Work methods measurement—a comparison between robot and human task performance

Abstract

SUMMARY The industrial robot, already an accepted element in modern manufacturing, when coupled with sensors and controlled by a computer, is better modelled as an operator than as a machine. In this paper the basic characteristics of sensor controlled robots are defined : workspace, actuation, positioning, orientation, sensing and decision making. Actual values of these characteristics are given for the Stanford Arm running under the WAVE system. In order to compare a robot to a human operator we consider each of the task elements defined in an established methodology for human work analysis, method time measurement (MTM). We translate each of these work elements into robot program statements. From this comparison we find that a robot can be modelled as an operator but that a different set of work elements is appropriate. We develop a new methodology, which we call RTM (robot time and motion) and describe an actual robot assembly operation. The same assembly task is described using MTM for a human operator as a comparison. RTM differs from MTM in that element times are based on physical parameters of the robot, maximum torque-, resolution, sensors, etc., leading to an exact method of predicting task times, unlike MTM which must take human variability into account in providing estimates of work element times. RTM provides a method of comparing robots by comparing work element times for each robot. A translation table from MTM into RTM is also developed, allowing robot performance to be compared to human operator performance for existing tasks.