JPH02150865A - Image forming device - Google Patents

Abstract

PURPOSE:To image a laser beam on a photosensitive body while holding an invariably excellent spot diameter by detecting the focus position shift of the laser beam and adjusting the laser beam automatically. CONSTITUTION:A position adjusting means controls the driving of a moving means while a position shift detecting means monitors the output of a beam position detecting means 9 and the position of a light converging means 4 is moved forward and backward in the irradiation direction of the light beam and adjusted automatically to adjust the light convergence position of the light beam to a proper position. At this time, the position of the light converging means is adjusted automatically by detecting the intensity of light outputted by the beam position detecting means 9 or a pulse signal. If the light converging means 4 shifts in position from a reference position for some reason, the position can be adjusted to the best position at all times. Consequently, the light beam equivalently for recording a high-definition image can be imaged on the photosensitive body.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus that forms an image by irradiating a light beam, and more particularly to a device that adjusts the focus of the light beam.

[Conventional technology]

In recent years, there has been a demand for improvement in the image quality of image forming apparatuses such as laser beam printers, and the precision of printed images, that is, the resolution, etc., has progressed to 240, 300, and 400 DPI. For this reason, it has become necessary to reduce the size of the pixels to be printed, and it has become necessary to reduce the spot diameter of the light beam.

FIG. 15 is a perspective view illustrating the configuration of a conventional image forming apparatus.

In this figure, 51 is an image signal (VDO) which is manually input to a laser unit 52. 53 is a laser beam ON10 FF modulated by the laser unit 52;
A motor 55 rotates the polygon mirror 56 at a constant speed. A condensing lens 59 focuses the laser beam 53 onto the photosensitive drum 58. Reference numeral 57 denotes an fθ lens that performs fθ correction so that the laser beam 54 scans the photosensitive drum 58 at a constant speed. Therefore, the laser beams 53 and 54 modulated by the image signal 51 are horizontally scanned onto the photosensitive drum 58. Reference numeral 60 denotes a photoelectric conversion element constituted by a photodiode, which serves as a beam detection means, and outputs a light beam position detection signal (beam detect signal (BD scratch signal) 61 which serves as the image writing timing. Reference numeral 62 denotes transfer paper. , corresponds to a state where an image developed by a developing device and a transfer charger (not shown) is transferred.

FIG. 16 is a timing chart illustrating the image writing timing of the image forming apparatus shown in FIG. 15.

When the light beam position detection signal (BD scratch signal 61) is detected, after a predetermined time T elapses, image recording processing according to the image signal 51 is executed line by line, and the hard disk is processed through the development, transfer, and fixing processes. Get a copy.

(Problem to be Solved by the Invention) The conventional image forming apparatus is configured as described above, and in particular, the condensing lens 59 is adjusted in advance to a position where it focuses on the photosensitive drum 58 and is fixedly arranged. However, there was an extremely serious problem in that physical distortion caused by signals applied from outside, temperature changes, etc. caused the focus to shift.As a result, even if the focus position shifted slightly, the print quality could be significantly affected. This also causes a problem in that the printing quality deteriorates and it becomes impossible to meet the demand for higher definition printing quality.

This invention was made to solve the above problems, and by detecting the focal position shift of the laser beam and automatically adjusting it, the laser beam is directed onto the photoreceptor while always maintaining a good spot diameter. An object of the present invention is to obtain an image forming apparatus capable of forming an image.

[Means to solve the problem]

The image forming apparatus according to the present invention includes: a moving means for moving the condensing means back and forth with respect to the irradiation direction of the light beam; a beam position detecting means for detecting the position of a predetermined light beam that is main-scanned on the photoreceptor; A position adjusting means is provided for automatically adjusting the position of the converging means by controlling the drive of the moving means while monitoring the output of the beam position detecting means.

Further, there is provided a transport position detection means for detecting the transport position of the recording medium in a direction perpendicular to the transport direction of the recording medium, and a detection position of the beam position detection means based on the position of the recording medium detected by the transport position detection means. A timing control means for changing the image writing timing in the main scanning direction is provided.

Further, the position adjusting means adjusts the position of the condensing means by counting pulses output from the beam position detecting means or by detecting the light intensity of the light beam.

