JP3442869B2 - Optical absolute encoder - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical one-track absolute encoder, and more particularly to an optical one-track optical absolute encoder that simultaneously uses an absolute signal indicating an absolute position and an incremental signal indicating a relative position. Regarding

[0002]

2. Description of the Related Art An optical encoder is a device for detecting a position by reading a pattern formed by a slit formed in a code plate. Among them, an optical absolute encoder is a device for detecting the pattern at different positions in the code plate. The values shown by are set to be the same.

In such an absolute pattern, conventionally, a plurality of tracks having codes of 0 and 1 are arranged on a concentric circle, and the codes arranged in the diametrical direction are read, and n is read.
There is a multi-track type that obtains an n-bit value from each track.

However, in recent years, a one-track type absolute pattern 101 as shown in FIG. 6A, which can obtain a value of n bits in one track, has come to be used. This 1-track type absolute pattern is a pattern in which, when n consecutive codes on one track are read, the values made from the n codes are made different at all positions. Is stored in advance and the absolute position is obtained from the read value. Figure 7 (a)
FIG. 4 is a diagram showing this reading state, in which the light transmitted through the code plate 112 provided with the absolute pattern 101 is applied to four of the eight photodetection elements 113, and 1 light and 1 dark are displayed. When it is set to 0, the binary number <00111001> is being read.

Such an absolute pattern 101
There are many known code arranging methods based on a large number of methods such as a full-cycle series and an M series, and it is easy to downsize the code plate as compared with the above-described multi-track type. The method for discriminating patterns has become popular because it is simple.

Even in such an absolute pattern of the prior art, as shown in FIG.
Narrow slit 121 corresponding to 0 "and binary" 1 "
There is also a slit having a wide slit 122 corresponding to, but the slits are arranged at the same center distance d'with the light-shielding portion interposed therebetween.

In such a one-track type absolute pattern, it is premised that a predetermined number of consecutive codes can be correctly read, and dust is attached or scratched even on a part of the absolute pattern to be read. In some cases, it will read the wrong value. Then, if an incorrect value is read, an absolute position completely different from the correct position will be obtained, so a solution has been desired.

On the other hand, FIG. 6 (b) which has been conventionally used
The incremental pattern 102 as shown in FIG. This incremental pattern 1
As shown in FIG. 7 (b), reference numeral 02 denotes slits 115 arranged at equal intervals, which are arranged on the code plate 116, and between the light emitting element and the code plate 116, A mask 117 in which slits having the same size as the slits are arranged at the same intervals as the intervals is arranged, and the light transmitted through the mask 17 is counted as to whether it is transmitted through the code plate 116 or shielded. Then, the movement amount is obtained.

A plurality of slits are arranged on the mask 117 so that the light transmitted through the code plate 116 is condensed by the lens 118, and the threshold level for discriminating between the transmitted state and the shielded state is appropriate. By setting to 1, there is an advantage that even if a part of the code plate 116 is scratched or dust is attached, it is possible to correctly distinguish between the light-shielded state and the light-transmitted state.

In order to solve the inconvenience of the absolute pattern, which is vulnerable to dust and scratches, a composite pattern 103 as shown in FIG. 6C is known. In this composite pattern 103, an absolute pattern and an incremental pattern are arranged on concentric circles, and absolute coordinates obtained from the absolute pattern are compared with relative coordinates obtained from the incremental pattern to correct a reading error of the absolute pattern. Is what you are trying to do.

However, such a composite pattern 1
No. 03 inevitably becomes thicker than the width of the absolute pattern 101, and it becomes impossible to meet the demand for downsizing the code plate.

Further, since it is necessary to install a device for reading an absolute pattern as shown in FIG. 7A and a device for reading an incremental pattern as shown in FIG. 7B in parallel, the cost is increased. However, there is an inconvenience that the device becomes large.

[0013]

SUMMARY OF THE INVENTION The present invention was created in order to solve the above-mentioned disadvantages of the prior art, and its object is an optical system capable of detecting an absolute position and a relative position with a one-track type absolute pattern. It is an object to provide an absolute encoder.

