JP2007196427A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can realize positional delivering of a printing medium with a high speed and a high accuracy, and can suppress deterioration of the quality of an image without decreasing printing speed even in a mechanism which can not increase feedback gain. <P>SOLUTION: The image forming apparatus forms the image by moving a printing head in the main scanning direction and moving the printing medium in the sub-scanning direction. The image forming apparatus has a printing medium conveying apparatus (100) for moving the printing medium and a conveying controlling apparatus (20) for controlling operation of the printing medium. The conveying controlling apparatus (20) changes the operational mode of the printing medium conveying apparatus (100) so that the printing medium is moved to a specified position by feedback controlling and when it reaches the specified position, it is moved by a positional conveying operation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus in which a printing head is moved in a main scanning direction and a printing medium is moved in a sub scanning direction by a feeding mechanism.

  In an image forming apparatus in which a printing head is moved in the main scanning direction and the printing medium is moved in the sub scanning direction by a feeding mechanism, the printing medium is fed one by one from a mechanism that holds the printing medium such as a feeding tray. Is fed out by a paper feeding device or the like, and the head of the print medium is detected by a print medium detection sensor. The printing medium moved to a place where printing by the printing head can be performed by this paper feeding device is moved in a direction perpendicular to the scanning direction of the printing head at regular intervals by a printing medium feeding device such as a printing medium conveyance roller, and further printed. By moving the head, image formation on the print medium is realized.

Here, in the paper feeding operation of the printing medium feeding mechanism at regular intervals, a speed profile is created starting with JP 2001-224189 A (Patent Document 1) and JP 2002-345277 A (Patent Document 2). A method for realizing position feed by feedback control based on an encoder output attached to a print medium conveyance shaft based on the profile has been proposed.
JP 2001-224189 A JP 2002-345277 A

  However, in a consumer printer system, the feedback gain cannot be increased because the mechanism is not sufficiently rigid, and it is very difficult to achieve high-speed position feed. If the gain of the feedback loop is low, high-speed position feed cannot be realized, and the printing systems disclosed in Patent Literature 1 and Patent Literature 2 cannot increase the printing speed.

  Accordingly, the present invention provides an image forming apparatus that realizes high-speed and high-precision position feeding of a print medium even in a mechanism in which the feedback gain cannot be increased, and can suppress deterioration in image quality without reducing the printing speed. The purpose is to do.

  In order to achieve the above object, an image forming apparatus of the present invention is an image forming apparatus that forms an image by moving a printing head in a main scanning direction and moving a printing medium in a sub scanning direction. A printing medium conveying device to be moved; and a conveyance control device for controlling the operation of the printing medium. The conveying control device moves the printing medium to a predetermined position by feedback control and reaches the predetermined position. The operation mode of the print medium conveying apparatus can be switched so as to be moved by the position feeding operation.

  As a result, even in a mechanism in which the feedback gain cannot be increased, high-speed and high-precision position feeding of the print medium can be realized, and deterioration in image quality can be suppressed without reducing the printing speed.

  In the image forming apparatus according to the aspect of the invention, the transport control device may use a command value to the print medium transport device as an initial setting command value when the operation mode is switched, and switch to a position feed operation after a predetermined time has elapsed. .

  Thereby, it is possible to realize the movement of the print medium to a predetermined position, that is, to the vicinity of the target position.

  In the image forming apparatus of the present invention, the transport control device refers to a command value to the print medium transport device during the position feeding operation by a predetermined amount (hereinafter referred to as “increase predetermined amount”) from the initial setting command value. ) Can be increased step by step.

  As a result, the print medium conveying device gradually starts to operate, and continues this operation until it reaches the target position, whereby the print medium can be sent to a predetermined position.

  In the image forming apparatus according to the aspect of the invention, the initial setting command value may be the print medium transport when the command value to the print medium transport device is increased by a predetermined amount from the stop state of the print medium transport device. It may be a command value when the apparatus starts operation.

  As a result, it is possible to operate the print medium conveying apparatus with a minimum driving force and execute the position feeding operation based on this.

  In the image forming apparatus of the present invention, the transport control device can determine the predetermined increase amount based on a load applied to the print medium transport device.

  As a result, a position feed operation with good responsiveness to load fluctuations becomes possible.

  In the image forming apparatus according to the aspect of the invention, the transport control device can change the initial setting command value based on a load applied to the print medium transport device.

  This makes it possible to perform a position feed operation with better response to load fluctuations.

