Ball Screw Liquid Feeding Device Error Compensation

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Solution Overview

Problem

The use of a ball screw as a power mechanism in liquid feeding devices for TOC measurement instruments introduces variable errors in feed length, affecting conductivity measurement values due to machining inaccuracies, leading to increased costs and processing difficulties.

Innovation Solution

A liquid feeding device with a syringe driven by a ball screw, equipped with a rotation detection mechanism and control device that uniformizes the rotational cycles of the ball screw by starting each discharge process from an identical rotational angle, minimizing feed errors through precise control of the pulse motor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Extent of automation

If a ball screw is used as a power mechanism in liquid feeding devices, then the device can achieve automated liquid feeding control, but machining inaccuracies of the ball screw cause variable errors in feed length that affect measurement precision

Engineering Contradiction:

Improveautomated liquid feeding controlVSAvoidconductivity measurement value accuracy

Core Design Contradiction:

Extent of automationVSMeasurement precision

Solution Approach 1:

The patent employs feedback control by detecting the actual rotational angle of the ball screw with a rotation detection mechanism (encoder) and comparing it with the commanded rotational angle. The control device adjusts the pulse motor output based on the detected error, creating a closed-loop control system that compensates for ball screw machining inaccuracies and stabilizes liquid feed flow rate.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces open-loop mechanical positioning with a closed-loop control system that uses electrical signals (pulse motor control) and sensory feedback (rotation detection) to achieve precise positioning. This substitution of pure mechanical reliance with electromechanical control allows compensation for mechanical inaccuracies.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If the machining accuracy of the ball screw is increased to reduce feed errors, then measurement precision improves, but manufacturing costs and processing difficulty increase

Engineering Contradiction:

Improvefeed length accuracyVSAvoidball screw processing difficulty

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

Instead of improving mechanical manufacturing precision through more complex and expensive machining processes, the patent substitutes mechanical precision with control system precision. The ball screw can be manufactured with standard tolerances, and the control system compensates for the resulting errors through feedback control, thereby reducing manufacturing difficulty and cost while maintaining measurement precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Productivity

If liquid feeding is controlled by flow rate using a ball screw, then automated control is achieved, but variable errors in feed length per rotational angle cause flow rate variations that manifest as measurement errors

Engineering Contradiction:

Improveautomated liquid feedingVSAvoidconductivity measurement accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The rotation detection mechanism continuously monitors the ball screw's actual rotational position and feeds this information back to the control device. The control device adjusts the pulse motor's pulse output in real-time to compensate for deviations from the commanded position, ensuring accurate liquid feed flow rate control despite ball screw manufacturing variations.

Inventive Principle:

Principle #23Feedback

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 stabilizes the liquid feed flow rate, reducing measurement errors from ±20 μgC/L to ±1 μgC/L, enhancing the accuracy and reproducibility of TOC measurements.

Implementation Method 1

a ball screw 36 that moves a piston rod of a syringe, a pulse motor 32 that rotates the ball screw 36

Methodology Applied

Scientific EffectScrew mechanism: Screw

Implementation Method 2

a photo sensor 40 that is combined with the coupling 38 so as to detect a position of the slit 39 of the coupling 38

Methodology Applied

Scientific EffectPhotoelectric detection: Photoelectric Effect

Data Source

PatentUS9021899B2Liquid feeding device using ball screw, and analyzer

Publication Date: 2015.05.05 SHIMADZU CORP

AI summary

A control device controls driving of a pulse motor to cause liquid that is sucked into a syringe in a single suction process to be discharged over a plurality of discharge processes. The control method of the control device is a method that controls driving of the pulse motor so that rotation of a ball screw for executing each discharge process starts from an identical rotational angle position relative to a slit of a coupling.