SEED Guides Tutor's Guide - Cam Mechanisms < >

3.1 There are several different configurations of cam mechanism, each has many sub-types. See Grossjean, Jensen (1987), Reeve, Rothbart or ESDU "Item" 82024. [References are cited in Section 14 below]. 'Cam Mechanisms - Unit Design' Guide is restricted to the translating follower configuration [see 'Cam Mechanisms - Unit Design' Guide Figures 2a, 6, 7], with radial or offset path, because the complete specification requires fewer independent dimensions than alternative configurations, e.g., those with swinging-arm followers. These dimensions are defined in 'Cam Mechanisms - Unit Design' Guide, pages 8 & 9.

NB - the units quoted are those needed for rigorous analysis; for manufacture it is customary to use mm and degrees for the cam profile specification.

3.2 Within this restriction on the number of independent variables it is possible to re- arrange the equations defining critical parameters in non-dimensional form to derive graphical design data identifying limiting values and hence to optimise the dimensions of the mechanism for a specific case. These analyses form the bulk of the spreadsheet, see Section 10. Specific values defining the mechanism being designed are entered in dedicated cells, so that the non-dimensional values can be factored to obtain those for a trial result. This contrasts with the application of hardcopy design data which must be factored manually. Moreover typical hardcopy data gives merely the critical maximum or minimum; charts generated from the spreadsheet are considered superior for academic purposes as they show the change of a variable throughout a complete motion segment (i.e., a complete rise or fall action) providing a basis for sensitivity analysis.

3.3 The design should begin from a diagrammatic timing chart, e.g., 'Cam Mechanisms - Unit Design' Fig 3. The problem can be enhanced by involving the synchronisation of two or more mechanisms. In practice it is probable that some segment angles are not known; initially these should be made as large as possible. [To ensure correct synchronisation sequential movements should be separated by a clearance of, say, 2š].

3.4 In addition the lift and the envelope containing the camshaft, follower and swept volume will be known from the layout drawing. [it is unrealistic to decree that the cam mechanism be optimised and the remainder of the machine be constructed around it!] The consequent compromises provide opportunities for comparing the trade-offs.