FI61837B - TRYCKNING GENOM BLAECKSPRUTNING - Google Patents

Abstract

1519629 Selective printing SILONICS Inc 21 July 1975 [19 July 1974] 03901/78 Divided out of 1519627 Heading B6F The subject of this Specification is identical to that of Specification 1,519,627, but the claims are directed to the control of the ink pressure in the common chamber connected to each of the orifice containing chambers.

Description

rBl ADVERTISEMENT] PUBLICATION

jJHa ljk} utlAggningsskeuft 618 37 «ygNat c Patent granted ni /> * non • gÖ HS) Patent ncddelat 9“ “^ ^ ^ (51) Ky.lk?/int.a.3 BJJ / 04 // G 06 K 15 / 00 FINLAND —FINLAND (21) P »» nulh »k« mu «- Pxenttmöknlng 752081 * (22) H» k * ml »pllv4 - AnsOkningidag 10.07 * 75 ^ ^ (23) AlkupUvt - Glltighatsdig 18.07.7 5 (41) ) Tullut | ulkls «ksl - Bllvlt offentllg 20.01.76

National Board of Patents and Registration .... ...,,., „, 1 (44) Date of issue and hearing fee. -

Patent and registration authorities An «ek» n utl »gd and utl.» Krlften publkerad 30.06.82

(32) (33) (31) Caught privilege —Begird priorltet 19.0 7.7U

USA (US) I + 89985 (71) System Industries, Inc., Sunnyvale, California 9-086, USA (US) (72) Edmond L. Kyser, Portola Valley, California, Stephan B. Sears,

Belmont, California, USA (7 * +) Berggren Oy Ab (5M Inkjet Printing - Tryckning genom bläcksprutning

The present invention relates generally to a non-compression printing apparatus and method, and more particularly to an apparatus and method * in which printing ink is ejected out of a die using volume displacement.

Historically, printing has been accomplished by placing ink on a specially shaped font, i.e., a support, and mechanically pressing it against a deposit substrate such as paper to form an print on that substrate. Recently, non-compression printing devices have been developed in which data patterns (alpha numerals, graphics, etc.) are deposited on a storage medium.

This invention relates to a droplet ejection device in which a plurality of adjacent nozzles communicate with separate ink chambers connected by a common heart rate trap chamber to an ink reservoir. Each chamber has an electromechanical transducer for rapidly changing the volume of the chamber due to the electrical heart rate signal so that one drop of ink, the volume of which depends on the magnitude and duration of the electrical signal, ejects out of the respective nozzle asynchronously when the signal is required. The term "asynchronous" in this specification refers to the property that a specific rhythmic rate is absent. Essential to the printing of the material to be understood is that the dropout is asynchronous, given that the droplets follow a substantially straight flight path to the printing medium and do not change direction. The invention also relates to a printing apparatus using such a multi-nozzle printing head for printing various shapes, such as alpha-numeric and graphic data patterns, and to a method of printing such shapes.

Figure 1 is an exploded perspective view of an ink jet printing head according to the invention.

Figure 2 is a plan view of a part of a multi-chamber printhead according to the invention.

Figure 3 is a circuit diagram of an ink control circuit for use with the printhead of Figure 1.

Figure 4 is a schematic representation of a system incorporating an ink jet printing apparatus according to the invention.

Fig. 5 is a circuit diagram of a control circuit used in the system of Fig. 4.

Figure 6 is a horizontal partial sectional view of an alternative embodiment of the nozzle.

Figures 1 and 2 show a multi-nozzle coil 10 comprising seven ink jet printing devices constructed in accordance with the invention. The number of printing devices seven is compatible with commercially available character generators using a matrix five points wide and seven points high. However, the system also works well using matrices of other sizes and a battery with between five and sixteen printing devices for the vertical component of the matrix. Figure 2 shows the lower part of a radiator comprising a ceramic base plate 11 in which recesses are etched to form elements of a printing device. Thus, the base plate 11 has seven nozzles 12, seven necks 13 and seven ink chambers 14. On top of the ink chambers, at the top of each radiator in Figure 1, there is a cover strip 18 to which seven piezoelectric crystals 21-27 are attached. 16, which communicates with each ink chamber opposite the nozzles 12. The heart rate trap chamber 16, when filled with ink, serves to absorb the back pressure of the ink. As will be explained in more detail below, when one of the crystals 21-27 causes the cover strip 18 to bend into one of the ink chambers 1 * 1, a drop 7 ejects from the corresponding nozzle 12 while the ink is forced backwards towards the heart rate trap chamber 16. Thus, the volume displaced from the ink chamber must be larger than the volume of the ink ejected as a droplet.

