JPH09258596A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve fixing property of an OHP sheet and to prevent color developing property from being deteriorated by separating a pressure auxiliary member from an endless belt in the case an OHP sheet discriminating device discriminates that a recording sheet is the OHP sheet. SOLUTION: In the case the OHP sheet discriminating device(UI+C) discriminates that the recording sheet S is the OHP sheet, a pressure auxiliary member pressing force adjusting device(71 to 73+C) separates the pressure auxiliary member 56 from the endless belt 51. Thus, a toner image is prevented from being peeled in the midst of fixing based on the sudden decrease of pressing force in the case it is shifted from the press-contact area of the member 56 to a downstream area(area where pressing force between a pressure area and a pressure roller 54 is suddenly decreased) just behind the member 56. Namely, the parting and the peeling of toner on the recording sheet caused by the change of pressure distribution on a fixing nip area are prevented, and the excellent color developing property is held.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for fixing an unfixed toner image on recording paper by heating and pressurizing it.
In particular, the present invention relates to a belt nip type fixing device that uses a heat fixing roll and an endless belt that presses against the heat fixing roll. The fixing device of the present invention is used in image information recording devices such as copiers, printers and facsimiles.

[0002]

2. Description of the Related Art Several belt-nip type fixing devices using a heating roll and a belt pressed against the heating roll have been proposed. However, there is no mention of a measure for improving the fixing performance of the OHP sheet which is the subject of the present invention.

(J01) Technology described in JP-A-5-150679 In the technology disclosed in JP-A-5-150679, a plurality of (3 to 4) rolls are stretched around the surface of a heat fixing roll of a fixing device. The endless belt is in pressure contact, and one of these rolls is used as a pressure roll to press against the heat fixing roll from the inside of the endless belt to distort the elastic body on the surface of the endless belt, thereby eliminating the peeling device such as peeling claw In addition, it is characterized by a self-strip technique for separating the recording sheet from the heat fixing roll. On the other hand, the distortion of the toner on the recording sheet at the belt nip portion occurs due to the distortion of the elastic body of the heating and fixing roll necessary for this self-strip technique. The pressure assisting roll is applied to the belt nip so as to reduce the above-mentioned distortion.

(J02) Technology described in Japanese Utility Model Application Laid-Open No. 4-55056 In Japanese Utility Model Application Laid-Open No. 4-55056, a pressure plate is arranged on the back surface of a belt member so that the belt member is pressed against a heat fixing roll from the inside. The pressure plate is supported via a moving mechanism, and the force for pressing the paper against the pressure roll can be relatively changed. As a result, the pressing force of the pressure plate can be changed, and the fixing performance can be improved by this mechanism.

[0005]

[Problems to be Solved by the Invention]

(Problem of (J01) above) In the technology of (J01) above, O
Since the fixing speed is low in the fixing of the HP sheet, the pressure distribution in the process direction caused by the pressure assisting roll in the belt nip portion causes the separation of the OHP sheet and the fixing roll inside the nip portion, and the fixing roller rolls on the OHP sheet. Toner is divided, resulting in deterioration of image quality. In order to avoid this, there is a method of increasing the amount of the release agent oil to prevent the toner from being divided inside the nip portion, but there is a problem that the coloring property is deteriorated due to the increase in the amount of the oil.

(Problem of (J02)) Further, (J2)
In the technique of 02), in fixing the OHP sheet, no consideration is given to the fact that the toner on the OHP sheet is divided and the image quality is deteriorated due to the fluctuation of the pressure distribution in the process direction in the belt nip portion.

In view of the above circumstances and examination results, the present invention has as its subject the contents described in (O01) below. (O01) OHP in a belt nip type fixing device
To improve the fixing performance of the sheet. And preventing the deterioration of the color development of the OHP sheet.

[0008]

Next, the present invention devised to solve the above-mentioned problems will be described. Elements of the present invention are used to facilitate correspondence with elements of the embodiments described later. , The reference numerals of the elements of the embodiment are enclosed in parentheses. The reference signs in parentheses connected with a + sign indicate that a combination of a plurality of elements of the embodiments corresponds to an element of the present invention. The reason why the present invention is described in correspondence with the reference numerals of the embodiments described below is to facilitate understanding of the present invention, and not to limit the scope of the present invention to the embodiments.

(Invention) In order to solve the above-mentioned problems, a fixing device (F) of the present invention of the present application is provided with the following requirements: (Y01) recording sheet (S) sheet Elastic body surface layer (43 + 4) arranged on the transport path (29)
4) having a heating fixing roll (41), a (Y02) pressure roll (54), and a belt supporting roll (52, 53) which are rotatably movably stretched, and an outer surface of the belt has the heating fixing roll (41). 41) Endless belt (51) pressed against (41), (Y03) Pressure roll for pressing the pressure roll (54) toward the heat fixing roll (41) with a pressing force that deforms the elastic surface layer (43 + 44). Supporting devices (55), (Y04) A pressure assisting member (56) that is in contact with the inner surface of the endless belt (51) and that is arranged upstream of the pressure roll (54) in the recording sheet (S) transport direction, (Y05) A pressure assisting member supporting device (57) for pressing the pressure assisting member (56) toward the heat fixing roll (41), (Y06) the heat fixing roll (41) and The endless belt (5
The heat fixing roll (41) forms a fixing nip (N) by the pressure contact area of 1) and fixes the unfixed toner image (I) attached to the recording sheet (S) passing through the fixing nip (N). And the endless belt (51),
(Y07) OHP that determines whether the recording sheet (S) passing through the fixing nip (N) is an OHP sheet
Sheet discriminating device (UI + C), (Y08) The OHP sheet discriminating device (UI + C) is used to OH the recording sheet (S).
When it is determined that the sheet is a P sheet, a pressure assisting member pressing force adjusting device (71 to 73+) that reduces the pressing force of the pressure assisting member (56) against the heat fixing roll (41).
C).

(Explanation of Terms) The term “pressing force” is used not to mean “pressure” per unit area but to mean the sum of pressing forces, that is, “load”. Further, the expression “to decrease the pressing force” of the pressure assisting member with respect to the heat fixing roll (41) means “separate” from the heat fixing roll (41), that is, “move in a direction away from”. Including.

[0011]

Next, the operation of the present invention having the above features will be described. (Operation of the Present Invention) In the fixing device (F) of the present invention having the above-mentioned characteristics, the OHP sheet discriminating device (UI + C)
Is a recording sheet (S) passing through the fixing nip (N).
Is a OHP sheet. On the elastic surface layer (43 + 44) of the heat fixing roll (41) arranged in the sheet conveying path (29) of the recording sheet (S), the pressure roll (54) and the belt supporting rolls (52, 53) are provided.
The belt outer surface of the endless belt (51) stretched around and rotatably around is pressed against. The pressure roll support device (55) presses the pressure roll (54) toward the heat fixing roll (41) with a pressing force that deforms the elastic body surface layer (43 + 44). The pressure assisting member (56) arranged on the upstream side of the pressure roll (54) in the conveyance direction of the recording sheet (S) contacts the inner side surface of the endless belt (51). The pressure assisting member support device (57) presses the pressure assisting member (56) toward the heat fixing roll (41). The heat fixing roll (41) and the endless belt (51)
Forms a fixing nip (N) by the pressure contact area of the heat fixing roll (41) and the endless belt (51), and the unfixed toner adhered to the recording sheet (S) passing through the fixing nip (N). Fix image (I). The pressure assisting member pressing force adjusting device (71 to 73 + C),
When the OHP sheet discriminating apparatus (UI + C) discriminates the recording sheet (S) as an OHP sheet, the pressing force of the pressure assisting member (56) against the heat fixing roll (41) is reduced.

[0012]

Next, an embodiment of the present invention will be described. (Embodiment 1) Embodiment 1 of the fixing device (F) of the present invention is characterized in that the fixing device of the present invention has the following requirements. (Y09) The OHP sheet discriminating device is The pressure assisting member pressing force adjusting device (71 to 73 + C) for separating the pressure assisting member (56) from the endless belt (51) when it is determined that the recording sheet (S) is an OHP sheet.

