Make or brake with compact controllers

Saturday, 13 December, 2003

Integrated control solutions are at the heart of Pacifica Group Technologies' new brake caliper assembly machines, allowing unprecedented ease and versatility in the production process.

Of all the features that grace modern automobiles, few are as important as the disc brakes. Not only do they provide the crucial function of reducing travelling speed, their capabilities have implications for the very design of the vehicle: from the size of the chassis to the power of the engine. It is paramount that these devices are constructed with the utmost precision and care - the performance of the car and the safety of the occupants demand it.

One company that is very familiar with the challenges of producing reliable braking systems is PBR International, a subsidiary of Pacifica Group Ltd. For years, the automotive brake manufacturer has been delivering lightweight, high-performance braking systems to its customers from plants in Australia, the United States, Malaysia and Thailand.

When PBR needs the latest in assembly technology, it turns to the research and development efforts of Pacifica's Melbourne-based process technology and product development division, Pacifica Group Technologies (PGT), to produce streamlined and innovative assembly lines. The latest development by PGT in this area is a series of machines that can efficiently assemble any one of five different types of brake disc-caliper - an addition made possible through the use of advanced control technology from Rockwell Automation.

Calipers for export

A disc brake operates by applying drag with a 'caliper' to a 'rotor' disc that turns with the corresponding wheel. For the sliding calipers manufactured by PBR, the caliper itself consists of two main sub-assemblies: the fixed 'bracket' and the 'body', which moves relative to the bracket in order to engage or disengage the rotor. The contacting surfaces of the caliper are lined with special wear-resistant pads, and pressure is applied through the use of one or more hydraulic pistons.

In the world of disc brake calipers, one size does not fit all. Not only are front wheel brake calipers generally larger than the rear wheel equivalents to accommodate the distribution of weight in a car, each caliper design is strongly influenced by the desired braking performance. For this reason, PBR produces both one- and two-piston caliper brakes (referred to as 'single pot' and 'twin pot' respectively). Generally, the 'twin pots' are seen on larger or high-performance vehicles, such as the HSV Clubsports and FPV Falcon GT.

Producing such high-quality brake calipers, however, is no simple task. The assembly process must put together a large number of components to provide a range of different final products, given limited factory floor space and operator supervision.

Integrated detection

Each of the new caliper assembly lines, in essence, comprises three machines which must co-ordinate a sequence of tasks: one assembles the caliper body, another assembles the bracket, before the third machine combines these sub-assemblies and performs a final acceptance check prior to unloading.

Bruce Henshall, PGT Assembly Technology Development Manager, explains that this 'final validation' is necessary to confirm that all components have been put together properly. "Basically, we operate the caliper, then release it and measure the residual drag. What we want to know is that there is no friction between the rotor and the pads in the release condition. This is essential to confirming that both our assembly and machining processes are correct," he says.

Each machine is designed around a number of 'fixtures' in which different assembly operations are carried out. In the case of the eight-station 'body' and the four-station 'drag validation' machines, a central 'indexing table' rotates around a vertical axis to move each part to the appropriate fixture.

Not only are they responsible for putting together the sub-assemblies, but many of the machine fixtures are designed to perform validation and outcome verification functions - from the measurement of torque on bolts to high-pressure leak tests. These checks and tests are vital for maintaining quality, and necessitate the use of an impressive array of instrumentation, including hard probes, pressure and torque transducers, as well as infrared and optical laser detectors.

"The reason why we go through all the testing and checking is because our aim is zero defects. When the brake caliper is assembled, all the fitment points that the customer is going to use will have been checked. We have very tight first-off quality targets within the plant," says Henshall.

Automating the enterprise

Enabling the intricate train of operations of PGT's new caliper machines is a sophisticated automation system. "Most of our customers want different variations of the same caliper. The machines are quite complex, even though some of the tasks look simple," Henshall explains. "It's the detection side of the task which consumes considerable amounts of money. These assembly machines are special because they change from one product to another, and a lot of the cost is tied up in automation."

