JP3717101B2 - Inkjet recording head drive apparatus and drive method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a driving apparatus and driving method for an ink jet recording head used in, for example, a printer, a facsimile machine, a copying machine, a plotter, and the like, and more particularly to a technique for controlling the amount of ejected ink drops.
[0002]
[Prior art]
Conventionally, an ink jet recording apparatus is known. The ink jet recording head used in this recording apparatus includes a plurality of nozzles in the sub-scanning direction (paper traveling direction) and is moved in the main scanning direction (direction orthogonal to the paper traveling direction) by the carriage mechanism. . Then, ink droplets are ejected from the respective nozzles of the inkjet recording head at predetermined timings according to the dot pattern data obtained by developing the print data. As a result, ink droplets from each nozzle adhere to the recording paper, and printing is performed. As described above, in an ink jet recording apparatus, printing is performed depending on whether or not ink droplets are ejected, that is, by controlling on / off of dots.
[0003]
Accordingly, a method of expressing one pixel with a plurality of dots is used to express the intermediate gradation. For example, if one pixel is expressed by a 4 × 4 dot matrix, light and shade can be expressed by 16 gradations (17 gradations including all white). If the number of dots per pixel is increased, more detailed gradation expression can be performed. However, if the gradation is increased without changing the dot diameter, the substantial resolution decreases. Further, when the recording dot diameter formed on the recording paper is large, the graininess in the low density region is conspicuous and the print quality is deteriorated.
[0004]
These problems can be solved by reducing the weight of ink droplets to reduce the recording dot diameter. However, if the recording dot diameter is reduced, the printing speed decreases. In order to prevent this decrease in printing speed, it is only necessary to shorten the interval at which ink droplets are ejected or increase the number of nozzles, but this is not easy.
[0005]
In order to solve such a problem, for example, in Japanese Patent Laid-Open No. 9-11457, the size of recording dots can be changed by controlling the amount of ink droplets ejected from one nozzle, and gradation expression can be realized. An “inkjet recording head drive device” is disclosed. In this drive device, a drive signal is supplied to the piezoelectric body provided corresponding to each of the plurality of nozzles. The piezoelectric body expands and contracts according to the supplied drive signal, thereby causing a pressure change in a pressure chamber (ink is accommodated) provided corresponding to each of the plurality of nozzles. As a result, an amount of ink droplets corresponding to the pressure change is ejected from each nozzle.
[0006]
The driving signal used in this driving device is generated by simultaneously generating a plurality of waveform signals having different shapes and selecting one waveform signal from the plurality of waveform signals according to the print data. The As a result, the amount of ink ejected from the nozzles is controlled in accordance with the waveform signal, so that the diameter of the recording dots deposited on the recording paper can be changed.
[0007]
Japanese Laid-Open Patent Publication No. 10-81012 discloses an “inkjet printer head driving apparatus and driving method” that operates on the same principle as the above-described ink jet recording head driving apparatus. The driving signal used in this driving device includes four driving pulses in a printing cycle necessary for forming one recording dot. In each printing cycle, one or two or more drive pulses are sequentially supplied to the pressure generating element from the four drive pulses according to the print data.
[0008]
As a result, the pressure generating element causes a pressure change according to the drive pulse, and thus an ink droplet of an amount corresponding to the pressure change is ejected. Accordingly, when one driving pulse is supplied to the pressure generating element, one ink droplet is ejected within the printing cycle, and when a plurality of driving pulses are sequentially supplied to the pressure generating device, a plurality of ink droplets are discharged within the printing cycle. Is discharged. Thereby, the amount of ink deposited on the recording paper is controlled, and the diameter of the recording dot can be changed.
[0009]
Further, Japanese Patent Laid-Open No. 10-81014 discloses a drive composed of three drive pulses instead of a drive signal composed of four drive pulses as described in Japanese Patent Laid-Open No. 10-81012. An “ink-jet printer head driving apparatus and driving method” is disclosed in which a signal is used to control the amount of ink deposited on a recording paper, thereby changing the diameter of the recording dot.
[0010]
JP-A-57-160654 discloses that one or more ink particles having different particle velocities and particle diameters are driven from nozzles by selectively using appropriate pulses from a pulse train composed of a plurality of voltage pulses. A “recording method in an ink jet recording apparatus” is disclosed in which ink particles are ejected and the ink particles are combined to form dots on the recording medium with the combined particles.
[0011]
[Problems to be solved by the invention]
By using the ink jet recording head driving device disclosed in the above-mentioned JP-A-9-11457, the printing speed can be increased without increasing the number of nozzles. However, since it is necessary to provide hardware (more specifically, transfer gates) for selecting one waveform signal from a plurality of waveform signals in correspondence with each of the plurality of piezoelectric bodies, the amount of hardware is enormous. become. For example, when the ink droplet amount is varied in three stages, a transfer gate that is three times the number of nozzles is required. As a result, there is a problem that the drive device cannot be made compact and the cost is increased.
[0012]
Further, if the techniques disclosed in Japanese Patent Laid-Open Nos. 10-81012 and 10-81014 are used, the printing speed can be increased without increasing the number of nozzles, and one waveform signal can be selected from a plurality of waveform signals. Since there is no need to select a waveform signal, hardware for selecting the waveform signal is not necessary. However, since the number of driving pulses corresponding to the amount of ink droplets to be ejected is sequentially supplied to the pressure generating element from the plurality of driving pulses in the printing cycle, the ink droplets of the ink droplets depend on which driving pulse is supplied. Discharge timing is different. As a result, there is a problem that an ink droplet landing position shift occurs and print quality deteriorates. For example, since the time period between the first pulse and the third pulse is half of the printing period, the dot by the first pulse and the dot by the third pulse are shifted by a half pitch. If the dot pitch is 720 dots / inch (= 35 μm), the deviation is 18 μm.
