JPH07208922A - Fine displacement measuring instrument - Google Patents

Abstract

PURPOSE:To reduce the drift of a light source and an electronic circuit and to obtain a position measurement accuracy with a high resolution by feeding AC modulation power to a light source and changing 11 lighting intensity at a specific period and then converting the received reflection light into an electrical signal and then performing AC amplification. CONSTITUTION:An AC power from an AC modulation circuit 30 is fed to a light source using a high-brightness LED 31 and then lighting intensity is changed at a specific period, the light is applied to a fiber 1a for irradiation, light reflected by a surface to be measured is received by a photo diode 32 via a fiber lb for receiving light, and then the light is converted to a current (displacement) signal. On the other hand, the lighting intensity change in the LED 31 is received also by a photo diode 33 and is converted into current (reference) signal and is converted go voltage signals 34 and 35 along with the displacement signal. Then, the DC component is cut 36 and 37 and an offset signal is applied 38 and then is subjected to phase-sensitive detection 39 and, 40, then, the output ratio of both is output from a division circuit 41. The drift of the light source is reduced by an LED 31 and by dividing 41 the return intensity by a light source intensity and the drift of an electronic circuit is reduced by performing AC amplification of the light intensity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection photoelectric type micro-displacement measuring device which utilizes a phenomenon in which the amount of light reflected on a surface to be measured changes due to displacement (positional movement) of the surface to be measured.

[0002]

2. Description of the Related Art FIGS. 2 and 3 are views for explaining the measuring principle of an apparatus of this type. In the figures, reference numeral 1 is an optical fiber in which an irradiating fiber 1a and a receiving fiber 1b are bundled. It was Reference numeral 2 is a light source, 3 is an optical sensor, and 4 is a surface to be measured. In FIG. 3A, when the surface to be measured 4 is irradiated with a predetermined spread from the irradiation fiber 1a, the reflected light reflected from the surface to be measured 4 is also reflected with a predetermined spread, and the reflected light is reflected. Of these, the amount of reflected light that is substantially incident on the light receiving fiber 1b is
It is the product of the illuminance of reflected light and the receivable range of the shaded area shown by the dotted line where the end face b and the cross section of the reflected ray bundle overlap.

The distance Δd between the fiber end surface 1c and the surface 4 to be measured and the amount of reflected light entering the light receiving fiber 1b generally have a curve as shown in FIG. It is known that a minute displacement can be detected with high sensitivity by using the region of m in which the change rate of the light amount with respect to the displacement is high, and the displacement can be detected with a resolution of about several tens nm. (ROC
ooK and CWHamm: Fiber Optic Lever Displacement T
ransducer, Appl.Opt., 18, 19, (1979) 3230.). However,
In the device configuration as shown in FIG. 2, the amount of light that can be received by the optical sensor 3 is small, and the amplification factor of the signal is limited by the DC component unrelated to the displacement, so the detection sensitivity is poor. Therefore, as a device proposed to eliminate such a defect, there is a device shown in FIG.

FIG. 4 shows the journal of Precision Engineering Society (NO. 53 (19
June 1987) pp. 49-53, Igawa Naoya et al.) For explaining the apparatus, and in the figure,
Reference numeral 0 is a light source using a tungsten lamp, and a battery power source 11 is used for stabilizing the power source. Reference numeral 12 is a condenser lens, 13 is an optical fiber bundle formed by bundling optical fibers, and 14 is a reference optical system, which includes a fixed reference surface 15 and a reference photodiode 16. Reference numeral 17 denotes a measurement optical system, which is a surface to be measured 18 and a photodiode 1 for measurement.
9 and 9. As shown in the figure, the reference optical system 14 and the measurement optical system 17 are optical systems having the same characteristics. Two
0 is a differential amplifier.

Next, the operation of the apparatus shown in FIG. 4 will be described. In this apparatus, first, the optical fiber bundle 13 is used in the optical system so that a sufficient amount of measurement light can be obtained. The optical fiber bundle 13 includes, for example, two optical fiber bundles, one for measurement and one for reference, in which 1200 optical fibers each having a diameter of 25 μm are randomly bundled for irradiation and reception (about 2 mm in diameter). It has become one. Further, when a commercial power source is used, the SN ratio is lowered due to frequency pulsation, so the battery power source 11 is used for power source stabilization. As shown in FIG. 4, light is emitted from the same light source to the measured surface 18 and the fixed reference surface 15 through the irradiation optical fiber bundle, and the reflected light from each surface is transmitted through the light receiving fiber bundle. Are led to the photodiodes 16 and 19 having the same characteristics, where they are converted into electric signals corresponding to the received light intensity. Then, using the operational amplifier 20, the output of the photodiode 16 is subtracted from the output of the photodiode 19 to obtain a small displacement Δ.
Highly sensitive displacement output is obtained by amplifying and outputting only the signal component of d.

[0006]

The conventional micro-displacement measuring device is constructed as described above, and although the device shown in FIG. 4 can obtain a displacement output with relatively high sensitivity, it has a reference optical system and a measuring optical system. One optical system is required, there is a problem that the structure is complicated and it is not easy to incorporate it in other equipment.Because a tungsten lamp is used for the light source, it is necessary to constantly cool the light source, In addition, the life of a tungsten lamp is generally about 1,000 hours, which causes a problem in maintenance, and there is a problem that a change in light amount due to a temperature change is large. Further, since the DC amplification is performed, there is a problem that the resolution is deteriorated due to a drift at the time of amplification.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a micro-displacement measuring device capable of reducing the drift of a light source and an electronic circuit and obtaining high-resolution positioning accuracy. .

