Question:
Which drive concepts (mechanical + electrical principle) are used for SRU travelling drives?
Answer:
The drive power for the travelling drives of an SRU is predominantly determined by the acceleration component. The travelling drives must be capable of moving the entire mass of the SRU. The traction is transferred from the drives to the vehicle on the basis of various mechainical principles. The aspects described below relate to monorail travelling drives representing horizontal SRU axes.
Bearing, guidance on the floor via wheel on steel rail (wheels made from Vulcollan, other plastics, steel) --> moving drive.
Traction via friction wheels on Omega belts
Electrical principle
1 drive controller / 1 motor
1 drive controller / 2 motors (group drive) - for twin drive laterally on the rail
2 drive controllers / 2 motors (individual drives) - for twin drive on the rail (front + rear drive)
Length measuring system
Laser measuring systems with fieldbus interface (Profibus, CAN, SSI) or Hiperface (Sick/Stegmann)
Barcode system with CAN or SSI (e. g. Leuze, Stahltronik / Pepperl & Fuchs)
Fine positioning using sensors or initiators: (close to target positions) --> rough positioning using feedback systems on the motor side, fine positioning using initiators or photoelectric barriers to compensate for inaccuracies of the shelf system (steel construction) or changes in the stretching of the belt
Control concepts for drives
1 drive controller / 2 motors (group drive): This simple electrical concept is only possible with identical asynchronous motors. The torque is distributed via the slip characteristics of the motors. The power range features an upper limitation because high powers (>30 kW) feature little slip.
2 drive controllers / 2 motors (torque ratio control): In this case, two separate drive units acting on the same rail are coupled with each other. The torque setpoint of the master is transferred to the slave. In this way, the torque will be equally distributed to both drives.
This concept allows (dynamic) torque shifts between the two drives.
Search terms: Stacker crane; SRU; master; slave
The base project 'Stacker Crane' contains an application example for the '2 drive controllers / 2 motors (torque ratio control)' control concept. For more information, please see article 201015217.
