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Enhancing Friction Testing with Multi-Axis Sensors

Multi-axis sensors premier benefit is the ability to collect multiple data points to provide a more complete picture during product design and testing phases. The ability to measure on multiple axes at one time not only offers more accurate data, but it also speeds up the test process. Essentially it requires fewer variables, like using multiple load cells. One force testing application that benefits greatly from multi-axis sensors is friction force testing.

For purposes of definition, friction is the resistance a surface or object encounters when moving over another.

The coefficient of friction (fr) is a number that is the ratio of the resistive force of friction (Fr) divided by the normal or perpendicular force (N) pushing the objects together.

The force exerted by a surface as an object moves or attempts to move across it is what is called friction force.  Though it is not always the case, the friction force often opposes the motion of an object. A friction test will look to measure the resistance preventing the objects from moving without interference or restriction against each other. For purposes of measurement, sliding and static friction are the two most common.

Traditionally, the friction testing process for trying to measure multiple axes was completed using two or more single axis load cells that would measure force on each axis separately. Unfortunately, this process required the user to have multiple load cells of the same design on hand for such testing. Most importantly, this methods results could include parasitic losses to accuracy.

By introducing a multi-axis load cell like the 3-axis sensor, the user can get a more complete picture with less time and lower costs. The benefits of using a 3-axis sensor include the ability to eliminate parasitic losses and move the measurement closer to the specimen. Also, 3-axis sensors allow for simultaneous measurements of the x, y and z axis without additional load cells.

In our recent webinar Inventive Multi-Axis and Instrumentation Solutions, Keith Skidmore details a friction testing example and the benefits of using multi-axis sensors. He explains, in a friction test where you want to apply a weight to a specimen and then drag that specimen across a surface, that drag force could be measured with the single axis load cell. This works great assuming the weight is constant that you are pulling. The assumption in your testing accuracy is that the specimen doesn’t move during the test, so to prevent it from tipping over you probably have guides or an applied object. The issue is this type of application or guide might create parasitic loads and create a non-repeatability system.

How do you constrain the system without affecting the measurement in this type of friction testing? One way to do it would be using a three-axis sensor right above the specimen. Now you can use guides and it doesn’t matter because the sensor is sensing right at the test specimen. You can pull on it, the data channel shows the change in weight as you slide providing your fixed weight. Then you’ve got your friction force which tends to want to move side to side.

Users can also consider a 6-axis load cell for friction testing. 6-axis load cells provide even more data on all six axes, and also allows the user to adjust out of any off-axis components. Users that are interested in knowing the rotational component of the friction testing machine may also want to consider 6-axis. Using a 6-axis would allow you to measure tendencies in rotation or other effects from fixturing.  More data, better analysis and ability to control your testing specimens.

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

Friction Testing

A testing laboratory was looking to replace two single axis load cells used in their friction testing machine with one sensor that could measure force on the x, y, and z axis simultaneously. Interface suggest installing a 3A60 3-Axis load cell their existing machine with an Interface BSC4D-USB Multi-Channel PC Interface hooked directly to a PC laptop to monitor and log the data in real time. Using this solution, The testing laboratory was able to simplify their sensor set-up and improve their data collection, creating more value for their end customer.  You can read the entire application note on friction testing here.

 

Compression Force Testing 101

Compression is a type of force that we apply every day often without thinking and compression is intensely tested in many of the products we use on a daily basis.

Compression force is defined as the energy generated from compressing an object or substance. Compressive force is simply the direction of the force applied to the load cell. The compressive strength of materials and structures is an incredibly important engineering consideration in both designs and build.

Whether you are clicking the keys on your laptop at work or slamming on your brakes to avoid an accident on your morning commute, you are using the compression force. Testing of the compression force is essential in developing a reliable and sturdy product that can withstand the pressure applied to it many times over. Often, safety is at the core of compression testing.

Load cells incorporated into the testing process work by measuring the pushing force of an application on a single axis. The strain gage compresses to measure the load applied. The deformation of the strain gage provides the measurement data. Application tests measure the total compression force the products or structures can handle, as well as the effects of compression over time through stress tests. In both cases, original equipment manufacturers (OEMs) need accurate measurements to guarantee their products can withstand compression in the short and long-term.

Interface supplies a variety of compression-focused load cells and accessories for all types of applications, both for test and measurement, as well as for inclusion in originally manufactured products and solutions. These compression load cells are often used in vehicles, industrial automation, aerospace, and defense industries. Applications are wide-ranging, from testing the impact of drones dropping packages to the material strength of bridges during an earthquake. Interface load cells are highly-rated to provide the most accurate data and reliability over time, which is why engineers rely on Interface compression-only load cells.

Here are a few of the compression load cells available from Interface:

1601 Gold Standard® Calibration Compression-Only LowProfile® Load Cells – Interface’s Gold Standard® Load Cells are designed for calibrating other load cells. The 1601 load cell is compression-only and has options available for a second and third bridge and overload protection.

1201 Compression-Only Standard Precision LowProfile® Load Cells – The Interface 1201 LowProfile® load cell provides a “compression-only” force measurement. Its spherical-shaped top surface helps provide minimal off-axis loading. 1201 is our most popular load cell designed for static applications and has a higher output than most competitive load cells.

2101 Dual Range Standard Compression-Only Load Cells – The Interface Model 2101 consists of lower and higher capacity model 1200 type load cells which are stacked with overload protection built into the lower capacity load cell permitting the high resolution to be obtained at both low and high levels of capacity. The Model 1201 is LowProfile® moment compensated.

LBM Compression Load Button Load Cells – The Interface LBM Compression Load Button is constructed from stainless steel and has a small size for all types of sensor apps and testing. This product is available in capacities that range from 25 lbf up to 50K lbf.

There is a variety of other standard compression-only load cells, including modified and custom Interface compression testing options in multiple capacities. For more information on our compression-only products or any of Interface’s industry-leading force measurement solutions, contact our Application Engineers.