1. Introduction
The beer production process consists of several steps, including malt production, wort production, primary fermentation, secondary fermentation, filtration and sterilization, and packaging. The beer bottling and capping machines belong to the packaging process. After being filtered through a membrane, beer is piped into a rotary brewing tank, then through a valve into bottles, and finally capped to obtain bottled beer. The efficiency and automation level of the beer bottling and capping machines directly affect the daily beer production.
In order to meet the growing production scale of my country's beer industry and the high-speed filling requirements of modern beer filling machinery, domestic beer manufacturers are actively seeking or upgrading their beer filling production equipment to make it a modern beer filling machine with good performance, advanced technology, high production efficiency, stable and reliable operation, and low maintenance costs.
2. Working principle and control components of beer filling and capping machines
Liquid filling machines can be classified into atmospheric pressure filling machines, pressure filling machines, and vacuum filling machines according to their filling principle. Beer filling and capping machines use the pressure filling method, which involves filling at a pressure higher than atmospheric pressure. The pressure inside the storage tank is higher than the pressure inside the bottle, and the beer liquid flows into the bottle due to the pressure difference.
Currently, the basic bottling process at home and abroad is as follows: Utilizing the rotational motion of a rotary beer tank, an empty bottle placed in the tank's slot is used to open a vacuum valve fixed to the top of the tank via a mechanical mechanism. This allows for vacuuming of the sealed bottle. The external operating valve is then turned to open the gas valve, filling the bottle with CO2 gas. A vacuum cam continues to open the vacuum valve, extracting the air and CO2 mixture from the bottle. The gas valve reopens, filling the bottle with CO2 gas. The liquid valve inside the filling valve opens when the pressure inside the bottle approaches the back pressure of the gas, allowing the beer to flow down the bottle wall. Beer is then filled using a pneumatic or electric control of the filling valve.
The control system of today's advanced international beer filling and capping machines mainly consists of a photoelectric switch position detection unit, a bottle conveyor belt, a variable frequency speed control unit for the speed of the beer tank, and a main control unit composed of a programmable logic controller (PLC) and a touch screen. The mechanical structure of the filling and capping machine is fully integrated with modern automatic control technologies such as PLC programmable control, variable frequency stepless speed regulation, and human-machine interface, forming a mechatronics system.
3. Control System Modification Plan
The automation levels of the control systems used by many beer manufacturers in China for their bottling and capping machines vary considerably. All manual buttons and process switches are located on the control panel of a single control box. Most PLC controllers are early products from Japanese companies like OMRON or Mitsubishi. The equipment has few interlocking controls and protection features. In addition, the harsh environment and high humidity at beer bottling sites cause severe corrosion of contacts such as switches, resulting in a high failure rate in the system's signal detection components. This leads to low reliability of the equipment control system and short normal operating cycles.
Taking the control system of the filling and capping machine at Dandong Yalu River Beer Co., Ltd., which underwent actual modification, as an example, this paper introduces the modification method and clarifies the control concept and approach for modifying this type of equipment. Based on the actual on-site process conditions, the PLC operating program was rewritten. The PLC control system of the beer filling and capping machine was redesigned according to the actual situation of the on-site process conditions. This modification method and approach can also be applied to the modification of other liquid medium filling equipment.
3.1 System Hardware Configuration
The two OMRON C60PPLCs in the original system were replaced with a Mitsubishi FX2N128MR PLC. The original PLCs were older models, requiring a special communication converter for computer connectivity, and expansion modules were difficult to find when additional external I/O input points were needed. The FX2N128MR PLC is a box-type controller with 128 integrated I/O points, offering advantages such as fast processing speed, rich instruction set, high performance-price ratio, simple online programming, and convenient expansion. It is the most powerful small controller in the Mitsubishi FX series.
(1) The original system's panel buttons were replaced with Mitsubishi's 900 series 970GOT HMI touchscreen, which monitors and displays the operating parameters of the device. The 970GOTHMI is a high-brightness 16-color display that is directly connected to the CPU of the FX2N128MR PLC via a bus connection to achieve fast response. It has many maintenance functions, such as list editing function, ladder diagram monitoring (fault finding) function, and system monitoring function, which are used to find faults and maintain the PLC system.
(2) The frequency converters of the filling and capping machines were not replaced during the renovation. The on-site signal detection method still adopts switch detection. Since the detection switch works in a high humidity environment for a long time, a capacitor-type proximity switch is selected. According to the wiring method of the PLCI/O terminals, a PNP type proximity switch is selected.
3.2 System Programming
The core focus of the PLC controller program design revolves around controlling the rotation speed of the wine tank and detecting and shifting the positions of 60 bottles on the tank, as well as detecting and shifting the positions of broken and empty bottles and controlling related filling valves. The bottle shift detection program utilizes Mitsubishi PLC left-shift instructions, which execute an N2-bit shift each time the drive condition input changes from OFF to ON, where N2 represents the number of bits shifted.
(1) Bottle displacement subroutine 413LDX055; Machine counting pulse measurement and detection input point 414PLSM49; Main motor speed measurement and detection input point (take the bit after the differential of the rising edge) M49 416PLFM301; Main motor speed measurement and detection input point (take the bit after the differential of the falling edge) M301 418LDIM590; Bottle number detection 419ANIX005; Interlock protection point 420ANIX006; Emergency stop protection 421OUTM50; Bottle position detection 422LDM49; Main motor speed measurement and detection input point 423SFTLM50M500K60K1 Bottle displacement detection
The PLC uses a left-shift instruction, which is one of the core instructions of the entire sub-control program. The main motor and bottle position detection switches synchronously detect the moving bottles. Each revolution of the main motor corresponds to the wine tank passing through one bottle position. The PLC internal unit corresponding to these 60 bottle positions is designated as M500~M559. The number of units is set to K60 using the first letter K, and each change of one position is set to K1 using the second letter K. M50 reflects the empty or missing bottle position and shifts the detected position down at the frequency of the motor speed. The corresponding internal unit contains "1" or "0" to control the opening and stopping of the corresponding valve and the stirring cap motor. After continuously detecting 90 empty bottle positions, the system stops the stirring cap motor. The number of bottle positions detected can be arbitrarily set according to user requirements.
