This past semester, I was involved with a Mechanical Engineering capstone senior design course. Our group was assigned to perform an analysis on a paving machines hydraulic leveling sensor sensitivity. Working with another group, a test bench and sensor arm motivator were designed. My groups role was to design the sensor arm motivator.
As mentioned, the goal of this project was to perform analysis of an existing paver guidance system. A physical test system and method were expected deliverables. This project resulted in a functional prototype of a device which would motivate a paving sensor arm, as well as collect necessary data. To motivate the hydraulic sensor, a stepper motor was deemed most effective due to cost, precision and accuracy. An enclosure was then designed around the stepper motor to allow smooth linear motion. This enclosure consisted of an aluminum base plate and plastic top housing. The aluminum base plate was designed so the enclosure could be adjusted back and forth down the sensor wand. The complexity of the top housing lead to required use of 3D printing, whereas the bottom aluminum plate was simple enough to machine. A linear guide rail and bushing was added to the second design to constrain the motor from rotating about the z axis.
Control of the stepper motor was performed by using and Arduino Uno microcontroller, coupled with an Arduino motor controller shield. Limit switches were also installed to prevent the stepper motor from colliding with the top and base of the enclosure. To measure the displacement of the hydraulic piston, a string gauge potentiometer was used, and integrated to work with the Arduino. All programming of the Arduino was performed using the arduino based IDE software and was functioned with the CoolTerm interface.
After all was said and done, the entire cost of purchasing components totaled $910.68. Some of this was due to collaborative purchasing efforts with the other group working on the hydraulics of the system. Considering just the components necessary to the stepper motor system, the cost came out to $354.18 (with labor considered). This prototype was a relatively low cost solution for this problem.
Hydraulic test system
Stepper motor sensor motivator
Computer data output of sensor arm displacement vs piston displacement
String gauge potentiometer to measure piston displacement
Future Work
In the end, this project resulted in a working prototype which provided a proof of concept, as well as something that could be improved upon in the future. The enclosure of the system was made with an aluminum base plate which provided a solid durable base. The plastic top enclosure worked, but is not a good long term solution in such an industrial work environment. A more durable top enclosure, perhaps a nylon reinforced injection molding, or a simple bent piece of steel. The Arduino software/hardware should also be replaced by something more sophisticated for long term use. The Arduino for example can only output so many bits of information which resulted in rough plots of data. The Arduino software also should be replaced. Using different software which has an intuitive user interface would be helpful for the inexperienced user. It would also be helpful for the user to be able to see a live plot of excel data while testing is occurring.
Finally, a test method for determining the health/ functionality of a sensor would be very helpful. Several good sensors would have to be benchmarked and an acceptable range of sensitivity would have to be identified. Eventually, the system would be streamlined to a point of a go-no-go test. The tester could put a sensor on the bench, and then quickly determine the condition. The resulting test system lead to something that provided the paving company with something to improve upon and develop further. The above suggestions are things to consider for future improvement and would lead to a more sophisticated and reliable system.
Matt Szmurlo 