JPH0462076A - Automatic head gap adjustment mechanism of impact printer - Google Patents

Abstract

PURPOSE:To dispense with backlash elimination operation by allowing a platen to approach a printing head by a biasing force, and at the same time, allowing the platen to leave the printing head resisting the energization force by a driving force of a motor and adjusting a head gap. CONSTITUTION:A coil-like spring 40 which biases a platen 1 constantly in the direction of a printing head 6 is arranged below the platen 1. The platen 1 is allowed to ascend by elastic force of a spring 40 and is allowed to descend resisting the elastic force by a drive force of a pulse motor 22. Therefore, gears which transmit the driving force of the pulse motor 22 to the platen 1, that is, a power gear 23, an idle gear 21, a drive gear 19, pinion gears 16, 17 and rack gears 14, 15 are always free from a backlash. Consequently, a backlash elimination operation need not be carried out, and the platen 1 has only to come down from a medium contact position to an objective position when a head gap has to be adjusted rapidly to a specified value.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a mechanism for automatically adjusting the head gap between the tip of a print head and a medium mounted on a platen in an impact printer to a predetermined value.

(Prior art) Impact printers are equipped with a mechanism that automatically adjusts the head gap according to the thickness of the medium in order to maintain print quality by keeping the stroke of the wire ejected from the print head to the medium constant. There is.

FIG. 4 is a schematic perspective view of an impact printer equipped with a conventional head gap automatic adjustment mechanism, and FIG. 5 is a schematic diagram of the configuration of the adjustment mechanism.

As shown in the figure, in this printer, the platen 1 has vertically long notches 4 formed in the side frames 2 and 3 on both sides.
, 5, so that it can be moved up and down in a horizontal state. Above the platen l, a printing platen 6 is arranged with its tip facing downward and facing the platen l. This print head 6 is mounted on a carriage 7, and the carriage 7 is slidably attached to a carriage shaft 8 and a carriage guide 9 that are installed between the side frames 2 and 3 on both sides, and is moved by a space motor 10. It is connected to the spacing belt 11.

Also, the ink ribbon 1 runs along the tip of the print head 6.
2, a ribbon protector 13 is fixed to the carriage 7.

Then, the space motor 9 is activated to move the carriage 7.
By moving the print head 6, the print head 6 is moved along the platen 1, and printing is performed on the medium P mounted on the platen l.

The automatic head gap adjustment mechanism provided in the above impact printer moves the platen 1 up and down to adjust the print head 6.
It is configured to adjust the head gap HG between the tip of the print head 6 and the medium 2 by moving the print head towards or away from the print head. Adjustment of this head gap HG actually amounts to adjusting the air gap AG between the ribbon protector 13, which is fixed at a certain distance from the tip of the print head 6, and the medium P.

In order to move the platen 1 up and down, vertically long rack gears 14.15 are symmetrically fixed to both ends of the platen 1, and each rack gear 14.15 has a
Pinion gears 16 and 17 are engaged. These pinion gears 16.17 are fixed to both ends of a drive shaft 18 which is rotatably mounted to the sight frame 2.3. A drive gear 19 is fixed to one end of this drive shaft 18 together with a pinion gear 16, and the drive gear 19 is connected to a power gear fixed to the shaft of a pulse motor 22 via two reduction idle gears 20 and 21. 23
is engaged with. The above two idle gears 20, 21
is rotatably supported by one side frame 2, and the pulse motor 22 is fixed to the same side frame 2.

In the above configuration, when the pulse motor 22 is operated by a control circuit (not shown), its driving force is transmitted to the power gear 2.
3, the two idle gears 20, 21, the drive gear 19, and the drive shaft 18 to the pinion gears 16, 17, and the rack gears 14, 15 move up and down. Therefore, due to the driving force transmitted from the pulse motor 22 in this manner, the platen 1 is raised and lowered within the cutouts 4 and 5 of the side frames 2 and 3 according to the rotational direction of the motor 22, and the print head Approaching and moving away from 6. In this case, the platen l has pinion gears 16.17 and rack gears 14.17 fixed at both ends to the drive shafts 18. Is
Since it is driven symmetrically due to the combination with the 2-axis, it always moves up and down while maintaining a horizontal state.

