Patent Application
20200276809
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-037557, filed on Mar. 1, 2019, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a drive circuit for a liquid ejecting device and a liquid ejecting device.
A liquid ejecting device that supplies a predetermined amount of liquid to a predetermined position is known. The liquid ejecting device is used in, for example, an ink jet printer, a 3D printer, or a liquid dispensing device. An ink jet printer ejects ink droplets from an ink jet head to print an image or the like on a surface of a recording medium, such as a sheet of paper. A 3D printer ejects droplets of a pattern forming material from a material ejection head and the ejected droplets are then to form a three-dimensional object. A dispensing device supplies a predetermined amount of a sample material to a plurality of containers or the like.
An ink jet printer of one type includes an on-demand ink jet head that ejects ink from a nozzle. The ink is ejected from the nozzle by applying a drive signal to piezoelectric actuators that is selected from a plurality of piezoelectric actuators according to the data being printed by the printer. The drive signal includes a common drive waveform generated by pulse width modulation (PWM) or the like. The number of actuators to which the drive signal is applied is determined depending on the print data. Depending on the number of actuators, there may be a case where a large number of actuators are loads of a PWM drive circuit or a case where only a small number of actuators are loads of the PWM drive circuit. In either case, it can be difficult to stably drive an actuator as a capacitive load. When the capacitance value of a stabilizing capacitor is increased in order to stably drive the actuator, power loss may become large. In addition, it is difficult to select an inductance value for an output inductor of the PWM drive circuit that is suitable for both a case where the load is high and a case where the load is low.
Embodiments provide a drive circuit for a liquid ejecting device that can stably drive an actuator as a capacitive load whether the number of piezoelectric actuators that are driven at the same time is small or large.
In general, according to an embodiment, a drive circuit of a liquid ejecting device includes a load detection circuit configured to generate load number information corresponding to a number of actuators to be concurrently driven during liquid ejection according to liquid output information, such as image data to be printed or the like. A signal processing circuit is configured to compare a common drive waveform to a target common drive waveform and then generate a common drive signal to drive the actuators based on the load number information and the comparison of the common drive waveform and the target common drive waveform. A switching circuit is configured to selectively apply portions the generated common drive signal to an actuator according to liquid output information for liquid ejection.
Hereinafter, a drive circuit for a liquid ejecting device and an image forming apparatus according to certain example embodiments will be described with reference to the accompanying drawings. In the drawings, the same components/aspects will be represented by the same reference numerals.
An ink jet printer 10 that prints an image on a recording medium will be described as an example of an image forming apparatus on which a liquid ejecting device 1 according to a first embodiment can be mounted.
Image data to be printed on the sheet S is generated by, for example, a computer 2 that is an external apparatus. The image data generated by the computer 2 is transmitted to the control substrate 17 of the ink jet printer 10 through a cable 21 and connectors 22B and 22A.
A pickup roller 23 supplies the sheets S from the cassette 12 to the upstream conveyance path 13 one by one. Along the upstream conveyance path 13, feed roller pairs 13a and 13b and sheet guide plates 13c and 13d are provided. The sheet S is conveyed to an upper surface of the conveyance belt 14 through the upstream conveyance path 13. In the drawing, arrow A1 indicates a conveyance path of the sheet S from the cassette 12 to the conveyance belt 14.
The conveyance belt 14 is an endless belt comprising a mesh material having a plurality of through holes on a surface. Three rollers including a driving roller 14a and driven rollers 14b and 14c support the conveyance belt 14 such that the conveyance belt 14 is rotatable. A motor 24 rotates the driving roller 14a to rotate the conveyance belt 14. The motor 24 is an example of a driving device. In the drawing, A2 indicates a rotation direction of the conveyance belt 14. On a back surface of the conveyance belt 14, a negative pressure container 25 is arranged. The negative pressure container 25 is connected to a fan 26 for depressurization and adjusts the inside of the container to be in a negative pressure using air flow formed by the fan 26. Since the inside of the negative pressure container 25 is adjusted to be in a negative pressure container, the sheet S is adsorbed and held on the upper surface of the conveyance belt 14. In the drawing, A3 indicates the flow of air flow.