(Operation of First Embodiment) In the first embodiment of the fixing device (F) of the present invention having the above-mentioned structure,
When the HP sheet determining device (UI + C) determines that the recording sheet (S) is an OHP sheet, the pressure assisting member pressing force adjusting device (71 to 73 + C) causes the pressure assisting member (56) to endlessly move. Belt (51)
Keep away from Thereby, the pressure assisting member (5
During the fixing based on the sudden decrease in the pressing force during the transition from the pressing region of 6) to the downstream region immediately after the pressure assisting member (56) (the region where the pressing force between the pressing region and the pressure roll (54) sharply decreases) The peeling of the toner image is prevented.

(Embodiment 2) Fixing device (F) of the present invention
Embodiment 2 of the present invention is characterized in that the fixing device of the present invention or Embodiment 1 of the present invention has the following requirements. (Y010) The OHP sheet discriminating device sets the recording sheet (S) A fixing time control device that extends the fixing time by decelerating the rotation speed of the heating fixing roll (41) and the endless belt (51) that form the fixing nip (N) when it is determined that the sheet is an OHP sheet.

(Operation of Second Embodiment) In the second embodiment of the fixing device (F) of the present invention having the above-mentioned structure,
When the HP sheet determination device (UI + C) determines that the recording sheet (S) is an OHP sheet, the fixing time control device determines the heating fixing roll (41) and the endless end forming the fixing nip (N). Belt (5
The rotation speed in 1) is reduced to lengthen the fixing time. Thereby, the pressing force of the downstream region (the region where the pressing force between the pressure contact region and the pressure roll (54) sharply decreases) immediately after the pressure contact region of the pressure assist member (56) is increased. The decrease becomes gradual, and peeling of the toner image during fixing due to a sudden decrease in pressing force is prevented.

(Embodiment 3) Fixing device (F) of the present invention
Embodiment 3 of the present invention is characterized in that the fixing device of the present invention or the fixing device of Embodiment 1 or 2 of the present invention has the following requirements: (Y011) From the drive source (M1) of the fixing device The pressure assisting member pressing force adjusting device (71 to 73 + C) that changes the pressing force of the pressure assisting member (56) by the driving force transmitted through the driving force transmitting device and separates it from the endless belt (51). .

(Operation of Third Embodiment) In the third embodiment of the fixing device (F) of the present invention having the above-mentioned structure, the driving source (M1) is the pressure assisting member via the driving force transmitting device. The driving force is transmitted to the pressing force adjusting device (71 to 73 + C). The pressure assisting member pressing force adjusting device (71 to 73+
C) changes the pressing force of the pressure assisting member (56) by this driving force and separates it from the endless belt (51). As a result, the sheet (from the pressure contact region of the pressure assisting member (56) to the downstream region immediately after the pressure assisting member (56) (the region where the pressing force between the pressure contact region and the pressure roll (54) sharply decreases) ( Peeling of the toner image during fixing due to a sudden decrease in pressing force at the time of the transition of S) is prevented. Further, particularly in the third embodiment, since the pressure assist pad (56) is separated from the endless belt (51) by the drive source of the fixing device, it is not necessary to separately provide the drive source for the separation. Therefore, the device can be simplified.

(Embodiment 4) Fixing device (F) of the present invention
Embodiment 4 of the present invention is characterized in that the fixing device according to any one of Embodiments 1 to 3 of the present invention has the following requirements (Y012). The pressure assisting member pressing force adjusting device (71 to 73+) for separating the pressure assisting member (56) from the endless belt (51) by rotating.
C).

(Operation of Fourth Embodiment) In the fourth embodiment of the fixing device (F) of the present invention having the above-mentioned structure, the pressure assisting member pressing force adjusting device (71 to 73 + C) is the pressure assisting member. The member (56) is rotated to separate it from the endless belt (51). As a result, the pressure assisting member (56) is moved from the pressure contact region of the pressure assisting member (56).
6) The toner image is prevented from peeling off during fixing due to a sudden decrease in the pressing force at the time of transition to the downstream region immediately after.

(Fifth Embodiment) The fixing device (F) of the present invention
Embodiment 4 of the present invention is characterized in that the fixing device of the present invention has the following requirements. (Y013) The pressure assisting member (56) comes into contact with the endless belt (51) again after being separated. The pressure assisting member pressing force adjusting device (71 to 73 + C) for making the contact operation time at least 1.5 times the separation operation time.

(Operation of Fifth Embodiment) In the fourth embodiment of the fixing device (F) of the present invention having the above-mentioned structure, the pressure assisting member pressing force adjusting device (71 to 73 + C) is the pressure assisting device. After the member (56) is separated, the pressure assisting member (56) is brought into contact with the endless belt (51) for a contact operation time which is 1.5 times or more the separation operation time. This prevents the toner image from being peeled off during fixing due to a sudden decrease in the pressing force when the pressure assisting member (56) moves from the pressure contact region to the downstream region immediately after the pressure assisting member (56). Further, particularly in the fifth embodiment,
Impact and friction on the endless belt (51) at the time of re-contact of the pressure assisting member (56) can be reduced, and the service life of the endless belt (51) can be extended.

(Example) Next, an example (example) of an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following example. In order to facilitate understanding of the following description, orthogonal coordinate axes X axis, Y axis, and Z axis are defined in the directions of arrows X, Y, and Z that are orthogonal to each other in the drawings, and the arrow X direction is the front and the arrow Y direction is the Leftward, arrow Z direction is upward. In this case, the direction opposite to the X direction (front) (−X direction) is backward, and the direction opposite to the Y direction (left) (−Y
The direction is to the right, and the opposite direction (-Z direction) to the Z direction (upward) is the downward direction. The front (X direction) and the rear (-X direction) are referred to as the front-back direction or the X-axis direction, and the left (Y direction) and the right (-Y direction) are included in the left-right direction or the Y-axis direction. That is, the upper direction (Z direction) and the lower direction (−Z direction) are referred to as the vertical direction or the Z axis direction. Furthermore, in the figure, the ones with "・" in the "○" mean the arrows from the back of the paper to the front, and the ones with "X" in the "○" are from the front of the paper. It means an arrow pointing to the back.

(Embodiment 1) Next, Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram of an entire image processing apparatus including a first embodiment of a fixing device according to the present invention. In FIG. 1, an image forming apparatus U includes a digital copying machine A as an image forming apparatus main body having a platen glass (transparent document table) A1 on the upper surface, and an automatic detachable apparatus mounted on the platen glass A1. The document feeder B is provided. The automatic document feeder B sequentially takes out the documents stored in a document feed tray (not shown), conveys them to the copy position on the platen glass A1, and transfers the copied documents to the document discharge tray H. It is configured to discharge.

Next, a copying machine as the main body of the image forming apparatus will be described. The copying machine A includes an image input terminal IIT (hereinafter, IIT) as an image reading section and an image output terminal IOT (hereinafter, IOT) as an image recording operation section, which are sequentially arranged below the platen glass A1. have.

The IIT has an exposure scanning optical system 1 below the platen glass A1. The exposure scanning optical system 1 has an exposure lamp 2 for document illumination mounted on a full rate carriage and a first mirror 3. Further, the exposure scanning optical system 1 has a second mirror 4 and a third mirror 5 mounted on a half-rate carriage that moves at half the moving speed of the full-rate carriage. It has an imaging lens 6 supported. The imaging lens 6 reflects from the original on the platen glass A1 and further reflects the first, second,
It has a function of converging the reflected light of the original reflected by the three mirrors to a CCD (solid-state image pickup device). The CCD has a function of converting the original reflected light converged on the imaging surface into an electric signal. The IIT has an image data output unit 7 that receives an electric signal obtained by the CCD and outputs it as digital image data, and a user interface UI that allows a user to input an operation command signal such as copy start. The user interface UI has a display unit (not shown), and the display unit displays information relating to the current setting state of the image forming apparatus U. Further, when the OHP sheet is used as the recording sheet, the user interface UI is provided with an OHP sheet designation switch (not shown) for inputting that the recording sheet to be used is the OHP sheet.

Next, the IOT converts the image data output from the image data output unit 7 into a laser drive signal, and a laser drive circuit 8 outputs an image data according to the laser drive signal output from the laser drive circuit 8. It has a laser writing device 9 which emits an embedded laser beam L. The laser beam L emitted from the laser writing device 9 is projected onto the surface of the image carrier 11 at the latent image writing position Q1 set on the moving path of the surface of the image carrier 11 which rotates in the direction of the arrow in FIG. It is supposed to be incident. A charger 12 is arranged along the surface of the image carrier 11 on the rotationally upstream side of the latent image writing position Q1.

