JP2006076241A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that even when a medium to be recorded is highly accurately carried to a stopping position, the stopping position is changed by acting an external disturbance such as a back tension on the medium to be recorded during image forming operation to deteriorate quality of an image. <P>SOLUTION: After the medium to be recorded is carried to a target stopping position, when a printing is being practiced, the present position of the medium to be recorded is obtained from a positional speed detecting part 102. When the amount of deviation from the stopping position exceeds a preset amount of setting, an outputting value of a PID operating part 112 is changed in accordance with the amount of deviation so as to decrease the amount of deviation, to perform a control for holding the stopping position for returning the medium to be recorded to the original stopping position. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that performs feed control of a recording medium by feedback control.

  As various image forming apparatuses such as printers, facsimiles, copying machines, plotters, printer / fax / copier multifunction machines, etc., a recording head constituted by a droplet discharge head is mounted on a carriage, and the carriage is used as a recording medium (paper, paper, (Also referred to as a recording medium, etc.)) is scanned serially in a direction orthogonal to the conveying direction of the recording medium, the recording medium is intermittently conveyed according to the recording width, and recording is performed by alternately repeating conveyance and recording. A serial type that forms an image on a medium (recording, printing, printing, and printing are also used synonymously) and a recording head having a line width are provided on the recording medium while feeding the recording medium in sub-scanning. There is a line type that forms an image.

  In such an image forming apparatus, in order to continuously record an image on a recording medium by droplets ejected from a recording head that outputs an image having a certain constant width, the recording medium is intermittently conveyed (sub-recording). Scanning), the feeding accuracy of the recording medium and the stop positioning accuracy of the recording medium at this time affect the image quality. Therefore, in order to record a high-quality image at high speed, the recording medium must be conveyed and positioned at high speed and with high accuracy.

Therefore, in general, a driven body such as a conveyance belt or a conveyance roller for feeding a recording medium is rotationally driven by a drive motor, and the moving speed of the driven body is determined from an encoder output corresponding to the movement amount (rotation amount) of the driven body. Servo control is used to obtain speed information and position information related to the amount of movement, and to drive and control the drive motor based on these speed information and position information.
JP 2003-103857 A

Further, as disclosed in Patent Document 2, in the DC motor driving method controlled based on the digital position signal output from the detector that detects the rotation amount of the DC motor, the digital position signal is changed. Each time the signal confirmation step to confirm and each time the digital position signal is confirmed to change to a predetermined value, the first driving force is gradually reduced for the DC motor in accordance with the position error from the target position. Between each step of applying a driving force or reducing a driving force to stop driving, and after each first driving force is applied until it is confirmed that the digital position signal changes a predetermined amount, There is known a driving method including a driving force increasing step for increasing the driving force stepwise with respect to the driving force.
JP 2003-348878 A

  In the servo control as described above, the load to be controlled is not always constant, and it is necessary to grasp a state invisible to the control system such as inertia, frictional force, and rigidity (spring property). Therefore, it is possible to obtain a high-speed and high-quality printing result by detecting and controlling the speed at which these disturbance factors are directly connected without error.

  However, even if the recording medium is transported to the target position with high accuracy, the image forming (printing) is performed particularly when the recording medium is stopped and the droplets are ejected from the recording head. If a disturbance such as back tension from the paper feed roller acts on the recording medium and the position accuracy of the recording medium is disturbed, the droplet landing accuracy is disturbed and the image quality deteriorates. become.

  The present invention has been made in view of the above points, and an object thereof is to provide an image forming apparatus capable of obtaining high image quality by suppressing stop position fluctuation of a recording medium during image formation.

  In order to solve the above-described problem, the image forming apparatus according to the present invention is configured to record on the basis of the stop position fluctuation of the recording medium when the image forming unit performs an image forming operation for forming an image on the recording medium. A means for performing stop position holding control for returning the medium to a predetermined stop position is provided.

