# A Design Method for Multijoint Explosive-Proof Manipulators by Two Motors
## 1 Introduction  
Currently, manipulators act as \"right hands\", assisting humans in areas such as industrial production, agricultural engineering, medical treatment and rehabilitation, aerospace engineering, search-and-rescue, etc. In recent years, disasters and industrial accidents have occurred with high frequency, and the need for manipulators for search-and-rescue missions has increased accordingly. Manipulators can be especially helpful in emergencies where human activity is made complicated. In the radiation leak at the Fukushima Daiichi nuclear plant, the pump truck made by SANY GROUP helped rescuers inject water into the reactor using its manipulator [1]. However, the pump truck was designed to build buildings, and the nuclear plant had no prepared plans or resources for a rescue operation of this nature or scale. Therefore, they asked the SANY GROUP for help and the pump truck was transported from Changsha, Hunan Provence, China to the accident scene. Therefore, it is important to develop and prepare search-and-rescue manipulators for the prevention of different crises before disasters and industrial accidents emerge, and they should be specially designed for differentdisaster environments--for example, working in earthquake [2], explosive ordnance disposal [3; 4], and explosive environments. Coal mine disasters have happened frequently in the last ten years, and search-and-rescue missions can be carried out by explosive-proof robots to improve the safety of rescuers. The robots [5; 6; 7; 8] can only detect parameters of the explosive environment, because they are eventually blocked and become unable to continue detecting. Therefore, an explosive-proof manipulator is needed to help robots clear obstacles from their path. However, explosive-proof manipulators are very difficult to design. They should be specially designed in order to search and rescue in the explosive environment [9]. During operation, they should not ignite combustible gases by their electric components, making it is very difficult to ensure safety in the explosive environment. In an explosive environment, a working motor will lead to an explosion if it is not protected by an explosive-proof box. When a robot is searching and rescuing in an explosive environment, its explosive-proof boxes should not be damaged by an explosion caused by other factors. If the explosive-proof box is damaged, the motor or other electrical equipment will lead to a secondary explosion which will damage the environment again. After an explosion, the robot will be out of operation and will not affect the explosive environment, and the rescuers should use another new one to continue the search and rescue operation. Safer designs would make use of more mechanical components and fewer explosive-proof boxes for electric components. The choices of manipulator drive methods are various, including motor drive, pneumatic drive, and hydraulic drive methods. The manipulators using the hydraulic drive method have the largest power among the three drive methods, and are always applied to large-scale equipment to finish hard work. In the application of engineering machinery for the architectural industry (e.g., the pump truck mentioned above), the hydraulic drive method is the best choice for manipulator design because of its high power capacity [10; 11]. The pneumatic drive method is dexetrous and applied easily because it is light, but its power is lower than the others [12; 13]. It is usually used in industrial assembly lines, and the supply of the air resource can be concentrated conveniently. In recent years, the pneumatic drive method has been applied to the research of artificial muscles which can drive a manipulator in a manner similar to the human hand [14]. The motor driving method is the most widely used, and can be used more skilfully than the others. The methods of power transmission from the motor to the actuator are various (usually motor-reducer-actuator or motor-pulley-actuator).