JP7556307B2 - Droplet ejection device and image forming device - Google Patents

Description

The present invention relates to a droplet ejection device and an image forming device.

Conventionally, image forming devices have been known that include a transport unit that transports a medium and an ink ejection unit that ejects ink toward the medium transported by the transport unit. In such image forming devices, if there is variation in the speed at which the medium is transported by the transport unit, the ink ejected from the ink ejection unit may not land at the target position on the medium.

Therefore, there is a technique for correcting the ejection timing of the ink ejection unit based on the transport speed of the medium in order to keep constant the amount of deviation from the target position when the ink is ejected and lands on the medium (see, for example, Patent Document 1).

One method of correcting the ejection timing is to use the moving average value of the medium transport speed. However, the moving average value calculated based on past transport speeds includes a "delay" with respect to the current transport speed (transport amount). Therefore, with conventional technology that corrects the ejection timing based on the moving average value, there is an issue that the ink cannot land at the target position, resulting in reduced print quality.

The present invention has been made to solve these problems, and aims to provide a droplet ejection device that can reduce detection errors in the medium transport speed and land droplets at target positions.

In order to solve the above problem, one aspect of the present invention is a droplet ejection device including a transport unit that transports a medium, a droplet ejection unit that ejects droplets onto the medium transported by the transport unit, a transport speed sensor that outputs a detection value that correlates with the transport speed of the medium, and a controller that controls the timing of droplet ejection by the droplet ejection unit based on the detection value output from the transport speed sensor, wherein the controller calculates a moving average value of a plurality of the detection values most recently output from the transport speed sensor, corrects the calculated moving average value based on an amount of change in the plurality of detection values, generates the ejection timing based on the corrected moving average value, and causes the droplet ejection unit to eject droplets at the generated ejection timing.

The present invention makes it possible to reduce detection errors in the medium and land droplets at the target position.

1 is a schematic diagram of an inkjet recording apparatus according to an embodiment of the present invention. FIG. FIG. FIG. 2 is a diagram showing the hardware configuration of the inkjet recording apparatus. FIG. 2 is a functional block diagram of the controller. 4 is a flowchart of an image forming process. 5A and 5B are diagrams showing the correspondence relationships among a signal period, a pre-correction moving average value, a pre-correction error, a post-correction moving average value, and a post-correction error according to the embodiment. 13A to 13C are diagrams showing the transition of the conveying speed calculated based on an ideal signal period, the transition of the conveying speed calculated based on a pre-correction moving average value, and the transition of the conveying speed calculated based on a post-correction moving average value. 13 is a diagram showing the correspondence relationship between a signal period, a pre-correction moving average value, a pre-correction error, a post-correction moving average value, and a post-correction error according to Modification 1. FIG. 13 is a diagram showing the correspondence relationship between a signal period, a pre-correction moving average value, a pre-correction error, a post-correction moving average value, and a post-correction error according to Modification Example 2. FIG.

Below, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of an inkjet recording device (image forming device, droplet ejection device) 1 according to an embodiment of the present invention. As shown in FIG. 1, the inkjet recording device 1 includes a paper feed section 10, an image forming section 20, a drying section 30, and a paper ejection section 40. The inkjet recording device 1 forms an image by the image forming section 20 ejecting ink onto paper P (medium) fed from the paper feed section 10. Then, the inkjet recording device 1 dries the ink attached to the paper P in the drying section 30, and then ejects the paper P to the paper ejection section 40.

The paper feed section 10 includes a paper feed tray 11 on which multiple sheets of paper P are stacked, a feed device 12 that separates and sends out the sheets of paper P one by one from the paper feed tray 11, and a pair of registration rollers 13 that sends the sheets of paper P to the image forming section 20. The feed device 12 can be any known feed device with a feeding function, such as a device using rollers or rollers, or a device using air suction.

After the leading edge of the paper P sent from the paper feed tray 11 by the feeding device 12 reaches the pair of registration rollers 13, the pair of registration rollers 13 are driven at a predetermined timing, so that the paper P is fed to the image forming unit 20. In this embodiment, the configuration of the paper feed unit 10 is not particularly limited as long as it has the function of sending the paper P to the image forming unit 20.

