JP7275686B2 - Head driving device and image forming device - Google Patents

Description

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

2. Description of the Related Art A liquid ejection apparatus is known that includes a liquid ejection head that ejects liquid onto a recording medium. The liquid ejecting apparatus is also equipped with a head driving device for driving the liquid ejecting operation of the liquid ejecting head. An image forming apparatus (so-called inkjet printer) is also known as a liquid ejecting apparatus that ejects liquid ink onto a recording medium to form characters and images.

The liquid ejection operation of the liquid ejection head is controlled by applying a drive voltage waveform generated by a head driving device in accordance with the droplet size and ejection cycle to a piezoelectric element (piezo actuator) based on 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. It should be noted that a temperature rise can be cited as a factor that lowers the operational stability of the driver circuit.

In particular, the power amplifying part provided in the driver circuit is one of the structures where the temperature tends to rise. In order to equalize the amount of heat generated by the power amplifier, a recording head drive circuit has been disclosed that selects a driver circuit to be driven when there is a temperature difference between the two driver circuits (Patent Document 1). ).

The technology disclosed in Japanese Patent Application Laid-Open No. 2002-200001 selectively uses a driver circuit to drive the temperature difference of a plurality of driver circuits. Note that the head drive circuit generates a plurality of drive voltage waveforms, and the load associated with the generation of the drive voltage waveforms varies depending on the types of drive voltage waveforms generated and applied and the surroundings. That is, the temperature of the drive circuit varies depending on the load resulting from the generation and application of the drive voltage waveform.

Assuming a configuration including a plurality of head drive circuits, simply selecting a head drive circuit to be operated according to a temperature difference as in Japanese Patent Application Laid-Open No. 2002-200010 poses a problem in performing control in line with temperature changes. In addition, there is a problem in improving operational stability by more flexibly coping with temperature changes according to the degree of temperature rise, which differs depending on the type and combination of drive voltage waveforms generated by each head drive circuit.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a head drive device that switches the operation of each drive circuit according to the temperature of the drive circuits.

In order to solve the above problems, one aspect of the present invention provides a drive voltage waveform including a plurality of head drive units that generate drive voltage waveforms from drive waveforms based on drive waveform data and apply the drive voltage waveforms to liquid ejection heads. a waveform generation unit; and a head drive switching unit that generates the drive waveform from the drive waveform data and switches how to pass the drive waveform to each head drive unit based on a predetermined condition, wherein the drive The voltage waveform generation section includes a temperature detection section that detects the temperature of each of the plurality of head drive sections, and a storage section that stores in advance a temperature decrease rate of the drive voltage waveform generation section due to natural cooling or forced cooling. , the head drive switching section detects the operating status of each head driving section, and based on the operating status , the driving voltage waveform generating section as the operating load of each head driving section detects the temperature of each head driving section. switching the type of the drive waveform data input to each of the plurality of head drive units included in the drive voltage waveform generation unit when the calculated temperature increase rate or the temperature decrease rate exceeds a predetermined threshold; characterized by

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

1 is a schematic diagram showing the configuration of a printer that is an embodiment of an image forming apparatus according to the present invention; FIG. FIG. 2 is a side view showing the configuration of an embodiment of a liquid ejection head included in the printer; FIG. 2 is a bottom view showing an example of the structure of the liquid ejection head; FIG. 2 is a plan view showing an example of a nozzle port in the recording head; 1 is an exploded perspective view showing the configuration of an embodiment of a liquid ejection head provided in the printer; FIG. FIG. 3 is a functional block diagram of a head drive control section, which is one embodiment of the head drive section according to the present invention. FIG. 3 is a detailed functional block diagram of the head drive control section; FIG. 3 is a detailed functional block diagram of a head drive circuit switching section included in the head drive control section; 4 is a graph for explaining factors of temperature rise of a head drive circuit included in the head drive control section; Graph showing a setting example of a switching determination threshold in the head drive circuit switching unit 4 is a flow chart showing an example of a flow of switching processing in the head drive control section; 4 is a flowchart showing another example of the flow of switching processing in the head drive control section;

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

[Overall Configuration of 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 section 210, a paper feeding section 220, a registration adjusting section 230, a drying section 240, a recording medium reversing section 250, and a paper discharging section 290. ing. Next, an example of the flow of an image forming output operation (printing operation) in the inkjet printer 1000 having the configuration will be described. Note that the image forming unit 210 corresponds to an embodiment of the liquid ejection device.

