JP2012061690A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device having an inkjet recording head, capable of reducing wasteful power consumption by optimizing a power source voltage of a driving waveform amplifying circuit for amplifying a driving waveform for driving the head in accordance with ambient temperature and humidity.SOLUTION: The driving waveform obtained by performing D/A conversion of driving waveform data is input into the driving waveform amplifying circuit 202 from an input signal line 204, and is amplified, and a piezoelectric element 203 of the inkjet recording head is oscillated. The driving waveform data is tabulated for each of the ambient temperature and humidity, and is stored in ROM, and the waveform data is changed in accordance with the measurement data of the ambient temperature and humidity. An output voltage of a DC/DC converter 201 is variably set in accordance with the ambient temperature and humidity, and thereby, the optimum voltage in accordance with the ambient temperature and humidity is applied to an emitter of a transistor 202c, and wasteful power consumption of the driving waveform amplifying circuit 202 can be reduced.

Description

  The present invention relates to an image forming apparatus having an ink jet recording head, and more particularly to an image forming apparatus that reduces wasteful power consumption by optimizing a power supply voltage of a drive waveform amplifier circuit according to environmental temperature and humidity.

  In an image forming apparatus having an ink jet recording head, a technique in which a driving waveform generated by a driving waveform generating circuit is amplified by a driving waveform amplifying circuit and applied to the recording head, thereby driving the recording head to eject ink droplets. It has been known.

  The ink jet recording head has a built-in nozzle for discharging ink, and an actuator for discharging ink droplets is provided in the nozzle. A method using a piezoelectric element is known as an actuator. The piezoelectric element is an element whose volume varies depending on an applied voltage, and a voltage waveform called a drive waveform is input to obtain a target droplet size and ejection speed when ejecting ink droplets.

  FIG. 9 shows drive waveforms. The drive waveform mainly includes a “print waveform for ejecting ink to a recording medium and forming an image” shown in FIG. 9A, and an “empty ejection waveform for ejecting ink to a maintenance unit outside the recording medium” shown in FIG. 9B. 9C, there are three types of “fine drive waveforms for driving the actuator to such an extent that ink is not ejected”.

  The idle ejection waveform is used during a return operation when the ink in the nozzle dries in a state where it has been in contact with the atmosphere for a long time and normal ejection cannot be performed. The fine driving waveform is used as a maintenance operation for suppressing drying of the ink in the nozzle.

  When ink droplets are ejected, the steep volume increase / decrease of the actuator becomes a driving force. However, ink droplets can be ejected more efficiently by pulling out the liquid surface of the nozzle and then pushing it out. In this case, since the drive waveform is the operation to increase the voltage by lowering the voltage, it is efficient to start up and down the voltage from the reference intermediate potential, and the head drive is completed by slewing up to the intermediate potential in advance. Later, it is necessary to slew down to 0 potential. Since the reference potential of the drive waveform is mostly different depending on the type of drive (printing, idle ejection, fine drive), the through-up and through-down waveforms are also different for each drive. Also, the peak value of the drive waveform varies depending on the type of waveform, and the printed waveform differs depending on the environmental temperature because the peak value is corrected based on the measured value of the environmental temperature.

  In a drive waveform amplifier circuit using push-pull connected transistors, as shown in FIG. 10, a fixed voltage (a constant DC voltage) higher than the peak value of the drive waveform is always supplied to the transistors as the power supply voltage. ing. Since the peak value of the voltage necessary for driving the recording head (required maximum voltage) is the peak value of the drive waveform, the shaded area in the figure is wasteful power consumption. As described above, since the peak value of the drive waveform differs depending on the type of waveform and the environmental temperature, the fixed voltage is set to a high value with a margin so as to cope with the change of the type of waveform and the environmental temperature. For this reason, as the fixed voltage is higher than the voltage required by the recording head, the power that the transistor throws away as heat increases.

  There is an ink ejection amount control device having an ink save mode that saves ink ejection amount and power consumption by lowering the power supply voltage of the drive waveform amplification circuit by a DC / DC converter (Patent Document 1). The device does not consider the optimization of the power supply voltage according to the environmental temperature.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an image forming apparatus having an inkjet recording head and a driving waveform amplification circuit that amplifies a driving waveform for driving the inkjet recording head. It is to reduce wasteful power consumption by optimizing the power supply voltage of the drive waveform amplifier circuit according to the environmental temperature.