  Here, the stop position holding control is preferably performed by changing the output value for the drive source of the means for performing feedback control for the drive source of the recording medium with the predetermined stop position of the recording medium as the target position.

  In this case, a deviation amount between the current position of the recording medium and a predetermined stop position is detected, and it is determined whether or not to change the output value for the drive source based on the detected deviation amount and a preset set amount. It is preferable to have a means to do this.

  Furthermore, it is preferable to change the output value for the drive source according to the position deviation amount of the recording medium when the detected deviation amount exceeds a predetermined set amount.

  According to the image forming apparatus of the present invention, stop position holding control is performed to hold the recording medium at a predetermined stop position even during printing. Therefore, even if a disturbance is applied to the recording medium during printing, It is possible to form an image with high image quality by suppressing the stop position fluctuation of the recording medium.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an explanatory side view for explaining the overall configuration of the image forming apparatus according to the present invention, and FIG.
In this image forming apparatus, a carriage 3 is slidably held in a main scanning direction by a guide rod 1 and a guide rail 2 which are guide members horizontally mounted on left and right side plates (not shown), and a timing belt 5 is held by a main scanning motor 4. 2 is moved and scanned in the arrow direction (main scanning direction) in FIG.

  The carriage 3 includes, for example, four recording heads 7 each including a droplet discharge head that discharges yellow (Y), cyan (C), magenta (M), and black (Bk) ink droplets. The ejection ports are arranged in a direction crossing the main scanning direction, and are mounted with the ink droplet ejection direction facing downward.

  The droplet discharge head constituting the recording head 7 includes a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses film boiling of the recording liquid using an electrothermal transducer such as a heating resistor, and a metal phase change due to a temperature change. A shape memory alloy actuator to be used, an electrostatic actuator using an electrostatic force, or the like provided as energy generating means for discharging ink (liquid) can be used. Note that the recording head can also be configured by one or a plurality of liquid droplet ejection heads provided with a plurality of nozzle rows that eject different colors.

  The carriage 3 is equipped with sub-tanks 8 for each color for supplying ink of each color to the recording head 7. Ink is supplied to the sub tank 8 from a main tank (ink cartridge) (not shown) via an ink supply tube 9.

  On the other hand, as a paper feeding unit for feeding paper 12 stacked on a paper stacking unit (pressure plate) 11 such as a paper feeding cassette 10, a half-moon roller (for separating and feeding the paper 12 one by one from the paper stacking unit 11) A separation pad 14 made of a material having a large friction coefficient is provided facing the sheet feeding roller 13 and the sheet feeding roller 13, and the separation pad 14 is urged toward the sheet feeding roller 13 side.

  As a transport unit for transporting the paper 12 fed from the paper feed unit on the lower side of the recording head 7, a transport belt 21 for transporting the paper 12 by electrostatic adsorption, and a paper feed unit A counter roller 22 for transporting the paper 12 fed through the guide 15 between the transport belt 21 and the paper 12 fed substantially vertically upward is turned approximately 90 ° and copied onto the transport belt 21. A conveying guide 23 for adjusting the pressure and a tip pressing roller 25 urged toward the conveying belt 21 by a pressing member 24. In addition, a charging roller 26 as a charging unit for charging the surface of the transport belt 21 is provided.

  Here, the transport belt 21 is an endless belt, and is stretched between the transport roller 27 and the tension roller 28, and the transport roller 27 rotates from the sub-scanning motor 31 via the timing belt 32 and the timing roller 33. By doing so, it is configured to circulate in the belt conveyance direction (sub-scanning direction) of FIG. That is, the sub-scanning motor 31 is a drive motor, and the transport belt 21 (transport roller 27) is a driven body that is driven by the drive motor. A guide member 29 is disposed on the back side of the conveying belt 21 corresponding to the image forming area by the recording head 7.

  Further, as shown in FIG. 2, a slit disk 34 is attached to the shaft of the transport roller 27, and a sensor 35 for detecting the slit of the slit disk 34 is provided. An encoder 36 is configured. The encoder 36 is an encoder for detecting the amount of movement of the conveyor belt 21 that is a driven body (the amount of rotation of the conveyor roller 27).

