Inkjet type image forming apparatus

Abstract

An image forming apparatus (1) comprises a recording head (20), a drive waveform generation unit (15) that generates a pulsed drive waveform to be supplied to a piezoelectric element (T), a reverberation waveform detection unit (17) that is branched from a line electrically connecting the drive waveform generation unit (15) and the piezoelectric element (T) and that detects a reverberation waveform from the piezoelectric element (T) that occurs after the supply of the drive waveform, and a control unit (11) that controls the operation of the reverberation waveform detection unit (17) and the drive waveform generation unit (15), the control unit (11) setting the drive waveform generation unit (15) to high-impedance output when detection of the reverberation waveform is performed by the reverberation waveform detection unit (17).

Description

Inkjet image forming device

[0001] The present disclosure relates to an inkjet image forming apparatus.

[0002] 2. Description of the Related Art Conventionally, inkjet image forming apparatuses have been known that use a recording head that uses a piezoelectric element to discharge ink droplets onto a recording medium, thereby forming an image on the recording medium.

[0003] In this type of image forming device, a technique is known in which the physical residual vibrations that occur in the pressure chamber of the print head after the supply of a drive waveform are converted into an electrical signal using the characteristics of a piezoelectric element (i.e., the piezoelectric effect), and observed as a reverberation waveform. Note that the drive waveform refers to a drive voltage whose waveform has been controlled to ensure smooth ink ejection from the print head (the same applies hereinafter).

[0004] This reverberation waveform exhibits characteristics corresponding to the state of the pressure chambers and nozzles (i.e., channels) of the print head. Therefore, by observing the reverberation waveform, it is possible to determine whether ink droplets are being ejected normally or abnormally from the nozzles of the print head, or to determine the cause of abnormal ejection, such as the presence of air bubbles or increased viscosity of the ink. In other words, by observing the reverberation waveform, it is possible to inspect the state of the nozzles and pressure chambers of the print head. Note that this type of inspection is hereinafter referred to as "nozzle inspection using reverberation waveforms."

[0005] FIG. 1 is a diagram showing an example of a reverberation waveform from a piezoelectric element that occurs due to residual vibration in a pressure chamber. In a recording head, a drive waveform is supplied to the piezoelectric element, causing the pressure chamber to compress and ink to be ejected from a nozzle that communicates with the pressure chamber. At this time, a damped residual vibration occurs in the pressure chamber. This residual vibration propagates to the piezoelectric element and is observed as a reverberation waveform. Therefore, the reverberation waveform appears as a damped vibration waveform that occurs after a drive waveform is supplied to the piezoelectric element.

[0006] For example, Patent Documents 1, 2 and 3 describe various methods for detecting the state of the nozzles and pressure chambers of a print head based on observed reverberation waveforms.

[0007] JP 2005-185942 A JP 2017-043087 A JP 2011-178152 A

[0008] Meanwhile, due to demands for cost reduction and the like, the inventors of the present application are considering constructing a circuit for observing reverberation waveforms within an image forming apparatus without making major changes to the existing apparatus configuration. However, if an attempt is made to observe the reverberation waveform by reusing the drive line without making any changes to the print head or cable, the reverberation waveform will be affected by the drive waveform generation circuit, making it impossible to accurately detect the state of the pressure chambers and nozzles of the print head. Note that the "drive line" refers to a line that supplies a drive waveform from the drive waveform generation circuit to the piezoelectric elements of the print head, and is a line that electrically connects the drive waveform generation circuit to the piezoelectric elements (the same applies hereinafter).

[0009] Given this background, conventional technologies employ a configuration in which a dedicated line separate from the reverberation measurement switching unit and drive line is provided in the printhead or device main body. However, adding a switching unit requires the use of a large, slow-switching relay to enable switching of the high-current, high-voltage output from the drive waveform generation circuit. This poses a problem: nozzle inspection using reverberation waveforms cannot be performed during printing. Another problem with a configuration that requires a dedicated line is that the increased wiring increases the printhead size. Another possible configuration is to incorporate a reverberation waveform observation function into the existing head IC, but implementing such a configuration requires a design change to the existing head IC.

[0010] Furthermore, if the nozzles of the recording head dry out, the ink in the pressure chamber thickens, or air bubbles get trapped in the pressure chamber, the nozzles become clogged and are unable to eject ink droplets. When this happens, dots are missing from the printed image, causing a deterioration in the image quality of the printed matter. Therefore, there is a demand for nozzle inspections using reverberation waveforms to be performed even during printing, so that nozzle clogs and other issues can be addressed as necessary.

[0011] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a more suitable inkjet image forming apparatus that can implement a reverberation waveform observation function without significantly modifying the existing apparatus configuration.

[0012] The present disclosure primarily solves the above-mentioned problems and is an inkjet image forming apparatus comprising: a recording head having a nozzle, a pressure chamber communicating with the nozzle and containing ink, and a piezoelectric element arranged to form part of the wall of the pressure chamber; a drive waveform generation unit that generates a pulsed drive waveform to be supplied to the piezoelectric element; a reverberation waveform detection unit that is arranged branching off from a line electrically connecting the drive waveform generation unit and the piezoelectric element and detects a reverberation waveform from the piezoelectric element that occurs after the drive waveform is supplied; and a control unit that controls the operation of the reverberation waveform detection unit and the drive waveform generation unit, wherein the control unit sets the drive waveform generation unit to high impedance output when the reverberation waveform detection unit detects the reverberation waveform.

[0013] According to the image forming apparatus according to the present disclosure, it is possible to implement a reverberation waveform observation function in a more suitable manner without making significant changes to the existing apparatus configuration.

[0014] FIG. 1 is a diagram showing an example of a reverberation waveform generated from a piezoelectric element due to residual vibration in a pressure chamber. FIG. 2 is a block diagram showing an example of the configuration of an image forming apparatus. FIG. 3 is a diagram showing the external appearance of an image forming apparatus. FIG. 4A is a diagram showing an example of the configuration of a printhead (normal state). FIG. 4B is a diagram showing an example of the configuration of a printhead (pressure chamber expanded state). FIG. 5 is a schematic diagram showing a circuit configuration for detecting a reverberation waveform in an image forming apparatus. FIG. 6 is a diagram showing the configuration of an output stage of a drive waveform generating unit. FIG. 7A is a diagram showing an operating mode of the drive waveform generating unit (PUSH mode). FIG. 7B is a diagram showing an operating mode of the drive waveform generating unit (PULL mode). FIG. 7C is a diagram showing an operating mode of the drive waveform generating unit (Hi-Z mode). FIG. 8 is a circuit configuration for detecting a reverberation waveform in an image forming apparatus according to the prior art. FIG. 9 is a circuit configuration for detecting a reverberation waveform in an image forming apparatus according to the prior art. Fig. 10 is a diagram illustrating a period during which a drive waveform is applied to a piezoelectric element and a period during which a reverberation waveform is generated from the piezoelectric element. Fig. 11 is a diagram illustrating changes in the state of a pressure chamber when a drive waveform is supplied to a piezoelectric element. Fig. 12 is a flowchart showing an example of the operation of a control unit related to nozzle inspection using a reverberation waveform. Fig. 13 is a diagram schematically showing a circuit configuration for detecting a reverberation waveform in an image forming apparatus according to Modification 1. Fig. 14 is a diagram schematically showing a circuit configuration for detecting a reverberation waveform in an image forming apparatus according to Modification 2. Fig. 15 is a diagram schematically showing a circuit configuration for detecting a reverberation waveform in an image forming apparatus according to Modification 3.