  In the image forming apparatus of the present invention, the conveyance control device can change the predetermined increase amount when the print medium reaches a short distance from the target position.

  Thereby, it is possible to control the print medium to reach the target position more accurately.

  In the image forming apparatus of the present invention, the transport control device can set a command value to the print medium transport device to a predetermined value when the print medium reaches a target position.

  Thus, when the position of the print medium is moved by disturbance or the like after reaching the target position, control is easily performed so that the print medium is returned to the original target position. That is, it is possible to ensure that the print medium is aligned with the target position.

  Even in a mechanism with low rigidity and incapable of increasing the control feedback gain, the image forming apparatus of the present invention can switch between the feedback control operation and the position feed operation and parameterize the position feed operation, thereby achieving high speed and high accuracy. The position of the print medium can be realized, and the image quality deterioration can be suppressed without reducing the printing speed.

  Embodiments of the present invention will be described below with reference to the drawings.

[Configuration of printing medium transport device]
FIG. 1 is a configuration example of a print medium transport device incorporated in an image forming apparatus such as an ink jet printer. In the image forming apparatus, the print medium is fed one by one from a mechanism that holds the print medium such as a paper feed tray by a paper feed device such as a paper feed roller, and is transported by the print medium transport device 10 shown in FIG. An image is formed by a printing head that moves in a direction orthogonal to the conveying direction.

  The print medium conveyance device 10 includes a motor driven pulley 11, a driven pulley 12, a timing belt 13, a print medium conveyance roller 14, a pressure roller 15, a print medium conveyance plate 16, a printing head 17, It has a code wheel 18 and a sensor 19. The motor driven pulley 11, the driven pulley 12, and the timing belt 13 are means for driving the print medium conveyance roller 14 to rotate together. The print medium transport roller 14 and the print medium transport plate 16 are means for moving the print medium in the sub-scanning direction. The pressure roller 15 is a means for pressing the print medium placed on the print medium conveyance roller 14. The print head 17 is means for moving in the main scanning direction to form an image on the print medium. The code wheel 18 is mounted on the same axis as the print medium conveying roller, and is a means for installing the sensor 19. The sensor 19 is means for detecting the number of pulses of the code wheel 18.

  The motor-driven pulley 11 is driven by a motor (a motor 110 in FIG. 2 described later), and rotates the print medium transport roller 14 together with the driven pulley 12 and the timing belt 13. The print medium is rotated between the print medium conveyance roller 14 and the pressure roller 15 in the sub-scanning direction from the left to the right in FIG. And move on the printing medium conveyance roller 14 and the printing medium conveyance plate 16 to the printing start position. When the print medium reaches the print start position, the print head 17 positioned on the print medium ejects ink toward the print medium while moving in the main scanning direction orthogonal to the direction in which the print medium moves. An image is formed on a print medium. When the image formation for one main scanning direction by the print head 17 is completed, the print medium is moved to the next print start position by the same operation as described above. Thereafter, similarly, the print head 17 executes image formation for one main scanning direction on the print medium. By repeating such an operation, an image is formed on the print medium.

  Here, the printing medium conveyance operation by the printing medium conveyance roller 14 or the like requires the printing medium to be moved to a target position within a predetermined time. In order to realize this operation, it is necessary to convey the print medium at high speed and with high accuracy by a print medium conveyance roller or the like. The printing medium conveyance operation is based on the amount of movement of the printing medium in the sub-scanning direction according to the image to be formed. The amount of movement of the print medium is measured by detecting a pulse of a code wheel 18 mounted coaxially with the print medium conveyance roller 14 by a sensor 19. In this embodiment, the pulse signal count is increased or decreased according to the rotation direction of the code wheel 18.

[Measurement of printing medium movement and control of conveyance operation]
Measurement of the amount of movement of the print medium and control of the transport operation based on the pulse detection of the code wheel 18 by the sensor 19 of FIG. 1 will be described with reference to FIG. FIG. 2 is an example of a block diagram of a conveyance control device that controls the conveyance operation of the print medium by the print medium conveyance device of FIG.