  The charging roller 26 is disposed so as to contact the surface layer of the conveyor belt 21 and rotate following the rotation of the conveyor belt 21, and applies 2.5N to both ends of the shaft as a pressing force.

  As shown in FIG. 1, an encoder scale 42 having slits is provided on the front side of the carriage 3, and an encoder sensor comprising a transmissive photosensor that detects the slits of the encoder scale 42 on the front side of the carriage 3. 43 are provided, and an encoder 44 for detecting the position of the carriage 3 in the main scanning direction is configured by these.

  Further, as a paper discharge unit for discharging the paper 12 recorded by the recording head 7, a separation unit for separating the paper 12 from the conveyance belt 21, a paper discharge roller 52 and a paper discharge roller 53, and paper discharge And a paper discharge tray 54 for stocking the paper 12 to be stored.

  A double-sided paper feeding unit 61 is detachably mounted on the back. The double-sided paper feeding unit 61 takes in the paper 12 returned by the reverse rotation of the transport belt 21, reverses it, and feeds it again between the counter roller 22 and the transport belt 21.

  In the image forming apparatus configured as described above, the sheets 12 are separated and fed one by one from the sheet feeding unit, and the sheet 12 fed substantially vertically upward is guided by the guide 15, and includes the transport belt 21 and the counter roller 22. The leading end is guided by the conveying guide 23 and pressed against the conveying belt 21 by the leading end pressing roller 25, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately repeated from the high voltage power source to the charging roller 26 by a control circuit (not shown), that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 21 is alternating, that is, In the sub-scanning direction, which is the circumferential direction, plus and minus are alternately charged in a band shape with a predetermined width. When the sheet 12 is fed onto the conveyance belt 21 charged alternately with plus and minus, the sheet 12 is attracted to the conveyance belt 21 by electrostatic force, and the sheet 12 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 21. Is done.

  Therefore, by driving the recording head 7 according to the image signal while moving the carriage 3, the ink droplets are ejected onto the stopped paper 12 to record one line, and after the paper 12 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 12 has reached the recording area, the recording operation is finished and the paper 12 is discharged onto the paper discharge tray 54.

  In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 12 is fed into the double-sided paper feeding unit 61 by rotating the conveyor belt 21 in the reverse direction. The paper 12 is reversed (with the back surface being the printing surface), fed again between the counter roller 22 and the transport belt 21, controlled in timing, and transported onto the transport bell 21 as described above. Then, after recording on the back surface, the paper is discharged onto the paper discharge tray 54.

Next, an outline of the control unit of the image forming apparatus will be described with reference to the block diagram of FIG.
The control unit 80 includes a CPU 81 that controls the entire apparatus, a ROM 82 that stores a program executed by the CPU 81 and other fixed data, a RAM 83 that temporarily stores image data and the like, and a power supply for the apparatus. A rewritable NVRAM 84 for holding data and an ASIC 85 for processing image signals for performing various signal processing and rearrangement on image data and other input / output signals for controlling the entire apparatus are provided.

  The control unit 80 also includes an I / F 86 for transmitting and receiving data and signals to and from the host side, a head drive control unit 87 and a head driver 88 for driving and controlling the recording head 7, and the main scanning motor 4. The main scanning motor driving unit 90 for driving the sub-scanning motor 31, the sub-scanning motor driving unit 91 for driving the sub-scanning motor 31, the detection pulses from the encoders 36 and 44, and the detection from the temperature sensor 95 that detects the environmental temperature. An I / O 92 for inputting signals and detection signals from other various sensors is provided. The control unit 80 is connected to an operation panel 93 for inputting and displaying information necessary for the apparatus.

  The control unit 80 receives print data and the like from the host side such as an information processing apparatus such as a personal computer, an image reading apparatus such as an image scanner, and an imaging apparatus such as a digital camera via the cable or the network via the I / F 86.

