## 4 Proposed Design and Method
### Neck Securing Device  
Another critical concern about the ResQot 1.0 design is the loading process, which begins with the casualty's head. In our previous work, presented in [19; 23], we deemed the process to be safe and to satisfy the safety metrics, based on the experimental evaluations (we refer readers to [19; 23] for more details on the experiments). Nevertheless, this process still raises safety concerns in terms of potential damage to the casualty's head and neck upon initial contact (see Figure 2b). To address this safety issue, we propose a novel neck securing device (NSD) as a new safety feature of ResQot 2.0, which required a new and innovative design. The main purpose of the NSD module is to properly secure the neck and critical parts of the head to avoid excessive bending of the cervical spine and hard impact during loading. We propose an NSD that uses inflatable material. There are at least two main works (see Figure 7a,b) that inspired our design of the inflatable NSD module. In [30; 40], the authors proposed a head support system for the SAVER robot designed to grasp the injured person and stabilise the head and neck while gently pulling the casualty onboard. This mechanical system comprises a linear actuator, a tension spring, a string-rigged pulley differential mechanism, and a pair of head pads. The string-rigged pulley differential mechanism is a device that connects the head support pads in order to apply force equally to the right and left sides of the head. Each pad can assume an asymmetric final position, which gives the device the ability to stabilise the head and neck in the position in which the patient is originally encountered. The tension string minimises discomfort and allows a safe and stable hold while restricting the motion of the head. The concept for this head support mechanism is shown in Figure 7a. Inflatable systems such as airbags and life jacket mechanisms were investigated for possible implementation in the proposed NSD system. The Hovding inflatable cycling helmet presented in [59; 60] is one of the inflatable systems considered for the proposed NSD system. It has a collar that is worn around the neck that inflates when sensors indicate that a crash has occurred. Another option is the work presented in [61], which shows various inflatable objects that can be fabricated by the Printlatables platform. This work combines the design concept inspired by [30; 40] and the inflatable object technology shown in [59; 61] to develop the NSD for ResQot 2.0. Figure 7c illustrates the proposed concept, which uses inflatable material. We investigated several designs, all with the same fundamental concept that the inflatable device should cover and surround the casualty's head and neck up to the shoulders, as illustrated in Figure 7c. The requirement for the integration of the NSD in the stretcher bed (belt conveyor) system was that the NSD should be able to slide down along the bed to the ground and slide back up around the bed end. The NSD does not require a separate actuator for the sliding movement. The movement of the NSD relies on friction between the NSD and the conveyor belt. The NSD is placed on top of the conveyor and attached to linear guides on both sides of the NSD to constrain its movement only along the stretcher bed. Figure 8 illustrates the updated procedure to load casualties by means of the NSD system. This procedure is an extension of Step 4 in Figure 6.  
Figure 8: Illustration of the updated procedure to load casualties by means of the NSD system. This procedure is an extension of Step 4 in Figure 6. (**4a**) Once the robot achieves the desired loading configuration, the NSD module is sliding down, approaching the casualty. (**4b**) The NSD frame is placed in the desired position so that the casualty’s head and neck are in the NSD frame centre. (**4c**) The inflatable system of the NSD then slowly inflates and stabilises the casualty’s head and neck.