Printronix L5000 Series Maintenance Manual page 207

When the transfer elevator motor forward rotation instruction pulse is fed while the
transfer unit is in the lower position, the motor rotates so that the transfer unit is lifted
by cam action. When the transparent vinyl chloride cylinder installed over the cam
shaft rotates, and the tape on the cylinder surface blocks the light path between the
light emitter and receptor of the transfer unit upper-limit sensor (TUUL), the motor
stops. If the motor reversal instruction pulse is fed in this state, the motor reverses so
that the transfer unit is lowered by cam action, and when the tape blocks the light
path between the light emitter and receptor of the transfer unit lower-limit sensor
(TULL), the motor stops again.
Principles of Operation 5–47