[0013]
Further, in any case of the above-described ink jet recording head drive device, a plurality of drive waveforms are required to vary the ink droplet diameter, and the drive device is complicated, large, and high in cost. There is.
[0014]
The present invention has been made to solve the above-described various problems, and an object of the present invention is to increase the printing speed and to reduce the amount of ink droplets ejected from the nozzle so as to improve the printing quality. An object of the present invention is to provide a small-sized and low-cost driving device and driving method for an inkjet recording head.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, the ink jet recording head driving apparatus of the present invention provides: For ejecting one ink drop The basic waveform of the same shape Within one printing cycle Applying a part of the basic waveform to the piezoelectric element that is the drive source of the ink jet recording head by turning on and off the basic waveform generating means that generates a plurality of basic waveforms and a switch that turns on and off at a timing according to the print data Drive waveform extracting means for changing the amount of ink droplets ejected from the ink jet recording head by performing the operation of applying all, or not applying, and changing the amount of ink droplets ejected from the ink jet recording head.
[0016]
In order to achieve the above object, the ink jet recording head driving device of the present invention is provided with a driving waveform extracting means. Within one printing cycle The maximum voltage value of each of the plurality of waveforms to be output to may be ascending in time series.
[0017]
In order to achieve the above object, the ink jet recording head driving device of the present invention is provided with a driving waveform extracting means. Within one printing cycle The time intervals between the plurality of waveforms may be set so that the ink droplets ejected by the plurality of waveforms output to the recording medium are combined before landing on the recording medium.
[0018]
In order to achieve the above object, the ink jet recording head driving device of the present invention is provided with a driving waveform extracting means. Within one printing cycle The time interval between the plurality of waveforms may be set so that the ink droplets ejected by the plurality of waveforms output to the recording medium are combined on the recording medium.
[0019]
In order to achieve the above object, the ink jet recording head drive apparatus of the present invention is characterized in that the time of the rising portion of the basic waveform is 0.7 times or less the natural period of the ink flow path of the ink jet recording head. It is good.
[0020]
In order to achieve the above object, the ink jet recording head driving method of the present invention provides: Within one printing cycle In For ejecting one ink drop A step of generating a plurality of basic waveforms of the same shape and an on / off of a switch that inputs the basic waveforms and is turned on / off at a timing according to the print data, to a piezoelectric element that is a drive source of the ink jet recording head according to the print data Of the basic waveform And a step of changing the amount of ink droplets ejected from the ink jet recording head by performing an operation of applying a part of the waveform or applying all or not of the waveform.
[0021]
In order to achieve the above object, the ink jet recording head driving method of the present invention provides a driving waveform extracting means. Within one printing cycle It is also possible to drive such that the maximum voltage value of each of the plurality of waveforms to be output is in ascending order in time series.
[0022]
In order to achieve the above object, the ink jet recording head driving method of the present invention provides a driving waveform extracting means. Within one printing cycle The ink droplets ejected according to the plurality of waveforms output to the recording medium may be driven so as to merge before landing on the recording medium.
[0023]
In order to achieve the above object, the ink jet recording head driving method of the present invention provides a driving waveform extracting means. Within one printing cycle The ink droplets ejected by the plurality of waveforms output to the recording medium may be driven so as to be united on the recording medium.
[0024]
In order to achieve the above object, the ink jet recording head driving method of the present invention is driven so that the time of the rising portion of the basic waveform is 0.7 times or less the natural period of the ink flow path of the ink jet recording head. It may be characterized by.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a sectional view partially showing a mechanical structure of an ink jet recording head to which a driving apparatus according to an embodiment of the present invention is applied. This ink jet recording head employs a method of ejecting ink droplets by pressing a pressure chamber containing ink with a piezoelectric element.
[0026]
In this ink jet recording head, a vibration plate 12 is provided on a nozzle plate 10 via a pressure chamber plate 11, and piezoelectric elements 13 a, 13 b and 13 c are further provided on the vibration plate 12. As each of the piezoelectric elements 13a, 13b, and 13c, a stacked type piezoelectric element configured by stacking piezoelectric materials with an internal electrode interposed therebetween is used.
[0027]
As shown in the figure, a plurality of pressure chambers 14 a, 14 b and 14 c are formed by the nozzle plate 10, the pressure chamber plate 11 and the vibration plate 12. The nozzle plate 10 is formed with nozzles 10a, 10b, and 10c having R-shaped cross sections that communicate with the pressure chambers 14a, 14b, and 14c. Although not shown, each pressure chamber 14a, 14b, and 14c is provided with a supply port for supplying ink, and ink is filled into each pressure chamber 14a, 14b, and 14c through the supply port. Is done.
[0028]
In the ink jet recording head configured as described above, for example, when a voltage is applied to the piezoelectric element 13b, the piezoelectric element 13b extends downward in the figure and compresses the ink in the pressure chamber 14b. Thereby, the ink droplet 15 is discharged from the nozzle 10b. By moving a predetermined piezoelectric element at a predetermined timing based on print data supplied from outside while moving the inkjet recording head relative to a recording medium such as printing paper, characters, figures, etc. Recorded on a recording medium.
