JP2893851B2 - Absolute position detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a linear absolute value encoder used for measuring a moving distance, a speed, and the like of a directly moving device such as a machine tool.

[Conventional technology]

Conventionally, as this type of linear displacement detection device, an incremental type linear encoder is generally provided, which is provided with a slit corresponding to the resolution over the entire measurement length, and counts and detects divided pulses from an arbitrary origin. In this case, there is a problem that the operation is complicated because the absolute position is not known unless the position returns to the origin position every time the power is turned on.

In order to detect the absolute position, a linear absolute encoder consisting of a plurality of code tracks using a gray code or the like can be considered as in the case of the absolute encoder in the rotary encoder.In this case, a high resolution is required over the entire measurement length. Attempting to do so is not practical because the required number of bits increases and the number of code tracks on the scale increases.

A linear absolute value encoder for solving this problem includes a first low-resolution linear absolute value encoder for detecting an absolute position over the entire length as shown in Japanese Patent Application Laid-Open No. 61-182521, and a first linear absolute value encoder. There is known a method of obtaining a desired linear absolute value encoder by combining the absolute value encoder unit with a second high-resolution linear absolute value encoder unit that detects an absolute position within a measurement pitch of the absolute value encoder unit.

That is, in the conventional linear absolute value encoder, the value of the low-resolution first linear absolute value encoder unit and the second linear absolute value detection unit for detecting the absolute position with high resolution within the measurement pitch of the first linear absolute value encoder unit The absolute position is obtained by synthesizing the value of the absolute value encoder with the value of the absolute value encoder, for example, as shown in FIG. Here, the value of the first linear absolute value encoder is a first absolute value, the value of the second linear absolute value encoder is a second absolute value, and the second linear absolute value encoder is , The absolute position is detected within the measurement pitch of the first linear absolute value encoder with a resolution of P division. In this case, the synthesized output is obtained as N · P + (P−1) when the pitch is N−1.

[Problems to be solved by the invention]

However, in the linear absolute value encoder obtained by combining the first and second linear absolute value encoders as described above,
Since each linear absolute value encoder is an independent encoder, the position where the value of the first linear absolute value encoder changes and the position of the minimum value or the maximum value of the second linear absolute value encoder do not always match. .

Therefore, as shown in FIGS. 4 and 5, when obtaining the absolute position by combining, an error occurs in the combined output by one pitch of the first linear absolute value encoder. In FIG. 4, an error corresponding to one pitch of the first linear absolute value encoder occurs near the minimum value of the second linear absolute value encoder. In FIG. 5, the error of the second linear absolute value encoder is generated. An error occurs near the maximum value.

Accordingly, an object of the present invention is to provide the above-described absolute position detecting method in which an error of one pitch does not occur.

[Means for solving the problem]

In order to solve the above problem, the present invention has the same pitch resolution as that of the first linear absolute value encoder unit, and detects an absolute position shifted from the first linear absolute value encoder unit by 1/2 pitch phase. A third low-resolution linear absolute value encoder is provided, and when the second linear absolute value encoder is near a minimum value (or a maximum value), a value obtained by adding one to the value of the third linear absolute value encoder ( Or the subtracted value) to replace the value of the first linear absolute value encoder section,
When the second linear absolute value encoder is near the maximum value (or the minimum value), the value of the first linear absolute value encoder is replaced with the value of the third linear absolute value encoder.

(Operation)

By the above means, the first low-resolution linear absolute value encoder can be corrected in accordance with the second high-resolution linear absolute value encoder.

〔Example〕

An embodiment according to the present invention is shown in FIG. Here, the first
And a third linear absolute value encoder unit having the same pitch as that of the linear absolute value encoder unit and having a phase shifted by 1/2 pitch toward the maximum value side. And the second linear absolute value encoder section is less than L near the minimum value (for example, less than 1/4 pitch)
In the case of, the value X of the third linear absolute value encoder is 1
The added X + 1 is replaced with the value of the first linear absolute value encoder. The value Y of the encoder unit is replaced with the value of the first linear absolute value encoder unit. While the second linear absolute value encoder is between L and M, the value of the first linear absolute value encoder is used as it is. By the above means,
It is possible to correct the value of the first linear absolute value encoder so as to match the value of the second linear absolute value encoder.

FIG. 2 shows another embodiment of the present invention, in which the phase of the third linear absolute value encoder is shifted by a half pitch from the first linear absolute value encoder to the minimum value side. In this case, when the second linear absolute value encoder section is near the minimum value, the value X ′ of the third linear absolute value encoder section
Is replaced with the value of the first linear absolute value encoder, and the second
When the linear absolute value encoder of (3) is near the maximum value, the value Y 'obtained by subtracting 1 from the value Y' of the third linear absolute value encoder
The value of the first linear absolute value encoder is replaced with -1.