(Function) In the present invention, the position adjusting means controls the driving of the moving means while the positional deviation detecting means monitors the output of the beam position detecting means, and adjusts the position of the condensing means with respect to the irradiation direction of the light beam. Automatically adjust by moving back and forth to adjust the focusing position of the light beam to the appropriate position. At that time, the light intensity or pulse signal output from the beam position detection means is detected,
Automatically adjust the position of the light condensing means.

Further, when the conveyance position detection means detects the conveyance position of the recording medium in a direction perpendicular to the conveyance direction of the recording medium, the timing control means detects the detection position of the beam position detection means based on the detected position of the recording medium. to control the image writing timing in the main scanning direction.

(Embodiment) FIG. 1 is a block diagram illustrating the configuration of an image forming apparatus showing an embodiment of the present invention. Reference numeral 1 denotes an image signal, which is input from an external device (not shown). 2 is a laser unit,
Modulated beam 3 modulated by 0N10FF using image signal 1
emits. Reference numeral 4 denotes a condensing lens, which is configured to be movable back and forth in the laser emission direction by an 8-movement mechanism described later, and is automatically moved to a position where the modulated beam 3 emitted from the laser unit 2 is focused on the photosensitive drum 8. (The adjustment operation will be described in detail later).

A scanner motor 5 rotates a polygon mirror 6 at a constant speed to deflect the modulated beam 3. 7 is an fθ lens that performs fθ correction so that the modulated beam 3 scans the photosensitive drum B at a constant speed. Reference numeral 9 denotes a photoelectric conversion unit constituting the beam position detection means of the present invention, which converts the modulated beam 3 that is main-scanned.
It detects the image just before printing the image, and also detects the laser light that is scanned while being forcibly turned on at the start of printing.
The detection signal (also called BD○ signal (consisting of a plurality of pulse trains)) 10 is transmitted to a printer control means 23, which will be described later.
Output to.

Note that the CPU, which will be described later, also serves as a position adjustment means, and controls the drive of the 8-movement mechanism while monitoring the output of the photoelectric conversion unit 9, and adjusts the position of the condenser lens 4 back and forth with respect to the irradiation direction of the light beam. The light beam is moved and automatically adjusted 2 to adjust the focusing position of the light beam to an appropriate position.

Reference numeral 11 denotes a transfer paper serving as a recording medium, which is conveyed in the direction of the arrow. Reference numeral 12 denotes a transfer paper position detection means, which includes, for example, four light emitting diodes (LEDs) 12a and four phototransistors 1.
2b, and detects the position of the transfer paper 11 in a direction perpendicular to the conveyance direction. Note that the transfer paper position detection means 12
A light emitting diode (LED) 12a and a phototransistor 12b are arranged facing each other, and four sets are arranged at predetermined intervals in a direction perpendicular to the conveyance direction of the transfer paper 11. The transfer paper 11 is arranged to pass between the phototransistor 12b and the phototransistor 12b. The transfer paper position detection means 12 also serves as a conveyance position detection means, and detects the conveyance position of the recording medium in a direction perpendicular to the conveyance direction of the recording medium.
(constituting a timing control means) changes the detection position of the photoelectric conversion unit 9 based on the detected position of the recording medium, controls the image writing timing in the main scanning direction, and controls the image writing timing in the main scanning direction. Adjust the recording start position (
(detailed below).

FIG. 2 is a cross-sectional view illustrating the configuration of the photoelectric conversion section 9 shown in FIG.
It is composed of S4 and a light shielding part Sd. Note that the number of slits is not limited to four, but is determined depending on the number of beam positions to be detected. 9b is a photodiode,
Slit S.

.about.S4 are detected, and BDO signals 10 are sequentially outputted from the electrical signal conversion circuit shown in FIG. 3. Note that the arrow in the figure indicates the scanning direction of the laser beam.

FIG. 3 is a circuit diagram that converts the photodiode 9b shown in FIG.
The current flowing through the photodiode 9b is detected and converted into a detection voltage V.

14 is a comparator that compares the reference potential Vs and the detection voltage V at point A detected by the current detection resistor 13, and outputs the BDO signal 10, which is a pulse signal, to boat B (point B).
Output from

FIG. 4 is an operation explanatory diagram for explaining the operation of FIG. 3,
During normal operation, for example, four B
Outputs DO signal 10 (pulses BDO1 to BDO4).

FIG. 5 is a block diagram illustrating the print control mechanism of the image forming apparatus according to the present invention, and the same parts as in FIG. 1 are given the same reference numerals.

