Measurement of Contact Behavior Including Slippage of Cuff When Using Wearable Physical Assistant Robot

Abstract

Continuous use of wearable robots can cause skin injuries beneath the cuffs of robots. To prevent such injuries, understanding the contact behavior of the cuff is important. Thus far, this contact behavior has not been studied because of the difficulty involved in measuring the slippage under the cuff. In this study, for the first time, the relative displacement, slippage, and interaction force and moment at the thigh cuff of a robot during sit-to-stand motion were measured using an instrumented cuff, which was developed for this purpose. The results indicated that the slippage and relative displacement under the cuff was uneven because of the rotation of the cuff, which suggests that the risk of skin injuries is different at different positions. Especially, the skin closer to the hip showed larger dynamism, with a maximum slippage of approximately 10 mm and a displacement of 20 mm during motion. Another important phenomenon was the individual difference among subjects. During motion, the interaction force, moment, and slippage of some subjects suddenly increased. Such behavior results in stress concentration, which increases the risk of skin injuries. These analyses are intended to understand how skin injuries are caused and to design measures to prevent such injuries.

Developing Safety Measures for a Wheelchair-Compatible Physical Assistive System with Sit-To-Stand Movement Support

“…Moreover, it is important not only to develop safety measures, but also to verify safety of the device after the intervention experiment. In studies that developed a wearable physical assistive robot, skin injury resulting from excessive rubbing between the cuff of the robot and the surface of the skin was con rmed in intervention experiments [13,14]. In the present study, we con rmed that no skin injury occurred between the seat and buttocks, and that the users did not experience any pain while using the system [1,8].…”

“…Second, we identi ed additional dangers of injury due to hazardous device components and human physical, electrical, structural, and psychological factors. Next, we de ned the safety Ryoichiro SHIRAISHI, et al: Safety Measures of Sit-To-Stand Support System (13) conditions for the system and developed safety measures for each danger of injury and hazardous situation. At this step, it is important to properly record the methods used to develop the safety measures for submission to an ethical review committee.…”

Evaluation of effects caused by individual differences in human shape that affect the safe utilization of wearable robots

“…Because the interaction force exerted when rubbing on the uneven surface is affected by the normal force of the robotic cuff, the normal force of the manipulator was controlled to 20 N, which was the value exerted at the cuff when using a wearable robot in the previous study [17]. The surface of the robotic cuff was covered by a 40 mm × 40 mm × 15 mm sponge sheet, determined by considering the softness of the cuff used in commercial wearable robots.…”

“…1. In this process, first, the relative motion between the robotic cuff and human skin and the interaction force exerted at the contact area of the robotic cuff is measured [17,18]. Then, the relative motion and interaction force are reproduced by a 6-degree of freedom manipulator on dummy tissue [19].…”

A Three-Dimensional Skin-Shape Reproduction Mechanism for Evaluating the Risk of Wounds When Using a Wearable Robot

“…For our dummy, we utilized porcine skin, which is a common substitute for human skin [13], [14] because of its proven durability against repetitive shear force [15] and similarity to human skin [16], [17]. To identify whether skin injury occurs when using a wearable robot, we observed the relative motion and interaction force applied by a robotic cuff during use [18], [19] and reproduced them using manipulator on the dummy skin [20], [21]. An overview of this safety evaluation test is shown in Fig.…”