JPH0216523A - Optical scanner - Google Patents

Abstract

PURPOSE:To obtain a scanning light beam which has no difference in scanning length at a constant period and at a constant speed and to improve print quality by connecting a control circuit which varies the rotating speed of a scanner motor according to the time interval measured by sensors installed at two points in the scanning track of a laser printer to a motor driving circuit. CONSTITUTION:The motor rotation control circuit 22 which measures the time interval between the sensors installed at two points in the scanning track of the laser printer with their sensor outputs and varies the rotating speed of the scanner 6 is connected to the motor drive circuit 6. The scanner motor 6 is driven by a rotating speed control circuit 7 at a constant rotating speed and controlled so that the rotating speed in one rotation is constant, but a control signal generated by the motor rotation control circuit 22 is mixed with said control signal to vary the rotating speed of each reflecting surface in one rotation of a polygon mirror 1. Consequently, a mechanical variation component due to the deviation, etc., of the polygon mirror 1 is canceled to obtain the scanning light beam which has the constant period, the constant sped, and no difference in scanning length, thereby improving the print quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical scanning device for driving a polygon mirror that scans a laser beam in a laser printer or the like.

BACKGROUND OF THE INVENTION The present applicant has proposed the structure of a laser printer shown in FIG. 5 (Japanese Patent Application No. 1517-1983). That is, a polygon mirror 1 that is continuously rotated by a scanner motor is provided, and a laser beam irradiated from a signal light source 2 is reflected from a reflecting surface 3 of the polygon mirror 1 formed of an aspherical surface and transmitted through a correction lens 4. photosensitive drum 5
The image is formed on the .

The scanner motor is controlled so that its rotational speed is always constant by comparing a reference clock such as a crystal oscillator with a signal generated by its own rotation, such as an FG pulse. That is, in general, the reference clock and FG
The motor drive voltage is changed based on the phase difference and frequency difference to keep the rotation speed constant.
It is controlled by an LL control circuit.

The control circuit will be explained based on FIG. First, the scanner motor 6 is provided so as to be driven at a constant speed by a rotational speed control circuit 7, a mixing circuit 8, and a motor drive circuit 9 sequentially forming a loop.

Thus, the rotation speed control circuit 7 is connected to an FG synchronization circuit 10 receiving FG pulses from the scanner motor 6 and an AFC
A timing frequency divider 11 and a lock range detection circuit 12 are connected in series, and the lock range detection circuit 12 includes:
D/A converter 13 for frequency and D/A for phase
A converter 14 is connected in parallel to the mixing circuit 8. A reference signal generation circuit 15 having a built-in crystal oscillator is provided, and this reference signal generation circuit 15 is connected to the FG synchronization circuit 10 with a frequency divider 16 interposed therebetween. Further, a speed motor reversal detection circuit 17 is connected to the lock range detection circuit 12, and this speed motor reversal detection circuit 17 is connected to the D/A converter 14.

Further, a folding mirror 18 is provided at a start position within the locus of the laser beam scanned by each reflecting surface 3 of the polygon mirror 1, and a start sensor 19 is provided for detecting the laser beam reflected by the folding mirror 18. ing.

In such a configuration, the scanner motor 6 driven by the motor drive circuit 9 generates FC pulses. This FG pulse is compared with the reference signal circuit 15 in the FG synchronization circuit 10, and based on the result, the scanner motor 6 is controlled so as to keep the rotational speed of the scanner motor 6 constant.

Further, the signal detected by the start sensor 19 sets the start position of the laser beam, and sets the start position of the scanning light beam that forms an image on the photosensitive drum 5.

Problems to be Solved by the Invention In order to maintain the rotation speed of the polygon mirror 1 constant,
The rotation speed can be kept constant through the drive control described above. However, in this type of laser printer, the scanning speed of the scanning beam that forms an image on the photosensitive drum 5 is constant, and the timing of generation of the scanning beam by each reflective surface 3 of the polygon mirror 1 made of a hexahedron is consistent. This is required. This also depends on the rotational state of the polygon mirror 1 during one rotation, and simply controlling the number of rotations does not improve the functionality of the laser printer.

