JP2008203671A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which the time necessary for starting a first print is shortened by shortening the waiting time from the start of the driving of a polygon mirror to a stable steady revolution speed at which an image forming is possible. <P>SOLUTION: The image forming apparatus A is provided with: a polygon motor 54 which turningly drives the polygon mirror 55 which scanningly deflects a luminous flux output from a light source onto a face to be scanned; and a drive control means 59 which drives the polygon motor 54 so as to be a target revolution speed on the basis of a predetermined clock signal, wherein the drive control means 59 starts the polygon motor 54 on the basis of a first cock signal having a reference frequency f1 and has a clock signal switching means 512 which switches to a second clock signal having a frequency f2 lower than the reference frequency f1 for a predetermined time Te when the polygon motor 54 reached a predetermined revolution speed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  According to the present invention, a polygon motor that rotationally drives a polygon mirror that deflects and scans a light beam output from a light source toward a surface to be scanned, and the polygon motor is driven so as to reach a target rotational speed based on a predetermined clock signal. The present invention relates to an image forming apparatus including a drive control unit.

  In an electrophotographic image forming apparatus, a latent image is formed by irradiating a photoconductor with a uniformly charged surface to form a latent image, and the developed toner image is transferred to paper by attaching toner to the latent image. A laser beam or an LED is used as a light source for a light beam irradiated to the photosensitive member. The light beam emitted from the light source is scanned by a polygon mirror driven at a high speed by a polygon motor, and a latent image corresponding to an image to be printed is formed on the surface of the photoreceptor.

In Patent Document 1, a driving voltage higher than a reference voltage is supplied from a motor driving power source when starting a polygon motor, and when a predetermined time has elapsed from the starting of the polygon motor or when the polygon motor rotation speed reaches a predetermined rotation speed. A motor control device is proposed in which the drive voltage is sometimes switched to the reference potential and supplied, and the waiting time until the polygon motor rotation speed reaches the steady rotation speed can be shortened to shorten the time to start printing. Has been.
JP 2005-198468 A

  The technique described in Patent Document 1 can shorten the waiting time from the start of the polygon motor until it reaches the predetermined rotational speed, but cannot suppress overshoot and undershoot that occur in the polygon motor due to inertial force. . That is, there is room for further improvement in shortening the waiting time until the polygon motor rotation speed becomes stable at a printable steady rotation speed.

  In view of the above problems, an object of the present invention is to shorten the time required for starting the first print by shortening the waiting time from the start of driving of the polygon mirror until the polygon mirror is stabilized at a steady rotational speed at which image formation can be performed. It is in providing an image forming apparatus capable of performing the above.

  In order to achieve the above object, according to a first characteristic configuration of the image forming apparatus according to the present invention, the light bundle output from the light source is applied to the surface to be scanned as described in claim 1 of the claims. An image forming apparatus comprising: a polygon motor that rotationally drives a polygon mirror that performs deflection scanning toward the head; and a drive control unit that drives the polygon motor to have a target rotational speed based on a predetermined clock signal, The drive control means starts the polygon motor based on the first clock signal having a reference frequency, and when the polygon motor reaches a predetermined rotation speed, the drive control means applies a second clock signal having a frequency lower than the reference frequency for a predetermined time. The clock signal switching means for switching is provided.

  According to the above-described configuration, since the polygon motor has a deceleration effect during driving based on the second clock signal, it is possible to suppress the amplitude of overshoot or undershoot due to inertial force.

  According to the second characteristic configuration described in the second aspect, in addition to the first characteristic configuration described above, the clock signal switching unit performs a predetermined rotation after the polygon motor is started by the first clock signal. The predetermined time is variably set based on the time until the number is reached.

  According to the above-described configuration, it is possible to perform deceleration according to the number of revolutions of the polygon motor, and therefore it is possible to suppress the amplitude of overshoot or undershoot due to inertial force.

  In the third feature configuration, in addition to the first or second feature configuration described above, the drive control means is a PLL that drives the polygon motor based on a predetermined clock signal. Control means is provided for switching to the second clock signal when a synchronization signal for the first clock signal is detected.

  According to the above-described configuration, it is possible to shorten the waiting time until the rotation speed of the polygon motor is stabilized rather than controlling the rotation speed of the polygon motor only by PLL control.

