SEED Guides Tutor's Guide - Cam Mechanisms < >

11.1 Following the flowchart for the design process, 'Cam Mechanisms - Unit Design' guide , Fig 1, the simplest approach to finding the minimum cam size is to begin by finding the minimum prime circle radius for the case of a radial translating follower using the pressure angle criterion because the basic graphical data is derived independently of both the segment angle (D and the lift H. If acceptable then check the profile for undercutting. Work with the smaller of the rise and fall segment angles.

If either proves unacceptable then investigate the use of offsetting the follower path and/or blending the profile.

11.2 More advanced analyses involve more complex analysis.

Whilst it is possible to calculate contact stress on a spreadsheet using the Hertz equation for nominal "line" contact between two cylinders having parallel axes practical considerations suggest that this condition is improbable due to elastic deflections and accumulation of tolerances [including alignment of the cam and roller axes]. The author prefers the use of "barreled" rollers giving a realistic nominal "point" contact which becomes an elliptical surface between elastic members under load. The analysis of this condition involves the solution of elliptic integrals and hence beyond the capacity of a spreadsheet. [See ESDU hardcopy "Item" 93001 and software "ESDUpac" A9301.1

The dynamic load rating of needle bearing rollers during rise and fall actions is derived from the summation of a function involving the [continually varying] load and [continually varying] rotational speed of the roller about its centre [see ESDU hardcopy "Item" 91026 and software "ESDUpad' A91261.

The shear strength of the roller stud is another strength criterion.