Rockwell Automation Motion Analyzer Software - Manual (Page 87)

Rockwell Automation Publication MOTION-UM004B-EN-P - October 2012 87
Sizing Your System Chapter 2
2.1.3. Rotary Complex Loads
A complex rotary load is non-linear, which means that the load position is not
directly proportional to the input shaft position as it is with standard actuator
types. A simple example is a crank, where the load velocity is sinusoidal with a
constant shaft speed. The Crank and Four Bar Linkage templates are available for
these applications.
The main challenge with non-linear mechanisms is that the inertia value varies
with shaft angle. This means that even at constant shaft speed, a torque that varies
with the rate of change of inertia is required to maintain that speed. The same is
true of an unbalanced load in which external forces, such as gravity, induce torque
values that depend only on shaft angle, not velocity or acceleration.
The Rotary Complex load separates the dynamic inertia values from the motion
profile so that, having calculated inertia for a range of shaft positions, the motion
profile can be varied without having to re-calculate inertia at each shaft position.
Figure 69 - Rotary Complex Load Type