JPS60239621A - Deviation convertor - Google Patents

Abstract

PURPOSE:To obtain a deviation convertor of high resolving capacity and prompt response, by using a linear phase filter as a filter for removing higher hormonics involved in an input from an image sensor. CONSTITUTION:An output signal of an image sensor 4 is removed of its higher hormonics in a linear phase filter 61. Namely, in the filter 61, as group delay time becomes constant (A phase changes linearly against a frequency) in a constant frequency range, a phase error does not occur in a filter output, if the group delay time is assumed constant within a range: fsig=F0+ or -DELTAf, where DELTAf is defined as a fluctuation range of output frequency fsig. The output signal of the filter 61 is calculated on its phase shift quantity by the reference clock fC in a phase measuring circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a signal processing circuit in a displacement transducer that detects mechanical displacement using light.

(Prior Art) A displacement converter described in Japanese Patent Application No. 58-86391 is a type of optical displacement converter that improves the resolution and response speed of a conventional rotary encoder. This uses a photodiode divided into multiple parts as a light-receiving element that receives light that has passed through a light-transmitting slit, and a phase plate having light-transmitting slits arranged at a predetermined pitch is installed on the photodiode.
FIG. 2 is an explanatory diagram of its configuration. In this figure, 1 is a code plate, 11 is a plurality of translucent slits arranged in the circumferential direction with predetermined bits on the code plate 1, 3 is a light source, and 30 is a light beam from this light source 3 converted into a flat beam. 4 is an image sensor that receives the bright slit image from the light source 3 that has passed through the transparent slit 11. Here, for the sake of explaining the operation briefly, a photodiode divided into four parts is used. 43 and 44, and a phase plate 2 having slit holes arranged at a predetermined pitch is installed on the photodiode. SW+ to 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 that is applied via each switch SW + to SW4; 6 is an amplifier 5;
This is a bandpass filter that extracts the fundamental wave component of the output signal from the .

FIG. 3 shows light-transmitting slits 21°, 22.
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 the solid line 'g) is the same as that of the four-part photodiode 41 (42, 43°).
,44<indicated by a broken line'? The translucent slits (indicated by diagonal lines) that are equal to the array pitch of j) and provided in the code plate 1
It is formed so that the arrangement pitch P of 11 is r5/4P. Incidentally, the slit width of each of the slit holes 21 to 24 is set to P/2 here.

The operation of the apparatus configured as described above will now be described with reference to the operational waveform diagram of FIG. 4.

The light from the light source 3 becomes a parallel beam at the lens 3o, passes through the light-transmitting slit 11 of the code plate 1 and the light-transmitting slits i~21-24 of the phase plate 2, and is transmitted to the 4-split photodiode 4.
1 to 44'', the image of the transparent slit 11 is formed. Each switch SW + -SW4 is
) are sequentially turned on and off (on time is the key), and signals from each photodiode 1z41 to 44 are sequentially taken out. Amplifier 5 amplifies this signal. As a result, the output signal e5 of the amplifier 5 is as shown in FIG.
), a step waveform is formed in which the magnitude changes stepwise each time each switch SW + to SW 4 is turned on. When such a staircase waveform e5 is applied to the bandpass filter 6, a sine wave signal e6 as shown in FIG. 4(f) is obtained. The fundamental frequency of this sine wave signal e6 corresponds to the repetition frequency for sequentially driving each of the switches SW+ to SWa. Here, when the code plate 1 rotates according to the displacement to be measured, each photodiode 41
The image formed on ~44 moves, and the bandpass filter 6
The phase of the sine wave obtained from (g and e6 is the amount of movement of the image,
That is, in accordance with the displacement of the code plate, it is shifted by Φ, for example, as shown by the broken line. Code plate 1 has transparent slit 1
When the rotation J is increased by 1 pitch P of the arrangement pitch of 1, the phase shift ff)G of the sine wave signal e6 becomes 2π.

Therefore, by measuring this phase shift mΦ using a counting circuit or the like, it is possible to determine the rotation angle within the arrangement pitch P of the light-transmitting slits 11 formed in the code plate 1.

A displacement transducer with such a configuration has a relatively simple configuration,
Although it has the advantage of having high resolution, high-speed response, and being unaffected by changes in the intensity of the light source and changes in sensitivity of the elements constituting the image sensor, it has the following problems.

In a displacement transducer with the above configuration, a band pass filter (BPF) or a [1-pass filter (LP) is used to remove harmonic components from the stepped output waveform of the image sensor.
F), but since the output frequency from the image sensor 4 is FM modulated depending on the rotational speed and direction of the code plate 1, and changes within a range of, for example, t: 5kHz±2kHz, the above-mentioned filter 6 If the phase characteristic of is non-linear with respect to frequency, an error will occur in the displacement output as shown in FIG. That is, if the phases of the filter output and the output signal of the image sensor 4 match at the output frequency f0 of the image sensor 4, and the output frequency of the image sensor 4 changes by Δf, the group delay time of the filter changes depending on the frequency. Therefore, the output of the filter (ffi (dotted line)) has a phase delay of Δt=Δt corresponding to Δf (FIG. 5(a)).

