Estimating Pump Pressure via Motor Current Calibration
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Solution Overview
Problem
Conventional methods for measuring fluid pressure in fluid dispensing systems, especially those using electric motors, often require dedicated pressure sensors, which can be costly or impractical due to environmental or reliability concerns, prompting the need for alternative methods to estimate pump pressure.
Innovation Solution
The method involves using motor current measurements from H-bridge stepper motor controllers to estimate pump pressure by establishing a relationship through look-up tables and gain-corrected scaling factors, allowing for accurate pressure indication without the need for dedicated pressure sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dedicated pressure sensors are used to measure pump pressure, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses motor current as an intermediary parameter to indirectly measure pump pressure. Instead of directly measuring pressure with sensors, the system measures motor current which correlates with the torque required to drive the pump, and thus with pump pressure. This intermediary measurement approach avoids the complexity and cost of dedicated pressure sensors while maintaining measurement capability.
Solution Approach 2:
The patent replaces mechanical pressure sensing systems with an electrical measurement approach. By measuring the electrical current drawn by the motor and using the known relationship between motor torque and pump pressure, the system substitutes a simple electrical current measurement for a complex mechanical pressure sensing system, reducing device complexity while maintaining measurement precision.
2Measurement precision
If dedicated pressure sensors are used, then measurement precision is improved, but cost increases
Solution Approach 1:
The patent replaces expensive dedicated pressure sensors with a low-cost alternative using existing motor current measurement capabilities. The system leverages components already present in the motor controller (current sense resistors, microcontroller) to derive pressure information, eliminating the need for additional expensive pressure sensing hardware and reducing overall system cost.
Solution Approach 2:
The patent makes the motor current measurement system multi-functional. The same current sensing circuitry used for motor control and protection is also used to determine pump pressure. This universal use of existing components eliminates the need for dedicated pressure sensors, reducing system cost while maintaining measurement precision through software-based pressure calculation from current data.
3Device complexity
If motor current is used to estimate pump pressure, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent performs preliminary calibration to establish the relationship between motor current and pump pressure. During a calibration phase, the system collects data correlating motor current with actual pump pressure under various operating conditions. This pre-established relationship is stored and used during normal operation to accurately convert current measurements into pressure readings, ensuring measurement precision without requiring complex real-time calculations.
Solution Approach 2:
The patent implements feedback mechanisms to improve measurement accuracy. The system continuously monitors motor current and uses the calibrated relationship to determine pump pressure in real-time. This feedback approach allows the system to maintain accurate pressure measurements throughout varying operating conditions by continuously updating pressure estimates based on current measurements and the established current-pressure relationship.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides highly accurate pressure indications and can detect equipment failures or anomalies, ensuring reliable operation by correlating motor current with pump pressure, applicable to various motor-driven devices beyond pumps.
Implementation Method 1
Motor current is sensed by the voltage drop across these resistors
Data Source
AI summary
A system for measuring current in an H-Bridge motor drive circuit and using that current to determine the output of a device powered by the motor. A particular embodiment is disclosed for a motor-driven fluid pump. Motor current is measured at predetermined pump pressures and flow rates to create calibration tables relating motor current to pump pressure. Once calibrated, the system determines pump pressure based on motor current by referring to the calibration tables. In an embodiment, the pump is driven to achieve a predetermined fluid dispense profile. The system monitors pump pressure by measuring motor current and determines if the dispense profile is being achieved and sets alarms if predetermined thresholds are not maintained. The system also detects pump wear based on the current measurements and issues warnings to the user in such conditions.