JP2697159B2 - Absolute position detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device, and more particularly to an absolute position detecting device that can be used as an absolute encoder that detects an absolute position with high accuracy.

2. Description of the Related Art In recent years, digitization and complexity of control have increased the need for an absolute encoder that detects an absolute position as a position detection device.

Hereinafter, an example of the above-described conventional position detecting device will be described with reference to the drawings.

FIG. 3 shows the configuration of a conventional position detecting device. In FIG. 3, 101 is a light source, 102 is a collimating lens for converting the light of the light source into a parallel light beam, 103 is a scale attached to a moving body (not shown), 104 is a fixed mask, 1
05 is a fixed light receiving element array. FIG. 4A shows details of a pattern formed on the scale 103.
Gray code patterns C0 to C5, which are binary codes, are engraved on the scale 103. FIG. 4B shows details of the patterns M0 to M5 formed on the mask, and FIG. 4C shows signal waveforms S0 to S5 obtained from the light receiving element array 105, respectively.

The operation of the position detecting device configured as described above will be described below.

Light emitted from the light source 101 is converted into a parallel light beam by the collimator lens 102 and is irradiated on the scale 103. The scale 103 moves in the movement direction indicated by the scale movement direction. Light from the light source 101 transmitted through the scale 103 and the mask 104 is detected on the light receiving element array 105, and a change in transmitted light signal intensity accompanying a change in the position of the scale 103 from the light source 101 is detected by the light receiving element array 105. After being converted into an electric signal and digitized by a signal processing circuit (not shown) into values of 1 and 0 corresponding to each light receiving element, signal processing is performed to obtain a position signal.

However, in the above configuration, when detecting a highly accurate position, all bits from the most significant bit to the least significant bit area of the gray code are detected with the least significant bit detection accuracy. However, as the slit pitch of the scale and mask becomes smaller, the change in the amount of transmitted light becomes triangular with the change in position. Data may be misread. For example, at the position 4B shown in FIG. 4C, the digitized output of the light receiving element array is S5 = 0,
S4 = 0, S3 = 1, S2 = 0, S1 = 0, S0 = 1. On the other hand, the bit of S4 at the position of 4A is erroneously read at a position where it should originally be read as 1 because of a gradual change in the amount of light depending on the position due to the gradual change of the position. Output is S5 = 0, S4 = 0, S3 =
1, S2 = 0, S1 = 0, S0 = 1, which coincides with the pattern output at the position 4B.
A read error of 0 is output as including a 4-bit error of the minimum detection unit of the position with respect to the position where it should be. As described above, due to the reading error of 1 bit of 1 and 0 of the light receiving element array existing near the boundary of 1 and 0 of each bit of the gray code, the value of the actual position and the value of the position output from the detector may greatly differ. Therefore, there is a problem that a large error occurs in these detection positions. Further, when the gray code is used, there is a problem that the number of codes for detecting the absolute position increases and the size of the apparatus itself increases.

The present invention has been made in view of the above problems, and provides an absolute position detecting device capable of detecting an absolute position accurately and compactly without causing a detection error that the small detection error causes a large detection error.

Means for Solving the Problems In order to solve the above problems, a position detecting device according to claim 1 comprises a first position detecting means for detecting an absolute position with a predetermined minimum detection width, and the first position detecting means. Means for detecting an absolute position within a range twice as large as a minimum detection width by the means, and a boundary between a position detected by the first position detecting means and the second position. The boundaries between the detection positions detected by the detection means are shifted by a quarter pitch of the detection range of the second position detection means, and are obtained by the first position detection means and the second position detection means. It is characterized by comprising a correcting means for correcting the detection value based on the position information.

The first position detecting means may be constituted by a slit pattern extending obliquely to the displacement direction, and the second position detecting means may be constituted by a slit pattern extending obliquely to the displacement direction.

Operation Since the present invention has the above configuration, when the minimum detection pitch of the first position detection means is P ₁ and the minimum detection pitch of the second position detection means is P ₂ , detection error becomes possible to easily detect the correct absolute position in coarse detection error of _{± (P 1/2-P} 2) following.

Embodiment Hereinafter, a position detection method according to the present invention will be described with reference to the drawings.

FIG. 1 shows the overall configuration of an absolute position detecting device according to an embodiment of the present invention. In FIG. 1, 1 is a light source, 2 is a collimating lens that makes light from the light source substantially parallel, 3 is a scale attached to a moving body (not shown),
4 is a fixed mask, 5 is a fixed image sensor, 6 is a slit for detecting a first position for detecting an absolute position with a predetermined minimum detection width, and 7 is a minimum detection by the first position detecting means. A slit for detecting a second position for detecting an absolute position within the detection range with twice the width as a detection range, and a boundary between a detection position by the slit 6 for detecting the first position and the second position; The boundaries between the detection positions by the slits 7 for position detection are shifted by a quarter pitch of the detection range of the second position detection means. Reference numeral 8 denotes a reference slit that is used as a reference when correcting a measurement error due to vertical displacement due to movement of the scale in a direction not to be measured.

