DRYNESS DETECTION METHOD FOR CLOTHES DRYER BASED ON PULSE WIDTH

• US 20110088278A1
• Filed: 10/21/2009
• Published: 04/21/2011
• Est. Priority Date: 10/21/2009
• Status: Active Grant

• Current Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Hopkins, Thomas L.
• Granted Patent: US 8,549,771 B2
• Time in Patent Office: Days
• US Class Current: 34/443
• CPC Class Codes: D06F 2103/10 expressed as capacitance or resistance
• CPC Class Codes: D06F 2103/44 Current or voltage
• CPC Class Codes: D06F 2105/62 Stopping or disabling machine operation
• CPC Class Codes: D06F 34/18 Condition of the laundry, e.g. nature or weight
• CPC Class Codes: D06F 58/38 of drying, e.g. to achieve the target humidity
• CPC Class Codes: F26B 25/22 Controlling the drying process in dependence on liquid content of solid materials or objects

Abstract

A device and method are provided for detecting a root moisture content of clothing in a clothes dryer. The dryer has two conducting bars situated in the dryer bin. A pulse generator circuit is coupled to the conducting bars. A microcontroller is coupled to an output of the pulse generator circuit. The pulse generator circuit generates a pulse when wet clothing contacts the conducting bars in the dryer bin. The microcontroller receives the pulses and counts the pulses that are longer than a threshold length. The microcontroller issues a termination signal based on the number of counted pulses.

Claims

1. A clothes dryer, comprising:

a dryer bin;

a first conductor in the dryer bin;

a second conductor in the dryer bin;

a switch coupled to the first conductor and configured to generate a pulse when a resistance between the first and the second conductors is lower than a threshold resistance, a length of the pulse corresponding to a length of time that the resistance is lower than the threshold resistance; and

a microcontroller coupled to the switch and configured to receive the pulse from the output of the detection circuit and to output a termination signal based on a number of pulses that are longer than a threshold time.

2. The dryer of claim 1 wherein the microcontroller counts pulses during a plurality of counting periods and outputs the termination signal when the number is less than a threshold number in each of two or more consecutive counting periods.

3. The dryer of claim 1, comprising a capacitor coupled to the first and second conductors and to the switch, the capacitor configured to charge according to the resistance between the first and second conductors and to activate the switch when a voltage on the capacitor reaches a threshold voltage.

4. The dryer of claim 1 wherein each pulse triggers an interrupt at a processor of the microcontroller, the microcontroller being configured to count the pulse if the pulse is still present when the processor returns from the interrupt.

5. The dryer of claim 1 wherein the microcontroller is configured to start a timer at a leading edge of the pulse and to compare the length of the pulse to the threshold time as demarked by the timer.

6. The dryer of claim 1 wherein the microcontroller increments a counter if the pulse is longer than the threshold time.

7. A method, comprising:

sensing a resistance between two conductors in a dryer bin of a clothes dryer;

generating a pulse when the resistance is lower than a threshold resistance, a length of the pulse corresponding to a length of time that the resistance is lower than the threshold resistance;

comparing the length of the pulse to a threshold time; and

outputting a termination signal based on a rate of pulses that are longer than the threshold time.

8. The method of claim 7, comprising:

counting the number of pulses that are longer than the threshold time during a plurality of counting periods; and

outputting the termination signal if a number of pulses longer than the threshold time exceeds a threshold number during at least one of the counting periods.

9. The method of claim 7 wherein the termination signal ends the drying cycle.

10. The method of claim 7 wherein comparing comprises:

triggering an interrupt to a microcontroller on a leading edge of the pulse; and

counting the pulse if the pulse is longer than the interrupt to the microcontroller.

11. The method of claim 7 wherein comparing comprises:

starting a timer on a leading edge of the pulse; and

comparing the length of the pulse to the threshold time as counted by the timer.

12. The method of claim 7 wherein generating the pulse comprises:

charging a capacitor when the resistance between the two conductors is less than the threshold resistance, the capacitor being coupled to the two conductors; and

activating a switch when a voltage on the capacitor reaches a threshold voltage, the switch being coupled to the capacitor.

13. A method, comprising:

drying clothes in a dryer bin of a clothes dryer;

generating a pulse if the resistance of the clothes is less than a threshold resistance;

comparing a length of the pulse to a threshold time;

counting pulses which are longer than the threshold time; and

terminating a drying cycle if a rate of occurrence of counted pulses is less than a threshold rate.

14. The method of claim 13 wherein generating the pulse comprises:

charging a capacitor to a voltage dependent upon the resistance of the clothes;

turning on a transistor coupled to the capacitor when the voltage reaches a threshold voltage; and

outputting the pulse to a microcontroller when the transistor turns on.

15. A device, comprising:

a pulse generator circuit configured to generate a pulse when a resistance of an item is detected to be less than a threshold resistance;

a microcontroller configured to receive the pulse and to compare a length of the pulse to a threshold time; and

a counter coupled to the processor, the microcontroller being configured to increment the counter if the pulse is longer than the threshold time.

16. The device of claim 15 wherein the detection circuit is coupled to a first and a second conductor each positioned in a dryer bin of a clothes dryer.

17. The device of claim 15 wherein the item is clothes.

18. The device of claim 17 wherein a moisture content of the item is detected by sensing a resistance between the first and the second conductor when the first and the second conductor are in contact with the item.