JPH0452215B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to non-impact recording devices, and more particularly to inkjet recording devices in which droplets of ink are ejected from an orifice in a print head by varying the volume of a pressure chamber.

Inkjet recording devices are capable of high-speed printing with extremely low noise, can use inexpensive plain paper, and are easy to develop and print.
It does not require processing such as fixing, and has the advantage of not only character records but also the ability to enlarge records such as kanji and figures.

Conventional electrolytic control methods (Japanese Patent Publication No. 36-13768) and charge control methods (Japanese Patent Publications No. 42-4381 and 42-8350) have been known for this inkjet recording device since early on. In these systems, particularly in the means for forming ink droplets and the means for controlling the jetting direction (deflection) for forming characters,
Requires a complex and highly precise structure.

Therefore, methods with simpler structures have been developed in recent years and are attracting attention. As shown in Japanese Patent Application Laid-open No. 47-2006, each time an electric pulse is applied to the print head in response to an electric signal for printing, a droplet of ink is released from the orifice by a change in the volume of the pressure chamber. This is an inkjet recording device that ejects ink (hereinafter referred to as the ink-on-demand method), but since the ink-on-demand method does not require ink recovery, it does not require a complicated ink supply system such as a filter or an ink pump. This has the great advantage of not requiring a high voltage source to control the deflection of the ink droplets, which naturally results in less ink consumption.

The structure of a conventional print head of this type of ink-on-demand method (for example, the method described in the above-mentioned Japanese Patent Application Laid-Open No. 47-2006) is as shown in FIG. It sprays droplets. In the structure of this conventional print head, in order to efficiently print characters such as alphanumeric characters or figures on recording paper, for example, as shown in FIG. 9 or FIG. , multiple print heads must be placed side by side. The juxtaposition of multiple printheads has drawbacks such as increased manufacturing costs, reduced miniaturization, and limited ability to reduce the spacing between ink droplets.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inkjet recording device that can reliably obtain ink droplets with a simple configuration.

The present invention includes an ink reservoir, a communication pipe that guides ink from the ink reservoir, a plurality of nozzles, and a plurality of pressure chambers in which an electromechanical transducer is attached to a part of the wall.
an ink flow path that individually communicates the plurality of nozzles and the plurality of pressure chambers; and a common ink flow path that communicates with the plurality of pressure chambers and can distribute and supply ink guided through the communication pipe to each of the pressure chambers. a pulse trap chamber, the nozzle, the pressure chamber, the ink flow path, and the pulse trap chamber are constructed of a pair of substrates made of photosensitive glass; The present invention is an inkjet recording apparatus having a print head whose portion is made of a flexible member made of synthetic resin.

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

FIG. 1 is a diagram schematically showing a conventional ink-on-demand type recording apparatus (Japanese Patent Laid-Open No. 47-2006). In the figure, reference numeral 11 indicates a device provided to record information on a recording medium 12. As shown in FIG. Reference numeral 12 denotes a recording medium related to the device 11, which is stretched between a feed roller 13 and a take-up roller 14, and is configured to move as shown by the arrow. Here, the relative movement between the device 11 and the recording medium 12 can be performed by an appropriate method, such as by moving either the device 11 or the recording medium 12, or by moving both of them.

Reference numeral 16 denotes an ink reservoir for storing the specific recording liquid to be used, which communicates via a communication tube 17 with a device for ejecting droplets, that is, a printing head 18. 19 is an electronic pulse generator for supplying pulses to printhead 18 via suitable electrical connection means 21 such as wires. The generator 19
does not operate at a resonant frequency, but rather calls out the droplets according to a predetermined pattern to be printed.

Reference numeral 27 denotes a suitable flexible plate 27 which can be deflected into the pressure chamber 26 when receiving an electric signal from the generator 19, and is composed of piezoelectric crystals 29 and 30, which are connected to each other by a conductive thin film. Glued into an assembly. That is, when a suitable voltage is applied from the pulse generator 19 to both sides of the platen 27 via the electrical connection means 21, the upper crystal 29 contracts and the lower crystal 30 expands, thereby making it flexible. The entire plate 27 is bent inward to the pressure chamber 26.

The inward deflection of the flexible plate 27 is shown in dashed lines in FIG.

In this method, the precise positioning of the device 11 relative to the recording medium 12 or vice versa in relation to the recording medium is determined according to the signal generated by the electronic pulse generator 19, which is determined by the information to be recorded. This is carried out by causing droplets to collide with the recording medium in a pattern, and for details, please refer to the above-mentioned Japanese Patent Laid-Open No. 47-2006.

