Minako Hosono

A soft metal hydride actuator using LaNi 5 alloy and a laminate film bellows

Rehabilitation systems and assistive technology devices for people with motor disabilities caused by stroke or the aging process require a human-friendly actuator that is soft, compact, slow, noiseless, and environmentally benign. In order to realize these kinds of actuators, we designed a soft metal hydride (MH) actuator using a copper-coated LaNi5 alloy and a laminate film bellows. For the purpose of this study, we selected a suitable LaNi5 alloy and developed a soft and light end-effector for the soft MH actuator. As a result of experimental tests, the LaNi5 alloy that has a low plateau pressure at room temperature performs well for the MH actuator. Moreover, the end-effector applied to the soft bellows made of an aluminum laminate film is 20 times lighter and 30 times longer than the metal bellows used in a conventional MH actuator. These findings support the efficacy of the soft MH actuator using the LaNi5 alloy with low plateau pressure and laminate film bellows for the purpose of developing a portable rehabilitation system or a wearable force feedback device in virtual reality.

Dynamic performance analysis of a micro cantilever embedded in elastomer

This paper reports on the dynamic characteristics of a micro silicon standing cantilever embedded in a silicone elastomer, polydimethylsiloxane (PDMS). This combined structure, which consists of materials with significantly different Youngs moduli, is employed as a tactile sensor for shear-strain measurement. The frequency responses of the tactile sensor show no resonance near the intrinsic resonant frequency of the standing cantilever, whereas the resonant point was observed near the intrinsic resonant frequency of the PDMS covering. In addition, when the oscillation frequency is below the resonant frequency of the tactile sensor, the standing cantilever can follow the oscillating deformation of the PDMS covering with no delay, and the sensitivity of the tactile sensor does not change. The analytical and experimental results show that the PDMS covering has a dominant influence on the dynamic behavior of the embedded cantilever, and the tactile sensor can be applied to both static and oscillating input in the same way.

Shear force sensor using a cantilever with liquid-embedded hinges

We propose a shear force sensor using standing piezoresistive cantilevers with liquid-embedded hinges. The hinges of the cantilevers are positioned in elastomer compartments filled with liquid, while the tip and the root of them are buried in the elastomer shell of the compartments. This design allows most of the cantilever body to freely deform when the compartment shell is deformed with shear forces. Consequently, the stress concentration that is often found in conventional design of such type of sensor is effectively eliminated. The sensor therefore endures larger loading. We measured the relationship between the displacement of the tip of the cantilevers and their change in resistivity, and calculated the sensitivity of the sensors. We confirmed that the proposed design improved the measurement force range of such piezoresistive-cantilever-based force sensors.

Preliminary design of a simple passive toe exercise apparatus with a flexible metal hydride actuator for pressure ulcer prevention

In an aging society, social demands for home-based rehabilitation and assistive technologies by healthcare and welfare services are globally increasing. The progress of quality-of-life technologies and rehabilitation science is a very important and urgent issue for elderly and disabled individuals as well as for their caregivers. Thus, there is a substantial need to develop simple bedside apparatuses for both continuous exercise of joints and for power assistance for standing to prevent and manage disuse syndromes (e.g., pressure ulcers, joint contractures and muscular atrophy). Unfortunately, there are currently no commercially-available actuators compatible with the human requirements of flexibility, quietness, lightness and a high power-to-weight ratio. To fulfill the above demands, we have developed a novel actuation device using a metal hydride (MH) alloy and a laminate film, called the flexible MH actuator, as a human-friendly force generator for healthcare and welfare services. In this paper, we show the basic structure and characteristics of the flexible MH actuator used to create a passive exercise system for preventing disuse syndromes. To evaluate the efficiency of passive exercise for bedsore prevention, subcutaneous blood flow during passive exercise at common pressure-ulcer sites is measured by a laser blood flow meter. The force and range-of-motion angle required for a passive exercise apparatus is also examined with the help of a professional physical therapist. Based on these findings, a prototype of a passive exercise apparatus is fabricated using the flexible MH actuator technology, and its operation characteristics are preliminarily verified using a thermoelectric control system.

Application of metal hydride paper to simple pressure generator for use in soft actuator systems.

Metal hydride (MH) actuators have a simple structure and a number of features that make them attractive for use in rehabilitation engineering and assistive technology. The MH actuator provides a high power-to-weight ratio, high-strain actuation, human-compatible softness, and noiseless operation, while being environmentally benign. On the other hand, there remain technical challenges to be overcome to improve the MH actuator regarding its speed of operation and energy efficiency, given the low heat conductivity of the MH powder that is used as the pressure generator for soft actuation. To overcome the issues of low heat conductivity and the handling of MH powder, we developed an MH paper, which is a special paper incorporating MH powder and carbon fiber, for use as a new pressure-generating element for a soft MH actuator system. In addition, the basic properties and structure of the proposed MH paper were investigated through scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and several thermodynamic experiments. The results of these experiments showed that the hydrogen absorption and desorption rates of the MH paper were significantly higher than those of the MH powder around room temperature.