The image forming unit 20 includes a paper transport drum 21 (a rotating member), an ink ejection unit 22 (a droplet ejection unit), a receiving cylinder 24, and a transfer cylinder 25. The paper transport drum 21, the receiving cylinder 24, and the transfer cylinder 25 are examples of a transport unit. The receiving cylinder 24 receives the paper P from the paper feed unit 10. The paper transport drum 21 is a cylindrical rotating member that carries and transports the paper P received by the receiving cylinder 24 on its outer circumferential surface. The ink ejection unit 22 ejects ink toward the paper P transported by the paper transport drum 21. The transfer cylinder 25 transfers the paper P transported by the paper transport drum 21 to the drying unit 30.

The paper P transported from the paper feed unit 10 to the image forming unit 20 has its leading edge gripped by a paper gripper provided on the surface of the receiving drum 24, and is transported as the surface of the receiving drum 24 moves. The paper P transported by the receiving drum 24 is handed over to the paper transport drum 21 at a position opposite the paper transport drum 21.

A paper gripper is also provided on the surface of the paper transport drum 21, and the leading edge of the paper P is gripped by the paper gripper. In addition, multiple suction holes are formed and distributed on the surface of the paper transport drum 21. At each suction hole, a suction device 26 generates a suction air current toward the inside of the paper transport drum 21. The paper P is adsorbed to the surface of the paper transport drum 21 by this suction air current. The leading edge of the paper P transferred from the receiving cylinder 24 to the paper transport drum 21 is gripped by the paper gripper, and the paper P is adsorbed to the surface of the paper transport drum 21 by the suction air current, and is transported as the surface of the paper transport drum 21 moves.

The ink ejection unit 22 ejects ink of multiple colors, such as C (cyan), M (magenta), Y (yellow), K (black), white, and gold, to form an image. The ink ejection unit 22 is equipped with individual ejection heads 23A, 23B, 23C, 23D, 23E, and 23F for each ink color (type of droplet). The ejection heads 23A to 23F eject ink supplied from ink cartridges of each color mounted on the inkjet recording device 1. There are no limitations on the configuration of the ejection heads 23A to 23F, and any configuration can be used as long as they eject liquid.

The ejection operation of the ejection heads 23A to 23F is controlled by a drive signal corresponding to the image data. When the paper P transported by the paper transport drum 21 passes through the area facing the ink ejection section 22, each color ink is ejected from the nozzles provided on the lower surface (nozzle surface) of each ejection head 23A to 23F. As a result, an image corresponding to the image data is formed on the paper P. The ejection heads 23A to 23F can be of a known configuration.

In this embodiment, the image forming unit 20 only needs to have the function of depositing liquid onto the paper P to form an image, and there is no particular limitation on the configuration for ejecting or depositing the liquid.

The drying section 30 includes a drying mechanism section 31 and a suction transport mechanism section 32. The drying mechanism section 31 dries the ink that has adhered to the paper P in the image forming section 20. The suction transport mechanism section 32 transports the paper P transported from the image forming section 20 to the paper discharge section 40. That is, the paper P transported from the image forming section 20 is received by the suction transport mechanism section 32, and then transported by the suction transport mechanism section 32 to pass through the drying mechanism section 31 and delivered to the paper discharge section 40. When passing through the drying mechanism section 31, the ink on the paper P is subjected to a drying process, and the liquid content in the ink, such as water, evaporates, the ink is fixed on the paper P, and curling of the paper P is suppressed.

The paper discharge section 40 is equipped with a paper discharge tray 41 on which multiple sheets of paper P are stacked. The sheets of paper P transported from the drying section 30 by the suction transport mechanism section 32 are stacked and held in order on the paper discharge tray 41. Note that in this embodiment, the paper discharge section 40 only needs to have the function of discharging the sheets of paper P, and its configuration is not particularly limited.

The inkjet recording device 1 of this embodiment is composed of a paper feed unit 10, an image forming unit 20, a drying unit 30, and a paper discharge unit 40, but other functional units may be added as appropriate. For example, the inkjet recording device 1 may include a pre-processing unit between the paper feed unit 10 and the image forming unit 20 that performs pre-processing of the image formation, and a post-processing unit between the drying unit 30 and the paper discharge unit 40 that performs post-processing of the image formation.