The image carrier 11 is located downstream of the latent image writing position Q1 in the rotational direction along the surface of the image carrier 11.
A developing unit 13 for developing the electrostatic latent image formed on the surface into a toner image is arranged. The developing unit 13 has a red developing unit 13a and a black developing unit 13b. A transfer device 14 is arranged at a transfer position Q2 set further downstream of the developing unit 13. Further, a cleaner unit 16 is disposed further downstream in the rotation direction of the transfer device 14. Below the transfer device 14, paper feed trays 21 to 25 are arranged in multiple stages. The paper feed tray 23 is 1 for double-sided copying or multiplex copying.
This is an intermediate tray used when the recording sheet (hereinafter referred to as a sheet) S after the second copying is circulated and retransmitted to the transfer position Q2. The sheet S of each of the sheet feeding trays 21 to 25 passes through the first sheet conveying path 26 and is transferred to the transfer position Q2.
To be transported. The transfer device 14 is disposed at the transfer position Q2, and is configured to transfer the toner image I on the surface of the image carrier 11 to the sheet passing therethrough. Image carrier 11 that has passed the transfer position Q2
After the toner remaining on the surface is collected by the cleaner unit 16, the surface is again uniformly charged by the charger 12.

At the end of the first sheet conveying path 26, the conveyed sheet S is temporarily stopped at the upstream side of the transfer position Q2 in the sheet conveying direction, and then the transfer position Q2 is reached.
Roll 27 and register gate 28 for carrying in
Is arranged. The sheet S having the toner image transferred at the transfer position Q2 is conveyed to the fixing position Q3 through the second sheet conveying path 29 connected to the sheet discharge tray TR. A heating / pressurizing element (described later) of the fixing device F is disposed at the fixing position Q3, and is configured to heat and fix the unfixed toner image on the sheet S passing through the fixing position Q3. In the second sheet conveying path 29, the fixing position Q
A discharge roller 31 for discharging a sheet to the sheet discharge tray TR is provided on the downstream side of 3.

A switching gate 32 is arranged on the upstream side of the discharge roller 31 in the second sheet conveying path 29.
The switching gate 32 is used when switching the sheet conveyance direction on the second sheet conveyance path 29 to the sheet circulation path 33 or the sheet discharge tray TR. The sheet circulation path 33 is connected to the sheet inversion path 34 and the intermediate tray 23 via a switching gate 36. The switching gate 36 directs the sheet S in the sheet circulation path 33 to the sheet inverting path 34 when performing double-sided copying, and directly toward the intermediate tray 23 when performing multiplex copying. The sheet-shaped and comb-shaped Mylar gate 37 provided in the sheet inversion path 34 allows the sheet S to move downward due to elastic deformation when the passing sheet S is conveyed downward, When the sheet S passing through 37 is conveyed upward, the intermediate tray 2
It is configured to move in three directions. The sheet S temporarily stopped at a predetermined position on the intermediate tray 23 is configured to be transported from the intermediate tray 23 to the transfer position Q2 by the first sheet transport path 26.

Next, the fixing device F will be described. FIG. 2 is a detailed explanatory diagram of the first embodiment of the fixing device according to the present invention. 3A and 3B are detailed explanatory diagrams of a main part of the fixing device according to the first embodiment. FIG. 3A is a configuration diagram of a pressure roll supporting device, and FIG. 3B is a configuration diagram of a pad supporting device and a pad pressing force adjusting device. In the figure, the recording sheet (sheet) is represented by S, and the unfixed toner image transferred onto it is represented by I.

In FIG. 2, the fixing device F has a heating fixing roll 41. Core 42 of heat fixing roll 41
Is an aluminum cylinder having an outer diameter of 46 mm and an inner diameter of 42 mm. On the surface of the core 42, a hardness of 45 as a base layer 43.
2 (JIS-A) HUIV silicone rubber with a thickness of 2 mm
And a Viton rubber (registered trademark of DuPont) 30 as a top coat layer 44 on top of it.
It is coated with μm. An elastic body surface layer (43 + 44) is composed of the base layer 43 and the top coat layer 44. The top coat layer 44 is finished to have a surface close to a mirror surface. The rubber hardness of the base layer 43 is UIec.
With a lock type spring type A hardness tester,
This is the result of measurement with a load of 9.80 N added according to JIS K6301. Hereinafter, the hardness measured by the same measurement method is abbreviated as JIS-A.

The output of the halogen lamp 45, which is the heat source of the heat fixing roll 41, is 650 w, and the temperature sensor 46
A temperature controller (not shown) feedback-controls the halogen lamp 45 on the basis of the above signal to adjust the surface of the heat fixing roll 41 to 120 ° C. A release agent (amino-modified silicone oil having a viscosity of 300 cs) is applied to the surface by an oil supply device 47.
Are being supplied. On the other hand, the endless belt 51 is formed of a polyimide film with a thickness of 75 μm, a width of 300 mm, and a peripheral length of 188 mm. The endless belt 51 includes belt support rolls 52, 53,
And around the pressure roll 54 with a tension of 98.06 N. The belt support rolls 52 and 53 and the pressure roll 54 are made of stainless steel and have diameters of 18 mm, 18 mm, and 23 mm, respectively.

The belt supporting rolls 52, 53 and the pressure roll 54 are tapered so that the diameter of the central portion thereof is slightly larger than the diameter of the end portions thereof, whereby the tension of the endless belt 51 is increased. Therefore, even if these rolls are bent, the endless belt 51 is flat and does not undulate, so that the endless belt 51 can travel smoothly. Of these rolls, the pressure roll 54
Is pressed toward the center of the heat fixing roll 41 by a constant pressing force (load) by the pressure roll supporting device 55, whereby the endless belt 51 is pressed against the heat fixing roll 41. The heat fixing roll 41
The winding angle of the endless belt 51 on the is 45 °. The heat fixing roll 41 and the endless belt 5
The pressure contact area 1 forms a fixing nip N which is a place where fixing is performed. The width of the fixing nip N at this time is a contact width of the pressing area of the endless belt 51 pressed by the pressure roller 54 against the heating fixing roller 41, and is 3.6 m.
m.

Since the pressure roll 54 is made of stainless steel and is much harder than the top coat layer 44 of the heat fixing roll 41, it is pressed by the pressure roll 54 toward the elastic surface layer (43 + 44) of the heat fixing roll 41. The endless belt 51 is in a state of biting into the surface of the heat fixing roll 41. In this state, the endless belt 51 is unlikely to slip on the heat fixing roll 41,
The endless belt 51 can be conveyed at the same speed as the peripheral speed of the heat fixing roll 41. In this state,
The heating / fixing roll 41 is driven by the drive motor M1 to have a peripheral speed Vo.
Since the endless belt 51 is rotated at a speed of 200 mm / sec, the endless belt 51 can also travel at a speed Vo. In order to prevent the endless belt 51 from moving in the axial direction of the belt support rolls 52 and 53 and the pressure roll 54 and coming off from these rolls, the belt support roll 52 adjusts the direction of its axis. It is configured to be possible. That is, the shaft of the belt support roll 52 (the front end of the paper surface) is supported so as to be slightly displaceable to the left and right in the paper surface as indicated by the arrow in FIG.

2 and 3B, a pressure auxiliary pad (that is, a pressure auxiliary member) 56 arranged on the upstream side of the pressure roll 54 in the traveling direction of the sheet S has a thickness of 2. mm on a stainless support 56a having a width of 10 mm. A Teflon sheet 56 in which 5 mm of silicone sponge 56b (foam of silicone rubber) is covered, and glass fiber is impregnated with Teflon to reduce the contact resistance with the endless belt 51 at the upper layer.
It is covered with c. This pressure auxiliary pad 56
Is also pressed from the inside of the endless belt 51 toward the center of the heat fixing roll 41 by the pad supporting device (that is, the pressure assisting member supporting device) 57. The width of the fixing nip N is 18 mm due to the arrangement of the pressure assisting pad 56. As described above, when the pressure auxiliary pad 56 is separated from the endless belt 51, the pressure roll 54 of the fixing nip N is
The width of only the pressure contact area of is 3.6 mm.

