JP2002277809A - Planar galvanomirror driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar galvanomirror driving circuit which has a small circuit scale and surely drives a planar galvanomirror with a natural resonance frequency, without circuit adjustment while following up the change of the natural resonance frequency. SOLUTION: The planar galvanomirror driving circuit generates a pulse with a prescribed frequency in the initial stage of driving of the planar galvanomirror and drives the planar galvanomirror by the pulse and detects a counter-electromotive force from the planar galvanomirror after the start of driving the generates a drive timing of the planar galvanomirror from the detected counter-electromotive force waveform and generates a pulse at the obtained drive timing and drives the planar galvanomirror by this pulse.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for a planar galvano mirror used in a laser beam scanning system of a printer or the like.

[0002]

2. Description of the Related Art A planar galvano mirror is used for a laser beam scanning system for deflecting and scanning a laser beam, and operates on the principle that a mirror and a coil integrated with the mirror are arranged in a magnetic field. By passing a current through the mirror, an electromagnetic force is generated by the current and the magnetic field, the mirror and the 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 with the mirror and the mirror until the spring force of the holding member and the electromagnetic force obtained when a current flows through the coil are balanced. 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 through the coil and detect the presence or absence of the current and the amount of the current by the movement of the pointer. A planar galvanomirror using a semiconductor material has been proposed.

The above-mentioned planar galvanomirror is desirably rotated in a reciprocating manner in view of its use, and an alternating current is generally passed through the coil. That is, by passing an alternating current, an electromagnetic force according to the amount and direction of the alternating current is obtained, and the obtained electromagnetic force, that is, the rotational force is changed according to the amount and direction of the alternating current, and the mirror and the mirror are integrated. The coil is rotated back and forth.

FIG. 1 is a diagram for explaining the structure of a planar galvanomirror, and FIG. 2 is a timing chart of the operation of the planar galvanomirror. A movable plate 2 is formed on a silicon substrate 1, a mirror 3 is formed at the center of the movable plate 2, and a coil 4 is formed at a peripheral portion of the movable plate 2. The movable plate 2 is formed with the silicon substrate 1 hollowed out, and is held by torsion bars 5 and 6 formed integrally with the silicon substrate 1. The coil 4 obtains electrical connection with the outside by providing an electrode pattern on the torsion bars 5 and 6. A magnet 7 is provided outside the silicon substrate 1,
The movable plate 2 in the silicon substrate 1 is provided in a magnetic field. As shown in the timing chart of FIG. 2, when a current flows 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 repel or attract each other to generate an 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 performed by alternating current, the magnetic field generated by the coil 4 is also alternating current, and the electromagnetic force is also alternating current. 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 galvanomirror is
Due to the shape and weight of the movable plate 2 and the shapes of the torsion bars 5 and 6, there is a natural resonance frequency of rotation. The planar type galvanomirror is most efficiently operated at this natural resonance frequency, and it is easy to control the rotation angle. Therefore, it is general to drive the mirror at the natural resonance frequency.

[0006]

However, since the above natural resonance frequency is determined by each shape and weight,
It is difficult to accurately match a target frequency in manufacturing, and there is large variation. Therefore, the driving circuit must measure the natural resonance frequency of the planar galvanometer mirror in advance, and adjust the driving circuit in accordance with the measured frequency.

[0007] Further, since the sharpness (so-called Q) of the resonance of the natural resonance frequency is high, a slight frequency shift has a great effect on the rotation angle. Therefore, it is necessary to increase the frequency resolution of the drive circuit, and the circuit scale becomes large.

Further, the above natural resonance frequency depends on the environment used by the planar galvanomirror, for example, temperature, humidity,
Since it changes due to the atmospheric pressure or the like, it is almost impossible to change the driving frequency in accordance with the change in the natural resonance frequency.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and drives a planar galvanomirror without adjusting a circuit, has a small circuit scale, follows a change in a natural resonance frequency, and reliably drives at a natural resonance frequency. It is an object of the present invention to provide a galvanomirror driving circuit.

[0010]

In a driving circuit for a planar galvanomirror, a pulse is generated at a predetermined frequency in the initial stage of driving of the planar galvanomirror, and the planar galvanomirror is driven by the pulse. Back electromotive force from the galvanometer mirror
A driving timing of the planar galvanomirror is generated from the detected back electromotive force waveform, a pulse is generated from the obtained driving timing, and the pulse drives the planar galvanomirror.

