## 2 Related Work
Alternative designs using stretcher-type constructions or litters that aim for a smoother pick-up and transportation process of casualty extraction procedure have also been investigated. Examples of proposals for such systems are the robot presented by [PERSON] et al. in [36; 37; 38] and the Tokyo Fire Department [39]. These robots are designed to perform casualty extraction using a conveyor belt mechanism to pick up a casualty without having to move the body significantly in the process. Once the casualty is properly loaded on top of the robot, the conveyor belt base then properly supports the casualty's body so it can additionally serve as a stretcher bed. Thus, this robot design and method for casualty extraction is expected to be safer and would minimise the possibility of causing additional injuries to the casualty during the casualty extraction process. [PERSON] in [28] has also presented a similar design of a stretcher-type casualty ex-traction robot. A unique feature of this design is that it incorporates a wheel-legged structure that can be raised or lowered using linear actuators. The purpose of the design is to improve the robot's adaptability in a complex disaster scene. On the other hand, a very recently published work in [30; 40] presents a casualty extraction robot design called semi-autonomous victim extraction robot (SAVER) [41; 42]. This robot is equipped with two manipulator arms and a head support system. The arms are designed for the telemanipulation process to gently adjust the pose of the casualty prior to the loading process. The head support  
Figure 2: Casualty extraction procedures using two different types of casualty extraction robots. (**a**) Humanoid-type robot construction. The casualty extraction procedure has been presented in [29]. We found that there are at least three safety concerns in the typical humanoid-type robot construction procedure, the impact during the casualty scooping process could possibly bend the casualty’s body sideways, the lifting process could make the casualty’s body bend forward, and provide minimal support for the casualty’s head and neck during the transportation phase. (**b**) Stretcher-type robot construction. The presented casualty extraction procedure introduced as the loco-manipulation approach has been presented in [23]. system is designed to grasp the injured person and stabilise the head and neck while gently pulling the casualty on board. In our previous works presented in [19; 20; 21; 22; 23], we have developed a proof-of-concept mobile rescue robot for casualty extraction, called ResQbot (see Figure 1, ResQbot 1.0). This robot is a stretcher-type mobile rescue robot designed to safely load a casualty using the loco-manipulation approach [23] that uses a combination of the robot's wheeled locomotion and the belt conveyor mechanism to load a casualty (i.e., manipulation task), as illustrated in Figure 2b. The loco-manipulation approach allows the robot to load the casualty while ensuring that key safety thresholds (based on [43; 44]) are adhered to and avoiding potential causes of additional injury to the casualty, such as head, neck or spinal cord injuries [23]. The stretcher bed conveyor of this robot is also equipped with a stretcher strap mechanism to safely secure the casualty during transportation. Despite the promising results obtained from the evaluation experiments on the loco-manipulation approach using ResQbot 1.0 [23], ResQbot 1.0 is only capable of securing half the body of the casualty (i.e., upper body) onto the robot's stretcher bed module (see Figure 3a). During the casualty extraction mission, the robot will drag the casualty's legs during transportation (Videos of ResQbot 1.0 are available at [[https://www.imperial.ac.uk/robot-intelligence/robots/resQbot/](https://www.imperial.ac.uk/robot-intelligence/robots/resQbot/)]([https://www.imperial.ac.uk/robot-intelligence/robots/resQbot/](https://www.imperial.ac.uk/robot-intelligence/robots/resQbot/)) (accessed on 15 May 2021)).