JPH07309013A - Chip level control of spot size of ink jet printer - Google Patents

Abstract

PURPOSE: To hold droplets discharged from a plurality of tips to a constant size by providing a signal generator generating a pulse signal and a plurality of pulse signal modifiers. CONSTITUTION: A bias voltage divider circuit 160 provided with resistors 134-140 is inserted between an apparatus circuit 120 and a comparator 100. The resistors 134, 136 act as a voltage divider to reduce the magnitude of an inclination signal corresponding to control quantity corresponding to the values of the resistors 134, 136. The resistors 138, 140 act as a bias circuit to permit the addition of a bias value to the inclination signal corresponding to the values of the resistors 138, 140. By setting the channels of the resistors 134-140, the time width of the pulse signal applied to a heating element 26 is changed at every tip thereby to keep the constant spot size of droplets discharged from different tips.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a controller for an ink jet printer, and more particularly to a spot size controller for an ink jet print head, which controller controls a plurality of print heads on the print head based on the physical characteristics of each chip. The pulse signal applied to each of the chips is changed. In heated inkjet printing, ink droplets follow digital instructions to create the desired image on the copy surface.
It is selectively ejected from a plurality of drop ejectors on the pudding head. Typically, the printhead has ejectors arranged in a straight line for transferring ink to the copy sheet. The ejector is typically contained on multiple chips (known as a die module or integrated circuit). The pudding head moves back and forth with respect to the surface, for example to print characters. That is,
The linear array structure extends over the entire width of the copy sheet (eg, plain paper sheet) and is adapted to move with respect to the print head. Ejectors typically include capillary channels or other passages that are connected to one or more common ink supply manifolds. Ink from the manifold is held in each channel in response to an appropriate digital signal until the ink in the channel is rapidly heated and vaporized by a heater element located in the channel. This rapid evaporation of ink creates bubbles that cause a fixed amount of ink to be ejected through the nozzle onto the copy sheet. A patent showing a general shape of a typical inkjet print head is, for example, U.S. Pat. No. 4,774,530.

When a certain amount of ink in the form of droplets is ejected from the ejector onto the copy surface, the spots produced become part of the desired image. An important aspect of inkjet printing image quality is the spot size uniformity of large drops. This lack of uniformity would have a non-negligible effect on image quality if the volume of droplets ejected from the printhead was allowed to vary significantly during the production of a single document. Similarly, printing stability cannot be maintained if the volume of droplets ejected from the printing head is different during subsequent printing of the same document. This is especially important in color printing. An important factor in the change in volume of droplets ejected from the print head is the change in temperature of the print head during use. The temperature of the liquid ink before evaporation by the heating element is
It has a significant effect on the stored thermal energy and the viscosity of the ink. The properties of these two inks have a significant effect on the size of the spots that appear on the copy surface. Therefore, controlling the temperature of the print head has been a fundamental problem in the art. Various approaches have been tried to maintain a constant spot size from the inkjet printhead. One example is U.S. Pat. No. 4,89, assigned to the same assignee as the present application.
No. 9, 180. In this U.S. patent, the pudding head can incorporate many heater resistors and temperature sensors that operate to heat and maintain the pudding head to an optimal operating temperature despite local temperature changes.

US Pat. No. 5,223,853 (incorporated by reference herein) is a controller for a heated ink jet printer which selects the magnitude and duration of the input signal selectively applied to the heater element. Is disclosed. This device senses the temperature of the ink and selects the amplitude and time duration of the input signal that will provide the desired spot size on the copy sheet.