[0029]
In the ink jet recording head having such a configuration, the ejection ink droplets were evaluated by changing the drive waveform applied to the piezoelectric element. The ink jet recording head used has a natural period of pressure waves propagating in the pressure chamber (hereinafter referred to as an intrinsic period of the ink flow path) of 10 μs, and the volume change of the pressure chamber by the piezoelectric element is 2.3 fm. ^Three / V, the nozzle has a cross-sectional R shape with a diameter of 24 μm and a length of 70 μm, and the supply port has a cross-sectional R shape with a diameter of 27 μm and a length of 70 μm. Also, the viscosity is 3.3 × 10 ^-3 Pa · s ink was used. As shown in FIG. 2, the drive waveform applied to the piezoelectric element is a waveform having a portion that holds the voltage for a predetermined time t2 after being boosted for a predetermined time t1. The inclination of the boosting unit was 4 V / μs, and the ink was pressurized linearly.
[0030]
FIG. 3 shows the results of measuring the droplet volume and droplet velocity of the ejected ink droplets while changing the pressure increase time t1. The drop volume increases as the pressurization time t1 increases, but the drop speed increases up to about 7 μs, where the pressurization time t1 corresponds to 0.7 times the natural period of the ink flow path, but becomes almost constant when the drop time is exceeded. I understood that. In other words, in the range where the pressurization time t1 is 0.7 times or less the natural period of the ink flow path, the drop speed and the drop amount can be increased by increasing the pressurization time t1. In the present invention, the print dot diameter is varied using this feature.
[0031]
First, as shown in FIG. 4 as a basic waveform, a trapezoidal waveform is used which is boosted for 2.8 μs with a slope of 4 V / μs, then holds the voltage for 7.2 μs, and returns to the original voltage for 10 μs. When this waveform is applied to the piezoelectric element of the inkjet recording head described above, the droplet velocity is 7 m / s and the droplet volume is 17 fm. ^Three Ink droplets are ejected.
[0032]
Next, FIG. 5 shows a waveform obtained by cutting the waveform of FIG. The waveform in FIG. 5 is a trapezoidal waveform that boosts for 1.4 μs at a slope of 4 V / μs, then holds the voltage for 13.6 μs, and then returns to the original voltage at 5 μs. It is the same as FIG. When this waveform is applied to the piezoelectric element of the above-described ink jet recording head, the droplet velocity is 4 m / s and the droplet amount is 8.5 fm. ^Three Ink droplets are ejected.
[0033]
As shown in FIG. 6, when the waveform of FIG. 5 and the waveform of FIG. 4 are applied to the piezoelectric element of the ink jet recording head with a time difference of 86 .mu.s, the droplet velocity is initially 4 m / s and the droplet amount is 8.5 fm. ^Three Ink droplets, followed by a droplet speed of 7 m / s and a droplet volume of 17 fm ^Three Ink droplets are ejected. Then, 200 μs after the start of application of the first waveform, the two merged and fm of 25.5 ^Three Ink droplets are formed and land after 33 μs on the printing paper located 1 mm in front of the nozzles of the ink jet recording head.
[0034]
As described above, the ink droplets having three types of droplet amounts, that is, small droplets, medium droplets, and large droplets, can be deposited on the printing paper by the waveforms shown in FIGS. Further, after the waveform application is started, the small droplets land on the printing paper located 1 mm ahead of the nozzles of the ink jet recording head after 250 μs and the large droplets after 233 μs. By applying the waveform 86 μs after the application start timing of the waveform of the small droplet, the medium droplet is deposited on the printing paper located 1 mm ahead of the nozzle of the ink jet recording head after 229 μs. For this reason, the landing position deviation of small droplets, medium droplets, and large droplets is almost 11 μm between the small droplets and the medium droplets when the moving speed of the inkjet recording head in the main scanning direction is 0.508 m / s, for example. This level is negligible.
[0035]
FIG. 7 is a block diagram schematically showing the configuration of the drive device 20 for the ink jet recording head according to the embodiment of the present invention. The drive device 20 includes a basic waveform generation circuit 21 and a drive waveform extraction circuit 22. The basic waveform generation circuit 21 generates a basic waveform having the same shape. Within one printing cycle Multiple occurrences. The basic waveform generated by the basic waveform generation circuit 21 is supplied to the drive waveform extraction circuit 22. The drive waveform extraction circuit 22 generates a drive signal by extracting a part or all of the basic waveform from the basic waveform generation circuit 21 according to the print data. The drive signal generated by the drive waveform extraction circuit 22 is applied to the piezoelectric element group 13. Thereby, each piezoelectric element included in the piezoelectric element group 13 is driven.
[0036]
Next, the detailed configuration of the basic waveform generating circuit 21 will be described with reference to the circuit diagram shown in FIG. The basic waveform generating circuit 21 includes a charging constant current circuit 210, a discharging constant current circuit 212, a transistor Tr1, resistors R1, R2, and R5, a capacitor C, and a current amplifying circuit 214. The basic waveform generation circuit 21 is supplied with timing signals T1 and T3 from a timing generation circuit (not shown).
[0037]
The charging constant current circuit 210 includes transistors Q1 and Q2 and a resistor R10. The collector of the transistor Tr1 is connected to the control terminal Tc of the constant current circuit 210 for charging via a resistor R2. The emitter of the transistor Tr1 is grounded, and the timing signal T1 is input to the base via the resistor R1. The output terminal To of the charging constant current circuit 210 is connected to the first terminal of the capacitor C. The second terminal of the capacitor C is grounded. The charging constant current circuit 210 is activated when the timing signal T1 becomes a high level (hereinafter referred to as “H level”), and outputs a current having a predetermined magnitude.
