Inkjet recording device

Abstract

In low-resolution encoders, the ratio of the fluctuation amount per encoder pulse to the fluctuation amount of the transport speed, especially in the low-speed range, becomes large. This leads to large fluctuations in the output timing generated based on the encoder pulse, resulting in a problem of image quality degradation. [Solution] A correction value is obtained to correct the output of the encoder pulse while the transport means for transporting the recording medium is rotating at high speed, and the image is recorded at the ejection timing corrected by the obtained correction value.

Description

Technical Field

[0001] The present invention relates to an inkjet recording apparatus that records color images.

Background Art

[0002] Conventionally, an inkjet recording apparatus (hereinafter also referred to as a line printer) using a line head (recording head) has advantages such as being able to print color images at high speed and with low running costs, and thus is used as a printing means for various applications.

[0003] In a conventional line printer, since the lateral width and image quality of an image are determined by the length of the recording head and the resolution, the length of the recording head is often long and the resolution is often high. Further, when performing image recording with a recording head, a method is known in which the timing of ejecting ink from the recording head is determined based on a reference pulse signal output from an encoder provided in a conveyance mechanism (for example, conveyance rollers) of a recording medium for recording an image. Specifically, a method is known in which the reference pulse is multiplied by a predetermined multiplication factor according to the resolution of this encoder to generate a trigger according to the printing resolution in the conveyance direction.

[0004] Conventionally, when determining the ink ejection timing by multiplying the reference pulse from the encoder, it is desirable that the resolution of the encoder be as high as possible. If the resolution of the encoder is high, for example, when there is a speed variation during conveyance of the recording medium, the amount of variation per one reference pulse becomes small, and it is known that the followability of the ejection timing with respect to the speed variation becomes relatively good.

[0005] However, in a line printer, in order to increase the resolution of the encoder, for example, it is necessary to increase the diameter of a code wheel provided on the conveyance rollers, which has a demerit of leading to an increase in the size of the apparatus.

[0006] Furthermore, line printers require a wide speed range for transporting recording media, and in order to avoid complicating the transport mechanism, it was necessary to achieve the required speed range by using a single drive motor and drive gear for transport, and by using a low-resolution encoder.

[0007] However, with this configuration, when the transport speed of the recording medium enters the low-speed range, the drive motor is driven at a low frequency, which increases the rotational unevenness of the drive motor and the fluctuation in the transport speed of the recording medium. As a result, if the encoder resolution is low, the ability to track the ejection timing is impaired. To address these challenges, Patent Document 1 discloses an inkjet printer that, when generating an ink ejection trigger from a linear encoder that detects the position of a carriage movable along the main scanning direction, measures the output of the linear encoder in advance for pulses with a phase difference output from multiple light-receiving units of the linear encoder, and corrects the ejection trigger so that the intervals between ink ejection triggers are uniform based on the measured output of the linear encoder. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2015-74149 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, with conventional technology, there was a risk that the phase difference of pulses output from multiple light-receiving units of the encoder could not be accurately corrected when there were speed fluctuations due to rotational unevenness of the drive motor.

[0010] The present invention aims to provide an inkjet recording apparatus that can determine an ink ejection timing that can follow fluctuations in the transport speed of the recording medium, while reducing the resolution of the encoder and keeping the size of the apparatus down. [Means for solving the problem]

[0011] To solve the above problems, the inkjet recording apparatus according to the present invention comprises: a transport means for transporting a recording medium; an image recording means for recording an image by ejecting ink onto the recording medium; a rotary encoder for detecting the amount of movement of the recording medium transported by the transport means; a correction means for correcting the output pulse of the rotary encoder; a trigger generation means for generating a reference trigger that is uniform for each line based on the correction result of the correction means; and a control means for instructing the image recording means to record an image based on the reference trigger output from the trigger generation means. The control means is characterized in that, under the condition that the transport means is operating in a high-speed range, the pulse output from the rotary encoder is corrected by the correction means. [Effects of the Invention]

[0012] According to the present invention, even when the encoder resolution is reduced to a low resolution in order to miniaturize the device, it is possible to provide an inkjet recording device that has a wide transport speed range without compromising the uniformity of the ink ejection interval. [Brief explanation of the drawing]

[0013] [Figure 1] This is an external cross-sectional view showing an overview of the inkjet recording apparatus in this embodiment. [Figure 2] This is a block diagram showing the control configuration of the inkjet recording device in this embodiment. [Figure 3] This is a configuration diagram showing an overview of the rotary encoder in this embodiment. [Figure 4](a) This is a diagram showing an overview of the encoder sensor in this embodiment. (b) This is a diagram showing an overview of the encoder pulse in this embodiment. [Figure 5] This graph shows the relationship between transport speed and encoder pulse interval. [Figure 6] This is a flowchart showing the process for acquiring the correction value of the encoder pulse in this embodiment. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described in detail below with reference to the drawings. Figure 1 is an external cross-sectional view showing an overview of the inkjet recording apparatus in this embodiment. In this embodiment, as an example of an inkjet recording apparatus, a line printer that records image information on a roll-shaped recording medium using an inkjet method will be used for the description.