[0004]

[Problems to be Solved] It has been found that another cause of the variation in the volume of the ejected droplets is the physical characteristics of the plurality of chips constituting the print head. In the known conventional device, the pulse signal applied to each of the plurality of chips included in the print head is changed based on the physical characteristics of the chip to maintain droplets generated from different chips at a desired size. There is no. It is an object of the present invention to provide a method and apparatus for maintaining a constant spot size of droplets ejected from multiple chips located on the print head of a printer. Another object of the present invention is to control the pulse signal applied to each of the chips based on at least one physical property of each chip to maintain droplets originating from different chips at a constant spot size. It is to provide a device. Yet another object of the present invention is to provide a control device that allows for easy modification of the device for a variety of specific inkjet printing purposes.

The present invention achieves these and other features by a method and apparatus having a plurality of chips mounted on a printhead, each chip responsive to a selectively applied pulse signal. And has a plurality of heater elements that generate ink droplets. This device varies the pulse signal of each chip based on at least one physical property of each chip to maintain a constant spot size for droplets generated from different chips.

[0006]

DETAILED DESCRIPTION FIG. 1 is a cross-sectional view of a droplet ejector of an inkjet printhead, one of many ejectors found in one version of such an inkjet printhead. Typically, such ejectors are 300 per inch (2.54 centimeters).
To 600 in size, they are arranged so as to have a linear array structure. As used in the detailed description, a silicon member having multiple channels for a droplet ejector, which typically has 128 ejectors provided therein, is known as a "die module" or "chip". Although many devices include a small chip that moves across the copy sheet, such as in a typewriter format, or abuts the full width of the substrate to form a full width print head, the thermal ink jet device is The image extends across the width of the copy sheet on which it is printed, for example,
It may have a single chip of 8.5 inches or larger.
In a multiple chip design, each chip may have its own ink supply manifold, or multiple chips may share a single ink supply manifold. The full width color terminal jet printing device is equipped with 80 or more chips.

Each ejector 10 'has an orifice 1 at the head.
It has a capillary channel 12 having four. The channel 12 regularly stores a fixed amount of ink 16 retained in the capillary channel 12 until the time when the ink droplet is ejected. Each capillary channel 12 holds a supply of ink from an ink supply manifold (not shown). Channel 12 is typically constructed by combining several layers. In the ejector shown in FIG. 1, the main part of the channel 12 is constituted by an anisotropic groove etched in the upper substrate 18. The base 18 is made of crystalline silicon. The upper substrate 18 abuts the thick film layer 20, which in turn abuts the lower substrate 22. Between the thick film layer 20 and the lower substrate 22, an electric element for interposing ink droplets from the capillary channel 12 is interposed. A heater element 26 is arranged inside the recess 24 formed by the opening to the thick film layer 20. The heater element 26 is typically protected by a protective layer of tantalum, for example having a thickness of about 1 micron. The heater element 26 is electrically connected to the address electrode 30. Each of the multiple ejectors 10 'of the printhead includes a heater element 26 and an address electrode for each that is selectively controlled by a control circuit as described below. The address electrodes 30 are usually protected by a passivation layer 32.

When an electric signal is applied to the address electrode 30 to activate the heater element 26, the liquid ink immediately adjacent to the heater element 26 is rapidly heated to the vaporization point, and bubbles of vaporized ink are generated. Bubbles 36
The expansive force causes the ink droplets 38 to be ejected from the orifice 14 toward the surface of the copy sheet. A copy sheet is, for example, a paper sheet or a transparent sheet, on the surface of which droplet marks are made. The size of the spots produced by the droplets 38 on the copy sheet is determined by the physical quantity of ink at that location just prior to vaporization (which is a function that is highly dependent on ink temperature), the physical properties of each tip, and the ejection. Is a function of the kinetic energy of the droplets that are ejected, which is a function of the electrical energy to the heater element 26. Therefore, in the control device for the spot size of the droplet, the heater element 26
It is possible to change the electric power for the ink according to the physical characteristics of each chip as well as the temperature of the ink. The present invention operates on the principle of selecting an optimal or at least a suitable combination of power level and time duration of the input pulse signal to heater element 26 to obtain a spot of desired size on a copy sheet. Is. Many variables and parameters are taken into account in selecting the combination of pulsed signal power level and duration. That is, the temperature response characteristics of the temperature sensing means, the temperature of the liquid ink in the channel 12 of the droplet ejector 10 at the moment immediately before the heater element 26 is activated, and most importantly, the physical characteristics of the individual chips. 2 shows how a silicon wafer 40
Is divided into a plurality of chips 42 (also known as die modules or integrated circuits). One set of heater element 26, address electrode 3
0 and various logic circuits are patterned on each chip 42. In many inkjet printers, the plurality of chips 42 are aligned to form a printhead.

