JP2020146956A - Head drive device and image formation apparatus - Google Patents

Abstract

To provide a head drive device that switches an operation of each of drive circuits in accordance with temperatures of the drive circuits.SOLUTION: A head drive device comprises: a drive voltage waveform generation unit that generates a drive voltage waveform from a drive waveform based on drive waveform data and includes a plurality of head drive units each of which applies this drive voltage waveform to a liquid ejection head; and a head drive switching unit that generates a drive waveform from the drive waveform data and, based on a predetermined condition, switches a way of transfer of a drive waveform to each head drive unit. The head drive switching unit detects an operating state of each head drive unit, and based on this operating state, calculates operation load of each head drive unit. When deviation of this operation load exceeds a predetermined threshold, the head drive switching unit switches a type of drive waveform data to be transferred to each head drive unit so as to reduce the deviation of the operation load.SELECTED DRAWING: Figure 6

Description

The present invention relates to a head drive device and an image forming device.

A liquid discharge device including a liquid discharge head that discharges a liquid to a recording medium is known. The liquid discharge device is also equipped with a head drive device that drives the liquid discharge operation of the liquid discharge head. An image forming apparatus (so-called inkjet printer) is also known as a liquid ejection device that ejects liquid ink onto a recording medium to form characters and images.

The liquid discharge operation of the liquid discharge head is controlled by applying a drive voltage waveform generated by the head drive device according to the size of the droplet and the discharge cycle to the piezoelectric element (piezoactuator) based on the image data.

From the viewpoint of ensuring the stability of the droplet ejection state, the operational stability of the driver circuit that applies the drive waveform voltage to the liquid ejection head is important. A factor that lowers the operational stability of the driver circuit is an increase in temperature.

In particular, the power amplification unit provided in the driver circuit is one of the configurations in which the temperature tends to rise. Therefore, a recording head drive circuit that selects a driver circuit to be driven when a temperature difference occurs between the two driver circuits so as to equalize the amount of heat generated by the power amplification unit is disclosed (Patent Document 1). See).

The technique disclosed in Patent Document 1 selectively uses a driver circuit that drives a temperature difference between a plurality of driver circuits. The head drive circuit generates a plurality of drive voltage waveforms, and the load related to the generation of the drive voltage waveform differs depending on the type of drive voltage waveform to be generated and applied, the surroundings, and the like. That is, the temperature of the drive circuit differs depending on the load due to the generation and application of the drive voltage waveform.

Assuming a configuration including a plurality of head drive circuits, there is a problem in performing control according to a temperature change only by selecting a head drive circuit that operates by a temperature difference as in Patent Document 1. Then, there is a problem in more flexibly responding to the temperature change and improving the operation stability according to the degree of temperature rise that differs depending on the type and combination of the drive voltage waveforms generated by each head drive circuit.

An object of the present invention is to provide a head drive device that switches the operation of each drive circuit according to the temperature of a plurality of drive circuits.

In order to solve the above problems, one aspect of the present invention includes a plurality of drive waveform generators that generate a drive voltage waveform from drive waveform data and apply the drive voltage waveform to the liquid discharge head, and each drive waveform generator. It has a head drive switching unit that switches the drive waveform data to be input to based on a predetermined condition, and the head drive switching unit detects the operation status of each drive waveform generation unit and is based on the operation status. The operating load of each driving waveform generator is calculated, and when the bias of the operating load exceeds a predetermined threshold, the driving waveform data to be passed to each driving waveform generating unit is reduced so that the bias of the operating load is reduced. It is characterized by switching the type.

According to the present invention, the operation of each drive circuit can be switched according to the temperature of the plurality of drive circuits.

The schematic diagram which shows the structure of the printer which is one Embodiment of the image forming apparatus which concerns on this invention. The side view which shows the structure of one Embodiment of the liquid discharge head included in the said printer. The bottom view which shows the example of the structure of the said liquid discharge head. The plan view which the said recording head shows an example of a nozzle mouth. The exploded perspective view which shows the structure of one Embodiment of the liquid discharge head provided in the said printer. The functional block diagram of the head drive control part which is one practical form of the head drive part which concerns on this invention. A detailed functional block diagram of the head drive control unit. The detailed function block diagram of the head drive circuit switching part included in the head drive control part. The graph explaining the temperature rise factor of the head drive circuit included in the head drive control unit. A graph showing an example of setting a threshold value for switching determination in the head drive circuit switching unit. The flowchart which shows the example of the flow of the switching process in the head drive control unit. The flowchart which shows another example of the flow of the switching process in the head drive control part.

Hereinafter, embodiments of the head drive device and the image forming device according to the present invention will be described with reference to the drawings. First, the inkjet printer 1000, which is an embodiment of the image forming apparatus according to the present invention, will be described with reference to FIG.