Examples of the pre-processing section include a processing liquid application process that applies a processing liquid to the paper P that reacts with the ink to suppress bleeding. However, the contents of the pre-processing are not limited to the above-mentioned examples. Examples of the post-processing section include a paper inversion and transport process that inverts the paper P on which an image has been formed in the image forming section 20 and sends it back to the image forming section 20 to form images on both sides of the paper P, or a process that binds multiple sheets of paper P on which images have been formed. However, the contents of the post-processing are not limited to the above-mentioned examples.

In this embodiment, the inkjet recording device 1 is described as an example of an image forming device. However, the image forming device is not limited to one that visualizes meaningful images such as letters and figures with the ejected droplets, as long as it is equipped with a droplet ejection section that ejects liquid toward the surface of the sheet material to be dried. As another example, the image forming device may be one that forms patterns that have no meaning in themselves.

The medium is not limited to a particular material, and may be any material to which a liquid can be attached, even temporarily, such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, or ceramics. The medium may be, for example, a film product, a cloth product for clothing, building materials such as wallpaper or flooring, or leather products. In this embodiment, anything to which a liquid can be attached, even temporarily, is referred to as a "medium." In addition, a specific example of a "droplet" is not limited to the ink ejected from the ink ejection unit 22, but may be a processing liquid used in a pre-processing unit. In other words, the present invention can be widely applied to droplet ejection devices that cause droplets to land at a target position.

The "ejection head" is a functional component that ejects or sprays liquid from an ejection hole (nozzle). As an energy generation source for ejecting liquid, ejection energy generation means such as a piezoelectric actuator, a thermal actuator that uses an electrothermal conversion element such as a heating resistor, or an electrostatic actuator consisting of a vibration plate and an opposing electrode can be used. However, the ejection energy generation means used is not limited to the above examples.

Next, various sensors equipped in the image forming unit 20 will be described with reference to Figures 2 and 3. Figure 2 is a side view of the main parts of the image forming unit 20. Figure 3 is a plan view of the main parts of the image forming unit 20. Note that the plan views of the ejection heads 23A, 23B, 23C, 23D, 23E, and 23F are the same, so in Figure 3 they are represented by the term "ejection head 23". The image forming unit 20 is equipped with a first encoder 201, a second encoder 211 (conveyor speed sensor), and a leading edge position sensor 220.

The first encoder 201 is a rotary encoder composed of an encoder wheel 202 and an encoder sensor 203. The encoder wheel 202 is attached to the shaft 21a of the paper transport drum 21. In addition, N poles and S poles are arranged alternately in the circumferential direction on the outer circumferential surface of the encoder wheel 202. The encoder sensor 203 is disposed in a position facing the outer circumferential surface of the encoder wheel 202.

The encoder wheel 202 rotates together with the paper transport drum 21. The encoder sensor 203 reads the north and south poles arranged on the outer circumferential surface of the encoder wheel 202 and outputs a pulse signal (first detection value) to the controller 100 (see FIG. 4). The first encoder 201 is an example of a sensor that detects the amount of rotation per unit time (i.e., the rotational speed) of the paper transport drum 21.

The second encoder 211 is a linear encoder composed of an encoder scale 212 and a plurality of encoder sensors 213 corresponding to each of the plurality of ejection heads 23A to 23F. The encoder scale 212 is disposed at the axial end of the paper transport drum 21 (outside the area facing the ejection head 23). The encoder scale 212 also extends in the circumferential direction along the outer circumferential surface of the paper transport drum 21. The encoder sensor 213 is disposed at a position facing the encoder scale 212. The encoder sensor 213 is also disposed at the same position as the corresponding ejection head 23 in the circumferential direction of the paper transport drum 21. Furthermore, the encoder sensor 213 is disposed adjacent to the corresponding ejection head 23 in the axial direction of the paper transport drum 21.

The encoder scale 212 rotates together with the paper transport drum 21. The encoder scale 212 has north and south poles arranged alternately in the extension direction. The encoder sensor 213 reads the north and south poles arranged on the encoder scale 212 and outputs a pulse signal (second detection value) to the controller 100. The second encoder 211 is another example of a sensor that detects the amount of rotation per unit time (i.e., the rotational speed) of the paper transport drum 21.