That is, when the polygon mirror 1 is processed, if the eccentricity of the mounting hole formed at its center increases, even if the number of rotations is constant and the rotation speed is also constant,
- Periodic scanning speed errors occur with each rotation. Even if the start position of the scanning beam is fixed by the start sensor 19 as described above, the periodic error in the scanning speed that occurs every rotation changes the scanning length of the laser beam. Therefore, Figure 4 (a
), when a vertical line is drawn, it periodically changes in a meandering manner with each rotation as it approaches the end of the scanning beam, making it difficult to obtain high printing quality. Note that in FIG. 4, the scanning direction of the scanning light beam is the horizontal direction, and the numbers written at the left end indicate the order of the scanning light beams that are sequentially scanned.

In order to solve this problem, conventional methods have been to increase the processing precision and mounting precision of each component, but as a result, component costs have increased and yields have deteriorated.

Means for solving the problem A scanner motor is provided to drive a polygon mirror that scans a laser beam, and the FC pulses generated by the rotation of this scanner motor are compared with a reference clock to determine the phase and frequency deviations. In an optical scanning device, a rotation speed control circuit that generates a motor drive voltage for keeping the rotation speed of the scanner motor constant is connected to a motor drive circuit. A motor rotation control circuit was connected to the motor drive circuit for measuring the time interval between the two using sensor output and varying the rotational speed of the scanner motor according to the time interval.

The scanner motor is driven at a constant rotation speed by the operating rotation speed control circuit, and the rotation speed during one rotation is controlled to be constant. However, the control signal created by the motor rotation control circuit is mixed with the control signal. By doing this, the rotational speed of each reflecting surface during one rotation of the polygon mirror is varied, thereby canceling out mechanical fluctuation components due to eccentricity of the polygon mirror, etc. A scanning beam with no difference in scanning length can be obtained, improving print quality.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 to 4. Components that are the same as those described in FIGS. 5 and 6 are designated by the same reference numerals, and description thereof will be omitted.

First, in terms of structure, compared to the structure described with reference to FIG. 5, a folding mirror 20 is provided on the end side of the scanning beam, and an end sensor 21 is provided as a sensor that receives light reflected by the folding mirror 20.

Further, the circuit is different from the circuit shown in FIG. 6 in that a motor rotation control circuit 22 connected to the scanner motor 6 is connected to a motor drive circuit 9 via a mixing circuit 8.

The motor rotation control circuit 22 is configured as shown in FIG. That is, an exclusive OR 23 to which the start sensor 19 and the end sensor 21 as sensors are connected to the input side is connected to the first counter 24 . Terminals 22 and 21 of the first counter 24 are connected to the input side of an AND gate 25, and the output side of the AND gate 25 is connected to the clear terminal of the first counter 24. Therefore, when the count reaches 12, its contents are cleared. Further, the 2° terminal of the first counter 24 is connected to an AND gate 26 together with the system clock, and this A
ND gate 26 is connected to second counter 27 . This second counter 27 is connected to a memory 28,
This memory 28 is connected to a digital-to-analog converter 29. The second counter 27 is of a type that is cleared every time the polygon mirror 1 rotates once.

In such a configuration, the scanner motor 6 driven by the motor drive circuit 9 generates FG pulses. This FG pulse is compared with the reference signal circuit 15 in the FG synchronization circuit 10, and based on the result, the scanner motor 6 is controlled so as to keep the rotational speed of the scanner motor 6 constant.

The state of the scanning beam being scanned is detected by such control, but even if the rotation speed is constant due to the dimensional accuracy of the polygon mirror 1, and the rotation speed during one rotation is constant, the scanning beam The scanning state of is not necessarily constant as described above.