  An image forming apparatus according to the present invention includes an inkjet recording head, a drive waveform amplification circuit that amplifies a drive waveform for driving the inkjet recording head, a power supply voltage application unit that applies a power supply voltage to the drive waveform amplification circuit, and the power supply An image forming apparatus comprising power supply voltage setting means for variably setting the output voltage of the voltage application means, comprising environmental temperature measurement means for measuring environmental temperature, wherein the power supply voltage setting means is the environmental temperature measurement means The image forming apparatus variably sets the power supply voltage applied to the drive waveform amplifier circuit according to the measurement data.

[Action]
According to the present invention, the power supply voltage of the drive waveform amplification circuit that amplifies the drive waveform for driving the ink jet recording head is variably set according to the measurement data of the environmental temperature.

  According to the present invention, in an image forming apparatus having an inkjet recording head and a drive waveform amplification circuit that amplifies a drive waveform for driving the inkjet recording head, the power supply voltage of the drive waveform amplification circuit is optimized according to the environmental temperature. Therefore, useless power consumption can be reduced.

FIG. 2 is a side view for explaining a schematic configuration of a mechanism unit of the image forming apparatus according to the embodiment of the present invention. FIG. 2 is a plan view for explaining a main configuration of a mechanism unit of the image forming apparatus according to the embodiment of the present invention. FIG. 2 is a block diagram for explaining an outline of a control system of the image forming apparatus according to the embodiment of the present invention. 1 is a diagram illustrating a first example of a drive waveform amplifier circuit and a power supply voltage setting circuit thereof in an image forming apparatus according to an embodiment of the present invention. FIG. 5 is a diagram for explaining changing a drive waveform and a power supply voltage in accordance with a detection output of a temperature / humidity sensor in the image forming apparatus according to the embodiment of the present invention. It is a figure which shows the 2nd example of the drive waveform amplification circuit in the image forming apparatus of embodiment of this invention, and its power supply voltage setting circuit. It is a figure which shows the 3rd example of the drive waveform amplifier circuit in the image forming apparatus of embodiment of this invention, and its power supply voltage setting circuit. 6 is a flowchart illustrating processing that enables the power supply voltage to be forcibly reduced regardless of the peak value of the drive waveform in the image forming apparatus according to the embodiment of the present invention. It is a figure which shows the drive waveform of an inkjet recording head. It is a figure for demonstrating useless power consumption in a drive waveform amplifier circuit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
<Mechanism part of image forming apparatus>
FIG. 1 is a side view for explaining a schematic configuration of a mechanism part of an image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a plan view for explaining a main part configuration. The mechanism part of the image forming apparatus of this embodiment will be described with reference to these drawings.

  A carriage 33 is slidably held in the main scanning direction by a guide rod 31 and a stay 32, which are guide members horizontally mounted on the left and right side plates 21A and 21B constituting the frame 21, and is not shown by a main scanning motor (not shown). It moves and scans in the carriage main scanning direction via a timing belt.

  The carriage 33 is provided with a recording head 34 including four ink jet heads for ejecting ink droplets of yellow (Y), cyan (C), magenta (M), and black (Bk). They are arranged in a direction crossing the main scanning direction, and are mounted with the ink droplet ejection direction facing downward.

  As an inkjet head constituting the recording head 34, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses a phase change caused by film boiling of a liquid using an electrothermal transducer such as a heating resistor, and a metal phase change caused by a temperature change. It is possible to use a shape memory alloy actuator to be used, an electrostatic actuator using an electrostatic force, or the like provided as pressure generating means for generating a pressure for discharging a droplet.

  In the present embodiment, in addition to simultaneously driving all the ink discharge ports, it is also possible to drive by dividing in time. Driving all the ink outlets at the same time may cause disadvantages such as a decrease in recording quality due to the crosstalk between the ink outlets and an increase in the capacity of the power supply due to the temporary need for a large current. However, these disadvantages can be prevented by time-division driving.

  The recording head 34 is mounted with a driver IC (Integrated Circuit), and is connected to a control unit (not shown) via a harness (flexible print cable) 22. In addition, the carriage 33 is equipped with a sub tank 35 for each color for supplying ink of each color to the recording head 34. Each color sub-tank 35 is supplementarily supplied with ink of each color from the ink cartridge 10 of each color mounted in the cartridge loading unit 4 via the ink supply tube 36 of each color. The cartridge loading unit 4 is provided with a supply pump unit for feeding ink in the ink cartridge 10, and the ink supply tube 36 is engaged with the rear plate 21 </ b> C constituting the frame 21 in the middle of turning. It is held by the stop member 25.