In this figure, reference numeral 15 indicates transfer paper position information output from the transfer paper position detection means 12.

16 is image information, which is input manually from the host computer 18. 19 is a BD signal selection means, which outputs an appropriate D signal 21 from the BD selection signal (BSL) 17 output from the BD selection signal generation means 22 and the BDO signal 1o from the photoelectric conversion section 9 to the VDO signal generation means 2o. do. The BDD selection signal generation means 22 selects the BD number selection means 1 based on the transfer paper position information 15 output from the transfer paper position detection means 12.
A BDD selection signal (BSL) 17 is output to 9.

The VDO number generation means 20 generates the external host computer 1 in synchronization with the BDD number 21 of the BD signal selection means 19, etc.
The image information 16 manually input from 8 is outputted to the laser unit 2 as an image signal 1.

Note that 24 represents a host computer, and 27 represents a CPU.

The operation shown in FIG. 5 will be explained below.

The transfer paper 11 is normally discharged with one end in the direction orthogonal to the conveyance as a reference, and the transfer paper position detection means 1 is detected on the conveyance path.
2. The light from either of the LEDs 12a is blocked. Therefore, the conveyance position of the transfer paper 11 is detected based on the on/off state of the phototransistor 12b. The transfer sheet position information 15 obtained in this manner is transmitted to the BDD selection signal generating means 22.
Output to. The BDD selection signal generating means 22 outputs a BDD selection signal (BS) 17 for selecting the BDOD number 10 corresponding to the detected position based on the transfer paper position information 15 to the BDD number selection means 19. Then, BDD number selection means 1
9, the BDOD is selected based on the BDD selection signal (BSL) 17.
An appropriate pulse is selected from the four pulses No. 10 and outputted as BDD No. 21 to the VDOD signal generating means 20. VDO
The D number generating means 20 converts the image signal 1 based on the image information 16 output from the external host computer 18 into a BDD.
It outputs to the laser unit 2 in synchronization with No. 21. below,
This will be explained in detail with reference to FIG.

FIG. 6 is a timing chart for explaining the operation of FIG. 5.

For example, the edge of the transfer paper 11 is detected by the transfer paper position detection means 12 when the second phototransistor 12b from the outside shown in FIG. When detected, the BDD selection signal generation means 22 outputs a BDD selection signal (BSL) 17 corresponding to the second phototransistor 12b to the BDD number selection means 19.

The BDD number selection means 19 selects the BDOD from the photoelectric conversion unit 9.
Select the second signal from No. 10 and select BDD No. 21.
is output to the VDOD signal generating means 20. The VDO number generating means 20 converts the image information 16 into an image signal i (V
The electrostatic latent image is outputted to the laser unit 2 as a DOD number (also referred to as a DOD number) to form an electrostatic latent image on the photosensitive drum 8 corresponding to the transport position of the transfer paper 11.

As described above, the image writing position in the main scanning direction can be changed according to the paper transport position.

Further, the condenser lens 4 shown in FIG. 1 is configured to be movable back and forth in the irradiation direction of the laser beam 3, as shown in FIG.

FIG. 7 is a perspective view illustrating the movement mechanism of the condenser lens 4 shown in FIG. 1, and the same parts as in FIG. 1 are given the same reference numerals.

In this figure, 24 is a stepping motor, which is rotated by a predetermined number of pulses by a control means to be described later. Reference numeral 25 denotes a gear box, which is configured so that the amount of rotation of the condensing lens 4 becomes minute with respect to the rotation angle of the stepping motor 24.

Next, the focal position adjustment control operation of the condenser lens will be explained with reference to FIGS. 8(a) and 8(b).

FIGS. 8(a) and 8(b) show the photoelectric conversion section 9 shown in FIG.
2 is a diagram illustrating the output characteristics of BDOD No. 10 outputted from the BDOD. FIG. This corresponds to the case where the focal position of No. 4 is shifted.

The laser beam 3 scanned over the photoelectric converter 9 is detected by the photodiode 9b when it reaches the slit S, and the detected voltage at point A at that time (see Fig. 3) becomes the reference potential Vs, and B The output at the point becomes L level. Next, when the laser beam 3 reaches the light shielding part Sd after passing through the slit Sl, it is blocked by the light shielding part Sd, and A
The detected voltage V at the point becomes V<Vs, and the output at the point B becomes H level. Next, when reaching the slit S2 again, the detection voltage at point A detected by the photodiode 9b becomes Vs>Vs, and the output at point B becomes L. Therefore, if the focus is on, a total of four pulses (see FIG. 8 (-)) of the BDO signal 10 are output.

