Control method and system for clothes dryer

A control method and system for a belt-driven clothes dryer are disclosed. The control system includes a drum containing a load of wet clothes to be dried, a heater heating air flowing into the drum, a motor coupled to the drum by a power transmission system for rotating the drum, and a power supply supplying power to the motor and the heater during a dry operation of the dryer. The control system further includes a moisture sensor outputting a sensor signal during the dry operation, or a photo coupler outputting voltage pulses when the motor is in operation during the dry operation. Then, a microprocessor included in the control system detects a breakage of the power transmission system upon analyzing the sensor signal of the moisture sensor or the voltage pulses generated by the photo coupler. If the microprocessor detects such breakage, it interrupts the dry operation of the clothes dryer.

This application claims the benefit of Korean Patent Application No. P2003-0051346 filed on Jul. 25, 2003, Korean Patent Application No. P2003-0051351 filed on Jul. 25, 2003, and Korean Patent Application No. P2003-0059060 filed on Aug. 26, 2003, which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dryer, and more particularly, to a control method and system for a belt-driven clothes dryer that are able to automatically detect a breakage of a power transmission system coupled between a drum and a motor included in the dryer.

2. Discussion of the Related Art

A dryer is a device that automatically dries wet objects (e.g., clothes or shoes) by providing heated air under the control of a controller, and smarter and more efficient dryers that are able to meet the users' various requirements are in great demand. In general, a typical clothes dryer includes a tub (drum) containing the wet objects to be dried, a motor, and a power transmission system which is coupled between the motor and the drum for transmitting the power generated by the motor during a dry operation of the dryer. During the dry operation, the heated air flows into the drum and the drum continuously rotates so that the wet clothes inside of the drum could be dried. The moisturized air within the drum is continuously discharged from the drum and heated dry air flows into the drum simultaneously, while the drum rotates in the dry operation.

If there is a breakage in the power transmission system coupled between the motor and the drum, this could result very serious damages to the dryer and the objects within the drum. For example, if electric power is continuously supplied to the motor and the heater when a belt coupled between the motor and the drum for power transmission is broken, there is no motion of the drum and the objects within the drum. Therefore, the heated air will continuously make contact with same portions of the objects for a long time, and this could result serious damages to the objects. In order to substantially obviate the problems due to these limitations and disadvantages, many dryer manufactures have been trying to make clothes dryers capable of automatically detecting a breakage of the power transmission system and controlling operation of the dryer based on such breakage detection.

One of the examples of the existing breakage-detectable clothes dryers includes a mechanical breakage detection assembly including an arm which mechanically moves when the belt provided between the motor and the drum is broken, and a switch which automatically shuts off the power supply to the motor based on the motion of the arm. However, this detection assembly requires a complicated mechanical structure. For example, the arm must be provided at a predefined location within the dryer so as to accurately detect the breakage of the belt, and this could create a serious structural limitation when manufacturing the dryer. In addition, a slight dislocation of the switch which operates due to the rotation of the arm could result malfunction of the breakage detection assembly. Therefore, there are great necessities for a control system and method for a clothes dryer, which are able to detect the breakage of the power transmission system without requiring any complicate mechanical system.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a control method and system for a belt-driven clothes dryer that substantially obviates one or more problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a control method for a clothes dryer, which is able to detect a breakage of a power transmission system included in the dryer and to control the dry operation of the dryer based on the breakage detection.

Another object of the present invention is to provide a control system for a clothes dryer, which is able to detect a breakage of a power transmission system included in the dryer and to control the dry operation of the dryer based on the breakage detection.

To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a control method for a clothe dryer according to a first embodiment of the present invention includes the steps of performing a dry operation of the clothes dryer by supplying power to a motor for rotating a drum containing a load of wet clothes and to a heater for heating air flowing into the drum, which is coupled to a power transmission system driven by the motor, and receiving a sensor signal outputted from a moisture sensor provided within the drum during the dry operation. The moisture sensor outputs a voltage pulse each time it makes contact with the wet clothes during the dry operation. The control method further includes the steps of detecting a breakage of the power transmission system based upon analyzing the sensor signal, and interrupting the dry operation of the clothes dryer if the breakage of the power transmission system is detected. The breakage may be detected if the sensor signal received from the moisture sensor for a predetermined time includes no voltage pulse.

