JP7346913B2 - Image forming device and method of controlling the image forming device - Google Patents

Description

The present disclosure relates to an image forming apparatus and a method of controlling the image forming apparatus.

2. Description of the Related Art An image forming apparatus using an inkjet head that performs an ink ejecting operation by expanding or contracting a piezoelectric element is known.

In this type of image forming apparatus, generally, a drive signal is sent to the inkjet head from a drive signal generation section disposed in the main body of the image forming apparatus, and a drive voltage is obtained by voltage amplifying the drive signal. is used to operate the piezoelectric element. The rise time, fall time, pulse width, peak value, etc. of the voltage waveform of the drive signal are usually determined by optimal ink ejection timing and ink droplet diameter, taking into consideration the expansion or contraction mode of the piezoelectric element. Also, the settings are made so that the amount of mist generated when ink is ejected is reduced.

By the way, in this type of image forming apparatus, due to the capacitance of the piezoelectric element, the voltage waveform (hereinafter also referred to as "drive waveform") of the drive signal supplied to the piezoelectric element becomes dull, and the ink ejection timing and ink There is a known problem that the droplet diameter changes and print quality becomes unstable. In particular, when printing, the number of nozzles driven simultaneously differs for each line, so the voltage waveform of the drive signal supplied to the piezoelectric element is deformed from the voltage waveform of the drive signal set at the time of manufacturing, resulting in printing problems. It is known that quality deterioration occurs. Note that the state in which the drive signal is dull typically refers to a state in which the rise time and fall time of the voltage waveform are longer than set values.

Conventionally, in this type of image forming apparatus, a correction table prepared in advance is used to generate a drive signal that assumes a blunting of the voltage waveform due to the capacitance of the piezoelectric element, and the voltage waveform of the drive voltage supplied to the piezoelectric element is adjusted. A method has been adopted to stabilize the

For example, in Patent Document 1, in order to correct the blunting of the voltage waveform of a drive signal, the number of nozzles to be driven simultaneously in an inkjet head is calculated from image data, and a drive signal generation unit generates a signal according to the number of nozzles. It is described that the rise time and fall time of the voltage waveform of the drive signal are set. Note that Patent Document 1 employs a method of setting the rise time and fall time according to the number of nozzles to be simultaneously driven using a correction table determined in advance through experiments or the like.

Japanese Patent Application Publication No. 2014-200951

However, in conventional image forming apparatuses, drive waveforms caused by transmission lines (e.g., cables and connectors) connecting the image forming apparatus main body (here, a driver board housed in the main body) and the inkjet head It does not take into account the slowing down of

FIG. 1 is a diagram illustrating the blunting of the voltage waveform of a drive signal caused by a transmission line connecting an image forming apparatus main body P1 and an inkjet head P2 in an image forming apparatus P according to the prior art.

The main body P1 and the inkjet head P2 are typically connected to a cable P3 (for example, an FPC (Flexible Printed Circuit)) whose one end is connected to the connector P1c of the main body P1 and the other end is connected to the connector P2c of the inkjet head P2. electrically connected. When printing is executed, a drive signal generating section P1a housed within the main body P1 generates a drive signal specified by the CPU 1b and transmits it to the inkjet head P2 via a cable P3.

At this time, since the cable P3 connecting the main body P1 and the inkjet head P2 has a relatively large inductance component and resistance component, the voltage waveform of the drive signal generated by the drive signal generation section P1a (V1 in FIG. 1) When reaching the inkjet head P2, the voltage waveform changes to a dull voltage waveform (V2 in FIG. 1).

In addition, depending on this type of image forming apparatus P, a plurality of inkjet heads are often used in order to provide a wide printing width. Therefore, the cable length of the cable P3 connecting the main body P1 and the inkjet head P2 differs for each inkjet head P2. As a result, the degree of dullness of the drive signal when reaching the inkjet head P2 also changes for each inkjet head P2.

In this regard, in the conventional technology described in Patent Document 1, since correction data is set in advance at the time of manufacturing, it does not take into account the blunting of the waveform depending on the difference in cable length of the cable P3, and the inkjet head The drive signal when reaching P2 does not necessarily have an ideal voltage waveform. In addition, in the conventional technology described in Patent Document 1, the electrical characteristics of the transmission line (for example, the cable P3 and the connectors P1c, P2c) and the piezoelectric element of the inkjet head P2 change over time due to the usage conditions and aging of the image forming apparatus P. The problem is that it is difficult to deal with such situations.

The present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to provide an image forming apparatus and a control method for the image forming apparatus that can suppress deterioration of print quality due to blunting of the voltage waveform of a drive signal. shall be.

The main disclosure that solves the above-mentioned problems is:
An image forming apparatus having an inkjet head that performs an ink ejection operation by expanding or contracting a piezoelectric element,
a drive signal generation section that is disposed within the main body of the image forming apparatus and that generates a drive signal that forms a voltage waveform of a drive voltage that is supplied to the piezoelectric element;
a drive waveform detection section that is disposed within the inkjet head and detects a voltage waveform of the drive signal output from the main body side to the inkjet head via a cable;
The rise time and/or of the voltage waveform of the drive signal that is caused to be generated by the drive signal generation unit based on a pre-stored reference voltage waveform and the voltage waveform of the drive signal detected by the drive waveform detection unit. a drive waveform setting section that performs waveform settings related to fall time;
Equipped with
As a calibration process, the drive waveform setting section causes the drive signal generation section to sequentially generate a plurality of drive signals having different rise times and/or fall times,
The image forming apparatus performs the waveform setting by comparing the degree of coincidence between the voltage waveform of the drive signal detected by the drive waveform detection section and the reference voltage waveform.

