Gearing up for production control

Online since October 2006, SEW-Eurodrive's assembly facility at its Australian headquarters in Melbourne produces the MC Compact series of industrial gear units and has allowed the company to slash gear unit turnaround times.

The assembly facility comprises two key elements - a fixed assembly machine and a moveable track-based 100-tonne gear unit press. A one-tonne jib crane and a 10-tonne overhead gantry crane complement the assembly process, and allow rapid manoeuvring of the gear units and internals.

When it came to procuring the assembly machine, there were two choices - purchase an assembly machine from overseas at considerable expense or obtain a locally-made assembly machine. A locally-made off-the-shelf assembly machine with the precision positioning capabilities required simply did not exist.

As a result, the company teamed up with machinery designer-manufacturer, Andrew Engineering, to tailor a built-for-purpose assembly machine. The resulting machine is modelled on existing SEW-Eurodrive gear unit assembly machines already in operation around the globe and utilises a range of the company's own advanced drive and control solutions.

The resulting machine features a height-adjustable rotator that permits precise elevation and accurate orientation of the gear unit. The separate gear unit press moves back and forth to the stationery assembly machine and provides the force required to press the gear unit internals in place.

The mobile nature of the press ensures that it can be kept clear of the assembly process until needed. Both the gear unit assembly machine and press are operated via a single pendant controller.

The gear unit rotation and up/down motions realised at the gear unit assembly machine are achieved using three separate servo gear motors. An additional servo gear motor is employed to provide the 'travel' movement of the gear unit press. Four MOVIDRIVE 'B' application inverters (one per servomotor) are used to drive these four motors, and to provide advanced applications such as precision servo positioning.

All four inverters are interfaced with the MOVI-PLC, which provides central, single-point configurable control of all motion applications and enables programming time and costs to be reduced.

Integrated into the fixed assembly machine is a drive operations panel (DOP) operator interface, which allows plant-floor operators to select product 'recipes' and provides access to diagnostic data, such as load-sharing status.

Safety was a prime consideration during the project. Industrial lifting apparatus, such as the assembly machine, often employ hydraulic counter-weight systems in conjunction with a single-screw lifting mechanism.

The hydraulic component acts as a fail-safe mechanism in the event of power loss. It also reduces screw and motor size, and minimises screw-wear. Such hydraulic systems are often noisy, substantial in size, and can require regular costly maintenance. During the design process, Andrew Engineering developed another solution - a twin-screw lifting mechanism that incorporates advanced drive solutions to provide movement, control and counter-balance.

The two screws traverse the height of the gear unit assembly machine and are independently driven by two helical servo gear motors. A threaded nut on each screw links the screws to the rotator plate. As the screws turn, the nut and rotator are moved upwards and downwards. A lead screw is used to position the rotator, while a ball screw sustains the majority of the load.

The current draw of both screws can be monitored and the second screw programmed to take approximately 80% of the load. This load-sharing arrangement means the assembly machine can accommodate a range of gear unit weights.