JP2008229991A - Image forming system and motor drive control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problem: in a conventional image forming device, if disturbance such as soil exists on an encoder sheet etc., in spite that a carriage speed is set to a uniform rate, an actual carriage speed falls out of a target speed, and therefore the uniform rate cannot be ensured. <P>SOLUTION: In main scanning of the image forming system, a speed detecting cycle for detecting the carriage speed in a constant-speed moving zone (printing zone during constant-speed operation) and acceleration and deceleration zones, based on detection pulses from an encoder sensor 11, is set to a speed detecting cycle A when the carriage is accelerated or decelerated, and set to a speed detecting cycle B (A<B) when the carriage is operated at a constant speed, and the speed detecting cycle in the constant-speed operation zone is delayed from the speed detecting cycle in the acceleration and deceleration zones. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention particularly relates to an image forming apparatus that moves a carriage on which a recording head is mounted and a conveying unit that conveys a recording medium by a motor driven by servo control, and a motor drive control method.

  As various image forming apparatuses such as printers, facsimiles, copying apparatuses, plotters, printer / fax / copier multifunction machines, etc., a recording head composed of a liquid discharging head that discharges liquid droplets (hereinafter referred to as ink) is used as a carriage. The carriage is mounted on the recording medium (hereinafter also referred to as “paper”, but the material is not limited to paper, and is also referred to as recording medium, recording paper, transfer material, etc.). In addition, the recording medium is intermittently conveyed according to the recording width, and an image is formed on the recording medium by alternately repeating conveyance and recording (recording, printing, printing, The serial type is also used in the same meaning as printing), and the line type is a type in which recording is performed while the recording medium is conveyed without moving the recording head.

  For example, in a serial type image forming apparatus, in order to form a high-quality image by ejecting recording liquid droplets from a recording head to a predetermined position on a sheet, a constant velocity of a carriage or a conveying device It is important to ensure the accuracy of paper feeding, and in general, it is driven by servo control using a DC motor as a drive source for moving the carriage and transport means.

  However, when the speed of the carriage is controlled using DC servo motor control, if the linear encoder sheet for acquiring speed information is contaminated with an adhering material such as ink, the influence of disturbance such as contamination may depend on the control cycle interval. Therefore, the servo control may cause unevenness in the carriage speed control (constant speed).

Therefore, as described in Patent Document 1, control information for controlling the driving of the motor based on the first driving pattern is compared with a threshold value for determining an overload for the driving of the motor, and this comparison result The second drive pattern for changing the load for driving the motor based on the control information is set instead of the first drive pattern.
JP 2004-090267 A

Further, as described in Patent Document 2, when a carriage is moved by giving an output value (control value) of PID control to the motor, the motor is driven by a fixed output until the carriage detects movement from a stopped state. There is a motor control method that suppresses over-output of PID control due to mechanical feed at the start of startup by performing control.
JP 2004-166458 A

Further, Patent Document 3 includes a mechanical load measuring unit that measures the mechanical load state of the main / sub-scanning drive system at the time of turning on the power after the start of operation, every accumulated operation time of the apparatus, or every accumulated operation amount of the apparatus. There is something to prepare.
JP 2004-160873 A

In addition, there are driving methods and apparatuses as described in Patent Documents 4 to 6.
JP 2006-272770 A JP 09-131938 A JP 59-222780 A

  However, even in the devices described in Patent Documents 1 and 2 described above, since the speed control profile is created and the servo control is performed, there is a disturbance such as dirt on the encoder sheet, and the carriage speed is constant. However, if the input speed signal deviates from the profile, the servo control side determines the control amount based on the input signal, so the actual carriage speed deviates from the target speed. There is a problem of causing unevenness in control (constant velocity).

  The present invention has been made in view of the above problems, and performs stable speed control by reducing the influence of disturbance on speed control such as dirt on an encoder that detects the moving speed of a driven object. Objective.

  In order to solve the above problems, an image forming apparatus according to the present invention detects a moving speed of a driven object in an image forming apparatus that forms an image by moving the driven object by a motor driven by servo control. At least one of the detection cycle during acceleration and deceleration is configured differently during constant speed.