[0015] The printer 100 consists of a printer body 101 and a feeding unit 105 that supplies a recording medium P to the printer body 101. The recording data to be recorded on the recording medium P is transmitted from a host computer (hereinafter also referred to as a host PC) 700 to the printer body 101 via a print cable 701. The printer body 101 is equipped with an operation panel 103 for the operator to make various settings and to notify the operator of the status of the printer 100.

[0016] The printer body 101 is equipped with a four-color recording head 10, which has multiple ejection ports arranged over a range corresponding to the entire width of the maximum possible recording medium P. In this embodiment, by providing such recording heads 10 corresponding to four colors of ink, Y, M, C, and BK, a color image can be recorded on the recording medium P. In addition, a recovery unit 11 is provided for each color recording head 10 to maintain or restore the ink ejection conditions to a good state. The recovery unit 11 includes a cap that can cap the ejection port forming surface of the recording head 10 when not performing a recording operation, and can also receive the ink ejected during the recovery process.

[0017] In addition, the printer main body 101 is provided with an ink tank 30 for storing each color ink supplied to each recording head, and a recovery tank 40 for recovering the ink received by the cap. By rotationally driving the drive belt 21 by the driving force of the conveyance motor 25 in the conveyance unit 20, the conveyance roller 27 rotates, and the conveyance belt 24 stretched over a plurality of rollers including the conveyance roller rotates. As the conveyance belt 24 rotates, the recording medium P set in the feeding unit 105 is fed in the direction of arrow A and introduced into the printer main body 101.

[0018] The recording medium P introduced into the printer main body 101 is detected by the entrance sensor 22 and conveyed by the conveyance belt 24 toward the recording head 10. The conveyance belt 24 is provided with suction holes, and by applying a suction force by a suction fan (not shown) provided under the conveyance belt 24, the recording medium P is adsorbed onto the conveyance belt 24, and the recording surface is regulated to be flat. The conveyance position of the recording medium P is controlled based on the detection output of the rotary encoder 26 that rotates in synchronization with the rotation of the conveyance roller 27.

[0019] The recording medium P on which recording has been performed by the recording head 10 is detected by the exit sensor 23, and conveyance is stopped when the rear end of the recording page reaches the cutting position of the cutter unit 50. Then, after the rear end portion of the recording page is cut by the cutter, it is discharged page by page.

[0020] In addition, in FIG. 1, the roll paper-like recording medium P is illustrated, but it may be fan-fold paper-like, and in addition to those continuous paper-like ones, it may also be cut sheet-like.

[0021] Furthermore, the printer 100 includes a main control board 117 that controls the entire printer. The configuration of the main control board 117 in the present embodiment will be described in detail while referring to FIGS. 1 and 2.

[0022] The main control board 117 includes an SoC 201, a ROM 202, a RAM 203, and an FPGA 205. The SoC 201 controls the entire printer 100, including the FPGA 205, based on the control program and various history information of the printer 100 stored in the ROM 202, or the command signals and image information stored in the RAM 203. The RAM 203 stores the command signals and image information received by the SoC 201 from the host PC 700.

[0023] The FPGA205, acting as a control device, is connected to the SoC201 via a serial bus (not shown) and operates under the control of the SoC201. Specifically, the SoC201 receives image information from the host PC700, generates image data for each line in an image processing unit (not shown), and transfers it to the FPGA205. At this time, the SoC201 determines the timing of the image data transfer based on the ejection trigger received from the FPGA205.

[0024] The FPGA 205 receives multiple encoder pulses (encoder pulse A phase and encoder pulse B phase) corresponding to the amount of movement of the recording medium P detected by the rotary encoder 26, the speed management unit 303 counts the interval between the encoder pulses, and the storage unit 302 stores the count value.

