Abstract:
A toasting appliance includes a pair of elongate radiant elements, and provides relative movement between the radiant elements and the foodstuff to be toasted, so as to traverse the foodstuff with the elements, or vice versa. For faster operating speed and improved efficiency, a control circuit receives a toasting-control signal and controls a switch to energise the elements only during a portion of the amplitude of relative displacement produced between the carriage and elements, the portion being defined by the toasting-control signal. Correct movement of the elements is monitored by a control circuit that de-energises the elements when, due to a fault, one of the elements and the carriage departs from a defined velocity profile.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to toasting appliances, and more particularly to toasting appliances having elongate radiant elements, and which provide for relative movement between the radiant elements and the foodstuff to be toasted, so as to traverse the foodstuff with the elements, or vice versa. 
       BACKGROUND OF THE INVENTION 
       [0002]    U.S. Pat. No. 6,668,706 describes a toaster of the above-mentioned type, in which a pair of elongate radiant elements are arranged upright and scan back and forth across the foodstuff to simultaneously toast both sides. This arrangement provides high speed operation compared to conventional toasters incorporating planar elements. A window is provided in the body of the toaster for viewing the moving elements and the item being toasted. Owing to the regular movement required to complete each toasting cycle a visual indication is provided to the user of the remaining toasting time. While this toaster therefore offers advantages, there remains a need for improvements in the operating speed, efficiency and safety of toasting appliances of this type. It is an object of the present invention to address this need or, more generally, to provide an improved toasting appliance. 
       DISCLOSURE OF THE INVENTION 
       [0003]    According to one aspect of the present invention there is provided a toasting appliance for toasting a foodstuff, comprising:
       a carriage for supporting the foodstuff;   element means comprising either a pair of elongate radiant elements or a single elongate radiant element;   a switch controlling power supply to the element means;   a motorised drive for producing relative reciprocating displacement between the element means and the carriage in a direction substantially transverse to the element means so as to traverse the foodstuff with the element means, or vice versa;   a toasting-control signal generator for generating a toasting-control signal, and   a control circuit that receives the toasting-control signal and controls the switch to energise the element means only during a portion of the amplitude of relative displacement produced between the carriage and element means, the portion being defined by the toasting-control signal.       
 
         [0010]    Preferably the toasting appliance provides two-sided toasting simultaneously, and the element means comprises the pair of elongate radiant elements, between which the foodstuff is toasted. Preferably the elements of the pair are substantially parallel to one another, and most preferably the elements of the pair are linear. Preferably the element means is fixed at one end to the mount. Optionally, the element or elements may comprise a wire, ribbon or strip. 
         [0011]    Optionally, the toasting appliance toasts only a single-side of the foodstuff during the portion of the amplitude of relative displacement during which the element is energised, and the element means comprises only a single elongate radiant element. 
         [0012]    Preferably the toasting appliance further comprises a chassis, and the carriage is mounted for reciprocating movement relative to the chassis. Most preferably, the reciprocating movement is vertical such that the carriage is raised to eject the foodstuff. 
         [0013]    Preferably the toasting appliance further comprises a mount member reciprocated by the motorised drive, one of the carriage and the element means being mounted to the mount member, the other of the carriage and element means being mounted to the chassis. 
         [0014]    Preferably the portion of the amplitude of relative displacement during which the element is energised extends between a start position and an opposing end position, and the control circuit controls the switch to vary the start position, or the end position, between first and second spaced apart positions, according to the toasting-control signal, and controls the switch to de-energise the element means at the end position. 
         [0015]    Preferably the toasting-control signal generator comprises a user-actuable control for allowing the user to select between a plurality of discrete start or end positions corresponding to the size, or to the number, of items toasted. The user control may allow the user to select between the plurality of discrete start or end positions in a stepwise manner, alternatively the user control may allow the positions to be varied substantially continuously. Optionally the toasting-control signal generator may comprise sensors, such as optical sensors, for detecting the size or number of foodstuff items, and consequently the start or stop positions. 