In FIG. 3A, the outside of the pressure roll supporting device 55 is composed of a metal cylinder 61 and a thick bottom plate 62. A compression spring 63 is housed inside the cylinder 61. A slider 66 is supported on the upper portion of the cylinder 61 so as to be vertically slidable.
The slider 66 is a rotary shaft 54a of the pressure roll 54.
Is rotatably supported by a bearing case 67 and is connected by a connecting bolt 68. The pressure roll support device 55 is constituted by the elements indicated by the reference numerals 61 to 63 and 66 to 68. The pressure roll support device 55
Are arranged at both front and rear ends (both ends in the X-axis direction) in the copying machine A.

In the first embodiment, the slider 66 is rotatably housed in the cylinder 61. However, since the slider 66 is pressed against the pressure roll shaft 54 extending in the front-rear direction (X-axis direction) of FIG. 3A, it does not rotate in the cylinder 61. In order to prevent the rotation of the slider 66 in the cylinder 61 more reliably, a guide groove along the axial direction is provided in the cylinder 61, and a guided pin that slidably and non-rotatably engages with the guide groove is used as a slider. It is also possible to provide 66.

In FIG. 3B, the pad support device (ie, pressure member support device) 57 is the pressure roll 54.
Are arranged at both front and rear ends of the copying machine A in the same structure as the pressure roll supporting device 55. That is, the pad support device 57 in the first embodiment corresponds to the constituent elements of the pressure roll support device 55 shown by reference numerals 61 to 63 and 66 to 68 in FIG.
And 66'-68 '. However, among these, a pad connecting member 67 ′ for connecting the slider 66 ′ and the pressure assisting pad 56 is different from the bearing case 67. Further, slits 61a 'extending vertically are formed in the upper surfaces of the cylinders 61' facing each other 180 degrees apart, and a pin 66a 'fixed to the outer surface of the slider 66' is vertically extended in the slits 61a '. The slider 66 'is slidably engaged to regulate the rotation and vertical movement range of the slider 66' about the vertical axis.

In other respects, elements 61'-6
3'and 66'-68 'are constructed similarly to the elements 61-63 and 66-68. Reference numeral 61 'described above
63 'and 66' to 68 'constitute the pad supporting device 57 (61' to 63 '+ 66' to 68 '). On the outer side surface of the cylinder 61 ', a pair of solenoids 72 are fixed on the left and right side surfaces in FIG. 3B. The operating rod 72a of the solenoid 72 extends upward and is connected to the pad connecting member 67 '.

In FIG. 1, the user interface U
When the IHP OHP sheet designation switch (not shown) is pressed, a detection signal indicating that the OHP sheet designation switch is pressed is input to the controller C. Controller C
Determines that the sheet S is an OHP sheet based on the input detection signal. When it is determined that the sheet S is an OHP sheet, the controller C sets so that the fixing can be performed at the fixing speed set for the OHP sheet (generally reduced compared to the normal sheet S). The memory Me stores memory OHP sheet data corresponding to the rotation speed of the heating and fixing roll 41, the OHP sheet transport speed, and the like. And the controller C is a sheet S
Is determined to be an OHP sheet, the drive circuit 7 of the drive motor M1 for the heating and fixing roll 41, which operates according to the OHP sheet data and is connected to the controller C,
1 (see FIG. 2), the drive circuit 73 of the pair of solenoids 72 (see FIGS. 2 and 3), and the like are controlled.

The drive circuit 71 controlled by the controller C operates the drive motor M1 to a predetermined fixing speed. Further, the solenoid drive circuit 73
Drives a pair of solenoids 72 connected thereto, causing the pad support device 57 to move away.
In the first embodiment of the fixing device F of the present invention, the symbol U
OHP sheet discrimination device (UI) based on the elements indicated by I and C
+ C), and the pad pressing force adjusting device, that is, the pressure assisting member pressing force adjusting device (71 to 73 + C) is formed from the elements denoted by reference numerals 71 to 73, C.

(Operation of First Embodiment) Next, the operation of the first embodiment of the fixing device F of the present invention having the above-mentioned structure will be described. The automatic document feeder B has a user interface UI.
In response to a copy command signal input from, the originals stored in the original feed tray (not shown) are sequentially taken out and carried to the copy position on the platen glass A1. II
At T, the original is exposed and scanned by the exposure lamp 2 for illuminating the original of the exposure scanning optical system 1 arranged immediately below the platen glass A1, and the reflected light from the original is reflected by the first mirror 3 and the second mirror. The light is reflected by the fourth and third mirrors 5 and is focused on the CCD (solid-state image pickup device) through the imaging lens 6. The CCD converts the reflected light of the document converged on the image pickup surface into an electric signal and outputs the electric signal, and the image data output unit 7 receiving the electric signal converts it into digital document image data and outputs it. The automatic document feeder B discharges the copied document from the copy position to the document discharge tray H.

Next, in the IOT, the laser drive circuit 8 which receives the above image data converts it into a laser drive signal and sends it to the laser writing device 9. The laser writing device 9 responds to this signal by the laser beam L for image writing.
Is rotated in the direction of the arrow in FIG.
It is made incident on the latent image writing position Q1 on the surface. The surface of the image carrier 11 is uniformly charged in advance by the charger 12, and the electrostatic latent image corresponding to the original image is written by the irradiation of the laser beam L. Next, the red developing unit 13a or the black developing unit 13b of the developing unit 13 arranged on the downstream side of the rotation of the image carrier 11.
Develops a toner image by attaching toner to the electrostatic latent image. At the transfer position Q2 set further downstream, the transfer device 14 electrostatically attaches and transfers the toner image on the image carrier 11 onto the sheet S carried in by the registration roll 27. The remaining residual toner is scraped off by the cleaner unit 16 further on the downstream side in the rotation direction.

The transferred sheet S is conveyed to the fixing position Q3 through the second sheet conveying path 29. Here, the fixing device F causes the unfixed toner image I on the sheet S to be unfixed.
Is fixed (details will be described later), and when the fixing is completed, the sheet is conveyed to the second sheet conveying path 29 on the downstream side. The discharge roller 31 discharges the sheet S to the sheet discharge tray TR. On the other hand, I
Regarding the sheet feeding operation in the OT, the sheet S is taken out from the corresponding tray (excluding the sheet feeding tray 23) among the sheet feeding trays 21 to 25 in response to a copy command signal from the user interface UI, and the first sheet is conveyed. Road 26
The sheet is conveyed until it comes into contact with the registration gate 28 at its end. Further, the registration gate 28 allows the sheet S, which has been temporarily stopped, to pass in synchronization with the arrival of the toner image on the image carrier 11, and the registration roll 27 causes the transfer position Q to be transferred.
Send to 2.

Except in the case of the one-sided once-copy,
The switching gate 32 provided in the second sheet transporting path 29 is switched to transport the sheet S, which has been transferred on one side, to the sheet circulating path 33 below. Then, the lower switching gate 36 is operated to directly convey the sheet S to the intermediate tray 23 in the case of multiple copy. In the case of double-sided copying, the sheet S is once fed to the lower sheet reversing path 34 and returned again, and the sheet S whose sheet is turned upside down by switching the Mylar gate 37 is sent to the intermediate tray 23. In the intermediate tray 23, the sheet S is temporarily stopped at a predetermined position, and then the transfer position Q is passed through the first sheet conveying path 26.
Transport to 2 again.

Next, the operation of the fixing device F will be described. The sheet S conveyed to the fixing position Q3 from the right side of FIG. 2 is 200 mm / sec by the drive motor M1 immediately after the sheet S is discriminated by the OHP sheet discriminating device (UI + C). Is fed to the fixing nip N, which is a pressure contact region between the heating and fixing roll 41 and the endless belt 51 which are rotating at the peripheral speed. Therefore, the unfixed toner I is fixed on the sheet S by the heat of the heat fixing roll 41 and the sandwiching pressure between the heat fixing roll 41 and the endless belt 51. That is, first, the heating and fixing roll 41 is heated by the halogen lamp 45 arranged in the central portion, and the surface is heated uniformly. The surface temperature is detected by the temperature sensor 46, is feedback-controlled via the controller C, and is maintained at 120 ° C. On the surface of the heat fixing roll 41, a release agent of silicon oil is supplied from the oil supply device 47 on the upstream side to form a thin film, which transfers the unfixed toner I to the heat fixing roll 41. It's suppressed. The pressure required for the heat fixing is
The steady pressure due to the endless belt 51 being pressed against the heat fixing roll 41 at a wrapping angle of 45 ° with a tension of 98.06 N, and the pressure roll 54 and the pressure auxiliary pad 56 are included in the endless belt 51. It is obtained by the pressing force that presses the side surface.

