Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Reexamination Certificate
2001-12-21
2003-11-11
Leykin, Rita (Department: 2837)
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
C318S568160, C318S568190, C901S042000, C901S043000, C700S282000
Reexamination Certificate
active
06646404
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for controlling a robot which follows a moving object which is conveyed on a conveyor or the like and which performs a predetermined action on the moving object. The present invention also relates to a robot controller using the method.
2. Description of the Related Art
Hitherto, in conveyor tracking in which such a moving object (hereinafter referred to as a “work”) is followed, an external sensor such as a proximity switch determines as to whether the work has come into a region in which a robot can move, and the robot starts to follow the work at its finger tip (tool) in accordance with a determination signal and performs an action on the work when the hands reach the work. The known conveyor tracking has been applied mainly to welding of automotive bodies disposed on a conveyor. The known system of conveyor tracking has been formed such that the conveyor moves at a low speed and a small number of the works (generally one work) is processed at one time.
Recently, various applications have required conveyor tracking, and a processing of a plurality of the works have been required while they are conveyed on a conveyor at a certain level of speed. However, it has been difficult to realize applications by using a system such as that described above in which a small number of works are processed.
When the positions of the works change, a certain amount of computation in proportion to the number of works is necessary. Therefore, for example, when the robot is positioned so as to be inclined with respect to the conveyor instead of being parallel thereto, the current positions of the works must be computed by performing trigonometric computations based on the angle of inclination of the robot with respect to the amount of movement of the conveyor. Thereby, the amount of the computation becomes significantly increased because it is necessary to compute an x-coordinate value and a y-coordinate value in a robot coordinate system (a rectangular coordinate system (x, y, and z) in which the z-axis is a vertical axis having the origin at a mounting base of the robot). Therefore, there is a problem in that the number of works which can be processed at one time is limited, a high-speed CPU for processing numbers of the works is required, and so on.
In an operation program for the robot to follow the works on a conveyor, a targeted position of the tool of the robot is set in the robot coordinate system. Therefore, it is difficult to designate the position based on the conveyor (for example, to designate a position 5 mm upstream from the center of a work or a position 10 mm upward in the width direction of the conveyor from the center of the work), and therefore, the description of the program becomes complex.
Recently, a system which uses a camera for detecting the works has been known. It is expected that the system can be used when a plurality of the works are scattered on a conveyor because the camera can determine the positions and orientation of the works. However, the problem of the large amount of computation for updating the present positions of the works has not been overcome even in such a system.
In these known systems, the users must program processes for checking whether a work is positioned in an operational range of the robot or out of the operational range. Therefore, a process loop for monitoring whether or not the current position of the work is in the operational range must be described in the user program.
FIG. 20
shows an example of the description of a user program.
FIG. 21
is a flowchart corresponding to the user program shown in FIG.
20
. The same reference numerals are used for corresponding steps in
FIGS. 20 and 21
.
In this user program, it is checked by a process loop (DO . . . LOOP) whether or not the work is positioned in an operational range (step S
101
), and when the work is positioned in the operational range, a following path is formed and the robot follows the work (step S
102
). The following path is repeatedly formed until completion of handling of the work (step S
104
), while a process loop (REPEAT . . . UNTIL) checks whether or not the work moves outside of the operational range (step S
103
). When the robot moves outside of the operational range, the following motion is suspended and an error process is performed (step S
105
).
In the known technology, since it is checked, based on a user program, whether or not the work arrives in the operational range (handling region) of the robot, laborious work such as program creation is required of the user, and the program becomes complex thus less readable.
When the program is suspended for any reason while the robot is performing the following motion, there is a risk of the robot colliding against other devices disposed in the operational range of the robot or an error is caused by the robot trying to operate beyond its operational range.
A robot controller which controls a plurality of devices such as a camera and a robot is provided with a multi-tasking ability to perform at a high speed a parallel processing of a plurality of programs such as a program concerning determination of the position of the work and an operational program of the robot. However, some processes such as checking for arrival and deviation of the work which may enough function even by a simple checking at given intervals are processed excessively due to the process loops, whereby the operational speed of the other programs is decreased and the performance of the robot controller as a whole is lowered, that is, the multi-tasking ability is not used efficiently.
The known handling system generally includes a straight conveyor, and it is difficult to control motion to follow the works conveyed on a conveyor which has a curved conveying pathway for the works, such as a turntable or an arc-shaped conveyor. A technology is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 60-221805, which overcomes this drawback. However, the drawback of the large amount of computation required for determining the position of the work has not been solved.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for controlling a robot and a robot controller using the method in which the amount of computation for determining the present position of a work conveyed on a conveyor is decreased regardless of a moving path, a robot operation on a moving object can be described easily, and intuitive teaching is made possible.
It is another object of the present invention to provide a method for controlling a robot and a robot controller using the method in which a program can be described easily and the execution speed of the program can be increased by setting a handling region (following region) of the robot and by providing a function to check the relationship of the positions between the following region and the work.
(1) According to one aspect of the present invention, a method for controlling a robot, which follows a moving object conveyed by a conveyor and which performs a predetermined action on the moving object, is provided. The method comprises the steps of detecting the moving object; obtaining a detected position of the moving object in a conveyor coordinate system from the result of the detection; sequentially updating a current position of the moving object in the conveyor coordinate system on the basis of the detected position of the moving object and the amount of movement of the conveyor; transforming the current position of the moving object in the conveyor coordinate system to that in a robot coordinate system; and forming a following path for the robot to follow the moving object, on the basis of the transformed position.
(2) In the method for controlling a robot according to the present invention, the conveyor coordinate system may consist of an x-axis in the movement direction of the moving object, a y-axis which represents, together with the x-axis, a carrying surfa
Kameyama Takayuki
Okuyama Masayuki
Setsuda Nobuyuki
Leykin Rita
Seiko Epson Corporation
Watson Mark P.
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