In some fields of industrial production, because of work reasons, workers are often exposed to flammable, explosive, deadly gases and other factors, which increase the labor intensity of employees and even endanger their lives. Therefore, ensuring production safety, reducing production price and improving product quality and economic benefits are the most important problems that enterprises should face. Automatic mold unloading manipulator mainly frees workers from heavy and frequent operations in harsh environments such as inflammable and explosive. Although it is not as flexible as hands, it is characterized by repeated work and labor, ignorance of fatigue and fear of danger, and the strength of grasping heavy objects is greater than that of hands, especially when operating in harsh environments such as high altitude, dust, inflammable, explosive and high temperature. Therefore, its application is more and more extensive. Under remote observation, The emergence of mold unloading manipulator provides a reliable professional guarantee for the completion of mold unloading work and provides a reference for more comprehensive realization of unmanned operation of mold replacement.
 
Function analysis of manipulator
 
1. The structural characteristics of the mold
 
There are 6 sets of molds with similar shapes and different sizes, with a length of about 1250mm and a steel structure with a weight of about 500kg.
 
2. Composition of the manipulator
According to the characteristics of the mold mechanism and the layout of the workshop, the rectangular manipulator with a gantry structure is adopted to meet the requirements of mold loading and unloading space transportation. The manipulator is mainly composed of an actuator, drive system, control system and position detection device. The actuator includes the hand, wrist, arm, post and other parts. The driving device mainly includes an explosion-proof motor and a cylinder. The proximity switch is used to prevent collision between mechanical parts. The cylinder pulls the rack to complete the opening and closing of the gripper. The explosion-proof motor is used to drive the manipulator to move in all directions, and the mold can be assembled and unloaded through cooperation. The control system of the manipulator is usually composed of the program control system and electrical positioning (or mechanical stop positioning) system. If necessary, it can monitor the activities of the manipulator and send out alarm signals when errors or faults occur.
 
3. Unloading workflow
Before making the design scheme, it is necessary to sort out the management methods of the de-molding manipulator. First, the de-molding manipulator returns to the starting position from any position. In the whole process, the mechanical gripper opens to the maximum angle, the mechanical arm is lifted to the highest position, and the gantry frame also returns to the left origin. In manual mode, with the help of video observation, the operator starts the command button to operate. The lifting arm and sidearm of the mold unloading manipulator are equipped with proximity switches, which can accurately reach the planned stop position. For other motion mechanisms, inching fine adjustment is recommended for the position to be reached.
 
Design of Manipulator Gripper
 
The gripper is the main component of the manipulator's actuator, which realizes the opening and closing of the gripper through the up-and-down movement of the rack. According to the shape and quality of the mold, the gripper of the manipulator uses two mechanical clamp grippers to grab the mold back and forth to transport the workpiece. Various movements of the gripper are usually realized by driving mechanism and transmission mechanism, and the mechanical gripper uses an air cylinder as its power element. From the stress analysis, when it is working, it directly bears the static and dynamic loads of the mounting frame, hands and workpieces, and has extra self-movement. Therefore, the structure, working stroke and flexibility of the gripper directly affect the working performance of the mechanism.
 
1. Design and analysis of manipulator gripper
(1) The gripper should have a large bearing capacity, good rigidity and be lightweight;
(2) Section form and outline size should be selected according to the stress situation;
(3) Improve the supporting rigidity and reasonably choose the supporting distance;
(4) Hand movement should be flexible and inertia should be small.
 
2. Design and calculation of manipulator gripper

(1) the type of claw.
Claws commonly used by industrial manipulators can be divided into two types according to the principle of clamping workpieces: clamping type and adsorption type. The adsorption type is usually used to grab plate-like objects with flat surfaces and huge space, while the clamping type will drive the die with a heavy load, and the clamping degree is higher. According to the shape and size of the mold, the gripper of the clamping manipulator is selected in this design. So that the manipulator can operate the workpiece with ease, this design selects two clamping claws, and the clamping force is provided by two cylinders. The gripper is installed on the manipulator adjusting frame through the gripper fixing seat.

(2) Design and calculation of rack.
1) According to the designed transmission scheme, select rack and pinion transmission.
2) The explosion-proof manipulator is a general working machine, and its speed is not high, so it chooses Grade 7 precision.
3) Material selection. According to Table 10-1 of Mechanical Design, the pinion gear is 40Cr (quenched and tempered), the hardness is 280HBS, and the rack material 45 steel (quenched and tempered) is 240HBS and the hardness difference between them is 40HBS.
4) Closed gear transmission generally has a higher rotating speed. In order to improve the stability of transmission and reduce impact vibration, the number of pinion teeth Z1 is 20-40, so the number of pinion teeth Z1 is chosen to be 28. On the basis of compact structure and avoiding waste, the gear transmission device designed in this way can meet the contact fatigue strength of each tooth surface and the bending fatigue strength of the tooth root.

(3) Design of mounting base.
The side plate is mainly used to fix the gripper and cylinder of the robot and to determine the position of the gripper and rack, which is an important part of the manipulator.
 
(4) Pneumatic control design
The gripper of the explosion-proof mold unloading manipulator is controlled by pneumatic components, and the opening and closing of the cylinder is controlled by a three-position five-way solenoid valve, while the valve core is in the middle position, which can lock the cylinder for a long time and prevent the gripper from opening at the moment of gas failure. The throttle valve will change the airflow, resulting in slow clamping speed and stability of the manipulator. The PLC controls the pneumatic system, and the PLC logic output manages the on/off of the relay of the directional valve, realizes the action of the directional valve body and completes the on/off of the gas path to control the pneumatic circuit.
 
3. Calculation and verification of the opening angle of manipulator gripper
 
(1) Check the opening angle of the preliminary design.
At the initial stage of design, it is assumed that the cylinder model CDGPB15-150-D-B-97 is used, then the elongation of the cylinder piston rod is 150mm, and the rotation angle of the manipulator is 0, then the theoretical maximum vertical distance is 19.53mm, and finally, the upward-lifting distance is 169.53 mm < 240 mm (the diameter of the mold clamping position), so the opening angle is too small to clamp parts.
 
(2) Calculate and check the opening angle of the optimized manipulator gripper. Through analysis, it is necessary to adjust three parts: first, change the cylinder model and choose the cylinder of CDGPB15-200-D-B-97, and the cylinder piston rod elongation will be 200mm. Secondly, the hand-held part of the manipulator is reduced by 50mm, and the position of the third rotating pin is increased by 100 mm. The theoretical maximum vertical distance is 118.26mm if the grasping rotation angle of the manipulator is, then the upward-lifting distance can be finally 118.26+100+50 = 268.26 > 240 mm, then the opening angle meets the requirements, and the parts can be clamped.
 
Conclusion
 
An explosion-proof manipulator is an important tool for assembly in a harsh environment. In this paper, according to the characteristics of the mold, the composition of the manipulator is designed, the design and analysis of the mechanical gripper are made, the type of gripper is designed, and the opening angle of the mechanical gripper is preliminarily calculated and checked. By optimizing the design scheme, the opening angle can meet the requirements of the mold, and parts can be clamped.