JPH0769191B2 - Optical displacement meter - Google Patents

Description

[Detailed Description of the Invention] <Industrial field of application> The present invention relates to an optical displacement meter using an LED, the deterioration of the LED and the L
The present invention relates to an optical displacement meter that accurately measures displacement regardless of the characteristics of the ED itself.

<Prior Art> A photo interrupter shown in FIG. 4 is conventionally known as an optical displacement meter of this type.

In the figure, 1 is a light source composed of an LED or the like, and light from this light source passes through slits 7 and 8 formed in the first light shielding plate 2 and the second light shielding plate 3, and a photoelectric conversion element (for example, a photodiode ... Hereinafter, simply referred to as PD) 4. Reference numeral 5 is a displacement body that blocks light passing through the slit 8 by moving in the direction of the arrow. Therefore, the position of the displacement body 5 can be detected by measuring the change in the output of the PD4.

FIG. 5 shows the relationship between the position of the displacement body and the output of the PD having the above configuration, and shows the state in which the output of the PD increases as the displacement body moves leftward from the position indicated by a. . If such a photo interrupter is used for a simple displacement meter or zero point position detection, the structure is simple, so that it is easy to manufacture and cost effective.

<Problems to be Solved by the Invention> However, the above conventional example has the following problems.

The decrease in output due to aging of the LED affects the relationship between displacement and output, resulting in an error.

Since the characteristics of the LED itself differ from sample to sample, it is necessary to measure the characteristics of each device and create a calibration table.

 The moving direction of the displacement body is unknown.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide an optical displacement meter capable of determining a moving direction without being affected by variations and deteriorations in LED characteristics.

<Means for Solving the Problems> The structure of the present invention for solving the above problems includes a light source,
An amplitude modulator that amplitude-modulates the light intensity of the light source into a sinusoidal wave, a light diffusing unit that diffuses the light from the light source, a slit width and a light-shielding portion have the same width, and they are arranged at equal intervals. When the arranged displacement bodies and the gap between the slit width of this displacement body and the period of the light-shielding portion are d, four strips are arranged at equal intervals between the bands of light emitted from the gap d. A photoelectric conversion element, an I / V converter that converts each of the current outputs from these photoelectric conversion elements into a voltage, an adder that adds the output voltages from these I / V converters, and an output of this adder A low-pass filter that cuts the AC component, and a high-pass filter that cuts the DC component by inputting two outputs of the outputs from the I / V converters whose phases are adjacent to each other. Outputs a high or low level signal based on the output of the pass filter A comparator, peak value detection means for detecting the peak value of the output from the high pass filter, and a divider for dividing the output signal from the peak value detection means by the output signal from the low pass filter. And an inverse calculation table for calculating the displacement amount of the displacement body based on the output of the divider.

<Embodiment> FIG. 1 is a block diagram showing an embodiment of an optical displacement meter of the present invention.

In the figure, 1 is a light source, and 20 is an amplitude modulator for amplitude-modulating the light intensity of the light source 1 in a sinusoidal shape. 21 is a slit
The light from the light source 1 reaches the diffuser plate 23 through the slit 22 and becomes a diffused light and illuminates the displacement body 24.
A plurality of slits 24a are formed in the displacement body 24, and the slits 24a and the light shielding portions 24b are formed to have the same width. Reference numeral 25 denotes a photoelectric conversion unit in which four PDs 25a to 25d are arranged in a strip shape at equal intervals, and the interval between the slit 24a of the displacement body and the light shielding unit 24b is d (2
.pi.), four (two in the drawing are at the slit and the other two are at positions corresponding to the light shielding portion) are arranged at the interval d. For this reason, sinusoidal light is applied to the photoelectric conversion unit 25, and the relationship between the light intensity received by each photoelectric conversion element and the phase angle is as shown in FIG. (Note that it is necessary to increase the number of PDs in order to obtain a smooth sine wave as shown in Fig. 2). That is, the central portion of the slit 24a has the highest light intensity and the central portion of the light shielding portion 24b has the lowest light intensity. Therefore, the output signal I _1-
I ₄ is a signal that is 90 ° out of phase with each other, and these signals can be expressed by the following equation.

I ₁ = (sin θ + 1) a I ₂ = (cos θ + 1) a I ₃ = (-sin θ + 1) a I ₄ = (-cos θ + 1) a θ; A variable that changes according to the position of the displacement body 1, that is, the position of the displacement body Signal a: the light intensity of the light source 1. Incidentally, 1 is added to sin θ, cos θ, −sin θ, and −cos θ so that the light of the light source 1 does not have a negative value.

30a to 30d are I / V converters provided corresponding to the PDs of 4a to 4d, and convert the output current of the PD into a voltage. I / V converter 30a-30d
The output signals P _{1 to} P ₄ from the adder 31 are added by an adder 31, the output signal P ′ of this adder is input to a low-pass filter 32 to cut its AC component, and its output signal P _L is a divider. One of 33 inputs.