First, the recording media P stacked in the paper feed stack 221 of the paper feed section 220 are picked up one by one by the air separating section 222 and conveyed toward the image forming section 210 . When the recording medium P conveyed from the paper feeding section 220 reaches the registration adjustment section 230 , the registration roller pair 231 provided inside the registration adjustment section 230 corrects the inclination of the recording medium P with respect to the conveyance direction.

The recording medium P corrected (registration adjustment) by the registration roller pair 231 is sent to the image forming section 210 . A recording medium gripper 212 provided on the surface of a cylindrical drum 211 grips the leading end of the recording medium P, and the drum 211 rotates to transport the recording medium P to a position facing the head arrays 100K to 100P. be. In the image forming unit 210, head arrays 100K to 100P that eject ink by an inkjet method are arranged radially at angles along the surface of a cylindrical drum 211 while being filled with predetermined ink colors.

A plurality of head arrays 100K to 100P constitute a liquid ejection module, which is a liquid ejection section. Thus, an image is formed on the recording medium P. FIG. A blank ejection receiver 213 is provided on the outer peripheral surface of the drum 211 to receive ink that is blankly ejected when the head module 100 is not ejecting ink onto the recording medium P. After the image is formed, the recording medium P is transported to the drying section 240 .

A drying unit 241 is provided in the drying section 240, and the water content of the recording medium P evaporates as the recording medium P passes under the drying unit 241. FIG. Further, the drying section 240 is provided with a recording medium reversing section 250 including a recording medium reversing mechanism 251 . During double-sided printing, the recording medium P is reversed by the recording medium reversing unit 250 and conveyed again toward the image forming unit 210 by the reversing conveying unit 252 . The inclination of the recording medium P is corrected by a registration roller 253 provided inside the image forming unit 210 before reaching the drum 211 . The recording medium P that has been dried by the drying section 240 is conveyed to the paper discharging section 290 and stacked with the edges of the recording medium P aligned.

It is assumed that part of the control of the droplet ejection operation in the image forming section 210 is performed in the image forming control section 201 included in the image forming section 210 . Note that the image formation control unit 201 may control the overall operation of the inkjet printer 1000 . In addition, each of the paper feeding unit 220, the registration adjustment unit 230, and the drying unit 240 is provided with a control unit individually, and is configured to control the overall operation of the inkjet printer 1000 by cooperating with the image formation control unit 201. may

[Configuration 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. FIG. As shown in FIG. 2, the head module 100 mainly includes a head drive control section 110, an inkjet recording head 130, and a connection section 120 that connects the head drive control section 110 and the inkjet recording head 130. .

In the head drive controller 110 , a drive control IC 112 , a drive voltage waveform generation control IC 113 , and a nonvolatile memory element 114 are mounted on a 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 a cable 121 , and connects 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 driving IC substrate 134 for switching which piezoelectric element 142 to apply the driving voltage waveform, an ink tank 133 in the head, a rigidity and a plate 135 . If the configuration of the liquid ejection head provided in the inkjet printer 1000 is of a line scanning type, the direction intersecting the conveying direction of the recording medium P corresponds to the width direction of the recording medium P, and the width dimension of the recording medium P is Ink jet recording heads 130 are arranged. This configuration is called a line head configuration. The present invention is also applicable to a serial scanning type in which an image is formed while moving one or a plurality of inkjet recording heads 130 in the width direction of the recording medium P and conveying the recording medium P in the conveying direction. It is possible. It is also applicable to other types of liquid ejecting apparatuses.

