EP3494255A1

EP3494255A1 - Electrical household appliance having a moisture sensing circuit

Info

Publication number: EP3494255A1
Application number: EP17751312.4A
Authority: EP
Inventors: Ali Acar; Erdem Kara; Ihsan Ozan YILDIRIM; Ersin FIDANOGLU; Olcay KAPSIZ
Original assignee: Arcelik AS
Current assignee: Arcelik AS
Priority date: 2016-08-05
Filing date: 2017-07-26
Publication date: 2019-06-12
Also published as: WO2018024580A1; TR201610981A2

Abstract

An embodiment of the present invention relates to a moisture sensing circuit for a laundry treatment appliance and more particularly for a laundry drying appliance. An embodiment of the present invention more particularly relates to an electrical household appliance comprising a rotary drum in which laundry is placeable, conducting plates placed within said drum and a moisture sensing circuit (1) measuring resistance of the laundry.

Description

ELECTRICAL HOUSEHOLD APPLIANCE HAVING A MOISTURE SENSING CIRCUIT

The present invention relates to an electrical household appliance, such as a laundry treatment appliance and more particularly a laundry drying appliance, comprising a moisture sensing circuit.
It is well-known that in laundry drying appliances, moisture level of laundry is monitored by sensors during the drying cycle to determine when a moisture-free situation is reached within the drum of the household appliance. The desired level of dryness is generally determined by user input, depending on the type of laundry. When moisture sensors determine that the desired value is reached, the drying cycle is terminated.
Moisture sensors are placed in the drum of the dryer and generally operate by measuring the electrical impedance of wet fabric via electrodes. In the state of the art, moisture sensors make use of a number of electronic components to measure electrical impedance of wet fabric and associate this information with humidity level by means of a microprocessor. Moisture sensing circuits consist of several circuit elements and components such as operational amplifiers, resistors and capacitors which result in an overly complex system that is burdensome to design and costly to manufacture. In addition, this system is difficult to troubleshoot in case of breakdown of hardware or software due to its complexity.
Among others, a prior art publication in the technical field of the invention may be referred to as US7345491B2, which discloses a moisture sensing circuit for use in a laundry dryer which consists of a pair of spaced apart electrodes which measure the resistance of wet clothes. In addition, an active filter is used to suppress noise relating to the operating line frequency of the dryer and to obtain a voltage signal representing the voltage drop across the electrodes.
The present invention, on the other hand, addresses the situation where complex and costly circuits are not necessary to use in moisture sensors. To this end, the present invention provides a moisture sensing circuit consisting of fewer components than is found in the art to provide more efficient and inexpensive sensing of moisture levels of laundry. Also, use of filter circuits provides more effective sensing of moisture. The simple design of moisture sensing circuit allows ease of troubleshooting in case of breakdown.
The present invention provides an electrical household appliance having a moisture sensing circuit as provided by the characterizing features defined in Claim 1.
Primary object of the present invention is to provide a household appliance with a moisture sensing circuit comprising a simple circuit design and filter for more effective and inexpensive sensing of moisture levels of laundry.
The invention proposes an electrical appliance with a moisture sensing circuit as an electrical filter circuit electrically connected to sense laundry moisture within the drum through conducting plates. A pulse width modulated input signal’s duty cycle is changed at the end of an initial phase of moisture sensing operation when a predetermined value for laundry resistance is measured. Parameters such as frequency, resistance, capacitance or inductance of the electrical filter circuit can be changed from a first value to a second value at the end of said first stage to increase resolution of the second stage measurements. Said moisture sensing circuit is an RC, RL or RLC circuit and preferably an RC circuit where the reference resistance of the RC circuit is preferably in parallel electrical connection with said conducting plates.
Accompanying drawings are given solely for the purpose of exemplifying a moisture sensing circuit, whose advantages over prior art were outlined above and will be explained in brief hereinafter.
The drawings are not meant to delimit the scope of protection as identified in the Claims, nor should they be referred to alone in an effort to interpret the scope identified in said Claims without recourse to the technical disclosure in the description of the present invention.
Fig. 1 demonstrates a general flow diagram representation of the moisture level sensing implementation according to the present invention.
Fig. 2 demonstrates a simplified schematic circuit diagram of the moisture level sensing circuit according to the present invention.
The following numerals are assigned to different part numbers used in the detailed description:

Moisture sensing circuit
Laundry Resistance
Reference Resistor
Sensing point
Capacitor

