JPH01303085A - Rotation controlling circuit for scanner motor - Google Patents

Abstract

PURPOSE:To cancel mechanical fluctuation component due to the eccentricity or the like of a polygon mirror and enable the scanning beam of a constant period and a constant speed to be obtained, by connecting a rotational fluctuation generating circuit for fluctuating a rotational speed during one rotation of a scanner motor, to a motor driving circuit. CONSTITUTION:By a rotational frequency controlling circuit 7, the FG pulse of the output generated from a scanner motor 6 is compared with reference clock pulse, and the output of motor driving voltage for making the rotational frequency of the scanner motor 6 constant through the positional shift of phase and frequency is directed to a mixer circuit 8. In the meantime, when the input of pulse signal generated once per rotation on the scanner motor 6, to a rotational fluctuation generating circuit 18 is provided, then the pulse signal of a specified width is fed to the mixer circuit 8. The output of the mixer circuit 8 is fed to the scanner motor 6 via a motor driving circuit 9.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of Industry-42 The present invention relates to a scanner motor rotation control circuit for driving a polygon mirror that scans a laser beam in a laser printer or the like. 7. Prior Art The structure of a laser printer not shown in FIG. 6 has been proposed by Mr. Mizuide (Japanese Patent Application No. 151.7/1983). That is, a polygon mirror 1 that is continuously rotated by a scanner motor is provided, and the laser beam irradiated from the signal light source 2 is reflected from the reflective surface 3 of the polygon mirror formed of an aspherical surface and transmitted through the correction lens 4. The image is formed on the second part of the photosensitive drum 5.

The scanner motor is controlled so that the number of revolutions is always constant by comparing a reference clock such as a crystal oscillator with a signal generated by its own rotation, such as a PG pulse. That is, - inside the shell are the reference clock and F
The motor drive voltage is controlled by the pr-1, jliU control circuit to compare the G pulse and change the motor drive voltage based on the phase shift and frequency shift to keep the rotation speed constant.

In order to maintain the rotational speed of the apex polygon mirror at a constant value of 1.5 while the invention is being carried out, the rotational speed can be kept constant by 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 at which the scanning beam is generated by each reflective surface 3 of the polygon mirror 1 made of a hexahedron is fixed. A match is required. This also depends on the rotational state of the polygon mirror 1 during one rotation, and simply controlling the rotational speed cannot improve the functionality of the laser printer. .

That is, when the polygon mirror 1 is processed, if the eccentricity of the 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. This error causes a meandering line when a vertical line is written by a scanning beam that scans a photosensitive drum in a laser printer, making it impossible to obtain high print quality.

In order to solve this problem, conventional methods have been to improve the machining accuracy and mounting accuracy of each part, but as a result, the cost of the parts has increased by 20% and the yield has deteriorated. There is.

Means for solving the problem A scanner motor is provided to drive the polygon mirror that scans the laser beam, and the FG pulses generated by the rotation of the scanner are compared with the base FiQ clock to determine their phase deviation and frequency. In a scanner motor rotation control circuit, 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 the rotation speed of the scanner motor during one rotation. A rotational fluctuation generating circuit for varying the rotational speed was connected to the motor drive circuit.

The scanner motor is driven at a constant rotation speed by the operating rotation speed control circuit, and the rotation speed during rotation is also controlled to be constant, or the control signal is mixed with the control signal generated by the rotation fluctuation generation circuit. By doing this, the rotational speed of the polygon mirror during one rotation is varied, thereby canceling out mechanical fluctuation components due to eccentricity of the polygon mirror, etc., so that a scanning light beam with a constant period and constant speed can be obtained.

Embodiment A first embodiment of the present invention will be explained based on FIGS. 1 to 3. Structurally, the same as that explained with reference to FIG. 6 is used, and the explanation will be omitted. First, the scanner motor 6 is provided to form a loop with a rotational speed control circuit 7, a mixing circuit 8, and a motor drive circuit 9, and to be driven at a constant speed.

