Abstract:
Apparatus is provided for detecting and controlling an abnormal rise in temperature associated with a combination of a cooking utensil ( 10 ) and a cooking surface ( 4 ) overlying an electric heater ( 6 ). A temperature-responsive device ( 24 ) monitors the temperature of the cooking utensil ( 10 ), while cooking utensil detection means ( 26 ) detects the location of the cooking utensil ( 10 ). Control means ( 30 ) is adapted to control energising of the heater ( 6 ) whereby an abnormal rise in temperature associated with an event within the cooking utensil ( 10 ) is distinguished from an abnormal rise in temperature sensed by the temperature-responsive device ( 24 ) and associated with removal of the cooking utensil ( 10 ) from the cooking surface ( 4 ).

Description:
[0001]     This invention concerns apparatus for detecting an abnormal rise in temperature associated with a combination of a cooking utensil and a cooking surface, such as of glass-ceramic material, overlying an electric heater. Such abnormal rise in temperature may, in particular, result from a boil-dry event within the cooking utensil or an event in the cooking utensil in which a food product adheres to a base of the cooking utensil.  
       DESCRIPTION OF PRIOR ART  
       [0002]     It is known to provide an electric heater arranged at the underside of a cooking surface, such as of glass-ceramic material, and in which the heater incorporates at least one electric heating element spaced from the underside of the cooking surface. A cooking utensil is arranged to be supported on the cooking surface in a cooking zone overlying the heater. It is known to provide a first temperature-responsive device, for example in a cavity between the at least one heating element and the underside of the cooking surface, to monitor temperature within the cavity and of the cooking surface and to operate to de-energise the heater when a maximum permitted temperature is sensed, thereby preventing thermal damage from occurring to the cooking surface. Such first temperature-responsive device may be arranged to provide an electrical output as a function of the temperature sensed and may be arranged to be electrically connected to control means, which may be microprocessor-based circuitry.  
         [0003]     It is also known to provide a second temperature-responsive device arranged in contact with, or adjacent to, the underside of the cooking surface within the cooking zone and operating to provide an electrical output to the control means as a function of the temperature of the cooking utensil through the cooking surface within the cooking zone. Such second temperature-responsive device may be used to closely monitor the temperature of the cooking utensil and to provide a closed loop control system in which the heater is appropriately energised to provide a desired heating schedule for the cooking utensil.  
         [0004]     When a boil-dry event occurs in the cooking utensil, or a food product being cooked in the cooking utensil adheres to the base thereof, a rise in temperature occurs in the cooking utensil, which although small can be monitored by the second temperature-responsive device and used by the control means to instigate de-energising of the electric heater for safety purposes. Such de-energising will remain effective until a manual reset means is operated by the user.  
         [0005]     A problem exists in that if during a cooking cycle the cooking utensil is removed from the cooking surface, even temporarily such as for adding water thereto, the second temperature-responsive device will sense a rise in temperature. This rise in temperature will be seen by the second temperature-responsive device as an abnormal rise in temperature and indistinguishable from that associated with a boil-dry event in the cooking utensil or from that associated with adhesion to the base of the cooking utensil of a food product being cooked. As a result, the heater will be de-energised by the control means and will remain so after the utensil is replaced on the cooking surface, necessitating inconvenient operation of the manual reset means.  
         [0006]     A further problem exists in that incorrect location of the cooking utensil on a predetermined cooking zone of the cooking surface overlying the heater and the second temperature-responsive device may result in incorrect sensing of the temperature of the cooking utensil by the second temperature-responsive device.  
       OBJECT OF THE INVENTION  
       [0007]     It is an object of the present invention to overcome or minimise these problems.  
