Bottling with EPSI machines

PC based control yields better filling machine accuracy and speed

For those who work with liquid products, filling containers requires developing a balance between the problems of precision filling versus the speed of the filling process. Beverage companies such as Motts Apple Juice (Aspers,.PA), a division of Cadbury Beverages Inc., typically had to rely on volumetric or level filling systems which offered limited fill accuracy. To guarantee meeting stated minimum requirements, the company adjusted its filling process to add a little extra product to each container. This fractional overfill, can actually grow in to hundreds-of-thousands of dollars in added product cost per year. Slowing the machinery to enable more accurate fills also lowers system productivity, resulting in distribution headaches and lower return on capital investments, among other business issues.

This predicament exists because traditional filling machine manufacturers have been slow to recognize new technologies to control the filling process. Since machine downtime and the resulting lost production can cost a fortune, filling machine vendors have done little to increase filling accuracy or bottling speed when the result could be the loss of a customer due to problems with new designs; especially if a problem relates to software.

Once a supplier develops a filling machine with a proven service record, only incremental improvements would evolve over the machines product life. In microprocessor based designs for net weight control, decade old technology was often still alive.

A full filling opportunity

Engineered Products & Systems Inc. (EPSI) is a company consisting mostly of engineers and service people with more than 60 man years of experience designing, installing, and servicing liquid filling machines. Their goal is to build better filling machines and to retrofit existing machines with up-to-date "open-architecture" control technology that allow machines to fill containers at significantly higher speeds with a greater degree of accuracy. EPSI's customers save on product costs while increasing system productivity. The use of standard control and mechanical components also reduces the cost of downtime and maintenance.

Real-time focus

EPSI decided to develop a Window/PC-based real-time control and MMI system. This led to the selection of Wizdom Controls' Paradym-31 Soft-Logic for real-time machine control. It integrates a Windows-based program development environment, program simulation, and a real-time operating system for the PC. It includes the ability to handle floating-point numbers and the construction of your own, user defined function blocks.

Also, it lets you develop special procedures using "C", a powerful low level language, but yet allows someone who is familiar with typical PLC programming to write or modify programs used in the filling process. Automated program documentation and cross-referencing develops good documentation, and makes debugging easier. In simulation mode, one knows, which SFC block is active and operating. You can go into that block and monitor its operation or even monitor the variables used by an individual function block.

A typical configuration for the PC control system consists of two computers. One includes the operator interface and supervisory control connection to the SCADA package. The interface incorporates some line control, the ability to display alarms for the operator, and some Statistical Process Control (SPC) capabilities. EPSI's use allows their customers to add other options found in the HMI software and to integrate the filling machine into a total line control system as desired.

A second PC onboard the filler runs Paradym-31in DOS mode and controls the loadcells and other I/O. The operator uses the operator interface to select the different functions of the filling system. The two systems are linked via an ARCnet network.

The HMI software is tightly linked to the control part via a standard available drive.

Performance

With this filling system, the amount of overfills are significantly reduced, while improving significantly the performance of the typical production line.

Besides easily identifiable payback on investment, the system also offers flexibility in operation and alternative filling strategies. As a net weight machine they can also identify containers that are out of specification, and be setup to not fill them. In a particular application a container may be rinsed with a pre-fill solution, which becomes part of the product. To compensate for this the machine can be setup to use a fixed container weight. By doing this the residual product left in the container will have no effect on the tare weight of the container.

Paradym-31 Program Development

This package allows users to develop and debug real-time control operations on a personal computer off-line. Since the development environment is the same as the operating environment, the porting of the program to the target system is easier. It is based on the IEC 61131-3 standard which enables intelligent devices to be programmed in multiple languages. These programming languages can be combined to simplify programming.

In general, program development starts by laying out function blocks in order of operation. The function blocks can be connected in sequence, branched and even "looped back" to repeat the operation. The use of Sequential Function Charts (SFCs) allows users to logically lay out the broad levels of control system functionality. With SFC programming, only an active block is operational. EPSI's control system has three branches for production, maintenance and calibration, and CIP operations. Each branch is activated at the operator station, ensuring that the filling machine won't accidentally start running during CIP or maintenance.

At each function block, a program developer can use Ladder Diagram (LD), to program the electrical input and output functionality. Included are a library of standard symbols and functions, as well as for the SFC operation.

For special functions a function block library is included, supporting complex operations such as calculations, networking, interfaces to input/output devices and signal conversion. User-defined function blocks can be added to the ladder logic, also by using C++ programming.

As the program is written, the developer can simulate operation and use a cross-referencing capability to troubleshoot and debug the program; this can also be used for program documentation. When the program is ready, the developer compiles and ports the program to the target PC.

EPSI new 48-head filling machine for Motts is saving the company hundreds of thousands of dollars in product costs, thanks to better filling control. With the world's largest net weight filling machine, Motts has increased its line speed more than 50%.