FIG. 3 shows the electronic circuit of US Pat. No. 5,223,853 which accomplishes the task of providing a preselected desired shape of the ramp call pulse VA and which uses the call pulse in the operation of an ink jet printhead. Show.
First, it will be noted that the upper half of the circuit of FIG. 3, shown as device circuit 120, is applicable to an overall inkjet printing device in which many die modules (chips) can be used simultaneously. In contrast, the lower half 10 of the circuit
Shows the circuitry on each chip of each printhead of the device. As described above, each inkjet printing apparatus may include one circuit 120 and a large number of circuits 10. Each circuit 10 includes not only a respective heater element 26 (compare a cross-sectional view of the heater element 26 of FIG. 1 with a schematic view of this heater element 26) but also a temperature sensing diode such as the thermistor 102. A respective temperature sensing means for each chip in series with 110 is provided. As is apparent, the shape of the firing pulse VA is the same for all the chips of the print head, but each chip independently detects the temperature and changes the pulse width via each comparator 100. . The device circuit 120 includes a counter 122 and a read only memory (RO) as main elements.
M) 124, preferably various sets of desired waveforms V
A plurality of selectable lookup tables corresponding to A,
Digital-to-analog converter 126 (of 8-bit type)
And an amplifier 128. To reiterate, this central circuit is common to all the chips of the device and its output is a ramp firing pulse VA, which is delivered uniformly to each chip.

The circuit 10 is represented by each chip of the device, and the one shown in FIG. 3 is a single module circuit with hundreds or more ejectors. The main part of the circuit is the thermistor 1
02, a comparator 100 and a temperature detection diode 110. The output VC from the comparator 100 is now provided to a number of AND gates 130 each cooperating with the heater element 26 of the chip, each AND gate also accepting input digital data. This digital data is turned on or off depending on whether that particular ejector needs to be activated to produce a given pixel of the desired image on the copy sheet. If no data is input to the AND gate 130, the circuit
It is cut off between the comparator 100 and the heater 26.
In this example, instead of the output signal from AND gate 130 being directly input to the heating of heater element 26, the output of each AND gate 130 is used to activate switching transistor 132, which output signal In addition, it is used to control the energy applied to the heater element 26. In this method, the heater is energized according to the information to be printed,
It is not done.

When the device is in operation, the device circuit 120
It works as follows. The firing pulses are regularly input to the counter 122 in response to the operation of the printing process, ie the operation of the printhead with respect to the imaging surface, such as a paper sheet. During the firing pulse, the counter counts the pulses from the first clock (not shown). This gives an output of a series of uniformly increasing binary words. Then, this is sent to the ROM 124 as an address. Also, before this,
A user selection of a desired spot for a specific printing task is input to the ROM 124 by an input 125. This spot size value is
It can be specified as a function of the machine itself, or externally for a specific purpose, such as to use a different type of copy sheet as described below. Each time a pulse is input from the counter 122 to the ROM 124, the ROM 124 stores 1 of the VA waveform shown in FIG.
Outputs digital data giving two shapes. In the illustrated example, the desired firing pulse is represented as a word of digital data. The actual shape of the waveform generated by the digital data of the ROM is predetermined by the look-up table in the ROM 124. Actually, ROM
124 Random access memory that loads data before each execution. The shape of the VA pulse is determined empirically based on experiments by using a real machine. This pulse is loaded into the ROM 124 when the device is manufactured. This empirically obtained data generally relates to the required pulse width VC as a function of the detected temperature for a desired spot size, for example selected by the user.