The pressure roll 54 and the pressure auxiliary pad 56.
The pressing force by which each presses the inner surface of the endless belt 51 is generated by the pressure roll supporting device 55 and the pad supporting device 57. The pressing force of the pressure roll support device 55 and the pad support device 57 is generated by the compression springs 63 and 63 'incorporated therein, respectively, and the compression degree of each spring is adjusted in advance to use it. Good fixing performance, peeling performance (self-strip) corresponding to conditions such as the paper thickness of the sheet S and the toner density, and the avoidance of image shift are realized.

When the sheet S conveyed to the fixing nip N is discriminated as an OHP sheet by the OHP sheet discriminating device (UI + C), the controller C
Operates the image forming apparatus U at the rotation speed of the heating and fixing roll 41, the conveying speed of the OHP sheet, and the like set so that the fixing can be performed at the fixing speed set for fixing the OHP sheet. That is, the controller C controls the drive circuit 71 of the drive motor M1 to operate the drive motor M1 so as to achieve a predetermined fixing speed. Then, the conveyance speed of the recording sheet S and the like are also changed in accordance with the change in the fixing speed. Further, the controller C controls the solenoid drive circuit 73 for the solenoid 72 to turn on the solenoid 72. At this time, the operating rod 72a of the solenoid 72 descends from the upper limit position corresponding to the general seat shown in FIG. 3B, and the pressure assisting pad 56 is pressed from the position where it is pressed against the endless belt 51.
Separates downwards. In this state, the OHP sheet passes through the pressure contact areas of the heat fixing roll 41 and the endless belt 51 and is fixed.

By the way, when the pressure auxiliary pad 56 is pressed against the heat fixing roll 41, the pressure contact area between the heat fixing roll 41 and the endless belt 51 is the same as the pressure area of the pressure auxiliary pad 56. It is divided into a pressing region by the roll 45 and a region between both pressing regions (that is, a region immediately after the pressing region by the pressure assist pad 56 or a region immediately before the pressing region by the pressure roll 45). Thus, when the pressure auxiliary pad 56 is pressed by the heat fixing roll 41, the area immediately after the pressing area of the pressure auxiliary pad 56 (that is, the area immediately before the pressing area of the pressure roll 45). At, the pressing force suddenly decreases. In this case, OH
The toner I on the P sheet is separated and peeled off, and the image quality is deteriorated. However, in the present embodiment, when the OHP sheet is fixed, since the pressing force from the pressure assisting pad 56 is not applied, the area immediately after the pressing area of the pressure assisting pad 56 when it is applied (that is, the pressure The sudden decrease in the pressing force in the area immediately before the pressing area of the roll 45) is eliminated, the toner I on the sheet S is prevented from being separated and separated, and the image is fixed without deterioration in image quality. When the OHP sheet passes through the fixing nip N, the solenoid 72
Is turned off, the pressure assisting pad 56 is pushed up by the compression spring 63 ', and the endless belt 51
Is returned to the state of pressing against the heat fixing roll 41.

The findings of the results of experiments and studies conducted by the inventor regarding the relationship between the fixing property of the OHP sheet and the pressing force of the pressure assisting pad 56 are as follows. In this experiment, as the fixing temperature and the fixing speed, the values for the general sheet S were used. Further, the evaluation of color developability was performed visually. (Experiment 1) Coloring Experiment An OHP sheet is loaded with 0.65 mg / cm ² of toner per unit area, and the load on the pressure assisting pad 56 is set to a normal value (value in the case of a normal sheet S) and 0 (separated state). ) And was used to observe the change in toner color development. The result is shown in Figure 4.
Is shown in Table 1. In Table 1 of FIG. 4, the symbol x indicates that the toner has deteriorated in fixing and the color developability is poor, and the symbol ◯ indicates that the toner does not deteriorate and the color developability is good. From this result, in the case of fixing the sheet S of the OHP sheet, the pressure assisting pad 56 is attached to the endless belt 51.
It can be seen that the color developability of the toner is improved by separating the endless belt 51 in the running direction of the endless belt 51 from the abrupt distance from the toner so that the toner color develops.

(Experiment 2) Relationship between Load of Pressure Auxiliary Pad 56 and Toner Concentration Next, the load of the pressure auxiliary pad 56 is sequentially decreased, and finally the pressure auxiliary pad 56 is connected to the endless belt 51.
The change in color development from the separation to the separation was observed while changing the toner concentration (toner amount per unit area with 100% being 0.65 mg / cm ² ). The results are shown in Table 2 of FIG. In Table 2 of FIG. 5, the symbol x indicates that the toner fixing was deteriorated and the coloring property was poor, and the symbol ◯ indicates that the toner fixing was not deteriorated and the coloring property was good. Further, the toner density at which the image quality deterioration occurs is a value in% of the toner density value at which the image quality deterioration starts when the toner density on the OHP sheet is gradually decreased from the darker one in the experiment. According to the results of Table 2, the deterioration of the image quality is prevented only when the load of the pressure assisting pad 56 is 0, that is, when the pressure assisting pad 56 is separated from the endless belt 51. On the other hand, if the load of the pressure assisting pad 56 is increased,
It can be seen that due to a sudden change in the pressing force distribution in the fixing nip N portion, the thickness of the toner changes, so that the temperature differs between the toner surface and the toner surface, and the image quality begins to deteriorate from a higher toner concentration. This is because how the toner melts depends on the pressing force of the pressure assisting pad 56.

From the results of Experiments 1 and 2 described above, in the case of fixing the sheet S of the OHP sheet, the pressure assisting pad 5 is used.
Endless belt 5 in the fixing nip N part by separating 6
It can be seen that the color development is improved by preventing a sudden change in the pressure distribution in one traveling direction.

(Embodiment 2) FIG. 6 is a constitutional view of a pad supporting device and a pad pressing force adjusting device of a second embodiment of a fixing device according to the present invention, and is a view corresponding to FIG. 3B of the first embodiment. In the description of the second embodiment, the first embodiment
The same reference numerals are given to constituent elements corresponding to the above-mentioned constituent elements, and detailed description thereof will be omitted. The second embodiment differs from the first embodiment in the following points, but has the same configuration as the first embodiment in other points. In the second embodiment,
The configuration for vertically moving the slider 66 'is different from that of the first embodiment. That is, in place of the solenoid 72 of the first embodiment, in the second embodiment, a mechanism for vertically moving the slider 66 'by directly utilizing the driving force of the driving motor (that is, the driving source) M1 of the heating and fixing roll 41. Is provided.

In FIG. 6, the end of the rotary shaft of the drive motor M1 of the heat fixing roll 41 (the pad support device 57
A torque limiter 79 is mounted in the vicinity of (). The torque limiter 79 is based on a conventional technique such as containing magnetic powder or the like for transmitting the rotational torque, and its input portion (center portion) is fixed to the rotary shaft end of the drive motor M1 and its output portion. The (outer peripheral portion) is fixed to the gear G1. Then, an excessive amount of the rotational torque transmitted from the rotary shaft of the drive motor M1 to the input portion is absorbed by the flow of the magnetic powder inside the torque limiter 79, so that only a constant torque is transmitted to the gear G1 from the output portion. It has become. The torque limiter 79 prevents excessive contact pressure between the slit 61a 'and the pin 66a' slidably engaged with the slit 61a 'due to excessive vertical movement of the slider 66'. It is a thing.

A gear G2 meshes with the gear G1,
A disc-shaped connecting plate 78 is connected to the gear G2 via a clutch Cr.
However, both are coaxially coupled to the gear G2. That is, the input portion of the clutch Cr is fixed to the gear G2, and the connecting plate 78 is fixed to the output portion of the clutch Cr. Therefore, the connecting plate 78 is configured to rotate integrally with the gear G2 when the clutch Cr is engaged, but does not rotate when disengaging. In addition, a slit 78a is formed at one location near the outer edge of the connecting plate 78 from the outer edge toward the center of rotation. A small pin 67a 'fixed to the outer peripheral surface of the pad connecting member 67' so as to project at a right angle (front side of the drawing, in the X-axis direction) to the slit 78a is slidably fitted in the slit 78a. are doing. Thereby, the clutch Cr
When the connection plate 78 is connected and the connecting plate 78 is rotated by the rotational force of the drive motor M1, only the vertical movement is transmitted to the pin 67a ', and the pressing force of the pressure assisting pad 56 is reduced via the pad connecting member 67. Separation or (re) contacting is to take place.

