Patent Application
20110088279
The present disclosure relates to a method and a circuit for detecting the moisture content of articles in an automatic dryer.
Many clothes dryers allow the user to select a specific amount of time for the clothes dryer to dry a load of laundry. This selection can be made using a dial or a digital interface on the outside of the dryer.
Many dryers alternatively allow the user to select a level of dryness to which the dryer will dry a load of laundry. In this type of dryer there is typically some kind of mechanism for monitoring how dry the laundry is. When the dryer detects that the load of laundry has reached the level of dryness selected by the user, then the drying cycle ends.
In one system the humidity of the air exiting the dryer is monitored. As the dryer dries the clothes, water in the clothes evaporates and is expelled through the dryer vent. At first the air in the dryer is quite humid. But as the clothes become drier, the humidity in the air passing through the vent decreases. In such a system the dryer assumes that the clothes are dry once the humidity of the air passing through the vent has dropped below a threshold value. The dryer then turns off.
A challenge faced by automatic dryers is to ensure that the clothes do not stay in the dryer too long. This is countered by the need to ensure that the clothes are sufficiently dry. Over-drying clothes can damage certain types of delicate clothing and waste energy. A dryer that frequently continues to operate after the clothes are dry may also shorten its own lifetime.
In one embodiment, two conductors are positioned in the drying bin of a clothes dryer. The clothes dryer comprises a bin for drying the clothes and a sensor in the dryer bin. A capacitor is coupled to the sensor and configured to charge when the clothes are in contact with the sensor. A microcontroller is coupled to the capacitor and is configured to measure a charge time of the capacitor. The microcontroller is configured to output a termination signal to end the drying cycle based on the charge time. The charge time of the capacitor is proportional to the resistance of the clothing in contact with the sensor.
In one embodiment the sensor is two conducting bars in the dryer bin. When an item of clothing is in contact with both of the conducting bars, the item of clothing acts as a conductor having a resistance connected between the conducting bars and the capacitor is enabled to charge. If the resistance of the clothing is low enough, the capacitor will charge to a threshold voltage. A switch is coupled to the capacitor and configured to turn on when the capacitor reaches the threshold voltage.
In one embodiment, a microcontroller enables a discharge transistor to discharge the capacitor at the instance the switch turns on. The capacitor will then recharge and the microcontroller measures the time for the capacitor to recharge and enable the switch again. The microcontroller monitors the moisture content of clothes based on the charging rate of the capacitor in the RC circuit. Since the value of R in the RC circuit varies depending on how dry the clothes are, the capacitor charge time is a good indication of the moisture content of the clothes. The charge time is measured over a plurality of charge times. The microcontroller may issue a termination signal to end the drying cycle based on the one or more of the charge times.
One embodiment of a method for drying clothes in a clothes dryer comprises charging a capacitor when clothing in the dryer bin contacts a sensor in the dryer bin, measuring the charge time of the capacitor to reach a threshold voltage, and terminating the drying cycle based on the charge time.
In one embodiment the method further comprises discharging the capacitor once the capacitor reaches the threshold voltage and measuring a time to recharge the capacitor to the threshold voltage.
The user can use the user input 13 to select an automatic drying cycle and a desired level of dryness for the automatic drying cycle. The dryer 10 is configured to end the automatic drying cycle when clothes placed in the bin 12 have reached the level of dryness specified by the user.
The sensor 15 is coupled to a pulse generator circuit 18. When wet clothes contact the sensor 15, the pulse generator circuit 18 outputs a pulse to a processor 24. The processor 24 is coupled to a clock 26, a memory 28, a counter 30, and a timer 31. The memory 28 stores and retrieves data. The data includes information regarding pulses received from the pulse generator, software to enable execution of programs by the processor 24, or any other data which may be used by the processor 24 or other components.
The counter 30 counts a number of pulses received by the processor 24 from the pulse generator circuit 18. The timer 31 may be used to measure a time required for the pulse generator circuit 18 to change from a first state to a second state.