In the initialization of the firing pulse of the counter 122, which normally occurs every 3-5 microseconds, the counter 12
2 outputs a series of binary-incremented addresses to ROM 124, which outputs a 3-bit digital word to fast digital-to-analog converter 126. The speed required for this device is generally
Specialized digital-to-analog converter 1 because it exceeds what is allowed for analog conversion chips
26 is preferred. Generally, the output voltage of the ROM is not always a constant value when the data is logic high. Therefore, a clipping circuit is added to limit the amplification amount of the output pulse from the ROM 124 to one value. The output from the register network forming unit of the digital-analog converter 126 is weighted by the resistance and becomes a binary ratio according to the input digital signal, and then the output is the high speed operation amplifier 1
28 is input. The final output VA is then simultaneously input in parallel to all the chips of the printhead to generate the appropriate firing pulse VC in the manner described above. A certain amount of energy must be applied to the heater element 26 in order to fire the droplet from the printhead. Basically, there are two parameters that change to affect the transfer of thermal energy to the ink. That is, the voltage of the heater element 26 and the pulse width, that is, the time width of the signal. Said US Pat. No. 5,223,
The problem with the 853 device is that it does not take into account the differences in the physical properties of the multiple chips that make up the printhead, which gives the different spot sizes of the droplets ejected from the ejector to different chips. . Due to the different chips, the heater elements 26 often have different resistance values.

Furthermore, the driver transistors provided on the chip often accept different amounts of doping, which results in different transistor voltage characteristics. As a result, the voltage applied to the heater elements in different chips changes. Furthermore, the amount of heat transferred to the ink changes due to thermal, boundary, or manufacturing variations in the upper and lower layers of the heater element 26. FIG. 4 is a set of waveform diagrams. The input signals applied to the address electrode 30 and the ejector 10 '(as can be seen in FIG. 1) are the result of two simultaneous input waveforms, shown in FIG. 4 as VA and VC. VA is a ramp signal and is characterized by an initial steep voltage increase followed by a relatively gradual ramp down to base voltage. Other voltage shapes are used depending on the situation. This VA ramp firing pulse is initiated by the firing pulse for every cycle of the ink droplet to be ejected from the ejector. VB is a substantially constant voltage value related to the detected temperature of the liquid ink in the capillary channel 12 of the ejector 10 'just prior to firing. The voltage amplitude of VB is determined by the capillary channel 12
It gradually changes in response to changes in the ink temperature. The VB value remains approximately constant during the cycle of the ramp firing pulse VA. As shown in FIG. 3, the two waveforms VA and VB are both transmitted to the comparator 100. The output can be used as an input signal to the address electrode 30 of a particular nozzle of the printhead.

The firing pulse VA is combined in the comparator 100 with a relatively constant bias voltage VB shown by the dashed line intersecting the top waveform pulse VA of FIG. The constant voltage VB has a magnitude that is related to the sensed temperature of each particular chip of the printhead. Constant voltage V
B can be determined from the thermistor 102, a temperature sensing diode integrated for each chip of the printhead, or other temperature sensing device. Comparator 100 produces a constant voltage output when the VA input is greater than the VB input. Therefore, the output pulse VC from the comparator 100 begins with an initial abrupt increase in each pulse VA, and the gradually decreasing value of VA is greater than the VB value, as illustrated by the lower waveform VC shown in FIG. Continue until it gets smaller. In one spot size control technique,
It is desirable to use multiple pulses rather than a single pulse to ignite each jet. For example,
Two pulses of width d1 and d3 divided by the empty time d2 may be used. By changing the width of the three pulses, it is possible to change the volume of the droplet.
In such a control approach, d1 is used to preheat the ink and d3 is used to eject the droplet. In this case, for example, in logic 1 select a slope and d
It is possible to use an additional lead 127 for the ROM 124, such as determining a 1 and then selecting a slope to determine the idle pulse width d2 and the pulse width d3, for example in logic 0. it can.

