DE2531682A1 - Position recognition system using optical sensor - determines location and orientation of objects by means of circular optical scanning - Google Patents

Abstract

The optical sensor of the location and orientation of objects lying on a table, takes account of the centre of gravity of the area of the envelope of the object and the point of intersection of circles about the centre of gravity with the outline, in which a first scan determines the coordinates of the centre of gravity, after which a circular scan times the period elapsing before the scan meets the envelope. Comparison of the results of two such circular scans with stored reference times enables the nature and orientation of the position of the object and hence its location to be determined. The stored reference values may first be derived from a series of scans with the objects to be recognized in known positions.

Description

Optical sensors for detecting individual workpieces with industrial robots Most of the now known, practically used industrial robots own no optical sensors; they are therefore on a defined and known environment reliant. The present invention relates to a flexible optical sensor, the detection of previously separated workpieces, known types or tools enables.

For many applications of industrial robots, mechanical ones are sufficient Devices, simple optical presence checks or position measurements, around the arm of the robot with the gripper or tool in the desired way steer. For some important tasks in medium and small series production, assembly and these sensors are not sufficient for control; around workpieces, for example to be ordered or positioned are their angular orientation and their position coordinates capture.

With methods of artificial intelligence "the attempt is therefore made to to simulate the sensory abilities of humans / 1 /; the one after today State of the art of computing, required expenditure of computing time and storage space requirements prevent the practical use of these procedures.

The difficult sensory task is simplified when the number the degrees of freedom that a workpiece or a tool # can assume will and when the workpieces may be offered to the sensor in individual cases.

With incoherent optical methods, e.g. through optical correlation or by mask comparison / 2 /, and by using television methods with selection from a few lines of information / 3 / it is possible to capture workpieces, which are occasionally on one level and guided against a mechanical stop will. In particular, the degree of freedom of rotation is restricted by the stop.

The use of mechanical stops is undesirable because it does this for example, the flexible adjustment of the sensor when changing workpieces is impaired and because, in addition, not all workpieces are in defined positions by a stop can be brought.

It was therefore the realization of the unrestricted grip on the table "proposed / 4 / by first placing the workpiece with a television camera scanned and the scanned image is stored in a digital computer; afterward the center of gravity of the area formed by the outline is calculated arithmetically a circle of suitable radius placed around the center of gravity and from the location of the intersection points of this circle with the outline on the shape of the outline, i.e. the type of The workpiece is placed on the table and the angular orientation is closed. The storage space and computing time required for this process is high.

According to the invention, a method is therefore proposed that already in the scanning of the image of the workpiece, i.e. in the opto-electrical Transformation, a strong information reduction and thus the unrestricted Grip on the table "made possible with reasonable effort. The process works in two steps: first, when the image is first scanned, the coordinates the center of gravity of the area defined by the outline of the workpiece; then a circle around the center of gravity with a suitable Radius used and from the times at which these scanning movements the contour line cuts, on the type of support of the workpiece on the table and on the Angular orientation closed.

The proposed method therefore uses the same image features like / 4 /, but is essential due to the inventive implementation of the method less laborious.

An example serves to explain the two steps in more detail.

In Figure 1, a workpiece 1 is shown, which is in one of the its shape made possible types of support on the table surface 2 lies. One after one Image converter scanning a line raster scans the field of view 3.

Furthermore, the following applies: x-coordinate in line direction, y-coordinate vertical for line direction N1 the number of the first line that intersects the outline, N2 is the number of the last line that intersects the outline, n is the number of one any line xni> Xn2 the coordinates of the intersections of the line with the Outline; if there are more than two points of intersection, there are corresponding additional links on s is the distance between two lines.

The coordinates of the center of gravity of the area enclosed by the outline 4 thus result in The quantities involved in these relationships can easily be measured when scanning according to a television grid in a known manner with the aid of numerical counters and a clock frequency generator by deriving start-stop signals for the counters from the scanning signal when the line with the outline is cut.

