JPS63101813A - Laser beam printer - Google Patents

Abstract

PURPOSE:To bring a polarization beam splitter to a rotation control with high accuracy by feeding back a monitor output of an optical sensor to a rotation driving part of the polarization beam splitter, and controlling a rotational angle of this splitter. CONSTITUTION:As for a part of a laser beam which has passed through a polarization beam splitter 3 in the direction being parallel to the paper surface, by following up a light emission of a laser diode 1, an optical power is monitored by a laser power range adjusting optical sensor 15. A monitor output is brought to waveform shaping through a photoelectric converting circuit 24, and thereafter, inputted to one terminal of a comparison amplifier 25. To the other terminal of the amplifier 25, a setting signal of a density dial 26 is inputted in advance, and a signal of a difference of both input signals and applied to a motor driving circuit 27. Therefore, a servo-motor 14 rotates the splitter 3 until an output of the amplifier 25 becomes zero, and an optical power range which has coincided exactly with a set quantity of the dial 26 can be adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser beam printer, and more particularly to a laser beam printer that adjusts the optical power range on an image forming surface by rotating a polarizing beam splitter around an optical axis. .

In a laser beam printer, it is necessary to have a function to switch the optical power range on the image forming surface in order to respond to loft-to-loft variations in sensitivity of the sensitive material and to user needs. In this case, it is possible to change the optical power range on the imaging surface by changing the input to the drive circuit of the light source (laser diode), but this would complicate the video signal generation circuit, which is the input circuit of the drive circuit. There's a problem. Therefore, conventionally, a polarizing beam splitter is provided in the optical path leading to the image forming surface, and by rotating the polarizing beam splitter around the optical axis, the optical power range can be switched without changing the light source power.

FIG. 5 shows the principle of optical power range switching using a polarizing beam splitter. In FIG. 5, 61 is a laser diode as an example of a laser light source, and 62 is a polarizing beam splitter. The light emitted from the laser diode 61 is linearly polarized (
The polarization direction is indicated by 3). The polarizing beam splinter 62 transmits the P component (light whose electric field oscillates in a plane perpendicular to the reflecting surface; indicated by 4 in the figure) of the incident light, and transmits the S component (light whose electric field oscillates in a plane parallel to the reflecting surface). Vibrating light (indicated by 5 in the figure) has the property of being reflected, so the polarizing beam splitter 62 is used to maximize the amount of laser light transmitted.
When the beam splitter 2 is rotated around the optical axis from the state in which the
changes periodically with the rotation angle. At this time, the amplitude of the light transmitted through the polarizing beam splitter 62 is CO8, where θ is the rotation angle from the reference position of the polarizing beam splitter.
It is expressed as θ. Also, the intensity of the transmitted light at this time is cos
Similarly, the light intensity of the S component reflected by the polarizing beam splitter 62 is proportional to SIN θ.

Figure 6 is a graph showing changes in the light intensity of the P component and S component with respect to the rotation angle θ. In Figure 6, the solid line is the P component and the broken line is the S component.
Shows the light intensity of the components.

FIG. 7 shows a conventional device for switching the range of optical power using the polarized beam tin lifter 2. As shown in FIG.

The polarizing beam splitter 62 is embedded in the center of a rotatable disk-shaped base 81. A hole 82 is formed on the base 81 to indicate the reference position of the polarizing beam splinter 62 (generally the position of θ=0 in FIG. 6). This hole 82 is detected by the optical sensor 83 when the polarizing beam splitter 62 is at the reference position, and an enable signal is applied to the motor drive circuit 85 through the CPU 84. This signal enables the motor drive circuit 85. A stepping motor 86 is connected to the output side of the motor drive circuit 85, and a density dial 87 is connected to the input side. A driving gear 88 provided on the output shaft of the stepping motor 86 meshes with a sprocket 89 formed on the circumferential surface of the disc-shaped base 81, and rotates the polarizing beam splinter 62 around the optical axis to rotate the polarizing beam splinter 62 around the optical axis. Light power can be changed. In this case, the stepping motor 86
The lens used here changes the optical power on the imaging surface from the maximum value to the minimum value by rotating discretely in 8 to 16 steps. On the other hand, density dial 87
outputs digital signals corresponding to the 8 steps to 16 steps described above. When considering user operations, it is desirable that the image density change at the same rate when operating the density dial from 1 to 2 and from 2 to 3. The signal and the rotation angle of the stepping motor 86 are set to have a predetermined relationship of cos'' θ.