Thus, the rotation speed control circuit 7 has an FG synchronization circuit 10 that receives FG pulses from the scanner motor 6, and an AFG synchronization circuit 10 that receives FG pulses from the scanner motor 6.
A timing frequency divider]] and a lock range detection circuit]2 are connected in series, and the lock range detection circuit 12 includes:
D/A conversion converter for frequency D/A for 3 phases
A converter 14 is connected in parallel to the mixing circuit 8. A reference signal generation circuit 5 incorporating a crystal oscillator is provided, and a 20-base foil signal generation circuit 15 is connected to the FG synchronization circuit 10 with a frequency divider 16 interposed. Further, a speed motor reversal detection circuit 17 is connected to the lock range detection circuit 2, and this speed motor reversal detection circuit 7 is connected to the D/A converter 44.

A rotational fluctuation generating circuit 8 is connected between the scanner motor 6 and the mixing circuit 8. This rotational fluctuation generating circuit ] 8 is two mono-multivibrators 2 to which variable resistors respectively indicated as VRl, , VR2], , 9.20 are connected.

Variable resistor 2 consisting of 22 and marked as VR3 on the output side.
3 is connected.

In such a configuration, the scanner motor 6 driven by the motor drive circuit 9 generates FG pulses. This PG 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 to keep the rotation speed of the scanner motor 6 constant.

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

Therefore, by adjusting the variable resistors 19 and 20, the rotational variation generating circuit 18 generates a control signal to vary the rotational speed during one rotation of the polygon mirror 1, thereby canceling out variations in the scanning light beam due to mechanical errors.

That is, a signal generator (not shown) that generates one pulse per revolution is formed in the scanner motor 6 using a Hall element or the like, and the mono-multivibrator 21 is activated by the rise or fall of the signal. to generate an output with a pulse width t1, and at the rising edge of the output, the mono multivibrator 22 is activated to generate an output with a pulse width t2. Then, the variable resistor 20 is scanned and adjusted so that the relationship between t2 and the period T is t2/T-1/2. Further, the output level is adjusted by the variable resistor 23, inputted to the mixing circuit 8, and superimposed on the output from the rotation speed control circuit 7 to artificially cause fluctuations in the rotation of the scanner motor 6. This cancels out errors in the scanning speed of the scanning light beam.

Next, a second embodiment of the present invention will be described based on FIGS. 4 and 5. The tree embodiments each have an additional VR/1. , variable resistor 24.2 labeled VR5
5 are connected to the output side of the mono multivibrator 22.

Thereby, the final output is obtained as an acceleration/deceleration pulse.

Note that here, the variable resistor 24 adjusts the pulse width at t4, and the variable resistor 25 adjusts the pulse width at t5.

Effects of the Invention The present invention provides a scanner motor that drives a polygon mirror that scans a laser beam in a double series, and compares the FG pulse generated by the rotation of this scanner motor with a reference clock to determine the phase shift. In a scanner motor rotation control circuit, 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 difference between the rotation speed and the frequency,
Since a rotational fluctuation generation circuit for varying the rotational speed of the scanner motor during one rotation is connected to the motor drive circuit, the scanner motor is driven at a constant rotational speed by the rotational speed control circuit, and the rotational speed during one rotation is - However, by mixing the control signal with the control signal created by the rotation fluctuation generation circuit, the rotation speed of the polygon mirror during one rotation is varied. This has the effect that a scanning beam of constant period and constant speed can be obtained without increasing mechanical precision by canceling out mechanical fluctuation components due to eccentricity, etc.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG.
3 is a timing chart, FIG. 4 is a circuit diagram of a rotation fluctuation generating circuit showing a second embodiment of the present invention, FIG. 5 is a timing chart, and FIG. 6 is a circuit diagram of a rotation fluctuation generating circuit.
The figure is a plan view showing an optical system of a polygon mirror. ] Polygon mirror, 6 scanner motor, 7 rotation speed control circuit, ? ] Motor drive circuit, 18 Rotation fluctuation generation circuit Application Person: Tokyo Electric Co., Ltd.

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 a scanner motor rotation control circuit in which a rotation speed control circuit for generating a motor drive voltage for making the motor drive voltage constant is connected to a motor drive circuit, a rotation fluctuation generation circuit for varying the rotation speed during one rotation of the scanner motor is provided. A scanner motor rotation control circuit characterized by being connected to a motor drive circuit.