JP2013215958A - Driving device, liquid jetting head, liquid jetting recorder and driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving device for driving a liquid jetting head which avoids the occurrence of a failure such as cavitation in a nozzle even if the number of driven nozzles changes when driving the liquid jetting head.SOLUTION: In the driving device 110, the magnitude of a load capacity of a pressure generating element PZT is detected in advance by a load current detection part 116. A current supplied to the pressure generating element PZT is restricted by a variable charging current restriction part 117 in accordance with the detected level of the load capacity.

Description

  The present invention relates to a driving apparatus, a liquid ejecting head, a liquid ejecting recording apparatus, and a driving method for driving a liquid ejecting head that ejects liquid from nozzle holes to record images and characters on a recording medium.

In general, a liquid ejecting head to which ink (liquid) is supplied from an ink tank has a head chip. Recording is performed by ejecting ink from the nozzle holes of the head chip onto a recording medium.
FIG. 8 is a block diagram illustrating a configuration example of a drive unit of a liquid jet head chip built in the liquid jet head.
In the example shown in this figure, the liquid jet head chip 73 is configured to include 512 nozzles NZ1 to NZ512 (generically referred to as “nozzle NZ”). The pressure generating element PZT corresponding to each nozzle NZ in the liquid ejecting head chip 73 is driven by the driving unit 100 mounted on the control circuit board 80. The driving unit 100 includes four driver ICs 101 to 104 serving as driving devices for the liquid jet head chip 73, and each of the driver ICs (IC1 to IC4) 101 to 104 includes 128 nozzles NZ. The pressure generating element PZT corresponding to each is driven. The driver ICs (IC1 to IC4) 101 to 104 input various image signals for printing and various clock signals (shift CLK, pixel CLK, etc.) used when performing a printing operation via the connector 100A. .

  FIG. 9 is a diagram illustrating a configuration example of a driving device for the pressure generating element PZT. For example, FIG. 9 is a block diagram illustrating a configuration example of the driver IC illustrated in FIG. As shown in FIG. 9, the driving device (driver IC) 101 includes a selector 111, a set value storage element 112, a waveform generation circuit 113, a shift register 121, a latch circuit (latch) 122, and a waveform selection circuit (waveform selection) 123. And a level conversion circuit (level conversion) 124. The details of each component will be described in the section of the embodiment described later.

  In the driving device 101 shown in FIG. 9, the pressure signals corresponding to the n nozzles NZ in the liquid ejecting head chip 73 (see FIG. 8) are generated by the driving signals OUT1 to OUTn output from the level conversion circuit 124. The element PZT is driven.

By the way, this pressure generating element PZT has a very fast response speed to the drive signals OUT1 to OUTn. For this reason, as shown in FIG. 10A, when the pressure generating element PZT is driven by a rectangular wave having a peak value Vp, a sudden pressure change is generated inside the nozzle. For this reason, the meniscus operation cannot be controlled with high precision, satellites or mists may be generated, and the side wall of the pressure generating element PZT is rapidly deformed, which may cause cavitation. is there.
Therefore, as shown in FIG. 9 described above, a fixed resistor R is inserted between the level conversion circuit 124 and the drive power source Vd (for example, DC 30V power source). In this case, the pressure generating element PZT is a capacitive load (capacitor load), and a first-order lag circuit is configured between the fixed resistor R and the capacitance of the pressure generating element PZT.

  Therefore, as shown in FIG. 10B, the driving voltage of the pressure generating element PZT is gently lowered while drawing a curve by the first-order lag circuit composed of the fixed resistor R and the capacitance of the pressure generating element PZT. The voltage rises to Vp. Therefore, the drive voltage waveform of the pressure generating element PZT does not rise rapidly but rises gently from time t1 to t2. For this reason, the displacement of the pressure generating element PZT also becomes gradual, a sudden pressure change does not occur inside the nozzle NZ, and the occurrence of cavitation and mist can be suppressed.

An object of the ink jet head described in Patent Document 1 is to provide an ink jet head in which cavitation does not occur.
In the inkjet head described in Patent Document 1, a chamber serving as an ink chamber is provided on the piezoelectric plate, and a voltage is applied to the side wall of the chamber to eject ink using the reverse piezoelectric phenomenon of the piezoelectric plate. Predetermined electrical resistance is put on the driving circuit for driving the head chip and the wiring from the power source to the driving circuit, and the chamber side wall is prevented from abrupt deformation and the occurrence of cavitation is reduced.

JP 2008-207354 A

As described above, the pressure generating element PZT corresponding to each nozzle NZ becomes a capacitive load (capacitor load) when viewed from the drive circuit. Therefore, the driving current for driving the pressure generating element PZT is limited by the fixed resistor R.
However, the fixed resistor R becomes a common impedance when driving a plurality of nozzles. For this reason, when ejecting ink droplets simultaneously from a plurality of nozzles NZ, the drive current for driving each nozzle NZ is limited by the fixed resistor R having a common impedance. For this reason, for example, the time constant determined by the resistance value of the fixed resistor R and the capacitance of the piezoelectric actuator changes greatly when the number of nozzles to be driven is one and when the number of nozzles to be driven is plural. The rising waveform (waveform rising time) shown in FIG. Thus, when this fixed resistor R becomes a common impedance, when driving a plurality of nozzles, the drive current supplied to each nozzle NZ changes according to the number of nozzles to be driven, and the drive A large difference occurs in the rising waveform of the signal. For this reason, the printing state of an image changes according to the number of nozzles to drive.

  The present invention has been made to solve the above problems, and the object of the present invention is to generate defects such as cavitation in a nozzle even when the number of nozzles to be driven changes even when the liquid jet head is driven. It is an object to provide a driving apparatus, a liquid ejecting head, a liquid ejecting recording apparatus, and a driving method for driving a liquid ejecting head.

The present invention has been made to solve the above-described problems, and a driving device according to the present invention includes a plurality of nozzles in which a plurality of nozzle openings are arranged, and a pressure generation chamber communicating with each nozzle opening. And a pressure generating element that generates a pressure fluctuation in the pressure generating chamber when a driving signal is input, and a driving device that drives a liquid ejecting head that discharges ink droplets from the nozzle opening by the pressure fluctuation. A plurality of driving units that respectively drive the pressure generating elements, a detection unit that detects a magnitude of a load capacity of each of the pressure generating elements driven by the plurality of driving units, A setting unit that sets a limit value that limits the current supplied to the plurality of drive units according to the magnitude, and a current that is supplied to each of the plurality of drive units according to the limit value A current limiting unit that, characterized in that it comprises a.
Thus, the magnitude of the load capacity of the pressure generating element to be driven is detected in advance, and the drive current supplied to the pressure generating element is limited according to the detected magnitude of the load capacity. Thus, when the liquid jet head is driven, it is possible to avoid occurrence of problems such as cavitation in the nozzle even if the number of nozzles to be driven changes.

In the driving device according to the present invention, in the driving device described above, the detection unit supplies the driving unit with the magnitude of the load capacity of the pressure generating element driven by the plurality of driving units. Detection is based on a value.
With this configuration, the magnitude of the load capacity of the pressure generating element can be detected by measuring the current value supplied to the drive unit. For this reason, the magnitude of the load capacity of the pressure generating element can be easily detected by a simple method.

In the driving device according to the present invention, in the driving device, the detection unit detects a value of a current supplied to the plurality of driving units.
With this configuration, the magnitude of the load capacity of the pressure generating element can be detected by measuring the current value supplied to the drive unit. For this reason, the magnitude of the load capacity of the pressure generating element can be easily detected by a simple method.

In the drive device according to the present invention, in the drive device, the detection unit detects a total value of currents supplied to the plurality of drive units.
With this configuration, it is possible to detect the magnitude of the load capacity of the pressure generating element to be driven by detecting the total value of the load currents flowing through the pressure generating element to be driven. For this reason, the magnitude | size of the load capacity | capacitance which the pressure generating element used as a drive object has can be easily detected by a simple method.

In the drive device according to the present invention, in the drive device, the setting unit sets a limit value that limits a value of a current supplied to the plurality of drive units, and the current limit unit is configured according to the limit value. The total value of the current supplied to each of the plurality of driving units is limited.
With this configuration, the setting unit sets a limit value for limiting the current supplied to the driving unit according to the load capacity of the pressure generating element detected by the detection unit, and the current limit The unit limits the total value of the current supplied to the drive unit according to the limit value set by the setting unit.
Thereby, according to the magnitude | size of the load capacity | capacitance of the pressure generating element detected by the detection part, the electric current value supplied to a pressure generating element can be restrict | limited easily.

In the drive device according to the present invention, in the drive device, the setting unit sets a limit value that limits a total value of currents supplied to the plurality of drive units.
Thereby, according to the magnitude | size of the load capacity | capacitance of a pressure generating element, the total value of the electric current value supplied to this pressure generating element can be set.

In the driving device according to the present invention, in the driving device, the setting unit sets a limit value for limiting a current supplied to the plurality of driving units in proportion to a size of the load capacity. And
With this configuration, the setting unit sets a limit value that limits the current supplied to the drive unit in proportion to the load capacity of the pressure generating element detected by the detection unit.
Thereby, the current limiting value supplied to the pressure generating element can be set in proportion to the magnitude of the load capacity of the pressure generating element detected by the detection unit.

