JPH0493719A - Absolute-type encoder - Google Patents

Abstract

PURPOSE:To make it possible to perform accurate measurement of the amount of displacement and the amount of rotation by emitting coherent light on a small-pitch pattern, and emitting incoherent light on a pattern having a relatively large pitch. CONSTITUTION:The coherent light is emitted from a linear light source device 1 on a small-pitch pattern. The reflected light forms the shade pattern on an optical sensor 11. Lower-bit signals are generated in the light receiving parts of the sensor 11 in response to the movement of the corresponding shade pattern. Incoherent light is emitted from a light source 1' on an aperture 1A'. The light which is taken out of each opening part is cast into a pattern having the relatively large pitch. The shade pattern which is generated in the pattern having the relatively large pitch is received with a sensor 11'. Bit signals are generated in large light receiving parts in response to the movement of the corresponding shade pattern. Thus, the upper bit signals are obtained from the sensor 11'. The absolute position of a scale, i.e. a rotary shaft 7, can be detected by the combination of the bit signals corresponding to the code pattern.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an absolute encoder.

[Prior art] In an encoder that detects the amount of displacement or rotation of a moving object, a scale is integrated with the moving object and is displaced or rotated, and the displacement or rotation of a code pattern formed on the scale is optically detected. .

The scale of an encoder known as an absolute encoder is provided with a plurality of tracks so that the absolute position of the scale can be detected, and the pitch of the pattern formed for each track is different from each other. The entire pattern formed for each track is called a code pattern. As code patterns, binary coded decimal codes and Gray codes based on alternating binary codes are known.

Signals are detected from multiple tracks simultaneously, and the absolute position of the scale is known from a combination of the detected signals.

In this way, a plurality of patterns with different pitches are formed on the scale of the absolute encoder. The signal from the pattern with the smallest pitch is called the least significant bit signal, and the smaller the pitch of the pattern that provides the least significant bit signal, the more finely the amount of displacement or rotation can be detected.

Conventionally, the pitch of the pattern that provides the least significant bit signal in the scale of an absolute encoder is several tens of μm.
It was about.

However, recently, a method has been proposed in which a shadow pattern is generated by irradiating light onto a grating pattern with an extremely fine pitch, and the amount of displacement or rotation of the grating pattern itself is detected by detecting the displacement or rotation of this silhouette pattern. The pitch of the pattern giving the above least significant bit signal is 0.1μ
Up to about m is now allowed.

In other words, when coherent light from a linear light source or incoherent light extracted through an extremely fine slit or an elliptical or circular fine aperture is irradiated onto a fine-pitch grating pattern under predetermined conditions, the grating will form. The transmitted light or reflected light from the pattern creates a silhouette pattern that is an enlarged version of the lattice pattern, so by detecting the displacement or rotation of this shadow pattern, it is possible to measure the amount of displacement or rotation of the lattice pattern itself. be.

[Problems to be Solved by the Invention] When constructing an absolute encoder using a silhouette pattern as described above, if all of the plurality of light sources are laser light sources, the production cost of the encoder will be high.

The present invention was made in view of the above-mentioned circumstances, and
The purpose of the present invention is to provide a new absolute encoder that uses a scale with an extremely fine pitch pattern and is capable of extremely high-precision detection, and can be realized at low cost.

[Means for Solving the Problems] The absolute encoder of the present invention includes a scale having a code pattern, a light source device that irradiates light to the code pattern on the scale, and a light source device that emits light from the light source device according to the scale. and a light receiving device that detects a shadow pattern generated by reflected light or transmitted light.

The "light source device" includes a linear light source device that emits coherent light, a light source that emits incoherent light, and an aperture that converts the incoherent light from the light source into light that can generate a silhouette pattern.

A pattern with a small pitch on the scale is irradiated with coherent light from a "linear light source device", and a pattern with a large pitch is irradiated with "incoherent light from a light source extracted through an aperture".

The "linear light source" constituting the "linear light source device" is
This is disclosed in Japanese Patent No. 297513, and includes those in which the shape of the light emitting portion is not necessarily linear.

That is, as shown in FIG. 3, the pitch of the grating pattern 9 for generating the silhouette pattern is ξ, and the pitch of the light source 1 for irradiating the grating pattern with coherent light is ξ.
When the length of the light emitting section corresponding to the repeating direction of the grating pattern is d, a light source that satisfies 1/10≦(d/ξ)≦2(1) is called a linear light source. When the grating pattern 9 is irradiated with such a linear light source, the transmitted light or reflected light from the grating pattern 9 generates a pattern of strong and weak light intensity as shown in FIG. The period of the maximum value of the light intensity in this intensity pattern is the same as the lattice pitch in the lattice pattern, which is enlarged like a silhouette using a point light source. For this reason, this intensity pattern of light intensity is called a shadow pattern.