In another aspect of the present invention, a control system for a clothes dryer according to the first embodiment of the present invention includes a drum containing a load of wet clothes to be dried, a heater configured to heat air flowing into the drum so as to dry the wet clothes, a motor coupled to the drum by a power transmission system such as a belt for rotating the drum, and a driving unit supplying power to the motor and the heater during a dry operation of the clothes dryer. The control system further includes a moisture sensor provided within the drum for outputting a sensor signal, and a microprocessor configured to detect a breakage of the power transmission system based upon analyzing the sensor signal received from the moisture sensor. The moisture sensor outputs a voltage pulse each time it makes contact with the wet clothes during the dry operation. Then the microprocessor detects the breakage of the power transmission system if the sensor signal includes no voltage pulse for a predetermined time.

In another aspect of the present invention, a control method for a clothes dryer according to a second embodiment of the present invention includes the steps of performing a dry operation of the clothes dryer by supplying power to a motor for rotating a drum containing a load of wet clothes and to a heater heating air flowing into the drum, which is coupled to a power transmission system driven by the motor, and receiving voltage pulses which are outputted from a photo coupler coupled to the motor when the motor is in operation during the dry operation. The control method further includes the steps of detecting a breakage of the power transmission system based upon analyzing the voltage pulses, and interrupting the dry operation of the clothes dryer if the breakage of the power transmission system is detected. The breakage of the power transmission may be detected if a pulse width of the voltage pulses is less than a reference pulse width, or if a frequency of the voltage pulses is greater than a reference frequency.

In another aspect of the present invention, a control system for a clothes dryer according to the second embodiment of the present invention includes a drum containing a load of wet clothes to be dried, a heater configured to heat air flowing into the drum, and a motor mechanically coupled to the drum by a power transmission system for rotating the drum. The control system further includes a power supply configured to supply power to the motor and the heater during a dry operation of the clothes dryer, a photo coupler which outputs voltage pulses when the motor is in operation during the dry operation, and a microprocessor which detects a breakage of the power transmission system based upon analyzing the voltage pulses outputted from the photo coupler. The microprocessor interrupts the dry operation of the clothes dryer if the breakage of the power transmission system is detected.

In another aspect of the present invention, a control method for clothes dryer according to a third embodiment of the present invention includes the steps of initiating a dry operation of the clothes dryer by performing a pre-dry operation. During the pre-dry operation, power is supplied to a motor for predetermined time so as to accelerate a drum containing a load of wet clothes and the power is shut off thereafter, where the drum is coupled to a power transmission system driven by the motor. The control method further includes the steps of measuring a counter electromotive force generated by the motor during the pre-dry operation, detecting a breakage of the power transmission system if the measured counter electromotive force is greater than a reference level, and interrupting the dry operation of the clothes dryer if the breakage of the power transmission system is detected. The control method may further include the step of performing a main dry operation of the clothes dryer by supplying power to the motor and a heater only if no breakage of the power transmission system is detected during the pre-dry operation, where the heater is configured to heat air flowing into the drum. In addition, the counter electromotive force is measured based on a frequency of voltage pulses outputted from a photo coupler coupled to the motor. The voltage pulses are outputted when the motor is in operation during the pre-dry operation.

In another aspect of the present invention, a control system for clothes dryer according to the third embodiment of the present invention includes a drum containing a load of wet clothes to be dried, a motor mechanically coupled to the drum by a power transmission system for rotating the drum, and a power supply configured to supply power to the motor for a predetermined time and to shut off the power thereafter during a pre-dry operation of the clothes dryer. The control system further includes a photo coupler coupled to the motor to output voltage pulses when the motor is in operation after the power is shut off, and a microprocessor configured to measure a counter electromotive force generated by the motor during the pre-dry operation based on a frequency of the voltage pulses. The microprocessor detects a breakage of the power transmission system if the measured counter electromotive force is greater than a reference level. The microprocessor further performs a main dry operation of the clothes dryer only if no breakage of the power transmission system is detected during the pre-dry operation.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1illustrates an example of the belt-driven clothes dryer capable of detecting a belt breakage according to the present invention. According toFIG. 1, the dryer includes an outer case1, a drum2rotatably provided within the outer case1and containing a load of wet clothes to be dried, an entrance3through which the clothes can be loaded into or removed from the drum2, a door4which opens and closes the entrance3. The dryer further includes an electric motor5which is mechanically coupled to the drum2by a power transmission system. For example, when the motor5rotates, a belt6mechanically coupled between the motor5and the drum2forces the drum2to rotate simultaneously. In addition, a plurality of lifters7are provided on an interior wall of the drum2so that the clothes are continuously lifted and evenly distributed inside the drum2when the drum2rotates during a dry operation.