  On the other hand, as a paper feeding unit for feeding the papers 42 stacked on the paper stacking unit (pressure plate) 41 of the paper feeding tray 2, a half-moon roller (feeding) that separates and feeds the papers 42 one by one from the paper stacking unit 41. Opposite to the paper roller 43 and the paper feed roller 43, a separation pad 44 made of a material having a large friction coefficient is provided. The separation pad 44 is urged toward the paper feed roller 43 side.

  In addition, in order to feed the paper 42 fed from the paper feeding unit to the lower side of the recording head 34, a guide member 45 for guiding the paper 42, a counter roller 46, a transport guide member 47, and a tip pressure roller. And a holding belt 48 which is a conveying means for electrostatically attracting the fed paper 42 to a position facing the recording head 34.

  The transport belt 51 is an endless belt, and is configured to wrap around the transport roller 52 and the tension roller 53 and circulate in the belt transport direction (sub-scanning direction). The transport belt 51 is, for example, a surface layer that is a sheet adsorbing surface formed of a pure resin material having a thickness of about 40 μm that is not subjected to resistance control, for example, ETFE pure material, and resistance control by carbon using the same material as the surface layer. And a back layer (medium resistance layer, earth layer).

  A charging roller 56 is provided as charging means for charging the surface of the conveyor belt 51. The charging roller 56 is disposed so as to come into contact with the surface layer of the conveyor belt 51 and to be rotated by the rotation of the conveyor belt 51, and applies a predetermined pressing force to both ends of the shaft as a pressing force. The transport roller 52 also functions as an earth roller, and is in contact with the middle resistance layer (back layer) of the transport belt 51 and is grounded.

  In addition, a guide member 57 is disposed on the back side of the conveyance belt 51 so as to correspond to a printing area by the recording head 34. The guide member 57 has an upper surface that protrudes toward the recording head 34 from the tangent line of the two rollers (the conveyance roller 52 and the tension roller 53) that support the conveyance belt 51, thereby maintaining high-precision flatness of the conveyance belt 51. Like to do.

  The conveyance belt 51 rotates in the belt conveyance direction (sub-scanning direction) in FIG. 2 when the conveyance roller 52 is rotationally driven by a sub-scanning motor (not shown).

  Further, as a paper discharge unit for discharging the paper 42 recorded by the recording head 34, a separation claw 61 for separating the paper 42 from the conveying belt 51, a paper discharge roller 62, and a paper discharge roller 63 are provided. The paper discharge tray 3 is provided below the paper discharge roller 62. Here, the height from between the paper discharge roller 62 and the paper discharge roller 63 to the paper discharge tray 3 is increased to some extent in order to increase the amount that can be stored in the paper discharge tray 3.

  A double-sided unit 71 is detachably attached to the back surface of the apparatus main body. The duplex unit 71 takes in the paper 42 returned by the reverse rotation of the transport belt 51, reverses it, and feeds it again between the counter roller 46 and the transport belt 51. The upper surface of the duplex unit 71 is a manual feed tray 72.

  Further, as shown in FIG. 2, a maintenance / recovery mechanism 81 including a recovery means for maintaining and recovering the nozzle state of the recording head 34 is disposed in the non-printing area on one side of the carriage 33 in the scanning direction. Yes. The maintenance / recovery mechanism 81 includes a cap member (hereinafter referred to as “cap”) 82a to 82d (hereinafter referred to as “cap 82” when not distinguished) and a nozzle surface for capping each nozzle surface of the recording head 34. A wiper blade 83 that is a blade member for discharging, and an empty discharge receiver 84 that receives liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid. . Here, the cap 82a is a suction and moisture retention cap, and the other caps 82b to 82d are moisture retention caps.

  Then, the waste liquid of the recording liquid generated by the maintenance / recovery operation by the maintenance / recovery mechanism 81, the ink discharged to the cap 82, the ink attached to the wiper blade 83 and removed by the wiper cleaner, and the idle ejection receiver 84 are idled. The discharged ink is discharged and stored in a waste liquid tank (not shown).

