JP3334835B2 - Displacement sensor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement sensor device utilizing composite resonance of a laser.

[0002]

2. Description of the Related Art In a storage device such as a magnetic disk device and an optical disk device, accuracy of sub-micron or less is required. The same applies to micromachines. Development of such devices requires a displacement sensor with nanometer accuracy. Also, displacement detection is the basis of a sensor. If the displacement of the elastically supported object is measured, it becomes an acceleration sensor, and if the deformation displacement of the diaphragm due to pressure is measured, it becomes a pressure sensor. Also, the more accurate the displacement sensor used, the smaller the amount of displacement required for measurement. The smaller the required displacement, the wider the frequency band of these sensors.

An optical interference method is a principle of detecting displacement with high accuracy. However, the detection mechanism including the optical path system becomes large. Recently, a displacement sensor using the complex resonance of a laser has been developed (Katagiri et al., "Highly Sensitive Micro Displacement Sensor Based on Coupled-Cavity Laser", Measurement and Control, 34, 6).
No. 1995, p. 489).

FIG. 4 shows the configuration. This displacement sensor is composed of a semiconductor laser 1, a semiconductor photodetector 2, and a micro-sphere lens 3. The return light of the light emitted from the laser 1 from the observation surface 4 interferes with the laser light emission, and the light emission intensity changes the displacement of the observation surface 4. Is used to repeat the intensity for each half wavelength of the laser emission wavelength. The intensity is detected by a semiconductor photodetector 2 on the back surface of the semiconductor laser 1 (which also emits light on the back surface).

FIG. 5 shows the relationship between the displacement of the observation surface and the emission intensity in the case of a laser having a wavelength of 1.3 μm. λ / 2 = 650
The emission intensity repeats strength and weakness for every displacement of nm. A in FIG.
With the use of a slope, displacement measurement with high accuracy in the range of several hundred nanometers is possible.

Further, in order to enlarge the measurement range, as shown in FIG. 6, control is performed by using a piezo element 5 to drive the piezo element so that the output of the semiconductor photodetector 2 becomes constant in accordance with the displacement of the observation plane. Circuit 6 is installed. Piezo element 5
, The voltage applied to the piezo element 5 indicates the displacement of the observation surface. With this method, the displacement can be measured in the extension range of the piezo element 5 (usually several microns to several tens microns).

[0007]

SUMMARY OF THE INVENTION The present inventor has found the following problems as a result of studying the above conventional technology.

[0008] The emission intensity of the semiconductor laser 1 fluctuates greatly depending on the temperature. This intensity fluctuation appears as it is as an output fluctuation of the semiconductor photodetector 2, and it has been found that the value reaches several tens of nanometers per degree in terms of displacement in the experimental example. That is, this known sensor has a problem that a large error occurs with respect to a temperature change.

An object of the present invention is to provide a displacement sensor device capable of measuring with nanometer accuracy for a long time.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0011]

The following is a brief description of an outline of a typical invention among the inventions disclosed in the present application.

(1) A displacement sensor device comprising a semiconductor laser, a semiconductor photodetector, a microsphere lens, and a piezo element, wherein the piezo element corresponds to a displacement of the output of the semiconductor photodetector with respect to an observation surface. A displacement sensor device comprising: means for oscillating around the lowest value of the output voltage; and means for constantly controlling the center of oscillation to the minimum value by an integrated value of a photodetector output by the oscillating means.

(2) The displacement sensor device according to (1), further comprising control means for detecting an output fluctuation due to the temperature of the semiconductor laser and keeping the laser output constant regardless of the temperature.

According to the above-described means, control is performed such that the oscillation center of the piezo element is always maintained at a point where the output of the piezo element changes discontinuously with respect to the displacement (point B shown in FIG. 2). By doing so, the displacement of the observation surface can be detected from the center of PZT oscillation, and the occurrence of measurement errors due to the temperature of the laser beam is eliminated by controlling the intensity of the laser beam. Measurement can be enabled.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings together with its embodiments (examples).

FIG. 1 is a block diagram showing a schematic configuration of a displacement sensor device according to an embodiment (example) of the present invention. The displacement sensor device of this embodiment (example) includes a semiconductor laser 1, a semiconductor photodetector 2, a microsphere lens 3, an observation surface 4, a piezo element 5, a control circuit 6,
It comprises a laser control circuit 7, an integration circuit 8, a PZT control circuit 9, and an oscillator 10.

The laser control circuit 7 includes the semiconductor laser 1
Semiconductor photodetector 2 so that the light emission intensity of
Is a control circuit for controlling the laser output by the average value of the outputs (average value of the laser).

The integrator circuit 8 has a positive voltage rectangular wave of a positive pulse ON and a negative pulse OFF associated with the oscillation of the piezo element 5,
This is a circuit for integrating two types of rectangular waves of a predetermined voltage, that is, a negative voltage rectangular wave having a negative pulse ON and a positive pulse OFF.

The PZT control circuit 9 adds an oscillator 10 for generating a voltage for oscillating the piezo element 5 and a signal from the integration circuit 8 to oscillate the piezo element 5 and always keeps the oscillation center in FIG. This is a circuit that controls so as to be held at the indicated point B.

FIG. 2 shows the output of the semiconductor photodetector 2 in the displacement sensor device of the present embodiment (embodiment) (hereinafter referred to as the output).
FIG. 4 is a characteristic diagram showing a relationship between displacement and PD displacement.
Is a portion where the output changes almost linearly with respect to the displacement, and B is a point where the output changes discontinuously with respect to the displacement.

