Rubber bearings for precision positioning systems

Abstract

In this thesis we investigate the use of thin rubber sheets or laminates of metal and rubber sheets as bearings in precision positioning systems. Such bearings have the potential to replace more conventional flexures fabricated for instance from metal. Rubber bearings also potentially have advantages in for example ease and low-cost of fabrication, overload robustness, and compact form. To study the properties of these we have designed a test fixture. This fixture allows us to measure the shear and compression characteristics of these bearings in their static sense, as a function of frequency, and of various design parameters. The test fixture has been used to test several types of rubber material. The tests performed include compression and shear tests of rubber laminates' static stiffness, dynamic stiffness, preload effects, step response, hysteresis, fatigue tests, and manufactureability. Different low-cost manufacturing methods of the rubber bearings have been suggested and preliminary tests have been done. The feasibility of these manufacturing methods has been confirmed, and the advantages and disadvantages of each identified. On the basis of the experimental results a rotary precision positioning system utilizing a rotary laminated rubber bearing, was designed, fabricated and tested.

(cont.) The bearing of this device consists of multiple laminates of metal and rubber sheets packaged within a preload mechanism. This preload mechanism assures the bearing radial stiffness and compact form. It also assures a low cost alternative versus the use of conventional flexural bearings. Tests have shown that a steady-state angular travel of 2.5 mrad-pk can be accomplished and two types of controllers have been used to obtain a closed-loop bandwidth in the range of 1 kHz and 1.5 kHz.