With the improvement of the living standard of the population, the demand for beverages in China is growing rapidly. In order to adapt to this demand, beverage manufacturers continue to expand the scale of production. While expanding the scale, how to ensure product quality and improve production efficiency is particularly important. Beverage automatic filling machine is the main production equipment indispensable to the beverage industry, the liquid level control of the liquid filling process, filling pressure control, synchronized speed control is an important guarantee of filling quality. This paper proposes to control the multistage speed regulation of the frequency converter through the output of the programmable controller, so that the motor speed follows the detected feedback signal and realizes the automatic control of the speed of the conveyor belt of the filling beverage, which matches the speed of the filling machine and improves the efficiency of industrial production. The design of the programmable controller and inverter control is fully integrated, the switching output of the programmable controller is directly connected to the switching input of the inverter, which has many features such as easy operation, stable and reliable operation. And the use of configuration software designed automatic filling machine real-time monitoring screen, the production process of the parameters of the measurement and control points, the dynamic image of the process will be displayed in real time on the monitoring screen. Convenient for production managers to understand the production progress and equipment operation, to make timely and effective decision-making, to ensure the safety and efficiency of production.

1 system overall design

The filling system is based on PLC and inverter as the core, through a variety of sensors and I / O data acquisition card, the automatic filling machine actuators into the real-time control and adjustment of the automation control system. The filling system needs to control the object including the production station of the conveyor motor, protective gas valve, filling valve, under the cap mechanism, capping mechanism, need to collect data including storage tank, online bottle level, protective gas pressure, filling liquid flow rate, empty / full bottle conveyor belt speed, empty and full of bottles in place, stacking blockage, under the cap, open and close the state of loading piston valve. The automatic filling machine consists of conveyor belt and filling liquid tank, the conveyor belt is dragged by motor. The motor can be turned forward and reverse. When the motor is rotating positively, the conveyed cans pass through the 4 stations of empty can position, filling position, full can and terminal in sequence.

Control panel including metering filling machine console is equipped with ordinary lower machine control panel and upper machine HMI (human-machine interface) two kinds of equipment, respectively, can be implemented on the automatic filling machine control.

Lower machine control panel requirements: the lower machine using an ordinary control panel, the control panel requires the design of start and stop buttons, emergency stop button, lower (PLC) / upper (HMI) selector switch, manual / automatic selector switch, positive and negative rotation switch, fault reset buttons, counters, counter zero buttons and a variety of indicator lights.

Upper HMI: The upper HMI requires the HMI device to use TP177BcolorPN/DP touch screen as the control device.

Control device: the whole system requires the use of Siemens programmable controller S7-300 for control and management of the lower computer, the upper computer requires the use of configuration software WinccFlexible, the site status with graphics, tables, curves and other dynamic reproduced on the TP177BcolorPN/DP touch screen, the site to monitor!

Drive device: requires the use of Siemens MM440 series inverter drive conveyor belt motor, and requires programmable controller S7-300 through the Profibus-DP network and MM440 series inverter can communicate with the control, inverter drive motor.

Control mode: weighing and filling machine needs to be designed for manual and automatic two working modes. The manual mode is used for the commissioning of the equipment and the reset of the full tank count value. Automatic mode allows to start the weighing and filling machine operation.

System failure and alarm: the control system should be equipped with emergency handling and fault diagnosis and display reporting functions. When equipment failure occurs, the control system can respond immediately, in the control panel or HMI on the corresponding indicator light flashes, after the fault is eliminated, only press the fault reset button, the filling machine can run automatically.

Other requirements of the control system: emergency stop protection and counting and display functions, liquid level monitoring function in the filling tank.

The working principle of the system: the site speed sensor, pressure transmitter, pile blocking photoelectric sensors, liquid level sensors and a variety of on-site switching devices will be collected signals to the PLC, the PLC according to the status of the collected signals. Call the corresponding control program or algorithm for data processing, and then the control object for real-time control and regulation. At the same time in the control, PLC will through the industrial Ethernet will control the real-time status of the object and the collection of devices to the upper PC server, and dynamic display in the monitoring screen.

