GB2105974A - Improvements in or relating to electric toasters - Google Patents

Abstract

An electric toaster (1) has the duration of a toasting operation determined by an integrated circuit timing device. The device has a manual control (6) enabling a user to set the device to measure a toasting operation of a required duration, and another manual control (7) enabling a user to terminate a toasting operation before the end of a set duration. The device produces an output used to energise an electromagnet at the beginning of a toasting operation to hold a toast platform in a toast position. The output terminates at the end of the set duration or earlier if the user actuates the other control. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electric toasters This invention relates to electric toasters which have at least one compartment into which a slice of bread to be toasted is inserted and which contains a platform that supports the slice. When moved against one or more springs, the platform brings the slice into close proximity to electric radiant heating elements which toast that slice.

Conveniently, the period of time during which toasting takes place is determined by a bimetal strip exposed to the temperature in the or one of the toasting compartments. The bimetal strip is arranged to release the platform at the end of the period and to de-energise the heating elements. A manual control is normally provided which gives a user some control over the toasting period.

The arrangement just described is not entirely satisfactory. The same setting of the manual control does not ensure consistent results and, in many cases, the range of variation provided by the manual control is inadequate.

It has also been proposed to employ electronic devices to control the duration of the toasting period. Such devices employ some form of timer which is set into operation when the platform is positioned at the commencement of toasting and which relases the platform and de-energises the heating elements at the end of a preset period. A manually-operable control is provided to enable a userto set (within limits) the toasting period.

Such devices as have been proposed do not meet fully the requirements of an effective toaster and, in some cases, have been expensive to manufacture.

It is an object of the present invention to overcome the disadvantages referred to above.

According to the present invention, an electric toaster having a platform for supporting a substance to be toasted includes a Type 555 or equivalent integrated circuit timing device, means for initiating operation of the device at the commencement of a toasting period, a platform retaining device for retaining the platform in a "toast" position, said retaining device being controlled by the timing device to hold the platform in a "toast" position at the commencement of a toasting period and to release the platform at the end of that period, a manually-operable control for setting the duration of the toasting period, and a further manually-operable control for terminating a toasting operation before the end of the set toasting period.

Preferably, the further manually operable control operates to apply a terminating signal to the timer.

In one embodiment of the invention, the timer is energised from tapping points on one of the heating elements. The tapping points are so arranged to supply the low voltage input required by the timer.

The platform retaining device may comprise an electromagnet which co-operates with an armature forming part of or secured to the platform. Preferably, the electromagnet is energised from the timer.

By way of example only, an electric toaster embodying the invention will now be described in greater detail with reference to the accompanying drawings of which: Fig. 1 is a perspective view of the toaster, and Fig. 2 is a circuit diagram of a control unit.

Fig. 1 shows, in diagrammatic form only, a "pop-up" toaster 1 of conventional external appearance. The toaster has two internal compartments for receiving slices of bread to be toasted, the compart ments being accessible via slots 2 in the upper surface 3 of the toaster. Within the toaster are the conventional radiant heating elements, there being one between the compartments and one on each outside compartment face.

Movable up and down in each compartment is a platform, the two platforms being linked together for movement, in a downward direction, by a finger plate 4 located on one end face of the toaster 1 and joined to the linked platform through a slot 5 in the end wall. Downward movement of the linked platforms takes place against springs located within the toaster.

The duration of a toasting period is determined by the control circuit shown in Fig. 2. The principal component of the circuit is an integrated circuit IC1 typically a Type 555 timer, for example the NE555P manufactured by Texas Instruments or the type MC1555 manufactured by Motorola Inc., connected to operate as a monostable RC timer. Pin 1 of the IC1 is grounded and a control voltage of 12v derived from suitable tapping points on one of the radiant heating elements-for example one of the outer one and rectified and smoothed by diode D1 and capacitor C1 respectively is applied to pin 8.

The timer is triggered by voltage pulse applied to pin 2 and derived from the mid-pointofthe resistor capacitor combination R1, C3.

IC1 is arranged to power, on output pin 3, the coil HM of an electromagnet suppression diodes D2 and D3 being connected as shown to protect the integrated circuit from voltage peaks that arise before and afterenergisation and de-energisation of the coil HM.

Pin 4, the "reset" input, is connected via resistor R2 to the main rectified low voltage power line and via interrupt switch SW to earth.

Discharge and threshold pins 6, 7 are both connected to the junction of thermistor T- and capacitor C2, T1 and C2 being in series connection with potentiometer P1 across the main rectified low voltage supply.

Pin 5-the control voltage pin-is left "floating" but could, alternatively, be decoupled to earth via a capacitor of suitable value if more accurate control of the threshold voltage of l.C.1. is required.

Potentiometer P1 has a manual control knob 6 mounted on an end face of the toaster 1 below the lower limit of movement of the finger plate 4. A push button 7 positioned on the same end wall adjacent the knob 6 actuates the interrupt switch SW. The switch SW is spring biassed to its "OFF" position.

