Automated test stand ensures axle quality

Citation

(2007), "Automated test stand ensures axle quality", Industrial Robot, Vol. 34 No. 2. https://doi.org/10.1108/ir.2007.04934baf.002

Automated test stand ensures axle quality

Automated test stand ensures axle quality

Drivers of luxury cars built in the UK can be confident that the axle and differential assembly, known as the final drive unit (FDU), is as quiet and smooth as in any vehicle in the world. It is because a first-tier supplier in the Midlands has installed a robotically- loaded test stand to inspect rigorously each FDU for noise, vibration and harshness (NVH) as it comes off the production line, rejecting any that do not meet car makers' stringent standards.

Designed and built by Geo Kingsbury in Gosport, Hampshire, UK, the production test stand operates around the clock, five days a week and frequently at weekends. It is one of the most advanced ever built, employing a six-axis articulated-arm robot from Motoman to load and unload the FDUs, of which there are currently four types weighing up to 65kg each, in a floor-to-floor time of one minute (Figure 1).

Operators are thus spared having to handle 50tons of material a day, avoiding strain injury and other potential health and safety problems. During changeover from one assembly to another, which takes place up to five times a day, the robot automatically changes its own grippers to handle the next FDU model and also exchanges the heavy, bespoke fixtures that clamp them in the rig.

Figure 1 Final drive units are loaded and unloaded by robot in the Geo Kingsbury production test stand at a tier 1 supplier in the Midlands

Instead of using subjective analysis by an operator, full NVH testing of vehicle transmission components is being specified more and more by automotive OEMs in response to higher levels of expectation from drivers. What sets this test stand apart is the use in production of a new system whereby the vibrations of the input and output shafts are measured as the pinion gear engages with the crown wheel, allowing the quality of gear meshing to be determined very accurately. It allows the level of refinement of the gear teeth when in contact to be determined, leading to an accurate prediction of how quiet the FDU will be in operation in the vehicle.

As it arrives by conveyor at the test stand, the axle is recognised by an electronic “handshake” with the production line control. Provided that the correct fixtures are in place, the robot automatically loads the FDU onto one side of the test stand's rotary table and waits for it to index to give access to the tested FDU. If it has passed, it is picked up and placed onto the conveyor to complete its journey to the dock audit section ready for delivery.

Meanwhile, the new FDU is automatically clamped in the Geo Kingsbury stand at an in-vehicle mounting position. In the case of a rear axle, the differential input shaft that simulates the drive from the engine is engaged and so also are the two output shafts that will, when the FDU is in the car, be connected to the back wheels.

At the same time, the differential is filled automatically with temperature- controlled oil, the type and amount of which varies according to FDU variant. Double metering ensures that the correct amount of oil enters the unit, as the axle will be shipped in this condition and it is important that the differential is neither overfilled nor underfilled.

As the oil fill cycle finishes, the shafts start to rotate, taking the assembly through a sequence of tests at different speeds. Scenarios include varying the speed at constant torque, varying the torque from positive to negative at constant speed, and combining the two. In this way, the gear set is monitored for NVH under heavy load in both directions and also when the gears are only lightly meshing.

System control software writing and programming of the test stand were carried out in-house at the Gosport factory. Anthony Best Dynamics' software is employed for analysing the output signals from the transducers.

Web site: www.testrigs.com