Probe Station Project

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

Iteration 1 - Single

slide-handler design responsibilities passed from gantry-station co-worker

Iteration 2 - Dual

early attempt to incorporate a "reference slide" of known conductivity/geometry

note the slight banana-fication from curing process

Iteration 3 - Single w/ Calibration Cover

space efficient solution with minimal calibration geometry

Conductivity Probe Design

Iteration 1 - Electrode Printing

original prototype, designed with a different workflow in mind

test printing of NanoAg electrodes and traces on glass

Iteration 2 - 4 Point Conductivity

simple 4-point probe prototype

To be replaced by Signatone 4-Point Probe after kinematics are deemed safe.

Software

System Block Diagram

• 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