Head unit and liquid dispensing device

Abstract

To provide a head unit that can stop the heater's operation in the event of a temperature anomaly. [Solution] A head unit comprising: a head including a discharge section that ejects ink according to the displacement of a piezoelectric element that displaces in response to the application of a drive signal; a heater that heats the ink; a temperature abnormality detection section that detects an abnormal temperature and outputs an abnormality detection signal; a heater stop section that stops the operation of the heater according to the abnormality detection signal; and a head board connected to the head, wherein the heater stop section is analogously mounted on the head board.

Description

Technical Field

[0001] The present invention relates to a head unit and a liquid ejection device.

Background Art

[0002] In recent years, there has been an increasing demand for inkjet printers that heat and eject high-viscosity ink using a heater. In an inkjet printer that ejects high-viscosity ink, for example, as described in Patent Document 1, the ink is heated using a heater provided in the head unit, and the viscosity is controlled to suppress a deterioration in image quality. If current continues to flow through the heater due to some abnormality, the temperature of the head unit may rise, and the head unit may malfunction. Therefore, conventionally, a control unit on the main body side upstream of the head unit acquires temperature information of the head unit and stops supplying current to the heater when a temperature abnormality occurs.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, if an abnormality occurs in the transmission of temperature information from the head unit to the control unit, the control unit may not be able to stop supplying current to the heater. Further, in Patent Document 1, the temperature of an ink sub-tank provided near the head is controlled by the heater, but in order to heat the ink at a position closer to the head, for example, it is preferable to provide a heater on a head substrate disposed above the head. However, the head substrate directly connected to the piezoelectric element inside the head may be disposed in a very narrow area, and it is difficult to mount an IC having a function of stopping current to the heater in the limited area on the head substrate. [Means for solving the problem]

[0005] One embodiment of the head unit according to the present invention is: A head includes a piezoelectric element that displaces in response to the application of a drive signal, and a dispensing unit that ejects ink in response to the displacement of the piezoelectric element, A heater for heating the aforementioned ink, A temperature anomaly detection unit that detects temperature anomalies and outputs an anomaly detection signal, A heater stop unit that stops the operation of the heater in response to the abnormality detection signal, A head board connected to the aforementioned head, Equipped with, The heater stop unit is analogously mounted on the head board.

[0006] One embodiment of the liquid dispensing device according to the present invention is: A liquid dispensing device comprising a head unit and a power supply circuit, The head unit is A head includes a piezoelectric element that displaces in response to the application of a drive signal, and a dispensing unit that ejects ink in response to the displacement of the piezoelectric element, A heater for heating the aforementioned ink, A temperature anomaly detection unit that detects temperature anomalies and outputs an anomaly detection signal, A heater stop unit that stops the operation of the heater in response to the abnormality detection signal, A head board connected to the aforementioned head, Equipped with, The power supply circuit outputs a heater drive signal to drive the heater, The heater stop unit is analogously mounted on the head board. [Brief explanation of the drawing]

[0007] [Figure 1] This is a perspective view showing the schematic configuration of a liquid dispensing device. [Figure 2] This is a block diagram showing the electrical configuration of a liquid dispensing device. [Figure 3]It is a cross-sectional view showing a schematic configuration of a discharge unit. [Figure 4] It is a diagram showing an example of a drive signal COM. [Figure 5] It is a block diagram showing an electrical configuration of a drive signal selection circuit. [Figure 6] It is a circuit diagram showing an electrical configuration of a selection circuit. [Figure 7] It is a diagram showing decoding content in a decoder. [Figure 8] It is a diagram for explaining the operation of a drive signal selection circuit. [Figure 9] It is a diagram showing an example of a configuration of a temperature detection circuit. [Figure 10] It is a diagram showing an example of a configuration of a protection circuit in the first embodiment. [Figure 11] It is a plan view of a head substrate. [Figure 12] It is a diagram showing an example of a configuration of a protection circuit in the second embodiment. [Figure 13] It is a diagram showing an example of a configuration of a protection circuit in the third embodiment. [Figure 14] It is a diagram showing an example of a configuration of a protection circuit in the fourth embodiment. [Figure 15] It is a diagram showing another example of a configuration of a protection circuit in the fourth embodiment. [Figure 16] It is a diagram showing another example of a configuration of a protection circuit in the fourth embodiment.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The drawings used are for convenience of explanation. Note that the embodiments described below do not unduly limit the content of the present invention described in the claims. Also, not all of the configurations described below are essential constituent elements of the present invention.

[0009] 1. First Embodiment 1-1. Configuration of Liquid Discharge Device An example of a liquid ejection device according to this embodiment is an inkjet printer that ejects ink according to image data input from an external host computer to form dots on a printing medium such as paper, and prints an image including characters, figures, etc., corresponding to the image data.

[0010] Figure 1 is a perspective view showing the schematic configuration of the liquid dispensing device 1. Figure 1 illustrates the direction X in which the medium P is transported, the direction Y in which the mobile body 2 reciprocates intersecting direction X, and the direction Z in which the ink is dispensed. In this embodiment, directions X, Y, and Z are described as mutually orthogonal axes, but it is not limited to the various components of the liquid dispensing device 1 being arranged mutually orthogonally. Also, in the following description, the direction Y in which the mobile body 2 moves may be referred to as the main scanning direction.

[0011] As shown in Figure 1, the liquid dispensing device 1 comprises a movable body 2 and a moving mechanism 3 that reciprocates the movable body 2 along direction Y. The moving mechanism 3 includes a carriage motor 31 that serves as the driving source for the movable body 2, a carriage guide shaft 32 fixed at both ends, and a timing belt 33 that extends substantially parallel to the carriage guide shaft 32 and is driven by the carriage motor 31.

[0012] The carriage 24 included in the mobile body 2 is supported on the carriage guide shaft 32 so as to be able to reciprocate. It is fixed to a part of the timing belt 33. The carriage motor 31 drives the timing belt 33, and the carriage 24 is guided by the carriage guide shaft 32 and reciprocates along direction Y. A head unit 20 with numerous nozzles is provided in the part of the moving body 2 that faces the medium P. Control signals and the like are input to the head unit 20 via the cable 190. Based on the input control signals, the head unit 20 ejects ink as an example of a liquid from the nozzles.

[0013] The liquid dispensing device 1 includes a conveying mechanism 4 that transports the medium P on a platen 40 along direction X. The conveying mechanism 4 includes a conveying motor 41 which is the drive source, and conveying rollers 42 which are rotated by the conveying motor 41 to transport the medium P along direction X.

[0014] In the liquid dispensing device 1 configured as described above, the head unit 20 dispenses ink at the time the medium P is transported by the transport mechanism 4, thereby forming an image on the surface of the medium P.

[0015] 1-2. Electrical Configuration of Liquid Dispensing Device Figure 2 is a block diagram showing the electrical configuration of the liquid dispensing device 1. As shown in Figure 2, the liquid dispensing device 1 includes a control unit 10 and a head unit 20. The control unit 10 and the head unit 20 are electrically connected by a cable 190 such as a flexible flat cable (FFC).

[0016] The control unit 10 includes a control circuit 100, power supply circuits 90 and 91, and drive circuits 50a and 50b. The control circuit 100 generates multiple control signals, etc., for controlling various configurations based on image data input from the host computer and outputs them to the head unit 20.

[0017] Specifically, the control circuit 100 outputs a clock signal SCK, print data signals SIa and SIb, latch signals LATa and LATb, and change signals CHa and CHb to the head unit 20. The control circuit 100 also outputs drive data signals DATAa and DATAb to the drive circuits 50a and 50b, respectively.

[0018] Although not shown in the diagram, the control circuit 100 controls the carriage motor 31 and the transport motor 41. This controls the movement of the carriage 24 in direction Y as shown in Figure 1, and the movement of the medium P in direction X as shown in Figure 1.

[0019] The power supply circuit 90 generates a heater drive signal VHT and supplies the heater drive signal VHT to the protection circuit 300 included in the head unit 20. The heater drive signal VHT is a signal that drives the heater 260 included in the head unit 20.

[0020] The power supply circuit 91 generates voltages VHV_H and VHV_A, for example, DC 42V. The power supply circuit 91 supplies voltage VHV_H to the print head 22 included in the head unit 20, and voltage VHV_A to the drive circuits 50a and 50b. The power supply circuit 91 also generates voltage VDD and supplies voltage VDD to the liquid ejection modules 21a and 21b and the protection circuit 300 included in the head unit 20.

[0021] The drive circuit 50a generates a drive signal COMa and a reference voltage signal VBSa based on the voltage VHV_A and the drive data signal DATAa, and outputs them to the head unit 20. The drive circuit 50b generates a drive signal COMb and a reference voltage signal VBSb based on the voltage VHV_A and the drive data signal DATAb, and outputs them to the head unit 20. Here, the reference voltage signals VBSa and VBSb are signals with constant voltage, for example, ground potential. These are voltage signals such as DC 5V and DC 6V.

[0022] The head unit 20 includes a print head 22, a head board 23 connected to the print head 22, and a protection circuit 300. The print head 22 includes liquid ejection modules 21a and 21b.

[0023] The liquid dispensing module 21a includes a drive signal selection circuit 200a, a plurality of dispensing units 600a, and a temperature detection circuit 250a. Each dispensing unit 600a also includes a piezoelectric element 60a. The drive signal selection circuit 200a receives a clock signal SCK, a print data signal SIa, a latch signal LATa, a change signal CHa, a drive signal COMa, and a voltage VHV_H as inputs. Based on the clock signal SCK, print data signal SIa, latch signal LATa, change signal CHa, and voltage VHV_H, the drive signal selection circuit 200a generates a drive signal VOUTa by selecting or deselecting the drive signal COMa.

