JPS6076613A - Displacement converter - Google Patents

Abstract

PURPOSE:To obtain a displacement converter, which does not have errors and phase fitter due to delay in a circuit system and does not require adjustment, by detecting light transmitted through a code plate by a specified image sensor, counting the detected signal by a counter through a bandpass filter, and processing the result. CONSTITUTION:Image sensor 4 is driven by a reference clock fc and detects light transmitted through a code plate. The detected signal undergoes phase modulation through a bandpass filter 6. A signal e6 becomes a rectangular wave signal e7 through a wave shaping circuit 51 of a phase measuring means 50. The signal e7 is inputted to the D terminal of an FF52, which receives the reference clock fc as a clock input. An output e8 of the FF52 is inputted to a control circuit 53. A pulse e9 is generated at every cycle of the signal e7 and inputted to a counter 54. The clocks fc of the one cycle are counted. Output D1 of the counter is inputted to an operation circuit 55, where operation is performed. Then the output corresponding to the change in the code plate can be obtained. Since the signal e8 is synchronized with the clock fc, errors are not computed.

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 provides a plurality of light-transmitting strips arranged at a predetermined pitch.

The present invention relates to an optical displacement converter including a code plate in which a slit is formed, a phase plate, a light source and a light receiving element that emit and receive light through the light-transmitting slit of the code plate.

[Prior art]

A displacement transducer of Japanese Patent Application No. 58-86591 is an improved version of the conventional displacement transducer as described above. FIG. 1 is an explanatory diagram of the configuration of an example of the device. In this figure, 1 is a code body, 11 is a plurality of translucent slits arranged in the circumferential direction at predetermined widths in this code body, 3 is a light source, and 30 is a parallel beam for converting the light beam from the light source 3 into a parallel beam. 4 is a light source 3 that passes through a transparent slit 11.
An image sensor that receives light (slit image) from
Here, for the convenience of simply explaining the operation, a photodiode 41, 42, 43, 44 divided into four parts and a phase plate 2 having slit holes arranged at a predetermined pitch are placed on the photodiode. SWl, SW2.
SW3. SW4 is each photodiode 4 divided into four parts.
This is a switch that sequentially takes out signals from 1 to 44 at a fixed timing. 5 is an amplifier that amplifies the signal from the image sensor 4 applied via each switch SW1 to SW4, and a bandpass filter that extracts the fundamental wave component of the output signal from the trtd amplification H5.

FIG. 2 shows the transparent slits 21° 22 provided in the phase plate 2,
23.24 and photodiodes 41 to 4 divided into four
FIG. 4 is a diagram showing the arrangement relationship of No. 4. As shown in this figure, the arrangement pitch of the light-transmitting slits 21, 22, 23, 24 (indicated by solid lines) is 41.42°43
, 44 (indicated by the broken line), and has a rich arrangement pitch, and also,
Transparent slit provided with code body IK (shown with diagonal lines) 1
The arrangement pitch is 5/4P with respect to an arrangement pitch P of 1. In addition, the slit width of each slit hole 21-24 is set to P/2 here.

The operation of the apparatus configured as described above will be explained next with reference to the fourth operation waveform chart.

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 to 24 of the phase plate 2, and is transmitted to the four-divided photodiodes 41 to 24.
An image of the transparent slit 11 is formed on the slit 44. In the four-divided photodiodes 41 to 44, each switch 3W1
~SW4 is turned on and off (on time is T) sequentially at the timing shown in FIG. Amplify this signal.

As a result, the output signal e5 of the amplifier 5 has a staircase waveform whose magnitude changes stepwise every time each switch 8W1 to SW4 is turned on, as shown in FIG. 3(, ). When such a staircase wave signal e5 is applied to the bandpass filter 6, a sine wave signal e6 as shown in FIG. 3(r)K is obtained. The fundamental frequency of this sine wave signal e6 corresponds to the repeating frequency that sequentially drives each of the switches SWI 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 obtained from the bandpass filter 6 changes from that of the image. Depending on the amount of movement, the cord body is shifted by Φ, for example, as shown by the broken line. When the code body 1 rotates by one pitch P of the arrangement pitch of the transparent slits 11, the phase shift amount of the sine wave signal e becomes 2π.