[Overall configuration of the inkjet printer 1000]
The inkjet printer 1000 is, for example, an image forming apparatus that employs an on-demand line scanning type. As shown in FIG. 1, the inkjet printer 1000 includes an image forming unit 210, a paper feeding unit 220, a resist adjusting unit 230, a drying unit 240, a recording medium reversing unit 250, and a paper ejection unit 290. ing. Next, an example of the flow of the image formation output operation (printing operation) in the inkjet printer 1000 having the configuration will be described. The image forming unit 210 corresponds to the embodiment of the liquid discharge device.

First, the recording media P loaded on the paper feed stack 221 of the paper feed unit 220 are picked up one by one by the air separation unit 222 and conveyed in the direction of the image forming unit 210. When the recording medium P conveyed from the paper feeding unit 220 reaches the resist adjusting unit 230, the inclination of the recording medium P with respect to the conveying direction is corrected by the resist roller pair 231 provided inside the resist adjusting unit 230.

The recording medium P corrected (resist adjustment) in the resist roller pair 231 is sent to the image forming unit 210. Then, the tip of the recording medium P is sandwiched by the recording medium gripper 212 provided on the surface of the cylindrical drum 211, and the recording medium P is conveyed to a position facing the head arrays 100K to 100P by the rotation of the drum 211. To. In the image forming unit 210, head arrays 100K to 100P for ejecting ink by an inkjet method are arranged at a radial angle along the surface of the cylindrical drum 211 in a state of being filled with a predetermined ink color.

A liquid discharge module, which is a liquid discharge unit, is configured by a plurality of head arrays 100K to 100P, and ink (liquid) is discharged from the liquid discharge module to the outer peripheral surface of the recording medium P held on the surface of the drum 211. As a result, an image is formed on the recording medium P. An empty ejection receiver 213 is provided on the outer peripheral surface of the drum 211 so that the empty ejection receiver 213 receives the empty ejection ink when the head module 100 is not ejecting ink to the recording medium P. When the image is formed, the recording medium P is conveyed to the drying unit 240.

A drying unit 241 is provided in the drying unit 240, and the water content of the recording medium P evaporates when the recording medium P passes under the drying unit 241. Further, the drying unit 240 is provided with a recording medium reversing unit 250 including a recording medium reversing mechanism 251. At the time of double-sided printing, the recording medium P is inverted by the recording medium inversion unit 250 and conveyed again in the direction of the image forming unit 210 by the inversion transport unit 252. Before reaching the drum 211, the inclination of the recording medium P is corrected by the resist roller 253 provided inside the image forming unit 210. The recording medium P that has been dried by the drying unit 240 is conveyed to the paper ejection unit 290 and loaded in a state where the ends of the recording medium P are aligned.

Part of the control of the droplet ejection operation in the image forming unit 210 shall be performed in the image forming control unit 201 included in the image forming unit 210. The image formation control unit 201 may control the overall operation of the inkjet printer 1000. Further, each of the paper feed unit 220, the resist adjustment unit 230, and the drying unit 240 is individually provided with a control unit, and is configured to control the entire operation of the inkjet printer 1000 by cooperating with the image formation control unit 201. You may.

[Structure of head module 100]
Next, the configuration of the head module 100 will be described. FIG. 2 is a side view of the head module 100. As shown in FIG. 2, the head module 100 is mainly composed of a head drive control unit 110, an inkjet recording head 130, and a connection unit 120 that connects the head drive control unit 110 and the inkjet recording head 130. ..

In the head drive control unit 110, a drive control IC 112, a drive voltage waveform generation control IC 113, and a non-volatile storage element 114 are mounted on the head control board 111.

The connection unit 120 has a drive control board connector 122 and a head side connector 123 attached to both ends of the cable 121, and is between the head board 132 mounted on the inkjet recording head 130 and the head drive control unit 110. Responsible for analog signal communication and digital signal communication.

The inkjet recording head 130 mainly includes a residual vibration detection module 131, a head substrate 132, a head drive IC substrate 134 that switches which piezoelectric element 142 the drive voltage waveform is applied to, an ink tank 133 in the head, and rigidity. It is composed of a plate 135. If the configuration of the liquid ejection head included in the inkjet printer 1000 is a line scanning type, the direction intersecting the transport direction of the recording medium P corresponds to the width direction of the recording medium P, and extends over the width dimension of the recording medium P. Inkjet recording heads 130 are arranged side by side. This configuration is called a line head configuration. The present invention is also applied to a serial scanning type that forms an image while moving one or more inkjet recording heads 130 in the width direction of the recording medium P and further transporting the recording medium P in the transport direction. It is possible. It is also applicable to other types of liquid discharge devices.