The dryer shown inFIG. 1further includes an air circulation duct8connected between an air outlet and an air inlet provided on the rear and front sides of the drum2, respectively, for supplying heated dry air into the drum2. In the air circulation duct8, a heater11is provided near the air inlet14for heating the air flowing into the drum2, and a fan9is provided near the air outlet for discharging the moisturized air from the drum2such that the air circulates through the air circulation duct8. The fan9is also mechanically coupled to the motor5. When the motor5rotates, a belt6coupled between the motor5and the belt6forces the fan9to rotate simultaneously. In addition, the dryer further includes an air supply duct12and a water discharge duct13coupled to the air circulation duct8. The air supply duct12supplies outside air into the drum2, and the water discharge duct13discharges the water condensed from the moisturized air circulating within the circulation duct8.

Reference will now be made in detail to the preferred embodiments of the control systems and methods for a belt-driven dryer according to the present invention.

FIG. 2illustrates a control system for a belt-driven clothes dryer, an example of which is illustrated inFIG. 1, according to a first embodiment of the present invention. The control system shown inFIG. 2includes a power supply unit101which supplies power to the motor5and the heater11during a dry operation of the clothe dryer. The control system further includes a moisture sensor102provided within the drum2for generating a voltage pulse each time it makes contact with the wet clothes during the dry operation, a pulse detector103detecting each voltage pulse generated by the moisture sensor102and generating a corresponding sensor signal, and a microprocessor104which detects a breakage of the belt6shown inFIG. 1based upon analyzing the sensor signal received from the pulse detector103. During the dry operation of the clothes dryer, the microprocessor104generate an interruption signal to a driving unit105which drives the motor5and the heater11if the belt breakage is detected. When the driving unit105receives the interruption signal, it automatically interrupts the dry operation of the dryer by shutting off the power being supplied to the motor5and the heater11.

When the drum2of the belt-driven clothes dryer shown inFIG. 1rotates during a dry operation, the wet clothes are continuously lifted and dropped within the drum2. When a portion of the wet clothes makes contact with the moisture sensor102provided on the interior surface of the drum2during the dry operation, the moisture sensor102generates an analog voltage pulse indicating a moisture level of the portion of the clothes. When the portion of the wet clothes is in contact with the moisture sensor102, a resistance of the moisture sensor102changes due to the moisture contents of the clothes in contact. Therefore, the amplitude of the voltage pulse indicates the moisture level of the portion of the clothes in contact. Thereafter, the pulse detector103detects the analog voltage pulses generated by the moisture sensor102, and it generates a corresponding digital sensor signal including digital voltage pulses corresponding to the detected analog voltage pulses, respectively. Therefore, if there is no analog voltage pulse generated by the moisture sensor102, the digital sensor signal does not include any digital voltage pulse.

If the belt6mechanically coupled between the motor5and the drum2is in a normal condition (e.g., no breakage) during the dry operation of the clothes dryer, the drum2containing the wet clothes rotates simultaneously with the motor5and the wet clothes are continuously lifted and dropped within the drum2.FIG. 3Aillustrates an example of the sensor signal generated by the pulse detector103during a dry operation, where the belt6is in a normal condition. As it is shown in the figure, the sensor signal includes a plurality of voltage pulses because the wet clothes continuously make contact with the moisture sensor102. In other words, the amplitude of the sensor signal is High during the time a portion of the wet clothes is in contact with the moisture sensor102. On other hand, the amplitude of the sensor signal is Low when the wet clothes are not in contact with the moisture sensor102. Since the clothes are continuously lifted and dropped within the drum2, the wet clothes continuously make contact with the moisture sensor102as shown inFIG. 3A.

FIG. 3BandFIG. 3Cillustrate examples of the sensor signals generated by the pulse detector103during a dry operation, where there is a breakage in the belt6. If a breakage in the belt6exists, the power generated by the motor5is not properly transmitted to the drum2. In other words, the drum2does not rotate during the dry operation, and there is no motion of the wet clothes within the drum2. Therefore, there is no change in the sensor signal generated by the pulse detector103because there is no action within the drum2. The amplitude of the sensor signal is continuously High if any portion of the wet clothes is in contact with the sensor as shown inFIG. 3B, or it is continuously Low if there is no contact between the clothes and the moisture sensor102as shown inFIG. 3C. The amplitude of the sensor signal remains unchanged since there is no motion of the drum2and the wet clothes.

