JP2002195809A - Optical dimension measuring method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the sudden change of a measurement value by a temperature change. SOLUTION: In the measurement of the dimension or displacement of a measuring object by use of a laser beam 10 oscillated by a semiconductor laser 20 of single mode with concentrated oscillation spectrum, the working current of the semiconductor laser 20 is subjected to high frequency modulation and made into a multi mode to minimize the influence by mode hop.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical dimension measuring method and apparatus, and more particularly to a single mode semiconductor having a concentrated oscillation spectrum, which is suitable for use in a laser scanning type external measuring instrument and an optical displacement meter. The present invention relates to an improvement in an optical dimension measuring method and apparatus for measuring dimensions and displacement of a measurement object using laser light oscillated by a laser.

[0002]

2. Description of the Related Art As described in Japanese Patent Application Laid-Open No. 2000-88528, an apparatus for measuring the size and displacement of an object to be measured by using a laser beam uses an object arranged within a parallel scanning range of the laser beam. As described in Japanese Patent Publication No. 4-49048, a laser-scanning outer shape measuring device that measures the outer shape of a measurement object by measuring the length of a shadow that occurs.
An optical displacement meter of a triangulation method for measuring a change in the position of the reflected light of the laser beam projected on the measurement target surface due to the displacement of the measurement target surface using a position detecting element such as a PSD, As described in US Pat. No. 43148, there is a focusing optical displacement meter that measures the displacement of a measurement target surface from a change in focusing position using an autofocus mechanism.

In a dimension measuring apparatus using such a laser beam, a multi-mode semiconductor laser whose oscillation spectrum is diffused has been used in the past.
With the consolidation of products, the types of semiconductor lasers that can be used are decreasing. As shown in FIG. 1, single-mode semiconductor lasers having a concentrated oscillation spectrum have become mainstream, and it has become difficult to obtain multi-mode semiconductor lasers. ing.

[0004]

However, an example of the relationship between the oscillation wavelength and the case temperature characteristic in a single mode semiconductor laser is as shown in FIG. 2, and the oscillation mode changes due to a change in ambient temperature, and the oscillation wavelength changes. Change,
Since a so-called mode hop phenomenon occurs, this has been a serious problem particularly in a dimension measuring device that requires precise measurement.

For example, in a laser scanning type external shape measuring instrument, as shown in FIG. 3, a laser beam 10 emitted from a semiconductor laser (not shown) is applied to a rotating polygon mirror 1.
2 and the parallel scanning light 1 by the f-θ lens 14.
After that, when the oscillation wavelength changes due to mode hopping, parallel scanning for scanning at a constant speed due to aberration of the f-θ lens 14 due to a change in the wavelength of the laser beam. The light 16A changes like 16B or 16C, causing an error in the shadow time T of the measurement object 8,
When the parallel scanning light spreads outward as in 16B,
When the parallel scanning light is narrowed in the direction in which the outer shape of the measuring object 8 is reduced, as opposed to 16C, an error occurs in the direction in which the outer shape of the measuring object 8 is increased. In particular, when a mode hop appears due to a subtle temperature change at a specific temperature, the mode hop appears as a sudden change in the measured value, giving the user the impression that the external shape measuring device has failed.

In the former external shape measuring instrument, the repeatability was relatively poor, so the mode hop phenomenon was not a problem. However, as a result of the advancement of the accuracy, the mode hop phenomenon became conspicuous, and the major problem was that Has become.

Further, in the optical displacement meter of the triangulation method, when the oscillation wavelength changes due to mode hop, the refraction angle of the lens changes with the wavelength, so that the position where the reflected light hits the PSD changes. Since the focus type optical displacement meter uses the direct focal length, if the oscillation wavelength changes due to mode hopping, the refraction angle of the lens changes with the wavelength. Appear. In addition, since there is no multimode in the visible light laser, the visible light laser cannot be used, and since the invisible laser is employed, the measuring point cannot be seen, and there is a problem that a lamp for confirming the measuring point is separately required. .

If the temperature characteristic shown in FIG. 2 is, for example, linear and constant, it may be possible to detect and correct the temperature. However, the temperature characteristic is not linear but has a step-like shape. Moreover, since the staircase characteristic changes for each product, it is practically impossible to detect and correct the temperature.

