Human-robot Interaction Force Research Articles

An event-controlled online trajectory generator based on the human-robot interaction force processing

Purpose– The problem of robotic co-manipulation is often addressed using impedance control based methods where the authors seek to establish a mathematical relation between the velocity of the human-robot interaction point and the force applied by the human operator (HO) at this point. This paper aims to address the problem of co-manipulation for handling tasks seen as a constrained optimal control problem.Design/methodology/approach– The proposed point of view relies on the implementation of a specific online trajectory generator (OTG) associated with a kinematic feedback loop. This OTG is designed so as to translate the HO intentions to ideal trajectories that the robot must follow. It works as an automaton with two states of motion whose transitions are controlled by comparing the magnitude of the force to an adjustable threshold, in order to enable the operator to keep authority over the robot's states of motion.Findings– To ensure the smoothness of the interaction, the authors propose to generate a velocity profile collinear to the force applied at the interaction point. The feedback control loop is then used to satisfy the requirements of stability and of trajectory tracking to guarantee assistance and operator security. The overall strategy is applied to the penducobot problem.Originality/value– The approach stands out for the nature of the problem to be tackled (heavy load handling tasks) and for its vision on the co-manipulation. It is based on the implementation of two main ingredients. The first one lies in the online generation of an appropriate trajectory of the interaction point located at the end-effector and describing the HO intention. The other consists in the design of a control structure allowing a good tracking of the generated trajectory.

Human-Walking-Intention-Based Motion Control of an Omnidirectional-Type Cane Robot

An intelligent cane robot is designed for aiding the elderly and handicapped people's walking. The robot consists of a stick, a group of sensors, and an omnidirectional basis driven by three Swedish wheels. Recognizing the user's walking intention plays an important role in the motion control of our cane robot. To quantitatively describe the user's walking intention, a concept called “intentional direction (ITD)” is proposed. Both the state model and the observation model of ITD are obtained by enumerating the possible walking modes and analyzing the relationship between the human-robot interaction force and the walking intention. From these two models, the user's walking intention can be online inferred using the Kalman filtering technique. Based on the estimated intention, a new admittance motion control scheme is proposed for the cane robot. Walking experiments aided by the cane robot on a flat ground and slope are carried out to validate the proposed control approach. The experimental results show that the user feels more natural and comfortable when our intention-based admittance control is applied.

Experimental Research on Trajectory Control of Walking Rehabilitation Training Robot

In order to improve the effect of smooth motion, the impedance control is introduced into the control system of walking rehabilitation training robot. An impedance control strategy for active rehabilitation training model is proposed and analyzed, and an adaptive control algorithm is proposed on that basis. The experimental tests of three control methods including PD position servo control, impedance control and adaption control are implemented on the robot prototype. The experimental results show that the robot can continuously adjust its gait trajectory according to the human-robot interaction force to meet the expected gait characteristics under the latter two control strategies. The feasibility and validity of the two control strategies is proved, which will be used in active rehabilitation training.

Effects of Impedance Reduction of a Robot for Wrist Rehabilitation on Human Motor Strategies in Healthy Subjects during Pointing Tasks

Studies on human motor control demonstrated the existence of simplifying strategies (namely 'Donders' law') adopted to deal with kinematically redundant motor tasks. In recent research we showed that Donders' law also holds for the human wrist during pointing tasks and that it is heavily perturbed when interacting with a highly back-drivable state-of-the-art rehabilitation robot. We hypothesized that this depends on the excessive mechanical impedance of the pronation/supination (PS) joint of the robot and in this work we analyzed the effects of its reduction. To this end we deployed a basic force control scheme, which minimizes human–robot interaction force. This resulted in a 70% reduction of the inertia in the PS joint, and in decrease of 81 and 78% of the interaction torques during 1- and 3-d.o.f. tasks. To assess the effects on human motor strategies, pointing tasks were performed by three subjects with a lightweight handheld device, interacting with the robot using its standard PD control (setting impedance to zero) and with the force-controlled robot. We quantified Donders' law as two-dimensional surfaces in the three-dimensional configuration space of rotations. Results revealed that the subject-specific features of Donders' surfaces reappeared after the reduction of robot impedance obtained via the force control.

Symmetry-based resistance as a novel means of lower limb rehabilitation

Robotic devices hold much promise for use as rehabilitation aids but their success depends on identifying effective strategies for controlling human–robot interaction forces. We developed a robotic device to test a novel method of controlling interaction forces with the intent of improving force symmetry in the limbs. Users perform lower limb extensions against a computer-controlled resistive load. The control software increases resistance above baseline in proportion to lower limb force asymmetry (balance between left and right limb forces). As a preliminary trial to test the device and controller, we conducted two experiments on neurologically intact subjects. In experiment 1, one group of subjects received symmetry-based resistance while performing lower limb extensions ( n=10). A control group performed the same movements with constant resistance ( n=10). The symmetry-based resistance group improved lower limb symmetry during training (ANOVA, p<0.05), whereas the control subjects did not. In experiment 2, subjects ( n=10) successfully used symmetry-based resistance to alter their lower limb force production towards a target asymmetry (ANOVA, p<0.05). These studies suggest that symmetry-based resistance may hold rehabilitation benefits after orthopedic or neurological injury. Specifically, performing strength training therapy with this controller may allow hemiparetic individuals to focus better on increasing strength and neuromuscular recruitment in their paretic limb while experiencing symmetric limb forces.