2 Hardware design

According to the filling equipment control and process requirements, after analyzing the control relationship of the field control equipment, this system uses HP PC, Siemens PLC (S7-300) and frequency converter (MM440) to form the upper and lower two-level automatic control system. The upper PC is located in the main control room, the main role is to communicate with the S7-300 real-time communication, access to real-time data on the automatic filling machine, and display the filling process, prompting alarms, report curve generation and printing, real-time data storage for querying.PLC for the lower device control layer, mainly on the system logic, inverter speed section, the start and stop of the control broad, liquid level data acquisition and other control. PLC is the lower equipment control layer, mainly controlling the system logic, inverter speed section, start and stop of each control broad, liquid level data collection, etc. And through the industrial Ethernet and host PC communication, transmission of various parameters in the production process.

2.1 PLC selection

The system selects SMIATICS7-300 series PLC, which is equipped with rich instruction system, easy for users to program, with a wealth of special modules and communication capabilities, very suitable for application in automated production control system.S7-300 series PLC has six basic CPU models, according to the system needs to detect and control parameters, the system selects CPU315-2DP, which can be connected with 32 expansion modules with RS-485 interface and ProfibusDP interface. According to the requirements of control and Yuan Yu configuration, the choice of 32 points of input modules, a 32-point output module. Because of the liquid level, pressure and other analog signals for measurement and control, it is selected 8-point analog input and output hybrid module. As the measurement and control points are located in various different positions of the automatic filling machine, the distance is far away, direct control with S7-300 will be subject to electromagnetic signal interference to reduce the reliability of the system, so the system adopts a distributed I / O control device ET200M. It is as a slave of the S7-300, real-time data communication with the master station through ProfibusDP.

2.2 Selection of frequency converter

The frequency converter selects Siemens MM440 type frequency converter, this type of frequency converter supports both cyclic data communication with the master station and non-cyclic communication with the master station, in order to be able to realize the communication between S7-300 and the frequency converter through ProfibusDP protocol, the system selects CB communication module to be added on the MM440.

3 software design

According to the beverage filling process and control requirements, the system software design is divided into PLC control and monitoring screen software design. all the functions of the PLC control system are realized inside the main loop OB1. OB1 according to the control needs, call each function function module to achieve the control functions 3. the system main program flowchart is shown in Figure 4. Limited to space, here mainly introduces the PLC and inverter communication program and monitoring screen software design.

3.1 PLC and inverter communication design

The communication between PLC and inverter in this system adopts ProfibusDP bus mode. The communication medium adopts shielded twisted pair cable or fiber optic cable.S7-300 uses function block SFC14/SFC15 to read and modify the parameter values of MM440 so that the inverter can control the motor according to the system requirements and read the current voltage, current and frequency values of the motor in real time.

3.2 Monitoring configuration software design

As a sub-system of the upper computer control information management system of the automatic beverage filling machine, the monitoring screen plays a very important role. It realizes the remote control and real-time monitoring of the whole filling process. The system selects wincc6.2 industrial configuration software as the upper computer control software development platform.

The main monitoring screen of the automatic filling machine collects the working status of the transfer motor, protective gas valve, filling valve, capping mechanism, capping mechanism, storage cylinder, online bottle level, protective gas pressure, liquid flow rate during filling, speed of the conveyor belt of empty/full bottles, the status of empty/full bottles in place, stacking and blocking, capping, and opening/closing of the piston valve in real time, and the management personnel are able to monitor the operation status of the entire automatic filling machine equipment through the main monitoring screen. The manager is able to monitor the running status of the whole automatic filling machine equipment through the main monitoring screen. When the liquid level, gas pressure and belt speed exceed the alarm limit, the monitoring system can display the alarm information through the alarm interface. The system report will record the historical information of each signal collection point and reflect the trend of information change in the form of curve. Parameter setting can modify the liquid level, gas pressure, belt speed, frequency converter frequency and other parameters, the operator can operate according to the actual situation.

4 Conclusion

In this paper, the use of PLC, frequency converter and configuration software design of liquid filling, gives the system software, hardware design and communication design process method. The actual application results show that the system is safe, reliable and easy to operate. As a modern industry in the filling production line of the main control equipment PLC, inverter with its excellent characteristics in the actual control engineering has been widely used.