JPS63158579A - Laser beam printer - Google Patents

Abstract

PURPOSE:To compensate a variation error of a printing magnification generated by variation of a galvanomirror with simple constitution, by providing a reference frequency generating means of a copy machine driving motor for synchronizing the revolving speed of the copy machine driving motor with a resonance frequency of the galvanomirror. CONSTITUTION:A home pulse 12 for showing a fact that light has passed through a home sensor is inputted to a reference time pulse generating circuit 18, and a reference time pulse 14 is generated. This reference time pulse 14 and an end pulse 13 for showing a fact that light has passed through an end sensor are compared by a phase comparing part 19a, and when the reference time pulse 14 has risen earlier than the end pulse 13, an output voltage 15 of the phase comparing part 19a outputs a high voltage, and in case of the contrary, a low voltage is outputted. A speed control system is formed so that the resonance frequency of the galvanomirror obtained in such a way coincides with a speed signal 21 generated by frequency-dividing or multiplying by a reference frequency generating part 66. In such a way, a variation error of a printing longitudinal magnification generated by variation of a galvanomirror resonance frequency can be compensated with simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a galvano-mirror one-type laser beam printer that deflects and scans a light beam at the resonant frequency of a torsion bar having a natural frequency.

Using the signal obtained by dividing or multiplying the resonant frequency of the galvanometer mirror as a reference frequency, the number of rotations of the copy machine drive motor is controlled, and the pulse signal that detects the number of rotations of the copy machine drive motor is used as an electronic servo. The present invention relates to a laser beam printer that compensates for fluctuation errors in copy machine printing vertical magnification caused by fluctuations in the galvanometer mirror resonance frequency by feeding back into a loop and locking the copy machine drive motor reference frequency.

[Conventional technology]

Conventionally, this type of device is a combination of dot recording technology using laser beam scanning and electrophotography technology, and the laser light generated from the laser is turned on and off according to image information using an optical modulator, and is turned on and off using an optical deflector. This device scans a photosensitive drum to form a latent image, obtains a visible image through toner development, transfers it to paper, and then performs a fixing process to obtain a record.

A polygon mirror, in which a prismatic or pyramidal polygon mirror is rotated at high speed by a motor, has generally been used as the optical deflector.

The manufacturing cost of this polygon mirror is high, and even at a relatively low price, there are 6 to 8 surfaces, each of which is precisely polished to an optical level. Therefore, ultra-precision processing technology is required, and in addition, an optical system that corrects the tilt angle error requires a linear lens, and in order to keep the beam speed in the horizontal scanning direction constant and to form an image from a spherical imaging system on a flat surface. Optical systems such as f/θ lenses are incorporated from time to time to correct this.

Incidentally, since uneven rotation of the high-speed motor described above causes image unevenness, the bearing should not have a short lifespan (air bearings, etc.).

Furthermore, the drive source for the polygon mirror that scans in the horizontal direction is a frequency generator (hereinafter referred to as X'tal) that uses an optical encoder or magnetic encoder to convert the reference signal, which is the clock of a crystal oscillator (hereinafter abbreviated as X'tal), and the rotational speed of the motor. , F.G.
A frequency feedback circuit type phase-locked loop (hereinafter abbreviated as PLL) that compares the detected pulse signal with the pulse signal detected in The motor drive source of a copy machine that scans in the vertical direction is also X't as described above.
This is a constant speed paper transport mechanism using a PLL comprised of Al, and synchronizes the paper transport system such as paper feeding, paper ejection, and fixing with the surface speed of the photosensitive drum.

The speed is set via a transmission mechanism such as a gear or a timing belt to equalize the length of one dot in the horizontal direction and the length of paper feed in the longitudinal direction in one scan.

The horizontal scanning, vertical scanning, and data clocks having frequencies corresponding to the horizontal scanning speed are each operated at a reference frequency consisting of independent X'tal, but the accuracy of the X'tal depends on the system. The accuracy needed to be two or more orders of magnitude higher than the accuracy that would be problematic as an error.