There is no particular restriction on the length of the light emitting part of the linear light source 1 in FIG. 3 in the direction perpendicular to the drawing. Therefore, the two-dimensional shape of the light emitting part of the linear light source 1 can be appropriately selected for d that satisfies the above relationship (1).

Silhouette patterns can also be generated by incoherent light. However, even if the grating pattern is directly irradiated with light from a light source that emits incoherent light, no shadow pattern is generated. In this case, incoherent light is extracted through the opening of the aperture and irradiated onto the grating pattern.

The "length in the direction corresponding to the repeating direction of the grating pattern" dA in this opening is 1/10≦(dA/ξ)≦2, as in the case of the linear light source described above.
If the relationship (2) is satisfied, a shadow pattern can be generated.

Therefore, the shape of the opening in the aperture is as follows:
For example, as shown in Figure 5, a narrow slit with a length dA (Figure 5 (a)), an elliptical shape with a major or minor axis diameter of dA (Figure 5 (b)), or a circular shape with a diameter dA. (Same figure (C
)) etc. are allowed.

As the shape of the scale, various shapes conventionally known or proposed as encoder scales are possible. That is, the scale may be a "linear scale" (claim 2), a "disk shape" (claim 3), a "cylindrical shape" or a "conical shape" (claims 4 and 5).

``Function'' As mentioned above, even with incoherent light, a shadow pattern can be generated by irradiating the light extracted through an appropriate aperture, but when the pitch of the grating pattern becomes small, the incoherent light The contrast of the generated shadow pattern will be low.

Therefore, in the present invention, patterns with a narrow pitch in the scale are irradiated with coherent light to generate a shadow pattern with high contrast, and patterns with a relatively large pitch are irradiated with incoherent light to generate a shadow pattern with a high contrast. It generates patterns.

As methods for forming scale patterns, printing can be applied for patterns with large pitches, well-known laser beam interferometry and photolithography can be applied for patterns with relatively fine pitches, and magnets can be used to form patterns with extremely fine pitches. - Lithography is suitable.

Magnet lithography forms an in-plane magnetized film such as Fe2O3 or a perpendicularly magnetized film such as CoCr on a substrate, writes a pattern as a magnetized pattern on this magnetized film with a magnetic head, and visualizes this magnetized pattern with a magnetic fluid. , is a method that will become established.

Examples of magnetic fluids include "magnetic colloidal fluid" in which fine ferromagnetic powder is dispersed in a surfactant, and "photocurable magnetic fluid" in which the fine powder is dispersed in a photocurable resin together with a surfactant. A "thermosetting magnetic fluid" dispersed in a thermosetting resin can be used.

As the ferromagnetic material, iron, Mn ferrite, Ba ferrite, CO ferrite, magnetite, etc. can be used. As the photocurable resin, N-vinylcarbazole, polyvinyl chloride, polystyrene, etc. can be used. As the thermosetting resin, epoxy resin, silicone resin, melamine resin, etc. can be used.

Since the photocurable resin is cured by light irradiation, when the magnetized pattern is visualized with a photocurable magnetic fluid, the code pattern can be fixed to the magnetized film simply by irradiating the visualized code pattern with light. Thermosetting resins harden when heated, so when the magnetization pattern is visualized with thermosetting magnetic fluid,
The code pattern can be fixed on the magnetized film simply by heating the visualized code pattern.

[Example] Specific examples will be described below.

FIG. 1(a) shows one embodiment of the present invention.

A rotating shaft indicated by reference numeral 7 in the figure is supported by a bearing 6 and is rotationally driven by a motor (not shown). This embodiment is an example of an absolute encoder configured using the rotary shaft 7 itself as a scale.

As shown in FIG. 2, a magnetized film is formed on a part of the circumferential surface of the rotating shaft 7. A part of this magnetized film is perpendicularly magnetized film region 1
5A, the other portion is formed as an in-plane magnetized film region 15B. A code pattern is written as a magnetization pattern in the magnetization film, but the perpendicular magnetization film region 15A has a code pattern of 0.
A pattern with a fine pitch of 1 to 10 μm is written, and a pattern with a medium fine pitch of about 10 μm or more is written in the in-plane magnetized film region 15B. A pattern with a large pitch is written in the in-plane magnetized film region 15B so that one pattern unit is "consisted of fine striped patterns in a direction crossing the track direction." The magnetization pattern written in correspondence with the code pattern is visualized using magnetic fluid,
By fixing the visualized pattern, a desired scale 8 as shown in FIG. 1(a) can be obtained.

FIG. 1(a) shows an absolute encoder composed of the scale thus obtained, a light source, and an optical sensor.

FIG. 1(b) shows a fine pitch pattern formed in the perpendicularly magnetized film region. Three tracks are shown in the figure. Each arrow indicates a track direction.

