A Kinematic Model of a Humanoid Lower Limb Exoskeleton with Hydraulic Actuators

Abstract

Although it is well-established that exoskeletons as robots attached to the extremities of the human body increase their strength, limited studies presented a computer and mathematical model of a human leg hydraulic exoskeleton based on anthropometric data. This study aimed to examine lower limb joint angles during walking and running by using Inertial Measurement Units. The geometry and kinematic parameters were calculated. Twenty-six healthy adults participated in walking and running experiments. The geometric model of a human leg hydraulic exoskeleton was presented. Joint angle data acquired during experiments were used in the mathematical model. The position and velocity of exoskeleton actuators in each phase of movement were calculated using the MATLAB package (Matlab_R2017b, The MathWorks Company, Novi, MI, USA). The highest velocity of the knee actuator during walking and running was in the swing phase, 0.3 and 0.4 m/s, respectively. For the ankle and hip joints, the highest velocity of actuators occurred during the push-off phase. The results with 26 healthy subjects demonstrated that the system's compliance can be effectively adjusted while guiding the subjects walking in predefined trajectories. The developed mathematical model makes it possible to determine the position of lower limb segments and exoskeleton elements. The proposed model allows for calculating the position of the human leg and actuators’ characteristic points.

Dynamic Model of a Humanoid Exoskeleton of a Lower Limb with Hydraulic Actuators

“…This is especially important when designing this type of device. The starting and ending position of the wearable device was calculated with the determination of the movement trajectory based on the method presented in [ 37 ]. The proposed mathematical model of each part of the exoskeleton takes into account the weight of an element of the wearable device and each part of the user’s body.…”

“…The model of a hydraulic exoskeleton with three actuators is shown in Figure 1 a. A kinematic description and mathematical model with the movement simulation are presented in [ 37 ].…”

“…If the following parameters are known: angle of initial position (squat), angle of final position (standing position), velocity and acceleration values for start and end of the movement, and time of movement. Then, we can determine the locations of individual points with the application of the forward kinematics [ 37 ]. The sum of individual angles in the hip joint , knee joint , and ankle joint and the sum of individual velocities , , and angular accelerations , , can be defined by …”

“…Thus, the aim of this research was to create a mathematical model of the hydraulic exoskeleton. Hip, knee, and ankle gait angles were obtained by using inertial measurement units (IMUs) implemented in the proposed model and were presented in previous work [ 37 ]. This paper is focused on the dynamical model of a hydraulic exoskeleton.…”

Improved Single Inertial-Sensor-Based Attitude Estimation during Walking Using Velocity-Aided Observation

“…Recent gait analysis studies show the increasing use of wearable inertial sensor instead of camera-based laboratory systems for measuring attitude during gait [ 21 , 22 , 23 ]. However, most of the works focus on analysis by monitoring the angle of various joints on the lower extremities (e.g., foot, shank, calf or thigh) whereas only a small number of studies have analyzed upper limb function despite the fact that the upper limbs play an important role in balance and stability maintenance, reduction of mechanical loads on tissue, and improved gait efficiency [ 24 , 25 , 26 ].…”