[Structure of Inkjet Recording Head 130]
FIG. 3 is a schematic view showing an example in which the inkjet recording head 130 is arranged in a line head configuration. The head module 100 according to the present embodiment is an aggregate of components that are distinguished for each color of the liquid ink to be ejected. The head module 100 illustrated in FIG. 3 shows a configuration example different from that of the head module 100 shown in FIG. The head module 100 illustrated in FIG. 3 includes a black head array 100K for ejecting black ink droplets, a cyan head array 100C for ejecting cyan ink droplets, and a magenta head array for ejecting magenta ink droplets. This is an example composed of four elements: 100M and a yellow head array 100Y for ejecting yellow ink droplets. Each head array included in the head module 100 is arranged in a direction (generally orthogonal to each other) that intersects with the transport direction (black-painted thick arrow direction) of the recording medium. By arranging the inkjet recording heads 130 in an array in this way, a wide printing area is secured.

FIG. 4 is a bottom view of the inkjet recording head 130. On the bottom surface of the inkjet recording head 130, printing nozzles 137, which are a plurality of nozzle ports 29, are arranged in a staggered pattern. The nozzle surface 136 is formed by the plurality of printing nozzles 137. Droplets are ejected from each of the printing nozzles 137 arranged on the nozzle surface 136 based on the expansion and contraction of the piezoelectric element 142. By arranging the print nozzles 137 in a staggered arrangement, the resolution of the image formed by the discharged liquid can be increased.

[Detailed Configuration of Inkjet Recording Head 130]
Next, the detailed configuration of the inkjet recording head 130 will be described with reference to FIG. The inkjet recording head 130 is mainly composed of a nozzle plate 31, a pressure chamber plate 33, a restrictor plate 35, a diaphragm plate 38, a rigid plate 135, and a piezo element group 46 which is a piezoelectric element. There is.

A nozzle plate 31 in which a large number of printing nozzles 137 are arranged in a staggered pattern, a pressure chamber plate 33 forming an individual pressure chamber 32 corresponding to each printing nozzle 137, a common ink flow path 39, and an individual pressure chamber 32 are communicated with each other. The restrictor plate 35 having the restrictor 34 for controlling the ink flow rate to the individual pressure chamber 32, the diaphragm 36, and the diaphragm plate 38 provided with the filter 37 are sequentially overlapped, positioned and joined. A flow path plate is formed by the above. This flow path plate is joined to the rigid plate 135 so that the filter 37 faces the opening of the common ink flow path 39.

The upper opening end of the ink introduction pipe 139 is connected to the common ink flow path 39 of the rigid plate 135, and the lower opening end of the ink introduction pipe 139 is connected to the ink tank 133 in the head filled with ink.

A piezo element drive IC 44 is mounted on the piezo element support substrate 143, and a piezo element group 46 composed of a large number of piezoelectric elements 142 arranged is inserted through an opening 138 provided in the rigid plate 135, and each of them is inserted. The inkjet recording head 130 is configured by adhering and fixing the free end of the piezoelectric element 142 to the diaphragm 36. In FIG. 5, parts such as the printing nozzle 137, the individual pressure chamber 32, and the restrictor 34 are reduced for simplification.

[Embodiment of Head Drive Device]
Next, the configuration of the head drive control unit 110 according to the embodiment of the head drive device according to the present invention will be described with reference to FIG. The head drive control unit 110 includes an image processing unit 10, a head drive circuit switching unit 20, a storage unit 30, and a drive voltage waveform generation unit 40.

[Image processing unit 10]
The image processing unit 10 generates drive data based on the image data received from the image formation control unit 201 that controls the image formation operation for operating the head module 100 to form an image on the recording medium P, and the head It is passed to the drive circuit switching unit 20. Further, the image processing unit 10 generates a timing control signal for controlling the operation timing of the inkjet recording head 130 based on the image data received from the image formation control unit 201, and notifies the inkjet recording head 130 of the timing control signal.

A driver IC that drives a piezoelectric element based on a timing control signal and a drive voltage waveform is mounted on a head drive IC substrate 134 (see FIG. 2) that constitutes the inkjet recording head 130. The driver IC applies a drive voltage waveform to the piezoelectric element based on a period based on the timing control signal to execute a liquid discharge operation.

[Head drive circuit switching unit 20]
The head drive circuit switching unit 20 reads out the drive waveform pattern stored in the storage unit 30 based on the drive waveform data passed from the image processing unit 10 and generates a drive waveform based on the drive waveform pattern. Is passed to the drive voltage waveform generation unit 40.

The head drive circuit switching unit 20 generates a plurality of types of drive waveforms composed of a combination of a plurality of waveforms according to the number of head drive units included in the drive voltage waveform generation unit 40. In the present embodiment, the drive voltage waveform generation unit 40 includes two head drive units. Therefore, the head drive circuit switching unit 20 generates two types of drive waveforms based on the drive waveform data, and passes each of them to the drive voltage waveform generation unit 40. In the following description, the two types of drive waveforms will be described as "first drive waveform (drive waveform A)" and "second drive waveform (drive waveform B)".

