# A Motion Control of Soft Gait Assistive Suit by Gait Phase Detection Using Pressure Information
## 2 Soft Gait Assistive Suit  
### Mechanical Design of Soft Gait Assistive Suit  
Figure 1 shows the PARMs attached on the trainee's leg. The target muscles of the proposed suit are vastus lateralis, semitendinosus, gastrocnemius and tibialis anterior as shown in Figure 1c. By assisting these muscles, the suit can efficiently aid the motion of the hip, knee, and ankle joints. The PARMs are placed on the anterior and posterior surfaces of the trainee's thigh and calf. Figure 1a shows a leg link system attached the PARMs, and Figure 1b shows an illustration of the trainee's leg wearing the gait assistive suit. For attaching the PARMs to the legs, the trainee wears a waist supporter, knee supporters, and shoes. The foot, knee and pelvis are the key anchors for the PARMs, which can be seen in other exoskeletons as well (e.g., [11]). Figure 2 shows the attachment unit of the novel gait assistive suits. The parameters of the novel gait assistive suit are shown in Table 1. Compared with the previous suit [18] which has a rigid link system, the novel suit consists of only lightweight and soft parts as PARMs, waist supporter, knee supporters, nylon belts and shoes, and the whole weight of the attachment unit is about 1 kg. The attachment unit has no electrical devices. The supporters are made of soft textiles contain polyester, nylon, polyurethane and natural rubber. They attach the PARMs to the trainee's body securely and comfortably. The waist supporter is fixed on the pelvis by tightening force of the textile and the nylon belt. The knee supporters are fixed on the knee joints in the same manner. These supporters and shoes are connected to each other by the nylon belts and the PARMs not to slip on the body surface, and the PARM contraction force will be effectively transmitted to the leg motion. The time to take on the suit is a short time, about 5 min. Because electrical sensors are not needed to be attached to the trainee, and the suit is soft and lightweight, it has the advantage of being easy and safe to use compared with the previous suit. The 8 PARMs are placed on the surfaces of the legs. The PARMs on the right leg are named as the right thigh front (RTF), right thigh back (RTB), right calf front (RCF), and right calf back (RCB). The PARMs on the left leg are named in the same manner (LTF, LTB, LCF, LCB). The thigh front (TF) PARMs support vastus lateralis. The thigh back (TB) PARMs support semitendinosus. The calf back (CB) PARMs support gastrocnemius. These target muscles are the biaarticular muscles, therefore these PARMs are also attached on the trainee's body across the 2 rotational joints as shown in Figure 1a. When the TF PARMs contract, the contraction force flexes the hip joint and extends the knee joint. On the other hand, when the TB PARMs contract, the contraction force extends the hip joint and flexes the knee joint. In addition, when the CB PARMs contract, the contraction force flexes the knee joint and plantar flexes the ankle joint. The calf front (CF) PARMs support tibialis anterior. When the CF PARMs contract, the contraction force dorsiflexes the ankle joint. Next, parameters of the attachment unit shown in Table 1 are discussed. The suit was designed for supporting an average Japanese adult male with a height of about 170 cm and a weight of about 65 kg. Since the average thigh length is about 400 mm and the lengths of the thigh surface change about 60 mm, the thigh PARM lengths were designed as 300 mm whose stroke length is 75 mm. The average calf length and its amount of change are almost same or small compared with the thigh, therefore the same PARMs are used on the thigh and calf to simplify the suit design. In addition, the normalized maximum output torque of the human leg joints during walking is about 1.40 Nm/(kg m) of the ankle joint torques [37]. In the case of the target trainee with 170 cm and 65 kg, the maximum output torque is about 155 Nm.