A system utilizing metal hydride actuators to achieve passive motion of toe joints for prevention of pressure ulcers: a pilot study.

This paper describes the influence of human toe movement on blood flow and the design of a toe joint passive motion system for preventing pressure ulcers. First, we measured lower extremity blood flow in the foot during active and passive motion of the toe to facilitate the design of new rehabilitation equipment. Also, the flexion and extension angles and the force of the toe joints were measured to determine appropriate specifications for the system. Increases in blood flow were observed at the external malleolus during movement. Flexion and extension angles and the force of the toe joints were found to differ significantly among participants. It is shown that a toe joint passive motion system can be effective in preventing pressure ulcers. On the basis of these results, a device using alloys of metal hydride (MH) as an actuator that is suitable for the system to initiate toe motion, was developed.

Surplus heat drive actuators using MH alloys for assistive devices

A metal hydride (MH) actuator that uses the reversible reaction between the heat energy and mechanical energy of a hydrogen absorbing alloy is characterized by its small size, low weight, noiseless operation and mechanical compliance. Though the moving speed of the MH actuator is slow, this actuator is a suitable as a power source for rehabilitation or assistive devices. Prototype assistive devices using the MH actuator were reported, such as a wheelchair with a seat lifter and a robotic transfer aid to assist sit-to-stand motion. The main characteristic of the MH actuator includes a heat drive. This allows the MH actuator to be driven by surplus heat present in the surrounding environment. When only a high-temperature heat source is available, the surplus heat drive of the MH actuator requires rapid hydrogen absorbing to the MH alloy. This paper describes the means to improve the hydrogen absorption characteristics of the MH alloys. Three compositions of MH alloys were tested. One of these alloys obtained sufficient hydrogen absorption under natural cooling of the MH module. This means that the surplus heat source provides repeating absorption and release of hydrogen on the MH alloy. Maintaining this cycle forms an MH air compressor in which the air pressure is produced by converting the hydrogen pressure in the MH actuator. The advantages of this air compressor are that the small size and easily altered shape have the potential for the realization of unprecedented assistive technology devices for persons with disabilities.

A Preliminary Study of a Power Assist System for Toe Exercise using a Metal Hydride Actuator

In an aging society, there is concern that the population of bedridden elderly people will increase due to diseases and injuries such as cerebral strokes and bone fractures. From this social background, we have been developing a power assist system using a soft MH actuator for home health care to help prevent disuse syndromes. The soft MH actuator, which uses a laminate film bellows, has suitable properties for use as home-based motor rehabilitation equipment. To examine the preventive effect on bedsore formation of a passive motion exercise machine, we measured the skin blood flow of the lower limb. Results have shown a significant blood flow increase at sites frequently associated with decubitus ulcers. Thus, passive motion at toe joints may be useful for the prevention of disuse syndromes. Furthermore, we demonstrate a prototype of a power assist system using the soft MH actuators electrically controlled by Peltier devices. This system has performed moderate slow extension and flexion motion for toe joints. The soft MH actuator seems to provide a key solution to develop a human-friendly power assist system for motor rehabilitation and quality-of-life technology.

Designing a Metal Hydride Actuator with Human-Compatible Softness and High Power-to-Weight Ratio for Future Quality-of-Life Technologies

Japan faces a rapidly growing elderly population that is unprecedented in the world. As a result, there are emerging needs for quality-of-life technologies, such as rehabilitation equipment, long-term care, and assistive devices. In particular, elderly people who are bedridden due to physical illnesses, such as cerebral stroke or bone fractures caused by a fall, may suffer awkward disuse syndromes (e.g., pressure ulcers, joint contracture, cardiac hypofunction, and mental depression). It is difficult for them to actively participate in rehabilitation exercises by themselves. Thus, to manage these disuse syndromes, we have developed a light and soft actuator device with metal hydride materials. This actuator device has a high power-to-weight ratio, adequate softness for human body support, noiseless motion, and a clean hydrogen energy system. The three apparatuses in which the metal hydride actuator is applied are a joint rehabilitation device for the hand, a seat lifter for a wheelchair or toilet, and a toe exercise apparatus for bedsore prevention.

Development of a metal hydride actuator driven only by solar heat

A metal hydride (MH) actuator provides mechanical work by applying the hydrogen pressure transition that originates from the reversible reaction of the MH alloy as it absorbs and desorbs hydrogen gas. The MH actuators that have been reported employ a Peltier element or an electrical heating resistance wire as a heat source. This paper describes the design of an MH actuator that is driven by low-quality heat sources, such as solar heat. A certain composition of a LaNi5-based alloy that produces desorbing and absorbing reactions through a low-temperature difference is specified. This alloy composition can provide a large amount of hydrogen desorption using solar heat and a large amount of hydrogen absorption by natural air cooling in an adequate reaction time. To improve the moving speed and to control the performance, a reciprocating air compressor that applies this solar heat-driven MH actuator is proposed. These findings support the efficacy of an MH actuator operating without electric or fossil fuel energy consumption.