Academic Journal of Science and Technology ISSN: 2771-3032 | Vol. 7, No. 1, 2023 125 Design of Control System for Pusher Plate Automatic Loading and Unloading Machine Shenghu Pan*, Meichang Cai and Pengjie Lv Department of Mechatronics Engineering, Southwest Petroleum University, Chengdu 610500, China * Corresponding author Abstract: Aiming at the problem that the automatic loading and unloading system of the lathe is controlled by the electric control, which leads to the aging of the coil and the complicated wiring, this paper designs a control system that can automatically load and unload the material to meet the requirements of high efficiency automatic processing, stability and reliability of the lathe. This system uses Delta PLC as the controller and touch screen control to realize the automatic transmission from the loading machine to the lathe for processing, and then from the lathe to the blanking machine after processing. Equipped with pneumatic system, it can quickly and reliably realize the push and discharge actions. The system can be used in production, reduce the time of loading and unloading, and improve production efficiency. Keywords: Loading and unloading machine, Control system, PLC. 1. Introduction With the arrival of the new era of intelligent manufacturing and the significant development of artificial intelligence, smaller factories are undergoing transformations and upgrades to become automated factories in order to enhance production efficiency [1]. As a result, the application of automated processing equipment is becoming increasingly widespread. Currently, the push-pull type loading and unloading machine used in the CNC workshop of our company is controlled by electrical circuits. However, the circuit stability is not reliable. For example, the relays, which actuate the executive components when energized through their coils, can experience aging issues over time [2-3]. Ultimately, this can affect the control circuit. Sometimes, when there is a need for minor changes, additional electrical components such as relays and wiring are required, and at times, an additional control cabinet needs to be considered due to severe space constraints. Due to production requirements, it is necessary to set parameters and display certain signals, which cannot be achieved through the electrical control circuit alone. In order to ensure reliable control of the system and considering the reliability and maintainability of the control system, a highly automated loading and unloading equipment has been designed [4-6]. This push-pull type automated system is based on PLC (Programmable Logic Controller) control, offering faster loading and unloading speeds, thereby enhancing production efficiency. It holds significant value for widespread application [7]. 2. Overall System Design As shown in Figure 1, the push-pull type automatic loading and unloading mechanism is a critical component of the automated CNC machine tool, aiming to achieve automation on the production line [8]. The push-pull type automatic loading and unloading mechanism consists of three parts: the push-pull loading mechanism, the loading and unloading motor, the conveyor belt, and the unloading pushing mechanism. The workflow of the push-pull type automatic loading and unloading mechanism is as follows: The operator initially places the bar workpieces into the loading mechanism, with a maximum of 50 pieces at a time. After completing all necessary checks, the operator activates the power supply. At this point, the feeding cylinder of the loading mechanism pushes the bar materials to station 1. Upon receiving the signal from the sensor at station 1, the loading motor drives the conveyor belt, which stops rotating when the bar material reaches station 2. This loading process continues in a cyclic manner. Once the bar material is processed on the CNC lathe, the sensor at station 3 detects its presence. Subsequently, the unloading motor drives the conveyor belt, delivering the processed bar material to station 4. After a 5-second delay, the blocking cylinder automatically retracts, allowing the processed bar material to slide into the unloading bin. 1—Feeder motor; 2—Pusher feeder mechanism; 3— Conveyor belt 1; 4—CNC lathe; 5—Conveyor belt 2; 6— Unloading pusher mechanism; 7—Unloading motor Figure 1. Pusher-type Loading and Unloading Mechanism. 