The amount of rotation of the paper transport drum 21 per unit time correlates with the amount of transport per unit time of the paper P carried and transported by the paper transport drum 21 (i.e., the transport speed). In this embodiment, the output interval of the pulse signal by the second encoder 211 (hereinafter referred to as the "signal period") is described as a detection value that correlates with the transport speed. In other words, the shorter the signal period, the faster the transport speed, and the longer the signal period, the slower the transport speed.

However, the detection value correlated with the conveying speed is not limited to the above example, and may be the number of pulse signals output from the second encoder 211 per unit time. Also, instead of the pulse signal of the second encoder 211, the pulse signal of the first encoder 201 may be used as the detection value. Furthermore, the first encoder 201 and the second encoder 211 are not limited to being magnetic, and may be optical.

The leading edge position sensor 220 is disposed upstream of the ejection heads 23A to 23F in the transport direction of the paper P, facing the paper transport drum 21. The leading edge position sensor 220 detects the position of the leading edge of the paper P carried and transported by the paper transport drum 21, and outputs the detection result to the controller 100.

Figure 4 is a hardware configuration diagram of the inkjet recording device 1. As shown in Figure 4, the inkjet recording device 1 has a configuration in which a CPU (Central Processing Unit) 101, a RAM (Random Access Memory) 102, a ROM (Read Only Memory) 103, a HDD (Hard Disk Drive) 104, and an I/F 105 are connected via a common bus 109.

The CPU 101 is a computing means and controls the operation of the entire inkjet recording device 1. The RAM 102 is a volatile storage medium capable of reading and writing information at high speed, and is used as a working area when the CPU 101 processes information. The ROM 103 is a read-only non-volatile storage medium in which programs such as firmware are stored. The HDD 104 is a non-volatile storage medium with a large storage capacity that allows information to be read and written, and in which the OS (Operating System), various control programs, application programs, etc. are stored.

The inkjet recording device 1 processes a control program stored in ROM 103, an information processing program (application program) loaded from a storage medium such as HDD 104 to RAM 102, and the like, using the calculation function of the CPU 101. This processing constitutes a software control unit including various functional modules of the inkjet recording device 1. The combination of the software control unit thus constituted and the hardware resources mounted on the inkjet recording device 1 constitutes a functional block that realizes the functions of the inkjet recording device 1. In other words, the CPU 101, RAM 102, ROM 103, and HDD 104 constitute a controller 100 that controls the operation of the inkjet recording device 1.

The I/F 105 is an interface that connects the paper feed unit 10, the image forming unit 20, and the drying unit 30 to a common bus 109. That is, the controller 100 controls the paper feed unit 10, the image forming unit 20, and the drying unit 30 through the I/F 105 to execute an image forming process that forms an image indicated by image data on paper P. The image data may be received, for example, from an external device (e.g., a PC) through a communication interface, or may be generated by a scanner mounted on the inkjet recording device 1 reading a document.

Figure 5 is a functional block diagram of the controller 100. As shown in Figure 5, the controller 100 includes a detection value acquisition means 501, a moving average value calculation means 502, a moving average value correction means 503, an ejection timing generation means 504, and an ejection control means 505.

The detection value acquisition means 501 acquires the output interval of the pulse signal from the second encoder 211 as a signal period (detection value) and stores the acquired signal period in the RAM 102. The signal period is the difference (sec) between the output times of two temporally adjacent pulse signals. The detection value acquisition means 501 starts acquiring the signal period when the leading edge of the paper P is detected by the leading edge position sensor 220. The detection value acquisition means 501 also continues acquiring the signal period until the formation of an image on the paper P is completed.

The signal period acquired by the detection value acquisition means 501 may vary due to, for example, variations in the pitch of the encoder scale 212 or external noise. In other words, the signal period stored in the RAM 102 may contain an error with respect to an ideal signal period (not shown).

The moving average calculation means 502 calculates the moving average of multiple signal periods stored in the RAM 102, and stores the calculated moving average (hereinafter referred to as the "pre-correction moving average") in the RAM 102 in association with the signal period. In this embodiment, the average of the most recent four signal periods is set as the moving average. However, the number of signal periods for calculating the moving average is not limited to four, and can be set to any number equal to or greater than two.