  Here, it is preferable that the speed detection cycle during constant speed is longer than the speed detection cycle during acceleration and deceleration. In this case, when the driven object is moved at a constant speed, the detected speed can be changed to a speed detection cycle before the threshold is exceeded when the detected speed exceeds a predetermined threshold with respect to the target speed.

  In each of the image forming apparatuses according to the present invention, the driven object has a configuration in which a recording head is mounted and a configuration in which the recording target is a conveying unit that conveys a recording medium. For example, the conveying unit is a conveying belt. The configuration and the conveyance means may be a conveyance roller.

  The motor drive control method according to the present invention is a motor drive control method in which a motor for moving a driven body is driven and controlled by servo control, and the movement speed of the driven object is detected when the driven object is accelerated or decelerated. The speed detection cycle is different from the speed detection cycle for detecting the moving speed of the driven object when the driven object is moved at a constant speed.

  According to the image forming apparatus of the present invention, the speed detection cycle for detecting the moving speed of the driven object is different between at the time of acceleration and at the time of deceleration. The influence of disturbance can be reduced, and stable speed control can be performed without excessively reacting to the speed detected by each control face (acceleration / deceleration, constant speed) of servo control.

  According to the motor drive control method of the present invention, when the driven object is accelerated or decelerated, the speed detection cycle for detecting the moving speed of the driven object and the driven object when the driven object is moved at a constant speed. Since the speed detection cycle for detecting the moving speed of the servo motor is different, the influence of disturbance such as dirt on the encoder is reduced, and the speed detected by each control face (acceleration / deceleration, constant speed) of servo control is excessive. Stable speed control can be performed without reacting to.

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an outline of an ink jet recording apparatus as an image forming apparatus to which the present invention is applied will be described with reference to FIGS. 1 is an explanatory plan view showing a schematic configuration of the ink jet recording apparatus, FIG. 2 is an explanatory front view, and FIG. 3 is an explanatory side view.
In this ink jet recording apparatus, a carriage 3 is held by a guide lot 1 horizontally mounted on left and right side plates (not shown), and main scanning is performed by a main scanning motor 5 via a timing belt 8 passed between a driving pulley 6 and a driven pulley 7. Move and scan in the direction.

  The carriage 3 includes, for example, recording heads 4y, 4m, 4c, four liquid ejection heads that eject ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (K). 4k (hereinafter referred to as “recording head 4” when colors are not distinguished) is arranged in a direction perpendicular to the main scanning direction (sub-scanning direction) on the nozzle surface on which a plurality of ink discharge ports (nozzles) are formed. The ink discharge port direction is directed downward. In addition, although the independent liquid discharge head is used here, it is also possible to employ a configuration in which one or a plurality of heads having a plurality of nozzle rows that discharge droplets of recording liquid (ink) of each color are used. Further, the number of colors and the arrangement order are not limited to this.

  The liquid discharge head constituting the recording head 4 includes a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses a phase change caused by liquid film boiling using an electrothermal transducer such as a heating resistor, and a metal phase change caused by a temperature change. A shape memory alloy actuator using an electrostatic force, an electrostatic actuator using an electrostatic force, and the like provided as pressure generating means for generating a pressure for discharging a droplet can be used.

  Further, an encoder scale 10 having slits is provided on the back side of the carriage 3 along the main scanning direction, and an encoder sensor 11 for detecting the slits of the encoder scale 10 is provided on the carriage 3, so that the carriage 3 A linear encoder 12 for detecting the position and speed in the main scanning direction is configured.

  On the other hand, in order to transport the paper P, a transport belt 15 that is a transport means for electrostatically attracting the paper P and transporting it at a position facing the recording head 4 is provided. The transport belt 15 is an endless belt, and is configured to wrap around the transport roller 16 and the tension roller 17 so as to circulate in the belt transport direction (sub-scanning direction). 17 is charged (charged).

  The transport belt 15 may be a single-layer belt or a multi-layer (two or more layers) belt. In the case of a single-layer conveyor belt, it contacts the paper or charging roller, so the entire layer is formed of an insulating material. In the case of a transport belt having a multilayer structure, it is preferable that the side that contacts the paper and the charging roller is formed of an insulating layer, and the side that does not contact the paper and the charging roller is formed of a conductive layer.

