Hydraulic materials-testing system with 10-nm positional accuracy

Abstract

Due to inherent impertections, mainly in the servo valve, the piston of hydraulic materials-testing systems typically fluctuates about the prescribed position by 1 μm. Hydraulic bearings in the cylinder, together with a careful selection of oil temperature and pressure can improve the accuracy to 0.2μm. Further improvements can be realized by compensating these unwanted movements with the help of the electrically controlled expansion of piezo crystals. The mechanical design of the piezo crystals as well as the electric-control circuitry are described. With the prototype system, an accuracy of better than 10 nm was obtained for piston speeds up to 0.3 mm/s.