Many circuit board drilling machines still use obsolete frequency converters to drive their very high speed spindles. These typically have a maximum speed of 80,000RPM and pre-date the modern general purpose types that now go that fast.
It can be difficult to retro fit these old machines with new drives for a number of reasons. Some of the spindles are 2-phase types, and these types of converters are no longer manufactured. Others use low voltage 3-phase motors that are not capable of withstanding the high voltage PWM pulse produced by modern drives.
The frequency converter pictured also has an unusual interface which uses a square wave to determine the speed of the drive as well as being a low voltage drive.
There is no documentation for this drive so it was reverse engineered to obtain a schematic. This wouldn't normally be necessary, but the drive in question had a fault that was difficult to trace without a deeper understanding of how it worked.
The are still a good number of machines using Sieb & Meyer, Kavo and Precise frequency converters driving a variety of spindle types. All of these can be supported even though they are obsolete.
Frequency converter repairs
Wessel frequency converter for Jaeger low voltage 60,000 RPM spindles
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