  The conveyor belt 15 is rotated by the sub-scanning motor 19 when the conveyor roller 16 is rotationally driven via the drive belt 20 and the timing roller 21. An encoder wheel 22 having a slit is attached to the shaft of the conveying roller 16, and a transmission type photosensor 23 for detecting the slit of the encoder wheel 22 is provided. 24 is constituted.

Next, an outline of the control unit of the ink jet recording apparatus will be described with reference to FIG.
The control unit includes a main control unit 101 including a CPU, a ROM, a RAM, and the like, a RAM 102, a ROM 103, a print control unit 104, a host I / F 105, an I / F 106, 107, and controls the entire inkjet recording apparatus. A printer controller 100 to perform, a head driver 111 for driving the recording head 4, a driver 112 for driving the main scanning motor 5 and the sub-scanning motor 18, an AC bias supplying unit 113 for applying an AC bias voltage to the charging roller 18, and the like. The main control unit 101 receives detection signals from the encoder sensor 11 of the linear encoder 12 that detects the position and speed of the carriage 3 and the encoder sensor 23 of the rotary encoder 24 that detects the position and speed of the conveyor belt 12. .

  Through the I / F 105 of the printer controller 100, print data from the host side such as an information processing device such as a personal computer, an image reading device such as an image scanner, and an imaging device such as a digital camera is received via a cable or a network. . The RAM 102 is used as various buffers and work memories and stores various data. The ROM 103 stores various control routines executed by the main control unit 101, font data and graphic functions, various procedures, and the like. The print control unit 104 includes a drive signal generation circuit that generates a drive waveform for the recording head 24, and print data and drive waveform developed in dot pattern data (bitmap data) via the I / F 106 to the head driver 111. To send.

  The main control unit 101 detects the speed and position of the carriage 3 in the main scanning direction based on the detection signal from the encoder sensor 11 to control the movement stop of the carriage 3, and based on the detection signal from the encoder sensor 23. The movement stop control of the conveyor belt 15 is performed.

  The main control unit 101 reads and analyzes the print data in the reception buffer included in the I / F 105, stores the analysis result (intermediate code data) in a predetermined area of the RAM 102, and stores the analysis result in the ROM 103. Using the stored font data, dot pattern data for outputting an image is generated and stored again in a predetermined area of the RAM 102. Note that when image data is developed into bitmap data and transferred to this recording apparatus by the printer driver on the host side, the received bitmap image data is simply stored in the RAM 102.

  When the main control unit 101 obtains dot pattern data corresponding to one row of the recording head 4, the main control unit 101 outputs the dot pattern data for one row to the I / F 106 in synchronization with the clock signal from the transmission circuit. The serial signal is sent to the head driver 111 as serial data, and a latch signal is sent to the head driver 111 at a predetermined timing.

Next, details of a portion related to the drive control of the main scanning motor in the control unit will be described with reference to the functional block diagram of FIG.
A speed profile (acceleration table target speed) of the main scanning motor 5 is stored in the speed profile storage unit 201, and a target speed is given to the motor control unit 202. The speed profile storage unit 201 is configured by the ROM 102.

  The speed detection unit 203 counts the detection pulse output from the encoder sensor 11 and converts it into a carriage speed (speed detection value), and the speed is detected at the speed detection period (sampling period) set by the speed detection period setting unit 204. The detected value is given to the comparison calculation unit 205. The speed detection cycle setting unit 204 sets a speed detection cycle according to whether the carriage 3 is accelerating, decelerating, or constant speed based on the speed profile stored in the speed profile storage unit 201. In another embodiment, the speed detection cycle setting unit 204 sets a speed detection cycle according to whether the carriage 3 is accelerating, decelerating, or constant speed based on the speed profile stored in the speed profile storage unit 201. When the detection speed from the speed detection unit 203 exceeds a predetermined threshold during constant speed, the speed detection period during constant speed is set to the speed detection period before exceeding the threshold.