[0008]

In the micro-displacement measuring device according to the present invention, the drift of the light source is reduced by dividing the reflected light intensity by the light source intensity, and the drift of the electronic circuit is amplified by AC amplification. The circuit configuration is reduced.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which 1a is a fiber bundle for irradiation, 1b is a fiber bundle for receiving light, 30 is an AC modulation circuit, 31 is a light emitting diode,
32 and 33 are photodiodes, 34 and 35 are current-voltage conversion circuits, 36 and 37 are HPFs (high-pass filters), 38 is an offset signal, 39 and 40 are lock-in amplifiers, 41 is a divider circuit, and 42 is an output terminal. is there.

Next, the operation of this embodiment will be described. In this embodiment, the light source drift is reduced by using the light emitting diode 31 and the return light intensity is divided by the light intensity of the light source, and the drift of the electronic circuit is reduced by AC amplification of the light intensity. That is, a high-intensity light emitting diode 31 (for example, GL5UR3K1) is used as a light source, AC power from an AC modulation circuit is supplied to the light emitting diode 31, the luminous intensity is changed at a predetermined cycle, and the light is incident on the irradiation fiber bundle 1a. . The light emitting diode 3
1 is a light emitting diode which does not have a condenser lens, in which the condenser lens portion provided at the tip is removed in order to increase the amount of light incident on the fiber bundle. The irradiation fiber bundle 1a to the emission fiber bundle 1b have the same configuration as in FIG. 2 (however, both the irradiation and reception light fiber bundles are used), and the incident light is reflected by the measured surface 4. Then, the reflected light is emitted from the light receiving fiber bundle 1b, and the reflected light is received by the photodiode 32 and converted into a current signal (displacement signal).

On the other hand, the change in luminous intensity of the light emitting diode 31 is
The photodiode 33 also receives the light, converts it into a current signal (reference signal), and amplifies and converts each output signal into a voltage signal in the current-voltage conversion circuits 34 and 35, respectively, and cuts the DC component through the HPFs 36 and 37, respectively. Then, an appropriate offset is applied by taking the difference between the displacement signal and the reference signal, and the distance Δd between the fiber end face 1c and the measured face 4 when the output voltage is zero is adjusted so as to be in the measurable region. After that, the displacement signal and the reference signal are phase-sensitively detected by separate lock-in amplifiers 39 and 40 to form a DC signal, and then a dividing circuit 41 outputs the ratio of both outputs. According to the experimental results of the applicants, the maximum measurement range is about 40 μm and the maximum sensitivity is 70 nm / V.
Was obtained.

In the above embodiment, the lock-in amplifier is used as the means for performing the phase sensitive detection of the displacement signal and the reference signal, but a demodulation circuit similar to the amplitude modulation wave demodulation circuit may be used. Further, the calculation by the division circuit 41 may be performed before the phase sensitive detection, and the division circuit may be a circuit that is numerically performed through an AD conversion circuit.

[0013]

As described above, in the minute displacement measuring apparatus of the present invention, the drift of the light source is reduced by dividing the reflected light intensity by the light source intensity, and the drift of the electronic circuit is reduced by AC amplification. With the configuration, it is possible to obtain a high-sensitivity, simple and compact device with extremely small drift. Also,
Since the light emitting diode is used for the light source, the amount of heat generated is extremely smaller than that of a tungsten lamp or the like used in the conventional apparatus, and therefore, there is an effect that the light source does not need to be cooled and can be used semipermanently.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining the measurement principle of this type of device.

FIG. 3 is a diagram for explaining the measurement principle of this type of device.

FIG. 4 is a diagram for explaining an example of a conventional device of this type.

[Explanation of symbols]

 1a Irradiation fiber 1b Receiving fiber 30 AC modulation circuit 31 Light emitting diode 32,33 Photodiode 34,35 Current-voltage conversion circuit 36,37 HPF (high-pass filter) 39,40 Lock-in amplifier 41 Division circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norio Yasuda 1603-1 Kamitomioka Town, Nagaoka City, Niigata Prefecture Nagaoka University of Technology

Claims (3)

[Claims] 1. Light emitted from an end face of an irradiation optical fiber (or fiber bundle) to a surface to be measured, and reflected light at an end face of a light receiving optical fiber (or fiber bundle) provided at the same position as the end face of the irradiation optical fiber. In a small displacement measuring device that receives the received light and detects the received reflected light intensity with an electric signal to measure the small displacement of the surface to be measured with respect to the end face of the optical fiber. A micro displacement measuring device comprising: a unit for changing a light intensity by converting the received light into an electric signal and performing AC amplification to reduce a drift at the time of amplification. 2. The micro displacement measuring device according to claim 1, further comprising means for dividing the intensity of the received reflected light by the intensity of the light source for irradiation to reduce the influence of the change in the light amount of the light source. 3. The micro displacement measuring device according to claim 1, wherein a light emitting diode having no condenser lens is used as the irradiation light source.