Flexure-based 60 degrees stroke actuator suspension for a high torque iron core motor

Abstract

For the actuation of flexure-based precision systems direct drive actuators are used to allow for precise manipulation. For this purpose, often iron-less direct drive actuators are used which do not suffer from parasitic magnetic forces. In contrast, actuators with iron core can provide a higher power density, but require high off-axis stiffness normally too demanding for flexure-based mechanisms, especially when combined with a large range of motion. In this paper, a flexure-based suspension for an iron core direct drive torque motor with a range of motion of 60 degrees and a maximum output torque of 55 Nm is presented. The system provides the required high off-axis stiffness (more than 1000 N/mm) and is able to withstand the high pull-in forces caused by the iron core over the full range of motion. Furthermore, the design is made robust by limiting the deflections in the support directions, effectively rerouting excess forces from the flexures into the frame parts. Experimental validations confirm the high support stiffness and show that the system is able to withstand high actuation and reaction forces. Due to the friction-free mechanical design, only the current noise from the motor driver limits the stand-still performance and the repeatability of the system, resulting in a RMS positioning error of 1.1μrad for an inertia of 0.066 kgm2.