The clutch Cr is on / off controlled by a clutch drive circuit 74 operated by the controller C. Therefore, in the second embodiment, reference numerals 71 and 7
2, 74, 78, 79, C, Cr, G1, G2, M1, etc. are used to reduce the pressing force of the pressure auxiliary pad 56 and to separate the pad pressing force adjusting device (71 to 74 + 7).
8 + 79 + C + Cr + G1 + G2 + M1).

(Operation of Second Embodiment) Next, the operation of the second embodiment of the fixing device of the present invention having the above-described structure will be described. The clutch Cr is normally off. When the clutch Cr is off, the connecting plate 78 is free to rotate. This connecting plate 7
The rotational position of 8 is the pin 67a 'which engages with the slit 78a.
It depends on the position of. The pad connecting member 67 'that supports the pin 67a' is constantly urged upward by the compression spring 63 ', and the pressure assisting pad 56 is held at a position where it comes into pressure contact with the heating and fixing roll 41. That is, the clutch C
When r is off, the pressure assisting pad 56 is held at the raised position where it is pressed against the heating and fixing roll 41. If the sheet S conveyed from the right side of FIG. 2A to the fixing position Q3 is not an OHP sheet, fixing is performed while the clutch Cr is off. That is, the fixing is performed in a state where the pressure assisting pad 56 is held at the raised position where it is pressed against the heating and fixing roll 41.

When it is judged that the sheet S conveyed to the fixing nip N is an OHP sheet (that is,
When the OHP sheet designation switch (not shown) of the user interface UI is pressed), the controller C turns on the clutch Cr. That is, the clutch Cr is connected, and the torque limiter 79, the gears G1 and G are connected from the rotation shaft of the drive motor M1 of the heating and fixing roll 41.
Rotational force transmitted via 2 causes the connecting plate 78 to rotate in the clockwise direction shown in FIG. Therefore, the pin 67a slidably fitted in the slit 78a on the connecting plate 78 is pushed down, and the slider 66 'and the slider 6 which fix and hold the pin 67a are held.
The pad connecting member 67 'and the pressure assisting pad 56, which are sequentially connected to 6', also move downward. As a result, the pressing force from the pressure assisting pad 56 to the heating and fixing roll 41 is reduced, and the pressing force is separated from the endless belt 51.
That is, when the sheet S is an OHP sheet, fixing is performed in a state where the pressure assisting pad 56 is not in pressure contact with the heat fixing roll 41. Therefore, in the second embodiment, the OHP
When fixing the sheet, since the pressing force from the pressure assisting pad 56 is not applied, the area immediately after the pressing area of the pressure assisting pad 56 when it is applied (that is, immediately before the pressing area of the pressure roll 45) is applied. The sudden decrease in the pressing force in the area) is eliminated, the toner I on the sheet S is prevented from being separated and separated, and the image is fixed without deterioration in image quality.

After fixing the OHP sheet, clutch C
When r is off, the connecting plate 78 is free to rotate and the force pushing the pin 67a downward disappears, so that the slider 6 is driven by the reaction force of the compression spring 63 '.
6 ', the pressure assisting pad 56 and other members are pushed up, and the pressure assisting pad 56 returns to the state of pressing the heat fixing roll 41 via the original endless belt 51. If the pin 66a 'reaches the lower limit of the slit 61a' when the clutch Cr is on, excessive torque is absorbed by the torque limiter 79, and the pin 66a 'is absorbed.
The force pressing the slit 61a 'downward is kept below a certain value.

(Third Embodiment) Next, referring to FIG. 7, a third embodiment of the present invention (an example of the third embodiment) will be described. FIG. 7 is a block diagram of a pad supporting device and a pad pressing force adjusting device of a third embodiment of the fixing device according to the present invention, and is a view corresponding to FIG. 3B of the first embodiment. In the description of the third embodiment, components corresponding to the components of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The third embodiment differs from the first embodiment in the following points, but is configured similarly to the first embodiment in other points.
That is, instead of the solenoid 72 for separating the pressure assist pad 56 in the first embodiment, the pad support device 5 is used.
A mechanism (described later) for rotating 7 to separate the pressure assist pad 56 is provided.

A cylinder 61 'of the pad supporting device 57 is fixed to a disc-shaped connecting plate 82 whose rotational position can be controlled by a step motor M2 which rotates forward and backward by a motor drive circuit 81. Rotating shaft 83 of connecting plate 82
Are arranged below and to the right of the right end of the upper surface of the pressure assisting pad 56 in FIG. When the connecting plate 82 rotates counterclockwise in the state shown in FIG. 7, the pad supporting device 5
7 and the pressure assist pad 56 rotate counterclockwise around the rotary shaft 83. The state shown in FIG. 7 is the position where the pressure assisting pad 56 is in pressure contact with the heating and fixing roll 41, and when the rotating shaft 83 of the connecting plate 82 rotates counterclockwise from this state of FIG. It rotates clockwise and separates from the heat fixing roll 41.

As described above, since the rotary shaft 83 is arranged below and to the right of the right end of the upper surface of the pressure assisting pad 56 in FIG. 7, the rotary shaft 83 rotates counterclockwise in the state of FIG. In this case, the upper surface of the pressure assisting pad 56 (the pressure contact surface with the endless belt 51) is
It will only move away from. Therefore, when the pressure assisting pad 56 is separated, the pressure assisting pad 56 can be pulled out to the left without receiving resistance. In the third embodiment, the rotational position of the connecting plate 82, that is, the rotational position of the pressure assisting pad 56 is the step motor M2.
Can be detected by the rotational drive amount of. Therefore, the rotational position of the pressure assisting pad 56 is determined by the step motor M2.
By controlling the amount of rotational drive of the endless belt 51, a pressure contact position (position in FIG. 7) contacting the endless belt 51 and a separated position (position counterclockwise rotated from the position in FIG. 7) separated from the endless belt 51 are set. It is possible to control the position between. The pad pressing force adjusting device (81 to 83 + M2 + C) of the third embodiment of the fixing device of the present invention is constituted by the elements indicated by the reference numerals 76 to 78, M2 and C.

(Operation of Third Embodiment) Next, the operation of the third embodiment of the fixing device of the present invention having the above-described structure will be described. When it is determined that the sheet S conveyed to the fixing nip N is an OHP sheet (that is, when an OHP sheet designation switch (not shown) of the user interface UI is pressed), the controller C drives the motor. The circuit 81 is operated to rotationally drive the step motor M2. At this time, the step motor M2 rotates at a predetermined speed. The rotation causes the connecting plate 82 to rotate counterclockwise from the state of FIG. 7. The pad support device 57, the pressure assisting pad 56, and the like fixed to the connecting plate 82 also integrally rotate in the counterclockwise direction. Therefore, the pressure assisting pad 56 is pressing the endless belt 51.
To the left of the paper surface, the pressing force on the heat fixing roll 41 disappears. Therefore, in the third embodiment, when the OHP sheet is fixed, the pressing force does not suddenly decrease in the area immediately before the pressing area of the pressure roll 45, so that the toner I on the sheet S is prevented from being separated and separated, and the image quality is improved. It is fixed without deterioration.

(Embodiment 4) This embodiment 4 is different from the above-mentioned embodiment 2 in the following points, but is configured similarly to the above-mentioned embodiment 2 in other points. The fourth embodiment is different from the second embodiment in that the pad supporting device 57 is configured to have a shock absorbing damper function when the pressure assisting pad 56 re-contacts. The pad support device 5
A piston 84 is arranged below the slider 66 'in the cylinder 61' of No. 7, and the slider 66 'and the piston 84 are connected via a piston rod 85.
The compression spring 63 'pushes the lower surface of the piston 84 upward.