Also, the rotation of the pulse motor 22 is detected and the platen l is
In order to control the amount of movement of the motor 22, a slit circle g/L24 is fixed to one axis of the motor 22, and a slit sensor 25 is arranged to optically detect the slit 24a of the slit disk 24. Furthermore, in order to detect the home position of the platen L, one of the rack gears 1
A position sensor 26 is arranged to optically detect the lower end of 4. Detection signals from these sensors 25 and 26 are sent to the control circuit.

In the adjustment mechanism configured as described above, the head gap HG is adjusted using the step-out of the pulse motor 22. The head gap automatic adjustment operation will be explained with reference to FIG. 5 and an explanatory diagram of FIG. 6 showing time changes in the position of the platen l.

First, set the medium P on the platen 1 with the platen 1 located at the home position HP, then operate the pulse motor 22 to raise the platen 1, bring the medium P into contact with the ribbon protector 13, and then set the medium P on the platen 1. 22 out of step. At this time, although the control circuit is generating drive pulses to the pulse motor 22, the slit disk 2
Since the rotation of the pulse motor 4 stops and the detection signal from the slit sensor 25 disappears, the step-out of the pulse motor 22 is detected.

Move platen 1 to step-out position P□. After the pulse motor 22 is reversed, the target position P is reached at which a predetermined head gap HG, that is, a predetermined air gap AG is obtained. Lower the platen l toward the Then, in order to eliminate gear backlash between the pulse motor 22 and the platen L and eliminate adjustment errors, the platen L is temporarily moved to the target position P.

Lower it further down and then raise it again to the target position P.

to stop it. That is, the platen 1 is moved to the target position P. The rotation direction of the pulse motor 22 when stopped at is the same as when the platen 1 is raised to the step-out position P1o, which is the reference for head gap adjustment. This target position P. Then, the platen 1 is held by applying a holding current to the pulse motor 22.

After adjusting the head gap HG to a predetermined value in this manner, printing is started.

FIG. 7 is a schematic configuration diagram showing another conventional example.

As shown in the figure, in this adjustment mechanism, a linear sensor 30 is mounted on the carriage 7 of the print head 6, and the sensor section 3 moves up and down.
1 is fixed in a state of protruding toward the platen l. This linear sensor 30 sends a detection signal according to the amount of movement of the sensor section 31 to the control circuit.

In the case of this adjustment mechanism, the platen 1 is raised from the home position and the medium P is
The platen 1 is stopped at a position where the sensor section 31 of is pushed up by a certain amount. That is, the medium P is not brought into contact with the ribbon protector 13. Thereafter, as in the case of the prior art example, the platen 1 is lowered to below the target position and then raised again to eliminate backlash and adjust the head gap HG to a predetermined value.

<Problems to be Solved by the Invention> Even in the case of the adjustment mechanism described above, in order to eliminate the backlash of the gear between the pulse motor 22 and the platen 1, the platen 1 is once lowered below the target position. It is necessary to perform a backlash removal operation of lowering the head and then raising it again, which poses a problem in that it takes time to adjust the head gap.

Furthermore, in the case of an adjustment mechanism that utilizes step-out of the pulse motor 22, the ribbon protector 13 is displaced by the pressing of the platen 1, and the pressing force is also affected by changes in the load of the platen drive system due to changes in temperature and humidity, etc. Since the out-of-step torque of the motor 22 is not constant due to instability, etc., there is a problem that the out-of-step position, which is a reference for head gap adjustment, varies, and as a result, the adjusted head gap varies.

