Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1994-12-14
1996-04-16
Swann, Glen
Communications: electrical
Condition responsive indicating system
Specific condition
340679, 901 13, G08B 3100
Patent
active
055086861
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an overtravel detecting device for an industrial robot. More particularly, it relates to an overtravel detecting device, for an industrial robot, which can determine and detect limit positions during a rotation of the robot about an axis of rotation, and permits setting of a limit to the rotating motion of the robot which is more than 360 degrees.
PRIOR ART
In industrial robots, especially in a multi-articulated industrial robot, movable elements thereof are allowed to perform respective rotating motions about a plurality of axes, and accordingly, a foremost movable element of the robot, e.g., a robot end effector such as a robot hand, is made to perform a desired amount of motion by rotating several movable elements.
In the multi-articulated industrial robot, the rotating motion of each movable element about its own axis or articulation is usually driven by a drive source comprised of an electric motor. The rotating motion performed by each movable element of the robot about its own axis in the clockwise and the counterclockwise directions is limited to a predetermined angle to prevent the robot from being excessively moved so as to ensure the safety of an operator and to avoiding mechanical interference between the robot and equipment installed near the robot to thereby prevent the robot or the equipment being damaged.
One method conventionally used to prevent the robot moving excessively is to provide an overtravel detecting device on each articulation axis of the robot so as to limit the motion of each movable element around its own articulation axis.
One of the conventionally used overtravel detecting devices is constituted by mechanical dogs attached to each movable (rotatable) element of the robot, and a detecting unit such as well known limit switches and proximity switches attached to a stationary element of the robot confronting the movable element. The overtravel detecting device operates in such a manner that the detecting unit is actuated by the mechanical dogs when the movable element of the robot is moved through a predetermined motion range with respect to the stationary element, and a signal indicating the limit of motion of the movable element is transmitted by the detecting unit.
Another conventional overtravel detecting means is constituted by an encoder unit incorporated in a drive motor for each movable element comprised of a servo motor. The encoder unit constantly detects the amount of rotation of the movable element, and transmits a signal, to a robot control unit, as a feedback signal which the control unit uses to detect overtravel of the movable element.
Nevertheless, in the former conventional overtravel detecting means using mechanical dogs and a detecting unit for detecting the limit of rotation of a movable element of the robot about an axis of rotation, since the dogs are arranged so as to be brought into physical contact with the detecting unit to detect the limit of rotation, the dogs and the detecting unit must be arranged in a common plane extending perpendicularly to the axis of rotation of the movable element.
As a result, when a detecting actuator of the detecting unit is arranged at an origin position of the rotation of a movable element, only two dogs can be used and must be arranged at two positions distant less than 180 degrees in the clockwise and counterclockwise directions from the origin position of the rotation, respectively. Namely, if one of the dogs is arranged so as to detect a limit of rotation of a movable element from the origin position in one of the clockwise and the counterclockwise directions, which is larger than 180 degrees, the dog becomes in contact with the detecting unit when the movable element rotates less than 180 degrees in the other of the clockwise and the counterclockwise directions. Thus, the other dog must be arranged so as to detect a limit of rotation of the movable element from the origin position, which is obviously less than 180 degrees. Thus, there occurs such a defect that
Nihei Ryo
Otsuka Kazuhisa
Sugiyama Hideki
Fanuc Ltd.
Swann Glen
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