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An adjustment for five degrees of freedom as an alternative for a hexapod mechanism

Author: Klinkhamer, J.F.F.
Type:article
Date:2003
Institution: Technisch Physische Dienst TNO - TH
Source:Hatheway, A.E., Optomechanics 2003, 7-8 August 2003, San Diego, CA, USA, 5176, 108-113
series:
Proceedings of SPIE - The International Society for Optical Engineering
Identifier: 237449
Keywords: Electronics · Constraint of rotation · Hexapod · Opto-mechanics · Actuators · Degrees of freedom (mechanics) · Kinematics · Mirrors · Natural frequencies · Optical telescopes · Sensors · Stiffness · Systems analysis · Imaging optics · Optical engineering

Abstract

Modem mirror optics often consists of a limited number of elements, in which many aberrations may be attacked by adjusting only one element in five degrees of freedom, i.e. all degrees of freedom except the rotation around the optical axis. When the adjustment has to be reusable and mass and stiffness are of importance, a hexapod mechanism is 'the mechanism of choice' for this function. This choice holds even though the hexapod controls six degrees of freedom, while control of only five degrees of freedom is required, simply because there was no known configuration that does only control the required five degrees of freedom while maintaining the superior mass and stiffness properties of the hexapod. In this paper a mechanical configuration is presented that offers a worthwhile alternative for the simultaneous adjustment of five degrees of freedom (one rotation constrained), in the sense that: The rotation around one axis is constrained by the mechanical configuration, meaning that only the required five degrees of freedom have to be controlled. This means only five instead of six actuators are needed, which results in an increase in reliability. The mass and stiffness of the mechanism are comparable with the hexapod. From a mechanical and control point of view the configuration is less complex than the hexapod.