JP2003322507A - Absolute position detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for detecting unmovedly the present absolute position without returning mechanically a sensor element to the origin and counting from the edge. <P>SOLUTION: In order to specify either of X2 and X3, when, for example, P2 is lit and an output R is acquired, P2 is put out and W2 and W3 are lit alternately, and the magnitudes of outputs T2 and T3 corresponding respectively are compared. T2 becomes the maximum at a singular point overlapping a light shielding part between P1 and P2, and all the other P values become on the zero level. When Wi can be specified, the position of A-A' is necessarily positioned on the center of the light shielding part of pixels P, and thereby the distance is calculated by adding a 1/4 wavelength. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a current absolute position of a detector without using a liquid crystal or other electro-optical effect. The present invention is, for example, a numerical control machine, a machine, a semiconductor substrate transfer device, a three-dimensional drawing device, an endoscopic surgery device, a μ machine manufacturing device, an articulated robot, a gene therapy drug manufacturing device, position control non-contact shape measurement. It can be used for position control of drive system actuators such as devices, optical disk inspection devices, DNA inspection / analysis devices, and the like.

[0002]

2. Description of the Related Art Conventionally, as an apparatus for detecting an absolute position, for example, a scale on which information about a position is recorded at a constant cycle and a position recorded on the scale by moving relative to the scale. A device having a sensor element for reading information is known. Most of the current sensor elements are of optical type and magnetic type, and the former is a method of detecting changes in transmission / reflection characteristics of light using LEDs and LDs.
The latter is a method of detecting the magnetism from a magnetic body with a coil or the like. In order to realize high resolution, both of them have conventionally been a method of causing a phase shift in a sensor signal by arranging a multi-element detector and multiplying by a logic element or quantizing a detection analog signal. Is used. This method of multiplication is important for position detection on the nano-order, and the cause of error due to software processing is
It can be said that it depends on the quality of the output. At present, the method that is said to have the highest detection resolution is an optical multiplication method, and the resolution is increased by quantizing the analog signal from the pickup.

[0003]

However, the optical position detection is generally affected by the disturbance of the diffracted light, and the finer the patterning of the positional information of the scale, the more the interference of the diffracted light due to transmission or reflection. However, it is inevitable that the accuracy will be adversely affected. Also, in multiplication to increase resolution, the accuracy of multi-element arrangement is required, the position-to-signal output characteristic from the pickup is not linear, and reproducibility is poor. The point that the above burden is very large remains as an issue.

In terms of materials, it is required to consider the quality of the scale, which is an element of the position detector, especially heat and environmental temperature. For example, in the nanoscale manufacturing method, it is possible to manufacture a small precision scale by using micromachining technology or vapor deposition technology, but it is difficult to give a sufficient thickness, so it is easily deformed by subtle residual stress or thermal stress. As a result, sufficient reliability cannot be obtained due to dynamic deformation when driving at high speed. Therefore, conventional optical detection has a limit in high resolution and high reliability, and a new scale material has been required. In the case of the magnetic method, the magnetic flux density changes with time, and the detection sensitivity does not reach that of the optical method.

Further, when a scale in which position information is recorded in a fixed cycle is used, it is possible to measure the position within one cycle, but with respect to detection of position over a plurality of cycles (detection of movement amount) It is necessary to integrate the number of times the detected signal is repeated. The detection of the position over a plurality of cycles is not very high in reliability because an error in the number of signal repetitions or the like is likely to occur. Moreover, two-dimensional (XY
When making a scale of (axis), if two absolute one axes are combined, two-dimensional is possible, but since cumulative error occurs, adjustment such as alignment takes a very long time and yield is poor.

Further, conventionally, it was not possible to know the current position when the sensor element is stopped. By moving the sensor element, it is possible to read the coded coordinates created on the scale, so that the current position is detected. However, moving the mechanical part may cause a runaway, so in order to ensure safety, it is necessary to provide a plurality of sensors and limit circuits installed near the origin, CW and CWW limits, and the origin. there were. In addition, since the movement for knowing the current position is not originally necessary, the work takt time becomes longer than necessary. Therefore, the more complicated the process, the more immovable the method for knowing the current position is required.

Therefore, an object of the present invention is to eliminate the method of mechanically returning the sensor element to the origin and counting from the end, and to provide a new method of detecting the current absolute position without movement. And Another object of the present invention is to provide a method that enables absolute detection on a two-dimensional plane, which cannot be achieved by conventional methods.