  The CPU 81 reads and analyzes the print data in the reception buffer included in the I / F 86, performs necessary image processing, data rearrangement processing, and the like in the ASIC 85, and transfers the image data to the head drive control unit 87. To do. The dot pattern data for image output may be generated by storing font data in the ROM 82, for example, or the image data is developed into bitmap data by a host-side printer driver and transferred to this apparatus. You may do it.

  When the head drive control unit 87 receives image data (dot pattern data) corresponding to one row of the recording head 7, the dot pattern data for one row is serialized to the head driver 88 in synchronization with the clock signal. Data is sent out, and a latch signal is sent to the head driver 88 at a predetermined timing.

  The head drive control unit 87 includes a ROM (which can be configured by the ROM 82) storing pattern data of a drive waveform (drive signal), and a D / A converter for D / A conversion of drive waveform data read from the ROM. A waveform generation circuit including an A converter and a drive waveform generation circuit including an amplifier and the like are included.

  In addition, the head driver 88 is a shift register that inputs a clock signal from the head drive control unit 87 and serial data that is image data, and a latch circuit that latches the register value of the shift register using a latch signal from the head drive control unit 87. A level conversion circuit (level shifter) that changes the output value of the latch circuit, an analog switch array (switch means) that is controlled to be turned on / off by the level shifter, and the like, and controls on / off of the analog switch array. As a result, a required drive waveform included in the drive waveform is selectively applied to the actuator means of the recording head 7 to drive the head.

  The main scanning motor driving unit 90 calculates a control value based on a target value given from the CPU 81 side and a speed detection value obtained by sampling a detection pulse from the encoder 44, and passes the main scanning motor via an internal motor driver. 4 is driven.

  Similarly, the sub-scanning motor drive unit 91 calculates a control value based on a target value given from the CPU 81 side and a speed detection value obtained by sampling a detection pulse from the encoder 36, and passes through an internal motor driver. The sub-scanning motor 31 is driven.

Therefore, a portion related to the drive control of the sub-scanning motor in this image forming apparatus will be described with reference to the functional block diagram of FIG.
A speed profile (acceleration table target speed) of the sub-scanning motor 31 is stored in the speed profile storage unit 101, and a target speed is given to the sub-scanning motor driving unit 91 by the CPU 81. The speed profile storage unit 101 is configured by a ROM 82.

  The position speed detection unit 102 counts the rising edge of the A-phase detection pulse output from the encoder 36 and detects the feed speed of the transport belt 21 corresponding to the rotational speed of the transport roller 27, so that the current speed is reached. While converting to a certain detection speed, the rising edge and falling edge of the detection pulses of the A phase and B phase are detected and counted, and the relative movement amount of the conveyance belt 21 corresponding to the rotation amount of the conveyance roller 27 is detected. Convert to position.

  The sampling unit 103 samples the speed information and the position information output from the position / velocity detection unit 102 at a predetermined sampling cycle, and supplies the sampled information to the sub-scanning motor driving unit 91. The speed detection unit 102 and the sampling unit 103 are configured by the encoder 36, the CPU 81 of the control unit 80, and the like.

  The sub-scanning motor drive unit 91 includes a comparison calculation unit 111, a PID control calculation unit 112, a motor driver 113, and a low speed calculation unit 114. Here, the comparison calculation unit 111 compares the target speed corresponding to the target position given from the speed profile 101 with the detection speed (current speed) output from the position speed detection unit 102 and given by the sampling unit 103. A deviation (speed deviation) between the two is calculated and given to the PID control calculation unit 112.

  The PID control calculation unit 112 performs PID (proportional, integral, differentiation) control on the speed deviation from the comparison calculation unit 111 or the speed deviation from the low speed calculation unit 114 and controls the sub scanning motor 31 that is a DC servo motor. Calculate the control value. Here, assuming that the sub-scanning motor 31 is driven by PWM (Pulse Width Modulation) control, the PID control calculation unit 112 performs PID control on the speed deviation to obtain the PWM duty ratio, and this PWM Is supplied to the motor driver 113 and the motor 31 is driven by PWM control to drive the conveyor belt 21 to a target position at a target speed.