[0009] Although high-frequency superposition similar to that of the present invention is performed in DVDs and MDs, servos are applied to DVDs and MDs so as to follow the warpage and deformation of the disc, and the purpose is different from that of the present invention. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and has as its object to prevent a measured value from suddenly changing even when an ambient temperature changes.

[0011]

SUMMARY OF THE INVENTION The present invention relates to an optical size measuring method for measuring the size and displacement of an object to be measured using a laser beam oscillated by a single mode semiconductor laser having a concentrated oscillation spectrum. An object of the present invention is to solve the above-described problem by performing high-frequency modulation on an operating current of a semiconductor laser to make the semiconductor laser multimode so as to reduce the influence of mode hop.

The present invention also provides an optical size measuring apparatus for measuring the size and displacement of an object to be measured by using a laser beam oscillated by a single mode semiconductor laser whose oscillation spectrum is concentrated. Another object of the present invention is to solve the above-mentioned problem by providing a high-frequency superimposing circuit for applying high-frequency modulation to a current, making the semiconductor laser multimode, and reducing the influence of mode hop.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In the present invention, as shown in FIG. 4, for example, a semiconductor laser (LD) 20 whose output is kept constant by an automatic output adjustment circuit (APC) 24 including a photodiode (PD) 22, The operating current of the laser
A high-frequency superimposing circuit 26 for modulating at a high frequency of several hundred MHz, for example, 400 to 500 MHz is provided.

FIG. 5 shows an example of the relationship between the driving forward current of the semiconductor laser 20 and the light output.

When the high frequency is not superimposed, the oscillation spectrum of the single mode as shown in FIG. 1 is changed to the oscillation spectrum of the multi mode as shown in FIG. 6 by superimposing the high frequency. Therefore, a multi-mode oscillation spectrum can be obtained using a single-mode semiconductor laser.

Hereinafter, a first embodiment of the present invention applied to a laser scanning type outer shape measuring device will be described in detail.

This embodiment is configured as shown in FIG. In the figure, a light emitting unit 30 irradiates a scanning beam 16 to a measurement range in which a measurement target 8 is arranged. The light receiving unit 50 receives a part of the scanning beam 16, that is, a beam that is not blocked by the measurement object 8, and transmits a light receiving signal corresponding to the part. Then, the dimensions of the measurement object 8 are measured by the calculation unit 60 based on the received light signal.

The light emitting section 30 includes a semiconductor laser 20, and a laser beam 10 is output from the semiconductor laser 20. The semiconductor laser 20 has the same A
The PC 24 and the high-frequency power supply circuit 26 according to the present invention are connected.

The laser beam 10 is polarized by a mirror 32 and guided to a polygon mirror 12. Polygon mirror 1
2 is rotated by a motor 34 arranged coaxially therewith. A clock pulse is output from the clock circuit 62, and a drive signal synchronized with the clock pulse is output from the motor synchronization circuit 36. Based on the output of the motor synchronization circuit 36, the motor drive circuit 38 supplies electric power to the motor 34 and drives it. Therefore, the polygon mirror 12 rotates at a speed having a predetermined relationship with the clock pulse.

The laser beam 10 is reflected by the rotating polygon mirror 12 and further passes through the f-θ lens 14, whereby a parallel scanning beam 16 is formed.

In the light emitting section 30, a light receiving element 40 is arranged outside the f-θ lens 14. The light receiving element 40 is arranged at a position for receiving the laser light after one scan of the range in which the laser light passes through the f-θ lens 14, and outputs a pulse signal when receiving the light.
Therefore, the light receiving signal of the light receiving element 40 is output once each time one scan of the laser beam is completed.

In the light receiving section 50, the parallel scanning beam 16 is focused on a light receiving element 54 by a lens 52. The light receiving element 54 sends a signal that goes high when the scanning beam 16 is received and goes low when the scanning beam 16 is not received, and this signal is amplified by the amplifier 56,
The data is sent to the calculation unit 60. If the scanning beam 16 is blocked by the measuring object 8 and does not reach the light receiving element 54, the light receiving element 54 outputs a low signal. Therefore, scanning beam 1
Even when 6 scans within the measurement range, by measuring the period during which the signal is a low signal, it is possible to measure the dimension of the measuring object 8 in the scanning direction in the scanning plane. The dimension measurement is performed by the calculation unit 60.

