JPH01291114A - Absolute position detector - Google Patents

Abstract

PURPOSE:To shorten the read-out time of one frame and to improve the responsiveness by reading out only a necessary pitch element without reading out all picture elements. CONSTITUTION:A signal charge from a photodiode 5 is transferred to a vertical shift register, and the signal charge is transferred to a head register 6. To the register 6, a switching element 7 of an FET is connected, and also, by the next clock which the signal charge of the register 6 has reached, the signal charge is swept out to a ground line 8. The element 7 is set to ON state selectively by an output signal of a horizontal address decoder 9, and the signal charge which has passed through the element 7 is supplied to a comparing circuit 11 through a charge voltage converter 10. To the circuit 11, a threshold voltage is supplied 12, and a binarized image pickup signal is taken out. This image pickup signal is supplied to the decoder 9, and an address of a picture element for executing read-out is designated. In such a way, only the picture element required for deriving absolute position information is read, therefore, the read-out time of one frame is shortened, comparing with reading out all the picture elements of an image pickup element 21, and an output delay time can be shortened remarkably.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an absolute position detection device suitable for use, for example, in detecting the angle of an arm of an industrial robot or detecting the position of a machine tool when feeding a table.

[Summary of the Invention] The present invention provides an absolute position detection device that detects an absolute position by capturing an image of a code plate pattern using a two-dimensional image sensor and processing the image signal.
A switching element that is selectively turned on by the output of the address generation circuit is provided between the exit of the transfer register of the dimensional image sensor and the output terminal, and the signal charge at the exit of the transfer register is swept out at the next clock. The responsiveness is improved by using the address generation circuit to search for a necessary read address based on the signal from the output terminal.

[Conventional technology]

Absolute position detection devices are often used to detect the angle of industrial robots and the feeding position of machine tool tables.
As described in the specification of No. 26, a numerical pattern is formed on a code plate serving as a scale plate, and a stripe-like pattern is also formed, and this code plate is read by a two-dimensional imaging device composed of a CCD. proposed an absolute position detection device that detects a position with coarse precision from a numerical pattern and a position with precision from a striped pattern by processing the output signal of an image sensor.

FIG. 5 shows a schematic configuration of the above-mentioned absolute position detection device, which includes a code plate 20 as a scale plate, and a code plate 20 as a scale plate.
At least one of the image sensors 21 disposed opposite to the image sensor 0 is movable. The code plate 20 has a sixth
As shown in the figure, numerical pattern area 2 showing gray code
2 and a striped pattern area 23 are provided. Gray code is one of the codes that express binary numbers, and is also called alternating binary code or reflective binary code, and has the characteristic that only one bit always changes between two adjacent numbers. are doing. Striped pattern area 23
, a plurality of stripe-like patterns P each having a width W are formed parallel to each other and spaced at equal intervals. The arrangement direction Z of these striped patterns P is perpendicular to the extending direction of the pattern P, and the arrangement pitch thereof is defined as Pz. Gray codes in the numerical pattern area 22 are attached corresponding to each pattern P, and by reading these gray codes, the absolute position in two directions can be known.

An image sensor 21 disposed facing the code plate 20 described above
is a two-dimensional imaging device using a CCD. code board 2
The direction of relative movement between 0 and the image sensor 21 is parallel to the arrangement direction Z. The axial direction of the image sensor 21 itself is provided so as to have a slight inclination angle θ with respect to the arrangement direction Z. In FIG. 6, the angle between the vertical axis V of the horizontal and vertical coordinate axes H1 of the image sensor 21 and the arrangement direction Z is defined as θ.

The image sensor 21 is arranged in each pattern area 22 .
23 are simultaneously imaged, and the image signals are sent to the detection circuit 24 shown in FIG. As will be described later, the coordinates of a predetermined point are read from the live pattern P. These read data are supplied to the coordinate conversion circuit 25. The coordinate conversion circuit 25 calculates absolute position information in the Z-axis direction based on the value of the gray code and the coordinates of a predetermined point of the striped pattern P. That is, according to the Gray code, the pattern P
Positional information with relatively coarse accuracy is obtained in units of arrangement pitch Pz, and positional information with even higher accuracy can be obtained based on the coordinates of a predetermined point of pattern P (by coordinate transformation).

In addition, in FIG. 5, the LE is connected from behind the code board 20.
Light from a light source 26 such as D is irradiated, and an example is shown in which a so-called transmissive type code plate 20 is used. good.

