JP2000071509A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To write a light minutely at a high speed while constantly maintaining a spot irradiation interval of a plurality of light beams to be directed on a photosensitive member according to a recording density without being influenced by the temperature change in a light source part in a multi-beam writing system image forming apparatus. SOLUTION: A thermister 130 for detecting the temperature change in a light source part is provided. A temperature detection value is inputted to a CPU 133 via an AD converter 132. The CPU 133, which stores correction coefficients preliminarily determined according to the temperature detection value, reads out the correction coefficient corresponding to the value when a temperature detection value is inputted, and calculates a driving step number P of a stepping motor 126 appropriate for the recording density designated by a recording density instruction part 135 at the time, using the correction coefficient. The stepping motor 126 is rotated in a predetermined direction for the step number P by a stepping motor driving circuit 134.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms an image to be printed out by irradiating a photoreceptor with a laser beam, and prints out the image through a series of image forming steps such as development, transfer and fixing. TECHNICAL FIELD The present invention relates to a digital image forming apparatus such as a laser printer, a copying machine, etc., and more particularly, to an image forming apparatus having a multi-beam writing device for forming an image by simultaneously irradiating a plurality of laser beams to a photosensitive member surface using a plurality of laser light sources. It concerns the device.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic digital image forming apparatus such as a digital copying machine or a laser printer, a laser beam from a laser light source is irradiated onto a rotating polygon mirror (optical deflector) called a polygon mirror and reflected. Thereby, while scanning (scanning) the laser beam in the main scanning direction, the sub-scanning direction (direction orthogonal to the main scanning direction)
A latent image of an image to be output is formed by irradiating the surface of the photosensitive member moving to the surface. Since the intensity of the laser beam is modulated according to the image to be output, an electrostatic latent image corresponding to the image to be output is formed on the photoreceptor, and the electrostatic latent image is developed into a toner image. . In such a digital image forming apparatus, in order to output an image at a speed comparable to that of an analog high-speed machine, the rotation speed of a polygon mirror that deflects a laser beam and scans on a photoconductor is increased, It is necessary to increase the modulation speed of the semiconductor laser that modulates the laser beam, but there is a limit to the drive speed of the motor that rotates the polygon mirror and the modulation speed of the semiconductor laser. Therefore, various multi-beam writing devices have been proposed which increase the recording speed by simultaneously scanning a plurality of laser beams on the photoreceptor (JP-A-06-331913, JP-A-07-181411, JP-A-07-181411).
181412). FIG. 7 shows a configuration example of a multi-beam writing apparatus mounted on a conventional image forming apparatus. In FIG. 7, reference numeral 10 denotes a writing device mounted on a laser printer or the like. This writing device 10 rotates two laser beams L1 and L2 emitted from the light source unit 20 through a cylindrical lens 11 at a high speed. The mirror is deflected by being reflected by a mirror surface whose angle changes with rotation and is repeatedly scanned in the main scanning direction. The laser beams L1 and L2 deflected by the polygon mirror 12 further enter the folding mirror 14 provided along the photosensitive drum 15 via the fθ lens 13 and are reflected by the mirror 14 to be reflected by the photosensitive drum 15 Scanned up. At this time, the laser beam L
1, L2 are emitted from the light source unit after being modulated in accordance with image data, and are simultaneously spot-irradiated on the photosensitive drum 15 at a predetermined distance X in the rotation direction (sub-scanning direction) of the photosensitive drum 15. Thus, an electrostatic latent image is formed, and the recording speed is increased by recording the image data two lines at a time. FIG. 8 is a cross-sectional view illustrating a configuration example of the light source unit 20.
In FIG. 8, reference numerals 5 and 6 denote collimating lenses for converting the laser beams L1 and L2 emitted from the semiconductor lasers 1 and 2 into substantially parallel light beams.
The laser beams L1 and L2 are deflected by the beam combining prism 7 and emitted close to each other. The semiconductor lasers 1 and 2 are held at a predetermined position of the collimating lens holder 3 while being held by a fixture 8. The beam synthesizing prism 7 is housed and held in a housing 9. The housing 9 is screwed onto the collimating lens holder 3 and attached to a predetermined position with respect to the semiconductor lasers 1 and 2 and the collimating lenses 5 and 6. Is held. The collimating lens holder 3 is attached to the LD control board 4 by screwing.

