# A Parcel Transportation and Delivery Mechanism for an Indoor Omnidirectional Robot
## 1 Introduction  
Growths in e-commerce have consistently risen worldwide in the last decade, with a global increase of 6.5% in 2022 relative to 2021 [1]. Worldwide, 19% of all retail sales came from e-commerce during the same period [1]. The increment in online sales has resulted in the intensification of parcel deliveries [2, 3] which is a challenge for parcel service providers and city logistics [4]. Currently, delivery vehicles are responsible for up to 20% of vehicular congestion and almost 60% of total emissions [5], operate inefficiently, and accumulate unnecessary mileage [6]. Indeed, the main challenges faced in last-mile delivery are sustainability, costs, time pressure, an increasing volume, and an aging workforce [7]. Since modern city logistics should be efficient and cause as few negative externalities as possible [8], conventional delivery based on vans is not considered a viable option for the future [9]. Hence, efforts on parcel shipments in urban areas are focused on reducing traffic volumes and proposing alternative delivery concepts. For instance, researchers are evaluating several alternative delivery options to identify efficient delivery systems for urban areas [10, 11]. Among the innovative ideas, the benefits of using robots for last-mile delivery is a topic of interest [12]. Autonomous mobile robots have high capabilities such as autonomous trajectory planning, dynamic response to changes in the environment, and direct machine-to-machine interaction [13]. Therefore, autonomous robots can automate repetitive actions such as the transportation and delivery of parcels [14] because they are able to compute and implement efficient sequences of actions to transport and deliver packets from a pick-up to a drop-off point [15]. So far, the main research trend related to delivery robots has been focused on outdoor last-mile delivery [14, 15, 16, 17, 18]. Specifically, last-mile delivery refers to the logistical operations involved in delivering parcels to customers' households [19]. Whilelast-mile delivery is considered an outdoor problem that deals with transportation from depots to customers' homes (single-family houses) [20], the problem rests unsolved for residential multi-story buildings with many apartments or offices per floor. Despite the requirements of robotic delivery systems operating outdoors and indoors are different, some works extrapolate the proposals and conclusions from outdoor parcel delivery works to applications related with indoor parcel delivery [21; 22]. The scientific literature on indoor delivery is usually focused on the design of the robot or the algorithms used to navigate within a building [23]. For example, [PERSON] et al. [24] presented an autonomous delivery robot to prevent the spread of infectious diseases in product delivery during the coronavirus pandemic. The package was transported inside a password-protected container, and when the robot reached its destination, it waited for the customer to unlock the container and extract the product. [PERSON] et al. [25] developed an indoor delivery robot for multi-floor environments. The system included a parcel box with a small door that remained closed during transportation, and when the robot arrived at the destination, if the recipient confirmed that they would receive the parcel, the robot opened the door, and the parcel could be picked up. In case the consignee did not respond, the robot moved to the next destination. In this case, parcel loading into the robot was automatic: the robot went to a hub with a manipulator that put the parcels into the mobile robot. [PERSON] et al. [26] proposed three heterogeneous mobile platforms that cooperated among themselves in domestic, condominium, and outdoor environments in order to transport items from outdoors to consignees' apartments and vice versa.