JP2005134634A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in which an abnormal rotation of a polygon mirror is accurately detected with software even when instantaneous lock disengagement occurs. <P>SOLUTION: The optical scanner is so composed that a polygon lock signal XSCRDY is generated by extending the high level (ineffective state) of the lock signal by adding a predetermined term to the term in which the lock signal is set in the High level (ineffective state). Thus, the polygon lock signal XSCRDY is surely detected with the software and the abnormal rotation of the polygon mirror is accurately detected even when the instantaneous lock disengagement occurs. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical scanning device and an image forming apparatus.

  An image forming apparatus is an apparatus that forms an image by, for example, an electrophotographic process method. Normally, a laser beam emitted from a light source is exposed and scanned on a photoconductor by deflecting it with an optical deflector such as a polygon mirror. An optical scanning device for forming an electrostatic latent image on the body is provided.

  The optical scanning device includes a polygon motor that rotationally drives a polygon mirror during image formation, and controls the rotational speed (number of rotations) of the polygon motor. That is, the optical scanning device compares the outputs of the encoders that detect the rotational speed with respect to the reference clock signal (the type that detects light, the type that detects coil current, the type that detects magnetic field, etc.), and the two match. Thus, the drive current of the polygon motor is controlled (see Patent Document 1).

  In such an optical scanning device, since it is necessary to rotate the polygon mirror at a predetermined rotation speed during image formation, it is detected whether or not the rotation speed of the polygon mirror is rotating at a predetermined rotation speed. For example, when the polygon mirror does not rotate at a predetermined speed, that is, when the polygon mirror deviates from the predetermined rotation speed, a lock signal is output (lock signal is invalid) and this lock signal is detected. The rotational speed of the polygon mirror is monitored by (see Patent Document 2). That is, when the lock signal is in a valid state (for example, Low state), it is determined that the polygon mirror is rotating at a predetermined rotation speed. When the lock signal is in an invalid state (for example, High state), the polygon mirror is It is determined that the motor is rotating out of a predetermined rotational speed (unlocked).

JP-A-5-333280 JP-A-6-148551

  However, there is a limitation that the period of the software timer cannot be set short when software unlocking (lock signal invalid state), which is an abnormal rotation of the polygon mirror, is detected. At this time, when the momentary unlocking occurs, there is a problem that the abnormality cannot be detected by software because the period during which the lock signal is abnormal (the invalid state of the lock signal) is short.

  An object of the present invention is to provide an optical scanning apparatus and an image forming apparatus capable of accurately detecting a rotation abnormality of an optical deflector such as a polygon mirror by software even when an instantaneous unlocking occurs. is there.

  According to a first aspect of the present invention, there is provided an optical scanning device comprising: a light source that emits laser light; a drive motor that is a drive source; and a rotational drive by the drive motor to deflect and scan the laser light emitted from the light source. An optical deflector, a motor control unit that rotates the drive motor at a predetermined rotation speed, and an effective state when the drive motor is rotated at a predetermined rotation speed by the motor control unit, and A lock signal generating means for generating a lock signal that becomes invalid when the drive motor deviates from a predetermined rotational speed; and a predetermined period during a period when the lock signal generated by the lock signal generating means is in an invalid state. An extension means for extending the invalid state of the lock signal by adding a period; and an abnormality detection means for detecting a rotation abnormality of the optical deflector based on the lock signal. That.

  According to a second aspect of the present invention, in the optical scanning device according to the first aspect of the present invention, the optical scanning device includes a temperature detection unit that detects a temperature inside the device, and the extension means is based on the temperature detected by the temperature detection unit, A period during which the lock signal is in an invalid state is controlled to be constant.

  According to a third aspect of the present invention, in the optical scanning device according to the second aspect, the extension means is detected by an adder circuit having a plurality of resistors and a capacitor connected to the plurality of resistors, and the temperature detector. And a selection circuit that selects one resistor to be used from the plurality of resistors according to temperature.

  According to a fourth aspect of the present invention, in the optical scanning device according to the first, second, or third aspect, the extension means extends an invalid state of the lock signal so as to mask chattering of the lock signal.