  In addition, as shown in FIG. 2, in the non-printing area on the other side in the scanning direction of the carriage 33, idle discharge is performed to discharge liquid droplets that do not contribute to recording in order to discharge the recording liquid thickened during recording or the like. An empty discharge receiver 88 for receiving the droplets at the time is disposed, and the empty discharge receiver 88 is provided with an opening 89 along the nozzle row direction of the recording head 34.

  Further, a communication circuit unit (interface) such as a USB for transmitting / receiving data to / from the host is provided on the inner rear side of the apparatus main body, and control constituting a control unit that controls the entire image forming apparatus. A circuit board is provided.

  In the image forming apparatus configured as described above, the sheets 42 are separated and fed one by one from the sheet feed tray 2, and the sheets 42 fed substantially vertically upward are guided by the guide member 45, and are conveyed to the conveyor belt 51 and the counter. It is sandwiched between the rollers 46 and conveyed, and further, the leading end is guided by the conveying guide member 47 and pressed against the conveying belt 51 by the leading end pressing roller 49, and the conveying direction is changed by approximately 90 °.

  At this time, a charging voltage pattern in which a positive voltage and a negative output are alternately repeated from the AC bias supply unit to the charging roller 56 by a control unit (not shown), that is, an alternating voltage is applied, and the conveying belt 51 alternates. That is, plus and minus are alternately charged in a band shape with a predetermined width in the sub-scanning direction which is the circumferential direction. When the paper 42 is fed onto the conveyance belt 51 charged alternately with plus and minus, the paper 42 is attracted to the conveyance belt 51, and the paper 42 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 51.

  Therefore, by driving the recording head 34 according to the image signal while moving the carriage 33, ink droplets are ejected onto the stopped paper 42 to record one line, and after the paper 42 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 42 has reached the recording area, the recording operation is finished and the paper 42 is discharged onto the paper discharge tray 3.

  Further, during printing (recording) standby, the carriage 33 is moved to the maintenance / recovery mechanism 81 side, and the recording head 34 is capped by the cap 82 to keep the nozzles in a wet state, thereby preventing ejection failure due to ink drying. . In addition, the recording liquid is sucked from the nozzle by a suction pump (not shown) with the recording head 34 capped by the cap 82 (referred to as “nozzle suction” or “head suction”), and the recovered recording liquid and bubbles are discharged. Perform the action. In addition, an idle ejection operation for ejecting ink not related to recording is performed before the start of recording or during recording. As a result, the stable ejection performance of the recording head 34 is maintained.

<Control system of image forming apparatus>
FIG. 3 is a block diagram for explaining the outline of the control system of the image forming apparatus according to the embodiment of the present invention. In this figure, the same reference numerals as those in FIGS.

In FIG. 3, a control unit 100 executes a central processing unit (CPU) 102 that also serves as a unit that controls the sheet conveyance operation and the carriage 33 movement operation, which controls the entire image forming apparatus, and the CPU 102 executes the control unit 100. ROM (Read Only Memory) 103 for storing programs and other fixed data, and RAM (Random for temporarily storing image data and the like)
(Access Memory) 104, rewritable non-volatile RAM (NVRAM) 105 for holding data even while the apparatus is powered off, and various signal processing and rearrangement for image data. An ASIC (Application Specific Integrated Circuit) 106 for processing image processing and other input / output signals for controlling the entire apparatus is provided.

  The control unit 100 generates a host I / F (interface) 108 for transmitting and receiving data and signals to and from the host device 180 side, and a drive waveform for driving the recording head 34, and the recording head. A head control unit 109 that outputs image data for selectively driving the pressure generating means and various data associated therewith to the head driver 120, a main scanning motor driving unit 110 for driving the main scanning motor 130, and a sub-scanning motor 150. Sub-scanning motor driving unit 112 for driving, AC bias supplying unit 111 for supplying AC bias to charging roller 56, detection pulses from linear encoder 140 and wheel encoder 160, and detection signals from various other sensors. An I / O (Input / Output) 107 for inputting is provided.

  Each unit in the control unit 100 is connected to the bus 101. The control unit 100 is connected to an operation panel 170 for inputting and displaying information necessary for the image forming apparatus.

  Here, the control unit 100 transmits print data generated by the printer driver 181 of the host device 180 such as an information processing device such as a personal computer, an image reading device such as an image scanner, an imaging device such as a digital camera, or the like via a cable or a network. Via the host I / F 108.