[Configuration of inkjet recording head 130]
FIG. 3 is a schematic diagram showing an example in which the inkjet recording heads 130 are arranged in a line head configuration. The head module 100 according to the present embodiment is a collection of constituents distinguished for each color of liquid ink to be ejected. The head module 100 illustrated in FIG. 3 shows a configuration example different from the head module 100 illustrated in FIG. The head module 100 illustrated in FIG. 3 includes a black head array 100K that ejects black ink droplets, a cyan head array 100C that ejects cyan ink droplets, and a magenta head array that ejects magenta ink droplets. 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 that intersects (substantially orthogonal to) the conveying direction of the recording medium (the direction of the thick black arrow). By arraying the inkjet recording heads 130 in this way, a wide print area is ensured.

4 is a bottom view of the inkjet recording head 130. FIG. Print nozzles 137 that are a plurality of nozzle ports 29 are arranged in a zigzag pattern on the bottom surface of the inkjet recording head 130 . A nozzle surface 136 is formed by the plurality of print nozzles 137 . Liquid droplets are ejected from each print nozzle 137 arranged on the nozzle surface 136 based on expansion and contraction of the piezoelectric element 142 . By arranging the print nozzles 137 in a zigzag arrangement, it is possible to increase the resolution of the image formed by the ejected liquid.

[Detailed Configuration of Inkjet Recording Head 130]
Next, a 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 group of piezoelectric elements 46, which are piezoelectric elements. there is

A nozzle plate 31 in which a large number of print nozzles 137 are arranged in a zigzag pattern, a pressure chamber plate 33 in which individual pressure chambers 32 corresponding to the print nozzles 137 are formed, a common ink flow path 39, and the individual pressure chambers 32 are communicated with each other. A restrictor plate 35 formed with a restrictor 34 for controlling the flow rate of ink to the individual pressure chambers 32, a diaphragm plate 36, and a diaphragm plate 38 provided with a filter 37 are sequentially stacked and positioned and joined. A channel plate is configured by The channel plate is joined to a rigid plate 135 to align the filter 37 with the opening of the common ink channel 39 .

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

A piezoelectric element driving IC 44 is mounted on the piezoelectric element support substrate 143, and a piezoelectric element group 46 configured by arranging a large number of piezoelectric elements 142 is inserted through an opening 138 provided in a rigid plate 135, and each The inkjet recording head 130 is constructed by bonding and fixing the free end of the piezoelectric element 142 to the vibration plate 36 . In FIG. 5, for the sake of simplification, parts such as the print nozzle 137, the individual pressure chamber 32 and the restrictor 34 are omitted.

[Embodiment of Head Driving Device]
Next, the configuration of the head drive controller 110, which is an embodiment of the head drive device according to the present invention, will be described with reference to FIG. The head drive control section 110 has an image processing section 10 , a head drive circuit switching section 20 , a storage section 30 and a drive voltage waveform generation section 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 which controls the image forming operation for forming an image on the recording medium P by operating the head module 100, and generates drive data. It is passed to the drive circuit switching unit 20 . The image processing unit 10 also 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 head driving IC substrate 134 (see FIG. 2) that constitutes the inkjet recording head 130 is mounted with a driver IC that drives the piezoelectric element based on the timing control signal and the driving voltage waveform. The driver IC applies a drive voltage waveform to the piezoelectric element based on the period based on the timing control signal to execute the liquid ejection operation.

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

The head drive circuit switching section 20 generates a plurality of types of drive waveforms, which are combinations of a plurality of waveforms, according to the number of head drive sections included in the drive voltage waveform generation section 40 . In this embodiment, the drive voltage waveform generation section 40 includes two head drive sections. Therefore, the head driving circuit switching section 20 generates two types of driving waveforms based on the driving waveform data, and passes each of them to the driving voltage waveform generating section 40 . In the following description, the two types of driving waveforms will be described as "first driving waveform (driving waveform A)" and "second driving waveform (driving 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. be. The head driving circuit switching unit 20 generates these driving waveforms so as to apply the ejection operation controlled by the timing control signal in one cycle, and transfers the driving voltage waveform to the driving voltage waveform generating unit 40 . In the following description, of the two types of drive waveforms, the drive waveform consisting of a combination of large droplets and medium droplets will be referred to as a "first drive waveform (drive waveform A)", and the drive waveform consisting of a combination of small droplets and fine droplets will be referred to as "first drive waveform (drive waveform A)". This will be described as "second driving waveform (driving waveform B)".

