Ballast is widely used as a control device for starting and limiting the current of gas discharge lamps. It contains an iron core made of silicon steel, and the iron core is wound with enameled wires. When working, the ballast always has current passing through it, which is easy to generate vibration and heat. When the gas discharge lamps are illuminated outdoors, the ballast also faces the risk of rain invasion. Asphalt has the functions of heat dissipation, insulation, waterproof, dustproof, shockproof and noise reduction. In actual production, the ballast shell is filled with asphalt by an asphalt filling machine, which can improve the performance of the ballast, such as enhancing the insulation strength and reducing the working temperature, thus prolonging the service life. According to a foreign-funded enterprise that produces ballasts in Suzhou, most ballast manufacturers are equipped with asphalt filling machines, which use manual hand-held ballasts for asphalt filling. The two-shift production has high labor costs, and the heated asphalt also emits some pungent odor, which has potential health hazards after long-term contact. In order to save costs, improve efficiency and maintain the health of employees, automatic filling equipment is also needed to replace manpower in actual production.
 
1. Automatic filling scheme of rectifier asphalt
All equipment serves the production process, and automation equipment is no exception. To design the scheme of automatic filling equipment for rectifier asphalt, it is necessary to understand the production process of rectifier asphalt filling and the action flow of manual filling as the basis and the necessary basis for designing the scheme of automatic filling equipment for asphalt, so that the designed automatic filling equipment can better cooperate with the filling machine and better integrate into the original production line.
 
1.1 Manual asphalt filling process description
The process of manually filling asphalt is as follows: manually pick up the ballast from the conveyor belt to the filling port of the filling machine, and start the filling machine on foot. During the filling process, the ballast is moved back and forth manually, so that the asphalt is evenly distributed in the ballast in the shortest possible time. At the same time, because the asphalt is viscous, the reciprocating movement can prevent overflow. When the filling time reaches the set value, the filling machine automatically stops, and the ballast-filled with asphalt is manually transferred to the workbench to complete a production process of manual filling. The asphalt flow speed and filling time are tested according to different types of ballasts, and the appropriate parameters are obtained and stored in the filling machine, and the relevant process data are directly transferred during production.

1.2 Asphalt automatic filling scheme
The purpose of adding automatic filling equipment is to replace manual workstations and to reduce investment and minimize changes to the original production line. In this way, it is convenient for the equipment to imitate manual filling actions. According to the action process of manually filling asphalt, a manipulator similar to a human hand is needed to grasp the ballast, then accurately move to the filling port of the filling machine, reciprocate relative to the filling port, and move to the next station of the production line after the filling is completed. The manipulator puts down the ballast and the filling is finished. A three-degree-of-freedom manipulator is designed, which is composed of a lifting cylinder, rotating cylinder and air claw, and is installed on a ball screw to realize the moving function. In order to cope with the moving position of ballasts of the same series with different sizes and facilitate debugging and operation, servo motor drive and PLC control are adopted.
 
The initial state of the equipment is that the manipulator is at the ballast position to be grasped on the right side. The action flow of automatic asphalt filling equipment is as follows: a ballast is in place → manipulator descends → air claw closes and grabs ballast → manipulator ascends → manipulator rotates 90 clockwise and moves to the filling position to the left → asphalt filling reciprocates → filling ends → manipulator rotates 90 clockwise and moves to the conveyor belt to the left → manipulator descends.
 
Open the claw and place the workpiece → the manipulator rises → the manipulator rotates 180 counterclockwise and moves to the ballast grasping position at the same time.
 
