CA1263681A - Power control arrangement for automatic surface unit - Google Patents

Abstract

PATENT - 9D-RG-16419 - Payne IMPROVED POWER CONTROL ARRANGEMENT FOR AUTOMATIC SURFACE UNIT

ABSTRACT
An improved electronic power control arrangement for a cooking appliance equipped with an automatic surface unit operable in a Fry Mode to heat a utensil to a steady state temperature range corresponding to the temperature setting selected by the user. Two error signals are established by the electronic controller as functions of the difference between the user selected temperature and the sensed utensil temperature. The controller controls energization of the automatic surface unit as a function of the first error signal during the heat-up phase to rapidly bring the sensed utensil temperature to the selected steady state temperature range and as a function of the second relatively larger error signal during operation in the steady state phase to rapidly return the sensed utensil temperature to the selected range if it should drop below the selected range during steady state operation.

Description

3L2 ~3~i~3~L PATE~r - 9D-RG-16419 - Payne -BACKGROUND OF THE INVENTION
-This invention relates generally to an improved power control arrangement for an autornatic surface unit in a co~ing appl;ance such as a dcmestic electric range. More specifically, this invention is an 5 improvement to the power control arrangement disclosed and claimed in commonly assigned U.S. Patent 4,4g3,980 to Thomas R. Payne, -~hic~ patent issued Januar~r 15, 1985.
The electronic control arrangement of the above referenced patent provides a significant improvement in the temperature control lC ~erform2 oe of automat c surrace units over tile coln~entional electromechanical sensing and control devices con~ellcionally used or such surface units. In that control arrangement the applied power level for the surface unit is adjusted as a function of an error signal which is directly proportional to the difference between the selected utensil temperature range and the sensed utensil temperature range.
This error signal is large early ;n the transient heat up phase when .
the differential is large resulting in a relatively high applied power level and goes to zero as the differential goes to zero with the applied power level diminishing accordingly. Consequently, the unit is greatly overdriven initially to heat up the utensil rapidly, but only slightly so.as the sensed temperature approaches the selected steady state temperature range to minimize overshoot. This arrangement works well for relatively small and average thermal loads. Ho~ever, for relatively large thermal loads, during steady state operation, that is operation after having initially reached the selected steady state temperature range, the utensil temperature may drop below the desired minimum steady state temperature, a condition referred to as undershoot. When such conditions occur the error signal at least ;nit1ally is relatively small, and consequently the applied power level :, .~, ' ` ~L~ 3~ L PATENT - 9D-RG-16419 - Payne for the surface unit is such that utensil temperature may be undesirably slow in returning to the selected ranye.
Therefore, it is an cbject of the present invention to provide an improved power control arrangement which will retain the rapid thermal response with minimum overshoot during the transient heat up phase provided by the arrangement of the'980 patent , yet which will provide a more rapid thermal response to undershoot conditions occurring during operation in the steady state phase.
SUMMARY OF THE INYENTIO~
.
The present invention provides an improved power control arrangelnenl for a cooking appliance -,ncorpoYatin3 an automatic ~urfare unit for which the user may select a FRY mode for heating food loads to one of a plurality of user selectable steady state temperature ranges.
The automatic surface unit ;ncludes temperature sensing means for sensing the temperature of a cooking utensil being heated on the surface unit. User operable selector means are provided, enabling the user to select one of a plurality of different temperature settings for the FRY mode, each setti~g in having associated with it a predetermined steady state temperature range defined by a predetermined minimum and maximum sensed utensil temperature. Electronic control means controls energi~ation of the surface unit in response to inputs from the temperature sensing means and the user input selector means. In accordance with the improvement of the present invention, the control means is operative in the FRY mode to generate first and second error signals, as functions of the difference between the sensed utensil temperature and the steady state temperature range for the selected heat setting. The control means operates the surface unit at an applied power level determined as a function of the first error signal during the transient heat up phase, prior to the sensed utensil .

~ L PATENT - 9D-RG-16419 - Payne temperature first reaching the selected steady state ternperature range, and operates the surface unit at an applied power level which is determined as a function of the second error signal during operation in the steady state phase after the sensed utensil temperature has first reached the selected steady state utensil temperature range. The second error signal is larger than the first error signal whereby undershoot conditions occurring during the steady state phase such as may result from a relatively large thermal load are corrected rapidly.
While the novel features of the invention are set forth ~ith particularitJ in the appYnded claims, the invention, uoth ~s to organization and oontent, will be better understood and appreciated from the following detailed description taken in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DR~IINGS
15 - FIG. 1 is a front perspective view of a portion of an electric range illustratively embodying the power control arrangement of the .
present invention;
FIG. 2 is a greatly enlarged view of a portion of the control panel of the range of Fig. 1 showing the details of one of the control knobs thereof;
FIG. 3A is a sectional side view of a surface unit of the type incorporated in the range of Fig. 1 showing the temperature sensor;
FIG. 3B is a graphic representation of the resistance Y5.
temperature characteristic for the temperature sensor of Fig. 2A;
FIG. 4 is a greatly simplified functional block diagram of the control arrangement employed in the range of Fig. 1 incorporating the power control arrangement of the present invention;
' FIG. 5 is a simplified schematic diagram of the control circuit illustratively embodying the power control arrangement of the present invention as used in the range of Fig. l;