       SUMMARY OF THE INVENTION  
       [0008]     According to the present invention there is provided apparatus for detecting an abnormal rise in temperature associated with a combination of a cooking utensil and a cooking zone of a cooking surface overlying an electric heater and for controlling energising of the heater, the apparatus comprising: a temperature-responsive device adapted to be arranged in contact with or adjacent to an underside of the cooking surface within the cooking zone, for monitoring temperature of the cooking utensil and providing an electrical output as a function thereof; cooking utensil detection means for detecting location of the cooking utensil relative to the cooking surface, the cooking utensil detection means being provided in structural combination with the temperature-responsive device; and control means cooperating with the temperature-responsive device and the cooking utensil detection means and adapted to control energising of the heater from a power supply in dependence upon detection by the detection means of the cooking utensil overlying the temperature-responsive device on the cooking surface, and in dependence upon detection by the temperature-responsive device of an abnormal rise in temperature, whereby an abnormal rise in temperature sensed by the temperature-responsive device associated with an event within the cooking utensil while located on the cooking surface is distinguished from an abnormal rise in temperature sensed by the temperature-responsive device and associated with removal of the cooking utensil from the cooking surface.  
         [0009]     The control means may be adapted whereby occurrence of the abnormal rise in temperature associated with the event within the cooking utensil and sensed by the temperature-responsive device, with the cooking utensil located on the cooking surface, results in de-energising of the heater. Such de-energising of the heater may be arranged to be effected until a reset means is operated by a user of the apparatus.  
         [0010]     The control means may be adapted to return energisation of the heater to its previous level in the event of removal of the cooking utensil from the cooking surface followed by relocation of the cooking utensil on the cooking surface within a predetermined short time period. Such predetermined short time period may result in an abnormal rise in temperature being sensed by the temperature-responsive device, which abnormal rise in temperature may be included in a temperature range associated with that resulting from the event within the cooking utensil. The short time period may be less than about 5 minutes.  
         [0011]     The control means may be adapted not to return energisation of the heater to its previous level in the event of removal of the cooking utensil from the cooking surface followed by relocation of the cooking utensil on the cooking surface in a time period in excess of a predetermined long time period. Energisation of the heater may not be returned to its previous level until a reset means is operated by a user of the apparatus. Such long time period may be in excess of about 5 minutes.  
         [0012]     The cooking utensil detection means may comprise an arrangement providing an electrical parameter which changes as a function of location of the cooking utensil relative to the cooking surface and detectable by the control means. Such electrical parameter may comprise electrical inductance or capacitance or an electrical signal resulting from receipt by a receiving means of an optical, infrared, sonic or ultrasonic signal transmitted by a transmitting means and reflected from a base of the cooking utensil.  
         [0013]     The cooking utensil detection means may suitably comprise an inductively-operating sensing coil or loop which may be supported on or surrounding at least part of the temperature-responsive device. Such sensing coil or loop may be electrically connected to a resonant circuit arrangement associated with the control means.  
         [0014]     The temperature-responsive device may comprise a component whose electrical resistance changes as a function of temperature and may comprise a platinum resistance component. Such component may be provided on a supporting means, such as of ceramic material.  
         [0015]     The temperature-responsive device and the cooking utensil detection means may be located in the heater at a peripheral region thereof and such that they underlie a region of the cooking utensil when the cooking utensil is located for heating on the cooking surface.  
         [0016]     The control means may comprise microprocessor-based circuitry.  
         [0017]     The event within the cooking utensil resulting in the abnormal rise in temperature may be a boil-dry event or an event in which a food product adheres to a base of the cooking utensil.  
         [0018]     The cooking surface may comprise glass-ceramic material.  
         [0019]     The electric heater may incorporate at least one electric heating element, which may be selected from a radiant electrical resistance heating element and an electrical inductance heating element.  
         [0020]     A further temperature-responsive device may be provided, adapted to monitor temperature of the cooking surface, and may be arranged to be electrically connected to the control means.  
         [0021]     The further temperature-responsive device may be adapted to monitor temperature of the cooking surface sensed with time.  
         [0022]     The further temperature-responsive device may alternatively or additionally be adapted to operate to cause de-energising of the heater when it senses a predetermined maximum permitted temperature of the cooking surface, and/or to operate to provide a predetermined set-point temperature for the cooking surface.  
         [0023]     The further temperature-responsive device may comprise a component whose electrical resistance changes as a function of temperature and may comprise a platinum resistance component.  
