## 2 Materials and Methods
### Structure Design
#### 2.2.2 Electrical Structure Design  
In order to accomplish the exoskeleton control scheme, sensors are not only placed on the back-support plate of the exoskeleton, but also on the actuation unit of the exoskeleton joint. Each exoskeleton joint is equipped with both kinematic (angular position, velocity and acceleration) and kinetic (interaction force between limb and exoskeleton) sensors. The hip exoskeleton operates with the following physical sensors:  
1. Absolute position magnetic encoders (AS5600) measure the joint angle at each joint output shaft.
2. One IMU (Inertia Measurement Unit) (MPU6050) placed in the back-support plate to estimate the pitch angle of the upper body of the wearer.
3. A force sensor at each powered joint is used to measure the interaction force between the body and the exoskeleton joint.  
The electrical structure is the bridge connecting the control and mechanical structure in the system design, which mainly consists of three parts: the drive board at the left and right thighs and the main control board at the back. In addition to driving the motor and reading the encoder to obtain the current position, the driver board also puts DSP (Digital Signal Processing) to obtain the interactive force information output by the interactive force sensor during the movement. The instructions sent by the master, the actuator information and the interaction force information of the left and right leg joints are transmitted through CAN (Controller Area Network) communication (Figure 5), and the baud rate of its communication is 1000 K. During the movement, except for the sampling frequency of interaction force and the sampling resistance being 1K Hz, the rest of the sensor's data update frequency is 200 Hz.  
Figure 4: The hip active exoskeleton ‘MeBot-EXO’. (**a**) Prototype in SolidWorks. (**b**) This member. (**c**) Supporting mechanism of the waist. (**d**) Binding structure. 1. Battery. 2. Back-support plate. 3. Removable cushion. 4. Shoulder straps. 5. Waist straps.  
Figure 5: Electrical hardware structure.  
In the current state, the power is supplied by 24-V DC lithium batteries at the lower end of the back-support plat, with a maximum discharge current of up to 15 A. It can meet the maximum current required by the exoskeleton system to assist adult men (170 \(\pm\) 10 cm, BMI (Body Mass Index) \(<\) 25) from squatting to standing.  
In particular, in addition to placing a sampling resistor on the lower bridge circuit of the three-phase inverter circuit of the motor driver, a sampling resistor is also placed on the bus of the driver for the collection and analysis of the induced current. The purpose of this is to make a quick judgment of the standing state, as can be seen from the Figure 6; when the subject wears the exoskeleton and moves in the EXO-OFF state, the induced current generated by the motor's rotation of the human body changes faster than the angle obtained by the magnetic encoder, which can be used to solve the problem of rapidly capturing the motion intention of human body in the process of the human-computer interactive motion, so as to improve the subject's sense of experience in the process of motion.