# Development of a Humanoid Nursing Care Robot and Realization of Quantitative Pouring Operation
## 4 Realization of Quantitative Pouring Operations
### Experiments and Results  
We conducted a verification experiment by pouring a certain amount of water from a PET bottle into a cup and measuring the force sensor of the hand holding the cup of the robot. Specifically, a PET bottle with a capacity of 650 g was filled with 300, 450, or 600 g of water, and the cup was held in one of the robot's hands. The robot was operated to pour water from the PET bottle into a cup with a 150 g target value of pouring volume. The mass of the water poured into the cup was measured using a scale. In the verification experiment, the robot was operated according to the flowchart shown in Figure 10. In other words, the flow of robot motion in the verification experiment consisted of the following steps 1 to 5. However, the resolution of the force sensor was only 17 g.  
Figure 9: Flow of the process of pouring a drink. 1. Tilt the hand holding the plastic bottle by 1\({}^{\circ}\);
2. The mass of the water in the cup is measured by a force sensor in the hand holding the cup;
3. Determine whether the measured amount of water in the cup reaches the target value of 150 g. If it has, proceed to 1. If it has reached it, go to 1. If it has not been reached, go to 1;
4. Compare this measurement with the previous one. If the difference between this and the previous measurement is greater than the force sensor resolution of 17 g of the hand holding the cup, it is judged that the amount of water poured by tilting the bottle 1\({}^{\circ}\) has not flowed completely, and the angle of the hand holding the PET bottle is not changed; that is, wait until it pours out at the same angle, and return to 1. If the difference between this and the previous measurement is smaller than or equal to the force sensor resolution of 17 g, we could judge that the bottle has been poured out at the same angle, and the process is returned to 1. The hand holding the PET bottle is tilted by another 1\({}^{\circ}\);
5. The amount of water in the cup reaches the target value of 150 g, and the angle of the hand holding the plastic bottle returns to 0\({}^{\circ}\). Figure 10: Flow of actions for pouring 150 g of water into a cup. Figure 11 shows the verification experiment of the robot pouring a certain amount of water from a PET bottle into a cup. Experiments to verify the robot's behavior when pouring 150 g of water from PET bottles containing 300, 450, and 600 g into a cup were conducted three times each. The results of these experiments are presented in Table 1.  
When the PET bottle was filled with 300 g of water, the average value of the three robot pouring motions with a target value of 150 g was 139.7 g. When the PET bottle was filled with 600 g of water, the average value of the pouring motions of the three robots was 143 g. When the PET bottle was filled with 450 g of water, the average value of the pouring motions was 140.3 g. When the PET bottle was filled with 600 g of water, the average pouring motion of the three robots was 143.3 g. The results of the validation experiment showed that the average value for each condition fell within approximately 10 g of the injection target value; that is, the force sensor mounted on the robot wrist could be measured accurately, and the robot pouring motion was well realized. \begin{table}
\begin{tabular}{c c c c c} \hline
**Bottled Water** & **First Time** & **Second Time** & **Third Time** & **Mean Value** \\ \hline
300 g & 122 g & 162 g & 135 g & 139.7 g \\
450 g & 158 g & 129 g & 134 g & 140.3 g \\
600 g & 161 g & 118 g & 151 g & 143.3 g \\ \hline \end{tabular}
\end{table} 
Table 1: Results of pouring 150 g of water into a cup. Figure 11: Robot pouring 150 g of water into a cup. In addition, a verification experiment was conducted using a force sensor for the hand holding the cup, as shown in Figure 12, to verify the operation of filling a paper carton with milk and pouring it into the cup at a fixed amount. Milk (300 g) was placed in a paper carton with a capacity of 1000 g and held in one hand by the robot, which also held the cup in the other hand (Figure 12).