| Ultra-precision positioning technology is a key technology in a wide range ofhigh-tech fields such as precision optical engineering, microassembly, ultra-precisionmachining, biomedicine, aerospace engineering etc. With the rapid development ofmodern scientific technology, there are increasing needs for the precision actuatorswith compact structure and high positioning accuracy. Piezo-driven stepping actuatoris a new type of precision actuator based on bionic motion principle. With theadvantages of high positioning accuracy, good working stability, strong loadingcapacity and so on, the piezo-driven stepping actuator has become an important branchof the ultra-precision driven technology.The working principles of the bionic piezo-driven rotary actuator have beensystematically analyzed. There is a high requirement of processing accuracy for theexisting piezo-driven stepping rotary actuators, and it’s very difficult to assemble theactuators. Besides, the existing actuators also have the disadvantages of low resolution,low loading capacity, and low rotary speed and so on. In order to resolve theseproblems, a bionic piezo-driven stepping rotary actuator with the changeable radius isproposed in this paper. The structure and working principle of the actuator is designedand analyzed.The proposed novel bionic piezo-driven rotary actuator is inspired by themovement of natural inchworm and it’s mainly composed of the clamping mechanism,driving mechanism and elevating mechanism. The structural design process andworking principle of these components are described, and the forces applied on themare analyzed. Lever-type mechanism is used to amplify the micro displacement of theclamping piezoeletric stack, and a geometric model of the lever-type mechanism isestablished. The deformation and stress distribution, strength, stiffness and modalmode of the developed actuator are analyzed via finite element method and the resultsare evaluated. Dynamic simulation analysis of the stepping motion process is made base on the finite element software Abaqus, and the reasonability of the mechanicalstructure and load sequence of the rotary actuator has been demonstrated.The bionic piezo-driven rotary actuator takes the piezoelectric stack and flexurehinge as the driving unit and transmitting unit respectively. The piezoelectric stacktransforms the electrical energy into mechanical energy and provides the source powerfor precision positioning combined with the transmission function of flexure hinge.Basic characteristics of the piezoelectric stack are analyzed and its structure andworking principle are described in this paper. Besides, hysteretic characteristic of thepiezoelectric stack is also analyzed and tested. Detailed analysis on the flexure hingeare given in this paper, including the structure-types of the flexure hinge, thecommonly used material and processing method, the calculation of mechanical model.The right-angle flexure hinge and right-circle flexure hinge are chosen to be theprecision transmitting units for linear displacement and rotation displacementrespectively by comparing the performances of different types of flexure hinge.A prototype of the bionic precision rotary actuator is developed and anexperimental system is established to test the output performance of the actuator. Thecomponents and working principle of the experimental system are presented in details.In order to investigate the output performance of the rotary actuator, a series ofexperiments have been carried out. Experimental results show that the actuator willachieve a highest rotation resolution of0.25μrad while the driving voltage is8V, it canrotate at a highest speed of77488μrad/s with no load and the maximum output torqueis37Nmm while the actuator can work in stable condition. Besides, the clamping forceof the clamping mechanism, working stability and rotation speed of the rotary actuatorare also studied by experiments. Experimental results confirm that the proposed bionicprecision rotary actuator has the advantages of high rotation displacement resolution,good working stability, strong loading capacity, high positioning accuracy, etc. A novelrotation speed adjustment mode named variable clamping radius is presented in thispaper, and experimental results indicate the rotation speed of the actuator can beadjusted easily through changing the clamping radius.Rotation displacement of the rotary actuator is measured using the inclined laser triangulation method. A relative error model of the rotation displacement is establishedbased on the detailed analysis of the measurement process. It’s found that the lineardisplacement captured by the laser displacement sensor can be approximatelyconsidered as the arc length of the sampling point. The relative error of the rotationdisplacement is just0.077%while the actual rotation angle is1000μrad. A specialmechanical structure is designed for measuring the rotation displacement combine themeasuring principle of the inclined laser triangulation method and the structuralcharacteristics of the rotary actuator.The clamping radius of the existing piezo-driven rotary actuators is constant.Therefore, the rotation speed of the rotary actuators can only be adjusted by the drivingvoltage and driving frequency. These characteristics restrict their application inultra-precision positioning. A novel rotation speed adjustment mode named variableclamping radius is firstly presented in this paper to solve the above problems of theexisting rotary actuators. An elevating mechanism is designed for adjusting theclamping radius and the clamping radius can change from10.6mm to25mm. Therotation displacements of the rotary actuator under different clamping radiuses aretested and it’s found that there is an obvious inverse relationship between the clampingradius and rotation displacement. The accumulated rotation displacement is about3260μrad when the rotary actuator works continuously for ten steps with a drivingvoltage of100V and a clamping radius of23mm and the rotation displacement isabout5480μrad when the clamping radius decreases to14mm. Experimental resultsverify the feasibility of the new variable clamping radius speed adjustment mode. |
