5. Dynamic control

A robot manipulator is a complex mechanical structure whose inertias relative to the joint axes vary not only with the end load, but also with the configuration. The effects of gravity also vary with the configuration. When the joints ("axes") are actuated via high reduction ratios, the inertia seen by the motors varies little. This is because the inertia of the load brought back to the motor is divided by the square of the reduction ratio (see the articles on servo-controls [R 7 500] and following in this treatise). In these cases, axis-by-axis control can be provided by conventional networks, such as PID (proportional-integral-derivative). However, increasing reduction ratios leads to a loss of efficiency and oversized motors.

For drives with low reduction ratios or even "direct-drive",...