Honda cuts downtime 90% with PC control of process
By scrapping programmable logic control and going with a single PC running a materials handling system, the auto maker raises productivity and gains flexibility.
By Staff -- Modern Materials Handling, 6/1/1998
Engineers at Honda of America Manufacturing Inc.'s engine and power train plant in Anna, Ohio are replacing programmable logic controllers (PLCs) with PCs. A PC-controlled system now runs a scrap metal sorting process with great success: Downtime is down 90%. Engineering time spent making line changes is cut 75%."We simply could not achieve productivity improvements like these with the same old approach [of using PLCs]," says Honda engineering coordinator Bryan Burns.
With help from a leading supplier of PC-based control systems (Steeplechase Software) Burns led engineers in Honda's Ferrous Casting Department in the development of the plant's first PC-controlled gating returns system. This system sorts iron gating from two molding lines and transports it to a cupola charging area for remelt (see sidebar, p. 36).
One of the most obvious differences in the new system is that the controller is now local. Previously, control devices were hard-wired and piggy-backed to a remote PLC. "This set-up was very inconvenient," says Burns. "When problems occurred, getting diagnostic data meant calling operators in another office who had access to the PLC."
Of course, Honda could have purchased another PLC and dedicated it to the returns system. However, Burns was convinced that "no PLC system could deliver the level of time- and cost-savings or the added flexibility that could be achieved with PC control."
Using the supplier's software suite [Visual Logic Controller (VLC)], a device-level bus network, and a single PC, the Ferrous Casting Department has reduced error recovery time from an average of 20 minutes to less than two minutes. The flexibility inherent with the new system is credited with reducing engineering time devoted to line modifications by 75%.
Combining functions
Unlike a PLC, the VLC combines programming, control, control maintenance, and operator interface functions on a single PC. Designed for use in industrial and process applications, the VLC moves the core of a PLC into a PC for robust, reliable control capable of surviving Windows faults, errant Windows applications, and even hard disk crashes.
In contrast to PLC-based systems, which require separate hardware and multiple databases for control programming, control maintenance, and operator interfaces, the VLC provides a single, common database across all of its integrated tools. This eliminates one of the greatest sources of human error when configuring or changing parameters in a PLC system, which may have four separate databases to maintain.
If any changes are made in a PLC-based system, each database has to be modified and tested against the other databases. The VLC does away with all that data entry and greatly reduces the chance for error.
Windows programming
Being able to program in a Windows environment was one of the advantages of PC control that first interested Burns. "I really couldn't believe how easy it was to write a program in the flowchart language," recalls Burns.
"I had no training, just the manual. I did call [the VLC supplier] a couple of times with questions but, coming from a relay ladder logic background, I knew this software was going to be important as soon as I created my first subroutine."
With the VLC's assurance of hard real-time control and the open architecture platform of a PC, Honda was able to select and apply a device-level bus network from one supplier, remote I/O blocks from another, and devices from a variety of manufacturers. The bus network connects I/O to the VLC through a PC interface card. Not only does it support the use of smart devices to provide more diagnostic information, but it also replaces hard-wiring with neat plug-and-play cabling.
"We are working in a foundry environment," explains Burns. Returns are shuttled from the molding lines to the remelt furnace through a long tunnel. Instead of running wires for each device through the tunnel as they did in the hard-wired system, Burns and his team just attached the bus cabling to the tunnel wall.
"Once the bus cabling is in place, you can drop devices in anywhere along the line with branch cables," says Burns. "This approach gives us diagnostic capabilities throughout the entire system and makes the installation process a lot safer, simpler, and faster."
Productivity gains
Seven months after the installation, it's the operational productivity improvements that are most impressive to Burns. "With flowcharts, error recovery happens differently," stresses Burns. "It's lightening fast."
The flowchart language provides programmers with an easy way to have many programs executing in parallel. Using subroutines, processes are broken down into many small, independent flowcharts. Unlike a PLC, which runs a long, continuous scan cycle, the VLC cycle executes many flowcharts at once, each with their own error-recovery instructions.
"I've developed one error-recovery subroutine as a template that I use in all the flowcharts," explains Burns. "When an error occurs, the control program loops back to that step in the process. We had to wait 20 minutes for the PLC's ladder logic to cycle through and get us back on track. With the VLC, we've got error-recovery down to under two minutes."
With the system's diagnostic capabilities, Honda gets into a recovery mode more quickly, too. The VLC's integrated operator interface displays diagnostic messages for the operator. Composing these message in the Windows-based VLC programming tool is as simple as typing.
"The diagnostics enable us to differentiate between a problem with the bus and a problem with a device," says Burns. "This takes troubleshooting time way down. The diagnostic message gives us the nature of the problem and its exact location, so we can take care of the issue and get right into recovery."
Making modifications
With the PC's flexibility and the VLC's Windows-based tools, line modifications also are faster and easier. When Honda needed to make a 60-ft equipment modification, Burns just had to scan through the specific flowchart subroutines that needed changes. Since the VLC's database is global, tag names are automatically updated across the entire system.
Future outlook
Looking back at the decision to replace the PLC-based system with PC control, Burns is confident that Hon-da is moving in the right direction. "PCs are cropping up everywhere on the plant floor, especially in the automotive industry [and probably will continue in many other industries]."
While Burns says the gating returns' control system doesn't take advantage of all the benefits of PC control, he knows the additional capabilities are there. For instance, diagnostic messages can include high-level graphics, even animation. Programmers can automate the handling of diagnostic events by incorporating a flowchart that does anything from printing a report to calling a pager number. Machine control systems can be linked to higher-level distributed control systems and information systems through a simple, off-the-shelf cable. "If something goes wrong with my motherboard, I can run out to the nearest discount electronics outlet and pick one up in a half hour," says Burns. "You just don't have that option with a PLC."
While the immediate productivity and flexibility gains are extremely advantageous, Burns says Honda of America and other users are just beginning to capitalize on the powerful capabilities of a PC. "The PC is not only advancing industrial control, it's simplifying it," says Burns, "and the flexibility of PC control provides us with an open-ended platform that prepares us to make future improvements, regardless of where the future takes us."
Overview: materials handling system controlled by PC
Now PC-controlled, Honda's materials handling system sorts iron gating from two molding lines and transports it to a cupola charging area for remelt.
Included in this gating returns system are two vibratory weigh hoppers equipped with load cells, a tunnel-located bucket car, a bucket-transfer shuttle, a gantry/hoist, and storage bunkers. The system handles sprues and risers from grey iron casting processes.
After separation from cast parts, the gating returns are fed into the weigh hoppers. When the weigh hopper is full, the bucket car travels to that hopper and the hopper load is transferred. The loaded bucket car then returns to the shuttle, which transfers the bucket to the gantry/hoist.
On the hoist, the bucket is emptied into one of ten storage bunkers. Different bunkers are used for different products in a sortation process related to the differing chemistry of a variety of iron parts.
When the bunker is full, the sorted material in it may be used for remelt. Materials are selected for remelt through remote panels located in the areas where gatings are separated from cast parts.
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