Also, in other situations,
A method for controlling an image forming apparatus having an inkjet head that performs an ink ejection operation by expanding or contracting a piezoelectric element, the method comprising:
a step of generating a drive signal that is disposed within the main body of the image forming apparatus and forms a voltage waveform of a drive voltage that is supplied to the piezoelectric element;
detecting a voltage waveform of the drive signal disposed within the inkjet head and output from the main body side to the inkjet head via a cable;
Waveform settings related to the rise time and/or fall time of the voltage waveform of the drive signal to be generated based on a reference voltage waveform stored in advance and the voltage waveform of the drive signal detected on the inkjet head side. and the steps to
has
The step of generating the drive signal includes, as a calibration process, sequentially generating a plurality of the drive signals having different rise times and/or fall times,
The step of setting the waveform includes the step of setting the waveform by comparing the degree of match between the voltage waveform of the drive signal detected during the step of sequentially generating the drive signal and the reference voltage waveform.
This is a method of controlling an image forming apparatus.

According to the image forming apparatus according to the present disclosure, it is possible to suppress deterioration in print quality due to blunting of the voltage waveform of the drive signal.

A diagram illustrating the blunting of the voltage waveform of a drive signal caused by a transmission line connecting an image forming apparatus main body and an inkjet head in a conventional image forming apparatus. A block diagram showing an example of the configuration of an image forming apparatus according to the first embodiment A diagram showing the appearance of a transport mechanism of an image forming apparatus according to a first embodiment A diagram showing an example of a voltage waveform of a drive signal generated by the drive signal generation unit according to the first embodiment A diagram showing an example of the configuration of a drive control IC according to the first embodiment A diagram showing an example of a drive signal arrangement pattern determined by the drive control IC according to the first embodiment A diagram illustrating an example of the calibration process performed by the drive waveform setting unit according to the first embodiment. Flowchart showing an example of calibration processing performed by the drive waveform setting unit according to the first embodiment Block diagram showing the configuration of an image forming apparatus according to a second embodiment

Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that in this specification and the drawings, components having substantially the same functions are designated by the same reference numerals and redundant explanation will be omitted.

(First embodiment)
[Configuration of image forming apparatus]
An example of the configuration of the image forming apparatus according to this embodiment will be described below with reference to FIGS. 2 to 6.

FIG. 2 is a block diagram showing an example of the configuration of the image forming apparatus U according to the present embodiment. FIG. 3 is a diagram showing the appearance of the transport mechanism 100R of the image forming apparatus U according to the present embodiment. FIG. 4 is a diagram showing an example of a voltage waveform of a drive signal generated by the drive signal generation section 140 according to the present embodiment.

The image forming apparatus U includes an image forming apparatus main body (hereinafter abbreviated as "main body") 100 and an inkjet head 200. Although only one inkjet head 200 is shown here, if the image forming apparatus U is a color printer that ejects a plurality of ink colors, the inkjet head 200 may be configured to eject a plurality of ink colors (for example, yellow, They are provided corresponding to each of the four colors (magenta, cyan, and black). Furthermore, a plurality of inkjet heads 200 that eject ink of the same color may be provided.

The main body 100 and the inkjet head 200 are connected by, for example, a cable 300. The cable 300 is, for example, an FPC (Flexible Printed Circuit), and has one end connected to a connector (not shown) of the main body 100 and the other end connected to a connector (not shown) of the inkjet head 200.

In the image forming apparatus U, the main body 100 transports the recording medium P using a transport mechanism 100R (for example, a transport roller). Then, the main body 100 forms a desired image on the recording medium P by ejecting ink droplets from the inkjet head 200 disposed to face the recording medium P while conveying the recording medium P. .

The main body 100 includes a control section 110, a storage section 120, a line memory 130, and a drive signal generation section 140. Note that the control section 110, the storage section 120, the line memory 130, and the drive signal generation section 140 are configured, for example, on a driver board within the casing of the main body 100.

The control unit 110 performs arithmetic processing and performs various controls related to image forming operations in the image forming apparatus U. The control unit 110 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input port, an output port, and the like. The functions of the control unit 110 are realized, for example, by the CPU referring to control programs and various data stored in the ROM or RAM.

The control unit 110 includes a transport control unit 110a that controls the transport mechanism 100R described above, a drive command unit 110b that controls the operation of the inkjet head 200, and a drive waveform setting unit that sets the waveform of a drive signal to be supplied to the inkjet head 200. 110c.

The storage unit 120 stores various data. The storage unit 120 calibrates, for example, image data 120a to be printed on the recording medium P, drive waveform data 120b that defines the voltage waveform of the drive signal generated by the drive signal generation unit 140, and the drive waveform data 120b. Reference waveform data 120c that defines a reference voltage waveform to be used is stored.