In the drive device according to the present invention, in the drive device, the setting unit may be configured to supply current supplied to the plurality of drive units when the detection unit detects the magnitude of the load capacity. Is set to a predetermined value such that the pressure generating element is charged by the current, and the detection unit is based on a voltage value that has changed during a predetermined period in the voltage charged to the pressure generating element. Then, a total value of currents supplied to the plurality of driving units is detected.
With this configuration, when detecting the magnitude of the load capacity, the pressure generating element is charged with a fixed current for a predetermined period, and the charging voltage of the pressure generating element that has changed during the predetermined period is Based on the value, the magnitude of the load capacity of the pressure generating element is detected.
Thereby, the magnitude of the load capacity of the pressure generating element can be easily detected.

The liquid jet head according to the present invention is driven by the drive device described above.
Thereby, even if the number of nozzles to be driven changes, the liquid ejecting head can avoid occurrence of problems such as cavitation in the nozzles.

A liquid jet recording apparatus according to the present invention includes the liquid jet head described above.
Accordingly, the liquid jet recording apparatus can avoid occurrence of problems such as cavitation in the nozzles even when the number of nozzles to be driven is changed when printing an image with the liquid jet head.

The driving method according to the present invention includes a plurality of nozzles in which a plurality of nozzle openings are arranged, a pressure generation chamber communicating with each nozzle opening, and a pressure fluctuation in the pressure generation chamber by inputting a drive signal. A liquid ejecting head that ejects ink droplets from the nozzle opening by the pressure fluctuation, wherein a plurality of driving units respectively drive the pressure generating elements. And detecting the magnitude of the load capacity of each of the pressure generating elements driven by the plurality of driving sections, and supplying the plurality of driving sections according to the magnitude of the load capacity. The method includes a step of setting a limit value for limiting a current to be supplied and a step of limiting a current supplied to each of the plurality of driving units according to the limit value.
Accordingly, even when the number of nozzles to be driven changes when driving the liquid jet head, it is possible to avoid the occurrence of problems such as cavitation in the nozzles.

  According to the present invention, the magnitude of the load capacity of the pressure generating element is detected, and the current supplied to the pressure generating element is limited according to the detected magnitude of the load capacity. Therefore, when driving the liquid ejecting head, even if the number of nozzles to be driven changes, it is possible to avoid occurrence of problems such as cavitation in the nozzles.

FIG. 3 is a perspective view of a liquid jet recording apparatus equipped with a liquid jet head including the driving device of the present invention. FIG. 3 is a partially broken perspective view of a liquid ejecting head. It is a block diagram which shows the structure of the drive device in 1st Embodiment of this invention. It is a figure which shows the structural example of the variable charging current limiting part 117 and the variable discharge current limiting part 118. 6 is a time chart showing an ink droplet ejection cycle in the first embodiment. It is a block diagram which shows the structure of the drive device in 2nd Embodiment of this invention. 10 is a time chart showing an ink droplet ejection cycle in the second embodiment. FIG. 6 is a block diagram illustrating a configuration example of a driving unit of a liquid jet head chip. It is a figure which shows the structural example of the drive device of the pressure generating element PZT. It is a figure which shows the example of the drive signal of the pressure generating element PZT.

[First Embodiment]
(Configuration of liquid jet recording apparatus)
FIG. 1 is a perspective view of a liquid jet recording apparatus 1 showing an example of a liquid jet recording apparatus equipped with a liquid jet head equipped with a driving device of the present invention.
The liquid jet recording apparatus 1 includes a pair of transport mechanisms 2 and 3 that transport a recording medium S such as paper, a liquid jet head 4 that ejects ink droplets onto the recording medium S, and supplies ink to the liquid jet head 4. And a scanning unit 6 that scans the liquid ejecting head 4 in a direction (sub-scanning direction) substantially orthogonal to the conveyance direction (main scanning direction) of the recording medium S.
In the following description, the sub-scanning direction is the X direction, the main scanning direction is the Y direction, and the direction perpendicular to both the X direction and the Y direction is the Z direction.

  The pair of transport mechanisms 2 and 3 includes grid rollers 20 and 30 that extend in the sub-scanning direction, pinch rollers 21 and 31 that extend in parallel with the grid rollers 20 and 30, respectively, and grid grids, although not shown in detail. And a drive mechanism such as a motor for rotating the rollers 20 and 30 around the axis.

  The liquid supply means 5 includes a liquid container 50 that contains ink, and a liquid supply pipe 51 that connects the liquid container 50 and the liquid ejecting head 4. A plurality of liquid containers 50 are provided. Specifically, ink tanks 50Y, 50M, 50C, and 50B containing four types of inks of yellow, magenta, cyan, and black are provided side by side. Each of the ink tanks 50Y, 50M, 50C, 50B is provided with a pump motor M, which can press and move the ink to the liquid ejecting head 4 through the liquid supply pipe 51. The liquid supply pipe 51 is formed of a flexible hose having flexibility that can correspond to the operation of the liquid ejecting head 4 (carriage unit 62).

  The scanning unit 6 includes a pair of guide rails 60 and 61 provided extending in the sub-scanning direction, a carriage unit 62 slidable along the pair of guide rails 60 and 61, and the carriage unit 62 in the sub-scanning direction. And a drive mechanism 63 to be moved. The drive mechanism 63 rotates a pair of pulleys 64 and 65 disposed between the pair of guide rails 60 and 61, an endless belt 66 wound between the pair of pulleys 64 and 65, and one pulley 64. And a drive motor 67 to be driven.

  The pair of pulleys 64 and 65 are disposed between both end portions of the pair of guide rails 60 and 61, respectively, and are disposed at an interval in the sub-scanning direction. The endless belt 66 is disposed between the pair of guide rails 60 and 61, and the carriage unit 62 is coupled to the endless belt 66. A plurality of liquid jet heads 4 are mounted on the base end portion 62 a of the carriage unit 62. Specifically, liquid jet heads 4Y, 4M, 4C, and 4B that individually correspond to four types of inks of yellow, magenta, cyan, and black are mounted side by side in the sub-scanning direction.

(Liquid jet head)
FIG. 2 is a partially broken perspective view of the liquid ejecting head 4.
As shown in the figure, the liquid ejecting head 4 includes an ejecting unit 70 that ejects ink droplets onto the recording medium S (see FIG. 1), and a control circuit board 80 electrically connected to the ejecting unit 70. The pressure buffer 90 interposed on the bases 41 and 42 is provided between the jetting unit 70 and the liquid supply pipe 51 via connection parts 93 and 94, respectively. The pressure buffer 90 is for allowing the ink supply to flow from the liquid supply pipe 51 to the ejection unit 70 while buffering fluctuations in ink pressure.

  The ejection unit 70 includes a flow path substrate 71 connected to the pressure buffer 90 via a connection unit 72, and a liquid ejection head chip that ejects ink as droplets onto the recording medium S when a voltage is applied. 73, and a flexible wiring 74 that is electrically connected to the liquid jet head chip 73 and the control circuit board 80 and transmits a drive signal to the liquid jet head chip 73. The control circuit board 80 includes a drive unit 100 that generates a drive pulse for the liquid jet head chip 73 based on a signal such as pixel data from a main body control unit (not shown) of the liquid jet recording apparatus 1.

The liquid ejecting head chip 73 includes a substantially rectangular piezoelectric actuator having a longitudinal direction in the Z direction in FIG. 2 and a plurality of nozzles in which a plurality of nozzle openings are arranged in the Y direction. The piezoelectric actuator is made of, for example, PZT (lead zirconate titanate) as a pressure generating element. The piezoelectric actuator has a pressure generating chamber communicating with each nozzle opening and a drive electrode portion extending in a plate shape.
The drive electrode portion is electrically connected to the control circuit board 80 via the flexible wiring 74, whereby a drive signal is input from the control circuit board 80 to the liquid ejecting head chip 73. When a drive signal is input, a pressure fluctuation in the pressure generating chamber is generated, and an ink droplet is ejected from the nozzle opening by the pressure fluctuation.

In addition, a nozzle plate made of polyimide or the like is provided on the front end surface of the piezoelectric actuator (the end surface on the lower side in the Z direction in FIG. 2). One main surface of the nozzle plate is a bonding surface to the piezoelectric actuator, and the other main surface is coated with a water-repellent or hydrophilic water-repellent film for preventing adhesion of ink or the like.
In addition, as described above, a plurality of nozzle holes (nozzle openings) are formed in the nozzle plate at predetermined intervals (intervals equal to the pressure generating chamber pitch) in the longitudinal direction. A nozzle hole is formed in nozzle plates, such as a polyimide film, using an excimer laser apparatus, for example. These nozzle holes are respectively arranged in agreement with the pressure generating chambers.

  Under such a configuration, a predetermined amount of ink is supplied to the flow path substrate 71 from the storage chamber in the pressure buffer 90 (see FIG. 2) via the connection portions 72 and 94. Further, the flow path substrate 71 communicates with the pressure generation chamber of the liquid jet head chip 73 and has a structure that allows ink to be distributed from the connection portions 72 and 94 to the pressure generation chamber. That is, the pressure generation chamber functions as an ink chamber filled with ink, while the flow path substrate 71 functions as a common ink chamber that communicates the pressure generation chambers.

(Configuration of Drive Device of First Embodiment)
FIG. 3 is a block diagram showing the configuration of the drive device according to the first embodiment of the present invention. The driving device shown in FIG. 3 is a device built in the liquid jet head 4 provided in the liquid jet recording apparatus 1 shown in FIG. More specifically, the driving device is mounted as a driver IC on the control circuit board 80 of the liquid jet head 4 shown in FIG. The driving device 110 drives the piezoelectric actuator in the liquid jet head chip 73 described above.

