Direct Drive Precision Linear Actuator for Space Interferometry Mission (SIM) Siderostat Pointing

Abstract

SIM PlanetQuest will exploit the classical measuring tool of astrometry (interferometry) with unprecedented precision to make dramatic advances in many areas of astronomy and astrophysics." (1) In order to achieve the required pointing precision of SIM, a gimbaled Siderostat (SID) pointing mechanism with coarse and fine stage actuators is being employed. In order to better understand the coarse pointing accuracy, a team of engineers set out to design, build, and test a linear ballscrew actuator that can perform submicron incremental steps for 10 years of continuous operation. Point tracking and low disturbance requirements lead the team to implement a ballscrew actuator with a direct drive DC motor and a piezo brake. By using an off the shelf motor, Hall effect sensor, ballscrew, and glass scale encoder, repeatable 20 nm incremental steps (actuator resolution) over a 120mm range was achieved. The results exceed expectations by a factor of 50 times and prove linear nanometer positioning requires no gears, levers, or hydraulic converters.12

Design Method for Buckling Amplified Piezoelectric Actuator Using Flexure Joint and its Application to an Energy Efficient Brake System

“…Additionally, for a given length, L, the flexure properties affect the output properties including the energy transfer efficiency, R E , which is defined by Eq. (12). Greater R E yields higher output force for the same maximum displacement.…”

“…In Eq. (12), ‫ܧ‬ is the maximum output energy from the piezoelectric stack with the ideally preloaded mechanism which is the integral over both the push and pull actuation. ‫ܧ‬ ௨௧ is the maximum output energy from the buckling actuator which is the integral over both the push and pull actuation from the maximum actuation of the piezoelectric stack.…”

“…Some types of piezo brakes are presented conventionally focusing on the energy efficiency of piezoelectric actuators. Most of them employ some kinds of displacement amplification mechanisms [12,13,14]. Targeting EM motors, the hydrostatic amplification [14] can have sufficient properties but is hard to apply because of the need for maintenance.…”

“…Targeting EM motors, the hydrostatic amplification [14] can have sufficient properties but is hard to apply because of the need for maintenance. In contrast, the conventional geometric methods [12] don't need maintenance with adequate flexure design, but have limited displacement performance properties which can't substantially compensate for the wear at the brake plates for commercial products. Our buckling type actuator has potential to satisfy the specifications of commercial products due to their potential high energy transfer rate.…”

Air-LUSI: an autonomous robotic telescope for high-altitude lunar spectral irradiance measurements

“…7 Linear actuators were used as a variable length linkages to incite rotation about each degree of freedom. [8][9][10] The ARTEMIS control system uses a simplified approach to control the pointing of the telescope when compared to other inertially stabilized systems that are commonly implemented for target tracking. 11 The simplified system treats both the azimuth and elevation axes as completely independent degrees of freedom and implements two distinct single input single output controllers for both axes.…”