When printing an image on the recording medium P, the line memory 130 temporarily stores image data 120a to be ejected from each nozzle of the nozzle row 210 of the inkjet head 200, out of the image data 120a stored in the storage unit 120. It is a memory that stores information. The line memory 130 holds, for example, data for one line of the image data 120a, and sequentially transfers the data to the drive control IC 220 of the inkjet head 200. Note that data transfer of the image data 120a from the storage section 120 to the line memory 130 is executed under the control of the control section 110.

The image data 120a transferred from the line memory 130 to the drive control IC 220 has, for example, a data structure in which pixel data is arranged in the order of addresses within the image to be printed. "Pixel data" has a configuration in which, for example, 3 bits represent the pixel value (i.e., gradation) of one pixel area, and the 3-bit data is transmitted from the line memory 130 to the drive control IC 220 via three signal lines. pixel data is transferred in parallel. Note that the image data 120a defines the ejection timing and amount of ink ejected from each nozzle of the nozzle array 210.

The drive signal generation unit 140 generates a drive signal that defines the waveform of the drive voltage supplied to the nozzle array 210 (piezoelectric element), and sends it to the drive control IC 220 of the inkjet head 200.

The drive signal generation unit 140 generates a drive signal with a voltage waveform instructed by the control unit 110 (drive command unit 110b). As shown in FIG. 4, the control unit 110 (drive command unit 110b) outputs, for example, the rise time T-up, fall time T-down, pulse width T-mid, and peak value of the voltage waveform of the drive signal. Vf etc. are commanded. Note that the control section 110 (drive command section 110b) reads out the drive waveform data 120b stored in the storage section 120 and instructs the drive signal generation section 140 to generate a voltage waveform.

The drive signal generation section 140 includes, for example, a D/A converter and a power amplifier. The drive signal generation unit 140 generates a drive signal (analog signal) using a D/A converter, for example, based on a command signal (digital signal) related to a drive waveform commanded from the control unit 110, and outputs the drive signal to the power amplifier. and amplify the drive signal.

The drive signal generation unit 140 is configured to be able to output three types of drive signals: a drive signal used when ink is ejected, a drive signal used when ink is not ejected, and a drive signal used when the nozzle is not in operation. .

The inkjet head 200 includes a nozzle array 210, a drive control IC 220, and a drive waveform detection section 230.

The nozzle row 210 has, for example, a plurality of one-dimensionally arranged nozzles (here, 256 nozzles) 210-ch1 to 210-ch256 (see FIG. 5). Each nozzle is constituted by a piezoelectric element that expands or contracts according to the drive voltage supplied from the drive control IC 220 (FIG. 5 shows a piezoelectric element operating in shear mode). Each nozzle has an electrode film separately connected to the output line of the drive control IC 220. Each nozzle bends and deforms its own piezoelectric element by being supplied with a drive voltage from the drive control IC 220, and ejects ink droplets from the nozzle hole.

The drive control IC 220 selectively applies one of the three types of drive signals input from the drive signal generation unit 140 to each nozzle ( piezoelectric element).

FIG. 5 is a diagram showing an example of the configuration of the drive control IC 220 according to this embodiment. FIG. 6 is a diagram showing an example of a drive signal arrangement pattern determined by the drive control IC 220 according to this embodiment.

The drive control IC 220 includes a shift register 221, a latch circuit 222, a waveform selection section 223, and a buffer amplifier 224.

The shift register 221 is, for example, a FIFO type memory that stores 3-bit data for 256 channels (the number of nozzles in the nozzle array 210). The shift register 221 stores each 3-bit pixel data input in parallel from the line memory 130 in synchronization with the transfer clock signal CLK. The 256 3-bit data stored in the shift register 221 are output in parallel to the latch circuit 222 all at once at a predetermined timing.

The latch circuit 222 holds the 3-bit data for 256 channels output from the shift register 221 until the timing specified by the latch signal LAT, and outputs it to the waveform selection section 223.

For each of the 256 channels, the waveform selection unit 223 determines a drive signal array pattern that defines the operation mode of the channel based on the 3-bit pixel data output from the latch circuit 222, and selects a drive signal array pattern corresponding to the drive signal array pattern. The drive signals are sequentially output to the buffer amplifier 224. In addition to the pixel data, the waveform selection unit 223 receives three types of drive signals output from the drive signal generation circuit 140, the clock signal GSCLK output from the control unit 110, the reset signal RST, etc. .

The drive signal array pattern is, for example, as shown in FIG. This defines three types of drive signal arrangement patterns: a drive signal and a drive signal used during ink ejection. The data defining the drive signal array pattern is stored in the waveform selection unit 223 in advance in association with 3-bit pixel data, for example.

FIG. 6 shows eight types of drive signal array patterns associated with 3-bit pixel data, and the waveform selection unit 223 selects eight types of drive signal array patterns based on the 3-bit pixel data input from the latch circuit 222. One of the drive signal array patterns is selected, and drive signals corresponding to the drive signal array pattern are sequentially output to the buffer amplifier 224. Although the voltage waveform of the drive signal is shown in a rectangular shape in FIG. 6 for convenience of explanation, the voltage waveform of the drive signal actually has a predetermined rise time and fall time as shown in FIG. is set.

