Highly Integrated Self-compensating Hydraulic Feed Axis for Small Machine Tools

Current machine tools for the machining of small workpieces show a remarkable disproportion of the machines’ size and the size of the components they produce. When trying to miniaturise such machine tools, feed axes play an important role. They position the workpiece and tool relative to each other and are, therefore, crucial for the accuracy and productivity of the machining process. The research and development of a highly accurate feed axis with a compact build space was the task of this project in the priority program SPP1476. Within the two phases of the priority program, different demonstrators for compact feed axis systems have been developed and evaluated. The final system uses a hydraulic fluid in order to realise a feed axis with a combined guidance system in a compact body. The use of piezoelectric valves enables a precise and highly dynamic control of the oil flows in the axis. In contrast to conventional hydrostatic guidance systems, the axis can not only absorb forces of the machining process and component movements but also provide functionalities for an active compensation of geometric errors. This compensation can be achieved by actively controlling the oil flow in the guidance system with piezoelectric orifices. The oil flow affects the gap widths between fixed guidance prisms and the moving housing of the axis. It can, therefore, compensate geometric errors by making small correctional movements in five degrees of freedom. An evaluation of the developed axis system shows that it meets the specified requirements and can provide highly accurate and dynamic movements within the desired build space.