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Couplings 101

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One of the biggest challenges in the force measurement is dealing with misaligned loads. Misaligned loads can result in bad data and damaged test equipment. Therefore, it’s important to understand the affect these types of loading conditions can have on a force test and know of the ways to fix or account for it.

For every force test, there is typically a piece of equipment designed to deal with misaligned loads. Whether it’s simply applying the force device properly or if misaligned loads are unavoidable, using the right tools to reject misaligned load. Learning more about couplings is a great place start in knowing how to this power tool is designed to deal with misaligned loads in torque testing.

Couplings are a critical component to be used alongside torque transducer that ensures the isolation of torque loads. A coupling is a mechanical element that connects two shafts together to accurately transmit the power from the drive side to the driven side while absorbing the mounting error of misalignment of the two shafts. Essentially, they allow and compensate for misalignment in a torque test. It is one of the topics we discuss in our online webinar, New Twist on Torque.

For instance, if two shafts are coupled together and the center shafts aren’t aligned, measuring torque without a coupling may ruin the test, affecting the longevity of the parts and the performance of the measurement. With a coupling, the shafts don’t have to be perfectly aligned in length and can still provide an accurate torque test.

There are two main categories of couplings used in force measurement and the biggest difference in the two is the degree of freedom needed for the application. The categories are single-jointed and double-jointed. A single-jointed coupling allows for angular and axial misalignment, while double-jointed coupling allow for an additional radial misalignment. For floating mount installations, Interface recommend single-flex disk couplings. For fixed mount installations, double-flex disk couplings are required.

Couplings should be used in all applications and the selection of the coupling type is based on the speed of the application. For higher speed applications, Interface recommends a high-quality coupling with a flexible, yet sturdy construction made from premium metals.

Interface offers a wide variety of torque transducers and can provide couplings off the shelf or in a custom solution when necessary. One of our most popular torque solutions, which includes a coupling, is the Interface Model T1 Torque Coupling Rotary Torque Transducer. This solution integrates torque measurement with a robust double flex coupling.  The coupling and sensor are completely hollow, allowing the shortest possible distance between the coupled shaft ends. On-board digital electronics provide a ±5V output, low-noise signal. Powered by 12-28V DC, the strain gage based T1 Torque Coupling offers precision rotary torque measurement in a bearing-less, contact-free design. Covering ranges from 50 to 1000 Nm (443 to 8.85K lbf-in), the T1 ships with factory bored hubs to mate precisely with the customer’s shaft ends.  Both smooth and keyed shaft style hubs are available.

Examples of a torque solutions using a coupling in the field can be found in our application notes section of the website. We’ve provided an example of one such application below.

Fuel Pump Optimization – Rotary Torque

A nationally renowned race team was using a flow bench to measure fuel pump performance. They wanted to determine if they could reduce the power consump­tion of the pump by further analyzing the precise torque it produced. An Interface Model T25 High Speed Rotary Torque Transducer was integrated into the pump drive to directly measure the torque required to spin the pump. Interface Shaft Style Torque Transducer Couplings we’re also used to marry the shafts to the T25. Using this data collected from the T25 in conjunction with the pressure and volume measurements of the fuel flow, the race team was able to characterize fuel pump performance versus drive line torque, and then minimize the required drive power while maintaining the needed pressure and flow for efficient fuel delivery.

Couplings are an integral part of any torque test project. To learn more about couplings and their application in a wide variety of projects, reach out to Interface at 480-948-5555 or contact us here. We can suggest a combination of off-the-shelf transducers, couplings and data acquisition devices or work with you to develop a custom solution necessary for your goals.

ADDITIONAL READING: TORQUE TRANSDUCERS 101

Source: Keith Skidmore

Addressing Off-Axis Loads and Temperature Sensitive Applications

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As technology progresses, one of the main differences we see over years and years of iteration on a wide range of consumer and commercial technology is miniaturization. There are hundreds of thousands of examples of advancing technology that went from the room-size of a mainframe decades ago, to a handheld device today. As technology grows more compact and convenient, the equipment used to design, test and manufacture these devices has to follow suit.

This is one of the driving factors for Interface to increase the product types and capabilities in our Load Button Load Cells and Interface Mini Load Cell products. Interface’s Load Button Load Cells are designed for customers who require the measurement of forces in a very confined space. They provide the most accuracy in as little space as possible. Diameters range from 1 inch to 3 inches, with heights from 0.39 inch to 1.5 inches.

For many years, load button load cells have been sensitive to off-axis, eccentric or misaligned loads. This means that if the load is not exactly perpendicular to the surface it’s resting on, the data could become skewed or inaccurate. All on-axis load generates some level, no matter how small, of off-axis extraneous components. This can cause a variety of challenges including slight inaccuracies and reduction of the load cells overload capacity.

With Interface’s family of load button load cells, we bring premium accuracy and repeatability, even under eccentric angular loading. The shaped load button has a spherical radius to help confine misaligned loads to the primary axis of the cell. Our design engineers and force measurement experts have purposefully tested applications under a wide variety of load conditions to ensure that the our load button series can continue to deliver premium performance. We have been extremely pleased with the results and continue to advance our offerings, including the soon to be released precision focused ConvexBT load button load cells.

The load button load cells’ size has in the past precluded the use of internal temperature compensation. We have redesigned our ultra precision product line of load buttons to ensure that this is no longer something the user has to account for when testing a product in certain environmental conditions.

Interface engineers have eliminated this issue by taking the technology out of the load button load cells cable and designing it back into the product. This ensures that temperature-sensitive applications do not suffer from errors caused by the load cell being exposed to different environmental conditions than the cable.

These new features open new possibilities to test compression force on a broader range of products and environments. To learn more about our ultra precision Load Cell Load Buttons and how it can make a difference in your design and testing process when dealing with tight and confined spaces, contact our Application Engineer experts here.

To see the complete line of Load Button Load Cells, visit here.  Watch for the release announcement of our new ultra precision ConvexBT product coming out this month.

Contributors:  James Richardson, Interface Mechanical Engineering Manager and Ted Larson, VP Product Management and Marketing

Source:  Interface Load Cell Field Guide