Evolving Design Challenges with Piezoelectric Motion Devices (Part 3 of 3)
A Python API and a serial command set can be used, which can be sent to the driver board via RS232 interface. In this way motor control can be established in any customer control platform for devices and instruments.
With closed-loop control there are different algorithms to optimize motor speed and position control, leading to quiet and accurate motor motion and positioning.
Continuous-frequency algorithm – Medium to high speeds of 2 rpm to 100 rpm are regulated by varying the excitation frequency along the resonance characteristic of the piezo motor within its medium-frequency region during medium- to high-speed motion.
- Hysteresis algorithm – Low speeds of 1 rpm to 2 rpm are regulated by varying the excitation frequency along the resonance characteristic of the piezo motor within its high-frequency region during lower-speed motion.
- Modulation algorithm – Slow speeds of 0.2 rpm to 1 rpm are regulated by the formation of train excitation packets with specific fixed repetition rates. The packets are internally frequency modulated during slow-speed motion.
- Frequency modulation algorithm – Very slow speeds of 0.01 to 0.2 rpm are regulated by the formation of train excitation packets (similar to modulation algorithm), but with a varying repetition rate during very slow speed motion.
Being a direct drive, once the motor has attained its rotary or linear position the power is turned off and the motor holds position at full blocking torque or blocking force, unlike a dc solution, which will continuously consume power to maintain that position. In some circumstances, dc solutions may dither around the set point dependent upon the control schema being used, whereas the piezo solution will maintain a fixed stationary holding position.
An initial range of rotary devices offering torque from 0.2 mN.m to 30 mN.m and a range of linear devices with forces from 0.2 N to 10 N has been established. Product development continues and the range will continue to expand with extended performance.
Developments include adjustable travel linear motion actuators. In this derivative the piezoceramic resonator is attached to a carriage on a linear bearing system and can drive the carriage with a force of 10 N along any length of track. The carriage can be moved at up to 200 mm/sec and can be controlled in 50-nanometer incremental steps. This embodiment of a linear piezo motor system offers a useful design solution for very precise 3D-biomedical printing applications.
Piezo motors offer technical benefits and are now an affordable alternative to DC motors for rotary and linear motion requirements. They are direct drive and offer high precision with fast response times, plus good power density and light weight. With zero power to hold they offer the possibility of very efficient overall duty. They can be designed to offer low magnetic permeability for use in MRI fields, are immune from EM and RF interference, and have no emissions.
Piezo motors offer a unique alternative design solution for engineers to consider in a multitude of applications.