The ink jet heads 1A, 1B, 1C, and 1D are arranged to face the sheet S on the conveyance belt 14 across a small gap of, for example, 1 mm. The ink jet heads 1A to 1D each eject ink droplets on to the sheet S. When the sheet S passes below the ink jet heads 1A to 1D, an image is printed on the sheet S. In this example, the ink jet heads 1A to 1D have the same structure except that the color of inks to be ejected are different from each other. The colors of the inks are, for example, cyan, magenta, yellow, and black.
The ink jet heads 1A, 1B, 1C, and 1D are connected to corresponding ink tanks 3A, 3B, 3C, and 3D and ink supply pressure adjusting devices 32A, 32B, 32C, and 32D through ink flow paths 31A, 31B, 31C, and 31D, respectively. The ink flow paths 31A to 31D are, for example, tubes formed of a resin. The ink tanks 3A to 3D are containers where the inks are stored. The ink tanks 3A to 3D are arranged above the ink jet heads 1A to 1D, respectively. In a sleep mode, the ink supply pressure adjusting devices 32A to 32D adjust the ink jet heads 1A to 1D to have a negative pressure internally of, for example, −1 kPa with respect to the atmospheric pressure, such that leakage of inks from nozzles (refer to
After image formation, the sheet S is conveyed from the conveyance belt 14 to the downstream conveyance path 15. Along the downstream conveyance path 15, feed roller pairs 15a, 15b, 15c, and 15d, and sheet guide plates 15e and 15f that regulate the conveyance path of the sheet S are provided. The sheet S is conveyed from a discharge port 27 to a discharge tray 16 through the downstream conveyance path 15. In
Next, a configuration of the ink jet head 1A will be described with reference to
A piezoelectric actuator 8 (also referred to as “actuator 8”) is an example of a capacitive actuator that is a drive source in an operation of ejecting ink. In this example, an actuator 8 is provided for each of the nozzles 51. These actuators 8 are formed in an annular shape and are arranged such that the nozzles 51 are positioned at the centers thereof. One set of nozzles 51 and the actuators 8 form one channel. Regarding the size of the actuator 8, for example, the inner diameter is 30 μm, and the outer diameter is 140 μm. The actuators 8 are electrically connected to individual electrodes 81, respectively. Further, eight actuators 8 arranged in the Y direction are electrically connected to each other through a common electrode 82. The individual electrodes 81 and the common electrode 82 are further electrically connected to mounting pads 9, respectively. The mounting pad 9 functions as an input port that applies a drive signal (electrical signal) of a drive waveform to the actuator 8. The individual electrodes 81 apply drive waveforms to the actuators 8, respectively, and each of the actuators 8 is driven according to the applied drive waveform. For convenience of description, the actuators 8, the individual electrodes 81, the common electrodes 82, and the mounting pads 9 are indicated by solid lines in
The mounting pad 9 is electrically connected to a wiring pattern formed on the flexible substrate 6 through, for example, an anisotropic contact film (ACF). Further, the wiring pattern of the flexible substrate 6 is electrically connected to the head drive circuit 7. The head drive circuit 7 is, for example, an integrated circuit (IC). The head drive circuit 7 applies the drive waveform to the actuator 8 selected according to print data.
The diaphragm 53 is formed of an insulating inorganic material. The insulating inorganic material is, for example, silicon dioxide (SiO2). The thickness of the diaphragm 53 is, for example, 2 μm to 10 μm and preferably 4 μm to 6 μm. The diaphragm 53 and the protective layer 52 are curved inward by d31 mode deformation of the piezoelectric body 85 when a voltage is applied to the piezoelectric body 85. When the application of a voltage to the piezoelectric body 85 is stopped, the diaphragm 53 and the protective layer 52 return to the original states. Due to this reversible deformation, the volume of a pressure chamber 41 expands and contracts. When the volume of the pressure chamber 41 changes, the ink pressure in the pressure chamber 41 changes.
