JPH04142510A - Beam scanner - Google Patents

Abstract

PURPOSE:To obtain superior temperature stability and to enable highly accurate angle control by connecting a 1st thermistor which is incorporated in a galvanometer and a 2nd thermistor which is provided externally and controlling the temperature of the galvanometer so that the composite resistance value of the two thermistors becomes constant. CONSTITUTION:Position control over the beam scanner is performed according to an angle control signal 101, which is converted into a specific driving signal 102 through a driving amplifier 21 and applied to the coil of the galvanometer 1 to rotate a mirror 11. At this time, negative feedback control is so performed that the detected angle signal 103 outputted by the galvanometer 1 becomes equal to the angle control signal 101. The 1st thermistor 13 which is put in the galvanometer 1 to detect the internal temperature and the 2nd thermistor 14 which is placed outside so as to ambient temperature are connected in series. A voltage applied to a surface heater 12 fitted to the external housing of the galvanometer 1 is so controlled that the composite resistance value of the two thermistors becomes constant.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to galvanometer type beam scanners used in laser processing machines and laser applied measuring instruments that perform various processing and measurements using laser beams. and in particular its stabilization method.

[Conventional technology]

For laser processing machines and measuring instruments that use laser beams, it is almost always necessary to either move the position of the workpiece or measured object or move the position of the light beam. be. From the viewpoint of processing speed, beam scanners are often used in which the moving parts are lightweight and compact and can move at high speed, and among these, galvanometer type beam scanners, which can move at even higher speeds, are often used.

This type of beam scanner using a galvanometer moves the laser beam by minutely rotating the mirror of the galvanometer in response to a position control signal, but the only movable parts are the rotor of the galvanometer and the mirror, so the moment of inertia is small. Therefore, it has the advantage that it is possible to move the focusing position at a high speed of, for example, 10 meters/second, and is widely used mainly in applications that require high-speed beam movement, such as laser trimmer devices.

In order to obtain high angular accuracy in such a beam scanner, it is essential to accurately control the angle by detecting the rotor angle by some method and performing feedback control. An angle detection method called the capacitance bridge method is usually used, and is described in the literature (E, P, Grenda and P.
J. Brosens, “Closing theLOO
P on Galvanometer 5canner
s″, EO8D Magazine, Aρotsu 1974.
As described in detail on page 32), there are electrodes attached to the rotor and multiple fixings placed around it! Changes in capacitance between the poles and the poles are differentially detected using a bridge-connected detection circuit.

This detection method allows you to obtain minute resolution, but since the gap between the electrodes is very small, even a slight temperature change will create a gap between the electrodes due to the difference in thermal expansion in that area, causing a change in capacitance. This results in a large angle detection error. This detection error also changes depending on the angle of the rotor, that is, the detection angle, and does not exhibit a constant temperature coefficient, so it is impossible to compensate for temperature changes by electrical methods or the like.

Therefore, in order to obtain high angular accuracy, it is a reliable and optimal method to maintain the temperature of the galvanometer constant. -As an option, it is possible to use a galvanometer placed in a constant temperature bath, but this is not practical due to structural limitations and economical problems. Therefore, in practice, a method of heating the galvanometer by attaching a planar heater to the outer casing is generally used. Specifically, in addition to attaching a surface heater to the outer casing of the galvanometer,
A thermistor, which is a temperature sensing element, is built inside, and the voltage applied to the surface heater is feedback-controlled so that the resistance value of the thermistor remains constant.

FIG. 6 is a block diagram showing the configuration of a conventionally used beam scanner, which includes a galvanometer 1 equipped with a mirror 11 mounted on the rotor axis, a control circuit 2 equipped with a drive amplifier 21 and a temperature control circuit 22. It consists of A thermistor 13 is used as a temperature sensing element built into the galvanometer, and the voltage applied to a surface heater 12 attached to the outer casing of the galvanometer is controlled so that its resistance value is constant.