When considering what platform to use for automation, PGT was faced with the need to realise both sequential and single-axis motion control. The equipment also needed to be able to record and communicate key performance indicator (KPI) data that would be passed to the US-based PBR Columbia management system - from process pass/fail information and pressure and torque readings, through to part numbers and 'pack weigh-out' details. Moreover, the engineers at PBR wanted a 'single source' solution whose equipment was consistent throughout its entire brake assembly plant.

The decision was made to opt for a complete Rockwell Automation solution that would interface well with the existing PBR management system based on the Rockwell Software RSBizware data integration and analysis package. "Our idea is that we should focus on one technology and we considered the Allen-Bradley suite because, not only were they considered the best electromechanical resource at the time, but they were also nominated as the most user-friendly," says Henshall.

According to Jim Christopher, PGT Electrical Engineer, the new high-level control platform offered key advantages to the development group. "We went to ControlLogix because it was the latest innovation, and had drive capabilities, high-resolution analog and seamless integration. Importantly, it allowed us to meet the requirement that the assembly lines be able to communicate with the management system. It also means that we can sit in Melbourne and monitor the factory across the network," he explains.

Driving considerations

The assembly machines use drive systems for a variety of applications - from PowerFlex 70 AC variable speed drives (VSD) for the indexing tables, to the servo positioning system for final assembly unloading. Christopher says that one of the benefits of the Rockwell Automation system was the ease with which the controllers could be interfaced with the drives.

"These lines are the first where we've used the full Allen-Bradley drive system. Previously, we've had to go in with other software to set up the drive and its parameters. This time we wanted it to be seamless, so we opted for a system that allows us to program and change everything straight through the processor. They're also a lot smoother and quicker," says Christopher.

One of the most striking benefits from the drive integration was the servo positioning system application. Located at the end of the drag validation machine, the positioning system is responsible for unloading each caliper along one of six exit conveyors, ensuring that the correct part is transported to the correct 'pack-out' station. By connecting a ControlLogix to an Ultra 3000 digital servo drive with fibre-optic cable, PGT has been able to meet all of its motion control needs without the requirement for a separate motion controller.

Philosophy and footprints

According to Christopher, the use of distributed I/O linked via DeviceNet was behind a lot of the key savings realised in the construction of the machines. "There are two main advantages as far as we are concerned. The first is that it's not as labour-intensive to wire-up, and the I/O is distributed around the machine as and where it is required. Secondly, it provides space savings - put simply, we don't require a huge electrical cabinet in which to put the I/O," he says.

Henshall adds that PGT was able to support PBR's philosophy of locating the equipment in such a way as to optimise process flow, from the casting and machining through to assembly. By keeping its control cabinets down low in order to allow easier, 360° access to the equipment, PGT has ensured that its machines maximise free floor space and reduce the 'walk distance'.

"Distributed I/O helped us to reduce the size of the footprint. By putting the I/O on the tooling, this helps with diagnostics and makes it more accessible to maintenance people," says Henshall.

Assembly online

PGT completed construction of the new disc caliper assembly machines in the second quarter of 2003, and Henshall weighs the benefits of the single-source automation solution. "The installation, commissioning and implementation of the Rockwell Automation system has saved in time and money, because they don't have to go and write special code to interface with other systems and gather all the information. That has been a definite saving - to do it any other way it would cost 30 per cent more."

Christopher also points out that the use of CompactLogix on the bracket sub-assembly machine has in itself helped to achieve PGT's needs with less expense: "Its easier for the maintenance people to be able to understand the program. In using the Logix5000 programming platform, we've been able to implement CompactLogix and cost-reduce one of the machines considerably; it led to 15 per cent off the cost of the machine."

Once they are shipped to PBR Columbia, the new caliper machines will be able to integrate seamlessly into the wider brake assembly plant. As part of one common automation platform for operations, maintenance and technical training, they will thus facilitate the streamlining of brake production. In addition, the seamless system design enhances the on-site ability of the OEM to carry out diagnostics and a number of maintenance functions, while being remotely supported from PGT in Australia.

Ironically, according to Henshall, PGT went down this path originally to ensure that the system would integrate easily into the US plant. But the use of the system has actually allowed PGT to improve the performance and quality of the assembly process, enabling an ultimate reduction in capital cost per part. The impact of this will be experienced on many levels, beginning with more efficient manufacturing for PBR Columbia and ending with better braking systems for customers worldwide.

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