         [0024]     By means of the apparatus of the present invention, a detected rise in temperature resulting from an event within a cooking utensil, such as a boil-dry event or adhesion of a food product to the base of the cooking utensil, is distinguished from a rise in temperature associated with removal of the cooking utensil from the cooking zone of the cooking surface, during a cooking cycle and unnecessary manual re-energising of the heater is avoided when a cooking utensil is temporarily removed. Correct location of a cooking utensil on the cooking surface overlying the temperature-responsive device is also ensured.  
         [0025]     For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]      FIG. 1  is a plan view of an embodiment of a cooking arrangement incorporating apparatus according to the present invention for detecting abnormal rise in temperature associated therewith;  
         [0027]      FIG. 2  is a cross-sectional view of the arrangement of  FIG. 1 ;  
         [0028]      FIG. 3A  is a perspective view of an embodiment of a temperature-responsive device in combination with an embodiment of a cooking utensil detection means, for use in the arrangement of  FIGS. 1 and 2 ; and  
         [0029]      FIG. 3B  is an exploded view of the device of  FIG. 3A . 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0030]     Referring to  FIGS. 1 and 2 , a cooking arrangement  2  comprises a cooking surface  4 , such as of glass-ceramic material, at an underside of which is supported an electric heater  6 . A cooking zone  8  is provided on the cooking surface  4 . A cooking utensil  10  containing, for example, water and/or a food product to be heated, is located on the cooking surface  4  at the cooking zone  8 .  
         [0031]     The heater  6  comprises a dish-like support  14  containing a base layer  16  of thermal insulation material and supporting at least one radiant electrical resistance heating element  18 . Instead of the at least one radiant electrical resistance heating element  18 , at least one electrical induction heating element of known form could be provided. The at least one heating element  18  is spaced from the underside  20  of the cooking surface  4 , such that a cavity  22  is formed.  
         [0032]     A temperature-responsive device  24  is provided, located in contact with, or adjacent to, the underside  20  of the cooking surface  4 , within the cooking zone  8  and is adapted to provide an electrical output as a function of temperature of the cooking utensil  10  through the cooking surface  4  within the cooking zone  8  at a peripheral region thereof. As will be described in detail hereinafter, the temperature-responsive device  24  suitably comprises a component, such as a platinum resistance component, whose electrical resistance changes as a function of temperature.  
         [0033]     A cooking utensil detection means  26  is provided in structural combination with the temperature-responsive device  24 . The cooking utensil detection means  26  comprises an arrangement providing an electrical parameter which changes as a function of location of the cooking utensil  10  relative to the cooking surface  4 . In particular, the electrical parameter comprises electrical inductance, with the cooking utensil detection means  26  comprising an inductively-operating sensing coil or loop  28  supported on or surrounding at least part of the temperature-responsive device  24  and consisting of one or more turns of electrically conductive material, such as in the form of wire or ribbon.  
         [0034]     Other forms of cooking utensil detection means  26  could alternatively be provided. For example an arrangement could be employed which provides a change of electrical capacitance as a function of location of the cooking utensil  10  relative to the cooking surface  4 . Other arrangements may be employed which provide an electrical signal resulting from receipt by a receiving means of an optical, infrared, sonic or ultrasonic signal transmitted by a transmitting means towards a base of the cooking utensil  10  and reflected from the base of the cooking utensil  10 .  
         [0035]     The cooking utensil detection means  26  need not necessarily be provided in structural combination with the temperature-responsive device  24 .  
         [0036]     A microprocessor-based control means  30 , containing processing and control circuitry and operating with appropriate software algorithms, is electrically connected to the temperature-responsive device  24  by leads  32  and to the cooking vessel detection means  26  by leads  34 . An appropriate resonant circuit arrangement  36  of known form is suitably provided, operating in association with the control means  30  for processing signals from the inductively-operating sensing coil or loop  28  of the cooking utensil detection means  26 .  
         [0037]     The control means  30  is also electrically connected by leads  38  to the at least one heating element  18 , by way of a terminal block  40  provided at an edge of the heater  6 , and is arranged to control energising of the at least one heating element  18  from a power supply  42 .  
