# Electromagnetic Switching Multiple Grasping Modes Robot Hand
## 3 Structure of the ESMGM Hand
### Mechanical Structure of the ESMGM Finger  
The ESMGM hand consists of a palm and several ESMGM fingers. The ESMGM finger is the basic functional unit of grasping movement. Although the size and appearance of each finger of humans are different, for the robot hand, to simplify the design, all the ESMGM fingers adopt the same structure. According to the above design concept of the switchable CPS mechanism and the partial effective transmission mechanism, the specific structure of the ESMGM finger was designed. The ESMGM finger has a two-joint structure, and its appearance and specific parts structure are shown in Figure 4.  
Figure 3: Partial Effective Transmission Mechanism: (**a**) Initial position; (**b**) Idle-stroke stage; (**c**) Effective-stroke stage. The only motor is fixed on the base and powers the whole device through a worm gear transmission mechanism. The partial effective transmission mechanism, which consists of the torsion spring, the driven gear, the partial effective driven disc, and the bump, is embedded in the proximal phalange. The partial effective transmission mechanism connects with the proximal phalange through a torsion spring on one side and connects with the switchable CPS mechanism on the other. The power and torque from the motor are transferred to the driving gear of the partial effective transmission mechanism. Then it transfers the power to the proximal phalange and the switchable CPS mechanism during the effective-stroke stage. The switchable CPS mechanism mentioned above is also set in the proximal phalange. When the partial effective transmission mechanism is in the idle-stroke stage, one of the two parallel setting switchable transmission gear trains will be limited by the tension spring, depending on under which grasping mode stage the electromagnetic switch device is triggered, and the other transmission gear train is in the follow-up state. When the partial effective transmission mechanism is in the effective-stroke stage, the bump on the driving gear drives the partial effective driven disc to rotate. Therefore the distal phalange, fixed with the third gear, will rotate with the same angular velocity, meaning the ESMGM finger enters the self-adaptive grasping mode. The switching device can realize the switching of different working modes and the limit function of gears. It has different implementation methods, one of which is an effective embodiment of the electromagnetic switching device, which will be introduced in the next subsection. Figure 5 shows the grasping movement process of the ESMGM finger. Due to its switchable function, it has two modes of operation, namely parallel and self-adaptive grasping mode (PASA mode) and coupled and self-adaptive grasping mode (COSA mode). Figure 4: Mechanical structure of the ESMGM finger: (**a**) Overall structure; (**b**) left side stereoscopic view; (**c**) right side stereoscopic view. Components: 1—base; 2—proximal phalange; 3—distal phalange; 4—proximal joint axis; 5—distal joint axis; 6—worm; 7—worm gear; 8—transition gear; 9—driving gear; 10—partial effective driven disc; 11—bump; 12—parallel grasping gear train; 13–15—first gear to third gear; 16—coupled grasping gear train; 17–20—fourth gear and seventh gear; 21—electromagnetic switching device; 22—torsion spring; 23—tension spring; 24—string; 25—reeling sleeve; 26—motor. When the ESMGM finger is under PASA mode, the whole grasping process includes three stages. Besides the parallel grasping stage and the self-adaptive grasping stage, there is still an idle-stroke stage between them. That is because in most situations it is not possible that the time during which the proximal phalange touches the object matches the finishing time of the idle stroke perfectly. The whole process can be described as follows: the ESMGM finger begins with the parallel grasping mode (PA mode), the proximal phalange rotates, and the distal phalange keeps parallel to the initial attitude. If the distal phalange contacts the object earlier, the whole process will end.