JPH0360043B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a displacement transducer that detects mechanical displacement using light. More specifically, the present invention includes a code plate and a phase plate in which a plurality of light-transmitting slits arranged at a predetermined pitch are formed, a light source and a light-receiving element that transmit and receive light through the light-transmitting slits of the code plate. This invention relates to an optical displacement transducer.

[Prior art]

The displacement converter disclosed in Japanese Patent Application No. 58-86391 is an improved version of the conventional displacement converter as described above.

FIG. 1 is a configuration explanatory diagram showing an example of the device. In this figure, 1 is a code body, 11 is a plurality of translucent slits arranged circumferentially at a predetermined pitch on this code body, 3 is a light source, and 30 is a lens for converting the light beam from the light source 3 into a parallel beam. , 4 is an image sensor that receives the light (slit image) from the light source 3 that has passed through the transparent slit 11. Here, for the sake of explaining the operation briefly, it is divided into four photodiodes 41, 42, 43, and 44. , a phase plate 2 having slit holes arranged at a predetermined pitch is installed on the photodiode. SW
1, SW2, SW3, and SW4 are switches that sequentially take out signals from each of the four divided photodiodes 41 to 44 at a constant timing. 5 is an amplifier that amplifies the signal from the image sensor 4 applied via each switch SW1 to SW4, and 6 is a bandpass filter that extracts the fundamental wave component of the output signal from the amplifier 5.

Figure 2 shows the transparent slit 2 provided in the phase plate 2.
1, 22, 23, 24, and a diagram showing the arrangement relationship of photodiodes 41 to 44 divided into four. As shown in this figure, transparent slits 21, 22, 2
The arrangement pitch of photodiodes 3 and 24 (indicated by solid lines) is equal to the arrangement pitch of 4-divided photodiodes 41, 42, 43, and 44 (indicated by broken lines), and )11
The array pitch P is 5/4P. Note that the slit width of each of the slit holes 21 to 24 is set to P/2 here.

The operation of the apparatus constructed in this manner will now be described with reference to the operational waveform diagram in FIG.

The light from the light source 3 is turned into a parallel beam by the lens 30, passes through the light-transmitting slit 11 of the code plate 1 and the light-transmitting slits 21-24 of the phase plate 2, and forms the light-transmitting slit 11 on the four-divided photodiodes 41-44.
Form an image of 4-division photodiode 41
~44, each switch SW1~SW4 is turned on in sequence at the timing shown in FIG. 3a~d.
The photodiodes 41 to 44 are turned off (on time is T), and signals from each of the photodiodes 41 to 44 are sequentially taken out. Amplifier 5 amplifies this signal. As a result, amplifier 5
As shown in FIG. 3e, the output signal _e5 has a step waveform whose magnitude changes stepwise each time each switch SW1 to SW4 is turned on. When such a staircase wave signal e ₅ is applied to the bandpass filter 6, a sine wave signal e ₆ as shown in FIG. 3f is obtained. The fundamental frequency of this sine wave signal _e6 corresponds to the repetition frequency for sequentially driving each of the switches SW1 to SW4. Here, when the cord body 1 rotates according to the displacement to be measured, the images formed on each of the photodiodes 41 to 44 move, and the phase of the sine wave signal e ₆ obtained from the bandpass filter 6 changes as follows.
Depending on the amount of movement of the image, that is, the displacement of the code body, it is shifted by Φ, for example, as shown by the broken line.
When the cord body 1 rotates by one pitch P of the arrangement pitch of the transparent slits 11, the amount of phase shift of the sine wave signal _e6 becomes 2π.

Therefore, by measuring this phase shift amount Φ, the rotation angle within the arrangement pitch P of the transparent slits 11 formed in the cord body 1 can be determined.

