Page 18 - MetalForming Magazine May 2023

To implement the hydraulic con- trols, Aleksandra Spiess, an engineer at Dayton Die Cushions, selected an RMC75 electrohydraulic motion con- troller (Fig. 3) from Delta Computer Systems, Inc.
“The RMC75 can run four separate task-execution engines simultaneous- ly,” Pederson explains, noting that with- in Delta’s RMCTools software, each task also can run any of several user pro- grams, one at a time. “We assigned one of the tasks to be a dedicated compu- tation engine working in the back- ground. A PLC wouldn’t have been fast enough to perform like the RMC.”
The motion controller connects to two servo valves, with each assigned to a separate control axis of the RMC75, which can control as many as two axes simultaneously and independently.
“If needed, we can move extra oil to the tank in order to quickly move the die cushion,” Pedersen says. “The ram moves quickly when the cushion first hits, and then slows down as the compression operation completes.”
Correct Pressure Timing a Must
The new die cushion uses two Bal- luff magnetostrictive linear displace- ment transducers (LDTs) with synchro- nous serial-interface inputs to the Delta motion controller and Hydac high- speed pressure sensors. One LDT measures ram position and the other measures cushion position. Just prior to the ram contacting the cushion, the RMC75 opens the valves and begins moving oil through the manifold. Then, at ram contact the RMC75 runs a pres- sure-control loop as the cushion descends. At the bottom of the press stroke, as the ram reverses direction and ascends, the RMC is programmed to switch to position-control mode. This causes the die cushion to rise quickly, just in time to meet a robotic arm that picks the finished part out of the die.
“The cushion must ascend in a cer- tain time window, repeatably, to meet the transfer arm,” says Pedersen. “This required adaptive closed-loop control occurs as the temperature and, hence,
Fig. 3—A motion controller from Delta Computer Systems, Inc., incorporated to control die-cushion pressure precisely, enables needed pressure throughout the press stroke to aid forming operations.
the flow properties of the hydraulic oil are changing dynamically.”
Another challenge met by the Delta controller: the ability to work with exist- ing off-the-shelf valves used by Dayton Die Cushions, as lead times for man- ufacture of new valves stretched too long to meet project goals.
The Dayton Die Cushions team undertook three iterations to complete the motion-control program for the Delta controller.
“As we went through the iterations, Delta’s engineers provided tremendous help,” Pedersen says. “For example, they taught us how to use the RMC75’s S-curve instruction, which initiates a smooth acceleration and deceleration to avoid hydraulic shock. They also helped to incorporate feed-forward parameters into the control loop—pre- dictive terms that help speed response of the control algorithm.”
The team used Delta’s RMCTools Plot Manager software to prove the functionality of the system graphically and optimally tune the control-loop gains. Saving time in completing the design was important, as Spartanburg Steel Products sought to add tooling quickly in support of part production for the new automotive model year.
The die cushion design developed by Dayton Die Cushions provides an example of how hydraulic control sys- tems have become smarter in order to meet the increased productivity and quality demands of modern automo- tive manufacturing. A key component of the new machines making this pos- sible: the programmable electro- hydraulic motion controller. MF
16 MetalForming/May 2023
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