~ 3~L PATENT - 9D-RG-16419 - Pa~ne FIG. 6 is a fla~ diagram cf the User Input Scan routine incorporated in the control prograM for the microprocessor in the circuit of Fig. 5;
FIG. 7 is a flow diagram of the Temperature Scan routine incorporated in the control program for the microprocessor in the circuit of Fig. 5;
FIG. 8 is a flow diagram of the Sensor Filter and Timing routine incorporated in the control program for the microprocessor in the circuit of Fig. 5;
lQ FIG.--~ is a ;l ~ diagram of the Fry rou~ine incorpolated in the control program of the microprocessor in the circult of Fig. 5;
FIG. 10 is a flo~ diagram of the Warm routine incorporated in the control program of the microprocessor in the circuit of Fig. 5;
FIGS. llA and llB depict the flow dlagram of the Power Compare routine incorporated in the control program for the microprocessor in the circuit of Fig. 5; and .
FIG. 12 is a flow diagram of the Pcwer Out routine incorporated in the control program of the microprocessor in the circuit of Fig. ~.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODI~EN~
Fig. 1 illustrates an electric range 10 incorporating a control arrangement illustratively embodying the present invention.
Range 10 includes four conventional electric surface units comprising resistive heating elements 12, 14, 16 and 18 supported from a substantially horizontal support surface 20. Each of elements 12-18 are adapted to support cooking utensils, such as frying pans, sauce pans, tea kettles, etc., placed thereon for heating. Heating element 12 is arranged to function as an automatic surface unit, that is, energization of element 12 is automatically controlled as a function of .

~6~3~3~ PATENT - 9D--RG-1~419 - Payne the sensed temperature of the utensil being heated thereon and the user selected heat setting. Heating elements 14, 16 and 18 may be arranged to be duty cycle controlled in conventional manner to provide a predetermined output power level corresponding to the user selected heat setting. hhile, as is common practice, the range of the illustrative embodiment is provided with only one automatic surface unit, it will be appreciated that multiple automatic surface units could be provided.
Mode selection switch 22 on control panel 24 enables the user iO t~ select the Fry Mode or the general Boil Mode for heating element 12. Manually operable rotary control knobs 26~ 28, 30 and 32 are mounted to control panel 24. Control knob 26 is illustrated in greater detail in Fig. 2. Control knob 26 enables the user to select a plurality of heat settings corresponding to various cooking temperatures for the Fry Mode, and to select Warm, Simmer and Lo, Med and~ Hi Boil Modes for the general 3Oil mode.
The utensil temperature sensing arrangement employed with the automatic surface unit in the illustrative embodiment will now be described with reference to Fig. 3A. Surface unit heating element 12 is supported on spider arms 33. The temperature sensor apparatus designated generally 34 includes a housing 36 mounted on one end of an elongated, generally L-shaped tubular arm 38.
A cylindrical shield 40 of low thermal mass meta~ forms the central core to which the radial spider arms 33 are attached and also serves to shield sensor housing 36 from radiated heat from heating element 12. Arm 38 extends through a slot 4~ in shield 40, and bears against the upper end of the slot to hold housing 36 in the proper position slightly above the element 12 so as to cause the uppermost surface 37 of housing 36 to resiliently contact the bottom of a cook;ng 8~L
9~-RG-16419 utensil when it is placed on heat:ing ele-ment 12. ~rhe temperature sensitive element (not shown) of the sensor contained within housing 36 is a conventional negative temperature coefficient thermistor having a resistance vs. temperature characteristic as shown in Fig. 3B. ~he structural details of this sensor arrangement do not form any part of the subject invention and are thus described only to the extent necessary for an understand mg of the present invention. Such devices are described in greater detail in commonly assigned U.S. Patent No. 4,241,289.
A generalized functional block diagram of the control arrangement for automatic surface unit 12 of range 10 is shown in Fig. 4.
Heating element 12 is energized by a standard 60 Hz AC power signal which can be either 120 or 240 volts supplied to terminals Ll and L2. Power to element 12 is controlled by switch -means 44. The switching device of switch means 44 is switched into and out of conduction by control signals generated by electronic control means 46.
Electronic control means 46 generates power control signals for element 12 in response to inputs from the user operable input ælection means 48 and 50 signifying mode and heat setting selections respec~ively and inputs from temperature sensing means 52 which senses the temperature of the utensil being heated by element 12.
In the illustrative embodiment, electronic control means 46 controls the output power level of heating element 12 by controlling the duty cycle, i.e., the percentage of time power is applied to the heating element. A predetermined control period comprising a fixed number of control intervals is employed as the time base for power control. The ratio of conductive control intervals to the total number of control intervals Ln the control period, expresæ d as a percentage, is hereinafter referred to as the duty cycle. Preferably each control ` ~2~3~i~31 PATENT - 9D-RG-16419 - Payne interval comprises eight full cycles of the standard 60 Hz 240 volt AC
power signal corresponding to a time period of approxirnately 133 milliseconds. Each control period comprises 32 control intervals corresponding to a time period of approximately 4 seconds. The duration for the control interval and control period selected provide a satisfactory range of heat settings for desired cooking performance and can be programmed to make efficient use of microprocessor memory. It is understood, however, that control intervals and control periods of greater and lesser duration could be similarly employed.
iO . ' ' ' TABLE I
On Control Intervals Hex Rep Power Level % On Time Per Control Period M(KB) OFF O O O
l 3

2 6.5 2 2

3 9 3 3

4 12.5 4 - 4 7 25 ~3 7 8 31.5 10 8 9 37.5 12 9 ll 50 16 B
12 62.5 20 C

14 87.5 28 ` E
loo 32 F

~L~ 3~L PATENT - 9D-RG-16419 - Payne Electronic control means 46 selectively implements one of sixteen different duty cycle power levels, including a zero duty cycle or OFF level. Table I shows the percentage ON time, i.e. the duty cycle and the number of conductive control intervals per control period for each of the available power levels.
Only the Fry mode, which is the mode implemented by the improved control arrangement of the present invention, will be described herein. A power control arrangement implementing the Boil mode is described and claimed in commonly assigned hereinbefore ïO re~erenced U.~. Patent 4,~93,980.
The Fry Mode is intended to rapidly bring the temperature of the utensil to the selected relatively narrow operating temperature range while avoiding extensive temperature overshoots and undershoots which can adversely affect co~ing performance. Relatively tight control over the steady state operating temperature of the heating element is desired in the heating of a wide variety of food loads. To this end, a relatively narrow steady state temperature range is provided for each of the Fry Mode heat settings. The temperature range associated with each heat setting for the Fry Mode ;n the illustrative embodiment is shown in Table II.
The user selects the Fry Mode by manipulation of mode switch 22. To facilitate rapid thermal response to an increase in heat setting, either from OFF or from a previously selected heat setting, the heating element is operated at a transient p~ler level determined by the electronic control means as a function of the difference between the steady state temperature range and the sensed utensil temperature when the sensed utensil temperature is less than the steady state temperature range for the selected heat setting. `

~ 3~L PATE~IT - 9D-RG-16419 - Payne The power level applied to the heating element exceeds the stead~ state power level for the selected heat setting by a number of power levels, which number of levels is a function of the difference between the sensed utensil temperature and the steady state t~mperature range for the selected heat setting. As the temperature difference approaches zero, the applied power level approaches the steady state level. By operating the heating element at relatively high power levels when the difference between the desired temperature range and the sensed utensil temperature is large, the utensil temperature 1~ ~nr~2ases rapidly. By perating the heating elemen~ at poher levels which decredse toward the s~eady state level as the sensed temperature increases toward the desired temperature range, the desired rapid thermal response is achieved with minimal temperature overshoot. For steady state operation each Fry Mode heat setting has associated with it a steady state duty cycle or power level which is intended to maintain typically loaded cooking utensils within the corresponding steady state temperature range following the transient heat-up period.
I~hen the sensed utensil temperature exceeds the steady state temperature range the heating element is de-energized.
The control arrangement described thus far is the control arrangement of the hereinbefore referenced 4,493,980 patent. The control arrangement provides very satisfactory transient heat up phase performance for all types of thermal loads. Loads are brought to the selected state temperature rapidly with minimal overshoot. However, it will be recalled that an object of the present invention is to provide improved temperature control when operating ;n the steady state phase while retaining the highly satisfactory performance in the transient phase.~ A problem particularly with large th`ermal loads such as large, heavily loaded utensils is that the utensil temperature tends to ~ i36~3~ PATENT - 9D-RG-16419 - Payne undershoot, that is drop below the selected steady state temperature range, because the normal steady state power level is insufficient to maintain the utensil temperature within the selected steady state range. When the power level is adJusted in the same manner as during the transient heat up phase, an undesirably slow response results.
More specifically, in the control arrangement of the 4,4g3,980 patent an error signal is established as a function of the temperature differential. The power level is then increased as a function of this error signal. However, the increase may not be enough to return the 10 ~ `nsil temperature to th~ desired`stead~ state-range 2S 4uickly as desired. The improvement of the present invention contemplates establishing a second error signal as a different function of the temperature differential, which weighs the differential more heavily resulting in a greater increase in the power level upon the occurrence of an undershoot condition after the steady state temperature range has initially been reached. This second error signal is employed in lieu of the first in adJusting the power level during operation in the steady state operating phase. In a preferred form of the invention the error signal is at least a factor of two larger than the first error signal and is preferably further increased by two power levels. An error signal of this re~ative magnitude, if used during the transient heat up phase, could result in an undesirably large overshoot.
However, it has been empirically determined that when this larger error signal is employed in the steady state phase with the range of the illustrative embodiment, the utensil t~mperature is rapidly returned to the selected range without overshoot. The means for implementing this arrangement in thè control of the range of the illustrative embodiment .

i2~;3~31 PATE~T - 9D-P.G-16419 - Payne is hereinafter described wi~ reference to the control program flow diagrams .

TAB LE I I
Fry Mode Stea dy Stea dy Sta te Sta te HexadecimalSelected Utensil Power Representati on Heat Temp . Level of Setting (KB) Setting Range F. M(KB) .
O ' OFF - O
. ~ Wm 116-140 2 2 Wm 116-140 200 ~91-215 7 _ 1 1 _ ~ 2 6~3Ç~3~L PATENT - 9D-P~G-16419 - Payne .
Circuit Description A control circuit illustratively implementing the improved pu~er control arrangement of the pr~ enk invention is represented in simplified schematic form in Fig. 5. Power to heating element 12 is proYided by application of a standard 60 Hz AC power signal of either 120 or 240 volts across terminals Ll and L2. Heating element 12 is connected across lines Ll and L2 via normally open relay contacts 78 of ON/OFF relay 80 and power control triac 82. Coil 84 of ON/OFF relay 80 is serially connectedjbetween DC reference voltage supply YR and ~0 system ground via ON,~'OFF switch ~. Switch 86 is mechar,;call~ coupled in conventional manner (i'iustrated schematically) to control knob 26 such that switch 86 is in its open position when control knob 26 is in its OFF position. Movement of control knob 26 from its OFF position places switch 86 in its closed position, energizing coil 84 which in turn closes associated contacts 78 thereby enabling power control triac 82 to control energization of heating element 12.
Microprocessor 72 controls the switching of power control triac 82 by trigger signals pr wided at output port R7. The trigger signal at R7 is coupled to pin 2 of opto-isolator device 88 via inverting buffer amplifier 90. Pin 1 of opto-isolator 88 is coupled to DC reference voltage supply via current limiting resistor 92 and switch 86. The output return pin 4 of opto-isolator 8~ is coupled to p~ler line L2 via current limiting resistor 94. Pin 6 is coupled to the gate terminal 82A of power control triac 82 which is connected 1n series with heating element 12. The trigger s;gnal at R7 is inverted by amplifier 90 forward biasing light emitting diode 96 of opto-isolator 88 which in turn switches the bi-polar switch portion 98 of opto-isolator 88 into conduction to apply a gate signal to pcwer control triac 82 switching it into conduction.

~ % ~3~i~3~L PATENT - 9~-RG-1641~ - Payne A 60 Hz p~llse train is generated by conventional zero crossing detector circuit 100 coupled between Ll and input port K8 of microprocessor 72 to Facilitate synchron;zation of triac triggering and other control system operations with zero crossings of the 60 Hz AC
power signal applied across Ll and L2.
Utensil temperature inputs are provided to microprocessor 72 via temperature sensing means 52 comprising a thermistor device 104 connected in parallel with linearizing precision resistor 106 and in series with precision resistor 10~ forming a voltage divider network energized bv a regulated +9 Yolt dc voltage supply. The divider network is coupled to ground through transistor Ql. The junction of thermistor 104 and resistor 108 is coupled to microprocessor input port A1. The analog voltage at this point is proportional to the temperature sensed by the thermistor. Microprocessor 72 has an internal 8-bit A/D converter which operates bet~een voltage rails AVSS
and AVDD which are set at 9 volts DC and 4 volts DC respectively by regulated voltage sources connected to input ports AYSS and AVDD of microprocessor 72, to provide a 5 volt voltage swing. The internal A/D
con~erter measures the input voltage signal at Al and converts this signal to a corresponding digital value. Table III lists representative values of the thermistor resistance, and corresponding temperature and analog voltage values. Also shown in Table III is the Hexadecimal representation of the corresponding 8 bit binary code resulting from the A/D conversion of the analog voltage values.
Transistor Q and biasing resistors 110 and 112 function as a disabling circuit. Output port R12 of microprocessor 72 is coupled to the base of Ql via resistor 110. Resistor 112 is connected between the emitter and the base of transistor Ql. The function of the disabling circuit is to only allow current flow through thermistor 10~ when ~6~3~i~3~ PATENT - 9D-P~G-1641g - Payne temperature measurements are being made. To this end, microprocessor 72 sets output R12 causing a positive voltage to be applied to the base of Ql via resistor 110 switching Ql into conduction. After the temperature input is obtained, R12 is reset rendering Ql and thermistor 104 non-conductive.

TABLE I II
TemperatureResistance Analog Yolts Hex ~ep F ~J~) _ _ .. . .
10 115 22,000 4.71 24 140 11,500 4,86 2C
165 7,600 5.04 35 190 5,000 5.33 44 215 3,300 5.63 53 15 240 23`100 6.02 67 265 1,500 6.41 7B
290 1,050 6.82 90 315 740 7.16 Al 340 560 7.47 Bl 20 365 410 - 7.77 C0 390 320 7.96 CA
415 250 8.14 D3 440 200 8.27 DA
465 150 8.45 E3 User inputs are provided to microprocessor 72 via Boil~Fry Mode selection switch means 22 and heat setting selection means 50 comprising input potentiometer 102. Mode selection switch 22 is ~2Çii;36~3~ PATENT - 9D-RG-16419 Payne directly coupled between output port R2 and input port K4 of microprocessor 72. The open and closed states of switch 22 signify selection of the general Boil Mode and Fry Mode, respectively.
Microprocessor 72 determines the state of switch 22 by periodically generating a logical high signal at R2 and monitoring the input signal at K4.
Input potentiometer 102 is coupled between regulated g volt dc and regulated 4 volt dc reference voltage supplies. Wiper arm 102A, coupled to A/D input port A2 of microprocessor 72, is positioned by user rotation of control bnob 26. The voltage between the wiper arm and the 4 vc;t supply is an analog signal representing the selected heat setting. The internal A/D converter of microprocessor 72 described briefly above for processing the temperature inputs also processes analog voltages appearing at A2 representing the user input ~5 settings.
The processing of the resultant digitized temperature and pcwer setting input signals will be described in conjunction ~ith the following description of the control program.
The follcwing component values are believed suitable ~or use in the circuit of Fig. 5. These values are illustrative only, and are -l 5-PATENT - 9D-RG-16419 - Payne not intended to limit the scope of the claimed invention.

Fixed Resistors ~IL) Transistor Ql 92 lK 2N2222 94 220 - Integrated Circuits 106 2.21K 88 MDC 3020 Integrated Circuit 108 2.21K 90 ULN 2004A Integrated Circuit ~10 22~

117 lOK
119 lOK
Potentiometer (Q ) Thermistor ( Q ) Microprocessor 104 50K 72 Texas Instruments TMS 2300 Triac 82 General Electric SC 147 Surface Unit 12 General Electric WB 30 X 218 , Control Program Description ~ croprocessor 72 is customized to perform control functions in accordance with this invention by permanently configuring the Read Only Memory (ROM) of microprocessor 72 to ;mplement predetermined control instructions. Figs. 6 through 12 are flow diagrams which illustrate the control routines incorporated in the control program of ~ $~3L PATENT - 9D-RG-16419 - Payne microprocessor 72 to perform the control functions in accordance with the present invention. From these diagrams one of ordinàry s~ill in the programming art can prepare a set of control instructions for permanent storage in the ROM of microprocessor 72. For the sake of simplicity and brevity, the control routines to follow will be described with respect to the implementation of the control algorithms of the present invention It should be understood that in addition to the control functions of the present control arrangement herein described there may be other control functlons to be performed in conjuncticn \;it" other operating c"dracterist ~s oF 'rhe app,i~nce Instructions for carrying out the routines described in the diagrams may be interleaved with instructions and routines for other control functions which are not part of the present invention.
USER INPllT Routine - Fig. 6 The function of this routine is to read in the user selected -- heat settinq input signals at input port A2 ~Fig. 5), and to determine whether Boil or Fry has been selected for the automatic surface unit.
The state of mode select switch 22 is determined by setting output R2 tBlock 130). Inquiry 132 then scans input port K4 to determine whether switch 22 is open ~K4=~) or closed ~K4=1) If K4=1, signifying selection of the Fry Mode, a Mode ~ ag is set for future reference in a subsequent routine ~Block 134). If K4=0, signifying selection of the Boil Mode, the Mode Flag is reset ~Block 136).
It will be recalled that there are 16 possible heat settings, each represented by a corresponding digital signal. The internal A/D
conversion routine provided in microprocessor 72 will convert the analog voltage at pin A2 to an eight bit digital code capable of establishing 256 levels. Sixteen wiper arm positions corresponding to 16 power settings are evenly spaced along the potentiometer, By this ~6~36~3~ PATENT - 9D-RG-1641g - Pa~ne arrangement the user selected input setting may conveniently be represented by the four high order bits of the 8 bit A/D output signal. The analog input at pin A2 i5 read in (B10ck 138) and converted to its corresponding digital signal. The four high order bits of this signal designated A/D HI are stored as the new input power setting variable KBI (Block 140). Inquiry 1~2 compares the new input KBI with input variable KB representing the previously stored power setting read in during the previous pass through the program to detect a change in setting. If KBI equals KB signifying no change in power settir,g selection, the program branches ~Block 144) to the Temp Input Routine (Fig. 7). If ~I differs from KB signifying a change in setting, the new setting is stored as KB (Block 146) and a flag designated the SS Flag utilized in the Fry routine is reset (Bloc~
148). By this arrangement the SS Flag is reset in response to each change in power setting selection. The program then branches from the User Input routine to the Temp Input routine.
.
TEMP INPUT Routine - Fig. 7 The function of this routine is to convert the analog voltage ` at pin Al representing the sensed utensil temperature to a digital signal representative of the sensed utensil temperature. More speci ff cally, this routine determines within which of 15 predetermined temperature ranges the present sensed utensil temperature falls. A
hexadecimal value is assigned to the variable SENINP (and also SENOUT) corresponding to the appropriate one of the 15 temperature ranges shown in Table IV. The hexadecimal value for the upper temperature threshold ~L PATENT - 9~-RG-16419 - Payne value for each temperature range is also included in Table IV.

TABLE IV
Hex Rep Hex Code SENINP & SENOUT Temp. Range F.Upper Threshold O T~115 24 1 115C T '140 2C
2 140 ~ T ~165 35 3 165 ~ T '190 44 4 - 190 '.T ~ 215 ~ - 53 215 ~ T ~ 240 6/
6 240 ~ T_ 265 7B
7 265 ~ T~ 290 90 8 290 ~T~ 315 Al 9 315 ~ T~ 340 Bl A 340 C T~ 365 CO
B 365 cT~ 390 CA
C 390< T ' 415 D3 D 415 ~T ~ 440 DA
E 440 ~T ~465 E3 F 465 ~T

Referring now to Fig. 7, R12 is set (Block 170~ to turn on transistor Ql (Fig. 5) thereby enabling energization of thermistor 104. Next the analog voltage representing the sensed temperature is read in and converted to its 8 bit digital representation (Block 172).
The variable TC in the f~ow diagram represents the digital value of the analog signal. Inquiries 174-202 determine the temperature range in _l g .

PATE~iT - gD-RG-1641~ - Pa~ne ~L2~3~i8~

which tne sensed temperature falls and Blocks 204-234 assign the appropriate Yalue to the temperature variable SFNINP in accor~nce with Table Y. After establishing the appropriate value for SENI~P, R12 is reset (Block 236) to turn off Ql, de-energizing thermistor 10~, and the program branches (Block 237) to the Sensor Filter and Timing routine (Fig. 8).
S~SOR FILTER and TIMING Routine - Fig. 8 This routine performs the dual function of iteratively filtering the sensor output temperature signal SENINP and also controlling the 'iming of the updating of tile tempera,ure si~nal w~ich is actually used ,n the co,trol routines yet ~o be describea~ The filter function is implemented to minimize the impact of aberrant temperature measurement inputs from the temperature monitoring circuit;
the timing function is implemented to minimize the effect of radiant energy from the heating element 12 impinging on thermistor 104 on the accuracy of the temperature measurements.
The iterative filter portion of this routine attaches relatively little weight to each individual input. Hence, isolated erroneous inputs are averaged out so as to have little effect on the accuracy of the cumulative average signal provided by the filter routine. Referring to Fig. 8, the filter function is performed by Block 238. It will be recalled that SENINP is the hexadecimal representation of the temperature ran~e for the sensed utensil temperature determined in the previously described TEMP INPUT routine.
One-sixteenth of the new SENINP input is added to 15/16 of the filter output variable designated SUM 1 from the previous pass through this routine. The resultant sum becomes the new value for the filter output variable SUM 1.

3~ ~ ~ PATE~iT - sD-RG-l6~lg - Pa~ne A new temperature input signal S~INP is processed by the filter portion o~ this routine to generate a new SUM 1, during each pass through the control routine, i.e. once every 133 milliseconds corresponding to 8 cycles of the 60 Hz power signal. However, to minimize the effects of radiant energy for heating elernent 12 on sensor 50, the sensed utensil temperature signal which is input to the power control portion of the control program is only updated during selected portions of the 4.4 second duty cycle control period.
A counter designated the ZCM counter operates as a 32 count ring courlter, counting from 0-31 and resetting to G5 In the duty cycle control implemented in the Power Compare and Power Out rGutine hereinafter described, for duty cycles less than 100~ the heating elernent is energized during the first part of the control period when the ZCM count is relatively low and de-energized while the Z~ count is relatively high. Since, except when operating at the lOOg power level, the heating element is always de-energized for count 31, radiant ener~y effects on the sensor are minimum at ZCM count 31. Thus, radiation effects are minimized by updating SENOUT, the temperature signal utilized in implementation of the Power Control routine only at count 31. It is desirable, however, to have at least two updates of SENOUT
during each 4.4 second control period, to limit oscillations between inputs. Hence, SENOUT is also updated at the midpoint of the control period, i.e. at count 16. There is potentially more error due to radiation effects for tnis measurement; however, the heating element is de-energized at this point for the eleven lower power levels. Hence, the effects of radiation even on this measurement are minimum except at the highest 4 power levels.
~ hen the heating element is operated at 100~ duty cycle, the radiation effects are the sarne at all counts; hence, for maximum , PAT~NT - 9~-RG-16419 - Payne ~ 3~ L

accuracy SENOUT is updated during each execution of the control program, i.e. every 133 milliseconds.
Referrin~ again to the flow diagram oF Fig. ~, Inquiries Z39 and 240 lo~ for ZCM counts of 16 and 31, respectively. Upon the S occurrence of either count, SENOUT is updated by the then current value of SUM 1 (Block 241). Otherwise, Inquiry 242 checks to determine if the power level presently being implemented is the 100~ power level ~M(KB)=15). If it is, SENOUT is updated by SUM 1 (Block 241) regardless of the count; if not, Block 241 is bypassed, and S~OUT is not updated during this pass. In this fashion for p~wer levels l~er than 15, SENOU~ ,s updated only on counts 16 ~}nd 31~ and when power level 15 is being implemented SENOUT ;s updated every count. Upon completion of this routine the program branches (Block 243) to the Fry routine (Fig. 9).
FRY Routine - Fig. 9 The function of this routine is to implement the Fry ~ode. It will be recalled that in accordance with the present invention, the pcwer level applied to the surface unit in the FRY Mode is established as a function of the selected temperature setting and a first error signal during the transient heat-up phase and as a funct;on of the selected power level and a second error signal during operation in the steady state phase. The appropriate power level to be applied is established in this routine. A flag designated the SS n ag is used in - this routine to ind;cate whether or not the sensed utensil has first reached the steady state temperature range for the selected temperature. The SS Flag is set on the F;rst pass through this routine after the selected steady state range is reached. The SS ~ ag is reset in the prev;ously described User Input routine ;n response to changes ;n the temperature selection.

~2~i3~;8~ PATENT - D-~G-16419 - Pa!/ne Referring na" to the flow diagra" of Fig. 9, Inquiry 382 checks for an OfF setting (K~=0). If OFF is 5elected, M(KB), the pa~er control variable utilized in the P~er Compare routine, is set to ~ero (Block 384) and the program branches (Block 386) to the Pc7tler Compare

5 routine, Fig. llA. Otherwise, Inquiry 388 determines if one of the Warm settings l~m(l ) or l~m(2) corresponding to K3 less than 3 has been selected (KB 3). If so, the program branches (Block 390) to the llarm routine, Fig. 12. Otherwise, Inquiry 392 co:npares the sensed utensil temperature SENOUT with the reference value representing the steady 1(~ state temperature range for tne selected heat setting ~ich ,s defined as (KB-l). For SENOUl greater than (KB-l), signifying that the sensed utensil temperature exceeds the selected range, Power Level zero is implemented (Block 384)~ and the program branches (Block 386) to the Power Compare routine (Fig. llA).
If the sensed utensil temperature is not greater than the desired temperature range, Inquiry 394 determines if (KB-l ) equals .
SENOUT signifying that the sensed utensil temperature is within the selected steady state temperature range. If so, the SS Flag is set (Block 396). By this arrangement the SS Flag is first set when the 20 sensed temperature first reaches the selected steady state range signifying for power control purposes, the transition from the heat up phase to the steady state phase for surface unit 12. Once set, SS
remains set unless the selected temperature setting is changed.
Next the appropriate error signal is determined. Inquiry 398 25 checks the state of the SS Flag to determine whether the surface unit is in the heat up phase (SS reset) or the steady state phase (SS set).
If SS is reset, a first error signal (ERR) is computed (Block 400~ as a function`of the difference between the desired temperature range represented by (KB-l) and the sensed utensil temperature represented by ~L~ L PATE~T - gD-P~G-16419 - Payne SENOUT, by computing the difference between KB-l and SENOUT and dividing this difference by two. If ERRl equals a fraction, it is rounded off to the next laryer integer. IF the SS Flag is not set, a second error signal (also labeled ERR) is calculated. Inquiry 401 determines if SENOUT equals KB~l, signifying that the sensed utensil temperature is in the desired steady state range. If so, the error signal ERR is set to zero (Block 402). Otherw;se, the second error signal is set equal to the difference be~ween (KB-l) and SENOUT plus a constant 2 (Block 403). By this arrangement the error signal employed ~o ~hen operatiny in the steady state phase is at least a ~actor of two greater than the error signal employed when operating in the heat up phase under undershoot conditions, that is, when the sensed utensil temperature is lo~er than the selected steady state range. As will be apparent from the following description, this results in the surface unit being operated at a power level which is at least two levels higher in the steady state phase than in the transient heat-up phase during undershoot conditions except when the error signal would result in a level higher than the maximum level of 15. Since the SS ~ ag is reset in the User Input routine (Fig. 6) each time the user selected setting is changed, the first error signal computed in Block 400 is used foll~Ying each change in power setting, until the SS ~ ag is again set as a result of the sensed utensil temperature first reaching the steady state temperature range for the newly selected heat setting.
After computing the error signal, Inquiries 404-410 determine the selected heat setting. A variable Y, corresponding to the steady state power level for the selected heat setting, is introduced in Blocks 412-420. The error signal (ERR) is summed with steady state power`level variable Y to generate a signal representing the power level to be applied, which ;s temporarily stored in the accumuiator ~63~i81 PATENT - ~D-RG-1641g - Payne (ACC) (Block 422). Inqulry 424 and Block 426 limit the maximuM value to 15 in the event the sum of ERR-~Y is greater than 15. The value stored in ACC is then transferred to M(KB) to implement the appropriate power level in the Power Cornpare routine and the program branches ~Block 394) to tne Power Compare routine (Fig. llA).
To further speed the temperature response of the system in the Fry Mode, power level 15 is implemented when the sensed utensil temperature is less than 116 F. This is implemented by Inquiry 430 which checks the sensed utensil temperature. If the sensed utensil temperature is less than 116 ~. (SENOUT=O)z ACC is set to 15 ~P'~ck 426), resulting in M(KB) being set to 15 (BLock 428), and the program then branches (Block 394) to the Power Compare routine, Fig. llA.
WARM Routine - Fig. 10 This routine is entered from the Fry routine whenever KB is less tnan 3. The function of this routine is to implement tne Warm Mode.
For heat settings KB=l and KB=2, the maximum warm temperature limit is 140 F corresponding to SENOUT=2. For KB=3, the maximum warm temperature limit is 165 F corresponding to SENOUT=3. Inquiry 432 checks for KB=l representing the Wm(l) setting. For KB=l, Inquiry 433 determines ;f SENOUT is less than 2. If not, M(KB) is set to ~ero (810ck 434) to de-energize the surface unit. If SENOUT is less than 2 signifying a sensed utensil temperature less than the maximum for K8=1, M(KB) is set to 2 (Block 435), and the program branches (Block 436) to the Pcwer Compare routine (Fig. llA).
Returning to Inquiry 432, if KB is not equal to one, Inquiry 437 determines if the sensed utensil temperature variable SENOUT is less than KB=l. If SENOUT is less than KB-l, power level 6 is implemented by setting M(KB) to 6 (Block 438). The program then branches (Block 436) to the Power Compare routine (Fig. llA).

~ L PATENT - 9D-RG-1641~ - Payne -If the sensed utensil temperature is not less than (KB-l), the program proceeds to Inquiry 439 which checks for the upper temperature limit for KB=2 and KB=3 which is represented by SENOUT=2, and 3 respectively.
If Inquiry 439 determines that the sensed utensil temperature is less than the maximum warm reference temperature for the selected heat setting (SENOUT< KB), M(KB) is set to (KB+l) (Block 440). This implements the steady state power levels 2, 3 and 4 for heat settings 1, 2 and 3, respectively, corresponding to duty cycles of 6.5~, 9~ and ~ 12.5Z, respectively ~See Tables I and II~. If the sensed utensil temperature is not ~ess than the maximum warm reference tempera~ure, M(KB) is set to O ~Block 434) corresponding to the zero or OFF pcwer level. M(KB) having been set, the program then branches (Block 436) to the Power Compare routine (Fig. llA).
POWER COMPARE Routine - Figs. llA and llB
The function of the Power Compare routine is to determine, based upon the power level designated by power level variable M(KB), whether or not the power control triac should be triggered into conduction for the next eight cycle control intervals.
It will be recalled that there are 16 possible power levels including OFF. The % duty cycle for each power level corresponds to the ratio of conductive control intervals to 32, the total nu~ber of control intervals in the control period. A ZCM counter functioning as a 32 count ring counter is incremented once for each pass through the control program. The power control decision is made by comparing the Z~l count with a reference count associated with the power level represented by M(KB). The reference count for each powe. level ~represents the number of conductive control intervals per control period corresponding to the desired duty cycle. When the ZCM count is ~2~ 1 PATENT - 9D-RG-16419 - Pa~ne less than the reference, a Power Out Latch (POL) is set, signifying that power control triac 82 is to be swi tched into conducti on;
otherwise, POL is reset, signifying that the associated power control triac is to be non-conductive.
Referring to Figs. llA and B, Inquiries 540-568 determine the value of M(KB). The appropriate one of Inquiries 572-598 corresponding to the identified M(KB) performs the comparison of ZCM to the associated reference count. If ZCM ;s 1 ess than the reference, the ~er Out Latch is set by the appropriate one of Blocks 602 and 606, siqnifying that the surface unit for which the control progr~rn is presently executing is to be energized during the next control interval. Otherwise, the PGwer Out Latch is reset by the appropriate one of Blocks 604 and 608, signifying that associated surface unit is to be de-energized during the next control interval.
Having made the power control decision, the program branches to the P~er Out Routine, Fig. 12.
POWER OUT Routine - Fig. 12 The function of the Power Out routine is to synchronize the firing of power control triac 82 with zero crossings of the 60 Hz AC
20 power signal applied across Ll and L2 (Fig. 5).
Referring now to Fig. 12, input port K8 receives zero crossing pulses from zero crossing detector circuit 100 (Fig. 5). Positive half-cycles are represented by K&l and negative half~ycles by K8=0.
Inquiry 620 determines the polarity of the present pat~er signal 25 half-cycle. If the signal is presently in a positive half~ycle, (K8=1), Inquiry 622 waits for the beginning of the next negative half~ycle, (K&O). Upon detection of K&l, the program proceeds to I`nquiry 624. If the answer to Inquiry 620 is NO (K8=0), Inquiry 634 waits for the beginning of the next positive half~ycle (K8=1), then 30 proceeds to Inquiry 624.
.

~L~ 3 3~3 PATENT 9D-RG-16419 - Payne Inquiry 624 checks the state of the Power Out Latch (POL). If POL is reset, signifying that surface unit lZ is not to be energized during the next control interval, output port R7 is reset (Block 6~6);
if POL is set, signifying that the corresponding surface unit is to be energized, R7 is set (Block 628); the program delays (el ock 630) and then returns (Block 632) to the Start Routine (Fig. 6) to repeat the control program for the next control interval.
In the illustrative enbodiment, execution of the control program uses less than one-half cycle of the power signal. The ~lrat-ion of the ~ontrol inte~val is ei-ght cycles. ~nus, 31O^k ~32 -delays the program for 15 half-cycles and then returns (Block 634) to the User Input routine to begin execution for the next control interval.
While in accordance with the Patent Statutes, a specific embodiment of the present invention has been illustrated and described herein, it is realized that numerous modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit and scope of the invention.

Claims (7)

PATENT - 9D-RG-16419 - Payne The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. In a cooking appliance of the type including at least one surface unit for supporting and heating a cooking utensil placed thereon and adapted for energization by an external power supply, temperature sensing means for sensing the temperature of a utensil supported on the surface unit, user operable input selector means enabling a user to select a FRY mode, and to select for the FRY mode one of a plurality of different heat settings, each heat setting having associated with it a predetermined steady state temperature range defined by a predetermined minimum and maximum temperature and electronic control means responsive to the temperature sensing means and the input means for controlling energization of the surface unit, an improvement wherein said electronic control means comprises:
means for establishing first and second error signals as functions of the difference between the sensed temperature and the selected steady state temperature range; and means operative to control energization of the surface unit as a function of the first error signal during the transient heat up phase prior to the sensed utensil temperature first reaching the steady state temperature range and as a function of the second error signal during the steady state phase after the sensed utensil temperature first reaches the steady state temperature range, whereby tighter control of the utensil temperature during the steady state phase is achieved while maintaining minimal overshoot in the transient heat up phase.

2. The improved control arrangement of Claim 1 wherein said first error signal is proportional to the difference between the PATENT - 9D-RG-16419 - Payne selected steady state temperature range and the sensed utensil temperature and wherein said second error signal is larger than said first error signal.

3. The improved control arrangement of Claim 2 wherein said second error signal is at least a factor of two larger than said first error signal.

4. The improved control arrangement of Claim 1 wherein said electronic control means includes means for generating a first digital signal representing the steady state temperature range associated with the selected heat setting; means for generating a second digital signal representing the sensed utensil temperature, and wherein said first error signal is proportional to the difference between said first digital signal and said second digital signal and said second error signal is at least a factor of two larger than said first error signal.

5. In a cooking appliance of the type including at least one surface unit for supporting and heating a cooking utensil placed thereon and adapted for energization by an external power supply, temperature sensing means for sensing the temperature of a utensil supported on the surface unit, user operable input selector means enabling a user to select a FRY mode, and to select for the FRY mode one of a plurality of different heat settings, each heat setting having associated with it a predetermined steady state temperature range defined by a predetermined minimum and maximum temperature, and electronic control means responsive to the temperature sensing means and the input means for controlling energization of the surface unit, an improved power control arrangement wherein said control means is PATENT - 9D-RG-16419 - Payne operative to generate a first error signal equal to one-half the difference between a signal representing the selected utensil temperature range and the signal representing the sensed utensil temperature range and a second error signal at least equal to the difference between the signal representing the selected utensil temperature range and the signal representing the sensed utensil temperature range, and wherein said control means is operative to control energization of the surface unit as a function of said first error signal prior to the sensed utensil temperature first reaching the selected steady state temperature range and as a function of said second error signal thereafter whereby the utensil temperature is rapidly brought to the selected steady state temperature range with minimal overshoot during the transient heat up phase and minimum undershoot during the steady state phase.

6. An improved method of controlling the energization of an automatic surface unit in a cooking appliance comprising the steps of:
at least periodically sampling the temperature of a utensil being heated by the surface unit and assigning it a value representative of a corresponding temperature range;
periodically computing a first error signal as a first function of the difference between a value representing the selected steady state utensil temperature range and a value representing the sensed utensil temperature range;
periodically computing a second error signal as a second function of the difference between the selected steady state utensil temperature range value and the sensed utensil temperature range value;
detecting when the sensed utensil temperature first reaches the selected steady state temperature range; and controlling energization of the surface unit as a function of the first error signal until the sensed utensil temperature first reaches the selected steady state range and as a function of the second error signal thereafter.

7. The method of claim 6 wherein the first error signal is proportional to the difference between the selected steady state utensil temperature value and the sensed temperature value and the second error signal is greater than the first error signal by at least a factor of two.