JP4346828B2 - Planar type galvanometer mirror drive circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a driving circuit for a planar galvanometer mirror used in a laser beam scanning system such as a printer.
[0002]
[Prior art]
Planar galvanometer mirrors are used in laser beam scanning systems that deflect and scan laser beams. The principle of operation is that a mirror and a coil integrated with the mirror are placed in a magnetic field, and a current flows through the coil. Thus, an electromagnetic force due to a current and a magnetic field is obtained, the mirror and a coil integrated with the mirror are rotated by the obtained electromagnetic force, and the laser beam irradiated by the rotation of the mirror is deflected and scanned. Since the mirror and the coil integrated with the mirror are fixed by the holding member, the mirror and the mirror are integrated to an angle at which the spring force of the holding member and the electromagnetic force obtained when a current is passed through the coil is balanced. The coil rotates. There is a galvanometer that uses the same principle to rotate a pointer and a coil integrated with the pointer by a current flowing in the coil, and detect the presence and the amount of current by the movement of the pointer. Planar type galvanometer mirrors using semiconductor materials have been proposed.
[0003]
The planar galvanometer mirror is desirably rotated in a reciprocating manner for its use, and an alternating current is generally applied to the coil. That is, by passing an alternating current, an electromagnetic force corresponding to the amount and direction of the alternating current is obtained, and the rotational force is changed according to the obtained electromagnetic force, that is, the amount and direction of the alternating current, and is integrated with the mirror and the mirror. Rotate the coil back and forth.
[0004]
FIG. 1 is a diagram illustrating the structure of a planar galvanometer mirror, and FIG. 2 is a timing chart of the operation of the planar galvanometer mirror.
A movable plate 2 is formed on the silicon substrate 1, a mirror 3 is formed at the center of the movable plate 2, and a coil 4 is formed at the periphery of the movable plate 2. The movable plate 2 is formed with the silicon substrate 1 being hollowed out, and is held by torsion bars 5 and 6 formed integrally with the silicon substrate 1. The coil 4 is electrically connected to the outside by providing electrode patterns on the torsion bars 5 and 6. Magnets 7 and 8 are installed outside the silicon substrate 1, and the movable plate 2 in the silicon substrate 1 is present in the magnetic field.
As shown in the timing chart of FIG. 2, when a current is passed through the coil 4, a magnetic field is generated by the coil 4. The magnetic field generated by the coil 4 and the magnetic field generated by the magnets 7 and 8 are repelled or attracted to generate electromagnetic force. The generated electromagnetic force rotates the movable plate 2 by the torsion bars 5 and 6.
When the current flowing through the coil 4 is AC, the magnetic field generated by the coil 4 is AC and the electromagnetic force is AC. Therefore, the rotation of the movable plate 2 is also a reciprocating rotation. The rotation angle is determined by the amount of current flowing through the coil 4 and the spring force of the torsion bars 5 and 6.
[0005]
Such a planar galvanometer mirror has a natural resonance frequency of rotation due to the shape and weight of the movable plate 2 and the shapes of the torsion bars 5 and 6. The planar galvanometer mirror is most efficiently operated at this natural resonance frequency, and it is easy to control the angle of rotation, so it is generally driven at the natural resonance frequency.
[0006]
[Problems to be solved by the invention]
However, since the natural resonance frequency is determined by each shape and weight, it is difficult to accurately match the target frequency in manufacturing, and the variation is large. Therefore, the driving circuit must also measure the natural resonance frequency of the planar galvanometer mirror in advance and adjust the driving circuit according to the measured frequency.
[0007]
Further, since the resonance sharpness (so-called Q) of the natural resonance frequency is high, a slight frequency shift greatly affects the rotation angle. Therefore, it is necessary to increase the frequency resolution of the drive circuit, and the circuit scale also increases.
[0008]
Furthermore, since the natural resonance frequency changes depending on the environment in which the planar galvanometer mirror is used, for example, temperature, humidity, atmospheric pressure, etc., it is impossible to vary the driving frequency in accordance with changes in the natural resonance frequency. Close to.
