Doors to perfection

Citation

(2001), "Doors to perfection", Sensor Review, Vol. 21 No. 3. https://doi.org/10.1108/sr.2001.08721caf.002

Doors to perfection

Doors to perfectionKeywords: Inspection, Automotive industry

A machine for automatically assembling vehicle door casings has had its error checking systems upgraded so that Land Rover can be confident of improved delivery to its just-in-time assembly plant in Solihull, where the Freelander, Discovery, Range Rover and Defender platforms are made.

The doors must be assembled correctly and the machine runs a check to ensure that all the equipment – window mechanisms, locks, handles, speakers, trims, etc. – has been put in place, screws are tightened to the optimum torque and that everything is in the correct colour and trim. Land Rover has something in the order of 500 different door specifications to cover its entire production, so the checking system has to accommodate a great many variables while simultaneously exchanging data with the high level production control system to ensure the correct specification doors are being produced at any given time (Plate 3).

The actual checking is done through a series of photocells, proximity switches, other sensors and torque screwdrivers. Each of these feeds a signal back to a PLC which compares the results of the check sequence with the "recipe" for the given door specification read from a barcode into the PLC. If all the correct signals are received, the PLC passes the door, if not, the errors are highlighted to the operator and the door remains at the workstation for the necessary reworking.

Plate 3 With over 500 different door specifications, Land Rover uses Omron control equipment to ensure each door passes stringent checks before it is approved to be fitted to a vehicle

For the upgrade, all existing devices and i/o were left in place and more were added. This necessitated replacing the original PLC with a more powerful Omron CQM1H (the removed PLC, an Omron SRM1, being redeployed to another job). Soon the way in which pass/fail and error details are presented to the operator will be enhanced: the CQM1H will be configured to drive an easy-to-understand graphics presentation on an Omron NT30C human-machine interface touchscreen, which shows clearly and instantly any errors. The screen was fitted at the time of the upgrade, and will be brought on line in a few months.

The upgrade was designed and implemented by control systems specialists Theocrest of Coventry. The machine uses a rotating carousel to bring the various items to the workstation where they are inserted into the main body of the door. It is run by Textron Automation in Birmingham and can produce doors in the various specifications required for all the models, colours and variants in the Land Rover range.

Just-in-time production is vital for the success of many industries, including automotive manufacture, and requires very high levels of co-operation right along the supply chain to be effective. Deliveries have to be to a strict schedule and every item of every delivery has to be perfect, otherwise the production line is likely to come grinding to a halt. Even greater co-operation and pre-planning is required when new production machinery is to be installed or existing machinery reconfigured. In order to not disrupt production, the Land Rover/Textron/Theocrest/Omron project had to be completed in a specified four-day window.

"Setting that window was a defining moment in the project," recalls Theocrest's Garry Frere. "Before we had the date the whole thing was almost like an academic exercise, but once it was set it was more like a military operation. There was no option for going back, we had to have every detail planned, prepared and scheduled ready for the window to open. The tension grew as we counted down to the window, and then it was total dedication to complete everything within the allotted four days.

"We have since been welcomed back regularly to complete further mods and upgrades. For instance we have added a number of colour sensors to further enhance the error checking. We have also interfaced the CQM1H with the PLC on a nearby water jet machine which cuts the door trims, for data exchange so that the two machines always work in perfect synchronism."