Yulei Hou

Analysis of a Pre-stressed Six-component Force/Torque Sensor Based on Stewart Platform

In this paper, the structure analysis and finite element analysis (FEA) of a novel pre-stressed six-component force/torque sensor based on the Stewart platform are presented. The structure feature of the sensor is analysed in comparison with the traditional Stewart platform-based sensor. The measure principle of the sensor is introduced briefly and the mathematical expression of the sensors force mapping matrix is built by using the screw theory. With the objective of achieving high measurement sensitivity, good isotropy and least effect of frictional moment, the key structural parameters of the sensor are determined and the prototype of the sensor is manufactured. The finite element method is employed for the analysis of the static and dynamic characteristics of the prototype. The finite element model of the prototype is built and the stress distribution of the elastic legs of the sensor is achieved. The natural frequencies and the natural vibration mode shapes of the prototype are obtained, which provide a reference basis for the sensors dynamic analysis. The results of the theoretical deduction and the finite element analysis indicate that the structure is suitable for six-component force/torque sensor and the validity of the finite element model.

Isotropic Design of Stewart Platform-Based Force Sensor

The modified isotropy indices of Stewart platform-based force sensor are proposed by introducing the orthogonality condition, the physical meanings of the modified isotropy indices, the orthogonality condition and the concept of full isotropy are given. The isotropy performance of the general 6-6 Stewart platform-based force sensor is studied in detail based on the modified isotropy indices, the result indicates that it is impossible to realize full isotropy in theory, and the best comprehensive isotropy performance is obtained by compromising the isotropy indices. A novel 6/3-3 Stewart platform-based force sensor which can achieve full isotropy is proposed and a numeric example is given. The research results are useful for structure design of the six-axis force sensor.

Orientation Precision Monitoring and Homing Strategy of the Subreflector Adjusting System for 65 Meters Radio Telescope

The subreflectors adjusting mechanism of the 65 meters radio telescope in Shanghai observatory is a Stewart parallel robot.In order to find out the problems of this robots precision decline in time,caused by mechanical wear or error accumulation,inclinometers are used to measure the orientation of the mobile robot platform.Comparing the RMS (root mean square) error of the measured platform orientation with the expected orientation precision,thereby the user can judge whether maintenance or homing is required.For improving the easy maintenance of the parallel robot,two ways of homing are set up,by using photoelectric sensor and magnetic linearity displacement transducer(MLDT) respectively.The principles of the two ways of homing are analyzed,particularly that of calibrating the precision of the photoelectric sensor and the MLDT by using the homing operation.Whats more,different conditions under which the parallel robot needs homing operation are summarized,and the corresponding homing control strategies are proposed.Test shows that the homing strategy proposed is an effective tool to solve homing problem of the parallel robot.

Configuration and isotropy study of a novel fully pre-stressed and double-layer six-component force/torque sensor

A novel fully pre-stressed six-component force/torque sensor based on double-layer Stewart platform is proposed, and the parameter optimization of the sensor structure with genetic algorithms (GA) is presented. The structure characteristic of the fully pre-stressed sensor is analyzed in comparison with the traditional Stewart platform-based sensor. The number of the elastic limbs is determined by using Carathodorys theorem and Steinitzs theorem in convex analysis. In order to achieve the best performance, the static mathematical model is built by using screw theory, and the isotropy indices of the sensor are studied systematically. By compromising all the isotropy indices, the optimal design of the sensor structure is performed based on genetic algorithms, and the best comprehensive index of Stewart platform-based force sensor is obtained. The research results of the paper are useful for the design and further research of the six-component force/torque sensor.

Calibration of a Pre-stressed Stewart Platform-based Forcre/Torque Sensor

This paper presents the calibration of a novel parallel architecture of pre-stressed six-component force/torque sensor based on the Stewart platform. The structure feature of the sensor is analysed in comparison with the traditional Stewart platform-based sensor. The mathematical expression of the sensors force mapping matrix is built by using the screw theory. The static calibration device for the sensor is designed and the signal processing system is developed. Two different calibration methods are proposed and applied to the static calibration experimentation of the prototype. The calibration and error matrices of the prototype are worked out. The computed results prove the correctness of the theoretical analysis and the validity of the calibration methods

Task-oriented design of a fully pre-stressed double-layer six-component force/torque sensor

This paper presents a method to study and design a fully pre-stressed double-layer six-component force/torque sensor. The structure characteristic of the fully pre-stressed sensor is analyzed. In order to achieve the best performance, the static mathematical model is built by using screw theory. Based on the task ellipsoid, the task model of the pre-stressed force sensor is built. The relationship between the sensor and the task is studied systematically. And the mathematic description of task-oriented performance evaluation of the fully pre-stressed sensor is proposed. The key parameters of the fully pre-stressed force sensor satisfying the purpose of the task are obtained. The research results of this paper are useful for the further research and practical application of the six-component force sensor.