The two drive waveforms generated by the head drive circuit switching unit 20 are, for example, a first drive waveform for ejecting large droplets and medium droplets and a second drive waveform for ejecting small droplets and fine driving. is there. The head drive circuit switching unit 20 generates these drive waveforms so that the discharge operation controlled by the timing control signal becomes a drive voltage waveform applied in one cycle, and passes it to the drive voltage waveform generation unit 40. In the following description, of the two types of drive waveforms, the drive waveform consisting of a combination of large drops and medium drops is referred to as "first drive waveform (drive waveform A)", and the drive waveform consisting of a combination of small drops and fine drives is defined as This will be described as "second drive waveform (drive waveform B)".

The load on the head drive unit is higher when the drive voltage waveform of the first drive waveform is applied than when the drive voltage waveform of the second drive waveform is applied. Therefore, when the operation related to the first drive waveform is performed, the amount of heat generated by the head drive unit is larger and the temperature is more likely to rise than when the operation related to the second drive waveform is performed.

Further, the head drive circuit switching unit 20 switches the drive waveform to be passed to each of the two head drive units included in the drive voltage waveform generation unit 40 based on the temperature information from the drive voltage waveform generation unit 40. That is, which drive waveform is to be passed to which head drive unit, and how to pass it, depending on the temperature and temperature rise due to heat generated as a result of the discharge operation related to the first drive waveform or the second drive waveform. Switch. In other words, the head drive circuit switching unit 20 switches the type of drive waveform to be passed to each of the head drive units included in the drive voltage waveform generation unit 40. The head drive circuit switching unit 20 constitutes a head drive switching unit.

[Storage unit 30]
The storage unit 30 stores a drive waveform pattern for generating a drive waveform based on the image data. The drive waveform pattern is classified to correspond to the droplets that need to be ejected to the recording medium P in order to form an image based on the image data. For example, there are drive waveform patterns of "large droplet", "medium droplet", and "small droplet" corresponding to each of the sizes of droplets ejected by the liquid ejection operation. Further, the drive waveform pattern includes a "fine drive" drive waveform pattern for vibrating the piezoelectric element to the extent that droplets are not ejected in order to adjust the state of the nozzle port 29 of the inkjet recording head 130.

The drive waveform pattern stored in the storage unit 30 corresponding to the image data is read out as a drive waveform pattern required for operating the inkjet recording head 130. The head drive circuit switching unit 20 generates a drive waveform using the read drive waveform pattern.

In addition, the storage unit 30 stores past temperature information for calculating the temperature rise rate in the temperature prediction unit 24, which will be described later.

Further, in the storage unit 30, the temperature decrease rate due to natural cooling is stored in each of the head drive units (first head drive unit 41 and second head drive unit 42). When the head drive unit is provided with a forced cooling mechanism (fan, etc.), the temperature decrease rate in consideration of forced cooling is stored.

Further, the storage unit 30 also stores a threshold value used for the switching determination process in the switching determination unit 25, which will be described later.

[Drive voltage waveform generator 40]
The drive voltage waveform generation unit 40 generates a drive voltage waveform by performing voltage amplification and current amplification on the drive waveform passed from the head drive circuit switching unit 20, and passes it to the driver IC included in the inkjet recording head 130. The driver IC passed the drive voltage waveform executes a liquid discharge operation based on the drive voltage waveform. The drive voltage waveform generation unit 40 includes, for example, two head drive units as illustrated in FIG.

The drive voltage waveform generation unit 40 includes a first head drive unit 41, a second head drive unit 42, a first temperature detection unit 43, and a second temperature detection unit 44. The first head drive unit 41 and the second head drive unit 42 each amplify the drive waveform passed from the head drive circuit switching unit 20 as described above to generate a drive voltage waveform, and each generated drive voltage. The waveform is passed to the driver IC. The note that the drive voltage waveform is passed from the first head drive unit 41 and the second head drive unit 42 to the driver IC is synchronized with the cycle of the inkjet recording head 130 based on the timing control signal. Therefore, within one cycle of the operation of the inkjet recording head 130 based on the timing control signal, the drive voltage waveform based on the two types of drive waveforms is applied to the inkjet recording head 130.

The first temperature detection unit 43 measures the temperature of the first head drive unit 41 and feeds back the measurement result to the head drive circuit switching unit 20 as temperature information. The second temperature detection unit 44 measures the temperature of the second head drive unit 42, and feeds back the measurement result to the head drive circuit switching unit 20 as temperature information. The first temperature detection unit 43 and the second temperature detection unit 44 may have a configuration capable of detecting the temperature of the first head drive unit 41 and the second head drive unit 42 and notifying the detection result as temperature information. The first temperature detection unit 43 and the second temperature detection unit 44 are configured by using, for example, a temperature detection element such as a thermistor.

