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Compact controllers put on the brakes

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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.

One company that is very familiar with the challenges of producing reliable braking systems is automotive brake manufacturer, PBR International, a subsidiary of Pacifica Group. When PBR needs the latest in assembly technology, it turns to Pacifica’s Melbourne-based process technology and product development division, Pacifica Group Technologies (PGT).

The most recent development by PGT in this area is a series of machines that can efficiently assemble any of five different types of brake disc-caliper.

For the sliding calipers manufactured by PBR, the caliper consists of two main sub-assemblies: the fixed ‘bracket’; and the ‘body’ that moves relative to the bracket to engage or disengage the rotor. The contacting caliper surfaces are lined with special wear-resistant pads. Pressure is applied through the use of one or more hydraulic pistons.

Brake calipers vary in shape and size, depending on whether they are for front (larger calipers) or rear (smaller calipers) wheels, and on the desired braking performance. PBR produces both one-piston and two-piston caliper brakes; in Australia, the ‘twin pots’ are seen on larger or high performance vehicles, such as the HSV Clubsports and FPV Falcon GT.

At its brake assembly plant in the US city of Columbia, PBR required machines for three new disc caliper assembly lines. PGT was called on todevelop the machines that would be able to handle of three types of front caliper and two different kinds of rear caliper on each compact production line.

In response to PBR Columbia’s needs, PGT began constructing the new caliper assembly machines. For each line, three machines complete a sequence of tasks: one assembles the caliper body as another assembles the bracket. The third machine then combines the sub-assemblies and performs a final acceptance check prior to unloading.

Each machine is designed around a number of ‘fixtures’ in which different assembly operations are carried out. In the case of the 8-station ‘body’ and the 4-station ‘drag validation’ machines, a central ‘indexing table’ rotates around a vertical axis to move each part to the appropriate fixture.

As well as putting together the sub-assemblies, many of the fixtures can perform validation and outcome verification, from the measuringtorque on bolts to high-pressure leak tests.

Automation system

A sophisticated automation systems enables the intricate train of operations of PGT’s new caliper machines, allowing them to change between products. The brains behind this automation is Rockwell Automation ’s Logix family of controllers.

Both the ControlLogix system (used for the body sub-assembly and drag validation machines) and the smaller CompactLogix system (for the bracket sub-assembly machine) offer powerful control capabilities. Both allow access via Rockwell Software RSLogix 5000 programming software.

According to PGT’s electrical engineer, Jim Christopher, the new high-level control platform allows the assembly lines to communicate with the management system. “It also means that we can sit in Melbourne and monitor the US factory across the network,” Christopher explained.

The assembly machines utilise drive systems for a variety of applications--from Allen-Bradley PowerFlex 70 ac variable speed drives (VSD) for the indexing tables, to the servo positioning system (based on an Allen-Bradley ULTRA 3000 digital servo drive) for final assembly unloading.

Christopher asserts that, in addition to being smoother and quicker, a benefit of the Rockwell Automation system was the ease with which the controllers could be interfaced with the drives, leading to striking benefits for the servo positioning application.

By using a SERCOS digital servo interface module and fibre-optic cable to connect to the ULTRA 3000 servo drive, the ControlLogix has been able to meet all motion control needs, with no need for a separate motion controller.

Providing a simple communications conduit for the many field devices located about the machines was the DeviceNet device-level network. The fact that DeviceNet allows the use of field-located, or ‘distributed’, input/output (I/O) provided distinct advantages.

“The first is that its not as labor-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,” Christopher said.

According to PGT’s assembly technology development manager, Bruce Henshall, the single-source automation solution, installation, commissioning and implementation, has saved time and money. “To do it any other way, it would cost 30% more.”

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