Figure 8 shows a flowchart of a conventional laser beam printer.When the printer's power is turned on, it executes a self-diagnosis (Sl).In the self-diagnosis, the machine itself checks the operation and status of each part of the printer. The polarizing beam splitter also performs a rotation operation to set the initial position. When the self-diagnosis is completed, the printer is ready to print, and the user can set the image density using the density dial on the operation panel (S2), prepare the photosensitive material, prepare the video input from the host computer, etc. After completion, when the user presses the print button (S3),
As the various parts necessary for image formation begin, after a certain period of time, an enable signal is issued from the CPU, the polarizing beam splitter rotates based on the setting value of the density dial (S4), and then exposure is performed ( S5), scanning is performed with a predetermined optical power, the photosensitive material is discharged, and the photosensitive material is stored in the magazine (S6), and one cycle is completed.

1. By the way, the conventional laser beam printer described above has a configuration in which the stepping motor is simply rotated a predetermined number of steps from the reference position based on the setting value of the density dial, that is, a so-called open loop configuration. Therefore, it is difficult to finely control the image density, and there is a problem that it cannot be applied when the sensitivity of the photosensitive material used is extremely high.In other words, if the sensitivity of the photosensitive material is high, the laser beam printer cannot be If uncontrolled, differences in image density will occur between lofts, resulting in poor image reproducibility, but conventional printers are unable to deal with this problem.

In addition, in color printers that rotate the polarizing beam splitter installed in each optical path in order to correct the color balance of each wavelength, if the rotation is done in an open loop configuration, delicate color balance correction is required. There is also the problem that it is not possible.

SUMMARY OF THE INVENTION In view of these problems, it is an object of the present invention to provide a laser beam printer that can control the rotation of a polarizing beam splitter with high precision.

In order to achieve the above-mentioned object of solving the problem of voice, the present invention provides a laser beam printer in which the optical power range on the image forming surface is adjusted by rotating a polarizing beam splinter disposed in the optical path around the optical axis. The laser beam reflected by the polarizing beam splitter is monitored by an optical sensor that rotates integrally with the polarizing beam splitter, and the output of this monitor is fed back to the rotation drive section of the splitter to control the rotation angle of the polarizing beam splitter. It is characterized by

Since the optical sensor rotates together with the polarizing beam splitter, the laser beam power reflected from the polarizing beam splitter can be constantly monitored. The monitored results are then fed back to the rotation drive section of the polarizing beam splitter through the optical sensor, thereby realizing highly accurate control of the rotation angle of the polarizing beam splitter.

FIG. 1 shows an embodiment of the laser beam printer of the present invention. Reference numeral 1 denotes a laser diode, and the amount of light emitted is modulated by a video signal applied from a video signal source not shown. 2 is a collimator lens that converts the laser beam emitted from the laser diode into parallel light; 3 is a polarizing beam splinter for changing the power range of the laser beam on the imaging surface; 4 is a reflecting mirror; 5 is a polygon mirror; By rotating the laser beam on the imaging plane
Scan in the direction. 6 is an F/θ lens, 7 is a reflecting mirror, and the laser beam reflected by the mirror is irradiated onto a photosensitive material 9 between two small diameter rollers 8.8. Sensitive material 9
is conveyed in the direction a between the small diameter roller 8.8 and the large diameter roller 10. The laser beam is scanned in the A direction on the photosensitive material, and the photosensitive material itself is transported in the a direction, so that an image corresponding to the light modulation of the laser diode is formed on the photosensitive material.

Reference numeral 11a denotes a mirror provided on the optical path corresponding to the starting end side of the image forming surface, and a part of the laser beam reflected by this mirror passes through lens llb and is sent to an optical sensor (SOS sensor) 12 for controlling image start timing. This detection signal is used to control the image start timing on the image forming surface based on this detection signal.

The polarizing beam splitter 3 is embedded in the center of a disc-shaped base 13, which has a sprocket 13a carved in one quarter of its circumference. A notch groove 13b is provided in a part of the base 13 from which reflected light is emitted from the polarizing beam splitter 3.
is formed.

An optical sensor 15 for laser power range adjustment is attached to the cutout groove 13b with an adhesive in such a manner that it can receive the reflected light from the polarizing beam splitter 3. The laser power range adjusting optical sensor 15 is connected to a control circuit to be described later by a flexible cable 16. The sprocket 13a formed on the circumferential surface of the base is meshed with a drive gear 14a of a servo motor 14, and rotation of the servo motor 14 moves the polarizing beam splinter 3 and the optical sensor 15 for adjusting the laser power range 9 around the optical axis.
The optical power range on the image forming surface can be changed by rotating within a range of 0@. The amount of rotation of the polarizing beam splitter 3 around the optical axis, in other words, the laser beam power reflected by the polarizing beam splitter 3 is constantly monitored by the optical sensor 15 for adjusting the laser power range, and the rotation amount is as shown in FIG. It is input to the control circuit. In Fig. 2, 21 is a video signal source;
2 is a laser diode drive circuit, L from CPU23.
After the D ON signal is applied, the video signal emitted from the video signal source 21 causes the laser diode l to emit light. The video signal is kept at a partial level when adjusting the optical power range. In this embodiment, this partial level is set to the signal level required for the laser diode to output half the maximum power. There is. A part of the laser beam that passes through the polarizing beam splitter 3 in a direction parallel to the plane of the paper as the laser diode 1 emits light has its optical power monitored by the laser power range ffl adjustment optical sensor 15, and is converted into a waveform through the photoelectric conversion circuit 24. After being shaped, it is input to one input terminal of the comparison amplifier 25. The setting signal of the density dial 26 is input to the other input terminal of the comparator amplifier 25, and a signal representing the difference between the two human power signals is outputted and applied to the motor drive circuit 27. Therefore, the servo motor 14 rotates the polarizing beam splitter 3 until the output of the comparator amplifier 25 becomes zero.
It is possible to precisely adjust the optical power range according to the setting amount of the density dial 26. The motor drive circuit 27 is enabled to operate by an enable signal from the CPU 23, and performs the above-described adjustment control of the optical power range.

