Seamless sequence

Factory simulation software can give firms an edge in working out the best way to assemble new products. The ability to model programmable logic controllers used to automate processes is the latest development, says Douglas Friedli

As product life-cycles get shorter and manufacturing processes more complex, firms can gain a big competitive advantage by cutting the time it takes to set up or reconfigure a plant for a new product. A milestone in recent years has been factory simulation software, which enables manufacturers to work out the best way of organising each stage in the assembly process.

The latest component to get the simulation treatment is the programmable logic controller (PLC), used to control automated factory operations.

Tecnomatix, whose Robcad software has been used extensively by companies such as Rover to model production lines, has added a new module to the suite of programs. Robcad-PLC can model and test a sequence of operations in manufacturing cells controlled by PLCs before the cell is physically built.

It enables production and process engineers to design manufacturing processes, create programs to run PLCs, robots and machines, and to validate and optimise programs in advance. These programs can then be downloaded on to machines on the shopfloor.

According to Yoav Tomer, product manager at Tecnomatix Technologies, the idea of a seamless path from process design to shopfloor is now a reality. `Everything that can be done with robots can also be done with PLCs,’ he says.

Robcad-PLC was developed with Siemens’ automation and drives group at the instigation of BMW. Siemens dominates the European PLC market with an estimated 70% market share. Europe is also the largest market for Tecnomatix.

Alfons Kiermeier, BMW’s PLC program manager, says the company was looking for a way to speed up new model launches and cut costs. `We have to know exactly the functionality and behaviour of the product lines early in the production engineering phase,’ he says. `These critical factors can be achieved by generating automatically the PLC programs concurrently with the design process, and then using these programs to simulate the production lines in a virtual environment.’

One benefit is that changes in design which would be difficult and costly to try in a real factory can easily be tested. Tecnomatix northern Europe manager Gareth Watts says: `In the past, the production engineer would ask the design engineer to make changes in the product to make it easier to manufacture. The design engineer would say: “change the way you build it”.’ Now these conflicts can be addressed at the design stage.

There is also a saving in paperwork, says Tomer. `At the moment, the sequence of operations in a manufacturing cell is transferred to control engineers on paper. They add more information to do with safety, novel operations and so on. But there is no feedback to the process or mechanical engineers.’

An electronic system means, in theory, automatic feedback and less paperwork. This is likely to be even more true when PLC simulation software starts to become Windows NT-compatible. At the moment Robcad-PLC works only under Unix, but the company plans a Windows NT version for July.

BMW is expected to start installing Robcad-PLC at its plant in Dingolfing, Bavaria when the NT version comes out. It is encouraging suppliers such as production systems manufacturer Comau to start working with the same software.

Only Siemens PLCs are now compatible with Robcad, but in the longer term Tecnomatix will probably have to work with other PLC makers, especially outside Europe, where Siemens has a lower market share. `Ford in the US is pushing us to talk to other manufacturers,’ says Tomer.

DaimlerChrysler is also looking at PLC simulation as part of the wider question of factory simulation. The US-based Chrysler part of the company has been working on what it calls control program generation analysis (CPGA) since last year.

Working with Rockwell Automation and manufacturing software firm Deneb, Chrysler has developed CPGA to generate and validate control programs before tooling is made.

The software has built-in libraries with data on robots, common production equipment and tooling. This, with process and resource models from Chrysler’s digital manufacturing production system, creates a basis for creating a virtual factory.

Frank Ewasyshin, Chrysler’s vice-president of advanced manufacturing engineering, says: `CPGA will cut the time it takes to program a typical workcell by thousands of hours, shave two to four months off the development time of cars and save upwards of $20m (£13m) per assembly plant.

`It will also more readily identify and eliminate process variation in the build process for better vehicle quality. And it will improve communication among manufacturing, engineering and supplier personnel.’

The motor industry is leading the way on PLC simulation, but other sectors will not be far behind. Watts says: `The automotive sector tends to be ahead on most things. Plastics firms have been investing more in robots recently, but the actual applications are just too trivial to make PLC simulation worth it. But we expect industries with complex processes such as electronics or aerospace to be interested.’