To best record information, the droplets should be of precise and predetermined shape and volume. That is, each droplet follows exactly the electrical signal from the pulse generator 19, and the evenly spaced signals produce equally spaced, uniform droplets.

Now, the droplet 22 is ejected from the print head 18 by a sudden decrease in the volume of the pressure chamber 26, and thus this sudden decrease in volume displaces enough ink to form the droplet 22. up to pressure chamber 2
This is accomplished by flexing the flexible plate 27 within 6.

The deflection must be sudden enough to impart sufficient kinetic energy to the ink within the nozzle 28 to accelerate a portion of it beyond the escape velocity. Minimum escape velocity is the minimum velocity at which a column of ink protruding from a nozzle can be severed from the nozzle to form a single, separated droplet. The minimum escape velocity is determined by equating the energy required to form the droplet's surface and the droplet's kinetic energy.

Minimum escape velocity = [12σ/μD] ^1/2 where σ is the surface tension constant of the ink, μ is the density of the ink, and D is the diameter of the droplet.

As an example, the minimum escape velocity for a water droplet with a diameter of 0.015 cm is 167 cm/sec. To accomplish this, the flexible plate must set a minimum velocity to force the ink in the nozzle out of rest by the end of the liquid's travel so that the ink projects a column of ink approximately equal to the diameter of one droplet from the orifice. Pressure must be created in the ink to accelerate it to a speed that exceeds that of the ink. This minimum pressure is obtained by the following equation:

Minimum Pressure = 6Kσ/D where K is a dimensionless constant that defines the effective length of the nozzle for a given printhead, σ is the ink surface tension constant, and D is the droplet diameter. K is usually 4~
Between 40 and 40. If a 0.015 cm water droplet is ejected from the head with K = 10, the minimum pressure is 2.8 x
10 ⁵ DYne/cm ² or nearly 4 per square inch
It is a pound. The flexible plate 27 must also displace a larger amount of ink than the amount of droplets being ejected, since a portion of the ink displaced by the flexible plate will flow backwards through the inlet. It is. The action of the flexible plate produces a negative pressure pulse having a magnitude approximately equal to the magnitude of the positive pressure pulse as the flexible plate returns to its rest position.

A negative pressure pulse reverses the direction of ink flow within the nozzle. It promotes fragmentation of the column of ink protruding from the nozzle, producing separate droplets. The maximum pressure when the head is operating is
It is determined by the cavitation vacuum created in the liquid when a negative pressure pulse is applied.

The occurrence of cavitation depends on frequency and ink viscosity among various parameters, so it is very difficult to explain it analytically.
The practical upper limit for pressure in the print head is 3.5×
10 ⁶ Dyne/cm ² or approximately 50 points per square inch. In this way, when one pulse voltage is received from the pulse generator 19, the print head 18
ejects a discrete ink droplet 22 from an orifice 24. Each applied pulse voltage causes a single droplet 22 with a limited droplet volume to be deposited on the recording medium 12 as it passes through the print head 18, independently of the preceding signal. After the droplet has been ejected, following a substantially straight trajectory and forming a line 23 on the recording medium 12, the flexible plate 27 is in its normal position. and the ink meniscus is pulled back into the orifice by approximately the diameter of the droplet.
This ink must be in its original position before the print head again ejects another droplet, but capillary action of the liquid within the orifice provides the necessary force. The maximum speed at which the droplet group is ejected during this return process is approximately expressed by the following equation.

Maximum Drop Frequency [σ/ρKD ³ ] ^1/2 Taking a water droplet with a diameter of 0.015 cm again as an example, and assuming that this droplet is ejected by a print head with dimensions such that K = 10, the maximum drip frequency is about
It is 1440 drops. Smaller droplet sizes increase the maximum drop velocity and the maximum printing speed in characters per second. If K is 44 and the droplet diameter is
If printing at 0.0025cm, the maximum printing speed is per second
If the droplet size increases by 10 times (0.025 cm), the maximum print speed will decrease to 500 characters per second.
Although maximum drop frequency is discussed as the best condition in this example, faster jetting operations are possible even if the ink within the nozzle is not fully restored.

In other words, even though the shape, size, etc. of each droplet are not perfect, a higher jetting speed can be achieved in practice. Also, during a jetting operation, the momentum of the liquid in the print head causes the ink in the nozzle to rapidly return to the orifice.