Further, the signal line indicated by a broken line in FIG. 2 is not used when adjusting the optical power range, but is used as a transmission line for an image start timing signal when forming an image.

FIG. 3 shows a flowchart for explaining a laser beam printer system including such an optical power range adjustment process. The difference from the flowchart in Figure 9 is that the test emission process for adjusting the optical power range has been increased, and the initial setting of the polarizing beam splitter (rotation to return to the reference position) is required in the self-diagnosis step. Since the other points are the same as the flowchart of FIG. 9, detailed explanation will be omitted. Note that the initial setting of the polarizing beam splitter is not required in the self-diagnosis step because the laser beam power reflected from the polarizing beam splitter is monitored by a laser power range adjustment sensor and fed back to the motor drive circuit via a comparator amplifier. For this reason, the polarization beam cover rotates to accurately follow the setting value of the density dial.

Figure 4 shows three laser diodes 41a and 4 with different wavelengths.
1b, 41c is shown, and 4
2a, b, c are laser diode drive circuits, 43a
, b, c are collimator lenses, 53a, b, c are bases, and on the bases 53a, b, c, polarizing beam splitters 44a, b, c and the polarizing beam splitters 44a,
Laser power range adjustment optical sensors 52a, b, and c are provided to monitor the laser beams reflected from the laser beams b and c, respectively. 45a, b, c are beam splitters, 4
6 is a cylindrical lens, 47 is a polygon mirror, 4
8 is a toroidal lens, 49 is an F/θ lens, 50 is an SOS sensor for controlling image start timing, and 51 is a sensitive material. Although not shown, each of the polarizing beam splitters 44a, b, and c is connected to a control circuit similar to that shown in FIG. 2.

In this color beam printer, the color balance is corrected by each laser diode 41a,b.

This can be done in a state where C is emitted at the same time.

In this case, since the optical power range on the imaging plane for each wavelength can be controlled with high precision by a control circuit provided for each wavelength, delicate color balance correction can be performed precisely.

Further, as explained above, according to the present invention, by providing an optical sensor for adjusting the laser power range that rotates integrally with the polarizing beam splitter, the laser beam reflected from the polarizing beam splitter can be adjusted. Since it is possible to constantly monitor the optical power, and this monitor output is fed back to the rotation drive unit of the optical beam splitter, the laser power range on the image forming surface can be adjusted with extremely high precision. There is an effect like this.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the laser beam printer of the present invention, Fig. 2 is a diagram showing a control circuit connected to the configuration of Fig. 1, and Fig. 3 explains the operation of the printer of the present invention. Flowchart, FIG. 4 is a diagram showing the configuration of a color beam printer, FIGS. 5 and 6 are diagrams explaining the operation of changing the optical power range by a polarizing beam splitter, and FIG. 7 is a diagram showing the polarizing beam in a conventional laser beam printer. FIG. 8, which shows a rotation control circuit for a splitter, is a flow chart explaining the operation of a conventional laser beam printer. 3.44a, 44b, 44c... Polarization beam splitter, 15, 52a, 52b, 52c... Optical sensor for laser power range adjustment, 27.42a, 42b, 42c
...Rotary drive unit of polarizing beam splitter. Patent applicant: Minolta Camera Co., Ltd. Fig. 3 Fig. 4 Fig. 6

Claims (1)

[Claims] (1) In a laser beam printer that adjusts the optical power range on the image forming surface by rotating a polarizing beam splitter placed in the optical path around the optical axis, the laser beam reflected by the polarizing beam splitter is What is claimed is: 1. A laser beam printer characterized in that a photo sensor that rotates integrally with the laser beam monitor monitors the printer, and controls the rotation angle of the polarizing beam splitter by feeding back the output of the monitor to a rotation driving section of the polarizing beam splitter.