Integrated Force Sensor based on Optical Distance Measurement for a Modular Actuator used in Active Optics

This paper presents a modular actuator with an integrated force sensor for the utilization in an active optics support system for primary mirrors in the meter-class. The actuator uses a commercial stepper motor together with an arrangement of helical springs. The force measurement of the individual actuators required for the active optical system is based on an optical proximity sensor which measures the distance between the components connected by the springs. This way, the force sensor is highly integrated into the actuator and for the developed system a precise force measurement with an RMS error of 4.5 mN over a range of 24 N is achieved.