JPH0421812A - Beam scanner - Google Patents

Abstract

PURPOSE:To execute a counterplan for readjustment before practical oscillation by extracting and detecting the high frequency component of a rotational drive signal and detecting the abnormal resonance phenomenon of a galvanometer based upon the detected output level. CONSTITUTION:A ringing is generated in a driving signal waveform 204 outputted from a practical circuit after a pulse in a deceleration period, and in accordance with approach to the state to be easily oscillated, the amplitude of the ringing is increased and its attenuation is also delayed, causing the long continuation of ringing. When a high frequency component is extracted by a capacitor C2 and detected by a diode detecting circuit consisting of two diodes D1, D2 and the capacitor C2, a detection signal 205 is obtained. The peak value of the signal 205 is increased in accordance with approach to the state to be easily oscillated and maximized at the time of oscillation. Thereby, the probability of oscillation can be previously detected by outputting an alarm through a comparator 35 when the peak of the signal 205 exceeds a certain set level Vr. Consequently, the probability of oscillation can be previously detected and a counterplan such as readjustment can be executed.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a beam scanner, and more particularly to a beam scanner used in the optical parts of laser processing machines, laser application equipment, etc. that perform various processing and measurements using laser beams. .

Conventional technology In almost all cases, laser processing machines and measuring machines that use laser beams either control the movement of the position of the workpiece or object to be measured, or control the movement of the light beam position. Such means are indispensable. Generally, from the viewpoint of processing speed, a beam movement method is adopted, which allows the moving part to be lightweight and compact, and allows for high-speed movement. Among these, galvanometer type beam scanners, which are capable of faster movement and control, are widely used.

FIG. 6 is a diagram showing a schematic configuration of a two-dimensional scanning optical system using a conventionally used galvanometer type beam scanner. Two sets of galvanometers 11 and 13 each having a mirror 12 and 14 rotatably supported are arranged so that their scanning directions are perpendicular to each other. Incident light beam]6
are successively reflected by mirrors 12 and 14 attached to galvanometers 11 and 13, respectively, and then incident on an fθ type objective lens 15. The light beam passing through the fθ objective lens 15 is focused on a predetermined position proportional to the incident angle on the processing surface.

With this configuration, the focusing position is controlled by two orthogonal axes (X.

This is done by slightly rotating the mirrors 12 and 14 of the galvanometers 11 and 13, respectively, in accordance with the position control signals 17 and 18 of the Y. The only movable parts are the galvanometer's rotor and the mirror, and because the moment of inertia is small, it is possible to move the focusing position at a high speed of 10 meters/second, for example, and is useful for laser processing machines, etc. It is widely used mainly in applications that require high-speed beam movement.

As for the driving method of the galvanometer used in such a beam scanner, there is usually a method of driving the galvanometer used in the reference document 1 ("G-300P").
D 5CANNERAND CCX-1005ERVO
C0NTR0LLER”, GENERAL 5CANN
ING INc, company catalog) and literature 2 (B, P
,Grenda and P,J,Brosens,”
Closing the Loop on Galvan
ometer 5canners”, EO3D Mag
azlne, April, 1974. p. 32).

That is, an error signal is obtained from the difference between the input angle control signal and the detected angle signal of the galvanometer, and at the same time, the detected angle signal is passed through a high-pass filter to obtain the angular velocity signal obtained by differential processing, and these errors are calculated. After amplifying the signal and the angular velocity signal to appropriate levels,
A driving method is used in which the current applied to the galvanometer is controlled by negative feedback using a difference signal between the two signals.

FIG. 7 shows the circuit configuration of a beam scanner using such a driving method, which includes a control circuit section consisting of a DA converter 21, an angle detection circuit 22, and a drive circuit 23, and a galvanometer 11 and a control circuit section attached to its rotating shaft. It is composed of a mirror 12.

