Examples of Diagnostic Tools in Action
In our last article, we discussed how Simbex’s approach to diagnosing and resolving performance issues throughout the medical device development process, using design techniques such as building in error logging and debugging features, allows us to create safe and reliable products. In this article we take a deeper dive into the techniques and tools we use to make the invisible visible and pinpoint the source of an anomaly within the complexity of the design.
NRF Connect is a powerful software tool developed by Nordic Semiconductor, which is used for developing, testing, and debugging Bluetooth Low Energy (BLE) and other wireless applications. Its capabilities range from basic device discovery and connection management to advanced packet sniffing and emulation. The NRF Connect tool proved integral in one project with a sensor-based device that includes an inertial measurement unit worn on the leg. The tool helped us solve an issue with the position-in-space portion of their algorithm. Our team had identified that the algorithm required the sensor to know its orientation in 3D space in order to provide accurate output metrics. However, at a system level, the output metrics were not being reported for unknown reasons. To assess the root cause, we started by looking at the sensor orientation component because it was a low effort method to providing meaningful results. We added a Bluetooth characteristic to the firmware that reports if the sensor orientation was successfully determined. If yes, then we knew the issue was further down the algorithm or communication chain. The position was either not being determined or was being reported inaccurately per the NRF connect output results. This pointed the team to the orientation algorithm as the source of the problem. With this insight, the team was able to zero in on the issue and address it.
The Ellisys Bluetooth Tracker is a software tool designed for Bluetooth Low Energy (BLE) development and debugging. It allows developers to capture and analyze Bluetooth communication data between devices, providing insights into device behavior, timing, and performance. In one project with a wearable sensor-based device, the Simbex team needed to resolve an issue with the mobile app’s ability to communicate with multiple sensors used simultaneously on different people in near-real time. Certain sensors had a significant communication delay with the mobile app, for unknown causes. To address this, we utilized the Ellisys Bluetooth Tracker, which has the capability to analyze Bluetooth network traffic at a highly detailed level and from multiple devices simultaneously. The tracker revealed that the mobile app was holding on to connections with specific devices, which was not expected behavior, and creating a communication traffic jam. This pointed to an issue with the mobile app architecture, which our team was able to subsequently address.
In this example, we apply the technique of destructive prototyping to determine the root cause of a physical malfunction resulting in water leakage. A client came to us with an existing wearable device that is often used outdoors in which the wireless components are protected by plastic housings that seal with a gasket to prevent water damage. These sealed units, however, were getting water inside them from unknown locations during submersion testing. Since the client wished to make fundamental changes to the product design modularity and assembly methods, along with the need for serviceability and cost reduction targets, that also necessitated rethinking how the sealing was designed. To determine the source of the leakage and ensure it wasn’t transferred into any new design, we conducted a series of tests on the existing device using the destructive prototyping technique. First, we added water-contact color-change paper at likely ingress points, conducted testing, and documented results. This homed in on a more specific region which we investigated further by conducting destructive testing with video inspection. We cut a hole in the device, and using a video microscope, were able to pinpoint the leak site at a location where the gasket spanned a discontinuity in the inner wall that helps hold the gasket captive. This discontinuity resulted from injection molding limitations in the existing design and led to a prototype redesign of the snaps that hold the housings together. This allowed for a continuous inner wall and removal of some of the water ingress points. However, a third test series on new prototype iterations indicated that we hadn’t yet resolved all ingress points; additional microscope inspection revealed small leaks at sharp geometric transitions. The need to satisfy other product requirements meant that these small leaks couldn’t be easily designed away.
The level of ingress protection (IP rating) indicates how well a device is protected against water and dust and is a primary input to the mechanical design. We revisited the original ingress protection requirement and found it was based on older assumptions that were no longer valid. The client agreed that a relaxed IP rating was sufficient for the redesigned device. The product was then tested to the new standard and the client approved the design.
Our holistic approach to medical device design involves using built-in diagnostics as well as tools and techniques throughout the design and development process to ensure the highest quality and reliability. But resolving individual issues as they occur is only a part of product development. At Simbex we stress the importance of maintaining a systems perspective in everything we do.
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About the Authors:
Jesse Kuhn is the Systems Team Lead at Simbex. Jesse is a hands-on, highly self-motivated Mechanical Engineer with an emphasis on electromechanical product development from concept through volume production. Jesse has 15 years of professional experience including systems design for an ultra-pure distilled water device, complex rehabilitation powered wheelchair systems, and high-volume industrial grade LED lighting systems. Jesse has a BS in Mechanical Engineering from Northeastern University.
Jay Avis is a Systems Engineer at Simbex. He has a mechanical engineering degree from Northeastern University, with 14 years of professional expertise. His early career focused on consumer product development with lots of ideation and concept iteration using CNC machining, rapid prototyping, and manual manufacturing technologies. He has extensive 3D modeling experience in Solidworks, often with a focus on design for injection molding. His efforts at Simbex have mostly focused on developing and supporting football helmet technologies, and has led scrum events for a team of engineers. He has served as a liason to domestic and overseas vendors and contract manufacturers, including off-site assembly and testing support. Jay also owned a small design consulting business and developed production processes and physical products for his own entrepreneurial ventures.