To accurately store information on the storage tray 15, the droplets follow a substantially straight flight path from the nozzles 12 of the printhead 10 to the storage tray 15. In this manner, careful positioning of the storage tray relative to the printhead 10 or vice versa causes the droplets to collide as a predictable determined by the information to be printed. To best store information, the droplet must be accurate and predictable in shape and volume. In other words, each drop must carefully follow the electronic signals from the controller so that evenly spaced, uniform signals cause evenly spaced, uniform droplets.

The rush of each drop from the end 10 is caused by a sudden decrease in volume in one of the chambers 14 in the selected chamber. This sudden decrease in volume is achieved by shrinking the crystals on top of the chambers due to the electrical signal, thus bending the cover strip plate 18 in the selected chamber 14 so as to displace enough ink to form a drop. The bending must be sudden enough to provide a sufficient amount of kinetic energy to the fluid in the relevant nozzle 12 to accelerate a portion of the droplet to a rate greater than the release rate. The release rate is the lowest rate that causes the ink "plug" protruding from the nozzle to detach from the nozzle and form a droplet.

The release rate can be determined by plotting the kinetic energy of the droplet equal to the energy required to form the droplet surface: - | l / 2 12σ release rate = ^ where σ is the surface tension constant of the liquid, P is the density of the liquid and D is the diameter of the droplet. For example, a water droplet with a diameter of K 61837 0.015 cm has a release rate of 167 cm per second.

To accomplish this, the crystal on the bent lid 18 must develop a pressure in the liquid that is capable of accelerating the liquid in the nozzle from rest to a rate greater than the release rate until the liquid has moved so much that a "droplet" plug protrudes from the nozzle. This minimum pressure is obtained from the equation 6K σ

minimum pressure = D

where K is the dimensionless constant depending on the geometric shape of the device, σοη is the surface tension constant and D is the droplet diameter. K is usually between 4 and 40. With a 0.015 cm diameter drop of water pushed from an end with a K equal to 10, the minimum pressure is 2.8 x 10 6 dynes / cm 2, i.e. 0.28 kg / cm 2.

The bent lid strip 18 must also displace a larger amount of liquid than the volume of the droplet ejecting, as some of the liquid displaced by the lid strip flows back into the heart rate trap chamber 16.

When the droplet is ejected, the plate returns to its normal position and the end surface of the liquid is retracted in the nozzle by approximately one droplet diameter. This amount of liquid must be replaced before the printing device can be made to eject a new drop again, and the capillary action of the liquid in the nozzle provides the necessary force. During this replacement process, the maximum speed at which a droplet can be ejected is approximately 1/2. . . σ maximum point frequency = - _ρΚϋ3_ In this system, point frequencies as high as 50,000 drops per second can be reached, depending on the value of the constant K, which in turn depends on the geometric shape of the device.

The crystal on the lid 18 operates in such a way that when the crystal returns to its rest position, a negative pressure heart rate is generated which is approximately equal to the positive pressure heart rate. A negative pressure pulse reverses the direction of fluid flow in the nozzle, which helps the "plug" protruding from the nozzle to detach to form a free droplet. The maximum pressure at which the printhead can be operated is determined by the occurrence of cavitation during the corresponding negative pressure pulse. The occurrence of cavitation is quite difficult to express analytically, as it depends not only on other parameters for frequency and viscosity. The practical upper limit of the print head pressure can be considered to be 3.5 x 10 ° dynes / crrm, i.e. 3.5 kg / cm.

