A torsional MRE joint for a C-shaped robotic leg

Abstract

Serving to improve stability and energy efficiency during locomotion, in nature, animals modulate their leg stiffness to adapt to their terrain. Now incorporated into many locomotive robot designs, such compliance control can enable disturbance rejection and improved transition between changing ground conditions. This paper presents a novel design of a variable stiffness leg utilizing a magnetorheological elastomer joint in a literal rolling spring loaded inverted pendulum (R-SLIP) morphology. Through the semi-active control of this hybrid permanent-magnet and coil design, variable stiffness is realized, offering a design which is capable of both softening and stiffening in an adaptive sort of way, with a maximum stiffness change of 48.0%. Experimental characterization first serves to assess the stiffness variation capacity of the torsional joint, and through later comparison with force testing of the leg, the linear stiffness is characterized with the R-SLIP-like behavior of the leg being demonstrated. Through the force relationships applied, a generalized relationship for determining linear stiffness based on joint rotation angle is also proposed, further aiding experimental validation. Disciplines Engineering | Science and Technology Studies AbstractServing to improve stability and energy efficiency during locomotion, in nature, animals modulate their leg stiffness to adapt to their terrain. Now incorporated into many locomotive robot designs, such compliance control can enable disturbance rejection and improved transition between changing ground conditions. This paper presents a novel design of a variable stiffness leg utilizing a magnetorheological elastomer joint in a literal R-SLIP (Rolling Spring Loaded Inverted Pendulum) morphology. Through the semi-active control of this hybrid permanent-magnet and coil design, variable stiffness is realized, offering a design which is capable of both softening and stiffening in an adaptive sort of way, with a maximum stiffness change of 48.0%. Experimental characterization first serves to assess the stiffness variation capacity of the torsional joint, and through later comparison with force testing of the leg, the linear stiffness is characterized with the R-SLIP-like behavior of the leg being demonstrated. Through the force relationships applied, a generalized relationship for determining linear stiffness based on joint rotation angle is also proposed, further aiding experimental validation.

Evolving optimal learning strategies for robust locomotion in the spring-loaded inverted pendulum model

“…21,22 Some work has investigated how the shape of the leg can be used to achieve variable stiffness and relative leg length changes during the stance phase. 23,24 Similarly, Owaki et al…”

“…21,22 Some work has investigated how the shape of the leg can be used to achieve variable stiffness and relative leg length changes during the stance phase. 23,24 Similarly, Owaki et al investigated different nonlinear stiffness functions and identified the ones that are beneficial, 25 although this was done using a compass gate, rather than the SLIP model. Andrews et al explored changing the length of the spring, rather than its stiffness in their work.…”

Development and Vibration Control of Frequency Adjustable Tuned Mass Damper Based on Magnetorheological Elastomer

“…It can quickly change its storage modulus with the change of the external magnetic field, and has the ability to change stiffness in real time [ 32 ]. As a stiffness adjustable element, MRE has been used in many applications, such as stiffness-adjustable spring elements [ 33 ], stiffness-adjustable differential mounts of vehicles [ 34 ] and Mechanical leg, using MRE joints [ 35 ]. It can be seen that MRE has a good stiffness adjustment ability and can be used to make intelligent vibration reduction devices.…”

Analysis of Styrene-Butadiene Based Thermoplastic Magnetorheological Elastomers with Surface-Treated Iron Particles

“…Magnetorheological elastomers (MRE) are viscoelastic smart composites that show variable stiffness upon application of an external magnetic field. These compounds find applications in dampers for vibration absorption [ 1 , 2 ], in robotics, electronics [ 3 , 4 ], and force/acceleration sensors [ 5 , 6 , 7 ]. Depending on how magnetoactive particles are distributed in the matrix, two types of MRE are distinguished in literature: (1) isotropic MREs have homogeneously distributed particles within the matrix.…”