# Electromagnetic Switching Multiple Grasping Modes Robot Hand
## 3 Structure of the ESMGM Hand
### Components of the ESMGM Hand  
A healthy hand has five fingers and 24 degrees of freedom. However, for a robot hand, an overly complex structure and redundant degrees of freedom will inevitably mean higher cost and difficulty with control methods. Adhering to the practical concept of the underactuated hand, this research proposes an ESMGM hand with the structure of three fingers. The mechanical structure of the ESMGM hand is shown in Figure 7; it mainly consists of three ESMGM fingers, a base, a palm, and the transmission system. As the essential functional component, the ESMGM finger is mainly composed of several gear sets which transmit multiple grasping modes mo  
Figure 6: Mechanical structure of the electromagnetic switching device: (**a**) structure of the electromagnetic switching device; (**b**) function diagram. Components: 61—first gear; 71—fourth gear; 8—electromagnetic switching device; 81—switching sleeve shell; 82—electromagnet 1; 83—electromagnet 2; 84—ande; 85—cathode; 86—conductor; 92—tensor spring; 93—string; 94—reeling sleeve. Figure 7: Mechanical structure of the ESMGM hand: (**a**) left isometric view; (**b**) right isometric view; (**c**) bottom view. Components: 101–103—ESMGM fingers; 104—palm; 105—base; 106—palm motor; 107—palm worm; 108—palm worm gear; 109—first rotating gear set; 110—s rotating gear set. characteristics of gears ensure the high efficiency, sufficient grasping forces, and good grasping stability of the ESMGM hand. The switchable CPS mechanism which integrates three grasping modes ensures the effectiveness of the function. Based on the partial effective transmission mechanism in each ESMGM finger, large strokes are reserved for various grasping modes; thus, a large grasping motion range is guaranteed, and the ESMGM finger can achieve grasping action to a specific position with a different gesture. The electromagnetic switching method makes the ESMGM hand achieve fast and smooth switching without friction resistance. Its good property ensures that once a certain grasping mode is selected, the other transmission components will be completely in an idle condition without movement obstruction. Therefore, the ESMGM hand has good motion smoothness. The ESMGM hand is designed with a three-finger structure; the three ESMGM fingers are perpendicular to the palm and distributed on both sides of the palm. One finger is fixed on the base, while the other two are movable fingers. To give the robot hand better grasping characteristics, two fingers are set to be able to rotate around the rotation axis. The rotation of the two ESMGM fingers is realized through the transmission system. The motor provides the power to the two fixed shaft gear drive systems, and the end gears are fixed to the corresponding ESMGM fingers. If the motor starts, two ESMGM fingers will rotate at the same time and speed and in the opposite direction; the rotation range of each finger is 90 degrees. Figure 7a shows the initial position of the ESMGM hand, in which the two movable fingers are opposite the fixed finger. Figure 7b shows the state after the two movable fingers turn 90 degrees when they are opposite each other and perpendicular to the fixed one. In this way, the robot hand can grasp objects in the palm in all directions and is also endowed with wider grasping space, more dexterous movement, and better grasping stability. Thus its function can basically replace a robot hand with five fingers. Some parameters of the ESMGM robot hand compared with a human hand are shown in Table 1. According to various parameters, the size of the ESMGM robot hand is slightly larger than that of a human hand. However, its proportions are the same as that of human hands, with a high degree of personification. The ESMGM hand has greatly reduced the number of dofs, so its action is simpler than that of a human hand, but using an underactuated mechanism ensures self-adaptability.