Shelby Township, Michigan-based Fori Automation Inc., a specialist in automatic conveying and handling systems, is modernizing the assembly line of a large U.S. automobile plant with rail guided carts, fail-safe SIMATIC S7-1200 controllers, and IWLAN.
The requirements of the automotive industry are tough and ever-changing. Take the demands of a large automobile plant in the U.S. for its new assembly line manufacturing suspension modules. “Our customer must be able to introduce additional products onto the line without the usual long retooling times,” says Dean Colwell, controls engineering manager for assembly and welding systems at Fori Automation.
The aim of the project was to replace the existing conveyor belt-based system with a flexible rail-guided one. The new, flexible assembly solution, which also had to be more cost-efficient than the line it was replacing, enables the customer to respond efficiently to changing product demands and other general requirements.
Because floor-running carts are able to move much more easily in different directions than conventional conveyor systems, Fori opted for rail-guided carts (RGCs) to make the assembly line scalable and flexible. While perfect for this automotive application, RGCSs can meet the demands of other industries as well.
Flexible Communications and Integrated Safety
Fori supplied the customer with a highly flexible system in which the pallets on the existing rail system were made “smart.” The pallets were fitted with Poka-Yoke mechanisms, with the necessary data being processed by a PLC on the cart. This also required a flexible communications platform.
Key project requirements included:
- Fast roaming
- An integrated approach to all control and safety functions in the RGC system
To meet the specified goals, Fori relied on technology from Siemens: The TIA Portal engineering framework permits commissioning and configuration of all system components from one central location. For example, Fori installed fail-safe SIMATIC S7-1200 controllers as well as SCALANCE access points and client modules for wireless communication. This satisfied one of the main requirements, because the RGCs are autonomous and cannot be connected to a fieldbus system for the transfer of control signals or warnings.
Since the SIMATIC CPUs feature the necessary communication functions as standard, all connections within the system architecture and to the higher-level host system can be made in a cost-efficient way. SCALANCE offers real-time communication and fast roaming, key features considering the frequently long RGC lines that require multiple access points.
Another major factor was the integration of safety functionality into the PLC, because the individual RGCs have a safety bumper, an emergency stop switch, and optional safety scanners.
Despite the fact that each safety-switching device has to have a specific function, the parameters might change frequently depending on the RGC’s working range. With conventional hard-wired safety systems, that would not be feasible.
Keeping Costs in Line
Price was another key factor in the switchover from conveyor systems to rail guided carts. “The flexible cart system costs the same as a conventional conveyor system,” remarks Dan Connelly, head of the Fori Assembly Lines division. “Yet it combines all the benefits of such a conventional conveyor system, incorporating pallets with the advantages of 360-degree operator access.”
Further, the installation process is also much more economical, as it reduces the time and labor required by 25 percent. The assembly line can be configured as desired, in keeping with the process at hand or the available space. The material racks can be located both outside and inside the line.
“We can also configure the line with stops, or as a single continuous line,” Connelly adds. “That makes the process in general much more flexible, productive, and cost-efficient.”
Since the PLCs communicate with each other, the system permits the creation of loading lists as well as improved production monitoring. (An existing installed controller from another manufacturer was also easily integrated into the system.)
The fail-safe SIMATIC S7-1200 controllers offer system-integrated diagnostic and safety functions. Diagnostic data are continuously available via the HMI and on the web server—in this case, TIA Portal. All error messages are displayed in plain text. The system is comprehensively protected against unauthorized modifications to code or process values, both in the PLC and in TIA Portal.Have an Inquiry for Siemens about this article? Click Here >>