# A Parcel Transportation and Delivery Mechanism for an Indoor Omnidirectional Robot
## 6 Discussion  
This paper presents the design and implementation of a parcel transportation and delivery mechanism aimed at converting a general-purpose indoor omnidirectional robot into an indoor delivery robot. In general, the scientific literature on indoor delivery robots is usually focused on the control of the robot [23] without paying much attention to the transportation mechanism or the delivery of the packages transported. The design of this new transportation and delivery mechanism considered the best placement in the robot and the limitation of not exceeding the diameter of the original robot to which it was attached. The final design of the mechanism was placed behind the robot and in the upper half of its body. The design consists of a basket with a lid, articulated with servomotors, which allow the manual loading and the automatic unloading of parcels. Compared with the transportation mechanism proposed by [PERSON] et al. [25], this new mechanism design is able to transport and automatically unload parcels onto predefined delivery areas without human intervention. Compared with the delivery mechanism proposed by [PERSON] et al. [30], this new mechanism is not limited to the delivery of cups, and no additional stabilization is needed thanks to the passive suspension embedded in the original omnidirectional mobile robot. Compared with the robotic delivery system proposed for home apartments by [PERSON] et al. [26], this new mechanism is designed to operate in multi-story office buildings, while both proposals are conceived to allow for the collection and return of any envelope or package garbage. The design of the transportation and delivery mechanism considered the size of 1797 packages received within four months in a five-story educational building with  
Figure 9: Sequence of one experiment on parcel transportation and delivery. The arrows represent robot movements (yellow) and parcel delivery (blue). \begin{table}
\begin{tabular}{c c c c c} \hline
**Mobile Robot** & **(Step) Action** & **Parcel** & **Experiments** & **Success** \\ \hline Performing parcel & (3) Manual load & SP & 25 & 100\% \\ \cline{2-5} transportation and delivery & (7) Automatic unload & SP & 25 \({}^{\dagger}\) & 100\% \\ \hline \end{tabular} \({}^{\dagger}\) In 3 experiments, the robot could not reach destination and returned the parcel to the reception.  
\end{table} 
Table 5: Results of the experiments on mobile robot parcel transportation and delivery. 174 possible delivery destinations. The analysis of the size of the packages received showed that the parcels most frequently received were large envelopes (36%), followed by small envelopes (23%) and small (14%) and medium (12%) parcels. Based on this information, the size of the basket of the mechanism was able to accommodate up to 90% of the packages received in the building. The design of the mechanism allows the following delivery operation: (1) the packages are manually received in the reception of the building, (2) the delivery robot is called, (3) one package is manually loaded onto the transportation mechanism of the robot, (4) the destination of the package in the building is manually selected, (5) the robot moves autonomously from the reception point to the destination point, (6) the delivery robot automatically unloads the package into a predefined delivery area, and (7) the delivery robot returns to its charging point. In cases where the route or the delivery cannot be completed, the robot returns the package to the reception. The transportation and delivery mechanism was empirically validated by conducting 125 static manual loading experiments, 150 static unloading experiments, and 50 complete parcel delivery experiments. All static manual parcel loading experiments were successfully completed, but preliminary parcel unloading experiments revealed unloading problems because some parcels did not slide out of the basket. This problem was solved by considering what a person would do, defining an oscillation (shake) around the delivery position of the basket.