         [0038]     The temperature-responsive device  24  is adapted to measure small increases in temperature of the cooking utensil  10  through the cooking surface  4  resulting, for example, from a boil-dry event occurring within the cooking utensil  10  or an event in which a food product adheres to a base of the cooking utensil  10  during a cooking cycle.  
         [0039]     A further temperature-responsive device  44  may be provided, extending across the heater  6  in the cavity  22  and electrically connected to the control means  30  by means of leads  46 . Such further temperature-responsive device  44  may extend beneath and/or be combined with and/or secured in common with the temperature-responsive device  24 . The further temperature-responsive device  44  is adapted to monitor temperature of the cooking surface  4  and may monitor temperature sensed with time. Alternatively or additionally, the further temperature-responsive device  44  may be adapted to operate to cause de-energising of the heater  6  when it senses a predetermined maximum permitted temperature of the cooking surface  4 , and/or to operate to provide a predetermined set-point temperature for the cooking surface  4 .  
         [0040]     The further temperature-responsive device  44  may comprise a component, such as a platinum resistance component, whose electrical resistance changes as a function of temperature.  
         [0041]     The construction of the temperature-responsive device  24  in combination with the cooking utensil detection means  26  is shown in detail in  FIGS. 3A and 3B .  
         [0042]     Referring to  FIGS. 3A and 3B , the temperature-responsive device  24  comprises a substantially planar thin elongate substrate  48 , such as of ceramic or other electrically insulating material, having an upper surface  50  provided at a first end region  52  thereof with a temperature-sensitive electrical resistance element  54  of film form and suitably comprising platinum. The resistance element  54  may be deposited onto the surface  50  of the substrate  48  by a thick film printing technique, although other deposition techniques may be applied. The ceramic substrate  48  suitably has a thickness of from about 0.5 to 1 mm and suitably comprises alumina. A suitable electrical resistance value for the temperature-sensitive electrical resistance element  54  is from about 50 to about 1000 ohms at 0 degrees Celsius and preferably from about 100 to about 500 ohms.  
         [0043]     Electrical connecting leads  56 ,  58 , also of film form, are provided on the upper surface  50  of the substrate  48  and are electrically connected to the temperature-sensitive electrical resistance element  54 . The electrical connecting leads  56 ,  58  suitably comprise the same or similar material as the electrical resistance element  54  and extend to terminal pads  60 ,  62  provided at a second end region  64  of the substrate  48 . The terminal pads  60 ,  62  may comprise substantially the same or a similar material as the electrical connecting leads  56 ,  58  or may comprise a different material, such as gold. Holes  66 ,  68  are provided through the pads  60 ,  62  and through the substrate  48 .  
         [0044]     An elongate support member  70 , arranged as a beam, is adapted to extend at least partly across the heater  6  from a peripheral region of the heater, across an aperture or recess in a peripheral wall  72  and a rim of the dish-like support  14 , with a first end  74  of the support member  70  secured externally of the heater at the peripheral region of the heater and with a second end  76  thereof located within the heater. The support member  70  suitably comprises a ceramic material, such as steatite, cordierite or alumina, and is provided with an elongate recess  78  into which is received the substrate  48 . The temperature-sensitive electrical resistance element  54  is located at or near the second end  76  of the support member  70  within the heater  6  at a peripheral region thereof, and the terminal pads  60 ,  62  are located externally of the heater, at the first end  74  of the support member  70 , where they are subjected to a relatively low temperature.  
         [0045]     The support member  70  is shaped in such a way as to provide waist-like regions  80  which locate the support member  70  where it crosses the aperture or recess in the peripheral wall  72  of the heater  6 .  
         [0046]     Thermal insulation means  82  is provided in the recess  78  in the support member  70 , interposed between the support member  70  and a lower surface  84  and side edges  86 ,  88  of the substrate  54 . The thermal insulation means  82  preferably comprises a thin layer of microporous thermal insulation material, suitably of a thickness from 1 to 4 mm and preferably from 2 to 3 mm. Alternatively or additionally, the thermal insulation material  82  could comprise granular thermal insulation material, such as vermiculite or calcium silicate.  
