JPS6073418A - Displacement transducer - Google Patents

Abstract

PURPOSE:To easily realize a displacement transducer which has a small nonlinear error by forming slits in either of a phase plate and a code plate. CONSTITUTION:When the phase plate 2 having diamond slits are used, the signal waveform (c) that respective outputs of a photodiode show in different phases for the displacement of the code plate 1 has less higher harmonics and is closer to a sine waveform than a triangular wave (a). Consequently, use of this phase plate reduces the influence of higher harmonic components to reduce the nonlinear error of the displacement transducer greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an improvement in a displacement transducer that detects mechanical displacement using light.

[Prior art]

A type of such displacement converter, which is an improved version of the conventional tube-tally encoder, is disclosed in Japanese Patent Application No. 58-8659.
This is the displacement transducer described in No. 1. This uses a plurality of divided photodiodes as a light receiving element that receives light that has passed through one transmissive slit, and a translucent transducer arranged at a predetermined pitch on these seven photodiodes. A position plate with slots and grooves is installed, and Figure 1 is an explanatory diagram of its configuration.
In this figure, 1 is a hood plate, 11 is a plurality of transparent slits arranged circumferentially at a predetermined pitch on this code plate, 3 is a light source, and 30 is a light beam for making the light beam from the light source 3 into a parallel beam. A lens 4 is an image sensor that receives light (slit image) from a light source 5 that has passed through a transparent slit 11. Here, for the purpose of briefly explaining the operation, a photodiode divided into four parts is used. .44, and a phase plate 2 having slit holes arranged at a predetermined pitch is installed on this photodiode. SWl, SW
2, SW5, and SW4 are switches that sequentially take out signals from each of the four divided photodiodes 41 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 6 is a bandpass filter that extracts the fundamental wave component of the output signal from the amplifier 5.

FIG. 2 shows the transparent slits 21° 22 provided in the phase plate 2,
23.24 and photodiodes 41 to 44 divided into four
FIG. As shown in this figure, the arrangement pitch of the light-transmitting slits 21, 22, 23, 24 (indicated by solid lines) is 41, 42°, 45°.
．． 44 (indicated by broken lines), and the translucent slits and grooves (indicated by diagonal lines) 11 provided on the code plate 1
The arrangement pitch P is 5/M. Note that the slit width of each slit hole 24 is set to P/2 here.

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

The light from the light source 3 is converted into a parallel beam by the bins 30, and then passes through the light-transmitting slots of the code plate 1, the light-transmitting slots of the code plate 1, the light-transmitting slots of the phase plate 2,
) 21M-24, and the 4-split photodiode 41
An image of the light-transmitting pickpocket 11 is formed on .about.44. In the four-divided photodiodes 41 to 44, each switch s'
w1-8W4 are turned on and off (on time is T) sequentially at the timings shown in FIGS. 3(a)-(d), and signals from each photodiode 41-44 are sequentially taken out. Amplifier 5 amplifies 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(,). In such a staircase wave signal e5, the number of bandpasses 7 corresponds to the repeating frequency that sequentially drives each of the switches SW1 to SW4. Here, when the code plate 1 rotates in accordance with 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 6 obtained from the intrusion filter is changed to Depending on the amount of movement of the image, that is, the displacement of the code plate, the image is shifted, for example, by Φ as shown by the broken line. When the code plate 1 rotates by one pitch P of the arrangement pitch of the light-transmitting slits 11, the amount of phase shift of the sine wave signal e6 becomes 2π.

Therefore, by measuring this phase shift amount Φ, it is possible to determine the rotation angle within the arrangement pitch of 2 of the light-transmitting slits 11 formed in the code plate 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 e6 obtained from the bandpass filter 6 by 100 to 10
The operation is to interpolate about 00. That is, the sine wave signal e6 is passed through a phase-locked loop (PLL) 7 having a frequency divider 72 with VN (N is a division ratio) in the feedback circuit.
1, and here N times f is applied to the up/down counter 9 after passing through the simultaneous pulse inhibiting circuit 8.

The frequency of the signal f multiplied by N by PLL71 is higher than f by 1
When the cord body 1 rotates in the direction (f+Δf) in which g
, is lower than f (f - Δf) 111g
When the e-do body 1 rotates, it counts down. Therefore, from the output of the up/down counter 9, the amount of phase shift, that is, the rotation angle of the code plate 1, can be interpolated with a high resolution of 1P □000, for example, if the frequency division ratio N is 1000. .