  Based on the position information given from the sampling unit 103 to the comparison calculation unit 111, the low-speed calculation unit 114 has a difference (movement amount deviation) from the previously sampled position larger than a predetermined movement amount (predetermined value). It is determined whether or not it is small. When the movement amount deviation is equal to or less than a predetermined value, it is determined that the low speed control is being performed, and based on the detection speed and detection position provided from the position / speed detection unit 102, The converted speed is converted into a predetermined speed, the speed deviation between the converted speed and the target speed is calculated, and the calculated speed deviation is given to the PID calculation unit 112. That is, the low speed calculation unit 114 is for performing speed control substantially without using the speed information obtained from the encoder output.

Therefore, first, the control for feeding the recording medium (paper) to the target position will be described.
In this embodiment, at low speed, speed control different from that at normal time is performed using the low speed calculation unit 114. This is due to the contradiction between the speed information and the position information during the low speed control.

  That is, referring to FIG. 5, the encoder 36 outputs an A-phase detection pulse (pulse signal) and a B-phase detection pulse (pulse signal) as shown in FIGS. These pulses are collectively referred to as “encoder output”. The position / velocity detection unit 102 generates and outputs position detection pulses by latching position detection at the rising and falling edges of the detection pulses of the A phase and the B phase, as shown in FIG. Also, as shown in FIG. 5E, the speed detection latch is generated and output by latching for speed detection at the rising edge of the A-phase detection pulse.

  On the other hand, the sampling unit 103 performs sampling (denoted as a latch) at a predetermined sampling period to obtain the count value of the position detection pulse as position information, as shown in FIG. As shown in f), sampling is performed (denoted as latch), and the count value of the speed detection pulse is acquired as speed information.

  Therefore, for example, as shown in FIG. 5, when the sampling is performed by the sampling latch 1 by the sampling 103, the position acquisition in the latch 1 is “5” (for example, 5 pulses = 26.5 μm), and the speed acquisition is “a1”. (For example, 26.5 mm / sec). On the other hand, if the sampling period is elapsed from the latch 1 and sampling is performed in the latch 2, the position acquisition in the latch 2 is “2” (for example, 2 pulses = 10.6 μm). On the other hand, since the speed detection latch is not performed during the speed acquisition, “a1” (for example, 26.5 mm / sec) at the time of the latch 1 remains.

  Thus, a contradiction in the detection speed with respect to the movement amount occurs. This occurs when the movement amount within a predetermined sampling period (for example, 1 msec) of the sampling unit 103 is a movement amount (for example, 8 pulses) during which the speed detection latch cannot be performed twice. However, such a contradiction between the amount of movement and the detected speed (position information and speed information) occurs, as shown in FIG. 6, that the speed at the previous sampling and the speed at the current sampling are larger than a predetermined value. This is a case where a large speed deviation occurs, and no contradiction occurs because there is almost no speed deviation when the constant speed control is performed.

  Therefore, based on the amount of movement, it is determined whether or not it is during deceleration control that causes a large speed deviation and greatly affects the position accuracy. During deceleration control, speed control is performed using a predetermined speed regardless of the encoder output. To do.

Accordingly, drive control of the sub-scanning motor at the time of paper feeding in this image forming apparatus including such speed control will be described with reference to FIG.
First, when the sheet feeding is started, the control unit 80 reads the speed profile stored in the speed profile storage unit 101 and gives the target position and the target speed to the comparison calculation unit 111 of the sub-scanning motor driving unit 91 (target). Position and target speed setting). An initial control amount is output from the sub-scanning motor driving unit 91 and driving of the sub-scanning motor 31 is started. As a result, information corresponding to the current position and current speed of the conveyor belt 21 is output from the speed detection unit 102 and sampled by the sampling unit 103 (current speed and position detection). The comparison calculation unit 111 is provided.