  The conveyance control device 20 is incorporated in the image forming apparatus and controls the printing medium conveyance operation by the printing medium conveyance device 10 in FIG. 1, and includes a multiplier 21, a counter 22, an arithmetic device 23, and the like. Have The multiplier 21 is a unit that performs binarization by four on the pulse signal detected by the sensor of the print medium transport device. The counter 22 is means for counting the signals binarized by the multiplier 21. The arithmetic device 23 calculates the amount of movement of the print medium from the count value of the counter 22, the diameter of the print medium conveyance roller, and the like, and based on the calculation result, the drive command for controlling the print medium conveyance operation by the print medium conveyance device A device that outputs a value.

  In FIG. 2, the print medium transport apparatus 100 includes a sensor 19, a motor 110, and a motor drive circuit 120. The sensor 19 is the same as the sensor 19 in FIG. The motor 110 is means for driving the motor driving pulley 11 of FIG. The motor drive circuit 120 is a circuit that receives a drive command value from the transport control device 20 and controls the motor 110 in response thereto.

  In the print medium conveying apparatus 100, the sensor 19 detects a pulse signal of the code wheel 18 of FIG. The pulse signal detected by the sensor 19 is input to the multiplier 21 of the transport control device 20. The multiplier 21 performs quadruple binarization on the input pulse signal. Next, the counter 22 counts the signal binarized by the multiplier 21. The arithmetic unit 23 reads the count value of the counter 22 and outputs a drive command value based on the difference value between the count value and the set value of the speed profile according to the present invention to the print medium conveying apparatus 100. In this embodiment, the drive command value is output as a voltage value. The drive command value output from the arithmetic device 23 is input to the motor drive circuit 120 of the print medium transport device 100. The motor drive circuit 120 controls the motor 110 according to the input drive command value. That is, the motor 110 changes the rotation speed according to the drive command value. The motor 110 is a means for driving the motor drive pulley 11 of FIG. 1, and the motor drive pulley 11 is a means for rotationally driving the print medium transport roller 14 which is a means for transporting the print medium. The printing medium conveyance operation is controlled. The conveyance control device 20 performs feedback control on the print medium conveyance device 100 until the print medium moves to the vicinity of the predetermined target position, and executes a position feeding operation after the print medium moves to the vicinity of the target position. Do the control.

[Speed profile until the print medium moves near the target position]
A transport operation of the print medium transport device until the print medium moves to the vicinity of a predetermined target position will be described. The print medium conveyance device is feedback-controlled by the conveyance control device until the print medium moves near a predetermined target position. As an example, a speed profile until the print medium moves near the target position is shown in FIG.

In the speed profile of FIG. 3, the vertical axis represents the conveyance speed, and the horizontal axis represents time. The speed profile includes an acceleration area (a), a constant speed area (b), a deceleration area (c), and a low speed constant area (d). In the acceleration region (a), the transport speed is accelerated to a speed v1 at a constant acceleration by the transport control device during time T1. Next, in the constant speed region (b), the transport control device performs feedback control of the transport speed with the speed v1 as the target speed. Here, assuming that the number of pulses corresponding to the target position obtained by converting the moving distance of the printing medium from the diameter of the printing medium conveyance roller and the like is P _ref , the conveyance control device counts this from the start of conveyance in the arithmetic unit 23 of FIG. The difference from the number of pulses P is calculated. When the difference P _ref −P reaches a predetermined value P1, that is, the moving distance of the print medium transported by the print medium transport apparatus sets the difference value P1 of the number of pulses to the target position as the print medium transport roller. When reaching the position converted from the diameter or the like, the transport speed is switched from the constant speed region (b) to the deceleration region (c) by the transport control device. In the deceleration area (c), the transport speed is decelerated at a constant deceleration, and when the difference P _ref −P reaches a predetermined value P2, that is, the travel distance of the print medium transported by the print medium transport device. However, when the difference value P2 of the number of pulses with respect to the target position reaches a position converted from the diameter of the printing medium conveyance roller, the conveyance control device changes the deceleration area (c) to the constant low speed area (d). Can be switched. Next, in the low speed constant region (d), the transport control device performs feedback control on the print medium transport device so as to transport the print medium at the speed v2, and the difference P _ref −P is a predetermined value P3. That is, when the moving distance of the printing medium conveyed by the printing medium conveying device reaches a position where the difference value P3 of the number of pulses is converted from the diameter of the printing medium conveying roller with respect to the target position. Then, the printing medium conveyance operation by the feedback control is finished, and the drive command value to the motor drive circuit 120 in FIG. 2 is changed to zero or a constant value.

  By controlling the transport speed of the print medium by the print medium transport apparatus using such a speed profile, a transport operation for moving the print medium to a vicinity of a predetermined target position is realized.