Conversely, when the output frequency of the image sensor 4 changes by 1 Δf, a phase delay of Δ[-8T' occurs in the output No. 3 of the filter (FIG. 5(b)). Such a difference in delay time causes a Qgt difference in the displacement output, so it is preferable to minimize it as much as possible.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned problems, and realizes a displacement transducer using light that detects mechanical displacement without dynamic errors in output. The purpose is to

(Means for Solving the Problems) The displacement converter of the present invention includes a code plate in which a plurality of transparent slits are formed arranged in a predetermined bit, and a light beam that projects parallel light onto the transparent slits of the code plate. This image is an image sensor consisting of a plurality of light-receiving elements, a phase plate having slit holes placed on each light-receiving element and arranged at a predetermined pitch, and a switch means for sequentially extracting signals from each light-receiving element. A linear phase filter extracts the fundamental wave component from the signal obtained from the sensor, and a reference clock synchronized with the output signal of the linear phase filter and the drive signal of the image sensor is input, and the phase shift of the fundamental wave component is calculated based on the phase shift of the fundamental wave component. The present invention is characterized by comprising phase measuring means for measuring the displacement of the code plate.

(Function) By using a linear phase filter as a filter for removing harmonics contained in the output from the image sensor, it is possible to eliminate phase errors in the filter and realize a displacement converter without dynamic errors.

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

FIG. 1 shows one embodiment of the displacement transducer according to the present invention.
FIG. 2 is an explanatory diagram of a main part configuration of an improved signal processing circuit in the displacement converter shown in the figure. 61 is the image sensor 4 (
7 is a phase measuring circuit that counts the phase shift m of the output signal of the linear phase filter 61 using a reference clock fc, and 8 is a reference clock. fc
This is a switch drive circuit consisting of a frequency dividing line and the like that sends a scanning signal synchronized with the image sensor 4 to the image sensor 4.

Next, its operation will be explained. A linear phase filter 61 removes harmonic components from the output signal of the image sensor 4. FIG. 6 is a characteristic curve diagram showing gain characteristics (a) ci, i and group delay time characteristics (b) of the beam near-phase filter. As is clear from (b), in the linear phase filter, the r-group delay time is constant within a certain frequency range (1, that is, the phase changes linearly with the frequency, so the output frequency f519 of the image sensor 4 changes). If the range is Δ[, then if the group delay time is constant within the range of fstg=f□±Δf, no phase error will occur in the filter output. The phase shift m is counted with high resolution.

In the above embodiment, a four-division photodiode is used, but the number of divisions may be three or more.

Furthermore, although each of the above embodiments assumes application to a rotary encoder, it can also be applied to a linear displacement encoder.

(Effects of the Invention) As described above, according to the present invention, a displacement converter with no dynamic error in output can be realized with a simple configuration using a method of detecting mechanical displacement using light. It also has features such as high resolution and fast response.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the main part configuration of one embodiment of the displacement converter according to the present invention, FIG. 2 is an explanatory diagram of the configuration of a conventional displacement converter, and FIG. 3 is a partial explanation of the displacement converter of FIG. 2. Figure 4 is the second
Figure 5 is an operating waveform diagram to explain the operation of the device shown in Figure 5. Figure 5 is an operating waveform diagram to illustrate the operating characteristics of a conventional filter. Figure 6 is a characteristic curve diagram to illustrate the operating characteristics of a near-phase filter. be. 1... Code plate, 2... Phase plate, 3... Light source, 4
...Image sensor, 7...Phase measurement means, 8...
・Switch drive circuit, 11...transparent slit, 21~
24... Slit hole, 41-44... Light receiving element, 6
1...Linear phase filter, SWI~SW4...
- Switch means, fC... reference clock.

Claims (1)

[Claims] 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 to the light-transmitting slits of the code plate, a light-receiving element divided into multiple parts, and a light-receiving element installed on each of the light-receiving elements at a predetermined pitch. An image sensor consisting of a phase plate having slit holes arranged in a phase plate and a switch means for sequentially extracting signals from each light receiving element, a linear phase filter for extracting a fundamental wave component from a signal obtained from this image sensor, and a linear phase filter for extracting a fundamental wave component from a signal obtained from this image sensor. A displacement converter comprising phase measuring means for inputting a reference clock synchronized with an output signal of a phase filter and a drive signal of the image sensor and measuring the displacement of the code plate based on the amount of phase shift of the fundamental wave component.