3. Hardware Design of The Control SystemDue to the high reliability, strong anti-interference capability, and low cost of use, the Delta PLC is selected [9- 10]. The programmable controller chosen is the DVP32ES200T model. It has 16 digital inputs and 16 digital outputs, with NPN-type outputs and a maximum passing current of 0.5A. The power supply connected is AC. For the 126 HMI (Human Machine Interface), the Kunlun Tongtai touchscreen with a 7-inch display, model TPC7032kt, is chosen. It offers powerful functionality, easy programming, an attractive appearance, and high touch sensitivity. The electrical control system architecture, as shown in Figure 2, is the equipment for human-machine interaction. The touchscreen functions to set, control, and debug relevant parameters. It communicates with the PLC via an Ethernet cable, with the touchscreen and PLC having the same IP address in the network segment. The PLC's IP address should be set as the gateway. Once the settings are completed, instructions are sent to the PLC, and the information returned by the PLC is displayed in real-time [11-12]. The PLC acts as the controller, similar to the brain of the control system. Its crucial functions include signal and data acquisition and management, control of the stepper motor, control of the cylinder, and control of indicator lights [13]. Since the PLC's outputs are transistor type with low current, intermediate relays are used to connect to the actuators. When the PLC receives signals from sensors or buttons, it outputs control signals to the intermediate relays, which then control the solenoid valves and subsequently control the cylinders. The lathe sends alarm signals to the PLC, and the PLC's loading and unloading alarm signals are also transmitted to the lathe via intermediate relays. The PLC controls the stepper driver through pulses and direction signals, ultimately controlling the rotation of the stepper motor and the movement of the conveyor belt. Table 1: Input/Output Address Allocation Table. Figure 2. Control System Structure. Table 1. Input/Output Address Allocation Table. input side signal source output side signal source X0 start button Y0 pulse signal for the feeder's stepper motor X1 stop button Y1 direction signal for stepper motor of the feeder X2 emergency stop button Y2 pulse signal for stepper motor of the unloader X3 preparation signal from machine tool to feeder Y3 direction signal for stepper motor of the unloader X4 preparation signal from machine tool to unloader Y4 alarm signal from the feeder X10 waiting station detection Y5 alarm signal from the unloader X11 loading station detection Y6 feeder cylinder extends X12 discharging station detection Y7 unloader cylinder extends X13 unloading station detection Y10 start indicator light Y11 stop indicator light Y13 feeder cylinder retracts Y14 unloader cylinder retracts 127 4. Design of Pneumatic Control System The pusher-type automatic loading and unloading machine is commonly used in factories, especially in environments with high dust and strong magnetic fields. Considering safety, reliability, and the need for rapid pneumatic actions, an air pressure control system is employed. The pneumatic control system of the pusher-type automatic loading and unloading machine is illustrated in Figure 3. Magnetic switches are used to detect the proximity of the bar stock and transmit the detection signals to the PLC [14].All cylinders in the system are pneumatically controlled. When the bar stock approaches the magnetic switches mounted on the cylinders and the loading/unloading device, the detected signals are promptly sent to the PLC in the control cabinet. Upon receiving the information, the PLC commands the solenoid valves installed on the valve manifold to change the cylinder's direction. The blowing valve is a two-way three-position valve connected to the pneumatic nozzle located adjacent to the CNC lathe's outer side. When the two-way three-position solenoid valve is energized, the pneumatic nozzle blows air to clean the waste generated by the bar stock during production. When the power to the two-way three-position solenoid valve is cut off, the blowing operation stops. To ensure that the cylinders immediately stop their actions when power is cut off, three- way four-port valves are chosen for the solenoid valves. Figure 3. Pneumatic Control System. 5. Software Design of The Control System 5.1. Touch screen interface design In order to interact with the PLC and control its functions, a touchscreen is used for parameter settings and displaying certain signals. The touchscreen interface design includes the main interface, debugging interface, parameter setting interface, and sensor display, allowing various functions of the loading and unloading system to be implemented. The main interface, as shown in Figure 4, displays the "Working Status" indicating whether the loading and unloading machine is running. The "Current Loading Count" displays the total number of materials transported since the machine was turned on. There is a reset button to reset the "Current Loading Count" to zero. When a fault occurs in the loading and unloading machine, the alarm label changes to red. Figure 4. Main Interface. During the design process, many factors need to be taken into consideration, such as the interlocking functionality between manual operation and automatic operation [15]. The debugging interface is shown in Figure 5, where you can click the corresponding buttons to activate the respective actions. 