# A Motion Control of Soft Gait Assistive Suit by Gait Phase Detection Using Pressure Information
## 1 Introduction
### Contribution of This Paper  
Considering these issues, we aim to develop a novel assistive device using the PARMs and its control method. The concept of our proposed device is to reduce wearable sensors from an easy wearing point of view. Our proposed device does not require for the wearer to attach any electric sensors on their body as same as the device of [18]. In addition, we solve the issues of the conventional device [18] mentioned above.  
We develop a hardware of a soft gait assistive suit actuated by the PARMs and propose its motion control method by a modified detection method using pressure and pressure derivative. The target task is to assist the wearer's forward walking, and the PARMs are placed on the anterior and posterior surfaces of the wearer's thigh and calf. The developed gait assistive suit consists of an attachment unit and a control unit, and these units are separated physically and only connected by air tubes. The control unit supplies compressed air and detects the assist timing using the measured pressure information. After the detection, the suit assists the wearer's leg motion as raising up the toe and landing the foot. The assist force is generated by the controlled PARM pressure, and the pressure input time is changed appropriately considering the walking cycle time. The assist force will decrease the walking load of the leg muscles.  
Considering the issue 1 in Section 1.1, the attachment unit has a lightweight soft structure, and it has no electrical devices. Because sensors are not needed to be attached to the wearer's body, and the suit is soft and lightweight, therefore, it has the advantage of being easy and safe to use compared with the previous device in [18]. Considering the issue 2, the novel phase detection method is proposed which can detect only one desired timing in one gait cycle. The previous and novel phase detection methods are compared, and advantages of the novel phase detection method are described. Considering the issue 3, we propose a control method of the pressure input time considering the gait cycle time. Proper phase detection and gait assistance can be achieved in an arbitrary gait cycle time by using this method. The calculation method of the gait cycle time using the detection timing is proposed, and the proper pressure input times are obtained from the calculation result.  
On the other hand, reducing sensors also have a disadvantage that will increase the responsibility of each sensor. Our developed suit is actuated by the PARM and it has backdrivability which will be an accident precaution of our suit. For example, when the pressure sensor is broken, the proposed suit will fail the proper detection or assist. When the PARM generates unpredictable force, the wearer will feel large leg load. However, a critical accident will be avoidable since the wearer can move against the PARM force thanks to the PARM's backdrivability.  
We focused on the usage of the proposed gait assistive suit as a training tool for health promotion, for example, a walking on a treadmill. The assistance of the suit will be useful especially for the elder persons who want to maintain their healthy locomotorium, and the suit provides the proper training menu in each trainee. By modulating the assistive force properly along with the training progress, the gait assistive suit will help to improve the trainee's walking ability.  
To confirm the performance of the proposed gait assistive suit, we conduct treadmill walking experiments of the trainees wearing the suit. In the experiments, we measured the pressure data and the trainees' electromyogram (EMG) signals for the performance evaluation.  
This paper is organized as follows. Section 2 describes the mechanism of the proposed suit. Section 3 describes the novel gait phase detection method. In Section 4, we describe the gait assistive control method. In Section 5, we describe the experiments conducted to confirm the effectiveness of the proposed suit and its control method. Concluding remarks are made in Section 6.