FIG. 7 shows an enlarged view of a part of the image captured by the image sensor 21. The pattern P of the striped pattern area 23 is binarized for each pixel (cell) S of the image sensor 21. It has a video pattern. In this case, the image sensor 2
Since the v-axis direction of the pattern P and the arrangement direction Z of the striped pattern P have an angle θ, the edge E of the pattern P has a stepped shape as shown in FIG. This stepped boundary line E occurs at the upper edge Ea and lower edge Eb of the pattern P. Pixels Sal, Sa2, etc. on the stepped portion of the upper edge Ea can be detected as pixels that change from white to black when scanning in the H direction, and pixels Sbl, Sb2, etc. on the stepped portion of the lower edge Eb can be detected as pixels that change from white to black when scanning in the H direction. It can be detected as a pixel that changes from black to white during scanning.

Here, if the coordinates in the H-axis and V-axis directions of the image sensor 21 are expressed in units of the number of pixels S, the coordinates of the pixel Sal at a predetermined stepped portion of the upper edge Ea are (Hal, Val), and The coordinates of the pixel Sbl on the stepped portion of the lower edge Eb corresponding to the pixel Sat are (Hbl, Vbl), and the coordinates of the center position of the line segment connecting these pixels Sal and Sbl are (H
l.

Vl) is Hl-(Hal+Hbl)/2 V l - (Va 1 + Vb 1) /2.

The point of this coordinate (Hl, Vl) is, as shown in Fig. 8,
It is located on the center line C of the striped pattern P, and the absolute position Zc of this pattern center line C in two directions can be read from the gray code.

Furthermore, since each coordinate value is expressed using the number of pixels S as a unit, if each pitch of the pixel S in the H-axis and v-axis directions is PM and Pv, respectively, it becomes a reference point for reading the position of the image sensor 21. Coordinates (Hl, Vl) relative to the origin (0,0)
The actual distance is HI PH in the H-axis direction and VIPv in the V-axis direction. Therefore, the absolute position Z0 of the origin (0, O) in the Z-axis direction is determined by the absolute position Zc of the pattern P, each coordinate value H1, Vl, each pitch P, , Pv, and inclination angle θ of the pixel S, as follows: Zo = Z c −(HIPM sin θ+VIP
vcos θ). As a result, in principle, the absolute position can be read with an accuracy of the minimum unit P, sin θ.

Note that the coordinates of each pixel S are all expressed as integer values, but the coordinates of the center position (Hl, Vl), etc. are values that are integral multiples of 0°5.

[Problem to be solved by the invention]

In the above-mentioned absolute position detection device, since the image sensor 21 reads out all pixels, the readout time for one frame becomes long.
There was a problem that the output delay time of the current position information became long.

If the output delay time is long, the range of use will be limited. The output delay time is expressed by the following formula.

(Output delay time>-'A<exposure time)+(pixel signal transfer processing communication time) When the image sensor 21 is of an interline type, the order in which the charges of each pixel are read out is performed as follows.

■Transfer the charge of the photosensor diode to the vertical shift register.

■Execute the shift operation of the vertical shift register.

At the same time, the first horizontal line charge is transferred to the horizontal shift register.

■Execute the shift operation of the horizontal shift register.

At the same time, the leading charge is read out.

The above operations are executed in the order shown in FIG. In FIG. 9, Nh indicates the number of horizontal pixels, Nv indicates the number of vertical pixels, the shift time required for the operation of ■ is T1, the shift time required for the operation of ■ is T2, and the shift time required for the operation of ■ Assuming that T3 is T1, T1 is sufficiently short compared to T2 and T3 and can be ignored, and the time T required to read out the charges of all pixels of the CCD image sensor 21 is T'', (T2+T3XNh) ・Nv. Become.

As an example, if the horizontal shift operating frequency is 10MHz (T3
-0.1μ5ec), and the vertical shift operating frequency is IM
Hz (T 2-1 μ5ec), (300X300
), the readout time T for one frame is approximately 9.3 m5ec as shown in the equation below.

(1 μsec +0.1 μsec x300) x3
00 = 9.3 m5ec By the way, when focusing on the image of the image sensor 21, the portions that provide the information necessary to output absolute position information are only a small portion such as the edges of the striped pattern P. That is, the coordinate values of points that change from white to black or from black to white at the edges of the striped pattern P, and the pixel data values (0 or 0) near the center of each track of the numerical pattern on the horizontal line where the change point is located. 1) is required.

Therefore, an object of the present invention is to provide an absolute position detection device that does not read out all pixels but only reads out necessary pixels, thereby shortening the readout time for one frame and improving responsiveness.

[Means to solve the problem]

In this invention, a switching element that is selectively turned on by the output of the address generation circuit is provided between the output terminal and the output terminal of the transfer register of the two-dimensional image sensor, and the signal charge at the output of the transfer register is The address generation circuit searches for a necessary read address based on the signal from the output terminal.

