Pump Backlash Compensation Using Limit Sensor Overshoot
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Solution Overview
Problem
Existing point-of-care (POC) coagulation monitoring and platelet function devices suffer from inaccurate pumps, high pump current draw, excess pump heat, and difficulties in visualizing clot or platelet aggregation, leading to inaccurate measurements and variable patient responses to anticoagulant medications.
Innovation Solution
A method of operating a pump that reduces or eliminates backlash errors by advancing a stepper motor additional steps after detecting a limit sensor change, overshooting the sensor, and reversing direction until the sensor indicates movement away, ensuring accurate piston travel and improving pumping accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a pump changes direction rapidly to improve productivity, then productivity increases, but backlash errors increase reducing measurement precision
Solution Approach 1:
The system performs preliminary actions by detecting limit sensor changes and advancing the motor additional steps before reversing direction. This preliminary overshooting action ensures the piston fully clears mechanical play and backlash zones before the next measurement-critical movement, preventing accuracy degradation while maintaining rapid cycling
Solution Approach 2:
The system uses limit sensors to provide real-time feedback on piston position. By monitoring when the piston reaches extreme positions and using this feedback to trigger additional overshoot steps before direction changes, the system dynamically compensates for backlash errors and maintains pumping accuracy throughout operation
2Productivity
If a pump operates continuously to improve productivity, then productivity increases, but pump heat increases causing harmful effects
Solution Approach 1:
The system employs periodic reciprocating motion with deliberate pause intervals at limit positions. The pump operates in cycles of forward motion, pause with additional overshoot steps, reverse motion, and pause, rather than continuous operation. This periodic action allows thermal dissipation during pause periods while maintaining high productivity through efficient use of active pumping time
3Power
If a pump uses high current to improve force and speed, then power increases, but energy consumption increases
Solution Approach 1:
The system dynamically adjusts motor operation by varying speed and current based on operational phase. High current is applied only during brief acceleration and direction-change phases where maximum force is needed to overcome inertia and backlash. During steady-state movement and pause periods, current is reduced or halted, optimizing the balance between power delivery and energy consumption
Data Source
AI summary
A method of operating a pump can include advancing a stepper motor one or more additional steps in a first direction after detecting a first change in a limit sensor state corresponding to a piston reaching an end of its travel in a first direction. After advancing the stepper motor the additional step or steps in the first direction, the stepper motor can be reversed and advanced in a second direction until a second change in the limit sensor state is detected. The stepper motor can then be advanced in the second direction a predetermined number of steps associated with a full travel of the piston.