Page 172 - Cam Design Handbook

THB6 8/15/03 2:40 PM Page 160

160 CAM DESIGN HANDBOOK

6.1 INTRODUCTION

This chapter introduces the physical factors and forces involved with the development of
the proper cam profile shape. This chapter is complemented by Chap. 7, which contains
algorithms for the establishment of the cam profile including manufacturing information.
The three basic factors for this kinematic study are:

• cam profile
• cam pressure angle
• cam curvature

In the past the cam profile was developed by observing the cam shape from the graph-
ical construction method explained below.

6.2 CAM PROFILE GRAPHICAL LAYOUT

Simple cam motions are easily produced by the graphical layout method. The graphic
construction is based on the principle of “inversion,” in which the cam is considered the
fixed member and the follower is then moved to its proper position (same relative motion)
corresponding to the number of cam angles selected. The cam profile is thus the envelope
of the follower profile as the follower is positioned around the cam. Note that the conju-
gate cam follower layout is similar, with the additional cam developed from the first cam
shape.
The cam and follower are shown in Fig. 6.1. Developing the cam profile by the graph-
ical layout method:
• Sketch the timing chart Fig. 6.1a, showing the cam follower action in 30 degree
increments.
• Locate cam center A, Fig. 6.1b, follower pivot B, and location of initial point O to
maximum rise point 4.
• At lowest point O draw the cam base circle (smallest circle to cam profile) and the prime
circle to cam center.
• Draw reference arc through follower center C.
• Locate points on reference arc C according to divisions in timing chart and number
accordingly.
• Draw a pivot circle through follower pivot B.
• Locate pivot points on pivot circle pertinent to each point on the reference circle and
number.
• From each of the pivot points, draw an arc with radius BC.
• Lay off the angle or arc on follower arc C related to points 0, 1, 2, 3, 4.
• Rotate each of the points on the arc to its proper position around the cam.
• Draw the roller follower outline at each of the points located.
• Draw a smooth curve tangent to the follower outline.