In the driving circuit of the planar galvanomirror, a pulse is generated at a predetermined frequency in the initial stage of driving of the planar galvanomirror, and the planar galvanomirror is driven by the pulse. The back electromotive force is detected, the driving timing of the planar galvanometer mirror is generated from the detected back electromotive force waveform, the phase is compared between the obtained driving timing and the oscillation frequency from the voltage controlled oscillator, and the planar galvanometer is compared. A signal having the same phase as the drive timing of the mirror is obtained from the voltage-controlled oscillator, a pulse is generated by the signal from the voltage-controlled oscillator, and the pulse drives the planar galvano mirror.

In the driving circuit of the planar galvanomirror, a pulse is generated by changing the frequency in the initial stage of driving of the planar galvanomirror, the planar galvanomirror is driven by the pulse, and the back electromotive force from the planar galvanomirror is detected. Then, the driving timing of the planar galvanomirror is generated from the detected back electromotive force waveform, a pulse is generated from the obtained driving timing, and the pulse drives the planar galvanomirror.

In the driving circuit of the planar galvanomirror, in the initial stage of driving the planar galvanomirror, a frequency is varied to generate a pulse, the pulse drives the planar galvanomirror, and the back electromotive force from the planar galvanomirror is detected. Then, the drive timing of the planar galvanomirror is generated from the detected back electromotive force waveform, the phase is compared between the obtained drive timing and the oscillation frequency from the voltage controlled oscillator, and the drive timing of the planar galvanomirror is performed. A signal having the same phase as that of the voltage-controlled oscillator is obtained, a pulse is generated by a signal from the voltage-controlled oscillator, and the pulse drives a planar galvanomirror.

[0014]

FIG. 3 is a block diagram showing a 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. 3 shows the waveforms of FIG. The planar galvanomirror driving circuit includes a predetermined frequency generating unit 31, a pulse generating unit 32, a current setting unit 3
3, 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. The detailed description of the operation will be described below with reference to the timing chart of FIG.

In the initial stage of driving of the planar galvanomirror 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 galvanomirror 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. Current setting unit 33
Now, the current corresponding to the target rotation angle is supplied to the pulse generator 3.
Only the "H" section of the pulse generated in step 2 flows through the planar galvanomirror 30. Here, a current flows through the planar galvanomirror 30, so that it rotates according to the above-described operation principle. However, since the current flows only in the "H" section of the pulse, it moves only in one direction. After performing the one-way rotation operation, the planar galvanomirror 30 repeats the reciprocating rotation to return to the original state by the spring force of the torsion bar. This reciprocating rotation is determined by the shape and weight of the movable plate and the shape of the torsion bar, and the reciprocating rotation cycle matches the natural resonance frequency. On the other hand, the coil provided in the planar galvanomirror 30 reciprocates in the magnetic field generated by the magnet due to the reciprocating rotation, so that a counter electromotive force is generated in the coil. Since this back electromotive force is generated by the reciprocating rotation, the period of the back electromotive force matches the natural resonance frequency. Therefore, a waveform in which the pulse generated by the pulse generator 32 and the waveform of the back electromotive force are mixed is observed from the planar galvanomirror 30 here.
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 matching the natural resonance frequency from the waveform. That is, since the planar galvano mirror 30 is driven by a pulse, the first half of the waveform is a pulse waveform, the second half is a back 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 a second-half zero crossing point and generates a timing pulse. Next, the timing generation unit 35 is connected to the pulse generation unit 32 by the switching SW 36, a pulse is generated by the timing pulse of the timing generation unit 35, and the planar galvanomirror 30 is driven.

This makes it possible to realize a circuit for driving the planar galvanomirror at the natural resonance frequency of the planar galvanomirror. The set frequency of the predetermined frequency generation unit does not need to be the natural resonance frequency, and can be set relatively freely since the rotation of the planar galvanomirror may occur even a little. Further, even if the natural resonance frequency of the planar galvanomirror changes, the change appears in the back electromotive force waveform, so that the drive circuit can always be driven at the natural resonance frequency of the planar galvanomirror.

FIG. 5 is a block diagram showing a second embodiment of the present invention. The planar galvanomirror driving circuit includes a predetermined frequency generating unit 31, a pulse generating unit 32, a current setting unit 3
3, back electromotive force detector 34, timing generator 35, switch SW 36, phase comparator 37, voltage controlled oscillator 38,
It comprises a frequency divider 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.

As in the first embodiment, at the initial stage of driving the planar type galvanometer mirror 30, the changeover switch 36
The pulse generator 32 and the current setting unit 33 are connected by a predetermined frequency generator 31, a pulse generator 32, and a current setting unit 33.
To drive the planar galvano mirror 30, the back electromotive force waveform is detected by the back electromotive force detector 34, and the timing generator 35 generates a timing pulse matching 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 1 / N by the frequency divider 39, and feeds back the result to the voltage-controlled oscillator 38. As a result, an N-fold 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 constant pulse width in a ratio with the natural resonance frequency.