The buffer amplifier 224 amplifies the drive signal output from the waveform selection section 223 (hereinafter, the amplified drive signal is also referred to as "drive voltage"). The buffer amplifier 224 supplies a driving voltage to each nozzle (piezoelectric element) of the nozzle array 210. Note that the buffer amplifier 224 is supplied with a power supply voltage VH for amplifying the drive signal.

The drive waveform detector 230 detects the voltage waveform of the drive signal output from the drive signal generator 140 to the inkjet head 200 via the cable 300. The drive waveform detection unit 230 detects the voltage waveform of the drive signal by, for example, detecting a temporal change in the voltage input to the input port of the drive control IC 220. The drive waveform detection section 230 then transmits the voltage waveform of the detected drive signal to the control section 110.

As the drive waveform detection section 230, it is preferable to use an A/D converter. This prevents the data from changing due to signal deterioration within the cable 300 when sending the data of the voltage waveform of the detected drive signal from the inkjet head 200 to the main body 100 (control unit 110). be able to.

[About how to set the drive waveform]
Next, a method for setting the voltage waveform of the drive signal of the image forming apparatus U according to the present embodiment will be described with reference to FIGS. 7 and 8. Setting processing of the voltage waveform of this drive signal is realized by the drive waveform setting section 110c.

As described above, the drive signal output from the drive signal generation unit 140 to the inkjet head 200 is generally caused by the capacitance of the piezoelectric element constituting the inkjet head 200, the inductance component and resistance component of the cable 300, etc. When reaching the inkjet head 200, it deforms into a blunt shape.

The drive waveform setting unit 110c performs calibration so that a drive signal that takes such waveform blunting into account is generated. Specifically, the drive waveform setting unit 110c acquires the voltage waveform of the drive signal detected by the drive waveform detection unit 230, and also acquires the reference waveform data 120c stored in the storage unit 120 in advance. Based on these, the drive waveform setting section 110c performs a process of calibrating the rise time and/or fall time of the voltage waveform of the drive signal generated by the drive signal generation section 140. That is, the drive waveform setting unit 110c generates a drive signal in a feedback manner by comparing the voltage waveform of the drive signal when it reaches the inkjet head 200 (drive control IC 220) with the reference voltage waveform of the reference waveform data 120c. Calibration processing is performed on the voltage waveform of the drive signal generated by the unit 140.

Note that the voltage waveform of the drive signal that is calibrated by the drive waveform setting unit 110c is typically the voltage waveform of the drive signal used during ink ejection.

The reference waveform data 120c referred to at this time is typically data that defines a target voltage waveform (i.e., an ideal waveform) of the drive voltage to be supplied to the piezoelectric element of the noise column 210, and is determined by experiment or the like in advance. stipulated. However, the reference voltage waveform of the reference waveform data 120c may be any waveform that can serve as a reference, and may be the voltage waveform of the drive signal output by the drive signal generation section 140 (that is, the drive waveform data 120b). , may be a square wave.

FIG. 7 is a diagram illustrating an example of the calibration process performed by the drive waveform setting section 110c.

During the calibration process, the drive waveform setting unit 110c, for example, causes the drive signal generation unit 140 to sequentially generate a plurality of drive signals V1a, V1b, V1c, and V1d having different rise times and/or fall times. let For example, the drive waveform setting unit 110c provides the drive signal generation unit 140 with a drive signal V1a having a rise time and a fall time of zero (that is, a rectangular wave), and a drive signal V1a that reduces the rise time and fall time from the drive signal V1a. A drive signal V1b, a drive signal V1c whose rise time and fall time are reduced from the drive signal V1b, and a drive signal V1d whose rise time and fall time are reduced from the drive signal V1c are sequentially generated. That is, the drive waveform setting unit 110c causes the drive signal generation unit 140 to sequentially generate drive signals V1a, V1b, V1c, and V1d whose voltage waveforms have decreasing slopes.

The drive waveform setting section 110c sets the drive waveform detected by the drive waveform detection section 230 when the drive signal generation section 140 outputs the drive signal V1a, and the drive waveform detected when the drive signal generation section 140 outputs the drive signal V1b. The drive waveform detected by the waveform detection unit 230, the drive waveform detected by the drive waveform detection unit 230 when the drive signal V1c is output from the drive signal generation unit 140, and the drive signal V1d from the drive signal generation unit 140. Each of the drive waveforms detected by the drive waveform detection unit 230 when output is compared with a reference voltage waveform (target voltage waveform here) of the reference waveform data 120c. Then, the drive waveform setting unit 110c determines, for example, from among the drive signals V1a, V1b, V1c, and V1d, the one that most matches the reference voltage waveform of the reference waveform data 120c as the voltage waveform of the drive signal used during printing. , corrects the drive waveform data 120b to the corresponding voltage waveform.

In this way, the voltage waveform of the drive signal to be generated by the drive signal generation unit 140 is determined in consideration of the waveform blunting caused by the capacitance of the piezoelectric element constituting the inkjet head 200 and the inductance component and resistance component of the cable 300. becomes possible. That is, this makes it possible to bring the voltage waveform of the drive voltage actually supplied to the piezoelectric elements of the nozzle array 210 closer to the ideal waveform.