  In the present embodiment, the piezoelectric actuator corresponds to each component of the piezoelectric actuator that is driven so as to eject ink droplets corresponding to each nozzle (corresponding to the drive electrode portion and the drive electrode portion corresponding to each nozzle NZ). In order to distinguish the part of the driving part) from the integrated piezoelectric actuator, it is called a pressure generating element PZT. The phrase “driving the nozzle” more precisely means that the pressure generating element PZT corresponding to the nozzle is driven.

  The driving device 110 shown in FIG. 3 is a driving device that performs image printing in a binary mode to be described later. The driving device 110 includes a selector 111, a set value storage element 112, a waveform generation circuit 113, a current limit value setting unit ( (Power supply side) 114, current limit value setting unit (GND side) 115, load current detection unit 116, variable charge current limit unit 117, variable discharge current limit unit 118, shift register 121, latch circuit (latch) 122, waveform selection circuit A (waveform selection) 123 and a level conversion circuit (level conversion) 124 are included.

  The selector 111 receives image data (or setting data), data IN which is an image data capture signal, and shift CLK which is a clock signal for performing data shift (data transfer) in the shift register 121. . The selector 111 captures image data in synchronization with the data IN signal, and generates and outputs a 2-bit signal D2b based on the captured image data.

  For example, the 2-bit signal D2b indicates that ink droplets are not ejected from the nozzle NZ when the bit value is “00”, and one ink droplet is ejected from the nozzle NZ when the bit value is “01”. “10” indicates that two ink droplets are ejected from the nozzle, and “11” indicates that three ink droplets are ejected from the nozzle. When the 2-bit data D2b is “10”, two ink droplets are continuously ejected from the nozzle. When the bit data is “11”, three ink droplets are continuously ejected from the nozzle. The plurality of ink droplets are ejected onto a sheet of paper as a single drop of ink by surface tension.

  When only “00” and “01” are used as the 2-bit signal D2b, either the ink droplet is ejected from the nozzle NZ or the ink droplet is not ejected from the nozzle NZ. This is called the binary mode in which images are selected and printed. On the other hand, when “00”, “01”, “10”, and “11” are used as the 2-bit signal D2b and the amount of ink droplets to be ejected is selected to perform image printing, the gray scale mode is set. be called.

  The driving device 110 according to the first embodiment is an example of the driving device 110 that performs printing in a binary mode.

  The 2-bit signal D2b output from the selector 111 is output toward the shift register 121 and the set value storage element 112. The selector 111 outputs the shift CLK to the shift register 121 and the set value storage element 112.

  The shift register 121 holds the 2-bit data indicated by the 2-bit signal D2b input from the selector 111 while sequentially shifting (transferring) the data in a cycle synchronized with the shift CLK. When all the data to be printed on the shift register 121 (n data to be printed by the liquid ejecting head chip 73) is input, the n pieces of image data (more accurately stored in the shift register 121 by the pixel CLK) are input. Are latched by the latch circuit 122. Further, the shift register 121 outputs the output 2-bit data to the data OUT while sequentially shifting (transferring) the held 2-bit data in a cycle synchronized with the shift CLK.

The set value storage element 112 receives the above-described 2-bit signal D2b and the shift CLK from the selector 111. The set value storage element 112 holds information on “charge current value per nozzle (reference value)” and information on “discharge current value per nozzle (reference value)”. The set value storage element 112 outputs this “charge current value per nozzle” information to the current limit value setting unit (power supply side) 114 as a signal Iup, and “discharge current value per nozzle (reference value)”. ) ”Is output to the current limit value setting unit (GND side) 115 as a signal Idp.
The set value storage element 112 generates a signal of a waveform set value (for example, a waveform height and a waveform output period) according to the content of the 2-bit data indicated by the 2-bit signal D2b. A set value signal is output to the waveform generation circuit 113.

The waveform generation circuit 113 generates a waveform signal Wave from the waveform setting value signal input from the setting value storage element 112 and outputs the waveform signal Wave to the waveform selection circuit 123.
The waveform generation circuit 113 includes a waveform signal Wave0 to be applied to the pressure generating element PZT when ink is not ejected from the nozzle NZ and a waveform to be applied to the pressure generating element PZT in order to eject ink droplets from the nozzle NZ. A signal Wave1 is generated.
The waveform signal Wave0 generated by the waveform generation circuit 113 is, for example, a waveform signal applied to the pressure generating element PZT in order to prevent ink sticking.

The waveform generation circuit 113 also generates a load detection waveform WaveD that is used to detect the load current of the nozzle NZ (pressure generating element PZT).
The waveform generation circuit 113 outputs the generated waveform signals Wave0, Wave1, and WaveD to the waveform selection circuit 123.
The load detection waveform WaveD is generated so as to be output at a timing different from the pulses (waveforms) included in the waveform signals Wave0 and Wave1. The load detection waveform WaveD can be handled as waveform signals Wave0 and Wave1 on which the load detection waveform WaveD is superimposed by time-division multiplexing the waveform signals Wave0 and Wave1, respectively.

  Based on the signal (2-bit data) input from the latch circuit 122, the waveform selection circuit 123 selects either the waveform signal Wave0 or Wave1 output from the waveform generation circuit 113 corresponding to each nozzle NZ, Output to the level conversion circuit 124.

  The level converting circuit 124 converts the voltage level of the waveform signal Wave0 or Wave1 set for each pressure generating element PZT input from the waveform selecting circuit 123 at the timing of printing an image by the power supply Vd, and drives the signals OUT1 to OUT1. Output as OUTn. Each pressure generating element PZT is driven by drive signals OUT1 to OUTn output from the level conversion circuit 124.

Further, the current limit value setting unit (power supply side) 114 receives the load current detection signal Idet of the nozzle NZ (pressure generation element PZT) detected by the load current detection unit 116 and “1” input from the set value storage element 112. Based on the information of “charging current value per nozzle”, a signal ILu for setting a limit current value (power supply side) when charging the pressure generating element PZT is generated and output to the variable charging current limiting unit 117.
Further, the current limit value setting unit (GND side) 115 receives the load current detection signal Idet of the nozzle NZ (pressure generating element PZT) detected by the load current detection unit 116 and “1” input from the set value storage element 112. Based on the information of “discharge current value per nozzle”, a signal ILd for setting a limit current value (GND side) when discharging the pressure generating element PZT is generated and output to the variable discharge current limiting unit 118.

  The load current detection unit 116 performs an operation of detecting the load current of the nozzle NZ (pressure generating element PZT) before discharging the ink liquid from the nozzle NZ. The load current detection operation in the load current detection unit 116 is performed in synchronization with the timing at which the load detection waveform WaveD is output from the waveform generation circuit 113 to the waveform selection circuit 123. The load current detection signal Idet detected by the load current detection unit 116 is output to the current limit value setting unit (power supply side) 114 and the current limit value setting unit (GND side) 115.

  When the load current detection unit 116 detects the load current (load capacity) of the pressure generating element PZT, the nozzle driven by the load detection waveform WaveD is later driven by the waveform signal Wave1 to actually detect the ink droplet. A plurality of nozzles for discharging. The load current detection unit 116 uses the detected load currents (load capacities) of the plurality of nozzles as a load current detection signal Idet, as a current limit value setting unit (power supply side) 114 and a current limit value setting unit (GND side) 115. Output to. As described above, the load current detection unit 116 detects the total value of the currents supplied to the level conversion circuits 124 (the plurality of drive units) that respectively drive the plurality of nozzles as the load current value.

The current limit value setting unit (power supply side) 114 has a waveform based on the load current detection signal Idet input from the load current detection unit 116 and the information of “charging current value per nozzle (reference value)”. When the nozzle NZ is driven by the signal Wave1 to eject ink droplets, the level of the signal ILu for setting the limit current value (power supply side) is set in order to limit the charging current according to the number of nozzles to be driven.
Further, the current limit value setting unit (GND side) 115 is based on the load current detection signal Idet input from the load current detection unit 116 and the information of “discharge current value (reference value) per nozzle”. In order to limit the discharge current according to the number of nozzles to be driven, the level ILd of the limit current value setting (GND side) is set.

The variable charging current limiting unit 117 limits the charging current value when charging the pressure generating element PZT according to the signal ILu of the limiting current value setting (power supply side) input from the current limiting value setting unit (power supply side) 114. To do.
The variable charging current limiting unit 117 is configured by a variable resistor (electronic volume) connected to the power supply Vd and the level conversion circuit 124 as shown in FIG. For example, as shown in FIG. 4B, the variable resistor (electronic volume) includes a constant current circuit composed of an operational amplifier AM11, an NPN transistor Q11, and a resistor R11, and a current composed of PNP transistors Q12 and Q13. And a mirror circuit.
By inputting the signal ILu of the limit current value setting (power supply side) to the normal input terminal of the operational amplifier AM11, a current I1 ′ proportional to the voltage of the signal ILu flows through the transistor Q11. When the current I1 ′ (reference current) flows through the transistor Q12 of the current mirror circuit, the current I1 (mirror current) flows from the transistor Q13 toward the level conversion circuit 124. The magnitude of the current I1 is limited to a value that is proportional to the magnitude of the current I1 ′. As described above, the variable charging current limiting unit 117 can limit the current I1 to a value of the charging current that flows through the level conversion circuit 124 to a value that is proportional to the voltage of the signal ILu. In the following description, it is assumed that the current I1 and the current I1 ′ are configured to be equal.