FIG. 5 illustrates how the present invention modifies the circuit of FIG. 3 to vary the duration of the input pulse applied to the heater element 26. This is a resistor 134 between the device circuit 120 and the comparator 100.
This can be achieved by inserting a bias voltage divider circuit 160 with -140. Resistance 134
And 136 act as voltage dividers to reduce the magnitude of the ramp signal by a controlled amount depending on the values of resistors 134 and 136. Resistors 138 and 140 act as a bias circuit, allowing bias values to be added to the ramp signal depending on the values of resistors 138 and 140. In general,
The values of resistors 134 and 136 are much larger than the values of resistors 138 and 140. The ramp signal input from the device circuit 120 can be represented by the function V (t) shown in FIG. 7, and the output from the bias voltage divider circuit 160 and
The resulting tilt used by the chip can be represented by AV (t) + B as shown in FIG.
In this case A is the effective reduction of the voltage divider and B is the effective bias constant voltage applied to the ramp signal. The size of A and B can be individually adjusted for each chip during manufacture or after the chip is assembled in the printhead. A and B do not have an exact linear relationship to resistors 134-140, but can be calculated by well known formulas. The resistor can be laser trimmed to adjust its value. If the resistance can be adjusted by using an adjustable resistance, or if it can be adjusted by laser trimming, it can be provided outside the chip. The bias voltage divider circuit 160 can be used to vary the ramp signal applied to the comparator 100, thus varying the duration of the pulse signal applied to the heater element 26 of each chip included in the printhead. In addition to compensating for variations in the physical characteristics of each chip, this keeps the spot size of droplets from different chips constant.

In determining the value of resistors 134-140, a predetermined input signal may be applied to each chip, and the measured value may be considered in determining the physical characteristics of each chip. In this manner, the characteristics of the transistor 132, basically the voltage drop across the transistor 132 as well as the resistance of the heater element 26 included in the chip herein, is determined, thereby determining the appropriate value of the resistors 134-140. You may make it set with respect to a chip. Other factors that can be measured and compensated for include variations in channel width, front channel length, and heater thermal conductivity. By setting the channel 12 of the resistors 134-140, the time width of the pulse signal applied to the heater element 26 is varied from chip to chip, thereby maintaining a constant spot size for droplets emitted from different chips. can do. In practice, the resistors 134-140 are responsive to the measured physical properties, or depending on the size of a typical droplet ejected from each chip when the printhead is at a given temperature.
The value of can be adjusted. FIG. 6 is a circuit showing how the amplitude of the pulse signal is modified to compensate for the physical properties of each chip of the printhead. The present invention allows the amplitude and / or the time width of the pulse signal to be changed. In FIG. 6, AND gate 130
Are shown connected to the pulse comparator 100. Therefore, in this embodiment, both the time width and the amplitude of the pulse signal are changed to compensate the physical characteristics of each chip. The circuit for changing the amplitude of the pulse signal is the second
Bias voltage divider circuit 170 (resistors 142, 14
4, 146 and 148), a comparator 152 and an RC circuit 154. This bias voltage divider circuit performs the same function as shown in FIG. 5 and also changes the ramp signal input to the chip. The changed output slope is input to the comparator 152 similarly to the signal from the thermistor 110. The comparator 152
A pulse signal is output in response to the changed input slope and the signal from the thermistor 110, and this signal is output from the RC circuit 15
4 is input. The RC circuit 154 functions to control the actual burn voltage applied to each heater element 26 on the chip. RC circuit 154 is transistor 1
The constant voltage input to the source of 32 is output, and the voltage applied to the heater element 26 is changed by the amount of the voltage input to the source of the transistor 132. By changing the value of the resistors 142-148, the amplitude of the pulse signal applied to the heater element 26 is changed, and the physical characteristics of each chip included in the print head can be changed. As described above, the value of the resistors 142-148 can be determined by inputting various signals to each chip and performing measurement to determine various factors of the individual chips. In the preferred embodiment, the voltage divider circuit 170 can be provided directly on each chip, like the comparator 152 and RC circuit 154. However, the device can be easily modified to place these elements in locations that are not on each chip.