[Detailed configuration of head drive circuit switching unit 20]
Next, the detailed configuration of the head drive circuit switching unit 20 will be described with reference to FIGS. 7 and 8. As shown in FIG. 7, the head drive circuit switching unit 20 includes a D / A conversion unit 21 and a switch unit 22.

The D / A conversion unit 21 is composed of a digital-analog conversion circuit for converting drive voltage waveform data, which is a digital signal input from the image processing unit 10, into a drive waveform, which is an analog signal.

The switch unit 22 has two head drive units (first head drive unit 41 and second head drive unit 42) of two drive waveforms (drive waveform A and drive waveform B) output from the D / A conversion unit 21. It is composed of a switch circuit that switches the way of passing to.

In the state illustrated in FIG. 7, the first drive waveform (drive waveform A) is passed to the first head drive unit 41, and the second drive waveform (drive waveform B) is passed to the second head drive unit 42. ing. In the switching control described later, when the switch unit 22 operates and the switch state is switched, the first drive waveform (drive waveform A) is passed to the second head drive unit 42, and the second drive waveform (drive waveform B). Is switched to the state where is passed to the first head drive unit 41. That is, the type of drive waveform passed to a certain head drive unit is switched by the operation of the switch unit 22.

[Detailed functional configuration of head drive circuit switching unit 20]
Next, a more detailed configuration of the head drive circuit switching unit 20 will be described. As shown in FIG. 8, the head drive circuit switching unit 20 includes a D / A conversion unit 21, a switch unit 22, a cumulative drive time calculation unit 23, a temperature prediction unit 24, and a switching determination unit 25. ..

[D / A conversion unit 21]
The D / A conversion unit 21 generates a drive waveform specified by the drive waveform pattern stored in the storage unit 30 based on the image data input from the image processing unit 10, and passes it to the switch unit 22.

[Switch unit 22]
The switch unit 22 uses the drive waveforms (first drive waveform and second drive waveform) passed from the D / A conversion unit 21 as the drive voltage waveform generation unit 40 (first head drive unit 41) based on the state of the switch. It is passed to the second head drive unit 42). The switch unit 22 switches the switch based on the switching control signal notified from the switching determination unit 25 described later.

[Cumulative drive time calculation unit 23]
The cumulative drive time calculation unit 23 accumulates the applied operations performed by each head drive unit on the inkjet recording head 130 based on the type and number of drive waveforms passed to each head drive unit in the D / A conversion unit 21. Calculate the time. This cumulative time is a cumulative load calculated for each head drive unit. This cumulative time can be used as the operating status of the head drive unit. The cumulative drive time calculation unit 23 passes the calculated cumulative time to the switching determination unit 25.

[Temperature prediction unit 24]
The temperature prediction unit 24 is a first head drive unit 41 and a second head drive unit 42, respectively, based on temperature information from the first temperature detection unit 43 and the second temperature detection unit 44 included in the drive voltage waveform generation unit 40. Generates predicted temperature information that predicts the temperature or the degree of temperature rise (temperature rise rate). The timing of generating the predicted temperature information may be periodic with a predetermined time interval predetermined. Further, the time interval until reaching a predetermined temperature or the temperature rise rate is lengthened, and the predicted temperature information is generated according to the degree of approaching the threshold value (specific temperature or time) opposite to the switching in the switching determination unit 25 described later. The time interval may be shortened.

The temperature prediction unit 24 passes the generated predicted temperature information to the switching determination unit 25. The temperature prediction unit 24 corrects the temperature based on the temperature information based on the cumulative time calculated by the cumulative drive time calculation unit 23 when predicting the temperature or the temperature rise rate of each head drive unit. May generate predicted temperature information. For example, even if the temperature based on the temperature information is the same, if there is a difference in the cumulative time, this is taken into consideration and the temperature of the head drive unit having a longer cumulative time is predicted to be higher.

The temperature prediction unit 24 stores the predicted temperature information generated at a certain timing. Then, the difference between the predicted temperature information generated at the next timing and the stored past predicted temperature information is calculated, and the temperature rise rate (degree of change in the temperature environment) is calculated. The calculated temperature rise rate is included in the predicted temperature information and passed to the switching determination unit 25.

The temperature prediction unit 24 may calculate the predicted temperature information and the like in consideration of the number of continuous prints defined by the image data which is the input data from the image formation control unit 201 to the head drive control unit 110.

