Research On Multi-dof Force Feedback Technology With Magnetorheological Damper

Force feedback interaction is a unique bilateral sensory modality.It can simulate the force that people feel in real environment,create a realistic interactive experience,and improve the immersion and telepresence of interaction.As the medium between the operator and the virtual/remote environment,force feedback device utilizes mechanical structures and actuators to deliver force stimuli and displays properties such as material,texture,and stiffness of the objects in the virtual/remote environment.Focusing on the disadvantages of commercially available force feedback devices and MR(magnetorheological)dampers,a six-DOF(degree-of-freedom)force feedback device with large workspace,high translational force and rotational torque output capabilities was developed as well as its finger mechanism supporting multi-finger force feedback.The multi-finger force feedback mechanism based on MR(magnetorheological)damper and the multi-drum MR damper were emphatically studied.A six-DOF force feedback device with hybrid structure was designed,evaluated and validated in this paper.The device has features in terms of large workspace,high translational force and rotational torque output capabilities.In addition,the device has simple kinematics due to its decoupled structures.At first,the mechanical design of the device was analyzed.The kinematics and static force models of the device were derived.Then,the position tracking performance and the force output performance of the device were evaluated.The results showed that the workspace of the device reached 500×500×420 mm.The position tracking error within the workspace was less than 0.8 mm.The peak translational force reached 20 N and the peak rotational torque reached 0.6 N.m.The peak force for fingers was about 3.5 N.At last,based on the force feedback device,a human-machine interaction system with two-handed force feedback was constructed.The system layout and architecture were introduced.An application example was also programmed.The example task results showed that the subject could move the target object faster and more accurately with two-handed force feedback than with one-handed force feedback and without force feedback.Focusing on the insufficient output capability of the DC(direct current)motor-based finger force feed-back mechanism,the finger force feedback mechanism based on MR damper was studied in this paper.The MR damper was in triple-disk structure.The FEA(finite element analysis)was adopted in damper optimiza-tion.The optimal damper was 36 mm in diameter,18 mm in height.Its off-state torque and peak torque were 5.5 and 480 m N.m,respectively.It had the dynamic range of 39 d B and the time constant of 60 ms.The damper-based finger force feedback mechanism adopted the design scheme and the wearing method similar to those of the DC motor-based finger force feedback mechanism.The damper-based finger force feedback mechanism had dimensions of 82×82×134 mm and weighed 550 g.The test results showed that the workspaces for the three fingers(thumb,index and middle fingers)were larger than 95?,the backlashes were less than 0.09?,and the peak force reached 8 N.In addition,an application example was designed to verify the effectiveness of the damper-based finger force feedback mechanism.In order to further increase torque density and realize a small damper with a large range of control-lable torque,a multi-drum structure was proposed,as well as a multi-drum MR damper parameter evaluation method based on FEA.The multi-drum MR damper has several drum-like rotors and stators in its structure.Compared with the drum damper,the multi-drum damper can activate more effective shear areas in a limited volume,thus making the damper more compact.The multi-drum MR damper has several fluid gaps.Under the same excitation,each fluid gap has its own flux density and shear area.Therefore,the number of drums and the fluid gap selection in optimization are two important parameters to be considered in a multi-drum damper design.In addition,the hollow casing radius also has a significant influence on the damper perfor-mance.In order to quantitatively evaluate the influence of these three parameters,the dampers with different numbers of drums,different gap selection in optimization,and different hollow casing radii were optimized via FEA.After obtaining the optimal designs of all dampers,they were evaluated according to torque,vol-ume,mass,and power consumption as well as torque-volume,torque-mass,and torque-power ratios.Based on the evaluation results,the suggestions on the three parameters were given.Based on the multi-drum structure,a small-scale multi-drum MR damper and a multi-drum MR damper with hollow casing were developed in this paper.In order to obtain good sealing effect and reduce the off-state torque,the ferro-fluidic sealing technique was used in both dampers.The two multi-drum dampers were optimized via FEA.Then,the damper prototypes were manufactured according to the optimal designs and their torque output and step response performances were evaluated.The optimal small-scale multi-drum MR damper was 28 mm in diameter and 23.5 mm in height.It could provide the minimum and maximum torque of 4 and 403 m N.m,respectively.It had the torque-volume ratio of 27.864 k N/m~2,the dynamic range of 40d B,and the time constant of 54 ms.The optimal multi-drum MR damper with hollow casing was 40 mm in diameter and 28 mm in height.It could provide the minimum and maximum torque of 11.04 and 1263.39m N.m,respectively.It had the torque-volume ratio of 41.252 k N/m~2,the dynamic range of 41.17 d B,and the time constant of 35 ms.