JP2017102207A - Optical scanner and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanner that is manufactured at a low cost and can appropriately control the magnitude of a bias current to be supplied to a light source, such as a laser diode, and an image forming apparatus including the optical scanner.SOLUTION: An optical scanner 313 comprises: a light source 61; a light source driving part 62; a temperature detection part 65; and a bias current control part 64. The light source driving part 62 supplies, to the light source 61, a driving current where a modulated current according to image data is superimposed on a bias current. The temperature detection part 65 detects the temperature of the light source 61. The bias current control part 64 controls the magnitude of the bias current according to the temperature detected by the temperature detection part 65.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical scanning device that irradiates a photosensitive drum or the like with light from a light source such as a laser diode, and an image forming apparatus including the optical scanning device.

  In an electrophotographic image forming apparatus such as a printer, a copier, or a facsimile, an image is generally formed using light from a laser diode. In such an image forming apparatus, it is necessary to improve the responsiveness of the laser diode in order to realize high density printing and high speed printing. Therefore, in general, a bias current having a predetermined magnitude is supplied to the laser diode in addition to the modulation current corresponding to the image data.

  In addition, a laser diode driving device is known that can change the magnitude of the bias current using a volume variable resistor or the like (see, for example, Patent Document 1).

JP 2002-127499 A

  Incidentally, it is known that the relationship between the drive current supplied to the laser diode and the light amount of the laser diode changes depending on the temperature of the laser diode and the like. Therefore, in the above driving device, even if the bias current is changed to an optimum value using a volume type variable resistor or the like, if the temperature of the laser diode is changed thereafter, the bias current is optimum. There is a problem that it is no longer in size.

  There is also a drive device having a function (so-called auto-bias function) that always maintains the magnitude of the bias current by detecting the light amount of the laser diode by a photodiode and performing feedback control. However, there is a problem that a drive device having an auto bias function is more expensive than a drive device that does not.

  An object of the present invention is to provide a low-cost optical scanning device and an image forming apparatus capable of appropriately controlling the magnitude of a bias current supplied to a light source such as a laser diode.

  An optical scanning device according to one aspect of the present invention includes a light source, a light source driving unit, a temperature detection unit, and a bias current control unit. The light source driving unit supplies a driving current in which a modulation current according to image data is superimposed on a bias current to the light source. The temperature detection unit detects the temperature of the light source. The control unit controls the magnitude of the bias current according to the temperature detected by the temperature detection unit.

  An image forming apparatus according to another aspect of the present invention includes the optical scanning device, an image carrier, a developing unit, and a transfer unit. The image carrier is irradiated with light from the optical scanning device. The developing unit forms a toner image on the image carrier. The transfer unit transfers the toner image formed on the image carrier to a sheet.

  According to the present invention, a low-cost optical scanning device and an image forming apparatus capable of appropriately controlling the magnitude of a bias current supplied to a light source such as a laser diode are provided.

FIG. 1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing a system configuration of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a block diagram showing a configuration of the optical scanning device according to the embodiment of the present invention. FIG. 4 is a diagram illustrating an example of a control table stored in the optical scanning device according to the embodiment of the present invention. FIG. 5 is a diagram illustrating an example of the bias current set in accordance with the temperature of the light source in the optical scanning device according to the embodiment of the present invention. FIG. 6 is a flowchart illustrating an example of a procedure of bias current control processing executed by the optical scanning device according to the embodiment of the present invention. FIG. 7 is a block diagram showing a configuration of an optical scanning device according to a modification of the embodiment of the present invention. FIG. 8 is a diagram illustrating an example of a control table stored in the optical scanning device according to the modification of the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. In addition, the following embodiment is an example which actualized this invention, Comprising: The thing of the character which limits the technical scope of this invention is not.

  First, a schematic configuration of an image forming apparatus 10 according to an embodiment of the present disclosure will be described with reference to FIGS. 1 and 2. Here, FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus 10.