The single printhead of the embodiment described above is well suited for multiple printhead arrays, as shown in FIG. FIG. 2 shows a cross section of one print head similar to FIG. In FIG. 2, the flexible plate consists of two parts: a cover slip (flexible wall) 31 and a piezoelectric crystal 32 adhered to the cover slip. When a voltage is applied to the crystal, the crystal contracts and the contracting action of the crystal 32 on the coverslip 31 causes the flexible plate to deflect inside the pressure chamber 33 and eject a droplet from the orifice 34 through the nozzle 36. Reduce the volume enough to cause

Cover slip 31 is glued to base plate 37. Since crystal 32 and coverslip 31 must be related to provide sufficient volume change and pressure for droplet ejection,
There are some clear relationships that always work optimally. That is, it is desirable that the neutral axes (points of zero tension) of the crystal, coverslip, and assembly lie in the midplane between them. This condition is satisfied by the following equation.

E ₁ · t ₁ ² = E ₂ · t ₂ ² where E ₁ and t ₁ are the elastic modulus and thickness of the crystal E ₂ and t ₂ are the elastic modulus and thickness of the coverslip, and E ₁ ≒ E ₂ If you choose a material that is
It is clear that t ₁ ≒ t ₂ in this equation. Third
The figures show a plan view and a partial sectional view of the print head shown in FIG. FIG. 4 is a sectional view taken along line A-A' of the print head shown in FIG. It will be seen that in width the width of the crystal 32 is smaller than the width of the pressure chamber 33. The difference in width between the two is selected to maximize the amount of deformation that can be achieved with a given width. We have found that the crystal only needs to be about 50-90% of the width of the pressure chamber, preferably about 70%, and should be centered so that the gaps on both sides are equal. Ta.

The pressure chamber 33 and the crystal 32 have a long rectangular shape. In this shape, the width (short side of the rectangle) is determined to provide sufficient pressure, and the length (long side) is determined to provide sufficient volumetric deformation. If the long side is greater than 20 times the width, the constant K becomes undesirably large, lowering the maximum drip frequency and increasing the required minimum pressure. On the other hand, the long sides should be greater than twice the width to minimize the area that has less than the maximum deflection at each end of the crystal. Therefore, the shape of the piezoelectric crystal to be attached to the flexible wall should be determined so as to satisfy the following conditions.

2a＜b＜20a Here, a is the width of the electromechanical transducer, b is the length of the electromechanical transducer, It is.

The diameter of the orifice 34 is preferably small to speed up the recovery of the ink caused by capillary action and to maintain consistent droplet size. Nozzle 3
6 must be long enough so that the droplet follows a substantially straight trajectory in the same direction as the nozzle and from the center of the nozzle, but without increasing the constant K and the required pressure and reducing the maximum printing speed. It should not be so long that it becomes a problem. We have found that the length of the nozzle should be between 2 and 4 times the diameter of orifice 34.

We have also found that when a group of droplets hits the printing surface, the diameter of the droplet in flight is
Produces 4 times as many print spots. It is clear that the smaller the droplets, the more efficient the printing action will be in terms of the ink required to cover a given area. In addition, resolution and maximum printing speed are increased when the ejected ink droplets are small. In FIG. 4, a state in which the crystal 32 and the cover slip 31 are deformed inwardly into the pressure chamber by voltage application is shown by two-dot chain lines.

FIG. 5 shows a perspective view of a set of printheads consisting of seven ink ejection systems. The seven inkjet groups can utilize a commercially available character generator using a 5x7 dot matrix. However, the printing device works well with other dot matrices and with a set of printheads consisting of groups of ink ejection systems in which the vertical component of the matrix is between 5 and 16. Each ink jetting system consists of the same elements as described in detail for a single jetting system (FIG. 2).
FIG. 5 shows a portion of a printhead consisting of a ceramic base plate 61 having etched cavities to form the elements of the jetting system.
In this way, the plate 61 has seven nozzles 62,
7 nets 63 and 7 ink pressure chambers 64
has. Cover slip 68 is glued to base plate 61. Moreover, seven piezoelectric crystals 71 to 77 are bonded to the upper part of the cover slip above the pressure chamber.