         [0047]     The substrate  48  and thermal insulation means  82  may be press-moulded into the recess  78  in the support member  70 .  
         [0048]     Holes  90 ,  92  are provided through the support member  70  at the first end  74  thereof. The holes  90 ,  92  are aligned with the holes  66 ,  68  in the ceramic substrate  48  and are arranged to receive electrically connecting members  94 ,  96 , suitably comprising bolts, pins or rivets, for electrically connecting the terminal pads  60 ,  62  to terminal tabs or pins  98 ,  100  and for mechanically securing the ceramic substrate  48  to the support member  70 . The terminal tabs or pins  98 ,  100  are arranged for electrically connecting the temperature-sensitive electrical resistance element  54  to the control means  30  by means of the leads  32 . When the electrically connecting members  94 ,  96  comprise bolts, such bolts suitably comprise brass, plated with silver or nickel. When the electrically connecting members  94 ,  96  comprise rivets, such rivets suitably comprise copper, plated with gold.  
         [0049]     A thermally conducting, electrically insulating member  102 , in the form of a substantially planar tile or thin beam, may be provided, arranged to overlie and contact the temperature-sensitive electrical resistance element  54  and its electrically connecting leads  56 ,  58  at least at a region within the confines of the heater  6 . The electrically insulating member comprises a suitable ceramic material and serves to electrically insulate the temperature-sensitive electrical resistance element  54  and the connecting leads  56 ,  58  from the cooking surface  4 , which exhibits significant electrical conductivity when hot. The electrically insulating member  102  is suitably recessed into the support member  70  such that it provides an upper surface substantially coplanar with that of the support member  70 .  
         [0050]     The cooking utensil detection means  26  has its inductively-operating sensing coil or loop  28  of wire or ribbon form supported on or surrounding at least part of the second end  76  of the supporting member  70  and such that it substantially surrounds the region of the temperature-sensitive electrical resistance element  54 . The sensing coil or loop  28  is provided with opposite end regions  104 ,  106 , which are electrically connected to terminals  108 ,  110  at the first end  74  of the support member  70 . The sensing coil or loop  28  is electrically connected to the resonant circuit arrangement  36  in the control means  30  by means of the leads  34 , the leads  34  being connected to the terminals  108 ,  110  at the first end  74  of the support member  70 .  
         [0051]     A metal mounting bracket  112  is provided for the temperature-responsive device  24 . The mounting bracket  112  suitably comprises stainless steel and has a first portion  114  arranged with clip means  116  securely engaging portions  118  of the first end  74  of the support member  70 . The engaging portions  118  are suitably provided as recesses or rebates in the support member  70 . The mounting bracket  112  has a second portion  120  arranged to be secured to the rim of the dish-like support  14  of the heater  6  by means of a threaded fastener  122  passing through a hole  124  in the second portion  120  of the mounting bracket  112 . The mounting bracket  112  is suitably provided of cantilevered form from a single bent sheet or strip of metal and such that the second end  76  of the support member  70  is spring-biased towards the underside  20  of the cooking plate  4 . In this way, the upper surface of the temperature-responsive device  24  can be maintained substantially in contact and good thermo-conducting relationship with the underside  20  of the cooking plate  4 . The mounting bracket  112  may be constructed to incorporate alternative spring-loading means.  
         [0052]     The mounting bracket  112  may be adapted to support the further temperature-responsive device  44 , which may have a rod-like or beam-like sensing portion  126  adapted to be secured to the mounting bracket  112  by clip means  128  provided on the bracket and arranged to extend beneath the support member  70  at least partly across the heater  6  from a peripheral region of the heater. The further temperature-responsive device  44  is arranged to be electrically connected to and to cooperate with the control means  30  by way of the connecting leads  46 , terminal tabs or pins  130 ,  132  and electrically connecting members  134 ,  136 .  
