Piezo-electric drive and adjusting elements are already known. In their simplest form, a piezo-electric element can be supported on a stationary mount and can press against an adjustable component. If an electrical voltage is applied to the piezo-electric element, this element moves and the adjustable component is deflected. Such piezo-electric elements have achieved certain usage as driving or adjusting elements. However, the small movement of a piezo-electric component, even in stacks formed from individual elements with stack heights of 20 mm, is not greater than about 20-30 .mu.m with the maximum permissible excitation voltage, and is generally considered a deficiency or disadvantage. Attempts have been made to compensate for a small movement by coupling the piezo-electric element(s) to lever structures which increase or even compound the movement.
Such a piezo-electric element and lever arrangement is widely used as a precision drive, for example, for adjustment tasks (cf. company catalogue from the Physik Instruments Company, Waldbronn 1994!). The disadvantages of such arrangements, particularly when they are installed in an apparatus, are that the piezo-electric element always has to carry out work against the lever structures and corresponding restoring means, and that fluctuating forces and temperatures produce changes in the length of the piezo-electric element. In particular, different thermal coefficients of expansion of the piezo-electric material and of the material of the rest of the apparatus, for example, steel, have a disadvantageous effect. In order to compensate for this effect, the actuating elements must either be readjusted in the event of temperature changes or else must be reset automatically, by means of a sensitive position measurement system, at the expense of the available actuation range. However, these measures require an additional outlay which is sometimes considerable.
Furthermore, because of the restoring means, these types of arrangements have a low intrinsic stiffness so that they can operate only quasi-statically with short reaction times.
In order to overcome these problems, piezo double-stack drives have already been proposed, in which two identical piezo-electric stacks act on one side of a toggle lever arrangement (F&M, Journal for Electronics, Optics and Microsystem Engineering, 104th Year 1996, page 70 ff.). Such arrangements lead to extremely prestressed stiff structures which exhibit good dynamic characteristics even without any loss of their own travel or movement. A further advantage is the intrinsic thermal compensation of these systems. To produce a sufficient drive travel with adequate drive forces, the toggle levers which are used must, however, be designed to be sufficiently robust to allow them to absorb the bending forces which act on them. This means that the toggle levers must have a suitable mass, so that adequate resonant frequencies can no longer be achieved for a predetermined travel and a predetermined step-up ratio for some applications.
USPTO Backgrounds
USPTO Backgrounds