         [0016]    Preferably the appliance further comprises a housing having a window through which the element means is visible. 
         [0017]    Preferably the motorized reciprocating drive comprises a reversible rotary electric motor connected to turn a screw, the mount having an internal thread engaged with the screw, and further comprising a rotary encoder in the control circuit for determining an angular position of the screw. Optionally the rotary encoder may comprise a disc portion which rotates with the screw, the disc portion comprising a regular angularly spaced array of apertures, and a cooperating optical emitter and receiver on opposing sides of the disc portion. The disc portion may be a portion of a gear arranged for transmitting torque between the rotary electric motor and the screw. 
         [0018]    Preferably the screw extends upright, and the carriage is mounted on a guide fixed to the chassis to move up and down in use, the screw and guide being disposed at opposing ends so the carriage, the appliance further comprising a spring for urging the carriage upwardly and an electromagnetic latching mechanism for holding the carriage in a lowered position. 
         [0019]    Preferably the elements are fixed to the mount member such that the motorized reciprocating drive reciprocates the pair of elements, and the carriage is secured to the chassis by a guide which restrains the carriage to reciprocate linearly relative to the chassis. Alternatively, if the carriage is fixed to the mount, the pair of elements may be fixed to the chassis, such that the motorised reciprocating drive reciprocates the carriage. 
         [0020]    In another aspect the invention comprises a toasting appliance for toasting a foodstuff, comprising:
       a carriage for supporting the foodstuff;   element means comprising a pair of elongate radiant elements or a single elongate radiant element;   a switch controlling power supply to the element means;   a motorized drive for producing relative reciprocating displacement between the element means and the carriage in a direction substantially transverse to the element means so as to traverse the foodstuff with the element means, or vice versa;   a control circuit that controls the switch to energize the element means only during a portion of the amplitude of relative displacement produced between the carriage and element means, and that controls the motorized reciprocating drive for producing the relative reciprocating displacement according to a velocity profile, and   monitoring means in the control circuit for monitoring the motorized reciprocating drive to provide a safety interlock whereby the control circuit de-energizes the element means when the monitoring means indicates that the relative reciprocating displacement has varied from the velocity profile.       
 
         [0027]    Preferably the motorised reciprocating drive includes a rotary DC electric motor for moving one of the elements and the carriage, and the monitoring means comprises a rotary encoder. 
         [0028]    Optionally, the motorised reciprocating drive includes a stepper motor for moving one of the elements and the carriage, the stepper motor having an open loop driver and the monitoring means comprising a feedback from the open loop driver to the control circuit. 
         [0029]    Preferably the velocity profile comprises a constant velocity and a power output of the elements is maintained substantially constant. Optionally, the velocity profile comprises a variable relative velocity between the carriage and element means, and element power is varied in a compensatory manner in proportion to the variable velocity. 
         [0030]    Preferably the elements of the pair are linear and parallel. Preferably radiant power output per unit length of the element is substantially constant throughout the length of the elements. 
         [0031]    In yet another aspect the invention comprises a single pass method of toasting a foodstuff, comprising:
       receiving a toasting-control signal;   adjusting one of a start position setting and an end position setting according to the toasting-control signal, the start position setting and end position setting defining a start position and an end position respectively;   energising element means comprising a pair of elongate radiant elements or a single elongate radiant element;   actuating a motorised reciprocating drive to move one of the energised element means and the foodstuff linearly relative to the other of the energised element means and the foodstuff from the start position to the end position, so as to traverse the foodstuff with the energised element means, or vice versa; and   de-energising the element means in the end position.       
 
         [0037]    Preferably the element means are energised only during a portion of an amplitude of relative displacement produced between the foodstuff and element means, the portion being defined by the toasting-control signal. 
         [0038]    By energising the element means only during a portion of the amplitude of relative displacement by adjusting one of the start position and end position according to the toasting-control signal an energy-efficient and flexible toasting method is provided, particularly suitable for toasting foodstuffs of varying sizes, as well as toasting a varying number of items. 
