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The quality of the product, as well as the optimal use of resources and energy, are all dependent on the stability of a filling cylinder’s level and back pressure. Analysis indicated that these two factors were determinants of a fill process’s stability. The main reason for inconsistencies with liquid levels is lagging control over an inlet proportional valve; similarly, instability regarding backpressure is rooted in unsteady liquid levels compounded by delayed regulation over the said valve. Therefore it is essential to ensure consistent results when dealing with such cylinders.
Through PID control analysis, we can observe the liquid level is regulated by a filling cylinder pressure detection sensor and an inlet regulating valve for adjustment. An identical model manages the pressure control with a CO2 inlet regulating valve (see Figure 1). As both processes are similar, this paper mainly focuses on liquid-level regulation; however, it should be noted that the same principles apply to pressure control as well.
When disruption occurs with the filling machine or bottles stop, there’s a sharp decrease in raw material usage within the fill cylinder. The liquid level adjustment valve will not be able to react swiftly enough to reduce this level, leading to elevated pressure and increased liquid volume that may open up an exhaust valve and cause extra CO2 consumption.
When all is functional again, filling volumes spike quickly but will result in low-pressure levels as it takes time for the regulation valve openings to adjust accordingly, impairing quality control of output products. In such cases, PID parameters cannot solve these issues alone – more drastic measures must be taken.
When the filling machine runs at a constant rate and bottle type, such as 300B/M with 1000ML capacity, the liquid level and pressure of the filling cylinder will stay steady around their set values. Additionally, those in charge can precisely record how much to open the CO2 and liquid regulating valves – OL (for level) and OP (CO2). This ensures continual production without hindrance or stoppage.
Factors such as speed and volume of filling are recorded when observing the filling process. Analysis reveals that there is a fixed proportion between regulating valve opening and the number of bottles filled simultaneously when it comes to the same bottle type and speed. Consequently, if either production speed or the number of bottles increases, more stations will be needed to complete the task – this can be regulated via feedforward control about the current quantity being filled. Similarly, coefficients related to both filling velocity and capacity would have to be adjusted for feedforward coefficient KL (as well as pressure KP) to reach 1; meanwhile, SUBL (pressure SUBP) records how many containers are currently full while liquid level DL together with pressure DP act as additional data sources during feedforward regulation.
To accurately determine the number of stations needed to fill at various capacities, we utilize SL. This method establishes a total station count using a liquid-level pressure feedforward calculation equation. With this formula, filling speeds can be adjusted as desired and accurately.
To simplify and streamline the implementation of field setup and maintenance, two coefficients, the filling speed coefficient, and the filling capacity coefficient, are used in conjunction with the SL-tested condition to generate a level pressure feedforward formula.
When bottles enter the filling machine, the feedforward value steadily rises by the current SUBL until it reaches its maximum stable point. The regulating valve is opened just before changes to the cylinder level occur, and then PID control is fed through feedback levels which cancel out any impact of feedforward control on output. As soon as the machine has stopped adding bottles, this same process happens but is reversed; simply put – feedforward values fall back down to 0 while gradually decreasing the opening size from the regulator valve until it completely closes off again. Consequently, a balance between pressure and level is accomplished for optimal regulation stability.
This program is created to provide a formula for calculating filling speed and volume coefficients so that only one SL needs to be tested per condition. Doing so will generate feedforward values which can then be automatically utilized in other speeds and volumes – making it unnecessary to repeatedly test the SL each time.
Incorporating the data from Figure 2 into our DB block enables independence between a function program and its associated information and direct integration of necessary functions into filling equipment. Parameter settings such as level/pressure regulating valve opening, feedforward coefficient, volume coefficient, starting position of the opening valve, and the number of open positions can be directly adjusted via HMI, while other processed data obtained by programming is also integrated for later use.
Before any non-volume filling machines can function correctly, the speed ratio and final destination must first be computed. An HMI (Human Machine Interface) only performs this essential process. Failing this procedure will cause these machines to work incorrectly.
To accurately measure the exact amount of full and empty bottles, we use a bottle detection technique that counts both their initial quantity as well as how many were left in the end, thus giving us an accurate final count.
Figure 4 illustrates the shiftdb.shift1[“disdb”.SL1] data is the bottle signal at the start of a valve opening. This figure also outlines how to convert and store this information in terms of its real data type for program calculation purposes. Moreover, shiftdb.shift1 array data originating from an original shift program plus input.sync_pulse (which generates one pulse per rotational cycle) are incorporated into machine filling operations too!
The feedforward formula is programmed into the software, and its resulting output, calculated feedforward, is incorporated into the PID control.
Enhance the HMI screen with pressure feedforward coefficients, valve opening volume coefficients, and other pertinent additions, as indicated in Figure 6.
Precise real-time counting was conducted for each filling valve head to optimize the feeder control. After fine-tuning the system, an astonishing result emerged; it became feasible to regulate the level of liquid inlet cylinder within 6mm without any venting caused by bottle stop/stop after instigating a new program! As Figure 7 depicts below – which compares the liquid levels before and after optimization on one particular site – there is a marked decrease in deviation.
iBottling, with over 25 years in manufacturing beverage filling machine, has developed an integrated feedforward control system engineered to streamline the filling process for better production efficiency. With our system, you can ensure utmost precision and accuracy with every pour. Contact us today to find out how we can revolutionize the way you fill your beverages.