[Switching determination unit 25]
The switching determination unit 25 determines whether or not to switch the state of the switch unit 22 based on the predicted temperature information passed from the temperature prediction unit 24, and when it is determined to "switch", switches the state of the switch unit 22. Take control.

Further, the switching determination unit 25 states the state of the switch unit 22 based on the predicted temperature increase rate calculated based on the difference between the past predicted temperature information stored in the storage unit 30 and the latest predicted temperature information. Judge whether to switch. When the switching determination unit 25 determines to "switch", the switching determination unit 25 controls to switch the state of the switch unit 22.

The switching determination unit 25 uses a threshold value stored in advance in the storage unit 30, and the temperature included in the predicted temperature information, the predicted temperature rise rate calculated from the predicted temperature information, and the like exceed the threshold values corresponding to these. Whether or not it is determined, and if it exceeds the threshold value, a switching control signal is notified to the switch unit 22.

As described above, according to the head drive circuit switching unit 20, the operation of the head drive unit is switched according to the information (information about temperature) that changes depending on the operating load of each head drive unit and the information of the cumulative load (cumulative drive time). .. As a result, the amount of heat generated by the plurality of head drive units that generate the drive voltage waveform and apply it to the inkjet recording head 130 can be made uniform, and the operation stability can be improved.

Further, since the head drive circuit switching unit 20 according to the present embodiment switches the operating state of the head drive unit using the expected temperature and the expected temperature rise rate based on the temperature measurement result of the head drive unit, the temperature environment changes. The followability of the is improved, and the operation stability can be further improved.

[Relationship between the operating status of the head drive unit and temperature]
Here, the relationship between the operating state of the head drive unit and the temperature will be described. Further, the setting of the threshold value used for the determination of the switching determination unit 25 and the type of information included in the predicted temperature information will also be described.

The heat generation factor of the head drive unit (first head drive unit 41 and second head drive unit 42) is the type of drive waveform pattern (large drop, medium drop, small drop, fine drive) included in the drive waveforms passed to them. ), The current amplification operation of the drive waveform, the idling current, and the like. Further, since the temperature of the head drive unit decreases due to natural cooling, the temperature decrease rate corresponding to this is stored in the storage unit 30 in advance. Further, when a forced cooling mechanism such as a fan is installed, the temperature drop rate due to forced cooling by the fan is also stored in the storage unit 30.

FIG. 9A is a graph illustrating the relationship between the driving amount, which is a factor affecting the temperature of the head driving unit, and the heat generation amount due to the combination of various elements. As shown in FIG. 9A, the amount of heat generated in the drive operation for ejecting large droplets is larger than that in the drive operation for ejecting small droplets or performing fine drive. Further, as the number of times of driving increases, the amount of heat generated increases. On the other hand, as the number of drives increases (as time elapses), the amount of heat generated due to cooling also decreases more. Therefore, the net calorific value increases with the operating condition of the head drive unit (what kind of droplets are ejected how many times), and decreases with cooling. In this way, the temperature of the drive unit can be predicted by adding the type (content) of the drive voltage waveform generated in the head drive unit, the number of times thereof, and the temperature reduction rate due to cooling.

FIG. 9B is a graph illustrating the relationship between the drive frequency and the amount of heat generated when the same drive unit is operated under the same conditions (generation of the same drive voltage waveform). As shown in FIG. 9B, as the drive frequency increases, the amount of heat generated increases and the temperature rise rate also increases even if the elapsed time is the same.

Therefore, the temperature prediction unit 24 calculates the temperature information notified from the drive voltage waveform generation unit 40, the past temperature information stored in the storage unit 30, the cooling efficiency, the estimated calorific value for each drive waveform pattern, and the cumulative drive time. The predicted value (predicted temperature, predicted temperature rise rate) of the temperature or the temperature rise rate is calculated using the past drive waveform stored in the unit 23 and its operating frequency.

Therefore, even if the responsiveness of the first temperature detection unit 43 and the second temperature detection unit 44 is low, more accurate temperature prediction can be performed, and control (switching control) for ensuring the operational stability of the head drive unit can be performed. The accuracy can be improved.

[Relationship between switching judgment threshold and switching operation]
Next, an example of a threshold value for making a switching determination based on the predicted temperature and the predicted temperature rise rate in the switching determination unit 25 will be described with reference to FIG.

FIG. 10A illustrates the elapsed operation time and temperature rise of the first head drive unit 41 and the second head drive unit 42. A drive voltage waveform for ejecting large droplets is applied to the first head drive unit 41, and a drive voltage waveform for ejecting small droplets is applied to the second head drive unit 42. To do.

