Improved friction testing with multi-axis sensors

The main advantage of multi-axis sensors is the ability to collect multiple data points to provide a more complete picture during the product development and testing phases. The ability to measure on multiple axes simultaneously not only provides more accurate data, but also speeds up the testing process. Essentially, fewer variables are required, like using multiple Load cells. One application of force testing that benefits greatly from multi-axis sensors is friction force testing.

For definition:
Friction is the resistance that one surface or object experiences as it moves over another.

The coefficient of friction (fr) is a number obtained from the ratio of the frictional resistance force (Fr) divided by the normal or perpendicular force (N) that pushes the objects together.

The force exerted by a surface when an object moves or attempts to move over it is called the friction force. Although not always the case, the force of friction often counteracts the movement of an object. A friction test measures the resistance that prevents objects from moving freely and unhindered against each other. For measurement purposes, sliding and static friction are the two most common.

Traditionally, the friction testing process for multi-axis measurement was performed using two or more single-axis load cells that would measure the force on each axis separately. Unfortunately, this method required the user to have multiple load cells of the same design available for such testing. Most importantly, the results of this method may involve parasitic losses in accuracy.

By introducing a multi-axis load cell such as the 3-axis sensor, the user can get a more complete picture with less time and lower cost. The advantages of a 3-axis sensor include the ability to eliminate parasitic losses and bring the measurement closer to the sample. In addition, 3-axis sensors enable simultaneous measurement of the x, y and z axes without additional load cells.

In our recent webinar, Inventive Multi-Axis and Instrumentation Solutions, Keith Skidmore explains an example of friction testing and the benefits of using it Multi-axis sensors. He explains that in a friction test that involves applying a weight to a sample and then pulling that sample across a surface, this pulling force can be measured using a single-axis load cell. This works great provided the weight you are pulling is constant.

Test accuracy

Test accuracy assumes that the sample does not move during the test. So, to prevent it from tipping over, you probably attached guides or an object. The problem is that this type of application or guidance can create parasitic loads and create an unrepeatable system.

How to limit the system without affecting the measurement in this type of friction test? One possibility would be to use a three-axis sensor directly above the sample. Now you can use guides and it no longer matters because the sensor measures directly on the test object. You can pull it and the data channel will show the weight change as you slide and provide the fixed weight. Added to this is the force of friction, which tends to move from side to side.

A 6-axis load cell can also be used for friction testing. 6-axis load cells provide even more data across all six axes and also allow the user to compensate for any off-center components. Users interested in the rotation component of the friction testing machine should also consider 6-axis. With a 6-axis machine you can measure rotation tendencies or other effects of the clamping device. More data, better analysis and the ability to control your test specimens.

Recently, Interface presented an application note describing the use of a 3-axis load cell to measure and test a friction force machine. Check it out below:

Friction test

A testing lab wanted to replace two single-axis load cells in its friction testing machine with a sensor that could measure force on the x, y, and z axes simultaneously. Interface suggested installing a 3A60 3-axis load cell into the existing machine and connecting an Interface BSC4D-USB Multi-Channel PC Interface directly to a PC laptop to monitor and record the data in real time. With this solution, the testing lab was able to simplify sensor setup and improve data collection, providing added value for the end customer.