JP2011046064A - Method for preventing malfunction of light quantity control apparatus of image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that in adjusting and controlling light quantity of a surface emitting laser, when the maximum light quantity of the light quantity of the laser does not reach a target light quantity, a light quantity control apparatus increases a driving electric current, and it sticks that the electric current reaches the maximum electric current as it does, and adjustment of the light quantity cannot be properly performed. <P>SOLUTION: In the light quantity control apparatus of an image forming apparatus, which when the driving current a light quantity adjusting and controlling means feeds to a laser element reaches a predetermined upper limit, the driving electric current is got out of a condition that the driving electric current sticks the maximum value as it does by lowering the driving electric current once, and an appropriate light quantity adjustment control is performed again by starting again the light quantity adjustment and control thereafter. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that scans a photoreceptor with a laser beam to form an image.

  Conventionally, an edge emitting laser is used as a light source of an image forming apparatus such as a printer. FIG. 3 shows the current-light quantity characteristics (hereinafter referred to as IL characteristics) of the edge emitting laser. When the amount of current is increased from 0 and the oscillation threshold is reached, laser light emission is started. Then, the light quantity increases almost linearly as it is raised. When further increased, the device enters a destruction mode and the device is destroyed.

  As is well known, auto power control (APC) for determining the current to be injected into the semiconductor laser is known as the light amount control. By adjusting the light amount with this APC circuit, the light amount of the semiconductor laser can be easily adjusted. The current determination by the APC circuit is a feedback circuit that increases the injection current until the light amount of the emitted laser light becomes the reference light amount.

  As shown in FIG. 4, the beam output from the laser light source 100 is received by the light detection unit 101, and the light detection unit 101 outputs a photocurrent corresponding to the received light amount. This photocurrent is converted into a voltage by the current-voltage conversion unit 102, input as a monitor voltage to the comparison unit 103, and compared with a reference voltage Vref output from a control unit (not shown). Based on the comparison result, the comparison unit 103 controls the sample hold circuit 104 for increasing or decreasing the output light amount of the laser light source 100 and feeds it back to the constant current source 105. The above sequence is repeated until the monitor voltage becomes equal to the reference voltage Vref, and the amount of drive current is adjusted to obtain a desired amount of light. Thus, the negative feedback amplification operation is performed.

  In recent years, it has been proposed to use a surface emitting laser as a light source in a printer in order to meet the demand for high speed and high resolution for a printer (see Patent Document 1).

  FIG. 5 shows the IL characteristic of the surface emitting laser. When the amount of current is increased from 0 and the oscillation threshold is exceeded, light emission starts. The amount of light increases as the amount of current increases, but reaches the amount of current Ipmax maximum amount of light Pmax, and the amount of light attenuates conversely even if the amount of current is further increased therefrom. Even if Ipmax is exceeded, the device will not be destroyed.

  The situation when the conventional light quantity control is used for the surface emitting semiconductor laser having such IL characteristics will be described with reference to FIG. When in the state (1), it is controlled by the current amount Ip that generates the target light amount P. When the surface emitting semiconductor laser instantaneously changes from state (1) to state (2) due to the influence of temperature change, the APC circuit increases the current amount from Ip to obtain the target light amount. Without exceeding the laser current point (Ip). Even when the state (2) returns to the state (1), the control is performed in the positive feedback amplification operation region in which the laser current is further increased. As a result, there is a possibility that the laser light quantity cannot be controlled to the target value.

  For this reason, a method has been proposed in which the amount of current that outputs the maximum amount of light is acquired and stored by detection operation so that the amount of light is not adjusted beyond the maximum amount of light, and the amount of current is controlled as the upper limit of the amount of current (patent) Reference 2).

JP-A-5-294005 JP 2001-308449 A

  However, in the conventional technology, although it is mentioned that the light amount is controlled below the upper limit value of the drive current, the upper limit of the current is due to an instantaneous change in IL characteristics during image formation or noise in the control circuit. When the value is reached, it is processed as an abnormal state, and it is necessary to replace the light source to resume image formation.

  The present invention has been made to solve the above-described problems, and it is an object of the present invention to prevent malfunction of light quantity control and to perform appropriate light quantity control with a simple configuration.

  In order to achieve the above object, according to the first aspect of the present invention, an image is formed on the scanned object by scanning the scanned light with a plurality of light beams emitted from a plurality of light sources. An image forming apparatus configured to detect a light amount of the plurality of light beams, and change a light source driving current by negative feedback control so that a detection value by the light amount detection unit becomes a predetermined value. A light amount control means for controlling the light amount of the light beam and a current monitor means for monitoring a light source driving current amount generated by the light amount control means, and when it is determined that the current monitor means has reached a predetermined current amount The light source driving current is temporarily lowered.

