CA1294311C

CA1294311C - Power control for appliance having a glass ceramic cooking surface

Info

Publication number: CA1294311C
Application number: CA000581472A
Authority: CA
Inventors: Thomas Roy Payne
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1987-11-13
Filing date: 1988-10-27
Publication date: 1992-01-14
Anticipated expiration: 2009-01-14
Also published as: GB2212303A; FR2623356B1; KR970003212B1; IT1229948B; JPH01206590A; DE3837096C2; FR2623356A1; JP2878698B2; IT8822615A0; US4816647A; GB2212303B; KR890009219A; GB8826466D0; DE3837096A1

Abstract

IMPROVED POWER CONTROL FOR APPLIANCE HAVING
A GLASS CERAMIC COOKING SURFACE

ABSTRACT
An improved power control system for a household cooking appliance of the type having a glass ceramic cooking surface and at least one radiant heating unit disposed beneath the cooking surface operable at a plurality of user selectable power settings. At least one of the power settings has associated with it predetermined maximum and minimum reference temperatures defining a temperature band representative of the steady state temperature range for the glass ceramic support surface proximate the heating unit when heating normal loads at that power setting. The power control system includes an arrangement for sensing the temperature of the glass ceramic cooking surface proximate the heating unit and is operative to operate the heating unit at a power level other than the power level corresponding to the user selected power setting when the sensed glass ceramic support surface temperature is outside the predetermined reference temperature band associated with the selected power setting to more rapidly bring the temperature within the band and thereby causing the heating unit to respond quickly to changes in user selected power setting.

Description

~ 9~-MA-17021 I~PROV~D POWER CONTROL FOR APPLIANCE AAVING
A GLASS CERl~'~IC COOKING SURFA OE
BACRGROUND OF T~E INVENT~ON
~hls lnventlon relates geDerally to gla~ cera~ic cooktop appliances and partlcularly to electronlc power control 6ystem~ for such appllances.
S Commonly asslgned co-pendlng Canadian Patent Application Serial No. 559,189, filed February 18, 198R, by Payne et al, discloses a coolctop appliance equipped with hea~lng unlts ~hlcn rad~ate substantlally ln thc lnfrarcd reglon ~1-3 mLcrons) in comblnation with a glass cera~ic cooktop supporr sur~ace whlch ls ~ubstantlally transparent to lnfrared ratlatlon. Utenslls placed on the cooktop surface are hcat-d prlmarlly by radlatlon dlrectly ~rom the heatlng unit rather than by conduction from the glass ceramic ~aterlal. Though the glasA cera~ic is substantlally transparent to ehe rat~atlon, a portlon of the encrgy ratiatlng from the heating unit ls a~sorbed by the glasfi cer~ic, as ls a portion of the eDergy reflected by the utensll belng heated. a..~ transfer fro~
the glass ceramlc is primarily by conductlon to the utensll.
The pover control system dlsclosed ln the afor mentlonet Payne et al appllcation, using gLass cera~lc CeYperaeUre ~nformatlon derlved from a temperature sen~or located dlrectly o~er each heatlng unlt contro1s the output powcr of esch hcatlng unlt to protect the glass ccra~lc agalnst overhcatlng cau8e~ by abnormal loat condlt~ons 6uch as operatlng the unlt wlth no ueensl1 present, use of badly ~arped utenslls, or he-tlng an empty utensil.
~ that arrangemcnt ~he temper~ture mc-Jurcoen~s are obtained by measurlng the reslstanc- of the bottom surfacc of the glSJ8 ceramlc ~aterlal abo~e ehe heatl3g unlts. The tccperature lnformat~on so obtalned ls sufflclently accurate for protectlng the glass cer~m1c agalnst overheatlng.

PA~E~ - 9D-MA-170Zl - Payne 1~J~ 3~
Slnce radlatlon ls the prlmary heat transfer mechanlsm for utenslls belng heated on such cooktops, the syE~tem responda more qulckly to changes ln user selected power settlngs than the conventlonal cooktops relylng on conductlon heatlng. However, the thermal inertlal of the glass cera~ic materlal results in 8 slouer response than that achlevable with closed loop automatlc surface unlt systems which measure utensll temperature d~ret:tly and control the output power of the heatlng unlt to achleve and maintaln the user selected utens~l temperature. Inherent lnaccuracies in thls temperature measurement system due to the temperature gradient through the glass ceramic materlal, the temperature gradlent from the top of the glass ceramic material to the bottom of the potentially warped pan, and other sources of error, render thls temperature sensor arrangement lncompatlble wlth such closed loop systems. Locating a sen60r to directly sense utensll temperature would add cost and complexlty to the manufacturing process and by protruding above the cooktop would negate at least to some extent the appearance and cleanability advantages of the smooth cooktop surface. Hence, there exists a need for a control arrangement which provides a faster response to changes in power setting than that of typical open loop control systems while retaining the advsntages in cost, cleanability and appearance of the smooth glass ceramic cooktop surface.
Therefore, it is a primary object of the present invention to provide an lmproved power control system for a glass ceramic cooktop appliance ~hich reduces the time requlred for the syste~ to reach steady state conditions ln response to changes ln the user selected power settlng uslng a temperature sensor mounted to the bottom or lnner surface of the glass ceramic cooktop support surface.

PATENT - 9D-MA-17021 - Payne In ~ccordance ~lth the pr~sent ~nventlon an lmproYed power coDtrol sy~te~ ls provlded for a hou~ehold cooklng appllance of the type havlng a gla8s ceramlc cooklng surface fGr s~pportlng loads to be heated and ~t lea~t one radlant heatlng unit df6posed beneath the glass ceramlc cooklng surfsce to heat loads supported thereon. U8er actu8ble lnput selectlon means enables the user to select one of a plurality of power sett~ngs for the heatlng unlt. The power control system includes temperature senslng means for sensing the temperature of the glass ceramic cooklng surface proxlmate the heatlng unlt, and power control means responsive to the input select~on means and to the temperature sensing means and operatlve to Dormally operate the beating unit at a power level corresponding to the user selected power settlng.
Advantageous use is made of the novel discovery that for at lesst some of the user selectable power settings, the steady state temperature of the glass ceramic surface will come wlthin 8 predictable te~perature band for substaDtially all normal loads when the heating unlt is operated at the corresponding power level. To this end, at least one of the plurality of power settings has associated with it predetermined max~mum and minimum reference t~mperatures deflnlng a temperature band representative of the steady state temperature range for the underside of the glass ceramic support surface proximate the heating unit when heatlng normal loads at that power setting. The power control means is further operative to operate the heating unit at a power level other than the power level corresponding to the user selected power settlng when the sensed glass ceramic support surface temperature is outside the predetermined reference temperature band associatet wlth the selected power setting to more rapidly brlng the temperature within the ~ant and thereby causing the heatlng unit to respond quickly to changes in user selected power settlng.