432LDX052 Bottle Discharge Position Detection
During the process of filling bottles with wine by back-pressing them with pressure in a rotary vat, an empty bottle may suddenly burst due to cracks or other reasons after back-pressing. In this case, it is necessary to detect the location of the burst bottle, open the purge solenoid valve at the location, spray compressed air to blow the broken bottle fragments away from the position, and after purging several bottle locations, open the spray solenoid valve to spray high-pressure water jets to spray several bottle locations around the broken bottle location.
(2) Stepper control for realizing bottle burst detection and control 482LDX055; Machine counting pulse measurement and detection input point 483PLSM49; Main motor speed measurement and detection input point (take the bit after the differential of the rising edge) M49 485PLFM309; Main motor speed measurement and detection input point (take the bit after the differential of the falling edge) M309 486LDIM70; Bottle breakage position detection 487ANIM071; Continuous bottle breakage position detection 488ANIX052; Bottle inlet position 489SFTLM52M600K20K1
The broken bottle detection and bottle position detection switches synchronously detect moving broken bottles. Each revolution of the main motor corresponds to the wine tank rotating through one bottle position. The PLC internal unit corresponding to these 20 broken bottle positions is designated M600~M619. The number of units is set to K20 using the first letter K, and K1 using the second letter K for each position change. M52 reflects the broken bottle position and shifts the detected position down at the frequency of the motor speed. Internally, the corresponding unit contains "1" or "0" to control the opening and stopping of the corresponding spray and purge solenoid valves. The opening and stopping times of the continuous spray and purge solenoid valves can be arbitrarily set according to process requirements.
The reliable guarantee for the automated operation of the system is the synchronous tracking of the bottle cap entering and exiting, which involves accurately detecting three conditions: the motor speed detection switch, the bottle breakage detection switch, and the bottle entry detection switch.
(3) The software of the 970GOT human-machine interface touch screen terminal adopts the GTWORKS software package from Mitsubishi Corporation, of which GTDesigner is a drawing suite software used throughout the GOT9000 series. This software package is easy to operate and can be configured and simulated on a personal computer beforehand, and then downloaded to the human-machine interface terminal. At the same time, since the human-machine interface also functions as a touch screen, commonly used switches are placed on the display screen for easy operation. Some functions can also be added, such as setting alarm information.
4. Functions of the modified control system
When the system is running normally, the machine is automatically controlled. It operates at a set speed or slow speed based on the fullness of the bottles on the inlet/outlet conveyor belt. It features functions such as bottle stopping, no capping without a bottle, automatic rinsing in case of bottle bursting, automatic back pressure at the filling position, and coordinated interlocking of the automatic start/stop of the cap conveyor system and safety protection mechanisms. All operations that were previously performed by buttons are now controlled via a touchscreen.
5. Monitoring function of the control system detection status
The bottle inlet detection switch and the bottle breakage detection switch generate photoelectric pulse outputs by detecting the position of the small iron pieces on each bottle pressing section. The PLC then collects the pulses. Since the position of the small iron pieces on each bottle pressing section is movable, after the machine has been running for a period of time, the positions of the small iron pieces on the bottle pressing section and the detection switches may shift, causing the detection switches to misjudge, such as misjudging a bottle when there is none, missing or misjudging a broken bottle, etc. This leads to output errors, causing the PLC to malfunction, resulting in faults such as back pressure, broken bottle blowing, washing, and malfunction of the bottle cap stirring system.
Before the upgrade, when this phenomenon occurred during daily production, operators could only switch all function switches or buttons to manual control, leaving the machinery unmonitored and losing its automatic control function. This resulted in significant waste of production materials such as gas, water, and alcohol. Only during production breaks could maintenance fitters and electricians adjust the installation position of the small LED on the detection switch (which has a displacement distance of only 5-8mm) to correct the gap between the detection switch and the small metal plate, based on the on/off status of the LED. This detection method was extremely outdated, and the effect of the adjustment was delayed, failing to reflect the results promptly.
In response to this detection situation, this detection function was added to the modified filling and capping machine control system and integrated into the human-machine touch screen to complete bottle position detection.
The human-machine interface touch screen displays the status of 60 bottles in real time and the status of bottles when they explode. The status of detection switches such as bottle presence, no bottle, bottle explosion, back pressure switch, and solenoid valves such as stirring motor are displayed in different colors, which is very intuitive.
When the position of the detection switch and small metal piece needs to be adjusted, maintenance personnel can make adjustments online without stopping the machine under normal production conditions, simply by checking the bottle position on the display screen, and immediately see the effect of the adjustment. In routine maintenance, it can also be used as a status monitoring device to observe the operating status of the output equipment. This system function was specifically designed to ensure the normal operation of the automated control system of the filling and capping machine.
6. Conclusion
The upgraded control system significantly simplifies the complex mechanical structure. Field operation and control performance testing have verified that the system's automation level meets design requirements, greatly reducing the workload of operators and increasing daily beer canning output by over 30% while significantly reducing the failure rate. It embodies modern automatic control technology and is currently the most advanced filling control system in China, developed through innovation based on the digestion and absorption of advanced industrial control technologies.
