Abstract:
The present invention provides a device for signal control of a switch which outputs a first signal in response to a turning operation thereof and outputs a second signal in response to a depressing operation thereof. If one of the first and second signals is outputted in response to a corresponding one of the switch turning operation and the switch depressing operation and the other signal is thereafter outputted in response to the other operation within a predetermined period, the control device nullifies the other signal. With this arrangement, a heating cooker provided with the switch is prevented from performing an under-heat or over-heat cooking operation on the basis of a misoperation of the switch. Further, the need for resetting a cooking period is obviated which may otherwise arise from the misoperation of the switch.

Description:
This application is based on Application No. 2000-163753 filed in Japan, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a heating cooker and, more particularly, to a microwave oven. The invention further relates to a switch control device and method to be employed in such a heating cooker. 
     2. Description of Related Art 
     Hitherto known as a switch for use in a microwave oven is a combination switch which functions as a push switch for outputting a cooking start signal in response to depression of the switch and as a rotary switch for outputting a cooking period signal according to the amount of turning of the switch. 
     The known switch for the microwave oven has two functions and, therefore, is contributable to an easy-to-handle design of the microwave oven with a reduced number of switches. However, the switch has drawbacks with a tendency toward the following misoperations due to its two functions as the push switch and as the rotary switch. 
     When a user depresses the switch to start a cooking operation after having set a cooking period by turning the switch, a misoperation of the switch is liable to occur with the switch inadvertently turned. Particularly, the user is liable to depress the switch while inadvertently turning the switch, whereby the cooking period once set is changed at the start of the cooking operation. 
     Further, the user may inadvertently depress the switch when turning the switch for the setting of the cooking period. 
     With either of the misoperations of the switch, over-heating or under-heating occurs because the cooking period is not set as intended by the user at the start of the cooking operation. 
     If the user becomes aware of the misoperations of the switch, the user may interrupt the cooking operation to reset the cooking period, but such a resetting operation is troublesome. Therefore, a switch is desired which requires no resetting operation. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to improve the operability of a depressible rotary switch for use in a heating cooker. 
     It is another object of the present invention to provide a switch control device and method which ensure an improved operability of a depressible rotary switch by rejecting an output signal generated due to a misoperation of the switch. 
     It is further another object of the present invention to improve the operability of a heating cooker having a depressible rotary switch. 
     In accordance with the present invention, there is provided a device for signal control of a switch which outputs a first signal in response to a turning operation thereof and outputs a second signal in response to a depressing operation thereof. If one of the first and second signals is outputted in response to a corresponding one of the switch turning operation and the switch depressing operation and the other signal is thereafter outputted in response to the other operation within a predetermined period, the control device nullifies the other signal. 
     With this arrangement, a heating cooker provided with the switch is prevented from performing an under-heat or over-heat cooking operation on the basis of a misoperation of the switch. Further, the need for resetting a cooking period is obviated, which may otherwise arise from the misoperation of the switch. 
     The foregoing and other objects, features and effects of the present invention will become more apparent from the following detailed description with reference to the attached drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view illustrating the appearance of a microwave oven according to one embodiment of the present invention; 
     FIG. 2 is a front view of an operation panel provided on a right side of a front face of the microwave oven shown in FIG. 1; 
     FIG. 3 is a block diagram illustrating the electrical construction of the microwave oven according to the embodiment; 
     FIG. 4 is a flow chart for explaining a control operation to be performed by a controller shown in FIG. 3; and 
     FIG. 5 is a flow chart for explaining another control operation to be performed by the controller shown in FIG.  3 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 is a perspective view illustrating the appearance of a microwave oven according to one embodiment of the present invention. The microwave oven  10  includes a main body housing  15 , and a door  16  covering a front opening of the main body housing  15  in an openable manner. With the door  16  being open, an object to be cooked is put into and taken out of a heating chamber (not shown) in the main body housing  15 . An operation panel  1  is provided on a right side of a front face of the main body housing  15 . 
     FIG. 2 is a front view of the operation panel  1 . A display  2 , a plurality of cooking mode selection switches  11 , a plurality of function switches  13  and an RP switch  12  are arranged on the operation panel  1  in this order from the top to the bottom thereof. The display  2  is comprised, for example, of a liquid crystal display panel (LCD), and is adapted to switchably display a present time and the remainder of a cooking period. Other information, e.g., a selected cooking mode and an error indication may be displayed on the display  2 . 
     The RP switch  12  has two functions as a rotary switch and as a push switch. The RP switch  12  outputs a cooking period signal in response to a turning operation thereof, and outputs a cooking start signal in response to a depressing operation thereof. 
     FIG. 3 is a block diagram illustrating the electrical construction of the microwave oven  10 . The operation of the microwave oven  10  is controlled by a controller  7 . The controller  7  comprises a microprocessor and the like, and incorporates a timer  8 . The timer  8  times a lapse of a predetermined period which will be described later. The timer  8  may be implemented as a hardware circuit or on a software basis. 
     Signals from the cooking mode selection switches  11 , the function switches  13  and the RP switch  12  provided on the operation panel  1  are applied to the controller  7 . The controller  7  performs predetermined operations on the basis of the signals from these switches. That is, the controller  7  controls a driver circuit  4  to drive a heating device  3 . The heating device  3  comprises, for example, a heater, a magnetron and the like. The object placed in the heating chamber within the main body housing  15  is heated by the heating device  3 . 