PATENT - ,D-MA-17021 - Payne In 8 preferred form of the lnventlon the mlnlmum reference temperature for each power settlng represents the temperature level whlch the glass ceramlc will normally at least reach under steady ætate condltlons when heatlng a relatlvely dark flat bottomèd utensll at the steady state power level for the selected power settlng. The ma~lmum reference temperature for that settlng corresponds to the temperature whlch would normally not be e~ceeded by the glass ceramlc ~aterlal when heatlng a shlny alumlnum utensil havlng a warped bottom surface at the correspondlng power level.
Whlle the novel features of the lnventlon are set forth with partlcularlty In the appended claims, the inventlon both as to organization and content uill be better understood and appreclated from the followlng detailed description taken In conjunctlon wlth the drawings.
BRIEF DESCRIPTION_OF T~E DRAWINGS
FIG. 1 ls a front perspectlve view of a portlon of a cooktop illustratlvely embodying the power control system of the present invention;
FIG. 2 is a sectional slde view of a portion of the cooktop of Fig. 1 showing details of one of the heating unlts;
FIG. 3 ls an enlarged top vlew of a portion of the cooktop of Fig. l showing details of the temperature sensor and the heating unit;
FIG. 4 is a functlonal block dlagram of the power control circuitry for the cooktop of Fig. l;
FIG. 5 illustrates power signals corresponding to varlous operator selectable power settlngs and a tlming signal for sychronizlng control system operation with the power signal;
FIG. 6 ls a graphic representation of the reslstance vs.
temperature characteristic for the glass-ceramic material forming the surface of the cooktop of Flg. l;

PATENT - gD-MA-17021 - Payne lZ~
FIG. 7 ls a simpllfled schematlc diagram of a control clrcult illustratlvely embodylng the power control system of the pre8ent lnventlon as embodled ln the cooktop of Flg. 1:
FIG. 8 ls ~ flow tlagram of the SC8~ routlne Incorporated ln the contr~l program for the microprocessor ln the clrcult of FLg. 7;
FIGS. 9A and 9B are flow tlagra~s of the Reyboard Decode routine incorporated in the control pro~ram for the microprocessor ln the circult of Fig. 7;
FIG. lO is a flow diagram of the Rate Calc routine lncorporated in the control program of the microprocessor in the clrcuit of Flg. 7;
FIGS. llA-llC are flow diagrams of the Temp FH/FC routlne lncorporated in the control program of the microprocessor ln the circuit of Flg. 7;
FIG. 12 ls a fl~w diagram of the PSET routine lncorporated ln the control progralm of the microprocessor in the clrcuit of Fig. 7; and FIG. 13 ls a flow diagram of the Power Out routine lncorporated ln the control program of the microprocessor in the clrcult of Fig. 7.
DETAILED DESCRIPTION OF ThE ILLUSTRATIVE EMBODr~ENT

Flg. l lllustrates a glass-ceramic cooktop appllance deslgnated generally lO. Cooktop appliance lO has a general~ ~)anar glas6-ceramic cooking surface 12. Circular patterns~i4-identlfy the relative lateral positions of each of four heating units (not sho~n) located directly underneath surface 12. A control and display panel generally deslgnated 15 lncludes a complete set of touch control keys 17 and a seven-segment dlgltal LED display element 19 for each heatlng unlt.

3il PATENT - gD-MA-17021 - Pagne The term glass-ceramic wlth reference to the materlal comprlsing cooktop ~urface 12 refers to a boron sllicste materlal such as the Ceran family of materlals. In partlcular in the illustrstive embodiment the glass-ceramic material is an infrared traDsmissive glass-ceramic material designated Ceran-85 manufactured by Schott J
Incorporatet.
A heating unit is dlsposed beneath each of the circular patterns 13(a) - 13~d). In the discussion to follow the designators 14(a) - 14(d) shall be understood to refer to the heatlng unlt tisposed under patterns 13(a) - 13(d) respectively. Surface unlt 14(a) is shown in greater detail in Flgs. 2 and 3. For purposes of lllustratlon only one of the heating units is shown. It will be understood that heatlng units 14(b) - 14(d) are similar ln structure to that shown in Figs. 2 and 3. Heatlng units 14(a) and 14(c) are 8 inches in diameter. Units 14(b) and 14(d) are 6 inches in diameter.

Referring agsln to Figs. 2 and 3, heating unit 14(a) comprlses an open coil electrical resistance element 16 of spiral configuration, which ls designed when fully energized to radiate primarily in the infrared (1-3 micron) region of the electromagnetic energy spectrum.
Element 16 is arranged in a concentric coil pattern and staked or otherwise secured to a support disk 18 formed of Mlcropore material such as is available from Ceramaspeed under the name Microtherm. Dlsk 18 is supported In a sheet metal support pan 20, by an lnsulatlng liner 22 formed of an aluminum o~ide, silicon o~ide composition. This insulatlng liner 22 lncludes an annular upwartly e~tentlng portlon 22(a) which serves as an insulating spacer between base 18 and the glass-ceramic cooktop 12. When fully assembled, pan 20 is spring loaded upwardly forcing the annular portion 22(a) of insulating llner 22 into abuttlng engagement with the underside of cooktop 12 by support PATENl ~ 17021 - Payne means not 6hown. ~eaeing unlts 14~a) -- 14~d~ are manufactured and sold commerclally by Cerama8peed under the part n~e Fa6t Start Radlant Heater wlth CGncentrlc Coil Pattern.
Flg. 4 lllu6~rates ln slDIplified 6chemstlc form sn embodiment of a sy~tem to be controlled ln accordance with the pregent inventlon.
Each of four heatlng unlts 14ta) - 14(d) i5 coupled to a 6tandard 240 volt, 60 ~z AC power source vla power liDes Ll and L2 through one of four trlacs 24(a~ - 24(d) respectlvely, the heatlng clrcults being J
connected ln parallel arrangement wlth each other. Trlacs 24(a) -0 24(d) are conventlonal thyrlstors capable of conductlng current ln either dlrectlon irrespectlve of the voltage polarity across their maln terminals when trl~gered by either a posltlve or negatlve voltage applled to the gate termlnals.
The power control system 26 controls the power applied to the 15 heatlng unlts by controlling the rate at which gate pulses are applied to the trlac gate terminals in accordance with power settlng selections for each heatlng unlt entered by user actuation of tactile touch membrane swltch keyboard 28. The columns of keys designated SUO
through SU3 provlde the control lnputs for heatlng unlts 14(a) - 14(d) 20 respectlvely. In the lllustratlve embodiment power pulses applied to the heatlng units are full cycles of the 240 volt, 60 Elz AC power signal; however, power signals of different frequencies and voltage levels such as 120 volts could be slmilarly uset.
A plurality of discrete power settings are provided, each 25 having uniquely assoclated wlth it a partlcular power pulse repetltion rate. In the lllustratlve embodlment sllne power settings plus Off and On are selectable for each heatlng unlt by user actuatlon of the keys in keyboard 2B. Table I shows the pulse repetltion rate associated with each power setting.

PATENT - gD-MA-17021 - Payne Look Up Table Power Power Power Pulse Settings Level Repetitlon Ra~e Address _ Power Pul6e Code 1 1 1/64 TBLADDR +8 8000 0000 0000 00QO

2 2 1/32 TBLADDR +10 8000 0000 8000 0000 3 3 a~f8 1//6 TBLADDR +18 8000 8000 8000 8000 4 4 ~ 4 ~ ~ TBLADDR +20 8000 8080 8080 8080 5 10/64 / TBLADDR +28 8088 8080 8088 8080 6 6 15/64 TBLADDR +30 8888 8888 8888 8880 7 7 21/64 TBLADDR +38 M 88 A888 A888 A888 8 8 28/64 TBLADDR +40 AA8A AA8A AA8A AA8A

9 9 36/64 TBLADDR +48 EAAA EAAA EAAA EAAA
A 41/64 TBLADDR +50 EEEA EAEA EAEA EAEA
B 45/64 TBLADDR +58 EEEE AEEE EAEE EEAE
C 51/64 TBLADDR +60 FEEE EEEE FEEE FEEE
D 55/64 TBLADDR +68 FEFE FEFE FEFE FEEE
E 59/64 TBLADDR +70 FFEF FEFF EFFE FFEF
F 64/64 TBLADDR +78 FFFF FFFF FFFF FFFF

The power pulse code in Table I represents 64-bit control words in hexadecimal format. The distrlbution of ON power cycles over a 64 cycle control period for each power setting is defined by the bit pattern of the associated control word. On and OFF cycles are represented by logical one and logical zero bits respectively. These repetition rates have been empirically established to provide a ran8e of power settings for good cooking performance in the appliance of the illustrative embodiment. The bit patterns have been selected to minimize the duration of idle or OFF cycles for each power level.
In Fig. 5 waveforms A-D represent the voltage applied to the heating element for each of power settings 1 through 4 respectively.

