RESUMO
With the rapid development of modern industrial technology and high performance technology products, ultra-precision machining technology becomes increasingly important. However, joint clearance of kinematic pairs, lack of feeding accuracy and overlarge contact stress still limit the further improvement of ultra-precision machining technology. In this study, a novel surface machining method utilizing structural elastic waves was proposed, and a machining tool using the piezoelectric actuating principle was presented for verifying the proposed method. Two vibration modes with a phase shift of π/2 in both space and time domains are exited simultaneously in the elliptical motion of points on the structural surface. By means of adjusting driving signal parameters, such as frequency, voltage amplitude and phase shift, different machining performances could be achieved. The configuration and working vibration modes of the proposed machining tool were firstly calculated by the finite element method, and then the optimal working frequency of the machining tool prototype was determined by vibration characteristic experiments. At last, machining characteristic experiments were conducted to validate the proposed machining method. Experimental results showed that the minimum working contact force between the machining tool and workpiece was 1N, and the chipped depth of 1.93µm was achieved at the same contact force after machining for 5min. And at the conditions of the contact force of 6N, two driving voltages of 400Vpp with a phase shift of π/2, and machining time of 5min, the prototype could achieve to machine the workpiece most efficiently and the roughness of the machined workpiece surface could be reached approximating 0.20µm. In conclusion, this proposed machining method could achieve a good quality machined surface with low residual stress and little damage by applying low contact force. Furthermore, it also had the advantage of no joint clearance error due to no kinematic pair in the structure, which improves the machining precision.
RESUMO
In this paper, a novel modal-independent ultrasonic motor with dual stator is proposed, in order to relieve the difficulty of adjustment for coincidence of modal frequencies of a stator for multi-modal coupling type ultrasonic motor (USM). It consists of two stators (an upper stator and a lower stator) and a rotor. The stators are excited the 3rd longitudinal vibration mode, by arranging the location of rotor and two stators, the rotor can realize rotary motion by friction effect with the stators. The rotor is mounted between the maximum deformation location of the upper stator and the nodal line of the lower stator. Since two stators are the same and are excited the same vibration mode, the modal-independent USM can adjust the coincidence of modal frequencies conveniently. Furthermore, the stator of the modal-independent USM has the characteristics of simple structure, which promised advantages of easy designing, manufacturing, miniaturizing and suitable for the mass production of USM. Modal test shows the disparity between the modal frequencies of the stators is 0.78%. Mechanical characteristic test shows the rotary speed of the USM is 75 revolutions per minute (clockwise) and 65.8 revolutions per minute (anti-clockwise) at the voltage of 400Vp-p. And at the same voltage, the maximum torque is 8.4N·mm. The resolution of the modal-independent USM can up to 0.34mrad at the applied voltage of 400Vp-p.