According to the present invention, moisture level of laundry is typically determined by two independent conducting plates (Sensing points, 4) placed on the front face of dryer drum of a laundry treatment appliance such as a dryer or combo washer and dryer. As is known, when wet laundry makes contact with conducting plates, impedance is measured by a moisture sensing circuit (1). Change in resistance of laundry leads to change in impedance in moisture sensing circuit (1), which causes a change in signal amplitude, frequency, or phase for every component of moisture sensing circuit (1). Moisture level is determined using the relationship between these changes and amount of moisture.
Moisture sensing circuit (1) of the present invention comprises a reference signal of modifiable or predetermined amplitude and frequency, components of variable values and RC, RL, RLC filter circuits where resistance of wet laundry (laundry resistance, 2) from contact with conducting plates placed on the front face of dryer drum connected parallel or in series to any and/or all components of said moisture sensing circuit (1) will cause a change in signal amplitude, frequency, or phase for every said component depending on amount of moisture in laundry whereby moisture level of laundry can be determined.
More particularly, the moisture sensing circuit (1) of the present invention advantageously affords a much less complex solution consisting of fewer components to provide more efficient and inexpensive sensing of moisture levels of laundry. This is achieved through use of an electrical filter circuit as the moisture sensing circuit (1) as will be delineated hereinafter.
In low frequency applications (up to 100 kHz), an electrical filter circuit having no amplifying elements (transistors, op-amps, etc.) can be realized making use of simple RC (Resistor-Capacitor) circuits. Higher frequency filters can be made from RLC (Resistor-Inductor-Capacitor) elements.
In reference to Fig. 2, the RC circuit’s response to an input signal that is a pulse width modulated signal of known period and duty cycle is such that the RC circuit typically converts the PWM output into a voltage corresponding to the percentage of the PWM waveform. As is apparent to the skilled worker, the capacitor (5) is charged by the external voltage source and then the applied voltage drops to zero and the capacitor is discharging through the reference resistor (3). The approach of the present invention relies on the concept that while a first set of parameters are used during an initial phase of the moisture sensing operation, a second set of parameters are used during the subsequent stage of the algorithm.
In a more specific manner, according to the present invention, during the initial stage of the laundry resistance (2) measuring operation, a first frequency value is used and the frequency value is dynamically changed at a certain laundry resistance (2) value to increase moisture measuring sensitivity. Increasing measurement sensitivity is crucial because the resolution of the measured data in an increased manner allows sensing of the dryness level during the subsequent stage of the measuring operation where the laundry resistance is at substantially higher levels. In sum, based on a stored pattern of corresponding data to precisely predict the level of dryness, measurements are carried out using different sets of parameters during subsequent stages in order to increase resolution of the measured data.
In reference to the RC circuit of Fig. 2, the parameters of reference resistance (R), RC, -t/RC, e^-t/RC, 1-(e^-t/RC) and Vo (Output voltage) change with the measured resistance. By way of example, according to a specific embodiment of the present invention in the case of an RC circuit, a frequency value of 400 Hz and a duty cycle of 10% are used in the first stage of the sensing operation. On the other hand, starting from a predetermined value of measured laundry resistance, a second set of parameters in the form of a frequency value of 50 Hz and a duty cycle of 20% are used.
It is to be noted that instead of the frequency value, the reference resistance or the capacitance values can also be dynamically varied. The electrical filter as the moisture sensing circuit can also be an RL or RLC filter circuit.
The following table demonstrates an exemplary non-complete listing of parameter value changes (units in F, Ohm and Volt) over time with respect to measured resistance (R-sensor).

Table 1

R-sensor	R	RC	-t/RC	e^-t/RC	1-(e^-t/RC)	Vo
1000	999,9545	1E-06	-250,0114	2,639E-109	1	5
2000	1999,818	2E-06	-125,0114	5,10804E-55	1	5
3000	2999,591	3E-06	-83,3447	6,36587E-37	1	5
4000	3999,273	4E-06	-62,51136	7,10656E-28	1	5
5000	4998,864	5E-06	-50,01136	1,90696E-22	1	5
6000	5998,364	6E-06	-41,67803	7,93344E-19	1	5
7000	6997,773	7E-06	-35,72565	3,05174E-16	1	5
8000	7997,092	8E-06	-31,26136	2,65071E-14	1	5
9000	8996,32	9E-06	-27,78914	8,53747E-13	1	5
10000	9995,457	1E-05	-25,01136	1,3731E-11	1	5
11000	10994,5	1,1E-05	-22,73864	1,33271E-10	1	5
12000	11993,46	1,2E-05	-20,8447	8,85652E-10	0,999999999	5
13000	12992,32	1,3E-05	-19,24213	4,39793E-09	0,999999996	5
14000	13991,1	1,4E-05	-17,86851	1,73703E-08	0,999999983	5
15000	14989,78	1,5E-05	-16,67803	5,71246E-08	0,999999943	5
16000	15988,37	1,6E-05	-15,63636	1,61888E-07	0,999999838	4,999999
17000	16986,87	1,7E-05	-14,71725	4,05865E-07	0,999999594	4,999998
18000	17985,28	1,8E-05	-13,90025	9,18749E-07	0,999999081	4,999995
19000	18983,61	1,9E-05	-13,16926	1,90838E-06	0,999998092	4,99999
20000	19981,83	2E-05	-12,51136	3,68454E-06	0,999996315	4,999982

