Time delays in iterative learning control schemes

Repeated accurate path tracking has many control applications. CNC machines in manufacturing or actuators in testing are examples. Repeated operations permits adjustments of control signals between cycles using trajectory error information. Learning control systems are well suited for this situation. Time delays in the plant or elsewhere can markedly affect control system stability even in repetitions. Calculation time by digital systems or by sampling techniques can cause delays. Sensor dynamics or sensor location can also cause delays. This paper proposes a stability condition for learning control where the plant exhibits a time delay