  Then, the CPU 102 of the control unit 100 reads and analyzes the print data in the reception buffer included in the host I / F 108, performs necessary image processing, data rearrangement processing, and the like in the ASIC 106, and sends it to the head control unit 109. The image data and the drive waveform are output from the head control unit 109 to the head driver 120 at a required timing.

  The dot pattern data for image output may be generated by storing font data in the ROM 103, for example, or the image data is developed into bitmap data by the printer driver 181 on the host device 180 side, and the control unit You may make it transfer to 100. Here, the printer driver 181 is used.

  The head control unit 109 includes a drive waveform generation unit. The drive waveform generation unit D / A converter (drive waveform generation circuit) converts the drive pulse pattern data stored in the ROM 103 and read by the CPU 102 from digital to analog. , And an amplifier (drive waveform amplifier circuit), etc., and outputs a drive waveform composed of one drive pulse or a plurality of drive pulses to the head driver 120.

  The head driver 120 forms a drive pulse that forms a drive waveform supplied from the drive waveform generation unit of the head control unit 109 based on image data (dot pattern data) corresponding to one row of the recording head 34 that is input serially. Is selectively applied to the pressure generating means of the recording head 34 to drive the recording head 34.

  The head driver 120 has, for example, a shift register for inputting a clock signal and serial data as image data, a latch circuit for latching a register value of the shift register with a latch signal, and an output value of the latch circuit for changing the level. A level conversion circuit (level shifter) and an analog switch array (switch means) whose on / off is controlled by this level shifter, etc., and the required drive pulse included in the drive waveform by controlling the on / off of the analog switch array Is selectively applied to the pressure generating means of the recording head 34.

<First Example of Driving Waveform Amplifying Circuit and its Power Supply Voltage Variable Setting Circuit>
FIG. 4 shows an example of a drive waveform amplifier circuit and its power supply voltage variable setting circuit. The drive waveform amplifier circuit 202 includes a pair of transistors 202a and 202b that are push-pull connected on the input side, and a pair of transistors 202c and 202d that are push-pull connected on the output side. Here, the transistors 202a and 202d are npn transistors, and the transistors 202b and 202c are pnp transistors.

  The collector of the input side transistor 202a and the base of the output side transistor 202c are connected, and the collector of the input side transistor 202b and the base of the output side transistor 202d are connected. A line connecting the emitters of the input side transistors 202a and 202b and a line connecting the collectors of the output side transistors 202c and 202d are connected.

  The bases of the transistors 202a and 202b are connected in common to the input signal line 204, and the line connecting the collectors of the transistors 202c and 202d is connected to the piezoelectric element 203 which is a pressure generating means constituting the recording head. The emitter of the transistor 202c is connected to a DC power source having a predetermined voltage V1 through the DC / DC converter 201, and the emitter of the transistor 202d is connected (grounded) to the ground. A voltage V1, which is an input voltage of the DC / DC converter 201, is a maximum voltage of a driving waveform necessary for head driving in consideration of various operating environments guaranteed by the product, and is set to 37 V, for example. Since the conversion efficiency of the DC / DC converter 201 is not 100%, it is actually desirable to input a voltage slightly higher than 37V.

  A drive waveform obtained by D / A conversion of the drive waveform data is input from the input signal line 204 to the drive waveform amplifier circuit 202 and amplified to vibrate the piezoelectric element 203 of the recording head 34. The drive waveform data is tabulated for each ambient temperature and humidity and stored in the ROM 103. As will be described later with reference to FIG. 5, the waveform data is changed according to the ambient temperature and humidity measurement data. Yes.

  Accordingly, since the maximum voltage (peak value) of the input drive waveform varies depending on the ambient temperature and humidity, the voltage applied to the piezoelectric element 203 also varies depending on the ambient temperature and humidity. The required maximum voltage for vibrating the piezoelectric element 203 is equal to the voltage applied to the emitter terminal of the transistor 202c. When the voltage applied to the emitter terminal of the transistor 202c is constant, as described above, a voltage higher than the necessary maximum voltage causes heat generation of the transistor, resulting in useless power consumption.

  Therefore, in this embodiment. By variably setting the output voltage of the DC / DC converter 201 according to the ambient temperature and humidity, an optimum voltage according to the temperature and humidity of the seed side is applied to the emitter terminal of the transistor 202c, and the drive waveform amplification circuit 202 is applied. Reduce wasteful power consumption.