However, such waveform dullness changes based on the number of nozzles driven simultaneously in the inkjet head 200. The reason for this is that the size of the parasitic capacitance seen from the drive signal generation unit 140 (that is, the parasitic capacitance of the piezoelectric elements of the nozzle array 210) changes depending on the number of nozzles driven simultaneously in the inkjet head 200.

From this viewpoint, it is preferable that the drive waveform setting unit 110c sets the rise time and/or fall time of the voltage waveform of the drive signal for each number of nozzles that are simultaneously driven in the inkjet head 200. For example, the drive waveform setting unit 110c temporally changes the number of nozzles driven simultaneously in the inkjet head 200, and executes the above-described calibration process (see FIG. 7) for each number of nozzles.

As a result, drive waveform data 120b is set in the storage unit 120 for each number of nozzles that are simultaneously driven in the inkjet head 200. In other words, it is thereby possible to appropriately set the voltage waveform of the drive signal, taking into account the degree of blunting of the voltage waveform caused by the difference in the number of nozzles to be driven.

FIG. 8 is a flowchart showing an example of the calibration process performed by the drive waveform setting section 110c. Note that the drive waveform setting unit 110c executes this calibration process, for example, when the image forming apparatus U is started or when the inkjet head 200 is replaced.

In step S1, the drive waveform setting unit 110c first sets the number of nozzles to be driven simultaneously among the nozzle rows 210 of the inkjet head 200. Then, the drive waveform setting unit 110c generates pseudo image data corresponding to the number of nozzles, and transfers the data to the line memory 130. Thereby, the inkjet head 200 starts a test ejection operation.

Note that when the execution of this flowchart is started, the number of nozzles to be driven simultaneously is set to N=1. Then, the drive waveform setting unit 110c increases the number of nozzles simultaneously driven in the inkjet head 200 by one each time it executes the processing of steps S2 to S6 (ie, loop processing).

In step S2, the drive waveform setting unit 110c sets the slope (that is, the rise time and fall time) of the voltage waveform of the drive signal as the test signal.

When step S2 is executed for the first time, the rise time and fall time of the drive signal are set to zero (ie, a square wave). Then, the drive waveform setting unit 110c sets the rise time and fall time of the drive signal to values that gradually increase each time the processing of steps S3 to S4 (ie, loop processing) is executed. Note that at this time, the degree to which the rise time and fall time are increased is arbitrary, but the degree is set such that, for example, the slope of the waveform increases by one degree.

In step S3, the drive waveform setting section 110c causes the drive signal generation section 140 to output a drive signal having a voltage waveform having the rise time and fall time set in step S2.

In step S4, the drive waveform setting unit 110c causes the drive waveform detection unit 230 to detect the voltage waveform of the drive signal output in step S3, and sends a detection signal related to the voltage waveform of the drive signal to the drive waveform detection unit 230. Get from.

In step S5, the drive waveform setting unit 110c compares the voltage waveform detected by the drive waveform detection unit 230 with a reference voltage waveform (for example, a target voltage waveform) of the reference waveform data 120c stored in the storage unit 120 in advance. Then, it is determined whether the shapes of the two match. Here, if both shapes match (S5: YES), the drive waveform setting unit 110c advances the process to step S6. On the other hand, if the two shapes do not match (S5: NO), the drive waveform setting unit 110c returns to step S2, resets the slope of the voltage waveform (that is, the rise time and the fall time), and performs the same procedure. Execute the process.

In step S6, the drive waveform setting unit 110c associates a voltage waveform with a slope that matches the reference voltage waveform (for example, a target voltage waveform) with the number N of nozzles that are simultaneously driven in the inkjet head 200, and sets it as drive waveform data 120b. Store it in RAM etc.

In step S7, the drive waveform setting unit 110c determines whether the number N of nozzles driven simultaneously has reached the maximum number (256 in this case). Here, if the number N of nozzles driven simultaneously reaches the maximum number (S7: YES), the drive waveform setting unit 110c advances the process to step S8. On the other hand, if the number N of nozzles driven simultaneously has not reached the maximum number (S7: NO), the drive waveform setting unit 110c returns to step S1 and increases the number of nozzles driven simultaneously by one (N→ N+1), the processes of steps S2 to S6 are executed again.

In step S8, the drive waveform setting unit 110c stores in the storage unit 120 data in which the number of nozzles to be simultaneously driven in the inkjet head 200 generated in the series of processes of steps S1 to S7 is associated with the drive waveform data 120b. .

The drive waveform setting unit 110c optimizes the voltage waveform of the drive signal generated by the drive signal generation unit 140 through the above processing.

Note that the flowchart in FIG. 8 shows a mode in which the drive waveform data 120b is set for each different number of nozzles. However, the drive waveform data 120b may be set for each number of nozzles that differs in units of 10 or for each number of nozzles that differs in units of 100.

When executing printing, for example, when transferring one line of image data 120a to the line memory 130, the drive command unit 110b counts the number of nozzles that are simultaneously driven in the inkjet head 200, and determines the number of nozzles that are simultaneously driven in the inkjet head 200. The drive signal generator 140 is instructed to select the drive waveform data 120b corresponding to the number and generate the drive waveform data 120b.