[0024] The drive signal VOUTa is supplied to one end of the piezoelectric element 60a included in each of the multiple ejection units 600a. A reference voltage signal VBSa is supplied to the other end of the piezoelectric element 60a. The piezoelectric element 60a is then driven by the potential difference between the drive signal VOUTa and the reference voltage signal VBSa, causing ink to be ejected from the ejection unit 600a. In other words, the liquid ejection module 21a has a piezoelectric element 60a driven by a drive signal COMa, and a drive signal selection circuit 200a that controls the supply of the drive signal COMa to the piezoelectric element 60a.

[0025] The temperature detection circuit 250a detects the temperature of the print head 22 and determines whether the temperature is above a predetermined threshold. If the temperature of the print head 22 is above the predetermined threshold, the temperature detection circuit 250a determines that a temperature anomaly has occurred in the print head 22 and outputs an L-level temperature anomaly signal XHa indicating a temperature anomaly in the print head 22.

[0026] The liquid dispensing module 21b includes a drive signal selection circuit 200b, a plurality of dispensing units 600b, and a temperature detection circuit 250b. Each dispensing unit 600b also includes a piezoelectric element 60b. The drive signal selection circuit 200b receives a clock signal SCK, a print data signal SIb, a latch signal LATb, a change signal CHb, a drive signal COMb, and a voltage VHV_H as inputs. Based on the clock signal SCK, print data signal SIb, latch signal LATb, change signal CHb, and voltage VHV_H, the drive signal selection circuit 200b generates a drive signal VOUTb by selecting or deselecting the drive signal COMb.

[0027] The drive signal VOUTb is supplied to one end of the piezoelectric element 60b included in each of the multiple ejection units 600b. A reference voltage signal VBSb is supplied to the other end of the piezoelectric element 60b. The piezoelectric element 60b is driven by the potential difference between the drive signal VOUTb and the reference voltage signal VBSb, causing ink to be ejected from the ejection unit 600b. In other words, the liquid ejection module 21b has a piezoelectric element 60b driven by a drive signal COMb and a drive signal selection circuit 200b that controls the supply of the drive signal COMb to the piezoelectric element 60b.

[0028] The temperature detection circuit 250b detects the temperature of the print head 22 and determines whether the temperature is above a predetermined threshold. If the temperature of the print head 22 is above the predetermined threshold, the temperature detection circuit 250b determines that a temperature anomaly has occurred in the print head 22 and outputs an L-level temperature anomaly signal XHb indicating a temperature anomaly in the print head 22.

[0029] On the head board 23, the wiring through which the temperature abnormality signal XHa propagates and the wiring through which the temperature abnormality signal XHb propagates are connected to form a single wiring, and the temperature abnormality signal XHOT, which is a combination of the temperature abnormality signals XHa and XHb, is input to the control circuit 100 of the control unit 10. When at least one of the temperature abnormality signals XHa and XHb is at an L level, the temperature abnormality signal XHOT is at a low level, and when the temperature anomaly signals XHa and XHb are at a high level, the temperature anomaly signal XHOT is at a high level. When the temperature anomaly signal XHOT is at a low level, the control circuit 100 stops the output of the clock signal SCK, print data signals SIa, SIb, latch signals LATa, LATb, and change signals CHa, CHb, and stops the output of the voltages VHV_H, VHV_A, and VHT from the power supply circuit 91. Note that the temperature anomaly signals XHa and XHb may be input to the control circuit 100 separately without being integrated.

[0030] In the following description, drive circuits 50a and 50b have similar configurations and may be referred to as drive circuit 50 unless otherwise specified. The various signals input to drive circuit 50 will be referred to as voltage VHV_H and drive data signal DATA. The various signals output from drive circuit 50 will be referred to as drive signal COM and reference voltage signal VBS.

[0031] Furthermore, the liquid dispensing modules 21a and 21b have similar configurations and will be referred to as liquid dispensing module 21 unless otherwise specified. The liquid dispensing module 21 will be described as having a drive signal selection circuit 200, a plurality of dispensing units 600, and a temperature detection circuit 250, with the plurality of dispensing units 600 including piezoelectric elements 60. In this case, the various signals input to the liquid dispensing module 21 will be referred to as the clock signal SCK, the print data signal SI, the latch signal LAT, the change signal CH, the drive signal COM, the reference voltage signal VBS, and the voltage VHV_H. The signal supplied to the piezoelectric element 60 will be referred to as the drive signal VOUT. The signal output by the temperature detection circuit 250 will be referred to as the temperature abnormality signal XH.

[0032] The heater 260 generates heat when a heater drive signal VHT is supplied, and heats the ink supplied to each ejection section 600a of the liquid ejection module 21a and each ejection section 600b of the liquid ejection module 21b. For example, the heater 260 includes a plurality of heating elements connected in series between the supply line of the heater drive signal VHT and ground, and current flows through these heating elements in response to the heater drive signal VHT, generating heat. For example, the heating elements are resistors. For example, the heater 260 is provided on the print head 22.

[0033] The protection circuit 300 receives a heater drive signal VHT and controls the supply of the heater drive signal VHT to the heater 260 depending on whether or not there is an abnormality in the temperature of the head unit 20. Specifically, if the temperature of the head unit 20 is normal, the protection circuit 300 supplies the heater drive signal VHT to the heater 260. If the protection circuit 300 detects an abnormality in the temperature of the head unit 20, it stops supplying the heater drive signal VHT to the heater 260. As will be described later, at least a part of the protection circuit 300 is mounted on the head board 23.

[0034] 1-3. Discharge section configuration Next, the configuration and operation of the discharge unit 600, including the piezoelectric element 60, will be described using Figure 3. Figure 3 is a cross-sectional view showing the schematic configuration of the discharge unit 600 when the liquid discharge module 21 is cut to include the discharge unit 600.

[0035] As shown in Figure 3, the liquid dispensing module 21 includes a dispensing unit 600 and a reservoir 641. Ink is introduced into the reservoir 641 from the supply port 661. Furthermore, a separate reservoir 641 is provided for each ink color.

[0036] The ejection unit 600 includes a piezoelectric element 60, a diaphragm 621, a cavity 631, and a nozzle 651. The diaphragm 621 is provided between the cavity 631 and the piezoelectric element 60. The diaphragm 621 is displaced by the movement of the piezoelectric element 60, which is located on its upper surface. In other words, the diaphragm 621 functions as a diaphragm that expands / contracts the internal volume of the cavity 631 by displacing. The inside of the cavity 631 is filled with ink. Furthermore, the cavity 631 functions as a pressure chamber whose internal volume changes when driven by the piezoelectric element 60. The nozzle 651 is provided on the nozzle plate 632 and is an opening that communicates with the cavity 631.

[0037] The piezoelectric element 60 has a structure in which a piezoelectric body 601 is sandwiched between a pair of electrodes 611 and 612. A drive signal VOUT is supplied to electrode 611, and a reference voltage signal VBS is supplied to electrode 612. A piezoelectric element 60 with this structure is driven according to the potential difference between electrode 611 and electrode 612. As the piezoelectric element 60 is driven, the electrodes 611 and 612 and the central part of the diaphragm 621 are displaced vertically relative to the ends. As the diaphragm 621 is displaced, the internal volume of the cavity 631 changes, and the ink filled inside the cavity 631 is ejected from the nozzle 651.

[0038] Here, the drive signal VOUT is a signal in which at least a portion of the drive signal COM is selected, the piezoelectric element 60 is displaced in response to the application of the drive signal COM, and the ejection unit 600 ejects ink to the medium P in response to the displacement of the piezoelectric element 60.

[0039] 1-4. Configuration of the drive signal selection circuit Next, the configuration and operation of the drive signal selection circuit 200 will be described. To explain the configuration and operation of the drive signal selection circuit 200, first, an example of the drive signal COM input to the drive signal selection circuit 200 will be described using Figure 4. After that, the configuration and operation of the drive signal selection circuit 200 will be described using Figures 5 to 8.

[0040] Figure 4 shows an example of the drive signal COM. Figure 4 shows the period T1 from when the latch signal LAT rises until the change signal CH rises, the period T2 after period T1 until the next rise of the change signal CH, and the period T3 after period T2 until the latch signal LAT rises. The period consisting of these periods T1, T2, and T3 is the period Ta for forming a new dot on the medium P. In other words, as shown in Figure 4, the latch signal LAT is a signal that defines the period for forming a new dot on the medium P, and the change signal CH is a signal that defines the switching timing of the waveform included in the drive signal COM.

[0041] As shown in Figure 4, the drive circuit 50 generates a trapezoidal waveform Adp during period T1. When the trapezoidal waveform Adp is supplied to the piezoelectric element 60, a predetermined amount, specifically a moderate amount of ink, is ejected from the corresponding ejection unit 600. The drive circuit 50 also generates a trapezoidal waveform Bdp during period T2. When the trapezoidal waveform Bdp is supplied to the piezoelectric element 60, a small amount of ink, less than the predetermined amount, is ejected from the corresponding ejection unit 600. The drive circuit 50 also generates a trapezoidal waveform Cdp during period T3. When the trapezoidal waveform Cdp is supplied to the piezoelectric element 60, the piezoelectric element 60 is driven to the extent that no ink is ejected from the corresponding ejection unit 600. Therefore, when the trapezoidal waveform Cdp is supplied to the piezoelectric element 60, no dots are formed on the medium P. This trapezoidal waveform Cdp is a waveform that prevents the ink near the nozzle opening of the ejection unit 600 from vibrating slightly and thus prevents an increase in ink viscosity. In the following explanation, driving the piezoelectric element 60 to the extent that ink is not ejected from the ejection section 600 in order to prevent an increase in ink viscosity is referred to as "micro-vibration."