  According to a second aspect of the present invention, there is provided an image forming apparatus for forming an image on the scanned object by scanning the scanned light with a plurality of light beams emitted from a plurality of light sources. The light quantity detection means for detecting the light quantity of the plurality of light beams, and the light source drive current is changed by negative feedback control so that the detection value by the light quantity detection means becomes a predetermined value, thereby reducing the light quantity of the light beam. A light amount control means for controlling, and a current monitoring means for monitoring a light source driving current amount generated by the light amount control means, and when the current monitoring means determines that the predetermined current amount has been reached, the light source driving current is temporarily An image forming apparatus characterized by setting to zero.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the timing for once decreasing the light source driving current is a non-image area during scanning.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect, the timing at which the light source driving current is once set to 0 is a non-image area during scanning.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the predetermined current amount is an upper limit of a driving current that can be supplied by the light amount control unit. .

  According to a sixth aspect of the present invention, in the image forming apparatus according to the first or second aspect, when the light source driving current amount is increased, the predetermined current amount decreases the light amount of the plurality of light sources. It is characterized by the amount of current to be generated.

  The invention described in claim 7 is characterized in that the light source described in claim 1 or 2 is a surface emitting semiconductor laser.

  According to the present invention, it is possible to prevent malfunction of light amount adjustment control of a surface emitting laser semiconductor. Further, the light amount adjustment control can be appropriately performed with a simple configuration. In addition, the downtime of the image forming apparatus can be reduced.

It is a block diagram which shows the structure of the laser light quantity control apparatus which concerns on this invention. It is a figure explaining the IL characteristic of a surface emitting laser element. It is a figure explaining the IL characteristic of a surface emitting laser element, and the control action of this invention. It is a flowchart explaining the control action of this invention. It is a figure which shows the IL characteristic of the conventional end surface emitting laser. It is a block diagram which shows the structure of the conventional laser control apparatus. It is a figure which shows the IL characteristic of a surface emitting laser element. It is a figure when the light quantity control method of the conventional laser element is used for the surface emitting laser element.

The image forming apparatus according to the present embodiment will be described below with reference to the drawings. The present invention will be specifically described below, but the present invention is not limited to these examples.
[First Embodiment]
[Image forming apparatus]
FIG. 1 is a block diagram showing a configuration of a laser light quantity control circuit of an image forming apparatus according to the present invention. In FIG. 1, reference numeral 200 denotes a surface emitting laser, and an output beam is received by a light detection unit 201. The light detection unit 201 outputs a photocurrent corresponding to the amount of light received. This photocurrent is converted into a voltage by the current-voltage conversion unit 202, input as a monitor voltage to the comparison unit 203, and compared with a reference voltage Vref supplied from a reference voltage source (not shown). Based on the comparison result, the comparison unit 203 controls the sample hold circuit 204 for increasing / decreasing the output light amount of the surface emitting laser unit 200 and feeds it back to the constant current source 205. By performing a negative feedback operation that repeats the above circuit operation until the monitor voltage becomes equal to the reference voltage Vref, a desired light amount is obtained.

  The IL characteristics of the surface emitting laser 200 are shown in FIG. Here, three lasers will be described as an example. As shown in FIG. 2, the IL characteristic varies depending on the beam. The light amount Pa required for image formation is set to a light amount lower than the peak light amount of all the beams. The drive currents that generate the light amount Pa are Ia1, Ia2, and Ia3, respectively. As described above, according to the operation of the laser light quantity control circuit shown in FIG. 1, the drive currents of LD1, LD2, and LD3 are set to Ia1, Ia2, and Ia3, respectively, and image formation is performed with a necessary light quantity Pa.

  Semiconductor lasers are generally sensitive to temperature in electrical / optical conversion efficiency. FIG. 3 shows IL characteristics when the temperature of the surface emitting laser 200 is changed in three stages. Here, the LD 3 in FIG. 2 will be described as an example.