[0009]
The present invention solves the above-described problems, and the planar galvanometer mirror that drives the planar galvanometer mirror without adjusting the circuit, has a small circuit scale, follows the change in the natural resonance frequency, and reliably drives at the natural resonance frequency. An object is to provide a drive circuit.
[0010]
[Means for Solving the Problems]
For this reason, the present invention
A planar frequency galvanometer mirror drive circuit; a predetermined frequency generator for generating a predetermined frequency signal whose frequency is sequentially varied in the initial stage of driving the planar galvanometer mirror;
A pulse generator for generating a pulse having the predetermined frequency at the initial driving of the planar galvanometer mirror;
Based on the pulse generated from the pulse generation unit, a setting current unit that drives the driving current of the planar galvano mirror by passing a setting current; and
A back electromotive force detection unit that detects a back electromotive force generated in the drive coil after the start of energization of the drive coil;
A timing generator for generating a driving timing signal for a planar galvanometer mirror from the detected back electromotive force waveform;
A changeover switch for switching the signal output to the pulse generator from the predetermined frequency signal to the drive timing signal;
The planar galvanometer mirror is driven by a pulse generated from the pulse generator at the drive timing after the signal is switched by the changeover switch.
[0011]
In addition, a voltage controlled oscillator,
A frequency divider for frequency-dividing the oscillation frequency from the voltage-controlled oscillator;
A phase comparator that compares the phase of the drive timing signal and the oscillation frequency divided by the frequency divider and feeds back the result to the voltage controlled oscillator;
Based on the signal fed back from the phase comparator and the frequency divided in synchronization with the drive timing signal oscillated by the voltage controlled oscillator, and based on the drive timing signal, the pulse width and the planar galvanometer mirror A pulse and a pulse width setting unit that generates a pulse having a constant pulse width ratio to the natural resonance frequency of
And further comprising
The changeover switch may be configured to switch from the predetermined frequency signal to the pulse signal generated by the pulse and pulse width setting unit instead of the drive timing signal.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 3 is a block diagram showing the first embodiment of the present invention, and FIG. 4 is a time chart for explaining the operation of the first embodiment of the present invention, showing waveforms at points A to D in FIG. The planar galvanometer mirror driving circuit includes a predetermined frequency generation unit 31, a pulse generation unit 32, a current setting unit 33, a back electromotive force detection unit 34, a timing generation unit 35, and a switching SW 36. The planar galvanometer mirror 30 is connected to a current setting unit 33 and a back electromotive force detection unit 34. A detailed description of the operation will be described below together with the timing chart of FIG.
[0015]
In the initial driving stage of the planar galvanometer mirror 30, the changeover switch 36 connects the predetermined frequency generator 31 and the pulse generator 32. The predetermined frequency generator 31 generates a frequency close to the natural resonance frequency of the planar galvanometer mirror 30 to be driven. The pulse generator 32 generates a pulse having a certain pulse width based on the frequency from the predetermined frequency generator 31. In the current setting unit 33, a current that matches the target rotation angle is allowed to flow through the planar galvanometer mirror 30 only in the “H” section of the pulse generated by the pulse generation unit 32.
Here, the planar galvanometer mirror 30 rotates in accordance with the above operating principle because a current flows. However, since current flows only in the “H” section of the pulse, it moves only in one direction. After performing the unidirectional rotation, the planar galvanometer mirror 30 repeats the reciprocating rotational movement to return to the original state by the spring force of the torsion bar. This reciprocating rotational motion is determined by the shape and weight of the movable plate and the shape of the torsion bar, and the reciprocating rotational period coincides with the natural resonance frequency.
On the other hand, the reciprocating rotational motion causes the coil provided in the planar galvanometer mirror 30 to reciprocate in the magnetic field of the magnet, so that a counter electromotive force is generated in the coil. Since this counter electromotive force is generated by reciprocating rotational motion, the period of the counter electromotive force coincides with the natural resonance frequency.
