Servo-Drives Out?

As standard AC drives approach their 40th birthday and move into their fifth generation, the technology they use has already evolved to challenge the dominance of other methods of variable speed – such as hydraulic, pneumatic and DC drives. Now, it would appear, it is the turn of the servo drive to do battle with AC drive technology.

“Replacing servo drives with conventional AC drives is a dream of several manufacturers,” says Professor Pacas from the Siegen University, Germany. “To some extent it is truly possible, but you need to be quite clear which applications you are talking about. You also need to be clear about the differences and limitations of each technology.”

A NEW CATEGORY OF DRIVE

The term ‘machinery drive’ has been coined for this new drives category. This term draws together drives with motion control software, used in machinery applications. They are not technically servo drives, however, as the technology is based on standard AC drives.

Until recently, many machine builders relied on servo drive technologies to meet their demands for positional variable speed control. Now they are being encouraged to look at the emerging machinery drives. Because machinery drives are able to drive any type of AC motor, including standard squirrel cage motors, and because these drives use components that are produced in high volumes, they promise the machine builder improved reliability at a lower cost. The transition has been underway for the last five years, but the main change happened when very high open loop performance became available in ordinary drives. This has resulted in servos and, generally speaking, closed loop systems being replaced by low cost inverters in certain applications. It’s all down to shaft performance: low speed torque performance and dynamic response – are the key features.