The opening 17 is connected between the ink source 5 and the valve combination described below. As shown in Fig. 1, there is a cover strip 18 on the base plate 11, which is attached to it so as to close the chambers, nozzles and necks described above. Unlike the plate 11, in which the chambers are etched, the cover strip 18 has only two openings: a large opening delimiting the heart rate trap chamber 16 and a valve opening 19 · Both of these ceramic plates 11 and 18 can be suitably made of "Photoceram" made by Corning Glass Corp ., Corning, New York. Attached to the cover strip 18 are seven piezoelectric crystals 21-27. The underside of the lower plate 11 has a pipe connection 28 which fits into the opening 17 (Fig. 2). The tubes 6 connect the ink source 5 to the connection 28.

Above the radiator, at the valve opening 19, a valve seat 29 is attached. On the cover strip 18, at said two openings 16 and 19, there is a membrane 31. The membrane 31 is preferably made of a flexible material such as Saran plastic (trade name of Dow Chemical Co., Midland, Michigan). ). The membrane 31 forms the upper wall of the heart rate trap chamber 16. On top of the diaphragm 31 is a pressure regulator frame 32, which is preferably made of steel. The frame 32 is suitably made to generally outline the outline of the diaphragm 31 because both cover both the chamber 16 and the valve opening 19. The frame 32 is stamped with an opening at the opening 19 in the plate 11 and a second U-shaped cut to form a long tongue 33. The tongue 33 is formed by folding its sides up into a U-shape so as to obtain a long torque arm. The movement of the tongue 33 is limited by a rod 34 attached to the frame 32. The base of the tongue 33 has two strain gauges 36 and 37, one of which serves to measure tension at the point where the tongue 33 joins the rest of the frame 32 and the other serves as a reference. As will be explained below, the strain gauges detect the pressure in the heart rate trap chamber 16. As the ink flows into the heart rate trap chamber 16 at a higher pressure, 6 61837 it lifts the membrane 31 and the tongue 33 thereon.

When the strain gauge 37 indicates a stress corresponding to the change in pressure, it generates an electrical signal which, as will be explained in detail below, causes the spool valve to open relative to the detected pressure. This spool valve regulates the flow of ink through the opening 19. The spool valve consists of a plug 38 attached to the valve beam 39, a diaphragm 31 and a seat 29. · When the plug 38 rises from the opening 19, ink can flow out through the opening 19 into the heart rate trap chamber 16 under the membrane 31.

The adjusting plug 38 is guided by a beam 39. The beam 39 is preferably a stainless steel reaction plate fitted immediately over the cover strip 18. Attached to the beam 39 is a piezoelectric crystal 41 which is electrically controlled by the strain gauges 36 and 37 by means of the circuit shown in FIG. When the strain gauge 36 detects a change in tension due to the rise or fall of the tongue 33, it generates an electrical signal in the circuit which causes the piezoelectric crystal 41 to shrink or swell according to the detected tension, which opens or closes the slide valve. The positioning wool 40 can be positioned on the beam 39 so that no ink flows through the opening 19 when no voltage is applied to the crystal 41.

Figure 3 shows a circuit diagram of the pressure control circuit. Voltage meters 36 and 37 are connected in series across a +5 volt DC power supply and their connection point is connected to the second input terminal of the differential amplifier circuit 30. A variable resistor 20 in series with a standard resistor 35 is connected in parallel with the voltmeters 36 and 37 across said +5 volt DC power supply. The connection point of the resistors 20 and 35 is connected to the second input terminal of the differential amplifier circuit 30. The output signal of the amplifier circuit 30 is applied to the crystal 41 and depends on the difference of the input signals of the amplifier circuit 30. The variable resistor 20 is thus the control device by which the system can be calibrated to the normal resting state of the system pressure, which pressure is measured in the heart rate trap chamber 16 (Figure 1). It is usually preferable that the pressure in the chamber 16 of the heart rate trap 7 61837 be slightly negative so that the end face of the ink in the nozzle is convex inwards. However, any pressure is appropriate as long as the ink remains in the nozzle and does not drip out of it. When the resistor 20 is set to the desired value, the strain gauge 36 is calibrated to measure the stress caused by the deflection of the membrane 31. The output signal of the pressure control circuit of Figure 3 is applied to a piezoelectric crystal 41 which moves the beam 39 to open and close the ball valve 38 against the valve seat 29.

