Due to the advantages of more intensiveness, long duration, repeatability, and task-orientation, robot-assistant training has become a promising technology in stroke rehabilitation. Regarding the upper extremity, the natural coordination called shoulder rhythm is the most challenge to the design of ergonomic shoulder exoskeleton. Based on kinematic analysis of movement of shoulder complex, a 10-degree-of-freedom (DoF) exoskeleton rehabilitation robot with six-DoF shoulder actuation mechanism driven by pneumatic muscle through Bowden cable transmitting force is proposed. The kinematic relationship between shoulder girdle motion and the humerus flexion/retroflexion and abduction/adduction was described. The compact mechanisms for cable tension and cable disconnect/connect respectively were proposed to realize the cable automatic tension and drive-unit/manipulating-unit detachment. In order to verify the manipulability of the proposed robot during assisting patient with performing activities of daily living (ADLs), the performance criteria, i.e., normalized dexterity measure and manipulability ellipsoid, are used to evaluate and compare with human upper extremity. The evaluated results confirm the ergonomic design of shoulder mechanism of the rehabilitation robot that can provide approximate dexterity of human upper extremity in ADLs.

Категория: Ищем научные статьи | Нет комментариев »

Spinal cord injury (SCI) affects over 1000 people a year in the UK and has severe consequences for their independence and quality of life. Treatments to address SCI focus on techniques that aim to restore some degree of walking or locomotor activity. One such technique is treadmill training of SCI patients. This paper reviews the use of treadmill training in the recovery of locomotor ability in patients with SCI. Outcomes from treadmill training are variable; for patients with incomplete SCI (where some degree of connection between the brain and the spinal cord is spared from injury), treadmill training only enabled limited full weight-bearing locomotion. In patients suffering a complete SCI (where communication between the brain and spinal cord is lost), no weight-bearing locomotion at all was achieved with training. However, treadmill training does influence the activity of the leg muscles in the acute patients, observed by recordings made from the muscles (electromyography). The impro-vements achieved by treadmill training are not significantly different from other techniques such as over-ground training and functional electrical stimulation. The most effective way of restoring locomotion is through complete repair; however, regeneration techniques are still being developed. For regeneration to take place, the neurons within the spinal cord that are important in generating rhythmic movements (the central pattern generator (CPG) circuits) still need to be functioning, as these circuits have been shown to decline through long periods of inactivation. Treadmill training has therefore an important role in keeping neurons active until regenerative techniques become viable. Furthermore, in spinalized rats, it has been shown that by combining treadmill training with pharmaceutical and electrical stimulation therapies, greater improvements are seen. This suggests that the treatment of spinal cord injury should not be limited to one method. Techniques that repair the damage are the ultimate goal and it is important that patients keep active in order to increase chances of recovery.

(далее…)

Категория: Научные статьи | Нет комментариев »

Many of the current implementations of exoskeletons for the lower extremities are conceived to either augment the user’s load-carrying capabilities or reduce muscle activation during walking. Comparatively little research has been conducted on enabling an exoskeleton to increase the agility of lower-limb movements. One obstacle in this regard is the inertia of the exoskeleton’s mechanism, which tends to reduce the natural frequency of the human limbs. A control method is presented that produces an approximate compensation of the inertia of an exoskeleton’s mechanism. The controller was tested on a statically mounted, single-degree-of-freedom (DOF) exoskeleton that assists knee flexion and extension. Test subjects performed multiple series of leg-swing movements in the context of a computer-based, sprint-like task. A large initial acceleration of the leg was needed for the subjects to track a virtual target on a computer screen. The uncompensated inertia of the exoskeleton mechanism slowed down the transient response of the subjects’ limb, in comparison with trials performed without the exoskeleton. The subsequent use of emulated inertia compensation on the exoskeleton allowed the subjects to improve their transient response for the same task.

(далее…)

Категория: Научные статьи | Нет комментариев »

In the research field of robot-assisted gait rehabilitation there is increased focus on the improvement of physical human-robot interaction by means of high-performance actuator technologies and dedicated control strategies. In this context we propose a combination of lightweight, intrinsically compliant, high-torque actuators (pleated pneumatic artificial muscles) with safe and adaptable guidance along a target trajectory by means of proxy-based sliding mode control. We developed a powered knee exoskeleton (KNEXO) to evaluate these concepts. In addition to the trajectory-based controller a torque controller was implemented with a view to minimizing the interaction during unassisted walking. First, various treadmill walking experiments were performed with unimpaired subjects wearing KNEXO to evaluate the performance of the proposed controllers. Test results confirm the ability of KNEXO to display low actuator torques in unassisted mode and to provide safe, adaptable guidance in assisted mode. Subsequently, a multiple sclerosis patient participated in a series of pilot experiments. Provided there was some patient-specific controller tuning KNEXO was found to effectively support and compliantly guide the subject’s knee.

Категория: Ищем научные статьи | Нет комментариев »

Within the context of impedance controlled exoskeletons, common actuators have important drawbacks. Either the actuators are heavy, have a complex structure or are poor torque sources, due to gearing or heavy nonlinearity. Considering our application, an impedance controlled gait rehabilitation robot for treadmill-training, we designed an actuation system that might avoid these drawbacks. It combines a lightweight joint and a simple structure with adequate torque source quality. It consists of a servomotor, a flexible Bowden cable transmission, and a force feedback loop based on a series elastic element. A basic model was developed that is shown to describe the basic dynamics of the actuator well enough for design purpose.

Further measurements show that performance is sufficient for use in a gait rehabilitation robot. The demanded force tracking bandwidths were met: 11 Hz bandwidth for the full force range (demanded 4 Hz) and 20 Hz bandwidth for smaller force range (demanded 12 Hz). The mechanical output impedance of the actuator could be reduced to hardly perceptible level. Maxima of about 0.7 Nm peaks for 4 Hz imposed motions appeared, corresponding to less than 2.5% of the maximal force output. These peaks were caused by the stick friction in the Bowden cables.

Spring stiffness variation showed that both a too stiff and a too compliant spring can worsen performance. A stiff spring reduces the maximum allowable controller gain. The relatively low control gain then causes a larger effect of stick in the force output, resulting in a less smooth output in general. Low spring stiffness, on the other side, decreases the performance of the system, because saturation will occur sooner.

Категория: Ищем научные статьи | Нет комментариев »