Energy-efficient application advice
While best practice energy efficiency tips are always helpful in identifying steps to energy management improvements, it can often be more helpful to look at specific processes within a plant to identify the low-hanging, energy savings fruit. Peter P. Fischbach, manager of component sales for Bosch Rexroth Corp., offers the following specific suggestions for three common applications:
Converting/Printing: In continuous web applications, direct drive motors and electronic line shafting controls help eliminate inefficient mechanical shafts, transmissions, and tensioning brakes. “By replacing the inefficient induction motor, mechanical drive train, and tensioning systems of a printing machine with a multi-axis servo drive system, users can reasonably expect to achieve around 30% savings in energy,” Fischbach says. How? The common dc Bus of the drive system distributes the regenerative energy from the tensioning axis to the driving axis, lowering the net power consumed from the grid (see “Reusing energy via a common DC bus” sidebar in the January 2009 article).
Packaging/Handling: In production lines with fast, cyclical motion and repetitive start/stop operations, DC capacitor modules can be used to store excess energy from slowing or stopping until the next acceleration phase of the motion axis. “This reduces the net power used by the packaging/handling system,” says Fischbach. ”It is possible to reduce energy usage in such applications by up to 20% by replacing mechanical cams, induction motors, and variable frequency drives with a common dc bus servos system and capacitor modules.”
Hoisting/ Lifting/Palletizing: Regenerative energy is created during an application where the load possesses more energy than the motor, as is often the case when lowering or stopping heavy loads like pallets, hoists, or centrifuges. While motors are used to convert electrical power into mechanical power for the machine, servo motors have the potential to generate electricity, too. “As a heavy load decelerates or stops, the braking motor turns into a generator converting mechanical power back into electrical power, which needs to be removed,” says Fischbach. “Traditionally, most motor systems would take this excess energy and burn it off using a brake resistor or other mechanical ways, which generate heat and in many cases uses even more energy for cooling off the control cabinet and building. Servo drives connected via a common dc bus to a regenerative power supply can convert the excess energy back to ac power, which then can be reused by other equipment in plant.”
For more energy efficiency tips, see the two-part energy management articles in the January and February 2009 issues of Control Engineering, online at www.controleng.com .
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