Page 32 - Cam Design Handbook

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20 CAM DESIGN HANDBOOK

(a) Roller follower (b) Flat-faced follower
(60 deg. pressure angle). (zero pressure angle).
FIGURE 1.27. Significance of pressure angle.

1.8 OTHER METHODS THAN CAMS

Other methods than cams may employ mechanical, electrical, or fluid devices individu-
ally or in combination to satisfy the design requirements. Cam-follower systems and other
methods have specific functional applications where they are selectively applied. The fol-
lowing are some of the major systems utilized and their performance compared to cam-
follower systems: (a) linkage mechanisms; (b) servo valve-controlled hydraulic cylinder;
(c) stepper motor and controller, and (d) industrial adjustable mechanism.
The linkage mechanism may be of either four-bar or multiple-bar construction depend-
ing on the complexity of the designed motion. These mechanisms cannot produce exact
dwell action (only an approximation), with poor force transmission and high torque exist-
ing in the cyclical action.
A servo valve-controlled hydraulic cylinder yields equivalent performance to cam-
follower systems for high force level requirements. This machinery has limited control
and speed application.
The servo motor (stepping motor), programmable servo controller (stepper controller),
and ball-screw combination is another replacement for cams. Motion controls can be
changed easily. This mechanism has the advantage of programmability in small force and
low power applications but has speed limitations.
The last alternate method involves the use of adjustable mechanisms in industrial appli-
cations. To achieve flexibility, the cams are replaced by multi-degree-of-freedom systems
with multi-actuators and logic controllers. The adjustable or programmable mechanisms
are utilized in flexible fixturing and flexible assembly systems. Their design is often com-
plicated and costly.
In general these devices are easier to manufacture but have limited speeds and limited
force levels and are more costly. Cam-follower systems in comparison are complex in con-
struction, are smaller, have better dynamic properties, carry a heavier load, and transmit
more power over a longer time period. The applications are high-speed automobile valve
controls, indexing tables, and industrial machinery such as paper converting and textile
machinery. Designing cams and forecasting their performance is easy.