The protective layer 52 is formed of, for example, polyimide having a thickness of 4 μm. The protective layer 52 covers one surface of the bottom surface side of the nozzle plate 5 and further covers an inner circumferential surface of a hole of the nozzle 51.
Next, the drive waveform applied to the actuator 8 and an operation of the actuator 8 that ejects ink from the nozzles 51 will be described with reference to
The head drive circuit 7 applies a bias voltage V1 to the actuator 8 from time t0 to time t1. That is, the voltage V1 is applied between the upper electrode 86 and the lower electrode 84. The voltage to be applied is decreased to a voltage V0 (e.g., voltage V0=0 V), and the voltage V0 is applied from time t2 to time t3. Next, the voltage to be applied is increased to a voltage V2, and the voltage V2 is applied from time t4 to time t5 so as to eject ink. After the end of ejection, the voltage to be applied is increased up to the voltage V1 to attenuate residual vibration in the pressure chamber 41. The voltage V2 is lower than the bias voltage V1, and the voltage value of voltage V1 is determined based on, for example, an attenuation rate of the pressure vibration of the ink in the pressure chamber 41. For example, the length of the period of time from time t1 to time t3 and the length of the period of time from time t3 to time t5 are respectively set to a half-period of a natural vibration period λ, which is determined by ink characteristics and the inkjet head internal structure. The half-period of the natural vibration period λ is also referred to as “acoustic length (AL)”. During the series of operations, the voltage of the common electrode 82 is fixed to 0 V.
At time t2, when the voltage V0 (=0 V) is applied as an expansion pulse, the actuator 8 returns to a non-deformed state as schematically illustrated in
At time t4, when the voltage V2 is applied as a contraction pulse, as schematically illustrated in
After the ink is ejected, the voltage V1 is applied as a cancel pulse at time t6. The ink pressure in the pressure chamber 41 decreases when a droplet of ink is ejected. However, the vibration associated with the ink ejection remains in the pressure chamber 41. Therefore, by increasing the voltage from the voltage V2 to the voltage V1, the actuator 8 is driven such that the volume of the pressure chamber 41 contracts, the ink pressure in the pressure chamber 41 becomes substantially zero (0), and the residual vibration of the ink in the pressure chamber 41 is forcibly attenuated.
The drive waveform illustrated in
The head drive circuit 7 includes a shift register 71, a latch circuit 72, a level shifter 73, and a select switch 74. The select switch 74 comprises, for example, a transistor that is provided for each of the actuators 8. The control unit of the printer on the control substrate 17 loads the image data in the image memory 94 as a dot pattern and transmits, for example, image data corresponding to the number of nozzles 51 in
In addition, the control unit of the printer as the control substrate 17 supplies signal LATCH (including a latch signal and a channel signal)o the latch circuit 72. The latch circuit 72 latches a signal stored in the shift register 71 at a timing of the latch signal. The level shifter 73 converts the signal latched by the latch circuit 72 into a voltage signal at a level at which the select switch 74 can be turned on and off. As a result, a select switch 74 that is connected to the actuator 8 of the nozzle 51 ejecting the ink is turned on, and the drive waveform COM generated by the common drive waveform generation circuit 101 is thereby applied to the actuator 8. In the drawing, HGND represents a ground terminal of the actuators 8.