Another type of optical deflection scanner is a single-sided galvano mirror. In this one-type galvano mirror, a torsion bar made of a metal with an elastic modulus is equipped with a portrait mirror, and the temperature dependence of the metal has a large effect on its natural frequency, so the scanning speed can be kept constant. Correct the speed, and
Some kind of device was required to synchronize the vertical scanning speed of the photoreceptor, etc.

[Problem that the invention seeks to solve]

Problems have been pointed out from various sources in the polygon mirror type laser beam printer as described above, such as not only the device configuration being large and complicated, but also the manufacturing cost being high.

The present invention was devised in view of the above-mentioned problems, and instead of the polygon mirror type optical system of the optical beam deflector described above, a galvano mirror type having the natural frequency of a torsion bar is adopted. This is what I did.

That is, the laser beam printer of the present invention is configured with a mirror sensor that detects the vibration phase of a galvano mirror that polarizes and scans a light beam at a frequency that resonates with the natural frequency of the torsion bar, and the output waveform of the mirror sensor is A band-pass filter (hereinafter abbreviated as BPF) removes out-of-band signals, and a comparator compares and processes the signal.The control signal is used to switch the galvanomirror drive circuit only during the energization phase and energization time. - constitutes a resonant frequency drive means having a frequency of vibration of the galvano mirror, and constitutes a reference frequency generating means for rotationally driving the copy machine having the photosensitive drum by dividing or multiplying the resonant frequency of the galvano mirror; It is an object of the present invention to provide a laser beam printer that compensates for fluctuation errors in printing vertical magnification caused by frequency fluctuations.

[Means for solving problems]

In order to achieve the above object, the laser beam printer of the present invention includes a light beam generating means, a light beam modulating means for on-off modulating image information, and a light beam deflecting and scanning means using a galvanometer mirror that vibrates back and forth at a resonant frequency. and a copy machine having a photosensitive drum that is exposed by scanning with the light beam, the copy machine comprising: a copy machine having a photosensitive drum exposed by scanning the light beam, the number of rotations of the copy machine drive motor being synchronized with the resonant frequency of the galvanometer mirror that vibrates back and forth. This constitutes a reference frequency generating means for the drive motor.

[Effect]

In the laser beam printer of the present invention configured as described above, the frequency obtained by synchronizing the resonant frequency of the galvano mirror using the torsion bar is used as the reference frequency of the copy machine drive motor, and Compensate for fluctuation errors in print magnification that occur.

〔Example〕

Hereinafter, a preferred embodiment of the present invention will be described in detail based on the drawings, but the present invention is not limited to the following example unless it exceeds the gist of the invention. Figure 1 shows the laser beam of the present invention. FIG. 1 is a perspective view of an example of the configuration of a Φ printer. In the diagram, 1 is a laser element, and in this example a semiconductor laser is used, and the wavelength of this laser and the wavelength sensitivity characteristics of the photosensitive drum, which will be described later, are 780.
Matching is achieved at around 1m.

Reference numeral 2 denotes a converging optical system, which is composed of lenses, prisms, apertures, etc. The converging optical system 2 focuses the light beam generated from the semiconductor laser element 1 onto the photosensitive drum, increasing the energy density to achieve high speed. On/off control can be easily performed.

Reference numeral 3 denotes an optical deflector, which in this embodiment is a single-sided galvano mirror. The laser beam, which has been focused very narrowly by the converging optical system 2 and has a high energy density, is incident on a mirror 30 whose surface is made of a magnetic material and coated with a high reflectance thin film and is reflected.

The mirror 60 is provided at the center of a torsion bar 61 made of a highly elastic metal material, and a fixed yoke 66 having drive coils 62 on both sides is placed near the torsion bar 61, and its magnetic attraction force causes the mirror 60 to move. The torsion bar 6
Coupled with the elastic torsional vibration of 1, the mechanism resonates at the natural frequency.