As shown in FIG. 10A, the temperature of the first head drive unit 41, which requires a higher load for the discharge operation, is higher in a shorter time. Then, at some point, the temperature threshold is reached. Here, the switching determination unit 25 notifies the switch unit 22 of the switching control signal, and the switch unit 22 performs the switching operation. Then, the method of passing the drive waveform A and the drive waveform B to the drive voltage waveform generation unit 40 changes, and the drive waveform A (large drop discharge) is passed to the second head drive unit 42 and becomes the drive waveform B (small drop discharge). Is passed to the first head drive unit 41. As a result, the temperature of the first head drive unit 41 naturally decreases due to cooling, and the temperature of the second head drive unit 42 rises.

As described above, by detecting that the temperature condition has changed by comparing the threshold value and the temperature, the generation of the drive voltage waveform in each head drive unit is switched in a timely manner, and the temperature is controlled to be uniform. be able to.

In FIG. 10B, a predetermined time interval is set as a time threshold value so that the temperature of the specific head drive unit does not rise and exceed the temperature threshold value, and the head drive unit is used using this time interval. This is an example of switching the content of the drive waveform generation operation in each case. As shown in FIG. 10B, the temperature rise rate can be made uniform by switching the destination to which the drive waveform A having a high load (which easily causes a temperature rise) is passed at regular time intervals.

[First Embodiment of Control Method]
Next, an example of the flow of switching control in the head drive control unit 110 according to the present embodiment will be described with reference to the flowchart of FIG. When the image data from the image formation control unit 201 is input (S1101), the image processing unit 10 generates the drive waveform data (S1102).

The drive waveform data generated by the image processing unit 10 is converted by the D / A conversion unit 21, converted into a drive waveform which is an analog signal, and passed to the switch unit 22. The image processing unit 10 generates a timing control signal at the same time as generating the drive waveform data, and notifies the drive voltage waveform generation unit 40. As a result, the temperature information detected by each of the first temperature detection unit 43 and the second temperature detection unit 44 included in the drive voltage waveform generation unit 40 is notified to the temperature prediction unit 24.

The temperature prediction unit 24 calculates the predicted temperature or the predicted temperature rise rate for each head drive unit based on the notified temperature information and the past temperature information stored in the storage unit 30, and passes it to the switching determination unit 25. (S1103). The temperature prediction unit 24 may calculate the predicted temperature or the predicted temperature increase rate in consideration of the cumulative driving time calculated by the cumulative driving time calculation unit 23.

Subsequently, the switching determination unit 25 determines whether or not there is a head drive unit in which the predicted temperature or the predicted temperature rise rate exceeds the threshold value (S1104). If there is a head drive unit that exceeds the threshold value (S1104 / YES), the switch unit 22 is notified of the switching control signal, and the switch unit 22 switches the method of passing the drive waveform to change the load distribution (S1105). If there is no head drive unit exceeding the threshold value (S1104 / NO), S1105 is skipped.

Subsequently, it is determined whether or not the liquid ejection operation (printing operation) based on the input image data is completed (S1106), and if the printing operation is not completed, the process is returned to S1102 (S1106 / NO). .. If the printing operation is completed (S1106 / YES), the process is terminated.

As described above, according to the head drive control unit 110 according to the present embodiment, the predicted temperature or the predicted temperature rise rate thereafter is calculated using the result of detecting the temperature of the head drive unit, and the head drive unit Estimate the calorific value. As a result, when it is predicted that the calorific value (temperature, temperature rise rate) that may lack the stability of the operation is reached, the operation content can be switched to control the calorific value to be reduced.

Further, since the temperature and the temperature rise rate can be predicted and the switching determination can be performed in synchronization with the timing control signal, the temperature responsiveness is high and the switching operation can be performed in a timely manner based on the accurate prediction.

[Second Embodiment of Control Method]
Next, another example of the flow of switching control in the head drive control unit 110 according to the present embodiment will be described with reference to the flowchart of FIG. The content of the determination operation in the switching determination unit 25 is different from that described with reference to FIG. Since there are many common parts in other processes, the explanation of common processes will be simplified.

The image processing unit 10 generates drive waveform data based on the image data input from the image formation control unit 201, is converted into a drive waveform by the D / A conversion unit 21, and is passed to the switch unit 22 (S1201, S1202).

At the timing when the drive waveform is passed from the D / A conversion unit 21 to the switch unit 22, the type of drive waveform passed to each head drive unit and the cumulative drive time of each head drive unit based on the drive waveform are calculated as the cumulative drive time. It is calculated by the unit 23 and notified to the switching determination unit 25 (S1203).

Subsequently, the switching determination unit 25 determines whether or not the cumulative drive time exceeds the threshold value (S1204). If the threshold value is exceeded (S1204 / YES), the switch unit 22 is notified of the switching control signal, the method of passing the drive waveform is switched, the load distribution is changed, and the amount of heat generated is made uniform (S1205). If the threshold value is not exceeded (S1204 / NO), S1205 is skipped.

