Background. Variable structure parallel mechanisms, actuated with low-cost motors with serially added elasticity (series elastic actuator - SEA), has considerable potential in rehabilitation robotics. However, reflected masses of a SEA and variable structure parallel mechanism linked with a compliant actuator result in a potentially unstable coupled mechanical oscillator, which has not been addressed in previous studies. Methods. The aim of this paper was to investigate through simulation, experimentation and theoretical analysis the necessary conditions that guarantee stability and passivity of a haptic device (based on a variable structure parallel mechanism driven by SEA actuators) when in contact with a human. We have analyzed an equivalent mechanical system where a dissipative element, a mechanical damper was placed in parallel to a spring in SEA. Results. The theoretical analysis yielded necessary conditions relating the damping coefficient, spring stiffness, both reflected masses, controller's gain and desired virtual impedance that needs to be fulfilled in order to obtain stable and passive behavior of the device when in contact with a human. The validity of the derived passivity conditions were confirmed in simulations and experimentally. Conclusions. These results show that by properly designing variable structure parallel mechanisms actuated with SEA, versatile and affordable rehabilitation robotic devices can be conceived, which may facilitate their wide spread use in clinical and home environments.
COBISS.SI-ID: 1081449
Numerous haptic devices have been developed for upper-limb neurorehabilitation, but their widespread use has been largely impeded because of complexity and cost. Here, we describe a variable structure pantograph mechanism combined with a spring suspension system that produces a versatile rehabilitation robot, called Universal Haptic Pantograph, for movement training of the shoulder, elbow, and wrist. The variable structure is a 5-degree-of-freedom (DOF) mechanism composed of 7 joints, 11 joint axes, and 3 configurable joint locks that reduce the number of system DOFs to between 0 and 3. The resulting device has eight operational modes: Arm, Wrist, ISO (isometric) 1, ISO 2, Reach, Lift 1, Lift 2, and Steer. The combination of available work spaces (reachable areas) shows a high suitability for movement training of most upper-limb activities of daily living. The mechanism, driven by series elastic actuators, performs similarly in all operational modes, with a single control scheme and set of gains. Thus, a single device with minimal setup changes can be used to treat a variety of upper-limb impairments that commonly afflict veterans with stroke, traumatic brain injury, or other direct trauma to the arm. With appropriately selected design parameters, the developed multimode haptic device significantly reduces the costs of robotic hardware for full-arm rehabilitation while performing similarly to that of single-mode haptic devices. We conducted case studies with three patients with stroke who underwent clinical training using the developed mechanism in Arm, Wrist, and/or Reach operational modes. We assessed outcomes using Fugl-Meyer Motor Assessment and Wolf Motor Function Test scores showing that upper-limb ability improved significantly following training sessions.
COBISS.SI-ID: 1138793
Background: Repetitive task training, delivered either by a therapist or haptic robot is core of modern rehabilitation of movement. In the current rehabilitation, robotics-based movement training the level of haptic support assisting the movement is rather stationary and may remain the same for periods of days. The aim of this paper was to investigate the influence of haptic support algorithms (HSA) dynamics on the outcome of motor learning. Methods: Twenty-seven neurologically intact participants, divided into three groups supported by dynamically different HSA, played a rather demanding two degrees of freedom motor task (virtual reality based table football) to learn wrist movements with their inferior arm. The evaluation before training without support was followed by the training sessions and concluded with evaluation after training without robotic support. Results: The results showed significant improvement in all three groups, but the statistical analysis reveals the difference within groups. The selection of the HSA that is appropriate for the given motor task had a significant influence on the level of acquired motor skils after the training period. Conclusions: The results of this study suggest that for every motor task or equivalently for every motor ability of a particular subject such a HSA scheme exist and should be implemented that maximizes training effects in a limited number of training attempts.
COBISS.SI-ID: 1189993