Wave form E represents the power signal appearing across lines Ll and L2. Power pulses or ON cycles are represented 'oy full lines. Those cycles of the power signal durlng which the triac is non-conductive sre shown in phantom lines. As shown in Table I and Fig. 5, the pulse 12~31~
PAT~ ~ gD-~A-17021 - Payne repetltlon rate for the first four power sett~ngs range from 1 pulse per 64 power cycles for power settlng 1, the lo~est non-Off power settlng to 1 power pulge for every 8 cycles for power level 4.
The ma~lmum user selectable power settlng, level 9, corresponds to a repetltlon rate of 36 cycles per 64 cycles to permlt the heating unit to be designed for seeady state operation at an effectlve voltage wh$ch ls lower than the 240 volt line voltage as i5 described ~n greater deta~l ln commonly ass$gned co-pending Canadian Patent Appli~ation Serial Number 553,188 filed February 18, 1988, for Thomas R. Payne.
A temperature sensor for messurlng the temperature of the glass ceramic support surface is provided in the illustratlve embodiment in the form of four pairs of precious metal strlps 30 formed on the underside of glass-ceramic plate 12. One palr is associated wlth each heatlng unit. Strlps 30 serve as electrical contacts and the glass-ceramlc material in the gap 32 between the strlps is a reslstance, the value of which varies as a function of the temperature of the glass.
Strlps 30 may be silk screened and fired onto the underside of the glass-ceramlc cooktop 12 at a temperature of about 1300F.
Strips 30 are built up to a thlckness of about 50 to 100 angstroms and extend from the outer edge of cooktop surface 12 nearly to the center of each of the circular patterns 13(a) - 13(d). The strips are spaced apart a dlstance of approximately 0.3 inche~. The approximate length of each strip is 3 lnches and 4 lnches for the 6 and 8 heating units respectlvely. The mlnlmum wldth of each strlp is 0.1 inches. Such a construction gives a flnlte measurable resistance value for each strip conductor. The resistance of the 6trips ls not critical provlded lt ls small, but a value in the range of 1-10 ohms ls preferred. Gold ls PATENI - gD-MA-l7~21 - Payne used ln the ~llustratlve embodlme~t tO for~ the strlps 30; ho~e~r, lt wlll be appreclated that other precious metal6 imd comblnatlons thereof such as gold palladlu~ co~blnatlons or the like could be slmllArlg e~ployed. The partlcular tapered pattern for strlps 30 1D the illustratlve embodimeot wa6 selected 80mewhat arb~trarlly fo~ enhanced appearance slnce that portlon of the 6trlps whlch extends over the heatlng un~t will be vlslble through the cooktop when the heatlng unlts are operatLng. Thls pattern is not essentlal for proper operatlon.
An improved method for applying strlps to the glass ceramlc surface ls disclosed ln commonly asslgned co-pendlng Canadian Patent Application Serial Number 573,839, .iled August 4, 1988.

The reslstance between strlps 30 ls a functlon of the distance between the strlps, the length, glass-ceramlc thlckness, cooktop material as well as the temperature. The temperature vs. reslstance characterlstlc of the glass-ceramic material comprising the temperature sensor of the illustratlve embodlment ls graphlcally represented ln Flg. 6. At the maximum temperature of 1300F (700C) the reslstance of the glass-ceramic ls approxlmately 250 ohms. At room temperature the resl5tance of the glass-ceramlc ls ln the multl megaohm range-As herelnbefore briefly described, the maln heat transfermechanlsm ln the cooktop of the lllustratlve embodiment ls radlatlon from the heatlng unlt to the utensll through the glass. The glass-ceramic ls substaDtlally transparent to infrared radlation;
however, not totally so. Thus, a portlon of the energy radlatlng from the heatlng unit ls absorbed by the glass-ceramlc. Simllarly, a portlon of the energy reflected from the utensil is also absorbed by the glass-ceramic. Consequently, the conduction from glass ceramlc surface to the utensll makes a slgnlflcant contrlbutlon to the heatlng -1~

12~3 ~311 9D-MA-17021-Payne of the utensil. Thus, the thermal inertia of the glass ceramic material slows the response of the heating system to changes in the user selected power setting.
It will be recalled that an object of the present invention is to cause the system to respond more quickly, that is, to reach steady state heating conditi-ons more quickly in response to changes in the selected power setting. To meet this objective, advantageous use is made of a novel and unexpected empirical observation that for each power level, under steady state conditions the temperature of the underside of the glass ceramic material supporting a utensil load to be heated will come within a corresponding relatively wide but predictable temperature band or range for substantially all normal utensil loads being heated of the glass ceramic surface.
Table II shows the minimum and maximum temperatures which define the bands for power levels 4-7 of the illustrative embodiment.
As used herein, the phrase "normal load" refers to a range of utensils likely to be heated on the cooktop. At one extreme are dark flat bottomed Corningware type pans and at the other extreme are warped shiny aluminum pans.
The dark flat Corningware type of pans provide the most efficient heat transfer from the glass ceramic material.
The phrase "Corningware type" refers to pans made of ceramic material available under a variety of names. For a given power wetting the measured glass ceramic temperature will be lowest for this type of pan. The warped bright metal pan provides poor heat transfer by conduction and also tends to reflect radiant energy back toward the glass ceramic and thus establishes the high temperature end of the band.

,j --11--s ~ATENT - 9D-~A-17021 - ~ayne 12~9r3i~
TABLE II

Steady State Overdrlve Underdrive Past ~eat Paat Cool Pouer Level Level Level Threshold Threshold g _ _ _ _ The minimum temperatures in Table II were derived from empirlcal testing uslng a 8~ slze flat dark Everware pan containing 2 llters of water; the ma~imum temperatures were derived using a 6" size shiny aluminum pan wlth a severely warped bottom contalning 1/4 liter of water.
In sccordance with the present invention, the control system includes means responsive to the temperature sensing means operative to apply a power level other than the 6teady state power level corresponding to the user selectet power setting, when the sensed temperature of the glass ceramic material is outside the corresponting steaty state temperature bant. When the sensed glass ceramic temperature is less than the minimum thresholt temperature defining the lower limit of the temperature bant for the selected power setting, the heatlng unit is overdrlven, that ls, a power level higher than the steady state power level for the selected power settlng is applied to PAT~h~ - gD-MA-17021 - Pa7ne 12~'~3-ll the unit. Slmllarly, when the sensed glass ceramlc temperature is ~reater than the ~axl~u~ threshold temperature ,~efin~ng upper limlt o~
the temperature band for the 6elected power settlng, the heatln~ un~t i5 underdrlven, that is, a power level less thsn the ~teady state power level ls applied to the heating unlt. When the sensed glass ceramlc temperature ls within the corresponding steady state temperature band, the power level corresponding to the selected power settlng is applled to the heating unlt. By thls arrangement, the glass temperature is more rapidly brought within the temperature band associated with the selected power level than would be the case with a conventional open loop control arrangement.
In the illustrative embodiment, resistance of the glass when operating at the power levels 1-3 is so high that rellable measurement of usable temperatures requires very expensive clrcuitry. Thus, the overdrive or fast heat mode is not implemented for these power settlngs. The maximum reference temperature for power level 3 is used to implement the unterdrive or fast cool mode for power levels 1-3.
Power setting 9 is the maximum setting for which the unit ls designed.

