# Development of a Body Weight Support System Employing Model-Based System Engineering Methodology
## 2 Materials and Methods  
A Body Weight Support System allows patients with lower limb disabilities to reduce a percentage of their weight while performing physical therapy exercises. Additionally, the BWS needs to integrate closely with other equipment, such as treadmills or elliptical machines, to enhance the rehabilitation system and physical therapy exercises. General requirements support the BWS prototype design according to the user's needs. Figure 1A shows those requirements in a SysML Requirements Diagram (req). The main requirement is \"to Support the lower limb disability patient's weight partially and actively\". Other requirements include population type, workspace, and methods to support weight. These requirements initiate the development process and facilitate traceability. Upon prototype completion, they help estimate compliance with the objectives and results. According to Figure 1, requirements are essential for conceptualizing the system and serve as a precursor to obtaining the use case diagram (route 1 in Figure 1). This diagram establishes the interactions between the BWS and everyone involved in the process. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type of** & **Conceptual** & **Analytic** & \
\begin{tabular}{c} **Analytic** \\ **Verification-** \\ **Experimental** \\ \end{tabular} &
\begin{tabular}{c} **Mechanic and** \\ **Control Systems** \\ \end{tabular} \\ \hline Theoretical & X & X & & \\ Theoretical and practical & X & X & X & X \\ \hline \hline \end{tabular}
\end{table} 
Table 1: BWS Literature Review Classification. \begin{table}
\begin{tabular}{c c} \hline \hline
**Field** & **Research** \\ \hline Aerospatiate & [61; 62; 63; 64; 65] \\ Software architecture & [66; 67] \\ Industrial & [68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78; 79; 80; 81] \\ Control & [82] \\ General & [83; 84; 85; 86] \\ Models & [87] \\ Education & [88] \\ Automotive & [68; 89; 90; 91] \\ Software \& Hardware & [18; 22; 92; 93] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: SysML literature review classification. Figure 1C presents the general use cases according to the requirement of active weight support, considering the device users and their interactions with the BWS. Figure 1: Flux diagram of the global development of the BWS in SysML form. (**A**) General requirements diagram. (**B**) System layout diagram. (**C**) Use Case Diagram. (**D**) Pack diagram. (**E**) General structure of the system. This diagram helps identify parameters for the prototype's development, such as protocols for supporting the patient during physiotherapy exercises, parameters the therapist must set for the exercises, and system operation parameters. Use Case Diagrams are crucial for system development as they indicate which users interact with the system and help recognize the possible consequences of their actions. With the requirements and use cases, the next step is to follow and enter the information into development route 2--Figure 1. The BWS conceptual design begins with this action, setting up the main configuration. According to the requirements, the BWS needs the assistance of a treadmill to perform the therapy exercises and actively support the weight. Additionally, the data collected from the rehabilitation process can be saved and sent to other devices, allowing the therapist to analyze each patient's clinical history offline and from the comfort of a desk. Figure 1B presents the system layout, highlighting the controller, which manages information between devices and users within the BWS system and facilitates signal transmission for weight unloading. According to the Use Cases Diagram (uc) in Figure 1C, there are three fundamental system users: patient, therapist, and support engineer. The support engineer configures the equipment and manages its maintenance, the therapist sets up the weight support and the rehabilitation exercise parameters, and the patient interacts directly with the BWS and the treadmill.