Henry Ford is popularly remembered as the man who invented the automotive assembly line. In fact, that distinction properly belongs to Ransom E Olds, whose Curved Dash Oldsmobile was mass-produced by the method as early as 1901. Ford’s revolution was to marry the concept to conveyor belts. His moving chassis assembly line, which commenced operations in 1913, reduced the time it took to put together a car from twelve hours to two and a half.
It was, then, not the assembly line per se that gave birth to the modern car factory so much as it was this crucial first step towards automation: the substitution of mechanised work (movement of components) for human labour (walking between them).
The automotive industry has pioneered forms of automated process ever since. The first industrial robot, Unimate, was installed at a General Motors diecasting plant in New Jersey in 1959. And it was General Motors, again, who in the 1990s commissioned the development of the first smaller collaborative robots (or cobots).
Today’s car assembly plants – together with the part manufacturers and subassembly plants that supply them – are the inheritors of this tradition. And a century on, conveyor movement is still at the heart of the factory system, though now diversified and augmented by elevators, hoists, carrier vehicles and automated storage/retrieval systems.
Now, too, the vehicle under construction is conveyed around as many robotic processes as human: from spot and arc welding, through assembly tasks such as windshield installation and wheel mounting, to the bodywork spray painting that, following precise programming, produces exactly the desired finish.
The number of drives and motors used in these operations can run into the hundreds. To give an example, as part of its 2006 revamp, DaimlerChrysler’s Sprinter production facility in their east German Ludwigsfelde plant was supplied by Control Techniques with over 800 AC drives. In particular, the versatile Unidrive SP was deployed as standard throughout the facility for all applications over 1.1kW.
The applications thus powered require varying degrees of control. Relatively simple processes, such as shunting car body shells along storage rails, can be driven in open loop mode. More complex operations involve exact positioning in three dimensions and necessitate controlled movement in a closed loop system.
The automated storage operation at Ludwigsfelde, for example, where almost 200 body shells are stowed between the paint shop and final assembly, requires vertical lifting power of 55kW, forward movement power of 37kW and lateral movement of 2.2kW. Control along all three axes is achieved through encoder feedback and where necessary enhanced through the additional processing of laser signals.
The majority of drives on the shop floor at Ludwigsfelde are fitted with Interbus communication modules, with the protocol used depending on the application. In final assembly, CANopen runs over the network of floor conductors that supplies power to the automated guided transport vehicles. This twenty-first-century development of the conveyor system calls upon the combined action of several pairs of motors to effect the complex manoeuvres required by the appropriate movement profile.
As an alternative to fixed bus bars, and in order to overcome some of their constraints, wireless technology has elsewhere been used to refine assembly line conveyor control yet further. Ethernet/IP networks have been employed with PACs and supporting peripherals, including I/O and variable speed drives, to program the movement of shop floor carriers independently and at a range of speeds.
With the automotive industry more than ever seeking ways to improve efficiency and tighten points of design, it is essential that the drives of a system be as flexible and open to preferred types of programming as possible. And, as the shortage of skilled engineers grows ever more acute, it is equally important that drives’ operation and maintenance be straightforward and transparent.
But will the automation of the car factory ever become so total that the whole thing will equate to one giant, programmable machine – capable, as they say, of running with the lights out? Will the story begun by Henry Ford’s conveyor belt necessarily end with Elon Musk’s alien dreadnought?
Perhaps not yet. One trend in the automotive industry that actually pulls counter to the build towards full automation is the emergence of relatively short-term product cycles. As the marketplace for vehicles has become less uniform and passive, as it has instead grown more complex and diverse, car manufacturers have found a competitive edge in being able to respond quickly to consumer demand with different models.
It is increasingly common, in consequence, for factories to produce more than one model of vehicle, turning from one to another according to the call of the market. It is a dynamic to which humans inevitably respond more naturally than programmed robots. And it means that final assembly plants, in particular, have already come up against certain automatable limits.
None of this is to say, of course, that ongoing advances in digitization need stall or plateau. On the contrary: with car factories increasingly exploiting the close integration of human, robotic and IoT process, the flow and management of data for improved overall system control has never been more important.
In this context, the drives and motors used in automotive manufacture may be seen as indispensable aspects of larger networks, or complete automation solutions as they are coming to be called – their functional openness and flexible programmability underpinning the coherent functioning of the complete system.