Yarn exchange and doffing device in two-for-one twister

A yarn exchange and doffing device for use on a two-for-one twister having a plurality of spindles for feeding yarn from a yarn feed package to a wound package, comprising:

• propelling means for moving the device past the spindles;
• exchange means for effecting yarn exchange and doffing;
• detector means for detecting a location of a spindle where yarn is not being fed from the yarn feed package to the wound package and for stopping the device at a detected location;
• sensor means for sensing the absence of yarn on the yarn feed package at the detected location;
• and
• a controller including means, responsive to a failure by the sensor means to sense the absence of yarn on the yarn feed package at the detected location, for preventing the exchange means from effecting yarn exchange and doffing and for restarting the device, means for storing a detected location at which the sensor means has failed to sense the absence of yarn on the yarn feed package as a broken yarn location, and means for preventing the detector means from subsequently stopping the device at the broken yarn location.