There, the scanning light beam is detected by the start sensor 19 and the end sensor 21. These outputs are ORed by exclusive OR 23 and input to first counter 24 . As described above, this counter 24 is cleared at the sixth end pulse (the 12th as a counter output). And the counter 24
The output of 2@ corresponds to the time interval from the start sensor 19 to the end sensor 21, and this is ANDed with the system clock and input to the second counter 27, and the time interval signal for each reflective surface 3 is generated. It is stored in the memory 28 as . In addition, the F/V is
A stepped disturbance signal is created according to the frequency.

This disturbance signal is applied to the motor drive circuit 9 of the PLL circuit, and is added to the control loop with a value corresponding to the scanning speed before l scanning. Therefore, the timing (phase) of adding the amplitude of this disturbance signal
can be changed, and a disturbance signal is applied to each reflecting surface 3 so as to cancel out the error in the scanning speed corresponding to each reflecting surface 3.

That is, the phase of the disturbance signal applied is shifted due to the frequency characteristics of the scanner motor 6 and the like.

In this way, a disturbance signal corresponding to the scanning speed unevenness one rotation before is applied to the rotation speed control circuit 7 (PLL control circuit), thereby reducing the scanning speed unevenness. Therefore, even if there is a partial deviation of 17 n dots in the middle of the scanning beam, overall the lengths of all the scanning beams are approximately the same, as shown in Figure 4(b). In this way, a meander-free condition can be obtained at the terminal end.

Effects of the Invention As described above, the present invention includes a scanner motor that drives a polygon mirror that scans a laser beam, and compares the FG pulse generated by the rotation of this scanner motor with a reference clock to determine the phase shift and frequency. In an optical scanning device in which a rotation speed control circuit is connected to a motor drive circuit to generate a motor drive voltage for making the rotation speed of the scanner motor constant based on the deviation of A motor rotation control circuit for measuring the time interval between the two using the installed sensor output and varying the rotation speed of the scanner motor according to the time interval is connected to the motor drive circuit, so that the rotation speed control circuit The scanner motor is driven at a constant rotation speed and the rotation speed during one rotation is controlled to be constant. However, by mixing the control signal with the control signal created by the motor rotation control circuit, the polygon mirror The rotational speed of each reflecting surface during one rotation is varied, thereby canceling out mechanical fluctuation components due to eccentricity of the polygon mirror, etc., and scanning length on the photosensitive drum surface at a constant period and at a constant speed. This has the effect that scanning light beams with no difference can be obtained and printing quality can be improved.

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a plan view showing the optical system of the polygon mirror, Fig. 3 is a circuit diagram of the motor rotation control circuit, and Fig. 4 shows the state of printed dots. In the explanatory diagrams shown, (a) is a plan view showing the conventional state, and (b)
) is a plan view showing the state of this embodiment, FIG. 5 is a plan view showing an optical system of a polygon mirror showing a conventional example, and FIG. 6 is a block diagram thereof.

l... Polygon mirror 6... Scanner motor, 7
... Rotation speed control circuit, 9... Motor drive circuit,
22...Motor rotation control circuit application Person Tokyo Electric Co., Ltd.

[Brief explanation of the drawing]

-Brother figure (Item 4 side 1)

Claims (1)

[Claims] A scanner motor that drives a polygon mirror that scans a laser beam is provided, and the FG pulse generated by the rotation of this scanner motor is compared with a reference clock, and the rotation speed of the scanner motor is determined from the phase shift and frequency shift. In an optical scanning device in which a rotation speed control circuit that generates a constant motor drive voltage is connected to the motor drive circuit, the time interval between the two points is determined by the outputs of sensors installed at two points within the scanning locus of the laser printer. An optical scanning device characterized in that a motor rotation control circuit for measuring the rotation speed of the scanner motor and varying the rotation speed of the scanner motor according to the time interval is connected to the motor drive circuit.