FIG. 1C shows three tracks of patterns with large pitches formed in the in-plane magnetized film region.

Each arrow indicates a track direction. Each unit of each pattern is composed of fine striped patterns that are repeated in a direction perpendicular to the track direction.

The fineness of the stripes may be set arbitrarily within a range that satisfies the condition that a desired bit signal can be generated from one unit of the pattern thus formed. That is, when one pattern unit is large, instead of filling it out, one pattern unit is formed by hatching "a fine striped pattern in a direction perpendicular to the track direction."

Note that the perpendicular magnetization film region and the in-plane magnetization film region may be made separately by changing the materials, but there are some cases in which they can be made separately depending on the substrate temperature and film thickness during film formation. The manufacturing process is also easy if a suitable manufacturing method is used.

The light source device includes a linear light source device 1 having an array of semiconductor lasers such as GaAs or AlGaAs, a light source 1' using an LED, and an aperture IA'.

The longitudinal direction of the light emitting portion of each semiconductor laser constituting the linear light source device 1 is made to correspond parallel to the lattice arrangement direction of the patterns in the code pattern 8, that is, the direction of movement of the code pattern 8 due to rotation of the shaft 7. Linear light source device 1
Coherent light is irradiated onto patterns with a fine pitch of 0.1 to 1100 IL, and the reflected light from these patterns with a fine pitch forms a silhouette pattern on the optical sensor 11 that enlarges each pattern like a silhouette. The optical sensor 11 has light receiving sections equal in number to the number of types of silhouette patterns to be generated, and each light receiving section emits a lower bit signal in accordance with the movement of the corresponding shadow pattern.

The light source 1' is composed of one or more LEDs, and incoherent light from the light source 1' is irradiated onto the aperture LA'. The aperture IA' is provided with the necessary number of apertures described above to convert the incoherent light into light capable of generating a silhouette pattern, and the light extracted from each aperture has a relatively large pitch of 100 μm or more. is irradiated onto a pattern with

Shadow patterns generated from these patterns with relatively large pitches are received by the optical sensor 11'. The optical sensor 11' also has light receiving sections equal in number to the number of types of silhouette patterns to be generated, and each light receiving section emits a bit signal in accordance with the movement of the corresponding shadow pattern. In this way, a high-order bit signal is obtained from the optical sensor 11'. The scale, that is, the absolute position of the rotating shaft 7 can be detected by a combination of bit signals corresponding to the code pattern.

The optical sensor 11.11' constitutes a light receiving device.

In the above example, the entire code pattern of the scale was formed by magnetic lithography, but not limited to this example, medium pitch patterns and large pitch pattern parts were formed by photolithography, laser light interferometry, or It may be formed by printing or the like.

Furthermore, the shape of the scale is not limited to the cylindrical one described above, but may also be a disk shape as shown in FIG. 4(a), a conical shape as shown in FIG. 4(b), or a well-known linear scale. But it goes without saying that it's a good thing.

[Effects of the Invention] As described above, according to the present invention, a novel absolute encoder can be provided. Since this encoder is constructed as described above, it is possible to measure displacement and rotation amounts extremely accurately.

Furthermore, since an inexpensive light source that emits incoherent light can be used as a part of the light source device, it can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of the present invention, FIG. 2 is a diagram for explaining the production of a scale in the embodiment of FIG. 1, and FIG. 3 is a diagram for explaining a silhouette pattern. , FIG. 4 is a diagram showing two examples of scales, and FIG. 5 is a diagram for explaining an aperture for obtaining light for generating a silhouette pattern from incoherent light. 100. Linear light source device, l', , light source, LA',...
Aperture, 700. Rotation axis as a scale, 81
0. Code pattern, 11.11 "90. Optical sensor that constitutes the light receiving device Akira Honda et al.] Cause (a) P) 4 Figure Karasu 2 Ku Ryo 5゜

Claims (1)

[Claims] 1. A scale having a code pattern, a light source device that irradiates light to the code pattern on this scale, and light generated by reflected light or transmitted light from the scale of the irradiated light from the light source device. The light source device includes a linear light source device that emits coherent light, a light source that emits incoherent light, and a light source that can generate a shadow pattern by using the incoherent light from this light source. and an aperture for illuminating a pattern with a small pitch in the scale with coherent light from the linear light source device, and a pattern with a large pitch being extracted through the aperture using incoherent light from the light source. An absolute encoder characterized by irradiation with light. 2. The absolute encoder according to claim 1, wherein the scale is a linear scale. 3. The absolute encoder according to claim 1, wherein the scale is disc-shaped. 4. The absolute encoder according to claim 1, wherein the scale is cylindrical. 5. The absolute encoder according to claim 1, wherein the scale is conical and the code pattern is formed on a conical surface.