  At this time, as described above, it is determined whether or not the difference (position difference) between the position information at the previous sampling and the position information at the current sampling is equal to or larger than a predetermined value, and the position difference is predetermined. When the value is greater than or equal to the value, a speed deviation between the target speed based on the speed profile and the current speed is set from the comparison calculation unit 111 and is given to the PID control calculation unit 112, and the target speed and the current speed are calculated from the PID control calculation unit 112. A PWM control value (control amount) corresponding to the speed deviation is output, and the sub-scanning motor 31 is rotationally driven at a speed according to the set speed profile.

  On the other hand, when the position difference is not greater than or equal to the predetermined value, that is, when the difference between the previously sampled position and the current sampling position is smaller than the predetermined value, it is determined that the vehicle is in the low speed region during deceleration. Thus, a speed deviation corresponding to a predetermined speed is given from the low speed calculation unit 114 to the PID control calculation unit 112, and a PWM control value (control amount) corresponding to the set speed is output from the PID control calculation unit 112, The scanning motor 31 is rotationally driven at a speed according to the set speed profile.

  When the target position is reached, the driving of the sub-scanning motor 31 is stopped.

  Instead of fixing the speed at the low speed, for example, in the low speed calculation unit 114, the movement amount within the sampling period (for example, 1 msec) by the sampling unit 103 is the movement amount “1” (for example, 1 pulse = 5). .29 μm), the actual speed can be regarded as 5.29 mm / sec. Therefore, the speed deviation with respect to the target speed is obtained as the current speed, and this speed deviation is given to the PID control calculation unit 112. In this way, by performing speed control at a speed corresponding to the amount of movement based on position information within a predetermined time, it is possible to obtain a stable speed until stopping in deceleration control. Become.

Next, stop position holding control when the sheet is sent to the target position and stopped will be described with reference to FIG.
First, as described above, the control unit 80 drives the sub-scanning motor 31 to rotate with respect to information on the target position and target speed when starting to feed the recording medium. As a result, information corresponding to the current position and current speed of the conveyor belt 21 is output from the position detection unit 102, sampled by the sampling unit 103, and provided to the comparison calculation unit 111 of the sub-scanning motor driving unit 91, A PWM control value (control amount) is output from the PID control calculation unit 112 in accordance with the speed deviation, and the sub-scanning motor 31 is rotationally driven at a speed according to the set speed profile, and a recording medium at a given target position. And stop position holding processing is started.

  Then, as described above, the carriage 3 is main-scanned, and the recording liquid droplets are ejected from the recording head 7 according to the image data to form an image on the paper 12 as a recording medium (printing). A print scan end determination is performed to determine whether (scan) has ended (printing is in progress).

  If printing is being performed, the current position is acquired from the position / velocity detection unit 102, and is there a deviation amount between the target position when the recording medium is stopped, that is, a predetermined stop position and the current position? Stop position deviation amount determination processing is performed to determine whether or not.

  At this time, if there is no deviation amount between the predetermined stop position and the current position, that is, if there is no change in the stop position on the recording medium, the process returns to the print scanning end determination.

  On the other hand, if there is a deviation amount between the current position of the recording medium and a predetermined stop position, the positional deviation amount exceeds a predetermined set amount, for example, ± 1 pulse (= ± 5.29 μm). Control execution presence / absence determination processing for determining whether or not to perform feedback control for holding the stop position is performed.

  At this time, if the position deviation amount exceeds the set amount (for example, if it exceeds one pulse), the position deviation amount between the predetermined stop position and the current position is given to the PID control calculation unit 112 to perform PID control. By changing the PWM control value output from the calculation unit 112, that is, the output value for the sub-scanning motor 31 for feeding the recording medium, the sub-scanning motor 31 is rotationally driven in accordance with the position deviation amount so that the recording medium is An operation of returning to a predetermined stop position (target position) is performed.

