Dynamic Ride Height Testing Rig
SharkNinja Fall 2021
Problem Statement:
At SharkNinja, the finite interaction between vacuum nozzles and the floor while in motion is mostly unstudied. Any change in the distance between the nozzle and the ground greatly affects overall performance by varying the suction and changing the geometry. The goal was to create something that will measure and report this change in distance between nozzle and ground, called ride height, over an active stroke of any vacuum unit at SharkNinja.
Goals and Conditions:
Two initial product types were identified that could benefit from something to measure ride height and two units for me to focus my development on:
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SharkNinja VacMop
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the competitor unit multisurface cleaners
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Bissell Crosswave Max
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Tineco S3
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The final test should therefore be adaptable to many units and product lines.
Two conditions were required to be studied:
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The nozzle behavior over a flat surface
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The nozzle behavior over disruptive debris
And eventually, correlate these behaviors to 'good' or 'bad' scores on SharkNinja tests to guide the development of new products.
Goals for Final Rig:
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Easy read graphical output of the height of the nozzle over the stroke, little to no set up by a user
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Modular and can be attached to many different products
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Desired resolution of 0.01mm or 0.1mm, the difference of which was past proven to change testing results by +/-5%
Units that were studied during the development of the dynamic ride height rig. Left to Right: SharkNinja VacMop, Tineco S3, Bissell Crosswave Max
Initial Testing:
Two test situations were identified for the use of the final rig:
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The Push-Pull Rig, a SharkNinja machine that moved a unit forward and back a certain distance across a flat floor at a constant speed
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The flat surface was used to study the 'dig' of the unit into the floor or the natural rock of the nozzle
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An array of cheerios based on the ASTM Bare Floor test, shown below, 11 x 4 array on a testing floor the width of the nozzle minus 2cm
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Disruptive debris could show how a nozzle would jump or shift as it traveled over large pieces.
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Example set up of the cheerio array used to study disruptive debris affect on the ride height.
Design Iteration
1
Hall Effect Sensor
A Hall Effect Sensor works by changing the amount of voltage through the sensor based on the proximity to a magnetic field. With calibration, the distance from a magnet can be determined. The Arduino program written for the study in this section would output the cm distance from the ground. The sensor itself was attached hanging off the side of units.
Initial sketch of the rig attachment on a SharkNinja VacMop.
VacMop attached to Push-Pull rig with the Hall Effect sensor over a magnetic strip.
Results
The response rate was determined to be optimal every 50ms and the results of a stroke over cheerio debris is shown in the orange graph:
Moving floor design, the floor moved on track and unit was stationary over a powerful magnet. Inconsistent placement and floor speed eliminated this concept.
Tineco S3 Unit with the Hall Effect sensor over the large cheerio debris set up.
Possible Improvments
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Based on voltage output, the Hall Effect sensor could only be calibrated to give out data in steps of 0.34mm
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While small, this unit of measure is the full displacement of a unit on a flat surface so the Hall Effect sensor could only work well with larger debris/displacement
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This can be seen in the steps shown on the graph
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Using a magnetic strip created a very small area that the magnetic field was even over the strip
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In a study, movement even 1cm off the center could change the reading of the sensor by 1-2mm
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Manual calibration makes this a tricky sensor to work with, especially as we are assuming that every point along the magnet strip is the same magnetic field
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A sensor with standard calibration would be ideal
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The 11 peaks correspond to the Tineco S3 going over 11 rows cheerios and the average peak height was recorded to be 4-5mm of displacement (the height of a cheerio) which makes sense because the Tineco S3 has a roller in contact with the floor going over the debris.
2
Digital Dial Indicator
The second idea for recording the changing height was through a manual reading, like a dial indicator. Typically these output values physically, certain digital versions can be modified to output data to an Arduino, connected to a computer, and output to a graph. This is the approach I had and ended up designing and wiring a circit.
Small Unit Mount
Large Unit Mount
A Bissell competitor product with an attached manual dial indicator, I would record the face for the dial over the motion and record the reading on the face where it passed the tick marks. This created a rough outline for the motion of the unit.
Proof of concept a dial indicator would work.
I researched digital dial indicators and chose a Mitutoyo unit that allowed SPC output through a USB connection with a laptop. I then programmed in Arduino to convert the output over a certain time frame into a graph.
Example of Dial indicator mounted to a prototype vacuum.
Circuit diagram of the Arduino set up. Arduino would 'ping' the Dial Indicator and convert the hex code signal into a numerical output of the height the indicator reads at that moment in time.
While the Arduino can 'ping' very quickly, the Mitutoyo Dial cannot output faster than ~5 times a second.
Results
Graphical results of the height over the motion of the stroke are shown below. This method was extremely accurate (+/- 0.01mm) and could be used over a range change of 0-12.4mm with factory calibration. The Dial is the Blue lines on this graph.
Possible Improvments
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As mentioned in the above diagram caption, the Arduino would 'ping' the Indicator for a value, but the Indicator could only output every 0.2 s
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Since the stroke I was testing with only lasted ~3 s there was very few data points per stroke
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The resolution of the result did not capture fine movements (low response rate)
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Possibly use another type of Dial Indicator or a different way of accessing the information
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Sturdier mount that could hold the Indicator steady
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Unfortunately, my co-op ended before I completed a more formal mount
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Tip of the dial indicator rubs along the ground, possibly causing a drag effect that changes the measured value
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Create a sled or new contact point with the ground
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Note: the Dial Indicator has fewer data points and does not track the motion over the 11 peaks where the 11 cheerios are.
Again, the 11 orange peaks correspond to the Tineco S3 going over 11 rows cheerios.
Future Applications:
Both the Dial Indicator and the Hall Effecto Sensor give valuble information about the height and behavior of a vacuum nozzle in motion. Ultimately the goal would be to correlate a certain measured response with 'good' performance of a unit to help development in the future.
The Dial could be used for finer measurements and slow motion:
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Study stationary nozzle tilt when a handle is manipulated
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Behavior when a user moves the unit in a non uniform direction
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Detailed differences in nozzle height (ex. effect of added weight or change in geometry)
The Hall Effect Sensor can give general motion with high resolution:
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Tracking the response to different debris (similar to the 11 rows of cheerios shows 11 peaks on the graph)
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Change in nozzle height as a response to quick use of a vacuum, how tilt changes based on jerkiness of a user
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Another metric to have for any testing that involves straight line motion
Next Steps & Documentation:
Since I was unable to complete the goal before the end of my work experience, I typed up detailed instructions on the wiring, use, and plan for the rig for the next co-op to build off of.
The main future goals are: to create a sturdy mount for the dial indicator, translate the results into 'good' and 'bad' behavior for a unit, create a standalone program that would be easy for an engineer not well versed in Arduino code to operate.