Edsko E.G. Hekman

Self-Aligning Exoskeleton Axes Through Decoupling of Joint Rotations and Translations

To automatically align exoskeleton axes to human anatomical axes, we propose to decouple the joint rotations from the joint translations. Decoupling can reduce setup times and painful misalignment forces, at the cost of increased mechanical complexity and movement inertia. The decoupling approach was applied to the Dampace and Limpact exoskeletons.

Dampace: dynamic force-coordination trainer for the upper extremities

According to reviews, training with upper-extremities rehabilitation robotics is at least as good as regular stroke rehabilitation, probably because the robotics increase the training intensity for the patients. As an alternative to the functional approach mimicking activities of daily living, targeted force-coordination training may also have its benefits. Our passive exoskeleton, the Dampace, has controlled braking on the three rotational axes of the shoulder and one of the elbow. It is designed to combine functional training of activities of daily living with force-coordination training. The Dampace exoskeleton can assist in identifying causes behind the movement disorders of stroke patients, tackle these causes with isolated force-coordination training, possibly simultaneously over multiple joints, and then integrate the isolated training back into a functional, task-specific training protocol. Not needing to align the Dampace axes to the human shoulder and elbow axes overcome some of the difficulties traditionally associated with exoskeletons. Although it adds more complexity, the reduction of setup times to a few minutes and the absence of static reaction forces in the human joints, are major advantages and have been well received by therapists and physicians. Controlled braking instead of actively assisting actuators, has the advantage of inherent safety and always actively participating patients, at the cost of not being able to assist movements or create all virtual environments.

Design of an electric series elastic actuated joint for robotic gait rehabilitation training

Robotic gait rehabilitation is at least as effective as conventional gait training in stroke survivors. Patients must be assisted as needed in order to improve affected gait patterns. The combination of impedance control and series elastic actuation is a viable actuation principle to be used for human robot interaction. Here, a new promising electric series elastic actuated joint is developed. The large torque bandwidth limit at 100 Nm is 6.9 Hz. With a total weight of 3.175 kg it is possible to directly mount the actuator on the exoskeleton frame. The actuator is capable of providing sufficient torque at normal walking speed. Full patient assistance during gait and free motions without impeding the gait pattern are possible. The actuator allows isometric measurements up to 100 Nm and the patients progress in robotic rehabilitation can be evaluated.

Design of a Rotational Hydroelastic Actuator for a Powered Exoskeleton for Upper Limb Rehabilitation

The goal of this study was to validate the suitability of a novel rotational hydroelastic actuator (rHEA) for use in our new rehabilitation exoskeleton for the upper limbs, the Limpact. The rHEA consists of a rotational hydraulic actuator and a custom-designed symmetric torsion spring in a series-elastic configuration. For rehabilitation therapy and impairment quantification, both compliant impedance control and stiff admittance control modes are possible. In the validation experiments, the torque bandwidth of the rHEA was limited to 18 Hz for a desired 20 N·m reference signal (multisine, constant spectrum) due the transport delays in the long flexible tubes between the valve and cylinder. These transport delays also required changes to existing theoretical models to better fit the models on the measured frequency response functions. The (theoretical) measurable torque resolution was better than 0.01 N ·m and the (validated) delivered torque resolution below 1 N· m. After the validation experiments, further iterative improvements resulted in a spring design capable of a maximum output torque of 50 N·m with an intrinsic stiffness of 150 N· m/rad and a slightly higher bandwidth. With the design locked, the maximum measurable isometric torque is 100 N ·m. In conclusion, the rHEA is suitable for upper limb rehabilitation therapy as it matches the desired performance.

Freebal: dedicated gravity compensation for the upper extremities

In most upper-extremity rehabilitation robotics, several components affect the therapy outcome. A common component is gravity compensation which alleviates upper-extremity movements. Gravity compensation by itself could improve motor control further or faster, separate from other effects of robotic therapy. To investigate the rehabilitation value of gravity compensation separately, we created the dedicated gravity compensation system, Freebal. The sling systems with ideal spring mechanisms in the Freebal are well suited for providing compensation forces. The device has steplessly scalable forces, a large range of motion with constant compensation forces, independent control of the compensation of the lower and upper arm, and low movement impedance. It also does not need external power, force sensors or active controllers. Finally, the Freebal can be easily moved, serviced and used in arm rehabilitation with either sitting or standing subjects.