[0003]

However, in a writing apparatus that forms an image using a plurality of light beams as described above, the interval between the spot irradiation positions of the plurality of light beams changes due to a change in the temperature of the light source unit. This is because the mutual distance between a plurality of light emitting elements provided in the light source unit, the mutual distance between the collimating lenses, and the like change due to expansion and contraction of the support due to temperature change. In the example of FIG.
The positional relationship between the semiconductor lasers 1 and 2 and the collimating lenses 5 and 6 changes due to thermal expansion and contraction of the collimating lens holder 3 and the like.
The distance X between the light spots of the laser beams L1 and L2 changes. Although it depends on the overall optical characteristics of the writing device 10, the semiconductor lasers 1 and 2 and the collimating lens 5,
Even if the relative positional relationship of 6 is shifted on the order of microns, the change in the interval X between the light spots on the photosensitive drum 15 may be enlarged to 10 microns or more, which is a major factor that causes image quality deterioration. The recording density on the photosensitive drum 15 by the writing device 10 is changed by controlling the modulation operation of the semiconductor lasers 1 and 2 by a controller. At this time, the recording density on the photosensitive drum 15 is changed according to the recording density. The interval X between the light spots is also changed. For this reason, the degree of influence of the shift of the interval X between the light spots on the photosensitive drum 15 on the image changes depending on the recording density. Since the interval X between the light spots becomes smaller as the recording density becomes higher, the influence of the shift of the interval X between the light spots is likely to occur.
For example, when the recording density is 200 dpi, the spot interval X on the photosensitive drum 15 is 127 μm, and when the recording density is 600 dpi, the spot interval X on the photosensitive drum 15 is 42.3 μm. Therefore, the latter has a greater degree of image deterioration due to the deviation of the spot interval X than the former. The present invention has been made in order to solve the problems of the above conventional technology, the spot irradiation interval of a plurality of light beams irradiated on the photoreceptor, without being affected by the temperature change of the light source unit, It is an object of the present invention to provide an image forming apparatus including a multi-beam writing device capable of performing optical writing at high speed and with high precision while always maintaining a constant value according to the recording density.

[0004]

According to a first aspect of the present invention, there is provided a collimating lens for converting a plurality of laser light sources and light beams from the plurality of laser light sources into substantially parallel light beams. And a light source unit having a beam combining unit that emits these light beams close to each other or overlapped with each other, and a plurality of light beams separated from the plurality of light beams emitted from the light source unit in the sub-scanning direction. In an image forming apparatus that forms an image on the photoconductor by simultaneously scanning in the main scanning direction while condensing the light on the photoconductor as a light spot, a recording density specification that specifies a recording density of the image on the photoconductor Means, pitch changing means for changing the pitch of the light spot in the sub-scanning direction on the photoconductor, according to the recording density specified by the recording density specifying means, A temperature detecting unit such as a thermistor for detecting the temperature of the source unit; and a pitch correcting unit for correcting a pitch set value corresponding to each recording density by the pitch changing unit in accordance with the temperature detected value by the temperature detecting unit. It is characterized by that. According to a second aspect of the present invention, in addition to the configuration of the image forming apparatus of the first aspect, the image forming apparatus further includes a memory storing and holding correction data in which a temperature detection value and a correction coefficient are associated with each other. And reading out a correction coefficient corresponding to the temperature detection value from the memory, and correcting the pitch set value based on the correction coefficient. According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the memory stores and holds correction data in which a recording density and a correction coefficient are associated with each other, and the pitch correction unit stores the correction data from the memory. A correction coefficient corresponding to the recording density is read, and the pitch setting value is corrected based on the correction coefficient. According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, the memory stores and holds correction data in which a temperature detection value and a correction coefficient are associated with each other for each recording density, Is
A correction coefficient corresponding to the temperature detection value is read from the memory for each recording density, and the pitch set value is corrected based on the correction coefficient. Claim 5
The invention described in the above description is characterized in that, in the image forming apparatus according to any one of the first to fourth aspects, the temperature detection unit is provided on a collimating lens holding member of the light source unit.

