Research On Typical Stick-Slip Actuated Micromanipulator

Micro-nano manipulator is one kind of structure that can handle and move the object in micro and nano scale. With the development of research in micro-nano scale, higher requirements are put forward for higher controlling and positioning accuracy of micro-nano manipulator. Most of the micro-nano manipulators used in micro-nano scale research are actuated by stick-slip theory, which can make the manipulator reaching millimeters stroke with the step size of nanometers. Since the stick-slip structure is in fact motivated by friction and inertia, the structure will have a strong residual vibration and backlash at the end of driving cycle, because of the nonlinear characteristics of friction and some drawback of stick-slip actuation. So in order to restrain and even eliminate the vibration and backlash during stick-slip actuation, it is necessary to study the process of stick slip actuation, research the characteristics of friction, and describe the process of actuation with a reasonable friction model.Some research work about the contact situation and deformation between two surfaces have been done in this paper, a new friction model is proposed, and one experiment structure is designed and built at last. The main research contents are shown as follows:(1) The contact situation and tangential deformation between two contact surfaces and the characteristics of friction in presliding region are investigated through some experiments, and the maximum elastic deformation is found existing between two contact surfaces. If the tangential relative displacement between two contact surfaces is smaller than the maximum elastic deformation, all the displacement can be recovered by themselves when the tangential external force is removed. If sliding happens between the contact surfaces, only a short distance, which equal to the maximum elastic deformation, can be recovered. After measuring and comparing the size of friction force and relative displacement, the relationship between friction force and displacement is proved to be nearly linear in presliding region. Then, the relationship between surface roughness, normal pressure and maximum elastic deformation is investigated through one particular experiment. It was found that, the relationship between normal pressure and maximum elastic deformation is nearly linear. For the smoother surfaces, the relationship is more linear, and for the rougher surfaces, the relationship is stronger nonlinear.(2) Many classical friction models are investigated for their performance on describing the characteristic of presliding. The existing asperity models are divided into two categories, and a novel asperity model is proposed, which can describe the tangential and vertical contact situation reasonably. Based on the new asperity model, a novel friction model is proposed. This novel friction model assemble the advantages of many friction models, and can describe the pure elastic deformation and hysteresis with non-local memory reasonably, compared with the single-state friction models, and also can describe the vertical characteristics of hysteresis force, which is better than the traditional multi-state friction models. Compared with GMS friction model, the novel friction model has a brief structure and can be integrated into manipulator control system conveniently.(3) The stick-slip actuation is simulated by the novel asperity based mixed friction model, and the movement of slider during backlash is analyzed. The reason of slider’s residual vibration and the condition that slider doesn’t have backlash are proposed and analyzed too. A stick-slip experimental prototype is built and its dynamic model is calculated. Then, the control system of this prototype based on the novel friction model is designed.(4) A stick-slip actuation experiment system is designed and built at the last part of this paper. The large scale residual vibration of basement at the end of one actuation period is suppressed by an improved band reject filter. In order to isolate slider’s residual vibration in the last actuation period from the next actuation period, the waveform of driving signal is optimized. In order to suppress the residual vibration of slider, which is increased after suppressing the residual vibration of basement, a specific sine wave signal is added to the driving signal according to the simulation of novel friction model. Compared with the original performance of stick-slip structure with no vibration control, the actuation stability and positioning accuracy are improved by vibration control.