128 Figure 5. Debugging Interface. By utilizing the touchscreen's numerical input functionality, operators can input desired parameters in the parameter setting interface. At this point, a keyboard will pop up on the touchscreen interface for the operator to use [16]. The motor speed setting interface for the feeding motor is shown in Figure 6, allowing the adjustment of the conveyor belt speed by debugging the feeding motor speed. Figure 6. Parameter Setting Interface. 5.2. Program design of the control system This pusher-type automatic loading and unloading equipment adopts two working modes: automatic mode and manual mode. The control of the working mode is selected through a combo box option on the main interface. In the automatic mode, which is the normal operating mode of the pusher-type automatic loading and unloading equipment, when the bar stock is at the starting position of the machine, the start button is pressed, and the bar stock starts to move immediately. When the position detection proximity switch sends a signal to the PLC, the PLC controls the electromagnetic directional valves to achieve the complete loading process [17]. The working process of the pusher-type automatic loading and unloading equipment in automatic mode is as follows: the loading cylinder extends → the loading cylinder reaches the top position (5s delay) → the loading cylinder retracts → the conveyor belt runs (motor rotates clockwise) → the motor stops; after the bar stock is processed by the machine, the conveyor belt runs (motor rotates counterclockwise) → the motor stops → the unloading cylinder extends → the unloading cylinder reaches the top position (5s delay) → the unloading cylinder retracts. The pusher-type automatic loading and unloading machine completes one work cycle, and then repeats the above actions. Below is the program diagram for automatic operation. Figure 7 shows the start and stop program. Figure 7. Start and Stop Program. 129 When using the manual debugging mode, as shown in Figure 8, manual adjustment is generally used for the inspection and maintenance of the pusher-type automatic loading and unloading machine. In the debugging interface, the loading cylinder is controlled by the start button and stop button of the loading cylinder. Similarly, the feeding motor is controlled using the start button and stop button of the feeding motor. By selecting the manual debugging mode through the combo box option on the main interface, the system automatically enters the debugging interface. Figure 8. Automatic running program. When using the inching mode, as shown in Figure 9, for example, when the loading cylinder is running, and the manual debugging mode is selected, the input terminal M40 is connected to initiate the action of the loading cylinder. When the stop button of the loading cylinder is pressed, the input point M41 is connected to stop the operation of the loading cylinder. The control for other components follows a similar process. The design of the manual adjustment control program is relatively simple. The ladder diagram for manual debugging is shown in Figure 4 . Figure 9. Manual Operation Program. The manual control program and the automatic operation control program of the pusher-type automatic loading and unloading machine are isolated from each other. Therefore, a conditional jump is used to execute the corresponding control program. If the input terminal M3 is disconnected, the system will choose the manual adjustment mode and execute the automatic operation program section. On the other hand, if M3 is connected, the system will select the manual adjustment program mode and execute the manual adjustment program, skipping the automatic operation section. 