More than 800 AC drives have been installed in the new 'Sprinter' production facility in DaimlerChrysler’s Ludwigsfelde plant, near Berlin.
All drives above 1,1 kW used in the new factory were supplied by Control Techniques. Technical Engineer, Mr Wagner explains, “Programming flexibility and openness are the main reasons for this selection. We particularly liked the Unidrive SP’s versatility”.
The drives are used in open loop and closed loop applications – for both synchronous motors and induction motors, and all position-controlled axes in the entire facility. This embraces control of conveyor belts, scissor lifts, automated guided transport vehicles and advanced compact storage systems, up to ventilation and extraction systems.
Most of the Unidrive SP drives in the Ludwigsfelde plant are fitted with an application module for additional onboard processing and Interbus communication. Profibus DP or CANOpen bus protocol is used on some axes. Others have an additional encoder module to enable a second transmitter signal, from a laser measuring instrument, for example, to be processed
The drives control essential functions throughout the three core areas of the facility: body shop, paint shop and final assembly.
Body shop
Sprinter bodies are built from preformed sheet metal, using welding robots and a fully automatic material transport system. Over 200 Unidrive SP drives are used in this area. They are operated in open loop mode for transport tasks (in the buffer store, for example, where up to 86 body shells are stored temporarily on 11 rails) and in closed loop mode for hoist units. A typical precision application can be seen in the automatic welding cells where two drives coupled with servo motors are used in a master/slave configuration for the lifting mechanism, synchronised with a third drive with Unimotor in position control.
Paint shop
Around 200 more drives – rated at up to 110 kW – are used in the Dürr paint shop for ventilation and extraction tasks. Added to this, a number of blowers and pumps for hydraulic axes have to be controlled. Most of these drives run in open loop mode, with Interbus communication links to the corresponding PLCs. Synchronous motors with resolver feedback to the controlling Unidrive SP drives are used in the 15-workstation cathodic electro dip coating plant, not only for forward movement, but also to rotate the body shells within the dip.
Final assembly
The most demanding drive applications are found in final assembly, where approximately 400 drives are used.
Each of the open-loop transport units in the overhead conveyor system is supplied with DC power for its onboard drive/motor system via a specially designed busbar system that also enables CANbus communication. Automated guided transport vehicles, used for carrying components such as the complete power transmission system of a Sprinter – engine, gearbox, drive shaft and axles – are supplied by induction from conductors laid in the floor. In addition the six Unidrive SP inverters (1,1 to 1,5 kW) are supplied at 500 V d.c. Two induction motors are used for movement and steering, whereas two Unimotor type 142 UMD synchronous servo motors are required for the scissor lift and two Unimotor type 115 UMD motors for trim. Control signals are picked up from feed points let into the floor, so the vehicle is instructed when it should move and which movement profile it should follow. A CANbus/Interbus gateway is located in the interior of the vehicle and communication with all six inverters takes place via Interbus.
A body shell storage facility with 198 positions over two tracks and four-high racks is used as a call-off point between the painting and assembly operations, and demands precision movements in three axes. Additional feedback signals are provided for both longitudinal and lifting axes – a long-range laser for the distance along the rail and an absolute encoder fitted on a wheel of the lifting axis, which both enable monitoring and error correction, where necessary.
In the small components storage system, around 10 000 different components are accommodated in four magazines.
Two vehicles are used there, each fitted with four Unidrive SP giving 3-axis servo control (18,5 kW for lifting, 11 kW for longitudinal and lateral motion) as well as a small, integral 1,5 kW conveyor for the picking process.
For more information contact Bill Tedd, Control Techniques, +27 (0)11 462 1740, [email protected], www.controltechniques.com
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