Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Reexamination Certificate
1998-11-25
2001-03-27
Martin, David (Department: 2837)
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
C318S567000, C318S568160, C901S002000, C901S009000
Reexamination Certificate
active
06208105
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a robot controller for controlling an industrial robot, and more particularly to a robot controller having an erroneous motion detecting function.
BACKGROUND ART
Robots used in factories and the like sometimes make an abnormal motion due to a failure in a hardware component or a software defect; for example, a robot sometimes makes a motion at a velocity exceeding a value specified by a program or manually specified by a user, or moves toward an unexpected position.
Emergency stop buttons are provided on robots, but since servomotors of high power are mounted on recent robots, it is difficult to immediately stop a robot which has started an abnormal motion by merely depressing the emergency stop button. In addition, an operator tends to be late in depressing the emergency stop button.
In view of the above, there has been proposed a method in which a motion amount of each axis of a robot is periodically monitored by a robot controller and when the motion amount exceeds a predetermined limit value, the robot is automatically stopped, independently of the emergency stop button. This method, however, includes the following problems.
In performing a path control for straight-line or circular-arc, it is natural that velocities of axes greatly differ from one another, and particularly in a control for a path passing near a singular point, the maximum velocity is often required for a wrist axis etc. to maintain a designated orientation of the robot. Therefore, it is not appropriate to set a lower limit value for the detection of abnormal motions so as to avoid erroneous detection of abnormal motions. Consequently, even when an unexpected motion actually occurs, such a motion sometimes can not be determined to be abnormal and the robot is unable to be stopped automatically.
Further, with the above method, in the case where an abnormality occurs as to a position of a robot in motion, for example, a substantial deviation of the robot position from a taught path or a manual feed (Jog feed) direction occurs, such abnormality can not be detected to automatically stop the robot, as long as the velocities of motion of the respective axes are not abnormal.
Thus, the conventional technique is not sufficiently capable of immediately and surely responding to robot motions (abnormal state of motion or abnormal position in motion), posing problems in securing safety of the operator and protection of peripheral equipment.
SUMMARY OF INVENTION
An object of the present invention is to provide a robot controller capable of immediately and automatically sensing an abnormality and stopping a robot to avoid danger when a point representing a robot position is taking an abnormal velocity, an abnormal acceleration or an abnormal motion path in space when the robot operates in a program playback operation mode or in a manual operation mode such as a jog feed.
A robot controller according to the present invention comprises: abnormal motion detection index creating means for periodically creating an abnormal motion detection index for detecting an abnormal motion in space of a point representing a position of a robot, based on present position data of respective robot axes obtained from outputs of position detectors of the robot axes while the robot is in motion; determination means for comparing the abnormal motion detection index with a predetermined reference abnormal motion detection reference, and determining that an abnormal motion has occurred when the abnormal motion detection index exceeds the predetermined abnormal motion detection reference; and stopping means for immediately stopping motion of the robot when an abnormal motion of the robot is detected by the determination means.
Abnormal motion which can be detected with the robot controller according to the present invention is abnormal motion of the robot position-representative point during a program playback or manual feed (jog feed) operation, and the abnormal motions are classified into motion abnormality types stated below. Abnormalities 1 to 4 can be collectively referred to as “abnormality of motion” and abnormality 5 as “abnormality of position”. The term “robot position-representative point” used hin this specification denotes a point set in a fixed relation with respect to end effectors such as a robot hand, a welding torch or the like.
Typically, the robot position-representative point is the origin (tool center point) of a tool coordinate system set with respect to an end effector to be mounted, or the origin of a faceplate coordinate system set with respect to a tool mounting face. In the following description, the robot position-representative point is set at the tool center point (TCP) for convenience sake, but may be set at some other point. (Abnormality 1) Abnormality in Moving Velocity of Tool Center Point: The tool center point moves at a velocity exceeding a limit velocity. (Abnormality 2) Abnormality in Acceleration of Tool Center Point: The tool center point moves at an acceleration exceeding a limit acceleration. (Abnormality 3) Abnormality in Angular Velocity of Wrist Axis: The wrist axis moves at an angular velocity exceeding a limit angular velocity. For example, a state in which the final axis of a 6-axis robot rotates at an abnormally high velocity. (Abnormality 4) Abnormality in Direction of Movement of Tool Center Point: During path control, the tool center point moves beyond a limit in a direction away from the direction of a trajectory calculated from position data in the program. (Abnormality 5) Abnormality in moved Position of Tool Center Point: During path control, the tool center point moves beyond a limit to a position apart from a trajectory calculated from position data in the program.
In a preferred embodiment of the present invention, all of these motion abnormalities can be detected, but some of the abnormalities alone may be detected according to circumstances. For example, only abnormalities 1 and 5 may be detected, and even in this case many of abnormal robot motions can be detected.
The abnormal motion detection index is created within the control device so as to match abnormal motion to be detected and is compared with a corresponding abnormal motion detection criterion, and if an abnormal motion is detected, a process for stopping the robot is executed. Preferably, the abnormal motion detection criterion is automatically created within the control device in accordance with data in a taught motion program or manual feed conditions.
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Kato Tetsuaki
Shirahata Toru
Fanuc Ltd.
Martin David
Staas & Halsey , LLP
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