Abstract:
A method and apparatus for monitoring voltage input to an appliance, such as a dryer, sensing when power input to the appliance is lost. In addition, a controller in the appliance pulses relay coils controlling motors and/or heating devices within the appliance to conserve energy on a backup capacitor that supplies the control circuit of the appliance in the event of power loss. Further, a voltage sense circuit outputting a square wave effects monitoring of the input voltage to the appliance by outputting the square wave signal whose cycle period is monitored to determine power outage. The controller stores current operation settings at the time of power outage in a memory device and ensures proper storage through the extra energy conserved from the capacitor by the pulsing of the relay coils.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method and apparatus for detecting a power loss to an appliance and storage of current operation settings of the appliance when the power loss occurs. 
     Some appliances such as washing machines and dryers include a feature that allow the appliance to retain current operation settings in the event of a power outage. This is accomplished by monitoring the AC power input to the appliance, detecting when the AC power is lost and saving the current operation settings in a memory device such as a EEPROM so that when power is restored the washing machine cycle or dryer cycle will resume at the point in the cycle when power was lost. The period of time between loss of AC power and saving of the operation settings is critical since during this time a microprocessor or controller within the appliance is powered by a charged capacitor. Hence, the quicker that the current operation settings can be saved the more likely that the settings will actually be stored within the EEPROM. 
     In order to ensure that there is sufficient charge on the capacitor during power outage to store the current operation settings, an approach has been to increase the size of the capacitor so as to store more charge. However, larger capacitors are more expensive. 
     Additionally, appliances such as a washing machine or a dryer typically have a motor that turns a washing drum or a drying chamber, respectively. Other appliances, such as dishwashers, include motors which drive pumps. Microwave ovens often times include motors which drive rotating turntables. Most other domestic appliances also include motors and/or heating elements. During the power outage, the motor within the appliance continues to rotate for a short time, especially given a large washing or drying load, which increases the mass and, hence, the momentum of the washing drum or the drying chamber. This continued rotation of the motor after power outage causes transient voltages to be generated from the motor on the incoming line, that, in turn, cause noise to be present in the supply to a control microprocessor that is supplied with power by the incoming line through a power supply circuit. This noise creates a problem in that the microprocessor senses this noise and, thus, does not quickly recognize that power on the incoming AC line has been lost. Furthermore, by the time that the microprocessor recognizes power loss, the capacitor used to store the current operation settings of the appliance has been partially discharged due to continued operation of other loads such as a relay coil driving a contact to the motor or a heater element. The partial discharge of the capacitor during the time that the microprocessor does not recognize power loss leads to the inability of the microprocessor to save current operation settings since enough charge on the capacitor does not remain to effect this storage. 
     SUMMARY OF THE INVENTION 
     There is therefore a need for an apparatus and method for more quickly recognizing loss of input power to a device, such as an appliance, so that operation settings will not be lost in the event of transient noise generated from an electromechanical device within the device. Additionally, the need exists for faster recognition of AC power loss in order to reduce the discharge time of a capacitor and, hence, allowing the capacitor to have a smaller value. 
     These and other needs are met by the present invention including a method for monitoring power input to a device where at least a voltage signal on an incoming line to the device is monitored. Variations of a frequency of at least the monitored voltage signal from a prescribed frequency are sensed and a power loss signal is issued when a variation of the frequency from the prescribed frequency exceeds a first predetermined amount. The power loss signal indicates a detected loss of power input on the incoming line. By sensing variations of the frequency of the monitored voltage signal, the present method is able to take into account transient noise generated by a motor after power loss more quickly than the known art. 
