Hydraulic Motion Control
The market for powder compacting press equipment is highly competitive, with machine manufacturers vying for market share using a variety of cost/performance options. Original equipment manufacturers (OEMs) succeed by reducing costs, adding features, increasing productivity, or combining all three. A case in point is Precision Compacting Technologies of Bentonville, AR.
The market for powder compacting press equipment is highly competitive, with machine manufacturers vying for market share using a variety of cost/performance options. Original equipment manufacturers (OEMs) succeed by reducing costs, adding features, increasing productivity, or combining all three.
A case in point is Precision Compacting Technologies of Bentonville, AR. The company got its start re-building presses from other manufacturers and has been building its own presses since 1999. Its strategy with its newest line, called the Hydra Chief, is to use best-in-class PC-based motion-control tools to provide world-class capabilities is less expensive machines.
Precision Compacting's customers produce items such as carbide cutting and mining tools, transmission and gear components for heavy equipment or automotive applications, and energy-absorbing ceramic products for armor applications. Its machines range in capacity from 15 to 1,200 tons of pressure (the largest is 20 ft tall and weighs 100,000 lbs).
Hydraulic system diagram shows how the motion controller connects to the motion axes. Source: ABB
Planning a new machine
When Precision's executives began planning a new machine that was to go into production in 2005, they didn't want to break new technological ground. They sought to improve on the technologies incorporated in older presses by making proven modular design modifications. The “smart” machine they developed used a multi-axis electro-hydraulic motion controller and PC working together to replace the PLC-based control systems of the past.
The PLC systems worked satisfactorily, but the new PC-based system works better in function and performance. New strengths contributed by the use of the PC architecture include support for networking, flexible/expandable data storage for parts “recipe” management and data acquisition, and an operating environment that enables the hosting of powerful/flexible operator interfaces.
Precision Compacting used the PC's networking interconnectivity in the new machine to provide two network interfaces: Ethernet for connection to Precision's customers' plant-wide networks, enabling remote monitoring of machine processes; and Profibus as an expansion fieldbus to add machine options to the press.
Precision's engineers see Profibus as more robust than Ethernet, making the addition of optional robotics subsystems virtually a “plug-and-play” operation. For example, in some applications, Precision uses a pick-and-place robot to unload the system and weigh parts coming out of the press. Then another robot stacks the parts on a pallet. A laser module can also be added to measure the dimensions of production parts.
Using dynamic product weight and size information from these systems, the machine automatically adjusts and tunes itself to optimize the process. Although presses from international manufacturers can do this, Precision says it can do it for a fraction of the cost.
When selecting a motion controller to operate the Hydra Chief's hydraulics, Precision wanted maximum functionality from one compact motion controller module. The controller would need special capabilities, such as the ability to control applied pressure to drive hydraulic axes smoothly. The machine designer also wanted one controller that was easy to program and tune, and could coordinate the motion of multiple axes simultaneously.
After evaluating alternatives, Precision's engineers chose the RMC100 motion controller from Delta Computer Systems Inc., Vancouver, WA. “It stood out as the hydraulic motion control leader,” said Precision Compacting President Bill Fergus.
Coordinating five axes
The typical compacting press has five axes of motion. The upper and lower compression rams are position- and pressure-controlled. The powder filling shoe and the side punches require only position control (see diagram). The side punches, which are used in conjunction with the upper and lower rams, ensure that even powder density is maintained within multi-level parts.
The filling system and punches can be positioned as needed, depending on the parts being manufactured. Different shapes require different shaped cavities, and that, along with different powder formulas, dictate separate motion “recipes” for each part made. A major benefit of the powder compacting process is the ability to create complex parts that perform like machined parts, but for a lower cost.
The Delta RMC100 motion controller can control up to eight axes operating simultaneously with variable profiles. In the Hydra Chief, both rams move simultaneously. They need to accelerate and decelerate smoothly in a coordinated fashion to maintain part quality during compression, and when a part is being released. Precision's software engineer built the capability into the HMI, allowing the machine to move the axes to a target position or a target pressure on a part-by-part basis.
The engineer had designed compacting presses in the past, and has always viewed the coordination of multiple axes as a challenge. He attended a motion-controller training class at Delta Computer Systems' facility, and also received some hands-on training from a Delta applications engineer at his site. Then, he developed the control programs starting with simple steps, adding more functionality as needed.
One at a time, he proved out the individual paths through the event step table of Delta's RMC controller that corresponds to simultaneous motion sequences. He tried out Delta's automated tuning wizard for modeling his application. In the end, he did most of the final system tuning by hand, using plots of actual versus target position profiles provided by Delta's RMCWin software.
The engineer was able to incorporate the motion plots into his machine's HMI as well, providing a tool for his support personnel to use to diagnose problems. Precision's customers also may e-mail plots to Precision and have the company diagnose problems.
As a result of Precision's attention to design details, U.S. customers have a new press that, the company says, is much easier to understand and use than presses from international competitors. Using best-in-class control technologies, Precision Compacting is able to deliver world-class capabilities and improve support for their customers.
ABB's new PSR model softstarters offer a full set of knob-adjustable functions for starting and stopping 3 to 45 A, three-phase motors, up to 600 V ac in a compact package that easily mounts in small control panels and equipment enclosures.
The PSR range includes three physical sizes from 1.77 to 2.13 inches (45 to 54 mm) wide, and control voltages of 24 V dc or 100-240 V ac. All sizes include a “Run” signal relay, while sizes from 25 to 45 A add a signal relay for “TOR” or full voltage. These can be attached to an automation control system to provide closed-loop control or operator indication.
PSR's wider operating voltage range reduces back-up inventory required to support multiple applications, according to the company. www.abb.com ABB
Ethernet motion controls
With the launch of Ethernet Powerlink three-phase AC drives, Baldor Electric Company says it offers all the major motion control functions. The 3-phase AC drives allow users to build all- Ethernet systems with the optimum choice of motor technology for each axis, from small to large loads. Rotary and linear versions of brushless servo, and AC vector motors are all software selectable.
Ethernet, the company says, does not force a machine builder to adopt any particular control architecture. Systems can still have the traditional central controller (coordinating all drives in profiled torque, speed or position modes), or can have self-controlled positioning devices (DS402 compatible positioning drives) that respond on command.
In addition, intelligent (programmable) drives can be employed in a system to implement more complex standalone axes, or to implement the complete motion system.
Ethernet's 100 Mbits/second bandwidth merges the functionality of a fieldbus and a motion bus into one system. Functionality normally reserved for the device service port (such as firmware updates, configuration, and diagnostics) can be done through the machine-control network. www.baldor.com Baldor Electric Co.
Rick Meyerhoefer is a regional applications specialist at Delta Computer Systems.
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