The operation of the position detection position configured as described above will be described below with reference to FIG. Light emitted from the light source 1 is converted into a parallel light beam by the collimator lens 2 and is irradiated on the scale 3. The scale 3 moves in the arrow direction shown as the scale moving direction. Immediately behind the scale 3, a mask 4 is provided. The light from the light source 1 that has passed through the scale 3 and the mask 4 is detected by an image sensor 5, and transmitted through the scale 3 from the light source 1 with a change in the position of the scale 3. The position in the direction substantially perpendicular to the direction of movement of the light scale 1 is read by the image sensor 5, converted into an electric signal, and subjected to signal processing by a signal processing circuit (not shown) to detect an absolute position.

Hereinafter, the above-described position detection method will be described in detail with reference to FIG. The distance interval between the slits 6 and the reference slit 8 is detected by the image sensor 5, the digital minimum detection pitch P ₁ = d _1/8 the detection area d ₁ region divided into eight slits 6 by digitizing performs arithmetic position as the smallest unit of reduction is detected by an integer in the range of -4 to 3, the detection position of the detection value in the i region and i * d _1/8. Likewise, the minimum detection pitch P ₂ = d _2/8 the area of the detection area d ₂ of the slit 7 8 divided by digitizing performs detection calculated by the image sensor 5 the distance interval of the slit 7 and the reference slit 8 Is the minimum unit of digitization and the position is -4.
It detected an integer ranging from 3 to detect the position of the detected width in the j region and j * d _2/8 from. Here, d ₂ = d _1/8
* 2. The end edge of the slit 7 of the slit 6 are spaced apart by d _2/4.

If i is even here, the position X becomes _{X = i * d 1/8} + j * d 2/8 (1).

If i is odd and j is 0 or more, the position X becomes _{X = i * d 1/8} + j * d 2/8-d 2/2 (2).

If i is odd and j is less than 0, the position X becomes _{X = i * d 1/8} + j * d 2/8 + d 2/2 (3).

For example, at the position A in FIG. 2, the first position detection means outputs the main body i = −3, j = −3, and the equation applied in this case corresponds to the case of the equation (3), position X by using the equation _{X = -3 * d 1/8} + (- 3) * d 2/8 + d 2/2 = {- 3 * 4/8 + (- 3) / 8 + 4/8} * d 2 = −11 / 8 * d ₂ where i = −2 is output, the equation applied in this case corresponds to the above equation (1), and by using this equation, position X is _{S = -2 * d 1/8} + (- 3) * d 2/8 = {- 2 * 4/8 + (+ 3) / 8} * d 2 = -11 / 8 * d 2 , and the upper Even if the bit value is misread by one bit, if the detection error of the upper position from the boundary of the detection position by the first position detection means is ± (P ₁ / 2−P ₂ ) or less,
You can get the right position.

As described above, according to the present embodiment, accurate reading can be performed even when the value of the high-order bit is misread by one bit, so that there is no error in reading the position in the detection of the absolute position, and the scale is also small. The absolute position can be detected with a simple configuration.

The present invention can be configured in various modes in addition to the embodiments described above.

In the embodiment, the number of interpolations of the slits 6 and 7 is set to 8, but other numbers may be used.

Further, in the embodiment, the number of slits for position detection is described as two, but the number of slits may be two or more.

Further, in the embodiment, as a means for detecting an absolute position with a predetermined minimum detection width, a slit is used obliquely to the moving direction, but a moire fringe or the like may be used.

In the embodiment, the position is detected by an optical method as a means for detecting the absolute position with a predetermined minimum detection width. However, the position may be detected by using another method such as a magnetic method or a mechanical method. Good.

As described above, according to the present invention, the first position detecting means for detecting an absolute position with a predetermined minimum detection width, and the detection range is set to twice the minimum detection width by the first position detection means. And a second position detecting means for detecting a position in the second position detecting means, wherein a boundary between a position detected by the first position detecting means and a boundary between positions detected by the second position detecting means is the second position detecting means. And a signal processing circuit for calculating a detection value based on the position information obtained by the first position detection means and the second position detection means. The minimum detection pitch of the upper
P _1, ± detection error from the boundary of the position detected by the first position detecting means located in the upper when the minimum detection pitch of the lower and _{P 2 (P 1/2-} P 2) hereinafter referred to as a coarse detector It is possible to easily detect a correct position even with an error.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of a position detecting device according to one embodiment of the present invention, FIG. 2 is an explanatory diagram showing an operation principle of a position detecting method according to one embodiment of the present invention, and FIG. FIGS. 4A to 4C are explanatory views showing a slit pattern, a mask pattern and a signal waveform in a conventional position detecting device. 1 ... light source, 2 ... collimating lens, 3 ... scale, 4 ... mask, 5 ... image sensor, 6 ... first
Slit for position detection, 7... Slit for second position detection, 8... Reference slit.

Claims (2)

(57) [Claims] 1. A first position detecting means for detecting an absolute position with a predetermined minimum detection width, and an absolute position within the range is set as a detection range twice as large as the minimum detection width by the first position detection means. And a boundary between a position detected by the first position detecting unit and a boundary between positions detected by the second position detecting unit are set to four times the detection range of the second position detecting unit. An absolute position which is displaced by one-half pitch and further comprises a correcting means for correcting a detection value based on position information obtained by the first position detecting means and the second position detecting means. Detection device. 2. The method according to claim 1, wherein the first position detecting means comprises a slit pattern extending obliquely with respect to the scale displacement direction, and the second position detecting means comprises a slit pattern extending obliquely with the scale displacement direction. The first,
2. The absolute position detecting device according to claim 1, further comprising a signal pattern serving as a reference when measuring the position in the second position detection.