[0014]

In order to solve the above-mentioned problems, the invention according to claim 1 is provided with a code plate having an absolute pattern and a code plate which is relatively movable in a pattern forming direction of the code plate. In an optical absolute encoder having a detection unit for detecting a light-dark pattern made of light transmitted through a plate, and a signal processing unit for extracting an absolute signal indicating an absolute position on the absolute pattern of the detected light-dark pattern, The absolute pattern has a plurality of types of coding elements having different widths, and one end of the coding elements is arranged at equal intervals, and the signal processing unit detects the one end and detects the relative position of the code plate. The invention according to claim 2 is characterized by further comprising an auxiliary signal processing section for generating an incremental signal indicating a position. Of the optical absolute encoder, wherein the moving amount of the code plate obtained from the absolute signal is compared with the moving amount of the code plate obtained from the incremental signal to detect an error in reading the absolute signal. The invention according to claim 3 is characterized by comprising a device.
The optical absolute encoder according to claim 1, wherein the width of at least one coding element of the predetermined number of coding elements forming the absolute signal is different from the width of a predetermined number of other coding elements. Characterize.

[0015]

The optical absolute encoder is constructed so that only the light transmitted through the absolute pattern formed on the code plate can reach the detection section, and the light and dark pattern according to the absolute pattern is formed on the detection section. Since it is formed, it is possible to read a bright and dark pattern of a predetermined length by the detection unit.

In the absolute pattern, since the light and dark patterns formed when the predetermined length is taken are made different at any position on the absolute encoder, all the light and dark patterns of the predetermined length different from each other are Since each bright and dark pattern and its absolute position are associated and stored in advance, the absolute position of the detected pattern can be known by detecting the bright and dark pattern of a predetermined length.

In this case, the absolute pattern is composed of a plurality of types of coding elements having different widths,
If one ends of the coding elements are arranged at equal intervals d, when the code plates move relatively in the pattern forming direction, the one ends of the coding elements arranged at the same intervals will be simultaneously on the detection unit. Therefore, among the light receiving elements on the detection unit, the light receiving elements arranged at the interval d change from bright to dark or from dark to bright all at once.

By detecting the number of simultaneous changes and whether each change is a change from dark to bright or a change from bright to dark, an incremental signal indicating a relative position is obtained from the absolute pattern. Can be generated.

Since the amount of movement of the absolute pattern can be known from this incremental signal, once the absolute position has been obtained, the absolute position can be subsequently calculated from the incremental signal.

Then, by comparing the absolute position obtained from the incremental signal with the absolute position obtained by reading the absolute pattern, the reading error of the absolute signal can be detected.

[0021]

1 (a) shows an optical absolute encoder according to an embodiment of the present invention, which has a code plate 3 having an absolute pattern 2, a detecting section 4, and a signal processing section 5. .

The code plate 3 is constructed so as to be rotatable about a rotation axis 7, and the absolute pattern 2 is provided in the circumferential direction of the code plate 3, so that the code plate 3 is attached. Since the code plate 3 also rotates when the object to be measured rotates, the code plate 3 and the detection unit 4 are configured to relatively rotate.

The absolute pattern 2 is provided with a plurality of slits which are light-transmitting elements, which are coding elements.
Each slit is separated by a light blocking portion that blocks light.
As shown in Fig. 1 (c), this slit has a binary ""
There are two types of slits, a narrow slit 11 indicating 0 "and a wide slit 12 indicating binary" 1 ". For example, in the case of the arrangement shown in FIG. The binary number "01110010" is indicated.

When the code plate 3 is irradiated with the laser light from the light source 6, the light and dark patterns are formed in the detecting section 4 through the absolute pattern 2 and the detecting section 4 absolutely forms the light and dark pattern. It is possible to output the signal as a signal and convert the absolute signal into a binary number by the encoding device 9 provided in the signal processing unit 5.

When eight consecutive slits on the absolute pattern 2 composed of the narrow slit 11 and the wide slit 12 are taken, the corresponding 8-bit binary number is the absolute number. Pattern 2
It is configured to be different at every position above (same 2
Since it is configured so that a decimal number does not appear, 2
If a binary number and an absolute position on the absolute pattern from which the binary number can be read are associated and stored in the computing device 8, the binary number obtained from the absolute signal output from the detecting device 4 is stored in the computing device. By inputting in 8, it is possible to search the correspondence and obtain the absolute position corresponding to the binary number. The absolute position is configured to be displayed on the display device 10.