In the arithmetic section 60, the signal of the amplifier 56 is first input to an edge detection circuit 64. The edge detection circuit 64 detects both a rising edge that changes from low to high and a falling edge that changes from high to low. The edge detection circuit 64 sends an edge detection signal to the gate circuit 66 when either the rising edge or the falling edge is detected. The pulse signal from the clock circuit 62 is also input to the gate circuit 66,
In accordance with the input of the edge detection signal, start and stop of transmission of the clock pulse to the counter 68 are controlled. If it is desired to measure the dimension of the measurement object 8, the clock pulse may be counted from when the falling edge is detected until when the next rising edge is detected.

When the laser beam 10 is detected by the light receiving element 40 provided in the light emitting section 30, a light receiving signal is sent to the reset circuit 70. The reset circuit 70 sends a square pulse wave reset signal to the gate circuit 66, and the gate circuit 66 receives the signal and stops the operation of all counters. The reset signal is also sent to a CPU (Central Processing Unit) 72 via a bus, and the CPU 72 reads the count value of the counter 68 and calculates the dimensions of the measuring object 8. Since the scanning of the traveling beam 16 is performed in synchronization with the clock pulse, the number of clock pulses counted by the counter 68 corresponds to the length (dimension) from the position where the counting was started to the position where the counting was stopped. are doing. It also corresponds to the time from when counting is started to when it is stopped.

The calculated value is sent to an external output device such as a display device or a printing device via the input / output circuit 74.
The CPU 72 includes a storage device 76 such as a ROM or a RAM in which a program for dimension calculation is stored, and a keyboard 7 for inputting constants and the like required for dimension calculation.
8 are connected via a bus.

FIG. 8 shows an example of a waveform measured by the light receiving element 52.

Before superimposing the high frequency, the outer diameter measuring device having the temperature characteristic of the measured diameter value as shown in FIG. The temperature characteristics of the measured diameter values were obtained, which could be greatly improved.

Further, since the spectrum is diffused by the multi-mode operation and the spectrum is not concentrated on the peak, the interference becomes small, and the position of the measuring object 8 due to the deviation of the threshold shown in the lower part of FIG. The up-down error at the time of occurrence also becomes small.

The amplitude and frequency of the high frequency superimposed by the high frequency superimposing circuit 26 are adjusted so as to obtain data as shown in FIG.

Next, a second embodiment of the present invention applied to a triangulation optical displacement meter is shown in FIG. In this embodiment, the semiconductor laser 20, the PSD 80, and the PSD 80
An optical displacement meter comprising: a center-of-gravity calculating circuit 84 for calculating the center of gravity of the above received light-receiving waveform; 20 is provided with a high-frequency superimposing circuit 26 in addition to the APC 24.

Next, a third embodiment of the present invention applied to a focusing type optical displacement meter is shown in FIG.

In this embodiment, a displacement meter main body 90, an objective lens holder 94 for holding the objective lens 92 movably in the vertical direction with respect to the displacement meter main body 90, and the objective lens holder 94 And a linear encoder 98 for detecting the vertical position of the objective lens holder 92.

The voice coil 96 is composed of a magnet 96A fixed to the displacement meter main body 90 and a coil 96B fixed to the objective lens holder 94.

The linear encoder 98 includes a scale 98A having one end fixed to the objective lens holder 94,
It comprises a detector 98B fixed to the displacement meter main body 90 so as to face the scale 98A.

The semiconductor laser 2 is mounted on the displacement meter body 90.
0, a beam splitter 100 that reflects the light emitted from the semiconductor laser 20 toward the measurement target surface 9, and a collimator that directs the light whose traveling direction has been changed by the beam splitter 100 to the objective lens 92 as a parallel beam. A lens 102, an imaging lens 104 that forms an image of the reflected light from the measurement target surface 9, a beam splitter 106 that splits the light passing through the imaging lens 104, and each of the split reflections split by the beam splitter 106. Pinhole plates 108A and 108B arranged before and after the light focus position, and each pinhole plate 108A,
Photodetectors 110A and 110B are provided for detecting the amounts of the divided reflected lights that have passed through 108B.

