Tumble Dryer Cycle Control Using Conductivity Noise and Air Temperature
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Solution Overview
Problem
Existing tumble dryers face inefficiencies due to fixed-duration drying cycles, which can result in under-dried or over-dried laundry, especially with variable loads and humidity levels, and traditional humidity sensing methods restrict drum design and are unreliable for small loads and damp cycles.
Innovation Solution
A method that estimates the weight of laundry by analyzing the noise level in the electrical resistance/conductivity signal between arc-shaped electrodes fixed to the door, combined with temperature sensing to determine when to stop the drying cycle, allowing for flexible drum design and improved reliability across various load sizes and humidity conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed-duration drying cycle is used, then the drying process is simple to control, but the drying effectiveness is poor for variable loads and humidity levels
Solution Approach 1:
The patent implements feedback control by continuously monitoring the electrical resistance between the drum and metal inserts during the drying cycle. The control unit adjusts the drying process based on real-time resistance measurements, automatically determining when the laundry has reached the desired dryness level. This resolves the contradiction by maintaining simple operation while significantly improving drying effectiveness through automatic feedback-based control.
2Measurement precision
If conductivity is measured between drum and metal inserts, then humidity sensing is effective, but the drum must be made of conductive material and cannot be lined with soft materials
Solution Approach 1:
The patent introduces metal inserts as intermediary elements that provide the necessary conductive contact points without requiring the entire drum to be conductive. These inserts are strategically positioned to ensure reliable electrical contact with the laundry during the drying cycle, enabling accurate humidity sensing while preserving the ability to use soft, non-conductive drum linings for gentle laundry treatment.
3Adaptability or versatility
If electrodes are fixed to the inside of the door with limited contact surface, then drum design is unrestricted, but the system is unreliable for small loads and damp cycles
Solution Approach 1:
The patent extracts the humidity sensing function from the door-mounted electrode system and relocates it to the drum itself through metal inserts. This extraction allows the door electrodes to be removed or minimized, eliminating the reliability problems associated with limited contact surface area while maintaining drum design freedom. The metal inserts provide robust, reliable contact points that work effectively for all load sizes and humidity conditions.
4Measurement precision
If the drum is divided into two halves for conductivity measurement, then humidity measurement is reliable, but the drum construction becomes complex and restrictive
Solution Approach 1:
The patent uses metal inserts as intermediary contact points that eliminate the need to divide the drum into two halves. These inserts provide the necessary conductive pathways for measuring electrical resistance between the drum and the laundry, maintaining measurement reliability while preserving simple, unified drum construction. The inserts are easily integrated into the existing drum structure without requiring complex modifications.
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 enables accurate determination of when to stop the drying cycle, ensuring efficient energy use and effective drying performance without the design restrictions of traditional systems, maintaining reliability even with small loads and damp cycles.
Implementation Method 1
measuring a electrical resistance/conductivity signal between a pair of arc-shaped electrodes
Implementation Method 2
combined with temperature sensing to determine when to stop the drying cycle
Data Source
AI summary
A method of controlling a tumble laundry drier (1), the method including the steps of: starting a drying/ironing cycle and feeding drying air into the drum (5) from a drum input to a drum output; continuously measuring the electrical resistance/conductivity between two electrodes (25) located on the inside of the door; estimating the weight of the laundry inside the drum (5); measuring a temperature of the drying air at the drum output; stopping the drying/ironing cycle, if the weight of the laundry is above a weight threshold, when the electrical resistance/conductivity between the two electrodes (25) is above/below a resistance/conductivity threshold; and stopping the drying/ironing cycle, if the weight of the laundry is below a weight threshold, when the electrical resistance/conductivity between the two electrodes (25) is above/below a resistance/conductivity threshold and also when the temperature of the drying air at the drum output is above a temperature threshold.