A torsion bar 6 in which the mirror 60 is arranged in the center.
1 and the fixed yoke 66 are arranged at right angles to each other on the support frame 64, and their torsion bars 61 are at right angles to the lateral scanning plane.

65 is a mirror sensor that detects the vibration phase of the mirror 60.

Reference numeral 4 denotes an f.theta. lens, which is an optical system lens that keeps constant the beam velocity in the horizontal scanning direction of the light beam reflected by the mirror 60 and converts the spherical imaging system into a planar imaging system. Furthermore, f
A lens (focal lens) or only a θ lens may be used.
Further, uniform velocity can be obtained by appropriately selecting the amplitude of the light beam, so correction may not be necessary.

Reference numeral 5 denotes a mirror for changing the optical path, which is installed as needed.

6 is a copy machine (hereinafter sometimes abbreviated as RPC), which has a photosensitive drum 6 uniformly charged by corona discharge.
A latent image is formed by turning on and off the laser beam according to the information, a visible image is obtained by toner development, and after being transferred to the printing paper 61, a fixing roller 66 having a fixing heater 62 and an idle roller 64 are activated. This is a device that fixes and records images.

A home sensor S-1 and an end sensor S-2 for detecting the light beam are arranged on both sides at centrally symmetrical positions of the light beam which draws a sinusoidal locus by main scanning on the photosensitive drum 60.

FIG. 2 is a block diagram showing the electrical system of FIG. 1. In FIG. 2, a mirror sensor 65 in this embodiment emits light from an LED lamp 65b, which is an optical semiconductor element, and the light beam is reflected by the mirror 60 and received by a phototransistor 55a to detect the vibration phase. The phase of the output waveform of the mirror sensor 65 is determined by the torsion bar 61 in the phase circuit section 16 consisting of a BPF and a phase circuit 16a1 and a comparator 16b.
The galvanomirror drive unit 17 is tuned so that it resonates.
is switched by an electronic switch 68 to send a current to the drive coil 32, and the magnetic field created by the drive coil 62 is applied to the mirror 6.
Drive 0.

Note that this reflective detector can be used with light emitting diodes, photodiodes, and CDs as long as the mirror position can be detected.
Further, any non-contact detection means such as an element capable of magnetically detecting the position may be used without hindering the spirit of the present invention.

65 is a copy machine drive motor. This motor 65
is driven to rotate at the reference frequency generated by the reference frequency generator 66. The reference frequency generator 66 generates the galvano mirror 6.
The frequency obtained by dividing or multiplying the resonant frequency and synchronizing with the resonant frequency is used as the speed signal. This resonance frequency can be obtained by using the number or frequency of periodic pulses such as the home pulse, end pulse, mirror pulse, etc. detected by the sensor.

Here, an example of the galvanometer mirror resonance frequency generating means and the copy machine drive motor reference frequency generating means will be described with reference to FIG.

The resonance frequency generating means inputs a home pulse 12 indicating that light has crossed the home sensor S-1 to a reference time pulse generation circuit 18 set by X'tal, and generates a reference time 20 by the reference time pulse generation circuit 18. A reference time pulse 14 is created that rises after the elapse of time. The reference time pulse 14 and the end pulse 16 indicating that the light has crossed the end sensor S-2 are compared by the phase comparator 19a. Reference time pulse 1
4 rises earlier than the end pulse 13, that is, when the optical scanning speed is slower than the reference, the phase comparator 19a
The output voltage 15 of outputs a high voltage 15-1, and in the opposite case outputs a low voltage 15-2.

