# Quasi-Passive Resistive Exosuit for Space Activities: Proof of Concept
## 2 Materials and Methods
### Proof of Concept
#### 2.2.1 Exosuit Platform and Actuation Unit  
The XoSoft exosuit has been iteratively developed to meet the safety critical requirements, and it is certified as class 1 medical device in conformity with the standard UNI ISO 60601. The exosuit can control up to six pneumatic actuators and weighs only 4 kg with a compact (200 \(\times\) 400 \(\times\) 150 mm) external backpack. The backpack includes a battery (4 Ah and 24 V) that allows the system to run for 6 h continuously (continuous operation of four active actuators, at a walking speed of 3 km/h). The system can, if required, be equipped with a pressure tank to support completely untethered operation. This adds only an additional 1.5 kg. Figure 1 shows the XoSoft Gamma exosuit, the actuator arrangement, sensing integration, and the garment physical structure. In particular, Figure 1 shows the arrangement of the four knee actuators, two coupled to the knee extension and two to the knee flexion. This actuation configuration is employed specifically for the assessment of the proof of concept presented in this work. The main technological elements composing this exosuit platform are presented in Figure 2, and some of the main characteristics are summarized as follows:  
* Quasi-Passive Actuation (QPA): is composed of a soft clutch (or textile based clutch [88] and Elastic bands (EB). The soft clutch (SC) creates controlled storage and release of energy. The EB stores the user generated mechanical energy. * Body Attachment: Body attachment is required to transmit the forces from the actuators to the wearer's body. The body attachments consist of shoulder straps, fixation straps, belt, and actuation attachments. * Wearable Sensors: Sensors are used as an input for the motion segmentation. Insole sensors and two versions of knee angle displacement measuring sensors (details are reported in Section 2.2.3) are employed. Figure 1: The system overview of the XoSoft Gamma exosuit used during the experimental evaluation. Written informed consent was obtained from the individual pictured in figure. Figure 2: Overview of the system components and layout for the “XoSoft Gamma prototype”. The following components form the experimental platform: (1) Xsens and BTS-EMG logging for motion tracking sensors and EMG recording; (2) Logging controller for the exoskeleton state measurement sensors; (3) Air supply; (4) Central processor; (5) Valve controller board; (6) Valves; (7) Soft Clutches (SCs); (8) Shoe sensors; (9) IMUs; (10) Compressed air; (11) Vacuum lines; (12) CAN bus 1; (13) CAN bus 2; (14) Wi-Fi network 1; (15) soft sensors; (16) CAN bus 3; (17) Elastic Bands (EBs). Main hardware components of the exoskeleton are described in Section 2.2.1. The QPA is composed of an EB and the SC connected in series. The actuation principle is based on modulation of a passive element (i.e., EB), which stores mechanical energy, and an active element (i.e., SC), regulating the storage and release of this mechanical energy between gait phases. QPA refers to any controllable element that cannot apply a non-conservative, motive force [89]. The SC is based on a combination of granular and textile jamming, with the electromagnetic clutch functionality mounted in series with the elastic element [88]. From the functional point of view, this is equivalent to an electromagnetic clutch mechanism, but it is soft, and directly mounted on the human joint without the need for any dedicated transmission (e.g., bowden cables). From the wearability viewpoint, the flexible nature of the pneumatic systems gives important advantages. The SC is a variable stiffness actuator, which controlling vacuum it ensures a controllable increase in the internal friction forces thanks to plastic grooves (while retaining the same volume), to modify the linear stiffness of the element. When the vacuum is applied, the SC is engaged, with the SC stiffness characteristic changing from elastic to rigid along the direction of pull (the relative motion of the two sliding parallel structures is blocked).