Electronic Motion Controller Simplifies Hydraulic Press Controls
- Wednesday, 01 October 2008
What do you do if you’re in the business of producing a wide variety of metal presses to meet special customer requirements? You choose your system components wisely, and flexibility of function plays a large part.
Multipress, Inc. of Columbus, Ohio, is a leader in design and production of hydraulic press technology based on flexible architectures, The company has been producing hydraulic presses since the 1920’s, for applications as diverse as high-speed stamping of self-locking nuts (3-4 nuts/second to a +/- 10 pound tolerance), metal extrusion, and forming of metal components. Over the years, Multipress has continually focused on evolving and enhancing the technologies employed in their presses.
Multipress’ two most recent presses will be used to form metal components for the automotive industry. These presses needed to move quickly, but also precisely. Multipress’ system designers met the challenge by setting up the press to operate at three different speeds. At the start of a press cycle, the hydraulic ram needs to move very quickly. Then, it needs to slow down as the business end of the press ram approaches the work piece.
The faster steps in the process use open-loop moves for maximum speed, and when the machine slows down near the end of the cycle, it does precise positioning by making minute, precision flow control adjustments via a servo valve. Though each press uses a 31-inch cylinder, closed-loop position control is only needed for the final 3 inches of motion. Under closed-loop control, final positioning of the axis is accomplished to within .001 inch of target values.
Flexibility the key
There are three key types of components in the typical press: mechanicals, hydraulics, and electrical/control elements. Correct decisions must be made in each area. If the mechanical design isn’t right, there may be no way for the hydraulics to make it work effectively. If the hydraulic components aren’t selected and sized correctly, an electronic motion controller may not be able to maintain precise control.
The hydraulics and electronic controls for the Multipress machines were designed in conjunction with Advanced Industrial Products, Inc. of Plain City, OH. Multipress strives for simplicity and flexibility in the designs they do and a track record of success proves that this approach works.
To control the hydraulics, Multipress needed a programmable electronic motion controller that was capable of smoothly transitioning between several different modes of operation. The company selected the RMC75, manufactured by Delta Computer Systems, Inc. of Vancouver, Washington (see Figure 1).
For maximum flexibility in the hydraulics, the Multipress machine (see Figure 2) uses an open loop regenerative circuit for fast advance and fast feed speeds. A small servo valve is used to do final press positioning on the main ram cylinder. The position of the ram is controlled using a Balluff transducer. The Delta controller enables this system to run in both open and closed-loop modes, allowing a cost savings and energy savings by not having to use large servo valves.