1 Introduction
Machine tools are an indispensable piece of equipment in the machinery manufacturing industry. The precise coordination of their various mechanical transmission systems and electrical control systems is essential to ensure the normal or even excessive completion of workloads. Furthermore, only through continuous optimization and updating of the PLC design within the control system can we promote the vigorous development of China's manufacturing industry and elevate the level of machine tool control to a higher level.
2. Principle of Mechanical Press Control System
Figure 1 Control principle diagram
As shown in Figure 1, the PLC is the core of the control system. Input signals include sensors and proximity switches, movement buttons, limit switches, cam switches, two-hand output operating stations, pressure switches, and level switches. Its output signals control intermediate relays, contactors, solenoid valves, and indicator lights. It can perform fine-tuning, inching, single-stroke, and continuous preset stroke control; it can perform timed control and monitoring of the lubrication system; it can perform hydraulic overload protection control and automatic adjustment and monitoring of the balancer's air pressure; and it utilizes cams to achieve single-stroke anti-repetition. This simplifies the system structure, facilitates the operation and monitoring of the press, and improves safety performance analysis. The press should not be placed in an exposed external environment. The ambient temperature should be between -5 and 40℃, and the environment should be dry, well-ventilated, and free from acid and alkali corrosion. The press has necessary operating, indicating, interlocking, and safety protection devices, conforming to GB5226-2002 "General Technical Conditions for Electrical Equipment of Machine Tools" and JB3350-83 "Safety Technical Conditions for Mechanical Presses".
3. System Overall Control Scheme Design
3.1 Hardware System Design
The core of the press control system is an Omron CJ2M-CPU33 programmable controller, a D-network communication tab, two safety relays (PZHZ X4P, PNOZ X2.8P), an OMRON RS-422/485 option board, a power module, an I/O control unit, a 0.7m connecting cable, an I/O interface unit, a temperature control unit, an analog module, a relay output module, a DC input unit, a bus module, and a DeviceNet communication module, all installed in the electrical control cabinet. For ease of machine operation and maintenance, in addition to necessary indicator lights, the control panel is equipped with a PRO-FACE GP4501TADW touchscreen, rated at DC24V and 10.4 inches in size, used to indicate the operating status and parameter settings of the press's main control circuits, such as control pressure, mold height, and air cushion stroke. This press adopts a series of mechatronics technologies. The main motor is an AC variable frequency motor, and the stroke control and other auxiliary actions are controlled by electronic cam switches. It has a lubrication frequency detection function, which can display the number of oil supply to key lubrication points on the touch screen. It also uses digital measurement and control technology and has a mold height adjustment function.
The PLC and frequency converter are connected. The pressure flywheel and transmission system are implemented by a three-phase asynchronous motor with a rated voltage of AC380V and a rated frequency of 50Hz. The PLC communicates with the frequency converter through an Ethernet local area network. The speed control and feedback of the actual current speed, as well as the monitoring of start/stop, three-phase line voltage, and current, are achieved through messages with set tag names and addresses. The standard topology of Ethernet is a bus topology, a computer local area network technology. The IEEE 802.3 standard, organized by the IEEE, defines the Ethernet technology standard, specifying the content including physical layer connections, electronic signals, and media access layer protocols. This makes node connection faster, more stable, more accurate, and more effective in industrial environments. The connection between the PLC and the touch screen also uses Ethernet communication to create a touch screen display, monitor corresponding address information, and change various parameter values. DeviceNet is a fieldbus standard for automation technology manufactured by Allen-Bradley, Inc. The PLC carries a DeviceNet module, and the PLC connects to the electronic cam and angle indicator through the DeviceNet communication module to monitor the slider angle in real time. Figure 2 shows the network communication diagram. Figures 3 and 4 are the I/O address allocation tables for the operator station. The hardware wiring is configured by the wiring diagram and schematic diagram. The schematic diagram and wiring diagram are not shown here.
