Repair Bulletin Detail

Whatever Happened to the BDS Servo Drive?

What was the BDS Servo Drive? The BDS Servo Drive series was well ahead of the completion when it was introduced to the market by 1986.

In addition to being a brushless drive with resolver feedback, it also featured a sine current profile when many of the competitors were using trapezoidal current control. (Sinusoidal current control more closely approximates alternating current, keeping the motor from generating extra heat not related to actual work.)

The BDS series was also the first to electronically change the rotor flux and the stator flux, known as torque angle or phase advance, thereby widening the speed range. When Kollmorgen patented the phase advance technology, many prominent competitors found themselves in violation of Kollmorgen’s protections. Some of these competitors ended up incurring substantial judgements as defendants in court.

The BDS drive was originally offered by Industrial Drives, at that time part of Kollmorgen Corporation. (We now know that group as simply Kollmorgen.) The BDS drive was offered in 3 degrees of sophistication: BDS3, BDS4, and BDS5. The BDS3 was a basic analog velocity drive, in which a zero-volt signal would normally cause the motor to mostly be at rest. The drive would command full speed of the motor in a positive direction at 10 volts, whereas -10 volts would command full speed in a negative direction.

At the other end of the BDS product spectrum was the BDS5 full-position control drive. The BDS amplifier modules were available in sizes of 3, 6, 10, 20, 30, 40 and 55 amps RMS/phase continuous. The BDS drives used Kollmorgen’s PSR power supplies to provide the bus power that the drive required, and were typically paired with Kollmorgen’s Goldline brushless motors.

The BDS proved to be a very successful offering for Kollmorgen, finding strong acceptance across the machine tool industry. Kollmorgen would even private label the BDS for some of their major customers. Meanwhile, competitors like Pacific Scientific had to play catch up to achieve the level of sophistication and breadth of products represented by BDS. It’s worth noting that Pacific Scientific later became a sister company to Kollmorgen.

So what happened?

The analog-designed BDS drives were ultimately replaced by digital models that were shown to be far easier to commission with more repeatable behavior. The BDS series soon gave way to digital designs such as the Servostar S, Servostar CD, and the Servostar S300/400/600. Kollmorgen eventually ceased BDS production in 2002.

Some of you may be surprised to learn that BDS drives continue to be in full operation today. Having been the factory-authorized BDS servo drive repair service for the past ten years, Motor Systems Inc. is proud to have helped prolong the lifespan (and value) of these important drives for many of our customers.

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