[0038]
The discharging constant current circuit 212 includes transistors Q3 and Q4 and a resistor R20. The timing signal T3 is input to the control terminal Tc of the discharging constant current circuit 212 via the resistor R5. Further, the input terminal Ti of the discharging constant current circuit 212 is connected to the first terminal of the capacitor C. The discharging constant current circuit 212 is activated when the timing signal T3 becomes H level, and inputs current from the input terminal Ti.
[0039]
The first terminal of the capacitor C is connected to the output terminal To of the charging constant current circuit 210 and the input terminal Ti of the discharging constant current circuit 212 as described above, and further to the input terminal of the current amplification circuit 214. It is connected. The electric charge stored in the capacitor C is charged by charging the constant current circuit 210 for charging, and the current from the charging constant current circuit 210 is activated. On the other hand, when the discharge constant current circuit 212 is activated, a current flows to the discharge constant current circuit 212 and is discharged.
[0040]
The current amplifying circuit 214 includes transistors Q7 and Q8, and amplifies the current flowing through the first terminal of the capacitor C. The signal amplified by the current amplification circuit 214 is supplied to the drive waveform extraction circuit 22 as a basic waveform.
[0041]
Next, the operation of the basic waveform generating circuit 21 will be described with reference to the timing chart shown in FIG. As shown in FIG. 9A, a timing generation circuit (not shown) generates a timing signal T1 that becomes H level only for a time t1 corresponding to the rising portion of the basic waveform. Further, as shown in FIG. 9B, a timing signal T3 that rises after a time t2 corresponding to the holding unit and changes to the H level for a time t3 corresponding to the falling unit from the change in the falling of the timing signal T1 is generated. .
[0042]
The charging constant current circuit 210 is activated when the timing signal T1 is set to H level, and the current from the power source + V is output from the output terminal To via the resistor R10 and the transistor Q2. Thereby, the capacitor C is charged at a speed according to the time constant of the CR circuit formed by the resistor R10 and the capacitor C in the charging constant current circuit 210. By this charging, as shown in FIG. 9C, a rising portion having an inclination corresponding to the time constant is formed. Note that if the CR time constant is made sufficiently larger than t1, the slope of the voltage can be made substantially constant.
[0043]
Next, when the timing signal T1 falls and becomes a low level (hereinafter referred to as “L level”), the output of the current from the charging constant current circuit 210 is stopped, and the charge stored in the capacitor C is held as it is. . This state is maintained until the timing signal T3 becomes H level next time. As a result, a holding portion that maintains the level of the end portion of the rising portion for the time t2 is formed.
[0044]
Next, when the timing signal T3 becomes H level as shown in FIG. 9B, the discharging constant current circuit 212 is activated, and the electric charge held in the capacitor C passes through the transistor Q4 and the resistor R20. To the ground. As a result, the capacitor C is discharged at a speed corresponding to the time constant of the CR circuit formed by the resistor R20 and the capacitor C in the discharge constant current circuit 212. By this discharge, as shown in FIG. 9C, a falling portion having a slope corresponding to the time constant is formed. In this case, as shown in FIG. 9C, the charge accumulated in the capacitor C during the time t1 is completely discharged at the time t3. In other words, at the time t3, the level reaches the top level of the basic waveform. Thus, the time constant, that is, the value of the resistor R20 is determined.
[0045]
The current flowing through the first terminal of the capacitor C due to the charging / discharging of the capacitor C as described above is amplified by the current amplification circuit 214 and supplied to the drive waveform extraction circuit 22 as a basic waveform.
[0046]
Next, the detailed configuration of the drive waveform extraction circuit 22 will be described with reference to the block diagram shown in FIG. Note that the drive waveform extraction circuit 22 generally generates a drive signal for driving several hundred piezoelectric elements, but here, in order to simplify the description, the four piezoelectric elements 13a, 13b, 13c and 13d are connected. A drive signal for driving is generated.
[0047]
The drive waveform extraction circuit 22 includes a system control circuit 23, shift circuits 24a, 24b, 24c and 24d, latch circuits 25a, 25b, 25c and 25d, level conversion circuits 26a, 26b, 26c and 26d, and switch circuits 27a, 27b, 27c and 27d.
[0048]
The system control circuit 23 controls the entire drive device 20. That is, the system control circuit 23 generates a clock signal and supplies it to the shift circuits 24a to 24d. In addition, a latch signal is generated and supplied to the latch circuits 25a to 25d. Further, external data is sequentially supplied to the shift circuit 24a as serial print data. Further, a start signal for instructing the start of generation of the drive waveform is generated and supplied to the basic waveform generation circuit 21. Also, a reset signal for clearing the contents of the shift circuits 24a, 24b, 24c and 24d is generated.
[0049]
Each of the shift circuits 24a to 24d is configured by, for example, a 1-bit D-type flip-flop. The shift circuit 24a stores the print data supplied from the system control circuit 23 in synchronization with the clock signal, and the shift circuits 24b, 24c and 24d respectively receive the print data clock signals from the preceding shift circuits 24a, 24b and 24c. Store in sync with. Thus, the shift circuits 24a to 24d form a 4-bit shift register that sequentially shifts print data from the system control circuit 23 in synchronization with the clock signal. The print data stored in each of the shift circuits 24a to 24d is supplied to the latch circuits 25a to 25d, respectively.
[0050]
The latch circuits 25 a to 25 d latch the print data from the shift circuits 24 a to 24 d in synchronization with the latch signal from the system control circuit 23. The print data latched by the latch circuits 25a to 25d is supplied to the level conversion circuits 26a to 26d, respectively.