         [0039]    Preferably the method further comprises manually actuating a user control to generate the toasting-control signal. Optionally sensors, such as mechanical or optical sensors, for detecting the size or number of foodstuff items may generate the toasting-control signal. 
         [0040]    The user control may allow for the user to select between a plurality of discrete start or end positions. Alternatively, the user control may allow for the user to select between a plurality of discrete start and end positions. 
         [0041]    Preferably the motorized reciprocating drive moves the one of the elements and the foodstuff linearly at a substantially constant velocity, and a power output of the elements is maintained substantially constant. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]    Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: 
           [0043]      FIGS. 1 and 2  are perspective views from opposing sides of a toaster according to an embodiment of the invention; 
           [0044]      FIG. 3  is a perspective view of the toaster of  FIGS. 1 and 2 , with an outer part of the housing removed; 
           [0045]      FIG. 4  is a schematic drawing of the motorised reciprocating drive of the toaster of  FIGS. 1 and 2 , and 
           [0046]      FIG. 5  is a schematic drawing of the control circuit of the toaster of  FIGS. 1 and 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0047]    Referring to  FIGS. 1 and 2 , a toaster according to the invention comprises a housing  10  at the top of which is a slot  11  for receiving a foodstuff such as a slice of bread. The slot  11  extends generally between longitudinally opposing first and second ends  22 ,  23  of the toaster. The foodstuff is supported upon a carriage  12  visible through windows  15 ,  16  that are disposed in opposing sides of the housing  10 . The toaster is of the pop-up type, with a carriage  12  mounted upon an upright guide  50  at the first end  22 , allowing the foodstuff to be lowered for toasting, and automatically raised upon completion of toasting. The carriage  12  may be of a cantilever type, being supported only on the upright guide  50  and extending horizontally to support the foodstuff in a cantilevered manner. A spring  14  is connected at one end to the carriage  12  and at the other end to the chassis  17 , so as to urge the carriage  12  upwardly. A handle  13  projecting from an upright slit in the housing is provided for lowering the carriage  12 . The toaster may incorporate an electromagnetic latching mechanism (not shown) for holding the carriage  12  in its lowered toasting position, and releasing the carriage  12  upon completion of toasting. 
         [0048]    Two radiant elements  20 ,  21  may be linear, and extend parallel to one another along either side of the slot  11 . The pair of elements  20 ,  21  are spaced apart sufficiently for the item to be toasted to pass between them. One longitudinal end of each of the elements  20 ,  21  may be fixed at the second end  23  to a mount  24 , supporting the elements  20 ,  21  in a cantilevered manner. The elements  20 ,  21  may be of tubular form, with reflectors (not shown) for focussing the radiant energy inwardly, toward the slot  11  and the item to be toasted, and away from the windows  15 ,  16 . The power output of the elements is maintained substantially constant and power output per unit length of the elements is substantially constant throughout the length of the elements  20 ,  21 . As shown, both elements  20 ,  21  lie generally in a horizontal plane. 
         [0049]    A screw  28  is mounted upright, with its opposing ends supported in journals (not shown) provided in the chassis  17  allowing the screw to turn about its longitudinal axis. The mount  24  may include an internal thread engaged with the screw  28  for reciprocating the mount  24 . The mount  24  may include clamping fixtures  60  for holding ends of the elements  20 ,  21 . The mount  24  is restrained by upright surfaces  61  so as to move up and down without rotation. 
         [0050]    As shown in  FIGS. 3 and 4 , a motorised reciprocating drive for turning the screw  28  comprises a reversible DC motor  29  connected by a gear train  30  to transmit torque to the screw  28 . The gear train  30  may comprise an output pinion  32  fixed on the motor output shaft and a driven gear  34  fixed to rotate with the screw  28 , with three intermediate gears  33   a,    33   b,    33   c  transmitting torque between the output pinion  32  and driven gear  34 . Each of the intermediate gears  33   a,    33   b,    33   c  may comprise integral large and small diameter wheels for providing a speed reduction, for instance with the large diameter wheel of intermediate gear  33   a  being meshed with the output pinion  32 , the small diameter wheel of intermediate gears  33   c  meshed with the driven gear  34 , and with the respective small and large diameter wheels of the intermediate gears  33   a,    33   b,    33   c  meshed together. Of course this gear train  30  is only an example, and many other combinations achieving a speed reduction and torque multiplication may be used. 