  As shown in FIGS. 1 and 2, the image forming apparatus 10 includes an ADF 1, an image reading unit 2, an image forming unit 3, a paper feeding unit 4, a control unit 5, an operation display unit 6, and a communication unit 7. The image forming apparatus 10 is a multifunction machine having a plurality of functions such as a scan function, a facsimile function, and a copy function, in addition to a printer function that forms an image based on image data. The present invention is also applicable to image forming apparatuses such as printers, facsimile machines, and copiers. The image forming apparatus 10 is a monochrome-compatible image forming apparatus, but may be a color-compatible image forming apparatus.

  The ADF 1 is an automatic document conveyance device that includes a document setting unit, a plurality of conveyance rollers, a document pressing unit, and a paper discharge unit, and conveys a document read by the image reading unit 2. The image reading unit 2 includes a document table, a light source, a plurality of mirrors, an optical lens, and a CCD (Charge Coupled Device), and reads an image data from a document placed on the document table or a document conveyed by the ADF 1. It is possible to execute a reading process.

  The control unit 5 includes control devices such as a CPU, ROM, RAM, and EEPROM (registered trademark) (not shown). The CPU is a processor that executes various arithmetic processes. The ROM is a non-volatile storage unit in which information such as a control program for causing the CPU to execute various processes is stored in advance. The RAM is a volatile storage unit, and the EEPROM is a non-volatile storage unit. The RAM and the EEPROM are used as a temporary storage memory (working area) for various processes executed by the CPU. Then, the control unit 5 performs overall control of the image forming apparatus 10 by executing various control programs stored in advance in the ROM using the CPU. The control unit 5 may be an electronic circuit such as an integrated circuit (ASIC), and is a control unit provided separately from the main control unit that controls the image forming apparatus 10 in an integrated manner. May be.

  The operation display unit 6 is a display unit such as a liquid crystal display that displays various types of information in response to control instructions from the control unit 5, and an operation key or touch panel that inputs various types of information to the control unit 5 in response to user operations. And so on.

  The communication unit 7 performs wired or wireless data communication with a communication device such as an external information processing device via a communication network such as the Internet or a LAN.

  The image forming unit 3 is an image forming process (printing process) that forms an image by an electrophotographic method based on image data read by the image reading unit 2 or image data input from an information processing apparatus such as an external personal computer. ) Can be executed.

  Specifically, as shown in FIG. 1, the image forming unit 3 includes an image forming unit 31, a fixing device 32, and a paper discharge tray 33.

  The image forming unit 31 includes a photosensitive drum 311, a charging device 312, an optical scanning device 313, a developing device 314, a transfer roller 315, and a cleaning device 316. The photosensitive drum 311 carries a toner image. The charging device 312 charges the surface of the photosensitive drum 311 to a predetermined potential. The optical scanning device 313 irradiates the surface of the photosensitive drum 311 with light based on the image data, and forms an electrostatic latent image corresponding to the image data on the photosensitive drum 311. Details of the optical scanning device 313 will be described later. The developing device 314 stores toner and develops the electrostatic latent image formed on the photosensitive drum 311 using the toner. The transfer roller 315 transfers the toner image formed on the photosensitive drum 311 to a sheet supplied from the paper feeding unit 4. The cleaning device 316 removes toner remaining on the surface of the photosensitive drum 311. Here, the photosensitive drum 311 is an example of an image carrier in the present invention. The developing device 314 is an example of a developing unit in the present invention. Furthermore, the transfer roller 315 is an example of a transfer portion in the present invention.

  The fixing device 32 includes a heating roller and a pressure roller, and melts and fixes the toner image formed on the sheet by the image forming unit 31 to the sheet.

  The paper feed unit 4 includes a paper feed cassette and a plurality of transport rollers, and discharges sheets stored in the paper feed cassette via a toner image transfer position by the image forming unit 31 and a fixing position by the fixing device 32. Transport to paper tray 33. The sheet is a sheet material such as paper, coated paper, postcard, envelope, and OHP sheet.