The above-mentioned seven crystals 21-27 are each attached to the cover strip 18 each at its own inner chamber of the radiator plate 11. Crystals 21-27 are electrically connected to the printed circuit board 42 by appropriate conductors (not shown). Similarly, from the plate 42, conductors lead to the strain gauges 36 and 37 and the piezoelectric crystal 41 to control the system. The printed circuit board 42 is connected by a 14-wire flat cable 43 to a printed resistor circuit board 44 and then to a fourteen-pin plug connector 46. The entire combination shown in Figure 1 forms a single print head assembly equipped with a battery of seven ink jet printers.

To match the commercially available brand developers (5x7 dot groups) and generally accepted weight sizes (each brand 0.25 cm high), the seven different nozzles of the press coil must be 0.036 cm apart. Of course, the printing method according to the invention can be adapted to other types of font sizes, and the die number and droplet size can be changed within the limits set by the various components. The spacing of the nozzles can be selected from 0.050 cm (maximum practical point size) to 0.012 cm (the smallest nozzle spacing that can be made by the manufacturing technique of the system of Figure 1). To facilitate manufacture, a series of seven nozzles 12 can be made so that the diameter of the nozzles is between 0.005 and 0.025 cm. The distance between the first and last nozzle of the series must not exceed 0.25 cm to fit a standard font size. For example, in most typewriters, the height of the font is approximately 0.25 cm, and the device according to the invention strives for approximately the same size.

The crystals can be made of any suitable material that deforms due to an electrical impulse. One suitable material is lead-8,61837 zirconate-lead titanate ceramics, which are commercially available. Others include Rochelle salt, ammonium dihydrogen phosphate, lithium sulfate and barium titanate. When a voltage is applied across one of the crystals 21-27, the crystal shrinks, and the effect of the shrinking crystal on the lid strip 18 causes it to bend inwardly into the chamber 14 below the shrinking crystal, reducing the chamber volume enough to drop a drop out of the corresponding nozzle 12. be 1-3 times the average cross-sectional dimension of the nozzle.

Since the crystal and the lid strip must interact to displace the droplet to achieve the required volume displacement and pressure, there are a number of precise conditions that must be met to achieve the best performance. It is desirable that the neutral axis (zero stress line) of the crystal-lid-strip assembly be at the interface between them. This condition is met provided that (Et2) crystal = (Et2) cover strip where E is the modulus of elasticity of the component in question and t is its thickness.

As can be seen from the drawing, the crystals 21-27 are narrower than the rectangular pressure chambers 1 * 1, and this dimensional difference is chosen so that the displacement achievable at a given width is as large as possible. Crystals 21-27 must be centered with respect to the chambers 1 * 1 so that the clearances are equal on both sides. Pressure chambers 14 and crystals 21-27 are selected to have long rectangular shapes. The width of this shape (smaller dimension of the rectangle) is chosen to provide the required pressure, and the length (larger dimension) is selected to provide the necessary volume displacement. If the length exceeds 20 times the width, then the geometric factor K becomes harmfully large, which lowers the maximum point frequency and increases the required minimum pressure. On the other hand, the length must be greater than twice the width to minimize the area at the ends of the crystal that bends less than the maximum deflection. The volume of each pressure chamber 33 should be between 1.6 x 10 5 and 1.6 x 10 2 cm 2.

If "A" represents the length of the shorter side of this hypothetical rectangle and "a" and "b" the width of the crystal on it and the corresponding length, respectively, the dimensions of the crystal must be chosen so that they satisfy the conditions: 0,5A ^ a ^ O , 9A and 2a - =: b <r20a

The diameter of the orifice of the nozzle is preferably small to promote ink replacement due to the capillary effect and to determine the droplet size. The nozzle 12 must be long enough to ensure that the droplet follows a substantially straight, parallel and concentric trajectory of the nozzle, but not too long, which would increase the geometric factor K, increase the required pressure and reduce the maximum weight velocity.

It has been found that the length of the nozzle should be 2-4 times the diameter of the nozzle orifice.