  In the fourth feature configuration, as described in claim 4, in addition to any of the first to third feature configurations described above, the reference frequency is a frequency corresponding to a target rotational speed of the polygon motor. There is a point.

  According to the above configuration, it is sufficient that two types of clock signals, the first clock signal and the second clock signal, can be used as the clock signal used by the drive control means for the polygon motor drive control, thereby preventing the clock signal output circuit from becoming complicated. This can contribute to cost reduction.

  According to the present invention, there is provided an image forming apparatus capable of shortening a time required for starting a first print by shortening a waiting time from when a polygon mirror starts driving until the polygon mirror is stabilized at a steady rotational speed at which image formation can be performed. Can now be offered.

  Hereinafter, an electrophotographic copying machine as an image forming apparatus to which the present invention is applied will be described.

  As shown in FIG. 2, the copying machine A according to the present invention sequentially reads a series of documents set on the operation unit 1 on which a color display unit, hardware keys, and the like are arranged, and the document placing unit 2 to read electronic data. The image reading unit 3 that converts the image data into image data, performs predetermined image processing, and stores the image data in the memory; and the image data stored in the memory on the paper that is the recording medium conveyed from the paper feed cassette 4 And an image forming unit 5 that forms and outputs a toner image corresponding to the image and a system control unit 6 that controls the digital copying machine 1 in an integrated manner.

  The development of the toner image in the image forming unit 5 will be described. As shown in FIG. 1, the image forming control unit 50 that controls the image forming unit 5 receives an operator's image formation start request, and performs charging by a charger (not shown). The image data of the document read by the image reading unit 3 and stored in the memory 57c is read into the buffer 57b for several lines on the surface of the photosensitive member 58, which is the surface to be scanned, charged in the manner described above. The LD 57 driven by the driver 57a irradiates the corresponding light beam, deflects and scans the polygon mirror 55 driven at high speed by the polygon motor 54, and the original is applied to the surface of the photoconductor 58 via the fθ lens 57d. A latent image corresponding to the image is formed, and a developing device (not shown) attaches toner to the latent image and develops it. The image forming control unit 50 drives the LD 57 when the rotation speed of the polygon motor 54 is stabilized near the target rotation speed ft at which image formation is possible.

  The drive control of the polygon motor 54 will be described. The image formation control unit 50 receives the operator's image formation start request and receives the PLL control of the present invention from a clock signal output circuit (hereinafter referred to as “CLK signal output circuit”) 51. A PLL circuit (Pulse-Locked loop: phase synchronization circuit) 52, which is a means, outputs a first clock signal (hereinafter referred to as “first CLK signal”) having a reference frequency f1. The PLL circuit 52 receives a first CLK signal input from the CLK signal output circuit 51 and a rotation speed signal having a rotation frequency fm which is the rotation speed of the polygon motor 54 detected and output by the encoder 56 attached to the polygon motor 54. The polygon motor 54 is driven and controlled by controlling the motor driving current from the motor driver 53 so as to be in phase. Here, the reference frequency f1 is a frequency corresponding to the target rotational speed ft of the polygon motor 54.

  The CLK signal output circuit 51 includes a clock generation circuit, a frequency division circuit, and the like. The clock signal generated by the clock generation circuit is frequency-divided by the frequency division circuit, and the first CLK signal having the reference frequency f1 or the frequency f2 lower than the reference frequency f1. The second clock signal (hereinafter referred to as “second CLK signal”) is output to the PLL circuit 52. That is, the CLK signal output circuit 51 includes a first clock signal generation unit 510 that generates a first CLK signal, a second clock signal generation unit 511 that generates a second CLK signal, and a clock signal switching unit (hereinafter referred to as “CLK signal switching unit”). 512), and the CLK signal switching means 512 outputs the first CLK signal or the second CLK signal to the PLL circuit 52 at the time of image formation in accordance with the control signal from the image formation control unit 50 to form the image. At the end, the clock signal output is stopped.

  The PLL circuit 52 includes a phase comparison circuit, and controls the motor drive current to the polygon motor 54 by comparing the phase between the reference frequency f1 of the first CLK signal and the rotation frequency fm of the rotation speed signal, and also the rotation speed signal. Accordingly, when the rotational frequency fm of the polygon motor 54 is a predetermined rotational speed set in advance and is within a predetermined range (hereinafter referred to as “lock signal output range”) in the vicinity of the target rotational speed ft where image formation is possible. A lock signal, which is a synchronization signal as shown in FIGS. 3A and 3B, is output to the image formation control unit 50. The PLL circuit 52 is configured to control the motor drive current to the polygon motor 54 in response to the second CLK signal when the CLK signal output circuit 51 receives the second CLK signal.