[0051]
Each level conversion circuit 26a-26d is comprised, for example with an amplifier, converts the level of the signal from each latch circuit 25a-25d, and supplies it to switch circuit 27a-27d, respectively. As a result, a gate control signal having a level sufficient to control the switch circuits 27a to 27d is supplied to the switch circuits 27a to 27d.
[0052]
Each of the switch circuits 27a to 27d includes a gate circuit that is turned on / off according to a gate control signal. The basic waveforms from the basic waveform generating circuit 21 are input to the input terminals of the switch circuits 27a to 27d, and the control signals from the level converting circuits 26a to 26d are input to the gate control terminals. Output terminals of the switch circuits 27a to 27d are connected to one terminals of the piezoelectric elements 13a to 13d. And the signal from each switch circuit 27a-27d is supplied to each piezoelectric element 13a-13d as a drive signal. The other terminals of the piezoelectric elements 13a to 13d are grounded.
[0053]
Next, the operation of the drive waveform extraction circuit 22 configured as described above will be described with reference to the timing charts shown in FIGS.
[0054]
First, the case of droplet ejection will be described with reference to the timing chart shown in FIG. In the case of this small droplet ejection, the system control circuit 23 generates the significant data (in this embodiment, “1”) as print data twice in succession. (The data corresponding to the nozzles to be ejected is 1, the data corresponding to the nozzles that are not ejected is 0, and all the nozzles are simultaneously 1).
That is, as shown in FIG. 11E, when the system control circuit 23 sequentially outputs “1111B” (the last digit “B” represents a binary number, the same applies hereinafter) as print data in the section TM0. As shown in FIG. 11C, the shift circuits 24a to 24d take in the print data while sequentially shifting in synchronization with the clock signal. Then, the shift operation stops in a state where “1” is stored in all the shift circuits 24a to 24d.
[0055]
Next, as shown in FIG. 11B, the system control circuit 23 makes the latch signal active (H level) at the head of the section TM1. As a result, the print data “1” stored in the shift circuits 24a to 24d is latched by the latch circuits 25a to 25d. The data “1” latched by the latch circuits 25a to 25d is converted in signal level by the level conversion circuits 26a to 26d and supplied to the switch circuits 27a to 27d.
[0056]
As a result, each of the switch circuits 27a to 27d is turned on, and a drive signal having the same inclination as the basic waveform as shown in the section TM1 in FIG. 11G is supplied to each of the piezoelectric elements 13a to 13d.
[0057]
In the interval TM1, in parallel with the output of the drive signal described above, the system control circuit 23 activates the reset signal (H level) as shown in FIG. 11D, thereby shifting the shift circuits 24a, 24b, The contents of 24c and 24d are cleared.
[0058]
Next, as shown in FIG. 11B, the system control circuit 23 activates the latch signal at the beginning of the interval TM2, that is, during the rise of the basic waveform. Accordingly, each of the switch circuits 27a to 27d is turned off, and a constant voltage is held as shown in a section TM2 in FIG.
[0059]
In the section TM2, in parallel with the output of the drive signal described above, the system control circuit 23 sequentially outputs “1111B” as the next print data as shown in FIG. The print data is taken into the shift circuits 24a to 24d in the same manner as described above, and the shift operation is stopped in a state where “1” is stored in all the shift circuits 24a to 24d.
[0060]
Next, as shown in FIG. 11B, the system control circuit 23 activates the latch signal at the head of the section TM3. As a result, as in the section TM1, the switch circuits 27a to 27d are turned on. As shown in the section TM3 in FIG. 11G, the drive signals having the same falling shape as the basic waveform are displayed. It is supplied to the piezoelectric elements 13a to 13d. Thereby, ink droplets are ejected from the nozzles 10a to 10d.
[0061]
Next, the case of middle droplet ejection will be described with reference to the timing chart shown in FIG. This middle drop is generated when the system control circuit 23 outputs significant data “1” as print data once.
[0062]
(A), (B), (C), and (D) in FIG. 12 are the same as (A), (B), (C), and (D) in FIG. When the system control circuit 23 sequentially outputs “1111B” as the print data in the section TM4 as shown in FIG. 12E, the shift circuits 24a to 24d receive the print data as shown in FIG. Are captured while sequentially shifting in synchronization with the clock signal. Then, the shift operation stops in a state where “1” is stored in all the shift circuits 24a to 24d.
[0063]
Next, as shown in FIG. 12B, the system control circuit 23 makes the latch signal active (H level) at the head of the section TM5. As a result, the print data “1” stored in the shift circuits 24a to 24d is latched by the latch circuits 25a to 25d. The data “1” latched by the latch circuits 25a to 25d is converted in signal level by the level conversion circuits 26a to 26d and supplied to the switch circuits 27a to 27d.
[0064]
As a result, each of the switch circuits 27a to 27d is turned on, and a drive signal having the same shape as the basic waveform as shown in a section TM5 in FIG. 12G is supplied to each of the piezoelectric elements 13a to 13d. Thereby, ink droplets are ejected from the nozzles 10a to 10d.
[0065]
Next, the case of large droplet ejection will be described with reference to the timing chart shown in FIG. This large droplet discharge occurs by outputting significant data from the system control circuit 23 as print data three times in succession.
[0066]
That is, when the system control circuit 23 sequentially outputs “1111B” as the print data in the section TM0 as shown in FIG. 13 (E), the shift circuits 24a to 24d receive this as shown in FIG. 13 (C). Print data is captured while sequentially shifting in synchronization with the clock signal. Then, the shift operation stops in a state where “1” is stored in all the shift circuits 24a to 24d.