[0005] As described above, the image forming apparatus according to the first aspect includes the temperature detecting means for detecting the temperature of the light source unit, which is a factor for changing the interval between the light spots on the photosensitive member,
According to the temperature detection value of the light source unit by this temperature detection means,
Since the pitch set value by the pitch changing means at each recording density is changed, the spot interval of the plurality of light beams irradiated on the photoconductor is adjusted according to the recording density without being affected by the temperature change of the light source unit. Can always be kept constant. Further, in the image forming apparatus according to the second aspect, correction data in which the detected temperature value and the correction coefficient correspond to each other are stored and held in a memory in advance, and the correction coefficient corresponding to the detected temperature value of the light source unit by the temperature detecting means is provided. Is read from the memory, and the pitch set value by the pitch changing means at each recording density is corrected based on the value. The distance between light spots on the body can be kept constant. Further, in the image forming apparatus according to the third aspect, correction data in which the recording density and the correction coefficient correspond to each other are stored and held in a memory in advance, and the correction coefficient corresponding to the recording density specified by the recording density specifying unit is stored. Is read from the memory, and the pitch set value by the pitch changing means at each recording density is corrected based on the value, so that the interval between the light spots on the photoconductor can be more accurately kept constant. Further, in the image forming apparatus according to the present invention, correction data in which a temperature detection value and a correction coefficient are made to correspond to each recording density is stored and held in a memory in advance, and the temperature detection value of the light source unit by the temperature detection means is stored. The corresponding correction coefficient is read from the memory for each recording density, and the pitch set value by the pitch changing means is corrected based on the value. It is possible to accurately keep the distance between the light spots on the photosensitive member constant without performing the above operation.
Further, in the image forming apparatus according to the fifth aspect, a temperature detecting member such as a thermistor is provided on a holding member of the collimating lens in order to detect a position change of the collimating lens which most contributes to a change in the interval between the light spots, and the temperature is determined according to the detected value. By correcting the distance between the light spots, the distance between the light spots can be kept constant with high accuracy.

[0006]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is an exploded perspective view showing a configuration example of a light source unit of a multi-beam writing device mounted on an image forming apparatus according to the present invention. As shown, the light source unit 100 includes two semiconductor lasers 10 as laser light sources.
1 and 102; collimating lenses 111 and 112 for converting the two laser beams L1 and L2 emitted from the semiconductor lasers 101 and 102 into substantially parallel light beams; and narrowing the laser beams L1 and L2 to a predetermined beam diameter. Aperture plate 10
5, the laser beam L1, which has passed through the aperture plate 105,
A beam combining prism 106 is provided as a beam combining unit that emits the beams L2 overlapping each other. Also,
The light source unit 100 rotates the optical system itself including the semiconductor lasers 101 and 102, the collimating lenses 111 and 112, the stop plate 105, the beam combining prism 106, and the like around substantially the optical axis of the light emitted from the beam combining prism 106. Accordingly, a pitch variable mechanism 150 for changing the interval X between the light spots on the photosensitive drum is provided. The two laser beams L1 and L emitted from the light source unit 100
Like the writing device described with reference to FIG. 8, the light 2 is incident on a polygon mirror that rotates at a high speed via a cylindrical lens, and is deflected by being reflected by a mirror surface whose angle changes with rotation. Scanning is repeatedly performed in the scanning direction.

The semiconductor lasers 101 and 102 are integrally fixed on a substrate 109 on which a laser drive circuit is formed. The semiconductor lasers 101 and 102 are fixed to holder members 107 and 108, respectively.
07 and 108 are fixed to the back surface of the collimating lens holder 110 with screws 113 and 114, so that the pn junction surfaces of the collimating lenses 111 and 108 are matched.
It is provided so that the optical axis coincides with 112. The collimating lenses 111 and 112 are respectively housed in lens barrels, fitted in fitting holes 110a and 110b of the collimating lens holder 110, and fixed to the holder 110 by bonding. The aperture plate 105 and the beam combining prism 106 are provided at predetermined positions on the back side of the rotating member 151 of the variable pitch mechanism 150, and the collimating lens holder 110 is
By being fixed to the back side of the rotating member 151 with 7 or the like, it is fixed to the rotating member 151. Then, the substrate 10 on which the laser drive circuit is formed on the back side of the rotating member 151
9 is fixed by screws or the like, so that the semiconductor laser 10
The members from 1, 102 to the beam combining prism 106 are integrally held in a form accommodated between the rotating member 151 and the substrate 109. Hereinafter, the “light source unit 100”
Denotes the one integrated in this manner.