However, more preferably, the drive command unit 110b determines in advance, based on the image data 120a to be printed, the number of nozzles to be simultaneously driven in the inkjet head 200 when printing each line of the image data 120a before printing. Keep it counted. This makes it possible to increase the calculation speed compared to a method in which the number of nozzles that are simultaneously driven is counted each time the ink is ejected. That is, this makes it possible to cope with the case where the ejection cycle of the inkjet head 200 is fast.

[effect]
As described above, in the image forming apparatus U according to the present embodiment, the drive waveform setting unit 110c uses the reference waveform data 120c stored in advance, and the voltage waveform of the drive signal detected by the drive waveform detection unit 230. Based on this, the waveform setting related to the rise time and/or fall time of the voltage waveform of the drive signal to be generated by the drive signal generation unit 140 is performed.

Therefore, according to the image forming apparatus U according to the present embodiment, the voltage waveform of the drive signal generated due to the resistance component and inductance component of the transmission path (in particular, the cable 300) connecting the main body 100 and the inkjet head 200 It is possible to optimally set the voltage waveform of the drive signal to be generated by the drive signal generation section 140, assuming the dullness of the curve. That is, this makes it possible to bring the voltage waveform supplied to the piezoelectric element of the inkjet head 200 closer to the target waveform (that is, the ideal waveform).

(Modification 1)
The drive waveform setting section 110c determines an appropriate voltage waveform of the drive signal through arithmetic processing based on the difference between the voltage waveform of the drive signal detected by the drive waveform detection section 230 and the reference voltage waveform of the reference waveform data 120c. A rise time and/or a fall time may be calculated.

In this case, for example, the difference between the voltage waveform of the drive signal detected by the drive waveform detection unit 230 and the reference voltage waveform of the reference waveform data 120c can be used to set an appropriate voltage waveform of the drive signal. It is desirable to obtain an appropriate correspondence relationship between the rise time and/or fall time of the voltage waveform of the drive signal in advance using experimental data.

As a result, it is possible to set an appropriate rise time and/or fall time of the voltage waveform of the drive signal from a single drive signal generated by the drive signal generation unit 140, thereby shortening the time for the calibration process. is possible.

Further, this also enables the drive waveform setting unit 110c to perform calibration processing of the drive waveform generated by the drive signal generation unit 140 in the image forming apparatus U during printing. During printing, the internal temperature of the image forming apparatus U increases, and the component characteristics of the drive signal generation unit 140 and the inkjet head 200 and the resistance value of the cable 300 change. Therefore, by executing the calibration process during printing, it may be possible to more appropriately set the rise time and/or fall time of the voltage waveform of the drive signal.

(Modification 2)
The drive waveform setting section 110c sets the voltage waveform of the drive signal to be generated by the drive signal generation section 140 based on the voltage waveform of the drive signal detected by the drive waveform detection section 230 and the reference voltage waveform of the reference waveform data 120c. A wave height value may also be set.

This makes it possible to set the voltage waveform of the drive signal generated by the drive signal generation section 140 in consideration of the attenuation of the drive signal due to the resistance component of the cable 300. Thereby, it is possible to bring the voltage waveform supplied to the piezoelectric element closer to the ideal waveform.

(Modification 3)
The drive waveform setting unit 110c may independently set the rise time and fall time of the voltage waveform of the drive signal.

In the above embodiment, the calibration process was described on the premise that the drive waveform setting unit 110c sets the rise time and fall time to be the same. However, the electrical characteristics (typically, capacitance characteristics) of a piezoelectric element differ during expansion (i.e., when the voltage waveform of the drive signal rises) and when it contracts (i.e., when the voltage waveform of the drive signal falls). And it often changes.

Therefore, the drive waveform setting unit 110c independently sets the rise time and fall time of the voltage waveform of the drive signal, taking such characteristics into consideration. This makes it possible to set both the rise time and fall time of the voltage waveform of the drive signal to optimal values, making it possible to bring the voltage waveform supplied to the piezoelectric element closer to the ideal waveform.

In this case, the drive waveform setting section 110c first causes the drive signal generation section 140 to sequentially generate a plurality of drive signals having different rise times, and at that time, the drive waveform detection section 230 detects the drive signal. A first calibration process is performed to set a waveform related to the rise time based on the comparison result between the voltage waveform and the reference voltage waveform. Then, the drive waveform setting section 110c causes the drive signal generation section 140 to sequentially generate a plurality of drive signals having mutually different fall times, and at this time, the voltage of the drive signal detected by the drive waveform detection section 230. A second calibration process is performed to set the waveform regarding the fall time based on the comparison result between the waveform and the reference voltage waveform.

(Modification 4)
The drive waveform detection section 230 may be configured with a voltage detection circuit (for example, a voltage dividing circuit) and a buffer circuit (for example, a source follower) instead of the A/D converter. That is, the detection signal related to the voltage waveform from the drive waveform detection section 230 to the main body 100 (control section 110) may be transmitted as an analog signal.

Even in such a configuration, if the drive waveform detection section 230 has a buffer circuit, it can be configured to output low impedance, so it is possible to suppress signal deterioration of the detection signal. This eliminates the need to provide an A/D converter within the inkjet head 200, making it possible to secure a component mounting area within the inkjet head 200.

