JP2003247864A - Scale for absolute encoder, its manufacturing method, and absolute encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a small-sized absolute encoder by using a scale which generates an absolute signal by a single track. <P>SOLUTION: A change in the amplitude of a signal caused by changing the scale depth (h) on the scale 20 is used as a long-period track signal, and is used together with a plane signal obtained from a short-period scale. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an absolute encoder scale for outputting a detected position as absolute data, a manufacturing method thereof, and an absolute encoder, and more particularly to an absolute encoder scale capable of generating an absolute signal in a single track, The present invention relates to a manufacturing method and an absolute encoder.

[0002]

2. Description of the Related Art There are two types of encoders for detecting the position of a machine movable part such as a tool or a table of a machine tool, an incremental type and an absolute type (absolute value type).

The incremental type position detecting encoder obtains the movement displacement from the number of repetitions of a periodic signal generated when the scale and the detector are moved relative to each other, the interpolated signal of the signal, or the combination thereof.

On the other hand, in the absolute type position detecting encoder, as shown in FIG. 1, a plurality of tracks 11, 12, 13, 14 formed on the same substrate 10 and capable of generating signals of different periods or different waveforms. The signals obtained from ... Are combined, or a signal obtained by combining them by some method is taken out, and a unique signal is detected at each position within the measurable range (range) for detection.

[0005]

In the former incremental type position detection encoder, the current position of the mechanical movable portion disappears when the power is turned off. For this reason, after the power is turned on, the machine moving part is returned to the origin, and the contents of the current position counter are cleared to 0 so that the current position of the machine moving part matches the contents of the current position counter. I was trying to do. However, the method of returning to the origin each time the power is turned on is not preferable because the operation becomes complicated.

On the other hand, according to the latter absolute type position detecting encoder, the current position of the movable part of the machine does not disappear even if the power is cut off, and the origin returning operation after the power is turned on is unnecessary. This has the advantage that position control can be performed immediately.

However, in the absolute position detecting encoder, a plurality of tracks 11, 12,
Since 13 must be provided on the same substrate 10, there is a problem in that the scale area increases, which is disadvantageous in terms of downsizing the encoder.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to be able to generate an absolute signal with a single track.

[0009]

According to the present invention, in an absolute encoder scale, a change in signal amplitude caused by changing the scale depth or optical density on the scale in the longitudinal direction is used as a long period track signal, and a short period scale signal is used. The problem is solved by using it together with the phase signal obtained from the above.

According to the present invention, a lattice material is formed on a support, a resist is applied to the surface of the lattice material after the film formation, and graduation stripes having a desired pitch are exposed by changing energy for each graduation. ,
Using the resist pattern after the development process as a mask,
It is intended to provide a method for manufacturing a scale for an absolute encoder, which comprises etching a grating material and peeling off the remaining resist.

The present invention further provides an absolute encoder including the above scale.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a vertical sectional view of the scale 20 used in this embodiment, and FIG. 3 is a plan view thereof. This scale 2
Reference numeral 0 is composed of a support 22 such as glass, and a thin film 24 that has been etched.

As shown in FIG. 3, the pitch p of the scales (phase grating) 26 formed parallel to the scale width direction is constant, but the grating depth h is a film forming the scales as shown in FIG. In the range of thickness, while slightly different between adjacent lattices,
It changes sequentially in the longitudinal direction.

Since the diffraction efficiency of the scale depends on the grating shape, the light source wavelength of the encoder, the polarization plane grating period, the duty, etc., when determining the grating depth h, the diffraction efficiency changes monotonically with the grating depth. To select each parameter. In this embodiment, the lattice shape is rectangular.

The scale 20 can be produced by a process as shown in FIG. 4, for example.

That is, first, in step 100, the support 22
A lattice material such as the metal thin film 24 is formed thereon by a method such as vacuum deposition or sputtering.

Next, at step 102, a resist is applied to the surface of the lattice material after film formation. As the resist, a photo resist, an electron beam (EB) resist, or the like is selected according to the exposure method.

Next, at step 104, a grid pattern having a predetermined pitch is exposed by changing the exposure energy for each pattern. The difference in the depth of the resist groove obtained in this step is
This is reflected in the final lattice depth h. Here, as a method of changing the exposure energy, for example, in the case of mask exposure using light, a halftone mask having a different light transmittance for each grating is used, and in the case of EB drawing, a variable dose dose exposure is used. The dose (exposure energy) may be changed for each grid.

