Biomimetic compliant lower limb exoskeleton (BioComEx) and its experimental evaluation

Abstract

Exoskeleton robots are generally used for rehabilitation and load-carrying applications. Stable and flexible walking with minimal energy consumption of the human body is achieved by the compliant operation of the human joints. Essentially, the stiffness of the human ankle joint varies continuously, while the stiffness of the knee and hip joints remains nearly constant during loading phases of the walking cycles. With inspiration from the human leg biomechanics, a new biomimetic compliant lower limb exoskeleton robot (BioComEx) was constructed and its preliminary experimental tests were carried out in this paper. A variable stiffness actuator was developed for the ankle joint of BioComEx, and series elastic actuator designs were employed in the knee and hip joints of the robot. The joint actuators of BioComEx were designed longitudinally in order to be embedded inside of the thigh and shank leg segments for the compactness. Separate force sensors were employed in each segment of the robot for the modularity of the control strategies. Since the exoskeletons can be used for both load-carrying and rehabilitation, the developed robot was tested in both human-in-charge and robot-in-charge modes, respectively. The robot needs to mimic movement of healthy user joints in the human-in-charge mode and maximize the compliance between the user and robot; thus, the interaction forces should be reduced as possible. Hence, a modular closed-loop impedance control algorithm was developed for this mode. On the other hand, in the robot-in-charge mode, the robot joints need to track predefined gait references to make the patient walk. PID position control algorithm was chosen for preliminary test of the robot in this mode. Experimental results show that BioComEx is sufficiently satisfactory for walking applications of healthy and paralyzed users.

Methodologies for evaluating exoskeletons with industrial applications

“…The analysis of muscular activity with electromyography (e.g., [Wang et al 2020, Pillai 2020) is predominantly applied for evaluating the physical relief for selected (in particular supported) muscle groups. The analysis of movement patterns (e.g., recorded with force sensors [Baser et al 2019], inertial measurement units [Maurice et al 2020], video camera [Wang et al 2018], optical marker system [d 'Elia et al 2017]) focused mainly on kinematic aspects or working speed comparisons. Modelling (e.g., musculoskeletal simulations [Blanco et al 2019, Nelson et al 2020, Weston et al 2018, mathematical/numerical calculations [Aoustin and Formalskii 2018, Han et al 2020, Pan et al 2014] addressed mainly the system's support as well as the movability and motions during its use.…”

“…All these criteria were respectively subsumed under working speed and quality of work.  Kinematic aspects comprise principally the movability with the exoskeleton, since the user's range of motion should not be impaired [Baser et al 2019] or changed in motion sequences in terms of movement patterns [Baltrusch et al 2019] or load transfers (i.e., postural control, risk of falling [Maurice et al 2020]). Ideally, the system features a synchronicity with the user's dynamics (i.e., acceleration and velocity [Yong et al 2019]) and motion trajectories (i.e., position, direction, and orientation [Li et al 2018a]).…”

State of the Art Lower Limb Robotic Exoskeletons for Elderly Assistance

“…With the integrated interface and the modular structure, the proposed exoskeleton provides variety of control methods such as electroencephalograph (EEG) and the joystick to manipulate the system. The exoskeleton called ''BioComEx'' described in the work by Baser et al represented in figure 2 (d), assists walking of people with paralyzed limbs or healthy people by reducing the load [27]. Basically, it applies series elastic type of actuation for the knee and hip joints, however for the ankle joint variable stiffness actuator has been employed.…”

Low-Cost Force Sensors Embedded in Physical Human–Machine Interfaces: Concept, Exemplary Realization on Upper-Body Exoskeleton, and Validation

“…In this case, evaluators can choose from a pool of applicable methods such as surveys, modeling, and simulation, or the analyses of muscular activities or movement patterns. However, the analyses of applied interaction forces in interfaces might enable a multidimensional evaluation with only one tool regarding the exoskeletal support (e.g., [14][15][16][17]), comfort (e.g., [14,18,19]), motion synchronicity (e.g., [15,20]), or movability (e.g., [21]). Additionally, and in case of being permanently embedded in the interface, the respective sensory data might be analyzed in real-time in order to detect poor system configurations and initiate system-sided adjustments [22].…”