Controllers ease hydraulic integration

Farmington Hills, MI —When Lance Lemon began integrating the components of a hydroforming machine for one of his customers in the automotive business, he thought the task might be difficult. "I'm an experienced hydraulics engineer, but have limited experience with motion controllers," says Lemon, a designer of machines for Behco, an industrial equipment supplier. Multiple vendors supplied the components, which didn't make matters any easier.

Hydroforming is a single-step process used in the automotive industry for forming metal parts and components. Hydroforming machines use high-pressure water inside a tubular blank that forces expansion of the tube until it fills a die cavity. For one large automotive manufacturer, Lemon's challenge involved integrating a PLC from Mitsubishi (Vernon Hills, IL), pump motors from Lincoln Electric (Cleveland, OH), cylinders from Sheffer Corp. (Cincinnati, OH), and hydraulic motion controllers from Delta Computer Corp. (Vancouver, WA).

Delta controllers -- RMC1 and RMC2 -- control hydraulic cylinders and water pressure inside the tube of the hydroforming machine.

In Lemon's resulting system, the first controller—RMC1—controls hydraulic cylinders that close the water seals at the end of each tubular blank. RMC1 maintains the proper hydraulic pressure at the ends of the blank. The controller also activates proportional hydraulic valves for cylinder position control using inputs from magnetorestrictive displacement transducers mounted on the hydraulic pistons. Too much pressure on the end seals damages the tube. Too little pressure allows water leakage.

The second controller—RMC2—controls water pressure inside the tube. It monitors pressure against a desired profile and drives the hydraulic piston inside the intensifier by way of a proportional valve.

Maintaining control of the process requires sampling from the transducers once every two milliseconds. Delta RMC's can sample once every millisecond. However, speed wasn't Lemon's only concern—he had to make the Delta controllers communicate with a Mitsubishi PLC. He solved the problem by programming the parallel interfaces of the RMCs with the PLC.

"Within a few hours of installing the Delta Modules, I had them up and running using the information Delta provides," he says. Initially, Lemon's PLC didn't download the necessary parameters. Delta helped him by reading the command log and then reconfiguring the digital input card. "The RMC has a wealth of connection options, including a PROFIBUS Fieldbus interface, but we chose the parallel interface because a PROFIBUS connection was not available for the Mitsubishi PLC."