[0067]
Next, as shown in FIG. 13B, the system control circuit 23 makes the latch signal active (H level) at the head of the section TM1. As a result, the print data “1” stored in the shift circuits 24a to 24d is latched by the latch circuits 25a to 25d. The data “1” latched by the latch circuits 25a to 25d is converted in signal level by the level conversion circuits 26a to 26d and supplied to the switch circuits 27a to 27d.
[0068]
As a result, the switch circuits 27a to 27d are turned on, and drive signals having the same inclination as the basic waveform as shown in the section TM1 in FIG. 13G are supplied to the piezoelectric elements 13a to 13d.
[0069]
In the interval TM1, in parallel with the output of the drive signal described above, the system control circuit 23 activates the reset signal (H level) as shown in FIG. 13D, so that the shift circuits 24a, 24b, The contents of 24c and 24d are cleared.
[0070]
Next, as shown in FIG. 13B, the system control circuit 23 activates the latch signal at the beginning of the interval TM2, that is, during the rise of the basic waveform. Accordingly, the switch circuits 27a to 27d are turned off, and a constant voltage is held as shown in a section TM2 in FIG.
[0071]
In the section TM2, in parallel with the output of the drive signal described above, the system control circuit 23 sequentially outputs “1111B” as the next print data as shown in FIG. The print data is taken into the shift circuits 24a to 24d in the same manner as described above, and the shift operation is stopped in a state where “1” is stored in all the shift circuits 24a to 24d.
[0072]
Next, as shown in FIG. 13B, the system control circuit 23 activates the latch signal at the head of the interval TM3. As a result, as in the section TM1, the switch circuits 27a to 27d are turned on. As shown in the section TM3 in FIG. 13G, the drive signals having the same falling shape as the basic waveform are displayed. It is supplied to the piezoelectric elements 13a to 13d. Thereby, first, a small ink droplet is discharged from each of the nozzles 10a to 10d.
[0073]
Subsequently, when the system control circuit 23 sequentially outputs “1111B” as the print data in the section TM4 as illustrated in FIG. 13E, the shift circuits 24a to 24d are configured as illustrated in FIG. The print data is captured while being sequentially shifted in synchronization with the clock signal. Then, the shift operation stops in a state where “1” is stored in all the shift circuits 24a to 24d.
[0074]
Next, as shown in FIG. 13B, the system control circuit 23 makes the latch signal active (H level) at the head of the section TM5. As a result, the print data “1” stored in the shift circuits 24a to 24d is latched by the latch circuits 25a to 25d. The data “1” latched by the latch circuits 25a to 25d is converted in signal level by the level conversion circuits 26a to 26d and supplied to the switch circuits 27a to 27d.
[0075]
As a result, each of the switch circuits 27a to 27d is turned on, and a drive signal having the same shape as the basic waveform as shown in a section TM5 in FIG. 13G is supplied to each of the piezoelectric elements 13a to 13d. As a result, medium ink droplets are ejected from the nozzles 10a to 10d. And it combines with the small droplet discharged previously, and forms a large droplet.
[0076]
As described above, according to the present embodiment, the number of switch circuits may be the same as that of piezoelectric elements, and the drive device can be significantly reduced in size compared to the conventional device, and the cost can be reduced. In addition, small droplet (small dot), medium droplet (medium dot), and large droplet (large dot) are generated by generating a small droplet waveform and a medium droplet waveform individually or simultaneously within one printing cycle. Can be obtained. Furthermore, the waveform generated by the drive waveform generating means is input to the waveform extracting means, and a necessary portion is taken out by the waveform extracting means and applied to the piezoelectric element, so that small droplets, medium droplets, large droplets can be obtained from a single basic waveform As many as three types of droplets can be discharged, and the drive circuit is low in cost.
[0077]
In the above-described embodiment, an example has been described in which a small droplet and a medium droplet combine to form a large droplet during flight before reaching the recording medium, but the time difference between the small droplet waveform and the medium droplet waveform is 107 μs. If so, small droplets and medium droplets can be combined to form large droplets on the printing paper located 1 mm ahead of the nozzles of the inkjet recording head.
[0078]
In the above-described embodiment, Within one printing cycle Although an example of generating two basic waveforms has been described above, it is possible to further expand the variable range of the droplet diameter by generating three or more basic waveforms.
[0079]
From the drive waveform extraction means Within one printing cycle Since the maximum voltage value of each of the plurality of waveforms output to is in ascending order in time series (in the above-described embodiment, the first is 5.6 V and the second is 11.2 V). The droplet landing position deviation is small and preferable.
[0080]
In the above-described embodiment, an example using a trapezoidal wave as a basic waveform has been shown. However, as shown in FIG. 14, a waveform that rises after a slight initial pull-in (after falling) is used. The effect of the present invention is also exhibited in the same manner.
[0081]
In the embodiment described above, the multilayer type piezoelectric element as shown in FIG. 1 is used as the ink jet recording head. However, the present invention is not limited to the ink jet recording head using the multilayer type piezoelectric element. The present invention can also be applied to an ink jet recording head using a single plate type piezoelectric element as shown in FIG.
[0082]
An example of an inkjet recording head using a single plate type piezoelectric element is shown in FIG. The ink jet recording head includes a nozzle plate 201 for forming the nozzle 101, an ink pool plate 202 for forming an ink pool, an ink supply port plate 203 for forming the ink supply port 103, and a pressure chamber 104. Therefore, the pressure chamber plate 204, the vibration plate 205, and the piezoelectric element 206 are laminated and joined.
