Patent Publication Number: US-6335521-B1

Title: Microwave oven

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accuring under 35 U.S.C. §119 from my application MICROWAVE OVEN filed with the Korean Industrial Property Office on Oct. 11, 2000 and there duly assigned Serial No. 59845/2000. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to microwave ovens, and more particularly, to a microwave oven having an improved grill cover. 
     2. Description of Related Art 
     Referring to FIG. 6 which is an exploded perspective view of a conventional wall-mounted microwave oven, the conventional microwave oven is comprised of a main body  101  formed with a cooking compartment  103 , and an outer casing  105  surrounding the main body  101 , to define an outer appearance of the microwave oven. 
     A tray  107  upon which food rests is placed within the cooking compartment  103 . In front of the cooking compartment  103  is installed a door  109  opening and closing the cooking compartment  103 , through which a user can put in and pick out the food. Beside the door  109  is installed a control panel  111  formed with a plurality of buttons by which the user can control the microwave oven. In the rear of the control panel  111  is installed a magnetron  115  supplying electromagnetic waves into the cooking compartment  103 . 
     The outer casing  105  is comprised of an upper casing  117 , a lower casing  121  and a rear casing  119 . The upper casing  117  takes a shape of inverse ‘U,’ surrounding the upper part and both side parts of the main body  101 , the lower casing  121  is installed in the lower of the main body  101  and the rear casing  119  is installed in the rear of the main body  101 . 
     On the lower casing  121  are installed a pair of air inlet ports  127  and a pair of hood lamps  129 . Through the air inlet ports  127 , air flows into the lower casing  121 , according to operation of a blowing fan  125  installed to the rear casing  119 , and the hood lamps  129  is installed adjacent to the air inlet ports  127 , to illuminate below the microwave oven. 
     On the top face of the upper casing  117  is formed an exhaust port  123  through which the air drawn through the air inlet ports  127  is exhausted outside the main body  101 . Between the upper of the main body  101  and the upper casing  117  is formed a grill member  135  having a number of air passing holes  133 . On the top of the main body  101  is formed a holding bracket  131  holding the grill member  135 . In front of the grill member  135  is provided a grill cover casing  141 , taking a shape of rectangular box, having longitudinal openings in the front face and the rear face thereof. In the front opening of the grill cover casing  141  is installed a grill cover  143 . Between the grill member  135  and the grill cover  143  is provided a switch  161  opening and closing the grill cover  143  installed in the front opening of the grill cover casing  141 . 
     FIG. 7 is a partial, sectional view showing an assembly of the grill cover  143  and the switch  161  taken along line VII—VII of FIG. 6, and FIG. 8 is a view showing an operation state of the grill cover of FIG.  6 . As shown therein, the grill cover casing  141  is comprised of an inclination part  142  downwardly inclined toward the inside of the front opening thereof, with a predetermined inclination degree. On the outer upper surface of the grill cover casing  141  is formed an indentation part  141   a  indented from the surface thereof to a predetermine depth. On the outer lower plate of the grill cover casing  141  is formed a protrusion part  141   b  protruded transversely relative to the lower plate thereof. The grill cover casing  141  is allowed to closely contact an upper portion of the main body  101  and a lower surface of the upper casing  117  by means of the indentation part  141   a  and the protrusion part  141   b . On the grill cover  143  installed in the front opening of the grill cover casing  141  is formed a link supporter  147  protruded toward the grill member  135  transversely, relative to the grill cover  143 . 
     The link supporter  147  has an elongated guide hole  147   a  (see FIG. 8) formed in the lengthwise direction thereof. On opposite sides of the rear lower portion of the grill cover  143  is provided a hinge  149  coupled to the grill cover casing  141 , opening and closing the front opening of the grill cover casing  141 . In the middle of the grill cover casing  141  is formed a bracket  165  taking a shape of inverse ‘U.’ One side of the bracket  165  is opened and the other side thereof is coupled to the grill member  135 . The switch  161  opening and closing the grill cover has a step motor  163  having a rotational shaft to drive of opening and closing of the grill cover  143 , and a link shaft  167  coupled to the rotational shaft of the step motor  163 . The step motor  163  is coupled to an external side of the bracket  165 . On one end of the link shaft  167  is formed a motor shaft accommodating part  167   a  coupled to the rotational shaft of the step motor  163 . On the other end of the link shaft  167  is formed a connection pin  167   b  connected to the elongated guide hole  147   a  of the link supporter  147 . 