If the gear ratio of the platen drive system is set so that the rotation of the pulse motor 22 is largely decelerated in order to improve the accuracy of position adjustment of the platen l, the pressing force of the platen l increases in proportion to the gear ratio. If the material and structure of the ribbon protector 13 are made strong enough not to be displaced by the large pressing force of the platen l, the cost will increase as well as the weight. Furthermore, when copying paper is used, the large pressing force of the platen 1 causes indentations.

In order to avoid increasing the pressing force of the platen 1, it is necessary to reduce and finely adjust the current value of the pulse motor 22 that flows when the platen 1 loses synchronism, and this is extremely difficult.

On the other hand, in the case of an adjustment mechanism using the linear sensor 30,
Since the platen 1 is not pressed against the ribbon protector 13, there is no problem like the one described above in the adjustment mechanism that uses the step-out of the pulse motor 22. However, the linear sensor 30 is not cheap, so it is costly.

Further, in order to arrange the linear sensor 30, an extra space is required on the carriage 7 of the print head 6, and the shape and size of the ribbon cassette to be used or the running route of the ribbon are restricted. Moreover, the medium P may come into contact with the sensor portion 31 of the linear sensor 30 protruding from the lower surface of the carriage 7, causing skew or jam.

In addition, the linear sensor 30 must be mounted with high precision using a special jig, which poses a problem of poor assembly efficiency.

<Means for Solving the Problems> The present invention was proposed to solve various problems in the conventional head gap automatic adjustment mechanism as described above. Means is provided to constantly urge the print head toward the print head.

<Operation> In the adjustment mechanism configured as described above, the platen is moved closer to the print head by a biasing force, and the platen is moved away from the print head by the driving force of the motor against the biasing force to adjust the head gap. As a result, the backlash of the gear that transmits the driving force of the motor to the platen is always removed, and a backlash removal operation becomes unnecessary.

<Example) Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a schematic configuration diagram of an automatic head gap adjustment machine of the present invention, and FIG. 2 is a schematic perspective view of an impact printer provided with the adjustment mechanism. Incidentally, in FIGS. 1 and 2, components that are the same as those in the conventional example shown in FIGS. 4 and 5 are given the same reference numerals, and explanations thereof will be omitted.

A feature of the automatic head gap adjustment mechanism of the present invention is that it is provided with a means for constantly urging the platen l in the direction of the print head 6, and in the case of this embodiment, the urging means includes:
As shown in the figure, a coiled spring 40 is arranged below the platen 1.

The rest of the configuration is similar to the conventional adjustment mechanism that utilizes step-out of the pulse motor 22.

The spring 40 is fixed on a support piece 41 that is bent and protrudes inward from the lower end of the notch 4 of one side frame 2, and its elastic force is used to support the platen.
is constantly pressed upward. The elastic force of the spring 40 applied to the platen l in this manner is applied to the rack gears 14 provided on both sides of the platen l. Is and pinion gear 16.
17 , and the drive shaft 18 will span the ends of the platen l symmetrically. Therefore spring 40
Even if the plates are not placed on both sides of the platen 1, the platen 1 will not tilt.

Next, the automatic adjustment operation of the head gear and the knob by the adjustment mechanism having the above configuration will be explained with reference to FIG. 1 and FIG.

When the printer is not in use, the platen l is attached to the spring 40.
It is pushed up by the elastic force of and is in contact with the ribbon protector 13.

When starting to use the printer, the control circuit or pulse motor 22 is first activated to lower the platen l against the elastic force of the spring 40. Based on the detection signal from the position sensor 26, the platen 1 is stopped at the home position HP, and a holding current is applied to the pulse motor 22 to hold the platen 1 at this position. In this state, medium P is set on platen l.

Thereafter, the holding current of the pulse motor 22 is turned off to make the shaft free. Then, the platen l is pushed up by the elastic force of the spring 40 and stops at a position P□ where the medium P comes into contact with the ribbon protector 13.

