Iterative Learning Control for a Soft Exoskeleton with Hip and Knee Joint Assistance

Abstract

Walking on different terrains leads to different biomechanics, which motivates the development of exoskeletons for assisting on walking according to the type of a terrain. The design of a lightweight soft exoskeleton that simultaneously assists multiple joints in the lower limb is presented in this paper. It is used to assist both hip and knee joints in a single system, the assistance force is directly applied to the hip joint flexion and the knee joint extension, while indirectly to the hip extension also. Based on the biological torque of human walking at three different slopes, a novel strategy is developed to improve the performance of assistance. A parameter optimal iterative learning control (POILC) method is introduced to reduce the error generated due to the difference between the wearing position and the biological features of the different wearers. In order to obtain the metabolic rate, three subjects walked on a treadmill, for 10 min on each terrain, at a speed of 4 km/h under both conditions of wearing and not wearing the soft exoskeleton. Results showed that the metabolic rate was decreased with the increasing slope of the terrain. The reductions in the net metabolic rate in the experiments on the downhill, flat ground, and uphill were, respectively, 9.86%, 12.48%, and 22.08% compared to the condition of not wearing the soft exoskeleton, where their corresponding absolute values were 0.28 W/kg, 0.72 W/kg, and 1.60 W/kg.

A Semi-active Exoskeleton Based on EMGs Reduces Muscle Fatigue When Squatting

“…In order to evaluate whether the exoskeleton interfered with the subjects' movement in the following mode, such as walking between the workbenches of the assembly line. The wearable metabolic system (K5, COSMED, Italy) was adopted to measure the concentration and volume of the exhaled pulmonary gas, which are mainly carbon dioxide and oxygen (Chen et al, 2020).…”

A Novel Lightweight Wearable Soft Exosuit for Reducing the Metabolic Rate and Muscle Fatigue

“…The relatively easy control strategy is to provide a consistent force (about 50-100 N), simultaneously the executive force time starts from the maximum rotation angle of the hip joint in the positive direction to the end of the maximum rotation angle in the negative direction, which strategy is relatively simple and only needs to detect the changing conditions to provide the force. In some papers, many complex functions [29] are used as the function of the force, some of which are even difficult to express with mathematical formulas.…”

“…The joints of human body lower limbs will generate torque during walking, which can be referred to as the desired force. Our team used the Vicon (a device for capturing motion) to capture the motion state of the human body's lower limbs, and utilizes the human body model in Anybody (a kind of human motion simulation software, Denmark) to calculate the angle and torque of each lower limb joint in real time [29]. The biological torque of hip joint when walking on the ground is shown in Figure 4, where it can be discovered that in the first 1/2 cycle, which was a suitable assisting time, the biological torque of hip joint was similar to a sine curve.…”

“…where K p R 2×2 and K d R 2×2 denote respectively the coefficient matrices of the proportional and derivative controllers [29]. When the whole system started running normally, firstly, it obtained the Euler angle of the human body through IMUs, to analyze human gait information.…”

D-Type Iterative Learning Control for Open Container Motion System With Sloshing Constraints

“…It corrects the control signal according to the deviation between the output signal and the desired target, so as to improve the tracking performance of the system [37]. Iterative learning control is significant for nonlinear, strong coupling, difficult to model and repetitive motion of the controlled system [38], and it has been widely used in robot control, traffic flow control, industrial process, biomedical engineering and many other practical problems [39][40][41][42][43][44]. These practical problems have similar characteristics with the open container motion model with sloshing constraints, but the relevant research work is seldom reported at present.…”