 The principle of the present invention will be described below.

(1) In an ideal case (when accuracy is good) In an ideal case (when accuracy is good), as shown in FIG. 3, the second absolute value is:..., (P-2), (P-1) , 0, 1, ..., the first absolute value changes by one pitch from (N-1) to N at the same time as changing from (P-1) to 0.
In this case, when the detection position is, for example, at the origin 0 on the left side of the second absolute value in FIG. 3, the detection value of the first absolute value at that time is N, and the detection position of the combination is N · P. Become. Similarly, when the detection position is on the left side, the detection value of the second absolute value is (P-1), the detection value of the first absolute value is (N-1), and the detection position of the synthesis is ( N−1) · P + (P−1) = N · P−1.

(2) Actual case (when accuracy is poor) In actual position detection, the physical position such as mounting of the detection system is poor, so that the ideal positional relationship as shown in FIG. As shown in FIG. 4, the change position of the first absolute value and the change position of the second absolute value from (P-1) to 0 cannot be the same.

In this case, the original absolute position is the second finer step.
It is an object of the present invention to generate the original absolute position by correcting the first absolute value to generate the original absolute position.

In the case of FIG. 4, when the detection position is at the origin 0 on the left side of the second absolute value, the detection value of the first absolute value at that time is (N-1), and the detection position of the combination is (N -1) · P = N · P−P, and the position N · P to be originally detected is the first absolute value 1
The value is shifted by the pitch. Similarly, when the detection position is on the left side, the detection value of the second absolute value is (P-1), the detection value of the first absolute value is (N-1), and the detection position of the synthesis is ( N-1) .P + (P-1) = NP1 (the same as the original detection position). During this period, the continuity of the detection position is lost, and the absolute position detection fails.

In the embodiment of the present invention shown in FIG. 1, even in the case of FIG.
The detected value (N-1) of the absolute value of (N-1) is used, and (N-1) + 1 = N, the detection position of the combination becomes NP, which is a value to be originally detected.

As described above, in the present invention, even if there is some error in the detection system, failure occurs by selecting the first and third absolute values based on the second absolute value and creating a composite output. Without this, an effect of realizing continuous absolute position detection can be obtained.

〔The invention's effect〕

As described above, according to the present invention, it is possible to provide a linear absolute value encoder capable of detecting a position with high accuracy and having no error of one pitch.

[Brief description of the drawings]

1 is an absolute value composite diagram according to an embodiment of the present invention, FIG. 2 is an absolute value composite diagram according to another embodiment of the present invention, FIG. 3 is an absolute value composite diagram according to a conventional example, and FIG. FIG. 5 is a diagram showing another example of error occurrence in the conventional example.

Claims (2)

(57) [Claims] An output of a first low-resolution linear absolute value encoder for detecting an absolute position and a measurement pitch of the first linear absolute value encoder as one cycle are used as the first linear absolute value encoder. In the method of detecting the absolute position by synthesizing the output of the second high-resolution linear absolute value encoder for detecting the absolute position within the measurement pitch of the first linear absolute value encoder, it has the same pitch resolution as the first linear absolute value encoder. A third low-resolution linear absolute value encoder for detecting an absolute position shifted from the first linear absolute value encoder by a 1/2 pitch phase toward the maximum value side, and a second linear absolute value encoder. Is near the minimum value.
The value of the first linear absolute value encoder unit is replaced with a value obtained by adding one to the value of the linear absolute value encoder unit, and when the second linear absolute value encoder unit is near the maximum value, the value of the third linear absolute value encoder unit is replaced. An absolute position detection method, wherein a value of a first linear absolute value encoder is replaced with a value. 2. The first linear absolute value encoder unit, wherein the output of a first low resolution linear absolute value encoder unit for detecting an absolute position and the measurement pitch of the first linear absolute value encoder unit are defined as one cycle. In the method of detecting the absolute position by synthesizing the output of the second high-resolution linear absolute value encoder for detecting the absolute position within the measurement pitch of the first linear absolute value encoder, it has the same pitch resolution as the first linear absolute value encoder. A third low-resolution linear absolute value encoder for detecting an absolute position shifted by a 1/2 pitch phase from the first linear absolute value encoder to the minimum value side; a second linear absolute value encoder Is near the minimum value.
The value of the first linear absolute value encoder is replaced by the value of the linear absolute value encoder, and the value of the third linear absolute value encoder is reduced by 1 when the second linear absolute value encoder is near the maximum value. An absolute position detection method, wherein a value of a first linear absolute value encoder is replaced with a value.