Abstract
A robot runaway can be defined as an unexpected robot motion due to a failure of robot hardware or software. In the future robots will be required to work in unstructured environments, sharing their working area with humans or expensive machinery. In such environments safety considerations are important and a runaway should be prevented at all times. In order to reduce the probability of a runaway, redundancy in the sensor information and the control hardware is needed. This paper presents a new method of robot runaway detection. Our approach is to measure the accelerations of the robot wrist by means of three orthogonal accelerometers. An emergency stop is initiated if the difference between measured and expected wrist acceleration exceeds a certain limit. The expected acceleration, which is the second derivative of the accelerometer position, is calculated from the desired joint positions of the three main robot axes. Besides being rather inexpensive and small, accelerometers have the advantage of being easy to mount on a robot arm. The resulting runaway protection system can thus be applied to any existing (industrial) robot, requiring only a minimum of hardware changes. The idea has been implemented and tested on a PUMA 562 robot. The tests have shown this method to effectively detect a robot runaway, providing a short reaction time and good sensitivity.
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