Thus, no overdriving is implemented ln response to selection of this power level.

Table II also shows the power levels applied for overdriving and underdriving the units for each power setting. These power levels have been empirically selected to provide satisfactory performance in the cooktop of the lllustrative embodiment. The ob~ective in chooslng these levels ls to bring the temperature to withln the desired limits quickly but wlthout overshoot.
It will be appreciated that the speciflc temperature and power level parameters described in Tsble II are intended to be illustratlve only and not intended to be limltations on the invention.

PATEN~ - gD-MA-17021 - Payne ~Z~3:~
F~g. 7 schematlcally lllustrates an e~bodlment of a po~er control circult for the cooktop of Flg. 1 whlch performs the pow~r control functlon ln accordance vlth the present lnvention. I~ this control system power coDtrol is provlded electronically by mlcroprocessor 40. Mlcroprocessor 40 ls a M6~000 serles mlcroprocessor of the type commerclally avallable from Motorola. Microprocessor 40 has been customized by permanently conflguring lts reat only memory to implement the control scheme of the present lnventlon.
As pre~iously described with reference to Flg. 4, keyboard 28 ls a conventlonal tactile touch type entry system. The kegboard array comprises four columns of 11 keys each. Columns for controlling heatlng elements are deslgnated SUO through SU3 respectlvely. The keys enable a user to select power levels 1 through 9 ln addltlon to On and Off for each of the four heatlng unlts. Reyboard 28 has one lnput llne for each column com~only sharet by all keys in that column and ll output llnes, one for each row of keys. Each partlcular column of keyboard 28 is scanned by perlodica11y generatlng scan pulse sequentlally at outputs P400 through P403 of microprocessor 40. These pulses are transmltted as they appear to the corresponding column input lines of keyboard 28. Thls voltage 18 transmitted essentlally unchanged to the output llnes of all the untouchet keys. The output of an actuated key wi11 differ, signifying actuation of the key iD that row and column.
In thls manner each column of keyboard 28 ls scanned for a new lnput periodlcally at a rate determined by the control program stored ln the ROM of microprocessor 40. As wlll become apparent from the descrlptlon of the control routlnes whlch follow, esch column ls scanned once every four complete power cycles of the power slgnal appearlng on llnes Ll and N. The output from keyboard 28 18 coupled to PAT~NT - 9D-~A-17021 - Payne lnput ports PlI0-PlIA of mlcroprocessor 40 vla a 410 parallel port lnterface clrcult, A zero crosslng slgnal marking zero cro6slngs of the power signal appearlng on llnes Ll and N from the po~er 6upply ls lnput to mlcroprocessor 40 at ~nput pDrt PôIO fr~m a conventlonal zero crosslng detector circuit 44. The zero crosslng signal from circuit 44 ls lllustrated at wave form F of Fig. 5. The pulses mark the pos$tlve going zero crossings of the power slgnal across llnes Ll and N of the AC power supply. The zero crosslng slgnals are used to synchronlze the 1~ triggering of the triacs wlth zero crosslngs of the power slgnal and for tlmlng purposes in the control program e~ecuted by mlcroprocessor 40.
Glass cooktop temperature information ls provlded to mlcroprocessor 40 at input ports PAI0 through PAI3 via a standard VME
600 A-D converter circuit 46. An analog voltage signal representative of the temperature of the glass-ceramic in the vicinlty of each heating unlt is provLded vla temperature sensor voltage bridge network 48 comprising for each heatlng unit, a 2K resistor 49 connected in parallel with 200R resistor 50, vla an analog multiple~er circuit 51 serially connected to resistor 49, an isolating tiode 52, and a 10 uf filter capacitor 54. The resistance of the glas6-ceramic is represented schematically as variable resistor 56 coupled between the ~unction of resistor 50 and diode 52 and ground. The other side of resistor 50 is coupled to an AC 6upply 60urce 57. AC 6upply 57 is used to drive the glass-ceramic sensor resistance circuitry in order to minimize parasitic and diffusion affects. The analog voltage signal applied to the input of the A-D converter from each indivitual 6ensor circuit is converted internally to a digitized value which is stored ln the RAM of mlcroprocessor 40.

t3:t~
PATE~T - 9D-MA-17021 - Payne Analog multlplexer clrcult 51 ls connected ln serles with current llmltlng reslstor 49 to effecelvely e~pant the temperature range of the senslng clrcuit. Multlplexer clrcults 51 act as analog switches triggered by enable signals from output ports P404-P407 to selectlvely swltch the 2R ohm reslstor lnto the sensl~g circult. If only 2R reslstor 49 is employed, the temperature reatings at the low end of the range are dlfflcult to resolve. As will be hereinsfter descrlbed ln greater detall ln the descriptlon of the control routines, when the sensed temperature is above a predetermined threshold temperature ar~ltrarLly set at 750 F, an enable slgnal is transmitted from the approprlate one of I/O ports P404-P407 to lts assoclated multiplexer circuit 51 to swltch ln the lower reslstor 49 before reading in the temperature for measurement purposes. For temperacures less than the threshold temperature, the I/O port ls lS reset, effectlvely swltchlng reslstor 49 out of the circult.

Microprocessor 40 transmits triac trlgger signals from I/O
ports P500 through P503 to the gate terminals of triacs 24(a) - 24(d) respectively vla a conventional 615 triac drlver circuit. Triac driver circuit 64 amplifles the outputs from ports P500-P503 of microprocessor 40 and isolates the chip from the power line. Dlsplay data ls transmitted from I/O ports P200-P20F. Display 58 is a conventional four diglt display, each digit compsising a 7-seg~ent EED display.
Display information is coupled from I/O ports P200-P20F to the display segments via a conventlonal 410 parallel port interface circuit 60 and a conventional segment display decoder drlver circuit 62 in a manner well known in the art.
It will be recalled that microprocessor 40 is customized to perform the control functlons of thls lnvention by permanently conflguring the ROM to lmplement a predetermined set of instructions.

PATENT - gD-MA-17021 - Payne 3-t~
Flgs. 8-14 are flow diagrams whlch lllustrate the control routines lmplemented ln the microprocessor to obtaln, store and process the lnput data from the keyboard and generate control ælgnals for trlggerlng the trlacs in a manner whlch provldes the power pulse repetltlon rate requlred for the power settlng ~elected and the seDsed glass-ceramic temperature for each of the heating unlts. From these dlagrams one of ordinary sklll ln the program~lng art could prepare a set of lnstructions for permanent storage Ln the ROM of micrOprOCeSSOr 40 whlch would enable the mlcroprocessor to perform the control functlons ln accordance wlth thls lnvention.

The control pr~gram comprlses a set of predetermlned control lnstructlons stored ln the read only memory (ROM~ of mlcroprocessor 40. A separate file in the random access memory (RA~) of the mlcroprocessor ls assoclated wlth each of heatlng unlts 14(a) - 14(t).
Each file stores the control lnformatlon for lts assoclated heatlng unlt whlch ls acted upon by the lnstructions ln the RO~. Execution of the control program ls synchronized wlth the 60 Hz power slgnal such that the set of control lnstructlons ln the ROM ls cycled through once during each cycle of the power slgnal. A flle register common to all four flles functlonlng as a four count ring counter ls incremented once durlng each pass through the control program. The count of thls file reglster ldentifles the RAM flle to be operated on by the control lnstructions during the ensulng pass through the control program. By thls arrangement the control program ls executed for any one particular heatlng unit once every four cycles of the 60 Hz power slgnal.

