Per NDA restrictions, I am only able to present a subset of the work that I'm doing for Stanley Black & Decker. In general, the project is to create a testing rig for an unreleased SBD product and quantify a critical system performance metric to compare to a competitor's product.
Spring-Loaded Torsional Mount
Part of the testing rig requires us to precisely measure the linear motion of a device using a scale. The issue with taking this measurement is that the device under test is not perfectly planar, so the connections between it and the scale need to be designed such that the system is not overly constrained. The scale uses a sliding reader that needs to be mounted to the moving device in a way that allows no slop in the direction being measured, but has freedom in the other two directions.
I designed a mount that uses a torsional spring to add preload to the connection between the device and the
scale’s reader and uses a slot to allow freedom in the two directions that can’t be overconstrained. I milled the main part of the bracket, pressed in the oiled-embedded bushings, and mounted it to the device using a shoulder bolt so that it could rotate freely.
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Testing showed that it works as intended - only the direction of motion was fully constrained and all other directions allowed flexibility to account for the non-planarity of the moving device relative to the scale.
Electronics and System Integration
The testing rig uses a variety of sensors, buttons, and switches to get input from the user and the environment as well as collect data about the device being measured. A motor controller and motor are used to actuate the device. The system block diagram on the right shows an overview of how the various sensors and actuators connect to each other and to an Arduino Mega. The data is formatted and saved onto an SD card so that the testing rig can be run without a computer. Due to the fact that there is a motor actuating the device, an E-stop is included in the system that mechanically breaks current going to the motor. This ensures that even in the case of a software fault, a user will always be able to safely stop the device’s motion.
[Note: Sensitive information has been redacted from the block diagram.]
A finite state machine architecture is used to control the device while checking for user input asynchronously via the buttons with interrupts. The device can be run in a manual mode, where the user controls the motor’s motion, and automatic mode, where the motor's motion is semi-randomized. In both of these modes, data is collected periodically and saved to the SD card.
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Currently, this system has been prototyped and tested using a breadboard and the next step is to transition to a solder board and an electronics enclosure.