[0025] Furthermore, the FPGA 205 corrects the interval between multiple encoder pulses received from the rotary encoder 26 using the pulse correction unit 301. At this time, the pulse correction unit 301 adjusts the amount of correction for the encoder pulses according to the count value of the encoder pulse interval that has been measured in advance and is stored in the storage unit 302.

[0026] Subsequently, the trigger generation unit 305 transmits an ejection trigger to the SoC 201 based on the encoder pulse corrected by the pulse correction unit 301. The SoC 201 transmits line-by-line image data to the FPGA 205 according to the timing of the ejection trigger received from the FPGA 205. The FPGA 205 receives the line-by-line image data transmitted from the SoC 201 with the head drive signal generation unit 304, converts it into a signal format that the recording head 10 can receive, and then transmits a head drive signal to the recording head 10.

[0027] In addition, the main control board 117 is equipped with a CPU and actuator drive circuit (not shown), various sensor detection circuits, and performs overall control of the printer 100, including driving the transport motor 25, detecting the remaining amount of ink in the ink tank 30, and driving the cutter unit 50.

[0028] Next, the configuration of the rotary encoder 26 in this embodiment will be described in detail with reference to Figures 3 and 4. The rotary encoder 26 is capable of detecting the position of the recording medium P being transported along the sub-scanning direction via the transport roller 27. The rotary encoder 26 is composed of a code wheel 261 and an encoder sensor 262. The code wheel 261 has a plurality of slit-shaped marks 261a formed on a disc at predetermined intervals and dimensions to indicate the position in the rotation direction. The rotary encoder 26 is mounted on the rotation axis of the transport roller 27, which is driven by the transport motor 25.

[0029] The slit-shaped marks formed on the code wheel 261 consist of transparent, light-transmitting portions and black, light-impermeable portions, which are alternately arranged in pairs at equal intervals. The encoder sensor 262 optically detects these alternately arranged slit-shaped marks 261a. The encoder sensor 262 outputs the detection signal detected from the slit-shaped marks 261a as an encoder pulse to the FPGA 205. At this time, since the slit-shaped marks 261a formed on the code wheel 261 are formed at equal intervals and with equal width, the detection signal detected by the encoder sensor 262 from these slit-shaped marks is formed as a 50% duty cycle square wave and output as an encoder pulse.

[0030] Furthermore, as shown in Figure 4(a), the encoder sensor 262 has an LED 262a as a light-emitting part and multiple photodiodes 262b as light-receiving parts to generate a predetermined phase difference. In this case, the encoder sensor 262 receives transmitted light from the LED 261a at each of the four photodiodes 262b according to the position of the slit-shaped mark 261a, and outputs two detection signals with a phase difference as output signals to the FPGA 205. In other words, the encoder sensor 262 has four photodiodes 262b arranged at predetermined intervals so that the two detection signals have a predetermined phase difference, forming a photodiode array.

[0031] Furthermore, the encoder sensor 262 includes a signal processing circuit 262c and two comparators 262d for generating digital signals. The encoder sensor 262 can obtain signals A, -A, (overline A), B, -B, (overline B) by passing the outputs of multiple photodiodes 262b through the signal processing circuit 262c.

[0032] The encoder sensor 262 then uses two comparators 262d to receive these signals and generate A-phase and B-phase digital signals with a predetermined phase difference of 90° electrical angle. In other words, as shown in Figure 4(b), the encoder sensor 262 is configured with a photodiode 262b, a signal processing circuit 262c, and two comparators 262d such that the A-phase and B-phase digital signals are detected signals with a predetermined phase difference of 90°. The encoder sensor 262 outputs the two digital signals described above to the FPGA 205. The FPGA 205 receives these two-phase output signals and generates an ejection trigger.

[0033] However, in reality, due to various factors, the phase difference between the A-phase and B-phase of the encoder pulse may not be the expected phase difference (90° in this case) and pulse duty cycle (50% in this case), and errors may be present. These various factors include, for example, mounting errors of the multiple photodiodes 262b, manufacturing precision, offset voltage variations of the comparator 262d, mounting errors of the code wheel 261, misalignment of the slit-shaped mark 261a formed on the code wheel 261, and the mounting angle of the encoder sensor 262 relative to the rotation surface of the code wheel 261.

[0034] Thus, if the phase difference between phase A and phase B of the encoder pulse is not exactly 90°, and the pulse duty cycle of each phase is not exactly 50%, the interval of the discharge trigger generated based on the encoder pulse containing the phase difference error will also become uneven. Therefore, when using a detection signal with these two phase differences, pulse interval correction is necessary. The timing of this encoder pulse correction must be considered in relation to the transport speed of the recording medium P and the encoder pulse interval.

