To provide for extremely fast response of positioning of a positioned element (3) operating within a guide bore (2) formed in a housing (1), upon application of a force, for example by loading of a spring (14), the element (3) is a hollow body (4) within which a stack assembly (5) of piezoelectric disks (6) is located, the piezoelectric disks expanding or contracting under application of electrical energy from a cable (11) against an elastomer disk or cushion (9) which, consequently, will elastically expand the side walls of the body (4) to clamp the element (3) in the guide bore (2) and permit release, for example, at time of maximum applied force to result in abrupt, sudden high operating force and acceleration of the positioned element. Positioning times of between 10 to 100 microseconds can be obtained.