A system and method for controlling a needle motion of a material applicator are disclosed. The system includes an actuator assembly that contains a piezoelectric device, where the actuator assembly is connected to a needle and translates the needle along a vertical direction, and a sensor assembly that includes an emitter for emitting light, where a portion of the actuator assembly occludes a portion of the light. The sensor assembly also includes a receiver for receiving a non-occluded portion of the light and a sensor holder that secures the emitter and the receiver. The system further includes a controller in electrical communication with the piezoelectric device, emitter, and receiver, where the controller adjusts operation of the actuator assembly based on feedback received from the receiver.