     The connection pin  167   b  is accommodated in the elongated guide hole  147   a , so as to slidably elevate along the elongated guide hole  147   a . When the grill cover  143  is closed, the connection pin  167   b  is placed in the upper side of the elongated guide hole  147   a  of the link supporter  147 . 
     Referring to FIG. 8 again, in the case that the grill cover  143  is opened, if the step motor  163  is activated for a predetermined period of time according to a signal from a controller (not shown), so that, for example, the motor shaft is rotated counterclockwise in view of the motor  163 , the link shaft  167  coupled to the rotational shaft of the step motor  163  is rotated counterclockwise. If the link shaft  167  is rotated counterclockwise, the connection pin  167   b  of the link shaft  167  is slid downward along the elongated guide hole  147   a . If the connection pin  167   b  is slid downward, the grill cover  143  is forward rotated, to thereby open the front opening of the grill cover casing  141 . After a predetermined period of time has passed, the controller (not shown) activates the step motor  143  to stop its operation. If the step motor  163  stops, the grill cover  143  remains in the maximally opened state. At this time, the step motor shaft connected to the link shaft  167  supports the weight of the grill cover  143 . 
     In the case that the opened grill cover  143  is closed, if the rotational shaft of the step motor  163  is rotated clockwise by a control signal from the controller (not shown), the link shaft  167  coupled to the rotational shaft of the step motor  163  is rotated clockwise. If the link shaft  167  is rotated clockwise, the connection pin  167   b  of the link shaft  167  is slid upward along the elongated guide hole  147   a  of the link supporter  147 . If the connection pin  167   b  is slid upward, the grill cover  143  is rotated backward, to thereby close the front opening of the grill cover casing  141 . After a predetermined period of time has passed, the controller (not shown) activates the step motor  163  to stop its operation. If the step motor  163  stops, the grill cover  143  is closed. That is, the step motor  163  draws the grill cover  143  connected to the link shaft  167  by the rotation of the rotational shaft of the step motor  163 . 
     In the conventional microwave oven, while the operation to open the grill cover is being conducted, the weight of the grill cover is to be supported by the rotational shaft of the motor, thereby generating an excessive burden to the rotational shaft. Further, while the operation to close the grill cover is being conducted, the grill cover is to be drawn by the rotation force of the motor, thereby generating an over-load to the motor. 
     To open and close the grill cover, the motor has to be rotated reciprocally rather than unidirectionally, and frequent reciprocation of the motor is likely to cause the motor to be out of order. To open and close the grill cover, the connection pin connected to the link shaft should be slid up and down along the elongated guide hole of the link supporter, thereby preventing smooth open and close operations. In addition, since the grill cover is opened and closed by operating the motor for a predetermined period of time, it is not easy to maintain open and close range. Also, the conventional microwave oven requires a step motor that is more expensive than other motors, thereby increasing the cost of production. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made in view of the above-described shortcomings, and it is an object of the present invention to provide a microwave oven capable of smoothly opening and closing the grill cover, maintaining the open and close range, and reducing the cost of production. 
     This and other objects of the present invention may be achieved by a provision of a microwave oven comprising a main body formed with a cooking compartment, an outer casing surrounding the main body, to define an outer appearance of the microwave oven, a grill member provided between the main body and the outer casing, having a number of air passing holes, and a grill cover rotatably provided in front of the grill member, opening and closing the grill member, further comprising a main cam rotatably contacting with a rear face portion of the grill cover; a motor moving the main cam; and a switch sensing a rotational position of the main cam, the rotational position of the main cam being controlled to control the opening/closing operation of the grill cover when the motor operates. 