A displacement transducer with such a configuration has the advantage of being unaffected by its relatively simple structure.
24 is a characteristic curve diagram showing signal waves L e D outputted from each of the photodiodes 41 to 44 (with different phases) with respect to the displacement of the code plate 1 in the case of the slot shape of No. 24. FIG. . Each time the displacement θ of the code plate 1 increases by the pitch P, the same repeated triangular waveform a appears. If this triangular wave a is expanded into a 7-lier series, it becomes 3θ, 5θ, etc.
Since the shift amount Φ of the sine wave signal e in FIG. 3 is not exactly proportional to the displacement θ, the shift amount Φ of the sine wave signal e in FIG.

[Purpose of the invention]

The present invention has been made to solve these problems, and an object of the present invention is to reduce non-linear errors in the above-mentioned displacement converter.

[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 to the transparent slits of the code plate. , an image consisting of a plurality of divided photodiodes, a phase plate having slots and holes installed on each photodiode and arranged at a predetermined pitch, and means for sequentially extracting signals from each photodiode. A sensor, a band-pass filter that extracts a fundamental wave component from a signal obtained from the image sensor, an output signal of this band-pass filter and a driving signal of the image sensor are inputted, and the fundamental wave component is extracted based on the amount of phase shift of the fundamental wave component. A phase measuring means for measuring the displacement of the code plate is provided, and at least one of the phase plate and the code plate is arranged so that a change in the output signal of the photodiode corresponding to the displacement of the code plate has a waveform with few high frequency components. The present invention resides in a displacement transducer characterized by having one of the slit shapes.

〔Example〕

The present invention will be explained in detail below using the drawings.

FIG. 6 shows the slit shape of the phase plate 2 used in the displacement converter of FIG. FIG. 2 is a characteristic curve diagram showing a signal waveform C shown in different phases. Triangular waveform a in FIG. 5 is also shown for comparison. In signal waveform C, the equation of the curve in each range within one pitch is as follows.

P　P.

−kuθ〈 , e=4Aθ2+4Aθ once 4 2 DP
2 In other words, the curve C has a waveform closer to a sine wave with fewer harmonics than the triangular wave a. As a result, if such a phase plate is used in the displacement transducer shown in Fig. 1, the shift amount Φ of the sine wave signal e shown in Fig. 3 will be less influenced by harmonic components, and the nonlinearity of the displacement transducer will be reduced. Errors are significantly reduced.

Waveform C in FIG. 7 has a shape closer to the sine wave in FIG. 5 than the triangular wave α, but they do not match exactly. Fifth
Although the shape of the phase plate that produces the sine waveform shown in the figure is a curve with a complicated relationship, it does not contain any harmonic components, so it is possible to completely eliminate nonlinear errors in the displacement transducer. Therefore, in order to reduce the non-linear error of the displacement transducer, the waveform of the change in the output signal of the diode with respect to the displacement of the code plate 1 should be close to the sine wave shown in FIG. Any slit or groove shape that produces a shape with few harmonic components can be used.

In the above embodiment, only the slit shape of the phase plate 2 is devised, but the through-hole slit 1 of the code plate 1
A similar effect can be obtained by devising the shape of 1.

〔Effect of the invention〕

As described above, according to the present invention, a displacement transducer with small nonlinear errors can be easily realized. It also has a relatively simple configuration, and has features such as high resolution and fast response.

[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 operation waveform diagram. FIG. 4 is a configuration block diagram showing an example of a phase shift amount measuring circuit, FIG. 5 is a characteristic curve diagram showing changes in the output signal of the photodiode with respect to the displacement of the code plate 1, and FIG. 6 is an embodiment of the present invention. FIG. 7 is a characteristic curve diagram. 1... Code plate, 11... Translucent slit, 3...
Light source, 4... Image sensor, 41-44... 4-division photodiode, SW1-8W4... Switch,
6... Bandpass filter, θ... Displacement, eD...
・Photodiode output signal. "ζ, ° slander 2'

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 consisting of a phase plate having slots and holes arranged in a row and a switch means for sequentially extracting signals from each photodiode; a bandpass filter for extracting a fundamental wave component from the signal obtained from the image sensor; A phase measuring means is provided which inputs the output signal of the band-pass filter and the drive signal of the image sensor and measures the displacement of the code body based on the amount of phase shift of the fundamental wave component. A displacement transducer characterized in that at least one of the phase plate and the code plate has a slit shape so that a change in the output signal of the photodiode corresponding to displacement has a waveform with few high frequency components.