  The temperature of LD3 is higher in the order of LD3- (1), LD3- (2), and LD3- (3). That is, the higher the temperature of the element, the lower the electrical / optical conversion efficiency. For example, assume that image formation is started in the state of LD3- (1). The drive current at this time is Ia3- (1). If image formation is continued and the state of LD3- (2) is changed to the state of LD3- (2) due to self-temperature rise of LD3, it will be lower than Pa, but the laser light quantity control circuit sets the drive current to Ia3- (2) to increase the light quantity to Pa The image formation is continued without any problem. When a high-density image is continuously formed or when the laser light is instantaneously changed to the state of LD3- (3) due to laser thermal interference around the LD3, the laser light quantity control circuit increases the light quantity to Pa. Although the drive current is increased as much as possible, Pa cannot be reached even when the peak light quantity of IP3- (3) is reached, and the drive current is further increased, stuck to ILimit, and fixed by positive feedback operation. In such a state, even if LD3 returns to the states LD3- (2) and LD3- (1), it cannot return to the negative feedback operation.

  Even if the state of LD3- (3) does not occur, when some electrical noise is mixed in the light amount control circuit, for example, the reference voltage Vref and the monitor voltage input to the comparison unit 203 are fluctuated. In such a case, it may be erroneously detected that the amount of light is temporarily insufficient, and similarly, it may stick to the positive feedback operation.

  The control for automatically returning from the positive feedback operation to the negative feedback operation, which is a feature of the present invention, will be described. The constant current source 205 of the laser light quantity control circuit has a built-in current monitoring mechanism 206 that monitors the supplied current and notifies the CPU 207 as a current upper limit value arrival signal when the current upper limit value ILimit is reached. .

  The control flow will be described with reference to FIG. Assume that the image is in an image forming state. First, it is determined whether or not a current upper limit reaching signal is notified from the current monitoring mechanism 206 to the CPU 207 (step S01). When the current upper limit value arrival signal is notified (step S01 determination YES), the CPU 207 waits until the non-image section for image formation (step S02 determination NO), and when the non-image section is reached (step S02 determination YES), the constant current source 205. A current reduction signal is issued (S03). The constant current source 205 temporarily reduces the current value stuck at ILimit to 0 or near 0. By doing so, the light quantity control circuit can return to the negative feedback operation region of FIG.

  The current upper limit value may be the upper limit of the drive current that can be supplied by the constant current source.

  Further, the current upper limit value may be a current value in a positive feedback operation region in which the amount of light decreases when the current of all LDs of the surface emitting laser 200 is increased.

  As described above, the laser light amount control circuit monitors the LD drive current, and when it reaches a predetermined upper limit current value, the drive current is temporarily reduced to 0 or near 0, thereby performing positive feedback operation. The light quantity control circuit can be returned to the negative feedback region, and appropriate light quantity adjustment control can be performed with a simple configuration.

205 Constant current source 206 Upper limit current value detection mechanism

Claims (7)

  An image forming apparatus for forming an image on a scanned object by scanning a plurality of light beams emitted from a plurality of light sources on the scanned object, wherein the amount of light of the plurality of light beams is changed. A light amount detection unit for detecting, a light amount control unit for controlling a light amount of a light beam by changing a light source driving current by negative feedback control so that a detection value by the light amount detection unit becomes a predetermined value, and the light amount control unit An image forming apparatus having current monitoring means for monitoring the amount of light source driving current generated by the light source, and once reducing the light source driving current when it is determined that the current monitoring means has reached a predetermined current amount.   An image forming apparatus for forming an image on a scanned object by scanning a plurality of light beams emitted from a plurality of light sources on the scanned object, wherein the amount of light of the plurality of light beams is changed. A light amount detection unit for detecting, a light amount control unit for controlling a light amount of a light beam by changing a light source driving current by negative feedback control so that a detection value by the light amount detection unit becomes a predetermined value, and the light amount control unit An image forming apparatus comprising: a current monitoring unit that monitors a light source driving current amount generated by the light source; and, when the current monitoring unit determines that a predetermined current amount has been reached, the light source driving current is once set to zero. .   The image forming apparatus according to claim 1, wherein the timing at which the light source driving current is once lowered is a non-image area during scanning.   3. The image forming apparatus according to claim 2, wherein the timing at which the light source driving current is once set to 0 is a non-image area during scanning.   3. The image forming apparatus according to claim 1, wherein the predetermined amount of current is an upper limit of a drive current that can be supplied by the light amount control unit.   3. The image forming apparatus according to claim 1, wherein the predetermined amount of current is an amount of current that decreases a light amount of the plurality of light sources when the amount of light source driving current is increased. 4. Forming equipment.   3. The image forming apparatus according to claim 1, wherein the light source is a surface emitting semiconductor laser.

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