Reliability test design

Design a reliability test and corresponding test fixtures for a peristaltic pump subassembly in a dialysis cycler.

Role

Systems

Engineering Co-Op

Team

Unreleased Cycler Test & Systems

Company

Fresenius Medical Care

Date

Mar. 2019

 

Reliability Test Requirements

  • Test must simulate wear on subassembly equivalent to 7-year product life

  • Test must account for all relevant failure modes outlined in DFMEA document

    • Focused on mechanical and ​​electrical failures​

  • Test design must account for wear on replaceable pump tubing

  • Test must log test data in the case of a failure

  • Test fixture must be relatively compact

 

System

COnstraints

  • Fluid delivery from 7 years of pumping at the maximum treatments per day corresponds to 584 days of continuous pumping at maximum pump speed

  • Pump tubing wears out after about 72 hours of pumping

  • Cyler software not tuned to determine if the pump stalls or stops

  • Pump rotation resulted in a 1mm linear actuation on another part

Red Arrow Denoting 1mm linear actuation to be tracked

 

Fixture & Script

Due to a multitude of factors, the peristaltic pump subassembly could stall during testing, resulting in 0 mL/min fluid delivery. These failure cases, if not stopped immediately, could lead to system damage that would not be authentic to normal use.

 

To ensure that the reliability test would proceed without any unrealistic damage to the subassembly, the 1mm cyclic actuation of the 25mm diameter shaft which corresponded to proper pump rotation was used to prove proper pump operation.

 

I created a fixture that amplified the motion of the shaft by a factor of 2.5. This fixture was tracked using two photo-interrupt optical sensors and compared to the most recent pump command using onboard cycler test software that I created using JavaScript.

 

If the optical sensors did not register motion once the test had begun, the system had stalled. The error detection would command the pump to stop and all logged data would be saved. In addition to error detection, the script stepped testers through the test procedure and monitored leak detection and data logging.

 
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©2019 by Alexander Arcasoy