Electricity: motive power systems – Positional servo systems – With particular 'error-detecting' means
Patent
1989-10-25
1992-06-02
Ip, Paul
Electricity: motive power systems
Positional servo systems
With particular 'error-detecting' means
318587, 3185681, 3644742, 395 1, B25J 900
Patent
active
051190060
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a collision detecting method capable of prompt detection of a collision of machine operating parts driven by servomotors with a foreign object.
2. Description of Related Art
During operation of a machine, if a foreign object entering the working region of a machine operating part, the foreign object may interfere with the operating part. There is then a possibility of either impeding normal operation of the part or machine or damaging the machine. Conventionally, various methods have been employed to avoid such problems.
For example, a collision of a machine operating part with a foreign object is detected by using a touch sensor mounted to the outer surface of the machine operating part. The use of the sensor, however, entails an increase of the cost of the machine, and it is not possible to detect a collision of the machine operating part with a foreign object occurring outside the operable region of the sensor.
In those types of machines in which the machine operating parts thereof are driven by servomotors, it is known to detect a collision of a machine operating part with a foreign object has been detected by determining whether an increase in driving current for the corresponding servomotor exceeds a predetermined discrimination value. However, there is a passage of time from the detection of a collision until the servomotor driving current reaches the discrimination value. This time lag in collision detection can bring about greater damage to the operating part or machine than if the collision was detected more quickly after its occurrence.
In other types of machines, e.g., industrial robots, a collision discriminating process is carried out by a built-in computer utilizing either a sensor output or the detected value of the servomotor driving current. In these machines, the collision discriminating process is executed by the same computer which is used to control the robot. The robot control, however, involves a variety of complicated data processing operations; accordingly, the time required for the control process and the collision discriminating process of the computer becomes inevitably long. Consequently, additional time is required from collision detection until completion of the collision discriminating process in these machines.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method which is capable of promptly detecting a collision of a machine operating part driven by servomotor with a foreign object, thus preventing or limiting damage to a machine, etc., due to the collision.
To achieve the above object, the present invention utilizes the following a method of detecting a collision of a machine operating part driven by a servomotor, comprising the steps of: (a) obtaining a collision discriminating parameter relating to a driving force of the servomotor, at first predetermined periods; (b) obtaining an amount of change in the collision discriminating parameter at second predetermined periods; and (c) determining that a collision of the machine operating part has occurred when the amount of change of the collision discriminating parameter, detected in the step (b), becomes greater than a predetermined value.
Preferably, a torque command value supplied to the servomotor or a deviation between a velocity command supplied to the servomotor and an actual velocity of the servomotor is used as the collision discriminating parameter, and the first predetermined period at which the amount of change of this parameter is detected is set to a value shorter than a period of machine control action. Further, the difference between the value of the collision discriminating parameter detected in a previous period and the value of the same parameter detected in a current period is preferred to determine the amount of change in the collision discriminating parameter, at second predetermined periods equal to the first predetermined periods.
According to the present invention, a collision of
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Hamura Masayuki
Kato Tetsuaki
Naito Yasuo
Torii Nobutoshi
Fanuc Ltd.
Ip Paul
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