End Position Control of Long Non-Rigid Arms

The position control of a load at the far end of a long, non-rigid arm by an actuator at the near end is considered. The actuator must integrate two tasks: position control of the load and active absorption of vibration to steady it in position. A control strategy based on the launching and absorbing of mechanical waves by the actuator is presented. It is shown to work remarkably well for longitudinal waves in lumped mass spring systems, being robust, close to optimal and inherently adaptive. Only the first two masses and springs need to be characterised and observed to determine the required actuator movement. The approach also applies to related continuous systems. The case of flexural, transverse waves is under study and looks equally promising.