Washing Machine Drum Speed Control for Accurate Foam Detection
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Solution Overview
Problem
The formation of a closed liquid ring at the circumferential walls of the laundry drum during high-speed rotation in washing machines interferes with accurate foam monitoring and drainage, leading to incomplete washing cycles.
Innovation Solution
Detecting the liquid level and comparing it with a threshold value to reduce the rotational speed if it exceeds the upper threshold, thereby preventing the formation of a closed liquid ring, and initiating a foam-detecting procedure to manage foam levels effectively during dewatering and spinning phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the laundry drum rotates at high speed during spinning phase, then dewatering efficiency is improved, but a closed liquid ring forms at circumferential walls which prevents accurate foam monitoring
Solution Approach 1:
The control unit performs preliminary action by detecting the liquid level and comparing it with a threshold value before the spinning phase begins or while the drum is rotating at a lower speed. This allows the system to determine in advance whether foam monitoring will be compromised by closed liquid ring formation, and to take preventive measures by interrupting the spinning phase or adjusting operational parameters before the problem occurs.
Solution Approach 2:
The system implements feedback by continuously detecting the liquid level in the washing tub and using this information to control the drum rotation speed. When the liquid level exceeds the threshold value indicating potential closed liquid ring formation, the control unit receives this feedback and adjusts the drum speed accordingly to maintain both dewatering efficiency and foam monitoring accuracy.
2Reliability
If the liquid level exceeds the threshold during high-speed rotation, then a closed liquid ring forms which obstructs drainage, but reducing speed below threshold may reduce dewatering efficiency
Solution Approach 1:
The system applies dynamics by making the drum rotation speed variable rather than constant. The control unit dynamically adjusts the rotation speed based on real-time liquid level detection, increasing speed to enhance dewatering efficiency when liquid level is acceptable, and reducing speed when liquid level approaches the threshold to prevent closed liquid ring formation, thus maintaining both drainage reliability and dewatering efficiency.
3Extent of automation
If foam amount is monitored by detecting liquid level during spinning, then foam detection is possible, but the measurement becomes inaccurate when closed liquid ring forms
Solution Approach 1:
The system performs preliminary detection of liquid level at speeds where closed liquid rings do not form, establishing a baseline for accurate foam monitoring. By comparing liquid level measurements taken under different rotational conditions, the system can distinguish between actual foam-related level changes and artifacts caused by closed liquid ring formation.
Solution Approach 2:
The system changes the operational parameter of drum rotation speed to optimize measurement conditions. By varying the rotation speed and observing how liquid level measurements change, the system can identify conditions where measurements are reliable versus those where closed liquid rings distort the readings, thereby maintaining accurate foam detection capability.
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
Ensures accurate foam detection and reduction, preventing foam from obstructing drainage and allowing for uninterrupted washing cycles by avoiding closed liquid rings and ensuring effective foam management.
Implementation Method 1
when the drum is rotating at a certain rotation speed there is a threshold level of the liquid level in the washing tub at which the liquid starts rotating along the circumferential walls of the drum, in such a way to create a closed liquid ring
Implementation Method 2
the monitoring of the foam amount is performed by detecting the liquid level in the washing tub or in the draining region
Data Source
AI summary
A method for operating a washing machine (10) having a washing tub (24) containing a laundry drum (26). The method has the steps of:detecting a liquid level (44) in the washing tub (24) and/or in a draining region thereof while the laundry drum (26) is rotating at a first speed,comparing the detected liquid level (44) with an upper threshold value (48), wherein the excess of said upper threshold value (48) by the liquid level (44) while the laundry drum (26) rotates at a rotation speed equal or higher than the first speed generates a closed liquid ring at circumferential walls of the laundry drum (26), andif the detected liquid level (44) exceeds the upper threshold value (48), then reducing the rotational speed of the laundry drum (26) below the first speed and performing a foam-detecting procedure for detecting the amount and/or presence of foam inside the washing tub (24) and/or in the draining region thereof.