  According to a fifth aspect of the present invention, in the optical scanning device according to the first, second, third, or fourth aspect, the extension means is executed by hardware and software.

  An image forming apparatus according to a sixth aspect of the present invention includes the optical scanning device according to any one of the first to fifth aspects, and a scanned surface that is exposed and scanned by a laser beam emitted from the optical scanning device, And a photoreceptor carrying an electrostatic latent image on the surface to be scanned.

  According to the optical scanning device of the first aspect of the present invention, momentary unlocking occurs by extending the invalid state of the lock signal by adding a predetermined period to the period when the lock signal is in an invalid state. Even in this case, it becomes possible to reliably detect the unlocking, and it is possible to accurately detect abnormal rotation of the optical deflector such as a polygon mirror by software.

  According to the second aspect of the present invention, in the optical scanning device according to the first aspect, the ambient temperature is controlled by controlling the period during which the lock signal is disabled based on the temperature detected by the temperature detection unit. The rotation abnormality of the optical deflector such as a polygon mirror can be stably detected by software without being affected by the above.

  According to a third aspect of the present invention, in the optical scanning device according to the second aspect, by selecting one resistor to be used from a plurality of resistors included in the adder circuit according to the temperature detected by the temperature detector. With a simple configuration, it is possible to stably detect abnormal rotation of an optical deflector such as a polygon mirror by software without being affected by the ambient temperature.

  According to a fourth aspect of the present invention, in the optical scanning device according to the first, second, or third aspect, the light deflection of a polygon mirror or the like is performed by extending the invalid state of the lock signal so as to mask chattering of the lock signal. It is possible to prevent erroneous detection of abnormal rotation of the device.

According to the invention of claim 5, in the optical scanning device of claim 1, 2, 3 or 4, by extending the invalid state of the lock signal by hardware and software,
According to the image forming apparatus of the sixth aspect of the invention, the same effect as that of any one of the first to fifth aspects of the invention can be achieved.

  An image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal side view schematically showing an image forming apparatus according to the present embodiment.

  As shown in FIG. 1, the image forming apparatus 1 optically reads an original image on the contact glass 3 by an image reading unit 2, and an image forming unit 4 based on image data such as the optically read original image. An image is formed by an electrophotographic process, which is transferred from the recording material holding unit 5 to a sheet of recording material conveyed by the conveying unit 6 via the conveying path 7, and the transfer image of the sheet is heated and pressed by the fixing unit 8. Thus, the toner is fixed and discharged onto the paper discharge tray 9.

  The image reading unit 2 includes a scanner mechanism 10 that reads a document image on the contact glass 3 with a predetermined linear density. Further, the image reading unit 2 may include an ADF mechanism that automatically conveys a document toward a document reading position on the contact glass 3. The transport unit 6 includes a plurality of rollers such as a paper feed roller 11 and a transport roller 12 that feed paper from the recording material holding unit 5, and transports the paper along the transport path 7.

  The image forming unit 4 includes a drum-shaped photosensitive member 21 that is rotatably provided, a charger 22, an exposure unit 23 that is an optical scanning device, a developing unit 24, a transfer unit 25, a cleaner 26, and the like. The image forming unit 4 charges the photoconductor 21 with the charger 22 and exposes and scans the surface of the photoconductor 21 based on the image data with the exposure unit 23 to form an electrostatic latent image on the photoconductor 21. Then, a toner is attached to the electrostatic latent image on the photosensitive member 21 by the developing device 24 to form a visible toner image, and the toner image is transferred onto the paper by the transfer device 25. Thereafter, the image forming unit 4 scrapes off the toner that is not transferred onto the sheet and remains on the photosensitive member 21 with the cleaner 26.

  FIG. 2 is a plan view schematically showing the internal structure of the exposure unit 23. As shown in FIG. 2, the exposure unit 23 is provided with a light source unit 30 that is a light source that emits laser light. The light source unit 30 includes a semiconductor laser 31 that emits laser light and an optical component 32 such as a collimator lens that collimates the laser light emitted from the semiconductor laser 31.