[0008]

The present invention has been made to solve the above problems, and according to the present invention,
By using the electro-optical effect of liquid crystal, etc .: It is possible to know the current position easily. That is, for example, by utilizing the electro-optical shutter effect of the liquid crystal matrix arranged on the surface light source, it is possible to turn on and off any position by opening and closing the shutter pixel (pixel) of the liquid crystal. The optical sensor installed above the position of the liquid crystal pixel is scanned by opening and closing the liquid crystal pixel in order without mechanical drive such as returning to the origin. When the pixel at the position where the photo sensor is installed opens, the output of the photo sensor increases at that time. Thereby, the position of the optical sensor can be known. This is the same in the XY directions, that is, in the two-dimensional scanning. This makes it possible to know the absolute position without mechanically returning the optical sensor or liquid crystal matrix connected to the drive system to the origin.

That is, according to the present invention, the optical means is arranged on a scale having m (m ≧ 2) pixels of the transmission part in n columns (n ≧ 1), and m of any one column of n columns is arranged. Pixels are sequentially opened and closed for each pixel to estimate the address where the optical means is arranged among the m pixels, and the adjacent pixel in the next column corresponding to the estimated address is opened and closed to determine the adjacent pixel. There is provided an absolute position detection method characterized by comparing the output values from the above and thus detecting the absolute position of the optical means.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The scale used in the present invention has m (m ≧ 2) pixels arranged in at least one dimension.
The pixels have a width of 10 to 100 μm and a pitch of 10 to 100 μm. The dimension (column) in which the pixels are arranged is not particularly limited, but when arranged in multiple dimensions (n columns), the pattern is preferably a staggered pattern, but is not limited to this. In the case of two-dimensional (n = 2), it is preferable to shift by 1/2 wavelength as compared with the one-dimensional pattern.

The width of the pixel is 5 to 500 μm,
It is preferably 20 to 100 μm. This is because when the width of the pixel is 5 μm or less, the influence of the interference of the diffracted light cannot be ignored due to the Fraunhofer law as in the diffraction grating, and this becomes disturbance light, and a precise position cannot be specified. On the other hand, if the width of the pixel is wider than 500 μm, the linearity characteristic of position vs. output is distorted. Further, the pitch is 5 to 500 μm, preferably 2
It is 0 to 100 μm. This is for the same reason as the pixel width described above.

More specifically, the scale of the present invention is
A pair of transparent substrates are opposed to each other, and liquid crystal is sealed between them. A transparent electrode film is formed on one side of the transparent substrate in an amount of 5 to 500.
With a width of μm and a pitch of 5 to 500 μm, a similar transparent electrode film is vapor-deposited on the opposing transparent substrate in a pair with one side, and the light shielding film is short-circuited around the transparent electrode film. To form. The width and pitch are limited to the above-mentioned numerical values, as described above.

Here, examples of the transparent substrate include, but are not limited to, a glass substrate and a polyacrylic substrate. The transparent electrode film is, for example, I
It is preferable to use a TO (InSnO ₃ ) film, but not limited to this. The transparent electrode film is deposited by the CVD method or the like.

Further, the liquid crystal is, for example, a birefringent liquid crystal element, a transmission / scattering liquid crystal element, a TN (twisted nematic) liquid crystal, an STN (super TN) liquid crystal, a ferroelectric liquid crystal element, an antiferroelectric liquid crystal, a polymer. It may be composed of any of dispersed liquid crystals, but is not limited thereto. The distance (cell gap) between the facing substrates is 1 to 100 μm.
m, preferably 5 to 20 μm.

As the light-shielding film, for example, an aluminum vapor-deposited film can be used, but the material thereof is not limited as long as it can prevent the light from wrapping around. For example, as a method of manufacturing the light-shielding film, in addition to the aluminum vapor deposition method, it is possible to form it by a dry / wet etching method after forming a film by chrome vapor deposition or screen printing a gold paste and baking it. Vapor deposition, screen printing, etc. are also possible for the ITO film that corresponds to the window. The transparent substrate on the side where the light-shielding film is formed is preferably on the light-receiving side of the optical means described later.

The applied voltage to the transparent electrode is a frequency DC to 1 kHz when the cell gap of the scale is 5 to 20 μm,
It is preferable to apply a rectangular wave of DC to 300 Hz and 3 to 50 V, preferably 3 to 15 V. By changing the drive voltage within this range,
It is possible to adjust the height and / or width of the signal waveform. This is because the liquid crystal refractive index distribution, the viewing angle, the tilt angle, and the transmittance can be adjusted by adjusting the driving voltage of the liquid crystal. The drive voltage of the liquid crystal may be changed independently for each pixel, or may be changed collectively for a plurality of pixels as a set.

The changes in the liquid crystal pixels are read by optical means. The optical means includes a light projector that irradiates the scale with light, and a light receiver that detects the transmitted and scattered light from the scale. Examples of the light projector include, but are not limited to, a light emitting diode, a laser, a lamp, and an EL (electroluminescence). The wavelength range used is in the ultraviolet to infrared range, preferably
A wavelength range of 300 to 1500 nm can be used. The light projector may be either a point light source or a backlight for illuminating the entire surface of the scale.