The variable discharge current limiter 118 is a discharge current when discharging the charge of the pressure generating element PZT according to the signal ILd of the limit current value setting (GND side) input from the current limit value setting unit (GND side) 115. Limit the value.
The variable discharge current limiting unit 118 is configured by a variable resistor (electronic volume) inserted between the level conversion circuit 124 and the circuit ground G as shown in FIG. For example, as shown in FIG. 4D, the variable resistor (electronic volume) includes a constant current circuit composed of an operational amplifier AM21, a PNP transistor Q21 and a resistor R21, and a current composed of NPN transistors Q22 and Q23. And a mirror circuit. By inputting the signal ILd to the normal input terminal of the operational amplifier AM21, a current I2 ′ proportional to the voltage of the signal ILd flows through the transistor Q21. When the current I2 ′ (reference current) flows through the transistor Q22 of the current mirror circuit, the current I2 (mirror current) flows from the level conversion circuit 124 toward the transistor Q23. The magnitude of the current I2 is limited to a value that is proportional to the magnitude of the current I2 ′. As described above, the variable discharge current limiting unit 118 can limit the current I2 ′ to a value equal to or less than a value proportional to the voltage of the signal ILd. In the following description, it is assumed that the current I2 and the current I2 ′ are configured to be equal.

(Explanation of load capacity detection and ink droplet ejection)
The driving device 110 configured as described above drives the pressure generating element PZT (all nozzles NZ that ejects ink droplets later) with the load detection waveform WaveD before discharging the ink droplets, thereby generating a load current (load capacity). Based on the detected value of the load current, a limit current value corresponding to the number of nozzles that eject ink droplets is set.
When detecting the load current detection, the driving device 110 performs normal image printing using the current limit values (signals ILu and ILd) output from the variable charge current limiter 117 and the variable discharge current limiter 118. The load current is detected from the charge voltage value when the pressure generating element PZT is charged with a constant current by the load detection waveform WaveD. The load detection waveform WaveD is set to a short pulse width that does not affect the ejection of ink droplets from the nozzle NZ.

FIG. 5 is a time chart showing an ink droplet ejection cycle in the first embodiment, which is an example in the binary mode. Note that the binary mode is a mode for controlling whether or not to eject ink droplets without controlling the amount of ink droplets ejected from the nozzle NZ as described above.
The time chart shown in FIG. 5 shows the passage of time in the horizontal direction, the pixel CLK, the signal for limiting current value setting (power supply side), the signal for limiting current value setting (GND side), and the waveform in the vertical direction. The waveform Wave output from the generation circuit 113 and the drive signal OUT output from the level conversion circuit 124 toward the pressure generating element PZT are shown side by side.

  Further, in FIG. 5, the first half (between time t0 and t7) shows an example of an ink droplet ejection cycle when the number of nozzles to be simultaneously driven is small (when the overall capacity load is small). This part (after time t10) shows an example of an ink droplet ejection cycle when the number of nozzles to be driven simultaneously is large (when the overall capacity load is large).

  In the first half (time t0 to t7), the ink droplet ejection cycle includes a step of detecting the load capacity (load detection zone) performed between time t0 and time t3, and ink performed after time t4. A droplet ejection step (ink droplet ejection zone).

  In addition, before starting the load detection zone from time t1, the driving device 110 according to the present embodiment sets the limit current value setting (power supply side) to a constant value ILu1, and sets the limit current value setting (GND side) to a constant value. ILd1 is set, and the limit values of the charge current and the discharge current flowing through the pressure generating element PZT are set to a constant current limit value higher than that in the case of performing normal image printing. The driving device 110 continues the current limiting state based on the constant values ILu1 and ILd1 until time t3 when the load detection zone ends.

  When the pixel CLK is input at time t0, the waveform generation circuit 113 outputs the load detection waveform WaveD to the waveform selection circuit 123 at time t1 when a predetermined time has elapsed since the pixel CLK was input. . In this load detection waveform WaveD, the pulse width ΔT is set short so that ink droplets are not ejected from the nozzle NZ.

  The waveform selection circuit 123 outputs the load detection waveform WaveD to the level conversion circuit 124 in association with a nozzle that is later driven by the waveform signal Wave1. The level conversion circuit 124 generates and outputs a drive signal corresponding to the load detection waveform WaveD to the nozzle NZ driven with the load detection waveform WaveD.

  The pressure generating element PZT of the nozzle NZ rises to the voltage V1 during the period ΔT by performing constant current charging from time t1. That is, the drive current is limited to a predetermined current value ILu1, the pressure generating element PZT is driven by the load detection waveform WaveD, and the voltage V1 charged in the capacitance of the pressure generating element PZT during the pulse width period ΔT. Is detected. The voltage V1 charged in the pressure generating element PZT is peak-held by the load current detector 116 and detected.

The load current detection unit 116 can determine the total capacitance C of the nozzle (pressure generating element PZT) based on the limit current value ILu1, the period ΔT, and the charging voltage (charge voltage) V1, using the following equation.
Nozzle total capacitance C = ILu1 × ΔT / V1,
Based on the total nozzle capacitance C, the load current I1 of the nozzle can be determined by the following equation.
Nozzle load current I1 = a × C, where a is a predetermined constant,
The load current detection unit 116 generates a load current detection signal Idet corresponding to the magnitude of the load current I1 of the nozzle.
That is, the magnitude of the load current of the nozzle NZ (pressure generating element PZT) to be driven by the waveform signal Wave1 is determined by the magnitude of the total nozzle capacitance C, and the load current detection unit 116 is configured to load the nozzle NZ. A detection signal (load current detection signal) Idet corresponding to the magnitude of the current is generated, and this load current detection signal Idet is generated as a current limit value setting unit (power supply side) 114 and a current limit value setting unit (GND side) 115. Output for.

The current limit value setting unit (power supply side) 114 is based on the load current detection signal Idet input from the load current detection unit 116 and the “charging current value per nozzle” input from the setting value storage element 112. A limit current value setting (power supply side) V_Rn for appropriately driving the plurality of nozzles NZ (pressure generating elements PZT) is determined by the waveform signal Wave1. The current limit value setting unit (power supply side) 114 outputs a signal of the limit current value setting (power supply side) V_Rn to the variable charge current limit unit 117 at time t3.
Similarly, the current limit value setting unit (GND side) 115 receives the load current detection signal Idet input from the load current detection unit 116 and the “discharge current value per nozzle” input from the setting value storage element 112. On the basis of this, a limit current value setting (GND side) V_Fn for appropriately driving the plurality of nozzles NZ (pressure generating elements PZT) is determined by the waveform signal Wave1. The current limit value setting unit (GND side) 115 outputs a signal of this limit current value setting (GND side) V_Fn to the variable discharge current limit unit 118 at time t3.

  Then, at time t3, after the limit current value setting (power supply side) V_Rn is set in the variable charge current limiter 117 and the limit current value setting (GND side) V_Fn is set in the variable discharge current limiter 118, time t4 Ink droplet ejection is started.

  During the period from time t4 to time t6, the waveform generation circuit 113 outputs the waveform Wave1 for ejecting ink droplets to the waveform selection circuit 123. The waveform selection circuit 123 outputs the ink droplet ejection waveform Wave1 to the level conversion circuit 124 in association with the nozzle NZ that performs printing. The level conversion circuit 124 generates and outputs a drive signal OUT corresponding to the ink droplet ejection waveform Wave1 to the nozzle NZ that performs printing.

From time t4, charging is started by the drive signal OUT output from the level conversion circuit 124 to the pressure generating element PZT of the nozzle NZ that discharges ink droplets. In this case, since the charging current flowing to the pressure generating element PZT is appropriately limited by the level V_Rn corresponding to the load capacity by the variable charging current limiting unit 117, as shown in the charging waveform between time t4 and time t5. The charging waveform to the pressure generating element PZT is a smooth charging waveform. For this reason, a rapid pressure change does not occur in the nozzle NZ, and the occurrence of cavitation or the like can be avoided.
When the charging voltage of the pressure generating element PZT reaches the voltage Vu at time t5, charging to the pressure generating element PZT is stopped, and ink droplets are held in the nozzles NZ until time t6.

  When time t6 is reached, discharge of the charge charged in the pressure generating element PZT is started. In this case, since the discharge current flowing out from the pressure generating element PZT is appropriately limited by the level V_Fn corresponding to the load capacity of the pressure generating element PZT by the variable discharge current limiting unit 118, the discharge current is discharged so as not to generate cavitation or the like. It can be carried out. Thus, after time t6, ink droplets are ejected from the nozzle NZ. When the discharge from the pressure generating element PZT is completed at time t7, the ejection of ink droplets from the nozzle NZ stops.

In addition, the ink droplet ejection cycle starting from time t10 is an example in which the number of nozzles that are simultaneously driven is large. The operation of the ink droplet ejection cycle from time t10 to time t17 is basically the same as the operation of the ink droplet ejection cycle from time t1 to time t7.
That is, an ink droplet ejection cycle is started from time t10, load detection of the pressure generating element PZT is performed from time t11 to t12, and at time t13, the limit current value setting (power supply side) V_Rn is a variable charging current limiter. 117, the limit current value setting (GND side) V_Fn is set in the variable discharge current limiter 118. After that, charging is started for the pressure generating element PZT of the nozzle NZ that discharges ink droplets from time t14, ink droplets are held in the nozzle NZ from time t15 to time t16, and from the nozzle NZ after time t16. Ink droplets are ejected.