  Next, the configuration of the optical scanning device 313 will be described with reference to FIG.

  As shown in FIG. 3, the optical scanning device 313 includes a light source 61, a light source driving unit 62, a bias current setting resistor unit 63, a bias current control unit 64, a temperature detection unit 65, and a density detection unit 66.

  The light source 61 is a laser diode, for example, and emits light according to the drive current supplied from the light source drive unit 62. Light emitted from the light source 61 is guided to the photosensitive drum 311 while being scanned in a predetermined main scanning direction by an optical device such as a reflection mirror (not shown), a lens, and a polygon mirror.

  The light source driving unit 62 supplies a driving current corresponding to the input image data to the light source 61. Specifically, the light source driving unit 62 supplies the light source 61 with a driving current in which a modulation current corresponding to image data is superimposed on a bias current. The modulation current is generated by, for example, pulse width modulation (PWM) using image data. In this case, the drive current is a current that alternately repeats a low level (only the bias current) and a high level in accordance with image data. In addition, since this kind of drive device is generally known, description is abbreviate | omitted about the detailed structure of the light source drive part 62 here.

  Incidentally, it is known that the relationship between the drive current supplied to the laser diode and the light amount of the laser diode changes depending on the temperature of the laser diode and the like. Therefore, for example, even if the magnitude of the bias current is changed to an optimum magnitude using a volume type variable resistor or the like, if the temperature of the laser diode subsequently changes, the magnitude of the bias current becomes the optimum magnitude. There is a problem that will disappear. There is also a driving device having a function (so-called auto-bias function) for constantly maintaining the magnitude of the bias current by detecting the light amount of the laser diode by a photodiode and performing feedback control. However, there is a problem that a drive device having an auto bias function is more expensive than a drive device that does not. In contrast, the optical scanning device 313 can appropriately control the magnitude of the bias current supplied to the light source 61 such as a laser diode, as will be described below.

  The light source driver 62 is provided with a bias current control terminal 621 for controlling the magnitude of the bias current. By changing the voltage or current applied to the bias current control terminal 621, the magnitude of the bias current supplied to the light source 61 can be changed.

  A bias current setting resistor unit 63 is connected to the bias current control terminal 621. The bias current setting resistor unit 63 is configured to be able to change the combined resistance value, and includes, for example, at least one fixed resistor having one end connected to the switching element and the other end grounded. In the configuration example shown in FIG. 3, the bias current setting resistor unit 63 includes a fixed resistor R0 and a plurality of fixed resistors connected in parallel to each other, one end connected to the switching elements Tr1 to Tr4 and the other end grounded. And R1 to R4. The switching elements Tr <b> 1 to Tr <b> 4 are digital transistors, for example, and are on / off controlled by the bias current control unit 64.

  The bias current control unit 64 includes control devices such as a CPU, ROM, RAM, and EEPROM (registered trademark) (not shown). The CPU is a processor that executes various arithmetic processes. The ROM is a non-volatile storage unit in which information such as a control program for causing the CPU to execute various processes is stored in advance. The RAM is a volatile storage unit, and the EEPROM is a non-volatile storage unit. The RAM and the EEPROM are used as a temporary storage memory (working area) for various processes executed by the CPU. The bias current control unit 64 controls the magnitude of the bias current supplied to the light source 61 by executing a bias current control program stored in advance in the ROM using the CPU. The bias current control unit 64 may be configured by an electronic circuit such as an integrated circuit (ASIC), or may be a part of the control unit 5 that controls the image forming apparatus 10 in an integrated manner. .