Further, small holes 84a and 84b are formed in the vicinity of the outer periphery of the piston 84 so as to vertically pass therethrough.
The small hole 84b is larger than the small hole 84a, and one side is hinged to the upper surface of the small hole 84b. The small hole 84b is opened on the upper surface, but a one-way valve 84c that is in contact with the upper surface of the piston 84 and closes the small hole 84b is attached below. ing. Further, the cylinder 61 '
Oil O, which serves as a damping material, is filled therein so as to sufficiently cover the vertical movement range of the piston 84. By these components, resistance of the oil O passing through the small holes 84a and 84b to the piston 84 acts when the slider 66 'is pushed down and pushed up. In particular, when the oil O is pushed up, the oil O can only pass through the small holes 84a, so that the resistance is large.

Various dimensions such as the inner diameter of the cylinder 61 ', the length and elasticity of the compression spring, the small hole 84a of the piston 84, and the like.
And 84b, the viscosity of the oil O and the injection amount (relationship with the residual air volume), and the like, the push-up time of the piston 84 when the pressure assist pad 56 re-contacts with the endless belt, It can be set so that the pressing time of 84 is more than 1.5 times and the process is completed before the next fixing sheet arrives at the fixing nip portion. It should be noted that this oil damper function is not a built-in type in the pad support device 57, but may be combined with an independent type damper arranged in parallel therewith. Reference numeral 61 'described above
.About.63 ', 66' to 68 ', 84, 85, and O, the pad supporting device 57 (61') of the fourth embodiment.
.About.63 '+ 66' to 68 '+ 84 + 85 + O.sub.3). Further, the pad pressing force adjusting device (71 to 7
4 + 78 + 79 + C + Cr + G1 + G2 + M1) is the second embodiment.
Is configured similarly to.

(Operation of Fourth Embodiment) Next, the operation of the fourth embodiment of the fixing device of the present invention having the above-described structure will be described. When the sheet S conveyed from the right side of FIG. 2A to the fixing position Q3 is not an OHP sheet, fixing is performed in the state shown in FIG. 8 (the state where the pressure auxiliary pad 56 is in contact with the heating fixing roll 41). . When it is determined that the sheet S conveyed to the fixing nip N is an OHP sheet (that is, when an OHP sheet designating switch (not shown) on the user interface UI is pressed), the clutch Cr 'is turned on. . At this time, the rotational force of the drive motor M rotates the connecting plate 78, and as a result, the pressure assisting pad 56 is moved downward and separated. At this time, the piston 84 in the cylinder 61 'moves downward. When the pressure assisting pad 56 is separated from the piston 84 (that is, when the piston 84 is pushed down), the large one-way valve 84c of the small hole 84b provided in the piston 84 is also opened to open both the small holes 84a and 84b. Since the oil O passes therethrough, the resistance is reduced and does not hinder the rapid separation of the pressure assist pad 56. In this case, cylinder 6
The air left in the upper part of 1'is also compressed when being pushed down by the slider 66 ', which smooths the initial movement of the piston 84.

When the fixing of the OHP sheet is completed, the clutch Cr is disengaged (OFF). At this time, the pushing down force of the pin 67a of the connecting plate 78 disappears,
As a result, the slider 66 'is pushed up by the reaction force of the compression spring 63', and the pressure auxiliary pad 56 is re-contacted with the endless belt 51 (return to the pressed state).
Is performed. When the pressure assisting pad 56 is brought into contact with the endless belt 51 again, the movement of the piston 84 pushed up by the reaction force of the compression spring 63 ′ is moderated by the resistance of the oil O in the cylinder 61 ′. That is, the small holes 84a and 84b are opened in the piston 84, but when rising, 84b is blocked by the one-way valve 84c and passes only the small hole 84a where the oil O having high viscosity remains. A great resistance is given to the rise of the piston 84. Therefore, the abrupt rise of the piston 84 and (finally) the pressure assist pad 56 pushed up by the compression spring 63 'is alleviated. With the above operation, the push-up time of the piston 84 becomes 1.5 times or more the push-down time of the piston 84 when the pressure assist pad 56 is separated. For this reason, impact and friction at the time of re-contact with the endless belt 51 are reduced. This reduces wear of the Teflon sheet 56c of the endless belt 51 and the pressure assisting pad 56,
Has the effect of extending service life. In addition, the fourth embodiment is O
When fixing the HP sheet, since the pressing force does not suddenly decrease in the area immediately before the pressing area of the pressure roll 45, the toner I on the sheet S is prevented from being separated and separated, and the image is fixed without deterioration. .

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 9 is a configuration diagram of a pad supporting device, a pad pressing force adjusting device, and a compression spring adjusting device of a fifth embodiment of the fixing device according to the present invention. Example 5
Is different from the second embodiment in the following points, but is configured similarly to the second embodiment in other points. That is,
The only difference is that the pad support device 57 in the second embodiment is combined with the pressing force adjusting device (compression spring adjusting device) for the compression spring. A spring receiving piston 87 is housed below the compression spring 63 'in the cylinder 61' of the pad supporting device 57. A piston rod 88 is formed on the lower surface of the spring receiving piston 87 and extends downward so as to slide in the through hole 62a 'of the bottom plate 62'.
Are connected. A pressed plate 89 is fixed to the lower end of the piston rod 88. Above, the code 6
1'-63 ', 66'-68' and 87-89, the pad support device 57 (6) of the fifth embodiment is used.
1 '+ 63' + 66'-68 '+ 87-89).

The pressed plate 89 is supported by an eccentric cam 91 which is in contact with the lower surface of the pressed plate 89. The eccentric cam 91 is driven to rotate about an eccentric shaft 91a by a step motor 92. The step motor M
3 is driven by a drive circuit 92 connected to the controller C. The controller C includes
A detection signal of the sheet thickness detecting device T arranged on the upstream side of the fixing device F in the sheet S traveling direction is input. As the sheet thickness detecting device T, it is possible to use a conventionally known device described in JP-A-5-8900. Further, the controller C stores in the built-in memory Me sheet thickness for generating a pressing force of the pressure auxiliary pad 56 which is optimum for fixing property corresponding to the detected sheet thickness-optimal rotational position data of the step motor 92. have. With the above configuration, the controller C is configured to generate an optimum pressing force for the detected sheet thickness.
The stepping motor M3 is driven in response to a command from the eccentric cam 91 to rotate the eccentric cam 91, and the spring receiving piston 87 is moved up and down to expand and contract the compression spring 63 '. Reference numerals 91, C, M3 and UI '
The compression spring adjusting device (91 to 92 + C + UI ′) of the fifth embodiment is constituted by the elements indicated by the above.

(Operation of Embodiment 5) Next, the operation of Embodiment 5 of the fixing device of the present invention having the above-mentioned structure will be described. The sheet S sent to the fixing device F is detected by the OHP sheet discrimination device (UI + C) as a general sheet S that is not an OHP sheet, and the sheet thickness detection device T detects its thickness. Then, the controller C
Reads the optimum rotational position data of the step motor M3 corresponding to the detected sheet thickness from the storage table of the sheet thickness-optimal rotational position of the step motor M3 in the built-in memory Me, and operates the drive circuit 92. The drive circuit 92 causes the step motor M3 to rotate by a required angle, and the eccentric cam 91 also rotates about the eccentric shaft 91a by the same angle. As a result, the pressed plate 89, which is in contact with the upper surface of the eccentric cam 91, moves up and down, and therefore the spring receiving piston 87 also moves up and down by the same distance via the piston rod 88 connected thereto. As a result, the compression spring 63 'expands and contracts by a predetermined amount, and the pressing force from the corresponding pressure auxiliary pad 56 to the heat fixing roll 41 via the endless belt 51 changes. With the above operation, it is possible to generate an optimum pressing force that maintains good fixing performance even on general sheets S other than OHP sheets.

When it is determined that the sheet S is an OHP sheet, Cr is turned on as in the second embodiment, the connecting plate 78 is rotated clockwise, and the slit 78a is rotated.
Since the pin 67a 'engaging with is pushed down, the pressure assisting pad 56 is separated (moved downward) from the position (position shown in FIG. 9) where the pressure assisting pad 56 is in pressure contact with the heat fixing roll 41. Therefore, in the fifth embodiment, when fixing the OHP sheet, the pressing force does not suddenly decrease in the area immediately before the pressing area of the pressure roll 45, so that the toner I on the sheet S is prevented from being separated and separated, and the image quality is improved. It is fixed without deterioration.

