JPS63187919A - Absolute encoder - Google Patents

Abstract

PURPOSE:To execute an absolute position detection being free from a read mistake, by constituting a conventional waveform shaping circuit and code converting circuit of a small number of grating tracks and photoelectric converting elements, instead of a signal interpolating circuit and a data processing logic circuit, respectively. CONSTITUTION:A light beam which is transmitted through a first scale 103 transmits through the second scale 104 provided with plural gratings t1, t2 and t3 corresponding to grating tracks t1, t2 and t3, respectively of the first scale 103, and converted to an electric signal by plural provided photoelectric converting elements 105, 105 and 105, respectively. Subsequently, by a signal interpolating circuit 301 in a signal processing circuit 106, the transmission light is interpolated and divided in one pitch of the grating, respectively and becomes an absolute position data. Also, the absolute position data in one pitch of the grating from the signal interpolating circuits 301, 301 and 301 is collected as an absolute position data of a moving extent of the first scale by a data processing logic circuit 302 and outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an optical absolute encoder used for position measurement in machine tools and the like.

(Technical background and problems to be solved) There are generally two types of optical encoders used for position measurement: incremental type and absolute type. Fig. 7 shows a schematic 4R structure common to both types.

The optical encoder 100 consists of a light emitting element +01, a collimator lens 102, and parts where light can pass through and parts where it cannot pass through at a constant pitch.'']+Scale 1
03 and the second scale toll, and the photoelectric conversion element 10
5 and a signal processing circuit 106.

To explain the operation of this optical encoder 100, light emitted from a light emitting element 101 is made into parallel light by a collimator lens 102, and a first scale 103 and a second scale 104 are collimated.
The light that has passed through is converted by the photoelectric conversion element 105 into an electrical signal corresponding to the amount of light. Furthermore, when the first scale 103 moves in the longitudinal direction of the scale, the amount of light incident on the photoelectric conversion element 105 changes periodically, and the electric signal also changes periodically accordingly. This electrical signal is transmitted to the signal processing circuit 10
6, the data is converted into displacement data and position data in a predetermined format and output. In particular, in the absolute encoder 200, absolute position data of the first scale 103 is output.

Next, a schematic structure of a conventional absolute encoder 20° is shown in FIG. 8 in correspondence with FIG. 7.

The absolute encoder 200 has a first scale 10
2 on the first scale 103 to detect the absolute position of 3.
A plurality of first grid tracks representing decimal codes1. ．． 12.13
A plurality of second grating tracks t, J2 . t3
has been newly established. In addition, the signal processing circuit 106
is composed of a waveform shaping circuit 201 that converts a position signal into a binary digital signal, and a code conversion circuit 202 that converts this signal into a pure binary code or the like.

To explain the operation of this absolute echoder 200, light emitted from the light emitting element 101 is transmitted through the collimator lens 102.
, the first and second grating tracks j, , t2 . t3
The light transmitted through these grating tracks t, t2 . L3
A plurality of photoelectric conversion elements 101, 105, 105 corresponding to
The light is then converted into an electrical signal according to the amount of light. Typically, these grid tracks 1, . 12,13. . . .+jn uses a pattern called an alternating binary code (Dalay code) as shown in FIG. This is because in pure binary codes, the codes of multiple tracks may change at the same time, and misreading is likely to occur. The converted electric signal is sent to the waveform shaping circuit 201 in the signal processing circuit 106.
It is converted into a digital signal representing position data in binary numbers. FIG. 1O shows a digital signal representing position data obtained with the alternating binary code pattern shown in FIG. This digital signal is converted by a code conversion circuit 202 into a desired format such as pure binary code or D code.

However, since the above method requires many grating tracks for the absolute position detection stroke, the first scale 1
03 and the second scale 104, it is necessary to provide many photoelectric conversion elements 105, resulting in a problem that the device becomes large. For example, in the case of grating tracks with the shortest pitch of 10 μm on the first scale 103, at least 8 rows of grating tracks are required for an absolute position detection stroke of 1 mm. In addition, as another problem, 2
In a lattice pattern based on progressive codes, the change in the sign of the track on the long pitch side is as important as the change in sign of the track on the short pitch side, so particularly severe accuracy was required in reading the code on the long pitch side.

(Object of the Invention) The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to be able to be configured with a small number of grating tracks and photoelectric conversion elements, and to provide a system that can be configured with a small number of grating tracks and photoelectric conversion elements, and can be configured with a small number of grating tracks and photoelectric conversion elements. An object of the present invention is to provide an absolute encoder capable of detecting an absolute position without making reading errors that are likely to occur.

(Means for Solving the Problems) The present invention relates to an absolute encoder, and an object of the present invention is to provide a plurality of first grating tracks with different pitches, and to receive parallel light from a light source and encode the encoder in the longitudinal direction. A moving first scale, a plurality of second grating tracks corresponding to the plurality of first grating tracks are provided, a second scale provided to face the first scale, and the first and second grating tracks. The relationship between the plurality of photoelectric conversion elements that read the light transmitted through the scale and each grating pitch of the first and second grating tracks is 1:N (N is an integer of 3 or more), and each photoelectric conversion element from the optical TL conversion element a signal interpolation circuit that interpolates an electrical signal into N parts within one pitch of each grid to obtain absolute position data within one pitch of each grid; and a signal interpolation circuit that logically combines the absolute position data to determine the amount of movement of the first scale. This is achieved by providing a data processing logic circuit for determining absolute position data.