7 and 8 show how the device circuit 12
7 is a waveform diagram showing whether the input slope generated at 0 is modified by the voltage divider circuits 160 and 170 of FIGS. 5 and 6. FIG. 7 shows the input ramp signal generated by the device circuit 120. This input slope signal changes in response to user selection of the desired spot size, and device circuitry 120
Generated by. FIG. 8 shows the output slope V (t) output from the bias voltage divider circuits 160 and 170 of FIG. 5 or 6. As can be seen from FIG. 8, the output ramp signal has an effective damping (attenuation amplitude) similar to the bias value applied to the ramp signal. As mentioned above, the present invention provides accurate control of the spot size emitted from various chips by varying the pulse signal applied to the heater element 26 based on the physical characteristics of each chip of the printhead. What is provided is that the spot size of the droplets ejected from the different chips of the printhead can be kept constant.

[Brief description of drawings]

FIG. 1 is a sectional elevation view of a nozzle of an inkjet print head,

FIG. 2 is a schematic plan view showing how to cut a wafer into a plurality of chips,

FIG. 3 is a prior art simplified diagram showing an electronic circuit for providing a preselected desired shaped ramped firing pulse VA using firing in the operation of an inkjet printhead.

FIG. 4 is a waveform diagram showing how a variable firing pulse VA can be used in the circuit of FIG. 3 for generating a heater current pulse with a variable duration.

FIG. 5 is a simplified schematic diaphragm showing an electronic circuit that modifies the time width of a pulse signal of a chip to compensate for the physical properties of the particular chip.

FIG. 6 is a simplified schematic diaphragm showing an electronic circuit that modifies the magnitude of a pulse signal on a chip to compensate for the physical properties of the particular chip.

7 is a waveform diagram showing how the input ramp signal used in FIG. 4 is modified to produce an output ramp signal,

FIG. 8 is a waveform diagram showing how the input ramp signal used in FIG. 4 is modified to produce an output ramp signal.

[Explanation of symbols]

10 decentralized system, 12 interconnection mechanism, 14, 1
6, 18 and 20 workstations, 22, 24
Printer, 26, 28 Secondary Storage Device 30, 32, 34 and 36 Memory, 37 Test Tool.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Juan Jay Vessela New York, USA 14580 Webster Clarendon Court 453 (72) Inventor James Eaton, New York, USA 14568 Walworth Walworth Ontario Center Road 3041 (72) Inventor Gary Anie Nisel United States New York 14580 Webster Woodard Road 1819 (72) Inventor Richard Vie Radonna United States New York 14450 Fairport Grandview Drive 67 (72) Inventor Peter Jay John United States New York 14616 Rochester Ripplewood Drive 450 (72) Inventor Joseph F Stephanie, New York, USA 14589 Wilmington Lake Road 3369 (72) Inventor Joseph Jay Wysocky, New York, USA 14580 Webster Crest Circle 544

Claims (1)

[Claims] 1. A controller for an ink jet printing apparatus having a plurality of chips disposed on a printhead, each chip having a plurality of heater elements for producing ink droplets in response to a selectively applied pulse signal. A pulse signal for each of the chips is provided, the signal generator generating the pulse signal, and a plurality of pulse signal modifiers, each pulse signal modifier being based on at least one physical characteristic of each of the chips. To maintain a constant spot size for droplets generated from different ones of the chips.