The moving average correction means 503 corrects the pre-correction moving average stored in the RAM 102, and stores the corrected moving average (hereinafter referred to as the "corrected moving average") in the RAM 102 in association with the signal period. More specifically, the moving average correction means 503 corrects the pre-correction moving average based on the amount of change in the multiple signal periods used to calculate the pre-correction moving average. A specific method for correcting the pre-correction moving average will be described later with reference to FIG. 7.

The ejection timing generating means 504 generates the ejection timing (ejection frequency) of the ejection head 23 based on the corrected moving average value stored in the RAM 102. The ejection frequency (Hz) is generated, for example, by substituting the medium conveying speed V (mm/sec) determined based on the corrected moving average value and the image data resolution d (dpi) into the following formula 1.

F=V÷(25.4×d) (Formula 1)

The ejection control means 505 causes the ejection head 23 to eject ink droplets at the ejection timing generated by the ejection timing generation means 504. That is, the faster the transport speed, the earlier the ejection timing of the ejection head 23 (the higher the ejection frequency), and the slower the transport speed, the later the ejection timing of the ejection head 23 (the lower the ejection frequency).

The detection value acquisition means 501, the moving average calculation means 502, the moving average correction means 503, the ejection timing generation means 504, and the ejection control means 505 execute the above-mentioned processes in parallel for each of the multiple ejection heads 23A to 23F. That is, the controller 100 controls the ejection timing of each ejection head 23 based on the detection value of the encoder sensor 213 associated with that ejection head 23.

Next, the image forming process according to this embodiment will be described with reference to Figs. 6 to 8. Fig. 6 is a flowchart of the image forming process. Fig. 7 is a diagram showing the correspondence between the signal period, pre-correction moving average value, pre-correction error, post-correction moving average value, and post-correction error according to this embodiment. Fig. 8 is a diagram showing the progress of the conveying speed calculated based on the ideal signal period, the progress of the conveying speed calculated based on the pre-correction moving average value, and the progress of the conveying speed calculated based on the post-correction moving average value.

First, the controller 100 starts transporting the paper P received from the paper feed unit 10 via the receiving drum 24 by rotating the paper transport drum 21 (S601). Then, the controller 100 waits to execute subsequent processes until the leading edge of the paper P is detected by the leading edge position sensor 220 (S602: No).

Next, after the leading edge of the paper P is detected by the leading edge position sensor 220 (S602: Yes), the controller 100 executes each process of steps S603 to S607. That is, the detection value acquisition means 501 acquires the signal period (S603). Next, the moving average value calculation means 502 calculates the pre-correction moving average value (S604). Next, the moving average value correction means 503 corrects the pre-correction moving average value (S605). Next, the ejection timing generation means 504 generates the ejection timing (S606). Next, the ejection control means 505 causes the ejection head 23 to eject ink droplets (S607).

The controller 100 repeatedly executes the processes of steps S603 to S607 each time the second encoder 211 outputs a pulse signal until the formation of an image on the paper P is completed (S608: No). However, the processes of steps S604 to S606 are omitted until the number of signal periods stored in the RAM 102 reaches four. Furthermore, when there are no ink droplets to be ejected (for example, when the pixel at the target position is white), the process of step S607 is omitted.

Furthermore, the moving average value correction means 503 according to this embodiment calculates the corrected moving average value, for example, by the following method. Below, a method for calculating the corrected moving average value (=108.78) at the timing when the pulse signal [4] in FIG. 7 is output will be described. Note that in this embodiment, the feedback gain (coefficient) is G=0.5. However, the feedback gain G may be set to a different value depending on the characteristics of the inkjet recording device 1.

The moving average correction means 503 calculates the difference (=7.61) between the newest signal period (=107.61) and the oldest signal period (=100.00) of the four signal periods used to calculate the pre-correction moving average (=104.98). Next, the moving average correction means 503 multiplies the calculated difference (=7.61) by the feedback gain G (=0.5) to obtain a value (=3.80) to the corresponding pre-correction average (104.98). This results in the post-correction moving average (=108.78).