     The switch comprises a first micro switch operated to suspend the rotation of the main cam and the operation of the motor when the main cam is rotated to a predetermined degree to correspond to an open position of the grill cover; and a second micro switch operated to suspend the operation of the motor when the main cam is rotated to a predetermined degree from the open position, to correspond to a closed position of the grill cover. 
     The microwave oven further comprises first and second auxiliary cams to respectively activate the first and second micro switches when the main cam is rotated to correspond to the open and closed positions of the grill cover. 
     The main cam, the first auxiliary cam and the second auxiliary cam are provided coaxially. The microwave oven further comprises a spring provided at the rear of the grill cover, elastically biasing the grill cover from the open position to the closed position. 
     A reinforced steel plate is provided on the rear face of the grill cover, to prevent the grill cover from being deformed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood and its various objects and advantages will be more fully appreciated from the following description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is an exploded perspective view of a wall-mounted microwave oven according to the present invention; 
     FIG. 2 is a partial sectional view showing an installation state of a grill cover and a switch of FIG. 1; 
     FIG. 3 is an enlarged sectional view taken along line—of FIG. 2; 
     FIGS. 4 and 5 are views showing open and close states of the grill cover; 
     FIG. 6 is an exploded perspective view of a conventional wall-mounted microwave oven; 
     FIG. 7 is a partial sectional view showing an installation state of a grill cover and a switch of FIG. 6; and 
     FIG. 8 is a view showing open and close states of the grill cover. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinbelow, an embodiment of the present invention will be described in more detail with respect to a wall-mounted microwave oven, referring to the accompanying drawings. 
     Referring to FIG. 1, the wall-mounted microwave oven according to the present invention is comprised of a main body  1  formed with a cooking compartment  3  in which food is cooked, and an outer casing  5  surrounding an outside of the main body  1 , to define an outer appearance of the microwave oven. Within the cooking compartment  5  is installed a tray  7  upon which food rests. 
     In front of the cooking compartment  3  is installed a door  9  opening and closing the cooking compartment  3 , to allow a user to put in and pick out food to be cooked. Beside the door  9  is installed a control panel  11  having a number of buttons. In rear of the control panel  11  is installed a magnetron  15  supplying electromagnetic waves into the cooking compartment  5 . 
     The outer casing  5  is comprised of an upper casing  17  surrounding the top and both sides of the main body  1 , taking a shape of inverse ‘U’, a rear casing  19  installed in the rear of the main body  1  and a lower casing  21  installed in the lower of the main body. A space is formed between the top face of the main body  1  and the lower face of the upper casing  17  to allow air to pass through. 
     The lower casing  21  has an air inlet port  27  and a hood lamp  29 . Air is drawn through the air inlet port  27  by an operation of a blowing fan  25  installed in the rear casing  19 ; and the hood lamp  29  is installed adjacent to the air inlet port  27 , illuminating below the microwave oven. 
     On the top face of the upper casing  17  is formed an exhaust port  23  through which the air within the main body  1  and the air drawn in through the air inlet ports  27  are exhausted outside the main body  1 . Between the upper of the main body  1  and the upper casing  17  is formed a grill member  35  having a number of air passing holes  33 . Through the air passing holes  33 , air is exhausted outside the main body  1  or outdoor air flows into the main body  1 . On the top of the main body  1  is provided a holding bracket  31  holding the grill member  35 . In front of the grill member  35  is provided a grill cover casing  41 , having longitudinal openings in the front and rear thereof. To the front opening of the grill cover casing  41  is installed a grill cover  141  of a plate shape. Between the grill member  35  and the grill cover  43  is provided a switch  61  opening and closing the grill cover  43 . 