     The microwave oven  10  includes a power supply circuit  6  for supplying power to the microwave oven  10 . A voltage from a utility AC power source  5  (e.g., AC100V) is applied to the power supply circuit  6 . The power supply circuit  6  shapes the waveform of the utility AC voltage to supply a source voltage to the driver circuit  4  and the controller  7 . 
     The controller  7  further controls the display  2  to display various information on the display  2 . 
     The RP switch  12  which functions as the rotary switch and as the push switch includes a rotation shaft  21 , a knob  22  fixed to a front end of the rotation shaft  21 , a disk  23  fitted around a midportion of the rotation shaft  21 , a depression switch  24  disposed at a rear end of the rotation shaft  21 , and a rotation detector  25  disposed in association with the disk  23 . The rotation shaft  21  and the disk  23  are rotated when the knob  22  is turned. The rotation detector  25  detects the rotation of the disk  23 , and the direction and amount of the rotation. The amount of the rotation detected by the rotation detector  25  is applied to the controller  7 , and converted into a period. Thus, the switch  12  functions as the rotary switch. When the knob  22  is depressed rearward, the depression switch  24  is switched by the rear end of the rotation shaft  21 . Thus, the switch  12  functions as the push switch. 
     The construction of the RP switch  12  per se is known. 
     Next, an explanation will be given to a control operation to be performed by the controller  7  shown in FIG. 3 with reference to a flow chart of FIG.  4 . 
     When the power is turned on, it is judged in Steps S 1  and S 2  whether or not the RP switch  12  is turned. If the RP switch  12  is turned, a signal outputted in accordance with the turning operation is detected to set a cooking period in Step S 3 . More specifically, when the RP switch  12  is turned, a pulse signal of a 0.02-second cycle, for example, is applied to the controller  7  from the rotation detector  25 . The pulse signal corresponds to the amount of the rotation of the knob  22 , and the controller  7  converts the amount of the rotation into a period which is employed as the cooking period to be set. At the same time, the timer  8  is set for 0.2 second and started in Step S 4 . That is, a lapse of 0.2 second is timed after the setting of the cooking period. 
     If it is judged in Step S 2  that the switch is not turned, the process goes to Step S 5  from Step S 2 . 
     In Steps S 5  and S 6 , it is judged whether or not the RP switch  12  is depressed. If the RP switch  12  is not depressed, the process returns to Step S 1 . If the RP switch  12  is depressed, it is judged in Steps S 7  and S 8  whether or not the cooking period is set. If the cooking period is not set, the process returns to Step S 1 . That is, the cooking operation is not started even if the RP switch  12  is operated with the cooking period being not set. 
     If it is judged in Step S 8  that the cooking period is set, it is judged in Steps S 9  and S 10  whether or not the timer  8  expires. If the timer  8  does not expire, i.e., if 0.2 second has not elapsed after the setting of the cooking period, it is judged that the depressing operation of the RP switch  12  is erroneous, so that the cooking start signal outputted in response to the depressing operation of the RP switch  12  is rejected and the process returns to Step S 1 . 
     On the other hand, if it is judged in Step S 10  that the timer  8  expires, the depressing operation of the RP switch  12  is not considered erroneous but effective, so that the cooking start signal outputted in response to the depressing operation of the RP switch  12  is accepted and the heating device  3  is actuated (Step S 11 ). 
     As described above, the timer  8  starts timing a lapse of the predetermined period (0.2 second) upon completion of the turning operation of the RP switch  12  for the input of the cooking period and, if the RP switch  12  is depressed within 0.2 second after the setting of the cooking period, it is judged that the depressing operation is erroneous, so that the cooking operation is not started. Even if the RP switch  12  is erroneously depressed when the RP switch  12  is turned, the cooking operation is not started in response to the depressing operation. Therefore, the operability of the RP switch  12  is improved. In addition, the cooking operation is prevented from being started by the misoperation. 
     As a result, the cooking period is set as intended by the user, so that a cooking failure can be eliminated which may otherwise occur due to the misoperation. 
     FIG. 5 is a flow chart for explaining another control operation to be performed by the controller  7 . 
     Steps S 21  to S 28  in FIG. 5 are the same as Steps S 1  to S 8  in FIG. 4 and, therefore, no explanation will be given thereto to avoid duplication. 
     The process shown in the flow chart of FIG. 5 is characterized in that, if the timer  8  does not expire when the timer  8  is checked in Steps S 29  and S 30 , it is judged in Step S 31  whether or not the cooking period is set at least 0.2 second before the timer check. If the cooking period is not set at least 0.2 second before the timer check, the process returns to Step S 21 . On the other hand, if the cooking period is set at least 0.2 second before the timer check, the setting of the cooking period based on a signal inputted within 0.2 second after the timer check is canceled in Step S 32 , and the process goes to Step S 33 . 
     If it is judged in Step S 30  that the timer  8  expires, the process goes to Step S 33 , so that the heating device  3  is actuated to start the cooking operation. 
     In accordance with the control operation shown in FIG. 5, the cooking period once set by turning the RP switch  12  is not changed even if the user thereafter inadvertently turns the RP switch  12  when pressing the RP switch  12 . Therefore, the cooking operation is started with the cooking period set as intended by the user. As a result, a cooking failure can be eliminated which may otherwise occur due to the misoperation. In addition, the need for resetting the cooking period can be obviated, thereby improving the operability of the microwave oven. 
     It should be understood that the present invention be not limited to the embodiment described above, but various modifications may be made within the scope of the present invention defined by the appended claims. For example, the present invention is applicable not only to the microwave oven but also to an oven, a toaster and the like.