Pre-loaded actuator using piezoelectric element

A self-contained pre-loaded piezoelectric actuator unit, for repetitively displacing a work piece from a reference position, comprising:

• a piezoelectric element, including a plurality of laminations in an axial stack which is compressible by a predetermined axial amount by non-destructive compressive force, for displacing a work piece;
• a work piece positioned at a first end of said piezoelectric element;
• support means for supporting said said piezoelectric element and said work piece, including an end member for restraining a second end of said piezoelectric element, wherein a side portion of said support means is made of a combination of a first material having a higher thermal expansion coefficient than the piezoelectric element and a second material having lower thermal expansion than said piezoelectric element, said expansion characteristics and axial dimensions of first and second materials being chosen so that the overall thermal expansion characteristics match those of said piezoelectric element;
• resilient means, resiliently coupling said work piece and said piezoelectric element to said end member, for pre-loading said piezoelectric element by applying sufficient force to compress said piezoelectric element by substantially said predetermined axial amount;
• and
• attachment means for enabling attachment of said support means in an operating position;
• whereby, said actuator unit may be attached in an operating position to externally apply said work piece displacement and said pre-loading enhances full displacement of said work piece.

A self-contained pre-loaded piezoelectric actuator unit, for repetitively displacing a work piece from a reference position, comprising:

• a piezoelectric element, including a plurality of laminations in an axial stack which is compressible by a predetermined axial amount by non-destructive compressive force, for displacing a work piece;
• a work piece positioned at a first end of said piezoelectric element;
• support means, for supporting said piezoelectric element and said work piece, including an end member for restraining a second end of said piezoelectric element,
• wherein a side portion of said support means is made of a ceramic material having stiffer longitudinal elasticity than a ferrous material;
• resilient means, resiliently coupling said work piece and said piezoelectric element to said end member, for pre-loading said piezoelectric element by applying sufficient force to compress said piezoelectric element by substantially said predetermined axial amount;
• and
• attachment means for enabling attachment of said support means in an operating position;
• whereby, said actuator unit may be attached in an operating position to externally apply said work piece displacement and said pre-loading enhances full displacement of said work piece.

A self-contained pre-loaded piezoelectric actuator unit, for repetitively displacing a work piece from a reference position, comprising:

• a piezoelectric element, including a plurality of laminations in an axial stack which is compressible by a predetermined axial amount by non-destructive compressive force, for displacing a work piece;
• a work piece positioned at a first end of said piezoelectric element,
• wherein said work piece is made of a material having a stiffer longitudinal elasticity than a ferrous material so that the displacement of said piezoelectric element is transmitted to the work being processed;
• support means, for supporting said piezoelectric element and said work piece, including an end member for restraining a second end of said piezoelectric element;
• resilient means, resiliently coupling said work piece and said piezoelectric element to said end member, for pre-loading said piezoelectric element by applying sufficient force to compress said piezoelectric element by substantially said predetermined axial amount;
• and
• attachment means for enabling attachment of said support means in an operating position;
• whereby, said actuator unit may be attached in an operating position to externally apply said work piece displacement and said pre-loading enhances full displacement of said work piece.

A method for pre-loading a piezoelectric actuator unit to be attached to a press to enhance work piece displacement and cycling frequency range, comprising the steps of:

• a. providing a form of piezoelectric actuator unit including a form of laminated piezoelectric element whose axial length may be shortened by application of compressive force, a work piece, a support device, and spring means for resiliently holding said work piece and piezoelectric element against an end member of said support device;
• b. determining the amount of compressive force necessary to produce substantially the maximum shortening of said axial length of said piezoelectric element when subjected to non-destructive compressive force;
• c. providing spring means able to exert a pre-loading force of substantially said amount of compressive force as determined in step (b), wherein said spring means exerts a pre-loading force not less than the greater of 30 kilograms per square centimeter or the force necessary to limit the duration of piezoelectric actuator unit deactivation vibration to less than one period of said cycling frequency;
• and
• d. assembling said form of piezoelectric actuator unit as described in step (a) incorporating said spring means as provided in step (c) to provide a pre-loaded piezoelectric actuator unit which is substantially free of work piece displacement loss due to piezoelectric element compression under load.

A self-contained piezoelectric actuator unit adapted to be attached to a press for repetitively displacing a work piece from a reference position for producing a force on a load in response to a voltage and returning the work piece to said reference position, comprising:

• an elongate hollow cylindrical container being closed at a first end by an end member and closed at the opposite second end by a guide plate having a centrally located guide hole there through,
• a piezoelectric element comprising a stack of layers of piezoelectric material, which stack is axially compressible by a predetermined amount by a non-destructive compression force, said piezoelectric element being contained within said cylindrical container with a first end thereof engaging said end member,
• a cylindrical support member positioned within said container for axial longitudinal movement relative thereto and having a first surface engaging a second end of said stack of layers of piezoelectric material,
• an elongate work piece secured to a second surface of said support member opposite said first surface and extending through the guide hole in said guide plate, and
• spring means disposed between said guide plate and said second surface of said support member for applying a pre-loading compressive force to said piezoelectric element not less than the greater of 30 kilograms per square centimeter or the force necessary to limit the duration of piezoelectric actuator unit deactivation vibration of said piezoelectric element to less than one period of the frequency of said repetitive displacing of said work piece from said reference position to axially compress said element by said predetermined amount.