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Glass roof insertion system keeps the XJ assembly on track

02 August 2010

A robot-controlled panoramic roof insertion cell has recently been incorporated into the Jaguar XJ assembly line. The trick was to introduce the cell into the existing overhead conveyor system that brings bodies to the trim and final assembly without changing the functionality and efficiency of the transportation systems and downstream assembly processes

The new Jaguar XJ features among its generous list of standard equipment the first full-glass roof on a Jaguar. This specially toughened Webasto glass roof is a defining feature of the new model, adding ‘a visible architectural lightness’ to the car’s exterior. A special opening mechanism also gives the new XJ’s coupe styling the lowest exterior roofline in its class.

Positioning, inserting and bonding the panoramic glass roof to the aluminium body required a complex automated conveying and handling system that was developed as the result of cooperation between the engineering team at Jaguar Cars and materials handling and automation specialist, Exmac Automation. In order to deliver the project on a turnkey basis, Exmac formed a partnership with Expert Tooling, another established supplier in the field.

The partners – Exmac specialising in conveying, transfer systems, automation and control, and Expert in robotics, precision tooling and gluing systems – initially worked closely with the Jaguar team on a detailed simultaneous engineering project for the roof insertion system. Input from the partners helped Jaguar identify the best technical approach and a location within the existing production facility that would avoid disruption to current and future assembly line operations. Jaguar then used the results of this project to obtain open market tenders prior to making its final selection. Following the tender, Exmac and Expert were successful in winning the contract to implement the cell.

Jaguar XJ bodies are delivered by truck and trailer from the Castle Bromwich body store and at an assembly point they are transferred into a static ‘false’ trailer. The bodies enter the building on a series of roller beds and elevators, and then transported through an existing assembly system that serves both the previous and the new Jaguar XJ models.

A fundamental requirement of the project was that the new automated roof insertion cell be introduced into the existing overhead conveyor system that brings bodies to the trim and final assembly line – a specification that was achieved without changing the functionality and efficiency of the transportation systems and assembly processes. It was also achieved without any disruption to the production of the existing XJ model.

To facilitate the fitting of the glass roof, the structure and operation of one of the elevators in the body delivery conveyor has been modified to allow XJ bodies to be removed and lowered to ground floor level, where a robot-controlled panoramic roof insertion cell, designed by Expert Tooling, has been installed to bring roof and car together.

These changes involved decommissioning and removing the old elevator and introducing the new one through the roof of the building, using a 100 tonne telescopic crane. Exmac designed and manufactured the new elevator, which required an increased lifting stroke of approximately seven metres to enable it to service the ground floor and first and second floor levels. Exmac also project-managed the operation, including rewiring and re-commissioning, during a two-week shutdown period and the new elevator was operating successfully with the existing systems when the assembly line was restarted.

Sunroofs are introduced to the new cell on specially designed platens via an Exmac two tier chain conveyor and lifter system. They are positioned and inserted using proven mechanical centralising methods and robot techniques, rather than camera vision systems. This was the preferred option to ensure the accuracy and repeatability of this process, as Expert’s Terry Davidson explains:

“A vision system would measure the roof aperture, adjust the programming of the robot, then try to fit the roof based on those measurements. However, the absence of sharp body features on the flowing lines of the XJ, make it difficult for a vision system to operate effectively.”

The Jaguar XJ system centralises the roof panel using an ABB robot and a special gripper featuring a ‘floating’ joint. With this method the glass roof is always suspended above the car in a known position on the gripper, and the roof aperture of the car is also in a known position below. The gripper joint is programmed to unlock and move into position on the car, rather than trying to move the whole robot to the car.

Before insertion the roof is heated to the temperature required for the polyurethane adhesive used in the bonding process. The robot then positions the roof underneath an SCA Schucker applicator and the adhesive is applied. The completed roof unit, held within a specially designed fixture, is then lowered to meet the roof aperture of the XJ body below.

At this point the special joint on the gripper disengages, allowing it to ‘float’. The floating gripper ensures that the roof is in the correct position to locate accurately with the aperture in the vehicle body. Weights are then applied for four seconds to complete the gluing process and ensure that car and roof are perfectly bonded. With its roof fitted, the body is fed back up into the body delivery system via the Exmac conveyor to continue its journey through assembly.

The robot and the adhesive system that bonds the roof to the car body are both interfaced to a PLC via Interbus protocols, to create an integrated and reliable system that has proved extremely accurate and reliable.

When the roof insertion process is completed, the finished vehicle is transported back to the assembly line on the first floor via the modified elevator, where it undergoes the normal assembly process. Exmac managing director Gary Sweeney summarises:

“We take the XJ body out of the existing Jaguar overhead assembly system, bring it down to floor level, fit the roof and feed it back into the system in one totally unmanned operation. It really is quite a feat of engineering and we are proud to have worked as a team with Jaguar engineers from concept to finish. “

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