The load on the head driving section 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, the amount of heat generated by the head driving section increases and the temperature rises more easily when operating according to the first driving waveform than when operating according to the second driving waveform.

Further, the head driving circuit switching section 20 switches the driving waveform to be passed to each of the two head driving sections provided in the driving voltage waveform generating section 40 based on the temperature information from the driving voltage waveform generating section 40 . That is, which drive waveform is transferred to which head driving unit and how to transfer it is determined according to the temperature and temperature rise due to the heat generated as a result of the ejection operation according to the first drive waveform or the second drive waveform. switch. In other words, the head drive circuit switching section 20 switches the type of drive waveform to be passed to each of the head drive sections provided in the drive voltage waveform generation section 40 . The head drive circuit switching section 20 constitutes a head drive switching section.

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

Among the drive waveform patterns stored in the storage unit 30 , those corresponding to the image data are read out as drive waveform patterns necessary for operating the inkjet recording head 130 . Using the read drive waveform pattern, the head drive circuit switching section 20 generates a drive waveform.

The storage unit 30 also stores past temperature information for calculating a temperature increase rate in the temperature prediction unit 24, which will be described later.

The storage unit 30 also stores the rate of temperature decrease due to natural cooling in each of the head drive units (the first head drive unit 41 and the second head drive unit 42). When the head drive unit is provided with a forced cooling mechanism (such as a fan), the temperature drop rate is stored with the forced cooling taken into account.

The storage unit 30 also stores threshold values used for switching determination processing in the switching determination unit 25, which will be described later.

[Drive voltage waveform generator 40]
The drive voltage waveform generation unit 40 amplifies the voltage and current of the drive waveform passed from the head drive circuit switching unit 20 to generate a drive voltage waveform, and passes the generated drive voltage waveform to the driver IC included in the inkjet recording head 130 . The driver IC receiving the drive voltage waveform executes a liquid ejection operation based on the drive voltage waveform. The drive voltage waveform generation section 40 includes, for example, two head drive sections as illustrated in FIG.

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

The first temperature detection unit 43 measures the temperature of the first head driving unit 41 and feeds back the measurement result to the head driving circuit switching unit 20 as temperature information. The second temperature detection section 44 measures the temperature of the second head driving section 42 and feeds back the measurement result to the head driving circuit switching section 20 as temperature information. The first temperature detection unit 43 and the second temperature detection unit 44 may be configured to detect the temperature of the first head drive unit 41 and the second head drive unit 42 and notify the detection results as temperature information. The first temperature detection unit 43 and the second temperature detection unit 44 are configured by using temperature detection elements such as thermistors, for example.

[Detailed Configuration of Head Drive Circuit Switching Unit 20]
Next, a detailed configuration of the head drive circuit switching section 20 will be described with reference to FIGS. 7 and 8. FIG. As shown in FIG. 7 , the head drive circuit switching section 20 has a D/A conversion section 21 and a switch section 22 .

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

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

In the state illustrated in FIG. 7, the first driving waveform (driving waveform A) is passed to the first head driving section 41 and the second driving waveform (driving waveform B) is passed to the second head driving section 42 . ing. In switching control, which will be described later, when the switch section 22 operates to switch the switch state, the first driving waveform (driving waveform A) is transferred to the second head driving section 42, and the second driving waveform (driving waveform B) is transferred. is passed to the first head drive unit 41 . That is, the operation of the switch section 22 switches the type of drive waveform passed to a certain head drive section.

[Detailed Functional Configuration of Head Drive Circuit Switching Unit 20]
Next, a more detailed configuration of the head drive circuit switching section 20 will be described. As shown in FIG. 8, the head driving circuit switching section 20 includes a D/A converting section 21, a switching section 22, an accumulated driving time calculating section 23, a temperature predicting section 24, and a switching determining section 25. .