  That is, here, the stop position control of the recording medium is performed by changing the output value to the sub-scanning motor of the means (for example, the PID control calculation unit) that performs feedback control with the predetermined stop position of the recording medium as the target position. To do. Specifically, since the integrator output of the PID control calculation unit is responsible, the present invention can be similarly applied even when a differentiator is not used for feedback control.

  On the other hand, if the position deviation amount does not exceed the set amount, that is, if the deviation amount is within the set amount (for example, one pulse), the deviation amount is regarded as zero and the PWM control value is not changed. That is, even if stop position fluctuation occurs in the recording medium, if the fluctuation amount (position deviation amount) is equal to or less than the set amount, it is assumed that the stop position fluctuation does not substantially occur, and the output value to the sub-scanning motor 31 Do not change.

  In this way, by executing stop position holding control for holding the recording medium at the stop position by feedback control (servo control) based on the stop position fluctuation during printing (image forming operation), High quality because the recording medium can be immediately returned to the original stop position even when disturbances such as back tension act on the recording medium during printing and the recording medium stops. Images can be formed.

  In this case, the stop position of the recording medium actually fluctuates by determining whether or not to change the output value for the driving source of the recording medium based on a predetermined set amount and deviation amount. However, it is possible to prevent the recording medium from being overexposed from the stop position by misjudging that there is a deviation amount due to the vibration of the encoder slit disk due to vibration, etc. Control can be performed.

  The control for returning the recording medium can be performed by changing the output value for the drive source in accordance with the position deviation amount, so that the recording medium can be returned to the original stop position with high accuracy. Holding control can be performed.

  Although the sub-scan driving of the serial type image forming apparatus has been described in the above embodiment, the present invention can be similarly applied to the case where the recording medium is intermittently transported and driven in the line type image forming apparatus.

1 is a schematic explanatory diagram of a mechanism unit of an image forming apparatus according to the present invention. It is principal part plane explanatory drawing of the mechanism part. It is a schematic block explanatory drawing of the control part of the apparatus. It is a functional block explanatory drawing of the part which concerns on the motor drive control of the control part. It is explanatory drawing with which it uses for description of acquisition of the positional information and speed information in the motor drive control. It is explanatory drawing with which it uses for description of the speed undetectable area | region in a speed profile similarly. It is a flowchart with which it uses for description of an example of the paper feed control in the motor drive control. It is a flowchart with which it uses for description of an example of the stop position holding | maintenance control in the same motor drive control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Carriage 4 ... Main scanning motor 7 ... Recording head 21 ... Conveying belt 26 ... Charging roller 27 ... Conveying roller 31 ... Sub scanning motor 36 ... Encoder 91 ... Sub scanning motor drive part 101 ... Speed profile storage part 102 ... Position speed detection Unit 103 ... Sampling unit 111 ... Comparison calculation unit 112 ... PID control calculation unit 113 ... Motor driver 114 ... Low speed calculation unit

Claims (4)

  In an image forming apparatus that intermittently feeds a recording medium and forms an image on the recording medium by an image forming unit, when performing an image forming operation for forming an image on the recording medium by the image forming unit An image forming apparatus comprising: a stop position holding control for returning the recording medium to the predetermined stop position based on a change in the stop position of the recording medium.   2. The image forming apparatus according to claim 1, wherein the stop position holding control is performed on the drive source by means for performing feedback control on the drive source of the recording medium with a predetermined stop position of the recording medium as a target position. An image forming apparatus, wherein the output value is changed.   3. The image forming apparatus according to claim 2, wherein a deviation amount between a current position of the recording medium and a predetermined stop position is detected, and the drive source is detected based on the detected deviation amount and a preset set amount. An image forming apparatus comprising: means for determining whether or not to change an output value.   4. The image forming apparatus according to claim 3, wherein when the detected deviation amount exceeds a predetermined set amount, an output value for the drive source is changed in accordance with a positional deviation amount of the recording medium. An image forming apparatus.

Images