Novel magneto-rheological fluid damper for passive force/torque feedback

The damper is capable of providing a continuously variable dampering force/torque in response to a magnetic field. It consists of an upside cap and an underside cap with a rotor located between them, the magneto-rheological （MR） fluid is filled into the gaps between the rotor and the caps. When the viscosity of the MR fluid increases under the influence of the magnetic field, the movement of the rotor will be resisted. The output torque is made up of the torque caused by the magnetic field, the torque caused by the plastic viscosity of the MR fluid, and the torque caused by the coulomb friction. The viscous torque can be calculated by a simple method and the frictional torque can be obtained by experiments. The torque dependent on the magnetic field is obtained by electromagnetic finite dement analysis. Experiments are done on the damper prototype and the validity of the design is verified.

Development and Calibration of a Hyperstatic Six-component Force/Torque Sensor

The six-component force/torque sensor has become one kind of the most important sensors with the ability of measuring all the external forces and torques. A novel hyperstatic six-component force/torque sensor based on the Stewart platform structure, which can be used for the force measurement of the robot wrist, is proposed, and its structural optimal design, finite element analysis and calibration experimentation is presented. The characteristic of the sensor structure is analyzed in comparison with the traditional Stewart platform-based sensor. The mathematical expression of the sensor＇s force mapping matrix is introduced. The condition number and generalized amplifying coefficient defined by singular values of force Jacobian matrix are used to evaluate the performances of isotropy and sensitivity of the sensor respectively. The optimal design of the sensor structure is performed with the objective of achieving high measurement sensitivity and good isotropy. The sensor prototype is fabricated, and the static and dynamic characteristics of the sensor are analyzed with finite element analysis software package ANSYS. The calibration device is manufactured, and the data acquisition and processing system is developed. The theoretical and experimental study of the static calibration of the sensor prototype is carried out. The results of simulation analysis and calibration experimentation prove the feasibility of the hyperstatic sensor structure, and the contents of this paper possess theoretical significance and engineering value for the further research and practical application of the six-component force sensor.

Miniature 6-axis force/torque sensor for force feedback in robot-assisted minimally invasive surgery

In order to restore force sensation to robot-assisted minimally invasive surgery(RMIS),design and performance evaluation of a miniature 6-axis force/torque sensor for force feedback is presented.Based on the resistive sensing method,a flexural-hinged Stewart platform is designed as the flexible structure,and a straightforward optimization method considering the force and sensitivity isotropy of the sensor is proposed to determine geometric parameters which are best suited for the given external loads.The accuracy of this method is preliminarily discussed by finite element methods(FEMs).The sensor prototype is fabricated with the development of the electronic system.Calibration and dynamic loading tests for this sensor prototype are carried out.The working ranges of this sensor prototype are 30 N and 300 N·mm,and resolutions are 0.08 N in radial directions,0.25 N in axial direction,and 2.4 N·mm in rotational directions.It also exhibits a good capability for a typical dynamic force sensing at a frequency close to the normal heart rate of an adult.The sensor is compatible with surgical instruments for force feedback in RMIS.

Design and calibration of spoke piezoelectric six-dimensional force/torque sensor for space manipulator