The use of a volume displacement device in an ink jet printing device requires that the ink system be completely airless and that no cavitation occur. For this reason, it is desirable to remove gases dissolved in the ink that may separate from the solution during a negative pressure pulse. This can be done by boiling the ink or removing air by means of a vacuum. If such an “airless” ink is exposed to the atmosphere, it will rapidly re-absorb gases to their original equilibrium state, so a sealed container and a pressure generation system that isolates the ink from the atmosphere are preferably used.

Figure 4 is a schematic representation of a printing equipment control system. The source of alpha numeric characters 101 is input to decoder 102.

This source can be a typewriter font, a computer reading, or some other source of alpha-numeric characters. Decoder 102 provides the information necessary to define the relevant alpha-numeric character as a six-bit code. These six information bits are fed to the character generator 103 · Dot matrix character generators with 64 characters using five times seven bits are commercially available from a variety of sources. The signal generator is also supplied with a measurement signal heart rate sequence from clock 104. This heart rate sequence also enters the control circuit 106 as well as the seven outputs of the signal generator 103. The controller 106 sends trigger instructions to the various crystals to press the desired points to form alpha-numeric characters. The seven outputs of the control circuit 106 go to the crystals 21-27-

Figure 5 shows a control circuit for each crystal. The seven outputs of the character generator are connected to the inputs of seven separate AND gates 105, the second input of which is supplied with a control signal controlled by the measurement beats. The outputs of the AND gates are fed through separate resistors 110 to the base electrodes of separate NPN transistors 111. The emitter electrodes of transistors 111 are grounded. Each crystal 21-27 is grounded on one side and connected on the other side in series with a separate adjustable resistor RC61-EC67 to the collector electrode of its own separate transistor 111. Each collector electrode is also connected to a 130 volt source via a separate 10 KP resistor 112. Transistors 111 are all suitable high voltage low energy transistors.

The size of the dot and the rate at which it is ejected can be electronically adjusted in a variety of ways, such as by varying the energy content of the control heart rate or by changing the shape of the heart rate while the energy content remains substantially unchanged. The circuit shown in Figure 5 is designed to control the point size and speed by changing the shape of the control heart rate, more specifically by changing the rise time of the control heart rate, i. the rate at which the voltage is applied to the crystals. Crystals have an inherent capacitance according to their structure and shape. Thus, when a voltage of 130 volts "Source" is applied to the crystal by the switching effect of one of the transistors 111, the circuit functions like an RC circuit, with the resistors RC 61-67 acting as the variable to provide the control. Resistors 61-67 can be adjusted to give a time constant ranging from 5 to 100 microseconds, which is particularly advantageous in character printing applications where the speed of all seven drops must be equal while small variations in volume, i.e. size The size of the dots can be adjusted by changing the magnitude of the control voltage applied to the crystals.Increasing the control voltage increases the droplet size and decreasing it decreases the droplet size.This way, the darkness of the printed characters can be adjusted. The size of the dot printed from a 0 cm diameter nozzle can be varied from approximately 0.010 cm to 0.060 cm.

n 61837

When using the device, the information that determines which character to print comes from source 101 and is decoded into a six-bit code that selects the correct five times from the seven matrix character generator 103 · The character generator 103 causes the control circuit 106 to trigger the corresponding crystal as the battery moves relative to the substrate.

Each time the control heart rate is triggered, the ink volume in one or more closed chambers 1 * 1 decreases due to the associated crystal deflection, suddenly ejecting one drop asynchronously toward the printing substrate. This results in a note system that is fully controllable and does not operate during idle times between characters or when the printing device is not in use. The desired points may or may not be formed as the print head moves stepwise relative to the printing base. To move the print head, a stepper motor can be suitably used to generate each character on the X-axis, while points can be formed on the Y-axis by optionally triggering the private control crystals.

It has been found that droplets, when they collide with the printing surface, produce printed dots with a diameter of 2-H times the diameter of the flying droplet. Thus, it becomes apparent that the smaller the droplets, the more efficient the printing process is in terms of ink demand per specific surface area. In addition, when less ink is used per drop, the resolution is also improved and the maximum print speed achievable is increased.