  In the ink droplet ejection cycle starting from time t10, since the number of nozzles to be driven simultaneously is large, the voltage V2 charged to the pressure generating element PZT of the nozzle NZ is changed from time t1 between time t11 and time t12. During the time t2, the voltage V1 is lower than the voltage V1 charged in the pressure generating element PZT of the nozzle NZ.

  Thus, the drive device 110 can detect the magnitude of the load capacity of the pressure generating element PZT in the load detection zone based on the voltage value charged in the nozzle NZ (pressure generating element PZT). By detecting the load capacity of the nozzle NZ, the charging voltage waveform (rising waveform) during the time t4 to t5 when the number of driving nozzles is small and the time t14 to t15 when the number of driving nozzles is large. The charging voltage waveform (rising waveform) between them can be the same gentle waveform. Further, a discharge voltage waveform (falling waveform) between times t6 and t7 when the number of driving nozzles is small, a discharge voltage waveform (falling waveform) between times t16 and t17 when the number of driving nozzles is large, Can have the same gentle waveform. Thereby, a sudden pressure change does not occur inside the nozzle NZ, and the occurrence of cavitation and mist can be suppressed.

As described above, the driving device 110 can set an appropriate driving current waveform even when the number of nozzles to be driven changes and the load capacity changes.
As a result, the driving device 110 can suppress the occurrence of cavitation in the nozzle NZ, eliminate the occurrence of nozzle omission, and stabilize ink droplet ejection. Further, the driving device 110 can suppress the generation of satellites and mist, and can improve the print image quality. In addition, the driving device 110 can set a driving current waveform according to the ink characteristics, and can further set a driving current waveform according to the ink characteristics depending on the ambient temperature.

  In addition, when detecting the load capacity of the nozzle NZ, the driving device 110 of the first embodiment described above charges the pressure generating element PZT with a constant current with a current limited to a constant value, and a predetermined period ΔT has elapsed. The charging voltage V1 at the time of the detection is detected, and the load capacity of the pressure generating element PZT is detected based on the value of the charging voltage V1. The method for detecting the load capacity of the pressure generating element PZT is not limited to this. For example, the load capacity of the pressure generating element PZT can also be detected based on the slope of the voltage rise when performing constant current charging. .

Further, in the drive device 110 of the first embodiment described above, the total load capacity of the plurality of nozzles NZ is calculated based on the total value of the current detected by the load current detection unit 116 in the load detection zone, and this load Although the total value of the current limit is controlled based on the capacity, the current of each nozzle can also be controlled as follows.
For example, the driving device includes a charge / discharge limiting circuit for each nozzle, calculates the load capacity for each individual nozzle based on the total load current detected by the load current detection unit 116, ”Load capacity” and “Charge and discharge current value per nozzle” are controlled for each nozzle so that the current flowing to each nozzle is less than the current limit setting value. You can also
In addition, for example, the driving device includes a charge / discharge limiting circuit for each nozzle, calculates the load capacity for each nozzle based on the total value of the load current detected by the load current detection unit 116, Based on the “load capacity per nozzle” and the “charge and discharge current value per nozzle”, when the current flowing through each nozzle is controlled (limited), the total value of the current limit is less than the set value. It can also be controlled.

[Second Embodiment]
In the first embodiment described above, an example of the driving device 110 when performing printing in the binary mode has been described, but in the second embodiment of the present invention, an example of the driving device 110A when performing printing in the gray scale mode is described. explain.

In the gray scale mode, as shown in waveform signals Wave1 (1drop), Wave2 (2drop), and Wave3 (3drop) in FIG. 7 to be described later, the waveform signal Wave1 has only the pulse P1 for final driving, and the waveform The signal Wave2 has a pulse P1 and a pulse P2 for initial driving, and the waveform signal Wave3 has a pulse P1, pulses P2 and P3.
The waveform signal Wave1 is equivalent to one drop by one driving with the pulse P1, the waveform signal Wave2 is equivalent to two drops by two driving with the pulses P1 and P2, and the waveform signal Wave3 is three times with the pulses P1, P2, and P3. Three drops of ink are ejected by driving, and the recording medium is printed with inks of different sizes.
For example, in the case of the waveform signal Wave3, the first, second, and third drops of ink are discharged into the air like a daisy chain, and the discharged first, second, and third drops of ink are mutually connected. The ink is drawn by the surface tension of the ink, and is ejected as one ink drop in the amount of three drops. The same applies to the waveform signal Wave2.

(Configuration of Drive Device 110A of Second Embodiment)
FIG. 6 is a block diagram showing a configuration of a driving device 110A according to the second embodiment of the present invention. The drive device 110A shown in FIG. 6 is newly compared with the drive device 110 of the first embodiment shown in FIG. 3 and includes a selector (power supply side) 131, a timing control unit (power supply side) 132, and a selector (GND). Side) 133 and the timing control unit (GND side) 134 are newly added. Further, the set value storage element 112 shown in FIG. 3 is changed to the set value storage element 112A, the waveform generation circuit 113 is changed to the waveform generation circuit 113A, and the current limit value setting unit (power supply side) 114 is changed to the current limit value setting unit. The difference is that the current limit value setting unit (GND side) 115 is changed to the current limit value setting unit (GND side) 115A, and the waveform selection circuit 123 is changed to the waveform selection circuit 123A. Other configurations are the same as those of the driving device 110 shown in FIG. For this reason, the same code | symbol is attached | subjected to the same component and the overlapping description is abbreviate | omitted.

In the driving apparatus 110A shown in FIG. 6, the set value storage element 112A receives the above-described 2-bit signal D2b and the shift CLK from the selector 111. The set value storage element 112A includes information on “P1 charge (rising) current value (reference value) per nozzle” corresponding to the drive pulse P1, and “P1 discharge per nozzle (reference value) corresponding to the drive pulse P1. Information on “falling) current value (reference value)”.
In addition, the set value storage element 112A includes information on “P2 charge (rising) current value (reference value) per nozzle” corresponding to the drive pulse P2, and “P2 discharge (per nozzle) (reference value) corresponding to the drive pulse P2. Information on “falling) current value (reference value)”.
Further, the set value storage element 112A includes information on “P3 charge (rising) current value (reference value) per nozzle” corresponding to the drive pulse P3, and “P3 discharge per nozzle (reference value) corresponding to the drive pulse P3”. Information on “falling) current value (reference value)”.

  The set value storage element 112A outputs information on “P1 charging current value per nozzle” to the current limit value setting unit (power supply side) 114A, and information on “P1 discharge current value per nozzle” as a current limit. The value is output to the value setting unit (GND side) 115A. In addition, the set value storage element 112A outputs information on “P2 charge current value per nozzle” to the current limit value setting unit (power supply side) 114A and information on “P2 discharge current value per nozzle”. It outputs to the current limit value setting unit (GND side) 115A. Furthermore, the set value storage element 112A outputs information on “P3 charge current value per nozzle” to the current limit value setting unit (power supply side) 114A and information on “P3 discharge current value per nozzle”. It outputs to the current limit value setting unit (GND side) 115A.

  The set value storage element 112A generates a signal having a waveform set value (for example, the number of waveforms, the height of the waveform, the output period of the waveform, etc.) according to the data content of the 2-bit signal D2b. A set value signal is output to the waveform generation circuit 113A.

  The waveform generation circuit 113A generates each waveform signal Wave of the waveform signals Wave0, Wave1, Wave2, and Wave3 from the waveform setting value signal input from the setting value storage element 112A, and outputs the waveform signal Wave to the waveform selection circuit 123A. The waveform generation circuit 113A generates a load detection waveform WaveD used in a load detection zone, which will be described later, and outputs the load detection waveform WaveD to the waveform selection circuit 123A.

The waveform signal Wave0 generated by the waveform generation circuit 113A is a waveform signal to be applied to the pressure generating element PZT at the time of non-ejection in which no ink droplet is ejected from the nozzle. For example, the waveform signal Wave0 is a waveform signal applied to the pressure generating element PZT in order to prevent ink sticking.
Further, as shown in FIG. 7, the waveform signal Wave1 is a waveform signal of a pulse P1 for ejecting one ink droplet from the nozzle, and the waveform signal Wave2 is used when ejecting two ink droplets from the nozzle. The waveform signal Wave3 corresponds to the pulse P1, the pulse P2, and the pulse P3 that are used when three ink droplets are ejected from the nozzle. It is a waveform signal.

The waveform selection circuit 123A outputs the waveform signals Wave0 to Wave3 output from the waveform generation circuit 113A in response to the print data (print data indicated by the above-described 2-bit signal D2b) for each nozzle input from the latch circuit 122. Is output to the level conversion circuit 124.
The level conversion circuit 124 generates signals OUT1 to OUTn for driving the nozzles according to the output timings of the pulses P1, P2, and P3 according to the waveform signal input from the waveform selection circuit 123A. Output. The pressure generating element PZT of the nozzle NZ is driven by the drive signals OUT1 to OUTn output from the level conversion circuit 124.

  In addition, the current limit value setting unit (power supply side) 114A receives the detection signal Idet of the nozzle load current (load capacity) detected by the load current detection unit 116 and “pulses P1, P2 input from the set value storage element 112A. And the charge current value of P3 / 1 nozzle ”, the signal A1 of the limit current value setting (power supply side) for the pulse P1, the signal A2 of the limit current value setting (power supply side) for the pulse P2, A limit current value setting (power supply side) signal A3 for the pulse P3 is generated, and these signals are output to the selector (power supply side) 131.