[0015] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functions are designated by the same reference numerals, and redundant description will be omitted.

[0016] [Overall Configuration of Image Forming Apparatus] An example of the overall configuration of an inkjet type image forming apparatus 1 according to one embodiment of the present invention will be described below, which will be abbreviated as "image forming apparatus 1" hereinafter.

[0017] Fig. 2 is a block diagram showing an example of the configuration of the image forming apparatus 1. Fig. 3 is a diagram showing the external appearance of the image forming apparatus 1.

[0018] The image forming apparatus 1 includes an apparatus main body 10 and recording heads 20Y, 20M, 20C, and 20K corresponding to the colors yellow, magenta, cyan, and black, respectively.

[0019] The recording heads 20Y, 20M, 20C, and 20K are respectively equipped with head ICs 21Y, 21M, 21C, and 21K and head bodies 22Y, 22M, 22C, and 22K. In the following description, the recording heads 20Y, 20M, 20C, and 20K are assumed to have the same configuration and will be simply referred to as the "recording head 20," the "head IC 21," and the "head body 22."

[0020] The device main body 10 and the recording head 20 are connected by, for example, a cable L. The cable L is, for example, an FPC (Flexible Printed Circuit).

[0021] In the image forming apparatus 1, the apparatus main body 10 uses a transport roller to transport the recording medium P. While transporting the recording medium P, the apparatus main body 10 ejects ink droplets from a recording head 20 disposed opposite the recording medium P, thereby forming a desired image on the recording medium P.

[0022] The device main body 10 includes a control unit 11 , an interface 12 , a page memory 13 , a line memory 14 , a drive waveform generation unit 15 , a common voltage supply unit 16 , and a reverberation waveform detection unit 17 .

[0023] The control unit 11 is a microcomputer including, for example, a CPU, a ROM, and a RAM. In the control unit 11, the CPU loads a program stored in the ROM into the RAM and controls the operation of each part of the image forming apparatus 1 in accordance with the program.

[0024] The control unit 11 outputs, for example, a control signal to the head IC 21 to instruct the channel from which ink is to be ejected, and controls switching of a switching circuit (see FIG. 5) provided in the head IC 21. The control unit 11 also outputs, for example, a control signal to the drive waveform generation unit 15, and performs waveform control of the drive waveform generated by the drive waveform generation unit 15. The control unit 11 also outputs, for example, a control signal to the reverberation waveform detection unit 17, and causes the reverberation waveform detection unit 17 to detect a reverberation waveform at a desired timing.

[0025] The interface 12 is a means for transmitting and receiving data to and from an external device M such as a personal computer.

[0026] The page memory 13 stores image data to be printed that is transmitted from the external device M. When printing an image on a recording medium, the line memory 14 temporarily stores pixel data to be ejected from each nozzle of the head main body 22, out of the image data stored in the page memory 13. The line memory 14 then sequentially transfers the stored pixel data to the head IC 21.

[0027] The drive waveform generation unit 15 generates a drive waveform and supplies the drive waveform to the recording head 20. The head IC 21 selects an output destination for the drive waveform supplied to the recording head 20, and the drive waveform is supplied to the piezoelectric element of the channel in the head body 22 from which ink is to be ejected. The drive waveform generation unit 15 is configured, for example, by a DA conversion circuit. Under the control of the control unit 11, the drive waveform generation unit 15 generates a drive waveform of a predetermined voltage waveform.

[0028] The drive waveform generated by the drive waveform generating unit 15 is, for example, a pulse waveform, the rise time, fall time, pulse width, and peak value of which are appropriately set according to the characteristics of the recording head 20.

[0029] The common voltage supply unit 16 generates a common voltage and supplies the common voltage to the recording head 20. The common voltage supplied to the recording head 20 has its output destination selected, for example, by the head IC 21, and is supplied to the piezoelectric elements of the non-ejection channels of the head main body 22. The common voltage supply unit 16 is configured, for example, by a constant voltage circuit. Note that the function of the common voltage supply unit 16 may also be performed by the drive waveform generation unit 15.

[0030] The reverberation waveform detection unit 17 detects the physical residual vibrations that occur in the pressure chamber of the recording head 20 after the drive waveform is supplied as a reverberation waveform from the piezoelectric element of the recording head 20. The reverberation waveform detection unit 17 is configured, for example, by an AD conversion circuit etc. For example, the reverberation waveform detection unit 17 converts the current associated with the reverberation waveform that is generated from the piezoelectric element as a result of the residual vibration into a voltage, smooths it using a low-pass filter, and performs AD conversion.

[0031] The reverberation waveform detector 17 may be configured using analog circuits such as a comparison circuit and a waveform shaping circuit.

[0032] [Configuration of Head Main Body] Figures 4A and 4B are diagrams showing an example of the configuration of the recording head 20. Here, Figures 4A and 4B are cross-sectional views of the head main body 22 viewed from the top side. Note that Figure 4A shows the state of the pressure chamber Td when no drive waveform is applied to the piezoelectric element T (normal state). Also, Figure 4B shows the state of the pressure chamber Td when a drive waveform is applied to the piezoelectric element T (pressure chamber expanded state).

[0033] The head main body 22 has, for example, a plurality of channels Tc each of which ejects ink. Figures 4A and 4B show three channels Tc, Tc_ch1 to Tc_ch3.