Therefore, by measuring this phase shift amount Φ, it is possible to determine the rotation angle within the arrangement pitch 2 of the transparent slits 11 formed on the cord body 1.

FIG. 4 is a configuration block diagram showing an example of such a phase shift amount measuring circuit. This circuit adjusts the phase of the sine wave signal C obtained from the bandpass filter 6 by 100 to 100.
The operation is to interpolate by about 0. i.e. a sinusoidal signal. is a 7-speed p-squared loop CPLL with an I/N (N is the frequency division ratio) divider 72 in the feedback circuit.
1 and here multiplied by 8 is the signal fF3□-1 reference clock (this reference clock is used as the 4 drive signal of the image sensor 4). It is a mourning thing to give to someone.

When the code body 1 rotates in the direction (f+Δf) in which the frequency of the signal f multiplied by 8 by the PLL 71 becomes higher than f (sig c ), the up/down counter 9 counts up and "s
ig is f. When the cord body 1 rotates in the direction of becoming lower (f. - 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 determined by, for example, dividing the frequency division ratio N by 100.
If it is set to 0, it is possible to interpolate with a high resolution of 1P'-000.

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. (a) Since the PLL is a servo system, it causes errors and phase jitter when the input frequency changes, for example, in a 2-amp manner. (B)
Since 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 delay K in the circuit system and does not require adjustment.

[Summary of the invention]

In order to achieve the above-mentioned object, the gist of the present invention is to provide a code plate in which a plurality of transparent slits arranged at a predetermined pitch are formed, a transparent slit of the code plate, and a trap for projecting parallel light. It consists of a light source divided into a plurality of photodiodes, a phase plate having slit holes placed on each photodiode and arranged in predetermined widths, and a switch means for sequentially extracting signals from each photodiode. An image sensor, a bandpass filter for extracting a fundamental wave component from a signal obtained from the image sensor, an output signal of this bandpass filter and a drive signal of the image sensor are inputted, and based on the amount of phase shift of the fundamental wave component. In the displacement converter, the phase measuring means is configured to set a constant initial value for each period of the output signal of the band-pass filter, and to measure the displacement of the cord body using the drive signal. The present invention relates to a displacement converter comprising a counter that performs continuous counting, and an arithmetic η-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. Fifth
The figure is an embodiment of the present invention, and is a block diagram showing an improved version of the phase shift measurement circuit shown in FIG. 4 in the displacement transducer described in the conventional example. Components that are the same as those in FIG. 4 are designated by the same symbols, and their explanation will be omitted. 5o inputs the output signal e6 of the bandpass filter B and a reference clock f (this reference clock is also used as a drive signal for the image sensor 4), and also inputs the phase shift amount of the sine output signal e of the bandpass filter 6. 7) Phase measuring means for measuring the displacement of the code plate 11; 51 is a waveform shaping circuit using a comparator or the like for inputting the signal e6 and shaping the waveform; 52;
53 is a D-type flip-flop (hereinafter referred to as F-F) having the output e7 from the waveform shaping circuit 51 as the D input and the reference clock f as the clock input;
A control circuit 54 inputs the output e8 from the control circuit 53 and generates one pulse for each cycle of the signal e7, and 54 is a counter (a counter) which receives the output e from the control circuit 53 as a clear input and uses the reference clock f as a clock input. ). 55 is an arithmetic circuit that inputs the data output D□ from the counter 54 and calculates the displacement of the code plate 11;
Computing hardware etc. can be used.

The operation of the phase measuring means having such a configuration will be explained below based on the time chart shown in FIG. If there is no displacement in the code plate 11, the sine wave output e from the bandpass filter 6
6 is a reference clock f. is synchronized with. Sine wave output e6
The frequency f, 1. The value at this time is f. shall be. When the code plate uK is displaced, the sine wave output e6 undergoes phase modulation, and the phase shifts in accordance with the displacement. When the code plate 11 remains stationary with a constant displacement, the frequency f remains constant with a constant phase shift.