  The comparison calculation unit 205 compares the target speed given from the speed profile 201 with the detected speed value given from the speed detection unit 202, calculates the deviation between them, and gives it to the PI control calculation unit 206. The PI control calculation unit 206 calculates a control value by performing PI (proportional integration) control (in addition, PID (proportional, integration, differentiation) control, etc. can be performed) on the deviation from the comparison calculation unit 201.

  Here, assuming that the main scanning motor 5 is driven by PWM (Pulse Width Modulation) control, the PI control calculation unit 206 performs PI control on the deviation to obtain the PWM duty ratio, and this PWM By applying the duty ratio to the motor driver 112 and driving the main scanning motor 5 by PWM control, the carriage 3 is driven to a target position at a target speed.

  The movement speed, position determination, and movement distance calculation of the carriage 4 are read and determined by the encoder scale 11 arranged in parallel to the main scanning direction of the carriage 4 and the encoder sensor 11 installed on the carriage 4 as described above. . In the present embodiment, the encoder scale 11 of 300 dpi is used, and the output of the encoder sensor 11 is shifted by 90 ° to generate the A and B phases, and is used as a 1200 dpi position counter. For the speed information, the carriage passing time between encoder edges of 300 dpi is measured by a counter with a constant period (Hz in the embodiment), and the speed information is calculated from the counted value.

  As the above-described PI control, generally, a difference (deviation) between a current speed (detected speed value) detected at a constant control cycle (speed detection cycle), for example, 1 msec cycle, and a control target speed (target speed). Based on the above, the control value (PWM instruction value) calculated based on the following equation (1) is given to perform the speed control. In equation (1), P: proportional gain, I: integral gain, Vt: target speed, Vn: current speed.

  Control value (PWM instruction value) = P × (Vt−Vn) + I × Σ (Vt−Vn) (1)

Next, drive control of the main scanning motor will be described with reference to the flowchart of FIG.
First, control parameters that need to be set for each operation, such as a target speed and a stop position, and device information parameters unique to the device are set. Then, the driving of the main scanning motor 5 is started, and a control interrupt generated at a constant interval (speed detection cycle) is waited. When a control interrupt occurs, the current main scanning is detected from the detection pulse signal (encoder signal) from the encoder sensor 11. The position (current position of the carriage 3) is calculated, and the current speed of main scanning (current speed of the carriage 3) is calculated from the encoder signal.

  Thereafter, it is determined whether the current position is a stop position. When the current position is not reached, a speed deviation amount is calculated from the current speed, and servo control is performed from the calculated speed deviation amount. In this servo control, the rotation speed of the main scanning motor 5 is changed by calculating from the set parameters, the distance to the stop position, and the detected speed. When the current position becomes the stop position, the driving of the main scanning motor 5 is stopped.

  In the above description, the main scanning motor 5 is described, but the same applies to the sub-scanning motor 19.

  Here, the speed profile of main scanning by the main scanning motor 5, the speed profile of sub-scanning by the sub-scanning motor 19, and the speed detection cycle (sampling cycle) will be described with reference to FIG. 7A shows a main scanning speed profile, and FIG. 7B shows a sub scanning speed profile.

  The main scanning speed profile consists of an acceleration section that accelerates to a constant speed section, a constant speed section, and a deceleration section that decelerates from the printing end position (constant speed section end position). In some cases). When returning after stopping, acceleration, constant speed, and deceleration for returning are performed from the end of the stop section. The sub-scanning speed profile is also divided into an acceleration section, a constant speed section, a deceleration section, and the like that accelerate to the constant speed region.

Therefore, a first embodiment of the present invention will be described.
For main scanning, the speed detection cycle for detecting the carriage speed is switched based on the detection pulse from the encoder sensor 11 in the constant speed movement section (printing section, during constant speed) and the acceleration / deceleration section. That is, as shown in FIG. 7A, the speed detection cycle for detecting the carriage speed is changed from the period A to the period B when the detected carriage speed reaches the target speed of the carriage constant speed drive (time point T1). Change to (A <B).

  For example, the detection period A (acceleration / deceleration section) is set to 1 msec, the detection period B (constant speed section) is set to 2 msec, and the speed detection period in the constant speed section is delayed (set longer) than the speed detection period in the acceleration / deceleration section. .)

