Tumble Dryer Cycle Control Using Load and Conductivity Sensing
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Solution Overview
Problem
Existing laundry dryers face inefficiencies due to fixed-duration drying cycles, which can result in under-dried or over-dried clothes, and humidity-sensing systems that are unreliable with small loads or damp cycles, especially when the drum is lined with soft materials.
Innovation Solution
A method that measures the weight of laundry by evaluating the noise level in the electrical resistance/conductivity signal between arc-shaped electrodes fixed to the door, using a low-pass filter to stabilize the signal, and combining this with temperature data to accurately determine when to stop the drying cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a fixed-duration drying cycle is used, then the drying cycle duration is predetermined and simple to control, but the drying effectiveness is poor because the laundry may be under-dried or over-dried
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 cycle duration based on real-time resistance measurements, extending the cycle if resistance indicates under-drying or terminating it early if resistance indicates sufficient drying. This feedback mechanism resolves the contradiction by maintaining control simplicity while significantly improving drying effectiveness.
2Measurement precision
If conductivity is measured between drum and metal inserts, then humidity measurement is direct and effective, but the drum cannot be lined with soft insulating materials
Solution Approach 1:
The patent makes the drum serve multiple functions: it acts as both the rotating component for laundry processing and as one electrode for conductivity measurement. By using the drum itself (rather than separate electrodes) to measure resistance between the drum and metal inserts, the system maintains precise humidity measurement capability while allowing complete design freedom for drum lining materials, including soft insulating materials for gentle laundry treatment.
3Adaptability or versatility
If small electrodes are fixed to the inside of the door, then the drum design is unrestricted, but the drying cycle stopping reliability is poor especially with small loads
Solution Approach 1:
Instead of fixing electrodes to the door as in conventional systems, the patent inverts the measurement approach by using the drum itself as one electrode and measuring resistance between the drum and metal inserts. This inversion provides larger effective contact area between the measurement system and laundry, significantly improving reliability for small loads while maintaining complete drum design freedom including the ability to use soft linings.
4Measurement precision
If the drum is divided into two halves for conductivity measurement, then humidity sensing is reliable, but the drum structure becomes more complex
Solution Approach 1:
The patent extracts the conductivity measurement function from the drum structure itself, using the existing intact drum as one electrode and measuring resistance between the drum and separate metal inserts. This eliminates the need to divide the drum into two halves, maintaining measurement reliability while preserving the drum's simple, unified structure and allowing continuous rotation without structural interruptions.
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 allows for reliable determination of when to stop the drying cycle, even with small loads or damp cycles, without restricting drum design, ensuring efficient energy use and effective drying performance.
Implementation Method 1
measuring a weight of the laundry inside the drum by evaluating a noise level in an instantaneous values of an electrical resistance/conductivity signal between the two electrodes
Implementation Method 2
using a low-pass filter to stabilize the signal
Implementation Method 3
a heating arrangement, which draw air from the outside and, via an appropriate conduit arrangement, heat and blow the air into and through the laundry drying drum
Implementation Method 4
fed to condensing means to condense the moisture collected in the hot air
Data Source
Figure 1
Figure 2
Figure 3~4
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.