Referring back toFIG. 2, the microprocessor104receives the sensor signal generated from the pulse detector103and determines whether a breakage in the belt6exists based upon analyzing the sensor signal. If a breakage of the belt6is detected, the microprocessor104interrupts the dry operation of the clothes dryer shown inFIG. 1by transmitting interrupt signals to the driving unit105. When the driving unit105receives the interrupt signals, it stops supplying power to the motor5and the heater11in order to prevent any damages. The microprocessor104detects a breakage of the belt6by determining whether there are changes in the sensor signal. If the amplitude of the sensor signal remain constant and there is no change in the sensor signal for a predetermined period of time, the microprocessor104determines that a breakage of the belt6exists, and it interrupts the dry operation of the dryer to avoid any damage to the motor5, the heater11, or the clothes within the drum2. In addition, it may transmit a display control signal to a display unit (not illustrated) of the dryer shown inFIG. 1in order to display a warning message indicative of the detected breakage of the power transmission system. Furthermore, it may transmit another control signal to a sound generating unit (not illustrated) of the dryer in order to generate warning sound (e.g., beep sound) such that a user could be easily informed of the breakage of the power transmission system.

FIG. 4illustrates a control method of for a clothes dryer, an example of which is illustrated inFIG. 1, according to the first embodiment of the present invention. First of all, the microprocessor104shown inFIG. 2included in the dryer shown inFIG. 1determines whether a user inputs a command for powering on the dryer in step S101, and it further determines whether the user inputs a command for initiating a dry operation (e.g., activation of Start Key) in step S102. If the microprocessor104determines that both commands are inputted, it initiates a dry operation by transmitting corresponding control signals to the driving unit105for operating the motor5and the heater11, and determines whether a breakage of the belt6exists (S103). In order to determine an existence of the breakage, the microprocessor104determines whether a portion of the sensor signal, which is received from the pulse detector103for a predetermined period of time, includes one or more voltage pulses.

If it is determined in step S103that the portion of the sensor signal does include at least one voltage pulse or a predetermined number of voltage pulses, the microprocessor104determines that the belt6is in a normal condition (no breakage) and it continues performing the dry operation (S104). Thereafter, the microprocessor104further determines whether the dry operation is completed in step S105. On the other hand, if it is determined in step S103that the amplitude of the sensor signal remain constant (no voltage pulse in the sensor signal) for the predetermined time, the microprocessor104determines that a breakage of the belt6exists and it interrupts the dry operation of the dryer by transmitting interrupt signals to the driving unit105(S106). When the driving unit105receives the interrupt signals, it stops supplying power to the motor5and the heater11in order to prevent any damages to the dryer. Additionally, the microprocessor104may further transmit a display control signal to the display unit of the dryer shown inFIG. 1to display a warning message indicative of the breakage of the belt6in step S106. Similarly, it may further transmit a sound control signal to the sound generating unit of the dryer in order to generate warning sound for informing the user of the breakage of the belt6step S106.

As described above, the control system and the method of controlling operation for a dryer according to the first embodiment of the present invention provide an extremely, efficient way of detecting a breakage of the power transmission system of the dryer during a dry operation without using any additional mechanical system for detecting the breakage. For example, the microprocessor104of the control system shown inFIG. 2uses the moisture sensor102, which measures the moisture level of the clothes being dried for controlling the dry operation, to determine whether there is a breakage of the belt6.

FIG. 5illustrates a control system (control circuit) for a belt-driven clothes dryer, an example of which is illustrated inFIG. 1, according to a second embodiment of the present invention. The control system shown inFIG. 5includes a power supply unit200supplying power to the motor5and the heater11shown inFIG. 1during a dry operation of the clothes dryer, a switch201which switches (turn on/off) the power being supplied to the motor5and the heater11, and a photo coupler203coupled to the motor5to output voltage pulses when the motor5is in operation during the dry operation. The photo coupler203may include a light generating unit and a light sensing unit. The control system further includes a microprocessor202for detecting a breakage of the belt6, which transmits the power generated by the motor5to the drum, upon analyzing the voltage pulses generated by the photo coupler203and for interrupting the dry operation of the clothes dryer if such breakage of the belt6is detected.