[0042] Here, the voltage values ​​at the start and end timings of the trapezoidal waveforms Adp, Bdp, and Cdp are all the same at voltage Vc. That is, the trapezoidal waveforms Adp, Bdp, and Cdp are waveforms that start and end at voltage Vc. Therefore, the drive circuit 50 outputs a drive signal COM with a continuous waveform of trapezoidal waveforms Adp, Bdp, and Cdp over period Ta. Note that the waveform of the drive signal COM shown in Figure 4 is just an example, and the waveform of the drive signal COM may be different. Also, drive circuit 50a and drive circuit 50b may generate and output drive signals COM with different waveforms.

[0043] Figure 5 is a block diagram showing the electrical configuration of the drive signal selection circuit 200. The drive signal selection circuit 200 generates and outputs a drive signal VOUT supplied to the piezoelectric element 60 during period Ta by switching whether or not to select the trapezoidal waveforms Adp, Bdp, and Cdp included in the drive signal COM during periods T1, T2, and T3. As shown in Figure 5, the drive signal selection circuit 200 includes a selection control circuit 210 and a plurality of selection circuits 230.

[0044] The selection control circuit 210 is supplied with a clock signal SCK, a print data signal SI, a latch signal LAT, a change signal CH, and a voltage VHV_H. Each output unit 600 in the selection control circuit 210 is provided with a set of shift registers 212 (S / R), latch circuits 214, and decoders 216. That is, the head unit 20 is provided with the same number of sets of shift registers 212, latch circuits 214, and decoders 216 as the total number of output units 600, n.

[0045] The shift register 212 temporarily holds the 2 bits of print data [SIH, SIL] contained in the print data signal SI for each corresponding ejector unit 600. Specifically, the number of shift registers 212 corresponding to the number of ejector units 600 are connected in cascaded order, and the serially supplied print data signal SI is sequentially transferred to the subsequent stages according to the clock signal SCK. In Figure 5, the shift registers 212 are labeled as 1st stage, 2nd stage, ..., nth stage in order from the upstream side to which the print data signal SI is supplied, in order to distinguish them.

[0046] Each of the n latch circuits 214 latches the print data [SIH,SIL] held in the corresponding shift register 212 on the rising edge of the latch signal LAT. Each of the n decoders 216 decodes the 2-bit print data [SIH,SIL] latched by the corresponding latch circuit 214 to generate a selection signal S, which is supplied to the selection circuit 230.

[0047] A selection circuit 230 is provided corresponding to each of the output units 600. That is, the number of selection circuits 230 in one head unit 20 is the same as the total number n of output units 600 included in the head unit 20. Based on the selection signal S supplied from the decoder 216, the selection circuit 230 controls the supply of the drive signal COM to the piezoelectric element 60.

[0048] Figure 6 is a circuit diagram showing the electrical configuration of the selection circuit 230 corresponding to one discharge unit 600. As shown in Figure 6, the selection circuit 230 has an inverter 232 and a transfer gate 234. The transfer gate 234 also includes transistor 235, which is an NMOS transistor, and transistor 236, which is a PMOS transistor.

[0049] The selection signal S is supplied from the decoder 216 to the gate terminal of transistor 235. The selection signal S is also logically inverted by the inverter 232 and supplied to the gate terminal of transistor 236. The drain terminal of transistor 235 and the source terminal of transistor 236 are connected to terminal TG-In, which is one end of the circuit. The drive signal COM is input from terminal TG-In. When transistors 235 and 236 are controlled to be on or off according to the selection signal S, the drive signal VOUT is output from terminal TG-Out, which is the other end to which the source terminal of transistor 235 and the drain terminal of transistor 236 are commonly connected. Terminal TG-Out is electrically connected to electrode 611 of piezoelectric element 60, which will be described later. In the following description, when transistors 235 and 236 are controlled to be conductive, they are referred to as "on," and when transistors 235 and 236 are controlled to be non-conductive, they are referred to as "off."

[0050] Next, the decoding process of decoder 216 will be explained using Figure 7. Figure 7 shows the decoding process in decoder 216. Decoder 216 receives 2-bit print data [SIH,SIL], a latch signal LAT, and a change signal CH as inputs. Decoder 216 then outputs a selection signal S that is at H,L,L levels for periods T1, T2, and T3, for example, when the print data [SIH,SIL] is [1,0] which defines a "middle dot". Here, the logic level of the selection signal S is level-shifted to a high-amplitude logic based on the voltage VHV_H by a level shifter (not shown).

[0051] Figure 8 is a diagram illustrating the operation of the drive signal selection circuit 200. As shown in Figure 8, the print data signal SI is supplied serially to the drive signal selection circuit 200 in synchronization with the clock signal SCK, and is sequentially transferred in the shift register 212 corresponding to the ejection unit 600. When the supply of the clock signal SCK stops, each of the shift registers 212 holds the print data [SIH, SIL] corresponding to the ejection unit 600. The print data signal SI is supplied in the order corresponding to the last n stages, ..., 2nd stage, 1st stage of the ejection unit 600 in the shift register 212.

[0052] Here, when the latch signal LAT rises, each of the latch circuits 214 simultaneously latches the print data [SIH,SIL] held in the corresponding shift register 212. LT1, LT2, ..., LTn shown in Figure 8 represent the print data [SIH,SIL] latched by the latch circuits 214 corresponding to the 1st, 2nd, ..., nth stage shift registers 212.

[0053] The decoder 216 outputs a logic level selection signal S in each of the periods T1, T2, and T3, according to the content shown in Figure 7, depending on the size of the dots defined in the latched print data [SIH, SIL].

[0054] When the print data [SIH,SIL] is [1,1], the selection circuit 230 selects trapezoidal waveform Adp during period T1, trapezoidal waveform Bdp during period T2, and does not select trapezoidal waveform Cdp during period T3, according to the selection signal S. As a result, the drive signal VOUT corresponding to the large dot shown in Figure 8 is generated. Therefore, a medium amount of ink and a small amount of ink are ejected from the ejection unit 600. Thus, a large dot is formed on the medium P by the adhesion of this ink. Also, when the print data [SIH,SIL] is [1,0], the selection circuit 230 selects trapezoidal waveform Adp during period T1, does not select trapezoidal waveform Bdp during period T2, and does not select trapezoidal waveform Cdp during period T3, according to the selection signal S. As a result, the drive signal VOUT corresponding to the medium dot shown in Figure 8 is generated. Therefore, a medium amount of ink is ejected from the ejection unit 600. Thus, a medium dot is formed on the medium P. Furthermore, when the print data [SIH,SIL] is [0,1], the selection circuit 230, according to the selection signal S, does not select trapezoidal waveform Adp during period T1, selects trapezoidal waveform Bdp during period T2, and does not select trapezoidal waveform Cdp during period T3. As a result, a drive signal VOUT corresponding to the small dots shown in Figure 8 is generated. Therefore, a small amount of ink is ejected from the ejection unit 600. Thus, small dots are formed on the medium P. Also, when the print data [SIH,SIL] is [0,0], the selection circuit 230, according to the selection signal S, does not select trapezoidal waveform Adp during period T1, does not select trapezoidal waveform Bdp during period T2, and selects trapezoidal waveform Cdp during period T3. As a result, a drive signal VOUT corresponding to the micro-vibrations shown in Figure 8 is generated. Therefore, no ink is ejected from the ejection unit 600, and micro-vibrations occur.

[0055] 1-5. Configuration of the temperature detection circuit Next, the configuration and operation of the temperature detection circuit 250 will be described. Figure 9 shows the temperature detection circuit 2 This figure shows an example of the configuration of 50. As shown in Figure 9, the temperature detection circuit 250 includes a reference voltage generation circuit 251, a comparator 252, a transistor 253, diodes 254-1 to 254-k, and resistors 255 and 256. The temperature detection circuit 250 is also supplied with a voltage VDD.

[0056] The voltage VDD is input to the reference voltage generation circuit 251, one end of resistor 255, and one end of resistor 256. The reference voltage generation circuit 251 transforms the voltage VDD to generate a voltage Vref with a constant voltage value. The voltage Vref generated by the reference voltage generation circuit 251 is then input to the + side input terminal of comparator 252. The other end of resistor 255 is electrically connected to the anode terminal of diode 254-1. The cathode terminal of diode 254-i (where i is one of 1 to k-1) is electrically connected to the anode terminal of diode 254-(i+1). The cathode terminal of diode 254-k is connected to ground. In other words, diodes 254-1 to 254-k are connected in series between the other end of resistor 255 and ground.

[0057] Then, the voltage at the connection point where the other end of resistor 255 and the anode terminal of diode 254-1 are connected is input as voltage Vdet to the negative input terminal of comparator 252. The voltage at this connection point is the sum of the forward voltages of diodes 254-1 to 254-k. As the temperature rises, the forward voltages of each of diodes 254-1 to 254-k decrease, so the voltage Vdet decreases.

[0058] Comparator 252 compares the voltage Vref input to the + side input terminal with the voltage Vdet input to the - side input terminal. If voltage Vdet is greater than voltage Vref, comparator 252 outputs a low-level signal of ground potential, and if voltage Vdet is less than voltage Vref, it outputs a high-level signal of voltage VDD.

