Experience from the Development of a Silicon-Based MEMS Six-DOF Force–Torque Sensor

Abstract

A six-DOF (Degrees Of Freedom) force–torque sensor was developed to be used for interactive robot programming by so-called lead through. The main goal of the development was to find a sensor concept that could drastically reduce the cost of force sensors for robot applications. Therefore, a sensor based on MEMS (Micro Electro Mechanical System) technology was developed, using a transducer to adapt the measuring range needed in the applications to the limited measuring range of the silicon MEMS sensor structure. The MEMS chip was glued with selected epoxy adhesive on a planar transducer, which was cut by water jet guided laser technology. The transducer structure consists of one rigid cross and one cross with four arms connected to the rigid cross by springs, all in the same plane. For this transducer a German utility patent [Weiß M, Eichholz J Sensoranordnung. Pending German utility patent] is pending. The MEMS structure consists of one outer part and one inner part, connected to each other with beams obtained by DRIE (Deep Reactive Ion Etching) etching. On each beam four piezoresistors are integrated to measure the stress changes used to calculate the forces and torques applied between the outer and inner part of the MEMS structure. The inner part was glued to the mentioned rigid cross of the transducer and the outer part was glued to the four arms including the transducer springs. FEM (Finite Element Modeling) was used to design both the MEMS- and transducer part of the sensor and experimental tests were made of sensitivity, temperature compensation, and glue performance. Prototypes were manufactured, calibrated, and tested, and the concept looks very promising, even if more work is still needed in order to get optimal selectivity of the sensor.