Next, the operation of the displacement sensor device of this embodiment (example) will be described. In FIG. 1, light emitted from a semiconductor laser 1 is transmitted through a microsphere lens 3 to an observation surface 4.
Irradiates the laser light emitted from the semiconductor laser 1 and the return light of the laser light from the observation surface 4 to interfere with each other, and the light emission intensity repeats the intensity according to the displacement of the observation surface 4 every half wavelength of the laser emission wavelength. We are using. The intensity is detected by a semiconductor photodetector 2 on the back surface of the semiconductor laser 1 (which also emits light on the back surface).

As shown in FIG. 2, when the piezo element (sensor) 5 is swung at a small interval d around the point B where the PD output changes discontinuously with respect to the displacement, the left side of the point B is gently moved. The output of the semiconductor photodetector 2 (hereinafter, referred to as PD output) has characteristics as shown in FIG.

When the derivative of the PD output is calculated, the inclination becomes gentle near point B. The sine wave (si
nωt) and the center of oscillation is point B, the PD output and the differential waveform of the PD output are as shown in FIG. A sine wave (sin ωt) or a waveform similar to the oscillating waveform is desirable for ease of driving and position detection described later.

In the displacement sensor device of this embodiment (embodiment), as for the waveform obtained by time-differentiating the PD output, a sharp rising or falling pulse waveform is generated at the position of point B in FIG. When a flip-flop circuit (not shown) is operated using this pulse, as shown in FIG. 3, there are two types of a rectangular wave of a positive voltage of a positive pulse ON and a rectangular wave of a negative voltage of a negative pulse ON. It is possible to generate a rectangular wave having a predetermined voltage.

When the swing is performed around the point B in FIG. 2, the wavelengths of the two rectangular waves are the same, and the output obtained by adding and integrating the two becomes zero. When the point B deviates from the center of oscillation, the wavelengths of the two rectangular waves are different, and the output obtained by adding and integrating the two becomes either a positive or negative value. If this signal is used as an error signal and the piezo element 5 is operated so that this signal is always zero, the center of swing always remains at the position of point B in FIG. The operating voltage of the piezo element 5 changes according to the displacement of the observation surface 4,
The change operating voltage indicates the displacement of the observation surface 4.

In the displacement sensor device of the present embodiment, the integration circuit 8 uses the positive pulse ON / OFF associated with the oscillation of the piezo element 5.
The PZT control circuit 9 integrates the piezo element 5 with the PZT control circuit 9 by integrating two types of rectangular waves having a predetermined voltage, that is, a rectangular wave of a positive voltage with a negative pulse OFF and a rectangular wave of a negative voltage with a negative pulse ON and a negative voltage with a positive pulse OFF. By adding the output signal of the oscillator 10 that generates the voltage to be oscillated and the output signal of the integration circuit 8 to oscillate the piezo element 5 and always keeping the oscillation center at the point B shown in FIG. Since the displacement of the observation surface can be detected from the center of the PZT oscillation, and the occurrence of measurement errors due to temperature is eliminated by controlling the light intensity of the laser beam, it is possible to perform measurement with nanometer accuracy for a long time. it can.

As described above, the present invention is applied to the above embodiment (example).
However, the present invention is not limited to the above-described embodiment (example), and it is needless to say that various changes can be made without departing from the gist of the present invention.

[0028]

The effects obtained by typical aspects of the invention disclosed in the present application will be briefly described as follows.

By controlling the oscillation center of the piezo element to be always maintained at a point where the output of the piezo element changes discontinuously with respect to the displacement (point B shown in FIG. 2), the PZ is controlled.
The displacement of the observation surface can be detected from the center of the T swing, and the occurrence of measurement errors due to the temperature of the laser beam is eliminated by controlling the intensity of the laser beam. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a displacement sensor device according to an embodiment (example) of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between an output (hereinafter, referred to as a PD output) of a semiconductor photodetector 2 and a displacement in the displacement sensor device of the present embodiment (example).

FIG. 3 is a diagram for explaining the operation of the displacement sensor device of the present embodiment (example).

FIG. 4 is a diagram showing a schematic configuration of a conventional displacement sensor device using composite resonance of a laser.

FIG. 5 is a characteristic diagram showing a relationship between optical output and displacement in the conventional displacement sensor device using composite resonance of a laser shown in FIG.

FIG. 6 is a diagram showing a schematic configuration of a displacement sensor device in which a measurement range of a conventional displacement sensor device using composite resonance of a laser is enlarged.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Semiconductor photodetector, 3 ... Microsphere lens, 4 ... Observation surface, 5 ... Piezo element, 6 ... Control circuit, 7 ... Laser control circuit, 8 ... Integration circuit, 9 ... PZ
T control circuit, 10 oscillator.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-95167 (JP, A) JP-A-8-145634 (JP, A) JP-A-60-256079 (JP, A) 116412 (JP, A) JP-A-4-116402 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B 11/00

Claims (2)

(57) [Claims] 1. A displacement sensor comprising a semiconductor laser, a semiconductor photodetector, and a microsphere lens, and the displacement sensor is positioned with respect to an observation surface with respect to a minimum value of an output voltage corresponding to a displacement of the output of the semiconductor photodetector. A displacement sensor device comprising: means for oscillating; and means for constantly controlling the center of oscillation to the minimum value by an integrated value of a photodetector output by the oscillating means. 2. The displacement sensor device according to claim 1, further comprising control means for detecting a change in output of the semiconductor laser due to a temperature and keeping the laser output constant regardless of the temperature.