[Effect]

The address generation circuit detects the edge of the striped pattern by sequentially comparing the signal at the edge of the striped pattern from the binary output signal of each pixel of the image captured by the image sensor, Imaging signals outside the edge, which are used to search for the stepped portion within the edge, are unnecessary and are therefore swept away. The address of the stepped portion detected by the search operation is determined.

Therefore, the imaging signal outside the edge of the striped pattern is
Only the addresses at the edges are read, and even at the edges,
Since pixels other than the search point are not read out, the readout time of the image sensor is significantly shortened, and the delay time until absolute position information is output can be shortened.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. This embodiment is an application of the present invention to the previously proposed absolute position detection device mentioned above.

With this absolute position detection device, an image, a part of which is shown in FIG. 2, can be obtained. In FIG. 2, x represents a stepped portion generated at the edge of the pattern P in the striped pattern area 23,
・represents the reading point of the numerical pattern area 22, Gl,
G2. G3... indicates a gray code value that is a collection of pixel data values (0 or l) near the center of each track.

In the image shown in FIG. 2, the change point coordinate value (Hx) of the stepped portion is determined by the least number of pixel readouts.

A method for determining the gray code value and the gray code value will be described below.

First, addresses h and v are assigned in the horizontal direction H and vertical direction V, respectively, in order to distinguish each pixel.

h-0,1,2,...+hll yxQ, L, 2. ..., ■.

The address symbol for the read pixel in the horizontal direction is h2, h address hs + si at the right end of the varnish drive, when h address n-0 when searching for the change point coordinate value, h In
. : When search start h address n-1, h*+I: When first h address n-n after search start, )L@, @: nth (search end) h address after search start h@+L: Pixel address near the center of each track in the numerical pattern section 22 (t-1, 2, ..., t (number of tracks)) As shown in FIG. 1, the first readout of one frame is as follows:
Start from (h,,o). The read data value (0 or 1) is represented by (h,,0).

(A) Next, vertical shift operation to increase ■ by one) (h,
, , ), the outputs obtained from flip-flops 1 and 2, respectively, are supplied to an exclusive OR gate 3. In exclusive OR gate 3, (h,,v)
(2) The calculation (h,,v-1) is performed. When the output of this exclusive OR gate 3 is false, it is not the edge of the striped pattern P, so we return to (A), and when the output is true, it is the edge of the pattern P, so (hl, ., V) and starts the search operation.

(B) The next search point is found using the following equation.

hl+l =hs, e + (2((hs, o, v)■
(hr, v)・)-1] ・2″Kihs,, 1xL,, −, + (2((h@-R-1nv
)■(h,,V))-1) ・2″1 Here, () is 0 when the logic output of the exclusive OR gate 4 is false (not at a step), and the logic output is true (not at a step). Set to 1 when the final search point (hs,
m, v) and find the change point coordinate values (Hx, Vy).

Hx-(hs, * + (2((hs, a, v)■(h
-, v)) 1) ・2-') ・P) lHv
xv-P.

PH: Horizontal pixel pitch Pv: Vertical pixel pitch [ ] is either +1 or -1, so Hx-(
h, , ±2-')-Po, where Hx represents the intermediate position (switching point) of the pixel.

Next, as in the image shown in Fig. 2, if there are two coordinate change points on the same edge of the striped pattern P, the V on the left side is (→-1) more than the V on the right side. hs, 0 ・pH・sin θ+v−Pv−cos
θ=h,,,” −PH−5in θ+(v
+1) ・Pv −cos θ holds, where hl. ' is the search start address of the coordinate change point on the left side, which is (h, .', ■+1). hs,. )I
IT. The relationship with ' is expressed by the following formula % hs. The search operation starts from ' and returns to CB).

When the search operation is completed, pixels (he, t, v+i) near the center of each track in the numerical pattern area are read one after another to determine the gray code value G.

Once the coordinate value and Gray code value of the change point are determined as described above, return to (A), repeat the same operation, and obtain (
v-ve), the reading operation for one frame is completed.

Note that one coordinate change point (Hx, Vv) is 1+2 (
2”-1+2”-”+...+2°)=2 ” ' −
1, and when Hx is the upper limit or lower limit of Hx, it is assumed that the (Hx, Vy) point could not be searched, so H
The range of x is within the search range pixels.

As described above, in order to detect the edge of the striped pattern P, the pixel at address h is read out, the pixels at n search points in the detected edge portion are read out, and the pixels at address h19 are read out.
．． The gray code value is determined by reading out the pixels. Therefore,
The change point coordinate values (Hx, Vy) and the gray code value G can be determined by a method that minimizes the number of times of pixel reading.