The thermistor T1 is of the NTC type and is located in one of the toasting compartments thereby sensing the temperature in the latter and reducing, in a corresponding manner, the time taken to charge capacitor C2. in parallel with thermistor T1 is a resistor R3 which has the effect of "containing" the effect of the resistance of the thermistor. During low ambient temperatures, the initial resistance of the thermistor can reach a high value so increasing toasting time to an unacceptable level.

Also located within the toaster housing is a two-pole switch that controls energisation of the radiant heating elements via a power lead not shown in Fig. 1. The switch is linked to movement of the linked platforms in such manner that downward movement of the platforms at the commencement of a toasting operation closes the switch to energise the elements, whilst upward movement of the platform at the end of a toasting period opens the switch to de-energise the elements.

Coil HM has a core (not shown) which co-operates with an armature carried by the linked platforms.

The core is so positioned that when the finger plate 4 is depressed to lower the platforms, the armature contacts the core when the platform reaches the lower limit of its travel.

The components shown in Fig. 2 are mounted on a printed circuit board itself positioned within the toaster adjacent the end wall carrying the knob 6.

To use the toaster, it is first connected to the mains supply and a slice of bread is dropped into one or other or both of the slots 2. The finger plate 4 is then pushed down. That action closes the switch controlling the energisation of the radiant elements, and, via the tapping points on the one element 1 2v is applied to pin 8 and to the resistor-capacitor combinations P1,T1, C2, and R1, C3. As C3 charges up, a trigger voltage is applied to pin 2 which sets a "flip-flop" inside IC producing an output on pin 3 which energises coil HM and this holds down the linked platforms at the lower limit of their travel.

Capacitor C2 gradually charges up to a value determined by the setting of P1 and the value of T1 until the voltage on C2 reaches a value equal to a threshold voltage determined by the resistor chain within IC1. At that point, a comparator in IC1 resets the flip-flop and terminates the output on pin 3 so de-energising HM. That releases the platforms which travel upwardly underthe spring and which then open the switch controlling the energisation of the heating elements.

The rate of charging of capacitor C2 and hence the duration of the toasting period is present by the user by adjustment of P1 by meanss of knob 6 so that, at the end of the toasting period, the slices have acquired a required degree of "brownness': If, at any time during a toasting period, the user wishes to terminate the toasting process, button 7 is depressed to close switch SW. This resets the flip4lop and terminates the toasting process in the manner described above.

It will be appreciated that when only a single slice of bread is to be toasted, the slice may be dropped into either of the slots 2.

The invention can also be embodied in toasters able to toast more than two slices of bread at the same time. Such toasters may, for example, be built-up in units of two each unit having its own timing control as described above or a single timing control only may be used.

The invention can also be embodied in the so-called "serve sideways" electric toasters.

Claims (12)

1. An electric toaster having a platform for supporting a substance to be toasted, a type 555 of equivalent integrated circuit timing device, means for initiating operation of the timing device at the commencement of a toasting operation, a platform retaining device for releasably retaining the platform in a "toast" position, said retaining device being controlled by the timing device to hold the platform in a "toast" position at the commencement of a toasting operation and to release the platform at the end of a toasting operation, a manually-operable control for setting the duration of the toasting operation, and a further manually-operable control for terminating a toasting operation before the end of a set duration.

2. A toaster as claimed in claim 1 in which operation of the further control applies a terminating signal to the integrated circuit.

3. A toaster as claimed in claim 2 in which the furrther control comprises a switch interconnected between a reset terminal of the integrated circuit and ground.

4. A toaster as claimed in claim 1, 2 or 3 in which the platform retaining device comprises an electromagnet and a co-operating armature.

5. A toaster as claimed in claim 4 in which the armature is carried by the platform and in which the electromagnet is powered by the integrated circuit and is energised at the commencement of a toasting operation and is de-energised at the end of the set toasting period, and is also de-energised in the event of operation of the further control.

6. A toaster as claimed in any one of the preceding claims in which the timing device is powered from tapping points located on a heating element of the toaster.

7. A toaster as claimed in claim 6 in which the means for initiating operation of the timing device comprises a switch that controls energisation of the heating element.

8. A toaster as claimed in any one of the preceding claims and including means respective to the temperature in the toasting position within the toaster and operable to modify the duration of a set toasting period in accordance with the sensed temperature.

9. A toaster as claimed in claim 8 in which the temperature responsive means comprises a NTC resistor.

10. A toaster as claimed in claim 9 in which the NTC resistor is shunted by a further resistor of such resistance as to "contain" the resistance of the NTC resistor as herein described.

11. An electric toaster comprising a platform for supporting a substance to be toasted, a type 555 or equivalent integrated circuit timing device, an electromagnet powered by the timing device and energised thereby at the commencement of a toasting operation, an armature carried by the platform and co-operating with the electromagnet to retain the platform in a "toast" position at the commencement of a toasting operation, an electric heating element for toasting the substance, tapping points on said element connected to the timing device for powering the latter, switch means operable by the platform when moved into the "toast" position to permit energisation of the element, a manually-operable control for setting the duration of the toasting operation and a further manually-operable control for applying a reset signal to the timing device to terminate a toasting operation before the end of the set duration by resetting the timing device which de-energ ises the electromagnet.

12. An electric toaster substantially as hereinbefore described with reference to and as illustrated by the accompanying drawing.