The light receiver is an image pickup device (CCD, C-MO).
S, vision chip), a photodiode, a photomultiplier, a solid-state light receiving sensor, a pyroelectric sensor, a thermo-mobile, and various other infrared sensors.

Further, the light transmitter and the light receiver also correspond to those integrated such as a photo coupler and a photo interrupter. Furthermore, the projector and the receiver are multiple photointerrupters,
A plurality of devices may be installed like a PSD (posision sensing device). Also, the projector is a single point or surface light source,
The case where only a plurality of light receivers are connected and the opposite case are also included.

Further, a slit may be provided between the light projector and the liquid crystal display panel or between the liquid crystal display panel and the light receiver to prevent light from wrapping around. The slit width varies depending on the size of the liquid crystal pixel, but is 50 to 500 μm in the case of a scale, for example. Further, the scale of the present invention is not limited to liquid crystal, and a piezoelectric element such as PZT or a shutter array manufactured by micromachining can be used.

The present invention will be described in more detail below. First, a method of knowing a precise one-dimensional absolute position will be described, and problems in that case and a solution thereof will be described. In particular, by using an electro-optical shutter such as a liquid crystal and a point light source, it is possible to determine a precise position by utilizing the halftone in the pixel. For example, by arranging a pair of a light source having a width equal to that of a pixel and a sensor for inspecting the light in a sandwich of an electro-optical shutter matrix, it is possible to obtain a higher precision in a pixel by using a halftone. It is possible to detect various positions by arbitrarily dividing the pixels.
That is, the pixels in the matrix can be divided with higher accuracy. In that case, the pixels need to be staggered with the same width and only where they block light. However, if the position of the sensor-light source pair is detected immovably using electro-optical scanning, the position
Since the same level output is output at different positions and binarized, it is not possible to specify which position the output is located. Therefore, by providing another pixel row on the staggered pattern, the problem of binarization can be solved.

FIG. 1 shows a scale pixel array and a light source.
The positional relationship of a sensor pair is shown. In FIG. 1, (a) is a cross-sectional view of the first column of the scale pixel array 1, (b) is a view corresponding to a transmissive part (P1, ... P4) of the pixel array 1, and (c) is a sensor point. Represents In the figure, L is a light source, S is a sensor, and 2 is a signal amplifier. The scale pixel array 1 has a detailed cross-section omitted, but a pair of glass substrates are made to face each other and are spaced by a spacer (for example,
5 μm) and liquid crystal is sealed. Further, an ITO film is vapor-deposited on the glass substrate to form a liquid crystal drive electrode, and a voltage controlled by a control circuit is applied to the liquid crystal drive electrode. On one side of the glass substrate, an ITO film 30
The pattern for forming the light transmitting window of μm square is, for example, 30
It is formed with a pitch of μm (transmissive portions P1, ... P4), and a similar ITO film of 30μ is formed on the opposing glass substrate.
The m-square pattern is formed so as to form a pair with one side, and a chrome vapor-deposited film for light shielding is formed by short-circuiting around the ITO film (light shielding portion).

Center of the light source L-sensor S pair AA '
Let R be the sensor signal output when X reaches an arbitrary position X. Assuming that the signal output R receives a light amount corresponding to the size Q of the light receiving portion of the sensor, it corresponds to the signal amount in which AA ′ has moved and accumulated by the Q amount. Therefore, the relationship between the sensor position and the signal output V Shows the trace of output change when moving from the point X0 to Xe.

Therefore, the arbitrary position X of AA 'is set to the light source L.
-As a method of knowing the position without mechanically operating the sensor S pair, when the lighting of the pixels is sequentially turned on from the point P0 to the pixel P1, the light source L-sensor S
When P2 involved in the place where the pair is stopped lights up, the output of R is obtained (FIG. 3). This means that the stop position Pi can be determined from the output of R by storing the address of the pixel at the stage of lighting sequentially. It is also possible to determine a precise position within a pixel from the output amount of R.

However, an arbitrary pixel Pi can be determined, but from R, the position of the sensor is Xi or Xi + 1.
If it cannot be specified (in the case of FIG. 4A and FIG. 4B), and if R is at 0 level (that is, the light source-sensor pair is hidden by the light-shielded portion), even the pixel cannot be specified.