Next, at step 106, dry etching, which has high anisotropy in the depth direction, for example, ion etching is performed on the lattice material such as a metal thin film using the resist pattern that has undergone the development process as a mask. As a result, a phase grating having a step that reflects the resist film thickness is formed. The lattice step depends on the selection ratio between the lattice material used and the resist.

Then, in step 108, the remaining resist is stripped to complete the scale having the phase grating as shown in FIG.

FIG. 5 shows a conceptual diagram of a signal output using the detector including the scale 20 and the photoelectric sensor. Thus, as the scale and the detector move relative to each other, a repetitive signal due to the grating pitch is obtained, and at the same time, a signal whose amplitude changes according to the grating depth is obtained.

As shown in FIG. 2, two photoelectric sensors 28 provided with a 90 ° phase difference for identifying the moving direction.
A phase (0 °) signal obtained by A, 28B, B phase (90
Figure 6 shows the Lissajous locus based on the (phase difference) signal. In practice, a signal in a good S / N range can be obtained as a displacement signal by using a signal processing circuit described later.

The configuration of a signal processing circuit for obtaining position information from the output signals of the photoelectric sensors 28A and 28B is shown in FIG.
Shown in. The two-phase output signals from the photoelectric sensors 28A and 28B have a spatial phase difference of 90 ° with respect to the movement of the scale. One signal is called an A-phase signal and the other signal is called a B-phase signal.

A / D converter 3 for the A-phase signal and the B-phase signal
The data after A / D conversion by 0A and 30B is Va and Vb.
Then, the amplitude calculating means 34 in the MCU 32 can calculate the amplitude A by the following arithmetic expression.

A = √ (Va ² + Vb ² ) ... (1)

Further, the phase calculating means 36 can calculate the phase θ by the following arithmetic expression.

Θ = tan ⁻¹ (Vb / Va) (2)

However, in this calculation, θ is −π / 2.
Since it takes only a value from + π / 2 to + π / 2, the phase from −π to π is found according to the magnitude relationship between Va and Vb.

In the absolute phase synthesizing means 38, the phase θ is 2π.
By weighting the change in the amplitude A when turning the amplitude A and adding it to the phase θ, the phase information of the absolute value (ABS) signal as shown in FIG. 6 is obtained.

The phase position conversion means 40 converts 2π into the position information with the input signal pitch λ.

Although the present invention is applied to the reflection type scale in the above-described embodiment, the application of the present invention is not limited to this. For example, the optical density is changed so that the amount of transmitted light changes in the longitudinal direction. It is also possible to realize a transmissive scale by using a scale adapted to change in the longitudinal direction. Further, it is applicable not only to the linear scale but also to the rotary scale.

[0033]

According to the present invention, a scale capable of generating an absolute signal with a single track can be realized. Therefore, a small absolute encoder can be realized by using such a scale.

[Brief description of drawings]

FIG. 1 is a plan view of a scale showing a configuration of an example of a conventional absolute encoder.

FIG. 2 is a vertical sectional view showing a configuration of an embodiment of an absolute encoder scale according to the present invention.

FIG. 3 is a plan view of the same.

FIG. 4 is a flow chart showing a manufacturing procedure of a scale for an absolute encoder according to the present invention.

FIG. 5 is a time chart showing an example of an output waveform of an absolute encoder using the scale.

FIG. 6 is a diagram showing a Lissajous locus similarly obtained by the A-phase signal and the B-phase signal.

FIG. 7 is a block diagram showing a configuration of a signal processing circuit for obtaining position information from an encoder output signal in the embodiment.

[Explanation of symbols]

20 ... Scale 22 ... Support 24 ... Thin film 26 ... Scale (phase grating) 28A, 28B ... Photoelectric sensor (detector) 32 ... MPU 34 ... Amplitude calculation means 36 ... Phase calculation means 38. Absolute phase synthesizing means 40 ... Phase position conversion means

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Claims (3)

[Claims] 1. A change in signal amplitude caused by changing the graduation depth on the scale or the optical density in the longitudinal direction is used as a long period track signal and is used together with a phase signal obtained from a short period graduation. Scale for absolute encoder. 2. A film of a lattice material is formed on a support, a resist is applied to the surface of the lattice material after the film is formed, and graduation stripes having a desired pitch are exposed by changing energy for each graduation, and a developing step is performed. Using the finished resist pattern as a mask,
A method for manufacturing a scale for an absolute encoder, which comprises etching the lattice material and peeling off the remaining resist. 3. An absolute encoder comprising the scale according to claim 1.