The control program ls loglcally dlvlded lnto a set of sub-routlnes whlch lncludes the Scan routlne, the Reyboard Decode routine, the Rate Calc routlne, the Rate Control routine, the Steady State routlne, the TE~P FH/FC routine, the PSET routlne, and the Power PATENT - gDiMA-17021 - Payne Out routlne. It wlll be appreclated that other ~ub-routlne~ may also be incluted to perform control functlons unrelated to the pre6ent lnventlon, The Scan routlne (Flg. 8), ~hlch contaln6 the flle reglster ldentlfylng the RAM flle to be acted upon durlng the ensulng pass through the control program, sets the scan line for the keyboard column a6sociated wlth the heatlng unlt which i6 the sub~ect of the current pass through the routlne, reads the lnput from the keyboard, and stores the user selected power settlng 6electlon lnformatlon ln temporary memory. The Keyboard Decode routine validates keyboard entrles and updates the control varlable representlng the p~wer level selected by the user as appropriate to reflect the st recent valld user lnput.
The Rate Calc routlne reats in the glass-ceramic cooktop temperature lnformation, ant periotically calculates the rate of change of temperature. This lnformation ls used in the Rate Control and Steady State Control routines which perform a temperature limitlng function by making ad~ustments to the power level to be applied to the heating unit as a functlon of the glass-cera~lc temperature, the rate of change of glass-ceramic temperature ant the user selectet po~er setting. The TEMP F~IFC routine uses the glass ceramlc temperature information reat ln by the Rate Calc routlne to overdrive or unterdrlve the heatlng unlts when the senset temperature ls outside of the temperature band associatet wlth the selectet power setting to speed up the response of the appliance to power setting changes ln accordance wlth the present invention.
Whlle the determlnation of what power level to be applled to the surface unlt is determinet only durlng the pass through the program for that partlcular heatlng unlt, a power control declslon must be made for the ensuing power cycle for each of the unlts durlng each pass -lô-PATE~T - gD~M~-17021 - Payne through the program. The PSE~ routlDe obtalns powcr le~el lnfor~atlon from each flle durin~ each p~s through the rourlne, perfor~s a table lsok-up for each heatlng unlt to check the approprlate blt for the power level oontrol word for esch surface ~nlt, and generstec a four blt trlgger control word whlch lden~lfies whlch heatIng unlts are to be trlggered on snd whlch are to be off during the ne~t po~er cycle. ~hls four blt control word is then used by the Power Out routlne whlch monitors the lnput from the zero crosslng clrcult and trlgger6 those triacs as60ciated wlth surface unlts to be energlzed durlng the ne~t power cycle ~nto conductlon upon detectlon of the ne~t occurrlng positive golng zero crosslng of the power slgnal. Each of these control routlnes e~cept for the Rate Control and Steady State Control routlnes will n~w be descrlbed ln greater detall wlth reference to lts flow dlagram ln the dlscusslon to follow. Ihe Rate Control and Steady State routlnes, whlch implement the temperature limltlng functlon, are described in detail in the Canadian patent application serial no. 559,189 filed February 18, 1988.
SCAN Routlne - FIG. 8 The functlon of thls routlne ls to address the approprlate RAM
flle for the current pass through the program, set the approprlate scan llne for the keyboard, ant reat in the lnput lnformatlon from the keyboard for the heatlng unlt assoclatet with the teslgnated RAM flle.
RAM flle reglster SU functlon~ as a four count rlng counter whlch counts from 0 to 3. Counts 0 through 3 of the SU counter ldentlfy R~M
flles for curface unlts 14ta)-l4(d) respectively.
Upon enterlng the Scan routine the register SU ls lncremented (Block 102) and Inqulry 104 determlnes lf SU 1B greater than 3. If 80, the counter is reset to 0 (Block 106). Ne~t the address of the RAM
file to be acted upon durlng thls pas6 through the control program ls PATENT - gD-ffA-17021 - Payne set equal to SU (Block 108). The scan llne g~ durlng the prevlous pa65 through the control program deslgnated R(Su-l) lg reset (Block 110). The scan llne assoclated wlth the surface unit for the rurrent pass through the program deslgnated R(SU) 16 flet (Block 112). The data of lnput lines PlIA through 9 are read ln, conveylng the current lnput Informatlon for thls RAM flle from keyboard 28 (Block 114) and thls lnformatlon ls stored as varlable KB (810ck 116). The program then branches (Block 118) to the Reyboard Decode routine of Flg. 9A.

KEY~OARD DECODE Routlne - FIGS. 9A and 9B
The Keyboart Decode routlne valldates inputs from keyboard 28 and updates the user selected power settlng variable PWD accordlngly.
The routine first determines if the neu keyboard entry is a blank signifylng no input, an Off entry, an On entry, or one of the power levels l through 9. To be valid when suitching the heatlng unit from Off to another power setting, the On key must be actuated first followed by the desired power setting. The power setting must be entered within ô seconds of actuation of the On key. If not, the On key must be re-actuated.

The variable PWD represents the user selected power setting.
PWD is only changed in response to user inputs. ~owever, in accordance with the present invention the pouer level actually applied to the heating unit may be different from the level corresponding to the user selected power setting. The variable PLVL is introduced in this routine to represent the power level to be actually applied to the heating unlt. PLVL is initially assigned the value of PWD. ~owever, PLVL ls sub~ect to be changed in the control routlnes hereinafter described.
A flag designatet the On flag and a tlmer or counter deslgnated the ONTI~ER are used to establish the eight second perlod PATENT - gD-MA-17021 - Payne for enterlng a valld power settlng after actuat$on of the On key. The On flag ls set when the On key ls ~tuated and lS only reset ln response to actuatl~n of the Of key or ti~lng oue ~f ONTIMER.
ReferrLng to the flow dlagra~ of Fl~s. 9A and 9B~ Inqulry 120 first deter~lnes lf RB represents a blank signifylng that no key 18 presently actuated. If XB ls blank, the syste~ branches to the Decode 2 sub-routlne (Fig. 9B). In the Decode 2 sub-routlne I~quiry 122 determlnes if the On flag is set. If the Cn flag is not set, the power level stored ln PWD is assigned to the varlable PLYL (Block 124). If the On flag is set, Inquiry 126 determines if the prev$ously selected power setting presently stored as PWD ls the off settlng. If not, the system $s presently operating at one of power settings 1 through 9 and the program proceeds to asslgn the value of PWD to PLVL (Block 124) and branches (Block 128) to the Rate Calc routlne (Fig. 10). If Inqulry ~5 126 determlnes that PWD equals O representlng an Off power level, thls indlcates that the user has swltched from Off to On and the On timer ls decremented (Block 130). When On timer equals O as determinet at Inqulry 132 signlfying that the tlme to enter a valid power level has expired, the On flag is cleared (Block 134) and program proceeds to Block 124 as before.

