Liquid Delivery Device Pressure Control via Feedback
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Solution Overview
Problem
Conventional liquid delivery devices in chromatography face challenges in accurately controlling the pressure, leading to pulsation and errors due to difficulties in detecting when cylinder pressure equals discharge pressure, resulting in fluctuation and inaccurate liquid delivery.
Innovation Solution
A liquid delivery device with a control unit that measures and compares discharge pressure and cylinder pressure, controlling motor speed to establish a judgment point before pressure equality, allowing for precise control and minimizing pressure fluctuation by adjusting the compression and delivery phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the liquid is compressed until cylinder pressure reaches discharge pressure, then the liquid can be delivered, but pulsation occurs due to difficulty in detecting pressure equality
Solution Approach 1:
The control unit establishes a judgment point before the cylinder pressure actually reaches the discharge pressure. By anticipating the pressure equality point and controlling the motor speed based on the difference between cylinder pressure and discharge pressure, the system prevents pulsation before it occurs rather than reacting after pulsation has occurred.
Solution Approach 2:
The control unit continuously monitors both cylinder pressure (via cylinder pressure detector) and discharge pressure (via discharge pressure detector), and adjusts motor speed based on the pressure difference. This closed-loop feedback control ensures accurate pressure matching without relying on detecting the exact moment of pressure equality, thereby eliminating pulsation.
2Productivity
If the valve is opened as soon as cylinder pressure reaches discharge pressure, then liquid delivery is achieved, but detection errors prevent accurate control
Solution Approach 1:
Instead of waiting for and detecting the exact moment when cylinder pressure equals discharge pressure (which is difficult and error-prone), the control unit proactively establishes a judgment point before this equality occurs. The motor speed is controlled based on the pressure difference, ensuring smooth transition to delivery without relying on imprecise detection of the equality point.
Solution Approach 2:
The system replaces the mechanical/reaction-based valve opening mechanism with a controlled motor-driven plunger system. The motor speed is continuously adjusted based on pressure feedback, allowing precise control of the compression and delivery phases without relying on mechanical valve timing that is sensitive to detection errors.
3Productivity
If two cylinders reciprocate alternately, then continuous liquid delivery is achieved, but pulsation occurs in synchronism with plunger frequency
Solution Approach 1:
The system dynamically adjusts the motor rotation speed based on real-time pressure differences between the cylinder and discharge pressure. By continuously varying the speed rather than maintaining constant speed, the system can compensate for pressure fluctuations and eliminate pulsation while maintaining continuous delivery through the alternating cylinder mechanism.
Solution Approach 2:
The control unit uses feedback from both cylinder pressure detectors and discharge pressure detectors to continuously adjust motor speed. This feedback mechanism ensures that the plunger movement adapts to pressure conditions, smoothing out the flow and eliminating pulsation that would otherwise occur with simple alternating reciprocation.
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
The solution ensures minimal pressure fluctuation and accurate liquid delivery, reducing errors and pulsation, and maintaining stable flow rates even with varying eluent properties.
Implementation Method 1
a discharge pressure detector to measure the discharge pressure of the eluent being discharged from said cylinders
Implementation Method 2
a cylinder pressure detector to measure the pressure of said eluent flowing in said cylinders
Implementation Method 3
a plunger reciprocates, so that it delivers a liquid continuously, with two cylinders repeating sucking and discharging alternately
Implementation Method 4
the liquid is compressed when the liquid, which has been suck up into the cylinder, is forced out by the plunger
Data Source
AI summary
The present invention provides a liquid delivery device for liquid chromatographs which, by performing liquid delivery at an accurate flow rate with limited pulsation, gives accurate results of analysis. The present invention, with a view to preventing erroneous operation due to errors in measurements at the time of judgment of completion of compression of liquid, establishes the judgment point before the pressure measured by a cylinder pressure detector agrees with the pressure measured by a discharge pressure detector and also calculates the point of completion of compression. Control in this manner prevents pressure fluctuation. It also calculates for control the point of completion of compression from the history of compression performed previously.