Drive application: Storage and retrieval system with cornering capability
Large quantities are put into storage in a high-bay warehouse. There are many aisles but the material flow rate is low. In this case, the storage and retrieval system has to have cornering capability because it must travel along many aisles. Cornering capability means that there is a differential between the front and rear drives, and that high transverse force during cornering can be avoided by means of active cornering control. When the front wheel enters the corner, the rear wheel is still running on the straight and is decelerated. Then, when the rear wheel enters the corner, the front one is running on the straight again. This results in a significant acceleration of the rear wheel, which may be as much as a factor of 2 or more depending on the radius and the distance between the axes.
This puts the following requirements on the drive system:
- Load distribution, both wheels are driven
- Slip control
- Cornering capability, electronic differential
Intelligent inverters are needed particularly for cornering capability. The machine control cannot manage this task.
The basis for this is that the speed of both wheels is known. Both wheels of the storage/retrieval system are driven; the load is shared by both drives. The driving motors are equipped with an incremental encoder and each one is supplied by its own inverter.
Both wheels are driven and each one is supplied by its own MOVIDRIVE® inverter. The inverters are connected via the system bus (SBus) and via the RS-485 interface. Both are standard.
- Electronic differential with system bus (SBus)
- Load distribution with the RS-485 interface
A significant feature of MOVIDRIVE® drive inverters, the IPOSplus® positioning and sequence control system, now comes into play. An IPOSplus® program in MOVIDRIVE® calculates the setpoint speed of the master drive based on the speed specification for cornering and the actual speed of both drive wheels. The slave drive operates with torque control.
- The MOVIDRIVE® units exchange the data for speed control and load distribution via the system bus and the RS-485 interface.
- All movement control is carried out by the IPOSplus® program in MOVIDRIVE®.
- High overhung loads are avoided through the electronic differential, which ensures safer operation of the storage/retrieval system.
- Safe traction of the storage/retrieval system through slip control
- With active cornering control it is possible to negotiate corners 2.5 to 3 times as quickly
- Safe operation of asynchronous AC motors even in the field weakening range
- Simple integration into higher-level machine control systems is possible via fieldbus.