FIG. 4 is a block diagram showing an example of such a phase shift amount measuring circuit. This circuit operates to interpolate the phase of the sine wave signal e6 obtained from the bandpass filter ₆ by about 100 to 1000. That is, a sine wave signal e ₆ is applied to a phase locked loop (PLL) 71 having an I/N (N is a frequency division ratio) frequency divider 72 in a feedback circuit, and a signal f _sig multiplied by N is applied thereto. and a reference clock _fc (this reference clock is used as a drive signal for the image sensor 4) are passed through a simultaneous pulse inhibiting circuit 8 and then applied to an up-down counter 9. When the code body 1 rotates in the direction (f _c +Δf) in which the frequency of the signal f _sig multiplied by N by the PLL 71 becomes higher than f _c , the up-down counter 9 counts up and f _sig becomes lower than f _c When the cord body 1 rotates in the direction (f _c -Δf), it counts down. Therefore, from the output of the up-down counter 9, the phase shift amount, that is, the rotation angle of the code body 1, can be calculated as follows, for example, if the frequency division ratio N is 1000.
Interpolation can be performed with a high resolution of 1/1000 of 1P.

According to such a configuration, a displacement transducer having high resolution and high speed response can be realized with a relatively simple configuration, but it has the following drawbacks. (stomach)
Since the PLL is a servo system, not only errors occur when the input frequency changes in a ramp-like manner, but also phase jitter. (b) Since the PLL is an analog circuit, adjustment is troublesome.

[Purpose of the invention]

The present invention solves the above-mentioned problems, and aims to realize a displacement converter that does not generate errors or phase jitter due to delays in the circuit system and does not require adjustment.

[Summary of the invention]

In order to achieve the above object, the present invention provides a code plate having a plurality of transparent slits arranged at a predetermined pitch, and a light source that projects parallel light onto the transparent slits of the code plate. , an image sensor consisting of a plurality of divided photodiodes, a phase plate having slit holes placed on each photodiode and arranged at a predetermined pitch, and a switch means for sequentially extracting signals from each photodiode; A bandpass filter extracts the fundamental wave component from the signal obtained from the signal, and inputs the output signal of this bandpass filter and the drive signal of the image sensor, and calculates the displacement of the code body based on the amount of phase shift of the fundamental wave component. A displacement converter comprising a phase measuring means for determining a phase, wherein the phase measuring means is a counter that is set with a constant initial value for each period of the output signal of the bandpass filter and counts based on the drive signal;
The present invention resides in a displacement converter characterized by comprising an arithmetic circuit that integrates values related to data output from the counter for each cycle.

〔Example〕

Hereinafter, the present invention will be explained in detail based on the drawings. FIG. 5 is a configuration block diagram showing one embodiment of the present invention, which is an improved version of the phase shift amount measuring circuit shown in FIG. 4 in the displacement transducer described in the conventional example. The same parts as in FIG. 4 are denoted by the same symbols and their explanation will be omitted. Reference numeral 50 inputs the output signal e6 of the bandpass filter ₆ and a reference clock (this reference clock is also used as a drive signal for the image sensor 4) _fc , and calculates the amount of phase shift of the sine wave signal e6 of the bandpass filter ₆ . Based on code board 1
1, 51 is a waveform shaping circuit using a comparator or the like for inputting the signal _e6 and shaping the waveform; 52 is a waveform shaping circuit using the output _e7 from this waveform shaping circuit 51 as the D input; A _D -type flip-flop (hereinafter referred to as F.
), 53 is the output e ₈ from this F・F52
54 _is the output from this control circuit 53.
This is a counter that uses _e9 as a clear input and reference clock _fc as a clock input. 55 is an arithmetic circuit which inputs the data output _D1 from the counter 54 and calculates the displacement of the code plate 11, and can use a microcomputer, addition hardware, or the like.

The operation of the phase measuring means having such a configuration will be explained below based on the time chart of FIG. If there is no displacement of the code plate 11, the sinusoidal output _e6 from the bandpass filter 6 is synchronized with the reference clock _fc . Let the value of the frequency f _IN of the sine wave output e ₆ at this time be f ₀ . When a displacement occurs in the code plate 11, the sine wave output e ₆ undergoes phase modulation, and the phase shifts in accordance with the displacement. When the code plate 11 remains stationary with a constant displacement, it outputs a sine wave of frequency f ₀ with a constant phase shift. When the code plate rotates at a certain speed, it is continuously phase modulated and outputs a sine wave.
The frequency of e ₆ also changes like the Doppler effect.
That is, when the direction of rotation of the code plate is the same as the direction in which the photodiodes 41 to 44 are sequentially turned on, the frequency becomes low, and when it is in the opposite direction, the frequency becomes high. Therefore, the frequency f _IN is
When the rotational speed is n and the modulation component is Δf(n), it is expressed as f _IN =f ₀ ±Δf(n).