Here, the function of the beam combining prism 106 will be described. A 波長 wavelength plate 115 is attached to one incident surface of the beam combining prism 106,
One of the two laser beams L1 and L2 from the semiconductor lasers 101 and 102 (in this example, the semiconductor laser 1
01 from the half-wave plate 115
, The polarization plane thereof is rotated by 90 ° and enters the beam combining prism 106. Then, the laser beam L1 passes through the polarization beam splitter surface 106b of the beam combining prism 106. The laser beam L2 from the other semiconductor laser 102 is internally reflected by the inclined end surface 106a of the beam combining prism 106, further reflected by the polarization beam splitter surface 106b, and substantially combined with the laser beam L1. However, the emission directions of the two laser beams L1 and L2 from the beam combining prism 106 are set so as to deflect each other by a small angle θ in the main scanning direction. Light emitted from the beam combining prism 106 is transmitted to the cylindrical portion 1 protruding from the front surface of the rotating member 151.
The light is emitted to the outside of the light source unit 100 through the inside 51a.

The cylindrical portion 151a of the rotating member 151 is inserted with a play into a hole 118a formed in a side plate of an optical frame 118 fixed to a fixed structure (frame) of the image forming apparatus. A coil spring 1 having a diameter larger than that of the hole 118a is provided outside the cylindrical portion 151a from the distal end side.
After the mounting of the coil spring 19, the spring pressing plate 120 is engaged, so that it can be turned around the cylindrical portion 151a while being pulled toward the side plate of the optical frame 118 against the elastic force of the coil spring 119. It is supported by. More specifically, the spring pressing plate 1 is provided at the protruding end of the cylindrical portion 151a.
20 is provided with a flange portion 151d.
The spring pressing plate 120 is provided with a hole 120a for receiving the flange portion 151d and a pair of locking pins 120b. Then, the coil spring 119 and the spring pressing plate 120 are mounted on the cylindrical portion 151a inserted into the hole 118a of the optical frame 118.
0 by approximately 90 °, the spring pressing plate 120
The flange portion 151d is locked by the locking pin 120b and the peripheral edge of the through hole 120a. As a result, the light source unit 1
00 denotes an arrow α against the elastic force of the coil spring 119.
In the state of being pulled in the direction of
It is attached to the optical frame 118 so as to be rotatable about the axis 51a.

On both sides of the rotating member 151, a rotating arm 15 is provided.
1b and the rotation position detection arm 151c protrude substantially at the left and right target positions. A rotation mechanism 1 for rotating the rotation member 151 is provided on the rotation arm 151b side of the optical frame 118.
A home position sensor 156 for detecting the home position of the rotation member 151 is provided on the side of the rotation position detection arm 151c. The rotation mechanism 155 and the home position sensor 156 are main parts of the pitch variable mechanism 150. Rotating mechanism 15
Reference numeral 5 indicates that the rotating arm 151b is always downward (in the direction of the arrow β).
Spring 157 biasing the rotation arm 151
and a vertical movement mechanism 158 for supporting the lower end of b and moving it up and down. The vertical movement mechanism 158 includes a cylindrical member 159 having a substantially D-shaped inner peripheral shape, which is fixed to the bottom plate of the optical frame 118 by vertically penetrating the same, and slides vertically in the cylindrical member 159. A sliding member 160 having a screw hole 160a that is movably accommodated and has a substantially D-shaped outer periphery and extends in the sliding direction;
a feed screw 161, which is screwed into
And a stepping motor 162 that rotates the sliding member 160 up and down by rotating the sliding member 160 up and down at a fixed position. The stepping motor 162 includes a motor shaft 162
Is inserted into the cylindrical member 159 and is fixed to the lower surface side of the bottom plate of the optical frame 118, and the lower end of the feed screw 161 is press-fitted and fixed to the tip (upper end) of the motor shaft 162.