[0035] As shown in Figure 5, the lower the transport speed of the recording medium P, the larger the error in the encoder pulse interval becomes. This is because when the transport speed of the recording medium P is in the low-speed range, the input step to the drive motor 25 becomes low-frequency, and the rotational irregularities of the drive motor 25 become larger. In other words, when the rotational speed of the drive motor 25 is low, the rotational irregularities of the drive motor 25 become large, and the error in the encoder pulse interval also becomes a large value (for example, ±10% or more). Conversely, when the transport speed of the recording medium P is in the high-speed range, the input step to the drive motor 25 becomes high-frequency, so the rotation of the drive motor 25 becomes smoother, and the rotational irregularities of the drive motor 25 become relatively small. Therefore, the faster the rotational speed of the drive motor 25, the smaller the fluctuation in the transport speed of the recording medium P becomes, and the smaller the error in the encoder pulse interval can be (for example, less than ±3%). Thus, it is desirable to perform the encoder pulse correction timing when the rotational speed of the drive motor 25 is high.

[0036] This is because, when encoder pulse A and encoder pulse B, which are output with an ideal phase difference of 90° and pulse duty cycle of 50%, deviate from the 90° phase and 50% duty cycle due to errors, and when fluctuations in transport speed are superimposed, the calculations required to determine the phase shift and pulse duty shift of each phase become extremely complex. As a result, large calculation errors are introduced, making it difficult to perform more accurate correction processing.

[0037] Furthermore, regarding the correction timing of the encoder pulse, it is desirable that the load on the drive motor 25 remains constant. This is because fluctuations in the load on the drive motor 25 may lead to uneven rotation. Therefore, in the correction process of this embodiment... This procedure is performed under conditions where the rotational speed of the transport drive motor 25 is in the high-speed range, and where there is no recording medium P on the transport belt 24 in order to minimize factors causing load fluctuations on the drive motor 25.

[0038] Next, the acquisition of the corrected value of the encoder pulse according to an embodiment of the present invention will be described in detail with reference to the flowchart in Figure 6. First, the SoC201 sets the transport speed (transport motor drive pulse) for which the encoder pulse correction is performed, and transmits the set transport speed information to the CPU (not shown) and FPGA205. (Step S1) At this time, the transport speed set by the SoC201 is determined to be the transport speed in which the rotation speed of the drive motor 25 is in the high-speed range (here, 330 mm / sec), as described above.

[0039] Next, the CPU (not shown) confirms from various sensor information that the recording medium P is not present on the transport path (step S2Yes), and controls the transport motor drive circuit (not shown) to drive the transport motor 25 for a predetermined time at a predetermined transport speed (transport motor input step) determined in step S1. (step S3)

[0040] Next, after a predetermined time has elapsed since the transport motor 25 was driven, the FPGA 205 starts counting the encoder pulses output from the encoder sensor 262, which have two phase-shifted signals. (Step S4)

[0041] Next, the speed management unit 303 within the FPGA 205 stores the counted encoder pulse intervals in the storage unit 302. At this time, four intervals are stored for each pulse. These four intervals are the four time intervals of the encoder pulse: from the A-phase rising edge to the B-phase rising edge, from the B-phase rising edge to the A-phase falling edge, from the A-phase falling edge to the B-phase falling edge, and from the B-phase falling edge to the A-phase rising edge. The FPGA 205 counts these four time intervals with its internal clock and stores the count value in the storage unit 302. At this time, the CPU (not shown) drives the transport motor 25 for a predetermined time, so that the FPGA 205 stores the four time intervals corresponding to a predetermined rotation of the transport motor 25 in the storage unit 302. (Step S5)

[0042] Next, the correction unit 301 refers to the multiple count values ​​for each of the four time intervals stored in the storage unit 302 and calculates the average value for each of the four time intervals. (Step S6)

[0043] Next, the correction unit 301 calculates the difference between each of the four average values ​​calculated in step S5 and the theoretical value for each phase difference. (Step S7)

[0044] Next, the correction unit 301 stores the difference values ​​of the four time intervals calculated in step S7 back into the storage unit 302. (S8) Here, the difference values ​​of the four time intervals stored in the storage unit 302 become the pulse interval correction. Based on the encoder pulse corrected using the correction values ​​acquired here, the trigger generation unit 305 described above transmits an ejection trigger to the SoC 201. Then, the SoC 201 transmits line-by-line image data to the FPGA 205 according to the timing of the ejection trigger received from the FPGA 205. The FPGA 205 receives the line-by-line image data transmitted from the SoC 201 with the head drive signal generation unit 304, converts it into a signal format that the recording head 10 can receive, and then transmits a head drive signal to the recording head 10. This makes it possible to record the image onto the recording medium P at a timing corrected by the correction values ​​acquired by the correction unit 301.