Referring again to Fig. 9A, if KB is not a blank, Inquiry 135 determines if the new entry is the Off setting. lf 60, the On flag is cleared (Block 136) and the variable PWD is as6igned the value O

representing the Off power setting (Block 138). The variable PLVL ls a66igned the value of PWD (Block 140) and the program branches (Block 142) to the Rate Calc routlne of Fig. 10. If KB ls not Off, Inquiry 144 determlnes if the new entry ls the On settlng. If lt ls, the On timer is re-initiallzed (Block 146). Inqulry 148 checks the state of the On flag. If set, the program proceeds to Block 140. If not set, lZ~
PATENT - gD-HA-17021 - Payne the flag is set (Block 150) and the PWD ls assigned the value 0 whlch corresponds also to the On settlng (Block 152). The program then proceeds to block 140 as before.
If the answer to Inqulry 144 ls No, signlfying that the new entry 18 one of power levels 1 through 9, Inqulry 154 checks the state of the On flag. If lt ls not set, signlfylng the user has attempted to go from Off to a power level wlthout flrst actuatlng the On key, the new entry ls lgnored and the program proceeds to Block 140 with PWD
unchanged. If the On flag is set, the power settlng lnput ls valld, and varlable P~D ls asslgned the new value corresponding to the new entry RB (Block 156).
~aving assigned the value of PWD representlng the most recent valid user selected power settlng to the varlable PLVL the system proceeds to the Rate Calc routlne (Flg. 10).
RATE CALC Routlne - FIG. 10 The functlon of thls routlne ls to read ln the glass ceramic temperature data and to determine the rate of change of the glass-ceramic temperature. Pursuant to reading in the data, thls routine generates enable slgnal to swltch the lower resistance lnto the senslng network when the initial reading signifies a temperature hlgher than the threshold reference temperature which is set at 750 F. 0f course, the AtD readings will dlffer for the same actual sensed temperature dependlng upon whlch of the two resistors ls ln the clrcuit when making the reating. For e~ample, for a sensed temperature of 750 F, with the 200K ohm resistor 50 ln the clrcuit the sensor circuit voltage wlll measure 2.9 volts whlch ls converted by the A/D
circuit to an A/D readlng of 253; with the 2K ohm resistor 49 ln the clrcult, for the same actual temperature the sensor circult voltage wlll be 9.7 volts which converts to an A/D reading of 7C3. In the PATEUT - gD'UA-17021 - Payne mlcroprocessor lmplementatlon of the lllustrat:Lve embodiment, a look^up table ls employed when the 200K reslstor ls ~n the circuit to convert the AID reading to the readlng equlvalent to t~t generated by the A/D
circuit for the same temperature wlth the low valuet reslator 49 In the clrcult. In the prevlous example, the look-up table converts the A/D
readlng of 253 to 7C3.
The rate of change informatlon determined ln thls rout~ne ls used ln the temperature llmltlng routlnes descrlbed In the aforementloned patent appllcatlon Serlal No. ~ . The rate calculatlon ls repeated every two seconds to provlde a rapld control response. ~owever, the rate of change ls calculated by measurlng the tifference between glass-ceramlc temperature measurements separated by elght seconds. This elght second separation provldes a more accurate rate determlnatlon. These tlme lntervals provlde satlsfactory results ln the lllustratlve embodlment.
Referr~ng to the flow dlagram of Flg. 10, flrst that one of the I/O ports P404-P407 for the partlcular heatlng unit for whlch the program ls then executlng, ldentlfled by lnde~ (SU~4), is reset (Block 158). Next, the glass-ceram~c temperature lnput from A/D converter ls then read ln (Block 159) ant stored as the varlable deslgnated &LSTffP.
Inqulry 160 compares thls temperature to threshold temperature of 750 F represented by the varlable T~TMP. If the sensed temperature 18 hlgher than the threshold reference value, I/O port P40(SU+4) ls set (Block 161) to 6wltch low value reslstor 49 (Flg. 7) lnto the clrcult.
The temperature lnput from the A/D converter ls read ln agaln (Block 162) wlth the low valued resistor ln the clrcult and stored as varlable GLSTMP. If the sensed temperature is lower than T~TMP, the value of GLSTMP entered at Block 159 uslng the hlgh valued reslstor 50 (Flg. 7) ls converted vla the look-up table (Block 164). The converted value ls stored as GLSIMP and the program proceeds.

PA12NT ~ 17021 - P~ne A two second timer SLPCLK ls lncre~en~:ed (Block 163). At two second lntervals ~Inqulry 165) the timer 1B reElet (Block 166).
As shown at Block 168, when the rate of change i8 to be uptated, the current value of GLSTMP ls stored as GLSTMP0, the prevlou~
readlng ls ~tored as GLSTMPl; the prevlous GLSI~Pl 18 stored as G15IMP2; the prevlous GLSTMP2 ~s stored as GLs~MP3, and the prevlous GLSTMP3 ls stored as GLsIMP4. By storlng temperature mea~urements every two seconds ln thls fa6hion, the time span between the most recent temperature measurement GLSTMPO and the oltest stored temperature measurement GLSTMP4 is appro~lmately elght seconts.
The rate of change of temperature, TMPSLP, is calculated as the difference between the most recent measurement and the oldest stored measurement (Block 170). This dlfference ls proportlonal to the rate of change wlth a proportlonality factor of 1/8. After readlng in the temperature data and updating the rate of change calculatlon as approprlate, the program then branches ~Block 172) successlYely to the Rate Control routine (not shown) and then the Steady State routine (not shown) to implement a temperature limiting function. From the Steady State routine the program branches to the TEMP FF/FC routine (Fig. llA).
TEMP FL/FC Routine - FIGS. ll~-llC
The function of the TeMP F~/FC routlne ls to determine lf the sensed temperature of the glass cersmic surface ls within the steady state temperature range for the user selected power settlng and to ad~ust the power level applled to the heating unlt upwartly if the temperature ls below the temperature range and downwartly lf the temperature ls abo~e the temperature range. If the sensed temperature ls wlthln the temperature range, no ad~ustment ls made and the steady state power level 15 applled to the heatlng unlt.

