For backlash compensation, the Galil controller provides solutions by using either an open loop bias compensation method or using the dual loop approach (DV1). For open loop bias Galil provides this as a custom firmware option where the user programs in a desired directional bias to compensate. With standard firmware, Galil offers the dual loop approach. The key in effective dual loop operation is to have the motor feedback resolution equal to or higher than the load position feedback resolution. This minimum ratio is required to stabilize the system. Without enough inner loop resolution, the motor would be able to move significantly without being detected by the motor encoder when the load encoder changes. This effectively allows chatter since there is no damping within this range.

Galil also provides an �Advanced� dual loop method (firmware NRE option) which allows the KP term to apply to the inner motor loop. This allows for better stability in the case of systems with larger backlash or increased loads (inertia)

-EricK

Let's say hypothetically that there is 0.02 degrees of backlash (at the motor). The rotor's moment of inertia is 5e-5 when in the backlash region. When engaged with the load, the total moment of inertia is 55e-5. In the dual loop method, there is a PD inner loop with the motor's encoder as feedback. Moment of inertia is a component in loop gain, and thus effects PD tuning. If tuning is based upon a moment of inertia of 55e-5, the system will most likely be unstable (by linear criteria) when the system is in the backlash region (with an effective inertia of 5e-5). How is this typically remedied?