The detection circuit 120 is provided for each of the photodetectors 110
A, 110B, current-voltage (IV) converters 122A, 122B for converting output currents into voltages, and an amplifier 12 for amplifying the output voltages of the IV converters 122A, 122B.
4A, 124B, a difference calculator 126 for calculating the difference between the outputs of the amplifiers 124A, 124B, and the amplifiers 124A, 124A,
A sum calculator 128 for calculating the sum of the outputs of B 124B;
30.

If the distances from the in-focus position of each divided reflected light to each of the pinhole plates 108A and 108B are set to be equal to each other, each of the photodetectors 110A and 110B
Is as shown in FIG. At that time, the detection circuit 12
The focus error signal S obtained from 0 becomes an S-shaped curve as shown in FIG. 14 and becomes a signal corresponding to the displacement of the measurement target surface 10. Therefore, if the voice coil 96 is controlled so that the objective lens 92 always focuses on the measurement target surface 9 based on the focus error signal S, the output of the linear encoder 98 at that time can be output as a measurement value. it can.

In this embodiment, the semiconductor laser 20
In addition, a point that a high-frequency superimposing circuit 26 is connected in addition to the APC 24 is different from the conventional example.

In the above embodiment, the present invention is applied to a laser scanning type external measuring device and an optical displacement meter, but the present invention is not limited to this.

[0041]

According to the present invention, even when a single mode semiconductor laser is used, multimode operation can be achieved.
A sudden change in the measured value due to a temperature change can be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a single mode oscillation spectrum of a semiconductor laser for explaining a problem of the present invention.

FIG. 2 is a diagram showing an example of a mode hop.

FIG. 3 is a cross-sectional view showing an example of a measurement state in the laser scanning type external shape measuring instrument.

FIG. 4 is a block diagram showing a configuration example of a power supply circuit of a semiconductor laser of the dimension measuring device according to the present invention.

FIG. 5 is a diagram showing an example of a relationship between a driving forward current of a semiconductor laser and an optical output.

FIG. 6 is a diagram showing an example of an oscillation spectrum of the semiconductor laser.

FIG. 7 is a block diagram showing a first embodiment of the present invention applied to a laser scanning type external shape measuring instrument;

FIG. 8 is a diagram illustrating an example of an output waveform of a light receiving element according to the first embodiment.

FIG. 9 is a diagram showing an example of a temperature characteristic before a high frequency is superimposed.

FIG. 10 is a diagram showing an example of a temperature characteristic after a high frequency is superimposed and a multi-mode operation is performed.

FIG. 11 is a front view showing a second embodiment of the present invention applied to a triangulation optical displacement meter.

FIG. 12 is a sectional view showing a configuration of a third embodiment of the present invention applied to a focusing type optical displacement meter.

FIG. 13 is a diagram illustrating an example of an output waveform of a photodetector according to a third embodiment.

FIG. 14 is a diagram showing an example of a focus error signal.

[Explanation of symbols]

 8 Measurement Object 9 Measurement Surface 10 Laser Light 12 Polygon Mirror 14 f-θ Lens 16, 16A, 16B, 16C Parallel Scanning Light 20 Semiconductor Laser (LD) 22 Photodiode (PD) 24 ... Automatic output adjustment circuit (APC) 26 ... High frequency superimposition circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (2)

[Claims] An optical size measuring method for measuring the size and displacement of an object to be measured by using a laser beam oscillated by a single mode semiconductor laser whose oscillation spectrum is concentrated, wherein an operating current of the semiconductor laser is modulated to a high frequency. An optical dimension measuring method characterized in that a semiconductor laser is made multi-mode to reduce the influence of mode hopping. 2. An optical size measuring apparatus for measuring the size and displacement of an object to be measured using a laser beam oscillated by a single mode semiconductor laser having a concentrated oscillation spectrum. An optical dimension measuring device characterized by providing a high-frequency superimposing circuit for applying a laser beam, making the semiconductor laser multimode, and reducing the influence of mode hopping.