Instruments that enter the human body need to conform to some unique geometries. This sometimes requires very delicate mechanisms in tight spaces. Instrumenting these types of devices to troubleshoot performance issues can be challenging, but is often critical to quick, efficient, problem solving.
Medical Device, Product Development & Troubleshooting
A strain gage is a flat, flexible piece of elastomer with a thin foil wire pattern that can fit in very small spaces while not significantly affecting mass and stiffness. It measures stretch, and if we know some other parameters like cross sectional dimensions and material modulus, we can infer stress, force, moment, sheer, etc. This makes a strain gage ideal as a diagnostic sensor in some situations.
We will often need to modify the device to accommodate instrumentation, such as a strain gage, and in doing so we need to be certain that our modification does not significantly alter the dynamic behavior of the device under test and make the results invalid. Poor experimental test design can produce confounding results and steer the design team in the wrong direction.
Our customers rely on our experience to focus on the key set of dynamic parameters of the device and its "boundary conditions" so that we can design an experiment that will allow us to more closely characterize the actual problem and find a solution. We always characterize and understand our experimental setup first, before testing, so that we can have more confidence in our results.
For example, we recently worked on a device that is inserted into the body through a very small opening. The mechanism was thus very thin and was suffering from mechanical failures in a force carrying mechanism. We used a small strain gage to determine if the static strain due to the preload was a likely cause of failure, or if it was the dynamic strain that resulted from a spring loaded shock. We used the strain gage to estimate the static and dynamics forces passing through the mechanism and used these force estimates to compared to the levels of force expected given the design of the preloaded mechanism.
In reviewing our experimental setup, we knew that the wire routing was crucial to getting a good estimate of the dynamic response as the wire could both slow the shock pulse, and damp the resulting vibration response in an unrealistic way. Through careful experimental design we had confidence that our setup matched the actual device closely enough to distinguish the weak point of the system. We then had confidence in our recommendations, and helped the client improve their device.