Rotatable-drum laundry drier and method of controlling a rotatable-drum laundry drier
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Solution Overview
Problem
Existing rotatable-drum laundry dryers fail to achieve precise and stable final moisture levels due to variations in laundry quantity/weight, particularly with cotton and synthetic fabrics, leading to unacceptable differences in drying outcomes.
Innovation Solution
A control method that memorizes a time-variable comparison threshold with discrete profile values for different drying time intervals and laundry quantities, measuring moisture using electrodes, and determining the end of the drying cycle based on these thresholds, allowing for adjustment of the cooling stage duration based on calculated laundry weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed comparison threshold is used for impedance measurement, then the control method is simple, but the final moisture varies significantly with laundry quantity/weight
Solution Approach 1:
The comparison threshold is transformed from a fixed value to a dynamic value that varies with drying time. The threshold is defined as a function of drying time, allowing it to adapt automatically as the drying process progresses. This dynamic adjustment ensures that the threshold accurately reflects the changing moisture conditions throughout the drying cycle, achieving consistent final moisture regardless of laundry quantity.
Solution Approach 2:
The invention changes the parameter of the comparison threshold from a constant to a time-dependent variable. By defining the threshold as a function of drying time and storing discrete threshold values in memory, the system can select appropriate thresholds based on the current drying stage, thereby maintaining precision across different laundry loads without increasing hardware complexity.
2Manufacturing precision
If weight sensors are added to determine laundry quantity, then precise final moisture can be achieved, but the system becomes expensive and complicated
Solution Approach 1:
The system uses the existing impedance measurement data and drying time information to indirectly determine laundry characteristics. Instead of adding weight sensors, the invention leverages the moisture sensor readings combined with time-based threshold comparison to achieve precise control, allowing the system to self-adjust based on measurements already being taken during the drying process.
Solution Approach 2:
The invention introduces a time-based comparison threshold as an intermediary between the impedance measurement and the drying control decision. This intermediary threshold function acts as a reference that accounts for laundry quantity effects without requiring direct measurement of weight, thereby achieving precision without additional sensors or complex hardware.
3Ease of operation
If the drying cycle is stopped when impedance reaches a fixed threshold, then the control process is simple, but the drying time varies significantly with laundry quantity
Solution Approach 1:
The comparison threshold is made dynamic by defining it as a function of drying time. This allows the threshold to automatically adapt to the current stage of drying, ensuring that the stopping condition remains appropriate regardless of total drying duration. The simplicity of the control process is maintained while achieving consistent drying outcomes across different laundry quantities.
Solution Approach 2:
The invention performs preliminary action by pre-calculating and storing discrete threshold values corresponding to different drying time intervals in memory. This preparation allows the microprocessor to quickly retrieve and compare against the appropriate threshold during drying, eliminating complex real-time calculations while maintaining precision and reducing drying time variation.
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 method ensures a precise and stable final moisture level, regardless of laundry quantity/weight, by accurately determining the end of the drying cycle and adjusting the cooling stage, thus improving drying consistency and efficiency without requiring weight sensors or increasing complexity and cost.
Implementation Method 1
the impedance of the laundry is measured by measuring electrodes positioned contacting the laundry
Data Source
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Figure 2
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AI summary
Method for controlling a rotatable-drum laundry drier to dry laundry in a drum, the control method comprising the steps of: - memorizing a in a memory device of said laundry drier a comparison threshold variable in time according to a predetermined profile, and - at predetermined drying times in the laundry drying cycle: - measuring an electric quantity indicating the moisture in the laundry at the drying time; - comparing, at each drying time, the measured electric quantity with the memorized comparison threshold corresponding to the drying time; - determining the end of drying cycle time on the basis of this comparison.