     Referring to FIGS. 2 and 3, the grill cover casing  41  is comprised of an inclination part  42   a  downwardly inclined toward the inside of the front opening thereof, with a predetermined inclination degree. On the upper surface of the grill cover casing  41  is formed an indentation part  41   b  indented from the surface thereof to a predetermine depth. On the lower surface of the grill cover casing  41  is formed a protrusion part  41   c  protruded from the surface thereof. The grill cover casing  41  is allowed to closely contact an upper portion of the main body  1  and a lower surface portion of the upper casing  17  by means of the indentation part  41   b  and the protrusion part  41   c.    
     On the free end of the inclination part  42   a  of the grill cover casing  41  is formed a cover accommodating groove  41   a , accommodating therein the upper end portion of the grill cover  43  when the grill cover is closed. On the rear face of the grill cover  43  is mounted a reinforcement plate  45  having predetermined length and width, to prevent the grill cover  43  from being deformed. On the rear upper face of the grill cover  43  are installed a pair of spring holders  47 , taking a shape of ring. The spring holders are spaced with each other longitudinally relative to the grill cover  43 . On opposite sides of the rear bottom face of the grill cover  43  are provided a pair of hinges  49  to be coupled to opposite sides of the lower part of the grill cover casing  41 . The grill cover  43  is rotated around the hinges  49  to thereby open and close the front opening of the grill cover casing  41 . In the middle of the rear face of the grill cover  43  is formed a main cam contact groove  51  indented to a predetermined depth. The main cam contact groove  51  is permanently in contact with an outer circumference of a main cam  67 . 
     On an inner face of a second inclination part  42   b  formed in the lower of the grill cover casing  41  are formed a pair of spring couplers  53  corresponding to the spring holders  47 . The spring couplers protrude from the planar surface of the grill cover  43 . Between the spring holders  47  of the grill cover  43  and the spring couplers  53  of the grill cover casing  41  are provided a pair of springs  55 , elastically biasing the grill cover  43 , by coupling one end thereof to the spring holder  47  and the other end thereof to the spring coupler  53 . In the middle of the grill cover casing  41  is formed a bracket  65  taking a shape of “U.” One side of the bracket  65  is opened toward the grill cover  43 , and the other side thereof is coupled to the grill member  35 . 
     Referring to FIG. 3, the switch  61  installed between the grill member  35  and the grill cover  43 , is comprised of an AC motor  63 , cams  67 ,  71  and  73  and micro switches  75  and  77 . The AC motor  63  is activated to open and close the grill cover  43 . 
     The motor  63  is mounted on one side of the bracket  65 , and a main cam  67  is installed on a rotational shaft of the motor  63 . The main cam  67  is accommodated within the bracket  65 , taking an approximately elliptical shape having different curvature radii, and is rotated by an operation of the motor  63 . An outer circumference portion of the main cam  67  is contacted with the main cam contact groove  51  formed on the grill cover  43 . Under the state that the grill cover  43  is closed, an outer circumference of a protrusion part  67   a  having the maximum curvature radius, that is, the point where one end of the main cam  67  is positioned the farthest from the center of gyration, is directed toward the grill member  35 . 
     Outside of one side wall of the bracket  65  is provided a first auxiliary cam  71  and a second auxiliary cam  73  extended axially from the main cam  67 . The first auxiliary cam  71  is of an approximately elliptical shape and has a protrusion part  71   a  having the minimum curvature radius; and the second auxiliary cam  73  is of the same shape and dimension as that of the first auxiliary cam  71  and has a protrusion part  73   a  disposed opposite to the protrusion part  71   a  of the first auxiliary cam  71 . The first and second micro switches  75  and  77  having terminals respectively contacting the protrusion parts  71   a  and  73   a  of the first and second auxiliary cams  71  and  73  are disposed in parallel with each other. Each of the micro switches  75  and  77  is supported by an outer side of the bracket  65 . Under the state that the grill cover  43  is closed, the outer circumference of the protrusion part  71   a  of the first auxiliary cam  71  is in contact with the terminal of the first micro switch  75 , and the protrusion part  73   a  of the second auxiliary cam  73   a  opposite to the protrusion part  71   a  of the first auxiliary cam  71  is spaced from the terminal of the second micro switch  77 . 
