A novel finger rehabilitation method using an electromag-netic system

Hand rehabilitation and training systems generally utilize either robot hands or robotic gloves [1-3]. These devices generate the repetitive gripping motion of fingers. The configuration of robot hands, which consist of electrical motors, wires, gears, etc., is complex, making them difficult to wear. To avoid these problems, many researchers have been developing soft robotic gloves that utilize flexible materials with a pneumatic system. However, because this method also utilizes wired control, stroke patients can find the gloves difficult to wear. In this study, we propose a novel method for finger rehabilitation and/or hand training. The proposed system provides a simply configured wireless system in an easily wearable device that uses magnetic torque and force control, which is based on an electromagnetic system that uses a permanent magnet. The proposed system provides two assist modes: active mode, which is between the electromagnetic field and the permanent magnet, and passive mode, which is between the permanent magnets. Figure 1 shows the principles used for the generation of the gripping motion and the configuration of the proposed method. Fig. 1 (a) shows the electromagnetic (EM) mode. The applied alternating magnetic field generates rotation and parallel translation by magnetic torque and force. These actuations are a basic principle of finger gripping. Fig. 1 (b) shows the permanent magnet (PM) mode. To increase the gripping angle of the fingers, we use a permanent magnet on the palm. The two magnets between the driving magnet and the assist magnet on the palm generate an attractive force. Thus, the proposed method is a hybrid that is used to control the gripping movement of the fingers, as shown in Fig. 1 (c). Because of this hybrid, we can decrease power consumption. Figure 1 (d) shows the configuration of the proposed methods. The inner diameter of the driving coil is 10 cm, and the coil has 250 turns by a wire diameter of 1.6 mm. The size of the driving magnet is (width) 20 mm × (length) 10 mm × (thickness) 10 mm. The surface magnetic flux density is 302 mT. The assist magnet is a disc-type, and its diameter and height are 10 and 3 mm, respectively. The surface magnetic flux density is 209 mT. The hybrid method becomes the active control, whereas the passive control does not use the driving coil. Hence, the active control does not require additional gripping force from patients. However, the passive control does utilize a patient's gripping force. Once the hand grips, an attractive force between the driving magnet and the assist magnet is generated. When we open our hands, the fingers require a stretching force more than an attractive force. Therefore, the passive control is suitable for increasing the muscular power of the fingers. Under the active control, variations in magnetic torque cause a stretching motion without the addition of finger force from patients. In the fabricated system, the maximum attractive force was 1.5 N.