Shared with express permission of Curtis Berlinguette Research group
I was tasked with designing and implementing a conductivity characterization module for a new gantry slide-handling robot.
Design Process
Problem Definition - Requirements, Constraints, and Goals
Requirements and Constraints
Interfaces physically with slide-handling gantry system, may require collaboration with gantry system developer to work out details of slide manipulation.
Samples will be deposited on 3”x1” standard glass slides.
Reliably achieves ohmic contact with sample with >90% accurate validation.
Positional validation required (allows for correlation of conductivity and imaging).
Solution must be safe for humans and equipment.
Consider consequences of robot arm and module collision error.
Consider pinch points for humans.
Consider electrical hazards for instrumentation.
Can conduct 4-point resistance measurement on glass slide samples.
Can record measurements for human or computational analysis which are accessible to the rest of the experimental platform.
Reliable enough to enable automated experimentation runs of over 10 hours (20-40 samples) with over 95% success rate.
Goals
Design cost is minimized.
Consider designing a prototype contact board for testing before implementing more expensive Signatone probe head.
Consider utilizing 8020 materials to align with upcoming order.
Make use of switch-matrix to allow for additional instrumentation modules or multiplexing to multiple probe stations.
Probe station can capture hysteresis and response time data.
Provide a useful probe station API to the rest of the team which is easy to integrate.
Slide-handler Design
slide-handler design responsibilities passed from gantry-station co-worker
early attempt to incorporate a "reference slide" of known conductivity/geometry
note the slight banana-fication from curing process
space efficient solution with minimal calibration geometry
Conductivity Probe Design
original prototype, designed with a different workflow in mind
test printing of NanoAg electrodes and traces on glass
This project uses two off-the-shelf components: a digital multimeter to conduct measurements and a switch matrix to multiplex the multimeter.
These instruments have native automation features written in SCPI. I used PyVisa to send SCPI commands and receive data in Python.
I wrote separate classes for controlling each instrument (switch matrix controller and dmm controller).
After confirming probe/gantry integration details with project engineers I wrote a probe station controller class which coordinated the two instruments to carry out conductivity measurements on command.
I documented the project, integrated it with the gantry station control project and submitted it for review.
Outcomes
The module was completed and handed over to the gantry station project owner.
The gantry system continued to see development through until February 2021.
In June a scientist requested use of the probe station to make swept conductivity measurements of glass-deposited films. A custom sweep routine and JSON data-output program were written and put into use for 3 weeks. End user reported satisfaction with operation and end results.
configuration of the overall station before integration with the larger Ada platform
