## 3 Design of FWRMS
### Fingers Mechanism Design  
The mechanical parts of the finger's mover demonstrated in Figure 2(a). Some of the fingers mechanical parts are a follow-up to recently developed ([PERSON], 2020). From Figure 2(a), we can observe the linear dynamic model of the proposed mechanical structure and transmissions mechanism, which is composed of an electrical motor holder, the base, a mechanical coupling, leading screw, nut, supporting bearings, sliders, linear motion ball bearing, a worktable. The FMRMS finger's rehabilitation mechanism design has the following characteristics: adopting an indirect feed drive with leading screw and nut mechanism. The leading screw and the motor's shaft connected through mechanical couplers. The motor's torque operates a rotational angular velocity, which generates a dynamic force between the external thread of the leading screw and the nut's internal thread; at this point, once the revolution is provided, the screw and nut threads convey the thrust. In this design, the nut is positioned then fixed at the button of the worktable. The driven nut then induces a linear displacement to the worktable. Eventually, this mechanism makes the rotational torque convert into translational velocity.  
Figure 2: A general overview of the proposed FMRMS prototype, (**a**) 3D structure overview of the FMRMS prototype; (**b**) real healthy object’s hand integration with the proposed system.  
By taking advantage of produced linear displacement, the exoskeleton fingertips, as demonstrated in Figure 3b, were placed, and fixed on the top of the worktable, designed to be the exoskeleton fingertips holder. The same displacement will transfer to each exoskeleton fingertip. Furthermore, the exoskeleton fingertips designed to converts the driven displacement again into rotary motion, which is copying the finger's nature trajectory workspace; in other words, the exoskeleton rotation range will be limited to the patient's fingers ROM; this mechanism assists the patient to freely and neutrally move their fingers. This mechanism's advantage is that the patient places their hand (load) onto the machine, leading to fewer mechanical parts integrations; this is considered a safety and comfort feature, not the opposite, where the mechanical assemblies are placed on the patient's fingers and top palm. Moreover, the fingertip's holder is adjustable to fit different hand sizes and lengths for either right or left hand, as demonstrated in Figure 3b. Additionally,  
Figure 3: The grounded-exoskeleton of the fingers rehabilitation: mechanism design: (**a**), The Finger rehabilitation indirect feed drive screw and nut mechanism design with all parts; (**b**) front view of the worktable with exoskeleton fingertips design, since the fingers’ anthropometric and positions of the right and the left hand, are not the same, especially the pinky finger. Therefore, we designed five adjustable fingertips holder to be suitable for either hand’s pinky finger; (**c**), side view 3D structure model of the FMRMS device and human finger interaction; (**d**), Front view, 3D structure model of the human finger-robot interaction.  
since the exoskeleton fingertip is the integration part between the patient's fingers and FWRMS, they are designed to remove, changeable, and more hygien. The base limits the worktable's mechanical structure and exoskeleton fingertips to limit driven displacement with respect to the finger's workspace.  
Eventually, regarding the finger's rehabilitation, the end-users arm should be fixed and appropriately fastened from the lower side of the forearm by using woven belts throughout the therapy process. The hand forearm cuff support presented in Figure 3a; ultimately, Figure 3c,d shows the 3D structure of the proposed fingers grounded-exoskeleton design machine and end-user hand and fingertips integration.