     According to another aspect of the present invention, a method for monitoring power input to an appliance and storing current operation settings of the appliance when the power input is lost includes monitoring at least a voltage signal on an incoming line to the device and sensing variations of a frequency of at least the monitored voltage signal from a prescribed frequency. When a variation of the frequency from the prescribed frequency exceeds a first predetermined amount a power loss signal is issued. The power loss signal indicates that a loss of power input on the incoming line has been detected. Relay coils that control power input to at least one of an electromechanical device and heating device within the appliance are pulsed at a predetermined duty cycle in response to the power loss signal in order to increase a discharge time of an electric charge on a capacitor connected to the input line and also connected to the relay coil. Finally, current operation settings of the appliance are simultaneously stored in a memory using the charge of the capacitor. The pulsing of the relay coils allows the relay coils to still maintain closed contacts in order to avoid an unnecessary opening of the contacts in a situation such as a brown out, thereby mitigating deleterious effects to the relay coils in these situations. Additionally, since the relay coils are driven by capacitor power, the pulsing at a predetermined duty cycle conserves charge on the capacitor that is later or simultaneously used for storing the current operation settings. Hence, enough capacitor charge will be present to ensure proper storing of the current operation settings. A further advantage is that a smaller capacitor can be utilized since the pulsing of the relay coils affords conservation of capacitor charge, and, thereby, a minimization of capacitor cost. 
     According to yet another aspect of the present invention an apparatus is provided for monitoring power input to an appliance and saving current operation settings of the appliance in the event of a power input loss. The apparatus includes a power input line for supplying a power input to the appliance. In addition, a power supply circuit for converting a voltage of the power input into a plurality of supply voltages is included. A capacitor within the power supply circuit is connected between the first supply voltage and a ground. A voltage sensing circuit is connected to the second supply voltage and outputs a sensing signal having a frequency that corresponds to a power input frequency of the power input line. One or more relay coils that control power input from the power input line to at least one of an electromechanical device and a heating device within the appliance are included. Current operation settings of the appliance are stored by a provided memory device. A controller is included that is configured to detect the frequency of the sensing signal, control the relay coils and store current operation settings of the appliance in the memory device. The controller pulses the relay coils using an electric charge from the capacitor at a prescribed duty cycle and also stores current operation settings of the appliance in the memory device using the same electric charge from the same capacitor when the controller detects a change in the frequency of the sensing signal after a predetermined number of cycles of the sensing signal. 
     Additional advantages and novel features of the invention will be set forth, in part, in the description that follows and, in part, will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference is made to the attached drawings wherein: 
     FIG. 1 is a partly cutaway perspective view of a clothes dryer employing the power input monitoring and current operation setting memory storage of the present invention; and 
     FIG. 2 is a circuit diagram of the monitoring and control circuit according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is applicable to various appliances or devices that have the capability of storing current operation or cycle settings in the event of a loss of power input and, in particular, to appliances and devices also having an electromechanical device such as a motor that may potentially present transient voltages during the time period immediately following loss of a power input. The present invention, for purposes of explanation, will be described in the context of an automatic clothes dryer. However, the present invention is, as mentioned above, applicable to various appliances and devices. 
     In FIG. 1 of the drawings, an automatic clothes dryer  10  is illustrated that is controlled, in part, by the control apparatus  200  shown in FIG.  2 . Specifically in FIG. 1, the mechanical components of the clothes dryer are well known in the art and are, thus, not shown in great detail. The clothes dryer  10  has a cabinet  12  including a control console  14 . Within the cabinet  12  is rotatably mounted a drum  16  that is rotatably driven about a horizontal axis by a motor  18  through a drive system  20 , typically including a belt  21 . A front door  22  formed in the front of the cabinet  12  provides selective access to the clothes treatment chamber  24  defined by the interior of the drum  16 . 
     The drum  16  is provided with an inlet aperture  26  and an outlet exhaust aperture  28  having a removable lint screen  30 . A supply of air is circulated by a fan  32  driven by the motor  18 . A heating element  34  is selectively energized by a relay coil  220 , shown in FIG. 2, that is controlled by a controller  216  located within the control console  14 , for example. As is well known in the art, supply of the temperature controlled air is circulated by the fan  32  past the heating element  34  through the inlet aperture  26  into the clothes treatment chamber  24  within the drum  16  and subsequently output through the outlet exhaust aperture  28  including the lint screen  30 . 
     The control console  14  includes a user interface  37  having, for example, a start button  38 , a dryness selector  40  and a temperature selector  42  to permit a user to start a drying cycle, as well as select other operation settings and parameters of the drying cycle. Further, the user interface  37  may also include means to allow a user to set time settings (not shown) such as a period of time in which the dryer is allowed to operate. 