Structural design description of automatic filling machinery
 
The mechanical composition of asphalt automatic filling equipment is relatively simple, which consists of a frame, a manipulator and a lead screw. The equipment is light in weight and low in dynamic load and is built with 100X100 aluminum profiles. When designing the manipulator, the tooling design should be considered, and a large number of varieties should be considered, and the ballast types with more external dimensions should be adapted as much as possible. Commonly used ballasts provided by manufacturers are 167-248mm in length and 65-87mm in width. Manipulator clamping ballast is related to ballast length and width, the length direction is met by long arm-shaped tooling, and the width direction dimension affects the versatility of the manipulator. The ADEQ parallel air claw HFZ32 with opening and closing stroke of 22 mm is selected to adapt to ballasts with different widths and sizes, and the repeated action accuracy of 0.02 mm is also the tolerance of 11 mm when the manipulator grasps the position, which greatly reduces the requirements for the positioning accuracy of ballasts. Under the action of 0.5mpa gas pressure, the air claw can generate a clamping force of 160n, which is enough to cope with the ballast and asphalt weight. the relevant data of the above air claw comes from the product manual of adek company. In order to ensure the accuracy of the manipulator's movements during lifting and rotating, a rotary cylinder and a three-bar cylinder are selected, and the three-bar cylinder completes the movements of the lifting manipulator. The specific models and parameters are not described one by one. The three-bar air cylinder is connected with the lead screw, the rotary cylinder is connected with the three-bar air cylinder through a connecting piece, and the air claw is connected with the rotary cylinder through a connecting piece. The tooling is installed on the air claw to form a manipulator, and its structure is shown in Figure 2. The rotating cylinder has three working positions: grabbing position, filling the position and conveying position. The pneumatic system is unstable due to the compressibility of the air compressor and other factors. The two-bar cylinder is set to play a positioning role, which ensures the accurate position of the manipulator in grabbing and conveying the position of the filling machine. The manipulator is driven by compressed air, each pneumatic actuating element is controlled by an electromagnetic valve, and the movement speed is adjusted by exhaust throttling. Because the rotary cylinder has three working positions, an O-shaped functional three-position valve is selected.
 
Design of automatic filling control system for asphalt
 
On the basis of completing the asphalt filling manipulator, an automatic asphalt filling control system is designed, which is used to control the action of the filling manipulator, start the filling machine in time to cooperate with the manipulator, and finally complete the automatic asphalt filling. When designing the control scheme, it is necessary to meet the control requirements of the equipment. For example, in order to find out the displacement and speed of the suitable manipulator to the grasping position, filling the position and conveying position, as well as the reciprocating speed and displacement of ballasts of different models under the filling machine, these parameters can be set and saved, and the system can expand or delete the corresponding parameters when increasing or decreasing the ballast models; The working condition, operating parameters, fault detection and alarm information of the equipment can be visually displayed when the equipment is transported; The system has two forms: automatic operation and manual operation. Automatic operation is used for stable and continuous actual production, while the manual operation is used for debugging and equipment maintenance. During the operation of the equipment, the current action can be stopped at any time, and the action of the used equipment can be stopped at any time in case of failure or emergency; And the interaction of control information between asphalt canning equipment and filling machine should be considered. In the control system, programmable logic controller (PLC) and servo motor are selected to form high-precision position control, the touch screen is selected as a man-machine interface, and information interaction such as parameter setting is carried out with PLC in real-time. The pedal starting device of the filling machine is modified by a relay. When the filling machine needs to be started, the output of PLC energizes the relay coil, and the normally open contact is closed instead of the pedal to switch on the starting circuit of the filling machine. At the same time, when the set filling time of the filling machine is reached, the signal of the stopping filling machine is input to PLC and the relay coil is powered off.
 
3.1 Hardware selection of control system
3.1.1 PLC
As the core of the control system, the controller needs to be safe and reliable and can adapt to the continuous and long-term industrial environment. Because the controller wants to control the servo system, it needs to have pulse output. Meanwhile, according to the number of I/o (input/output) points in the control system, the programmable controller fx3u-48mt output by Mitsubishi transistor, which is stable in operation, rich in communication interface and simple in programming, has 24 I/o points each. according to the principle of I/o point distribution, the pneumatic system actuator detects the cylinder piston position sensor as the PLC input signal address X10-x21, and the PLC outputs the signal address y5-y13 for controlling the solenoid valve coil.
 
3.1.2 Touch screen
Through the communication between the touch screen and PLC, the operation of the equipment is monitored by using the produced control interfaces such as parameter setting, automatic operation, manual operation and alarm information, so as to realize the effective control of the equipment by the control system. Choose delta DOP-b10s615 color 10-inch touch screen, and connect with PLC through rs422 communication interface.

