A Pinch of SERCOS, a Dash of Ethernet

Manufacturers rely on packaging machine builders to provide a simple, unambiguous function. They need machines that reliably move products into containers without damaging the products or the containers.

To fill those packaging needs, many of these manufacturers turn to Triangle Package Machinery, a Chicago-based industrial OEM established in 1923. Triangle designs and builds packaging machinery and equipment to help food, industrial, medical, electronics, and other industries meet their demanding packaging requirements.

The Triangle/FlexCell cartoner (Figure 1) was designed to meet customer requirements for a bag-in-box cartoner with a small footprint that could run 90-100 cartons/min. with minimal changeover time. Before the introduction of the FlexCell, large continuous motion cartoners operating at speeds up to 250 cartons/min. were the only solution.

However, meeting throughput requirements with these cartoners often was costly and consumed too much floor space. To deal with the floor space requirements, intermittent-motion cartoners topping out at 50-60 cartons/min. were employed.

Triangle created its Triangle/FlexCell cartoner to fill the gap between continuous and intermittent-motion cartoners. The sidebar details the performance improvements.

The FlexCell features a completely different way of advancing cartons and loading bags into the cartons. Instead of using gearboxes and shafts to transport the carton through the machine--a traditional lineshaft approach--the machine uses integrated motion control with digital servo drives and motors (Figure 2).

Because the machine design featured many new components, it was necessary for us to choose a completely new control system. We were able to start with a blank slate and select the control system that best met our requirements for machine control, motion control, and communications.

As is the case with many industrial OEMs, our clients generally prefer one brand of control system components over another. Several of our major customers specify Rockwell Automation for machine controls. If Rockwell has a solution that fits our needs, we generally try to use their products to ease customer acceptance.

We were familiar with many of the older Rockwell controllers, but none of them met our design criteria. We reviewed Rockwell's ControlLogix controller and found it had most of the features we needed, including a single control platform for the integration of logic and motion control.

The cartoner also makes extensive use of advanced networking services for integration of control system components including an HMI, the controller, variable-frequency drives (VFDs), servos, and sensors.

The ControlLogix platform also has third-party options, which give it flexibility that we plan to use for future designs. A multiaxis stepper card is available from AMCI (www.amci.com) and a Pentium PC-compatible coprocessor card from Online Development (www.oldi.com) with full backplane communications are just two that we are currently testing.

One of the most important features of the ControlLogix controller is its ability to simultaneously support multiple communication protocols. We needed digital networking for a variety of tasks including communication with client computing systems, between the controller and the HMI, between the controller and the servo drives, between the controller and the VFDs, and between the controller and the sensors (Figure 3).

Our evaluation revealed that different network tasks were best performed by entirely different types of digital communications protocols (Table I). We looked at the communication requirements, and ended up employing different networks to meet our machine control and communication requirements.

Perhaps the most critical network in the FlexCell is the digital link among the controllers and the servo drives. We use six servo drives in our base model machine, and there are two common options that require servo drives, so our machine can employ up to eight servo drives.

The servo network had to be high-speed, noise-immune, and optimized for servo control and communications. SERCOS met all our communications requirements, and the protocol is fully supported by the ControlLogix platform.

We use an eight-axis motion control card with SERCOS communications to and among digital servo drives. The main processor has access to all the servo information because the motion controller is part of the PLC system.