When the sine wave signal e ₆ from the bandpass filter 6 is applied to the waveform shaping circuit 51, a rectangular wave e ₇ having a period equal to that of e ₆ is obtained (FIG. 6b). F・F52
generates an output e ₈ corresponding to the binary signal e ₇ at a timing synchronized with the reference clock f _c (FIG. 6 a) (FIG. 6 c), and the control circuit 53 outputs the output e 8 corresponding to the binary signal e 7 for each cycle of the signal e ₈ . A pulse is generated (e ₉ in Fig. 6d). The counter 54 is cleared (reset) by the pulse of the signal _e9 every cycle, and counts the time until the next pulse from the reference clock _fc . The arithmetic circuit 55 outputs data from this counter 54 for each period.
Input D ₁ (Fig. 6 e) and use this value to calculate the reference value f _c /
The value obtained by subtracting f ₀ (corresponding to the count value by the clock f _c during one cycle of the signal e ₇ when the code plate 11 is stationary), that is, D ₁ −f _c /f ₀ is integrated. The calculated data output D _OUT = Σ(D ₁ −
f _c /f ₀ ) is the sum of the phase changes for each period, so it is an output corresponding to the displacement of the code plate. The phase measuring means described above is of an incremental type, but since the signal _e8 is synchronized with the clock _fc , no errors are accumulated. 6th
Figure e shows that f _c =5MHz, f ₀ =5kHz or f _c /f ₀ =
In this example, data output D ₁ in each cycle changes from 1000 to 1020 to 990 due to displacement.
This is changing. At this time, the calculated data output D _OUT at each point in time is as follows.

Time t ₁ : D _OUT1 = 1000-1000 = 0 Time t ₂ : D _OUT2 = 1020-1000 + D _OUT1 = 20 Time t ₃ : D _OUT3 = 990-1000 + D _OUT2 = 10 In the above example, the counter is However, as a modification, if a down counter with a preset is used in place of the counter 54 and a method is used in which the reference value f _c /f ₀ is preset for each cycle, the arithmetic circuit shown in FIG. 55, there is no need to subtract f _c /f ₀ . At this time, signal _e9 is applied to the preset terminal of the preset counter.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to easily realize a displacement converter that is free from errors and phase jitter due to delays in the circuit system and does not require adjustment. The configuration is simple, and the number of circuit components is less than half that of conventional ones.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing an example of a conventional device, FIG. 2 is a diagram showing the arrangement relationship between the light-transmitting slit of the phase plate 2 and the four-division photodiode in the device shown in FIG. 1, and FIG. 3 is an operating waveform diagram. FIG. 4 is a configuration block diagram showing one row of the phase shift amount measuring circuit, FIG. 5 is a configuration block diagram showing one embodiment of the phase shift amount measuring circuit in the present invention, and FIG. 6 is the operation of the circuit shown in FIG. 5. This is a time chart to explain. 1... Code body, 11... Translucent slit, 3...
...Light source, 4...Image sensor, 41-44...
4-division photodiode, SW1 to SW4... switch, 6... band pass filter, 50... phase measuring means, 54... counter, 55... arithmetic circuit, _D1 ... data output.

Claims (1)

[Claims] 1. A code plate on which a plurality of light-transmitting slits are formed arranged at a predetermined pitch, a light source that projects parallel light onto the light-transmitting slits of the code plate, a photodiode divided into a plurality of parts, and a photodiode installed on each photodiode at a predetermined position. An image sensor consisting of a phase plate having slit holes arranged in pitch and a switch means for sequentially extracting the signals from each photodiode, a bandpass filter for extracting the fundamental wave component from the signal obtained from this image sensor, and In the displacement converter, the displacement converter includes a phase measuring means that inputs an output signal of a bandpass filter and a drive signal of the image sensor and determines the displacement of the cord body based on the amount of phase shift of the fundamental wave component. is a counter that is set with a constant initial value for each cycle of the output signal of the bandpass filter and counts based on the drive signal, and a value related to the data output from this counter for each cycle is integrated. A displacement transducer characterized by being equipped with an arithmetic circuit.