  In this case, the first detection timing after reaching the target speed is detected at the speed detection cycle before the change, and the speed detection is performed at the timing when the speed detection cycle is changed from the next detection. Therefore, the timing is not immediately changed when the switching timing (target speed reached) is reached.

  In addition, the speed detection period to be set varies depending on the apparatus configuration, such as the characteristics of the main scanning motor and the constant speed performance of the carriage speed with respect to the image quality. Therefore, the optimum value is determined by actually measuring the apparatus.

  In this way, by switching the speed detection cycle between the acceleration / deceleration section and the constant speed section, the influence of disturbance such as dirt on the linear encoder sheet is reduced, and at each control face (acceleration / deceleration, constant speed) of servo motor control, Stable speed control can be performed without excessive reaction to the detected speed. In this case, by making the speed detection period during constant speed longer than the speed detection period during acceleration and deceleration, in the acceleration / deceleration section where the speed fluctuation is severe, the constant speed with less speed fluctuation is maintained while maintaining the speed following characteristics of the control. The speed stability (constant speed) in the section can be improved, and the print image quality can be improved.

  Similarly, for sub-scanning, the speed detection cycle for detecting the conveyor belt speed is switched based on the detection pulse from the encoder sensor 23 in the constant speed movement section (printing section, during constant speed) and the acceleration / deceleration section. That is, as shown in FIG. 7B, when the detected belt speed reaches the target speed for belt constant speed driving, the speed detection period for detecting the belt speed is changed from the period C to the period D (C <D ). In this case, the first detection timing after reaching the target speed is detected at the speed detection cycle before the change, and the speed detection is performed at the timing when the speed detection cycle is changed from the next detection. Therefore, the timing is not immediately changed when the switching timing (target speed reached) is reached.

  In this case, the speed detection period to be set differs depending on the apparatus configuration, such as the characteristics of the sub-scanning motor and the constant speed performance of the belt speed with respect to the image quality. Therefore, the optimum value is determined by actually measuring the apparatus.

  In this way, by switching the speed detection cycle between the acceleration / deceleration section and the constant speed section, the influence of disturbance such as dirt on the rotary encoder sheet is reduced, and at each control face (acceleration / deceleration, constant speed) of servo motor control, Stable speed control can be performed without excessively reacting to the detected speed. In this case, by making the detection period of the constant speed section longer than the acceleration / deceleration section, in the acceleration / deceleration section where the speed fluctuation is severe, the speed stability in the constant speed section where the speed fluctuation is small while maintaining the control speed followability ( Iso-speed) can be improved, and the print image quality can be improved.

  As described above, the speed detection cycle for detecting the moving speed of the driven object when the driven object is accelerated or decelerated and the moving speed of the driven object are detected when the driven object is moved at a constant speed. By controlling the drive of the motor with a different speed detection cycle, the influence of disturbance such as dirt on the encoder is reduced, and it reacts excessively to the speed detected on each control face (acceleration / deceleration, constant speed) of servo control. Stable speed control can be performed without doing this.

  In the above embodiment, the speed detection cycle during acceleration and deceleration is the same, and both are described as being shorter than the speed detection cycle during constant speed, but the speed detection cycle during acceleration and deceleration is The speed detection period during acceleration or deceleration may be shorter than the speed detection period during constant speed.

Next, a second embodiment of the present invention will be described with reference to FIG.
In this embodiment, for example, when the conveying belt 15 is driven at a constant speed in the sub-scanning (during constant speed driving), the detection speed detected three times in succession (speed indicated by an asterisk in the figure). When the detection speed at the detection timing) exceeds a predetermined speed fluctuation threshold range (for example, within target speed ± 30 msec) with respect to the target speed, it is determined that the speed is abnormal.

  The criterion here is that when a speed outside the threshold is detected three times in a speed detection interval (for example, 2 msec), it is not due to dirt (dust, ink mist, etc.) on the encoder wheel 22, but paper jam, etc. It is assumed that the speed of the conveyor belt 15 is abnormal due to the above factors. In addition, the motor output and the change in the conveyor belt speed in this embodiment have a speed change of about 4 to 5 msec after the control voltage is changed, so that the speed detection cycle (control cycle) is 3 times (6 msec) continuously. When the speed information is detected at, it is determined that the speed is abnormal.