That is, the vertical movement mechanism 158 drives the stepping motor 162 to rotate the feed screw 161 together with the motor shaft 162, whereby the cylindrical member 15 is rotated.
The sliding member 160 whose rotation is restricted by fitting with the sliding member 9 is moved up and down.
0, the rotating arm 151b is pushed up by the sliding member 160 to be rotated upward (in the direction of the arrow γ), and the sliding member 160 is moved downward by the force of the spring 157. The turning arm 151b is turned downward (in the direction of arrow β). Thereby, the light source unit 10
Numeral 0 rotates around the cylindrical portion 151a which is a light emitting portion. The tip 151e of the rotation position detecting arm 151c is bent in an L-shape, and the home position sensor 156
Are attached to the U-shaped part of the sensor support 156a fixed to the side plate of the optical frame 118, by the rotation position detecting arm 151.
light emitting element 163a for detecting the tip 151e of
And a light receiving element 163b. Tip portion 1 of rotation position detecting arm 151c
51e, the position at the moment when the space between the light emitting element 163a and the light receiving element 163b is blocked is the home position (H.
P. ), Which is a reference position when the rotation angle of the light source unit 100 is adjusted by the pitch variable mechanism 150.

FIGS. 2A and 2B show the pitch variable mechanism 15.
It is explanatory drawing of the pitch variable operation by 0. H. in FIG. P. Indicates the home position, and indicates the position at the moment when the tip 151e of the rotation position detecting arm 151c blocks between the light emitting element 163a and the light receiving element 163b as described above. Position B is a position rotated from the home position by an angle θ1 about the optical axis (substantially the center of the cylindrical portion 151a) as the center of rotation. Rotational position detection arm 1
In order to rotate 51c from the home position to the position B, the stepping motor 162 is rotationally driven by a predetermined pulse number Pb set in advance. Similarly, position A is a position rotated from the home position by an angle θ2 about the optical axis as the rotation center. In order to rotate the rotation position detecting arm 151c from the home position to the position A, the stepping motor 162 is rotationally driven by a predetermined pulse number Pa set in advance. FIG.
FIG. 2B shows the positions of two light spots on the photosensitive drum corresponding to the respective rotational positions in FIG. 2A. The light spots on the photosensitive drum corresponding to the rotation angles θ1 and θ2 are shown. The intervals (pitch) in the sub-scanning direction are X1 and X2.

As described above, by changing the rotation amount of the light source unit 100 from the home position, the interval X between the light spots on the photosensitive drum can be changed, and the rotation amount is changed by the home position of the stepping motor 162. Can be controlled by the number of drive pulses P from Incidentally, the pitch X when the recording density is 400 dpi is 6
Pitch X when set to 3.5 μm and 600 dpi
Is set to 42.3 μm.

Normally, when the power of the image forming apparatus is turned on, the light source unit 100 is positioned at a predetermined position, for example, 60.
The rotation is controlled to a rotation angle at a recording density of 0 dpi. At this time, after the light source unit 100 is once returned to the home position when the power is turned on, the stepping motor 162 is rotationally driven in the predetermined direction (for example, the direction of the arrow CW in FIG. 1) by the number of pulses Pa, and the light on the photosensitive drum is changed. The light source unit 100 is rotated so that the interval between the spots becomes X2. The rotation angle of the light source unit 100 is sequentially recorded in a memory inside the CPU (FIG. 6) or the like. Thereafter, when a recording density of 400 dpi is required, the stepping motor 1 is moved from the position at 600 dpi.
By rotating 62 in the opposite direction (for example, the direction of the arrow CCW in FIG. 1) by the number of pulses Pb-Pa, the interval between light spots on the photosensitive drum can be changed to X1. However, even if the stepping motor 162 is driven to rotate by the same number of pulses P, the light source unit 100
Of the light spot on the photosensitive drum X
Will change. That is, as shown in FIG. 3, the interval X between the light spots is equal to the pulse number P of the stepping motor 162.
However, the degree (gradient) of the change varies with the temperature change of the light source unit 100. FIG. 3 illustrates a case where the temperature is changed to 10 ° C., 25 ° C., and 40 ° C. Therefore, in the present invention, the light source unit 10 which causes a change in the interval X between the light spots on the photosensitive drum is generated.
A temperature detecting unit for detecting a temperature change of 0 is provided, and a pitch set value at each recording density is changed according to a detected temperature value of the light source unit 100.