[0045] Subsequently, the CPU (not shown) stops the drive of the transport motor 25 (step S9) and terminates the control for acquiring the encoder pulse correction value. The control for acquiring the encoder pulse correction value described in this embodiment may be performed as pre-processing before recording to the recording medium P, or it may be performed when the recording medium P is set or replaced in the feeding unit 105.

[0046] The printer 100 according to the embodiment described above includes a transport belt 22 for transporting a recording medium P, a transport motor 25 for rotating the transport belt 24, a rotary encoder 26 attached to a driven roller that follows the rotational movement of the transport motor 25 via the transport belt 24 and detects the amount of movement of the recording medium P, a recording head 10 for recording an image on the recording medium P, and a control board 117 that controls the recording head 10 and the transport motor 25 and records an image on the recording medium P while repeatedly forming and transporting an image line by line based on the detection result of the rotary encoder 26. The rotary encoder 26 is configured to include a code wheel 261 and an encoder sensor 262, and the code wheel 261 has a plurality of slit-shaped marks 261a formed in a disc shape at predetermined intervals and dimensions to indicate the position in the direction of rotation. Furthermore, the encoder sensor 262 outputs two encoder pulses with a phase difference by optically detecting slit-shaped marks 261a arranged at predetermined intervals with multiple light-receiving units. The control board 117 includes a speed management unit 301 that detects the transport speed from the two encoder pulses output from the encoder sensor 262, a storage unit 302 that stores a correction value calculated from the encoder pulses, a correction unit 303 that corrects the encoder pulses by referring to the correction value stored in the storage unit 302, and a trigger generation unit 303 that generates an ejection trigger that determines the printing timing based on the encoder pulse corrected by the correction unit 303. The pulse correction unit 303 can correct the two encoder pulses, including the phase difference, output from the encoder sensor 262 under the condition that the transport motor 25 is driven in the high-speed range.

[0047] As a result, the printer 100 can make the ink ejection interval from the recording head 10 uniform, even in a low-speed printing environment with a low-resolution rotary encoder 26 and large speed fluctuations, thereby stabilizing the ink's impact position on the recording medium P and improving image quality.

[0048] It goes without saying that the present invention is not limited to the embodiments described above, and can be modified in various ways without departing from its essence. Furthermore, although the above embodiments use an inkjet printer to record image information on a roll-shaped recording medium, it may also be applied to image recording devices such as thermal transfer, thermal, or dot impact printers. [Explanation of Symbols]

[0049] 100 Printers (inkjet recording devices) 101 Printer body 103 Control Panel 117 Control Board 201 SoC 205 FPGA 10. Recording head (recording means) 21 Conveyor belt 25. Transport motor 26 Rotary Encoders P recording medium 700 host computers

Claims

1. A transport means for transporting a recording medium, An image recording means that records an image by ejecting ink onto the aforementioned recording medium, A rotary encoder for detecting the amount of movement of the recording medium being transported by the transport means, The rotary encoder has a correction means for correcting the output pulses, a trigger generation means for generating reference triggers that are evenly distributed for each line based on the correction result of the correction means, and a control means for instructing the image forming means to form an image based on the reference triggers output from the trigger generation means. The inkjet recording apparatus is characterized in that the control means corrects the pulses output from the rotary encoder by the correction means when the transport means is operating in a high-speed range.

2. The rotary encoder comprises a code wheel having a plurality of slit-shaped marks, and an encoder sensor for detecting the slit-shaped marks. The encoder sensor comprises a light-emitting unit that emits light onto the slit-shaped mark, and a plurality of light-receiving units that generate a predetermined phase difference with respect to the light from the light-emitting unit that passes through the slit-shaped mark. The inkjet recording apparatus according to claim 1, characterized in that the correction means corrects a plurality of pulses including the phase difference output from the plurality of light receiving units.

3. The image forming means includes a nozzle for ejecting ink and a heater for ejecting ink from the nozzle. The inkjet recording apparatus according to claim 1 or 2, characterized in that the control means outputs a drive signal to the heater to the image forming means in accordance with the interval of the reference trigger generated by the trigger generation means.

Images