  The bias current control unit 64 can control the combined resistance value of the bias current setting resistor unit 63 by controlling the switching elements Tr1 to Tr4. When the combined resistance value of the bias current setting resistor unit 63 changes, the voltage or current applied to the bias current control terminal 621 changes, so the magnitude of the bias current supplied to the light source 61 changes. That is, the bias current control unit 64 can control the magnitude of the bias current by controlling the switching elements Tr1 to Tr4.

  A temperature detector 65 is connected to the bias current controller 64. The temperature detector 65 is a thermistor, for example, and detects the temperature of the light source 61. It is desirable that the temperature detection unit 65 is provided at a location close to the light source 61.

  The bias current control unit 64 controls the magnitude of the bias current by controlling the switching elements Tr1 to Tr4 in accordance with the temperature of the light source 61 detected by the temperature detection unit 65. The bias current control unit 64 controls the switching elements Tr1 to Tr4 based on, for example, a control table as shown in FIG. The control table shows the correspondence between the temperature detected by the temperature detection unit 65 and the states of the switching elements Tr1 to Tr4. The control table is stored in advance in a nonvolatile storage unit such as the ROM or the EEPROM, for example.

  FIG. 5 shows an example of the relationship between the drive current supplied to the light source 61 such as a laser diode and the light quantity of the light source 61. In general, when the drive current is smaller than a threshold current, the ratio of the change amount of the light amount to the change amount of the drive current is very small, and the light amount is very small. On the other hand, when the drive current exceeds the threshold current, the ratio of the change amount of the light amount to the change amount of the drive current increases, and the light amount increases in proportion to the increase amount of the drive current. In order to improve the response of the light source 61, it is preferable to increase the bias current. However, if the bias current is too large, the amount of light when the modulation current corresponding to the image signal is at a low level increases, so that the image quality deteriorates due to fogging. Therefore, it is desirable that the magnitude of the bias current be smaller than the threshold current.

  Incidentally, it is known that the threshold current changes depending on the temperature of the light source 61. For example, as shown in FIG. 5, the threshold current is Ith0 when the temperature of the light source 61 is T0, but the threshold current is Ith1 when the temperature of the light source 61 is T1 (where T1> T0). Similarly, when the temperature of the light source 61 is T2 (where T2> T1), the threshold current is Ith2, and when the temperature of the light source 61 is T3 (where T3> T2), the threshold current is Ith3, and the temperature of the light source 61 is When T4 (where T4> T3), the threshold current is Ith4. Thus, the threshold current increases as the temperature of the light source 61 increases. Similarly to the threshold current, the drive current required for causing the light source 61 to emit light with a desired light amount also increases as the temperature of the light source 61 increases. Therefore, in order to keep the responsiveness of the light source 61 good, it is necessary to increase the bias current as the temperature of the light source 61 increases.

  Therefore, the bias current control unit 64 turns off all the switching elements Tr1 to Tr4 when the temperature of the light source 61 detected by the temperature detection unit 65 is within the range of T0 to T1 based on the control table shown in FIG. To. As a result, the bias current becomes Ib0. Similarly, when the temperature is within the range of T1 to T2, the bias current control unit 64 turns on only the switching element Tr1. As a result, the bias current becomes Ib1. Further, when the temperature is within the range of T2 to T3, the bias current control unit 64 turns on only the switching elements Tr1 and Tr2. As a result, the bias current becomes Ib2. Further, when the temperature is within the range of T3 to T4, the bias current control unit 64 turns on only the switching elements Tr1 to Tr3. As a result, the bias current becomes Ib3. When the temperature exceeds T4, the bias current control unit 64 turns on all the switching elements Tr1 to Tr4. As a result, the bias current becomes Ib4.

  As described above, according to the optical scanning device 313 of the present embodiment, the bias current can be increased in accordance with an increase in the temperature of the light source 61. Therefore, even if the temperature of the light source 61 changes, the responsiveness of the light source 61 is improved. Can be kept good. Further, since the bias current can be appropriately controlled even if the light source driving unit 62 does not have an auto bias function, the costs of the optical scanning device 313 and the image forming apparatus 10 can be suppressed.