(Operation of the Invention) The present invention provides a signal interpolation circuit of an absolute encoder in which the relationship between the grating pitches of the first and second grating tracks is 1:N (N is an integer of 3 or more). The electric signal corresponding to the second grating track is interpolated and divided into N parts within one pitch of each grating to create absolute position data within one bit of each grating, and a data processing logic circuit calculates the absolute position data within one pitch of each grating. The data are logically combined to create absolute position data of the amount of movement of the first scale.

(Embodiment of the invention) FIG. 1 shows an absolute encoder 300 according to the invention.
A schematic structural diagram is shown corresponding to FIG. 8. In the present invention, a signal interpolation circuit 3 is used instead of the waveform shaping circuit 201.
01, a data processing logic circuit 302 is provided in place of the code conversion circuit 202.

The absolute 1 encoder 300 of the present invention detects the absolute position of the first scale 103 (in the moving direction, not perpendicular to the plane of this paper). To explain this operation, the light emitted from the light emitting element 101 is made into parallel light by the collimator lens 102, and the first
Enter scale +03. The first scale 103 has
A plurality of grating tracks each having a different pitch1. ．． 12
,1. is provided. While the conventional pitch relationship between the grating tracks was 1:2, the relationship in the present invention is 1:N (N is an integer of 3 or more). FIG. 2 shows the pattern when the relationship between the respective grating tracks is 1=lO, that is, three rows of grating tracks tI+
t2. Bit P of t3:P2:P3 is l+IQ:10
The relationship is 0. At this time, the pitch of the grating track t3 having the largest pitch becomes the absolute position detection range of the absolute encoder 300.

The light transmitted through the first scale 103 is transmitted to the grating track 1. of the first scale 103. ．． 12,1. A plurality of grid tracks corresponding to each one.1. ．． The second scale has 12.13! 04 and each of the light transmitted by the plurality of photoelectric conversion elements 105, 105, 105 is converted into an electric signal. Note that the first scale is 10
2nd scale +0 corresponding to one grid track on 3
The number of grating tracks and photoelectric conversion elements 105 on 4 is 1.
The number is not limited to one, but there may be more than one depending on the interpolation method.

The converted electric signal is interpolated and divided within one bit of each grid by a signal interpolation circuit 301 in the signal processing circuit 106 (the number of divisions is the pitch ratio N of each grid track on the first scale 103). ) and becomes absolute position data. For example, when using the first scale 103 with an interpolation division number lO shown in FIG. The data are shown in Figure 3.

The absolute position data within one pitch of the grid from the respective signal interpolation circuits 301, 301, and 301 are summarized and output as absolute position data of the first scale movement amount by the data processing logic circuit 302.

The above-mentioned absolute encoder 300 is effective when the movement of the object to be measured is performed in steps over a certain fixed length in synchronization with the grid bits, but it is effective when the movement of the object to be measured is performed in steps over a certain fixed length in synchronization with the grid bits. When measuring a small range of data, incorrect data may be output.

For convenience of explanation below, when focusing on two grating tracks with similar grating pitch lengths among the plurality of grating tracks, the one with the larger grating pitch will be referred to as the upper digit, and the one with the smaller grating pitch will be referred to as the lower digit.

FIG. 4 shows a part of the data obtained by the absolute encoder 300 of the present invention, and if the interpolation division of the upper digits is not done evenly, two grid tracks like P and Q in the figure will be generated. The locations where the numbers change differ between the two. For example, P in the same figure should be read as 19 or 29, and Q
In this case, incorrect data may be output, such as when a value read as 3o is read as 20.

Therefore, 1. In order to eliminate the above-mentioned points, Figures 5 (8) and (B)
).

By setting the interpolation division number of the upper digits of two lattice tracks with a grating pitch ratio of 1:N to 3N, the length corresponding to one pitch of the lower digits is further divided equally into three parts A, B, and C. At the same time, the lower digits are interpolated into three or more. Next, the data processing logic circuit 302 outputs the absolute position data of the lower digit and the three parts of the absolute position data of the upper digit, B, C.
The correct value of the upper digits is determined by determining the degree of overlap between the two.

Figure 5 (8) shows that when the interpolation division number of the lower digit is lO,
The figure (8) shows the case where the upper digit shifts to the right in the figure, and (8) shows the case where the upper digit shifts to the left. In the figure (A), the upper digit of the part where the value of the lower digit is 0, 1.2 is 1, but originally it is 2. Similarly, in the same figure (B), the value of the lower digit is 7.
．． The upper digit of the 8.9 part is 3, but it was originally 2.
It is. Therefore, in the data processing logic circuit 302 that combines the absolute position data within the lattice l pitch of each lattice track, when the lower digit is 0.1.2 and the upper digit is C, the data of the upper digit is 1°' The function to add and the lower digit is 7.
8.9 and the upper digit is A, the data of the upper digit is °
Incorporate a function to add “-1”. As a result, it is possible to have a margin of 3096 of the pitch of the lower digits for deviations in both the left and right directions, and if the interpolation division of the lower digits is set to a multiple of 3, the margin can be increased for both the left and right directions. The length increases to a length corresponding to 173 of the pitch.

