Positive Displacement Pump Volume Dispensing Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Positive displacement pumps face challenges in accurately dispensing a set volume of fluid due to latency in motor speed changes and pulsatile flow rates, making conventional control techniques like PID controllers ineffective in achieving precise volume control.
Innovation Solution
A control method that employs a pump motion profile with an acceleration phase, a constant speed phase, and a deceleration phase, using a flow sensor to generate a calibrated mapping between pump speed and flow rate, allowing for rapid and precise dispensing of a target volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PID control techniques are used to control pump speed, then the control system is simple to implement, but the dispensing accuracy is poor due to latency in motor speed changes and pulsatile flow rates
Solution Approach 1:
The system performs a calibration procedure before actual dispensing to establish a mapping between motor speeds and flow rates. This preliminary action characterizes the pump-tubing-fluid system so that subsequent dispensing operations can achieve high accuracy without requiring complex real-time control algorithms.
Solution Approach 2:
The control system dynamically adjusts motor speed based on the calibrated mapping to maintain a target flow rate. Rather than using fixed PID parameters, the system adapts motor speed commands based on the specific characteristics of the pump-tubing-fluid combination, improving dispensing accuracy while keeping the control logic relatively simple.
2Productivity
If the pump operates at maximum speed to increase productivity, then the dispensing speed is fast, but the flow rate pulsations increase and accuracy decreases
Solution Approach 1:
The system changes the operating parameters (motor speed) based on the calibrated flow rate mapping. By selecting appropriate motor speeds from the calibrated data, the system can operate at high speeds for bulk dispensing while transitioning to more precise, lower-speed operation for final volume accuracy, thus resolving the contradiction between productivity and precision.
3Duration of action of stationary object
If tubing properties change during operation due to wear, then the pump can operate continuously for long periods, but the calibrated settings become inaccurate
Solution Approach 1:
The system uses a flow sensor to provide feedback on actual flow rate during operation. This feedback allows the system to detect deviations from expected performance due to tubing wear and adjust motor speed accordingly, maintaining accuracy over extended operational periods without requiring frequent recalibration.
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
Aspects are provided for positive displacement pumps and methods and systems for controlling such positive displacement pumps for accurate volume dispensing. The pump may run a calibration procedure to determine a mapping between a pump speed and a flow rate for a current configuration of the positive displacement pump, a tubing size, and a fluid characteristic. A pump controller may determine a pump motion profile based on the mapping. The pump motion profile includes an acceleration phase, a constant speed phase, and a deceleration phase such that a total volume pumped according to the pump motion profile and the mapping is equal to a target volume. The pump controller may determine an adjustment to the pump motion profile based on a constant flow rate measured during operation. The pump controller may decelerate the positive displacement pump according to the adjusted pump motion profile until the target volume is dispensed.