l~A~l i PAT~NT- 9D~A-17~21- Payne The ma~l~um nnd minimum reference te~p~ratures 115ted ln ~able II are used in thls routlne. The ma~lmum and mlnlmum reference ~alues for the nth power ~ettlng are ~s61gned the varlable namc8 M ~I~P (n) and HINTMP (n) respectlvely.
S Referrin~ now to the flow dla~ra~ 11~, Inquiry 174 deter~nes lf the selected power 6ettlng represented by the varlable PWD ls O
representlng the OFF sett~ng, in whlch ca5e no modiflcatlon8 to the power settlng ls to be made and the program branches immedlately (Block 175) to the PSET routlne of Fig. 12. If one of power settlngs 1-9 has been selected, the program proceeds to Inqulry 176.
Inquiry 176 determlnes lf the selected power setting ~s one of power settlngs 1-3. If so, Inquiry 178 compares the sensed glass temperature to the maxlmum reference temperature for power setting 3, GLSTMP3. If the temperature is greater than GLSTMP3, a fast cool de is lnitiated by settlng PLVL to 7ero (Block 180); if not, no change is made to PLVL. The program theD braDches (slock 182) to the PSET
routine of Fig. 12. If the selected power 6ettlng is hlgher than power settlng 3, Inqulry 184 determines lf power settlng 4 ha6 been selected. A No response to Inqulry 184 signlfles that power setting 4 haR been selected. If so, the program proceeds to Inqulry 186 whlch compares the ~lass temperature represented by the variable GLSIMP to the maxlmum temperature for power 6ettlng 4. If the gensed temperature 18 greater than the reference, the applied pouer level PLVL ~s reduced by two levels (Block 188) and the program branches (Block 190) to the PSET routine of Fig. 12. If the 6en6ed glass temperature ls not greater than the ma~l~um temperature for power settlng 4, Inquiry 192 comparefi the temperature to the mlnlmum temperature for power settlng 4. If the sensed temperature ls les6 than the m~nlmum temperature, the applled power level ls lncreased by 2 (Block 194). Otherulse, the PATENT - 9D-~A-17021 - Payne program brsnches (Block 190) to the PSET rout;lne. If the selected power settlng ls hlgher than power settlng 4, the program proceeds to entry polnt FHFC2 at Flg. llB. Inqulry 196 determlnes lf the gslected power 6ettlng ls greater than power settlng 5. A No response to Inqulry 196 signlfles power settlng 5 has been selected and the program proceeds to IDqulry 198, whlch compares the sen~ed temperature to the maxlmum reference temperature for power settlng 5. If the sensed temperature exceeds the maxlmum temperature, the applled power level ls reduced by 2 (Block 200). Otherwlse, Inqulry 202 compares the sensed glass temperature to the minimum reference temperature for power settlng 5. If the sensed temperature ls less than the mlnlmum, the power level to be applled ls lncreased by 2 (Block 20~); otherwise, no change ls made to the power level to be applled and the program branches (Block 206) to the PSET routlne of Fig. 12.
Referrlng agaln to Inqulry 196, lf Yes, the program proceeds to Inqu~ry 208. A No response slgnlfles that power setting 6 has been selected. Inquirles 210 and 212 compare the sensed glass temperature to the maximum and minimum reference te~peratures for power settlng 6 respectively. If the maxlmum reference is exceeded, the power level is reduced by 3 (Block 214). If the sensed temperature is less than the mlnlmum reference temperature, the power level is increased by 3 (Block 216). Otherwise, no change is made to the power level and the program branches (Block 217) to the PSET routlne.
Referrlng bsck to Inquiry 208, if the response to Inquiry 208 is a Yes slgnlfying a power settlng greater than 6 has been selected, the program proceeds to entry point F~FC3 of Flg. llC.
A No response to Inqulry 218 slgnifles power settlng 7 has been selected. Inqulrles 220 and 222 compare the sensed glass temperature to the maxlmum and minlmum reference temperatures for power ~f~
PAIENI -- gD--MA--17 0 21 ~yne settln~ 7 reqpectl~ely~ If the gla68 te~perature exceeds the ~a%lmum reference te~perature, the power level 1A decreased by 3 (~lock 224) and the program branches (Block 228) to the PSET routlne of Fig. 12.
If the sensed glass temperature ls less than the minlmum reference temperature for power 8ettlng 7, the power level 9 representlng an increase of 2 power level~ is applled (Block 226). Otherwlse, no ad~ustment ls ~ade to power level and the program branches to the PSET
routine (Block 228).
If the power sett1ng ls greater than 7, the program proceets to Inqulry 229 whlch checks for the selection of power setting 8. If the response to Inqulry 229 ls No, slgnifylng power setting 8 has been selected, Inquiries 230 and 232 compare the sensed glass temperature to the maximum and mlnlmum reference temperatures respectlvely for power sett~ng 8. If the glass temperature exceeds the maximum reference temperature, the power level is decreased by 3 (Block 234) and the program branches (Block 236) to the PSET routlne. If the glass temperature ls less than the minlmum reference temperature, the power level ls lncreased by 1 to maximum power level 9 (Block 238), and the program branches (Block 236) to the PSET routlne. If the sensed te~perature ls not less than the mlnlmum reference temperature, no at~ustment ls made to the power level and the program branches (Block 236) to the PSET routlne.
PSET Routlne - FIG. 12 Havlng eqtabllshed the approprlate power level to be applied to the heating unit, it remains to make the trlac trlggerlng declslon for the next occurrlng power slgnal cycle. Thl6 declslon ls made for each of the four heatlng units durlng each pass through the control program. Use ls made ln this routlne of information from each of the four heating unlt RAM flles each time through the routlne. It wlll be recalled that the power pulse repetltlon rate for each po~er level ls deflned by the blt pattern of a 64-blt word wlth the logical one blt representing an On cycle and loglcal zero representlng an Off cycle.
The blts of the word representlng the power level to be applled to the heatlng unlt are tested sequentlally with one blt belng tected each pass through thls routlne. The state of that te~ted blt determlnes whether the trlac for the correspondlng heatlng unlt wlll be trlggered on or not ln the next power slgnal cycle.

Thls routlne performs a Table Look-Up function to find the approprlate control word and then checks the state of the approprlate blt ln that word for each of the four surface unlts. The trlac trlggerlng lnformatlon ls then ~toret ln a four-blt word deslgnated T~PON, whlch ls used ln the Power Out routlne (Plg. 13) to generate the approprlate trlac trlgger signals.
The varlable TBIADD represents the address ln RA~ of the startlng locatlon for the look-up table containing the 64-blt control words. The address and assoclated blt pattern ln ~ex representatlon ls shown $n Tabie I. Each of the 16 dlglts ln the code as shown for each control word ls the hexldeclmal representation of four blnary blts.
The varlable deslgnated BITADD represents the locatlon wlthln the 64 blt control word of the bit to be tested w$th O and 63 correspondlng to the locatlon of the most slgniflcant blt and least slgnlficant blt re~pect$vely.

An lndexing varlable n ls used to lterate the table look-up loop four tlmes durlng each pass through the routine, once for each heatlng unlt. The varlable PWDA~D ls the address of the control word representlng the power level to be applled to the n heatlng unlt.
AB can be seen ln Table I, the address for any part$cular power word ls obtalned by multlplylng the value of n VL for lts assoclated power -2&-l~z~
PAS'E~ 9D ~--17 0 Z 1 -- P /~ e level, whlch ls a number O through 9, ~ultlpllet by a factor of 8 And ~dd1ng thl6 to TBLADD.
Referrlng to Flg, lZ~ on enterlng thls routlne the control word T~SPON i6 cleared (Block 272) and a rlng co~Dter whlch counts from 0 to 63 1B lncremented. Inqulry 276 determines lf the counter ls greater than lts ma~cl~ count of 63. If 80, lt ls reset to O (slock 278). Next BIrADD ls set equal to the count of the r~nt counter thereby definlng the location wlthin the control word for the bLt to be tested for each heatlng unit (810ck 280). The same oit location ls tested for each of the heating units.
The varlable n is lnltlallzed to zero at Block 282. PWDADD
for the power level to be applied to ehe nth heating unlt ls determined at Block 284. The state of the blt location defined by the varlable BITADD in the control word located at the addres6 P~DADD ls then tested (Inquiry 286). If the tested blt ls a logLcal 1, the n bit of the control word TMPON is set (Block 288). Otherwise, the n bit of TMPON will remain 0. After the inde~c n ls incremented (Block 290) the value of n ls checked tInqulry 292). If greater than 3, slgnifying that the loop comprising Blocks 284, 288 and 290 and Inquirles 284 and 286 has been lterated four tlmes, n ls reset (Block 294) and the program proceeds to the Power Out routlne (Fig. 13). If n ls not greater than 3, the program returns to Block 284 to test the bLt for the power word for the ne~t heating unit. After the appropriate state for all four blts of the variable TMPON have been establlshed, the program branches (Block 296) to the Power Out routine (Fig. 13).
POWER OUT Routine - FIG. 13 The function of this routine is to trlgger triacs 24(a) -24(d) to implement the triac triggerlng declslon for the ne~t power cycle for each of the four heating units. The triggering of the triacs PATE~r ~ -17021 - Payne 18 synchronlzed wlth the positlve going zero crosslngs of the power s~gnal .
Referrlng now t~ the routlne ln Pig~ 13, on enterlng thls routlne the output latches P500-P503, whlch coutrol the trLac8, art reset (Block 302). Next the program reads in the Lnput from the lnput port P8IO representlng the state of the zero cross tetector (Block 304) and ~nquiry 306 checks the state of thls lnput untll lt switches to-a logical 1 signifyin~ the occurrence of a po8itive going zero crossing of the power slgnal. When P8IO equals 1, the program proceeds to 0 Inqulry 308 to sequentially check the four bits of the power word DM~ON

