The number of people with a mobility disorder caused by stroke, spinal cord injury, or other related diseases is increasing rapidly. To improve the quality of life of these people, devices that can assist them to regain the ability to walk are of great demand. Robotic devices that can release the burden of therapists and provide effective and repetitive gait training have been widely studied recently. By contrast, devices that can augment the physical abilities of able-bodied humans to enhance their performances in industrial and military work are needed as well. In the past decade, robotic assistive devices such as exoskeletons have undergone enormous progress, and some products have recently been commercialized. Exoskeletons are wearable robotic systems that integrate human intelligence and robot power. This paper first introduces the general concept of exoskeletons and reviews several typical lower extremity exoskeletons (LEEs) in three main applications (i.e. gait rehabilitation, human locomotion assistance, and human strength augmentation), and provides a systemic review on the acquisition of a wearer's motion intention and control strategies for LEEs. The limitations of the currently developed LEEs and future research and development directions of LEEs for wider applications are discussed.

In this paper, a magnetorheological (MR) damper is optimally designed for use in smart prosthetic knees. The objective of optimization is to minimize the total energy consumption during one gait cycle and weight of the MR damper. Firstly, a smart prosthetic knee employing a DC motor, MR damper and springs is developed based on the kinetics characteristics of human knee during walking. Then the function of the MR damper is analyzed. In the initial stance phase and swing phase, the MR damper is powered off (off-state). While during the late stance phase, the MR damper is powered on to work as a clutch (on-state). Based on the MR damper model as well as the prosthetic knee model, the instantaneous energy consumption of the MR damper is derived in the two working states. Then by integrating in one gait cycle, the total energy consumption is obtained. Particle swarm optimization algorithm is used to optimize the geometric dimensions of MR damper. Finally, a prototype of the optimized MR damper is fabricated and tested with comparison to simulation.

The harvesting of energy from human motion for portable and wearable electronic devices has received considerable attention. This letter describes a lightweight macrofiber composite (MFC)-based energy harvester for capturing biomechanical energy through the natural motion of the human knee. In the proposed device, a slider-crank mechanism is used to transform the rotary motion of the knee joint to linear motion, and a bending beam is used to transform the linear motion to a bending motion. When walking, a bending deformation is induced in two MFC slices attached to the bending beam, generating electrical energy. To test the performance of the developed device, treadmill tests at various walking speeds and resistive loads are performed. Experimental results show that the lightweight harvester (weighing just 307 g) can generate 1.60 mW without increasing the human effort required for walking. This is expected to significantly promote the usage of biomechanical energy harvesters.

Active transtibial prostheses, orthoses, and exoskeletons hold the promise of improving the mobility of lower-limb impaired or amputated individuals. Locomotion mode identification (LMI) is essential for these devices precisely reproducing the required function in different terrains. In this study, a terrain geometry-based LMI algorithm is proposed. The environment should be built according to the inclination grade of the ground. For example, when the inclination angle is between 7 degrees and 15 degrees, the environment should be a ramp. If the inclination angle is around 30 degrees, the environment is preferred to be equipped with stairs. Given that, the locomotion mode/terrain can be classified by the inclination grade. Besides, human feet always move along the surface of terrain to minimize the energy expenditure for transporting lower limbs and get the required foot clearance. Hence, the foot trajectory estimated by an IMU was used to derive the inclination grade of the terrain that we traverse to identify the locomotion mode. In addition, a novel trigger condition (an elliptical boundary) is proposed to activate the decision-making of the LMI algorithm before the next foot strike thus leaving enough time for performing preparatory work in the swing phase. When the estimated foot trajectory goes across the elliptical boundary, the decision-making will be executed. Experimental results show that the average accuracy for three healthy subjects and three below-knee amputees is 98.5% in five locomotion modes: level-ground walking, up slope, down slope, stair descent, and stair ascent. Besides, all the locomotion modes can be identified before the next foot strike.

Magnetorheological (MR) fluid, whose rheological properties can be changed reversibly by applied magnetic field, offers superior capabilities and opportunities since its invention. The most crucial feature of MR fluid is its controllable and continuous yield stress. Taking this advantage, MR fluid is gaining popularity in various medical applications to meet their force/torque requirements. In this review article, progress of medical applications of MR fluid in the last two decades are systematically reviewed, mainly focused on six categories: lower limb prosthesis, exoskeleton, orthosis, rehabilitation device, haptic master, and tactile display. With MR fluid, natural and stable limb motions in lower limb prostheses, exoskeletons, and orthoses, flexible muscle trainings in rehabilitation devices, and high transparency and resolution haptic feedback can be realized. Relevant discussions and future perspectives are also provided.

In this paper, we design and experimentally validate a geometric nonlinear M-shaped tri-directional piezoelectric energy harvester. This harvester adopts a single structural design, which consists of a proof mass and a beam bent into an M shape with both ends fixed. Through structural parameter modification, the vibration directions of the first three resonant modes can be nearly orthogonal, which is beneficial to achieve tri-directional energy harvesting. Finite element analysis is performed to guide the design and analyse the working effectiveness of the proposed harvester. The influence of the geometric parameters on the nonlinear stiffness is investigated to broaden the bandwidth of energy harvesting. In the experimental validation, an obvious hardening effect can be observed in vertical excitation at 0.3 m s ⁻² base acceleration. On the other hand, the power output of the harvester in three directions is in similar level, indicating the capability of tri-directional energy harvesting.