As a result, the signal period, pre-correction moving average value, and post-correction moving average value in the table of FIG. 7 are stored in the RAM 102. On the other hand, the pre-correction error is the difference between the ideal signal period and the pre-correction moving average value. Also, the post-correction error is the difference between the ideal signal period and the post-correction moving average value. Note that the ideal signal period and the actual signal period of the second encoder 211 share a large tendency in common. Therefore, in this embodiment, for simplicity, the differences between the actual signal period of the second encoder 211 and the pre-correction moving average value and the post-correction moving average value are described as the pre-correction error and post-correction error in FIG. 7.

In all rows in FIG. 7, the post-correction error is equal to or less than the pre-correction error. That is, the processing of the moving average correction means 503 causes the moving average to approach the ideal signal period. The progress of the conveying speed calculated based on the ideal signal period (dashed line L1), the progress of the conveying speed calculated based on the pre-correction moving average (gray line L2), and the progress of the conveying speed calculated based on the post-correction moving average (black line L3) are as shown in FIG. 8. Referring to FIG. 8, the black line L3 is closer to the dashed line L1 compared to the gray line L2 (i.e., the delay is smaller).

According to the above embodiment, by correcting the pre-correction moving average value based on the amount of change in the signal period and generating the ejection timing based on the post-correction moving average value, it is possible to reduce detection errors in the transport speed of the paper P and to land ink droplets at the target position.

In addition, according to the above embodiment, by arranging the encoder sensor 213 at the same position as the ejection head 23 in the circumferential direction of the paper transport drum 21, it is possible to properly detect the variation in the transport speed at the position of the ejection head 23. Furthermore, by providing an encoder sensor 213 corresponding to each of the multiple ejection heads 23A to 23F, it is possible to properly detect the variation in the transport speed at the position of each ejection head 23.

The method of correcting the moving average value by the moving average value correction means 503 is not limited to the above example, so long as it is based on the amount of change in the multiple signal periods used to calculate the pre-correction moving average value. Below, the moving average value correction methods according to Modifications 1 and 2 are described with reference to Figures 9 and 10. Note that Modifications 1 and 2 differ from the above embodiment in the processing of the moving average value correction means 503, but share other configurations and processing with the above embodiment.

[Modification 1]
9 is a diagram showing the correspondence relationship between the signal period, pre-correction moving average value, pre-correction error, post-correction moving average value, and post-correction error according to Modification 1. A method for calculating the post-correction moving average value (=104.70) at the timing when the pulse signal [5] in FIG. 9 is output will be described below. In this embodiment, the feedback gain (coefficient) is G=0.5. However, the feedback gain G may be set to a different value depending on the characteristics of the inkjet recording apparatus 1.

The moving average correction means 503 according to the first modification calculates the difference (=-2.91) between the most recent signal period (=104.70) and the next most recent signal period (=107.61) of the four signal periods used to calculate the pre-correction moving average (=106.16). Next, the moving average correction means 503 multiplies the calculated difference (=-2.91) by the feedback gain G (=0.5) to obtain a value (=-1.46) to the corresponding pre-correction average (106.16). This results in the post-correction moving average (=104.70).

In all rows in FIG. 9, the post-correction error is equal to or less than the pre-correction error. In other words, even if the moving average value is corrected using the difference between the most recent two signal periods, the moving average value approaches the ideal signal period. As a result, even with the moving average value correction method according to variant 1, it is possible to reduce detection errors in the transport speed of the paper P and land ink droplets at the target position.

[Modification 2]
Fig. 10 is a diagram showing the correspondence relationship between the signal period, pre-correction moving average value, pre-correction error, post-correction moving average value, and post-correction error according to Modification 2. A method for calculating the post-correction moving average value (=106.03) at the timing when the pulse signal [4] in Fig. 10 is output will be described below. In this embodiment, the feedback gain (coefficient) is G = 0.1/0.2/0.3. However, the feedback gain G may be set to a different value depending on the characteristics of the inkjet recording apparatus 1.

The moving average correction means 503 according to the second modification calculates the difference (=4.7/2.91/0) between two signal periods that are adjacent in time for each of the multiple pairs (100.00, 104.70/104.70, 107.61/107.61, 107.61) of the four signal periods used to calculate the pre-correction moving average (=104.98). Next, the moving average correction means 503 multiplies the difference (=4.7/2.91/0) between each pair by the feedback gain G (0.1/0.2/0.3) to obtain a value (0.47/0.58/0) to the corresponding pre-correction moving average (=104.98). This results in the post-correction moving average (=106.03). The difference in signal periods is multiplied by a smaller feedback gain G for earlier pairs and a larger feedback gain G for more recent pairs.

