May 2010 - Multipress Inc., Columbus, Ohio, is a manufacturer of custom presses. One of its new customers ordered a deep-draw hydraulic press that had some unique requirements. It needed both flexibility and precision.

In a deep-draw press, as material is placed in the die, and depending on the ram’s position, the press has to hold down pressure on the material so it flows properly during the deep-draw cycle.

To do this, both the position and the velocity of the draw cylinder have to be controlled, along with the proportional control of pressure on the hold-down ram. This allows the customer to get a custom-formed part.

Meeting requirements
These needs drove the customer to look for a forming press that had a closed-loop, hydraulic-control solution based on a programmable, multi-axis, electro-hydraulic motion controller.

The controller was required to control both position and pressure and to support flexible I/O options for handling other control and communications needs. Press setup needed to be easy, and its functionality had to be optimized for a wide range of metalforming tasks.

To correctly produce parts, the press required an infinitely adjustable closed-loop position and velocity control for the stamping cylinder. Additionally, it needed a manual joystick control for the pressing cylinder for both manual tooling setups and part adjustments during part prototyping. It also needed to establish communications with the press’ supervisory PLC.

Controlling pressure precisely was a critical requirement of the press because variable pressure had to be applied by the clamping cylinders to avoid damage to the workpiece during the press cycle.

The right stuff
To help with system design, Multipress worked with hydraulics distributor Mike Joyce of Advanced Industrial Products Inc., Plain City, Ohio, who recommended the use of an RMC75 motion controller manufactured by Delta Computer Systems Inc., Battle Ground, Wash. For normal automatic press operations, Rick Snyder, electrical engineering manager at Multipress, programmed the controller to run a one-step repeating program that machine operators could call up through an input on the human-machine interface (HMI).

The HMI communicated with the supervisory PLC, which downloaded the appropriate pressure settings into the motion controller, along with position set points corresponding to hold-down pressure settings and position set points for the main ram that relate to a particular press operation.

Because the motion-controller program uses variable position and pressure set-point values the HMI can select, production changeovers are easy to accomplish. This was a key element of the flexibility of the machine. Another button on the HMI enabled a change between automatic and joystick modes.

Delta Computer Systems’ RMC75 motion controller was chosen "because no other product could do it," says Joyce. "There was no easier way to do a motion control application. Delta’s equipment allows us to run anywhere from two to eight axes of motion (three- to eight-axis systems would use Delta’s RMC150 controller). It has Ethernet, digital I/O communication or serial communication, and it’s just extremely fast. We have loop update times from 250 milliseconds to 4 milliseconds. It’s simple to work with. It uses drop-down GUI menus, and they have help applications already set within their equipment."

A software package, RMCTools, comes with the Delta RMC75 controller. It includes motion program development and automated tuning tools with simulation capability that enables programming and tuning of the system even before connecting the hydraulic hardware to the motion controller. FFJ

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