an accommodating linkage device which operates in three modes to provide , upon command , either : a standard , resetable , rigid linkage between two objects ; a flexible linkage which responds to relative motion between two objects ; or an arbitrary , rigid linkage between two objects . the device includes two ball joints which connect to the two objects , a pair of locking pistons , and a pair of alignment pistons . operation of the device is in response to either control signals or to forces generated by the relative motion of the two objects , depending upon operating mode .