In the example shown in FIG. 2, the position of the read pixels and the number of read pixels are shown in FIG. 3, and the read time for one frame in this case is determined. The vertical shift operation frequency of the CCD image sensor is 1MHz (1tL3), and the pixel charge readout time is 0.3
μs, n-6 (search range 127), number of tracks 10, number of striped edge lines 30, number of pixels (30
0x300), vertical shift operation time + h1 point read time + h, and 1 point read time = 3ooXi#+ (300-30)xo, 3as+ (
7+7+10)×30×0.3μ5-597μs, which can significantly shorten the time for reading signals from the image sensor.

Now, the reading of h,,h,,h,can be realized by a function of randomly reading in the horizontal direction. FIG. 4 shows the configuration of a CCD image sensor capable of horizontal random access.

The signal charge from the photodiode 5 shown with diagonal lines in FIG. 4 is transferred to the vertical shift register, and the signal charge is transferred to the first register 6 through the vertical shift register. A FET switching element 7 is connected to the first register 6 of the vertical shift register, and
The configuration is such that the signal charges are swept out to the ground line 8 by the next clock after the signal charges reach the first register 6.

The switching element 7 is selectively turned on by the output signal of the horizontal address decoder 9. switching element 7
The signal charge passing through the charge voltage converter 10 is supplied to a comparison circuit 11 . The comparison circuit 11 is supplied with a threshold voltage from a terminal 12, and the output terminal 13 of the comparison circuit 11 is supplied with a threshold voltage.
A binarized imaging signal is extracted. This imaging signal (h.

(2)] and is supplied to the horizontal address decoder 9. The horizontal address decoder 9 uses the address (h, , h, , h) of the pixel to be read by the above-described operation.

).

〔Effect of the invention〕

Since this invention reads only the pixels necessary to obtain absolute position information, the readout time for one frame is shortened compared to reading out all pixels of the image sensor, and the output delay time can be significantly shortened. I can do it. In addition, when there is regularity such as a constant stripe pitch, or when conditions such as only minute displacement hold, the search range can be predicted, the search range can be reduced (or omitted), and Frame readout time can be shortened.

[Brief explanation of the drawing]

FIG. 1 is a flowchart used to explain a horizontal address decoder in an embodiment of the present invention, FIG. 2 is an enlarged view showing a part of an image of an image sensor, and FIG. 3 is a route map showing read pixel points and their number. , FIG. 4 is a connection diagram of a horizontal random access CCD, FIG. 5 is a block diagram showing a schematic configuration of an absolute position detection device to which the present invention can be applied, and FIG. 6 is a plan view showing an example of a code plate pattern. FIG. 7 is a plan view showing an enlarged view of the striped pattern P imaged by the image sensor, and FIG. 8 is a route map for explaining the coordinate conversion operation. Explanation of main symbols in the drawings 6: Start register of vertical shift register, 7: Switching element, 8: Ground line, 9: Horizontal address decoder, 21: Image sensor, 22: Numerical pattern area, 23 Varnish drive-like pattern area. Agent: Tadashi Sugiura, Patent attorney
Daan Pψ is also public J swamp 7th figure 4 standing in 4 directions! π Encoder Tsuo e Tenshi NM Fig. 5 ■■■■−−−■■■■−−−■■■■−１−■−−−
■■■ - Figure 9 Cor 1'm (7tr-7L O and above) ayt) @ Turn row Figure 6 Procedural amendment recommendation form, September 7, 1988 Patent Application No. 120232 2 , Name of the invention Absolute position detection device 3, Relationship with the case of the person making the amendment Patent applicant address 6-7-35, Kitashina, Tokyo Parts Store Name (21
8) Sony Corporation Representative Director Noriyoshi Ohga 4, Agent 170 Address 1-48-10-7 Higashiikebukuro, Toshima-ku, Tokyo In the statement of contents of the amendment, page 19, line 20, ``On the route map for be."
is corrected as below. ``Route map for ``, Figure 9 is a route map for explaining the readout operation of the image sensor.''

Claims (1)

[Scope of Claims] A switching element that is selectively turned on by the output of the address generation circuit is provided between the output terminal and the output terminal of the transfer register of the two-dimensional image sensor, and a switching element that is selectively turned on by the output of the address generation circuit is provided, and a switching element that is selectively turned on by the output of the address generation circuit is provided, and An absolute position detection device characterized in that the charge is swept out at the next clock, and the address generation circuit searches for a necessary read address based on the signal from the output terminal.