Therefore, here, the planar galvanometer mirror 30 observes a waveform in which the pulse generated by the pulse generator 32 and the waveform of the back electromotive force are mixed. This waveform is detected by the back electromotive force detector 34 and input to the timing generator 35. The timing generator 35 generates a timing pulse that matches the natural resonance frequency from the waveform. That is, since the planar galvanometer mirror 30 is driven by pulses, the first half of the waveform is a pulse waveform, the second half is a counter electromotive force, and the period of the natural resonance frequency is from the pulse rising point to the second half zero cross point. The timing generator 35 detects the latter zero cross point and generates a timing pulse.
Next, the timing generator 35 is connected to the pulse generator 32 by the switching SW 36, and a pulse is generated by the timing pulse of the timing generator 35 to drive the planar galvanometer mirror 30.
[0016]
As a result, a circuit for driving the planar galvanometer mirror at the natural resonance frequency of the planar galvanometer mirror can be realized. The set frequency of the predetermined frequency generator does not need to be a natural resonance frequency, and can be set relatively freely because it is sufficient that the planar galvanometer mirror rotates even a little. Further, even if the natural resonance frequency of the planar galvanometer mirror changes, the change appears in the counter electromotive force waveform, so that the drive circuit can always be driven at the natural resonance frequency of the planar galvanometer mirror.
[0017]
FIG. 5 is a block diagram showing a second embodiment of the present invention. The planar type galvanometer mirror driving circuit includes a predetermined frequency generator 31, a pulse generator 32, a current setting unit 33, a back electromotive force detector 34, a timing generator 35, a switching SW 36, a phase comparator 37, a voltage controlled oscillator 38, a minute It consists of a peripheral 39 and a pulse and pulse width setting unit 40. The planar galvanometer mirror 30 is connected to a current setting unit 33 and a back electromotive force detection unit 34.
[0018]
As in the first embodiment, at the initial stage of driving of the planar galvanometer mirror 30, the pulse generator 32 and the current setting unit 33 are connected by the changeover switch 36, and the predetermined frequency generator 31, the pulse generator 32, and the current setting are connected. The planar galvanometer mirror 30 is driven by the unit 33, the back electromotive force waveform is detected by the back electromotive force detection unit 34, and the timing generator 35 generates a timing pulse that matches the natural resonance frequency from the waveform. The timing pulse is input to the phase comparator 37. The phase comparator 37 compares the phase of the input timing pulse with the frequency oscillated from the voltage controlled oscillator 38 and reduced to 1 / N by the frequency divider 39, and feeds back the result to the voltage controlled oscillator 38. As a result, N times the frequency synchronized with the timing pulse is obtained from the voltage controlled oscillator 38. From the obtained N times frequency and timing pulse, the pulse and pulse width setting unit 40 generates a pulse having a pulse width with a constant ratio to the natural resonance frequency.
[0019]
Here, a method for generating a pulse having a pulse width with a constant ratio to the natural resonance frequency will be described in more detail. For example, the frequency division ratio of the frequency divider 39 is set to 1/20. Then, the voltage controlled oscillator 38 can obtain a frequency 20 times the natural resonance frequency. The pulse and pulse width setting unit 40 first obtains a pulse generation timing by a timing pulse. Next, the frequency from the voltage controlled oscillator 38 is counted from the time of the pulse generation, and when the predetermined count number is reached, the timing of the end of the pulse is obtained. Assuming that the predetermined count number is 5, a pulse width of ¼ of the period of the natural resonance frequency is obtained. This ¼ pulse width can always be kept ¼ even when the natural resonance frequency changes.
[0020]
A pulse having a constant pulse width with the natural resonance frequency obtained as described above is input to the current setting unit 33 by the switching SW 36 to drive the planar galvanometer mirror 30.
[0021]
This makes it possible to realize a circuit that drives the planar galvanometer mirror with a pulse having a constant pulse width ratio even when the natural resonance frequency changes at the natural resonance frequency of the planar galvanometer mirror. Since the ratio of the pulse width to the natural resonance frequency affects the rotation angle of the planar galvanometer mirror, if the ratio of the pulse width to the natural resonance frequency is constant, the rotation angle does not change even if the natural resonance frequency changes. It goes without saying that the pulse width can be set more finely by changing the frequency dividing ratio of the frequency divider 39 and the count number in the pulse and pulse width setting section 40.