It is further to be noted that the electrical filter circuit can be connected with the conducting plates in series or in parallel.
In a nutshell, the present invention proposes an electrical household appliance comprising a rotary drum in which laundry is placeable, conducting plates placed within said drum and a moisture sensing circuit (1) measuring resistance of the laundry.
In one embodiment of the present invention, said moisture sensing circuit (1) is an electrical filter circuit in electrical connection with said conducting plates.
In a further embodiment of the present invention, a pulse width modulated input signal is applied to said electrical filter circuit and laundry resistance between said conducting plates is measured by a first set of parameter values set during an initial phase of moisture sensing operation and a second set of parameter values set during a subsequent stage of said moisture sensing operation in the manner that at least one of the parameters including frequency, resistance, capacitance or inductance of said electrical filter circuit is changed from a first value to a second value at the end of said first stage where a predetermined laundry resistance is measured.
In a further embodiment of the present invention, said moisture sensing circuit (1) is an RC, RL or RLC circuit in electrical connection with said conducting plates in the form of sensing points (4).
In a further embodiment of the present invention, said RC, RL or RLC circuit comprises a reference resistor (3) in parallel with said laundry resistance.
In a further embodiment of the present invention, said moisture sensing circuit (1) is an RC circuit in electrical connection with said conducting plates in the form of electrical sensing points (4).
In a further embodiment of the present invention, a first frequency value higher than a second frequency value is applied during said initial phase compared to said second frequency value applied during said subsequent phase.
In a further embodiment of the present invention, a duty cycle value lower than a second duty cycle value is applied during said initial phase compared to said second duty cycle value applied during said subsequent phase.
In a further embodiment of the present invention, frequency value of 400 Hz and a duty cycle of 10% are set during said initial phase of moisture sensing operation and a frequency value of 50 Hz and a duty cycle of 20% are set during a subsequent stage of said moisture sensing operation.
In a further embodiment of the present invention, said electrical household appliance is laundry dryer or combo washer and dryer appliance.
The invention is devised under the recognition that a moisture sensing circuits consist of a minimum number of circuit elements should be constructed, which is not overly complex to design and costly to manufacture. The parameter values of the filter circuit are dynamically changed to ensure more accurate readings at higher values of measured resistances.

Claims

An electrical household appliance comprising a rotary drum in which laundry is placeable, conducting plates placed within said drum and a moisture sensing circuit (1) measuring resistance of the laundry characterized in that;

said moisture sensing circuit (1) is an electrical filter circuit in electrical connection with said conducting plates,

a pulse width modulated input signal is applied to said electrical filter circuit and laundry resistance between said conducting plates is measured by a first set of parameter values set during an initial phase of moisture sensing operation and a second set of parameter values set during a subsequent phase of said moisture sensing operation in the manner that at least one of the parameters including frequency, resistance, capacitance or inductance of said electrical filter circuit is changed from a first value to a second value at the end of said first phase where a predetermined laundry resistance is measured.
An electrical household appliance as in Claim 1, characterized in that said moisture sensing circuit (1) is an RC, RL or RLC circuit in electrical connection with said conducting plates in the form of sensing points (4).
An electrical household appliance as in Claim 2, characterized in that said RC, RL or RLC circuit comprises a reference resistor (3) in parallel with said laundry resistance.
An electrical household appliance as in Claim 2 or 3, characterized in that said moisture sensing circuit (1) is an RC circuit in electrical connection with said conducting plates in the form of electrical sensing points (4).
An electrical household appliance as in Claim 4, characterized in that a first frequency value higher than a second frequency value is applied during said initial phase compared to said second frequency value applied during said subsequent phase.
An electrical household appliance as in Claim 4, characterized in that a duty cycle value lower than a second duty cycle value is applied during said initial phase compared to said second duty cycle value applied during said subsequent phase.
An electrical household appliance as in Claim 4, characterized in that frequency value of 400 Hz and a duty cycle of 10% are set during said initial phase of moisture sensing operation and a frequency value of 50 Hz and a duty cycle of 20% are set during a subsequent phase of said moisture sensing operation.
An electrical household appliance as in Claim 1, characterized in that said electrical household appliance is laundry dryer or combo washer and dryer appliance.