From the mechanical design point of view, maximizing the payload to manipulator inertia ratio is desirable. This can be done by using a gear reduction mechanism to allow for a smaller (and less expensive) actuator. The particular configuration of interest uses a Harmonic Drive (HD) and a brushless DC motor. Harmonic Drives are very compact and have a very high gear reduction ratio. In the previous talks, issues associated with using this configuration (such as Coulomb Friction and compliance) have been discussed.

This talk will focus on the compensation of actuator saturation. When either the desired payload to manipulator inertia ratio or the desired bandwidth is increased, actuator saturation becomes a limiting factor. Ignoring saturation in the design process may result in undesirable limit cycles, avoiding saturation may result in the inability to achieve the desired goal.

One class of approach called Linear Conditioning (LC) appends additional controller which uses the difference between demanded and achieved actuation as the input. The idea is to reduce the performance degradation due to saturation.

Weston & Poslethwaithe proposed a generalized structure that allows for an intuitive view of the LC approach. The implementation is done by first designing a controller that stabilizes the system without saturation, and then adding an LC compensator. In this talk, an additional requirement that the first controller does not induce limit cycles is imposed. This reduces both the set of stabilizing controllers as well as the "burden" to the LC compensator. To this date, an objective performance measure is yet to be proposed.