[0034] Each channel Tc is formed, for example, by a nozzle Te, a pressure chamber Td communicating with the nozzle Te and containing ink, and a piezoelectric element T arranged to form part of the wall of the pressure chamber Td. The piezoelectric element T is formed by a piezoelectric member Tf and a first electrode Tg and a second electrode Th sandwiching the piezoelectric member Tf from the left and right. When the potential difference between the first electrode Tg and the second electrode Th changes, the piezoelectric element T changes state, for example, as shown in FIG. 4B . The first electrode Tg is an electrode separated for each piezoelectric member Tf and serves as a drive electrode for each piezoelectric member Tf. The second electrode Th serves as a common electrode shared by all piezoelectric members Tf. The common electrode is, for example, grounded.

[0035] The recording head 20 changes the contracted state and expanded state of each piezoelectric element T using a drive waveform input from the drive waveform generating unit 15. That is, in a first mode (for example, a PUSH mode described later), the recording head 20 contracts the piezoelectric element T and expands the pressure chamber Td to reduce the pressure inside the pressure chamber Td, thereby supplying ink from a supply path (not shown) into the pressure chamber Td, as shown in FIG. 4B. In a second mode (for example, a PULL mode described later), the recording head 20 returns the piezoelectric element T from the contracted state to its original state, as shown in FIG. 4A, and contracts the pressure chamber Td to pressurize the pressure chamber Td, thereby ejecting ink from the nozzle Te. See FIG. 11 described later.

[0036] [Circuit Configuration for Detecting Reverberation Waveform] Fig. 5 is a diagram schematically showing the circuit configuration for detecting reverberation waveforms of the image forming apparatus 1. Fig. 6 is a diagram showing the configuration of the output stage of the drive waveform generation unit 15. Figs. 7A, 7B, and 7C are diagrams showing the operation modes of the drive waveform generation unit 15.

[0037] In the image forming apparatus 1 according to this embodiment, the piezoelectric element T in the recording head 20 is connected to the drive waveform generating unit 15, the common voltage supplying unit 16, and the reverberation waveform detecting unit 17 via lines L1 and L2. Specifically, the drive waveform generating unit 15 and the reverberation waveform detecting unit 17 are connected to the first electrode Tg of the piezoelectric element T via line L1. The common voltage supplying unit 16 is connected to the first electrode Tg of the piezoelectric element T via line L2. The second electrode Th of the piezoelectric element T is connected to a reference potential (ground in this case). Hereinafter, the line L1 will also be referred to as the "drive line L1." The line L2 will also be referred to as the "common voltage supply line L2."

[0038] A head IC 21 in the recording head 20 is provided with a switch 21a and a switch 21b. The switch 21a is provided in the drive line L1 and switches the connection state between the piezoelectric element T and the drive waveform generating unit 15. The switch 21b is provided in the common voltage supply line L2 and switches the connection state between the piezoelectric element T and the common voltage supply unit 16.

[0039] 5, a plurality of piezoelectric elements T are arranged within the recording head 20, and common lines L1 and L2 are connected to each of the piezoelectric elements T. The head IC 21 is provided with individual switches 21a for switching the connection state between each of the plurality of piezoelectric elements T and the drive waveform generating unit 15. The head IC 21 is also provided with individual switches 21b for switching the connection state between each of the plurality of piezoelectric elements T and the common voltage supply unit 16.

[0040] That is, the output destination of the drive waveform supplied from the drive waveform generation unit 15 is selected by the switch 21a of the head IC 21, and the drive waveform is supplied to the piezoelectric element T of the channel Tc from which ink is to be ejected in the head main body 22. Also, the output destination of the common voltage supplied from the common voltage supply unit 16 is selected by the switch 21b of the head IC 21, and the common voltage is supplied to the piezoelectric element T of the non-ejecting channel Tc of the head main body 22. With this configuration, the connection state between the piezoelectric element T of each channel Tc and the lines L1 and L2 can be switched on and off separately.

[0041] The switches 21a and 21b provided for each of the plurality of piezoelectric elements T are not shown in Fig. 5. For an example of such a configuration, see Fig. 13 described later.

[0042] When observing a reverberation waveform, the switch 21b is basically in an open state, and the piezoelectric element T is electrically disconnected from the common voltage supply unit 16. Therefore, in the following description of reverberation waveform observation, the common voltage supply unit 16 is assumed to be electrically disconnected from the piezoelectric element T, and a description thereof will be omitted.

[0043] The drive waveform generating unit 15 is a circuit that generates a drive waveform to be supplied to the piezoelectric element T. As described above, the drive waveform generating unit 15 is configured by, for example, a DA conversion circuit. Then, under the control of the control unit 11, the drive waveform generating unit 15 generates a drive waveform that depicts a predetermined voltage waveform. Then, the drive waveform generating unit 15 sends the generated drive waveform to the piezoelectric element T via line L1.

[0044] The drive waveform generating unit 15 also has, for example, a switching element drive circuit 15b and a push-pull circuit 15c at its output stage. The switching element drive circuit 15b generates a switching signal corresponding to a drive waveform generated by a DA conversion circuit or the like inside the drive waveform generating unit 15. The push-pull circuit 15c operates based on the switching signal input from the switching element drive circuit 15b. That is, the push-pull circuit 15c performs power amplification of the drive waveform generated by the DA conversion circuit or the like inside the drive waveform generating unit 15.

[0045] The push-pull circuit 15c is configured by, for example, two switching elements, a high-side switch 15ca and a low-side switch 15cb.

[0046] The high-side switch 15ca is, for example, an NPN transistor whose collector terminal is connected to a power supply of voltage +VCC and whose emitter terminal is connected to one end of the line L1, while the low-side switch 15cb is, for example, a PNP transistor whose collector terminal is grounded and whose emitter terminal is connected to one end of the line L1.

[0047] The high-side switch 15ca and the low-side switch 15cb are not limited to bipolar transistors, and may be configured with transistors such as MOS-FETs, etc. The push-pull circuit 15c may be configured with two or more transistors.

[0048] A switching signal corresponding to a drive waveform is input from the switching element drive circuit 15b to the base terminal of the high-side switch 15ca and the base terminal of the low-side switch 15cb.

[0049] The switching element drive circuit 15b operates the push-pull circuit 15c in, for example, one of a PUSH mode, a PULL mode, and a Hi-Z mode.

[0050] In the PUSH mode, the switching element drive circuit 15b turns on the high-side switch 15ca and turns off the low-side switch 15cb, causing the drive waveform generation unit 15 to supply a drive waveform to the piezoelectric element T (see FIG. 7A).

[0051] In the PULL mode, the switching element drive circuit 15b turns off the high-side switch 15ca and turns on the low-side switch 15cb, causing the drive waveform generator 15 to supply a ground voltage to the piezoelectric element T (see FIG. 7B). The ground voltage here corresponds to the reference voltage of the present invention.