During a dry operation of the clothes dryer shown inFIG. 1, the switch201performs a switching function so that the power supply unit200supplies power to the motor5, which is mechanically coupled to the drum2by the belt6for rotating the drum2, and to the heater11for heating the air flowing into inside of the drum2for drying the wet clothes. When the motor5is in operation during the dry operation, the photo coupler203coupled to the motor5continuously generates a plurality of voltage pulses. In other words, when the motor5operates to rotate the belt6, the photo coupler203detects the motion (rotation) of the motor5and outputs corresponding voltage pulses to the microprocessor202, which determines whether a breakage of the belt6exists based on the voltage pulses outputted from the photo coupler203.

FIG. 6Aillustrates an example of the voltage pulses generated by the photo coupler203, where the belt6is in a normal condition, andFIG. 6Billustrates an example of the voltage pulses generated, where there is a breakage in the belt6. When there is a breakage in the belt6, the belt6does not exert any force on the motor5, and therefore, the motion of the motor5in the dry operation is comparatively faster. For this reason, the pulse width of the voltage pulses shown inFIG. 6Bis less than that of the voltage pulses shown inFIG. 6B. In addition, the frequency of the pulses shown inFIG. 6Bis greater than that of the pulses shown inFIG. 6Adue to the same reason.

The microprocessor202may determine that a breakage of the belt6exists if the pulse width of the voltage pulses generated by the photo coupler203is less than a predetermined pulse width value (w1), which may be stored in a memory (not illustrated) coupled to the microprocessor202. Alternatively, it may determine that a breakage of the belt6exists if the frequency of the voltage pulses generated by the photo coupler203is greater than a predetermined frequency value (f1), which may also be stored in the memory. When the microprocessor202determines that a breakage of the belt6exists, it interrupts the dry operation of the dryer by transmitting an interrupt signal to the switch201to shut off the power being supplied to the motor5and the heater11in order to prevent any damages to the dryer. In addition, it may transmit a display control signal to a display panel (not illustrated) of the dryer in order to display a warning message indicative of the breakage in the power transmission system of the dryer. Furthermore, it may transmit a sound control signal to a sound generating unit (not illustrated) of the dryer in order to generate warning sound (e.g., beep sound) such that the user could be easily informed of the breakage of the power transmission system.

FIG. 7illustrates a control method for a belt-driven clothes dryer, an example of which is illustrated inFIG. 1, according to the second embodiment of the present invention. Referring toFIG. 7, the microprocessor202shown inFIG. 5initially determines whether a user inputs a command for initiating a dry operation (e.g., activation of Start Key) in step S201. If the microprocessor202determines that the command is inputted, it initiates a dry operation of the dryer by transmitting a corresponding control signal to the switch201to supply power to the motor5and the heater11(S202). When the power is supplied in step S202, the motor5rotates the drum2containing a load of wet clothes and the heater11heats the air flowing into the drum2, which is coupled to the belt6driven by the motor5. During the dry operation of the dryer, the microprocessor202continuously receives voltage pulses, which are outputted from the photo coupler203when the motor5is in operation, and it determines whether a breakage of the belt6exists based upon analyzing the voltage pulses (S203). For example, the microprocessor202may detect the breakage if a pulse width of the voltage pulses is less than a predetermined reference pulse width value (w1). Alternatively, it may detect the breakage if a frequency of the voltage pulses is greater than a predetermined reference frequency value (f1).

If no breakage of the belt2is detected by the microprocessor202in step S203, it continues performing the dry operation of the dryer (S204). Thereafter, the microprocessor202further determines whether the dry operation is completed in step S205. On the other hand, if the breakage of the belt2is detected in step S203, the microprocessor202interrupts the dry operation of the dryer by transmitting interrupt signals to the switch201to shut off the power being supplied to the motor5and the heater11(S206). In step S206, the microprocessor202may additionally transmit a display control signal to the display panel of the dryer to display a warning message so as to inform a user of the detected breakage of the belt6. Similarly, it may further transmit a sound control signal to the sound generating unit of the dryer for informing the user of the breakage of the belt6.