In one embodiment, the processor 24 monitors a time required for the pulse generator circuit 18 to change from a first state to a second state. If the time required to change from the first state to the second state is longer than a threshold time, then the processor 24 issues a termination signal to end the drying cycle. The memory 28 may store data regarding a plurality of pulses and the processor may issue the termination signal based on times from a plurality of pulses. Other embodiments may have fewer or more components than those shown in
The value of the bleed resistor R is selected to permit the capacitor to charge under normal operating conditions. The value R is usually a high resistance, such as in the mega ohm range; after the clothes are no longer in contact with the sensor, the capacitor will discharge through R to be ready for the next sensing event.
If the resistance of the clothes is low, then enough voltage is dropped across the resistor R to permit the capacitor to charge to the threshold voltage rapidly; if the resistance of the clothes is high enough, then enough voltage will be dropped across the clothes to prevent the capacitor from charging to the threshold voltage and the switch will not be activated.
In one embodiment the microcontroller 22 may include the processor 24, the clock 26, the memory 28, the counter 30, and the timer 31. The microcontroller 22 receives pulses from the switch 35. Counter 30 counts the pulses. The processor 24 monitors the counter 30 to determine if the number of counted pulses in a selected time period is smaller than a threshold number. If the number of counted pulses is less than a threshold number then the processor 24 issues a termination signal to end the drying cycle.
In one embodiment the microcontroller 22 is configured to measure a charge time of the capacitor C1. The charge of the capacitor C1 is indicative of a relative moisture content of the clothing or articles in the dryer bin. If the charge time is longer than a threshold time, then the microcontroller 22 issues a termination signal. In one alternative, the microcontroller 22 records in the memory 28 a plurality of charge times. The microcontroller may retrieve data regarding charge times of the capacitor C1 from the memory 28 and determine whether the clothes are dry based on data from a plurality of charge times.
Prior to the beginning of a drying cycle, wet clothes or other articles are loaded into the bin 12 of the dryer 10. The user then selects an automatic drying cycle at the user selection 13 and begins the drying cycle. During the drying cycle the bin 12 rotates, which tumbles the clothes. The clothes are thus moved about throughout the bin 12. As the clothes tumble, individual items of clothing randomly and momentarily come into contact with both conducting bars 16 and 17 below the door 14. If an item of clothing contacts both conducting bars 16 and 17 simultaneously, then the clothing momentarily acts as a conductor connected between the two conducting bars 16 and 17. Of course, two items of clothing that are in contact with each other, while each is in contact with respective conductive bars, will also act as a resistive electrical conductor between the conducting bars 16 and 17.
Wet clothing generally has a lower resistance than dry clothing. When wet clothing contacts the conductive bars 16 and 17 there is a lower resistance between the conducting bars 16 and 17 than if dry clothing contacts the conductive bars 16 and 17. This configuration can be utilized to sense a relative moisture content (RMC) of the clothing. When the RMC of the clothing drops below a threshold level, according to the automatic drying cycle selected, the dryer 10 automatically shuts off.
A resistor R1, for example 4 kΩ, is connected between a high positive voltage supply Vph, for example 17V, and the first conductive bar. The second conductive bar is not usually electrically connected to the first conductive bar as shown in the situation illustrated in
A resistor R2, for example 4 kΩ, is coupled between the second conductive bar and node N1. A capacitor C1, for example 3.3 nF, is coupled between node N1 and ground. A resistor R3, for example 5 MΩ, is coupled between N1 and ground. The base of transistor T1 is coupled to N1. Resistor R4, for example 750 kΩ, is coupled between the high positive voltage supply and the collector of T1. The emitter of T1 is coupled to node N2. A resistor R5, for example 68 kΩ, is coupled between N2 and ground. The base of transistor T2 is also coupled to N2. The emitter of T2 is coupled to ground. The collector of T2 is coupled to an input In1 of microcontroller 22. Resistor R6, for example 100 kΩ, is coupled between a low positive voltage supply Vp1, 5V for example, and In1. The bases of transistors T3 and T4 are connected to Out1 and Out2, respectively, of the microcontroller 22. The emitters of T3 and T4 are connected to ground. The collectors of T3 and T4 are connected to node N1 then resistors R7 and R8 respectively. R7 is for example 18 kΩ. R8 is for example 510Ω. The specific values and configuration of circuit components are given merely by way of example and are not limiting. The circuit components may be arranged in many other configurations and have many other values according to other embodiments of the invention. In particular, transistors T1, T2, T3 and T4 may be implemented as MOS transistors or any other suitable transistor according to other embodiments of the pulse generator circuit 18. Transistors T1 and T2 may also be replaced by a comparator circuit with a threshold set by a resistor divider network.