[0052] In this embodiment, for ease of understanding, the switching element drive circuit 15b selectively uses the push mode and the pull mode. However, in practice, it is preferable that the pulse-shaped drive waveform be a slope-shaped waveform with a predetermined rise time and fall time. In this case, the pulse-shaped drive waveform is formed by operating in both the push mode and the pull mode.

[0053] In the Hi-Z mode, the switching element drive circuit 15b turns off the high-side switch 15ca and the low-side switch 15cb, causing the drive waveform generator 15 to set the push-pull circuit 15c to a high-impedance output (see FIG. 7C).

[0054] The switching element drive circuit 15b operates the push-pull circuit 15c to alternately switch between the PUSH mode and the PULL mode over time when ink is ejected from the channel Tc of the recording head 20. On the other hand, the switching element drive circuit 15b operates the push-pull circuit 15c in the Hi-Z mode when the reverberation waveform detection unit 17 detects a reverberation waveform.

[0055] The control unit 11 inputs a mode switching signal to the switching element drive circuit 15b for use in observing reverberation waveforms. The switching element drive circuit 15b can change the operating mode of the push-pull circuit 15c at any timing in response to the mode switching signal. That is, the switching element drive circuit 15b is configured to be able to switch the push-pull circuit 15c to a high-impedance output at any timing.

[0056] The reverberation waveform detector 17 is disposed at a position branching off from the drive line L1 and detects, as a reverberation waveform, a change in the electromotive force of the piezoelectric element T that accompanies residual vibrations in the pressure chamber Td that occur after the drive waveform is supplied.

[0057] In this embodiment, the reverberation waveform detector 17 is disposed in the device main body 10. The reverberation waveform detector 17 detects the reverberation waveform output from the piezoelectric element T in the recording head 20 via the drive line L1.

[0058] Note that no switching circuit is provided at the position in the drive line L1 where it branches off to the reverberation waveform detection unit 17. In the image forming apparatus 1 according to this embodiment, when the reverberation waveform detection unit 17 detects a reverberation waveform, the drive waveform generation unit 15 is set to high impedance output. This makes it possible to suppress the electrical influence of the drive waveform generation unit 15 on the reverberation waveform detection unit 17 without electrically shutting it off with a switching circuit.

[0059] For comparison, two examples of circuit configurations for detecting reverberation waveforms in image forming apparatuses according to the prior art will be given with reference to FIGS.

[0060] 8, components similar to those of the image forming apparatus 1 according to the present embodiment are denoted by a "Q" next to the reference numerals of the components. Also, in FIG. 9, components similar to those of the image forming apparatus 1 according to the present embodiment are denoted by a "R" next to the reference numerals of the components. Detailed descriptions of components similar to those of the image forming apparatus 1 according to the above-described embodiment will be omitted here, but the same names will be used for the sake of convenience.

[0061] 8 is a circuit diagram showing a circuit for acquiring a reverberation waveform by providing a switching unit Q18 in a device main body Q10 of an image forming device Q1. For an example of this circuit diagram, see, for example, Japanese Patent Application Laid-Open No. 2003-222999.

[0062] In the circuit of Fig. 8, a line for applying a drive waveform from the drive waveform generator Q15 to the piezoelectric element QT and a line for acquiring a reverberation waveform from the piezoelectric element QT are shared. This shared line is represented by line QL1 in the circuit of Fig. 8. This configuration is the same as the circuit configuration of the image forming apparatus 1 according to the above embodiment.

[0063] However, this circuit includes a switching unit Q18 provided along the line QL1. The switching unit Q18 can be used to switch between connecting the piezoelectric element QT to the drive waveform generator Q15 or the reverberation waveform detector Q17. That is, when a drive waveform is supplied to the piezoelectric element QT, the switching unit Q18 closes the connection between the piezoelectric element QT and the drive waveform generator Q15 and opens the connection between the piezoelectric element QT and the reverberation waveform detector Q17. Furthermore, when a reverberation waveform is acquired from the piezoelectric element QT, the switching unit Q18 opens the connection between the piezoelectric element QT and the drive waveform generator Q15 and closes the connection between the piezoelectric element QT and the reverberation waveform detector Q17.

[0064] That is, in this circuit, by providing a dedicated switching section Q18 on the device main body Q10 side, it is possible to observe the reverberation waveform without changing the configuration of the recording head Q20.

[0065] However, this circuit configuration requires a switching unit Q18 to switch the output destination from the drive waveform generation unit Q15, which is subject to high current and high voltage. Therefore, an analog switch or a mechanical relay is required as the switching unit Q18. Mechanical relays have a problem with slow switching speed. Therefore, the circuit configuration of FIG. 8 makes it impossible to observe the reverberation waveform during printing, requiring printing to be stopped for inspection. Furthermore, while analog switches have a relatively fast switching speed, placing an analog switch in the drive line QL1 prevents a large current from flowing through the drive line QL1. That is, during printing, a large current must flow through the drive line QL1 to drive the multiple nozzles of the print head Q20, and such a large current may exceed the power resistance of the analog switch.

[0066] 9 is a circuit diagram in which a dedicated switching unit R21c is provided in the head ICR21 of the recording head R20 of the image forming apparatus R1, and a dedicated cable RL3 is provided between the apparatus main body R10 and the recording head R20. For an example of this circuit diagram, see, for example, Japanese Patent Application Laid-Open No. 2003-222999.

[0067] In the circuit of FIG. 9, by adding a dedicated switching unit R21c and a dedicated line RL3 for each piezoelectric element T, it is possible to observe the reverberation waveform without being affected by the drive waveform generating unit R15.

[0068] The dedicated switching unit R21c is provided for each piezoelectric element T, and can be realized by a small, high-speed switch such as a transistor. In other words, by adopting such a circuit configuration, it becomes possible to detect reverberation during printing.

[0069] However, the circuit configuration of Fig. 9 requires changes to both the printhead and the cable from the existing image forming apparatus, and there is also the problem that changing the head IC in particular requires high development costs.

[0070] Here, the circuit configuration of the image forming apparatus 1 according to this embodiment shown in FIG. 5 will be explained again.

[0071] 8, the circuit of the image forming apparatus 1 according to this embodiment does not include a switching unit Q18 at the position in the line L1 where the line L1 branches off to the reverberation waveform detection unit 17. Also, the circuit of the image forming apparatus 1 according to this embodiment does not include a dedicated switching unit R21c and a dedicated line RL3 in the recording head 20, unlike the circuit of FIG.

[0072] Therefore, in the image forming apparatus 1 according to this embodiment, when observing the reverberation waveform, it is necessary to electrically separate the drive waveform generating section 15 from the reverberation waveform detecting section 17 .

