# A Prototype Mechatronic Device for Upper Limb Rehabilitation and Analysis of Its Functionality
## 3 Concept and Design Solution for the Rehabilitation Device
### Prototype Solution of the Device  
The application of a mechatronic design approach throughout all stages of the development process enabled a detailed refinement of the proposed structural concept. Following the development of the prototype concept, a systematic design procedure was established to achieve the desired functional and ergonomic characteristics of the device. Based on the defined specifications, a topological shape optimisation process was conducted to determine the optimal structural configuration. The design process was implemented in a series of sequential stages, as illustrated in Figure 2. During both the design and prototyping phases, particular emphasis was placed on ensuring user comfort and safety, in accordance with the recommendations outlined in [85]. The device is intended for seated use at a table, and all drive mechanisms are fully integrated within the base structure, thereby minimising external protrusions and potential hazards. During the development of the device's construction, particular attention was given to ensuring comfort during use for individuals with diverse body types. The key anatomical features of the entire human upper limb were identified. Anthropometric data were collected for the adult population, including women aged 20-60 years and men aged 20-65 years [86; 87; 88]. Based on measurements for women in the 5 th percentile and men in the 95 th percentile, the necessary manipulation space for the upper limb was virtually modelled [89]. The selection of geometric features, and the corresponding development of the structural design, followed applicable standards [90; 91; 92]. A topological search was conducted, taking into account the initially assumed working space geometry and dimensionless parameters defined during the conceptual stage (Figure 3). The functional characteristics of the device were developed based on a mapped manipulation area accessible to the human upper limbs [93; 94; 95]. The lengths and placements of the robotic arms and storage containers were determined through an anatomical analysis of upper limb structures [89]. Figure 2: Characteristic stages of the device design process (FEM—Finite Element). Based on the established housing dimensions and accessible reach zones for hand movement--specifically for object retrieval (area \"1\" in Figure 4a)--the parameters l-h and l-w were defined. The minimum and maximum lengths of the arms (l\({}_{1}\), l\({}_{2}\)), along with the angular displacement of the external arms, were determined by mapping the potential positions of the storage and task container modules (Figure 4b). The actual accessible area for inserting objects into the container openings was smaller than the full range of the upper limb manipulation space. To ensure functional and collision-free operation between the storage and container modules, a safe distance (l\({}_{d}\), Figure 4b) was established. Once the length of the external arm was defined, its operational range could also be determined. In Figure 4b, coloured dashed lines represent sample hand trajectories--retrieving an object, placing it into a container opening, and pressing a button to confirm task completion. This process engages the user in grasping the object correctly, transferring it to a specific container (as displayed on the monitor), and performing a button-press motion to indicate the task's completion. The user maintains a grip on the object while positioning it in the designated slot, followed by extending the fingers to press a control button. Figure 4: Identification of characteristic dimensions: (**a**) length of the central arm (“1”) and the external arm (“2”), (**b**) determination of possible positions of the central object storage container (“1”) and the external object placement container (“2”). Figure 3: Identification of the hand access area: (**a**) Basic area. (**b**) Model of the hand manipulation area for individuals with disabilities.