     It is noted that the control circuitry of FIG. 2 may be located within the control console  14 . However, other locations within the appliance  10  for the control circuitry could be utilized. Typically, input power for the dryer  10  is supplied from a  208  V.A.C. or 240 V.A.C. power source by means of an input power supply  36 , such as via a three-wire pigtail. In the present embodiment shown in FIG. 2, a single phase line L 1  is input to the power supply and control circuitry  200 . This voltage typically is 120 V.A.C. 
     As shown in FIG. 2, an input voltage to the control circuit  200  is derived from line L 1  and a neutral, shown delivered to terminals  202  and  204 , respectively. The input power is delivered to a power supply circuit  203  within the control circuit  200  to a primary coil  206  of a transformer  205 . The line voltage L 1  is transformed down to approximately 5 volts in a preferred embodiment across the secondary coil  208 , although other voltages could be used. This voltage is rectified via diodes D 1  and D 2  to supply a full wave rectified alternating voltage V.A.C. In addition, a capacitor C 1  is connected from the output of the full wave rectifier (i.e., diodes D 1  and D 2 ) to a potential VSS connected to ground. The voltage VUNR at node  209  is also delivered to voltage regulator  210 , which outputs a steady state 5 volt signal. This 5 volts is split into a +5 volts source and a VDD source. 
     The control circuit  200  also includes a voltage sense circuit  212  comprised of a transistor T 1  diode D 5  and filtering capacitors C 4  and C 5 . The voltage V.A.C. from node  207  is input to the base of transistor T 1  via diode D 5 . Thus, this AC signal, which is typically 60 Hertz, turns on transistor T 1  during every other half cycle since diode D 5  acts as a half wave rectifier. When transistor T 1  is in an “on” state allowing conduction of the 5 volt source through resistance R 1  to ground potential VSS, the output  214  of the voltage sense circuit  212  is at a low state. During the next half cycle of the AC voltage V.A.C., the transistor T 1  is in an “off state preventing conduction through the transistor. At this point, the resistor R 1  pulls up the voltage on line  214  to 5 volts until the next half cycle of voltage source V AC. At that time, T 1  again becomes conductive and the voltage on line  214  is again brought to ground or zero potential. Accordingly, the output of the voltage sense circuit  212  is a square wave signal which is delivered to the V AC sense input of controller  216 . Since, during normal operation, the incoming line is operating at  60  Hertz frequency, the square wave signal out of voltage sense circuit  212  also has a frequency of 60 Hertz with a cycle of 16.66 milliseconds. Thus, a typical half cycle of the square wave is 8.33 milliseconds. 
     With the voltage sense circuit  212 , any change in the cycle length or, more particularly, the time between zero crossings of the square wave signal output from the voltage sense circuit, varying from a time period of 8.33 milliseconds can be sensed and such variation can be used to indicate that the incoming line voltage has either been lost or is undergoing a brown-out situation. Since capacitor C 1  maintains a charge even after line voltage L 1  is lost, the 5 volt signal is supplied to the voltage sense circuit  212  for a short period. As described previously, the motor  18  may continue to rotate for a short time after the line voltage L 1  is lost and, therefore, acts as a generator presenting transient voltages on the line L 1 . These transient noise signals are, in turn, transformed in the power supply circuit  203  and are present at the node  207  for voltage V.A.C. The motor  18  immediately begins to lose momentum as power on line L 1  is lost and causes the voltage V.A.C. to vary from the normal 60 Hertz or, in other words, the normal 8.33 millisecond half cycle period. Recognizing that this occurs, detection of variations in the zero crossing of the square wave signal output from the voltage sense circuit  212  may be used to quickly recognize either a power loss or a brown out on line L 1 . 
     The controller  216  contains internal software that is programmed to sense the period of the incoming square wave signal on line  214  and initiate an internal power loss signal when the half cycle period varies from 8.33 milliseconds. This controller is powered by voltage source VDD in normal operation. In the situation of a power loss or brown out, the capacitor C 1  provides energy to the controller for a short time period. The controller  216  also controls transistors T 2  and T 3  that drive relay coils  220  and  222 , respectively. Normally, the outputs OUT 1  and OUT 2  are a steady state voltage that holds transistors T 2  and T 3  in an “on” state. Relay coil  220  is supplied with the voltage VUNR and closes switch  224  to cause the heating element  34  to energize. Similarly, relay coil  222  is used to control the operation of motor  18  which is switched to line L 1  directly via switch  226  driven by relay coil  222 . 