3.1.3 Servo motor and servo driver
Servo control is composed of servo driver, servo motor with encoder, etc. It is a precise automatic control system with mechanical position or angle. According to the calculation flow of servo motor selection, the load inertia, speed and torque required for driving the load on the shaft of the servo motor are calculated respectively. According to the principle of servo motor selection, the continuous working torque is less than the rated torque, the instantaneous maximum torque is less than the maximum torque when the motor accelerates, the load inertia is less than 3 times the inertia of the motor rotor and the continuous working speed is less than the rated speed. Select Mitsubishi HF-kp23b servo motor and Mr-J3-20a driver with the power of 200w. According to the need of control, PLC provides pulse train, pulse direction and enable signal, and servo driver provides a servo alarm signal to PLC. Refer to Mitsubishi MR-J3-A servo amplifier technical data set for parameter setting and servo control wiring. The servo wiring is shown in Figure 5.
 
3.1.4 Sensors
Sensors are used to detect the current state of each action element, material, etc., and the information is transmitted to PLC in combination with the control program to realize the control of the equipment, which can improve the stability and safety of the control system. The pneumatic actuator of the manipulator selects the magnetic induction sensor matched by Yadeke to detect the position of the piston, the lead screw selects Omron EE-SX670 slot photoelectric switch as the limit and origin detection, and the workpiece detection in grasping position and conveying position selects Omron E3ZD61 photoelectric sensor. When there is a workpiece detected in grasping position, the manipulator descends to grasp, otherwise, it waits. When no workpiece is detected in the transfer position, the manipulator descends to release the workpiece, otherwise, wait.

3.2 Software design of control system
With the cooperation of the program, the hardware of the control system can monitor the action of the equipment. The design of the software should not only consider the action flow of the equipment, such as manual and automatic modes, so as to facilitate the operation during debugging, running and maintenance, but also consider the structure of the program itself, so as to make the program readable, easy to modify and extensible. After debugging and modification, the redundancy can be reduced as much as possible and the program execution efficiency can be improved. Taking the action flow of automatic asphalt filling by manipulator as a reference, combined with the control requirements and the requirements of the control program itself, the PLC control flow of the control system is obtained.
When the equipment is started, the program is initialized first, so that the equipment is in the initial state and ready for the subsequent automatic filling action. At the same time, the touch screen pops up the prompt interface of whether the filling machine is ready and the ballasted model selection in turn. After artificial selection, the stored ballast parameters and servo motion parameters of this model will be automatically called to ensure the correct action. For product updates, it is only necessary to re-select the corresponding model. Select the equipment operation mode. In automatic mode, press the touch screen to start and send an x4 alarm signal to PLC. Refer to Mitsubishi MR-J3-A servo amplifier technical data set for parameter setting and servo control wiring.
 
The start button can start the equipment, and the manipulator runs automatically according to the asphalt filling process. In the manual mode, the manipulator in the touch screen constitutes pneumatic elements and servo action buttons, which can realize the program running and corresponding actions, and realize the actions of manual, debugging or maintenance. When selecting the automatic mode, ensure that the touch buttons in the manual mode in the touch screen control interface do not work during programming, and the start and stop touch buttons in the system control do not work during the manual mode, so as to avoid misoperation. The use of touch screen editing software design mainly includes an initial interface, control interface, parameter configuration, alarm information and other interfaces. Some interfaces are shown in Figure 7. The interface design mainly matches the PLC program function and simplifies the PLC program.
 
4. Conclusion
 
According to the action of manual asphalt filling, the asphalt filling manipulator is designed. In order to meet the general requirements of the manipulator for filling multiple types of ballasts, with the help of the key design of the combination of long-arm tooling and parallel air claws, PLC, touch screen and servo system are adopted to form a control system, and the stored product parameters are directly called, thus innovatively realizing the automatic asphalt filling of manipulator multi-type ballasts instead of manpower. Practice shows that, except for the reciprocating movement time of filling asphalt, a working cycle takes 5-7 seconds. Compared with manual filling which is easy to fatigue, the production efficiency of one shift can be increased by about one time, and it is not affected by the pungent smell of asphalt. There are few wearing parts of equipment and low maintenance cost. Within the tolerance range of the manipulator, product data can be increased according to production needs to adapt to asphalt canning of new ballast. Because the equipment investment is lower than the annual salary of a local operator, the enterprise can recover the investment within one year. Filling manipulator not only improves the automation degree of equipment in enterprises but also brings certain economic and social benefits to enterprises.