34a and 34b are high-pass filters, and two of the outputs of the I / V converters of 30a to 30d whose phases are adjacent to each other (in the figure, the output of 30c and the output from 30d are 30a and 30b. , 30b and 30c, 30a and
Outputs P ₃ and P _{4 (} which may be 30d) are input respectively, and output signals P _H1 and P _{H2 from} which the DC component is cut are input to comparators 36a and 36b connected in the _subsequent stage. This comparator outputs a high or low level signal P _H φ, P _L φ based on the output of the high pass filter. Further, the output of the high-pass filter is switched by the switch 37 at a constant period much slower than the modulation period of the amplitude modulator 20 and input to the peak value detector 35 (thus, the signal modulated by the amplitude modulator is Can be considered static). This peak value detector outputs the signal from the high-pass filter to the divider 33 as a DC signal output P _P. The divider uses the input from the low-pass filter as the denominator and the input from the high-pass filter as the numerator for division. The output signal P ₀ of this divider 33
Is input to the inverse conversion table 41 via the A / D converter 40 and si
Convert from nθ to θ.

In the above configuration, the light intensity of the light source 1 is now changed to the amplitude modulator.
As shown in Fig. 2 by 20, a sine wave (sinωt + 1)
When was varied, the output of the output P ₁ to P ₄ of the I / V converter can be expressed by the following equation.

P ₁ = (sin θ + 1) (sin ωt + 1) a P ₂ = (cos θ + 1) (sin ωt + 1) a P ₃ = (− sin θ + 1) (sin ωt + 1) a P ₄ = (− cos θ + 1) (sin ωt + 1) a θ = at the position of the displacement body 1 A variable (phase angle) that changes according to: ω = modulation frequency of LED a = radiation intensity of LED Then, the sum P ′ of outputs obtained by adding P _{1 to} P ₄ by the adder 31 is P ′ = 4 (sin ωt + 1) a The output P _L passed through the low pass filter is P _L = 4a.

On the other hand, the output of P _H1 and P _H2 passed through the high-pass filter is P _H1 = asin θsinωt P _H2 = acos θsinωt, and the output P _P passed through the peak detector is P _P = asin θ or acos θ).

Therefore, the output P ₀ calculated by the divider 33 becomes P ₀ = asin θ / 4a = sin θ / 4, and the output changes sinusoidally with the displacement amount θ of the displacement body. This output P ₀ can be input to the inverse conversion table 41 to obtain the displacement θ.

This θ enables measurement in the range of −π / 2 <θ <π / 2 or π / 2 <θ <3π / 2. Although it is unclear which position of the signal θ is 0 to 2π, the position can be determined from the output of the comparator.

That is, as shown in FIG. 3, comparators 36a and 36b
Output P _Hpusai, in the position of 0~π / 2 If P _Erupusai are both high level, the output P _H phi a high level of the comparator 36a, 36
If b output P _L phi of the low level in the position of π / 2~π, when the output P _L phi of the output P _Hpusai of the comparator 36a is low comparator 36b is at a high level of π~3π / 2 Position and the output P of comparators 36a and 36b
It can be seen that when _H φ and P _L φ are both low level, they are in the position of 3π / 2 to 2π.

In FIG. 1 and FIG. 2, the arrangement width of PD ₁ to PD ₄ of the photoelectric conversion unit 25 is shown as being almost the same as the width of the slit and the light shielding unit, but as shown by the dashed line in FIG. In slit 24a
The band of light radiated from is widened with distance from the displacement body 24. In such a case, it is necessary to expand the array of PDs according to the bandwidth of light.

<Effects of the Invention> According to the present invention as specifically described above with reference to the embodiments, the light intensity of the light source is amplitude-modulated, and the light passing through the displacement body is detected by the photoelectric conversion element with an appropriate phase relationship. Therefore, it is possible to realize an optical displacement meter that can determine the moving direction without being affected by variations and deterioration of LED characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of an optical displacement gauge according to the present invention, FIG. 2 is a diagram showing a relationship between a light intensity and a phase angle when the light intensity of a light source is changed in a sinusoidal shape, and FIG. The figure shows the phase relationship between the output of the comparator and the displacement body. Fig. 4 shows the essential parts of the conventional optical displacement gauge. Fig. 5 shows the displacement body position and photoelectric conversion of the conventional optical displacement gauge. It is a figure which shows the relationship of the output of an element. 1 ... Light source, 20 ... Amplitude modulator, 21 ... Shading plate, 22 ... Slit, 23 ... Diffusing plate, 24 ... Displacement body, 25a to 25d ... Photoelectric conversion element, 30a to 30d ... I / V converter, 31 …… Adder, 32 ……
Low pass filter, 33 …… divider, 34a, 34b …… High pass filter, 35 …… Peak value detector, 36a, 36b …… Comparator, 37 …… Switch, 40 …… A / D converter, 41 ... Inverse conversion table.

Claims (1)

[Claims] 1. A light source, an amplitude modulator for amplitude-modulating the light intensity of the light source into a sinusoidal wave, a light diffusing means for converting the light of the light source into diffused light, and a slit width and a light-shielding portion have the same width. , And the displacement bodies arranged at equal intervals, and when the interval between the slit width of this displacement body and the period of the light shielding part is d, the intervals of the light irradiated from the interval d are evenly spaced. Four photoelectric conversion elements arranged in strips, an I / V converter that converts each of the current outputs from these photoelectric conversion elements into a voltage, and an adder that adds the output voltages from these I / V converters And a low-pass filter that cuts the AC component of the output of this adder, and two outputs of the outputs from the I / V converter whose phases are adjacent to each other. A high or low based on the output of the high pass filter and the high pass filter. A comparator for outputting a level signal; a peak value detecting means for detecting a peak value of an output from the high pass filter; and an output signal from the low pass filter for dividing the output signal from the peak value detecting means. An optical displacement meter, comprising: a divider for performing the above operation; and an inverse calculation table for calculating the displacement amount of the displacement body based on the output of the divider.