Lenze makes the AC Tech SMVector frequency inverter, a variable frequency drive (VFD). It is a controller that regulates the frequency (hertz (Hz)). The faster the frequency, the faster the RPM’s of a motor. If an application does not require a motor to run at full speed, a variable frequency drive (VFD) can be used to ramp down the frequency and voltage, changing the load.
In the case of this loom a lower frequency allows the loom to run at a slower, more regulated speed.
AC Tech (manuals) – http://www.actechdrives.com/PDF/AC-Tech/AC-Tech-SMVector-Drive-User-Manual.pdf