[0073] From this perspective, in the image forming apparatus 1 according to this embodiment, when observing a reverberation waveform, the drive waveform generation unit 15 is controlled to output a high impedance, which enables the reverberation waveform detection unit 17 to detect a reverberation waveform with high accuracy without being affected by the drive waveform generation unit 15.

[0074] Furthermore, in the image forming apparatus 1 according to this embodiment, high-speed control is possible because the drive waveform generating unit 15 can be electrically disconnected from the reverberation waveform detecting unit 17 simply by controlling the operation mode of the push-pull circuit 15c of the drive waveform generating unit 15. That is, in the image forming apparatus 1 according to this embodiment, it is possible to smoothly inspect the nozzles Te for clogging and the like using the reverberation waveform even during printing.

[0075] Data relating to the reverberation waveform detected by the reverberation waveform detector 17 is output to the controller 11. The controller 11 then determines the state of the nozzle Te.

[0076] The method by which the control unit 11 determines the state of the nozzle Te based on the waveform information of the reverberation waveform is similar to a conventionally known method, and therefore a description thereof will be omitted here. For example, see Patent Documents 1, 2, and 3.

[0077] 10 is a timing chart illustrating the operation of each part when observing a reverberation waveform, and FIG. 11 is a diagram illustrating the state change of the pressure chamber Td when a drive waveform is supplied to the piezoelectric element T.

[0078] 10, each chart represents the following: "Drive waveform": the drive waveform supplied from the drive waveform generating unit 15 to the piezoelectric element T. "Hi-Z mode switching signal": the timing at which the drive waveform generating unit 15 is set to high impedance output. "Reverberation waveform": the reverberation waveform generated from the piezoelectric element T.

[0079] In this embodiment, the period during which the PUSH waveform is applied to the piezoelectric element T is a pressure chamber expansion period during which the piezoelectric element T expands and the pressure chamber Td is depressurized. See FIG. 4B. At this time, ink is supplied from the supply path into the pressure chamber Td. Also, the period during which the PULL waveform is applied to the piezoelectric element T is a pressure chamber contraction period during which the piezoelectric element T contracts and the pressure chamber Td is contracted and pressurized. See FIG. 4A. At this time, ink is ejected from the nozzle Te.

[0080] That is, in this embodiment, ink is ejected when the mode is changed from PUSH mode to PULL mode. However, it is also possible to eject ink by changing the mode in the opposite direction, and this mode differs depending on the type of head, the type of ink, and the method of use.

[0081] When observing the reverberation waveform, the drive waveform generating unit 15 is controlled to have a high impedance output. As a result, the drive waveform is not input to the piezoelectric element T, and the piezoelectric element T is in a floating state. Therefore, after ink is ejected, residual vibrations generated within the pressure chamber Td are transmitted to the piezoelectric element T, inducing a reverberation waveform in the piezoelectric element T. This reverberation waveform is then detected by the reverberation waveform detecting unit 17 via line L1.

[0082] In this way, the state of the ink in the nozzle Te and the pressure chamber Td can be grasped from the reverberation waveform detected by the reverberation waveform detection unit 17.

[0083] Here, the control operation by the control unit 11 when observing a reverberation waveform will be described with reference to FIG.

[0084] The "first measurement operation pattern" and "second measurement operation pattern" shown at the bottom of Fig. 10 each represent an operation pattern of the drive waveform generation unit 15 when observing a reverberation waveform. Note that "normal driving" indicates a part of the operation of the drive waveform generation unit 15 during normal driving before observing a reverberation waveform. Normal driving is the timing when the piezoelectric element T is driven, for example, during printing, flushing operation, maintenance operation, etc.

[0085] The image forming apparatus 1 according to this embodiment is configured to observe the reverberation waveform during normal operation (for example, printing). Such control is performed under the control of the control unit 11.

[0086] In this embodiment, as described above, the recording head 20 ejects ink when the operation mode of the drive waveform generation unit 15 transitions from the push mode to the pull mode. That is, during printing, the drive waveform generation unit 15 operates the push-pull circuit 15c so as to alternately switch between the push mode and the pull mode over time.

[0087] However, there are times during printing when ink is not ejected (for example, when turning a page). At these times, the control unit 11 causes the drive waveform generation unit 15 to execute the first measurement operation pattern and / or the second measurement operation pattern. This makes it possible to appropriately inspect the nozzles Te for clogs, etc., without stopping the printing operation.

[0088] Here, the "first measurement operation pattern" is an operation pattern for observing a reverberation waveform that occurs when ink is ejected from the nozzle Te by transitioning from PUSH mode to PULL mode. In other words, the first measurement operation pattern is an operation pattern for detecting a reverberation waveform that occurs after the pulse-like drive waveform supplied from the drive waveform generation unit 15 to the piezoelectric element T falls. In the first measurement operation pattern, the control unit 11 changes the operation mode of the drive waveform generation unit 15 in the order of PULL mode, PULL mode, and Hi-Z mode. Then, the control unit 11 causes the reverberation waveform detection unit 17 to start detecting a reverberation waveform in synchronization with the timing at which the operation mode of the drive waveform generation unit 15 is switched from PULL mode to Hi-Z mode.

[0089] This makes it possible to effectively observe the residual vibration occurring in the pressure chamber Td immediately after ink is ejected from the nozzle Te.

[0090] In particular, it is possible to effectively observe residual vibrations occurring within the pressure chambers Td by appropriately setting the timing for switching from PULL mode to Hi-Z mode according to the type or characteristics of the recording head 20. Normally, the timing at which the peak voltage of the reverberation waveform is observed varies depending on the type of recording head 20 (i.e., the shape of the piezoelectric element T or the pressure chambers Td). From this perspective, the control unit 11 can arbitrarily change the timing at which the drive waveform generation unit 15 is set to high impedance, so that the timing for acquiring the reverberation waveform can be arbitrarily advanced or delayed.

[0091] 10 shows an embodiment in which the drive waveform supplied to the piezoelectric element T for inspection is generated separately from the drive waveform supplied to the piezoelectric element T for printing. However, the drive waveform generated for inspection and the drive waveform generated for printing may be the same waveform. This makes it possible to directly inspect the behavior of the channel during printing.