<Selecting drive waveform according to ambient temperature and humidity>
FIG. 5 is a diagram for explaining that the drive waveform and the power supply voltage are changed in accordance with the detection output of the temperature / humidity sensor. 5A is a block diagram, and FIGS. 5B and 5C are drive waveform data stored in the ROM 103. FIG.

  There are variations in the drive waveform depending on the ambient temperature and humidity. This is to cope with the difference in ink viscosity due to the temperature. Therefore, a plurality of drive waveform data corresponding to temperature and humidity is stored in the ROM 103 in advance. Then, a temperature / humidity sensor 190 is installed at an appropriate position in the vicinity of the recording head 34, and the ambient temperature and humidity are measured. The CPU 102 and the ROM 103 are connected by, for example, a 16-bit bus, and the CPU 102 reads the measurement data of the temperature / humidity sensor 190, checks the table information in the ROM 103 via the bus, and drives according to the ambient temperature and humidity. The waveform data is read and output to the head controller 109. The D / A conversion unit (drive waveform generation circuit) of the head control unit 109 D / A converts the drive waveform data and outputs it to the drive waveform amplification circuit 202. Thereby, an optimal drive waveform can be generated according to the measurement data of the temperature / humidity sensor 190.

  In addition, since the output voltage of the DC / DC converter 201 is variably set according to the detection output of the temperature / humidity sensor 190, the CPU 102 controls the output control terminal of the DC / DC converter 201 according to the detection output of the temperature / humidity sensor 190. Supply signal. At this time, if the data of the required maximum voltages (peak values) Va1 and Va2 of the drive waveforms 301 and 302 are also stored in the ROM 103, high-speed setting is possible.

<Second Example of Driving Waveform Amplifier Circuit and its Power Supply Voltage Variable Setting Circuit>
FIG. 6 shows a second example of the drive waveform amplifier circuit and its power supply voltage variable setting circuit. In this figure, the same reference numerals as those in FIG. 4 are given to the same components as those in FIG.

  That is, the circuit configuration of the drive waveform amplification circuit 202 itself and the connection relationship between the drive waveform amplification circuit 202 and the DC / DC converter 201, the input signal line 204, and the piezoelectric element 203 are the same as those in FIG. What is different from FIG. 4 is a circuit configuration for setting the output voltage of the DC / DC converter 201. The output voltage of the DC / DC converter 201 is divided by the resistor 210 and the resistor circuit 206 and input to the feedback terminal of the DC / DC converter 201. By changing the setting of the feedback voltage, the output voltage of the DC / DC converter 201 can be changed.

  Therefore, a switching circuit 207 comprising a plurality of transistors is connected to the resistance circuit 206, and the transistor is turned on / off by the ASIC 106, so that the resistance value of the resistance circuit 206 can be freely changed by software control.

  Here, the resistance circuit 206 is composed of three resistors, and the switching circuit 207 is also composed of three transistors. Each resistor acts as a voltage dividing resistor only when the transistor connected to it is turned on. When only one of the three transistors is selectively turned on, three different resistance values can be obtained by setting all the resistance values of the three resistors to different values. If two of the three are turned on or all three are turned on, two or three combined resistance values can be obtained. As the number of resistors is increased, it is possible to correspond linearly to the ambient temperature and humidity, and wasteful power consumption can be further reduced.

<Third Example of Drive Waveform Amplifying Circuit and its Supply Voltage Variable Setting Circuit>
FIG. 7 shows a third example of the drive waveform amplifier circuit and its power supply voltage variable setting circuit. In this figure, the same reference numerals as those in FIG. 6 are assigned to the same components as those in FIG. That is, the DC / DC converter can be changed by changing the circuit configuration of the drive waveform amplifier circuit 202 itself, the connection relationship between the drive waveform amplifier circuit 202 and the DC / DC converter 201, the input signal line 204, the piezoelectric element 203, and the feedback voltage. Changing the output voltage 201 is the same as in FIG.

  The difference from FIG. 6 is that a digital potentiometer 213 is provided instead of the resistor circuit 206 and the switching circuit 207 of FIG. The digital potentiometer 213 is a resistor whose resistance value can be changed by setting a digital value, and can be controlled by, for example, an I2C bus. Here, the ASIC 106 is connected by two bus lines 214 including a clock line and a data line, and when a value is set from the ASIC 106 side, a resistance value corresponding to the value is obtained. Since the voltage dividing resistance value can be set more finely than the combination of the resistance circuit 206 and the switching circuit 207 shown in FIG. 6, the output voltage of the DC / DC converter 201 can be set finely.