FIG. 4 shows a thermistor 130 as a temperature detecting means in the collimating lens holder 110 in the configuration of FIG.
Is an example in which is embedded. FIG. 5 illustrates a case where the thermistor 130 is embedded in the collimating lens holder 3 in the configuration of FIG. The output from the thermistor 130 is sent to the CPU on the controller board of the image forming apparatus via the LD control boards 109, 4 and the like.
(FIG. 6). Although the example in which the thermistor is provided in the collimator lens holder is shown here, the thermistor may be attached to the periphery of the light source unit or to another member in the light source unit. FIG.
FIG. 2 is a schematic block diagram showing a configuration of a control system in the present embodiment. As shown, the thermistor 130 is connected to a power supply together with a resistor 131,
The output at the midpoint of connection between 0 and the resistor 131 is the AD converter 1
The data is input to the CPU 133 via the CPU 32. The output at the connection midpoint is the collimating lens holder 11
This is a temperature detection value of 0. The CPU 133 stores in the internal memory a correction coefficient determined in advance according to the detected temperature value. When the detected temperature value is input, the CPU 133 reads out the correction coefficient corresponding to the value from the internal memory, and reads the correction coefficient. Is used to calculate the amount of rotation (the number of steps P) of the stepping motor 162 suitable for the recording density specified by the recording density specifying unit 135 at that time. Then, the stepping motor drive circuit 134 rotates the stepping motor 162 in a predetermined direction by the number of steps P obtained by the above calculation. Thereby, the interval X between the light spots by the two laser beams L1 and L2 irradiated on the photosensitive drum is changed to the collimating lens holder 1 of the light source unit 100.
It is possible to always maintain a constant according to the designated recording density without being affected by the temperature change of 10. In the above, the rotation amount (step number) of the stepping motor 162 from the home position (HP) detected by the home position sensor 156 is constantly monitored by the CPU 133. For example, when the recording density is switched, By rotating the stepping motor 162 at the number of steps calculated including the temperature correction amount, the ideal light spot interval X on the photosensitive drum is always obtained. Further, instead of obtaining the number of steps by calculation using the correction coefficient from the temperature detection value and the recording density as described above, a data table corresponding to the recording density and the temperature detection value of the light source unit 100 is provided in the CPU 133, The number of steps P may be obtained based on the value of the data table.

[0016]

As described above, according to the present invention, the following excellent effects can be exhibited. According to the first aspect of the present invention, the pitch at each recording density is determined according to the temperature detection value of the light source unit by the temperature detection unit that detects the temperature of the light source unit, which is a factor that changes the interval between the light spots on the photoconductor. Since the pitch setting value is changed by the changing means, the spot interval of the plurality of light beams irradiated onto the photoconductor is always kept constant according to the recording density without being affected by the temperature fluctuation of the light source unit. can do. Therefore, it is possible to prevent the image quality from deteriorating due to the temperature fluctuation of the light source unit, and to stably form a high-quality image. According to the second aspect of the present invention, in addition to the first aspect, correction data in which the detected temperature value and the correction coefficient are associated with each other is stored and held in a memory in advance, and the detected temperature value of the light source unit by the temperature detecting means is stored in the memory. Since the corresponding correction coefficient is read from the memory and the pitch set value by the pitch changing means at each recording density is corrected based on the value, a small amount of memory can be obtained without performing a calculation process for obtaining the correction coefficient from the detected temperature value. The amount can keep the distance between the light spots on the photoreceptor constant. Therefore, it is possible to prevent the deterioration of the image quality due to the temperature fluctuation of the light source unit at low cost.

According to the third aspect of the present invention, there is provided the second aspect.
In addition, correction data in which the recording density and the correction coefficient are made to correspond to each other is stored and held in a memory in advance, and the correction coefficient corresponding to the recording density specified by the recording density specifying means is read out from the memory, and based on the value, Thus, the pitch set value by the pitch changing means at each recording density is corrected, so that the distance between the light spots on the photosensitive member can be more accurately kept constant. In the invention according to claim 4,
In addition to claim 1, correction data (data table) in which a temperature detection value and a correction coefficient are made to correspond to each recording density is stored and held in a memory in advance, and the correction data corresponds to a temperature detection value of a light source unit by a temperature detection unit. The correction coefficient to be read is read from the memory for each recording density, and the pitch set value by the pitch changing means is corrected based on the value. Therefore, it is necessary to perform an arithmetic process for obtaining the correction coefficient from the temperature detection value for each recording density. Thus, the distance between the light spots on the photoconductor can be accurately kept constant. In addition, in the invention described in claim 5, in addition to claims 1 to 4, a temperature detecting member such as a thermistor is provided on the holding member of the collimating lens to detect a change in the position of the collimating lens which most contributes to the change in the interval between the light spots. Since the interval between the light spots is corrected according to the detected value, the interval between the light spots can be kept constant with high accuracy.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a configuration example of a light source unit of a multi-beam writing device mounted on an image forming apparatus according to the present invention.