[0092] In this case, the first measurement operation pattern is preferably set to overlap with a normal drive period (e.g., a printing period). That is, the control unit 11 may treat the drive waveform (PUSH mode) supplied to the piezoelectric element T during the normal drive period as the test drive waveform. In this case, the control unit 11 switches the operation of the drive waveform generation unit 15 from PULL mode to Hi-Z mode at an appropriate timing, for example, after the falling edge of the drive waveform supplied to the piezoelectric element T for printing. That is, after switching from PULL mode to PULL mode for printing operation, the control unit 11 immediately switches from PULL mode to Hi-Z mode. Then, the control unit 11 causes the reverberation waveform detection unit 17 to detect the reverberation waveform generated by the piezoelectric element T in accordance with the timing at which the drive waveform generation unit 15 is switched to Hi-Z mode.

[0093] In this embodiment, a second measurement operation pattern is provided after the first measurement operation pattern in order to inspect the behavior of the channel Tc of the print head 20 in more detail or from another perspective. However, the second measurement operation pattern is not necessarily required.

[0094] The "second measurement operation pattern" is an operation pattern for detecting a reverberation waveform that occurs immediately after the rise of the pulse-like drive waveform supplied from the drive waveform generating unit 15 to the piezoelectric element T. In other words, the second measurement operation pattern is an operation pattern for checking the behavior inside the pressure chamber Td when the pressure chamber Td is simply expanded.

[0095] In the second measurement operation pattern, measurement can be performed even if a PUSH pulse with the same voltage amplitude as that during ink ejection is applied to the piezoelectric element T. In other words, the second measurement operation pattern allows measurement without ejecting ink from the recording head 20, even if the drive waveform generation unit 15 can supply only one type of drive waveform for ejection. From this perspective, the second measurement operation pattern is preferably used when printing on long paper, for example. Furthermore, in the second measurement operation pattern, there is no need to wait for the falling timing of PUSH, thereby shortening the measurement time.

[0096] In the second measurement operation pattern, when detecting a reverberation waveform, the control unit 11 controls the operation of the drive waveform generation unit 15 so that the mode is switched to PUSH mode and then immediately switched to Hi-Z mode. This makes it possible, in the second measurement operation pattern, to observe the reverberation waveform that occurs at the rising timing immediately after transitioning from PULL mode to PUSH mode.

[0097] The control unit 11 may be capable of switching between a mode in which the nozzle test is performed using the first measurement operation pattern and a mode in which the nozzle test is performed using the second measurement operation pattern, depending on the printing target (plain paper, long paper, etc.), for example.

[0098] In this way, the control unit 11 controls the operation of the drive waveform generation unit 15 and the reverberation waveform detection unit 17 to observe the reverberation waveform during printing, and performs checks for clogging of the nozzles Te of the recording head 20. After performing such control, the control unit 11 resumes normal drive operation. Note that this series of operations can be achieved essentially by simply switching the mode of the drive waveform generation unit 15, and can be performed in a short time without stopping the normal drive operation (e.g., printing).

[0099] 12 is a flowchart showing an example of the operation of the control unit 11 related to nozzle testing using reverberation waveforms. The processes in this flowchart are executed sequentially by the control unit 11 in accordance with a computer program when starting printing, for example.

[0100] In step S1, the control unit 11 acquires specification information of the print head 20, such as type information and performance information of the print head 20 that has been initially set.

[0101] In step S2, the control unit 11 sets the timing for performing the nozzle inspection based on the specification information of the print head 20.

[0102] Here, the control unit 11 sets the timing for performing the nozzle test based on, for example, the number of printed sheets. The timing for performing the nozzle test may be determined, for example, by determining whether the number of printed sheets since the previous nozzle test exceeds a threshold. However, the timing for performing the nozzle test may also be determined based on the number of ink ejections or the elapsed time since the previous nozzle test.

[0103] At this time, the control unit 11 may set the timing of switching from PULL mode to Hi-Z mode in the first measurement operation pattern based on the type information of the print head 20. At this time, the control unit 11 may set the timing of switching from PUSH mode to Hi-Z mode in the second measurement operation pattern based on the type information of the print head 20.

[0104] At this time, the control unit 11 may also set the nozzles to be inspected (for example, representative nozzles) from among the nozzle groups included in the print head 20 .

[0105] In step S3, the control unit 11 sets image data to be printed, and also sets waveform data of the drive waveform to be generated by the drive waveform generating unit 15 for use during printing.

[0106] In step S4, the control unit 11 determines whether or not it is currently the timing to perform a nozzle inspection. If it is currently the timing to perform a nozzle inspection (S4: YES), the control unit 11 proceeds to step S5. On the other hand, if it is not currently the timing to perform a nozzle inspection (S4: NO), the control unit 11 proceeds to step S10. In step S4, the control unit 11 determines whether or not it is currently the timing to perform a nozzle inspection, in accordance with the criteria for the timing to perform the nozzle inspection set in step S2.

[0107] In step S5, the control unit 11 causes the drive waveform generation unit 15 to perform an operation related to the first measurement operation pattern or the second measurement operation pattern in order to carry out the nozzle inspection. That is, in step S5, the control unit 11 causes the drive waveform generation unit 15 to execute the PUSH mode and the PULL mode in sequence.

[0108] In step S6, the control unit 11 switches the operation of the drive waveform generation unit 15 from PULL mode to Hi-Z mode at an appropriate timing, and in response, the control unit 11 causes the reverberation waveform detection unit 17 to start detecting a reverberation waveform.

[0109] In step S7, the control unit 11 acquires information relating to the reverberation waveform from the reverberation waveform detection unit 17, and detects the state of the nozzles Te of the recording head 20 based on this information.

[0110] In step S8, the control unit 11 determines whether the state of the nozzle Te detected in step S7 is abnormal. The method by which the control unit 11 determines the state of the nozzle Te based on the reverberation waveform is the same as a known method (see, for example, Patent Documents 1, 2, and 3).

[0111] In step S8, if the control unit 11 determines that the nozzle Te is in an abnormal state (S8: YES), the process proceeds to S9. On the other hand, if the control unit 11 determines that the nozzle Te is in an normal state (S8: NO), the process proceeds to S10.

[0112] In step S9, the control unit 11 performs a recovery process for the nozzle Te. The control unit 11 clears the clogged nozzle Te, for example, by a flushing operation. In the flushing operation, the control unit 11 applies, for example, a drive waveform that is larger than a normal drive waveform to the piezoelectric element T. This operation allows dried ink to be expelled from the nozzle Te. This recovery operation can be performed immediately even during printing.

[0113] At this time, the control unit 11 may set the clogged nozzle Te as an unused nozzle instead of performing recovery processing on the nozzle Te. In this case, the control unit 11 corrects the job data so that other nozzles adjacent to the unused nozzle compensate for the ink ejection from the unused nozzle. At this time, the control unit 11 may also perform a wiping process on the nozzle Te using a cleaning device (not shown) provided in the image forming apparatus 1.