(Modifications) Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-mentioned embodiments, but is within the scope of the gist of the present invention described in the claims. Thus, various changes can be made. A modified embodiment of the present invention is illustrated below. (H01) By separating the pressure assist pad 56 and increasing the tension of the endless belt 51, it is possible to make up for the deterioration of the fixing performance due to the pressure decrease in the fixing nip region. In that case, the increase in the tension of the endless belt 51 causes the tension roll shaft to move
A means for urging (pressing) the endless belt 51 in the direction of increasing the tension may be provided. (H02) In addition to the means shown in Embodiments 2 and 3, various mechanical and electromagnetic means can be considered as means for separating the pressure assisting member from the heat fixing roll.
For example, there is a mechanism for pushing down a compression spring using an eccentric cam, and a solenoid valve. (H03) The means for increasing the operation time at the time of re-contact of the pressure assisting pad with the endless belt shown in the fourth embodiment can be applied in combination to all of the present invention and the first to third embodiments of the present invention. . The physical means is not limited to the oil damper method described in the fourth embodiment, and various mechanical and electrical means such as direct control of a step motor that drives a cam mechanism for expanding and contracting the compression spring can be considered. (H04) The OHP sheet discriminating apparatus can use an OHP sheet detection sensor that detects whether or not the passing sheet is an OHP sheet, instead of using the OHP sheet designating switch provided in the user interface UI. .

(H05) As the pressure assisting member, it is possible to use a pressure assisting roll instead of the pressure assisting pad 56. (H06) The compression spring adjusting device for the pressure auxiliary pad capable of generating the optimum pressing force for maintaining the good fixing performance even on the general sheet S described in the fifth embodiment is the compression spring adjusting for the pressure roll. It can also be used as a device. Thereby, it is possible to change the pressing force from the pressure roll to the heat fixing roll 41 via the endless belt 51. (H07) The compression spring adjusting device for the pressure assist pad and the compression spring adjusting device for the pressure roll are integrally and integrally controlled,
It is possible to configure a (integrated) pressing force adjusting device that automatically generates an optimum pressing force that automatically maintains good fixing performance for various sheet S thicknesses. In that case, the command values to both compression spring adjustment devices are read and converted from the table of the sheet thickness-step motor optimum rotation position stored in the memory in the control in advance based on the fixing performance holding experiment. can get.

[0075]

The fixing device according to the present invention has the following effects. (E01) When fixing an OHP sheet recording sheet in a belt nip type fixing device, the toner on the recording sheet is prevented from being cut off or peeled off due to a change in pressure distribution in the fixing nip area, and good color development is maintained. be able to. (E02) Maintaining the above-mentioned color development is due to the recording sheet peeling performance,
It can be realized without impairing other fixing-related performances such as fixing performance (holding glossiness) and avoiding image shift.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an entire image processing apparatus including a first embodiment of a fixing device according to the present invention.

FIG. 2 is a detailed explanatory diagram of Embodiment 1 of the fixing device according to the present invention.

FIG. 3 is a detailed explanatory view of a main part of the fixing device of Embodiment 1, and FIG. 3A is a configuration diagram of a pressure roll supporting device.
B is a block diagram of a pad support device and a pad pressing force adjusting device.

FIG. 4 is a table of color-developing test results in Example 1 of the fixing device according to the present invention.

FIG. 5 is a table of experimental results regarding the relationship between the load of the pressure assisting pad 56 and the toner concentration in the first embodiment of the fixing device according to the present invention.

FIG. 6 is a configuration diagram of a pad supporting device and a pad pressing force adjusting device according to a second embodiment of the fixing device according to the present invention.

FIG. 7 is a configuration diagram of a pad supporting device and a pad pressing force adjusting device of a third embodiment of a fixing device according to the present invention.

FIG. 8 is a configuration diagram of a pad supporting device and a pad pressing force adjusting device of a fourth embodiment of a fixing device according to the present invention.

FIG. 9 is a configuration diagram of a pad supporting device, a pad pressing force adjusting device, and a compression spring adjusting device of a fixing device according to a fifth embodiment of the present invention.

[Explanation of symbols]

F ... Fixing device, I ... Unfixed toner image, M1 ... Driving source (driving motor), N ... Fixing nip, S ... Recording sheet (sheet), UI ... OHP sheet discriminating device, 29 ... Sheet conveying path, 41 ... Heating Fixing roll, 51 ... endless belt,
52, 53 ... Belt support rolls, 54 ... Pressure rolls, 5
5 ... Pressure roll supporting device, 56 ... Pressure assisting member, 57 ...
Pressure assisting member supporting device (pad supporting device) (61 'to 63' + 66 'to 68') ... Pressure assisting member supporting device (pad supporting device), (61 'to 63' + 66 ')
˜68 ′ + 84 + 85 + O) ... Pressure assisting member supporting device (pad supporting device), (61 ′ to 63 ′ + 66 ′ to 6)
8 '+ 87 to 89) ... Pressure assisting member supporting device (pad supporting device), (71 to 73 + C) ... Pressure assisting member pressing force adjusting device (pad pressing force adjusting device) (71 to 74 + 78 + 79 + C + Cr + G1 + G2 + M1)
… Pressure assisting member pressing force adjusting device (pad pressing force adjusting device) (81 to 83 + M2 + C)… Pressure assisting member pressing force adjusting device (pad pressing force adjusting device) (71 to 74 + 78 + 79 + C + Cr + G1 + G2 + M1)
... Pressure assisting member pressing force adjusting device (pad pressing force adjusting device) (91 to 92 + C + UI ') ... compression spring adjusting device, (4
3 + 44) ... elastic body surface layer,

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[Procedure amendment]

[Submission date] July 30, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

FIG. 4 is a chart of a color-developing test result in Example 1 of the fixing device according to the present invention.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Fig. 5

[Correction method] Change

[Correction contents]

FIG. 5 is a chart of an experimental result of the relationship between the load of the pressure auxiliary pad 56 and the toner concentration in the first embodiment of the fixing device according to the present invention.

Claims (6)

[Claims] 1. A fixing device comprising: (Y01) a heat fixing roll having an elastic surface layer disposed in a recording sheet conveying path; (Y02) a pressure roll and a belt supporting roll. An endless belt which is rotatably stretched around, and whose outer surface is in pressure contact with the heat fixing roll, (Y03) The pressure roll is applied to the heat fixing roll by a pressing force that deforms the elastic surface layer. A pressure roll supporting device for pressing the pressure roll toward the end face of the endless belt, (Y04) a pressure assisting member disposed on the upstream side of the pressure roll in the recording sheet conveying direction, and (Y05) the pressure assisting member. A pressure assisting member supporting device that presses against the heat fixing roll, (Y0
6) The heating fixing roll and the endless belt for fixing an unfixed toner image adhering to the recording sheet passing through the fixing nip by forming a fixing nip by the pressure contact area of the heating fixing roll and the endless belt, (Y07 ) An OHP sheet discriminating device which discriminates whether or not the recording sheet passing through the fixing nip is an OHP sheet, and (Y08) the heating when the OHP sheet discriminating device discriminates the recording sheet as an OHP sheet. A pressure assisting member pressing force adjusting device for reducing the pressing force of the pressure assisting member against the fixing roll. 2. The fixing device according to claim 1, characterized in that the pressure assisting member is provided when the (Y09) OHP sheet discriminating device discriminates the recording sheet as an OHP sheet. The pressure assisting member pressing force adjusting device for separating the pressure assisting member from the endless belt. 3. The fixing device according to claim 1, further comprising the following requirements: (Y010) The OHP
A fixing time control device for extending the fixing time by decelerating the rotation speeds of the heat fixing roll and the endless belt forming the fixing nip when the sheet judging device judges that the recording sheet is an OHP sheet. 4. The fixing device according to claim 1, wherein the fixing device has (Y011) a driving force transmitted from a driving source of the fixing device via a driving force transmitting device, The pressure assisting member pressing force adjusting device for separating the assisting member from the endless belt. 5. The fixing device according to claim 1, further comprising the following requirements: (Y012) The pressure assisting member is rotated to separate the pressure assisting member from the endless belt. Auxiliary member pressing force adjustment device. 6. The fixing device according to claim 1, wherein (Y013) a contact operation time when the pressure assisting member comes into contact with the endless belt again after the pressure assisting member is separated from the fixing device. The pressing force adjusting device for the pressure assisting member, wherein the operating time is 1.5 times or more.