Lift Unit
General
The lift unit is mounted on a cross-tie welded to the fixed mast. AGV Electronics uses always an electromechanical design of the lift unit consisting of a ball screw with a ball nut, a DC motor, worm gear box and a brake. This is a very efficient design, which gives high positioning accuracy for the lift height position which is very important at high lift heights.
The lift unit is very quiet and requires very little maintenance.
Lift Screw
The lift screw is normally a SKF ball screw with a ball nut attached to it. The lift screw and ball nut requires very little maintenance. The lift screw is attached to the worm gear box in the top. The lift ball nut is attached to the fork carriage or the duplex mast in the AGV. The lift ball screw comes in different sizes, which are used depending of the load capacity of the AGV.
Worm Gearbox
The worm gearbox is mounted between the DC motor and the lift screw. The worm gear is efficient and requires normally no maintenance. It has also a electromechanical brake mounted to it. The brake is used at E-stops and as a parking brake for the lift.
DC motor
The DC motor of the lift unit is normally a permanent magnetized (PM) motor. The motor size is depending of load capacity and lift frequency of the AGV. The motor requires normally only brush changes as maintenance.
Encoder
An incremental encoder is mounted direct on top of the lift screw. The encoder gives pulses to the AGV control board, which is used for height measuring.
Controls
The lift motor is controlled by a special electronic lift control unit which is a one quadrant chopper with internal contactors for switching motor direction and emergency stop control. The lift control unit is located in the electrical control enclosure. The lift control unit gives smooth start and stops and makes it possible to stop the lift unit with high accuracy. At emergency stop is the lift motor disconnected from the power source by an internal contactor and the lift brake is braking as power disappears.