A Convenient and Inexpensive Quality Control Method for Examining the Accuracy of Conjugate Cam Profiles

Abstract

The cam mechanism, basically consisting of a frame, a cam and a translating or oscillating follower with a roller in contact with the cam, is a simple and reliable device for motion control in machinery. Being a high-value-added product, a conjugate cam mechanism consists of a pair of disk cams that their profiles must be mutually conjugate to contact their respective follower. The conjugate cam mechanism is therefore a positive-drive mechanism (Wu, 2003; Rothbart, 2004; Norton, 2009) that can eliminate the use of return springs. As a benefit of positive-drive, the conjugate cam mechanism can ensure the contact between the cam and the follower roller with lower contact stresses between them. Such a situation can further contribute to the reduction of excessive noise, wear and vibrations occurred in the mechanism. In other words, reasonably designed conjugate cam mechanisms are especially suited to high-speed applications. However, since a conjugate cam mechanism is a so-called kinematically overconstrained arrangement (Wu, 2003), to ensure its movability condition and its ability to run without backlash (Rothbart, 2004; Norton, 2009), its cam profiles must be accurately designed and machined. The machined cams must then be carefully examined to check whether their profile errors fall within a specified tolerance range in order to achieve high quality and performance of the mechanism. Up to the present time, using a highly sensitive and accurate coordinate measuring machine (CMM) to examine the accuracy of machined cam profiles is an industry-recognized technique, although it is still costly and time-consuming. For the quality control of machined cams, the cam profile must be directly measured by using a CMM, while the path planning and/or the coordinate measuring data are dealt with by some mathematical approaches to evaluate the profile errors (Lin & Hsieh, 2000; Qiu et al., 2000a; Qiu et al., 2000b; Qiu et al., 2000c; Hsieh & Lin, 2007; Chang et al., 2008). As an alternative quality control method, a special conjugation measuring fixture, which is improved from the one proposed by Koloc and Vaclavik (1993) and further investigated by Chang and Wu (2008), is developed by Chang et al. (2009) for indirectly evaluating the profile errors of conjugate disk cams. The conjugation measuring fixtures are based on the means of measuring the conjugate variation