The switching type common drive waveform generation circuit 101 is driven by PWM such that the drive waveform COM applied to the actuator 8 is a waveform corresponding to a target drive waveform WCOM. That is, a feedback control is performed such that, when the target drive waveform WCOM is an analog signal, the drive waveform COM and the target drive waveform WCOM are the same and, when the target drive waveform WCOM is a digital signal, the drive waveform COM and the target drive waveform WCOM are similar to each other. The common drive waveform generation circuit 101 includes: a switching circuit 107 as an output switch; an inductor L; a feedback line 113 and a filter 108 as an example of the voltage waveform detection unit that detects the voltage waveform COM to be applied to the actuator 8; and a digital signal processing unit 120. That is, the voltage waveform detection unit detects a voltage waveform generated from a capacitive actuator. The filter 108 filters the detected voltage waveform. A capacitor Cc is a stabilizing capacitor for stabilizing the feedback control. The digital signal processing unit 120 further includes a waveform memory 103 as a storage unit of the target drive waveform WCOM, a subtraction/comparison unit 104 as an arithmetic circuit, a comparator 105, a triangular wave generation circuit 106, and an A/D (analog-digital) converter 109. The comparator 105 functions as a pulse width modulation circuit. The switching circuit 107 further includes a gate driver circuit 110, a high side switch SW1 connected to a power supply Vdd, and a low side switch SW2 connected to the ground.
The waveform memory 103 stores information of the target drive waveform WCOM in, for example, as digital data. The waveform memory 103 applies the target drive waveform WCOM to an input terminal (A) of the subtraction/comparison unit 104. The filter 108 removes a high frequency noise from the drive waveform COM fed back from a common line, and the A/D converter 109 converts the drive waveform COM from which the high frequency noise is removed by the filter 108 into a digital signal to generate a comparative drive waveform dCOM. The comparative drive waveform dCOM is applied to an input terminal (B) of the subtraction/comparison unit 104.
The subtraction/comparison unit 104 performs subtraction comparison (A-B) between the target drive waveform WCOM and the comparative drive waveform dCOM. When an error is present between the target drive waveform WCOM and the comparative drive waveform dCOM as a result of the subtraction comparison, the subtraction/comparison unit 104 applies an error dWCOM output from an output terminal (A-B) to an input terminal (+) of the comparator 105. When the value of the comparative drive waveform dCOM is less than the value of the target drive waveform WCOM, the error dWCOM is a positive value, and when the value of the comparative drive waveform dCOM is more than the value of the target drive waveform WCOM, the error dWCOM is a negative value. On the other hand, when the absolute value of the error dWCOM is in a predetermined range as a result of the subtraction comparison (including when no error is present), the subtraction/comparison unit 104 applies a disable signal as a stop signal output from an output terminal (A≈B) to the gate driver circuit 110 of the switching circuit 107. The comparative drive waveform that is compared to the target drive waveform is not particularly limited to a filtered digital waveform as long as it represents a voltage waveform to be applied to the actuator 8.
While the disable signal is applied, the gate driver circuit 110 turns off the high side switch SW1 and the low side switch SW2. That is, the switching of the output switch is stopped. In addition, the absolute value of the error dWCOM being in the predetermined range represents being within 10% or 5% of the maximum amplitude of the target drive waveform WCOM. For example, when the drive waveform of
In the comparator 105, the error dWCOM is input to an input terminal (+), and a triangular wave Tri having a predetermined frequency is applied to an input terminal (−). The comparator 105 as the pulse width modulation circuit compares the error dWCOM to the triangular wave Tri and modulates a pulse signal MCOM. The pulse signal MCOM is applied to the gate driver circuit 110. The gate driver circuit 110 switches on and off the high side switch SW1 and the low side switch SW2 according to the applied pulse signal MCOM. The high side switch SW1 and the low side switch SW2 are, for example, MOS transistors, and a reflux diode is inserted in parallel with the MOS transistor. The high side switch SW1 and the low side switch SW2 are not necessarily connected to the power supply Vdd and the ground. That is, the high side switch SW1 and the low side switch SW2 may be a first switch connected to a first potential and a second switch connected to a second potential.
Signal ACOM is output from the switching circuit 107 and is converted into the drive waveform COM through the inductor L, and the drive waveform COM is applied to the select switch 74. As described above, the select switch 74 that is connected to the actuator 8 selected according to the image data is turned on, and the drive waveform COM is applied thereto. When the drive waveform COM is applied, the operation of the actuator 8 is as describe above.
