Exoskeleton of assist

Then, we introduce the assist type of exoskeleton. In this paper, our purpose is to design a lower limb assist device, the purpose of our assist device is similar to this type of exoskeleton. There are many functions in assist exoskeleton. For example, Honda developed the Walking Assist Device programs [16,17], University of Tsukuba developed Hybrid Assistive Limb [18], and Argo Medical Technologies developed the ReWalk which was the only exoskeleton system passed FDA (Food and Drug Administration).

Figure 1.4 shows the appearances of Honda’s Walking Assist Device. Honda didn’t call the device “exoskeleton,” they called it walking assist device since the purpose of this programs are assisting in walking not like armor wear on body. Figure 1.4(a) shows Walking Assist Device with Stride Management Assist (WADSM) which is a lightweight (about 2.8kg with battery), simple design with a belt worn around the hips and thighs was created to reduce the wearer’s load and to fit different body shapes. Figure 1.4(b) shows the patent of WADSM which has a special mechanism shown as Fig 1.4(c). Because of the special mechanism, the thigh can be lifted easily. Figure 1.4(d) shows the Honda’s second walking assist device - Walking Assist Device with Bodyweight Support Assist (WADBSA). It helps support bodyweight to reduce the load on the user's legs while walking, going up and down stairs, and in a semi-crouching position. This could lead to reduced fatigue and less physical exertion. Figure 1.4(e) shows the patent of this device.

Although this device is heavier than the first one, it has a very special design. Different from other exoskeleton which are worn on thigh or knee, the device is only worn on shoes as shown in Figure 1.4(e). There exists a place to be seat on and it has force sensors on feet. With the computer and sensors, the device can get specific information to control and drive the motor.

(a) (b)

(c) (d) (e)

Figure 1.4 HONDA walking assist device (a) Walking Assist Device with Stride Management Assist [17]. (b) Patent of Walking Assist Device with Stride Management Assist [17]. (c) Special mechanism of Walking Assist Device with Stride Management Assist. (d) Walking Assist Device with Bodyweight Support Assist [18]. (e) Patent of Walking Assist Device

Yoshiyuki Sankai and his research team developed the first HAL (Hybrid Assistive Limb) prototype in 1990. The third HAL prototype, developed in the early 2000s, was attached to a computer. Its battery weighed nearly 22 kg and required two helpers to put on, making it very impractical. By contrast, later HAL-5 model weighs only 10 kilograms and wears more conveniently [19]. Figure 1.5(a) shows HAL-5 which is divided into upper and lower limbs. HAL-5 consists of controller/computer, battery, myoelectricity sensors, angle sensors, force sensors, floor reaction force sensors (COP/COG sensors), etc. [20]. As shown in Fig 1.5(b), the patent of HAL-5 lower limbs shows myoelectricity sensors which are marked as 38a, 40a, 42a, and 44a on the thigh in the picture. The force sensor is marked as 45 and floor reaction force sensors are marked as 50a, 50b, 52a, and 52b in the picture. Angle sensors are mounted with power units. With the sensors and power units above, HAL-5 can enhance and upgrade the human capabilities, using sensors to obtain the information from human body and control the device. Actually, most applications of HAL-5 only use lower limb part. And HAL-5 was used in care for the elderly in Japan. Fig 1.5(c) shows the detailed illustrations of HAL-5, number 1 is the computer, number 2 is the controller used to adjust for comfort as shown in Fig 1.5(d), number 3 is the battery, number 4 is the myoelectricity sensor, number 5 is the motor, and number 6 is the reaction force sensor.

(a) (b)

(c)

(d)

Figure 1.5 Assist device : HAL (a) HAL: Hybrid Assistive Limb [21]. (b) Patent of Hybrid Assistive Limb [22]. (c) Introduction of Hybrid Assistive Limb [21]. (d) Controller of Hybrid Assistive Limb [21].

Finally, we want to introduce the exoskeleton which had gotten FDA-approved.

ReWalk^TM [23]is a wearable robotic exoskeleton that provides powered hip and knee motion to enable individuals with spinal cord injuries (SCI) to stand upright, walk, turn, and climb and descend stairs. Figure 1.6(a) shows ReWalk^TM and its pilot, ReWalk^TM was designed for all day use, the battery-powered system features a light, wearable exoskeleton with motors at the hip and knee joints. Combined with the tilt sensor, the ReWalk^TM controls movements using subtle changes in his/her center of gravity. Figure 1.6(b) shows the patent of ReWalk^TM, mark 23 is the tilt sensor which may be worn on a shoulder strap that holds controller pack (mark 22) to user’s torso, and thus senses the degree of tilt of the torso. The tilt sensor may include accelerometers and gyroscopes. The ground force sensors (mark 28) are mounted on each foot places (mark 26). With the sensors above, a forward tilt of the upper body is sensed by the system which initiates the first step, and repeated body shifting generates a sequence of steps which mimics a functional natural gait of legs. Currently, ReWalk^TM has already been sold in many countries, and cooperated with hospitals in Taiwan. But if you want to buy an own one, the cost is very high. The above walking assist devices are summarized into Table 1.2.

Figure 1.6 REWALK^TM (a) REWALK^TM and its pilot [23]. (b) Patent of REWALK^TM [24].

Table 1-2 Detail of assist device in introduction

Assist devices Type Function Characteristics

ExoHiker^TM Enhancement

Carry baggage and walking

Enhanced endurance / reduce the burden

ExoClimber^TM Enhancement Carry baggage and hiking

Enhanced endurance /

WADSM Assistance Assist walking Lightly

WADBSA Assistance Assist walking

Reduce the weight while

Although the assist devices above provided with multifunction have lots of sensors and excellent control systems, the price of the assist devices are very high. As a result, patients need lots of money to get the device. Since there will be a population explosion in the elderly. If the cost of the assist device is very high, there must be many elders who can’t afford assist devices. In our opinions, we want to design an assist device with safety on walking and prevention of falling. We use simplified mechanism and lower the cost in order to make the elderly be able to have their own walking assist devices so the elderly can take care of themselves.