Sustainable Compliant Physical Interaction in a Biped-Wheeled Wearable Machine

This paper deals with the problem of the physical human-machine interaction in biped-wheeled exoskeletons and underlines how the symbiosis between humans and machines may increase sustainability. Few exoskeletons in the world are designed with wheels, but the evolution of wearable machines in industries and the convenience of using wheels, underline the importance of the novel research sector of biped-wheeled exoskeletons. This paper shows the functional design and simulation of a novel biped-wheeled wearable machine, including sustainable compliant physical interaction with the subject on board. In particular, the multibody model of the proposed machine is studied and simulated with the subject model on board, including human-machine compliant interactions. The classical human walking cycle is implemented in the machine, varying the speed and the joint compliance of the subject on board and comparing the torque and power output of the motors of the biped-wheeled exoskeleton. The results of this study underline how the joint compliance of the subject on board of the biped-wheeled exoskeleton may influence the efficiency and sustainability of the biped-wheeled wearable machine.

Design of admittance controller with sliding mode based on disturbance observer for elbow joint actuated by pneumatic muscles

Purpose Active compliance control is the key technology for Tri-Co robots (coexisting–cooperative–cognitive robots) to interact with the environment and people. This study aims to make the robot arm shake hands compliantly with people; the paper proposed two closed-loop-compliant control schemes for the dynamic identification of cascade elbow joint. Design/methodology/approach The active compliance control strategy consists of inner and outer loops. The inner loop is the position control using sliding mode control with disturbance observer (SMCDO), in which a new saturation function is designed to replace the traditional signal function of sliding mode control (SMC) law so as to mitigate chatter. The outer loop is the admittance control to regulate the dynamic behaviours of the elbow joint, i.e. its impedance. The simulation is carried out to verify the performance of the proposed control scheme. Findings The results show that the chatter of traditional SMC can be effectively eliminated by using SMCDO with this saturation function. In addition, for the handshake task, the value of threshold force and elbow joint compliance is defined. Then, the threshold force tests, impact tests and elbow-joint compliance tests are carried out. The results show that, in the impedance model, the elbow joint compliance only depends on the stiffness parameters, not on the position control loop. Practical implications The effectiveness of the admittance control based on SMCDO can improve the adaptability of industrial manipulator in different working environments to some degree. Originality/value The admittance control with SMCDO completed trajectory tracking has higher accuracy than that based on SMC.

Bolted joint compliance analysis with account for the roughness of contact surfaces

Bolted joints are widespread in various industries. They are used both in detachable and in non-detachable connections. The main requirement for bolted joints is to ensure the strength of the connection and guaranteed contact pressure on the connected surfaces, i.e. joints, during the operation of the structure. As a rule, their design and calculation do not take into account the contact compliance of surfaces, which is determined by their macro- and microroughnesses. This problem leads to an overestimation of the joint strength and an underestimation of the predicted joint compliance. The study proposes a simple model which makes it possible by calculation to take into account the effect of the roughness of the contacting surfaces on the compliance of the joint without modifying the ANSYS application package. On the example of a flange connection, an experimental verification of the adequacy of the proposed model was carried out.

Sex and Stride Impact Joint Stiffness During Loaded Running

This study determined changes in lower limb joint stiffness when running with body-borne load, and whether they differ with stride or sex. Twenty males and 16 females had joint stiffness quantified when running (4.0 m/s) with body-borne load (20, 25, 30, and 35 kg) and 3 stride lengths (preferred or 15% longer and shorter). Lower limb joint stiffness, flexion range of motion (RoM), and peak flexion moment were submitted to a mixed-model analysis of variance. Knee and ankle stiffness increased 19% and 6% with load (P < .001, P = .049), but decreased 8% and 6% as stride lengthened (P = .004, P < .001). Decreased knee RoM (P < .001, 0.9°–2.7°) and increased knee (P = .007, up to 0.12 N.m/kg.m) and ankle (P = .013, up to 0.03 N.m/kg.m) flexion moment may stiffen joints with load. Greater knee (P < .001, 4.7°–5.4°) and ankle (P < .001, 2.6°–7.2°) flexion RoM may increase joint compliance with longer strides. Females exhibited 15% stiffer knee (P = .025) from larger reductions in knee RoM (4.3°–5.4°) with load than males (P < .004). Stiffer lower limb joints may elevate injury risk while running with load, especially for females.