On the other hand, the detection voltage ■ when the focus of the laser beam 3 is shifted is as shown in FIG. 8(b). At times, it is detected by the photodiode 9b, and the detected voltage V at point A at that time becomes V>Vs, and the output at point B becomes L level. Next, after passing through the slit SI, the laser beam 3 reaches the light shielding part Sd, but since the laser beam 3 is not focused at this time, the slit S
, S2, and the laser beam 3 enters from both A and S2.
The detected voltage (■) at the point remains V>Vs, and the output at the point B still maintains the L level state. Then, when the laser beam 3 reaches the slit S2, it is detected by the photodiode 9b, and the detected voltage V at point A becomes V>Vs, and the output at point B becomes L level.

Therefore, when the defocused laser beam 3 scans the photoelectric conversion section 9, the number of BDO signals 10 output from the photoelectric conversion section 9 is one.

By counting the number of outputs of the BDO signal 10 from these focus state output characteristics, the positional shift of the condenser lens 4 can be determined.

Further, the stepping motor 24 is operated until the number of outputs of the BDO signal 10 is detected for the preset number of slits.
By performing forward/reverse point drive control (for example, the flowchart shown in FIG. 10) using the control means shown in FIG. 9, it becomes possible to automatically position the condenser lens 4 at the proper focal position.

FIG. 9 is a control block diagram illustrating the configuration of the position adjustment means according to the present invention, and the same components as in FIG. 1 are given the same reference numerals.

In this figure, a counter 26 starts counting the BDO signal 10 output from the photoelectric conversion section 9 in synchronization with a sampling start signal (SAMP) 028 from the CPU 27. A predetermined count value (“4” in this embodiment) is set in advance in the counter 26, and the BDO
An error signal (ERR) 29 is output when the count value of the signal 10 and the set value do not match. 30 is a stepping motor drive means that drives the stepping motor 24 by a predetermined number of pulses in response to a stepping motor drive signal 31 from C, P U 27. Note that 32 indicates a forward/reverse signal.

FIG. 10 is a flowchart showing an example of the first focus adjustment control procedure according to the present invention. In addition, (1) to (15
) indicates each step.

First, the CPU 27 drives the scanner motor 5 at a predetermined timing.1) When the scanner motor 5 reaches a predetermined number of times, that is, it outputs a scanner ready signal (RDY).
2) Scanner ready signal (R)
DY) is output, force the laser unit 2 to O.
(3) Next, wait for the detection timing of the BD signal 21 (4), and set the counter 26 at the detection timing.
A sampling start signal (SAMP) 2B is output to (5). Next, it is determined whether the error signal (ERR) 29 is output (ON) from the counter 26.
) If YES, turn sampling start signal 28 to 0FF.
L(7), determine whether the forward rotation flag is set (ON) 8) N If Ott, rotate the stepping motor 24 one step forward.9), determine whether the condenser lens 4 has moved by a predetermined amount of $3. 10), if NO, return to step (4); if YES, turn off the forward rotation flag.
F (11) and return to step (4).

On the other hand, if the determination in step (8) is YES, the stepping motor 24 is reversely rotated by one step (12), and it is determined whether the condenser lens 4 has emitted a predetermined amount (13).
If NO, return to step (4); if YES, turn on the forward rotation flag (14) and return to step (4).

On the other hand, if the determination in step (6) is NO, the sampling start signal 28 is turned off (15) and the process is ended.

In this manner, when the counter 26 outputs the error signal 29, the CPU 27 outputs the forward/reverse signal 32 to the stepping motor drive means 30, and at the same time outputs the stepping motor drive signal 31 for one clock. After that, return to step (4), output the sampling start signal 28 to the counter 26 at the timing when the BDO signal 10 comes in,
Monitor error signal 29. If the error signal 29 is not resolved even if the stepping motor 24 is rotated a predetermined number of revolutions, that is, the condenser lens 4 is moved by a predetermined amount,
The forward/reverse signal 32 is reversed and the same operation is repeated. When the position where the error signal 29 from the counter 26 becomes false, that is, the position where four pulses of the BDO signal 10 can be detected, is detected, it is determined that the condenser lens is in focus, and the series of control routines is exited.

