Grip Strength Analyzer
This grip strength analyzer is possibly the world's first 3D printed-in-place mechanical measurement device in PLA. With an accuracy of +/- 2 kg, it measures the force that can be exerted by one hand. It was inspired by the desire to create a useful tool that does not require assembly or fancy equipment (the combined cost of printer and filament was $340).
Rack and Pinion
This gearing was chosen to provide a fine-grained, real-time indication of force applied. Squeezing the handles closer by 1 mm causes the indicator needle to rotate nearly 4 mm.
A significant challenge was printing the system vertically. This may be the first instance of a conical axle enabling a print-in-place gear that rotates about a horizontal axis.
These springs had to do three things: provide significant resistance, compress by at least 60 mm without cracking, and retain their performance profile over hundreds of compressions.
Achieving this in PLA required scores of break tests, iterating over pitch, radii, height, outer shells, infill, layer thickness, extrusion temperature, and extruder settings.
This timer had to tick for five seconds, the industry standard for grip strength test duration. While it was tempting to exploit the conical axles developed for our rack and pinion system, in the interest of simplicity we created a hairspring that takes five seconds to return to its resting state.
Thanks to the data analysis of KMBond, we were able to determine percentiles for grip strength (due to the focus of the video above, those for American Millennial males) and apply these, as an adapted bell curve, to the display.
In addition to the percentile, the indicator needle points to kilos of force exerted, making it easy for the user to evaluate their performance as they squeeze.
Questions about the build? Licensing inquiries? Suggestions for improvement?