  The setting of these speed fluctuation threshold values varies depending on the apparatus such as the motor characteristics and the constant speed performance of the conveying belt speed with respect to the image quality. Therefore, an optimum value is determined by actually measuring the apparatus.

  As a result of the above control, when it is determined that the speed fluctuation is outside the threshold, the speed detection cycle is changed to the same cycle C as the acceleration / deceleration section (for example, 1 msec) until the conveyor belt 15 stops thereafter. Speed detection. When the conveyance belt 31 stops without reaching the target position, it is determined that the recording paper jam has occurred. Once deviating from the speed fluctuation threshold, the speed detection cycle is not changed again (returned to 2 msec) until the conveyor belt 31 stops even when the detected speed returns to the speed fluctuation threshold. Then, speed control is performed as it is. Then, DC servo motor control is performed by setting the speed detection cycle in the acceleration section from the next driving of the conveyor belt 15.

  Although the sub-scan is described here, the same control is performed for the main scan.

  In this way, when the detected speed exceeds the speed fluctuation threshold during constant speed, the speed detection period is returned to a short period (for example, the same as when accelerating / decelerating), and an abnormality such as a jam occurs. Safety can be ensured without deteriorating the device stop accuracy (stopping the device as soon as possible when an abnormality occurs).

  In the above-described embodiment, the example in which the conveyance unit is a conveyance belt has been described. However, the present invention can be similarly applied even when a recording medium is conveyed by a simple conveyance roller without using a conveyance belt. it can. Further, even when performing the shortest printing control, the same can be applied.

FIG. 4 is an explanatory plan view illustrating an example of a mechanism unit of the image forming apparatus according to the present invention. It is front explanatory drawing similarly. It is a side explanatory view similarly. FIG. 2 is a block explanatory diagram illustrating an overview of a control unit in the image forming apparatus. It is block explanatory drawing with which it uses for description of the part in connection with the main scanning motor control in the same control part. It is a flowchart with which it uses for description of the servo control of a motor. It is explanatory drawing explaining the relationship between the speed profile and speed detection period which are provided for description of 1st Embodiment of this invention. It is explanatory drawing explaining the relationship between the speed profile and speed detection period with which it uses for description of 2nd Embodiment of this invention.

Explanation of symbols

3 Carriage (driven object)
DESCRIPTION OF SYMBOLS 4 ... Recording head 5 ... Main scanning motor 11, 23 ... Encoder sensor 13 ... Linear encoder 15 ... Conveyor belt 19 ... Sub scanning motor 24 ... Rotary encoder 201 ... Speed profile storage part 202 ... Speed detection part 203 ... Speed detection period setting part 205 ... Comparison calculation unit 206 ... PI control calculation unit

Claims (8)

In an image forming apparatus that forms an image by moving a driven object by a motor driven by servo control,
An image forming apparatus, wherein a speed detection cycle for detecting a moving speed of the driven object is different from that during constant acceleration at least one of acceleration and deceleration.   2. The image forming apparatus according to claim 1, wherein a speed detection period during the constant speed is longer than a speed detection period during the acceleration and deceleration.   3. The image forming apparatus according to claim 2, wherein when the driven object is moved at a constant speed, the speed before the threshold is exceeded when the detected speed exceeds a predetermined threshold with respect to the target speed. An image forming apparatus characterized by changing to a detection cycle.   4. The image forming apparatus according to claim 1, wherein the driven object is a carriage on which a recording head is mounted.   5. The image forming apparatus according to claim 1, wherein the driven object is a conveying unit that conveys a recording medium.   6. The image forming apparatus according to claim 5, wherein the transport unit is a transport belt.   6. The image forming apparatus according to claim 5, wherein the transport unit is a transport roller. In a motor drive control method for driving and controlling a motor for moving a driven body by servo control,
A speed detection period for detecting a moving speed of the driven object when the driven object is accelerated or decelerated, and a speed detection period for detecting a moving speed of the driven object when the driven object is moved at a constant speed. A drive control method for a motor, characterized in that

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