When there is no difference in rise time between the reference time pulse 14 and the end pulse 16, the output of the phase comparator 19H has high impedance. The output of the phase comparator 19a is an LPF.
is sent to the carbanomirror drive unit 17 via the buffer amplifier 19b and the electronic switch 68, and is sent to the drive coil 6.
The maximum deflection angle θm is adjusted by changing the current flowing to the end sensor S-1, and after the light crosses the home sensor S-1, the end sensor S-
Control is performed so that the time T required for the light to reach 2 is always constant. That is, when the output voltage 15 is high, a large amount of current flows through the drive coil 62, the maximum angle of view θm increases, the optical scanning speed is increased, and the time T is shortened to approach the value of the reference time 20. When the output voltage 15 is low, contrary to the above, the time T is increased to approach the value of the reference time 20. With these circuit configurations, the home sensor S-
1. Since fluctuations in the transit time of the light beam between the end station and the end station S-2 are compensated for, the main scanning time is always a stable resonance frequency generating means.

An encoder 67 detects the number of rotations of the copy machine drive motor 65 using a speed signal 21 generated by frequency-dividing or multiplying a detection pulse of the sensor, such as a home pulse, an end pulse, or a mirror pulse, by a reference frequency generator 66. input the output 22 to the phase detector 68a of the PLL,
The phase difference with the speed signal 21 is detected, and this is passed through the LPF6.
Output 26 with noise and high frequency components removed through 8b
A speed control system is formed so that the rotation of the motor 65 matches the speed signal 21 synchronized with the resonance frequency through the power amplifying section 69.

The rotational output of the copy machine drive motor 65 is transmitted to a constant speed paper transport mechanism 70 using gears, timing belts, etc., and transports the paper 61 in synchronization with the surface speed of the photosensitive drum 600.

The copy machine drive motor reference frequency generating means according to the present invention is constructed as described above.

〔Effect of the invention〕

As described above, the present invention provides a resonant frequency generating means for a galvanometer mirror using a torsion bar that is temperature dependent, and a reference frequency generating means for a copy machine drive motor that is synchronized with the resonant frequency obtained by the resonant frequency generating means. The frequency obtained by synchronizing with the temperature-dependent galvanomirror resonance frequency of the torsion bar is used as the copy machine drive motor reference frequency, and the variation of the galvanomirror resonance frequency is This is a device that compensates for fluctuation errors in printing magnification caused by
There is no need for large, complicated, and expensive equipment like the one-sided polygon mirror system, which was a problem with the conventional technology, and there is no need to use the highly accurate and expensive X'ta1. The drive motor reference frequency generating means has the advantage that it can be applied to optical systems other than those mentioned above and to other devices.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the configuration of the laser beam printer of the present invention, FIG. 2 is a block diagram showing the electrical system of FIG. 1, and FIG. 3 is a time chart for explaining the resonance frequency generating means. 1...Laser element, 2...Converging optical system, 6...Galvano mirror 1 4...F/θ lens, 5... Optical path changing mirror, 6...Copy machine, 30...Mirror, 61...Torsion bar, 65...Mirror sensor, 60...Photosensitive Drum, 66... Reference frequency generator, S-1... Home sensor, S-2... Work/do sensor.

Claims (4)

[Claims] (1) A copy comprising a light beam generating means, the light beam modulating means for turning on and off image information, the light beam deflection and scanning means using a mirror that vibrates back and forth at a resonant frequency, and a photosensitive drum exposed by the scanning of the light beam. A laser beam printer comprising: a reference frequency generating means for a copy machine drive motor which synchronizes the number of revolutions of the drive motor of the copy machine with a resonant frequency of the reciprocating mirror; . (2) The laser beam printer according to claim 1, wherein the light beam generating means is a semiconductor laser. (3) The laser beam printer according to claim 1 or 2, wherein the mirror that vibrates back and forth is a galvano mirror mounted on a torsion bar having a unique elastic coefficient. (4) A copy machine is comprised of a motor that rotates a printing paper conveyance system such as a photosensitive drum, a fixing device, and a series of paper feed and ejection at a constant speed using a reference frequency. The laser beam printer according to any one of Item 3.