Risk factors for falls of older citizens

OBJECTIVE Fall prevention is a major issue in the ageing society. This study provides an overview of all risk factors for falls of older citizens. METHOD A literature search was conducted to retrieve studies of the past 25 years. All participants from the studies lived in the community or institutions and were aged 60 or older. The following key word combinations were used, limited to the title: elderly or older people or older adults and fall and risk. The risk factors were categorised as relevant and amendable, relevant but non amendable, inconclusive or unsupported. RESULTS In total 30 publications were studied in 2013 in Enschede, the Netherlands. The relevant intrinsic risk factors are muscle strength, balance capacity, reactive power, dual tasking and sleep disturbance. Relevant extrinsic risk factors are home hazards, wrong use of assistive devices and bad footwear. Behaviour-related risk factors are hurrying, risk taking, physical inactivity and fear of falling. Relevant symptoms that could be caused by underlying risk factors are mobility problems, gait problems, vertigo, use of assisting devices and history of falls. CONCLUSIONS Several risk factors are determined to be relevant and amendable. The provided overview could be used to create fall preventive measures for elderly.

A passive exoskeleton with artificial tendons: Design and experimental evaluation

We developed a passive exoskeleton that was designed to minimize joint work during walking. The exoskeleton makes use of passive structures, called artificial tendons, acting in parallel with the leg. Artificial tendons are elastic elements that are able to store and redistribute energy over the human leg joints. The elastic characteristics of the tendons have been optimized to minimize the mechanical work of the human leg joints. In simulation the maximal reduction was 40 percent. The performance of the exoskeleton was evaluated in an experiment in which nine subjects participated. Energy expenditure and muscle activation were measured during three conditions: Normal walking, walking with the exoskeleton without artificial tendons, and walking with the exoskeleton with the artificial tendons. Normal walking was the most energy efficient. While walking with the exoskeleton, the artificial tendons only resulted in a negligibly small decrease in energy expenditure.

The effect of three-dimensional geometrical changes during adolescent growth on the biomechanics of a spinal motion segment.

During adolescent growth, vertebrae and intervertebral discs undergo various geometrical changes. Although such changes in geometry are well known, their effects on spinal stiffness remains poorly understood. However, this understanding is essential in the treatment of spinal abnormalities during growth, such as scoliosis. A finite element model of an L3-L4 motion segment was developed, validated and applied to study the quantitative effects of changing geometry during adolescent growth on spinal stiffness in flexion, extension, lateral bending and axial rotation. Height, width and depth of the vertebrae and intervertebral disc were varied, as were the width of the transverse processes, the length of the spinous process, the size of the nucleus, facet joint areas and ligament size. These variations were based on average growth data for girls, as reported in literature. Overall, adolescent growth increases the stiffness with 36% (lateral bending and extension) to 44% (flexion). Two thirds of this increase occurs between 10 and 14 years of age and the last third between 14 years of age and maturity. Although the height is the largest geometrical change during adolescent growth, its effect on the biomechanics is small. The depth increase of the disc and vertebrae significantly affects the stiffness in all directions, while the width increase mainly affects the lateral bending stiffness. Hence, when analysing the biomechanics of the growing adolescent spine (for instance in scoliosis research), the inclusion of depth and width changes, in addition to the usually implemented height change, is essential.

Prototype design and realization of an innovative energy efficient transfemoral prosthesis

In this paper, we present the prototype realization of the conceptual design of a fully-passive transfemoral prosthesis. The working principle has been inspired by the power flow in human gait so to achieve an energy efficient device. The main goal of this paper is to validate the concept by implementing in a real prototype. The prototype, in scale 1 ∶ 2 with respect to the average dimensions of an adult human, is based on two storage elements, which are responsible for the energetic coupling between the knee and ankle joints during the swing phase and for the energy storage during the stance phase. The design parameters of the prototype are determined according to the human body and the energetic characteristics of the gait. The construction of the prototype is explained in details together with a test setup that has been built to evaluate the prototype.

Freebal: Design of a dedicated weight-support system for upper-extremity rehabilitation

Most rehabilitation devices for the upper extremities include a weight-support system. In recent publications, weight support is shown to be effective for stroke rehabilitation. But current devices are often complex, have significant movement inertia, and/or limit the movement range. The goal of this study is to improve on current designs by introducing a novel, dedicated weight-support device, the Freebal. This passive mechanical device uses balanced spring mechanisms for constant-but-scalable forces to support the arm. It has a large workspace of roughly 1 m 3 , low movement impedance, and independent support at the elbow and wrist of up to 5 kg. An explorative cross-sectional study with eight patients shows the Freebal to instantly extend the range of motion of the affected arm by 7%. In conclusion, most requirements are met for patients to benefit from therapy with the Freebal, potentially progressing earlier to more motivating, functional training.