The pressing force of the platen 1 at this time is extremely stable because it is due to the elastic force of the spring 40 acting directly on the platen 1. Moreover, if the elastic force of the spring 40 is set appropriately small, the ribbon protector 13
Even if the material and structure of the ribbon protector 13 are not particularly strong, the ribbon protector 13 will not be displaced.

Furthermore, since the pressing force of the platen 1 is small, there is no impression on the copy paper.

When the control circuit detects the stoppage of the platen 1 at the medium contact position P1 based on the detection signal of the slit sensor 25 that detects the rotation of the pulse motor 22, the control circuit stops the pulse motor 22.
is activated to lower the platen 1 against the elastic force of the spring 40 to reach a target position P where a predetermined head gap HG, that is, a predetermined air gap AG is obtained. to stop it. From this medium contact point MP1 to the target position P. The amount of movement of the platen l up to is controlled based on the detection signal from the slit sensor 25.

After adjusting the head gap HG to a predetermined value in this manner, a holding current is applied to the pulse motor 22 to hold the platen 1 and printing is started.

In the above adjustment operation, the platen l is
Since the platen 1 is raised by the elastic force of 0 and lowered by the driving force of the pulse motor 22 against the elastic force, the backlash of the gear that transmits the driving force of the pulse motor 22 to the platen 1, that is, the power gear 23. idle gear 21,
20, drive gear 19. The backlash of the gears 16 and 17 and the rack gears 14 and 15 is always removed. Therefore, the platen l is temporarily moved to the target position P. The medium contact position P is simply moved without performing a backlash removal operation of lowering it further down and then raising it again.
Target position P from □. The head gap HG can be quickly adjusted to a predetermined value by simply lowering the head gap HG to a predetermined value. Furthermore, as described above, since the amount of movement of the platen l from the medium contact position P, which is the reference for gap adjustment, to the target position Po is always constant, the head gap HG can be adjusted accurately without variation.

<Effects of the Invention> As described above, the head gap automatic adjustment mechanism of the present invention does not require a backlash removal operation, so that the head gap can be adjusted accurately in a short time. or,
It is only necessary to add a platen biasing means of a simple configuration to a ready-made adjustment mechanism, and since an inexpensive spring can be used as the biasing means, it can be realized easily and at low cost.

Furthermore, unlike conventional adjustment mechanisms using linear sensors, the present invention does not restrict the shape or size of the ribbon cassette or cause media skew or jam.

That is, according to the present invention, it is possible to provide an excellent head gap automatic adjustment mechanism that solves all the problems of conventional adjustment mechanisms that utilize motor step-out or use near sensors.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention; FIG. 2 is a perspective schematic diagram of an impact printer in the embodiment; FIG. 3 is an explanatory diagram showing changes in the position of the platen over time in the embodiment; FIG. 4 is a schematic perspective view of an impact printer in the conventional example. FIG. 5 is a schematic configuration diagram showing the conventional example. FIG. 6 is an explanatory diagram showing changes in the position of the platen over time in the conventional example. 1 is a schematic configuration diagram showing another conventional example. l...Platen, 6...Print head. 14.15...Rack gear. 16.17... Pinion gear, 19... Drive gear. 20.21... Idle gear, 22... Pulse motor. 23...Power gear, 40...Spring. HG...Head gap. Patent applicant Oki Electric Industry Co., Ltd. Agent
Patent Attorney Funabashi Kuni Nori 2゛wob 66rujni ←'' 14, Hokutaku Ax 6, ζnirr door 1941 Nazuoto 20: p-y, xw〆゛jiru 22°//2 no f-ta 23:ノ/'7 doors) Le 4o: 22 Radik HG Neeee w/°dunk.

Claims (1)

[Claims] An automatic head gap for an impact printer that automatically adjusts the head gap by transmitting the driving force of a motor to the platen through a gear and moving the platen away from the print head using the transmitted driving force. An automatic head gap adjustment mechanism for an impact printer, characterized in that the adjustment mechanism includes means for constantly biasing the platen in the direction of the print head.