[0114] In step S10, the control unit 11 executes (i.e., continues) printing. In step S10, the control unit 11 proceeds to the next step S11 while printing continues, for example, in accordance with the standard for nozzle inspection timing. For example, the control unit 11 proceeds to the next step S11 each time printing of one page is completed.

[0115] In step S11, the control unit 11 determines whether printing has finished. If printing has finished (S11: YES), the control unit 11 ends the series of processes in the flowchart. On the other hand, if printing has not finished (S11: NO), the control unit 11 returns to S4 and determines again whether the current time is the timing for inspection.

[0116] Through the above-described series of steps, the control unit 11 performs the printing process while inspecting the nozzles Te of the recording head 20 for clogging.

[0117] [Effects] As described above, the image forming apparatus 1 according to this embodiment comprises: a recording head 20 having a nozzle Te, a pressure chamber Td communicating with the nozzle Te and containing ink, and a piezoelectric element T arranged so as to form part of the wall of the pressure chamber Td; a drive waveform generation unit 15 that generates a pulsed drive waveform to be supplied to the piezoelectric element T; a reverberation waveform detection unit 17 that is arranged branching off from a line electrically connecting the drive waveform generation unit 15 and the piezoelectric element T and that detects a reverberation waveform from the piezoelectric element T that occurs after the drive waveform is supplied; and a control unit 11 that controls the operation of the reverberation waveform detection unit 17 and the drive waveform generation unit 15, wherein the control unit 11 sets the drive waveform generation unit 15 to a high impedance output when the reverberation waveform detection unit 17 detects a reverberation waveform.

[0118] According to the image forming apparatus 1 of this embodiment, the reverberation waveform observation function can be implemented by utilizing the existing device configuration, without the need for additional switches for circuit switching. In other words, according to the image forming apparatus 1 of this embodiment, no changes are required to the existing configuration of the image forming apparatus 1, such as an increase in wiring, the addition of a switching circuit, or a change in the head IC for controlling the switching circuit. This reduces development costs and product costs, and also contributes to the widespread use of image forming apparatuses 1 equipped with the reverberation waveform observation function.

[0119] Furthermore, with the image forming apparatus 1 according to this embodiment, the reverberation waveform observation function can be realized essentially by simply switching the mode of the drive waveform generation unit 15. This is extremely useful in that nozzle inspections using reverberation waveforms can be performed sequentially during printing.

[0120] 13 is a diagram schematically illustrating a circuit configuration for detecting a reverberation waveform of the image forming apparatus 1 according to Modification 1. This circuit configuration differs from the circuit configuration shown in FIG. 5 only in that the reverberation waveform detector 17 is disposed inside the recording head 20, rather than on the device main body 10 side.

[0121] From the viewpoint of preventing the size of the recording head 20 from increasing, it is preferable to arrange the reverberation waveform detector 17 (for example, a control board having an AD conversion circuit and the like) on the device main body 10 side, as shown in the above embodiment. However, if the reverberation waveform detector 17 is arranged on the device main body 10 side, the distance between the reverberation waveform detector 17 and the piezoelectric element T increases. Therefore, there is a risk that the reverberation waveform signal from the piezoelectric element T will be deteriorated before it reaches the reverberation waveform detector 17.

[0122] From this perspective, the image forming apparatus 1 according to this modified example has a configuration in which the reverberation waveform detector 17 is disposed in the recording head 20 rather than in the apparatus main body 10 .

[0123] As with the image forming apparatus 1 according to the above embodiment, the image forming apparatus 1 according to this modification can also implement a reverberation waveform observation function in a more suitable manner without significantly changing the existing apparatus configuration. Furthermore, the image forming apparatus 1 according to this modification can prevent the signal related to the reverberation waveform from deteriorating on the line L1 from the piezoelectric element T until it reaches the reverberation waveform detector 17. This allows the reverberation waveform detector 17 to acquire a reverberation waveform with a good S / N ratio.

[0124] 14 is a diagram schematically illustrating a circuit configuration for detecting a reverberation waveform of the image forming apparatus 1 according to Modification 2. This circuit configuration illustrates a circuit configuration for detecting a reverberation waveform that is assumed when the recording head 20 has a plurality of piezoelectric elements T.

[0125] As described above, the recording head 20 generally has a plurality of channels Tc, and a piezoelectric element T that forms a pressure chamber Td is disposed in each channel Tc. The operation of each of the plurality of piezoelectric elements T is controlled independently. More specifically, each of the plurality of piezoelectric elements T is connected to a common drive line L1, and the head IC 21 in the recording head 20 can switch the connection state of the piezoelectric elements T to the drive line L1 between on and off.

[0126] That is, the output destination of the drive waveform supplied from the drive waveform generation unit 15 is selected by the switch 21a (21a-ch1, 21a-ch2 in FIG. 14) of the head IC 21, and the drive waveform is supplied to the piezoelectric element T (T-ch1, T-ch2 in FIG. 14) of the channel Tc from which ink is to be ejected of the head main body 22. Also, the output destination of the common voltage supplied from the common voltage supply unit 16 is selected by the switch 21b (21b-ch1, 21b-ch2 in FIG. 14) of the head IC 21, and the common voltage is supplied to the piezoelectric element T of the non-ejecting channel Tc of the head main body 22. With this configuration, the connection state between the piezoelectric element T of each channel Tc and the lines L1 and L2 can be switched on and off separately.

[0127] In the image forming apparatus 1 according to this modified example, the control unit 11 preferably controls the head IC 21 to separately detect the reverberation waveforms generated from each of the plurality of piezoelectric elements T. The states of the plurality of channels Tc (i.e., the states of the nozzles Te) of the recording head 20 differ depending on factors such as the frequency of ink ejection from the nozzles Te. Furthermore, the structure of each of the plurality of channels Tc also includes manufacturing errors. Therefore, the residual vibrations generated in each of the plurality of channels Tc are not completely identical. In other words, the reverberation waveforms generated from each of the plurality of piezoelectric elements T are not completely identical.

[0128] From this perspective, the image forming apparatus 1 (controller 11) according to this modification controls the head IC 21 to individually detect the reverberation waveforms generated from each of the plurality of piezoelectric elements T. In this case, for example, the controller 11 controls the head IC 21 to sequentially switch on / off the switching circuits connected to each of the plurality of piezoelectric elements T, thereby sequentially testing the nozzles of each of the plurality of piezoelectric elements T. This makes it possible to individually test the state of each of the plurality of channels Tc (e.g., the state of the nozzles Te) of the recording head 20.

