Optimal design and torque control of an active magnetorheological prosthetic knee

Abstract

Despite advances in assistive technology, existing prosthetic knees still have some limitations, such as weight, low active and braking torque, and high energy consumption. This paper presents an active magnetorheological knee (AMRK) actuator developed for transfemoral prostheses. The system consists of a motor unit comprising an EC motor, harmonic drive and magnetorheological (MR) clutch. The motor unit provides active motion, working in parallel with an MR brake. With this configuration, the AMRK possesses multiple functions; it can work as a motor, clutch, or brake, reproducing movements similar to those of a healthy knee in different activities. All components of the prosthetic knee are protected to avoid risk of accidents and to provide an aesthetically appropriate structure. To reduce weight, energy consumption and volume, the MR clutch/brake geometric design was optimized using a particle swarm optimization algorithm. A prototype was fabricated and tested to evaluate the AMRK performance. Dynamic models of the MR clutch, MR brake and motor unit were analysed, and torque control was implemented. The results show that the AMRK is promising for the proposed applications, which require multiple functions with compact size, low weight, low energy consumption, high active and braking torque, and quick response time.

Magnetorheology: a review

“…They already serve as interfaces between electronic and mechanical devices in multiple applications. 4,5 Additionally, they serve as model systems (with easily tunable interparticle interactions) for a better understanding of directed colloidal self-assembly 6 and glass transition. 7 Currently there exist many review papers in this field of research [8][9][10][11][12][13][14][15][16][17][18][19] as well as some books.…”

Transient Thermal Analysis of a Magnetorheological Knee for Prostheses and Exoskeletons during Over-Ground Walking

“…A pair of thin section bearings allows relative movement between the external and internal structures. The structures are made of 7075 aluminum alloy [5], as shown in Figure 1(a). Figure 1(b) displays the configuration of the MR clutch and MR brake.…”

“…Over the years, researchers seek to develop suitable actuators for assistive lower-limb devices such as prosthesis and exoskeletons [3,4]. In general, this kind of actuators can be divided into three major groups: passive, semi-active, and active [5,6]. Passive devices do not require a power source for operation, they are designed for each type of application and do not allow performance adjustments [6].…”

“…When the fluid is subjected to an external magnetic field, its particles begin to form columnar structures parallel to the magnetic flux lines; this behavior changes the rheological properties of the fluid, such as yield stress and others, in a reversible and proportional way to the induced magnetic field [16]; the response time is in order of milliseconds [17]. Due to these characteristics, MR fluids are used to develop devices for many applications in engineering and industry: vehicle suspensions [18], clutches [19], brakes [20], structural vibration damping [21], intelligent prosthesis [5,[22][23][24] and others. MR devices usually present low energy consumption and high torque-to-weight ratio [25,26], which is important to increase the energy efficiency and reduce the weight of prostheses and exoskeletons' actuators [27].…”

Biomimetic Design of a Planar Torsional Spring to an Active Knee Prosthesis Actuator Using FEM Analysis

“…Therefore, hence active prostheses are capable of providing positive power; their assistance and ability to replicate the joint kinetics and kinematics in the whole activity can reduce the metabolic energy dispended by the user [3]. Those intelligent prostheses give the user greater mobility, acceptance, autonomy, and a sense of possession over them [4,5].…”