     Referring to FIGS. 4 and 5, the switching operation of the grill cover will be described in more detail. 
     As shown in FIG. 4, where grill cover  43  is closed, if AC motor  63  is operated according to a signal from the controller (not shown), the outer circumference of main cam  67  coupled to the rotational shaft of motor  63  is moved along main cam contact groove  51 . As the outer circumference of main cam  67  is rotatably moved along main cam contact groove  51 , grill cover  43  is slowly rotated forward around hinges  49  to thereby open grill cover casing  41 . When the outer circumference of protrusion  67   a  of main cam  67  directed toward grill member  35  contacts main cam contact groove  51 , grill cover  43  is elastically biased by the pair of springs  55  connecting grill cover casing  41  and grill cover  43 ; this allows grill cover  43  to be partially opened by a predetermined degree, rather than being opened completely. 
     The first auxiliary cam  71 , in the state that the outer circumference of the protrusion part  71   a  is in contact with the terminal of the first micro switch  75  when the grill cover  43  is closed, is rotated according to the rotation of the main cam  67 . The terminal of the first micro switch  75  and the outer circumference of the first auxiliary cam  71  are accordingly separated from their mutual contacting state. To the contrary, the second auxiliary cam  73 , at the opposite position to the first auxiliary cam  71  when the grill cover  43  is closed, is rotated according to the rotation of the main cam  67 , and the outer circumference of the protrusion part  73   a  of the second auxiliary cam  73  becomes in contact with the terminal of the second micro switch  77 . When the second auxiliary cam  73  and the terminal of the second micro switch  77  are contacted with each other, a contact signal is transmitted to the controller (not shown). Then, the controller identifies from the contact signal the maximum open state of the grill cover  43 , and transmits a signal to suspend the operation of the AC motor  63 . Upon receiving the suspension signal, the motor  63  immediately suspends its operation, to thereby allow the grill cover  43  to remain at its maximally opened state. 
     Referring to FIG. 5, where the opened grill cover  43  is closed from the open state, if the motor  63  is operated according to an operation signal inputted from the controller (not shown), the main cam  67  coupled to the rotational shaft of the motor  63  is rotationally moved along the main cam contact groove  51 . The protrusion part  67   a  of the main cam  67  is slowly separated from the main cam contact groove  51  and directed toward the grill member  35 . The grill cover  43  is slowly rotated toward the grill member  35  by an elastic power of the pair of springs  55  coupled to the grill cover casing  41  and the grill cover  43 , contacting the grill cover accommodating groove  41   a  to thereby close the grill cover casing  41 . 
     While the closing operation of the grill cover  43  is being conducted, the protrusion part  73   a  of the second auxiliary cam  73  and the terminal of the second micro switch  77  are slowly separated from the contacting state, whereas the protrusion part  71   a  of the first auxiliary cam  71  and the terminal of the first micro switch  75  is slowly contacted with each other from their separation state. If the first auxiliary cam  71  and the terminal of the first micro switch  75  are contacted, a contact signal is sent to the controller (not shown). Then, the controller identifies the close state of the grill cover  43  based on the contact signal and transmits a suspension signal to the motor  63 . When the suspension signal is applied to the motor  63  by the controller, the motor  63  immediately suspends its operation, thereby allowing the grill cover  43  to be maintained at the close state. 
     Even if the user arbitrarily opens the grill cover  43  by hand, this causes no damages to the motor  63 , the main cam  67 , the first auxiliary cam  71  and the second auxiliary cam  73  by means of the elastic force of the springs  55  provided between the grill cover casing  41  and the grill cover  43 . 
     According to the present invention, a main cam and auxiliary cams are provided for opening and closing the grill cover, the main cam is rotated by an AC motor, and a rotation of the main cam is controlled in cooperation with a connection of the auxiliary cams and micro switches. With this configuration, the switching operation is facilitated, the range of switching operation is constant, and the cost of production is reduced. 
     Although the preferred embodiment of the present invention has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.