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

[Switch section 22]
The switch unit 22 converts the drive waveforms (the first drive waveform and the second drive waveform) passed from the D/A converter 21 to the drive voltage waveform generator 40 (the first head drive unit 41 and the drive voltage waveform generator 40) based on the state of the switches. It is passed to the second head driving section 42). The switch unit 22 switches switches based on a switching control signal notified from a switching determination unit 25, which will be described later.

[Cumulative drive time calculator 23]
The cumulative drive time calculation unit 23 calculates the cumulative amount of application operations performed by each head drive unit on the inkjet recording head 130 based on the type and number of times of drive waveforms passed to each head drive unit in the D/A conversion unit 21. Calculate time. This cumulative time is the cumulative load calculated for each head driving section. This accumulated time can be used as the operational status of the head driving section. The cumulative drive time calculator 23 passes the calculated cumulative time to the switching determination unit 25 .

[Temperature prediction unit 24]
Based on the temperature information from the first temperature detection unit 43 and the second temperature detection unit 44 provided in the drive voltage waveform generation unit 40, the temperature prediction unit 24 controls the first head drive unit 41 and the second head drive unit 42, respectively. Predicted temperature information is generated by predicting the temperature or the degree of temperature rise (temperature rise rate). The generation timing of the predicted temperature information may be regular with predetermined time intervals. In addition, the time interval until a predetermined temperature or temperature rise rate is reached is lengthened, and predicted temperature information is generated according to the degree of approach to a switching opposite threshold (specific temperature or time) in the switching determination unit 25, which will be described later. You can shorten the time interval.

The temperature prediction unit 24 passes the generated predicted temperature information to the switching determination unit 25 . Note that 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 temperature rise rate of each head drive unit. may be used to 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 accumulated time, the temperature of the head driving unit with longer accumulated time is predicted to be higher, taking this into consideration.

The temperature prediction unit 24 stores 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 to calculate the temperature increase rate (the degree of change in the temperature environment). The calculated temperature increase rate is included in the predicted temperature information and passed to the switching determination unit 25 .

The temperature prediction unit 24 may also calculate the predicted temperature information, etc., taking into account the number of continuous prints determined by image data, which is 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 switches the state of the switch unit 22 when determining to “switch”. control.

Further, the switching determination unit 25 determines 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. determines whether or not to switch When the switch determination unit 25 determines to “switch”, it performs control to switch the state of the switch unit 22 .

The switching determination unit 25 uses thresholds stored in advance in the storage unit 30 to determine whether the temperature included in the predicted temperature information, the predicted temperature rise rate calculated from the predicted temperature information, or the like exceeds the thresholds corresponding to these. It is determined whether or not there is, and if the threshold is exceeded, a switching control signal is notified to the switch section 22 .

As described above, according to the head driving circuit switching unit 20, the operation of the head driving unit is switched according to information (information about temperature) that changes depending on the operating load of each head driving unit and information on the cumulative load (cumulative driving time). . As a result, the drive voltage waveforms are generated and applied to the inkjet recording head 130 to equalize the amount of heat generated by the plurality of head drive units, thereby improving the operational stability.

In addition, the head drive circuit switching unit 20 according to the present embodiment switches the operation status 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. followability is improved, and operation stability can be further improved.

[Relationship between operating conditions of the head drive unit and temperature]
Here, the relationship between the operating conditions of the head driving section and the temperature will be described. Also, the setting of the threshold used for determination by the switching determination unit 25 and the types of information included in the predicted temperature information will be described.

Heat generation factors of the head driving units (first head driving unit 41 and second head driving unit 42) include types of driving waveform patterns (large droplet, medium droplet, small droplet, fine driving) included in driving waveforms passed to them. ), the current amplification operation of the drive waveform, the idling current, and the like. In addition, since the temperature of the head drive section drops due to natural cooling, the corresponding temperature drop rate is stored in advance in the storage section 30 . If a forced cooling mechanism such as a fan is installed, the storage unit 30 also stores the rate of temperature drop caused by the forced cooling by the fan.