(Second embodiment)
The image forming apparatus U according to the present embodiment is similar to the first embodiment in that it has a plurality of inkjet heads 200 and sets an appropriate voltage waveform of a drive signal for each of the plurality of inkjet heads 200. This is different from the image forming apparatus U.

FIG. 9 is a block diagram showing an example of the configuration of the image forming apparatus U according to the present embodiment.

The image forming apparatus U according to the present embodiment has first to fourth inkjet heads 200a, 200b, 200c, and 200d connected to the main body 100 by separate cables (first to fourth cables 300a, 300b, 300c, and 300d). have. The first to fourth inkjet heads 200a, 200b, 200c, and 200d are, for example, inkjet heads that eject ink of mutually different colors (for example, YMCK). The first to fourth inkjet heads 200a, 200b, 200c, and 200d each have the same configuration as the inkjet head 200 described in the above embodiment, and include nozzle rows 210a, 210b, 210c, 210d, drive control ICs 220a, 220b. , 220c, 220d, and drive waveform detection units 230a, 230b, 230c, and 230d.

Generally, in this type of image forming apparatus U, the distance between the main body 100 (ie, driver board) and the first to fourth inkjet heads 200a, 200b, 200c, and 200d differs for each inkjet head. In other words, the cable lengths of the first to fourth cables 300a, 300b, 300c, and 300d that connect the main body 100 and the first to fourth inkjet heads 200a, 200b, 200c, and 200d are different from each other. Therefore, the degree of blunting of the voltage waveform when the drive signal is sent from the main body 100 side to the first to fourth inkjet heads 200a, 200b, 200c, and 200d depends on the cable length of the cables 300a, 300b, 300c, and 300d. It will be different.

From this point of view, in the image forming apparatus U according to the present embodiment, the first to fourth drive signal generation units 140a, 140b, 140c, 140d, and first to fourth drive waveform setting sections 110ca, 110cb, 110cc, and 110cd are provided.

More specifically, the first drive signal generation unit 140a generates a drive signal to be sent to the first inkjet head 200a, and the second drive signal generation unit 140b generates a drive signal to be sent to the second inkjet head 200b. The third drive signal generation unit 140c generates a drive signal to be sent to the third inkjet head 200c, and the fourth drive signal generation unit 140d generates a drive signal to be sent to the fourth inkjet head 200d. Generate a signal.

That is, the operation of the first inkjet head 200a is controlled based on the image data 120a output from the first line memory 130a and the drive signal output from the first drive signal generation section 140a. The operation of the second inkjet head 200b is controlled based on the image data 120b output from the second line memory 130b and the drive signal output from the second drive signal generation section 140b. The operation of the third inkjet head 200c is controlled based on the image data 120c output from the third line memory 130c and the drive signal output from the third drive signal generation section 140c. The operation of the fourth inkjet head 200d is controlled based on the image data 120d output from the fourth line memory 130d and the drive signal output from the fourth drive signal generation section 140d.

The first drive waveform setting section 110ca is a first drive signal generation section based on the reference voltage waveform of the reference waveform data 120c and the voltage waveform of the drive signal detected by the drive waveform detection section 230a of the first inkjet head 200a. The rise time and/or fall time of the drive signal to be generated for 140a is set. The second drive waveform setting section 110cb generates a second drive signal generator based on the reference voltage waveform of the reference waveform data 120c and the voltage waveform of the drive signal detected by the drive waveform detection section 230b of the second inkjet head 200b. The rise time and/or fall time of the drive signal to be generated for 140b is set. The third drive waveform setting unit 110cc generates a third drive signal generator based on the reference voltage waveform of the reference waveform data 120c and the voltage waveform of the drive signal detected by the drive waveform detection unit 230c of the third inkjet head 200c. The rise time and/or fall time of the drive signal to be generated for 140c is set. The fourth drive waveform setting unit 110cd generates a fourth drive signal generator based on the reference voltage waveform of the reference waveform data 120c and the voltage waveform of the drive signal detected by the drive waveform detection unit 230d of the fourth inkjet head 200d. The rise time and/or fall time of the drive signal to be generated for 140d is set.

Although the image forming apparatus U according to this embodiment has four inkjet heads 200, the image forming apparatus U according to this embodiment can be applied to any number of inkjet heads 200. .

As described above, according to the image forming apparatus U according to the present embodiment, each cable 300 (300a, 300b, 300c, 300d) connects the main body 100 and the plurality of inkjet heads 200 (200a, 200b, 200c, 200d). ) It is possible to appropriately set the voltage waveform of the drive signal in consideration of the resistance component and inductance component in Thereby, it is possible to bring the voltage waveform supplied to each piezoelectric element of the plurality of inkjet heads 200 closer to the ideal waveform.

(Other embodiments)
The present invention is not limited to the above-described embodiments, and various modifications are possible.

In the above embodiment, as an example of the control unit 110, a mode is shown in which the control unit 110 is configured by a CPU, a ROM, a RAM, an input port, and an output port. However, the control unit 110 may be configured with a dedicated hardware circuit using a comparison circuit or the like instead of the CPU.

Further, in the above embodiment, a shear mode inkjet head is shown as an example of the inkjet head 100. However, the present invention can also be applied to types of inkjet heads other than shear mode inkjet heads, such as radial mode inkjet heads.

Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples illustrated above.