[0059] The output terminal of comparator 252 is connected to the gate terminal of transistor 253. Transistor 253 is an N-channel MOS transistor, with its drain terminal connected to the other end of resistor 256 and its source terminal connected to ground. The signal from the drain terminal of transistor 253 is output from the temperature detection circuit 250 as a temperature abnormality signal XH.

[0060] When a low-level signal is input to the gate terminal of transistor 253, the drain terminal and source terminal become non-conductive. As a result, the voltage at the drain terminal of transistor 253 is pulled up by resistor 256, and the temperature detection circuit 250 outputs a high-level temperature anomaly signal XH. On the other hand, when a high-level signal is input to the gate terminal of transistor 253, the drain terminal and source terminal become conductive. As a result, the voltage at the drain terminal of transistor 253 becomes ground potential, and the temperature detection circuit 250 outputs a low-level temperature anomaly signal XH. In other words, the temperature detection circuit 250 outputs a high-level temperature anomaly signal XH when the temperature is within a predetermined range, and outputs a low-level temperature anomaly signal XH when the temperature exceeds the predetermined range.

[0061] 1-6. Configuration of the protection circuit Next, the configuration and operation of the protection circuit 300 will be described. Figure 10 is a diagram showing an example of the configuration of the protection circuit 300. In Figure 10, the power supply circuit 90, the head board 23, and the heater 260 are also shown.

[0062] As shown in Figure 10, the head board 23 has terminals 23a and 23b. Terminal 23a is a power terminal connected to the positive terminal of the power supply circuit 90, to which the heater drive signal VHT that drives the heater 260 is input. Terminal 23b is connected to the positive terminal of the heater 260. This is the terminal. The negative terminal of heater 260 is connected to ground.

[0063] As shown in Figure 10, the protection circuit 300 includes a temperature abnormality detection unit 310 and a heater stop unit 320.

[0064] The temperature anomaly detection unit 310 includes a resistor 311 and a thermistor 312.

[0065] Resistor 311 has a voltage VDD supplied to one end and the other end connected to one end of thermistor 312. The other end of thermistor 312 is connected to ground. The signal at the connection point where the other end of resistor 311 and one end of thermistor 312 are connected is output to the heater stop unit 320 as an abnormality detection signal XT. In this way, the temperature abnormality detection unit 310 detects a temperature abnormality using resistor 311 and thermistor 312 and outputs the abnormality detection signal XT. Thermistor 312 is an NTC thermistor, and the resistance value of thermistor 312 decreases as the temperature increases. Therefore, the voltage of the abnormality detection signal XT decreases as the temperature increases.

[0066] The heater stop unit 320 includes a P-channel transistor 321, an N-channel transistor 322, a resistor 323, and a resistor 324. For example, transistor 321 is a P-channel FET (Field Effect Transistor), and transistor 322 is an N-channel FET.

[0067] The drain terminal of transistor 321 is connected to the positive terminal of heater 260, and the source terminal of transistor 321 is connected to terminal 23a of head board 23. Resistor 323 has one end connected to the source terminal of transistor 321 and the other end connected to the gate terminal of transistor 321. Resistor 324 has one end connected to the gate terminal of transistor 321 and the other end connected to the drain terminal of transistor 322. The source terminal of transistor 322 is connected to ground, and an abnormality detection signal XT is input to the gate terminal of transistor 322.

[0068] If the temperature of the head unit 20 is below a predetermined value, the voltage of the abnormality detection signal XT is above the threshold voltage of transistor 322, so conduction occurs between the drain terminal and source terminal of transistor 322. Also, the voltage at the connection point of resistors 323 and 324 is lower than the threshold voltage of transistor 321, so conduction occurs between the source terminal and drain terminal of transistor 321. Therefore, the heater drive signal VHT is supplied from the positive terminal of the power supply circuit 90 to the positive terminal of the heater 260 via terminal 23a, transistor 321, and terminal 23b, causing current to flow from the positive terminal to the negative terminal of the heater 260, and the heater 260 to heat up. As a result, the ink is heated.

[0069] The heater 260 generates heat, causing the temperature of the head unit 20 to rise. Normally, the temperature of the head unit 20 fluctuates within a range below a predetermined value, but for some reason, the temperature of the head unit 20 may rise above the predetermined value. In this case, the voltage of the abnormality detection signal XT becomes lower than the threshold voltage of transistor 322, and the drain terminal and source terminal of transistor 322 become non-conductive. As a result, the voltage at the connection point of resistors 323 and 324 becomes higher than the threshold voltage of transistor 321, and the source terminal and drain terminal of transistor 321 become non-conductive. Therefore, the supply of the heater drive signal VHT to the positive terminal of heater 260 stops, and the heat generated by heater 260 gradually decreases. In this way, the heater stop unit 320 stops the operation of heater 260 in response to the abnormality detection signal XT. This lowers the temperature of the head unit 20 and reduces the risk of head unit 20 failure.

[0070] Furthermore, as long as the temperature of the head unit 20 does not rise above a predetermined value, transistors 321 and 322 remain in an ON state with conduction between the source terminal and the drain terminal, and current continues to flow through transistors 321 and 322. Therefore, in order to reduce power consumption, it is preferable that the on-resistance of transistors 321 and 322 be low. In particular, the lower the on-resistance of transistor 321, the higher the heating efficiency of the heater 260, so it is preferable that transistor 321 has a lower on-resistance than transistor 322.

[0071] 1-7. Implementation of the protection circuit onto the head board Next, the mounting of the protection circuit 300 to the head board 23 will be described. Figure 11 is a plan view of the top surface of the head board 23 as seen in direction Z in Figure 1. The head board 23 is a four-layer board including, for example, layers L1 to L4, and in Figure 11, some of the wiring, electrodes, and openings of the L1 layer are shown. Also in Figure 11, components mounted on the head board 23 and components connected to the head board 23 are shown with dashed lines.

[0072] As shown in Figure 11, the component mounting surface 400 of the head board 23 is provided with multiple electrodes 401 to which multiple terminals of connector 501 are connected, and multiple electrodes 402 to which multiple terminals of connector 502 are connected. In addition, wiring 411 to 419, electrodes 421 to 428, and openings 451 to 454 are provided on the surface 400 of the head board 23. Furthermore, the surface 400 of the head board 23 is provided with multiple electrodes 431 to which multiple terminals of FPC (Flexible Printed Circuits) 511 inserted into opening 451 are connected, and multiple electrodes 432 to which multiple terminals of FPC 512 inserted into opening 452 are connected. Furthermore, the surface 400 of the head board 23 is provided with multiple electrodes 441 to 444 to which multiple terminals of the FPC 513 inserted into the opening 453 are connected, and multiple electrodes 445 to 448 to which multiple terminals of the FPC 514 inserted into the opening 454 are connected.

[0073] FPC511 has a single-chip IC mounted that includes a drive signal selection circuit 200a and a temperature detection circuit 230a. Similarly, FPC512 has a single-chip IC mounted that includes a drive signal selection circuit 200b and a temperature detection circuit 230b. Furthermore, FPC513 has a heating element 260a and a thermistor 312a mounted on it. Similarly, FPC514 has a heating element 260b and a thermistor 312b mounted on it.

[0074] Wiring 411 is connected to one of the multiple electrodes 401 and electrode 421. Wiring 411 is a drive signal propagation wire through which the drive signal COMa input from connector 501 is propagated. Electrode 421 is connected to wiring 411 and one of the multiple electrodes 431, and the drive signal COMa is input to the drive signal selection circuit 200a via electrode 431.

[0075] Wiring 412 is connected to one of the multiple electrodes 401 and electrode 422. Wiring 411 is the wiring through which the reference voltage signal VBSa input from connector 501 propagates. Electrode 422 is connected to wiring 412 and one of the multiple electrodes 431, and the reference voltage signal VBSa is input to the drive signal selection circuit 200a via electrode 431.

[0076] Wiring 413 is connected to one of the multiple electrodes 402 and electrode 423. Wiring 413 is a drive signal propagation wire through which the drive signal COMb input from connector 502 is propagated. Electrode 423 is connected to wiring 413 and one of the multiple electrodes 432, and the drive signal COMb is input to the drive signal selection circuit 200b via electrode 432.

[0077] Wiring 414 is connected to electrode 424. Wiring 414 is also connected to one of the multiple electrodes 402 via wiring provided in layers L2 to L4 (not shown). Wiring 414 is the wiring through which the reference voltage signal VBSb input from connector 502 propagates. Electrode 424 is connected to wiring 414 and one of the multiple electrodes 432, and the reference voltage signal VBSb is input to the drive signal selection circuit 200b via electrode 432.

[0078] Wiring 415 is connected to one of the multiple electrodes 401. Wiring 415 is also connected to terminal 23a of the protection circuit 300 shown in Figure 10 via wiring provided in layers L2 to L4 (not shown). Wiring 415 is the wiring through which the heater drive signal VHT input from connector 501 is propagated.

[0079] Wiring 419 is connected to electrode 425. Wiring 419 is also connected to terminal 23b of the protection circuit 300 shown in Figure 10 via wiring provided in layers L2 to L4 (not shown). Electrode 425 is connected to wiring 415 and electrode 441. Electrode 441 is connected to one end of the heating element 260a, and the other end of the heating element 260a is connected to electrode 442. Electrode 442 is connected to electrode 426. Electrodes 443 and 444 are connected to both ends of the thermistor 312a.

[0080] Electrode 426 is connected to wiring 417, and electrode 442 is connected to wiring 416. Wiring 416 is connected to wiring 417 via wiring provided in layers L2 to L4 (not shown). Wiring 417 is connected to electrode 427.

