If components in precision machines need to be subsequently adjusted, washers ground to exact distances are often the method of choice. However, they have the disadvantage that they have to be installed mechanically. With the piezo-based PI Rest washers, Physik Instrumente offers an alternative. Due to the resolution of the actuators of a few nanometers, the washers are not only suitable for applications in classic mechanical engineering, but also for the adjustment of optical components in astronomy, materials research in synchrotrons or in vacuum environments.

However, there is one point in which PI residual actuators differ from piezo actuators, which are not suitable for readjustment: With classic piezo actuators, the electrical voltage (offset voltage) must generally be maintained on the actuator as long as the deflection is required. This has disadvantages for adjustment applications: When equipping the machine, an additional power supply would have to be provided for this, and the service life of the actuators would also suffer. Although PI-Rest technology is based on piezo actuators, they maintain their deflection after adjustment in a stable and nanometer-precise manner even without an offset voltage thanks to a special control system.

Long-term stability in the nanometer range
The static distance can be adjusted by briefly applying a supply voltage to the actuator. A voltage connection is provided for this in the so-called "Active Shim", which only needs to be connected to a voltage source during the adjustment process. PI offers an easy-to-use power supply with the appropriate control for this purpose. The necessary cables can already be taken into account when designing the machine.

After adjustment, the actuator maintains the desired position without tension over the long term. The stability of the deflection depends only on the change in ambient temperature. Long-term tests in an environment with a temperature stability of 1 K have shown drifts of less than ±100 nm for an actuator with a nominal stroke of 10 µm, irrespective of the deflection. For standard products, the maximum deflection is between 5 and 35 µm, depending on the actuator size. The Active Shims simplify adjustment in inaccessible places, especially as the piezo-based shims can hold loads weighing several tons. If required, they can also be combined with classic piezo actuators, for example for dynamic vibration compensation.

Dr. Mathias Bach, Head of the Piezo Systems Product Division at Physik Instrumente. Ellen-Christine Reiff, M.A., editor at Redaktionsbüro Stutensee / am