<Process to forcibly reduce the power supply voltage of the drive waveform amplifier circuit>
As is apparent from the drive waveform shown in FIG. 5, even if the power supply voltage of the drive waveform amplifier circuit is changed according to the ambient temperature and humidity, there is still a voltage difference between the maximum voltage (Va1, Va2) and the others. As a result, power loss remains. For this reason, when sending a print job to a user who prioritizes power consumption over image quality, a mode is provided in which the required maximum voltage according to the environment at that time is ignored and the voltage is forcibly set to a low voltage. It was. FIG. 8 is a flowchart of the process. This process is performed by the CPU 102 executing a program stored in the ROM 103.

  As shown in the figure, a print job is set (step S1), and it is determined whether or not a mode for forcibly setting a low voltage is set (step S2). If not set (S2: NO), normal printing is performed to change the power supply voltage of the drive waveform amplifier circuit according to the environmental temperature and humidity (step S5 → S6), and if set (S2: YES), printing is performed after setting to lower the image quality rank (steps S3 → S4 → S6). With this processing, image quality degradation occurs in a waveform region that does not satisfy the required voltage, but wasteful power consumption can be suppressed in other waveform regions.

  As described above in detail, according to the image forming apparatus of the embodiment of the present invention, the temperature and humidity around the recording head 34 are measured, and the drive waveform stored in the ROM 103 in advance according to the measurement data. Since the power supply voltage of the drive waveform amplifier circuit 202 is variably set, optimization of the power supply voltage according to the environmental temperature and humidity is realized, and wasteful power consumption can be reduced.

  In addition, as a power supply voltage for the drive waveform amplifier circuit, a mode is provided in which the required maximum voltage according to the environmental temperature and humidity is ignored and a low voltage is forcibly set. Therefore, power consumption is more important than image quality. It can respond to user's request.

  In the above embodiment, the ambient temperature and humidity are measured, and the drive waveform data is selected and the power supply voltage of the drive waveform amplifier circuit is set according to the measurement data. However, only the ambient temperature measurement data is measured. The drive waveform data may be selected and the power supply voltage of the drive waveform amplifier circuit may be set according to the above.

  The present invention can also be realized as a drive waveform amplifier circuit and a power supply voltage setting circuit, a program corresponding to the process shown in FIG. 9, and a method corresponding to each step of the process.

  34 ... Recording head, 102 ... CPU, 103 ... ROM, 106 ... ASIC, 201 ... DC / DC converter, 202 ... Drive waveform amplification circuit, 202c ... pnp transistor, 202d ... npn transistor, 203 ... piezoelectric element, 190 ... temperature and humidity Sensor.

JP-A-2005-35062

Claims (5)

An ink jet recording head; a drive waveform amplifying circuit for amplifying a driving waveform for driving the ink jet recording head; a power supply voltage applying means for applying a power supply voltage to the drive waveform amplifying circuit; and an output voltage of the power supply voltage applying means being variable. An image forming apparatus comprising a power supply voltage setting means for setting,
Having environmental temperature measuring means for measuring environmental temperature,
The image forming apparatus, wherein the power supply voltage setting unit variably sets a power supply voltage to be applied to the drive waveform amplification circuit according to measurement data of the environmental temperature measurement unit. The image forming apparatus according to claim 1,
Having environmental humidity measuring means for measuring environmental humidity;
The power supply voltage setting unit variably sets a power supply voltage to be applied to the drive waveform amplifier circuit according to measurement data of the environmental temperature measurement unit and measurement data of the environmental humidity measurement unit. The image forming apparatus according to claim 1 or 2,
The power supply voltage applying means is a DC / DC converter, and the drive waveform amplifying circuit has a pair of push-pull connected transistors connected between an output side of the DC / DC converter and the ground, and An image forming apparatus in which a drive waveform applied to the ink jet recording head is output from a connection line between transistors. The image forming apparatus according to claim 3.
The pair of transistors is an pnp transistor having an emitter connected to the DC / DC converter and an npn transistor having an emitter connected to the ground. The image forming apparatus according to claim 1,
An image forming apparatus comprising low voltage setting means for forcibly setting an output voltage of the power supply voltage applying means to a voltage lower than a peak voltage of the drive waveform.

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