According to the image forming apparatus according to the present disclosure, it is possible to suppress deterioration in print quality due to blunting of the voltage waveform of the drive signal.

U Image forming apparatus 100 Main body 100R Transport mechanism 110 Control section 110a Transport control section 110b Drive command section 110c, 110ca, 110cb, 110cc, 110cd Drive waveform setting section 120 Storage section 120a Image data 120b Drive waveform data 120c Reference waveform data 130, 13 0a , 130b, 130c, 130d Line memory 140, 140a, 140b, 140c, 140d Drive signal generation section 200, 200a, 200b, 200c, 200d Inkjet head 210, 210a, 210b, 210c, 210d Nozzle row 220, 220a, 220b, 220 c. , 220d drive control IC
230, 230a, 230b, 230c, 230d Drive waveform detection section 300, 300a, 300b, 300c, 300d Cable

Claims (12)

An image forming apparatus having an inkjet head that performs an ink ejection operation by expanding or contracting a piezoelectric element,
a drive signal generation section that is disposed within the main body of the image forming apparatus and that generates a drive signal that forms a voltage waveform of a drive voltage that is supplied to the piezoelectric element;
a drive waveform detection section that is disposed within the inkjet head and detects a voltage waveform of the drive signal output from the main body side to the inkjet head via a cable;
The rise time and/or of the voltage waveform of the drive signal that is caused to be generated by the drive signal generation unit based on a pre-stored reference voltage waveform and the voltage waveform of the drive signal detected by the drive waveform detection unit. a drive waveform setting section that performs waveform settings related to fall time;
Equipped with
As a calibration process, the drive waveform setting section causes the drive signal generation section to sequentially generate a plurality of drive signals having different rise times and/or fall times,
At that time, the waveform setting is performed by comparing the degree of match between the voltage waveform of the drive signal detected by the drive waveform detection section and the reference voltage waveform;
Image forming device. having n (where n is a positive integer of 2 or more) inkjet heads connected to the main body via each separate cable;
The drive signal generation section, the drive waveform detection section, and the drive waveform setting section are provided in n pieces so as to correspond to each of the n inkjet heads, respectively.
The image forming apparatus according to claim 1. In the calibration process, the drive waveform setting section causes the drive signal generation section to sequentially generate a plurality of drive signals in which the rise time and/or fall time are sequentially increased or decreased.
The image forming apparatus according to claim 1 or 2 . The drive waveform setting section executes the calibration process when the image forming apparatus is started and/or when the inkjet head is replaced.
The image forming apparatus according to any one of claims 1 to 3 . The calibration process causes the drive signal generation unit to sequentially generate a plurality of drive signals having different rise times, and at that time, the voltage waveform of the drive signal detected by the drive waveform detection unit; a first calibration process that sets the waveform related to the rise time by comparing the degree of matching with the reference voltage waveform;
causing the drive signal generation unit to sequentially generate a plurality of drive signals having different fall times, and at that time, the voltage waveform of the drive signal detected by the drive waveform detection unit and the reference voltage waveform. a second calibration process for setting the waveform related to the fall time by comparing the matching degree of the second calibration process;
The image forming apparatus according to any one of claims 1 to 4 . The drive waveform setting section performs the waveform setting based on a difference between the voltage waveform of the drive signal detected by the drive waveform detection section and the reference voltage waveform.
The image forming apparatus according to any one of claims 1 to 5 . The drive waveform setting section performs the waveform setting based on the voltage waveform of the drive signal detected by the drive waveform detection section during printing in the image forming apparatus.
The image forming apparatus according to claim 6 . The driving waveform setting section performs the waveform setting for each number of nozzles that are simultaneously driven in the inkjet head.
The image forming apparatus according to any one of claims 1 to 7 . The drive waveform setting section temporally sequentially changes the number of nozzles simultaneously driven in the inkjet head, executes the calibration process for each number of nozzles, and performs the calibration process for each number of nozzles simultaneously driven in the inkjet head. performing the waveform settings;
The image forming apparatus according to any one of claims 1 to 5 . The waveform setting includes setting a voltage waveform related to a peak value of a voltage waveform of the drive signal generated by the drive signal generation unit.
The image forming apparatus according to any one of claims 1 to 9 . The drive waveform detection section includes an A/D converter.
The image forming apparatus according to any one of claims 1 to 10 . A method for controlling an image forming apparatus having an inkjet head that performs an ink ejection operation by expanding or contracting a piezoelectric element, the method comprising:
a step of generating a drive signal that is disposed within the main body of the image forming apparatus and forms a voltage waveform of a drive voltage that is supplied to the piezoelectric element;
detecting a voltage waveform of the drive signal disposed within the inkjet head and output from the main body side to the inkjet head via a cable;
Waveform settings related to the rise time and/or fall time of the voltage waveform of the drive signal to be generated based on a reference voltage waveform stored in advance and the voltage waveform of the drive signal detected on the inkjet head side. and the steps to
has
The step of generating the drive signal includes, as a calibration process, sequentially generating a plurality of the drive signals having different rise times and/or fall times,
The step of setting the waveform includes the step of setting the waveform by comparing the degree of match between the voltage waveform of the drive signal detected during the step of sequentially generating the drive signal and the reference voltage waveform.
A method for controlling an image forming apparatus.

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