  When the lock signal is input from the PLL circuit 52, the image formation control unit 50 quickly converges the rotational frequency fm of the polygon motor 54 within the lock signal output range, as shown in FIG. The second CLK signal is output from the CLK signal output circuit 51 for the predetermined time Te, and when the predetermined time Te has elapsed, the first CLK signal is output. Specifically, the second CLK signal is output from the CLK signal output circuit 51 for a predetermined time Te after the falling edge of the input lock signal is detected, and the first CLK signal is output when the predetermined time Te elapses. It is configured as follows. Here, in order to prevent the deceleration effect from becoming so large that the amplitude of overshoot or undershoot is increased, the next rising edge is detected after detecting the falling edge of the lock signal at the maximum time Te. It is set to the value until detection.

  When the clock signal output from the CLK signal output circuit 51 is fixed to the first CLK signal and output, the overshoot or undershoot amplitude is large as shown in FIG. When the clock signal output from is switched to the first CLK signal and the second CLK signal according to the control described above and output, the overshoot or undershoot amplitude decreases, as shown in FIG. The time Ts until the rotation frequency fm converges within the lock signal output range is shortened.

  Further, when the image forming control unit 50 cannot detect the falling edge even after a predetermined time Tj has elapsed after detecting the rising edge of the lock signal, the line frequency fm of the polygon motor 54 converges within the lock signal output range. It is determined that image formation can be started and image formation is started.

  As described above, the image formation control unit 50, the CLK signal output circuit 51, the PLL circuit 52, and the motor driver 53 constitute the drive control unit 59 in the present invention, and the drive control unit 59 includes the first CLK of the reference frequency f1. Based on the signal, the polygon motor 54 is started, and when the polygon motor 54 reaches a rotation speed in the vicinity of the predetermined rotation speed ft, the CLK signal is switched to a second CLK signal having a frequency f2 lower than the reference frequency f1 for a predetermined time Te. Means 512 are provided.

  Hereinafter, drive control of the polygon motor 54 of the copying machine A will be described with reference to the flowchart shown in FIG.

  When the operator operates the operation unit 1 to make an image formation start request (S1), the CLK signal output circuit 51 receives a control signal from the image formation control unit 50 that has received the image formation start request from the system control unit 6. Outputs the first CLK signal to the PLL circuit 52 (S2).

  When the lock signal is input from the PLL circuit 52 (S3), the image formation control unit 50 measures the time from when the rising edge of the lock signal is detected until the falling edge is detected (hereinafter referred to as “lock signal input time”). ”And comparison with the predetermined time Tj (S4).

  When the lock signal input time is equal to or shorter than the predetermined time Tj (S4), the image formation control unit 50 outputs a control signal to cause the CLK signal output circuit 51 to output the second CLK signal (S5), and the predetermined time Te has elapsed. Then (S6), the PLL circuit is switched to output the first CLK signal (S2).

  When the lock signal input time is greater than the predetermined time Tj (S4), the image formation control unit 50 determines that the rotation speed of the polygon motor 54 is stable and image formation can be performed, and starts scanning by the LD 57 (S7). When the image formation end command is received from the control unit 6 (S8), a control signal is output to stop the clock signal output from the CLK signal output circuit 51 to the PLL circuit 52 (S9).

  Another embodiment will be described below.

  In the above-described embodiment, the clock signal output from the C lock signal output unit 51 is described as being switched from the first CLK signal to the second CLK signal for a predetermined time Te fixed by the CLK signal switching unit 512. The predetermined time Te may be variable instead of being fixed. For example, the CLK signal switching means 512 starts from the first CLK signal for a predetermined time Te variably set to the second CLK signal based on the time until the polygon motor 54 driven by the first CLK signal reaches a predetermined rotation speed. It may be configured to switch to the second CLK signal.