Either the products are in the counters of the two fraction lines calculated during a line run or the coordinates of the intersection points corresponding counter readings are stored and then the values x5 and y5 are calculated. The storage space and computing time required for this is qering.

The second scan uses an image converter or a punctiform one Lighting device (flying spot) with which a circle around the previously measured Center of gravity (xs) Ys) is described with a given radius and starting point. In Figure 2 shows the center of gravity 5 and a scanning circle 6, which is at point 7 its movement begins at time = n and takes time T for one revolution. The scanning circle enters the area enclosed by the outline at the points 8, 10 and 12 on and off at points 9, 11 and 13; the associated times are tR, tlo and t12 and tgs t11 and t13, respectively. The times t8, t10 - t8, t12 - t8 or

t11 tgs tl3 -t9 are used with dinital counters that send their start-stop signals obtained from the sampling signal, measured in a known manner. These time sequences can be continued periodically with time T.

With the sizes measured in this way, the type of support of the workpiece on the table, the angle orientation and the position coordinates in simple arithmetic steps be determined. In a preliminary learning phase, the workpiece was dated from serving people in every possible type of support with a known angular orientation subjected to the two types of scanning according to a known position; it was under Use of a monitor also a suitable radius of the scanning circle chosen. The resulting center of gravity coordinates and guidelines were qstored (optical "teach in").

In the working phase, after the two scans, the first step is through Compare the measured time sequences with the nesstored time sequences the type of Support and the angular orientation, based on the angular orientation in the learning phase, determined. Subsequently, with the knowledge of the type of edition and the location of the surface center of gravity determines the position coordinates of the workpiece.

If the information obtained with a scanning circle for detection of the workpiece is not sufficient, additional scanning circles with different radii are required used.

For the implementation of the two consecutive scanning steps There are various technical options available. In addition to television tubes come flyina spot scanners and charge coupled photodiode arrays (CCD), the latter e.g. also in circular form, in question.

Literature: / 1 / Fischlein, 0. Intelligent machines are on the Fischler, M.A. way.

Coles, L.S. IEEE Spectrum 11, July 1974, Tenenbaum, J.M. P. 41 48.

There further literature / 2 / German patent application P 2426 199.2 Method for gripping workpieces by means of an automatically controllable handling device.

/ 3 / German patent application P 2513 655.4 Sensor system for control ven automatic handling systems using a television camera.

/ 4 / Heainbotham, W.B. The Nottinqham 'Sirch' Assembly Gatehouse, D.W. Robot.

Pugh, A. 1st Conference on Industrial Robot Kitchin, P.W. Technology, University of t! Otting-Page, C.A. ham, U.K. March 27th - 29th, 1973.

Claims (3)

Expectations Optical sensor for detecting workpieces separated on a table according to the type of support, angular orientation and position using the center of gravity of the area enclosed by the outline and the intersection points of circles around the Center of gravity with the outline, characterized in that the coordinates of the centroid are measured during a first image scan and that by using a circular image-scanning system, from counters and arithmetic units the times, at which the circularly moved scanning point intersects the outline, during a second scan, and that by comparing the measured times and coordinates with stored times and coordinates the type of support and the angular orientation and then the position of the workpiece can be determined. 2. Optical sensor for the detection of singles on a table Workpieces according to type of support, angular orientation and position using the center of gravity the area enclosed by the outline and the points of intersection of circles the center of gravity with the outline according to claim 1, characterized in that the required for comparison with the measured times and coordinates Times are determined according to coordinates in a learning phase in which the workpiece in all possible types of support with a known angular orientation and a known position is subjected to the two Pildscans and that thereby ~ through those monitoring the learning phase People through observation a monitor is used to determine the size of the scanning circle. 3. Optical sensor for the detection of singles on a table Workpieces according to type of support, angular orientation and position using the center of gravity the area enclosed by the outline and the points of intersection of circles the center of gravity with the outline according to claims 1 and 2, characterized in that that the coordinates of the centroid during the first image scan through Use of a line scanning system, counters and arithmetic units to be determined.