The system erects cardboard trays for packaging the cassettes, prints and applies the labels, and performs vision inspection on the applied labels—all on an extremely compact 3-by-3-foot floor area. The blood-testing cassettes are filled with a mix of glass beads and reagent, which is monitored by the vision-inspection system in order to guarantee correct filling, i.e. a proper fill mixture. To enable precise measurement of the fill ratio, Wierciszewski Controls developed an accumulation table with a 4-by-4-foot floor space for 600 cassettes and a throughput of 80 cassettes per minute. The table not only meets the customer's size and speed requirements, but also integrates a vision inspection and reject system.
Lots of data
The visual inspection requires a personal computer (PC) with human-machine interface (HMI) to display and analyze the results. The camera has to collect a significant amount of information, such as serial number, bar code grade and fill levels. “In previous systems, the communication speed between vision inspection to HMI and to the PLC (programmable logic controller) was a bottleneck,” explains Jerry Wierciszewski, owner of Wierciszewski Controls.
As for the tray erector itself, it has to tolerate some variability in the tray’s raw materials. If there are material changes, the timing to bend the flaps and fold the cardboard must change accordingly. The accumulation table complicates the challenge with an in-feed system that has very demanding precision requirements. The conveyor timing must be tightly controlled when the cassettes are moved through the system to facilitate gentle product handling. “It can be very tedious work to perfect the system timing, but it is a necessity when dealing with blood-testing products,” Wierciszewski notes. “This made it necessary to move to a new control system.”
For medical products, the U.S. Food and Drug Administration requires rigorous electronic record keeping. Both machines therefore have an SQL database for audit trails and detailed tracking for CFR 21 part 11 compliance, according to U.S. regulations. As this is one of the highest demands in the packaging industry, especially in medical applications, there must be a reliable system in place to keep track of all changes in production and to create detailed reports on these.
For the controls centerpiece, Wierciszewski selected a Beckhoff CP7202 Panel PC to handle the automation, motion control, SQL database and HMI functions for his two-machine systems. “The main reason for choosing the Panel PCs with TwinCat PLC software was the requirement for a small footprint. Even greater space savings resulted from the fact that the Panel PC did not require a housing, but is attached to a moveable mounting arm,” says Wierciszewski, adding, “The CP7202 is more than up to the task for the CPU-hungry vision system and the control functions for the two machines. Using TwinCat, huge amounts of data can be transferred between the HMI and PLC in real-time.”
Wierciszewski also developed his own HMI software using a Visual Basic .Net and C# platform. “The HMI can communicate very easily with TwinCat and display visual inspection results, counters and any other system information.”
Due to the limited space, Wierciszewski designed a stepper-motor system using Beckhoff KL2541 input/output (I/O) terminals that are wired directly to Beckhoff stepper motors. Integration in the bus terminal system dispenses with the need for additional amplifiers.
Wierciszewski networks the bus terminals via Ethernet TCP/IP. Additional bus terminal I/Os are used for relay outputs, motor starters on the conveyor and solenoids, each with 1 amp power consumption. “In the past, we were using separate analog outputs, thermocouple inputs or heating control units from various suppliers,” he says. “Now all these functions are covered by one I/O system.”
Time and cost
From concept to finished machine, the tray erector took about four months. The accumulation table was even faster, taking just two months to design and build. Both machines were fully programmed in only four days. In addition, costs for the control system and development time were significantly reduced. “Even with the integrated SQL server and comprehensive vision system, the new control platform cost is an average of 40 percent less than the devices I used previously,” says Wierciszewski. “Using one Panel PC to control two machines saves considerable time and money. The I/O wiring, which could take several days previously, is now significantly easier using bus terminals and Ethernet TCP/IP. In addition, the PC-based control enables remote access to the machine via Internet so that errors can be corrected quickly online.”
March 2011, Related Feature - Process and Packaging Integration: The Challenge and the Promise
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