  Further, the current limit value setting unit (GND side) 115A receives the detection signal Idet of the load current (load capacity) detected by the load current detection unit 116 and “pulses P1, P2, and P3 input from the set value storage element 112A. Based on the information of “discharge current value / nozzle”, the signal B1 of the limit current value setting (GND side) for the pulse P1, the signal B2 of the limit current value setting (GND side) for the pulse P2, and the pulse P3 And a signal B3 for setting a limit current value for (GND side) for the above-mentioned and outputting these signals to the selector (GND side) 133.

  The selector (power supply side) 131 inputs the signal A1, A2, A3 of the limit current value setting (power supply side) generated by the current limit value setting unit (power supply side) 114A, and sets these limit current value (power supply side) ) A signal corresponding to each pulse P1, P2, P3 is selected from the signals A1, A2, A3, a signal ILu for setting a limit current value (power supply side) is generated based on the selected signal, and the variable charging current Output to the limiting unit 117. The timing for generating and outputting the limit current value setting (power supply side) signal ILu is controlled by the timing control unit (power supply side) 132.

  The timing control unit (power supply side) 132 detects the timing at which the waveforms of the pulses P1, P2, and P3 are output from the level conversion circuit 124, and according to the output timing of the pulses P1, P2, and P3 (more accurately, At the timing before the pulses P1, P2, P3 are output), the selector (power supply side) 131 is controlled, and the selector (power supply side) 131 sets the limit current value according to the pulses P1, P2, P3 (power supply side) The signal ILu is output.

  The selector (GND side) 133 inputs the signals B1, B2, and B3 of the limit current value setting (GND side) generated by the current limit value setting unit (GND side) 115A, and these limit current value settings (GND side) ) From the signals B1, B2, and B3, a signal corresponding to each pulse P1, P2, and P3 is selected, and a signal ILd for setting a limited current value (GND side) is generated based on the selected signal, and variable discharge is performed. Output to the current limiter 118. The timing for generating and outputting the signal ILu for limiting current value setting (GND) is controlled by a timing control unit (GND side) 134.

  The timing control unit (GND side) 134 detects the timing at which the waveforms of the pulses P1, P2, and P3 are output from the level conversion circuit 124, and according to the output timing of the pulses P1, P2, and P3 (more precisely, At the timing before the pulses P1, P2, and P3 are output, the selector (GND side) 133 is controlled, and the limit current value setting (GND side) according to the pulses P1, P2, and P3 from the selector (GND side) 133 is controlled. ) Signal ILd is output.

The load current detection unit 116 performs an operation of detecting the load current of the nozzle NZ to be driven before ejecting ink droplets from the nozzle NZ. The detection of the load current of the nozzle NZ is performed by the nozzle NZ driven by the pulse P1 included in the waveform signals Wave1, Wave2, Wave3, the nozzle NZ driven by the pulse P2, and the nozzle NZ driven by the pulse P3. Done for each.
The detection of the load current in the load current detection unit 116 is performed in synchronization with the timing at which the load detection waveform WaveD is output from the waveform generation circuit 113A to the waveform selection circuit 123A. The detection values of the load current (load capacity) detected by the load current detection unit 116 are the current limit value setting unit (power supply side) 114A and the current limit value setting unit (GND side) 115A as the load current detection signal Idet. Is output for each of.

  The variable charging current limiting unit 117 is charged when driving the nozzle NZ (pressure generating element PZT) in accordance with the signal ILu of the limiting current value setting (power supply side) input from the current limiting value setting unit (power supply side) 114A. Limit the current value. Further, the variable discharge current limiting unit 118 is configured to drive the nozzle (pressure generating element PZT) according to the signal ILd of the limiting current value setting (GND side) input from the current limiting value setting unit (GND side) 115A. Limit the discharge current value.

(Explanation of load capacity detection and ink droplet ejection)
FIG. 7 is a time chart showing an ink droplet ejection cycle in the driving apparatus 110A of the second embodiment, and is an example in a gray scale mode.

  The time chart shown in FIG. 7 shows the passage of time in the horizontal direction, and in the vertical direction, the pixel CLK, the waveform signal Wave1 (1 drop; waveform when one drop is ejected by the pulse P1), and the waveform signal Wave2 (2 drop; Waveform when two drops are ejected using pulses P1 and P2), waveform signal Wave3 (3drop; waveform when ejecting three drops using pulses P1, P2 and P3), and limit current value setting (P3 power supply side) (P3 pulse) Power supply side limit current value at output), limit current value setting (P2 power supply side) (power supply side limit current value at P2 pulse output), limit current value setting (P1 power supply side) (power supply at P1 pulse output) Side limit current value), limit current value setting (P3, GND side) (GND side limit current value at P3 pulse output), limit current value setting (P2, GND side) (GND side control at P2 pulse output) Current value), limit current value setting (P1, GND side) (GND side limit current value at the time of P1 pulse output), limit current value setting power source side (after switching), limit current value setting GND side (after switching) ), Drive signal OUT (during 1 drop), drive signal OUT (during 2 drop), and drive signal OUT (during 3 drop) are shown side by side.

  Further, in the time chart shown in FIG. 7, a load capacity detection step (load detection zone) is performed between time t0 and time t4, and an ink droplet ejection step (ink droplet ejection zone) after time t5. Is done.

  In addition, before starting the load detection zone from time t1, the driving device 110A of the present embodiment sets the limit current value setting (P3 power supply side) to a constant value ILu3 and sets the limit current value setting (P2 power supply side) to a constant value. ILu2, limit current value setting (P1 power supply side) is a constant value ILu1, limit current value setting (P3, GND side) is a constant value ILd3, limit current value setting (P2, GND side) is a constant value ILd2, The limit current value setting (P1, GND side) is set to a constant value ILd1. As a result, in the load detection zone, the current limit value for driving the nozzle NZ is set to a constant current limit value that is higher than that for normal image printing. The driving device 110A continues the current limiting state based on the constant values ILu3 to ILu1 and ILd1 to ILd3 until time t5 when the load detection zone ends.

When the pixel CLK is input at time t0, the nozzle NZ (a plurality of nozzles driven later by the pulse P3; hereinafter) is output from the waveform generation circuit 113A at time t1 when a predetermined time has elapsed since the pixel CLK was input. A load detection waveform WaveD3 is also output to the waveform selection circuit 123A. In the load detection waveform WaveD3, the pulse width is set to be as short as the period ΔT so that ink droplets are not ejected from the P3 nozzle. The same applies to load detection waveforms WaveD2 and D1 described later.
The nozzles NZ driven by the load detection waveform Wave3 are all the nozzles NZ (P3 nozzles) to which ink droplets are ejected later by the pulse P3.

  The waveform selection circuit 123A outputs the load detection waveform WaveD3 to the level conversion circuit 124 in association with each of the P1 nozzles. The level conversion circuit 124 generates and outputs a drive signal OUT (3drop) corresponding to the load detection waveform WaveD3 for a period of ΔT from time t1 to the P3 nozzle to be driven.

  When the load detection waveform WaveD3 is output, a signal ILu3 for limiting current value setting (P3 power supply side) is output from the selector (power supply side) 131 to the variable charging current limiting unit 117 and flows to the P3 nozzle. The charging current is limited to a constant current value ILu3. Further, a signal ILd3 for setting a limit current value (GND side) is output from the selector (GND side) 133 to the variable charge current limiter 117, and the discharge current flowing out from the P3 nozzle is limited to a constant current value ILd3. The That is, constant current charging with a limited constant current ILu3 is performed on the P3 nozzle that is a capacitor load.

  The P3 nozzle rises to the voltage V3 during the period ΔT by performing constant current charging from time t1. That is, the drive current is limited to a predetermined current value ILu3 and the P3 nozzle is driven (constant current charging) by the load detection waveform WaveD3 (charge constant current), and the pressure generation element PZT of the P3 nozzle is charged during the period ΔT of the pulse width. The voltage V3 is detected. The voltage V3 charged in the P3 nozzle is peak-held by the load current detector 116 and detected.

The load current detection unit 116 can obtain the total capacitance C3 of the P3 nozzle by the following formula based on the current value ILu3, the period ΔT, and the charging voltage V3.
P3 nozzle total capacitance C3 = ILu3 × ΔT / V3,
Based on the total capacitance C3 of the P3 nozzle, the load current I3 required for driving the P3 nozzle can be determined by the following equation.
P3 nozzle load current I3 = a3 × C3, where a3 is a predetermined constant,
The load current detection unit 116 generates a detection signal Idet of a load current (load capacity) corresponding to the magnitude of the load current I3 of the P3 nozzle, and the detection signal Idet of the load current is set as a current limit value setting unit (power supply). Side) 114A and current limit value setting unit (GND side) 115A.

  Thereafter, at time t2 after a predetermined time has elapsed from time t1, the waveform generation circuit 113A generates a waveform WaveD2 for load detection for the nozzle NZ (a plurality of nozzles driven later by a pulse P2; hereinafter also referred to as “P2 nozzle”). It is output to the selection circuit 123A. In this load detection waveform WaveD2, the pulse width is set to be as short as the period ΔT so that ink droplets are not ejected from the P2 nozzle.

  The waveform selection circuit 123A outputs the load detection waveform WaveD2 to the level conversion circuit 124 in association with each of the P2 nozzles. The level conversion circuit 124 generates and outputs a drive signal OUT (2drop) corresponding to the load detection waveform WaveD2 to the P2 nozzle that is a load detection target during a period of ΔT from time t2.