Figure 2 Network communication diagram
Figure 3 Key Input Address Allocation Table for Operator Station
Figure 4. Dual-valve control output address allocation
3.2 Hardware Communication Configuration
(1) Because the selected frequency converter is the AB755 series, an intermediate EDS file is required for communication with the Omron PLC. First, connect the frequency converter and the PC with a network cable, set up a common IP network segment, install the EDS file using RS-Linx, scan the frequency converter nodes, and set the inherent IP address. Then, use the Network Configurator in the OMRON software to achieve communication via EIP. After scanning the network nodes and setting up the tag speed setting and feedback, the communication is completed.
Figure 5. Label name length setting
Figure 6 Configuration completion interface
Then, by matching the speed input and feedback address in the PLC symbol with the set label name, the inverter can be operated by setting the number of times the operator station is used. Below is the program segment for setting and feeding back the main motor speed.
advertise
closure
Application Case | Beckhoff TwinCAT TCP/IP Opens Up Infinite Possibilities for Network Communication Figure 7 Main Motor Control Program
(2) To achieve EIP communication between the Pro-face touchscreen and the PLC, connect the two with a network cable. Set the same IP address range on both the PC and HIM ends, and then download the edited touchscreen program to the touchscreen. At the same time, the offline HIM needs to input the PLC's IP address on the touchscreen. PLC IP: 192.168.1.99, Touchscreen IP: 192.168.1.10, Inverter IP: 192.168.1.5.
Figure 8. Relationship between the various screens in the human-computer interface
This section introduces some of the functional components and principles involved in creating visuals.
Position switches: used for signal input in the screen; function switches: used for switching between screens; indicator lights: used to distinguish between two different states; numerical displays and time displays: directly display the required values and time consistent with the system, making each screen more consistent and neat; text, images, etc.
By utilizing the dialogue function between the human-machine interface (HMI) and the PLC, input/output signals and some important relay signals are displayed on the touchscreen as text and color-changing diagrams, forming a workflow diagram of the working status. Work status flow nodes are displayed in green for continuity and red for interruption. Figure 9 shows the monitoring of important parameters for various parts of the machine tool, and Figure 10 shows the monitoring of main lubrication. When an abnormal number of lubrication cycles occurs, the touchscreen displays a red alarm indicator for the current lubrication fault. Figure 11 shows the operation prompt interface for each part. When the fault alarm indicator on the left changes from green to red, it indicates a fault in that part, requiring corresponding hardware checks and program tests. A screen switching switch for the main functions is located on the right, and the corresponding screen number content is added to the program for further detailed monitoring of all work steps, providing a reliable basis for the analysis of the press's working status.
Figure 9 Machine tool status monitoring interface
Figure 10 Lubrication status monitoring
Figure 11 Operation prompt interface
4. Main program segments and operation flow
The main lubrication process: The press lubrication system consists of an oil tank, oil pump, oil filter, pressure relay, and oil distributor. A set of high and low oil level detection switches, along with several oil pumps and oil filters, are mounted on the oil tank. Operation and status displays are centralized on the operator station. Pressing the "Oil Pump Start" button illuminates the "Oil Pump Running" indicator light. After one minute of pump operation, the "Normal Lubrication" indicator light illuminates, indicating that the lubrication system is working normally. If the "Filter Clogged" indicator light illuminates, it indicates that impurities in the lubricating oil have clogged the filter, which should be cleaned. During oil tank refilling, pay attention to the "High Oil Level" indicator light on the touchscreen; if it illuminates, the tank is full, and refilling should be stopped. After the oil pump starts running, the lubrication status of the main machine tool components is checked using proximity switches. Specifically, the main oil distributor and connecting rod secondary oil distributor undergo lubrication number checks. Once the required number of lubrication cycles for each component is met, lubrication is considered normal. Normal lubrication serves as a condition for interlocking the main motor and stroke actions.
(1) Lubrication frequency monitoring program segment and operation procedure
Figure 12 Lubrication monitoring program segment and operation flow
(2) As shown in Figure (13), the program segment of the double valve start relay and the start operation of the main motor are shown.
Figure 13 Clutch-brake valve assembly start-up procedure and main motor start-up