[0081] Electrode 427 is connected to wiring 417 and electrode 445. Electrode 445 is connected to one end of heating element 260b, and the other end of heating element 260b is connected to electrode 446. Electrode 446 is connected to electrode 428. Electrodes 447 and 448 are connected to both ends of thermistor 312b.

[0082] Electrode 428 is connected to electrode 446 and wiring 418. Wiring 418 is connected to ground via wiring provided in layers L2 to L4 (not shown). Heating elements 260a and 260b are connected in series between terminal 23b of the protection circuit 300 and ground, and the heating elements 260a and 260b constitute the heater 260. Wirings 415, 416, 417, 418, and 419 are heater wiring through which the heater drive signal VHT is propagated.

[0083] Although not shown in the illustration, the surface 400 of the head board 23 is provided with numerous wires, electrodes, vias, etc., limiting the area available for placing the protection circuit 300. Therefore, if the protection circuit 300 were implemented as a digital circuit using an FPGA or the like, there might not be any area on the surface 400 of the head board 23 that could be used for mounting. In this embodiment, as shown in Figure 10, the protection circuit 300 is implemented as an analog circuit using resistors 311, 323, 324, a thermistor 312, and transistors 321, 322. The resistors 311, 323, 324, thermistor 312, and transistors 321, 322 are each analogously mounted on the surface 400 of the head board 23 as individual electronic components. In this way, the protection circuit 300 is implemented with a small number of electronic components, making it possible to place it even in a narrow area on the surface 400 of the head board 23.

[0084] By the way, the method of driving the heater 260 differs depending on the model of the liquid ejection device 1, and depending on the driving method, the heater drive signal VHT may become a noise source for the head unit 20. The drive signals COMa and COMb are analog signals that control ink ejection and are susceptible to noise, so the wiring 411 and 413 through which the drive signals COMa and COMb propagate, respectively, It is preferable to position the heater drive signal VHT away from the wiring 415, 416, 417, 418, 419 and electrodes 425, 426, 427, 428, 441, 442, 445, 446 through which the VHT propagates. Therefore, in the example shown in Figure 11, region A1 exists between wiring 411 and wiring 415, 416, 419. To effectively utilize this region A1, at least the heater stop unit 320 of the protection circuit 300 is positioned in region A1. That is, the heater stop unit 320 is implemented between wiring 411, which is the drive signal propagation wiring, and wiring 415, 416, 419, which are the heater wiring. Furthermore, the temperature abnormality detection unit 310 may also be implemented between wiring 411 and wiring 415, 416, 419.

[0085] The heater stop unit 320 may be located in the area between wiring 413 and wirings 417 and 418. That is, the heater stop unit 320 may be implemented between wiring 413, which is the drive signal propagation wiring, and wirings 417 and 418, which are the heater wiring. Furthermore, the temperature abnormality detection unit 310 may also be implemented between wiring 413 and wirings 417 and 418.

[0086] However, a portion of the temperature anomaly detection unit 310 does not need to be mounted between the drive signal propagation wiring and the heater wiring on the surface 400 of the head board 23. For example, the thermistor 312 does not need to be mounted between the drive signal propagation wiring and the heater wiring, and may be mounted on the surface of the L4 layer, which is the lower surface of the head board 23. Alternatively, in the temperature anomaly detection unit 310, thermistor 312 may be replaced with thermistor 312a mounted on FPC 513, or thermistor 312b mounted on FPC 514.

[0087] Note that transistor 321 is an example of a "first transistor," and N-channel transistor 322 is an example of a "second transistor." Also, resistor 323 is an example of a "first resistor," and resistor 324 is an example of a "second resistor." Furthermore, the positive terminal of heater 260 is an example of a "first heater terminal," and the negative terminal of heater 260 is an example of a "second heater terminal."

[0088] 1-8. Effects As described above, according to the liquid dispensing device 1 and head unit 20 of the first embodiment, if the temperature abnormality detection unit 310 in the protection circuit 300 detects a temperature abnormality, the heater stop unit 320 stops the operation of the heater 260, thereby reducing the risk of the head unit 20 failing due to a temperature abnormality. Furthermore, according to the liquid dispensing device 1 and head unit 20 of the first embodiment, the heater stop unit 320 can be placed in a limited narrow area on the head board 23, which is equipped with wiring for numerous signals such as drive signals COMa and COMb for driving numerous piezoelectric elements 60 and on which numerous electronic components are mounted, by being analogously mounted. In particular, since the heater stop unit 320 shown in Figure 10 is realized with few electronic components, it can be analogously mounted in a limited narrow area on the head board 23.

[0089] Furthermore, according to the liquid ejection device 1 and head unit 20 of the first embodiment, the drive signal wiring on which the noise-sensitive drive signals COMa and COMb propagate is located away from the heater wiring on which the heater drive signal VHT, which can be a source of noise, propagates. This allows the heater stop unit 320 to be mounted by effectively utilizing the region A1 created between the drive signal wiring and the heater wiring. In addition, according to the liquid ejection device 1 and head unit 20 of the first embodiment, the influence of the heater drive signal VHT on the drive signals COMa and COMb is reduced, thereby improving the ink ejection accuracy.

[0090] 2. Second Embodiment In the following description of the second embodiment, the same reference numerals are used for components similar to those in the first embodiment, and descriptions that overlap with those in the first embodiment are omitted or simplified. The main points to be described are those that differ from the first embodiment.

[0091] The liquid dispensing device 1 of the second embodiment differs from the liquid dispensing device 1 of the first embodiment in the configuration and operation of the protection circuit 300 included in the head unit 20. Figure 12 shows an example of the configuration of the protection circuit 300 in the second embodiment. In Figure 12, the power supply circuit 90, the head board 23, and the heater 260 are also shown.

[0092] As shown in Figure 12, the head board 23 has terminals 23a, 23b, and 23c. Terminal 23a is a power terminal connected to the positive terminal of the power supply circuit 90, and is to which the heater drive signal VHT that drives the heater 260 is input. Terminal 23b is a terminal connected to the positive terminal of the heater 260. Terminal 23b is also connected to terminal 23a. Therefore, the positive terminal of the heater 260 is connected to terminal 23a via terminal 23b. Terminal 23c is a terminal connected to the negative terminal of the heater 260.

[0093] As shown in Figure 12, the protection circuit 300 includes a temperature abnormality detection unit 310 and a heater stop unit 320. The temperature abnormality detection unit 310 includes a resistor 311 and a thermistor 312, and its configuration and operation are the same as in Figure 10, so its explanation is omitted.

[0094] The heater stop unit 320 includes an N-channel transistor 322. For example, transistor 322 is an N-channel FET.

[0095] The drain terminal of transistor 322 is connected to terminal 23c. Therefore, the drain terminal of transistor 322 is connected to the negative terminal of heater 260 via terminal 23c. The source terminal of transistor 322 is connected to ground. An anomaly detection signal XT is input to the gate terminal of transistor 322.

[0096] If the temperature of the head unit 20 is below a predetermined value, the voltage of the abnormality detection signal XT is above the threshold voltage of transistor 322, so conduction occurs between the drain terminal and source terminal of transistor 322, and the negative terminal of heater 260 is connected to ground. As a result, the heater drive signal VHT is supplied from the positive terminal of the power supply circuit 90 to the positive terminal of heater 260 via terminals 23a and 23b, causing current to flow from the positive terminal to the negative terminal of heater 260, and heater 260 to heat up. This heats the ink.

[0097] On the other hand, if the temperature of the head unit 20 rises above a predetermined value, the voltage of the abnormality detection signal XT falls below the threshold voltage of the transistor 322, causing the drain terminal and source terminal of the transistor 322 to become nonconductive. As a result, the connection between the negative terminal of the heater 260 and ground is interrupted, and no current flows to the heater 260, causing the heat generated by the heater 260 to gradually decrease. In this way, the heater stop unit 320 stops the operation of the heater 260 in response to the abnormality detection signal XT. This lowers the temperature of the head unit 20 and reduces the risk of the head unit 20 failing.

[0098] Furthermore, as long as the temperature of the head unit 20 does not rise above a predetermined value, the transistor 322 will remain in an ON state with conduction between the source terminal and the drain terminal, and current will continue to flow through the transistor 322. Therefore, in order to reduce power consumption, it is preferable that the on-resistance of the transistor 322 be low.

[0099] The example of mounting the protection circuit 300 on the head board 23 in the second embodiment is the same as in Figure 11, so its illustration is omitted. In the second embodiment as well, the protection circuit 300 is realized as an analog circuit using a resistor 311, a thermistor 312, and a transistor 322, and the resistor 311, thermistor 312, and transistor 322 are each individual electronic components. The protection circuit is analogously mounted on surface 400 of the head board 23. Thus, since the protection circuit 300 in the second embodiment is realized with even fewer electronic components than the protection circuit 300 in the first embodiment, it can be placed in a narrower area of ​​surface 400 of the head board 23.

[0100] In the second embodiment, as in the first embodiment, the heater stop unit 320 is implemented between the drive signal propagation wiring 411 and the heater wirings 415, 416, and 419. Furthermore, the temperature abnormality detection unit 310 may also be implemented between the wiring 411 and the wirings 415, 416, and 419. Alternatively, the heater stop unit 320 may be implemented between the drive signal propagation wiring 413 and the heater wirings 417 and 418. Furthermore, the temperature abnormality detection unit 310 may also be implemented between the wiring 413 and the wirings 417 and 418.

[0101] The other configurations and functions of the liquid dispensing device 1 of the second embodiment are the same as those of the liquid dispensing device 1 of the first embodiment, so their description will be omitted.

