Ankle strategy assistance to improve gait stability using controllers based on in-shoe center of pressure in 2 degree-of-freedom powered ankle-foot orthoses: a clinical study.

BACKGROUND: Although the ankle strategy is important for achieving frontal plane stability during one-leg stance, previously developed powered ankle-foot orthoses (PAFOs) did not involve ankle strategies because of hardware limitations. Weakness of movement in frontal plane is a factor that deteriorates gait stability and increases fall risk so it should not be overlooked in rehabilitation. Therefore, we used PAFO with subtalar joint for frontal plane movement and tried to confirm that the existence of it is important in balancing through clinical experiments. METHODS: We developed a proportional CoP controller to assist ankle strategy or stabilizing moment and enhance eversion to compensate for the tilting moment with 2 dof PAFO. It was true experimental study, and we recruited seven healthy subjects (30 ± 4 years) who did not experience any gait abnormality participated in walking experiments for evaluating the immediate effect of subtalar joint of PAFO on their gait stability. They walked on the treadmill with several cases of controllers for data acquisitions. Indices of gait stability and electromyography for muscle activity were measured and Wilcoxon signed-rank tests were used to identify meaningful changes. RESULTS: We found that subjects were most stable during walking (in terms of largest Lyapunov exponents, p < 0.008) with the assistance of the PAFO when their electromyographic activity was the most reduced (p < 0.008), although postural sway increased when a proportional CoP controller was used to assist the ankle strategy (p < 0.008). Other indices of gait stability, kinematic variability, showed no difference between the powered and unpowered conditions (p > 0.008). The results of the correlation analysis indicate that the actuator of the PAFO enhanced eversion and preserved the location of the CoP in the medial direction so that gait stability was not negatively affected or improved. CONCLUSIONS: We verified that the developed 2 dof PAFO assists the ankle strategy by compensating for the tilting moment with proportional CoP controller and that wearer can walk in a stable state when the orthosis provides power for reducing muscle activity. This result is meaningful because an ankle strategy should be considered in the development of PAFOs for enhancing or even rehabilitating proprioception. Trial registration 7001988-202003-HR-833-03.

Development and assessment of a hand assist device: GRIPIT.

BACKGROUND: Although various hand assist devices have been commercialized for people with paralysis, they are somewhat limited in terms of tool fixation and device attachment method. Hand exoskeleton robots allow users to grasp a wider range of tools but are heavy, complicated, and bulky owing to the presence of numerous actuators and controllers. The GRIPIT hand assist device overcomes the limitations of both conventional devices and exoskeleton robots by providing improved tool fixation and device attachment in a lightweight and compact device. GRIPIT has been designed to assist tripod grasp for people with spinal cord injury because this grasp posture is frequently used in school and offices for such activities as writing and grasping small objects. METHODS: The main development objective of GRIPIT is to assist users to grasp tools with their own hand using a lightweight, compact assistive device that is manually operated via a single wire. GRIPIT consists of only a glove, a wire, and a small structure that maintains tendon tension to permit a stable grasp. The tendon routing points are designed to apply force to the thumb, index finger, and middle finger to form a tripod grasp. A tension-maintenance structure sustains the grasp posture with appropriate tension. Following device development, four people with spinal cord injury were recruited to verify the writing performance of GRIPIT compared to the performance of a conventional penholder and handwriting. Writing was chosen as the assessment task because it requires a tripod grasp, which is one of the main performance objectives of GRIPIT. RESULTS: New assessment, which includes six different writing tasks, was devised to measure writing ability from various viewpoints including both qualitative and quantitative methods, while most conventional assessments include only qualitative methods or simple time measuring assessments. Appearance, portability, difficulty of wearing, difficulty of grasping the subject, writing sensation, fatigability, and legibility were measured to assess qualitative performance while writing various words and sentences. Results showed that GRIPIT is relatively complicated to wear and use compared to a conventional assist device but has advantages for writing sensation, fatigability, and legibility because it affords sufficient grasp force during writing. Two quantitative performance factors were assessed, accuracy of writing and solidity of writing. To assess accuracy of writing, we asked subjects to draw various figures under given conditions. To assess solidity of writing, pen tip force and the angle variation of the pen were measured. Quantitative evaluation results showed that GRIPIT helps users to write accurately without pen shakes even high force is applied on the pen. CONCLUSIONS: Qualitative and quantitative results were better when subjects used GRIPIT than when they used the conventional penholder, mainly because GRIPIT allowed them to exert a higher grasp force. Grasp force is important because disabled people cannot control their fingers and thus need to move their entire arm to write, while non-disabled people only need to move their fingers to write. The tension-maintenance structure developed for GRIPIT provides appropriate grasp force and moment balance on the user's hand, but the other writing method only fixes the pen using friction force or requires the user's arm to generate a grasp force.

Evaluating the effectiveness of an active strap for wearable robot: A Mechanical and Physiological Study.