61 also has a pulse trap chamber 66 etched therein to connect with the nozzle 62 and its respective pressure chamber. When filled with ink, the pulse trap chamber 66 acts to absorb the return pressure of the ink. During printing, when a pulse voltage from the pulse generator 19 is applied to the crystals 71 to 77, the crystals and the coverslip are bent inward into the pressure chamber 64, rapidly reducing the volume of the pressure chamber. Apply a sudden pressure pulse to the ink inside the pressure chamber. This pressure pulse causes the ink in the pressure chamber to be ejected as a droplet from the corresponding nozzle 62, while at the same time pushing the ink back toward the pulse trap chamber 66. The volume thus displaced inside the pressure chamber 64 must necessarily exceed the amount of ink ejected as one droplet. Further, in FIG. 5, ink from the ink reservoir 16 is connected to a communication pipe 17 and a valve assembly (not shown).
An aperture 67 is shown for access to the pulse trap chamber 66 through the pulse trap chamber 66.

The ceramic base plate 61 and cover slip 68 are preferably made of a photosensitive glass material that can be precisely etched.

71-77 are seven piezoelectric crystals overlapping with and bonded to the cover slip 68. The crystal is made of a suitable material that can be deformed by electrical pulses. One suitable material is the available lead zirconate-salt titanate ceramic. Others include Rothsiel's salt, ammonium-dihydrogen-phosphate, lithium-sulphate and barium titanate.

FIG. 6 is a block diagram for controlling the print head. Alphanumeric information sources 101
is fed into the decoder 102.

The source of information may be typewriter keys, computer readouts, or other alphanumeric sources. Decoder 102 provides the information necessary to form alphanumeric characters in 6-bit codes. Various available decoders may be used. The 6-bit information or address is provided to character generator 103. Dot matrix character generators are available that use 5x7 bits and have 64 characters. The character generator is also supplied with a strobe pulse train from clock 104. The pulse train reaches the drive circuit 106 to effect the seven outputs of the character generator 103. The drive circuit 106
tells how the various crystals should be sprayed to print the German letters necessary to form the alphanumeric characters. Seven outputs from the drive circuit 106 reach crystals 71-77 located above the pressure chamber. The size of the droplet can be controlled by varying the magnitude of the drive voltage applied to the crystal.

The increased drive voltage generates larger droplets,
Reduced drive voltage produces smaller droplets.

This method allows the density of printed characters to be controlled. As an example, the size of a droplet printed on recording paper from a nozzle with a diameter of 0.010 cm is approximately 0.010 cm.
It can be changed from cm to 0.060cm. In operation of the injector, the information determining the symbol to be printed is converted into a 6-bit code coming from the information source 101 and selecting a 5.times.7 matrix in the character generator. A drive circuit activates particular crystals as the print head moves relative to the recording medium. Each time a drive pulse is fired, the amount of ink within one or more pressure chambers is reduced such that it is optionally ejected into a single droplet toward the recording medium. This is entirely in accordance with the requirements and provides a recording system that does not fire during idle times, ie between symbols being printed or when the print head is inactive. The desired droplet may form or not form as the print head advances relative to the recording medium. A translation motor is conveniently used to move the printhead to form each character on the X-axis. On the other hand, droplets can be formed on the Y axis by selectively activating specific drive crystals that are fired. As described above, if the apparatus according to the present invention is used, for example, printing out from a computer can be done without the high cost of the currently used impact printers.
Can be produced at high speeds (over 1000 characters per second) without noise and high power requirements.

FIG. 7 shows another embodiment of a print head having seven ink ejection systems, and is an exploded view showing the base plate 61 combined as one element. In the figure, 61 is a base plate which has a cover slip 68 glued onto the base plate for closing the chambers, nozzles and nets mentioned above. The cover slip 68 has two apertures, unlike the base plate 61 which has an etched chamber. The larger one forms a pulse trap chamber 66, and the other is a valve opening 69. Base plate 61 and cover slip 68 are manufactured by Corning Grass Corporation of Corning, New York under the trade name "Photoceram."

78 is a tube fitting that fits into the aperture 67 and is located at the bottom of the base plate. A tube (not shown) connects the ink reservoir to the fitting. A valve seal 79 having an opening in the center is attached to the upper part of the device where the valve opening 69 is located. Reference numeral 81 denotes a partition wall that overlaps the two openings and forms the upper wall of the pulse trap chamber 66. Further, the partition wall 81 is provided with a valve seal 7 so as to limit the deflection when a plug, which will be described later, operates to open and close the opening 69 from above the partition wall.
9 and has a circular raised portion 81' on the opposite side thereof.

Bulkhead 81 is made of a flexible material, such as Saran Plastic (Dow Chemical Company, Midland, Mich.).

82 is a control frame that overlaps with the partition wall 81;
Preferably made of steel. The frame 82
are the pulse trap chamber 66 and the valve opening 69.
It is made to have a shape substantially corresponding to the partition wall 81 so as to cover both sides.