[Speed profile after the print medium has moved to near the target position]
A transport operation of the print medium transport apparatus after the print medium has moved to the vicinity of a predetermined target position by feedback control using the speed profile of FIG. 3 will be described. The print medium conveyance device is controlled to execute a position feeding operation by the conveyance control device after the print medium has moved to the vicinity of a predetermined target position. As an example, a speed profile after the print medium has moved to the vicinity of the target position is shown in FIG.

A difference P _ref −P between a pulse number P _ref which is a pulse number corresponding to a target position obtained by converting the moving distance of the print medium from the diameter of the print medium transport roller and the pulse number P counted from the start of transport is a predetermined value P3. After that, the transport control device sets the drive command value to the motor drive circuit 120 in FIG. 2 as the initial set command value C0. C0 is constant. After the predetermined time Tw elapses, the transport control device increases the initial setting command value C0 by a predetermined amount C1 that is increased every predetermined time. Such an operation is called a “position feed operation” in this embodiment. The count value of the counter 22 in FIG. 2 during the position feed operation is as shown in FIG. In FIG. 5, the vertical axis represents the count value, that is, the number of pulses, and the horizontal axis represents time. By increasing the drive command value by a predetermined amount every predetermined time, the motor starts rotating gradually and continues this operation until the print medium reaches the stop target position, thereby achieving the target number of pulses. . After the print medium reaches the target position at time t ₁ , the conveyance control device does not set the drive command value to the motor drive circuit 120 in FIG. 2 to zero, but a value at the time of arrival or an arbitrary constant value C 2. And C2 is determined by the value S0 of the drive command value when the target position is reached, for example,
C2 = S0 × D (1)
Sought by. Here, D is a constant of 1 or less.

The print medium is stopped at the target position until the image formation for one main scanning direction is completed after reaching the target position. That is, since there is no movement in the sub-scanning direction, the number of pulses does not increase or decrease from the target number of pulses _Pref . However, even after the target position is stopped, the transport control device continues counting the number of pulses. If the count value changes for some reason after the target position stops, the conveyance control device drives the motor drive circuit according to the change in the count value. Change the command value. For example, in FIG. 5, when the count value decreases at time t ₂ , this means that the print medium has moved in the direction opposite to the feed direction with respect to the target position, and the transport control device moves the print medium to the target position. It is necessary to drive the motor to send to Therefore, as shown in FIG. 4, the conveyance control device adds C3 to the drive command value C2 to the motor drive circuit. On the other hand, in FIG. 5, when the count value at time t ₄ increases, the print medium is that it has moved in the feeding direction with respect to the target position, the transport control unit, so as to return the print medium to the target position It is necessary to drive the motor. Therefore, as shown in FIG. 4, the transport control device subtracts C4 from the drive command value C2 to the motor drive circuit. Here, C3 and C4 are the following equations:
C3 = C0
C4 = C0 / 2
The value may be changed according to the mechanical characteristics of the motor or the like. This process ensures that the print medium is aligned with the target position.

[Set command value]
Here, a method of determining the initial setting command value C0 will be described with reference to FIG. In FIG. 6, the left vertical axis indicates the drive command value output from the transport control device 20 in FIG. 2 to the motor drive circuit 120, and the right vertical axis indicates the count value of the counter 22 in FIG. The number of pulses corresponding to the moving distance of the medium is shown, and the horizontal axis shows time. In FIG. 6, assuming that the motor for transporting the print medium is in a stopped state when time t = 0, the drive command value is increased by a predetermined step width every predetermined time from the stopped state of the motor. At that time, as described above, the rotation amount of the motor is detected by counting through the sensor and the counter, and the drive command value when the motor starts rotating is set as the initial setting command value C0.

Next, a method for determining the increased predetermined amount C1 added to the initial setting command value C0 every predetermined time during the position feed operation will be described. In the constant speed region (b) of FIG. 3, the load amount that is constantly applied when the motor is driven from the torque constant Ke and the resistance value R of the motor is expressed by the following equation:
C1 ′ = (V _v1 −V _emf ) / R × Ke × A (2)
Is calculated by Here, V _v1 is a command voltage value output from the transport control device in the constant speed region (b). V _emf is the counter electromotive force of the motor in the constant speed region (b), and is obtained from V _emf = Ke × ω, where ω is the angular velocity of the motor. A is an arbitrary constant determined in advance by experience. By setting the load amount C1 ′ obtained from the equation (2) as the predetermined increase amount C1 during the position feed operation, it is possible to perform position feed with good response to load fluctuations.