Straps are the most commonly used elements in the wearable robotic field, where it is employed as a physical human robot interface (pHRI) between the wearable robot and wearer's body. The main role of the strap is to transmit power from the robot to the wearer by pressing and attaching onto specific body parts to reduce the relative motion. To maximize the efficiency and performance using the appropriate function, a high stiffness and tension is required in the strap. However, the continuous force applied by the strap on the wearer's body is one of the main factors that reduces the wearing comfort of the wearable robot. In this paper, an active strap applied to a hip orthosis is proposed to restrict the hip joint angle. The active strap was periodically controlled using the hip joint angle of the orthosis and was only tightened when the hip joint angle reached the target hip joint angle. The experimental results were then used to evaluate the performance of the proposed strap from a mechanical and physiological point of view. The results suggest that active strap is capable of effectively performing the tasks of a hip orthosis during periodic movement, demonstrating its potential use in wearable robots. Furthermore, the physiological response observed at the contact area during periodic strap tension can relieve discomfort caused by prolonged tension, thus enhancing the comfort of the wearable robot.

Usability study of a smart transfer-assistive robot with dual arms for care workers.

PURPOSE: The predicted global labor shortages and health problems for long-term care workers can be addressed by care robots. We have developed a smart transfer-assistive robot with dual arms to assist in patient transfers. This study aims to evaluate the effectiveness and usability of a transfer-assistive robot with dual arms for long-term care workers in the Living Lab of Kyung Hee University. METHODS: Long-term care workers (N = 15) transferred healthy adults using the transfer-assistive robot and subsequently reported the workload differences of manual care and the transfer-assistive robot, as measured by the Borg rating of the perceived exertion scale (RPE) and the NASA Task Load Index (NASA-TLX). They also completed questionnaires on the usability of transfer-assistive robots and open-ended interviews. The RPE and NASA-TLX values for each task were compared using the Wilcoxon signed-rank test, and descriptive statistics were used to calculate demographics and usability. RESULTS: The RPE scale indicated that the perceived physical burden was significantly reduced when using the transfer-assistive robot compared with the manual method. The robot-aided transfer method significantly reduced the physical demand in the NASA-TLX subscales. In the usability test, the averages for safety, operability, and satisfaction were all three points or higher, indicating a positive result. CONCLUSION: This study demonstrates that a transfer-assistive robot has the potential to reduce physical stress and the risk of work-related musculoskeletal disorders in long-term care workers. This study shows that the robot is effective for long-term care workers suffering from the burden of the transferring/lifting action, emphasizing the need to introduce a transfer-assistive robot into the care field in South Korea.

Transfer-assistive robots are expected to alleviate the burden of transferring and lifting actions for long-term care workers.These results emphasize the need to introduce transfer-assistive robots in the care field.Ongoing attention to the usability study of transfer-assistive robots may be valuable in improving the work environment of long-term care workers and the quality of care services provided to care receivers.

The effects of operating height and the passage of time on the end-point performance of fine manipulative tasks that require high accuracy.

Sustained shoulder abduction, which results from an inappropriate worktable height or tool shape and long task hours, leads to an accumulation of muscle fatigue and subsequent work-related injuries in workers. It can be alleviated by controlling the table height or ergonomic tool design, but workers who are doing some types of work that require a discomfortable posture, such as minimally invasive surgery, cannot avoid these situations. Loads to the shoulder joint or muscles result in several problems, such as muscle fatigue, deterioration of proprioception or changing movement strategies of the central nervous system, and these are critical to work that requires a high accuracy of the upper extremities. Therefore, in this paper, we designed and conducted an experiment with human participants to discuss how an inappropriate height of the work-table affects the task performance of workers who are performing a fine manipulative task that requires high accuracy of the end point. We developed an apparatus that can control the height and has four touch screens to evaluate the end-point accuracy with two different heights. Eighteen adults (9 women and 9 men) participated in the experiments, and the electromyography of their shoulder muscles, their movement stability, and task performance were measured for the analysis. We found that inappropriate height of a table brings about muscle fatigue, and time elapsed for conducting tasks accelerated the phenomenon. Task performance deteriorated according to increased fatigue, and improved movement stability is not enough to compensate for these situations.

Jointless structure and under-actuation mechanism for compact hand exoskeleton.

It is important for a wearable robot to be compact and sufficiently light for use as an assistive device. Since human fingers are arranged in a row in dense space, the concept of traditional wearable robots using a rigid frame and a pin joint result in size and complexity problems. A structure without a conventional pin joint, called a jointless structure, has the potential to be used as a wearable robotic hand because the human skeleton and joint can replace the robot's conventional structure. Another way to reduce the weight of the system is to use under-actuation. Under-actuation enables adaptive grasping with less number of actuators for robotic hands. Differential mechanisms are widely used for multi-finger under-actuation; however, they require additional working space. We propose a design with a jointless structure and a novel under-actuation mechanism to reduce the size and weight of a hand exoskeleton. Using these concepts, we developed a prototype that weighs only 80 grams. To evaluate the prototype, fingertip force and blocked force are measured. Fingertip force is the force that can be applied by the finger of the hand exoskeleton on the object surface. The fingertip force is about 18 N when actuated by a tension force of 35 N from the motor. 18 N is sufficient for simple pinch motion in daily activities. Another factor related to performance of the under-actuation mechanism is blocked force, which is a force required to stop one finger while the other finger keeps on moving. It is measured to be 0.5 N, which is sufficiently small. With these experiments, the feasibility of the new hand exoskeleton has been shown.