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Controller Leverages Electronics to Target Cost/Benefit Sweet Spot
Speed and control simplicity accommodate multiple applications
By Design News Staff -- Design News, September 22, 2003
Developments in high-power, solid state electronics have pushed performance of electric-motor driven servo systems. But these same developments allow similar improvements in controlling simpler servo pneumatic systems, which can fill many motion control needs with required performance at a lower cost.
If an application doesn't need high torque at low speeds, or stiffness and tolerances in the ten-thousandths of an inch range, then designers can avoid the cost of such electromechanical systems while still providing needed control loads, speed, and accuracy. Although accuracy suffers somewhat, pneumatic control doesn't require certain systems, such as a dynamic braking circuit needed by electric-driven systems, to function. In addition, a proportional flow valve is less complicated and costly than a comparable electric motor, and linear absolute feedback—as with a potentiometer—eliminates having to "home" an axis upon startup.
Leveraging these advantages is the Smart Positioning Axis Controller (SPC-200), a two-axis device (expandable up to four axes with a sub-controller) that benefits from electronic developments, which engineers have coupled with Windows®-based application development software (WinPISA) featuring NC commands compliant with DIN 66025. "The pneumatic-based system can provide high speeds, on the order of 2-3 m/sec, over lengths that allow that speed to be reached," says Product Management Specialist Nuzha Yakoob. "We can now use air with a feedback encoder to correct position so that a minimum step is 3% of the encoder length, up to ±0.004-inch accuracy." She cites this speed and positioning as being ideal for applications such as filling of containers or printer head positioning on multiple-row production lines. Other advantages of pneumatics that Yakoob mentions are no hydraulic oils—allowing use in food processing—nor electrics— providing explosion-safe operation.
SPC-200 features also include a single digital I/O module in the basic unit that provides 10 inputs (7 programmable) and 8 outputs (6 programmable). While capable of standalone operation, by using an expansion card, the axis controller can be fieldbus-linked to a command control system.
The SPC-200 is compatible with the company's CP (Compact Performance) valves and I/O devices, operating them via signal-conditioning interface modules over a CANbus network. Festo Corporation, www.festo-usa.com Enter 681
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