  When this load detection waveform WaveD2 is output, a limit current value setting (P2 power supply side) signal ILu2 is output from the selector (power supply side) 131 to the variable charge current limiting unit 117, and the charge flowing through the P2 nozzle The current is limited to a constant current value ILu2. In addition, a limit current value setting (GND side) signal ILd2 is output from the selector (GND side) 133 to the variable charging current limiting unit 117, and the discharge current flowing out from the P2 nozzle is limited to a constant current value ILd2. . That is, constant current charging with a limited constant current ILu2 is performed on the P2 nozzle that is a capacitor load.

  The P2 nozzle rises to the voltage V2 during the period ΔT by performing constant current charging from time t2. That is, the drive current is limited to a predetermined current value ILu2 and the P2 nozzle is driven (constant current charging) by the load detection waveform WaveD2, and the pressure generation element PZT of the P2 nozzle is charged during the pulse width period ΔT. The voltage V2 is detected. The voltage V2 charged in the P2 nozzle is peak-held by the load current detector 116 and detected.

The load current detection unit 116 can obtain the total capacitance C2 of the P2 nozzle by the following formula based on the current value ILu2, the period ΔT, and the charging voltage V2.
P2 nozzle total capacitance C2 = ILu2 × ΔT / V2,
Based on the total capacitance C2 of the P2 nozzle, the load current I2 necessary for driving the P2 nozzle can be determined by the following equation.
P2 nozzle load current I2 = a2 × C2, where a2 is a predetermined constant,
The load current detection unit 116 generates a detection signal Idet of a load current (load capacity) corresponding to the magnitude of the load current I2 of the P2 nozzle, and the detection signal Idet of the load current is set as a current limit value setting unit (power supply). Side) 114A and the current limit value setting unit (GND side) 115A.

  Thereafter, at a time t3 after a lapse of a predetermined time from the time t2, the waveform generation circuit 113A generates a waveform WaveD1 for load detection with respect to the nozzle NZ (a plurality of nozzles driven later by the pulse P1; hereinafter also referred to as “P1 nozzle”). It is output to the selection circuit 123A. In this load detection waveform WaveD1, the pulse width is set to be as short as the period ΔT so that ink droplets are not ejected from the P1 nozzle.

  The waveform selection circuit 123A outputs the load detection waveform WaveD1 to the level conversion circuit 124 in association with each of the P1 nozzles. The level conversion circuit 124 generates and outputs a drive signal OUT (1drop) corresponding to the load detection waveform WaveD1 for a period of ΔT from time t3 to the P1 nozzle that is a load detection target.

  When this load detection waveform WaveD1 is output, a signal ILu1 for limiting current value setting (P1 power supply side) is output from the selector (power supply side) 131 to the variable charging current limiting unit 117 and flows to the P1 nozzle. The charging current is limited to a constant current value ILu1. Further, a signal ILd1 for setting a limit current value (GND side) is output from the selector (GND side) 133 to the variable charge current limiter 117, and the discharge current flowing out from the P1 nozzle is limited to a constant current value ILd1. The That is, the constant current charging with the limited constant current ILu1 is performed on the P1 nozzle which is the capacitor load.

  The P1 nozzle rises to the voltage V1 during the period ΔT by performing constant current charging from time t3. That is, the drive current is limited to a predetermined current value ILu1 and the P1 nozzle is driven (constant current charging) by the load detection waveform WaveD1, and the pressure generating element PZT of the P1 nozzle is charged during the pulse width period ΔT. The voltage V1 is detected. The voltage V1 charged in the P1 nozzle is peak-held by the load current detector 116 and detected.

The load current detection unit 116 can obtain the total capacitance C1 of the P1 nozzle based on the current value ILu1, the period ΔT, and the charging voltage V1 using the following equation.
P1 nozzle total capacitance C1 = ILu1 × ΔT / V1,
Based on the total capacitance C1 of the P1 nozzle, the load current I1 necessary for driving the P1 nozzle can be determined by the following equation.
P1 nozzle load current I1 = a1 × C1, where a1 is a predetermined constant,
The load current detection unit 116 generates a detection signal Idet of a load current (load capacity) corresponding to the magnitude of the load current I1 of the P1 nozzle, and the detection signal Idet of the load current is set as a current limit value setting unit (power supply). Side) 114A and the current limit value setting unit (GND side) 115A.

  The current limit value setting unit (power supply side) 114A detects the detected values of the load currents I1, I2, and I3 of the P1, P2, and P3 nozzles, and “P1, P2, and P3 charging current values per nozzle (reference value). ) "Is generated based on the output timings of the pulse P1, the pulse P2, and the pulse P3 on the side of the limit current value setting power source (after switching).

Specifically, the current limit value setting unit (power supply side) 114A sets the limit current value setting (P3 power supply side) to level V_R3, and sets the limit current value setting (P2 power supply side) to level V_R2. The limit current value setting (P1 power supply side) is set to the level V_R1.
In this case, the level V_R3 of the limit current value setting (P3 power supply side) is set in proportion to the detection current I3, and the level V_R2 of the limit current value setting (P2 power supply side) is “detection current I3 + detection current I2”. The level V_R1 of the limit current value setting (P1 power supply side) is set in proportion to “detection current I3 + detection current I2 + detection current I1”.

  In addition, the current limit value setting unit (GND side) 115A is configured to detect the detection values of the load currents I1, I2, and I3 of the P1 nozzle, the P2 nozzle, and the P3 nozzle, and “P1, P2, and P3 discharge current values per nozzle ( Based on the information of “reference value)”, a signal on the limited current value setting GND side (after switching) corresponding to the output timing of each of the pulse P1, the pulse P2, and the pulse P3 is generated.

Specifically, the current limit value setting unit (GND side) 115A sets the limit current value setting (P3, GND side) to level V_F3, and the limit current value setting (P2, GND side) to level V_F2. The limit current value setting (P1, GND side) is set to the level V_F1.
In this case, the limit current value setting (P3, GND side) level V_F3 is set in proportion to the detection current I3, and the limit current value setting (P2, GND side) level V_F2 is “detection current I3 + detection current I2”. The limit current value setting (P1, GND side) level V_F1 is set in proportion to “detection current I3 + detection current I2 + detection current I1”.

  The selector (power supply side) 131 receives, from the current limit value setting unit (power supply side) 114A, signals of limit current value setting (power supply side) indicating level V_R3, level V_R2, and level V_R1, respectively, and pulse P1 Depending on the output timing of pulse P2 and pulse P3, one of level V_R3, level V_R2, or level V_R1 is selected, and the variable charge current limiter is used as a current limit value setting power source side (after switching) signal It outputs to 117.

  Further, the selector (GND side) 133 receives, from the current limit value setting unit (GND side) 115A, the limit current value setting (GND) signals indicating the level V_F3, the level V_F2, and the level V_F1, respectively, and the pulses P1, The variable discharge current limiter 118 is selected as a signal on the limit current value setting GND side (after switching) by selecting one of the level V_F3, the level V_F2, and the level V_F1 according to the output timing of the pulse P2 and the pulse P3. Output to.

  At time t5, after the setting of the limit current value in the current limit value setting unit (power supply side) 114A and the current limit value setting unit (GND side) 115A is completed, from time t6, the driving device 110A starts the nozzle by the pulse P3. Driving of NZ (a plurality of nozzles NZ driven by the pulse P3) is started.

At the time of nozzle driving by this pulse P3, the selector (power supply side) 131 outputs a signal on the limit current value setting power supply side (after switching) indicating the level V_R3 to the variable charging current limiter 117, and the selector (GND side) 133 outputs a signal on the limited current value setting GND side (after switching) indicating the level V_F3 to the variable discharge current limiting unit 118.
Thereby, in the ejection of the ink droplet by the pulse P3 started from time t6, the charging current is limited to the level V_R3, and the discharging current is limited to the level V_F3. For this reason, an appropriate charging current can be supplied to the P3 nozzle driven by the pulse P3, and the charging voltage of the P3 nozzle can be gradually raised.

  Thereafter, between time t6 and time t7, ink ejected after time t7 is filled into the P3 nozzle by the pulse P3. Ink droplet ejection starts at time t7 by discharging the charge of the nozzle NZ driven by the pulse P3. When discharging the charge of the nozzle NZ, the discharge current is limited by the level V_F3. For this reason, an appropriate discharge current can be supplied from the P3 nozzle driven by the pulse P3, and the charging voltage of the P3 nozzle can be gradually lowered according to a desired waveform.

  After the ink droplet ejection by the pulse P3 is completed, at time t8, ink droplet ejection from the P2 nozzle (a plurality of nozzles NZ driven by the pulse P2) by the pulse P2 is started. When the ink droplet is ejected by the pulse P2, both the nozzle NZ driven by the previous pulse P3 and the nozzle NZ newly driven by the pulse P2 are driven. (After switching) is set to level V_R2, and the limit current value setting GND side (after switching) is set to level V_F2.

At the time of nozzle driving by this pulse P2, the selector (power supply side) 131 outputs a signal on the limit current value setting power supply side (after switching) indicating the level V_R2 to the variable charging current limiter 117, and the selector (GND side) 133 outputs a signal on the limited current value setting GND side (after switching) indicating the level V_F2 to the variable discharge current limiting unit 118.
Thereby, in the ejection of the ink droplet by the pulse P2 started from time t8, the charging current is limited to the level V_R2, and the discharging current is limited to the level V_F2. For this reason, an appropriate charging current can be supplied to the P2 nozzle driven by the pulse P2, and the charging voltage of the P2 nozzle can be gradually raised.

