JP2003145830A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a laser from emitting light over a maximum rating even if the target value of optical output is set at a maximum level erroneously. SOLUTION: The imaging apparatus comprises means for detecting the optical output from each laser as a potential, means for detecting the optical output from each laser as a potential and amplifying the optical output potential arbitrarily, means for setting a target value of writing optical output at the time of emitting light from each laser, means for supplying a switching current, and means for controlling the switching current variably in order to emit light from each laser at the target value of writing optical output wherein the target value of optical output and the amplification factor of optical output potential are set at maximum levels and then the amplification factor is regulated such that the quantity of laser light has a specified level (<= absolute maximum rating) after the laser is lighted.

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus such as a photosensitive member or an electrostatic recording medium which uses a laser light modulated from a laser light source. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus suitable for a copying machine, a laser beam printer, a facsimile, or the like, which guides light on a surface to form image information such as an electrostatic latent image on the surface. 2. Description of the Related Art Conventionally, in this type of image forming apparatus, a laser chip composed of one laser and a PD sensor has been used for generating a laser beam, and a bias current source and a pulse have been used. By having two current sources, the emission characteristics of the laser are improved. And
In order to stabilize the laser emission, the laser emission at the time of image formation is fed back using the output signal from the PD sensor,
Automatic control of the amount of pulse current is performed (hereinafter referred to as APC). In addition, control is performed to prevent abnormal light emission by comparing an output signal from a PD sensor with a predetermined value.
The configuration as shown in FIG. 3 is adopted in the image forming apparatus. The laser chip 44 in FIG. 3 shows the internal configuration of the semiconductor laser 31 in FIG.
This is a single laser including a laser 42 and a PD sensor 41. 47 is a bias current source of the laser 42;
Is a pulse current source of the laser 42, and the light emission of the laser 42 is controlled by a switch 57 that is turned on / off by a signal output from DATA * as image data. The output signal of the PD sensor 41 is converted into a voltage signal by a current / voltage converter 49, input to a comparator 55 via an S / H circuit 51, and output to a pulse current source 45.
Control. Reference numeral 52 denotes a light amount setting unit for providing a target value for controlling the pulse current source. Light volume setting unit is volume 60
, The maximum light intensity value is determined by the volume 61, and the input of the 6-bit D / A converter 62
It outputs 64 light intensity setting values from the minimum value to the maximum value. 58, an image processing unit for generating the image data; 59, a 6-bit D / A converter 62; and a system controller for controlling the image processing unit 58. Further, the output signal of the PD sensor 41 is converted into a voltage signal by a current-to-voltage converter 49, input to a comparator, compared with a predetermined potential input from an electronic volume 52, and exceeds a predetermined potential. If so, an error signal is sent to the system controller 58. The system controller 58 that has received the error signal temporarily turns off the laser and then turns on the laser. FIG. 4 shows a sequence when outputting image data of an image forming apparatus using a conventional example, and FIG. 5 shows laser emission characteristics. The bias current IB is always supplied to the laser. Next, at timing t3, the switch 57 is turned on, and the laser 42 is turned on.
After the write APC is completed, the write current IT is held, and the switch 57 is turned off to cut off the write current IT. At timing T5, BD light emission is performed.
It irradiates the light receiving unit 36 with a timing and outputs image data. While performing the APC of the laser 42 (from t1 to t2)
The output signal of the PD sensor 41 is converted into a voltage signal by the current / voltage converter 49 and input to the comparator 63. The output signal is compared with a predetermined potential input from the light amount limit set value 53, and If it exceeds, a PD limit signal is issued. After receiving the PD limit signal, the system controller 58 temporarily turns off the laser and then turns on the laser. When APC ends, each current is held. FIG. 6 shows a conventional limit operation. When reaching the limit value L1 beyond the target value Ref1 at the timing t6, the comparator 63 becomes H, and starts lighting at a timing t7 after a fixed time. [0009] For the same light amount, PD
The monitor current has characteristics peculiar to each laser, has a temperature characteristic, and its output changes depending on the ambient temperature. Therefore, if the light amount limit value is determined based on the Typ value of the PD monitor current, a malfunction may occur due to variations or an ambient temperature. In addition, if the light amount limit value is determined with a margin, there is a problem that the limit circuit does not operate even if the laser is turned on beyond the maximum rating due to variations or ambient temperature. According to the first aspect of the present invention, there is provided an image forming apparatus in which laser light modulated from a laser light source using a laser is guided adjacently to an image bearing surface. In an image forming apparatus for forming an image on the image carrier, a unit that causes each laser to emit laser light in response to each input laser emission signal, a unit that detects an optical output of each laser as a potential,
Means for detecting the optical output of each laser as a potential, arbitrarily amplifying the optical output potential, means for setting a write light output target value at the time of each laser emission, means for supplying a switching current, and writing light output Means for variably controlling the switching current in order to emit light at the target value, the light output target value and the amplification factor of the light output potential are set to the maximum, and after the laser is turned on, the laser light amount becomes predetermined. It is characterized in that the amplification factor is adjusted so as to be a value (≦ absolute maximum rating). (Operation) According to the structure of the present invention, even if the amplification factor of the PD monitor current is preset and the laser light amount setting value is erroneously set to the maximum value, the laser exceeds the absolute maximum rating due to variations and ambient temperature. Lights to prevent deterioration or destruction. FIG. 1 is a sectional view of an entire image processing apparatus to which the present invention is applied. The basic operation will be described with reference to FIG. The originals stacked on the original feeder are sequentially conveyed onto the original platen glass surface 2 one by one. When the document is conveyed, the lamp of the scanner 3 is turned on, and the scanner unit 4 moves to irradiate the document. The reflected light of the original passes through the lens 8 via the mirrors 5, 6, and 7,