[0083]
On the diaphragm 205, a guide portion 107 for positioning the piezoelectric element 206 is formed in a portion other than a range in contact with the pressure chamber 104. The piezoelectric element 206 positioned by the guide portion 107 is on the diaphragm 205. It is joined to. The ink jet recording head is provided with an electric signal line for supplying an electric signal to the piezoelectric element 206 and an ink flow path for filling the ink pool 102 with ink through the ink suction port. It is omitted in FIG.
[0084]
Next, the operation of the inkjet recording head configured as described above due to the unimorph effect of the piezoelectric element 206 and the diaphragm 205 will be described with reference to FIG. 16 is a cross-sectional view taken along the line AA in FIG. Corresponding to each pressure chamber 104, a piezoelectric element 206 is provided on the vibration plate 205. The piezoelectric element 206 has a lower electrode 208a on the surface bonded to the vibration plate 205 and an upper surface on the opposite surface side. Electrodes 208b are respectively formed. Here, the piezoelectric element 206 is polarized in the direction from the upper electrode 208b side to the lower electrode 208a side (possible in the reverse direction). The lower electrode 208 a is electrically connected to the diaphragm 205, and the diaphragm 205 serves as a common electrode portion for each piezoelectric element 206 and is connected to one of the drive sources 207.
[0085]
The upper electrode 208b is connected to the other side of the drive source 207 via a switch circuit 209 that turns on / off electrical connection for each piezoelectric element. When a print command is input from a control unit (not shown), the switch circuit 209 is turned on, and the voltage from the drive source 207 is applied to the piezoelectric element 206. As a result, the piezoelectric element 206 tends to contract in the direction of “e” in FIG. 16 due to the piezoelectric effect. However, the amount of distortion on the surface side of the piezoelectric element 206 bonded to the diaphragm 205 is smaller than the amount of distortion on the opposite surface due to the load of the diaphragm 205. Due to the asymmetry of the strain amount, the joint between the piezoelectric element 206 and the diaphragm 205 is deformed in the direction of “f” in FIG. Thereby, the volume in the pressure chamber 104 is contracted and pressurized.
[0086]
By supplying a drive signal from the above-described drive device 20 as the drive source 207 of the ink jet recording head configured as described above, the same operation as described above is performed, and the ejection of ink from the nozzle 101 is controlled. Is done.
[0087]
Next, another embodiment of the present invention will be described. The drive device according to this embodiment drives a so-called strike-type ink jet recording head in which a pressure chamber containing ink is expanded and then contracted. As this ink jet recording head, for example, a print head described in JP-A-10-81012 can be used.
[0088]
The mechanical structure of this ink jet recording head is shown in FIG. The substrate unit 300 is configured by holding a flow path forming plate 305 between a nozzle plate 302 in which a nozzle hole 301 is formed and a vibration plate 304 in which an island portion 303 is formed. In the flow path forming plate 305, an ink chamber 306, an ink supply port 307, and a pressure generation chamber 308 are formed.
[0089]
A storage chamber 310 is formed in the base 309, and a piezoelectric vibrator 311 is attached in the storage chamber 310. The piezoelectric vibrator 311 is fixed via a fixed substrate 312 so that the tip thereof is in contact with the island portion 303 of the diaphragm 304. Here, for example, a piezoelectric element using a lateral effect is used for the piezoelectric vibrator 311, and contracts when charged and expands when discharged. Charging / discharging of the piezoelectric vibrator 311 is performed via the lead wire 313.
[0090]
When the piezoelectric vibrator 311 is charged, the piezoelectric vibrator 311 contracts and the pressure generation chamber 308 expands, the pressure in the pressure generation chamber 308 decreases, and ink flows from the ink chamber 306 into the pressure generation chamber 308. When the piezoelectric vibrator 311 is discharged, the piezoelectric vibrator 311 expands and the pressure generation chamber 308 contracts, the pressure in the pressure generation chamber 308 rises, and the ink in the pressure generation chamber 308 passes through the nozzle holes 301. It is discharged outside.
[0091]
In this type of ink jet recording head, the pressure chamber is pressurized by lowering the voltage applied to the piezoelectric element. Therefore, by applying a waveform as shown in FIG. Droplets) can be discharged. Further, when the waveform shown in FIG. 18B cut in the broken line portion in FIG. 18A is applied, smaller ink droplets (small droplets) are ejected than when the waveform in FIG. 18A is applied. be able to. Further, as shown in FIG. 18C, when the waveform of FIG. 18B is applied and the waveform of FIG. 18A is applied after a certain period of time, a small droplet is first ejected and then a medium droplet is ejected. The ink droplets can be combined while the ink droplets are flying or on the recording medium, and large droplets can be formed (large droplets).
[0092]
That is, even in this type of ink jet recording head, the ink droplets are basically ejected by pressurizing the ink in the pressure chamber, and the voltage applied to the piezoelectric element is lowered to pressurize the pressure chamber. Therefore, there is basically no difference from the embodiment of FIG.
[0093]
【The invention's effect】
As described above in detail, according to the present invention, a small and low-cost ink jet recording head capable of increasing the printing speed and controlling the amount of ink droplets ejected from the nozzle so as to improve the printing quality. A driving device and a driving method can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a mechanical configuration of an ink jet recording head to which a driving apparatus according to an embodiment of the present invention is applied.
FIG. 2 is a waveform diagram showing an example of a basic waveform used in the ink jet recording head driving apparatus according to the embodiment of the present invention.
