# A Prototype Mechatronic Device for Upper Limb Rehabilitation and Analysis of Its Functionality
## 3 Concept and Design Solution for the Rehabilitation Device
### Objects Used for Exercises  
Interviews with stroke survivors and rehabilitation therapists identified several contextual factors that influence the use of rehabilitation technologies by individuals post-stroke [81; 82; 83]. Particular emphasis was placed on the person's hands and their motor ability to grasp objects used during therapeutic exercises [96]. Depending on a patient's motor capabilities (see Figure 6), suitable objects can be selected for initial rehabilitation sessions. Each phase of the motor response required to grasp various objects engages different levels of hand musculature (Figure 6). Beyond retrieving an object from the storage module, the patient is also required to place the object into a designated slot within the task container module. Not every grasping method (Figure 7) facilitates correct object placement. For instance, the grasp shown in Figure 7(d-1) may not allow the object to be aligned horizontally relative to the container. Some post-stroke users may only be capable of generating a palmar-like grasp, involving predominantly the thumb and index finger, with limited use of the remaining digits (Figure 7(d-2,d-3)). Depending on the exercise instruction, these users  
Figure 5: Hand rehabilitation device: (**a**) Isometric view of the model. (**b**) Top view, left storage unit with one of the overlays. Figure 6: Successive phases of the anatomical system from an open to a clenched hand (**a–d**). may attempt to orient the object horizontally (Figure 7(d-2)) or vertically (Figure 7(d-3)) by manipulating the entire upper limb. Other users may find it easier to grasp spherical objects with elongated protrusions (Figure 7(c-1,c-2)). One of the more basic grasp patterns is the cylindrical grasp, where fingers curl around the object, as illustrated in Figure 6d. This grip requires refined motor control and even finger extension. For cubic objects with slightly elongated dimensions, a cylindrical-type grasp may be mimicked (Figure 7(e-1)), although successful placement into a container slot may necessitate switching to a more suitable grip (Figure 7(e-2,e-3)). This encourages users to consciously adjust their grasping strategy. In spherical grasps, the hand must be pre-positioned as shown in Figure 6c prior to engagement. While healthy individuals typically execute such movements without difficulty (Figure 7(b-1)), those with motor impairments may achieve only a partial grasping (Figure 7(b-3)). The grip in Figure 7(b-2) enables the lateral placement of a sphere. The pincer grip, which demands precise control and positioning of the fingertips, is particularly useful for manipulating small objects with protruding segments (Figure 7(c-3)). This grasp style enhances the insertion precision and can support task diversity. The surface texture of spherical objects significantly affects grip retention. For example, foam spheres with a closed-cell structure (Figure 7(a-1)) generate reaction forces upon compression that assist with grasping. To improve tactile control, some spheres feature protrusions adapted to fingertip pad sizes (Figure 7(a-2)) or recessed indentations proportioned for the average finger anatomy (Figure 7(a-3)) [97]. The Box and Block Test  
Figure 7: Examples of training objects and their respective grasp types: (**a**) surface structures of spherical objects, (**b**) grasp of a smooth sphere, (**c**) grasp of objects with tubular protrusions, (**d**,**e**) grasp of block-type objects. (BBT) method supports a high degree of task customisation, enabling the creation of varied and complex exercise sets. The designed rehabilitation objects include cubes, cuboids, cylinders (including those with rounded edges), and spheres. Their dimensions have been adapted to fit the containers mounted on the device's arms. Each object can vary in surface texture, which significantly influences the static friction between the skin and the object [98]. It is well established that the object shape affects BBT task performance [99], a conclusion validated across objects of differing weights.