The load counting circuit 102 counts the number of actuators 8 driven during the same period as the number of loads. The load counting circuit 102 is an example of the load number detection unit. Being driven during the same period represents not only a case where drive timings are exactly the same (simultaneous) but also a case where charge/discharge periods of the actuators 8 partially overlap each other even when the drive timings are different from each other. For example, in the case of a binary head, the number of loads is the total number of actuators 8 driven within the same period.
In the example of
Referring back to
The size of the amplitude of the triangular wave Tri determines the sensitivity to the error dWCOM. Accordingly, when the amplitude of the triangular wave Tri changes depending on the number of loads, the sensitivity of PWM can be changed depending on the size of the load. Specifically, in a case where the amplitude of the triangular wave Tri increases, when the error dWCOM is changed, a change in pulse width is small, that is, the sensitivity to the error dWCOM is low. In other words, when the amplitude of the triangular wave Tri increases, PWM becomes shallow. Contrarily, in a case where the amplitude of the triangular wave Tri decreases, when the error dWCOM is changed, a change in pulse width is large, that is, the sensitivity to the error dWCOM is high. In other words, when the amplitude of the triangular wave Tri decreases, PWM becomes deep. This way, when the sensitivity of PWM changes depending on the size of the load, the operation will be described in detail with reference to
While the actuator 8 is charged, for example, as illustrated in
When the high side switch SW1 is turned off during a period where the actuator 8 is charged, the output ACOM of the switching circuit 107 decreases to be lower than the ground potential by electromotive force generated by the inductor L. Therefore, during this period, there is no interference with the operation irrespective of whether the low side switch SW2 is turned on or off. In this embodiment, in order to simplify the description, both the high side switch SW1 and the low side switch SW2 are turned off while A≈B. However, in order to reduce the ON resistance during reflux, the gate voltage may be controlled such that the low side switch SW2 is turned on during a period where the current refluxes through the reflux diode on the low side switch SW2 side.
While the actuator 8 is discharged, for example, as illustrated in
When the low side switch SW1 is turned off during a period where the actuator 8 is discharged, the voltage waveform COM increases to be higher than a power supply voltage by electromotive force generated from the inductor L. Therefore, during this period, there is no interference with the operation irrespective of whether the high side switch SW1 is turned on or off. In this embodiment, in order to simplify the description, both the high side switch SW1 and the low side switch SW2 are turned off while A≈B. However, in order to reduce the ON resistance during reflux, the gate voltage may be controlled such that the high side switch SW1 is turned on during a period where the current refluxes through the reflux diode on the high side switch SW1 side.
Here, when the error dWCOM is a positive value (WCOM>dCOM), it is necessary to increase the output. When the number of actuators 8 driven during the same period is large, that is, when the total load is high and the load capacitance is high, a relatively longer time is required for the output to rise. Therefore, a required ON period of the high side switch SW1 is longer. In this case, unless the sensitivity of PWM to the error dWCOM is set to be high, the drive waveform COM cannot follow the target drive waveform WCOM. Conversely, when the number of actuators 8 driven during the same period is small, that is, when the total load is low and the load capacitance is low, the output rises within a shorter period. Therefore, a required ON period of the high side switch SW1 is shorter. In this case, when the sensitivity of PWM to the error dWCOM is low, the actuator 8 is stable.
When the error dWCOM is a negative value (WCOM>dCOM), the same can be applied. When the load is high and the load capacitance is high, unless the sensitivity of PWM to the error dWCOM is set to be high, the drive waveform COM cannot follow the target drive waveform WCOM. Conversely, in a case where the load is low and the load capacitance is low, when the sensitivity of PWM to the error dWCOM is low, the actuator 8 is stable.
According to the first embodiment, the amplitude of the triangular wave Tri changes depending on the number of loads of the actuators 8 driven during the same period, that is, the sensitivity of PWM changes depending on the number of loads. As a result, the actuators 8 as capacitive loads can be stably driven whether the number of actuators 8 driven during the same period is small or large. Further, when the size of loads that are charged and discharged during the same period is detected and the sensitivity of PWM is adjusted according to the size of the load, feedback can be stabilized, and the reproducibility of the drive waveform can be improved.
