Roomba PAD LIFT mechanism

iRobot | Mechanical Engineer | July - December 2022

OBJECTIVE

This was a system-level project that involved multiple component efforts. Some of those efforts included:

1. Worst-case current testing and risk mitigation

2. Gearbox assembly issue and solution

3. Redesigning a metal injection molded (MIM) gear to be co-molded for cost savings

SKILLS SNAPSHOT

DFM/DFA

PTC CREO

PLASTIC INJECTION MOLDING

SURFACE MODELING

ELECTROMECHANICAL SYSTEMS

RISK MANAGEMENT

FAILURE TESTING

PROCESS IMPROVEMENT

CURRENT TESTING

WORST-CASE CURRENT TESTING & RISK MITIGATION

I led the effort to assess a potential risk with the pad lift mechanism: as the wheels wear down over time and the robot rides lower, there is a risk that the bin drags over a threshold and causes damage to the home or the robot. This would also incur a current error that would stop the robot's cleaning pass and require human intervention.

Objective

Troubleshooting Steps

Went through the previous engineer's notes and set out to replicate his results
Taught myself to use iRobot's internal debugging and control software
Ran a robot over thresholds in the office without incurring the error
Ran a robot over the highest allowable threshold in the product specs without incurring the error
Expanded my fleet to five robots and conducted the threshold test with a full debris bin, but did not incur the error
3D printed two alternate bins (one with a lower profile, and another with "ramp" features) and tested, but saw no difference with the existing bin
Communicated with our manufacturing partners in China to procure 10X worn wheel modules from production lifetime testing to assemble into my fleet or robots, but did not incur the error

The robot riding low over a threshold. If it rides too low, the threshold or the robot could become damaged. The robot could also throw a high current error that requires manual intervention. (Photo credit: Youtube - Robot Master)

Worn wheels like those I procured from our Chinese manufacturers to sub into my fleet of robots (Photo credit: r/roomba)

RESULTS

My test results proved the risk was negligible, so redesigning parts and investing in new tooling was not worthwhile. I recommended against taking further action.
The effort contributed to my being approved for a promotion to Senior Mechanical Engineer
I received the following feedback:
- "Taylor takes ownership of her technical tasks. Her dedication to getting to the root of issues and fully understanding the solution set is commendable."
- "A colleague was impressed that Taylor ordered worn wheel modules to use in testing... this was an above and beyond way to bound the data set, and provided additional confidence in the decision to forgo a solution because the existing product issue is not subject to degradation over life."

Gearbox Assembly

GEARBOX ASSEMBLY ISSUE AND SOLUTION

To find the root cause of a series of unexpected and seemingly random current draw errors.

Objective

Troubleshooting Steps

Tore down multiple pad lift gearboxes (left and right on multiple robots)
Documented anomalies (amount of lubrication, debris, etc)
Determined that the Geneva gear could be assembled one tooth off, which caused one side's wheel lift shim to deploy ahead of the other
Alerted the manufacturing team of the assembly issue
Implemented a pokayoke feature to eliminate risk of assembling the geneva gear one tooth off

Results

The high current issue was resolved when I alerted the manufacturing team and implemented a pokayoke on the assembly fixture moving forward!

The pad lift mechanism (photo credit: eBay)

A pad lift gearbox: the geneva gear on one side was sometimes assembled one tooth off, so that one side's wheel lift shim deployed ahead of the other and caused a high current error

Gear Matl Change

GEAR MATERIAL TRANSITION

To redesign the driven gear from being metal injection molded (MIM) to being co-molded for cost savings.

Objective

Design Steps

Split the solid-body CAD into two separate bodies, a MIM core and a co-molded portion
Improved DFM with our manufacturing partners in China
- Added 11 passthroughs and validated adhesion in pre-production samples

Results

My co-molded version of the gear was fully validated for production
The material changes saved $0.442 per gear, or $0.884 per production robot

The original MIM compound gear

The final co-molded compound gear, front and back

Roomba PAD LIFT mechanism

"Taylor takes ownership of her technical tasks. Her dedication to getting to the root of issues and fully understanding the solution set is commendable."

"A colleague was impressed that Taylor ordered worn wheel modules to use in testing... this was an above and beyond way to bound the data set, and provided additional confidence in the decision to forgo a solution because the existing product issue is not subject to degradation over life."