The narrow slits 11 and the wide slits 12 of the absolute pattern 2 are arranged at the left ends at equal intervals d, and the light-shielding portion 1 is provided between the slits.
Separated in 3.

The detecting section 4 is fixed to a holder, while the code plate 3 is attached to a measuring object such as a transit, which has a rotating motion, with the rotation axis 7 being the same. The detection unit 4 uses a linear sensor in which a plurality of unit light receiving elements are arranged in a row, and the absolute pattern 2 is also rotated by the rotation of the measuring object,
Along with this, the bright and dark patterns formed on the unit light receiving elements arranged in a row in the detection unit 4 also move.

2 (a) to 2 (e) are views for explaining a state in which the absolute pattern 2 moves on the detection section 4, and among the unit light receiving elements arranged in a line, the interval Four unit light receiving elements A, B, C, D located at d
The change in lightness and darkness above will be described as an example.

FIG. 2A shows the light receiving elements A, B, C and D.
This is a state in which the light shielding portion 13 of the absolute pattern 2 is positioned above.

When the absolute pattern 2 is moved to the left from this state, as shown in FIG. 2B, all the left ends of the wide and narrow slits 12 ₃ , 11 ₂ , 11 ₃ , and 12 ₄ are moved to the above-mentioned positions. There are times when they are located on the unit light receiving elements A, B, C, and D.

When the absolute pattern 2 is further moved to the left from this state, the left end of each slit is removed from above the unit light receiving elements A, B, C and D. In that case, for example, as shown in FIG. 2C, the wide slit 1
When the right ends of 2 ₃ and 12 ₄ are located on the unit light receiving elements A and D, the right ends of the narrow slits 11 ₂ and 11 ₃ are not located on the unit light receiving elements B and C. On the other hand, when the right end of the narrow slit is located on the unit light receiving element, the right end of the wide slit is not located.

Then, when the absolute pattern 2 further moves to the left from the state of FIG. 2 (c), as shown in FIG. 2 (d),
A narrow slit 1 is formed on the unit light receiving elements A, B, and D.
The left ends of 1 ₂ , 11 ₃ and 11 ₄ are located, and the left end of the wide slit 12 ₄ is located on the unit light receiving element C. When the absolute pattern 2 is moved rightward from the state of FIG. 3D, the wide slits 12 ₃ and 12 ₄ are positioned on the unit light receiving elements A and D as in the case of FIG. 2B. Then, a narrow slit 11 is formed on the unit light receiving elements B and C.
₂ and 11 ₃ are located.

FIG. 3 shows changes in the light-dark pattern formed on each of the unit light receiving elements A, B, C and D of the light receiving section 4.
It is a time chart shown by the magnitude of the electric signal which each unit light-receiving element outputs.

Each of the unit light receiving elements A, B, C, and D outputs a high voltage when a slit is positioned above it and is irradiated with light, that is, when a bright pattern is formed, and the light shielding portion is positioned. Then, when the light is blocked, that is, when a dark pattern is created, a low voltage is output, and if a constant threshold voltage is set between the high voltage value and the low voltage value. By the auxiliary signal processing unit 19 provided in the signal processing unit 5, it is possible to detect the light and dark pattern change on each unit light receiving element.

2B, 2D, and 2E, if it is detected that the signals output from the respective light receiving elements simultaneously cross the threshold voltage, the binary number is 1. Can be detected. At this time, if the change from the low voltage state to the high voltage state is detected as shown in FIGS. 2B and 2D, the incremental signal in the counter 11 is incremented by 1 count. On the other hand, as in the case of FIG. 2E, if the change from the high voltage state to the low voltage state is detected, the incremental signal is decreased by one count, and thus the moving direction of the absolute pattern can also be detected. Thereby, the relative movement amount can be calculated.

At this time, the absolute pattern 2
It is assumed that the absolute position before the movement of k is ₀ and the absolute position obtained by the absolute signal after the movement is k ₁ . If the incremental signal calculated by this movement is m, the following equation, k ₁ = k ₀ + m (1) should be established if there is no reading error of the absolute signal. Therefore, the error detection device provided in the arithmetic unit 8 is configured to compare k ₁ and the value of (k ₀ + m), and k ₁ ≠ k ₀ + m (2) In the case of, it is possible to detect that there is an error in reading the absolute signal due to dust, scratches, or the like.