     The controller  216  also has a third output OUT 3  that is used to save current operation settings of the appliance in an EEPROM  218 , which is also supplied by voltage source VDD. The EEPROM is used to store the current operation settings in the event of a power outage on line L 1 . 
     In the event of a power loss or brown out on line L 1 , the voltage sense circuit  212  begins to output a square wave signal having a time between voltage zero crosses of greater than 8.33 milliseconds. Furthermore, if the motor  18  is operating at the time of power loss or brown out, transient noise voltages will be generated on line L 1 . As the motor slows, the time between zero crossings of the voltage of the output of voltage sense  212  will begin to increase to times of 9 milliseconds, 10 milliseconds, etc. In the present invention, the controller is programmed to sense any variation from a voltage zero-cross time of 8.33 milliseconds. After the first half cycle that varies from this time, the controller initiates pulsing of the output signals OUT 1  and OUT 2  at a prescribed duty cycle that is less than 100% or, in other words, less than a steady state voltage. This pulsing is performed in order to protect the relay coils  220  and  222  from excessive wear and damage that can be caused by simply allowing them to turn off. In the event of a complete power loss or a brown out where the line voltage L 1  drops below 120 volts, the charge on capacitor C 1  is used to supply the voltage VDD to the controller and also the voltage VUNR to drive the relay coils C 1  and C 2 . Additionally, the controller needs only pulse transistor T 2  or T 3  when either the heating element  34  or the motor  18  was required to be run at that particular point in the drying cycle. Pulsing of the relay coils is preferably accomplished with a 50% duty cycle, which enables the coils to still operate, yet consumes less of the capacitor energy of the capacitor C 1 . Furthermore, in the event of a brown out, pulsing the relay coils maintains the connection via switches  224  and  226  to the heater  34  or motor  18 , respectively during the dip in voltage occurring during the brown out such that when the voltage again rises to normal operating voltage, no disruption in the settings of these switches occurs. 
     In the event of a complete power loss, pulsing of the transistors T 2  and T 3  conserves the charge energy in capacitor C 1  for a longer period of time. In a preferred embodiment, the controller  216  waits for four detected cycles of the output of voltage sense circuit  212  before storing the current operation settings to the EEPROM  218 , the storage operation also using the charge energy of capacitor C 1  to perform this operation. Preferably, the controller is programmed to wait for four cycles of the square wave output (i.e., approximately 64 msec) from the voltage sense circuit  212  before storing the current operation settings in the EEPROM  218 . This time delay allows the controller  216  to accurately determine whether a loss of power on line L 1  has occurred or merely a brown out before saving the current settings. Hence, unnecessary storage of current operation settings is avoided. Greater or lesser numbers of detected longer periods could be used, depending on the appliance, typical motor loads and other power demands. However, the number should preferably not be so low that unnecessary storage operations are frequently performed nor should the number be so high that the capacitor charge is frequently discharged prior to the saving of the operation settings. 
     The pulsing of the relay coils is advantageous in conserving energy from capacitor C 1  which is used to supply power to the relay coils  220  and  222 , the controller  216 , the voltage sense circuit  212  and the EEPROM  218 . Preferably, the capacitor C 1  is of sufficient size to afford enough charge to both pulse the relay coils and to effect storage of current operation settings in the EEPROM  218 . In order to provide sufficient charge, the capacitor C 1  is set at a value of approximately 2200 μF to provide about 300 milliseconds of available charge, which is sufficient to effect operation of the above mentioned devices. It is noted, however, the value of the capacitor C 1  is set in conjunction with the effective resistance of the circuit in which the capacitor C 1  is contained in order to achieve an RC time constant to allow sufficient time to store the operation settings in the BEPROM  218 . The capacitor C 1  value however, is nonetheless much smaller than would be required absent the pulsing operation of the coils and the quick voltage sensing afforded by voltage sense circuit  212 . Thus, the capacitor C 1  is a “smaller value” than would otherwise be required, which also reduces the cost of the control circuit  200 . The above provides a detailed description of the best mode contemplated for carrying out the present invention at the time of filing the present application by the inventors thereof. It will be appreciated, however, by those skilled in the art that many modifications and variations, which are included within the intended scope of the claims, may be made without departing from the spirit of the invention.