  The control table is preferably set for each type of light source 61 or for each light source 61 in consideration of the type of light source 61 and individual differences of the light sources 61. For example, each threshold value (T0, T1, T2, T3, T4) of the temperature in the control table may be set to an optimum value for each light source 61.

  Further, when a plurality of light sources 61 are provided in the optical scanning device 313 as in the color-compatible optical scanning device 313, the bias current is individually controlled for the plurality of light sources 61. Is desirable. In this case, for example, the light source driving unit 62, the bias current setting resistor unit 63, and the control table are individually provided for each light source. The bias current control unit 64 controls the switching elements Tr1 to Tr4 of the bias current setting resistor unit 63 corresponding to each of the plurality of light sources based on the control table corresponding to each of the plurality of light sources 61. The magnitude of the bias current supplied to each of the plurality of light sources 61 is individually controlled.

  It is known that the characteristics of the light source 61 depend not only on the temperature of the light source 61 but also on the aging of the light source 61. Therefore, the optical scanning device 313 of this embodiment also includes a correction function capable of correcting the bias current determined based on the control table as necessary. Hereinafter, the correction function will be described.

  A concentration detector 66 is connected to the bias current controller 64. The density detection unit 66 is, for example, an ID sensor, and detects the density of an image formed based on light emitted from the light source 61. The density detector 66 is provided, for example, on the downstream side of the developing device 314 in the rotation direction of the photosensitive drum 311 so as to face the outer peripheral surface of the photosensitive drum 311.

  Hereinafter, an example of the procedure of the bias current control process executed in the bias current control unit 64 will be described with reference to FIG. Here, steps S1, S2,... Represent processing procedure (step) numbers executed by the bias current control unit 64.

<Step S1>
First, in step S <b> 1, the bias current control unit 64 acquires the temperature of the light source 61 from the temperature detection unit 65.

<Step S2>
In step S2, the bias current control unit 64 controls the switching elements Tr1 to Tr4 according to the temperature based on the temperature acquired in step S1 and the control table, and sets the bias current.

<Step S3>
In step S <b> 3, the bias current control unit 64 forms a test pattern toner image on the photosensitive drum 311. For example, the bias current control unit 64 reads out image data of a test pattern stored in the ROM or the like and supplies it to the light source driving unit 62. As a result, a driving current corresponding to the test pattern is supplied from the light source driving unit 62 to the light source 61, and finally, an image (toner image) of the test pattern is formed on the photosensitive drum 311.

<Step S4>
In step S <b> 4, the bias current control unit 64 acquires the density of the test pattern image formed on the photosensitive drum 311 from the density detection unit 66.

<Step S5>
In step S5, the bias current control unit 64 determines whether or not the density acquired in step S4 is sufficiently dark. By the way, when the magnitude of the bias current is appropriate, the response of the light source 61 is kept good, so that the density of the test pattern image is sufficiently high. On the other hand, when the magnitude of the bias current is too small, the responsiveness of the light source 61 is lowered, and the density of the test pattern image is lowered. If it is determined in step S5 that the concentration is sufficient (S5: Yes), the bias current control process ends. On the other hand, if it is determined that the density is not sufficient (S5: No), the process proceeds to step S6.

<Step S6>
In step S6, the bias current control unit 64 corrects the bias current. Specifically, the bias current control unit 64 further increases the bias current by, for example, one step so that the responsiveness of the light source 61 is improved. For example, when the current bias current is Ib2 shown in FIG. 4, the bias current control unit 64 turns on the switching element Tr3 so that the bias current becomes Ib3. Then, the process returns to step S3. Thus, the processes of steps S3 to S6 are repeated until a sufficient density is detected.

  As described above, the optical scanning device 313 according to the present embodiment has the correction function as described above. Therefore, even if the characteristics of the light source 61 change due to conditions other than temperature, the magnitude of the bias current is increased. Can be controlled appropriately.