By executing the control shown in steps (1) to (15) above, the laser beam 3 is applied onto the photosensitive drum 8.
can focus on.

(Second Embodiment) FIG. 11 is another circuit diagram for converting the photodiode 9b shown in FIG. 2 into an electric signal, and the same components as in FIG. 2 are given the same reference numerals. .

In this figure, OP is an operational amplifier, which constitutes a negative feedback circuit with a resistor R, and amplifies the output from the photodiode 9b. D is a diode that causes the BDO signal 10 to flow in ripples. A hold capacitor C holds the peak value based on the operation of the switch S which is turned on and off in response to the sample hold signal SH output from the CPU 27. 40 is an A/D converter which A/D converts the peak voltage charged in the hold capacitor C and outputs it to the CPU 27.

FIGS. 12(a) and 12(b) are diagrams for explaining the detection voltage characteristics of the photoelectric conversion unit 9. FIG. 12(a) corresponds to the case where the focal position of the condenser lens 4 is normal, b) is the condenser lens 4
This corresponds to the case where the focal position of the image is shifted.

As can be seen from this figure, when the focal position of the condensing lens 4 shifts, the light of the laser beam 3 is distributed over a wide range as shown in the figure (b), so that the laser beam 3 when passing through the slit is The amount of light is smaller (Vl>V2) compared to when it is in focus. Therefore, by capturing the change in the light intensity level of the laser beam 3 as a voltage signal and monitoring the voltage signal, the focal position of the condenser lens 4 can be determined by the circuit shown in FIG. 13.

FIG. 13 is a control block diagram illustrating the configuration of another position adjusting means according to the present invention, and the same components as in FIG. 1 are given the same reference numerals.

In this figure, 33 is a peak hold circuit which starts sampling the peak value of the detection voltage V of the photoelectric conversion unit 9 in synchronization with a sample hold signal 35 from the cpU 34. 36 is an A/D converter which A/D converts the peak value of the detection voltage held in the peak hold circuit 33 into a predetermined bit.
The signal is converted into D and output to the CPL 134.

Note that the CPU 34 stores digital data corresponding to the reference voltage value V1 shown in FIG. 12(a).

The operation will be described below based on the flowchart shown in FIG.

FIG. 14 is a flowchart showing an example of the second focus adjustment control procedure according to the present invention. In addition, (1) to (11
) indicates each step.

The CPU 34 drives the scanner motor 5 at a predetermined timing (1), waits for the scanner motor 5 to rotate at a constant speed (sends a ready signal (RDY)), and (2) forcibly turns on the laser unit 2 (3). ).

Next, wait for the timing when the BD signal 21 should come in (4), output (turn ON) the sample hold signal 35 to the peak hold circuit 33 at the timing when it should come in (5) send the detected voltage to the peak hold circuit 33 ■ Hold. The detection voltage V held in the peak hold circuit 33 is A/D converted by the A/D converter 36 and converted to C.
Sent to PU34.

Next, the CPU 34 reads the converted value and compares it with the memory contents (read value>memory value) (6).

Initially, the memory content is "0", so the converted value itself is stored in the memory (7). Next, the sample hold signal 35 is set to 0FFL (8), and the stepping motor 24 is set to 1.
Step forward rotation (9), return to step (4), and wait for the next BDO signal detection timing. And the next BD
Start sampling again at the O signal detection timing,
Compare the converted value and memory contents. If the current converted value is larger than the previous converted value, the memory contents are updated sequentially.

When the above operation is repeated and the converted value becomes smaller than the memory content for the first time, that is, when the hold voltage has passed the peak (if the judgment in step (6) is No), the value one step before will reach the peak. It is determined that the value is correct and the stepping motor 24 is rotated in the reverse direction by one step (10). Then, the sample and hold signal 35 is OF F L (11
), the process ends.

By controlling as described above, the laser beam 3 can be focused on the photosensitive drum 8.

Note that in the above embodiment, there is no particular limitation on the timing to execute the position adjustment control of the light condensing means, but in order to record an optimal image, it may be executed when the power is turned on, immediately before continuous printing starts, or while capturing environmental temperature fluctuations. This allows even more precise control.