Yet another example will be described.

Since the conventional absolute encoder 200 including multiple grating tracks precisely matches the phase of the signal between each grating, the manufacturing and mounting of the scales 103 and 104 requires very strict precision, and mechanical Electrical adjustment was required.

Therefore, in order to eliminate the above-mentioned points, Figure 6 (8) and (B)
Explain with reference to.

FIG. 6(A) shows data of an absolute encoder 200 manufactured without paying attention to the phase between grating tracks.
As in the previous modification, two grating tracks with similar grating pitch lengths among the plurality of grating tracks are shown, and the point where the upper digit changes from 1 to 2 is at the lower digit 5.

Although there is no limit to the actual location of the change point, the location of the change point can be easily determined by reading the absolute cover data of each grid track while moving the first scale. That is, Fig. 6 (
By adding 5'' to all the lower digits of the data shown in ^) or providing an offset value addition/subtraction function that adds ``-5'' in the data processing logic circuit 302, the data shown in (0) in the same figure is obtained. be able to.

(Effects of the Invention) As described above, according to the absolute encoder of the present invention, absolute position detection can be performed with a small number of grating tracks, no strict precision is required for interpolation of upper digits, and the phase difference between multiple grating tracks can be detected. Since no matching is required, costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an outline of the device according to the present invention, FIG. 2 is a diagram showing an example of the lattice bagoon used in the device of the present invention,
Figures 3 and 4 are diagrams showing examples of the output data, and Figure 5 is a diagram showing examples of the output data.
Figures (^) and (B) are diagrams showing output data for explaining another embodiment of the present invention, and Figures 6 (A) and (0) are output data for explaining still another embodiment of the present invention. Diagram showing data, 7th
The figure shows an outline of a general optical encoder device.
FIG. 8 is a diagram showing an outline of a conventional device U, FIG. 9 is a diagram showing an example of a lattice pattern used in the conventional device, and FIG. 1O is a diagram showing an example of output data thereof. +(II... Light emitting element, 102... Frimeter lens, 103... First scale, 104... Second scale, L+rL2.--Ln... Grating track, 10
5... Photoelectric conversion element, 1Qfi... Chair processing circuit, 301... F8 interpolation circuit, 302... Data processing logic circuit. 1st hard j! & 2nd day's sharp friend number 3rd day's sheep 4 times: : Sheep's 7th question processing [! Circuit 106 8th l fO factor

Claims (4)

[Claims] (1) A plurality of first grating tracks with different pitches are provided, and the first grating track moves in the longitudinal direction in response to parallel light from a light source.
A scale and a plurality of second grating tracks corresponding to the plurality of first grating tracks are provided, and a second scale is provided opposite to the first scale, and the second scale is transparent to the first and second scales. The relationship between the plurality of photoelectric conversion elements that read light and each grating pitch of the first and second grating tracks is 1:N (N is an integer of 3 or more), and each electric signal from the photoelectric conversion element is transmitted to each grating. a signal interpolation circuit that interpolates N divisions within one pitch to obtain absolute position data within one pitch of each grating; and logically combines the absolute position data to obtain absolute position data of the movement amount of the first scale. An absolute encoder characterized by being equipped with the desired data processing logic circuit. (2) The signal interpolation circuit converts the upper digits of any two of the first and second grating tracks into 3N within one pitch of the grating.
By interpolating and dividing the lower digits of the arbitrary two above, and interpolating and dividing the lower digits of the above arbitrary two within one pitch of the grid, it is possible to obtain absolute position data within one pitch of each grid of the arbitrary two grid tracks. and the data processing logic circuit compares the absolute position data within one pitch of the lattice of the upper digit from the signal interpolation circuit with the absolute position data within one pitch of the lattice of the lower digit, and Claims have a function of selecting an appropriate value at a change in the absolute position data within one pitch and combining it with the absolute position data within one pitch of the lattice of the lower digit to obtain the absolute position data of the movement amount of the first scale. The absolute encoder described in item 1. (3) The data processing logic circuit arbitrarily adjusts the phase between the first and second grating tracks by adding or subtracting an offset value to absolute position data within one pitch of each grating of the first and second grating tracks. The absolute encoder according to claim 1, having a function that can be set to . (4) The signal interpolation circuit converts the upper digits of any two of the first and second grating tracks into 3N within one pitch of the grating.
By interpolating and dividing the lower digits of the arbitrary two above, and interpolating and dividing the lower digits of the above arbitrary two within one pitch of the grid, it is possible to obtain absolute position data within one pitch of each grid of the arbitrary two grid tracks. and the data processing logic circuit arbitrarily adjusts the phase between the first and second grating tracks by adding or subtracting an offset value to absolute position data within one pitch of each grating of the first and second grating tracks. The absolute encoder according to claim 1, having a function that can be set to .