## 2 Materials and Methods
### Design Requirements  
The following list of Design Requirements has been developed to generate a proposal of new techniques that integrate the design, which are translated as characteristics of the mobility exoskeleton device. The design has been subdivided into three tables of requirements: the user (Table 2), the operative (Table 3) and the Security (Table 4). The user requirements of people affected by SCI are the most important factor. Figure 1: Block diagram problem derived from the state-of-the-art. **User Requirements**  
* Autonomous mobility system with rechargeable batteries for people suffering SCI in a standing upright position for use in urban and home infrastructure;
* The SCI user will move in standing upright position, loading their weight on their feet on a footrest of the exoskeleton device;
* Not applicable for motor rehabilitation of users lower limbs;
* Applicable for adults aged 18 to 65 years with spinal cord injury T9 to T11 with total leg disability and loss of sensitivity of the belly button down;
* Maximum weight: 80 kg;
* Maximum Height: 1.75 m;
* The Exoskeleton device must be worn and removed by the same user;
* The device will allow the entry to WC and withdraw to sit at a sanitary rate (where the dimensions of the toilet allows). It does not apply to performing bathing actions;
* Device free of external stability auxiliaries such as canes/crutches. **Operative Requirements**  
* One sagittal degree of freedom (DOF) in the waist for a tilting effect User/Chassis;
* Two sagittal DOF on each pair of wheels for tilting effect with respect to chassis;
* One sagittal DOF for hip, one sagittal DOF for knee;
* One coronal parallelogram DOF for frontal stability of the user;
* Chassis of two skids with parallelogram system for stability and user-supported tilting exoskeleton structure;
* Driving system with four pairs of wheels;
* Electronic control system of speed, stability, step detection, transmission system troubleshooting;
* Permissible movements: Braking device: sitting/standing/sitting;
* Moving device: forward with increment, backward with slow, left with slow, right with slow, left slow 180\({}^{\circ}\) turn, right slow 180\({}^{\circ}\) turn;
* Weight of the device: Maximum 50 kg;
* EXO structure can be modified to adapt to the user's height from 1.65 to 1.75 m;
* Maintain a center of gravity (CG) as low as possible coronal and sagittal centering according to human-machine interaction kinematics;
* Place the batteries, control management unit and Direct Current (DC) motors inside the skids for environmental protection, shock and vibration;
* General dimensions of the device: 95 cm long (derived from human/machine interaction kinematics), 65 cm wide (access by door and standard ramp), and 110 cm high (human anthropometric center of gravity and floor take-off);
* Control Interface, Status Information Graphic Interface;
* Brake mode for mechanical braking in slowdown or blocking;
* In Brake mode it can work as a work, food and social seat;
* Automatic electronic braking when the control interface is no longer being handled;
* Maximum travel speed: 5 km/h (Average human walking speed at a fast pace);
* When ascending/descending ramps, low speed will be applied by system and assisted by mechanical brake by the user;
* Ascending/descending of curbs and steps up to 15 cm in height;
* Ultrasonic sensor for measuring obstacles, curbs and steps;
* Tilting sensor with position encoder for detecting the maximum coronal inclination of 15\({}^{\circ}\);
* Mechatronic system for coronal stability on ramps with a maximum inclination of 15\({}^{\circ}\).