Subsequently, it is determined whether or not the liquid ejection operation (printing operation) based on the input image data is completed (S1206), and if the printing operation is not completed, the process is returned to S1202 (S1206 / NO). .. If the printing operation is completed (S1206 / YES), the process is terminated.

When the image processing unit 10 notifies the drive voltage waveform generation unit 40 of the timing control signal generated at the same time as the generation of the drive waveform data, the temperature information detected by the first temperature detection unit 43 and the second temperature detection unit 44 is obtained. The temperature prediction unit 24 is notified. Therefore, in S1203, the switching determination unit 25 may multiply the cumulative drive time as a coefficient by the predicted temperature or the predicted temperature rise calculated by the temperature prediction unit 24, and perform the switching determination using the value.

As described above, according to the head drive control unit 110 according to the present embodiment, in addition to the result of detecting the temperature of the head drive unit, the cumulative load amount (cumulative drive time) related to each head drive unit is used. , The switching of the head drive unit can be controlled in anticipation of the subsequent rise.

In addition, since the cumulative time can be calculated in synchronization with the timing control signal, the responsiveness to fluctuations in the operating status is high, and the switching operation can be performed in a timely manner based on accurate prediction.

According to the present embodiment described above, the discharge operation of the drive waveform generation circuit in which the temperature error has occurred is stopped, and the operation cycle of the drive waveform generation circuit that centrally processes the stopped discharge operation is lengthened. The relative speed of the object to be discharged is controlled to be slowed down according to the minute. Then, by performing the ejection operation of all the droplet types in the drive waveform generation circuit that operates normally, even if a temperature abnormality occurs, the ejection operation can be continued without stopping, improving productivity. Can be made to.

10: Image processing unit 20: Head drive circuit switching unit 21: D / A conversion unit 22: Switch unit 23: Cumulative drive time calculation unit 24: Temperature prediction unit 25: Switching determination unit 29: Nozzle port 30: Storage unit 40: Drive voltage waveform generation unit 41: First head drive unit 42: Second head drive unit 43: First temperature detection unit 44: Second temperature detection unit 46: Piezo element group 100: Head module 101: Head drive control unit 110: Head drive control unit 111: Head control board 201: Image formation control unit 210: Image formation unit 1000: Inkjet printer

Japanese Unexamined Patent Publication No. 2008-002870

Claims (8)

A drive voltage waveform generator including a plurality of head drive units that generate a drive voltage waveform from a drive waveform based on the drive waveform data and apply the drive voltage waveform to the liquid discharge head.
It has a head drive switching unit that generates the drive waveform from the drive waveform data and switches the method of passing the drive waveform to each head drive unit based on a predetermined condition.
The head drive switching unit detects the operating status of each head driving unit, calculates the operating load of each head driving unit based on the operating status, and when the bias of the operating load exceeds a predetermined threshold value, the head drive switching unit is concerned. The type of the drive waveform data to be passed to each head drive unit is switched so as to reduce the bias of the operating load.
A head drive device characterized by that. The drive voltage waveform generation unit includes a temperature detection unit that detects each temperature.
The head drive switching unit receives the drive waveform data input to each of the drive voltage waveform generation units when the temperature rise rate calculated based on the temperature of each drive voltage waveform generation unit exceeds a predetermined threshold value. Switch types,
The head drive device according to claim 1. It has a storage unit that stores in advance the temperature reduction rate of the drive voltage waveform generation unit due to natural cooling or forced cooling.
The drive voltage waveform generator also uses the temperature decrease rate in calculating the temperature increase rate.
The head driving device according to claim 2. When the temperature of each head drive unit calculated based on the operation status exceeds a predetermined threshold value, the head drive switching unit determines the type of drive waveform data input to each of the drive voltage waveform generation units. Switch,
The head drive device according to claim 1. When the temperature rise rate of each head drive unit calculated based on the operation status exceeds a predetermined threshold value, the head drive switching unit receives the drive waveform data input to each of the drive voltage waveform generation units. Switch types,
The head drive device according to claim 1. The head drive switching unit is a type of drive waveform data input to each of the drive voltage waveform generation units when the cumulative load of each head drive unit calculated based on the operation status exceeds a predetermined threshold value. To switch,
The head drive device according to claim 1. The head drive switching unit detects the operating state at regular time intervals.
The head drive device according to any one of claims 1 to 6. An image forming apparatus that ejects a liquid into a conveyed medium to form an image.
A liquid discharge unit that discharges liquid to the medium based on the drive voltage waveform,
A transport unit that transports the medium to the liquid discharge unit,
A head drive device that generates the drive voltage waveform based on image data input from the outside and applies the drive voltage waveform to the liquid discharge unit.
With
The image forming apparatus according to any one of claims 1 to 7, wherein the head driving device is the head driving device.