[0022]
Furthermore, when the counter electromotive force is detected by the counter electromotive force detecting unit 34, the generated frequency of the predetermined frequency generating unit 31 in the first embodiment and the second embodiment is sequentially changed in the initial stage of driving. It can also be driven by timing pulses from the counter electromotive force detector 34 and the timing generator 35.
[0023]
This makes it possible to realize a circuit that does not require initial frequency setting and drives the planar galvanometer mirror at the natural resonance frequency of the planar galvanometer mirror.
[0025]
【The invention's effect】
According to the present invention, it is possible to provide a planar galvanometer mirror driving circuit that does not require adjustment.
[0026]
It is possible to drive the planar galvanometer mirror at the most efficient natural resonance frequency.
[0027]
Even if the natural resonance frequency changes during driving, it is possible to drive the planar galvanometer mirror at a frequency following the change.
[0028]
Since there is no need to increase the resolution of the set frequency, the circuit scale can be reduced.
[0029]
Even if the natural resonance frequency changes, it can be driven without changing the pulse width with respect to the natural resonance frequency, that is, the driving condition, so that a stable rotation angle can be obtained.
[0030]
Since it is not necessary to measure the natural resonance frequency of the planar galvanometer mirror in advance, it is easy to manufacture a planar galvanometer mirror driving circuit.
[0031]
In the manufacturing process, it is not necessary to accurately match the natural resonance frequency of the planar galvanometer mirror with the target frequency, so that the planar galvanometer mirror can be easily manufactured.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a structure of a planar galvanometer mirror.
FIG. 2 is a timing chart of the operation of the planar galvanometer mirror.
FIG. 3 is a block diagram showing a first embodiment of the present invention.
FIG. 4 is a time chart for explaining the operation of the first embodiment of the present invention.
FIG. 5 is a block diagram showing a second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Movable plate 3 Mirror 4 Coil 5 Torsion bar 6 Torsion bar 7 Magnet 8 Magnet 30 Planar type galvano mirror 31 Predetermined frequency generation part 32 Pulse generation part 33 Current setting part 34 Back electromotive force detection part 35 Timing generation part 36 Switching SW
37 phase comparator 38 voltage controlled oscillator 39 frequency divider 40 pulse and pulse width setting unit

Claims (2)

A planar frequency galvanometer mirror drive circuit; a predetermined frequency generator for generating a predetermined frequency signal whose frequency is sequentially varied in the initial stage of driving the planar galvanometer mirror;
A pulse generator for generating a pulse having the predetermined frequency at the initial driving of the planar galvanometer mirror;
Based on the pulse generated from the pulse generation unit, a setting current unit that drives the driving current of the planar galvano mirror by passing a setting current; and
A back electromotive force detection unit that detects a back electromotive force generated in the drive coil after the start of energization of the drive coil;
A timing generator for generating a driving timing signal for a planar galvanometer mirror from the detected back electromotive force waveform;
A changeover switch for switching the signal output to the pulse generator from the predetermined frequency signal to the drive timing signal;
And a planar galvanomirror driving circuit configured to drive a planar galvanomirror by a pulse generated from the pulse generator at the drive timing after the signal is switched by the changeover switch . A voltage controlled oscillator;
A frequency divider for frequency-dividing the oscillation frequency from the voltage-controlled oscillator;
A phase comparator that compares the phase of the drive timing signal and the oscillation frequency divided by the frequency divider and feeds back the result to the voltage controlled oscillator;
Based on the signal fed back from the phase comparator and the frequency divided in synchronization with the drive timing signal oscillated by the voltage controlled oscillator, and based on the drive timing signal, the pulse width and the planar galvanometer mirror A pulse and a pulse width setting unit that generates a pulse having a constant pulse width ratio to the natural resonance frequency of
And further comprising
2. The planar type according to claim 1, wherein the changeover switch is configured to switch from the predetermined frequency signal to the pulse signal generated by the pulse and pulse width setting unit instead of the drive timing signal. Galvano mirror drive circuit.

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