The large manipulator outside the space cabin is a multi-degree of freedom actuator for space operations.In order to realize the automatic control and flexible operation of the space manipulator,a novel spoke structure piezoelectric six-dimensional force/torque sensor with redundancy ability,high stiffness and good decoupling performance is innovatively proposed.Based on the deformation coordination relationship,the redundancy measurement mechanism is revealed.The mathematical models of the sensor with and without branch fault are established respectively.The finite element model is established to verify the feasibility of structure and redundancy measuring principle of the sensor.Depending on the theoretical analysis and simulation analysis,the prototype of the sensor is developed.Static and dynamic calibration experiments are carried out.The actual output voltage signal of the six-dimensional force/torque sensor is collected to establish the equation between the standard input applied load and the actual output voltage signal.Based on ant colony optimized BP algorithm,performance indexes of the sensor with and without branch fault are analyzed respectively.The experimental results show that the spoke piezoelectric sixdimensional force/torque sensor with the eight-point support structure has good accuracy and reliability.Meanwhile,it has strong decoupling characteristic that can effectively shield the coupling between dimensions.The nonlinear errors and maximum interference errors of decoupled data with and without branch faults are less than 1% and 2%,respectively.The natural frequency of the sixdimensional force sensor can reach 2856.45 Hz and has good dynamic characteristics.The research content lays a theoretical and experimental foundation for the design,development and application of the new six-dimensional force/torque sensors with redundancy.Meanwhile,it will significantly improve the research level in this field,and provide a strong guarantee for the smooth implementation of force feedback control of the space station manipulator project.

The Velocity Synchronizing Control on the Electro-Hydraulic Load Simulator

This paper builds up an accurate nonlinear mathematical model of anelectro-hydraulic force/ torque servo control system, and provides a thorough theoretical analysison the feedforward compensation for extraneous force/torque, whose limitation is analyzed andrevealed. The nonlinear factors and the servo valve dynamics have much influence on the systemcharacteristics. Subsequently a velocity syn-chronizing-compensation method by using the controlsignal of the control actuator is proposed, which can reduce the lagging effects for the betterperformance. For the reason of similarity between the model of control actuator and that of the loadsimulator, the proposed method performs well against the influence of nonlinear factors. Thesimulations and the experiments confirm that this control scheme results in a quick response,robustness, and excellent ability against disturbance.

Ground demonstration system based on in-orbit assembly oriented manipulator flexible force control

To eliminate the load weight limit of carrier rockets and reduce the burden on support structures,in-orbit assembly is a key technology to make design of scattering a large diameter telescope into submirror modules,which requires smooth operation of assembly robots,and flexible force control technology is necessary. A ground demonstration system is presented for in-orbit assembly focusing on flexible force control. A six-dimensional force/torque sensor and its data acquisition system are used to compensate for gravity. For translation and rotation,an algorithm for flexible control is proposed. A ground transportation demonstration verifies accuracy and smoothness of flexible force control,and the transportation and assembly task is completed automatically. The proposed system is suitable for the development of in-orbit assembly robots.

Robotics and mechatronics for planetary surface exploration

The paper briefly addresses DLR' s ( German Aerospace Center) expertise in space robotics by handof corresponding milestone projects including systems on the International Space Station ISS. It then discussesthe key technologies needed for the development of an artificial "robonaut" generation with mechatronic ultra-light weight arms and multifingered hands. The third arm generation is nearly finished now, approaching thelimits of what is technologically achievable today with respect to light-weight and power losses. In a similar wayDLR' s second generation of artificial 4-fingered hands was a big step towards higher reliability, manipulabilityand overall performance.

Relative roll control of satellite docking using electromagnetic coils

An electromagnetic coil topology and its control strategy,which can be incorporated into the electromagnetic docking device,have been proposed for the relative roll control of two satellites in space.The target satellite and the chaser satellite are respectively embarked with four and six coils evenly arranged around the docking axis.All the coils on the target satellite are Direct Current(DC)energized,while the currents in the coils of the chaser satellite are regulated to achieve the relative roll control.The electromagnetic force/torque model is built by utilizing the frequentlyused far field model.Based on the fundamental components extracted from that model,this paper proposes a real-time magnetic moment vector distribution formula that simply generates a constant roll torque.This paper not only presents an equation for calculating the relative roll angle through the Euler angles of two satellites,but also an equation that converts the roll torque setpoint to the setpoints of the coil currents.A 3-closed-loop positioning controller composed of angle,angular velocity,and current loop is developed.The proposed topology is verified by finite element simulation,and the control strategy is validated by dynamics simulation and ground-based tests.