Research On Key Technology For Force/Torque Sensor Used In Space Manipulator

With the rapid development of space technology such as on-orbit service and deep space exploration,more and more space missions require human participation.The appearance of space manipulator has somewhat alleviated the task of space astronauts.However,the space manipulator system lacks the force/torque sensing capability,which limits its application.Therefore,it is necessary to install a force/torque sensor at the joint of the space manipulator to obtain the relevant force/torque information in real time,which helps the space manipulator system achieve smooth control.The space manipulator is carried by the spacecraft from the ground into the space,and has to withstand many harsh external environments,such as strong vibration,high impact strength,strong radiation,and high/low temperature in vacuum.Conventional force/torque sensors are not suitable for this type of application.In view of the above background,this paper studies the vibration,overload protection,fault tolerance and temperature drift compensation methods of force/torque sensors.The details are as follows:(1)To investigate the vibration response of the force/torque sensor at the joint of the space manipulator in the spacecraft mechanics environment,we firstly analyze the characteristics of the vibration environment of the space manipulator.to build a six-dimensional force sensor vibration mechanics model with the dynamic substructure method Then,we obtain the inherent characteristics of the sensor structure and the vibration response law in the spacecraft mechanics environment after performing numerical simulations of the modal,random vibration and sinusoidal vibration analysis of the sensor elastomer according to the actual vibration parameters This provides a basis for structural optimization and overload protection of the sensor.(2)To overcome the overload problem of the force/torque sensor at the space manipulator joint under the spacecraft mechanics environment,we firstly design a hook-and-loop type omnidirectional mechanical overload protection device for a six-dimensional force/torque sensor with double E-type membrane structure.Then we employ the finite element method to determine the limit gap of overload protection,and verify its overload capability by simulations.The simulation results show that this special design makes the overload capability of the sensor in the Fz and Mz directions increase,respectively,from 4.4 times and 4.5 times to 43 times and 14.3 times,and the capability in the Fx/Fy and Mx/My directions increase,respectively,from 5.2 times and 5 times to 10.2 times and 8.2 times.(3)For the fault-tolerant problem of the torque sensor at the space manipulator joint,we take the widely used spoke-type joint torque sensor as the research object.Firstly,we firstly analyze the stress and strain of the torque sensor according to the deformation characteristics of the torque sensor and the deformation coordination condition,to build an analytical model of the torsional stiffness of the sensor with higher precision.Then we design an integrated torque sensor with redundant characteristics using the joint flange of the space manipulator via optimizing the parameters in the above established model.The experimental results show that the performance indices are improved:the linear error of the sensor is less than 0.77%,the Repeatable error is less than 0.89%and the fault tolerance of the sensor is improved.(4)For the temperature drift problem of the force/torque sensor in space high/low temperature environment,we take the six-dimensional force/torque sensor with double E-type membrane structure as the research object.Firstly,we analyze the temperature characteristics of the strain gauge and the causes of the heat output of the strain gauge and the elastomer,and investigate the characteristics of performance changes of reference source,excitation source,amplifier and amplifier resistance affected by temperature and the influence of the above-mentioned changes on sensor measurement results.Then,we propose a temperature drift compensation algorithm based on segmented function according to the features of experimental data.The comparison with the overall linear temperature drift compensation algorithm show that the temperature drift error of the compensated sensor has different degrees of reduction,and the effect of segmented temperature compensation(measurement error less than ± 0.5%)is better than that of the overall linear temperature compensation(measurement error less than ± 1%).