         [0051]    In  FIG. 4 , the elements  20 ,  21  are shown at a position  300 , intermediate upper and lower limits of travel, indicated by the dashed outline of the elements at  100  and  200  respectively. The amplitude A of displacement of the elements  20 ,  21  is the distance between the upper and lower limits  100 ,  200 , while portion B illustrates a portion of the travel (upward from the lower limit  200 , for instance) during which the elements  20 ,  21  are energised. 
         [0052]    A rotary encoder  40  may be provided for feedback for defining the position of the elements  20 ,  21 . The rotary encoder  40  may comprise a regular angularly spaced array of apertures formed as in the driven gear  34  and a cooperating optical emitter  42  and receiver  43  on opposing sides of the driven gear  34 . 
         [0053]    User controls on the housing may include an array of colour-control switches  47 , each with a respective illuminated indicator such as a light-emitting diode (LED)  48 . The colour-control switches  47  may be used to define different toasting cycles, or toasting colours. The LEDs  48  serve to indicate the selected toasting cycle. The colour-control switches  47  may be push-to-make switches, and a respective LED  48  may be illuminated at one time to indicate the selected colour-control button  47 . The colour-control switches  47  may provide a toggle action, and two adjacent LEDs  48  may be simultaneously to indicate a toasting cycle setting between that defined by two adjacent switches  47 . 
         [0054]    An eject button  49  can be used to terminate toasting. The eject button  49  may also be a push-to-make switch. 
         [0055]    A rotary toasting-control switch  51  can be adjusted to make a selection corresponding to the size of the item to be toasted, in the manner described below. The toasting-control switch  51  may allow continuously variable size selection, or selection in a stepwise manner as between detent positions, each detent position corresponding to a size of item to be toasted. 
         [0056]    As shown in  FIG. 5 , the rotary encoder  40  is connected in a control circuit  45  to a microcontroller  46  which controls the toasting process. The microcontroller  46  also receives inputs from the colour-control switches  47 , the toasting-control switch  51  and the eject button  49 . The control circuit  45  further comprises a power input  52  connected to a relay  53  and rectifier circuit  54  for providing DC power to the component other than the elements  20 ,  21 . A flexible coupling  55  provides power to the moving elements  20 ,  21  via the relay  53 . A motor controller  56  connected to the motor  29 , controls the speed and direction of the motor  29  according to an output from the microcontroller  46 . The control circuit  45  includes a start switch  57  actuated by lowering the carriage to the toasting position, and a solenoid  58  of the electromagnetic latching mechanism, the solenoid  58  being actuated to latch and hold the carriage  12  in its lowered toasting position, and de-actuated to release the carriage  12  when the toasting cycle is completed. A position switch  59  is actuated by the mount  24  when the mount  24  is in a predefined starting position, such that the signal from the rotary encoder  40  can be used to define any position of the mount  24  relative to the starting position. 
         [0057]    In use, the item to be toasted is dropped through the slot  11  onto the carriage  12 , the user then pushing down the handle  13  to lower the carriage  12 . The start switch  57  is actuated, as by contact with the mount  24 , when carriage  12  in its toasting position, and the microcontroller  46  then energises the latching solenoid  58 , to latch down and hold the carriage  12  in position, allowing the handle to be released by the user. The toasting cycle is started by the microcontroller  46  sending a signal to the motor controller  56 , to drive the motor  29  at high speed to move the mount  24  and attached elements  20 ,  21  to their lowermost position  200 . The position switch  59  provides an output to the microcontroller  46  indicating that the mount  24  and elements  20 ,  21  are in the lowermost starting position  200 , and initialising a counter in a register in the microcontroller  46 . The microcontroller  46  may actuate the relay  53  to energise the elements  20 ,  21  before the position switch  59  indicates that the mount  24  and elements  20 ,  21  are in the starting position  200 , whereupon the elements  20 ,  21  are rapidly brought up to operating temperature. Optionally, a short pause may to allow the elements to reach operating temperature. 
