# Design of a Two-DOFs Driving Mechanism for a Motion-Assisted Finger Exoskeleton
## 6 Test Results  
The built finger exoskeleton prototype has been tested experimentally to prove its feasibility as a finger motion exercising device in terms of it kinematic and operation behaviors. Given the  
Figure 17: FEM factor of safety calculations based on maximum shear stress. Figure 18: The built prototype of the finger exoskeleton, front view (**a**), back view (**b**). expected slow speed operation, dynamic simulations and tests are not required at this proof-of-concept stage. The finger exoskeleton can be easily worn with Velcro fasteners. The connection between the finger and exoskeleton can be as tight as the subject wishes. Even after long use, it is still comfortable to wear. Also, the calibration procedure is very straightforward. It consists of the following steps: Attaching the exoskeleton to the finger, manually placing the finger in its desired straight configuration; registering this position as the initial configuration; manually placing the finger in its desired fully closed configuration; registering this position as the fully closed configuration. After the above steps, the device is ready to operate within the desired operation range. The exoskeleton movement has been compared with the reference motion of a healthy human finger, and the angular error has been calculated as also partially reported in [33]. The driving angle of joint D0 is called \(\delta\), and the driving angle of joint B0 is called \(\beta\). The angles of the joints of the finger from the grasping test have been used as an input for a multibody motion simulation of the CAD model on SolidWorks 2019. The simulation acquires the angles of the motor for each position during the finger motion. A comparison of the simulation and the motion of the prototype was used to determine if the exoskeleton prototype moves as planned. The desired path planning and angular joint coordinates are managed by using an Arduino control board, which is connected to the two servomotors that drive the exoskeleton. The angles of the driving links have been calculated and interpolated for each position that has been experimentally measured during a grasping test, as reported in Figure 4. Then, the obtained motor angles are sent to an Arduino controller, which drives the exoskeleton. The desired motion has been obtained by an offline video post-processing that is carried out with MATLAB, allowing us to measure the angular joint positions in each acquired video frame. This information is converted into a desired set of joint angles versus time. The controller is programmed to move both motors in each desired position with an interpolated step motion. Accordingly, the proposed motion planning consists of passing through a prescribed number of path points with a smooth interpolated motion to reach precision positions. A pause of half a second is set before proceeding with the next step desired precision position to keep the motion safe for the user. The user has the time to easily stop if he/she feels discomfort in any reached configuration. The maximum angular reaches of motors are limited via software limits that are well within the range of the servo motors being equal to 180\({}^{\circ}\). After completing the motion planning, videos of human finger exoskeleton-assisted motions were collected and analyzed. Tests were performed on the same subject as for the initial grasping test in Figures 1 and 3. Video captures were acquired by tracking both finger joints and exoskeleton joints during a grasping motion. Then, the driving angles and the angles of the finger were determined. The resulting movement of the prototype and the finger is shown in Figure 19. The movement takes approximately 16 s. The proposed tests are performed with a human sitting and his/her forearm fixed on a reference table. The first snapshot Figure 19a refers to the beginning of the movement.