[0129] In addition, the image forming apparatus 1 (control unit 11) according to this modified example may inspect several channels Tc together (for example, inspect 10 channels Tc together) instead of inspecting the state of each channel Tc individually.

[0130] 15 is a diagram schematically illustrating a circuit configuration for detecting a reverberation waveform of the image forming apparatus 1 according to Modification 3. This circuit configuration differs from the circuit configuration shown in FIG. 5 in that a switch 18 is provided in front of the reverberation waveform detector 17 in a branch line branching off from the drive line L1.

[0131] 5, when the drive waveform generator 15 outputs a drive waveform, the drive waveform generator 15 is connected to the reverberation waveform detector 17. Therefore, the drive waveform output from the drive waveform generator 15 must be set taking into consideration the electrical influence of the reverberation waveform detector 17.

[0132] In this regard, as in the circuit configuration of this modified example, when a drive waveform is sent from the drive waveform generation unit 15, the reverberation waveform detection unit 17 can be disabled from the perspective of the drive waveform generation unit 15 by opening the switch 18 and disconnecting the reverberation waveform detection unit 17 from the drive line L1. In other words, this simplifies the setting of the drive waveform to be generated by the drive waveform generation unit 15.

[0133] An analog switch, for example, can be used as the switch 18. The switch 18 may be configured to be switched on / off by, for example, a control signal from the control unit 11. The control unit 11 opens the switch 18 when the drive waveform generation unit 15 sends out a drive waveform, and closes the switch 18 when the reverberation waveform detection unit 17 detects a reverberation waveform.

[0134] As described above, the image forming apparatus 1 according to this modified example is useful in that it is possible to disable the reverberation waveform detection unit 17 from the perspective of the drive waveform generation unit 15 when sending a drive waveform from the drive waveform generation unit 15.

[0135] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

[0136] The disclosures of the specification, drawings and abstract contained in Japanese Patent Application No. 2024-010465, filed on January 26, 2024, are incorporated herein by reference in their entirety.

[0137] According to the image forming apparatus according to the present disclosure, it is possible to implement a reverberation waveform observation function in a more suitable manner without making significant changes to the existing apparatus configuration.

[0138] REFERENCE SIGNS LIST 1 Image forming apparatus 10 Apparatus main body 11 Control unit 12 Interface 13 Page memory 14 Line memory 15 Drive waveform generating unit 15b Switching element driving circuit 15c Push-pull circuit 16 Common voltage supply unit 17 Reverberation waveform detecting unit 18 Switch 20 Recording head 21a Switch 21b Switch 22 Head main body L1 Drive line L2 Common voltage supply line M External device T Piezoelectric element Td Pressure chamber Te Nozzle Tf Piezoelectric member Tg First electrode Th Second electrode Tc Channel

Claims

1. An inkjet image forming apparatus comprising: a recording head having a nozzle, a pressure chamber communicating with the nozzle to contain ink, and a piezoelectric element arranged to form part of the wall of the pressure chamber; a drive waveform generation unit that generates a pulsed drive waveform to be supplied to the piezoelectric element; a reverberation waveform detection unit that is arranged branching off from a line electrically connecting the drive waveform generation unit and the piezoelectric element and detects a reverberation waveform from the piezoelectric element that occurs after the drive waveform is supplied; and a control unit that controls the operation of the reverberation waveform detection unit and the drive waveform generation unit, wherein the control unit sets the drive waveform generation unit to high impedance output when the reverberation waveform detection unit detects the reverberation waveform.

2. The image forming apparatus according to claim 1, wherein a switching circuit is not provided at a position in the line where the line branches off to the reverberation waveform detection unit.

3. The image forming apparatus according to claim 1, wherein the drive waveform generating section has a push-pull circuit at an output stage, and the control section sets the drive waveform generating section to a high impedance output by turning off all of the multiple switching elements that make up the push-pull circuit.

4. The image forming apparatus according to claim 1, wherein the control section is configured to be able to change the timing at which the drive waveform generating section switches to high impedance output.

5. The image forming apparatus according to claim 1, wherein the control unit controls the drive waveform generation unit and the reverberation waveform detection unit so as to detect the reverberation waveform at the timing when the recording head enters a non-ink ejection state during printing.

6. The image forming apparatus of claim 1, wherein the control unit, when detecting the reverberation waveform in the reverberation waveform detection unit, changes the operation of the drive waveform generation unit in the following order: a first mode in which the drive waveform generation unit supplies the drive waveform to the piezoelectric element; a second mode in which the drive waveform generation unit supplies a reference voltage to the piezoelectric element; and a third mode in which the drive waveform generation unit is set to high impedance output; and causes the reverberation waveform detection unit to start detecting the reverberation waveform in accordance with the timing at which the operation of the drive waveform generation unit is switched from the second mode to the third mode.

7. The image forming apparatus according to claim 6, wherein the control unit sets a timing for switching from the first mode or the second mode to the third mode according to the type or characteristics of the recording head or the type of ink.

8. The image forming apparatus according to claim 1, wherein the control unit has a first measurement operation pattern and a second measurement operation pattern as operation patterns to be executed on the drive waveform generation unit for observing the reverberation waveform, the first measurement operation pattern is an operation pattern for detecting the reverberation waveform that occurs after the pulse-shaped drive waveform supplied from the drive waveform generation unit to the piezoelectric element has fallen, and the second measurement operation pattern is an operation pattern for detecting the reverberation waveform that occurs immediately after the pulse-shaped drive waveform supplied from the drive waveform generation unit to the piezoelectric element has risen.

9. The image forming apparatus according to claim 8, wherein the first measurement operation pattern is provided in a form that overlaps with the normal drive period.

10. The image forming apparatus according to claim 8, wherein the control unit is configured to be able to switch between a mode of performing a nozzle inspection in the first measurement operation pattern and a mode of performing a nozzle inspection in the second measurement operation pattern.

11. The recording head holds a plurality of the piezoelectric elements, the plurality of piezoelectric elements are each connected to a common line, and the connection state with the line can be individually switched on and off by a head IC in the recording head, and the control unit controls the head IC to individually detect the reverberation waveforms generated from each of the plurality of piezoelectric elements. The image forming apparatus according to claim 1.

12. The image forming apparatus according to claim 1, wherein the reverberation waveform detection unit is disposed in the main body of the image forming apparatus.

13. The image forming apparatus according to claim 1, further comprising a switch in the front stage of the reverberation waveform detection unit branched from the line, wherein the control unit opens the switch when sending the drive waveform from the drive waveform generation unit, and closes the switch when detecting the reverberation waveform by the reverberation waveform detection unit.

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