and set the approprlate one of output latches P500-P503. Index varlable n is agaln used to sequentially check blts O through 3. It wlll be recalled that prlor to branching from the PSET routine the n ls reset to 0. Inquiry 308 tests the nt bit for a 1. If it ls a l, the output P50(n) ls set (Block 310), n is incremented (Block 312) and Inquiry 314 checks for an n greater than 3. If n ls less than 3, the progra~ returns to Inquiry 308 to check the next bit and set the corresponding output port as appropriate. Those ones of output latches P500-P503 associated wlth bits In the variable DMPON which are in the logical one state are set. Those ones with output latches associated with zero blts ln TMPON are not set. In the latter case these latches remain ln the reset state slnce each of the latches is reset upon entering this routlne.
In this fashlon each blt of the control word IMPON is tested each pass through the Power Out routine, and a teclsion to trigger or not trlgger each trlac is carrled out during each pass chrough the control program. Once the loop comprlslng Inquirles 306 ant 312 and Blocks 308 and 310 is lterated four times, once for each heatlng unlt, the power contro7 decision for the next power cycle has been lmplemented and the program returns to the Scan routine to execute the program for the next heating unlt.

PATE~T - gD'MA-17021 - Payne 1~9~3 1~
In the power control arrangement herelD descrlbed, It 18 contempl8ted that the control functlons of the p~e~ent ln~entlon be lmplemented ln cooperation with the tempersture llmltlng functlons at le~ct t~ the extent that the temperature limitlng functlon overrldes ~he fast heat/fast cool functlonn. It wlll be appreclated, however, that the fast heat/fa5t cool functlon i6 readlly lmplementable ln a power control system ln whlch the temperature llmltlng functlon 15 performed in a totally different manner, if at all. For example, in the system of the lllustratlve embodlment, thls could be achleved by simply deletlng the Rate Control ant Steaty State Control routlnes entlrely from the ROM of mlcroprocessor 40 and retalnlng only that portlon of the Rate Calc routl~e ln ROM whlch reads ln and stores the glass ceramlc temperature measurement data.

Whlle ln accordance wlth the Patent Statutes a speclflc embodlment of the present inventlon has been lllustrated and descrlbed herein, it ls realizet that numerous modlflcatlons and changes wlll occur to those skllled in the art. For example, the lllustratlve embodlment employs lnfrared heatlng unlts. ~dowever, the invention could also be used ln conventlonal conductlon cooktops as well. It ls therefore to be understood that the appended clalms are lntended to cover all such modlficatlons and changes as fall ~ithin the true splrlt and scope of the ln~ention.

Claims

1. In n household cooking appliance of the type having a glass ceramic cooking surface for supporting loads to be heated, and at least one radiant heating unit disposed beneath the glass ceramic cooking surface to heat loads supported thereon, a power control system comprising:

temperature sensing means for sensing the temperature of the underside of the glass ceramic support surface proximate the heating unit;
user actuable input selection means for enabling the user to select one of a plurality of power settings for the heating unit;
at least one of said plurality of power settings having associated with it predetermined maximum ant minimum reference temperatures defining a temperature band representative of the steady state temperature range of the underside of the glass ceramic support surface proximate the heating unit when heating loads at that power setting; and power control means responsive to the input selection means, operative to operate the heating unit at a steady state power level corresponding to the user selected power setting;
said power control means including means responsive to said temperature sensing means for operating the heating unit at a power level other than the power level corresponding to the user selected power setting when the sensed glass ceramic support surface temperature is outside said predetermined reference temperature band associated with the selected power setting to cause the heating unit to respond quickly to changes in the user selected power setting.

PATENT - 9D-MA-17021 - Payne

2. The power control system of Claim 1 wherein said means responsive to said temperature sensing means for operating said heating unit at a power level other than the power level associated with the user selected power setting is operative to apply a power level higher than the power level associated with the user selected power setting when the sensed temperature is below said predetermined temperature band for the selected power setting and to apply a power level lower than the power level associated with the user selected power setting when the sensed temperature is above said predetermined temperature band.

3. A power control system for a household cooking appliance of the type having a glass ceramic cooking surface for supporting loads to be heated and at least one radiant heating unit disposed beneath the glass ceramic cooking surface to heat loads supported on the cooking surface, said power control system comprising:
temperature sensing means for sensing the temperature of the underside of the glass ceramic support surface approximate the heating unit;
user actuable input selection means for enabling the user to select one of a plurality of power settings for the heating unit;
at least one of said plurality of power settings having associated with it predetermined maximum and minimum reference temperatures defining a temperature band representative of the steady state temperature range of the underside of the glass ceramic support surface proximate the heating unit when heating loads at that power setting; and power control means responsive to the input selection means for operating the heating unit at a predetermined steady state power level corresponding to the user selected power setting including means responsive to said temperature sensing means operative to operate the heating unit at a power level higher than the power level corresponding to the user selected power setting when the sensed glass ceramic support surface temperature is less than said minimum reference temperature and to operate the heating unit at a power level less than the power level corresponding to the user selected power setting when the sensed glass ceramic support surface temperature is higher than the said maximum reference temperature to reach steady state operating conditions associated with the newly selected power setting.

4. The power control system of Claim 3 wherein said minimum reference temperature represents a temperature level which the system will normally at least reach under steady state conditions when heating a relatively dark flat bottomed utensil at the steady state power level for selected power setting and the maximum reference temperature corresponds to a temperature which would normally not be exceeded when heating a relatively bright aluminum utensil having a warped bottom surface when at said corresponding power level.

5. The power control system of Claim 4 wherein said means for operating the heating unit at power levels other than the power level corresponding to the selected power setting is operative to operate the heating unit at a predetermined number of power levels higher than the power level selected when the sensed glass ceramic support surface temperature is less than said minimum reference temperature and a predetermined number of power levels lower than the steady state power level associated with the selected power setting when the sensed glass support surface temperature is greater than said maximum reference temperature for the selected power setting.

6. A method of controlling the output power of a heating element in a cooking appliance of the type in which the radiant heating element is disposed beneath a glass ceramic cooking surface for supporting loads to be heated by the element, said method comprising the steps of:
sensing the temperature of the underside of the glass ceramic support surface proximate the heating unit;
comparing the sensed temperature to a predetermined temperature range associated with the selected power setting;
operating the heating unit at a power level higher than the steady state power level associated with the selected power setting when the sensed glass temperature is less than the predetermined temperature range;
applying a power level to the heating unit lower than the steady state power level associated with the selected power setting when the sensed glass temperature is greater than the predetermined range; and applying the steady state power level associated with the user selected power setting to the heating unit when the sensed temperature lies within the predetermined range associated with the selected power setting.

7. The method of Claim 6 wherein the predetermined glass ceramic support surface temperature range for each of said user selectable power settings is defined by a minimum reference temperature representing the temperature which will normally be reached when heating a relatively dark flat bottomed pan at the power level associated with the user selected power setting and a maximum reference temperature representative of the temperature which will normally not be exceeded by a pan having a relatively bright aluminum bottom surface when operated at the power level associated with the selected power setting.