Operation of the circuit of
where Rc is the resistance of the clothing between the bars 16 and 17.
The current I1 will charge the capacitor to a voltage Vc dependent on the resistance of the clothes Rc according to the following relationship:
If the voltage Vc on the capacitor C1 is greater than the base-emitter turn on voltage, Vbe1, of transistor T1, then T1 will turn on. If the voltage Vc on the capacitor C1 is greater than Vbe1 plus the base-emitter turn on voltage, Vbe2, of transistor T2, then T2 will turn on as well and the voltage at the base of T1 will be clamped to the sum of Vbe1 plus Vbe2. When T2 is turned on, current I2 flows from the low positive voltage source through resistor R6. This causes the voltage to drop at In1. This drop in voltage acts as a pulse at In1. The microcontroller 22 receives the pulses at In1.
In order for a pulse to be sent to the microcontroller 22, the voltage Vc on the node N1, on one plate of capacitor C1 must be equal to or greater than a threshold voltage Vt:
Vt=Vbe1+Vbe2
The rate at which the capacitor C1 charges is based on the RC time constant of the circuit. For the circuit of
The voltage to which the capacitor C1 may charge also depends in part on the resistance Rc of the clothing in contact with the bars 16 and 17. Thus, if the resistance Rc of clothing which has contacted the bars 16 and 17 is below a threshold resistance, the voltage on node N1 will exceed Vt, but if the resistance is high, it will not reach Vt.
The duration of a pulse corresponds to the length of time that the wet clothing contacts the bars 16 and 17. Once a pulse has been generated, the pulse will continue as long as the wet clothing remains in contact with the bars. Once the clothing is no longer in contact with the bars 16 and 17, the capacitor C1 discharges through the resistor R3 to ground. The discharge of the capacitor C1 causes the voltage Vc of the capacitor C1 to drop. Once the voltage Vc at N1 has dropped below the threshold voltage Vt, the transistor T2 turns off and current I2 no longer flows. When current I2 no longer flows, the voltage at In1 increases to the level of the power supply Vp1. The return of the voltage at In1 to Vp1 denotes the end or trailing edge of the pulse.
The microcontroller 22 comprises a processor 24, a clock 26, a system memory 28, a counter 30, a timer 31, and a filter 33 as shown in
When the pulse generator circuit 18 generates a pulse at the input In1, the processor 24 detects the pulse and causes the counter 30 to increment. The counter 30 thus counts the number of pulses generated by the pulse generator circuit 18.
In one embodiment, the processor 24 monitors the number of pulses generated during each of a plurality of defined counting periods. At the end of each counting period the processor 24 monitors the counter 30 to determine the number of pulses received during the counting period. The number of pulses received during the counting period defines a rate at which pulses are being received. At the end of the counting period, a new counting period begins and the rate of pulses is monitored again for the new counting period. In one embodiment, each counting period is about two seconds.
The rate at which pulses are being received corresponds to the RMC of the clothing in the dryer bin 12. If the clothes are wetter, then the pulses will be generated more frequently. If the rate at which pulses are received drops below a threshold pulse rate for a number of counting periods, then the processor 24 determines that the clothes are dry and issues a shutdown signal which terminates a drying cycle of the clothes dryer 10. In one embodiment the processor 24 issues the shutdown signal if the rate of pulses drops below the threshold rate for two consecutive counting periods. Of course, in other embodiments the processor 24 may issue the shutdown signal after more or fewer counting periods than two.