FIG. 9A is a graph illustrating the relationship between the drive amount, which is a factor that affects the temperature of the head drive section, and the amount of heat generated by a combination of various factors. As shown in FIG. 9A, the driving operation for ejecting large droplets generates more heat than the driving operation for ejecting small droplets or fine driving. Further, the amount of heat generated increases as the number of times of driving increases. On the other hand, as the number of times of driving increases (as the time elapses), the amount of heat generated by cooling also decreases. Therefore, the net amount of heat generated increases depending on the operating conditions of the head driving section (what kind of droplets are ejected and how many times), and decreases due to cooling. In this manner, the temperature of the driving section can be predicted by considering the type (content) of the driving voltage waveform generated in the head driving section, the number of waveforms generated, and the rate of temperature decrease 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 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 heat generation amount for each drive waveform pattern, and the cumulative drive time calculation. A predicted value of the temperature or temperature rise rate (predicted temperature, predicted temperature rise rate) is calculated using the past drive waveform and its operating frequency stored in the unit 23 .

Therefore, even if the responsiveness of the first temperature detection section 43 and the second temperature detection section 44 is low, the temperature can be predicted with higher accuracy, and the control (switching control) for ensuring the operational stability of the head driving section can be performed. Accuracy can be improved.

[Relationship Between Switching Determination Threshold and Switching Operation]
Next, an example of a threshold for switching determination based on the predicted temperature and the predicted temperature increase rate in the switching determination unit 25 will be described with reference to FIG. 10 .

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

As shown in FIG. 10A, the temperature of the first head drive section 41, which requires a higher load for the ejection operation, rises in a shorter period of time. At some point, the temperature threshold is reached. Here, the switching determination section 25 notifies the switching control signal to the switching section 22, and the switching section 22 performs a switching operation. Then, the way in which the drive waveform A and the drive waveform B are passed to the drive voltage waveform generation section 40 changes, and the drive waveform A (large droplet ejection) is passed to the second head drive section 42 and transferred to the drive waveform B (small droplet ejection). is passed to the first head driving section 41 . As a result, the temperature of the first head driving section 41 naturally decreases due to the cooling, and the temperature of the second head driving section 42 rises.

As described above, by detecting a change in the temperature state by comparing the threshold value with the temperature, the generation of the driving voltage waveform in each head driving section 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 in order to prevent the temperature of a specific head driving unit from rising and exceeding the temperature threshold, and using this time interval, the head driving unit This is an example of switching the contents of the drive waveform generation operation in each case. As shown in FIG. 10(b), the temperature rise rate can be made uniform by switching the destination of the drive waveform A with a high load (easily causing a temperature rise) 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 this embodiment will be described using the flowchart of FIG. 11 . When image data is input from the image formation control unit 201 (S1101), the image processing unit 10 generates drive waveform data (S1102).

The drive waveform data generated by the image processing unit 10 is converted by the D/A conversion unit 21 into a drive waveform that is an analog signal and transferred 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 of it. Thereby, temperature information detected by 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 a predicted temperature or a 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). Note that 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 driving unit whose predicted temperature or predicted temperature increase rate exceeds the threshold (S1104). If there is a head driving unit that exceeds the threshold (S1104/YES), a switching control signal is sent to the switch unit 22, and the switch unit 22 switches the method of passing the drive waveform to change the load distribution (S1105). If there is no head driving unit exceeding the threshold (S1104/NO), S1105 is skipped.

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

As described above, according to the head drive control unit 110 according to the present embodiment, the predicted temperature or the predicted temperature increase rate after that is calculated using the result of detecting the temperature of the head drive unit. Guess the calorific value. As a result, when it is predicted that the amount of heat generated (temperature, rate of temperature rise) will reach a level at which the stability of the operation may be lost, the contents of the operation can be switched and the amount of heat generated can be controlled to decrease.

