# Analysis, Design, and Experimental Research of a Novel Wheelchair-Stretcher Assistive Robot
## 4 Experimental Research of the Wheelchair-Stretch Assistive Robot
### Experiment Research of the Lifting Mechanism and the Toilet Mechanism  
(1) Experiment Research of the Lifting Mechanism  
The automatic lifting function experiment mainly tests the synchronization of the robot in the process of rising and fall on both sides. The experimental height is set in the range 0-100 mm; the curve is formed by the fifth order polynomial equation and the motion time is 8 s. The position and velocity curves of the lifting mechanism under the theoretical state can be obtained, as shown in Figure 27. The performance parameters of the milang electronic ruler and linear actuator are shown in Table 3. By comparing the parameters in Figure 27 and Table 3, it is found that the planned trajectory is within the range of motion. The position close loop control method is used to control the motion of the lifting mechanism, and the output voltage of the milang electronic ruler could be measured by applying the A/D conversion function in the STM32 chip. The sampling time is 10 ms, and the average voltage is calculated by collecting 10 times of data. The position difference between linear actuator \(L_{1}\) and \(L_{2}\) can be obtained by the conversion of the average voltage, and the value of linear actuator \(L_{2}\) is modified. The time interval of each updating data value is 130 ms; therefore, in the process of the whole movement, a maximum of 61 data samples could be saved. The curves of the position and velocity are formed by using 61 data samples, as shown in Figure 28.  
Observing Figure 28, the following conclusions could be obtained:  
(1) The real position trajectories of the linear actuators \(L_{1}\) and \(L_{2}\) are stable and fluctuation is not obvious. The position close loop control strategy is suitable for the lifting mechanism. (2) To ensure that the position of the linear actuator \(L_{1}\), the velocity of the linear actuator \(L_{2}\) slightly larger than the velocity of the linear actuator \(L_{1}\). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Name** & **Voltage** & **Range** & **Maximum Velocity** & **Resolution Ratio** & **Output Type** \\ \hline Milang electronic ruler & 12–24 V & 0–300 mm & 10 m/s & 0.01 mm & 0–5 V \\ Linear actuator & 24 V & 0–300 mm & 25 mm/s & — & — \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Performance parameters of the milang electronic ruler and linear actuator. Figure 27: Trajectory planning of the lifting mechanism. In addition, tests also are conducted by multiple groups of passengers and the results show that the robot runs smoothly and passengers do not feel the deviation of movement as shown in Figure 29. It also indicates that the control algorithm of the lifting mechanism is in line with the design requirements. (2) Experiment research of the toilet mechanism  
The control of the toilet mechanism is relatively simple. In order to test its function, the current test method is used to detect its movement process. Firstly, passengers on the robot stand up by relying on the armrest, and then hold the open button on the remote control for the opening and closing of the toilet mechanism, as shown in Figure 30a,b. In the process of moving, the current values of the left and right linear actuators of the toilet mechanism are recorded, and the corresponding experimental results as shown in Figure 30c. Observing Figure 30c, the following conclusions could be obtained:  
1. Excepting for the instantaneous impulse current in the initial stage, the curve of the left and right linear actuators is smooth in the process of moving. 2. In the opening process of the toilet mechanism, the current increases gradually; in the closing process of the toilet mechanism, the current decreases gradually. The reason for this phenomenon is mainly the lengthening of the force arm of the linear actuator. Figure 28: The position and velocity change in test experiment of the lifting mechanism; (**a**) the position change of the linear actuators \(L_{1}\) and \(L_{2}\); (**b**) the velocity change of the linear actuators \(L_{1}\) and \(L_{2}\).