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The Role of Actuators in Force Measurement

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One of the most common force measurement tests in the engineering and manufacturing world is called cycle testing. Cycle testing involves constant force being applied to a component or product over hours, days and even months. The goal is to test a product to find out how long it will last under the amount of force it will see in use in the real world.

Cycle testing is used throughout different industries. One of the most common applications of a cycle test is on something like airplane wings. The wings of an airplane are exposed to constant push and pull force to guarantee that they will hold up over many flights. Check out the wing fatigue testing application note here.

Another example is simple furniture tests, like a chair, to ensure it can withstand the weight of people of all sizes after years and years of use. These tests are designed to really push the limits on the product so engineers and manufacturers can confirm their designs and ensure safety and durability.

To carry out these tests, actuators are used to generate the force in cycle testing. An actuator is a component responsible for moving and controlling a mechanism or system. Actuators are small components that convert energy in a linear moment. There are a variety of different types of actuators including linear, rotary, hydraulic, pneumatic, and more. Each is designed to create force in different directions and on different axes.

Actuators are very important because force measurement is fed back into a control loop and the actuator allows you to accurately control how much force you’re putting on a test article. As a basic example, if you wanted to measure how much force it takes to close a door, you would use an actuator to provide the door closing force while the load cell measures the amount of force given off by the actuator.

Interface often integrates actuators into load cells for custom solutions to use in rigorous use and cycle testing. These types of custom solutions are used by equipment and product manufacturers, OEMs, as well as product design and testing labs. There is increasing frequency for OEMs to integrate actuators into load cells for testing their automated testing lines or products in use for continuous feedback.

For example, mobile device manufacturers use a miniature–sized load button load cell like the ConvexBT to test the pressure sensitivity of the touch screen. By using an actuator, phone manufacturers can set up an automated test lines with an actuator integrated in the load button load cell to test each screen as they go across a test line. You can read more about ConvexBT in this new white paper.

Another major application for actuators is in calibration machines. To test if a load cell is calibrated correctly, an actuator applies force to the load cell being tested and a calibration grade Gold Standard Load Cell simultaneously. These measurements can tell the user if the load cell needs to be recalibrated or not because the actuator allows the user to create a very precise force measurement. If measurements on the test load cell are not the same as the control load cell, the user knows it is off calibration and it’s time to schedule a calibration service.

From custom solutions to calibration, if actuators are necessary for your next project learn how Interface can work with you to find a solution that meets your precise needs.

Read more about Gold Standard Calibration Systems here.

Learn about how Interface is a preferred provider of OEM solutions here.

Interface Differentiator is Proprietary Strain Gage Manufacturing

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Interface products have been heralded for their accuracy, reliability, and quality for more than 50 years. We credit our vertically integrated approach to manufacturing as the most significant factor in our development of industry-leading force measurement products, meaning we control every part of the design, manufacturing and testing of our products before they are shipped to our customers.

The process for how we differentiate ourselves begins with Interface strain gages. By manufacturing our own proprietary strain gages here at our headquarters in Scottsdale, Arizona, we can optimize our load cells to a quality level very few providers can match.

Think of strain gages as the heart and soul of a load cell. These components power every aspect of the device and their quality dictates a significant portion of the load cells’ overall quality. In addition, customization of the strain gages is a critical factor in ensuring the load cell is meeting the specific requirements of a customer’s project.

The last point is critically important because Interface does not just provide one size fits all products. Yes, we have a large standard product line ready to ship. There are many times when we collaborate directly with our customers to understand their application and the challenges that may be present during a force measurement testing program or OEM design. This allows us to offer modified and custom products that are engineered to order.  Whether that comes in the form of an off-the-shelf product within our catalog of more than tens of thousands of options, or a new model using our strain gage technology to meet the needs of a unique application.

An example of our commitment to meeting customer needs is the way we develop our strain gages to compensate for temperature, an environmental factor that can drastically affect the accuracy of force data. Our strain gages are designed and manufactured to counteract the temperature characteristics of the modulus of the load cell structural material.

The benefit to this is that our load cells are temperature-insensitive and do not require modulus compensation resistors, ultimately producing a simpler and more reliable circuit with higher output signal. It also means no dynamic thermal mismatch errors from modulus compensation resistors which cannot be thermally connected with the load cell’s surface at the strain gage location.