In this case, since the temperature stability is inversely proportional to the strength of feedback, that is, the loop gain of the feedback circuit, it is desirable to set the loop gain as large as possible. However, in the case of temperature feedback control, heat conduction takes time and the response time is slow, so if the loop gain is increased, pulsation or oscillation will occur, so the feedback gain cannot be increased beyond a certain limit, and sufficient temperature stability cannot be achieved. It was difficult to obtain. Another possible method is to use a microprocessor for control, but this method has the drawbacks of being complicated and bulky, making it difficult to use for temperature control in galvanometers.

On the other hand, the objects processed by laser processing machines, to which such beam scanners are applied, are electronic circuits, etc., but in recent years there has been a trend toward miniaturization, and the angular accuracy required of beam scanners has also become stricter. Conventional beam scanners are no longer able to adequately handle these problems. In addition, there is no known beam scanner that uses a scanning mechanism of another type and has high-speed mobility comparable to that of a galvanometer.

[Problem to be solved by the invention]

Therefore, an object of the present invention is to improve the temperature control method in a beam scanner using a galvanometer, thereby achieving excellent temperature control with a simple configuration and at low cost, which has been difficult to achieve with conventional beam scanners. The objective is to realize a beam scanner that achieves stability and can perform high-precision angle control.

[Means to solve the problem]

According to the present invention, in a beam scanner including a galvanometer and a control circuit consisting of a drive circuit for the galvanometer and a temperature control circuit, a first thermistor built in the galvanometer and a second thermistor provided externally A beam scanner is obtained in which the temperature of the galvanometer is controlled so that the combined resistance value of the two thermistors is constant.

This invention focuses on the fact that the thermal resistance value of a galvanometer is almost constant, and makes it possible to compensate for the effects of changes in ambient temperature, which could not be completely eliminated with conventional methods, making it possible to control temperature with sufficient stability. , it is possible to construct a beam scanner with higher angular accuracy than conventional ones.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram showing the configuration of a beam scanner according to a first embodiment of the present invention, which includes a galvanometer 1 having a mirror 11 attached to a rotation axis, and a control circuit 2 having a drive amplifier 21 and a temperature control circuit 22. It is made up of.

In FIG. 1, the position control of the beam scanner is performed according to an angle control signal 101, which is converted into a predetermined drive signal 102 via a drive amplifier 21, and is then sent to a galvanometer 1.
The detected angle signal 10 output from the galvanometer 1 is applied to the coil to rotate the mirror.
Negative feedback control is performed so that 3 is equal to this angle control signal 101.

FIG. 2 is a block diagram showing the detailed configuration of the temperature control section used in the beam scanner of this embodiment.

A thermistor whose resistance value gradually decreases as the temperature rises is used as the temperature sensing element, and a first thermistor 13 is placed inside the galvanometer 1 to detect the internal temperature, and a first thermistor 13 is used to detect the ambient temperature. The second placed outside for
The thermistor 14 is connected in series. Then, the voltage applied to the surface heater 12 attached to the outer casing of the galvanometer 1 is controlled so that the combined resistance value of these two thermistors becomes constant.

Considering the operation in the case where there is no second thermistor in this configuration, the loop gain GI0°9 of the entire feedback loop of the temperature control system is approximated by the following equation (1).

GIoop-8XGsXKxRt11・・・・・・・・・
...(1) However, S: Detection voltage sensitivity of thermistor (V
/”C) G1 Nio amplifier gain (=R22/R2
1) K: Power/voltage coefficient of heater in normal use range (W/V) Rth: Thermal resistance of galvanometer ('C/W) As a specific value, S=0. OIV/℃, K=0, 3W
/ V - Rth = 5℃/W, (1
) The loop gain in equation 2) is expressed as in equation 2).

G10゜p=o, O15xG,・・・・・・・・・・・・
...(2) Also, when the gain G of the operational amplifier is set to 2000 times as a value that allows stable operation,
From equation (2), the loop gain G. G9 will be 30 times more.