In all rows of FIG. 10, the post-correction error is equal to or less than the pre-correction error. In other words, even if the feedback gain G is reduced to correct the moving average value for the older set of signal periods, the moving average value approaches the ideal signal period. As a result, the method of correcting the moving average value according to variant 2 can also reduce the detection error in the transport speed of the paper P, allowing ink droplets to land at the target position.

The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the technical gist of the invention. All technical matters included in the technical ideas described in the claims are covered by the present invention. The above-described embodiment shows a preferred example, but a person skilled in the art can realize various modifications from the disclosed contents. Such modifications are also included in the technical scope described in the claims.

1: Inkjet recording device 10: Paper feed section 11: Paper feed tray 12: Feeding device 13: Pair of registration rollers 20: Image forming section 21: Paper transport drum 21a: Shaft 22: Ink ejection section 23: Ejection head 24: Receiving cylinder 25: Delivery cylinder 26: Suction device 30: Drying section 31: Drying mechanism section 32: Suction transport mechanism section 40: Paper ejection section 41: Paper ejection tray 100: Controller 101: CPU
102: RAM
103: ROM
104: HDD
105: I/F
109: Common bus 201: First encoder 202: Encoder wheel 203, 213: Encoder sensor 211: Second encoder 212: Encoder scale 220: Tip position sensor 501: Detection value acquisition means 502: Moving average value calculation means 503: Moving average value correction means 504: Discharge timing generation means 505: Discharge control means

JP 2007-237402 A

Claims (7)

A transport unit that transports the medium;
a droplet ejection unit that ejects droplets onto the medium transported by the transport unit;
a conveying speed sensor that outputs a detection value that correlates with the conveying speed of the medium;
a controller that controls a timing of droplet ejection by the droplet ejection unit based on the detection value output from the transport speed sensor,
The controller:
Calculating a moving average value of a plurality of the detection values most recently output from the conveying speed sensor;
correcting the calculated moving average value based on the amount of change in the plurality of detection values;
generating the ejection timing based on the corrected moving average value;
The droplet ejection device is characterized in that the droplets are ejected from the droplet ejection section at the generated ejection timing. The droplet ejection device according to claim 1, characterized in that, in the process of correcting the moving average value, the controller adds to the calculated moving average value a value obtained by multiplying a coefficient by the difference between the most recent detection value and the oldest detection value among the multiple detection values used in calculating the moving average value. The droplet ejection device according to claim 1, characterized in that, in the process of correcting the moving average value, the controller adds to the calculated moving average value a value obtained by multiplying a coefficient by the difference between the two most recent detection values among the multiple detection values used to calculate the moving average value. The droplet ejection device according to claim 1, characterized in that in the process of correcting the moving average value, the controller adds to the calculated moving average value a value obtained by multiplying the difference between the two detection values by a coefficient that is smaller for the more recent pair, for each of a plurality of pairs of two detection values that are adjacent in time among the plurality of detection values. the transport unit includes a rotating member that rotates while supporting the medium on an outer circumferential surface,
the droplet discharge unit is disposed facing an outer circumferential surface of the rotating member,
The conveying speed sensor is
an encoder scale that rotates integrally with the rotating member;
an encoder sensor that reads the encoder scale and outputs the detection value,
5. The droplet ejection device according to claim 1, wherein the encoder sensor is disposed at the same position as the droplet ejection portion in the circumferential direction of the rotating member. the droplet ejection unit includes a plurality of ejection heads that are disposed at positions spaced apart from each other in a circumferential direction of the rotating member and each ejects a different type of droplet;
the conveying speed sensor includes a plurality of encoder sensors that are disposed at the same positions as the plurality of ejection heads in a circumferential direction of the rotating member,
6. The droplet ejection device according to claim 5, wherein the controller controls the ejection timing of each of the ejection heads based on the detection value output from the corresponding encoder sensor. A liquid droplet ejection device according to any one of claims 1 to 6,
The image forming apparatus is characterized in that the droplet ejection section forms an image on a medium by ejecting ink droplets.