Improvements in the output power and accuracy of an ultrasonic stepping motor

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This study was focused on the improvements of an ultrasonic stepping motor for its practical use. In this motor, a stepping motion is realized by shifting spatially the standing vibrations of a ring/disk stator.1) To support the stator firmly, a bending vibration mode of a disk with a nodal circle was introduced. An appropriate stator configuration was designed by Finite-Element-Method and made. We succeeded in fix the stator without reduction in vibration characteristics.2) An experimental investigation on the contact mechanism at the rotor/stator interface revealed that the accuracy of step position becomes high when the width of contact region is designed at a quarter wavelength of the stator vibration.3) A motor with 4.5 degree-step was designed and made being based on these new knowledge.4) A high speed operation algorithm for accurate positioning was developed, where a large step high spped coarse positioning and a small step fine positioning were used complementarily.It was clarified that the accuracy of the electrode pattern and the dimensions of the stator should be improved for much higher precision. A design for higher vibration amplitude is also important for larger mechanical output5) A principle of linear stepping motor was also proposed. A reversible stepping motion of 10 steps for 50 mm span was realized by exciting several bending vibration of a bar with different order.