JPS58157203A - Optical device for generating sinusoidal wave of low harmonic wave content - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Optical devices are often used to generate electrical signal waveforms that are subsequently processed by electronic circuitry. A position encoder is one example of a device that uses such a device, and usually includes two mutually movable members each bearing some type of pattern. A light source and a photosensitive device cooperate with the two members to generate electrical signals that can be used to determine the direction and extent of relative movement of the two members.

For most purposes, square wave signals are suitable, especially when used to operate digital circuits. However, complex analog electronic circuits may be used to operate on the signals. Under the circumstances described in item 7, it is preferable that the optically derived electrical signal be a sine wave with as little harmonic content as possible.

According to the present invention, an optical device that generates a sinusoidal waveform with low harmonic content includes a first member having a pattern in which the transmittance varies sinusoidally along the axis, and a width along the axis that is a second member with an aperture between % and % of the wavelength of the sinusoidal pattern; a photosensitive element that senses light passing from the light source through the aperture and the pattern; and a photosensitive element in a direction parallel to the axis. and a mechanism for producing relative movement between the first member and the second member.

According to the present invention, the first member is supported by one of two objects that can move relative to each other in a direction parallel to the axis, and the second member is supported by the other of the two objects. A position encoder is provided which includes the device described in the previous section carried thereon.

The invention will now be described with reference to the accompanying drawings.

Referring to FIG. 1, a first member 10 made of an opaque material or having an opaque coating comprises:
A pattern is formed in the form of variable width slits 11 with sinusoidal edges. The second member 12 is formed with an opening 1 having a width approximately equal to a half wavelength of the sine wave pattern. When the two members are moved relative to each other in a direction parallel to the length of the slit 11, as indicated by the arrow 14, the amount of light passing through both the pattern and the aperture varies sinusoidally.

FIG. 2 shows the other components necessary to generate the sinusoidal electrical signal. The two members 10 and 12 are arranged adjacent to each other and parallel to each other, with a light source 15 placed on one side,
On the other side is a photosensitive element 16. Such a configuration is well known, and optical elements such as lenses are omitted.

In order to generate the required waveform, it is necessary to create relative movement between the two members. This is most easily accomplished by making one of the members disk-shaped so that it can rotate, while the other member is fixed. Since the opening 15 is easier to make, one circular plate has many openings,
It is convenient to make the fixing member to have a sinusoidal pattern. The figure shows a device like ;f:, 17
There is a fixed member, ie, an index, at 18, and a rotating disk, ie, a scale, at 18.

In practice, a large number of apertures overlapping a large number of sinusoidal patterns on the index are scaled to avoid errors caused by non-uniformity of the light source or non-uniformity of the response of the photosensitive element over its sensitive area. It is convenient to have one. The centers of the apertures must be spaced apart by the wavelength of the Cζ sine wave pattern so that the amount of variation in light that passes through each aperture matches each other. In the case of a rotating scale, the apertures must be arranged radially, but not exactly parallel to each other, and the sinusoidal pattern must likewise be arranged at wavelengths commensurate with the spacing of the apertures. Figure 4 is.

A portion of such a scale and index is shown. As shown in FIG. 4, the index 17 is
It has three sinusoidal patterns arranged parallel to each other. Scale 18, only a portion of which is shown, contains a number of apertures, four in the illustrated case, each extending over a half cycle of each sinusoidal pattern. A single photosensitive element is sensitive to light passing through all four apertures. For this purpose, it is also possible to apply a well-known technique for removing the DC offset voltage from the 10 sine wave output, which is a well-known technique for removing the above-mentioned error. One technique involves using the same photosensitive element that is also sensitive to light passing through a second set of sinusoidally varying strips. These cooperate with a pair of slots in which the photosensitive elements are arranged so that the amount of variation in light received from the two sets of IJ tubes is in opposite phase.

The width of the aperture 1 need not be exactly half the wavelength of the sinusoidal pattern. The width between 1 wavelength and % is appropriate, but
The centers of the apertures must be one wavelength apart. A particular advantage of the half-wavelength aperture is the complete cancellation of even harmonics from the output of the detector and the reduction of odd harmonics by a multiple equal to their harmonic number. The presence of harmonics is due to imperfections in the shape of the sinusoidal pattern. When other slit widths are used, the degree of reduction in harmonic content becomes smaller.

As already suggested, the sine wave generation mechanism described above can be used as a position encoding device. In the case of the embodiments of FIGS. 3 and 4, they can be used as shaft angle encoders using suitable electronic circuits. However, in order to determine the direction of rotation of the five discs, it is necessary to add another pattern or set of patterns. These are also sinusoidal envelopes, but are % wavelength shifted to produce a cosine wave output in conjunction with independent sets of apertures and an independent photosensitive element. By combining the sine waveform and cosine waveform, it becomes possible to determine the rotation direction of the disk. FIG. 5 shows the scale and index relationships of an axial encoder that produces sine and cosine outputs. A similar device may be used in a linear position encoder, in which case the scale is a straight elongated member with parallel apertures, rather than a disk with radial apertures.

The required sinusoidally varying light transmission may be provided by means other than a transparent outer strip with sinusoidal edges. For example, many cases where the mark/space ratio changes.

It is possible to achieve the same effect using a number of parallel lines.

Alternatively, a film or coating with a sinusoidally varying density may be used.

The requirements for generating a low harmonic sine wave depend on the relative motion between the two aforementioned members, and it does not matter which member is moving and which is stationary. The generated sine (or cosine) waveform has very low harmonic content;
can be processed electrically with little or no distortion.

[Brief explanation of drawings]

FIG. 1 shows the shape of the pattern on the first member, and FIG.
An example of an optical configuration. 5 shows an actual form of the invention; FIG. 4 shows details of an alternative form of the embodiment of FIG. 5; FIG. : Shows part of the incorporated axis encoder. 1, 0 - Part 1 member 11 - Variable width slit 12 - Second member 1 Another part 2 member opening 15 - Light source 16 - Photosensitive element 17 -
Fixed member 18-one rotation disk. Fig・1・Fig, 2゜0 Fig, 4゜

Claims (1)

[Claims] 1. A first member having a pattern whose light transmittance varies sinusoidally along the axis, and a width along the axis between A and % of the wavelength of the sinusoidal pattern; a second member with an aperture; a photosensitive element sensitive to light passing through the aperture and the pattern from a light source; and a mechanism for generating relative motion between the
An optical device that generates a sine wave with low harmonic content. 2. The pattern of sinusoidally varying translucency comprises a transparent strip of variable width having edges formed by two sinusoidal waveforms of the same wavelength and opposite phase.
Optical device as described in section. The optical device according to claim 1 or 2, wherein one of the first member and the second member is in the shape of a rotating disk, and the other member is stationary. The stationary member is the first member provided with the pattern, and the rotating disk has a plurality of apertures, the centers of the apertures being spaced apart from each other by the wavelength of the pattern. The optical device described in item (3). 5. The optical device according to any one of claims 1 to 4, wherein the width of each aperture along the axis is half the wavelength of the sine wave pattern. 6. The optical system according to any one of claims 1 to 5, wherein the first member has a plurality of sinusoidal patterns that are in phase with each other, and a portion of each pattern is aligned at the same time as the opening. Device.