  A polygon that is an optical deflector that rotates at a high speed by a polygon motor 33 that is a drive motor and deflects and scans the laser light emitted from the light source unit 30 in a horizontal plane is provided on the emission surface side of the light source unit 30 where the laser beam is emitted. A mirror 34 is provided. The polygon mirror 34 is formed in a regular hexagon and has six reflecting surfaces that reflect the laser light. The polygon mirror 34 directs the laser light emitted from the light source unit 30 toward the periphery of the photosensitive member 21, that is, in FIG. Is deflected and scanned in the right direction. The scanning direction of the laser beam deflected and scanned by the polygon mirror 34 is the main scanning direction, which is the axial direction of the photosensitive member 21. Further, the direction orthogonal to the main scanning direction is the sub-scanning direction, which is the rotation direction of the photoconductor 21.

  In the deflection scanning direction of the polygon mirror 34, an fθ lens 35 that converts laser light deflected by the polygon mirror 34 from constant angular velocity light to constant velocity linear light, and a deflection mirror 36 that is an optical system that guides the laser light to the photosensitive member 21. These are positioned so as to irradiate the writing area on the photosensitive member 21 with the laser beam deflected and scanned by the polygon mirror 34. Thereby, an electrostatic latent image as an image is formed on the photosensitive member 21. Further, each laser beam deflected by the polygon mirror 34 has its fθ characteristic corrected favorably by the fθ lens 35 and is imaged on the photosensitive member 21 with a predetermined beam spot diameter. Here, the fθ lens 35 functions as a shaping lens that shapes the laser light into a predetermined beam spot diameter, but is not limited thereto.

  Further, the exposure device 23 is provided with a photodetector 37 that detects laser light outside the writing area on the photosensitive member 21 out of the laser light deflected and scanned by the polygon mirror 34. This photodetector 37 is used to generate a synchronization signal for taking the write timing of the laser beam in the main scanning direction.

  FIG. 3 is a block diagram schematically showing the electrical connection of each part provided in the image forming apparatus 1. As shown in FIG. 3, the image forming apparatus 1 is provided with a control unit 40. The control unit 40 includes a CPU 41, a ROM 42 that stores a control program and the like, an EEPROM 43 and a RAM 44 that store various information in a rewritable manner. It is configured. The control unit 40 executes control of each unit and various calculations. The control unit 40 is connected to an image forming unit driving circuit 45 for driving and controlling the image forming unit 4, an image reading unit driving circuit 46 for driving and controlling the image reading unit 2, and an external device such as a personal computer. A communication I / F (interface) 47 or the like to be enabled is connected by a bus line 48. The image forming unit drive circuit 45 includes an exposure unit drive circuit 49 that drives and controls the exposure unit 23.

  FIG. 4 is a block diagram schematically showing electrical connection of characteristic portions of the present invention provided in the image forming apparatus 1. As shown in FIG. 4, the exposure device drive circuit 49 includes a polygon motor driver 60 that is a motor control unit that drives and controls the polygon motor 33. The polygon motor driver 60 is connected to a polygon motor 33 and an FG sensor 61 that detects the rotation of the polygon motor 33 and outputs a rotation detection signal FG. Thereby, the rotational speed of the polygon motor 33 can be detected. However, the present invention is not limited to this. For example, the rotational speed of the polygon motor 33 may be detected by using the photodetector 37.

  The polygon motor driver 60 amplifies the rotation detection signal FG output from the FG sensor 61, the rotation detection signal FG amplified by the amplifier 62, and the reference clock signal CK generated by the clock generation circuit 63. A phase difference signal PD generated by phase comparison of the phase difference signal PD, and a PWM signal generation circuit 65 for generating a PWM (pulse width modulation) signal based on the phase difference signal PD generated by the PLL circuit 64 Etc. Such a polygon motor driver 60 increases or decreases the rotation speed (the number of rotations) of the polygon motor 33 by increasing or decreasing the pulse width of the PWM signal generated by the PWM signal generation circuit 65 depending on the magnitude of the phase difference signal PD. The polygon motor 33 is driven and controlled so that the rotation speed of the polygon motor 33 is constant. The clock generation circuit 63 includes an oscillator (OSC) 66 and a frequency divider 67 that divides a pulse generated by the oscillator 66, and generates a reference clock signal CK.