Digital data 1 that specifies the destination for this beam scanner using a controller using a computer, etc.
01 is sent, and this data is converted into an analog signal by the DA converter 21 and applied to the galvanometer 11 via the drive circuit 23 as the angle control signal 102.
The detected angle signal 201 output from the angle detection circuit 22 at that time is this angle control signal! Negative feedback control is performed so that it becomes equal to 02.

Specifically, in the configuration shown in FIG. 7, ideal signal waveforms of each part are shown as angle control signal 1 shown in (a) and (b) of FIG.
02 and the detected angle signal 201, voltage dividing resistors R1 and R2
Then, using the operational amplifier 31, a sum signal, that is, an error signal 202 in FIG. 8(c) is obtained.

On the other hand, the detected angle signal 201 in FIG. 8(b) is
A high-pass filter consisting of a resistor R3 and an operational amplifier 32
The angular velocity signal 203 shown in FIG. 8(d) is obtained by passing through the angular velocity signal 203, and the drive signal 204 shown in FIG. 8(e) is obtained by adding these two signals.

Note that when the galvanometer is driven with this drive signal, the detected angle signal shown in FIG. 8(b) is obtained, and negative feedback control is performed as a whole.

This drive method has traditionally been considered the best method, and by increasing the loop gain of the negative feedback control loop, it is possible to move faster than the time constant of the galvanometer itself and improve position accuracy.

However, since the loop gain is high, if a mismatch occurs in relation to the drive signal due to inertia or friction of rotating parts such as mirrors, inductance of the drive coil, or slight fluctuations in back electromotive force, etc., it will have no effect on the angle control signal 102. However, there is a problem in that the mirror 11 vibrates, which is a so-called abnormal phenomenon.

If this kind of oscillation phenomenon is left unattended for a long time, the bearing used in the galvanometer's rotor will rapidly deteriorate due to friction, leading to deterioration of beam position accuracy, so it is necessary to take measures to stop the oscillation as soon as possible. is necessary. If the detection of oscillation is done manually, it can be easily determined by visual inspection of a part of the mirror, touch with a finger, or the sound of the operation, but in order to detect oscillation automatically, it is necessary to distinguish between a normal operating state and an oscillating state. isn't it.

A reliable method for detecting electrical and automatic oscillations for such purposes is to check for fluctuations in the mirror angle while the mirror is stopped; however, this method During this period, it is necessary to periodically stop and detect oscillations, which is not practical because of the drawbacks such as a decrease in operating efficiency. Another drawback of this detection method is that it can only be detected after oscillation actually occurs.

OBJECTS OF THE INVENTION An object of the present invention is to detect oscillations at any time, even in normal operating conditions, without reducing efficiency, in a beam scanner using a galvanometer, and to detect oscillations even at a stage before actual oscillations, when oscillations are likely to occur. In this way, it is an object of the present invention to provide a beam scanner in which measures such as readjustment can be taken before actual oscillation.

Structure of the Invention According to the present invention, a mirror, a galvanometer that rotatably supports the mirror and drives the mirror in response to a rotational drive signal from the outside, and a galvanometer that drives the mirror in accordance with a rotational drive signal from the outside and a rotational drive signal from the outside. A beam scanner comprising: a drive circuit that generates the rotational drive signal according to a difference from a rotational angle control signal; means for extracting and detecting a high frequency component of the rotational drive signal; A beam scanner characterized in that it includes a detection means for detecting an abnormal resonance phenomenon of the galvanometer based on the output level.

Example The present invention will be described in detail below using the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and parts equivalent to those in FIG. 7 are designated by the same symbols. In this example, an oscillation detection circuit 24 for detecting an abnormal resonance phenomenon of the galvanometer using a drive signal 204 is added to the conventional configuration shown in FIG. The other configurations are the same as those shown in FIG. 7, and their explanation will be omitted.

