FUZZY CONTROL OF A CLASS OF HYDRAULICALLY ACTUATED INDUSTRIAL ROBOTS

Application of a fuzzy logic controller to a class of hydraulically ac tuated industrial robots is investigated in this paper, A simple, yet effective, set of membership functions and rules are described which m eets certain control requirements of such robots, An off-line routine based on the simplex method is then outlined to tune the controller ga ins for an optimum response, The fuzzy control gains are tuned by mini mizing the summation of absolute position errors over step input respo nses. The fuzzy logic controller is first examined through simulation of a two-link hydraulic robot, The robot has the same hydraulic config uration as many existing industrial manipulators, It is shown that the controller exhibits positive aspects which cannot be easily achieved by conventional control techniques, such as a PD controller with fixed gains, These aspects include a fast rise-time and a well maintained d amped response, The fuzzy controller is then applied to an instrumente d Unimate MK-II industrial hydraulic robot, The experimental results a re encouraging in that the best performing control gains are found for different links with a reasonable number of trials and produce step r esponses with fast response and few oscillations at the set point. The controller demonstrates robustness in the presence of load, variation of set points, and nonideal hydraulic actuation systems. Compared to the simulation studies, the application of fuzzy control in experiment s requires a reduction in the width of the zero output membership func tion to compensate for the effect of friction, leakage, and other nonl inearities inherent in the actual robot, The elimination of steady-sta te errors which were observed in both step and ramp input experimental responses is also addressed in this paper.