         [0053]     The temperature-responsive device  24  operates in association with the control means  30  to monitor the temperature of the cooking utensil  10  through the cooking surface  4 . The temperature-sensitive electrical resistance element  54  is shielded from the effect of direct thermal radiation from the heating element or elements  18  in the heater  6  by the thermal insulation means  82 . A region of the cooking surface  4  immediately overlying the temperature-responsive device  24  is also shielded from the direct thermal radiation from the heating element or elements  18  and heat from the cooking utensil  10  is conducted into this region. Small changes in temperature of the cooking utensil  10  are able to be monitored by the temperature-responsive device  24  and its associated control means  30 , during a cooking cycle. Such small changes may be abnormal small changes, in particular resulting from a boil-dry event occurring within the cooking utensil  10  or from an event in the cooking utensil  10  in which a food product adheres to the base of the cooking utensil  10 . When a small change in temperature of this nature is detected, the control means  30  operates to de-energise, or to reduce the energisation level of, the heater  6  as a safety measure. The heater  6  is then arranged to remain de-energised, or at a lower energisation level, until a reset means  138 , associated with the control means  30 , is manually reset by a user of the cooking arrangement. Such a reset means  138  may, for example, be operated by a suitable button.  
         [0054]     It is important for correct operation of the cooking arrangement  2  that the cooking utensil  10  properly overlies the temperature-responsive device  24  on the cooking surface  4 , regardless of the size of the cooking utensil  10 . It is particularly important to ensure correct operation of the cooking arrangement when a small cooking utensil  10  is provided and which may be smaller than the cooking zone  8 . Here there is a risk that such a small cooking utensil may be located on the cooking zone  8  of the cooking surface  4  offset from the region under which the temperature-responsive device  24  is provided. In such a situation, false monitoring of temperature of the cooking utensil  10  by the temperature-responsive device  24  results. This situation is avoided in the present invention. The cooking utensil detection means  26 , operating with its associated circuit  36  in the control means  30 , senses placement of the cooking utensil  10  on the cooking surface  4  and functions to enable energising of the heater  6  only when the cooking utensil  10  is properly located on the cooking surface  4  overlying the temperature-responsive device  24 .  
         [0055]     The cooking utensil detection means  26  further operates as follows. If during a cooking cycle the cooking utensil  10  is removed from the cooking surface  4  by a user for a short time period, for example in order to add further contents such as additional water to the cooking utensil  10 , a rise in temperature occurs in the region of the cooking surface  4  overlying the temperature-responsive device  24 . Hitherto this would be interpreted by the temperature-responsive device  24  and the associated control means  30  as if it were an undesirable abnormal rise in temperature within the cooking utensil  10 , resulting in de-energising or the like of the heater  6 . Operation of the manual reset means  138  by the user would then be required for re-energising of the heater  6  after replacement of the cooking utensil  10  on the cooking surface  4  at the end of the short time period. This inconvenience is overcome in the present invention in that if the cooking utensil  10  is removed from the cooking surface  4  for a predetermined short time period, for example less than 5 minutes, such removal is detected by the cooking utensil detection means  26  in association with the control means  30  and the heater  6  is de-energised or the like by the control means  30 . When the cooking utensil  10  is properly relocated on the cooking surface  4  before the end of the predetermined short time period, this is detected by the cooking utensil detection means  26  and the associated control means  30  operates to automatically re-energise the heater  6 . Such re-energising is effected even if the abnormal rise in temperature resulting from the activity is included in a temperature range associated by the control means  30  with that resulting from a boil-dry event within the cooking utensil  10  or from an event within the cooking utensil  10  in which a food product adheres to the base of the cooking utensil  10 .  
         [0056]     If the cooking utensil  10  is removed from the cooking surface  4  for a predetermined long time period, for example more than 5 minutes, this is detected by the cooking utensil detection means  26 , in association with the control means  30  and the heater  6  is de-energised or the like by the control means. However, in this case, because such a predetermined long time period has been detected, when the cooking utensil  10  is relocated on the cooking surface  4  at the end of the long time period the heater  6  is arranged to remain de-energised or the like until the reset means  138  is operated by the user.