Coulomb friction in feedback control systems

The presence of coulomb friction in servomechanisms often results in undesirable effects, such as an operating dead-zone, low-frequency wander, and poor dynamic performance for low level signals. Methods of compensation for these adverse effects are discussed and a specific example is presented. Also, a general procedure, using frequency-response techniques, is outlined for the synthesis of compensation in systems affected by coulomb friction. The methods employed are based on the recognition that coulomb friction in a control device has a describing function which reduces gain and introduces phase lag. The describing function is determined by both the amplitude and the frequency of the input signal to the device.