         [0058]    The colour-control switches  47  and toasting-control switch  51  can be actuated before, or after, these initial operations to start the toasting cycle if the user wishes to vary the toasting cycle from default values. Default values may include an intermediate colour setting for the colour-control switches  47  and a maximum setting on the toasting-control switch  51 . In the maximum setting of the toasting-control switch  51  the elements  20 ,  21  are energised for the full duration of their upward travel of amplitude A. Memory in the microcontroller  46  stores a plurality of predefined toasting cycles, each defining a respective constant motor speed. Depending upon the default or user-selected toasting cycle selected by the colour-control button  47 , the microcontroller  46  looks up a corresponding motor speed. 
         [0059]    The motor  29  is then driven at the looked up motor speed to raise the energised elements  20 ,  21  at a constant velocity. The toasting proceeds in a single pass of the foodstuff by the elements  20 ,  21  during which the counter is incremented by the output of the rotary encoder  41 . Toasting may be interrupted by the user actuating the eject button  49 , whereupon the microcontroller  46  simultaneously cuts power to the elements  20 ,  21 , the motor  29  and the latching solenoid  58 , the carriage then automatically rising to eject the foodstuff. 
         [0060]    During the pass of the elements  20 ,  21  the microcontroller  46  monitors the output of the rotary encoder  41  to provide a safety interlock, whereby if the output of the rotary encoder  41  indicates that the movement of the elements  20 ,  21  has stopped, or departed from the velocity profile, the microcontroller  46  then opens the relay  53  to de-energise the elements  20 ,  21 . Monitoring the proper movement of the elements  20 ,  21  in this manner mitigates potential safety problems, such as the possibility that, due to a fault such as jamming or failure of the reciprocating drive, the item being toasted could be burned, or even catch fire. 
         [0061]    Different toasting-control signals are received by the microcontroller  46  depending upon the position of the toasting-control switch  51 . The toasting-control signal defines a counter value for an end position setting i.e. the value to which the counter is incremented by the time that the elements  20 ,  21  reach the end position  300  at which the selected scanning movement is to be completed. The microcontroller  46  monitors the counter, and when the microcontroller  46  determines that the counter has reached the counter end position setting, then the relay  53  is opened by the microcontroller  46  to de-energise the elements  20 ,  21  and the latching solenoid  58  is released, completing the toasting cycle and allowing the now toasted item to pop up. With respect to  FIG. 4 , the counter end position setting may require the energised elements  20 ,  21  to be raised to end position  300  for toasting a smaller item. When the elements  20 ,  21  reach the end position  300 , the elements  20 ,  21  have moved a portion B of their maximum travel, or displacement amplitude A. 
         [0062]    By providing windows  15 ,  16  the user is able to observe the toasting operation, and he may also intervene. For instance, by actuating the colour-control switches  47  during movement of the elements  20 ,  21  the toasting colour can be varied across the item being toasted. Likewise, if the default setting of the toasting-control switch  51  is too high, the user can turn the toasting-control switch  51  to reduce the setting (and toasting time) when he observes that the item to be toasted has been traversed, thereby immediately terminating toasting. 
         [0063]    By varying either end  300  in the manner described, or by varying the start position  200 , according to the toasting-control signal from the toasting-control switch  51 , smaller size items are toasted more quickly than larger ones, and power is saved due to the elements  20 ,  21  scanning only the portion B of the amplitude A and being prevented from scanning beyond the limits necessary to toast the selected item. Likewise, for instance, in a toaster able to simultaneously toast two or more items sequentially, when it is desired to toast only a single item the start or end position may be selected so as to avoid wastefully scanning across empty space adjacent to the single item. 
         [0064]    Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof. For instance, it will be plain that the carriage may be driven relative to the elements to provide the requisite relative movement, and that the elements may extend vertically instead of horizontally.