  The PLL circuit 64 outputs a lock signal for detecting an abnormality in the rotational operation of the polygon mirror 34 when the polygon motor 33 is rotationally driven. When the polygon mirror 34 is rotating at a predetermined rotation speed, that is, when the polygon motor 33 is rotating at a predetermined rotation speed, the PLL circuit 64 sets the lock signal to a low level (valid state = normal state) When the polygon mirror 34 stops rotating at a predetermined rotation speed, that is, when the polygon motor 33 stops rotating at a predetermined rotation speed, the lock signal is set to a high level (invalid state = abnormal state). That is, it is determined that the rotation speed is normal when the lock signal is Low level, and the rotation speed is abnormal when the lock signal is High level. The PLL circuit 64 functions as a lock signal generation unit. Further, in the present embodiment, the predetermined rotational speed is, for example, a rotational speed within a predetermined range, and the fact that the rotational speed deviates from this range is said to be unlocked.

  The lock signal output by the PLL circuit 64 is input to the adder circuit 68. A CPU 41 is connected to the adder circuit 68 via an I / O port 69, and a temperature sensor 71 that is a temperature detection unit is connected to the CPU 41 via an A / D converter 70. The image forming apparatus 1 detects the temperature in the exposure unit 23 by the temperature sensor 71. The detected temperature detected by the temperature sensor 71 is converted into digital data by the A / D converter 70 and input to the adder circuit 68 via the I / O port 69.

  The adder circuit 68 increases the pulse width of the lock signal based on the port signal S1 (detected temperature) input via the I / O port 69, and outputs the lock signal with the increased pulse width to the polygon lock signal XSCRDY. Is output to the register 72. The register 72 temporarily stores the value (Low level / High level) of the polygon lock signal XSCRDY. The adder circuit 68 functions as an extension means. In addition, a register 72 and an operation unit 73 are connected to the CPU 41. The operation unit 73 is configured by, for example, a touch panel, receives operations from an operator, and further displays various images such as an abnormality notification image.

  FIG. 5 is a schematic diagram schematically showing an example of the configuration of the adder circuit 68. As shown in FIG. 5, the lock output (lock signal) LD of the polygon motor driver 60 is an open collector output of the transistor Tr1. The emitter of the transistor Tr1 is connected to GND, and its collector is connected to the base of the transistor Tr2. The emitter of the transistor Tr2 is connected to GND, and the polygon lock signal XSCRDY is output from its collector. The base of the transistor Tr2 is connected to GND via the resistor R2, and the collector of the transistor Tr2 is connected to the power supply 5V via the resistor R3. The adder circuit 68 includes a selector 80 that is a selection circuit for selecting either the resistor R1 or the resistor R4. In the present embodiment, the relational expression R1 <R4 holds for the resistance values of the resistors R1 and R4.

  Here, a case where the resistor R1 is selected by the selector 80 will be described. Since the capacitor C1 is discharged by a current flowing from the collector of the transistor Tr1 to the GND through the collector, the capacitor C1 is rapidly discharged. When charging the capacitor C1, since the transistor Tr1 is turned off, the capacitor C1 is charged by a filter having a time constant composed of C1 and R1, and therefore it takes time. Therefore, since the polygon lock signal XSCRDY is an inverted signal of the lock signal LD, the polygon lock signal XSCRDY becomes steep at the rising edge and becomes dull by the time constant composed of C1 and R1 at the falling edge.

  For example, when the lock signal LD becomes High level for 50 ms due to unlocking from the Low level, the polygon lock signal XSCRDY is added with a mask period of 50 ms when the time constant consisting of C1 and R1 is 200 ms, The signal becomes a high level only for 250 ms.