  In the configuration example shown in FIG. 3, the switching elements Tr1 to Tr4 are connected in series in the bias current setting resistor unit 63, but the present invention is not limited to this. For example, as shown in FIG. 7, in the bias current setting resistor unit 63A, the switching elements Tr1 to Tr4 may be connected in parallel. In this case, by making the resistance values of the fixed resistors R1 to R4 different from each other, it is possible to set the combined resistance value of the bias current setting resistor unit 63A to a maximum of 16 types (that is, 2 to the 4th power). . Therefore, the bias current can be controlled more finely according to the temperature of the light source 61, for example, as in the control table shown in FIG.

  In the present embodiment, the combined resistance value of the bias current setting resistor unit 63 is controlled by the four switching elements Tr1 to Tr4, but the present invention is not limited to this. For example, the bias current setting resistor unit 63 may include only one switching element. In this case, the bias current can be changed only in two ways, but the costs of the optical scanning device 313 and the image forming apparatus 10 can be further reduced.

3 Image forming unit 10 Image forming device 31 Image forming unit 32 Fixing device 33 Paper discharge tray 61 Light source 62 Light source driving unit 63 Bias current setting resistor unit 64 Bias current control unit 65 Temperature detection unit 66 Density detection unit 311 Photosensitive drum 312 Charging Device 313 Optical scanning device 314 Developer 315 Transfer roller 316 Cleaning device 621 Bias current control terminals R0 to R4 Fixed resistors Tr1 to Tr4 Switching elements

Claims (8)

A light source;
A light source driving unit that supplies a driving current in which a modulation current according to image data is superimposed on a bias current to the light source;
A temperature detector for detecting the temperature of the light source;
A bias current control unit for controlling the magnitude of the bias current according to the temperature detected by the temperature detection unit;
An optical scanning device comprising: A bias current setting resistor unit connected to the light source driving unit and capable of changing a combined resistance value;
The optical scanning device according to claim 1, wherein the bias current control unit controls the magnitude of the bias current by controlling a combined resistance value of the bias current setting resistor unit. The bias current setting resistor unit includes at least one fixed resistor having one end connected to the switching element and the other end grounded;
The optical scanning device according to claim 2, wherein the bias current control unit controls the magnitude of the bias current by controlling the switching element in accordance with at least a temperature detected by the temperature detection unit. The bias current setting resistor unit includes a plurality of fixed resistors connected in parallel to each other, one end of which is connected to the switching element and the other end is grounded.
The optical scanning device according to claim 2, wherein the bias current control unit controls the magnitude of the bias current by controlling the switching element according to at least a temperature detected by the temperature detection unit.   The bias current control unit controls the magnitude of the bias current based on a control table indicating a correspondence relationship between the temperature detected by the temperature detection unit and the state of the switching element. Optical scanning device. A plurality of the light sources, a plurality of the light source driving units respectively corresponding to the plurality of light sources, a plurality of the bias current setting resistor units, and a plurality of the control tables,
The bias current control unit controls the switching elements of the bias current setting resistor unit corresponding to each of the plurality of light sources based on the control table corresponding to each of the plurality of light sources. The optical scanning device according to claim 5, wherein the magnitude of the bias current supplied to each of the light sources can be individually controlled. A density detector for detecting the density of an image formed based on the light emitted from the light source;
The bias current control unit controls the switching element in accordance with the temperature detected by the temperature detection unit, and further controls the switching element in accordance with the concentration detected by the concentration detection unit. The optical scanning device according to claim 3, wherein the magnitude of the bias current can be corrected. An optical scanning device according to any one of claims 1 to 7,
An image carrier to which light from the optical scanning device is irradiated;
A developing unit for forming a toner image on the image carrier;
A transfer unit for transferring the toner image formed on the image carrier to a sheet;
An image forming apparatus comprising: