GB1598292A

GB1598292A - Method and arrangement for controlling an electric cooker

Info

Publication number: GB1598292A
Application number: GB1602578A
Authority: GB
Original assignee: Licentia Patent Verwaltungs GmbH; Licentia Oy
Current assignee: Licentia Patent Verwaltungs GmbH; Licentia Oy
Priority date: 1977-04-22
Filing date: 1978-04-24
Publication date: 1981-09-16
Also published as: DE2717888B2; DE2717888A1; DE2717888C3; FR2388450A1

Description

(54) METHOD AND ARRANGEMENT FOR CONTROLLING AN ELECTRIC COOKER (71) We, LICENTIA PATENT VER WALTUNGS G.m.b.H., of 1 Theodor Stern-Kai, 6 Frankfurt/Main 70, Federal Republic of Germany. a German body corporate, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method of digital control of the initial cooking and subsequent cooking phases of electrical cookers.

Electric cookers are already known having several cooking stations in which the desired cooking stages are set with the aid of manipulating devices; the most varied cooking stages result from a change in the resistance of the cooking station which has tappings; the number of cooking stages is thus limited. Furthermore, the fluctuations in the mains voltage of t 10% and more cause changes in the power of + 20% and more because of its quadratic dependence; time programming is not possible since, with a constant duration, the heat energy emitted by the cooking station fluctuates in the same ratio as the power; a reproducible cooking process on the other hand demands a defined emission of heat energy.

So-called control plates with mechanical sensors are also known which measure the temperature at the bottom of a pot etc.

placed on the plate, which temperature is supplied as an actual value to a controller. It is difficult to obtain perfect temperature measurement with the aid of the mechanical sensor. Incorrect measurement can easily arise owing to impurities or damage.

The invention seeks to provide a method by means of which cooking stations without controllable resistance should emit a medium constant power with a large variation range with a moderate technical expense independently of fluctuations in mains voltage. According to a first aspect of the invention, there is provided a method of controlling initial and subsequent cooking or heating phases of an electrical cooker or other heating appliances comprising producing two sets of successive digital words the value of which depends on the instantaneous value of the supply voltage, setting first and second heating contants in the form of digital words for the initial and subsequent cooking or heating phases, comparing, each set of successive digital words with a respective one of the set digital words and controlling the cooker in dependence on these comparisons.

Further according to this aspect of the invention there is provided a method for controlling an electrical cooking or like appliance powered from the mains power supply to follow a programme comprising at least an initial phase in which a predetermined total quantity of heat is to be determined, and a subsequent phase in which a predetermined average heating power is to be maintained, in which during the initial phase of plurality of digital words are derived from the instantaneous applied mains voltage, each digital word controlling the delivery of a predetermined quantity of heating power, summing the number of predetermined quantities of heat delivered comparing the sum with a first preset digital word representing the said total quantity of heat to be delivered in the initial phase and terminating the initial phase when identity between the preset digital word and the sum is detected and in the subsequent phase deriving a train of successive digital words dependent on the instantaneous applied voltage, counting these words down to zero with clock pulses, comparing the instantaneous value of these words with a second preset digital word representing a required heating power, and controlling the heating appliance to turn it on, for predetermined time periods each time identity between the second preset digital word and the successive digital words is detected.

According to a second aspect of the invention, there is provided an arrangement for controlling initial and subsequent cooking or heating phases of an electrical cooker or other heating appliance comprising means for producing two sets of successive digital words the value of which depends on the instantaneous value of the supply voltage, setting means for enabling setting of first and second heating constants in the form of digital words for the initial and subsequent cooking or heating phases, comparison means for comparing each set of successive digital words with a respective one of the set digital words and means for controlling the cooker or heating appliance in dependence on the comparison from the comparison means.

The advantage achieved by the invention consists more particularly in that solely the mains voltage supplying the cooking station is used for its control and thus special temperature sensors and controllers can be dispensed with.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which: Figure 1 shows a signal diagram during the course of control of a cooking station in the initial cooking phase and in the following subsequent cooking phase; Figure 2 shows a signal diagram of the course of control of a cooking station in the initial cooking phase with a fluctuating mains voltage; counting state and again assumes a high counting state dependent on the voltage UN and then counts down again; at the point in time t1 there is again coincidence of the words of the counter 15 and of the subsequent cooking power constant F so that the cooking station 10 is switched on; this remains switched on up to the point in time t12 and is then disconnected.The counter 15 assumes a new maximum state almost at the same point in time; with coincidence of the words of the counter 15 and the constants F the cooking station 10 is switched on again at the point in time tl3 and is disconnected at the point in time tl4.

Since the subsequent cooking phase follows the initial cooking phase, the counter 4 used for the initial cooking phase can be generally for the subsequent cooking phase after the initial cooking phase has expired.

As mentioned in the introduction, there are corresponding fluctuations in the temperature of the material to be cooked in the case of fluctuations in the mains voltage.

Mains voltage compensation is achieved in which the mean power emitted bv the cooking station is not influenced by mains voltage fluctuations as is described in greater detail together with Figures 2 and 3.

In the diagram according to Figure 2 it is assumed that mains voltage fluctuations arise in the initial cooking phase.

The rated alternating voltage (220 V-) is designated UN at a, said alternating voltage being converted into a proportional direct voltage as in Figure 1, an increased mains voltage is indicated by U1 and a reduced mains voltage is indicated by U2, corresponding to an increased or reduced direct voltage; the initial cooking energy fu2dt is plotted in b, whereby the broken line 100 (represents) the path of a non-fluctuating mains voltage and the line 101 a path which corresponds to the mains voltage in a; the predetermined initial cooking time N is designated by the horizontal chain line, in which it is assumed that a value 20 has been selected; the production of the time portions representing digital words can be seen from c; the sum of time portions formed with non-fluctuating mains voltage is shown in d and the sum of time portions formed with fluctuating mains voltage is shown in e with respect to the predetermined initial cooking time constant N; the disconnection of the cooking station 10 which is different in terms of time is shown in f.

As can be seen, the cooking station 10 is switched on at the point in time to with maximum power. If the mains voltage, and correspondingly the derived direct voltage UN, were constant, twenty time portions would be created regularly by the backward counter 4 in the time to to t4 as shown in d; the counter would always assume the same high counting state up to the twentieth time portion as is designated in c by 102; at the point in time t4 the digital word assigned to the time portion 20 would coincide with the predetermined initial cooking time constants N as can be seen from b and thus the cooking station would be disconnected.

If, however, the mains voltage fluctuates as indicated in a, then in the time to to t1 eight time portions of a certain duration are produced this duration being determined by the rated voltage present at that time; shortly before the point in time tl the mains voltage has risen and thus the derived direct voltage has also risen from Un to U1; for the time tl to t2 in which the voltage U1 is not changed ten time portions 9 to 18 are produced which have a fairly short duration in relation to the preceding time portions; in the same period of time only six time portions 8 to 14 were produced when a constant mains voltage UN was present, as can be seen from d; shortly before the point in time t2 a drop U2 in voltage has occurred whereby two time portions 19, 20 are produced which have a fairly large time duration in relation to the time portions produced in the period of time to to t1 (rated voltage UN); the time portion 20" is already achieved at the point in time t3 and thus there is coincidence of the digital words of this time portion and the initial cooking time constants N (20', 20") and the cooking station 10 is disconnected. The latter emits a predetermined initial cooking energy despite fluctuating mains voltage.

As already mentioned above, the subsequent cooking phase automatically follows the initial cooking phase. It is assumed in Figure 3 that mains voltage fluctuations also arise in this subsequent cooking phase.

If the voltage UN is present, then the counter 15 forming the time portions assumes a certain maximum counting state 103 and counts downwards therefrom; the subsequent cooking power constant F is predetermined as a digital word; when the words of counter 15 and constant F agree at the point in time tl the cooking station 10 is switchhd on; if the counter 15 assumes an equal maximum condition 103 at the point in time t2 (no change in UN) then the cooking station 10 is switched off; if at the point in time t3 there is again coincidence between the two digital words then the cooking station 10 is switched on again and if the counter 15 again assumes the same maximum condition 103 at the point in time t4 it is switched off etc.

The cooking station 10 is triggered by current clock pulses of constant duration t' and a certain period duration T.

At the point in time t5 the voltage increases from UN to U1; the counter 15, uninfluenced thereby, assumes its zero condition only at the point in time t6 and assumes a new and higher counting condition 104 immediately thereafter; thus the time duration until coincidence of the two digital words is achieved increases, i.e.

those words present at the point in time t, in which the cooking station 10 is switched on; at the point in time t8 the counter 15 again assumes the maximum condition 104 and the cooking station 10 is switched off; as can be seen, the current clock pulse i2 has the same time duration t" as the preceding current clock pulses il but a greater spacing, at the point in time t9 there is again coincidence of the two digital words and the cooking station 10 is switched on; at the point in time t1( the counter 15 assumes its maximum condition 104 and the cooking station 10 is switched off; at the point in time t11 the voltage UN is reduced to U2; the counter 15 passes to its zero counting condition; at the point in time t12 there is agreement of the two digital words and thus the cooking station 10 is again switched on; at the point in time t13 the counter 15 assumes its zero counting condition and, immediately thereafter, a new maximum condition 105, which is smaller than the rated maximum condition 103; as can be seen from the diagram the period duration T' of the current clock pulses i2 has been increased in relation to the period duration T of the current clock pulses i1 by the increased mains voltage U1.

The voltage U2, which has dropped from the point in time t11 onwards, causes the counter 15 to assume a correspondingly reduced maximum condition 105; thus coincidence of the two digital words to be compared is achieved more frequently; coincidence exists again at the point in time t14 so that the cooking station 10 is switched on; at the point in time t15 the counter 15 again assumes the maximum state 105 and the cooking station 10 is disconnected etc.

The time duration t"' of the current clock pulse i3 agrees with the preceding current clock pulses i1, i2; the period duration T" of these current clock pulses i3 is lowered however in accordance with the drop in the mains voltage.

Figure 4 shows a digital control device for a cooking station.

An analog-digital converter 1 obtains a measured direct voltage U derived from the phase voltage S, for example, and converts this into a digital word which is supplied to an arithmetic unit 2; this arithmetic unit emits a digital word which corresponds to the function (Ui-UN)2 = 2AU, whereby U1 is the measured value of the direct voltage derived from the mains voltage and UN is a digital word corresponding to the rated value (220 V) of the alternating voltage.

In order to produce the initial cooking time, the voltage difference multipled by 2 in the arithmetic unit 2 is subtracted in an arithmetic unit 3 connected thereafter from a constant corresponding to UN and the result is multiplied by a constant k; the word k (UN - 2AU) thus formed is supplied to a presettable and pulsed backward counter 4 which counts to zero from the counting state set by the digital word, as was explained together with Figures 1 and 2. With each zero counting state, the counter 4 passes a signal Z via a controllable switch 5 to a forward counter 6 connected thereafter, the counting speed of this counter 6 being determined by the counter 4 and the values k (UN-2AU) fed thereto.In accordance with the quadratic relationship between the mains voltage and the power emitted, the proportional deviation from the rated value enters twice into the calculation of the initial cooking time.

After each zero condition the presetting of the counter 4 is activated via line V and the digital work k (UN-2AU) present from the arithmetic unit 3 is taken over into the counter 4; the counter itself emits a signal via line M for interrogating the digital measured value.The initial cooking time issued by the forward counter 6 as a digital word is supplied to a comparator 7 which obtains selectable initial cooking time constants N from a program store 8 via a switch 9; as long as the value of the counter 6 is smaller than the predetermined initial cooking time constant N the comparator 7 passes a binary signal, via the line 11 to an electronic switch control 12, of such a value (L) that the cooking station 10 is connected to the alternating mains voltage; if the two compared words of the counter 6 and the store 8 coincide, then a binary signal arises at the line 13 of the comparator 7 having such a value (L) that the cooking station 10 is disconnected from the alternating voltage via the switch control 12, the switch 5 is opened and a switch 5' is closed whereby the initial cooking time control A is disconnected and there is a switchover to the subsequent cooking power control B.

The arithmetic unit 3, the counters 4, 6 and the comparator 7 with the initial cooking time store 8 form the initial cooking time control A for the cooking station 10.

Subsequent cooking power control B comprises an arithmetic unit 14, which forms a value k(UN+2AU) as a digital word, said word being supplied as a preset amount to a pulsed backwards counter 15 which counts down as can be seen from the diagrams according to Figures 1 and 3; the digital words arrive at a comparator 16 to which are supplied selectable subsequent cooking power constants F of a store 17 via a switch 9'.

After each zero counting state of the backward counter 15, presetting of the same is activated via the line V' and the word k(UN+2AU) of the arithmetic unit 14 which is present takes this over; the counter 15 itself passes a signal via line M' to the converter 1 for interrogating the digital measured value.

The comparator 16 always passes a binary signal (L) switching on the cooking station 10 via the line 18 to the switch control 12 if the digital word transmitted by the counter 15 is equal to or smaller than the digital word of the selected subsequent cooking power constant F and the comparator 16 always passes a signal (L) disconnecting the cooking station 10 via the line 19 to the switch control 12 if the digital word emitted by the counter 15 is greater than the digital word of the selected subsequent cooking power constant F.

Figure 5 shows a power control for four cooking stations 10, 20, 30 and 40, for example, which for reasons of uniform loading of the mains are divided up into two phases.

A common analog-digital converter 1 and a common arithmetic unit 2 are used for the cooking stations 10, 20; the arithmetic units 3, 14 and the counters 4, 15 in accordance with Figure 4 are provided for both cooking stations 10, 20; together; morover in each case a controllable electronic switch 5, 5' and 5", 5"' is assigned to each cooking station 10, 20 and in each case a counter 6 and 6' and two comparators 7, 16 and 7', 16- are assigned to each cooking station 10, 20, these comparators passing their signals to a switch control 12, 12' respectively.

The cooking station 10 is operated by the controls A, B and the cooking station 20 is operated by controls Al, B1.

An analog-digital converter la connected to the phase T as well as an arithmetic unit 2a and controls A9, B2 and A3, B3 agreeing with the initial cooking time controls A, Al and the subsequent cooking power controls B, B1 are assigned to the cooking stations 30, 40.

As already indicated above, the elements of the initial cooking time controls released after expiry of the initial cooking phases are used appropriately in the subsequent cooking power control (time multiplexing control).

Figure 6 shows the input of the cooking stages. A keyboard 50 is provided for the operator, this keyboard comprising an input key switch field 51 with the numbers 0 to 9 and four function keys 52 to 55 for the four cooking stations 10, 20. 30 and 40 in accordance with Figure 5; the symbol of these switches 52 to 55 indicates the respective cooking station by means of a black spot.

The circuits 102 to 105 which trigger storage are assigned to the function key switches 52 to 55, these circuits being arranged before the stores 202 to 205 for the cooking stages, the constant stores 8, 17 for the initial cooking times and subsequent cooking power are connected after these cooking stage stores 202 to 205 in accordance with Figures 4 and 5.

The mode of operation of input of the cooking stages is described in greater detail below.

Each cooking station 10, 20, 30 or 40 can be triggered by nine different power stages which cover a power range of 1 : 25.

Input of a cooking stage takes place by pressing one of the function keys 52 to 55 and subsequently inserting the desired cooking stage by pressing one of keys 1 to 9 of the input field 51; by input of a zero, a selected cooking stage is disconnected.

If for example the rear left cooking station of a cooker is to be switched on, the key switch 52 should be pressed for a short time whereby the circuit 102 is closed; all of the other circuits 103 to 105 are opened; all of the circuits are connected to the input field 51 via which an appropriate digital word reaches the cooking stage store 202, which is made available to the constant stores 8, 17 as an address, by pressing a key switch 1 to 9 corresponding to the desired cooking stage; the constant stores 8, 17 passing the constants N and F for the initial cooking time and for subsequent cooking power, which fall within the address, as digital words to the comparators 7 and 16.

If a function key switch 52 to 55 is selected and actuates the cooking stage selection via the input field 51 then the circuit 102 is again automatically opened; similarly the circuit 102 would also open if one of the key switches 53 to 55 were actuated.

Since it is possible to operate in time multiplexing operation as mentioned above already, the constant stores 8 and 17 are each present only once.

WHAT WE CLAIM IS: 1. A method of controlling initial and subsequent cooking or heating phases of an electrical cooker or other heating appliances comprising producing two sets of successive digital words the value of which depends on the instantaneous value of the supply voltage, setting first and second heating constants in the form of digital words for their initial and subsequent cooking or heating phases, comprising each set of successive digital words with a respective one of the set digital words and controlling the cooker in dependence on these comparisons.

2. A method for controlling an electrical cooking or like appliance powered from the mains power supply to follow a programme comprising at least an initial phase in which a predetermined total quantity of heat is to be determined, and a subsequent phase in which a predetermined average heating power is to be maintained, in which during the initial phase of plurality of digital words are derived from the instantaneous applied mains voltage, each digital word controlling the delivery of a predetermined quantity of heating power, summing the number of predetermined quantities of heat delivered, comparing the sum with a first preset digital word representing the said total quantity of heat to be delivered in the initial phase and terminating the initial phase when identity between the preset digital word and the sum is detected and in the subsequent phase deriving a train of successive digital words dependent on the instantaneous applied voltage, counting these words down to zero with clock pulses, comparing the instantaneous value of these words with a second preset digital word representing a required heating power, and controlling the heating appliance to turn it on, for predetermined time periods each time identity between the second preset digital word and the successive digital words is detected.

3. An arrangement for controlling initial and subsequent cooking or heating phases of an electrical cooker or other heating appliance comprising means for producing two sets of successive digital words the value of which depends on the instantaneous value of the supply voltage, setting means for enabling setting of first and second heating constants in the form of digital words for the initial and subsequent cooking or heating phases, comparison means for comparing each set of successive digital words with a respective one of the set digital words and means for controlling the cooker or heating appliance in dependence on the comparison from the comparison means.

4. An arrangement as claimed in Claim 3, and comprising an analog-digital converter for converting the mains voltage an arithmetic unit which forms the function (UI - UN)2 being connected after the analogdigital converter (Ul being the actual instantaneous value of the mains voltage and UN the rated value of the mains voltage), the digital output therefrom being supplied to an arithmetic unit forming the function k(UN - 2AU) which function is supplied to a presettable pulsed backward counter which determines the counting speed of a forward counter the counting condition of the forward counter being compared in a comparator with the predetermined initial heating constant.

5. An arrangement as claimed in Claim 4, in which in order to produce the subsequent cooking or heating phase the output 2AU) of the aritimetic unit is supplied to a further aritimetic unit forming K(UN + 2AU), the output of the said further aritimetic unit passing to a settable and pulsed backward counter the counting stage of which is compared with the second heating constant by a comparator.

6. A method of controlling initial and subsequent cooking phases of an electrical cooker substantially as described herein with reference to the drawings.

7. An arrangement for controlling initial and subsequent cooking phases of an electrical cooker substantially as described herein with reference to the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. word reaches the cooking stage store 202, which is made available to the constant stores 8, 17 as an address, by pressing a key switch 1 to 9 corresponding to the desired cooking stage; the constant stores 8, 17 passing the constants N and F for the initial cooking time and for subsequent cooking power, which fall within the address, as digital words to the comparators 7 and 16. If a function key switch 52 to 55 is selected and actuates the cooking stage selection via the input field 51 then the circuit 102 is again automatically opened; similarly the circuit 102 would also open if one of the key switches 53 to 55 were actuated. Since it is possible to operate in time multiplexing operation as mentioned above already, the constant stores 8 and 17 are each present only once. WHAT WE CLAIM IS:

1. A method of controlling initial and subsequent cooking or heating phases of an electrical cooker or other heating appliances comprising producing two sets of successive digital words the value of which depends on the instantaneous value of the supply voltage, setting first and second heating constants in the form of digital words for their initial and subsequent cooking or heating phases, comprising each set of successive digital words with a respective one of the set digital words and controlling the cooker in dependence on these comparisons.