In addition, since the temperature and 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 section 110 according to this embodiment will be described using the flowchart of FIG. The content of the determination operation in the switching determination unit 25 is different from that described using FIG. 11 . Other processing has many parts in common, so the description of the common processing 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, which is converted into a drive waveform by the D/A conversion unit 21 and transferred to the switch unit 22 (S1201, S1202).

At the timing when the drive waveform is transferred from the D/A conversion section 21 to the switch section 22, the type of drive waveform transferred to each head drive section and the cumulative drive time of each head drive section based on the drive waveform are used to calculate 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 driving time exceeds the threshold (S1204). If the threshold value is exceeded (S1204/YES), a switching control signal is sent to the switch unit 22 to switch the delivery method of the drive waveform, change the load distribution, and equalize the heat generation amount (S1205). If the threshold 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 has ended (S1206), and if the printing operation has not ended, the process returns to S1202 (S1206/NO). . If the printing operation has ended (S1206/YES), the process ends.

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 The temperature prediction unit 24 is notified. Therefore, in S1203, the switching determination unit 25 may multiply the cumulative drive time by the predicted temperature or the predicted temperature rise calculated by the temperature prediction unit 24 as a coefficient, and use that value to perform the switching determination.

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 to , the switching of the head driving section 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, responsiveness to fluctuations in operating conditions is high, and switching can be performed in a timely manner based on accurate prediction.

According to the present embodiment described above, the ejection 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 concentrates and processes the ejection operations corresponding to the stopped operation is lengthened. The relative speed of the object to be ejected is controlled to be slow corresponding to the minute. By performing ejection operations for all types of droplets with a drive waveform generation circuit that operates normally, ejection operations can be continued without stopping even when a temperature abnormality occurs, improving productivity. can be made

10: Image processing unit 20: Head drive circuit switching unit 21: D/A conversion unit 22: Switch unit 23: Cumulative driving 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 Patent Application Laid-Open No. 2008-002870

Claims (6)

a drive voltage waveform generation unit including a plurality of head drive units for generating a drive voltage waveform from a drive waveform based on drive waveform data and applying the drive voltage waveform to the liquid ejection head;
a head drive switching unit that generates the drive waveform from the drive waveform data and switches how to pass the drive waveform to each head drive unit based on a predetermined condition;
The drive voltage waveform generation unit includes a temperature detection unit that detects the temperature of each of the plurality of head drive units;
a storage unit for pre-storing the temperature reduction rate of the drive voltage waveform generation unit by natural cooling or forced cooling;
with
The head drive switching section detects the operating status of each head driving section, and the driving voltage waveform generating section as the operating load of each head driving section calculates based on the temperature of each head driving section based on the operating status. and switching the type of the drive waveform data input to each of the plurality of head drive units included in the drive voltage waveform generation unit when the rate of temperature increase or the rate of temperature decrease exceeds a predetermined threshold. A head drive device characterized by: The head drive switching section selects the type of the drive waveform data input to each of the drive voltage waveform generation sections when the temperature of each head drive section calculated based on the operating conditions exceeds a predetermined threshold value. 2. The head driving device according to claim 1, which switches. The head drive switching section changes the drive waveform data input to each of the drive voltage waveform generation sections when the temperature rise rate of each head drive section calculated based on the operating conditions exceeds a predetermined threshold. 2. The head driving device according to claim 1, wherein the type is switched. When the cumulative load of each head driving unit calculated based on the operating conditions exceeds a predetermined threshold value, the head drive switching unit selects the type of the driving waveform data input to each of the driving voltage waveform generating units. 2. The head driving device according to claim 1, wherein the switching is performed between . 5. The head drive device according to claim 1 , wherein said head drive switching unit detects said operation status at regular time intervals. An image forming apparatus that forms an image by ejecting a liquid onto a medium being conveyed,
a liquid ejection unit that ejects liquid onto the medium based on the drive voltage waveform;
a transport unit that transports the medium to the liquid ejection 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 ejection unit;
An image forming apparatus, wherein the head driving device is the head driving device according to claim 1 .

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