Dispenser with closed loop control

A method of controlling needle motion of a material applicator that includes an actuator assembly coupled to a needle, the method comprising:

• actuating a piezoelectric device of the actuator assembly such that the needle translates along a vertical direction;
• emitting light from an emitter to a receiver such that a portion of the actuator assembly or a portion of the needle occludes a portion of the light and the receiver receives a non-occluded portion of the light;
• and
• adjusting operation of the piezoelectric device based upon feedback from the receiver and a voltage waveform provided to the piezoelectric device.

A method of controlling needle motion of a material applicator that includes an actuator assembly coupled to a needle, the method comprising:

• actuating a piezoelectric device of the actuator assembly such that the needle translates along a vertical direction between 1) a first position where the needle is spaced from a valve seat of a nozzle;
• and 2) a second position where the needle contacts the valve seat to jet an amount of a material from the nozzle;
• emitting light from an emitter to a receiver such that a portion of the actuator assembly or a portion of the needle occludes a portion of the light and the receiver receives a non-occluded portion of the light;
• and
• implementing a control loop that includes feedback control, wherein the feedback control adjusts a voltage provided to the piezoelectric device of the actuator assembly based on a comparison between feedback received from the receiver and a desired voltage waveform provided to the piezoelectric device to maintain a constant size and shape of the material jetted from the nozzle.