[0102] Note that the positive terminal of heater 260 is an example of a "first heater terminal," and the negative terminal of heater 260 is an example of a "second heater terminal."

[0103] The liquid dispensing device 1 and head unit 20 of the second embodiment described above provide the same effects as the liquid dispensing device 1 and head unit 20 of the first embodiment.

[0104] 3. Third Embodiment In the following description of the third embodiment, the same reference numerals are used for components similar to those in the first or second embodiment, and descriptions that overlap with those in the first or second embodiment are omitted or simplified. The description will mainly focus on the differences from the first and second embodiments.

[0105] The liquid dispensing device 1 of the third embodiment differs from the liquid dispensing device 1 of the first or second embodiment in the configuration and operation of the protection circuit 300 included in the head unit 20. Figure 13 shows an example of the configuration of the protection circuit 300 in the third embodiment. Figure 13 also shows the power supply circuit 90, the head board 23, and the heater 260.

[0106] As shown in Figure 13, the head board 23 has terminals 23a, 23b, 23c, and 23d. Terminal 23a is a power terminal connected to the positive terminal of the power supply circuit 90, and is to which the heater drive signal VHT that drives the heater 260 is input. Terminal 23b is a terminal connected to the positive terminal of the heater 260. Terminal 23b is also connected to terminal 23a. Therefore, the positive terminal of the heater 260 is connected to terminal 23a via terminal 23b. Terminal 23c is a terminal connected to the negative terminal of the heater 260. Terminal 23d is a power terminal connected to the negative terminal of the power supply circuit 90.

[0107] As shown in Figure 13, the protection circuit 300 includes a temperature abnormality detection unit 310 and a heater stop unit 320. The temperature abnormality detection unit 310 includes a resistor 311 and a thermistor 312, and its configuration and operation are the same as in Figure 10, so its explanation is omitted.

[0108] The heater stop unit 320 includes an N-channel transistor 322. For example, transistor 322 is an N-channel FET.

[0109] The drain terminal of transistor 322 is connected to terminal 23c. Therefore, the drain terminal of transistor 322 is connected to the negative terminal of heater 260 via terminal 23c. The source terminal of transistor 322 is connected to terminal 23d. Therefore, the source terminal of transistor 322 is connected to the negative terminal of power supply circuit 90 via terminal 23d. The gate terminal of transistor 322 is different The normal detection signal XT is input.

[0110] If the temperature of the head unit 20 is below a predetermined value, the voltage of the abnormality detection signal XT is above the threshold voltage of transistor 322. As a result, conduction occurs between the drain terminal and source terminal of transistor 322, and the negative terminal of heater 260 is connected to the negative terminal of power supply circuit 90. Therefore, a heater drive signal VHT is supplied from the positive terminal of power supply circuit 90 to the positive terminal of heater 260 via terminals 23a and 23b. Current flows from the positive terminal to the negative terminal of heater 260, causing heater 260 to heat up. This heats the ink.

[0111] On the other hand, if the temperature of the head unit 20 rises above a predetermined value, the voltage of the abnormality detection signal XT falls below the threshold voltage of the transistor 322, causing the drain terminal and source terminal of the transistor 322 to become non-conductive. As a result, the connection between the negative terminal of the heater 260 and the negative terminal of the power supply circuit 90 is interrupted, and no current flows to the heater 260, causing the heat generated by the heater 260 to gradually decrease. In this way, the heater stop unit 320 stops the operation of the heater 260 in response to the abnormality detection signal XT. This lowers the temperature of the head unit 20 and reduces the risk of the head unit 20 failing.

[0112] Furthermore, as long as the temperature of the head unit 20 does not rise above a predetermined value, the transistor 322 will remain in an ON state with conduction between the source terminal and the drain terminal, and current will continue to flow through the transistor 322. Therefore, in order to reduce power consumption, it is preferable that the on-resistance of the transistor 322 be low.

[0113] The example of mounting the protection circuit 300 on the head board 23 in the third embodiment is the same as in Figure 11, so its illustration is omitted. In the third embodiment as well, the protection circuit 300 is realized as an analog circuit using a resistor 311, a thermistor 312, and a transistor 322, and the resistor 311, thermistor 312, and transistor 322 are each analogously mounted on the surface 400 of the head board 23 as individual electronic components. Thus, the protection circuit 300 in the third embodiment is realized with even fewer electronic components than the protection circuit 300 in the first embodiment, so it can be placed in a narrower area of ​​the surface 400 of the head board 23.

[0114] In the third embodiment, as in the first embodiment, the heater stop unit 320 is implemented between the drive signal propagation wiring 411 and the heater wirings 415, 416, and 419. Furthermore, the temperature abnormality detection unit 310 may also be implemented between the wiring 411 and the wirings 415, 416, and 419. Alternatively, the heater stop unit 320 may be implemented between the drive signal propagation wiring 413 and the heater wirings 417 and 418. Furthermore, the temperature abnormality detection unit 310 may also be implemented between the wiring 413 and the wirings 417 and 418.

[0115] The other configurations and functions of the liquid dispensing device 1 of the third embodiment are the same as those of the liquid dispensing device 1 of the first or second embodiment, so their description will be omitted.

[0116] Note that terminal 23a is an example of a "first power terminal," and terminal 23d is an example of a "second power terminal." Also, the positive terminal of heater 260 is an example of a "first heater terminal," and the negative terminal of heater 260 is an example of a "second heater terminal."

[0117] The liquid dispensing device 1 and head unit 20 of the third embodiment described above provide the same effects as the liquid dispensing device 1 and head unit 20 of the first embodiment.

[0118] 4. Fourth Embodiment The fourth embodiment is described below, and has the same configuration as any of the first to third embodiments. The same reference numerals are used for the same elements, and explanations that overlap with any of the first to third embodiments are omitted or simplified. The explanation will mainly focus on content that differs from any of the first to third embodiments.

[0119] The liquid dispensing device 1 of the fourth embodiment differs from the liquid dispensing device 1 of the first to third embodiments in the configuration and operation of the protection circuit 300 included in the head unit 20. In the protection circuit 300 of the first to third embodiments, the temperature abnormality detection unit 310 detects temperature abnormalities using a thermistor 312, but in the protection circuit 300 of the fourth embodiment, the temperature abnormality detection unit 310 detects temperature abnormalities based on the temperature abnormality signal XHOT.

[0120] Figure 14 shows an example of the configuration of the protection circuit 300 in the fourth embodiment. In the protection circuit 300 shown in Figure 14, the temperature abnormality detection unit 310 includes a resistor 311 and a capacitor 313.

[0121] Resistor 311 has a temperature anomaly signal XHOT input to one end and the other end is connected to one end of capacitor 313. The other end of capacitor 313 is connected to ground. The signal at the connection point where the other end of resistor 311 and one end of capacitor 313 are connected is output to the heater stop unit 320 as an anomaly detection signal XT. If the temperature of the print head 22 is normal, the temperature anomaly signal XHOT is at the high level of voltage VDD, and the anomaly detection signal XT is also at the voltage VDD. On the other hand, if the temperature of the print head 22 is abnormal, the temperature anomaly signal XHOT is at the low level of ground potential, and the anomaly detection signal XT is also at ground potential.

[0122] In the example shown in Figure 14, the configuration of the heater stop unit 320 and the connection relationships between the power supply circuit 90, the head board 23, and the heater 260 are the same as in Figure 10. When the abnormality detection signal XT is at a high level, the drain terminal and source terminal of transistor 322 conduct, and the source terminal and drain terminal of transistor 321 conduct. Therefore, the heater drive signal VHT is supplied from the positive terminal of the power supply circuit 90 to the positive terminal of the heater 260 via terminal 23a, transistor 321, and terminal 23b, causing current to flow from the positive terminal to the negative terminal of the heater 260, and the heater 260 to heat up. As a result, the ink is heated.

[0123] On the other hand, when the abnormality detection signal XT is at the L level, the drain terminal and source terminal of transistor 322 become non-conductive, and the source terminal and drain terminal of transistor 321 also become non-conductive. As a result, the supply of the heater drive signal VHT to the positive terminal of heater 260 stops, and the heat generated by heater 260 gradually decreases. In this way, the heater stop unit 320 stops the operation of heater 260 in response to the abnormality detection signal XT. This lowers the temperature of the head unit 20 and reduces the risk of the head unit 20 failing.

[0124] In Figure 14, transistor 321 is an example of a "first transistor," and N-channel transistor 322 is an example of a "second transistor." Resistor 323 is an example of a "first resistor," and resistor 324 is an example of a "second resistor." The positive terminal of heater 260 is an example of a "first heater terminal," and the negative terminal of heater 260 is an example of a "second heater terminal."

[0125] Figure 15 shows another example of the configuration of the protection circuit 300 in the fourth embodiment. In the protection circuit 300 shown in Figure 15, the configuration of the temperature abnormality detection unit 310 is the same as in Figure 14, the configuration of the heater stop unit 320 is the same as in Figure 12, and the connection relationship of the power supply circuit 90, head board 23 and heater 260 is the same as in Figure 12.

[0126] When the abnormality detection signal XT is at a high level, the drain terminal and source of transistor 322 are connected. Electroelectric current is established between the terminals, and the negative terminal of heater 260 is connected to ground. As a result, the heater drive signal VHT is supplied from the positive terminal of power supply circuit 90 to the positive terminal of heater 260 via terminals 23a and 23b, causing current to flow from the positive terminal to the negative terminal of heater 260, and heater 260 to heat up. This heats the ink.

