High-accuracy interference-fit assembly utilizing a hybrid actuator

This paper presents an innovative press-fitting station that combines a hydraulic cylinder and a piezoelectric actuator to reach micrometric accuracy in axial positioning. The hydraulic cylinder permits a long operation range, while the piezoactuator provides dynamic action and micrometric accuracy. The experimental characterisation of the prototype press is presented together with the physical phenomena influencing the system performance. The tests are done using cylindrical plugs and sleeves to replicate the insertion of shafts into holes. The test samples are designed and machined to obtain a known interference fit. The classic press-fit assembly process can barely reach micrometric accuracy because the deformation on the contact surface cannot easily be measured. The presented press-fit station can overcome these limits thanks to the developed control strategy: When the piezoactuator is driven by an amplitude-modulated sinusoidal signal, it can realize assemblies with a maximum error in the final positioning of +/- 2 mu m for an insertion force of up to 20 kN.