In the first embodiment, the voltage waveform applied to the actuator 8 is filtered and then is applied to the digital signal processing unit 120, and the above-described operation is performed by digital processing to control the output switch. Examples of the digital signal processing include a method of using a random logic such as a FPGA (field-programmable gate array) and a method of performing processing using a DSP (digital signal processor) or a CPU (central processing unit) and a program. The signal processing using a program has a high degree of freedom for control but has a disadvantage in that the processing speed is slow. When a random logic is used, signal processing can be performed at a high speed, and there is an advantage in that the switching frequency is high.
Next, the liquid ejecting device 1 according to a second embodiment will be described by using the ink jet head 1A as an example.
The common drive waveform generation circuit 201 that generates the drive waveform COM as the common drive waveform includes: a first switching circuit 107A and a second switching circuit 107B as output switches; a first inductor L1 and a second inductor L2; the feedback line and the filter 108 as an example of the voltage waveform detection unit that detects the voltage waveform COM to be applied to the actuator 8; and a digital signal processing unit 220. The filter 108 filters the detected voltage waveform. The capacitor Cc is a stabilizing capacitor for stabilizing the feedback control.
The digital signal processing unit 220 further includes the waveform memory 103 as a storage unit of the target drive waveform WCOM, the subtraction/comparison unit 104 as an arithmetic circuit, a first comparator 105A, a second comparator 105B, the A/D converter 109, and a determination circuit 111. That is, the common drive waveform generation circuit 201 according to the second embodiment includes two sets of circuits including the comparator 105, the switching circuit 107, and the inductor L (A or B is added to the end of each of the reference numerals). The first comparator 105A functions as a first pulse width modulation circuit, and the second comparator 105B functions as a second pulse width modulation circuit. Further, the first switching circuit 107A includes a first gate driver circuit 110A, a first high side switch SW1A connected to the power supply Vdd, and a first low side switch SW2A connected to the ground. The second switching circuit 107B includes a second gate driver circuit 110B, a second high side switch SW1B connected to the power supply Vdd, and a second low side switch SW2B connected to the ground.
The circuit including the first comparator 105A, the first switching circuit 107A, and the first inductor L1 is used when the load is low. The circuit including the second comparator 105B, the second switching circuit 107B, and the second inductor L2 is used when the load is high. Therefore, the inductance of the second inductor L2 is lower than the inductance of the first inductor L1 (L2<L1). Further, it is preferable that the capacitance of a transistor used for the second high side switch SW1B and the second low side switch SW2B (of the second switching circuit 107B) is higher than that of a transistor used for the first high side switch SW1A and the first low side switch SW2A (of the first switching circuit 107A). In addition, the amplitudes of a triangular wave Tri to be applied to the first comparator 105A and a triangular wave Tri to be applied to the second comparator 105B may be the same as each other but are preferably set to values such that an appropriate sensitivity can be obtained. In this embodiment, the inductors are switched depending on the number of loads. A time required to charge and discharge the load depends on both the size of the load and the inductance of the inductor. Therefore, unlike the first embodiment, when the load is high, the amplitude of the triangular wave Tri is not necessarily reduced to increase the sensitivity of PWM. For example, the amplitude of the triangular wave Tri to be applied to the first comparator 105A is set to be lower than that of the triangular wave Tri to be applied to the second comparator 105B. That is, contrary to the first embodiment, the amplitude of the triangular wave Tri on the second inductor L2 side used when the load is high is lower than the amplitude of the triangular wave Tri on the first inductor L1 side used when the load is low.
