portion 42 having a force receiving surface 43 also located within chamber 18 will be an actuating device 44 as represented in fig1 actuator device 44 is a stack of piezoceramic crystal elements such a piezoelectric stack will be formed generally as a lamination of a plurality of thin piezoelectric disk elements mounted to the roof of chamber 18 for example using an adhesive 46 electrical leads 48 and 50 are shown coupled to the piezoelectric stack or actuator device 44 and upon the application of an appropriate electrical signal stack 44 will be actuated to move or be driven either upwardly in the embodiment shown in fig1 or with appropriate adjustments downwardly additionally the amplitude of flexure of stack 44 will be accurately controlled by the strength of the applied electrical signal voltage while the rate of the movement will be controlled by the rate of change of the electrical signal in preferred embodiments such control will be provided by a servo feedback system of the type disclosed and detailed in u s pat nos 3 895 231 3 926 209 and 4 018 241 all of which are incorporated herein by reference as though set forth in their entirety attached to the lowermost surface of stack 44 will be stiffener 52 which will provide a planar force transfer surface 54 which will be positioned closely adjacent to but spaced from upper force transfer surface 43 of head component 42 of stem 40 thus a gap 56 will be defined between force transfer surface 54 of stiffener element 52 and upper force receiving surface 43 of stem 40 within gap 56 there will be.