  Further, by changing the value of the initial setting command value C0 according to the following equation (3) in accordance with the load amount calculated as described above, position feed with better response to load fluctuations. Is possible.

C0 ′ = C0 × (V _v1 −V _emf ) / R × Ke × B (3)
Here, B, like A, is an arbitrary constant determined in advance by experience.

In the above description, it has been described that the initial setting command value C0 is increased every predetermined time and increased by a predetermined amount C1 during the position feeding operation. However, when the print medium moves to the vicinity of the stop target position, the print medium is more accurately detected. The value of the increased predetermined amount C1 may be changed so as to reach the target position. For example, the difference P _ref −P between P _ref , which is the number of pulses corresponding to the target position obtained by converting the moving distance of the print medium from the diameter of the print medium transport roller, and the number of pulses P counted from the start of transport is 10. When the position feed operation is started from the time point until the difference value becomes 10 and approaches the target position and becomes 5, the value of the predetermined increase amount is C1, and until the difference value becomes 5 to 0, That is, the value of the predetermined increase amount is set to C1 / 2 until the target position is reached.

[Modification]
In the above-described embodiments, the present invention has been described with respect to an image forming apparatus in which the print head is moved in the main scanning direction and the print medium is moved in the sub-scanning direction by the feeding mechanism. However, the present invention is not limited to the image forming apparatus. The present invention can be applied to various devices that perform position control using the above driving device.

  Moreover, the said Example is applicable also to control circuits of any motors, such as a DC motor, an AC motor, or a stepping motor.

  The present invention may also be realized by a program stored in a memory such as a hard disk (HDD) or a read-only memory (ROM) of the image forming apparatus. That is, the image forming apparatus of the present invention can be realized by executing an image forming apparatus program that realizes the position feeding of the print medium of the image forming apparatus as described above by an information processing apparatus such as a computer.

1 is a configuration example of a print medium transport device incorporated in an image forming apparatus. FIG. 2 is an example of a block diagram of a transport control device that controls a transport operation of a print medium by the print medium transport device of FIG. 1. An example of a speed profile until the print medium moves near the target position is shown. An example of the speed profile after the print medium has moved to the vicinity of the target position is shown. FIG. 5 is a graph of the number of pulses when the print medium conveyance device operates based on the speed profile of FIG. 4. It is a figure explaining an example of the determination method of initial setting command value C0.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,100 Print medium conveyance apparatus 11 Motor drive pulley 12 Driven pulley 13 Timing belt 14 Print medium conveyance roller 15 Pressure roller 16 Print medium conveyance board 17 Print head 18 Code wheel 19 Sensor 110 Motor 120 Motor drive circuit 20 Conveyance control Device 21 Multiplier 22 Counter 23 Arithmetic device v1, v2 Transport speed C0, C1, C2, C3, C4 Drive command value

Claims (8)

In an image forming apparatus that forms an image by moving a printing head in a main scanning direction and moving a printing medium in a sub-scanning direction,
A print medium transport device that moves the print medium, and a transport control device that controls the operation of the print medium,
The transport control device moves the print medium to a predetermined position by feedback control, and switches the operation mode of the print medium transport device so as to move by a position feeding operation when the predetermined position is reached. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the transport control device uses a command value to the print medium transport device as an initial setting command value when the operation mode is switched, and switches to a position feed operation after a predetermined time has elapsed. apparatus.   The transport control device increases a command value to the print medium transport device by a predetermined amount (hereinafter referred to as “increase predetermined amount”) from the initial setting command value during the position feeding operation. The image forming apparatus according to claim 2.   The initial setting command value is a command value when the print medium transport device starts operating when the command value to the print medium transport device is increased by a predetermined amount from the stop state of the print medium transport device. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 3, wherein the conveyance control device determines the predetermined increase amount based on a load applied to the print medium conveyance device.   The image forming apparatus according to claim 5, wherein the conveyance control device changes the initial setting command value based on a load applied to the print medium conveyance device.   The image forming apparatus according to claim 3, wherein the conveyance control device changes the predetermined increase amount when the print medium reaches a predetermined distance from a target position.   The image according to any one of claims 2 to 7, wherein the conveyance control device sets a command value to the print medium conveyance device to a predetermined value when the print medium reaches a target position. Forming equipment.

Images