FIG. 8illustrates a control system (control circuit) for a belt-driven clothes dryer, an example of which is illustrated inFIG. 1, according to a third embodiment of the present invention. The control system shown inFIG. 8illustrates a power supply unit300supplying power to the motor5during a pre-dry operation of the dryer shown inFIG. 1, a switch301which switches (turn on/off) the power being supplied by the power being supplied to the motor5, and a photo coupler303coupled to the motor5to output voltage pulses when the motor5is in operation after the power is shut off by the switch301during the pre-dry operation. The photo coupler303may include a light generating unit and a light sensor unit. The control system further includes a microprocessor302for measuring a counter electromotive force generated by the motor5during the pre-dry operation based on a frequency of the voltage pulses. The microprocessor302detects a breakage of the belt6if the measured counter electromotive force is greater than a predetermined reference value.

During a pre-dry operation of the clothes dryer shown inFIG. 1, the microprocessor302transmits a switch control signal to the switch301to supply the power supplied by the power supply300to the motor5, which is mechanically coupled to the drum2by the belt6for rotating the drum2. After the speed of the drum2reaches a predetermined speed or a predetermined time is elapsed, the switche301shuts off the power being supplied to the motor5under the control of the microprocessor302. After the power is shut off, the drum2containing the wet clothes continuously operates (rotates) for a while due to the tendency of the drum2to continue to rotate. During the time when the motor2is in motion with no power supply, the photo coupler303detects the motion (rotation) of the motor5and outputs corresponding voltage pulses to the microprocessor302, which then measures a counter electromotive force generated by the motor5during the pre-dry operation based on a frequency of the voltage pulses.

When there is a breakage in the belt6, the belt6does not exert any force on the motor5. Therefore, the motion of the motor5during the pre-dry operation of the dryer is comparatively faster (higher frequency) and the counter electromotive fore generated by the motor5is comparatively higher. On the other hand, when the belt6is in a normal condition, the belt6coupled to the drum2exerts a force on the motor5. Therefore, the motion of the motor5during the pre-dry operation is comparatively slower (lower frequency) and the counter electromotive force generated by the motor5is comparatively lower. The motions of the motor5in both cases are described and compared earlier in detail with reference toFIGS. 6A and 6B.

Due to the above reasons, the microprocessor302then detects a breakage of the belt6if the measured counter electromotive force is greater than a predetermined force value, which may be stored in a memory (not illustrated) coupled to the microprocessor302. When the microprocessor302determines that no breakage of the belt6exists during the pre-dry operation, it generates control signals to perform a main dry operation of the clothes dryer, during which power is supplied to the motor5and the heater11configured to heat air flowing into the drum2. In addition, it may transmit a display control signal to the display panel of the dryer in order to display a warning message indicative of the breakage of the power transmission system of the dryer. Furthermore, it may transmit a sound control signal to a sound generating unit (not illustrated) of the dryer in order to generate warning sound (e.g., beep sound) such that the user could be easily informed of such breakage.

FIG. 9illustrates a control method for a belt-driven clothes dryer, an example of which is illustrated inFIG. 1, according to the third embodiment of the present invention. Referring toFIG. 9, the microprocessor302shown inFIG. 5initially determines whether a user inputs a command for initiating a dry operation (e.g., activation of Start Key) in step S301. If the command is inputted, the microprocessor302initiates a dry operation of the clothes dryer by performing a pre-dry operation, during which power is supplied to the motor5for a predetermined period of time so as to accelerate the drum2containing a load of wet clothes, and the power is shut off thereafter (S302). During the pre-dry operation, the microprocessor measures a counter electromotive force generated by the motor5and compares the measured counter electromotive force with a predetermined force value (C1) to detect a breakage of the belt6(S303). The counter electromotive force may be measured in step S303based on a frequency of voltage pulses, which are outputted from the photo coupler303coupled to the motor5when the motor is in operation during the pre-dry operation.

If the measured force is greater than the predetermined force value, the microprocessor302determines that there is a breakage of the belt6and interrupts the dry operation of the clothes dryer by shutting off the power supplies to the motor5and the heater11(S306). In step S306, the microprocessor302may additionally transmit a display control signal to the display panel of the dryer to display a warning message to inform a user of the detected breakage. Similarly, it may further transmit a sound control signal to the sound generating unit of the dryer for informing the user of the breakage of the belt6. On the other hand, if the measured force is determined to be equal or less than the predetermined force value in step S303, the microprocessor302determines that there is no breakage in the belt6and continues the dry operation by performing a main dry operation (S304). During the main dry operation, the microprocessor302generates control signals to supply power to the motor5and the heater11, which heats the air flowing into the drum2.