Drive Unit
General
The drive unit on a forklift AGV is located under the battery and behind the front bumper. It is an integrated unit with a drive motor and a fail-safe brake. The drive unit is mounted on a mounting plate, which is attached to a turntable. A steering motor is mounted to the mounting plate and rotates the complete unit when running. The drive unit is very reliable and requires very little maintenance.
Spring suspension
The drive unit is mounted with spring suspension on five-wheel forklift AGVs. The springs press the drive wheel to the floor with a constant force. This will ensure good contact and friction between drive wheel and floor surface at all times.
DC motors
The DC motors of the drive and steer unit are always permanent magnetized (PM) motors. The motor size is depending of load capacity of the AGV. The motor requires normally only brush changes as maintenance.
Encoder
An incremental encoder is mounted direct on the drive motor. The encoder gives pulses to the AGV control board, which is used for distance measuring and speed control.
Steering potentiometer
A potentiometer is located on top of the drive unit in the AGV. It is direct linked to the steering and gives a feedback signal to the AGV control board of the AGV, telling exact angle of the steering wheel.
Guide antenna
In an AGV used for inductive wire guided systems is a front main guide antenna located in front of the drive wheel. The antenna is mounted direct on the plate of the drive unit and follows the steering angles of the wheel. This antenna is used for guiding on main paths.
Cross antenna
In an AGV used for inductive wire guided systems is normally a cross antenna mounted next to the drive unit, in line with the wheel. The antenna is mounted perpendicular to the guide antennas and is used to detect cross wires that the AGV is passing or stopping over. By counting cross wires can the AGV move long distances controlled by a simple command telling how many cross wires to count. At stop positions where very high accuracy is required can the AGV stop with the cross antenna positioned exactly over a cross wire.
Control
The drive and steer motor are controlled by four quadrant choppers in the electrical control enclosure. The choppers gives smooth start and stops and makes it possible to stop the AGV with high accuracy. At emergency stop does a contactor disconnect the drive chopper and the drive brake is braking as power disappears.