FIGS. 2A and 2B are explanatory diagrams of a pitch changing operation by a pitch changing mechanism shown in FIG.

FIG. 3 is a graph showing how a degree (gradient) of a change in an interval between light spots on a photosensitive drum according to the number of drive pulses of a stepping motor from a home position of a light source unit (gradient) fluctuates due to a temperature change of the light source unit. is there.

FIG. 4 is an exploded perspective view illustrating a case where a thermistor is embedded as a temperature detecting means in the collimating lens holder in the configuration of FIG. 1;

FIG. 5 is a cross-sectional view illustrating a case where a thermistor is embedded as a temperature detecting means in the collimating lens holder in the configuration of FIG. 8;

FIG. 6 is a schematic block diagram of a control system showing an example of an embodiment of the image forming apparatus according to the present invention.

FIG. 7 is a perspective view illustrating a configuration example of a multi-beam writing device mounted on a conventional image forming apparatus.

8 is a cross-sectional view showing a configuration of a light source unit shown in FIG.

[Explanation of symbols]

L1: laser beam, L2: laser beam, 100: light source unit, 101: semiconductor laser (laser light source), 102:
Semiconductor laser (laser light source), 111: collimating lens, 112: collimating lens, 105: aperture plate, 10
6: Beam combining prism (beam combining means), 109:
LD control board, 118: optical frame, 130: thermistor (temperature detecting means), 133: CPU (pitch changing means, pitch correcting means), 134: stepping motor drive circuit, 135: recording density specifying section (recording density specifying means) , 150: variable pitch mechanism, 151: rotating member, 1
51a: cylindrical portion, 151b: rotating arm, 151c: rotating position detecting arm, 155: rotating mechanism, 156: home position sensor, 158: vertical movement mechanism, 162: stepping motor, 163: shielded optical sensor, 163
a: Light emitting element, 163b: Light receiving element.

Claims (5)

[Claims] 1. A laser apparatus comprising: a plurality of laser light sources; a collimating lens that converts light beams from the laser light sources into substantially parallel light beams; and a beam combining unit that emits these light beams close to each other or overlaps each other. A light source unit configured, and by simultaneously scanning in the main scanning direction while converging a plurality of light beams emitted from the light source unit on the photoconductor as a plurality of light spots separated in the sub-scanning direction, In an image forming apparatus that forms an image on a photoconductor, a recording density specifying unit that specifies a recording density of an image on the photoconductor, and a pitch in a sub-scanning direction of the light spot on the photoconductor, the recording density Pitch changing means for changing according to the recording density specified by the specifying means; temperature detecting means for detecting the temperature of the light source section; An image forming apparatus characterized in that the pitch setting value corresponding to the density, with a, a pitch correction means for correcting in accordance with the temperature value detected by said temperature detecting means. 2. A memory for storing correction data in which a detected temperature value and a correction coefficient are associated with each other, wherein the pitch correction means reads a correction coefficient corresponding to the detected temperature value from the memory, and The image forming apparatus according to claim 1, wherein the pitch setting value is corrected by a correction. 3. The memory stores and holds correction data corresponding to a recording density and a correction coefficient. The pitch correction unit reads a correction coefficient corresponding to the recording density from the memory, and The image forming apparatus according to claim 2, wherein the pitch setting value is corrected. 4. The memory stores and holds correction data in which a detected temperature value and a correction coefficient are associated with each other for each recording density, and the pitch correction means stores the detected temperature value from the memory for each recording density. 2. The image forming apparatus according to claim 1, wherein a correction coefficient corresponding to the pitch is read, and the pitch set value is corrected based on the correction coefficient. 5. The apparatus according to claim 1, wherein said temperature detecting means is provided on a collimating lens holding member of said light source unit.
5. The image forming apparatus according to any one of claims 1 to 4,