Reliability test design
Design a reliability test and corresponding test fixtures for a peristaltic pump subassembly in a dialysis cycler.
Unreleased Cycler Test & Systems
Fresenius Medical Care
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
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.
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.