When reading the n-bit code, the arrangement of the continuous n slits on the absolute pattern 2 may be a case where all n slits are wide slits, or all n slits are wide. When a narrow slit is formed, not only the left end of each slit but also the right end thereof are aligned. Therefore, when such an array pattern is avoided and the absolute pattern is composed of n coding elements, The width of at least one slit therein is n−
It is desirable that the slits are arranged so as to have a width different from that of the other slits.

FIG. 4 shows an optical absolute encoder which is another embodiment of the present invention. This optical absolute encoder has a code plate provided with the same absolute pattern as the absolute pattern 2 described above, but this code plate is omitted.

A line sensor is used for the detection unit 24 of the optical absolute encoder shown in FIG. The signal processing unit 26 included in the optical absolute encoder has a built-in arithmetic unit 25, and the arithmetic unit 25 is an A / D converter.
It is connected to the detection unit 24 via a converter 27.

A program is built in the storage device of the arithmetic unit 25, and the signal processing unit 26 is
In accordance with the processing procedure of this program, an absolute signal is obtained from the digital signal input from the A / D converter 27, and an incremental signal is calculated.

FIG. 5 is a flow chart showing this processing procedure. This process starts from step S ₁ ,
In step S ₂ , the digital signal output from the A / D converter 27 is read and the processing is branched to the absolute signal processing section 28 and the incremental signal processing section 29.

The absolute signal processing section 28 starts the processing from step S ₁₁ . The step S _11, the extracting dark pattern from the digital signal, the process proceeds to step S _12. In step S ₁₂ , the light / dark pattern is converted into a binary number r. The binary number r is converted into an absolute position a ₁ in step S ₁₃ by a correspondence table that stores the binary numbers and the absolute positions stored in advance.

[0043] Since the gap between the absolute position between stored in the correspondence table are rough, in step S _13, step S
The center of gravity of the light-dark pattern obtained in ₁₁ is calculated, the absolute position a ₁ is corrected, the more accurate corrected absolute position a ₂ is obtained, and the process proceeds to S ₃₁ .

On the other hand, the incremental processing section 29
Starts the process from step S ₂₁ . The encoding element that constitutes the absolute pattern of this optical absolute encoder is composed of a narrow slit and a wide slit, as in the above-described embodiment, and each encoding element is separated by a light-shielding portion. Since the left ends of the respective coding elements are arranged at equal intervals d, the step S
_{At 21} , from the digital signal input from the A / D converter 27, a signal corresponding to a predetermined unit light-receiving element group serving as a reference arranged at the same interval as the interval d is extracted,
If all the signal changes of the corresponding signals are across the threshold voltage, the process proceeds to the next step S _22.
Move to.

[0045] The step S _22, the change of the predetermined light receiving element group of the signal, determines whether a rising edge of the change from the low voltage to high voltage. If there was a rise, the process proceeds to step S _23, the process proceeds to step S ₂₄ to set the +1 counter variable f. If not the rise, the process proceeds to step S ₂₅ from the step S _22, the change of the signal at the step S ₂₅ it is determined whether or not falling from the high voltage to low voltage. If the was falling, the process proceeds to step S ₂₄ is set to -1 to the counter variable f at step S _26. Step S is ₂₄ proceeds to set to zero the counter variable f at step S ₂₆ if did not fall.

[0046] Step S ₂₄ is a value of the counter variable f is added to the value b of the incremental signal stored, and the value b of the new incremental signal, the process proceeds to step S _27. In the step S _27, the process returns if there is a request for signal processing in the step S _2, and reads the A / D converter of the signal, to continue the process. On the other hand, if there is a signal processing request, the processing is performed in S _31.
Move to.

In step S ₃₁ , the value b of the new incremental signal and the stored initial value a ₀ of the absolute position are added, and the position a ₁ obtained by the absolute signal processing unit 28 is calculated. If they are equal, it is determined that the absolute signal extracted from the digital signal has no reading error, and the display variable c is displayed in step S _32.
The corrected absolute position a ₂ is set to and the value of the display variable is displayed in step S ₃₃ .

On the other hand, if they are not equal, it is determined that the absolute signal contains a reading error, and the process proceeds from step S ₃₁ to step S ₃₅ to set the initial value a ₀ of the absolute position to the incremental signal. sets a value obtained by adding the value b to the display variable c, displayed in step S _33.