In addition, our proprietary strain gages provide several key benefits. Included below are a few of the differentiators available with Interface strain gages:

  • A higher output of 4mV/V, while competitors provide 3mV/V or less, which provides superior performance, flexibility, and accuracy.
  • The ability to perform hot and cold thermal compensation, from 15˚ – 115˚F, while competitors typically only provide heat compensation (60˚ – 160˚F).
  • Eight strain gages per load cell compared to our competitors four gages, which provides superior compensation of eccentric loads to further minimize resulting errors.
  • Our strain gages also offer:
    • Higher signal-to-noise ratio
    • Higher resolution in precision measurement applications
    • Superior fatigue life

Another factor in the development of our strain gages is our expertise and knowledge of the manufacturing process. We have always developed our own strain gages going all the way back to 1968. Therefore, we have learned everything there is to know about it and can guarantee the quality of our load cells in any environment based on this tenured expertise and having manufactured and calibrated millions of force measurement devices.

To learn more about our vertically integrated manufacturing process and the various forms of product and system customization we offer, contact our specialized application engineers.

 

Considerations for Fatigue-Rated Load Cells

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There are many products that are made to serve a single or limited use. Needs for these types of products, often consumable, are immediate and buying decisions usually require limited research or comparisons. On the other end of the spectrum, there are products that need to be extremely reliable, durable, and built to last a long time. The buying decisions for these types of products often require more research to make certain they are highly rated, safe, and made from sturdy and reliable materials.

How do original equipment manufacturers (OEMs) determine how long a product should last with consistent use? What design decisions need to be made to improve product reliability? The answer is often found in the defined fatigue requirements of a product. In the test and measurement and design phase of a product, answers to these questions frequently require product and component testing with fatigue-rated load cells.

Fatigue is the weakening of a material caused by repeatedly applied loads. Similar to if you repeatedly bend a paper clip, it will eventually weaken and then break. The only way to test fatigue is to put prototypes of the product through stress tests for long periods of time or use an apparatus that tests the lifetime “wear and tear” in a few hours. The tool that reports the data gathered from stress tests is the load cell.

With Interface fatigue-rated load cells, designers and engineers can predict the time and force it will take for wear and tear to take its toll on their products. They can then create safety instructions for customers or redesign the product for better results.

Interface Model 1000 series is a portfolio of fatigue-rated low profile load cells with 300% safe overload, extremely low moment sensitivity of 0.1%/in and higher fatigue life. If you need to measure 1 pound (4.45N) or 1 million pounds (4500kN) of force, Interface fatigue-rated load cells are built for this type of testing.

Interface fatigue-rated load cells are designed for an operational life of in excess of 100 million fully reversed cycles.

It’s also important to note that Interface fatigue-rated load cells are based on fully reversed load cycles, which means they are rated for two directions. This type of loading cycle is considerably more stringent than unidirectional loading. It is the more common application of load cells. If a fatigue load cell is repeatedly loaded in only one direction, it can be loaded to about 133% of the bidirectional fatigue-rated capacity with no degradation of its fatigue rating.

Interface works with customers to provide our fatigue-rated load cells for products that can’t fail. It is our mission to ensure precision products are safe, reliable and durable. If they do fail, it could result in significant harm.

Two examples of products dependent on fatigue-rated load cells for testing are aircraft wings and furniture stability. In aircraft wing testing, load cells test the materials used to build the wings to ensure they are strong and lightweight. The load cells are also used in wind tunnels to test the stress of high winds on the wings over time. Safety protocols manufacturing for furniture products require fatigue testing, seat testing, shock testing, and proof testing. These tests must be rigorously performed before entering the marketplace.

Force testing simulations using fatigue-rated load cells help the manufacturer define max loads in order to protect manufacturers from liability due to damages resulting in the misuse or overloading of their products. These types of applications require the most accurate data available provided by our load cells to ensure that testing results produce a quality product that lasts.

Fatigue-rated load cells are one of the many Interface force measurement tools available to help customers develop quality products. For information on all of the load cells we provide, please visit www.interfaceforce.com/product-category/load-cells/.

Contributor:  Jay Bradley, Sr. Electrical Engineer, Interface