Multi-Axis Motion Measurement Systems Based on Optical Beam Deflection

Abstract

Multi-axis motion measurement is indispensable for precision motion control, and characterization of dynamic response of mechanical structures. This work describes the development and applications of a 5-axis high bandwidth motion measurement system based on optical beam deflection. The system can measure in-plane and out-of-plane motion of both macro- and micro-scale objects, namely, one- axis out-of-plane linear displacement, two-axis in-plane linear displacement and two-axis out-of-plane angular displacement. The system can measure transient motion of a target with a measurement bandwidth of over 1MHz. The measurement resolution can be less than a nanometre along the linear degrees of freedom (DOF) and less than a micro-radian along the angular DOF. The design and analysis of the measurement system will be discussed first. The sensitivity of the system for displacements along 5 axes has been derived and subsequently employed to optimize the system. The achievable resolution with this system would also be discussed. Next, the development, calibration, and evaluation of the measurement system would be presented. This includes a discussion of a novel calibration strategy, along with estimation of the bandwidth and range of the system. Subsequently, development of multi-point motion measurement capability for the system would be discussed. In particular, the design and evaluation of a novel calibration stage that enables automated calibration and measurement of motion at multiple points on the target would be discussed. The system has been employed to capture the deformation profiles of a micro-cantilever beam as it was excited at its first and second Eigen modes. Finally, the applications of the system for measurement of in-plane and out-of-plane motion of various macro- and micro-scale devices, whose motion is otherwise difficult to characterize, would be presented. These include measurement and control of in-plane displacement of a high-speed XY nano-positioning stage, characterization of a piezo-based 2-axis nano-positioner and simultaneous characterization of rigid body translational and rotational transient responses of RF MEMS switches. Finally, the measurement system has been utilized as part of a novel atomic force microscope (AFM) which enables active cancellation of base vibration of cantilever beam. The applicability of this AFM for elimination of artifacts due to the vibration would be presented.