FIG. 2 is a circuit diagram showing a specific example of the oscillation detection circuit 24 shown in FIG. FIG. 3 is a signal waveform diagram of each part showing the operation.
Drive signal 204 and detection signal 205 shown in b) and (c)
Indicates the relationship between

In this configuration, the signal waveforms of each part are ideally as shown in FIG. , ringing occurs after the pulse of the deceleration period, and the easier it is to oscillate, the more the amplitude of the ringing increases, and its attenuation becomes slower and tends to last longer.

Therefore, as in the oscillation detection circuit shown in FIG.
When a high frequency component is extracted and detected using a diode detection circuit consisting of two diodes D1 and D2 and a capacitor C2, a detected signal 205 as shown in FIG. 3(c) is obtained.

In this detection signal 205, the peak value increases as it becomes easier to oscillate, and reaches its maximum value at the time of oscillation. Therefore, if the comparator 35 is used to issue an alarm when the peak of the detected signal 205 exceeds a certain set level V', the possibility of oscillation can be detected in advance.

FIG. 4 is a circuit diagram showing another example of the oscillation detection circuit 24, and FIG. 5 is a diagram showing signal waveforms in this example.

The oscillation detection circuit 24 in this example focuses on ripples included in the drive signal when the regalvanometer is stationary or moving at low speed, which is different from the example in FIG. 2, and the amplitude of this ripple is absent under normal conditions. Detection is based on the fact that the amplitude is extremely weak and increases as the oscillation becomes easier, reaching its maximum amplitude when oscillating.

Specifically, with the circuit configuration shown in FIG. 4, after amplifying the drive signal 204 shown in FIG. When envelope detection is performed using a circuit, (
A detected signal 20B as shown in C) is obtained.

This detected signal 206 is a signal that has a peak when moving and is minimum when stationary, but using the comparator 35,
An alarm is issued when the level at this minimum amplitude exceeds a certain set value.

With this method, as in the first embodiment, it is possible to detect oscillation and a state where oscillation is likely to occur, and issue a warning.

In each of the embodiments described above, the angle control input signal is a digital input, but it may be of a format in which an analog signal is directly input without a DA converter. On the other hand, in systems where a microcomputer is used as the controller, the user can be notified by sending an alarm signal to the controller and displaying a message, or by directly using the output of the detection circuit to sound an alarm buzzer. It is also possible to notify by lighting a warning lamp.

As described in detail, according to the present invention, the state of ringing and ripple included in the drive signal is constantly monitored, so there is no need to provide a specific oscillation detection period, and the ringing and ripple conditions included in the drive signal are not required. Oscillation can be detected at

In addition, this beam scanner can detect not only when oscillation is actually occurring, but also when it is likely to oscillate, so it can detect the possibility of oscillation in advance and take measures such as readjustment. There is an advantage that it can be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of the oscillation detection circuit 24 in FIG. 1, FIG. 3 is a waveform diagram showing the operation of the circuit in FIG. 2, and FIG. The figure is a circuit diagram showing another example of the oscillation detection circuit 24 in Figure 1, Figure 5 is a waveform diagram showing the operation of the circuit in Figure 4, and Figure 6 is the configuration of a two-dimensional scanning optical system using a galvanometer. 7 is a circuit diagram of a conventional drive control system for a galvanometer, and FIG. 8 is an operating waveform diagram of the circuit shown in FIG. Explanation of symbols of main parts 11... Galvanometer 12...
Mirror 22... Angle detection circuit 23...
...Drive circuit 24...Oscillation detection circuit 3
5... Comparators C1, C4... High frequency extraction capacitors DI, D2... Detection diode C2
...Capacity for detection

Claims (1)

[Claims] (1) A mirror, a galvanometer that rotatably supports the mirror and drives the mirror in response to an external rotation drive signal, and an angle detection signal of the mirror and an external rotation angle control signal. a drive circuit that generates the rotational drive signal according to the difference between the rotational drive signal and the rotational drive signal;
A beam scanner characterized in that it includes a detection means for detecting an abnormal resonance phenomenon of the galvanometer based on the detection output level.