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2866 |
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Development of a novel, ultra-precision spindle |
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Design of Precision Machines and Instruments |
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Abstract
Precision rotational spindles are used throughout manufacturing and quality control processes. Over the years, several types of spindles have been designed to achieve a high precision rotational axis. For example, contact bearings such as journal bearings and rolling element bearings generates 0.1 to a few micrometers of asynchronous error motion [1, 2, 3]. Non-contact based bearings such as magnetic [4, 5], aerostatic [6], hydrostatic [7, 8] or hybrid designs [9] produce spindles exhibiting axial deviations of better than 100 nm. However, the tradeoff is reduced stiffness and higher manufacturing costs to produce the spindle. Air bearings represent the most accurate spindle currently available. They are used in variety of applications such as machine tool spindles and are often employed within metrology equipment. However, precise tolerances and other manufacturing difficulties as well as the need for an air supply represent economic or practical barriers for some applications. On the other hand, a metrology spindle for roundness gauging instruments operates at relatively low speed and low, constant loads but does require very low asynchronous error motion. The synchronous error correlates to the repeatability of the spindle and can be mapped and subtracted from the actual measurements.
Alternative instrumentation spindle designs have recently been developed to employ contact pads and kinematic constrains [10, 11]. The aim of this paper is to discuss the development of an axially symmetric spindle design. In general, the spindle consists of a rotary shaft equipped with two hemispherical reference surfaces on the ends. The hemispherical references are constrained in the housing by a set of three polymeric pads on each end of the spindle with one of the pads providing force closure for a 5 degree of freedom kinematic constraint. Additionally, the spindle is equipped with a frameless Aerotech motor, precision angle encoder by Heidenhain, and in-house developed slip-rings providing 10 contacts to pass signals to and from attachable gauging instruments mounted on the rotary shaft. Additionally the spindle is equipped with signal conditioning electronics that can be employed to transmit precision signals through the spindle slip-rings. The whole assembly presented in this paper is housed in a compact 100 x 100 x 128 mm3 envelope. Currently available spindle characterization techniques demonstrate that, under appropriate running conditions, the repeatability of the asynchronous deviations of the newly constructed spindle is less then 10 nm comparable with an air bearing based spindle. The scope of applications where it can be beneficial include, high end metrology gauging, and vacuum compatible rotary block heads.
References (please follow provided link, and download file ASPE2009_References.doc)
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