6. System Application Effect After comparing the production before and after the modification, it was found that with normal employee working hours of 8 hours per day, the original production had a scrap rate of 5% caused by operator errors, a total loading and unloading time of 41 seconds, and 5 to 10 equipment failures. However, after the modification, the employee working hours were increased to 24 hours per day, the scrap rate was reduced to 1%, the total loading and unloading time was reduced to 20 seconds, and there were no equipment failures. After three weeks of continuous debugging and testing in the factory, the data shown in Chart 2 was obtained. The main advantages of this loading and unloading equipment system are the replacement of electrical controls. Using a PLC as the control system reduces labor costs, allows for increased working hours, and has an extremely low failure rate with no failures observed during testing.Figure 10: Physical Diagram 130 of Up/Down Feeding Machine. Table 2. Machining Data Before and After Modification (Three Weeks). Category Unit Production before renovation Production after renovation Total loading and unloading time s 41 20 Actual working time h 10 24 Defect rate % 5 1 Number of breakdowns times 5~10 none Figure 10. Physical Diagram of Up/Down Feeding Machine 7. Conclusion In summary, this article has designed a control system for loading and unloading specifically for lathes based on the requirements of equipping lathes with automatic loading and unloading systems. The control system is developed and researched based on the deficiencies of the loading and unloading machine. The system is PLC-based and achieves functions such as rapid automatic loading and unloading, and conveying control for the machine tool. Through practical operation in the factory, the system is capable of continuous and uninterrupted processing of 50 bars of material each time, demonstrating stable performance. This system can be applied in production to reduce labor costs and improve production efficiency. Additionally, it provides useful technology and experience for the research on control systems related to loading and unloading robotic arms in the mechanical industry. References [1] Liu Xudong, Li Xiaogang. Practice of NC lathe automation transformation [J]. Internal combustion engine and accessories, 2018 (17): 112-113. [2] Jie, Z. Fault Diagnosis Method of Relay Misoperation in Electrical Control System[J]. Internal Combustion Engine and Components, 2021(11):282-289.. [3] Z. Application of Electrical Engineering and Its Automation in Low-voltage Electrical Apparatus Relay [J]. Digital Technology and Application, 2022(05):127-129.. [4] Liu Linshan, Li Jianyong, Hao Ming. Design and implementation of a robot control system for automatic loading and unloading of truss for CNC machine tools [J]. Manufacturing Automation, 2019(a), 41 (9): 108-110. [5] Liang Yun, Tan Xiaoman. Electrical design of automatic loading and unloading system of machine tools [J]. Electromechanical Engineering Technology, 2019, 48 (6): 42- 45. [6] Junsong, Y., Jian, Z., Gonghai, F., et al. Design of Bulk Material Hoist[J]. Mechanical Engineering and Automation, 2010(2):98-100. [7] Kang Jian, Cao Guoqing, Fu Lin Mine. Optimization design and application of production process with steel ladder [J]. Shandong Coal Science and Technology, 2019, 35 (10): 113- 114+117. [8] Zheng Zedian, Chen Yinqing, Lin Wenqiang, et al. Research on the combined application of industrial robot loading and unloading technology and CNC lathe processing technology [J]. Modular machine tool and automatic processing technology, 2013 (7): 105-109. [9] Liu Linshan, Li Jianyong, Hao Ming. Design and implementation of a robot control system for automatic loading and unloading of truss for CNC machine tools [J]. Manufacturing Automation, 2019(b), 41 (9): 108-110. [10] Wei Yongqi, Ju Fengjuan. Wall-cleaning robot based on PLC [J]. Foreign Electronic Measurement Technology, 2019, 38 (9): 40-43. [11] Wang Xueliang, Zhang Qiuju. Design of PLC based manipulator automatic loading and unloading control system [J] China Manufacturing Informatization, 2012 (15): 59 – 62. [12] Chao, W., Jinyun, Y., & Dongqing, W. Study on Communication between Touch Screen and PLC in AC Charging Pile[J]. Journal of Qingdao University, 2015(03):64- 69. [13] Jifa, C., Pengfei, L., Peng, C., et al. Design of Automatic Loading and Unloading System for Vanadium Nitride Sintering Equipment Based on PLC Control[J]. Industrial Furnace, 2022(02):55-58. [14] Xiayun, L., Yong, Y., & Yulong, Y. Design and Application of Automatic Loading/Unloading System for Robot in Multi- Process Machining of Outer Ring of Bearing[J]. Modern Manufacturing Engineering, 2021(07):128-134. [15] Zeng Wenxuan, Fan Shengyao, Wang Xueliang. Research and development of automatic loading and unloading manipulator control system of gear grinding machine [J] Modular machine tool and automatic processing technology, 2012 (11): 71-74. [16] Wang Youwei, Qiu Zixue, Wang Guowei Design of temperature fuse automatic feeding machine based on PLC [J] Modular machine tool and automatic processing technology, 2015 (04): 115-118. [17] Qinzhan, T. Design of Control System for Loading and Unloading Manipulator of Key Shaft Machining Machine[J]. Journal of Guilin University of Aerospace Technology, 2019(02):200-203.