## 2 Magnetic Mechanism and Control System for a Wireless Operation
### Magnetic Device Mechanism for Finger Movement and Overall System Configuration  
For wireless finger training, we propose a multi-link magnet device a with wireless control method. Figure 2a1,a2 show the designed and fabricated magnet assist device, respectively; this device works to maintain the posture by limiting excessive magnetic attraction and repulsion through the magnetic forces of the inner-magnet. The multi-link magnet device consists of four containers, six links (I1 to I6), and 12 bearings (B1 to B9). Bearings B1, B4, and B7 are composed of pairs (two bearings) to connect link I1 and I2, I3 and I4, and I5 and I6, respectively. Their role is to maintain the angles between the fingers (\(\beta\)) that occur when the fingers are stretched and bent (extension and flexion), as shown 'in Figure 2a3,a4. The fabricated links are different lengths because of the different finger lengths: I1, I3, and I5 are 34.72 mm in length, while I2, I4, and I6 are 30.21 mm. The device is lightweight, weighing only 90.3 g. Individuals have differently sized hands and, thus, the \(\beta\) values differ. Therefore, in the fabricated device, an inter-link angle (\(\alpha\)) of a minimum of 15\({}^{\circ}\) to a maximum of 130\({}^{\circ}\) can be maintained by bearings B1, B4, and B7. When the hands are stretched, \(\beta\) is smaller than \(\alpha\). Therefore, the bearings B2, B3, B5, B6, B8, and B9 cause link rotation and produce natural hand movements. Because the inner diameter and depth of the fabricated four containers are 20 mm and 9 mm, respectively, we can mount up to three disc-type permanent magnets with diameters and thickness of up to 20 and 3 mm, respectively. The magnet type is N27 and remanence Br is 1.07 T. One, three, one, and three magnets are installed in each container, considering the force between the magnets. Figure 2b shows the overall control-system configuration. The system consists of the driving coil, 3-axis armrest, DC power supply, control circuit, and cooling system. As noted above, we developed a LabView-based control program for real-time observation of the driving coil and for hand motion analysis. Figure 2c shows the graphical user interface (GUI) developed using LabView. A gesture is tracked via a video camera for trajectory determination. Using the GUI, the hand movement speed and magnetic field strength can be controlled. Figure 2d shows the control block diagram. It is divided into three parts: control, power circuit, and cooling. The control part performs signal generation with control and image processing. The power circuit part converts unipolar current to bipolar current signal for the actuations. Figure 1: Principles of wireless assistive finger training: (**a**) overall configuration for finger movement; (**b**) finger flexion method using positive driving current, where \(F_{M1,2}\) is the magnetic force between M1 and M2 and \(F_{M1,E}\) is the magnetic force between M1 and the electromagnet (driving coil); (**c**) finger extension method using negative driving current, where \(F_{M1,E}\) is the magnetic force between M1 and the electromagnetic and \(F_{M1,3}\) is the magnetic force between M1 and M3. Figure 2: (**a**) Configuration and mechanism of multi-link magnet assist device for flexion and extension. (**b**) Control system configuration. (**c**) Developed control software: the software can control the magnetic field strength and speed and observe and display the trajectory of motion using a video camera and monitor. (**d**) Total control diagram for the system. (**e**) Configuration of the driving circuit for current direction control at the driving coil and SSR control sequence for generation of sine wave current.