  For example, when the copying machine A is in a stopped state for a long time and the polygon motor 54 is completely stopped, and when the stopped state after execution of image formation is a short time and the polygon motor 54 is rotated by inertial force. The torque required for driving the polygon motor 54 and the inertial force generated in the polygon motor 54 are different. Therefore, the torque required for the polygon motor 54 and the inertial force generated are determined based on the time required to reach a predetermined rotational speed, and the CLK signal output circuit 51 is operated by the CLK signal switching means 152 for a predetermined time Te corresponding to each. The first CLK signal output from the second CLK signal may be switched to the second CLK signal. Furthermore, by configuring the predetermined time Te to be variable, drive control according to the drive performance of the polygon motor 54 due to secular change is possible. In this case, table data of the optimum driving time of the polygon motor 54 corresponding to each situation obtained by experiment or the like is provided in the image forming control unit 50, and the clock signal switching by the CLK signal switching means 512 based on the table data. Can be done.

  Further, as shown in FIG. 5, when the drive control of the polygon motor 54 is started by the drive control means 59, the predetermined time Te is made variable according to the rotation speed fm of the polygon motor 54 deviating from the lock signal output range. It is also possible to set. The predetermined time Te in FIG. 6 is set to the time from when the image formation control unit 50 detects the falling edge of the lock signal until the rotation speed fm reaches the peak value or the bottom value.

  In the above-described embodiment, the reference frequency f1 is described as a frequency corresponding to the target rotation speed ft of the polygon motor 54. However, the reference frequency f1 of the first CLK signal may be higher than the target rotation speed ft. In this case, it is sufficient that the CLK signal output circuit 51 can output at least a clock signal having the target frequency ft, and the polygon motor 54 in the stopped state is driven based on the first CLK signal having the reference frequency f1 higher than the target rotational speed ft. By doing so, the time for the rotation speed fm to reach the lock signal output range can be shortened. At this time, the frequency f2 of the second CLK signal may be lower than the reference frequency f1 of the first CLK signal as shown in FIGS. 6A, 6B, and 6C, and may be higher than the target frequency ft. It may be low and may be the same as the target frequency ft.

  In the above-described embodiment, the present invention is not limited to PLL control, and may be applied to other control circuits that control the rotational speed fm of the polygon motor 54 by feedback.

  The plurality of embodiments described above are not limited to being configured alone, but may be combined as appropriate within the scope of the effects of the present invention.

  Each of the above-described embodiments is merely an example of the present invention, and the scope of the present invention is not limited by the description. The specific configuration of each part is appropriately changed within the scope of the effects of the present invention. It goes without saying that it can be done.

Block diagram of drive control means Illustration of copier Control characteristics diagram of polygon motor drive control Flow chart explaining drive control of polygon motor Control characteristics diagram of polygon motor drive control (A) An explanatory diagram of the relationship between the first clock signal and the second clock signal output from the clock signal output circuit (second clock signal> target frequency), (b) the first clock signal output from the clock signal output circuit and the second clock signal Explanatory diagram of relationship between two clock signals (second clock signal <target frequency), (b) Explanatory diagram of relationship between first clock signal and second clock signal output from clock signal output circuit (second clock signal = target frequency) )

Explanation of symbols

50: Image formation control unit 51: Clock signal output circuit 52: PLL control means (PLL circuit)
53: Motor driver 54: Polygon motor 55: Polygon mirror 56: Encoder 59: Drive control means 512: Clock signal switching means

Claims (4)

A polygon motor that rotationally drives a polygon mirror that deflects and scans the light beam output from the light source toward the surface to be scanned, and a drive control unit that drives the polygon motor to reach a target rotational speed based on a predetermined clock signal. An image forming apparatus comprising:
The drive control means starts the polygon motor based on a first clock signal having a reference frequency, and sets a second clock signal having a frequency lower than the reference frequency when the polygon motor reaches a predetermined rotation speed. An image forming apparatus comprising clock signal switching means for switching time.   2. The clock signal switching means is configured to variably set the predetermined time based on a time until the predetermined rotation speed is reached after the polygon motor is started by the first clock signal. Image forming apparatus.   The drive control means includes PLL control means for driving the polygon motor based on a predetermined clock signal, and switches to the second clock signal when a synchronization signal for the first clock signal is detected. 2. The image forming apparatus according to 2.   The image forming apparatus according to claim 1, wherein the reference frequency is a frequency corresponding to a target rotational speed of the polygon motor.

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