The process proceeds to step S ₃₄ from the step S _33, in the step S _34, as well as set the value of the display variable c to the initial value a ₀ of the absolute position, to clear the incremental variable b, the step S Return to ₂ to continue.

Although the intervals between the left ends of the slits are equal in the above embodiment, the right ends may be arranged at equal intervals. Further, not only when the absolute pattern is provided on the circular code plate, the absolute pattern may be linearly arranged on the linear code plate.

Further, in the present embodiment, the case where the binary code (binary number) is read by using two kinds of slits, that is, a wide slit and a narrow slit, is shown. Ternary code using width slit
It may read n-ary numbers such as (ternary numbers) and quaternary codes (quaternary numbers).

Furthermore, although the slit which allows light to pass through has been described as an example of the coding element, it is also possible to use a light shielding portion for blocking light to this coding element. In that case, as the light-shielding portion as the encoding element, a plurality of types having different widths are used, and each light-shielding portion is separated by a slit that transmits light, and one end of each light-shielding portion is arranged at equal intervals. It suffices to form an absolute pattern by using an optical absolute encoder having such an absolute pattern.

Furthermore, in this embodiment, the absolute signal is composed of continuous coding elements, but the absolute signal is composed of non-continuous coding elements such as every other coding element and every two coding elements. Those that obtain signals are also included.

Needless to say, a change between the voltage indicating the low state and the voltage indicating the high state can be detected by using a plurality of unit light receiving elements instead of one.

[0055]

According to the present invention, it is possible to extract not only the absolute signal but also the incremental signal from the absolute pattern, and it is possible to detect whether or not the absolute signal includes a reading error by the incremental signal.

If there is a reading error, the absolute position can be obtained from the incremental signal, and therefore the wrong absolute position will not be obtained.

[Brief description of drawings]

1A is an optical absolute encoder according to an embodiment of the present invention, FIG. 1B is a diagram showing an absolute pattern provided in the optical absolute encoder, and FIG. 1C is a diagram for explaining a coding element of the absolute pattern.

FIG. 2 is a diagram for explaining a state in which an absolute pattern moves on a detection unit.

FIG. 3 is a timing chart of signals output from a unit light receiving element due to the movement.

FIG. 4 is an optical absolute encoder according to another embodiment of the present invention.

FIG. 5 is a flowchart showing the processing procedure.

FIG. 6 (a) Prior art absolute pattern (b) Prior art incremental pattern (c) Composite pattern of prior art

FIG. 7 (a) is a diagram for explaining an apparatus for detecting an absolute pattern according to the related art (b) is a diagram for explaining an apparatus for detecting an incremental pattern according to the related art (c) An example of an absolute pattern according to the related art Enlarged view of

[Explanation of symbols]

2 ... Absolute pattern 3 ... Code plate
4, 24 ... Detection unit 5, 26 ... Signal processing unit 11, 12 ... Encoding element 19 ... Auxiliary signal processing unit

Continuation of the front page (56) Reference JP 63-33603 (JP, A) JP 63-134918 (JP, A) JP 63-290916 (JP, A) JP 5-187890 (JP , A) Actual development Sho 64-15116 (JP, U) Actual development Sho 54-86445 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01D 5/00-5/62 G01B 7/00-7/34 G01B 11/00-11/30

Claims (3)

(57) [Claims] 1. A code plate having an absolute pattern, a detection unit provided so as to be relatively movable in a pattern forming direction of the code plate, and detecting a bright-dark pattern formed by light transmitted through the code plate, In an optical absolute encoder having a bright and dark pattern, a signal processing unit for extracting an absolute signal indicating an absolute position on the absolute pattern, the absolute pattern has a plurality of types of encoding elements having different widths, and the code One end of the digitizing element is arranged at equal intervals, and the signal processing unit includes an auxiliary signal processing unit that detects the one end and generates an incremental signal indicating the relative position of the code plate. Optical absolute encoder. 2. An error detecting device for detecting a reading error of the absolute signal by comparing a moving amount of the code plate obtained from the absolute signal with a moving amount of the code plate obtained from the incremental signal. The optical absolute encoder according to claim 1, wherein: 3. A width of at least one coding element among a predetermined number of coding elements forming the absolute signal is different from a width of a predetermined number of other coding elements. The optical absolute encoder according to claim 1 or 2.