After that, it is input to the image sensor unit 9. The image signal input to the image sensor unit 9 is directly or
The image data is temporarily stored in an image memory (not shown), read out again, and input to the exposure control unit 10. The latent image formed on the photosensitive member 11 by the irradiation light is developed by the developing device 12 or 13.
The transfer paper stacking section 14,
Alternatively, the transfer paper is conveyed from 15, and the developed toner image is transferred in the transfer section 16. After the transferred toner image is fixed on the transfer sheet by the fixing unit 17, the toner image is discharged from the sheet discharging unit 18 to the outside of the apparatus. FIG. 2 is a block diagram of the exposure control section 10 of FIG. The light beam emitted from the semiconductor laser 31 is converted into substantially parallel light by the collimator lens 35 and the stop 32, and is incident on the rotary polygon mirror 33 with a predetermined beam diameter. The rotary polygon mirror 33 rotates at a constant angular velocity in a direction indicated by an arrow, and with this rotation, the incident light beam is reflected as a deflection beam whose angle continuously changes. The light that has become a deflected beam is condensed by the f-θ lens 34. On the other hand, the f-θ lens 34 simultaneously applies a light beam to the photosensitive member 11 shown in FIG. 1 as an image carrier in order to correct the distortion so as to guarantee the temporal linearity of scanning. Combined scanning is performed at a constant speed in the direction of the arrow in the figure. Photoconductor 11
Writing of data into the semiconductor laser 31 is performed by controlling the amount of light of the semiconductor laser 31. FIG. 5 shows the configuration of a laser drive circuit used in such an image processing apparatus. This laser drive circuit is provided in the exposure control unit 10, and the same reference numerals are given to the same portions as those in the conventional example of FIG. FIG. 3 shows this embodiment.
What is different from the conventional example is a volume 64 for adjusting the amplification factor of the current / voltage converter 49 for converting the voltage of the PD monitor current.
Is added, the light amount limit set value 53 and the comparator 6
4 is a deleted point. The laser chip 44 shown in FIG.
1 shows the internal configuration of the semiconductor laser 31, and is a single laser including a laser 42 and a PD sensor 41. 47 is a bias current source of the laser 42,
Reference numeral 45 denotes a pulse current source of the laser 42. Light emission of the laser 42 is controlled by a switch 57 which is turned on / off by a signal output from DATA as image data. The output signal of the PD sensor 41 is converted into a voltage signal by a current / voltage converter 49, input to a comparator 55 via an S / H circuit 51, and output to a pulse current source 45.
Control. Reference numeral 52 denotes a light amount setting unit for providing a target value for controlling the pulse current source. Light volume setting unit is volume 60
, The maximum light intensity value is determined by the volume 61, and the input of the 6-bit D / A converter 62
It outputs 64 light intensity setting values from the minimum value to the maximum value. 58, an image processing unit for generating the image data; 59, a 6-bit D / A converter 62; and a system controller for controlling the image processing unit 58. Next, a method for setting the amount of laser light will be described. First
In advance, the light volume setting volumes 60 and 61 and the PD monitor current amplification factor setting volume 64 are set to the maximum, and the laser is turned on. Then, the PD monitor current amplification factor setting volume 64 is adjusted to set the laser emission amount to a predetermined value (≦ maximum rating). The PD monitor current amplification factor setting volume 64 must be paint-locked after adjustment, or have a configuration that cannot be adjusted by a user or serviceman. Second
The light volume setting volumes 60 and 61 are adjusted to adjust the laser light emission amount to the write light amount. With the above configuration, even if the light volume setting volumes 60 and 61 are erroneously adjusted to the maximum when adjusting the laser light intensity, the laser will not emit light exceeding the maximum rating. For this reason, the light amount limit setting value 53 and the comparator 63 which have been conventionally used as the laser protection circuit are no longer necessary. As described above, according to the configuration of the present invention, even if the amplification factor of the PD monitor current is set in advance and the laser light amount setting value is erroneously set to the maximum value, the variation or the ambient temperature causes It is possible to prevent the laser from lighting beyond the absolute maximum rating and leading to deterioration or destruction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing a configuration of an image forming apparatus to which the present invention is applied. FIG. 2 is a configuration diagram of an optical system in an exposure control unit of FIG. 1 FIG. FIG. 4 is a circuit diagram showing the configuration of a laser drive circuit. FIG. 4 is a timing chart showing operation timings when laser image data is output using a conventional example. FIG. 5 is a diagram showing laser emission characteristics 1. FIG. 6 is a PD limit operation. FIG. 7 is a diagram showing a conventional example of APC at the time. FIG. 7 is a diagram showing laser emission characteristics 2. FIG. 8 is a circuit diagram showing a configuration of a laser driving circuit according to an embodiment of the present invention. Units 5, 6, 7 Mirror 8 Lens 9 Image sensor 10 Exposure controller 11 Photoreceptor 12, 13 Developing unit 14, 15 Transferred paper stacking unit 16 Transfer unit 17 Fixing unit 18 Discharge unit

Claims (1)

Claims: 1. An image forming apparatus for forming an image on an image carrier by guiding a laser beam modulated by a laser light source from a laser light source using a laser to an adjacent image carrier face. Means for causing each laser to emit laser light in response to each input laser emission signal, means for detecting the optical output of each laser as a potential, detecting the optical output of each laser as a potential, and optionally setting the optical output potential Amplifying means, means for setting a write light output target value at the time of each laser emission, means for supplying a switching current, and causing each laser to emit light at the write light output target value.
Means for variably controlling the switching current; setting the light output target value and the amplification factor of the light output potential to the maximum, turning on the laser, and then setting the laser light amount to a predetermined value (≦
An image forming apparatus characterized in that the amplification factor is adjusted so as to be an absolute maximum rating.