High Performance Open Loop Control of Scanning with a Small Cylindrical Cantilever Beam

Area of Science:

• Mechanical Engineering
• Dynamics and Control
• MEMS/NEMS

Background:

• Achieving precise unidirectional motion in base-excited cantilever beams with circular cross-sections is hindered by nonlinear effects and system asymmetries, leading to undesirable whirling.
• Previous research primarily focused on nonlinearities, overlooking the significant impact of small asymmetries and actuator cross-coupling on whirling onset in real-world systems.
• Whirling is identified as a pervasive issue in resonant beam scanner design, occurring even at low amplitudes of motion.

Purpose of the Study:

• To demonstrate that whirling in cantilever beams is a broader issue than previously understood, stemming from minor system asymmetries and actuator cross-coupling.
• To develop and present a novel technique for controlling whirling motion in cantilever beams.
• To achieve accurate open-loop control of unidirectional beam motion.

Main Methods:

• Identification of the two orthogonal eigen directions of the cantilever beam system.
• Implementation of base excitation using virtual electrodes aligned with these identified eigen axes.
• Utilizing two pairs of orthogonally placed actuator electrodes for combined actuation.

Main Results:

• The developed technique successfully generates tip vibration without whirl when base excitation is applied along the identified eigen directions.
• This method enables accurate open-loop control of the cantilever beam's motion.
• The findings indicate that whirling is the norm in practical systems due to inherent asymmetries.

Conclusions:

• A novel method for controlling whirling in cantilever beams has been successfully developed and demonstrated.
• Accurate unidirectional motion can be achieved by exciting the beam along its natural eigen directions, mitigating the effects of asymmetries.
• This research provides a pathway for improved design and control of resonant beam scanners and similar micro-mechanical systems.