Fig. 6 shows an alternative primary nozzle shape application, in which ink is fed from two common openings 83 and 8a delimited by a partition 85 from a common pressure chamber 1 * 4 'in the base plate 11. For each heartbeat of the compression plate (not shown), two drops 86 and 87 are ejected simultaneously in exactly the same way as a lone droplet would be ejected from an undivided nozzle 12.

Using the device according to the present invention, for example, a computer list can be produced at high speed (up to 1000 characters per second) without the cost, noise and energy requirements associated with current printing presses. The device is light in weight and very reliable.

Claims (15)

An ink jet writing device having a plurality of writing units, each comprising an ink chamber having an outlet opening, wherein actuating means are provided for providing pressure rises in the chambers by deforming a deformable wall of each chamber, characterized by the chambers (14) being provided common elongate housing (11) spaced from each other by elongated wall means (13) extending in the longitudinal direction of the housing, a common flexible wall element (18) spanning the chambers with sealing abutment against the edges of the wall means 61 to 837 to form said deformable wall of each . and each outlet chamber opening (12) is provided at one end thereof between the two elongated wall members which restrict the chamber. 2. Device according to claim 1, characterized in that the housing (11) also contains a pressure pulse scavenging chamber (16) arranged in direct fluid communication with the chambers spaced from the outlet openings, ink being supplied to the chambers via said pressure pulse scavenging chamber. Device according to claim 2, characterized in that an ink source (5) pressurized in fluid communication with the pressure pulse capture chamber. 4. Device according to claim 2 or 3, characterized by a pressure sensing device (33, 36, 37) arranged in cooperation with the pressure pulse capture chamber (16) for sensing the ink pressure therein. Device according to claim 4, characterized in that a valve (38) is arranged between the ink source (5) and the pressure pulse capture chamber (16), which valve is operable to the closed or open state depending on a control signal, and that the pressure sensing device (33, 36, 37) controlled means are provided to generate control signals for the valve to maintain the ink pressure in the pressure pulse capture chamber within a predetermined range. Device according to claim 5, characterized in that the predetermined pressure range lies between the maximum positive and negative capillary pressures which can be generated in the chamber outlet openings (12). Device according to any of the preceding claims, characterized in that each outlet opening is divided into a plurality of zones (83, 84) with parallel axes, whereby the ink is divided into smaller droplets upon ejection. Apparatus according to any one of claims 4, 5 or 6, characterized in that the pressure sensing device comprises a diaphragm (31) extending over an opening to the pulse pressure chamber 61837, the tongue (33) fixed outside the pressure pulse capture chamber to move. on it, when the diaphragm is actuated in response to altered ink pressure in the pulse pressure capture chamber, and means (36, 37) arranged to provide a mat corresponding to the movement of the tongue to the ink pressure in the pulse pressure capture chamber. Device according to any of the preceding claims, characterized in that said actuator for providing pressure rises for each chamber is constituted by a piezoelectric element (21-27), the width of which is smaller than that of the chamber. Device according to any of claims 1-8, characterized in that said actuator for effecting pressure rises comprises a plurality of piezoelectric elements (21-27), wherein an electric drive circuit (106) is connected to each of the piezoelectric elements via a independent resistance-capacitance circuit (RCgI-g4), at which each resistance is adjustable to allow adjustment of the drop ejection rate at each chamber. Device according to claim 10, characterized in that the resistance (61-67) of each resistance capacitance circuit is variable to provide a time constant of the circuit of between 5 and 100 microseconds. Device according to any of claims 1-8, characterized in that said actuator for effecting pressure rises comprises a plurality of piezoelectric elements attached to the outside of the common flexible wall element (18) over each of the chambers (14), thereby deforming it. flexible wall element inset against the chamber upon electrical activation. Device according to any of claims 9, 10, 11 or 12, characterized in that each of the chambers is rectangular with the outlet opening in liquid communication with one end, each piezoelectric element being arranged over such a rectangular chamber and having a rectangular shape corresponding on the following conditions: 0.5 A <a <0.9 A 2 A <b <20a