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Automated Test of Touch Device Force Sensors Using CompactDAQ

*As Featured on NI.com

Original Authors: Timothy Wiles, Peratech

Edited by Cyth Systems

Automated Test of Touch Device Force Sensors
Automated Test of Touch Device Force Sensors

The Challenge

Force sensing solutions help device makers create more natural, intuitive, and immersive user experiences for those using their kits. Measuring and utilizing the analog, non-linear output from force sensors is entirely different than integrating capacitive sensing or traditional buttons, so having the tools to make force sensing solution design and high-quality mass production as straightforward and reliable as current technologies is vital.


The Solution

Peratech used CompactDAQ hardware and LabVIEW software to develop a pioneering, data-driven testing system that assures customers that purchased sensors meet required specifications and will perform as expected.


Application

Different force sensing technologies have been around for decades, but Apple’s decision to incorporate force touch into the iPhone, Apple Watch, and the latest MacBook has raised its profile. Smartphones and trackpads are merely the tip of the iceberg. Force-sensing technology can now improve our interactions with a range of devices, from household appliances to medical and industrial equipment.

The NI CompactDAQ platform provides the data acquisition needs for force testing of device touch sensors.
The NI CompactDAQ platform provides the data acquisition needs for force testing of device touch sensors.

How Force Touch Sensors Transform Our Interactions With Everyday Machines

In addition to displays, phone and tablet makers can add interaction opportunities by incorporating force sensors into other parts of their devices, such as volume controls and power/home buttons. Some manufacturers are adding an area of force sensitivity to the sides or rear of devices to create additional interaction methods that do not involve your fingers obscuring parts of the display. A basic example of the improvements force sensing makes possible is that you do not have to repeatedly lift your finger from the button to get the button to advance repeated times, which is especially valuable for one-handed volume control.

Left Integrating appropriate force sensors into laptops and notebooks enables a more intuitive user experience.


Right: A complete force-resistance curve shows how a sensor will perform at different levels of force.

Personal computer manufacturers are exploring how to build force sensors into other parts of the hardware, including keyboards. Imagine a light press on the arrow keys moving your cursor along letter by letter, while a harder press jumps through a word at a time. Now, a deliberate, intuitive level of pressure, not an arbitrary measure of time, determines the difference in the two actions from the same button.

Force sensors can replace mechanical switches in many applications where analogue control can provide a more intuitive experience, for example variable speed power tools or automotive controls. Their ultrathin design and high durability can increase life and reduce the total cost of ownership over traditional switch systems.


Essential Characteristics of Force Touch Sensors

As these applications show, the uses for force sensors are many and varied, but all share common requirements:

  1. The sensor must be fit for purpose and the specification must directly and accurately correlate to desired performance, otherwise there is a danger of accurately measuring something that has no bearing on actual product performance. There is little value in knowing a sensor can offer variances of no more than 10 g at forces of 1 kg if the greatest force it faces is 100 g.

  2. Performance must be predictable and reliable. You need absolute confidence that each and every sensor can perform as expected, every time you use it in your product. This high level of assuredness is particularly important in safety-critical roles, in which the sensor output must be accurate to a specified variance throughout the usable force range.

  3. The sensors need to be able to be produced in volume, while still providing the quality assurance outlined. This requires accurate testing that is also simple to perform, fast, and scalable. All of this needs to be embodied in a cost-effective piece of test equipment.

Next-Generation Sensor Testing: Delivering High Customer Confidence

We had worked with NI tools in other roles, specifically with LabVIEW and FPGA. Errors that occurred during development were often made by the user. The ease of use of NI technologies, such as the seamless integration of LabVIEW with NI DAQ hardware, helped us achieve a faster development time and rapid prototyping. Both of these points benefitted us as we needed to develop a reliable test system quickly.

Combining best-in-class testing hardware and software from NI with a bespoke data infrastructure that uses cloud and business intelligence/analytics tools, we designed and implemented a secure automated testing and monitoring system that can be used in any facility manufacturing its sensors.

The system tests every single sensor that rolls off a production line, using NI hardware and LabVIEW. The process subjects each sensor to a wide range of forces in less than five seconds, collecting up to 50,000 data points per second to produce a complete force-resistance curve. We can ensure sensor quality and reliably demonstrate to a customer how its sensors will perform across the applicable force range for each specific application.

Data-Driven Decisions

Data from the tests is distilled down and securely stored in the cloud, where it can be analysed from anywhere in the world. This helps us identify and resolve problems in minutes instead of days, which provides instant and continuous assurance of quality levels.

For customers, this rigorous factory testing can reduce or even eradicate the need for their own testing to find a suitable sensor, and dramatically cut end-product testing time. Should unforeseen product issues arise, the system features product traceability, enabling high-speed forensics and problem solving. As a result, our product assurance and traceability solutions reduce risk and uncertainty, and help get a product from concept to mass production quicker, with higher quality at lower cost.

Conclusion

The rapid prototyping and development capability of CompactDAQ and LabVIEW helped us create a system that relentlessly tests sensors before they are released into the market. We used NI tools to develop an automated and scalable test approach that ensures every single sensor it produces is tested against a range of forces that apply exactly to a customer’s product application needs. The testing system can quickly be modified to test new product designs, without the need for complex, low-level coding, resulting in the setup for testing new sensors taking days rather than months.

The impacts of using NI tools include:

  • improved testing time and cost

  • deep insight into sensor performance

  • the ability of device manufacturers to specify sensor type, giving them the confidence that every sensor module they purchase can perform as they need it to

Original Authors:

Timothy Wiles, Peratech

Edited by Cyth Systems


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