Abstract
In a compliance control of a serial link manipulator, the independent joint control approach is quite important because its features include: (1) simple SISO controllers, (2) asymptotical stability for arbitrary PD control gain in an arbitrary arm configuration, (3) colocated sensors and actuators. However this approach inherently has the fatal problem that end-point compliance can not arbitrarily be set according to the arm configuration. This paper describes a new method called “Stable Negative Compliance Control (SNCC)”, based on the independent joint control approach, whereby arbitrary end-point compliance can be achieved in an arbitrary arm configuration. First, the conventional idea is reviewed and then the fatal problem mentioned above is clarified by comparing the other methods, such as Active Stiffness Control (J.K. Salisbury) or Direct Compliance Control (DCC). Then a new compliance concept called “stable negative compliance (SNC)”, based on the characteristics of a nonminimum phase shift system, is introduced. This is the key technology involved in this new method. Next, employing a normal 2nd order actuator, the necessary and sufficient condition for a dynamic compensator realizing SNC is given in a frequency domain, and some practical control system examples for a normal robot actuator are shown. Finally, the proposed method is applied to a planar 3-link arm and the successful simulation results are also presented.
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