FIG. 3 is a diagram showing characteristics when the slope of the rising portion of the drive voltage is constant in the ink jet recording head.
FIG. 4 is a waveform diagram showing an example of a drive waveform for driving a piezoelectric element used in the inkjet recording head drive device according to the embodiment of the present invention. During ~ When discharging droplets).
FIG. 5 is a waveform diagram showing an example of a drive waveform for driving a piezoelectric element used in the ink jet recording head drive apparatus according to the embodiment of the present invention. small When discharging droplets).
FIG. 6 is a waveform diagram (during large droplet ejection) showing an example of a drive waveform for driving a piezoelectric element used in the inkjet recording head drive device according to the embodiment of the present invention.
FIG. 7 is a block diagram schematically showing the configuration of an ink jet recording head driving apparatus according to an embodiment of the present invention.
FIG. 8 is a circuit diagram showing a configuration of a basic waveform generating circuit of the ink jet recording head driving apparatus according to the embodiment of the present invention.
9 is a timing chart for explaining the operation of the circuit diagram shown in FIG. 8. FIG.
FIG. 10 is a block diagram showing a configuration of a drive waveform extraction circuit of the inkjet recording head drive device according to the embodiment of the present invention.
FIG. 11 is a timing chart for explaining an operation when ejecting small droplets using a predetermined basic waveform in the inkjet recording head driving apparatus according to the embodiment of the present invention.
FIG. 12 is a timing chart illustrating an operation when ejecting a medium droplet using a predetermined basic waveform in the ink jet recording head driving apparatus according to the embodiment of the present invention.
FIG. 13 is a timing chart illustrating an operation when a large droplet is ejected using a predetermined basic waveform in the ink jet recording head driving apparatus according to the embodiment of the present invention.
FIG. 14 is a waveform diagram showing an example of a basic waveform.
FIG. 15 is a diagram showing a mechanical configuration of another ink jet recording head to which the driving device according to the embodiment of the invention is applied.
16 is a diagram for explaining the operation of the ink jet recording head shown in FIG. 15. FIG.
FIG. 17 is a diagram showing a mechanical configuration of another ink jet recording head to which the driving apparatus according to the embodiment of the present invention is applied.
18 is a waveform diagram showing an example of drive waveforms used in the inkjet recording head drive apparatus shown in FIG.
[Explanation of symbols]
10 Nozzle plate
10a, 10b, 10c, 101 nozzle
11, 204 Pressure chamber plate
12, 205, 304 Diaphragm
13 Piezoelectric elements
13a to 13d, 206 Piezoelectric element
14a-14c, 104 pressure chamber
15 ink drops
20 Drive device
207 Drive source
21 Basic waveform generator
210 Constant current circuit for charging
212 Constant current circuit for discharge
214 Current amplifier circuit
22 Drive waveform extraction circuit
23 System control circuit
24a to 24d shift circuit
25a to 25d latch circuit
26a-26d level conversion circuit
27a to 27d, 209 switch circuit
301 Nozzle hole
308 Pressure generation chamber
311 Piezoelectric vibrator

Claims (10)

By means of basic waveform generating means for generating a plurality of basic waveforms of the same shape for discharging one ink drop within one printing cycle, and by inputting the basic waveform and turning on / off a switch that turns on / off at a timing according to print data, A part of the basic waveform is applied to the piezoelectric element which is a driving source of the ink jet recording head, or all of the basic waveform is applied or not applied, and the amount of ink droplets ejected from the ink jet recording head is changed. A drive apparatus for an ink jet recording head, comprising drive waveform extraction means. 2. The ink jet recording head driving apparatus according to claim 1, wherein the maximum voltage values of the plurality of waveforms output from the driving waveform extracting unit within one printing cycle are in ascending order in time series. A time interval between the plurality of waveforms is set so that the ink droplets ejected by the plurality of waveforms output within one printing cycle from the drive waveform extracting unit are combined before landing on the recording medium. An ink jet recording head drive apparatus according to claim 1 or 2. The time interval between the plurality of waveforms is set so that the ink droplets ejected by the plurality of waveforms output within one printing cycle from the drive waveform extracting unit are combined on the recording medium. An ink jet recording head drive apparatus according to claim 1 or 2.  5. The ink jet recording head according to claim 1, wherein the time of the rising portion of the basic waveform is 0.7 times or less the natural period of the ink flow path of the ink jet recording head. Drive device. By generating a plurality of basic waveforms of the same shape for ejecting one ink droplet within one printing cycle, and inputting the basic waveforms, and turning on / off the switch at a timing according to the print data, the print data is In response, the piezoelectric element which is the drive source of the ink jet recording head is operated to apply a part of the basic waveform, or to apply all of the basic waveform, or not, and to control the amount of ink droplets ejected from the ink jet recording head. And a step of changing the ink jet recording head. 7. The ink jet recording head driving method according to claim 6, wherein driving is performed so that the maximum voltage value of each of the plurality of waveforms output from the driving waveform extracting unit within one printing cycle is in ascending order in time series. . 8. The ink droplets respectively ejected by a plurality of waveforms output within one printing cycle from the drive waveform extracting means are driven so as to merge before landing on the recording medium. The inkjet recording head driving method described. 8. The ink jet recording according to claim 6 or 7, wherein the ink droplets ejected by a plurality of waveforms output within one printing cycle from the drive waveform extracting means are driven so as to be united on the recording medium. Head drive method.  10. The driving according to claim 6, wherein the time of the rising portion of the basic waveform is driven to be 0.7 times or less of the natural period of the ink flow path of the ink jet recording head. Ink jet recording head driving method.

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