# Analysis, Design, and Experimental Research of a Novel Wheelchair-Stretcher Assistive Robot
## 4 Experimental Research of the Wheelchair-Stretch Assistive Robot  
### Experimental Research of the Walking Mechanism  
In order to evaluate the performance of the compound position control method and verify the correctness of the kinematic equations, experimental research of the walking mechanism is conducted. First of all, the design parameters of the walking mechanism are shown in Table 2.  
According these parameters, the corresponding jacobian matrix can be computed as:  
\[J_{1}=\left[\begin{array}{ccc}\frac{1}{63.5}&\frac{1}{63.5}&\frac{-723.5}{ 63.5}\\ -\frac{1}{1}&\frac{-1}{2}&\frac{-723.5}{23.5}\\ \frac{63.5}{63.5}&\frac{63.5}{63.5}&\frac{63.5}{63.5}\\ \frac{63.5}{63.5}&\frac{63.5}{63.5}&\frac{63.5}{63.5}\\ \end{array}\right] \tag{38}\]  
The motion profile exhibits 1.0 m parallel motions along the \(y\)-axis of the global coordinate frame. In addition, the trajectory consists of acceleration for 4 s followed by deceleration for 4 s. The profile is formed by a 5 th order polynomial equation, as shown in Figure 22a. Based on the profile, Equations (5) and (37), the theoretical curves for the velocity of the motor could be obtained, as shown in Figure 22b.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline The velocity of the motor & 4900 \(\mathrm{\SIUnitSymbolDegree}\)/min & Reduction ratio for reducer & 1:80 \\ Radius \(R\) of the mencanum wheel & 63.5 mm & Bias angle \(\alpha\) & 45\({}^{\circ}\) \\ \(m_{1}\) & 272 mm & \(m_{2}\) & 451.5 mm \\ \hline \hline \end{tabular}
\end{table}
Table 2: Parameter value list of the walking mechanism.  
Figure 22: Trajectory planning of the walking platform and the motor; **(a)** trajectory planning for the center of the walking platform; **(b)** the motion curve for four motors of the mecanum wheel.  
The following conclusions can be drawn from the Figure 22b:  
1. In the mobile process, the trajectories of the four motors for the mecanusm wheel are the same, which is identical to the theoretical analysis.
2. The maximum velocity of the motor is less than the rated velocity (4900 r/min \(\approx\) 81.6 r/s) and the motion curve is suitable to the experimental requirements.  
The simulation data is processed, and the corresponding binary files can be obtained. Then, the data are imported into the control system to control the robot's motion in the experimental environment under a normal position control method, which means position control without the feedback function) and compound position control method, as shown in Figure 23a. Data collection is conducted every 100 ms, so 80 data samples can be obtained during the whole movement (100 ms \(\times\) 80 = 8 s). These data can be processed to obtain the real position of the robot under normal conditions and under composite position control, as shown in Figure 23b.  
Observing Figure 23b, the following conclusions could be obtained:  
1. The waveform for the normal position control shows steady-state positioning error not only for the \(x\)-axis but also for the \(y\)-axis. On the contrary, the compound position control can achieve a successful result in no steady-state error.
2. In data node 80, the position of the robot for the compound position control is 995.6 mm and there is a 4.4 mm deviation from the theoretical value 1000 mm.  
Based on the above experiment analysis, we can understand that the compound position method is not suitable for the precise control requirements, but it is enough for the control of the walking mechanism of the stretcher-wheel assistive robot as control accuracy is undemanding.