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An actuator is required to change its speed and force depending on the situation. Using multiple actuators for one driving axis is one of the possible solutions; however, there is an associated problem of output power matching. This study proposes a new active joint mechanism using multiple actuators. Because the actuator is made of a flexible bag, it does not interfere with other actuators when it is depressurized. The proposed joint achieved coordinated motion of multiple actuators. This report also discusses a new actuator which has dual cylindrical structure. The cylinders are composed of flexible bags with different diameters. The joint torque is estimated based on the following factors: empirical formula for the flexible actuator torque, geometric relationship between the joint and the actuator, and the principle of virtual work. The prototype joint mechanism achieves coordinated motion of multiple actuators for one axis. With this motion, small inner actuator contributes high speed motion, whereas large outer actuator generates high torque. The performance of the prototype joint is examined by speed and torque measurements. The joint showed about 30% efficiency at 2.0 Nm load torque under 0.15 MPa air input.

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The aim of the present study was to investigate the consciousness among young people (n＝ 1000) of training body part(s) by showing participants a picture of trunk muscle exercises through a questionnaire-based survey. The participants were shown a picture of bent-knee situp (sit-up), back extension (back-EXT), and plank from elbows to toes (plank), and were asked which body part(s) they felt was being trained in each picture. As for the frequency of performing these exercises, only 3z and 8z of all the participants had never performed sit-up and plank exercises, respectively. On seeing the picture, 40-60z of the participants who had no experience doing a sit-up or back-EXT felt that these exercises were to train not only the agonist muscle but also the antagonist muscle. Approximately 40z of the participants who had no experience doing a plank exercise felt that it was not to train the epigastrium or hypogastrium area. Among the participants who experienced doing a plank exercise without a previous experience of strength training under professional supervision, more than half felt that plank exercise was appropriate to train not only the trunk but also the upper limb or lower leg. Furthermore, among the participants who had a previous experience of strength training under professional supervision, approximately 30z had such an opinion. Therefore, although the penetration rate of these trunk exercises are high, doing trunk exercises by referring to only a picture may result in the participants not properly understanding how the body part(s) should be trained during the exercise. Therefore, to enhance the beneˆts of trunk exercises, individuals (even those who had a previous experience of training under professional supervision) always need to be instructed through appropriate supervision on the correct technique and knowledge about the exercises.

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