Here, a method of producing a pulse having a pulse width having 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, a frequency 20 times the natural resonance frequency is obtained from the voltage controlled oscillator 38. The pulse and pulse width setting unit 40 first obtains a pulse generation timing by a timing pulse. Next, from the time of pulse generation, the frequency from the voltage controlled oscillator 38 is counted, and when a predetermined count is reached, the pulse end timing is obtained.
Assuming that the predetermined count number is 5, a pulse width of 1/4 of the period of the natural resonance frequency is obtained. This 1/4
Is always 1/4 even if the natural resonance frequency changes.
Can be kept.

A pulse having a pulse width having a constant ratio to 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 galvanomirror 30.

Thus, it is possible to realize a circuit for driving the planar galvano 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 galvanomirror. 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 division ratio of the frequency divider 39 and the number of pulses in the pulse and pulse width setting section 40.

Further, the generation frequency of the predetermined frequency generation unit 31 in the first embodiment and the second embodiment is sequentially changed in the initial stage of driving, and when the back electromotive force is detected by the back electromotive force detection unit 34,
It is also possible to switch the switching SW 36 and drive it by timing pulses from the back electromotive force detector 34 and the timing generator 35.

This eliminates the need for initial frequency setting,
In addition, a circuit that drives the planar galvanomirror at the natural resonance frequency of the planar galvanomirror can be realized.

In this embodiment, the driving of the planar galvano mirror and the detection of the back electromotive force are performed by the same coil. However, both the driving coil and the detecting coil are formed in the movable plate, and each of them is used. It is feasible.

[0025]

According to the present invention, it is possible to provide a planar galvanomirror driving circuit which does not require adjustment.

The planar type galvanometer mirror can be driven at the most efficient natural resonance frequency.

Even if the natural resonance frequency changes during driving, the planar galvanomirror can be driven at a frequency that follows the change.

Since it is not necessary to increase the resolution of the frequency to be set, the circuit scale can be reduced.

Even if the natural resonance frequency changes, the driving can be performed without changing the pulse width with respect to the natural resonance frequency, that is, the driving conditions, so that a stable rotation angle can be obtained.

Since it is not necessary to measure the natural resonance frequency of the planar galvanomirror in advance, it is easy to manufacture a planar galvanomirror driving circuit.

In manufacturing, it is not necessary to precisely match the natural resonance frequency of the planar galvanomirror to a target frequency, and therefore, the manufacturing of the planar galvanomirror becomes easy.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a structure of a planar galvanomirror.

FIG. 2 is a timing chart of the operation of a planar galvanomirror.

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]

 Reference Signs List 1 silicon substrate 2 movable plate 3 mirror 4 coil 5 torsion bar 6 torsion bar 7 magnet 8 magnet 30 planar type galvanometer mirror 31 predetermined frequency generating unit 32 pulse generating unit 33 current setting unit 34 back electromotive force detecting unit 35 timing generating unit 36 switching SW 37 Phase comparator 38 Voltage controlled oscillator 39 Divider 40 Pulse and pulse width setting unit

Claims (3)

[Claims] In a driving circuit of a planar galvanomirror, a pulse is generated at a predetermined frequency in the initial stage of driving the planar galvanomirror, and the planar galvanomirror is driven by the pulse. , A driving timing of the planar galvanomirror is generated from the detected counterelectromotive force waveform, a pulse is generated from the obtained driving timing, and the planar galvanomirror is driven by the pulse. Characteristic planar type galvanometer mirror drive circuit. 2. A driving timing of a planar galvanomirror is generated from a back electromotive force waveform, a phase comparison is made between the obtained driving timing and an oscillation frequency from a voltage controlled oscillator, and a driving timing of the planar galvanomirror is calculated. 2. The planar galvanomirror drive according to claim 1, wherein a signal having the same phase is obtained from a voltage controlled oscillator, a pulse is generated by a signal from the voltage controlled oscillator, and the pulse drives a planar galvanomirror. circuit. In the initial stage of driving the planar galvanomirror, the frequency is varied to generate a pulse, and the pulse drives the planar galvanomirror. When the back electromotive force from the planar galvanomirror is detected, the detected reverse voltage is detected. 3. The planar galvanomirror driving circuit according to claim 1, wherein a driving timing of the planar galvanomirror is generated from the electromotive force waveform, and the planar galvanomirror is driven based on the obtained driving timing.