The determination circuit 111 determines whether to drive the circuit on the first inductor L1 side or the circuit on the second inductor L2 side depending on the number of loads. For example, a threshold (for example, when the total number of nozzles 51 is 1200, the threshold is 600 or half of the total number of nozzles) of the number of loads is provided. When the number of actuators 8 driven during the same period is less than or equal to the threshold, the circuit on the first inductor L1 side is selected. When the number of actuators 8 driven during the same period is more than the threshold, the circuit on the second inductor L2 side is selected. The determination circuit 111 outputs a control signal HPsel for setting the circuit on the inductor side to be used to be active based on the determination result and applies the control signal HPsel to the first or second gate driver circuit 110A or 110B.
When the load is low, the circuit on the first inductor L1 side is selected, and charge is supplied to the actuator 8. Conversely, when the load is high, the circuit on the second inductor L2 side having a lower inductance than the first inductor L1 is selected, and charge is supplied to the actuator 8. That is, when the load is high, there may be a case where the first inductor L1 cannot supply the required amount of charge during the required period as compared to the second inductor L2. However, the second inductor L2 supplies a larger amount of charge than the first inductor L1 during a predetermined period. Therefore, a higher current (ICOM2>ICOM1) than that of the first inductor L1 flows such that charge can be supplied to the actuator 8.
On the other hand, in the second inductor L2, the current rises more steeply than the first inductor L1. Therefore, in a case where the load is low, when the circuit on the second inductor L2 side is selected, the ripple of the output may increase. In addition, there is a limit on the minimum ON time of the transistor used as the high side switches SW1A and SW1B and the low side switches SW2A and SW2B. The limit value of the minimum ON time increases as the capacitance of the transistor increases. Therefore, when the load is low, there may be a case where stable driving cannot be performed in the circuit on the second inductor L2 side. By reducing the frequency of PWM, the ON duty can be reduced even when the minimum ON time of the transistor is long. However, when the frequency of PWM is reduced, the reproducibility of the drive waveform COM deteriorates, which may affect ink ejection characteristics. Accordingly, according to the second embodiment, these problems are solved by selectively using the two inductors L1 and L2 depending on the number of loads. That is, the actuators 8 as capacitive loads can be stably driven irrespective of whether the number of actuators 8 driven during the same period is small or large. As a result, the reproducibility of the drive waveform COM for PWM driving at a higher frequency can be improved, and ejection characteristics can be improved.
Further, by using the two inductors L (L1, L2), the capacitance value of the stabilizing capacitor Cc can be made to be low, and thus power consumption can be reduced. By increasing the number of the inductors L having different inductances and the number of drive circuits thereof to three or four, the capacitance value of the stabilizing capacitor Cc can be made to be lower. Therefore, power consumption can be further reduced, and the drive waveform COM can be accurately controlled. In addition, heat generation and a temperature increase can be suppressed.
Next, the liquid ejecting device 1 according to a third embodiment will be described by using the ink jet head 1A as an example.
The common drive waveform generation circuit 301 that generates the drive waveform COM as the common drive waveform is configured by combining the functions of the common drive waveform generation circuit 101 according to the first embodiment and the common drive waveform generation circuit 201 according to the second embodiment. That is, the common drive waveform generation circuit 301 includes: the first switching circuit 107A and the second switching circuit 107B as output switches; the first inductor L1 and the second inductor L2; the feedback line 113 and the filter 108 as an example of the voltage waveform detection unit that detects the voltage waveform COM to be applied to the actuator 8; and a digital signal processing unit 320. The filter 108 filters the detected voltage waveform. The capacitor Cc is a stabilizing capacitor for stabilizing the feedback control.
The digital signal processing unit 320 further includes the waveform memory 103 as a storage unit of the target drive waveform WCOM, the subtraction/comparison unit 104 as an arithmetic circuit, the first comparator 105A, the second comparator 105B, the triangular wave generation circuit 106, the A/D converter 109, and the determination circuit 111. Further, the first switching circuit 107A includes the first gate driver circuit, the first high side switch SW1A connected to the power supply Vdd, and the first low side switch SW2A connected to the ground. The second switching circuit 107B includes the second gate driver circuit, the second high side switch SW1B connected to the power supply Vdd, and the second low side switch SW2B connected to the ground.