  Here, the adder circuit 68 selects either the resistor R1 or the resistor R4 by the selector 80 based on the port signal S1 input via the I / O port 69. The capacitance value of the capacitor C1 varies depending on the temperature. One of R1 and R4 is selected by the selector 80 based on the port signal S1 so that the amount of change in the time constant composed of C1 and R (R1 or R4) decreases even if the temperature changes. When the capacitance of the capacitor C1 decreases due to temperature change, the resistor R4 having a large resistance value is selected. When the capacitance of the capacitor C1 increases due to temperature change, the resistor R1 having a small resistance value is selected. Thereby, the amount of change in the time constant can be reduced. In the present embodiment, only two resistors R1 and R4 are provided. However, the present invention is not limited to this. For example, two or more resistors may be provided. Here, in the normal capacitor C1, when the temperature rises within the range of 0 ° C. to 70 ° C., the capacitance value of the capacitor C1 decreases.

  A resistance selection process executed by the CPU 41 of the image forming apparatus 1 based on a program stored in the ROM 42 will be described with reference to FIG. FIG. 6 is a flowchart showing the flow of resistance selection processing.

  As shown in FIG. 6, the CPU 41 measures the temperature in the exposure device 23 by the temperature sensor 71 (step S1), and determines whether or not the measured temperature (temperature in the exposure device 23) is lower than a predetermined reference temperature K. Judgment is made (S2). When it is determined that the measured temperature is lower than the predetermined reference temperature K (Y in S2), the resistor R1 having a small resistance value is selected (S3), and when the measured temperature is determined not to be lower than the predetermined reference temperature K (N in S2), the resistor R4 having a large resistance value is selected (S4). As a result, even if the temperature in the exposure unit 23 changes, the amount of change in the time constant composed of C1 and R (R1 or R4) is reduced. It can be controlled so as to be constant without being influenced by.

  Next, the relationship between the lock signal LD and the polygon lock signal XSCRDY will be described with reference to FIGS. 7 and 8 are explanatory diagrams showing the relationship between the lock signal LD and the polygon lock signal XSCRDY.

  As shown in FIG. 7, when the polygon motor 33 is unlocked and the lock signal LD becomes High level for the period T1, the adder circuit 68 causes the polygon lock signal XSCRDY to become High level for the period T2. A necessary period is added to the lock signal LD (T1 <T2).

  As shown in FIG. 8, when the lock signal LD chatters, such as when the polygon motor 33 is activated, the chattering is erased by the mask of the adder circuit 68, and Low pulses in the periods T3 and T4 are generated. Erased. As a result, the polygon lock signal XSRDY becomes a signal that is at a high level only during the period T5 without chattering (T3 + T4 <T5).

  Next, an abnormality detection process executed by the CPU 41 of the image forming apparatus 1 based on a program stored in the ROM 42 will be described with reference to FIG. FIG. 9 is a flowchart showing the flow of the abnormality detection process.

  As shown in FIG. 9, the CPU 41 waits for light emission of the semiconductor laser 31 (N in step S11), and when the semiconductor laser 31 is emitting light (Y in S11), reads the value of the register 72 (S12). Then, it is determined whether or not the register value is at a high level (S13). If it is determined that the register value is at the low level (N in S13), the process returns to step S11. When it is determined that the register value is at the high level (Y in S13), the value of the register 72 is read again (S15) after time T2 by the software timer (S14). Again, it is determined whether or not the register value is at a high level (S16). If it is determined that the register value is at the low level (N in S16), the process returns to step S11. If it is determined that the register value is at the high level (Y in S16), it is determined that an abnormal rotation speed of the polygon motor 33, that is, an abnormal rotation of the polygon mirror 34 has occurred, and the CPU 41 notifies the operation unit 73 of the abnormality. An image (SC337) is displayed and the semiconductor laser 31 is turned off (S17). Here, a function as an abnormality detection means is executed.