As shown in FIG. 5, Xi or Xi according to the first column
The problem is solved by providing a pixel array in the second column in order to specify +1 or to which pixel the light-shielding portion on the left side hides the light source-sensor pair. FIG. 5A shows an arrangement example of pixels in two columns, and the width of the pixel of W is the same as the width of the sensitive width Q of the light source sensor pair like P. That is, for example, in order to identify X2 or X3 when there is an output R when P2 is turned on as shown in FIG. 5B, P2 is turned off and W2 and W3 are switched on. This is possible by alternately turning on the lights and comparing the magnitudes of the outputs T2 and T3 corresponding to each (FIG. 5 (c)).

When R ≠ 0, the center of the light source-sensor pair is always P2 at the right missing portion, and the position shown in FIG.
This is because the relationship of T (2)> T (3) is established as follows. Right chipping means that the center AA 'of the light source-sensor is on the left side of the triangle. Incidentally, since the triangular vertex is a singular point that is not binarized from R by the pixel P, it can be uniquely obtained from the R output. In the case of R = 0, it is possible to know in which light-shielding portion the light-shielding portion is located if the lights are sequentially turned on from W1. That is, at a singular point overlapping the light shielding portion between P1 and P2, T2 becomes maximum and all other T values become zero level. When Wi can be specified, the position of AA ′ is inevitably located at the center of the light-shielding portion of the pixel P, so that the distance is calculated by adding ¼ wavelength.

The simplest structure of the light source-sensor pair is to install only a single element pair so that both the first and second rows can be detected as shown in FIG. If a twin pair is used, the above-mentioned algorithm of turning off the first column → turning on the second column can be omitted.

Since the problem of binarization is solved by the above,
It becomes possible to determine the fine current position in the pixel from the sensor analog output intensity corresponding to the halftone. The desirable arrangement of the second pixel row forming the zigzag pattern must be shifted by 1/4 wavelength.

FIG. 6 shows a flow sheet of a scanning method for opening and closing pixels. Scan the opening and closing of a row of pixels. The i-th pixel position where the output of the photo sensor exceeds a certain threshold is detected, a binarization value corresponding to the output is calculated, and the distance between the two candidates is selected. This threshold level has the same meaning as the zero level described above. For example, S
This is the output level when N ratio = 1, and is the minimum detection resolution. Next, the i-th column and the i + 1-th column are alternately opened and closed in the second column, and it is possible to determine which side of the apex of the triangular wave is depending on the magnitude. That is, W _i > W
_{If i + 1} , it becomes the i-th position, and if W _i <W _{i + 1} , it becomes the i + 1-th position, and the distance can be obtained as shown in FIG.

[0031]

According to the present invention, the current absolute position can be detected without movement without mechanically returning the sensor element to the origin and counting from the end.

[Brief description of drawings]

FIG. 1 is a diagram showing a positional relationship between a scale pixel array and a light source-sensor pair.

FIG. 2 is a diagram showing a change in output of a sensor.

FIG. 3 is an output diagram when P2 involved in a place where the light source-sensor pair is stopped is lit.

FIG. 4 is a diagram showing that the position of a sensor cannot be specified.

FIG. 5 is a diagram in which a pixel array in the second column is provided.

FIG. 6 is a flow sheet diagram of a pixel opening / closing scanning method.

[Explanation of symbols]

1 ... Scale pixel array 2 ... Signal amplifier L ... light source S ... sensor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Junya Kobayashi             2-10-9-2 Hyakurakuen, Nara City, Nara Prefecture F term (reference) 2F065 AA02 AA07 AA14 BB02 BB18                       DD03 DD06 FF02 FF23 GG02                       GG04 GG07 GG12 GG18 HH03                       HH15 JJ01 JJ03 JJ05 JJ09                       JJ17 JJ18 JJ26 LL30 LL36                       LL53 MM12 MM22 MM28 PP12                       PP22 QQ25                 2F103 BA37 CA02 CA06 DA07 DA09                       EA02 EA15 EA19 EA20 EB02                       EB06 EB07 EB08 EB12 EB14                       EB15 EB16 EB28 EB33                 2H079 BA01 CA12 CA22 DA08 EA13                       GA04 GA05 KA18 KA19                 2H088 EA22 EA33 GA10 HA02 HA28                       JA05 JA13 JA17 JA20 KA02                       MA20

Claims (3)

[Claims] 1. An optical means is arranged on a scale having m (m ≧ 2) pixels of a transmission part in n columns (n ≧ 1),
Sequentially opening and closing pixels for m in any one of the columns to estimate the address of the m pixels where the optical means is located, and the adjacent pixel in the next column corresponding to this estimated address. Is opened and closed to compare output values from adjacent pixels, and thus detect the position of the optical means. 2. The absolute position detecting method according to claim 1, wherein each pixel in n columns is arranged so as not to overlap with a pixel in an adjacent column. 3. The absolute position detecting method according to claim 1, wherein the scale is made of liquid crystal, and the optical means is made of a light projector and a light receiver.