Since stability is inversely proportional to loop gain, the influence of changes in ambient temperature can be reduced and stabilized to one-thirtieth. Therefore, if the ambient temperature drops by 15 degrees, the temperature of the galvanometer will drop by 0.5 degrees, and sufficient temperature stability is not achieved.

Next, consider the case where a second thermistor 14 is added to measure the ambient temperature, and its detection sensitivity is set to 1/30 of the detection sensitivity of the first thermistor 13. In this system, the ambient temperature is 15 degrees. The contribution of the second thermistor 14 to the decrease in temperature is to increase the temperature by 0.5 degrees, so the temperature decrease of 0.5 degrees can be offset.
It can be made unaffected by changes in ambient temperature. In order to set the detection sensitivities of the two thermistors so that they have such a canceling relationship, it is necessary to The nominal resistance value should be selected to be 1/1 of the loop gain of the first thermistor 13.If the relationship is set to 0 or more, the change in ambient temperature will be reduced even if the loop gain is not very high. Accurate temperature control is possible regardless of the temperature.

FIGS. 3 to 5 are block diagrams showing the configuration of the temperature control portion of beam scanners according to second to fourth embodiments of the present invention, respectively, and the configuration is similar to that of the beam scanner of the first embodiment. , only the connection method of the thermistor 14 is different.

A second embodiment of the present invention has a configuration in which second thermistors 14 are connected in parallel, as shown in FIG. Also with this connection method, the nominal resistance value of the second thermistor 14 is set higher than the nominal resistance value of the first thermistor 13, and the
If the contribution of the thermistor is selected to be 1/the loop gain of the detection sensitivity of the first thermistor, it is possible to perform offset compensation for changes in ambient temperature as in the first embodiment. The same effect as in the first embodiment can be obtained.

The third and fourth embodiments of the present invention differ from the first and second embodiments only in that a fixed resistor is connected in parallel or in series with the second thermistor 13.

In the first and second embodiments, it was necessary to select the nominal resistance values of the first and second thermistors to have a specific relationship determined by the loop gain; Resistors are connected in parallel or in series, and by selecting the resistors, the contribution of the second thermistor can be set to be 1/the loop gain. This has the advantage that even if thermistors having the same nominal resistance value are used, cancellation compensation can be performed in the same manner as in the first embodiment.

〔Effect of the invention〕

As explained above, according to the beam scanner of the present invention, a thermistor is placed as a temperature sensing element inside and outside the galvanometer, and the contribution of each thermistor to the detection sensitivity is set in a predetermined relationship. By simply controlling the temperature so that the combined resistance value that connects them remains constant, the effects of changes in ambient temperature can be offset and removed, making it possible to stabilize the temperature more stably and accurately than with conventional methods. , it is possible to configure a beam scanner that requires highly accurate angle control.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the functional configuration of a beam scanner according to the first embodiment of the present invention, FIG. 2 is a detailed block diagram of the temperature control circuit used in the first embodiment of the present invention, and FIG. 5 are connection diagrams of the temperature control circuit portions of the second to fourth embodiments of the present invention, respectively, and FIG. 6 is a block diagram showing the schematic configuration of a conventionally used beam scanner. 1... Galvanometer, 2... Control circuit, 11...
- Mirror, 12... Surface heater, 13... First thermistor, 14... Second thermistor, 21... Drive amplifier, 22... Temperature control circuit, R11-R12, R
2] ~R2,...resistor.

Claims (1)

[Claims] In a beam scanner including a galvanometer and a control circuit consisting of a drive circuit and a temperature control circuit for the galvanometer, a first thermistor installed inside the galvanometer and a second thermistor installed outside the galvanometer are connected. A beam scanner characterized in that the temperature of the galvanometer is controlled so as to keep the combined resistance value of the two thermistors constant.