Under some circumstances, the rate of pulses may falsely indicate that the clothing is wet when the clothing is in fact dry. These errors may arise due to static discharge of the clothing in the dryer bin 12 or noise from other sources. These last two very short pulses 40 and 41 are so short that they are considered to be due to static discharge from the clothing or local noise in the system.
A dryer circuit is in an electrically noisy environment and noise may be generated in the sensing circuit from a number of locations, such as from the 60 Hz power line, spiking in the power supplies, the switching control signals, the power for driving the motor that is rotating the drum, the electrical control panel, or even from such sources as the filter mesh, a person banging the lid, or other unexpected locations. It is therefore desired to prevent noise from various sources having an impact on the sensing of clothing moisture content.
As the clothing becomes drier, certain types of fabric tend to frequently build up a static charge. When an item of clothing that has a build up of static charge contacts the second conductive bar, the static charge discharges through the second conductive bar. This static discharge quickly charges the capacitor C1 beyond the threshold Vt and a pulse is generated as previously described. Thus as the clothes become drier, many pulses may be sent to the microcontroller 22 due to static discharge. These pulses increment the counter 30 and the microcontroller 22 may interpret the rate of pulses to mean that the clothing is wet. The pulses due to static discharge may cause the dryer 10 to continue drying after the clothes are already dry. The prolonged drying cycle needlessly wastes energy. The clothing may also be damaged if it remains in the dryer 10 longer than necessary.
The pulses generated due to static discharge are generally very short compared to the pulses generated due to contact of wet clothing with the conductive bars 16 and 17. The reason for this is that static charge discharges very rapidly. A static discharge will quickly charge the capacitor C1 and then cease delivering current. When current is no longer supplied, capacitor C1 discharges through the resistor R3. Pulses generated due to static discharge are thus much shorter than those due to wet clothing.
In
In
In one embodiment, the microprocessor 22 measures the charge time of the capacitor C1. The time required for the capacitor C1 to charge from ground to the threshold voltage is approximately proportional to the resistance Rc of the clothing. If Rc is higher, then a smaller current will flow through the conducting bars 16 to charge the capacitor C1. If Rc is lower, then a larger current will through the conducting bars 16 to charge the capacitor C1. A larger current will charge the capacitor more quickly. Thus the charge time of the capacitor gives an indication of the resistance Rc of the clothing. The rise time of the voltage Vc on node N1 therefore gives an indication of the moisture content of the clothes. The resistance Rc of the clothing gives an indication of the moisture content of the clothing.
The microcontroller 22 receives a pulse when the capacitor C1 has charged to the threshold voltage, but charge rate needs to be measured. The times at which the clothing contacts both conductors 16 to begin charging the capacitor C1 are somewhat random. The problem of monitoring or deducing when the capacitor C1 begins to charge can be overcome in many ways.
In one embodiment, the microprocessor 22 outputs a high voltage at Out1 when a leading edge of a pulse is received at In1. The high voltage turns on T3 which rapidly discharges the capacitor C1. This happens very quickly, on the order of microseconds or nanoseconds. The time to discharge the capacitor is C1 is very small compared to the typical duration for which an article of clothing remains in contact with the conducting bars 16. When the capacitor falls below the threshold voltage, In1 returns to the positive voltage and the pulse ends.
During and after discharge of the capacitor C1 by T3, the clothing is usually still in contact with the conducting bars 16 and 17. At the next stage, microprocessor 22 brings Out1 low and T3 turns off. If the clothing is still in contact with the bars 16 and 17, the capacitor C1 immediately begins to recharge. When the capacitor C1 recharges to the threshold voltage, a pulse is again generated at In1. The microprocessor 22 measures the time from Out1 going low (end of forced discharge) to In1 going low again (new pulse received) and uses this to determine the charge time for the capacitor C1. Since the discharge of capacitor C1 happened quickly, if the cause of signal In1 going low was clothes, the clothing will still be in contact with the bars 16 and 17, on the other hand, if the cause of In1 going low was noise, the effects are likely gone and the voltage will not begin to climb again on node N1.