  Thereafter, between time t8 and time t9, ink ejected after time t9 is filled into the P2 nozzle by the pulse P2. Ink droplet ejection starts at time t9 by discharging the charge of the P2 nozzle. When discharging the charge of the P2 nozzle, the discharge current is limited by the level V_F2. For this reason, an appropriate discharge current can be supplied from the P2 nozzle driven by the pulse P2, and the charging voltage of the P2 nozzle can be gently lowered according to a desired waveform.

  After the ejection of the ink droplets from the P2 nozzle by the pulse P2, the ejection of ink droplets from the P1 nozzle (a plurality of nozzles NZ driven by the pulse P1) by the pulse P1 is started at time t10. When the ink droplet is ejected by the pulse P1, the nozzle NZ driven by the pulse P3, the nozzle NZ driven by the pulse P2, and the nozzle NZ newly driven by the pulse P1 are driven. The limit current value setting power supply side (after switching) is set to level V_R1, and the limit current value setting GND side (after switching) is set to level V_F1.

At the time of nozzle driving by this pulse P1, the selector (power supply side) 131 outputs a signal on the limit current value setting power supply side (after switching) indicating the level V_R1 to the variable charging current limiter 117, and the selector (GND side) 133 outputs a signal on the limited current value setting GND side (after switching) indicating level V_F <b> 1 to the variable discharge current limiting unit 118.
Thereby, in the ejection of the ink droplet by the pulse P1 started from time t10, the charging current is limited to the level V_R1, and the discharging current is limited to the level V_F1. For this reason, an appropriate charging current can be supplied to the P1 nozzle driven by the pulse P1, and the charging voltage of the P1 nozzle can be gradually raised.

  Thereafter, between time t10 and time t11, ink ejected after time t11 is filled into the P1 nozzle by the pulse P1. The ejection of ink droplets at the time t11 is started by discharging the charged charge of the P1 nozzle. When discharging the charge of the P1 nozzle, the discharge current is limited by the level V_F1. For this reason, an appropriate discharge current can be flowed from the P1 nozzle, and the charging voltage of the P1 nozzle can be gradually lowered according to a desired waveform.

As described above, the driving device 110A can smoothly raise the charging voltage applied to the pressure generating element PZT when applying each of the pulse P1, the pulse P2, and the pulse P3 to the nozzle NZ. Each of the pulses P1, P2, and P3 can have the same charging waveform (rising waveform) when the pressure generating element PZT is applied. In addition, when discharging the charging charge of the nozzle NZ, the driving device 110A can smoothly raise the charging voltage of the nozzle NZ and can arrange the discharge waveforms (falling waveforms) between the nozzles.
Accordingly, the driving device 110A can set charging and discharging waveforms suitable for each of the pulse P1, the pulse P2, and the pulse P3 in the gray scale mode, and a rapid pressure change occurs in the nozzle NZ. The occurrence of cavitation and mist can be suppressed. Therefore, even if ink with a high dissolved gas amount is continuously ejected, ejection failure such as missing dots does not occur and ejection stability is improved.

  In addition, when detecting the load capacity of the nozzle NZ, the driving device 110A of the second embodiment described above charges the pressure generating element PZT with a constant current with a current limited to a constant value, and a predetermined period ΔT has elapsed. A method is used in which the charging voltage at the time point is detected and the load capacity of the pressure generating element PZT is detected based on the value of the charging voltage. The method for detecting the load capacity of the pressure generating element PZT is not limited to this. For example, the load capacity of the pressure generating element PZT can also be detected based on the slope of the voltage rise when performing constant current charging. .

  Although the embodiments of the present invention have been described above, the correspondence between the present invention and the above-described embodiments will be supplementarily described here. In the above embodiment, the driving device in the present invention corresponds to the driving device 110 shown in FIG. 3 or the driving device 110A shown in FIG. Further, the pressure generating element in the present invention corresponds to the pressure generating element PZT, the driving unit in the present invention corresponds to the level conversion circuit 124, and the detection unit in the present invention corresponds to the load current detection unit 116, The setting unit in the invention includes a current limit value setting unit (power supply side) 114 and a current limit value setting unit (GND side) 115 shown in FIG. 3, or a current limit value setting unit (power supply side) 114A and a current shown in FIG. The limit value setting unit (GND side) 115A corresponds. Further, the limiting unit in the present invention corresponds to the variable charging current limiting unit 117 and the variable discharge current limiting unit 118.

  In the above-described embodiment, the driving device 110 includes a plurality of nozzles NZ in which a plurality of nozzle openings (nozzle holes) are arranged, a pressure generation chamber communicating with each nozzle opening (nozzle hole), and a drive signal. This is a drive device 110 that has a pressure generating element PZT that generates pressure fluctuations in the pressure generating chamber when input, and drives a liquid ejecting head 4 that ejects ink droplets from nozzle openings (nozzle holes) due to pressure fluctuations. Thus, a plurality of drive units (level conversion circuit 124) that respectively drive the pressure generation elements PZT and a large load capacity of the pressure generation elements PZT that are respectively driven by the plurality of drive units (level conversion circuit 124). Detecting unit (load current detecting unit 116) for detecting the length, and electric power supplied to a plurality of driving units (level converting circuit 124) according to the magnitude of the load capacity. A setting unit (current limit value setting unit (power supply side) 114 and current limit value setting unit (GND side) 115) that sets a limit value for limiting the current value and a plurality of drive units (level conversion circuit 124) according to the limit value Current limiting units (variable charging current limiting unit 117 and variable charging current limiting unit 117) that limit the supplied currents.

  The drive device 110 having such a configuration detects in advance the magnitude of the load capacity of the nozzle NZ (pressure generating element PZT) to be driven, and according to the magnitude of the detected load capacity, Since the drive current supplied to the nozzle NZ is limited, this prevents the occurrence of problems such as cavitation in the nozzle even when the number of nozzles to be driven changes when the liquid jet head is driven. be able to.

  Although the embodiments of the present invention have been described above, the driving devices 110 and 110A of the present invention are not limited to the above illustrated examples, and various modifications are made within the scope not departing from the gist of the present invention. Of course you get.

DESCRIPTION OF SYMBOLS 1 ... Liquid jet recording apparatus, 4 ... Liquid jet head, 73 ... Liquid jet head chip, 100 ... Drive part, 110, 110A ... Drive apparatus, 111 ... Selector, 112, 112A ... Setting value storage element, 113, 113A ... Waveform Generation circuit 114, 114A ... current limit value setting unit (power supply side), 115, 115A ... current limit value setting unit (GND side), 116 ... negative current detection unit, 117 ... variable charge current limit unit, 118 ... variable discharge Current limiter 121, shift register, 122, latch circuit, 123, 123A, waveform selection circuit, 124, level conversion circuit, 131, selector (power supply side), 132, timing control unit (power supply side), 133, selector ( GND side), 134... Timing control unit (GND side)

Claims (11)

A plurality of nozzles in which a plurality of nozzle openings are arranged, a pressure generating chamber communicating with each nozzle opening, and a pressure generating element that generates a pressure fluctuation in the pressure generating chamber when a drive signal is input. A driving device that drives a liquid ejecting head that discharges ink droplets from the nozzle opening by the pressure fluctuation,
A plurality of driving units for respectively driving the pressure generating elements;
A detection unit for detecting the magnitude of a load capacity of each pressure generating element driven by each of the plurality of driving units;
A setting unit for setting a limit value for limiting the current supplied to the plurality of driving units according to the size of the load capacity;
A current limiting unit that limits a current supplied to each of the plurality of driving units according to the limit value;
A drive device comprising: The detector is
The drive according to claim 1, wherein a magnitude of a load capacity of the pressure generating element driven by the plurality of drive units is detected based on a current value supplied to the drive unit. apparatus. The detector is
The drive device according to claim 2, wherein a value of a current supplied to the plurality of drive units is detected. The detector is
The drive device according to claim 3, wherein a total value of currents supplied to the plurality of drive units is detected. The setting unit
Set a limit value to limit the value of the current supplied to the plurality of drive units,
The current limiting unit is
4. The drive device according to claim 1, wherein a total value of currents respectively supplied to the plurality of drive units is limited according to the limit value. 5. The setting unit
The driving apparatus according to claim 5, wherein a limit value for limiting a total value of currents supplied to the plurality of driving units is set. The setting unit
The drive device according to claim 5, wherein a limit value for limiting a current supplied to the plurality of drive units is set in proportion to a size of the load capacity. The setting unit
When the detection unit detects the magnitude of the load capacity, the current supplied to the plurality of driving units is set to a predetermined value that the current limiting unit limits,
The detector is
The pressure generating element is charged by the current, and a total value of currents supplied to the plurality of driving units is detected based on a voltage value changed in a predetermined period in the voltage charged in the pressure generating element. The drive device according to any one of claims 1 to 7, wherein: The liquid ejecting head, which is driven by the driving device according to claim 1. A liquid jet recording apparatus comprising the liquid jet head according to claim 9. A plurality of nozzles in which a plurality of nozzle openings are arranged, a pressure generating chamber communicating with each nozzle opening, and a pressure generating element that generates a pressure fluctuation in the pressure generating chamber when a drive signal is input. A driving method of driving a liquid ejecting head that discharges ink droplets from a nozzle opening by the pressure fluctuation,
A plurality of driving units respectively driving the pressure generating elements;
Detecting a load capacity of the pressure generating element driven by each of the plurality of driving units;
Setting a limit value for limiting a current supplied to the plurality of driving units according to the size of the load capacity;
Limiting the current supplied to each of the plurality of driving units according to the limit value;
A driving method comprising:

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