(Effects of the Invention) As explained above, the present invention provides a moving means for moving a condensing means back and forth with respect to the irradiation direction of the light beam, and a beam for detecting the position of a predetermined light beam that is main-scanned on a photoreceptor. The pulse output from the beam position detecting means is provided with a position detecting means and a position adjusting means for automatically adjusting the position of the condensing means by controlling the drive of the moving means while monitoring the output of the beam position detecting means. Since the position of the focusing means is adjusted by counting or detecting the light intensity of the light beam, the focal position of the focusing means can be automatically adjusted from the output of the beam position detection means that originally detects the beam position. can.

Therefore, even if the position of the focusing means deviates from the reference position for some reason, it can always be adjusted to the optimum position, and a light beam suitable for recording a high-definition image can be focused on the photoreceptor.

Further, there is provided a transport position detection means for detecting the transport position of the recording medium in a direction perpendicular to the transport direction of the recording medium, and a detection position of the beam position detection means based on the position of the recording medium detected by the transport position detection means. Since a timing control means is provided to control the image writing timing in the main scanning direction by changing the timing, it is possible to accurately detect the transport position of the recording medium that is transported orthogonally to the light beam scanning direction, and to adjust the timing corresponding to the transport position. The main scanning start position can be determined. Therefore, an excellent effect is achieved in that an image can always be formed from the optimum position on the recording medium, regardless of the state of the conveyance position of the recording medium.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating the configuration of an image forming apparatus showing an embodiment of the present invention, FIG. 2 is a sectional view illustrating the configuration of the photoelectric conversion section shown in FIG. 1, and FIG. FIG. 2 is a circuit diagram for converting the photodiode into an electrical signal; FIG. 4 is a diagram showing the output of the electrical conversion circuit shown in FIG. 3; FIG. 5 is a print control mechanism of the image forming apparatus according to the present invention. 6 is a timing chart for explaining the operation of FIG. 5, FIG. 7 is a perspective view illustrating the heart motion mechanism of the condensing lens shown in FIG. a) and (b) are diagrams explaining the output characteristics of the BDO signal output from the beam detection means shown in FIG. 1; FIG. 9 is a control block diagram explaining the configuration of the position adjustment means according to the present invention; FIG. 10 is a flowchart showing an example of the first focus adjustment control procedure according to the present invention, FIG. 11 is another circuit diagram for converting the photodiode shown in FIG. 2 into an electric signal, and FIG. 12(a) , (b) is a diagram explaining the detection voltage characteristics of the beam detection means 9, FIG. 13 is a control block diagram explaining the configuration of another position adjustment means according to the present invention, and FIG. 14 is a second focal point according to the present invention. 15 is a perspective view illustrating the configuration of a conventional image forming apparatus; FIG. 16 is a timing chart illustrating image writing timing of the image forming apparatus shown in FIG. 15. be. In the figure, 1 is an image signal, 2 is a laser unit, 3 is a modulated beam (laser beam), 4 is a condenser lens, 5 is a scanner motor, 6 is a polygon mirror 7 is an fθ lens, 8 is a photosensitive drum, and 9 is a photoelectric The converter 10 is a BDO signal. Figure 2] Figure BDO-1111 - Figure 2 Figure (a) (b)

Claims (4)

[Claims] (1) A light beam irradiation means for irradiating a light beam modulated by an image signal from an external device, a condensing means for condensing the light beam irradiated by the light beam irradiation means, and a condensing means for condensing the light beam irradiated by the light beam irradiation means; An image forming apparatus comprising: a scanning means for horizontally scanning a photoreceptor with a light beam; a beam position detection means for detecting the position of the predetermined light beam being scanned; and a position for automatically adjusting the position of the light condensing means by controlling the drive of the moving means while monitoring the output of the beam position detection means. An image forming apparatus comprising: an adjusting means. (2) A conveying position detecting means for detecting the conveying position of the recording medium in a direction perpendicular to the conveying direction of the recording medium, and a beam position detecting means detecting the position of the recording medium detected by the conveying position detecting means. 2. The image forming apparatus according to claim 1, further comprising timing control means for changing the position and controlling the image writing timing in the main scanning direction. (3) The image forming apparatus according to claim 1, wherein the position adjustment means counts pulses output from the beam position detection means to adjust the positional deviation of the light focusing means. (4) Claim (4) characterized in that the position adjustment means detects the light intensity of the light beam and adjusts the positional shift of the condensing means (
1) The image forming apparatus described above.