  Note that when the unlocking is detected by polling the software timer and the abnormality notification image is displayed on the operation unit 73 by detecting the unlocking a plurality of times, the time of the software timer is set to a very short value. There may be constraints that cannot be done. If the unlock detection is performed only once by software, an abnormality may be detected by the noise of the lock signal LD. That is, there is a possibility of erroneous detection that the rotation speed of the polygon motor 33 is normal but abnormal. At that time, if the lock signal period T1 of the polygon motor 33 is short, the rotational speed of the polygon motor 33 actually becomes abnormal, and even if the unlock occurs, the unlock may not be detected by software. . Further, the rotation of the polygon motor 33 is uneven at the time of activation, chattering occurs in the lock signal, and the software timer may not be able to detect the unlocking.

  According to the present embodiment, by making the high level period of the lock signal LD longer by the adder circuit 68, it is possible to reliably detect the unlock by the software timer. As a result, the rotation abnormality of the polygon mirror 34 can be accurately detected. Further, by controlling the period during which the lock signal LD is at a high level based on the temperature detected by the temperature sensor 71, the rotation error of the polygon mirror 34 is stably controlled by software without being affected by the ambient temperature. Can be detected. Further, by eliminating chattering of the lock signal LD by the adder circuit 68 and extending the High level period of the lock signal LD, the software timer can reliably detect the unlocking. As a result, erroneous detection of rotation abnormality of the polygon mirror 34 can be prevented.

  In this embodiment, the low level of the lock signal LD is set to the valid state (normal state) and the high level is set to the invalid state (abnormal state). However, the present invention is not limited to this. Inversion may be performed so that the low level of the lock signal LD is invalid and the high level is valid.

1 is a longitudinal side view schematically showing an image forming apparatus according to an embodiment of the present invention. It is a top view which shows roughly the internal structure of the exposure device with which an image forming apparatus is provided. FIG. 2 is a block diagram schematically showing electrical connection of each unit included in the image forming apparatus. FIG. 3 is a block diagram schematically showing electrical connection of characteristic portions of the present invention provided in the image forming apparatus. It is a schematic diagram which shows roughly an example of a structure of an addition circuit. It is a flowchart which shows the flow of resistance selection processing. It is explanatory drawing which shows the relationship between a lock signal and a polygon lock signal. It is explanatory drawing which shows the relationship between a lock signal and a polygon lock signal. It is a flowchart which shows the flow of an abnormality detection process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 21 Photoconductor 23 Optical scanning apparatus 30 Light source (light source part)
33 Drive motor (polygon motor)
34 Optical deflector (polygon mirror)
60 Motor control unit 64 Lock signal generation means (PLL circuit)
68 Extension means (adder circuit)
71 Temperature detector (temperature sensor)
80 selection circuit R1 resistor R4 resistor C1 capacitor

Claims (6)

A light source that emits laser light;
A drive motor as a drive source;
An optical deflector that deflects and scans the laser light emitted from the light source by being rotationally driven by the drive motor;
A motor controller that rotates the drive motor at a predetermined rotational speed;
The motor control unit generates a lock signal that is enabled when the drive motor is rotating at a predetermined rotation speed and is disabled when the drive motor is out of the predetermined rotation speed. A lock signal generating means;
An extension means for extending the invalid state of the lock signal by adding a predetermined period to the period when the lock signal generated by the lock signal generation means is in an invalid state;
An abnormality detecting means for detecting an abnormal rotation of the optical deflector based on the lock signal;
An optical scanning device comprising: It has a temperature detector that detects the temperature inside the device,
The extension means controls the period during which the lock signal is in an invalid state based on the temperature detected by the temperature detection unit,
The optical scanning device according to claim 1. The extension means includes
An adder circuit having a plurality of resistors and a capacitor connected to the plurality of resistors;
A selection circuit that selects one resistor to be used from the plurality of resistors according to the temperature detected by the temperature detection unit;
Comprising
The optical scanning device according to claim 2. The extension means extends an invalid state of the lock signal so as to mask chattering of the lock signal;
The optical scanning device according to claim 1, 2 or 3. The extension means is executed by hardware and software.
5. The optical scanning device according to claim 1, 2, 3 or 4. An optical scanning device according to any one of claims 1 to 5,
A photosensitive member having a scanned surface that is exposed and scanned by the laser beam emitted from the optical scanning device, and carrying an electrostatic latent image on the scanned surface;
An image forming apparatus comprising:

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