Alternatively, the microcontroller 22 can measure the charge time from the time that Out1 is brought high (beginning of forced discharge) to the time that In1 goes low. In this scenario, the microcontroller 22 can adjust the charge time to take into account the known period for which Out1 was high. In either way, the charge time of the capacitor C1 can be accurately measured and the RMC can be calculated. As the clothes become dryer, the charge time is longer. Based on the charge time of the capacitor, the microcontroller 22 can issue a termination signal to terminate a drying cycle.
In one embodiment, microcontroller 22 stores data from a plurality of measured charge times in the memory 28. The microcontroller 22 can monitor the plurality of charge times and calculate a relative moisture content of the clothing based on the plurality of charge times. The microcontroller 22 may then issue the termination signal based on data accumulated the plurality of charge times.
The microcontroller 22 can issue the termination signal if the charge time is greater than a threshold charge time. Alternatively the microcontroller 22 can assemble a database of charge times and issue the termination signal based on a plurality of charge times. Of course there are many other schemes available for measuring the charge time and issuing the termination signal as are apparent in light of the current disclosure. All such schemes fall under the scope of the present disclosure.
The embodiment for measuring charge time, described in relation to
In a first embodiment, the value of R7 is low, less than 10 kΩ, and the capacitor C1 discharges quickly. The signal Out1 is kept high for a threshold period of time selected to mask out noise. If a noise pulse of 10 ms is to be blocked, then Out1 remains high for about 10 ms, after which it goes low and permits the capacitor C1 to begin to charge. If the noise pulse is gone, then the rise time for the voltage at N1 will be based on the moisture content of the clothing and not on a noise signal. Thus, the first pulse is ignored and the second pulse is measured to determine the rise time. The selection of the time that Out1 remains high determines the length of the masking period. It can be programmed to be any range desired to block noise. In one embodiment, Out1 remains high for 10 ms, while in others it remains high for 5 ms or 30 ms.
In the alternative embodiment, the value of R7 is varied in order to vary the time for masking out noise. If it is desired to mask out noise lasting in the range of 5 ms to 10 ms, then a larger resistor R7 can be used in one embodiment. The larger resistor R7 will slow the rate that node N1 goes to ground and thus permits the circuit to filter out noise that is 5 ms, 10 ms, or 20 ms long, as desired by the end user.
In this alternative embodiment, Out1 will stay high until In1 goes low. The microcontroller will compare the incoming value of In1, and while it is low, keep Out1 high. When sufficient charge has bled off of N1 to turn off transistor T2, then In1 will go high based on the current from I2 pulling it back high at a rate based on the value of R6. By the time In1 is pulled high, node N1 will be fully grounded. When In1 goes high again, this causes output Out1 to go low. The rise time on node N1 is measured by sensing the time difference between Out1 going low and In1 going low. In this way, pulses shorter than a selected threshold can be filtered out and not counted. Full control of the threshold time can be selected by the person designing the circuit in which the chip is used. Thus in some embodiments, the masking time for noise is preset in the circuit as constructed, in other embodiments, it can be customer selected as the final circuit is constructed.
One benefit of the embodiment of the alternative system is that the value R7 can be selected by the customer who is designing the product in which the circuit will be used. If one circumstance calls for a masking period of 1 ms, while another calls for a masking period of 10 ms, the chip user can easily achieve this by changing the value of R7 as an external resistor to the circuit. All components, including transistor T1-T3 can be on chip and the resistor R7 can be off chip, permitting the user to select the noise masking time as desired.
In the various embodiments, for pulses based on noise, such as from static electricity or other noise, there will be no conduction between bars 16 and 17 at time t4 when the sensing begins again, so no rise time will be measured for noise created signals.
Of course, this circuit may also be applied to mask noise signals in other circuits, such as in cameras, scanners, voltage regulators, cell phones or other environments in which short noise pulses may be interpreted as real signal pulses. The short noise pulses can be blocked by this masking and only the real signals considered for further evaluation.
In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.