The frame 82 also has an aperture punched to fit the aperture 69 on the base plate 61 and a U-shaped notch forming a long tongue 83. The tongue 83 is formed by folding the sides of the tongue to form a channel with one long rotating arm couple.

84 is a bar that controls the upward movement of the tongue piece 83. Reference numerals 86 and 87 are strain gauges installed at the base of the tongue 83 and designed to sense the pressure inside the pulse trap chamber 66. It senses deflection and also plays a role in issuing control instructions. That is, as the strain gauge 87 exhibits a deflection corresponding to the change in pressure, it causes the gate valve to open in relation to the sensed pressure. 88
is a control plug regulated by a valve beam 89, which is reliably protected by the beam 89, the bulkhead 81 and the valve seal 79. balm beam 8
9 is provided on the cover slip 68 and is preferably a stainless steel reaction plate.

91 is one piezoelectric crystal electrically controlled by deflection gauges 86 and 87;
It is glued to the beam 89. When the deflection gauge 86 detects a change in deflection due to the rise or fall of the tongue 83, the piezoelectric crystal contracts or expands in proportion to the indicated deflection and opens or closes the gate in a proportionate manner. Close the barrel.
The gate valve regulates the outflow through the aperture 69. On the other hand, ink can flow into the pulse trap chamber 66 below the partition wall 81 through the aperture 69 and the flow path 69'. A set screw 90 serves to adjust the beam 89 so that ink does not flow through the aperture 69 when no voltage is applied to the crystal 91.

Seven piezoelectric crystals 71-77 are glued onto each chamber in the base plate 61 of the device. Similarly, leads from circuit board 92 connect flexure gauges 86, 87 to control the device.
and connected to a piezoelectric crystal.

The printed circuit board 92 has 14 conductive planar cables 9
Supplied by 3.

The cable 93 is connected to a printed resistor circuit board 94 and then to a 14 pin dip socket.

According to the configuration of the present invention, the nozzle, the pressure chamber, the ink flow path, and the pulse trap chamber are constituted by a pair of substrates made of photosensitive glass, so that the structure is extremely simple. Additionally, a pulse trap chamber equipped with a print head and whose wall was partially covered with a flexible member made of synthetic resin prevented mutual interference between the nozzles during ejection, making accurate printing possible.

Furthermore, this device can produce reliable droplets with a simple configuration. It should be noted that the present invention should not be limited to the above embodiments, but includes applications, modifications, etc. without departing from the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing a recording apparatus, and a cross-sectional view shows a droplet ejecting means. FIG. 2 is a sectional view of another embodiment of the print head used in the inkjet recording apparatus of the present invention. Figure 3 is the second
FIG. 3 is a top view and partial cross-sectional view of the print head shown in the figures; Figure 4 shows the printing bed A shown in Figure 3.
-A' sectional view. FIG. 5 is a schematic diagram of a print head having seven ink ejection systems. FIG. 6 is a block circuit diagram coupled to the print head of the present invention. FIG. 7 is an exploded parts arrangement diagram of still another embodiment of the printing bed. 11 is a device, 12 is a recording medium, 16 is an ink reservoir, 17 is a communication tube, 18 is a print head, 19 is an electronic pulse generator, 21 is an electrical connection means, 22 is an ink droplet, 24, 34 are orifices, 26,3
3 and 64 are pressure chambers, 27 is a flexible plate made of piezoelectric crystals 29 and 30, 28, 36
and 62 is a nozzle, 31 and 68 are coverslips, 32 and 71 to 77 are piezoelectric crystals,
37, 61 are base plates (lower plates) 6
6 is a pulse trap chamber, 67 is an opening communicating with 17, 102 is a decoder, 103 is a character generator, 1
04 is a clock, and 106 is a drive circuit.

Claims (1)

[Scope of Claims] 1. An ink reservoir, a communication pipe that guides ink from the ink reservoir, a plurality of nozzles, a plurality of pressure chambers each having an electromechanical transducer attached to a part of the wall, the plurality of nozzles and the plurality of The pulse trap chamber has an ink flow path that communicates with the pressure chambers individually, and a common pulse trap chamber that communicates with the plurality of pressure chambers and can distribute and supply ink guided through the communication pipe to each of the pressure chambers. , the nozzle, the pressure chamber, the ink flow path, and the pulse trap chamber are constructed of a pair of substrates made of photosensitive glass, and a part of the wall of the pulse trap chamber is made of a flexible synthetic resin. An inkjet recording device comprising: a print head made of a flexible material;