[0127] On the other hand, when the abnormality detection signal XT is at a low level, the drain terminal and source terminal of transistor 322 become non-conductive. As a result, the connection between the negative terminal of heater 260 and ground is interrupted, and no current flows to heater 260, causing the heat generated by heater 260 to gradually decrease. In this way, the heater stop unit 320 stops the operation of heater 260 in response to the abnormality detection signal XT. This lowers the temperature of head unit 20 and reduces the risk of head unit 20 failure.

[0128] In Figure 15, the positive terminal of heater 260 is an example of a "first heater terminal," and the negative terminal of heater 260 is an example of a "second heater terminal."

[0129] Figure 16 shows another example of the configuration of the protection circuit 300 in the fourth embodiment. In the protection circuit 300 shown in Figure 16, the configuration of the temperature abnormality detection unit 310 is the same as in Figure 14, the configuration of the heater stop unit 320 is the same as in Figure 13, and the connection relationship of the power supply circuit 90, head board 23 and heater 260 is the same as in Figure 13.

[0130] When the abnormality detection signal XT is at a high level, the drain and source terminals of transistor 322 conduct, and the negative terminal of heater 260 is connected to the negative terminal of power supply circuit 90. As a result, the heater drive signal VHT is supplied from the positive terminal of power supply circuit 90 to the positive terminal of heater 260 via terminals 23a and 23b, causing current to flow from the positive terminal to the negative terminal of heater 260, and heater 260 to heat up. This heats the ink.

[0131] On the other hand, when the abnormality detection signal XT is at a low level, the drain terminal and source terminal of transistor 322 become non-conductive. As a result, the connection between the negative terminal of heater 260 and the negative terminal of power supply circuit 90 is interrupted, and no current flows to heater 260, causing the heat generated by heater 260 to gradually decrease. In this way, the heater stop unit 320 stops the operation of heater 260 in response to the abnormality detection signal XT. This lowers the temperature of head unit 20 and reduces the risk of head unit 20 failure.

[0132] In Figure 16, terminal 23a is an example of a "first power terminal," and terminal 23d is an example of a "second power terminal." Also, the positive terminal of heater 260 is an example of a "first heater terminal," and the negative terminal of heater 260 is an example of a "second heater terminal."

[0133] The example of mounting the protection circuit 300 on the head board 23 in the fourth embodiment is the same as in Figure 11, so its illustration is omitted. In the fourth embodiment, the protection circuit 300 shown in Figure 14 is realized as an analog circuit using resistors 311, 323, 324, capacitor 313, and transistors 321, 322, and the resistors 311, 323, 324, capacitor 313, and transistors 321, 322 are each analogously mounted as individual electronic components on the surface 400 of the head board 23. Also, the protection circuit 300 shown in Figure 15 or Figure 16 is realized as an analog circuit using resistor 311, capacitor 313, and transistor 322, and the resistors 311, capacitor 313, and transistor 322 are each analogously mounted as individual electronic components on the surface 400 of the head board 23. In this way, since the protection circuit 300 in the fourth embodiment is realized with a small number of electronic components, it can be placed even in a narrow area of ​​the surface 400 of the head board 23.

[0134] In the fourth embodiment, as in the first to third embodiments, the heater stop unit 320 is implemented between the drive signal propagation wiring 411 and the heater wirings 415, 416, and 419. Furthermore, the temperature abnormality detection unit 310 may also be implemented between the wiring 411 and the wirings 415, 416, and 419. Alternatively, the heater stop unit 320 may be implemented between the drive signal propagation wiring 413 and the heater wirings 417 and 418. Furthermore, the temperature abnormality detection unit 310 may also be implemented between the wiring 413 and the wirings 417 and 418.

[0135] The other configurations and functions of the liquid dispensing device 1 of the fourth embodiment are the same as those of the liquid dispensing device 1 of the first to third embodiments, so their description will be omitted.

[0136] The liquid dispensing device 1 and head unit 20 of the fourth embodiment described above can be used to obtain the same effects as the liquid dispensing device 1 and head unit 20 of any of the first to third embodiments.

[0137] 5. Variations The present invention is not limited to this embodiment, and various modifications can be implemented within the scope of the gist of the present invention.

[0138] For example, in each of the above embodiments, the control unit 10 includes two drive circuits 50, but the number of drive circuits 50 included in the control unit 10 may be one or three or more. Similarly, the print head 22 includes two liquid ejection modules 21, but the number of liquid ejection modules 21 included in the print head 22 may be one or three or more.

[0139] Furthermore, in each of the above embodiments, the liquid ejection device 1 was described as a so-called serial inkjet printer in which a liquid ejection module 21 that ejects ink is mounted on a carriage 24, and printing is performed by the carriage 24 reciprocating over the medium P. However, it may also be a so-called line inkjet printer in which the liquid ejection modules 21 are arranged in a line in the width direction of the medium P, and printing is performed by transporting the medium P.

[0140] Although embodiments have been described above, the present invention is not limited to these embodiments and can be implemented in various forms without departing from its spirit. For example, the above embodiments can be combined as appropriate.

[0141] The present invention includes configurations substantially identical to those described in the embodiments, for example, configurations with the same function, method, and results, or configurations with the same purpose and effect. Furthermore, the present invention includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. Furthermore, the present invention includes configurations that produce the same effects or achieve the same purpose as those described in the embodiments. Finally, the present invention includes configurations that add known technology to the configurations described in the embodiments.

[0142] The following conclusions can be drawn from the embodiments described above.

[0143] One form of a head unit is: A head includes a piezoelectric element that displaces in response to the application of a drive signal, and a dispensing unit that ejects ink in response to the displacement of the piezoelectric element, A heater for heating the aforementioned ink, A temperature anomaly detection unit that detects temperature anomalies and outputs an anomaly detection signal, A heater stop unit that stops the operation of the heater in response to the abnormality detection signal, A head board connected to the aforementioned head, Equipped with, The heater stop unit is analogously mounted on the head board.

[0144] With this head unit, if the temperature abnormality detection unit detects a temperature abnormality, the heater stop unit stops the heater's operation, thus reducing the risk of failure due to temperature abnormalities. Furthermore, with this head unit, the heater stop unit can be placed in a limited, narrow area on the head board, which has wiring for numerous signals such as drive signals for driving piezoelectric elements and many electronic components mounted on it, by being analogously mounted.

[0145] In one embodiment of the head unit, The aforementioned head board is The drive signal propagation wiring through which the drive signal propagates, A heater wiring through which a heater drive signal for driving the heater propagates, It has, The heater stop unit may be implemented between the drive signal propagation wiring and the heater wiring.

[0146] With this head unit, the drive signal wiring, which carries the noise-sensitive drive signal, is positioned separately from the heater wiring, which carries the heater drive signal, a potential noise source. This allows for the effective use of the space between the drive signal wiring and the heater wiring to implement the heater stop unit. Furthermore, this head unit reduces the influence of the heater drive signal on the drive signal, thereby improving ink ejection accuracy.

[0147] In one embodiment of the head unit, The head board has a power terminal to which a heater drive signal for driving the heater is input, The heater has a first heater terminal and a second heater terminal, The second heater terminal is connected to ground. The heater stop unit is, A first transistor of the P-channel type, The second transistor is an N-channel type, The first resistor and, The second resistor and Includes The drain terminal of the first transistor is connected to the first heater terminal. The source terminal of the first transistor is connected to the power supply terminal. The first resistor has one end connected to the source terminal of the first transistor and the other end connected to the gate terminal of the first transistor. The second resistor has one end connected to the gate terminal of the first transistor and the other end connected to the drain terminal of the second transistor. The source terminal of the second transistor is connected to ground. The abnormality detection signal may be input to the gate terminal of the second transistor.

[0148] With this head unit, the heater stop function is implemented with fewer electronic components, allowing for analog implementation within the limited, narrow area of ​​the head board.

[0149] In one embodiment of the head unit, The head board has a power terminal to which a heater drive signal for driving the heater is input, The heater has a first heater terminal and a second heater terminal, The first heater terminal is connected to the power terminal, The heater stop unit is, Includes an N-channel transistor, The drain terminal of the transistor is connected to the second heater terminal. The source terminal of the transistor is connected to ground. The abnormality detection signal may be input to the gate terminal of the transistor.

[0150] With this head unit, the heater stop function is implemented with fewer electronic components, allowing for analog implementation within the limited, narrow area of ​​the head board.

[0151] In one embodiment of the head unit, The head board has a first power terminal connected to the positive terminal of the power supply circuit and to which a heater drive signal for driving the heater is input, and a second power terminal connected to the negative terminal of the power supply circuit, The heater has a first heater terminal and a second heater terminal, The first heater terminal is connected to the first power terminal. The heater stop unit is, Includes an N-channel transistor, The drain terminal of the transistor is connected to the second heater terminal. The source terminal of the transistor is connected to the second power supply terminal. The abnormality detection signal may be input to the gate terminal of the transistor.

[0152] With this head unit, the heater stop function is implemented with fewer electronic components, allowing for analog implementation within the limited, narrow area of ​​the head board.

[0153] In one embodiment of the head unit, The first transistor may have a lower on-resistance than the second transistor.

[0154] In this head unit, when the temperature abnormality detection unit does not detect a temperature abnormality, the source terminal and drain terminal of the first transistor conduct, supplying a heater drive signal to the heater. With this head unit, the on-resistance of the first transistor is small, so the current flowing to the heater increases, and the heating efficiency can be improved.