In the above-described circuit, the load counting circuit 102 counts the number of actuators 8 being driven during the same period. This counted number of actuators 8 is used as the number of loads. The load counting circuit 102 supplies the counted number of actuators 8 to the determination circuit 111 as the load number information. The determination circuit 111 determines whether to drive the circuit on the first inductor L1 side or the circuit on the second inductor L2 side depending on the number of loads, outputs the control signal HPsel for setting the circuit on the inductor side to be driven to be active, and applies the control signal HPsel to the first or second gate driver circuit 110A or 110B through a gate circuit 112A or 112B. The control signal HPsel is input to the gate circuit 112A by a negative logic and is input to the gate circuit 112B by a positive logic. Therefore, while the control signal HPsel is at an L level, the first gate driver circuit is active, and while the control signal HPsel is at an H level, the second gate driver circuit is active. Further, the load number information is applied to the triangular wave generation circuit 106. The triangular wave generation circuit 106 generates the triangular wave Tri having an amplitude adjusted according to the number of loads and applies the triangular wave Tri to the first or second comparator 105A or 105B on the side to be driven. For example, the determination circuit roughly classifies the number of loads and determines whether to drive the circuit on the first inductor L1 side or the circuit on the second inductor L2 side depending on the number of loads as in the second embodiment. In either case, depending on the number of loads, as in the first embodiment, when the number of loads is large (that is, when the total load is high), the amplitude of the triangular wave Tri is decreased; and when the number of loads is small (that is, when the total load is low), the amplitude of the triangular wave Tri is increased.
In addition, when the absolute value of the error dWCOM between the target drive waveform WCOM and the comparative drive waveform dCOM is in a predetermined range (including when no error is present), the subtraction/comparison unit 104 outputs an H level as a stop signal from an output terminal (A≈B).
The stop signal is input to one input terminal of the gate circuit 112A. The control signal HPsel is applied to the other input terminal of the gate circuit 112A. When one input is at an H level or the other input is at an H level, the gate circuit 112A sets an output disable 1 signal as the H level. While at least the H level as the stop signal is output from the output terminal (AB), the disable 1 signal is at the H level. While the disable signal is at the H level, the first gate driver circuit 110A turns off the first high side switch SW1A and the first low side switch SW2A.
The stop signal is input to one input terminal of the gate circuit 112B. The control signal HPsel is applied to the other input terminal of the gate circuit 112B. When one input is at an H level or the other input is at an H level, the gate circuit 112B sets an output disable 2 signal as the H level. While at least the H level as the stop signal is output from the output terminal (AB), the disable 2 signal is at the H level. While the disable signal is at the H level, the first gate driver circuit 110B turns off the first high side switch SW1B and the first low side switch SW2B.
According to the third embodiment, the functions of the common drive waveform generation circuit 101 according to the first embodiment and the common drive waveform generation circuit 201 according to the second embodiment are combined. As a result, the two inductors L1 and L2 can be selectively used depending on the number of loads, the sensitivity of PWM can be finely adjusted depending on the number of loads, and thus feedback is stable in a wider range. Further, by providing a dead band where switching is stopped, unnecessary switching can be reduced, and power consumption can be reduced.
In a modification example of ink jet head 1A, as illustrated in
In the above-described embodiments, the ink jet heads 1A and 101A of the ink jet printer 1 were described as an example of a liquid ejecting device. However, the liquid ejecting device may be a material ejection head of a 3D printer or a sample ejection head of a liquid dispensing device. In such cases, references to “image data” can be considered equivalent to “pattern data” in the context of a 3D printer or more generally “intended output data” in the context of a liquid ejection device. In general, particular configuration and arrangement of aspects and components for the above-described example embodiments are not particularly limited as long as the actuator 8 is a capacitive load. Furthermore, in some examples, pulse-density modulation (PDM) may be adopted instead of pulse width modulation (PWM).
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-037557 | Mar 2019 | JP | national |