Outputs a sine wave. When the code plate rotates at a certain rotation speed, it is continuously phase modulated, and the frequency of the sine wave output e 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 is low, and when it is in the opposite direction, the frequency is high. Therefore the frequency fI
N is expressed as follows, where n1 is the rotational speed and Δf(n) is the modulation component.

When the sine wave signal e6 from the bandpass filter 6 is applied to the waveform shaping circuit $351, a rectangular wave e7 having a period equal to that of e6 is obtained (FIG. 6(b)). F-F52 is the above 2
The output e8 corresponding to the value signal e7 is the reference clock f. (Fig. 6 (a)) The 6th
6(c)), the control circuit 53 generates a pulse at each period of the signal e8 (e in FIG. 6(d)). The counter 54 is cleared (reset) by the pulse of the signal e every cycle, and counts the time until the next pulse based on the reference clock fK. The arithmetic circuit 55 uses this counter 5
The data output D (Fig. 6 1 (e)) for each cycle from 4 is input, and the reference value f is determined from this value. /f. (corresponding to the count value by the clock f during one cycle of the signal e7 when the code plate 11 is stationary), that is, D□-f. Integrate lfo. The calculated data output obtained in this way. UT÷Σ(D yo -fc, 1fo) is the sum of the phase changes for each cycle, so it becomes an output corresponding to the displacement of the code plate. The above phase measuring means is of an incremental type, and the signal e8 is clocked f. Since it is synchronized with , errors are not accumulated. Figure 6 (,) shows f-5MIIz +fo
In this example, data output in each period changes from 1000 to 1020 to 990 due to displacement. At this time, the calculation data at each point is output. UT is
It is as follows.

Time tl: DoUT1= 1000-1000=
.

Time t2: DoTJII12=1020-1000+D
oUT1=20 time t3: DoUII13=990-1
000+Do[Jr2=10 In the above embodiment, the contents of the counter 54 are reset every cycle.
As a modification, a down counter with a preset is used in place of the counter 54, and the reference value f is calculated every cycle. If a method of presetting lfo is used, it becomes unnecessary to subtract folfo in the arithmetic circuit 55 in diagram M5. At this time, the signal e9 is applied to the preset terminal of the preset counter.

〔Effect of the invention〕

As described above, according to the present invention, there is no error or phase jitter due to delay K in the circuit system, and a displacement converter that does not require adjustment can be easily realized. 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, and FIG. 2 is a diagram showing a light-transmitting slit of the phase plate 2 in the device shown in FIG. Figure 3 shows the arrangement relationship between the photodiode and the 4-split photodiode.
4 is a configuration block diagram showing an example of the phase shift amount measuring circuit, FIG. 5 is a configuration block diagram showing an embodiment of the phase shift amount measuring circuit according to the present invention, and FIG. 6 is a diagram of operation waveforms. 6 is a time chart for explaining the operation of the circuit of FIG. 5. FIG. 1... Code board, 11... Translucent pickpocket, G, 3...
Light source, 4... Image sensor, 41-14... 4-division photodiode, swi~SW4,... Switch, 691. Bandpass filter, 50... Phase measuring means, 54... Counter, 55... Arithmetic circuit, Dl...
・Data output.

Claims (1)

[Claims] A code plate with a plurality of transparent slits arranged at a predetermined pitch, a light source that projects parallel light to the transparent slits of the code plate, a photodiode divided into multiple parts, and a photodiode installed on each photodiode at a predetermined pitch. An image sensor is composed of a phase plate having slit holes arranged in an array, and a switch means for sequentially outputting the signals from each photodiode. A displacement converter comprising a filter, a phase measuring means that inputs an output signal of the bandpass filter and a drive signal of the image sensor and measures the displacement of the cord body based on the amount of phase shift of the fundamental wave component, The phase measuring means includes a counter that is set with a constant initial value for each period of the output signal of the band-pass filter and counts according to the drive signal, and a data output from the counter for each period. A displacement transducer characterized by comprising an arithmetic circuit that integrates related values.