[0155] One embodiment of a liquid dispensing device is: A liquid dispensing device comprising a head unit and a power supply circuit, The head unit is A head includes a piezoelectric element that displaces in response to the application of a drive signal, and a dispensing unit that ejects ink in response to the displacement of the piezoelectric element, A heater for heating the aforementioned ink, A temperature anomaly detection unit that detects temperature anomalies and outputs an anomaly detection signal, A heater stop unit that stops the operation of the heater in response to the abnormality detection signal, A head board connected to the aforementioned head, Equipped with, The power supply circuit outputs a heater drive signal to drive the heater, The heater stop unit is analogously mounted on the head board.

[0156] In one embodiment of a liquid dispensing device, The aforementioned head board is The drive signal propagation wiring through which the drive signal propagates, The heater wiring through which the heater drive signal propagates, It has, The heater stop unit may be implemented between the drive signal propagation wiring and the heater wiring.

[0157] In one embodiment of a liquid dispensing device, The head board has a power terminal to which the heater drive signal is input, The heater has a first heater terminal and a second heater terminal, The second heater terminal is connected to ground. The heater stop unit is, A first transistor of the P-channel type, The second transistor is an N-channel type, The first resistor and, The second resistor and Includes The drain terminal of the first transistor is connected to the first heater terminal. The source terminal of the first transistor is connected to the power supply terminal. The first resistor has one end connected to the source terminal of the first transistor and the other end connected to the gate terminal of the first transistor. The second resistor has one end connected to the gate terminal of the first transistor and the other end connected to the drain terminal of the second transistor. The source terminal of the second transistor is connected to ground. The abnormality detection signal may be input to the gate terminal of the second transistor.

[0158] In one embodiment of a liquid dispensing device, The head board has a power terminal to which the heater drive signal is input, The heater has a first heater terminal and a second heater terminal, The first heater terminal is connected to the power terminal, The heater stop unit is, Includes an N-channel transistor, The drain terminal of the transistor is connected to the second heater terminal. The source terminal of the transistor is connected to ground. The abnormality detection signal may be input to the gate terminal of the transistor.

[0159] In one embodiment of a liquid dispensing device, The head board has a first power terminal connected to the positive terminal of the power supply circuit and to which the heater drive signal is input, and a second power terminal connected to the negative terminal of the power supply circuit. The heater has a first heater terminal and a second heater terminal, The first heater terminal is connected to the first power terminal. The heater stop unit is, Includes an N-channel transistor, The drain terminal of the transistor is connected to the second heater terminal. The source terminal of the transistor is connected to the second power supply terminal. The abnormality detection signal may be input to the gate terminal of the transistor.

[0160] In one embodiment of a liquid dispensing device, The first transistor may have a lower on-resistance than the second transistor. [Explanation of Symbols]

[0161] 1...Liquid dispensing device, 2...Mobile body, 3...Moving mechanism, 4...Transportation mechanism, 10...Control unit 20...Head unit, 21,21a,21b...Liquid ejection module, 22...Print head, 23...Head board, 23a,23b,23c,23d...Terminals, 24...Carriage, 31...Carriage motor, 32...Carriage guide shaft, 33...Timing belt, 35...Carriage motor driver, 40...Platen, 41...Conveyor motor, 42...Conveyor roller, 45...Conveyor motor driver, 50,50a,50 b...Drive circuit, 60, 60a, 60b...Piezoelectric element, 90...Power supply circuit, 91...Power supply circuit, 100...Control circuit, 190...Cable, 200, 200a, 200b...Drive signal selection circuit, 210...Selection control circuit, 212...Shift register, 214...Latch circuit, 216...Decoder, 230...Selection circuit, 232...Inverter, 234...Transfer gate, 235, 236...Transistor, 250, 250a, 250b... Temperature detection circuit, 251…Reference voltage generation circuit, 252…Comparator, 253…Transistor, 254-1~254-k…Diode, 255,256…Resistor, 260…Heater, 300…Protection circuit, 310…Temperature abnormality detection unit, 311…Resistor, 312,312a,312b…Thermistor, 313…Capacitor, 320…Heater stop unit, 321…Transistor, 322…Transistor, 323…Resistor, 324… Resistor, 400...head board surface, 401...electrode, 402...electrode, 411~419...wiring, 421~428...electrode, 431,432...electrode, 441~448...electrode, 451~454...aperture, 511~514...FPC, 600,600a,600b...discharge section, 601...piezoelectric element, 611,612...electrode, 621...diaphragm, 631...cavity, 632...nozzle plate, 641...reservoir, 651...nozzle, 661...feed port

Claims

1. A head includes a piezoelectric element that displaces in response to the application of a drive signal, and a dispensing unit that ejects ink in response to the displacement of the piezoelectric element, A heater for heating the aforementioned ink, A temperature anomaly detection unit that detects temperature anomalies and outputs an anomaly detection signal, A heater stop unit that stops the operation of the heater in response to the abnormality detection signal, A head board connected to the aforementioned head, Equipped with, The heater stop unit is analogously mounted on the head board. A head unit characterized by the following features.

2. The aforementioned head board is The drive signal propagation wiring through which the drive signal propagates, A heater wiring through which a heater drive signal for driving the heater propagates, It has, The heater stop unit is installed between the drive signal propagation wiring and the heater wiring. The head unit according to feature 1.

3. The head board has a power terminal to which a heater drive signal for driving the heater is input, The heater has a first heater terminal and a second heater terminal. The second heater terminal is connected to ground. The heater stop unit is, The first transistor is a P-channel type, The second transistor is an N-channel type, The first resistor and The second resistor and Includes The drain terminal of the first transistor is connected to the first heater terminal. The source terminal of the first transistor is connected to the power supply terminal. The first resistor has one end connected to the source terminal of the first transistor and the other end connected to the gate terminal of the first transistor. The second resistor has one end connected to the gate terminal of the first transistor and the other end connected to the drain terminal of the second transistor. The source terminal of the second transistor is connected to ground. The abnormality detection signal is input to the gate terminal of the second transistor. The head unit according to feature 1.

4. The head board has a power terminal to which a heater drive signal for driving the heater is input, The heater has a first heater terminal and a second heater terminal. The first heater terminal is connected to the power terminal, The heater stop unit is, Includes an N-channel transistor, The drain terminal of the transistor is connected to the second heater terminal. The source terminal of the transistor is connected to ground. The abnormality detection signal is input to the gate terminal of the transistor. The head unit according to feature 1.

5. The head board has a first power terminal connected to the positive terminal of the power supply circuit and to which a heater drive signal for driving the heater is input, and a second power terminal connected to the negative terminal of the power supply circuit, The heater has a first heater terminal and a second heater terminal. The first heater terminal is connected to the first power terminal, The heater stop unit is, Includes an N-channel transistor, The drain terminal of the transistor is connected to the second heater terminal. The source terminal of the transistor is connected to the second power supply terminal. The abnormality detection signal is input to the gate terminal of the transistor. The head unit according to feature 1.

6. The first transistor has a lower on-resistance than the second transistor. The head unit according to feature 3.

7. A liquid dispensing device comprising a head unit and a power supply circuit, The head unit is A head includes a piezoelectric element that displaces in response to the application of a drive signal, and a dispensing unit that ejects ink in response to the displacement of the piezoelectric element, A heater for heating the aforementioned ink, A temperature anomaly detection unit that detects temperature anomalies and outputs an anomaly detection signal, A heater stop unit that stops the operation of the heater in response to the abnormality detection signal, A head board connected to the aforementioned head, Equipped with, The power supply circuit outputs a heater drive signal to drive the heater, The heater stop unit is analogously mounted on the head board. A liquid dispensing device characterized by the following features.

8. The aforementioned head board is The drive signal propagation wiring through which the drive signal propagates, The heater wiring through which the heater drive signal propagates, It has, The heater stop unit is installed between the drive signal propagation wiring and the heater wiring. The liquid dispensing device according to feature 7.

9. The head board has a power terminal to which the heater drive signal is input, The heater has a first heater terminal and a second heater terminal. The second heater terminal is connected to ground. The heater stop unit is, The first transistor is a P-channel type, The second transistor is an N-channel type, The first resistor and The second resistor and Includes The drain terminal of the first transistor is connected to the first heater terminal. The source terminal of the first transistor is connected to the power supply terminal. The first resistor has one end connected to the source terminal of the first transistor and the other end connected to the gate terminal of the first transistor. The second resistor has one end connected to the gate terminal of the first transistor and the other end connected to the drain terminal of the second transistor. The source terminal of the second transistor is connected to ground. The abnormality detection signal is input to the gate terminal of the second transistor. The liquid dispensing device according to feature 7.

10. The head board has a power terminal to which the heater drive signal is input, The heater has a first heater terminal and a second heater terminal. The first heater terminal is connected to the power terminal, The heater stop unit is, Includes an N-channel transistor, The drain terminal of the transistor is connected to the second heater terminal. The source terminal of the transistor is connected to ground. The abnormality detection signal is input to the gate terminal of the transistor. The liquid dispensing device according to feature 7.

11. The head board has a first power terminal connected to the positive terminal of the power supply circuit and to which the heater drive signal is input, and a second power terminal connected to the negative terminal of the power supply circuit. The heater has a first heater terminal and a second heater terminal. The first heater terminal is connected to the first power terminal, The heater stop unit is, Includes an N-channel transistor, The drain terminal of the transistor is connected to the second heater terminal. The source terminal of the transistor is connected to the second power supply terminal. The abnormality detection signal is input to the gate terminal of the transistor. The liquid dispensing device according to feature 7.

12. The first transistor has a lower on-resistance than the second transistor. The liquid dispensing device according to feature 9.

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