CA2115580A1 - Infrared conveyor oven - Google Patents

Abstract

A conveyor oven (10) for cooking food products using infrared radiation includes upper and lower etched foil heater (38 and 40) which are disposed above and below the upper flight of a conveyor belt (36) passing therethrough. The oven also includes a controller (18) for governing the speed of the belt (36), the time of exposure to infrared radiation, and a range of radiation wavelength between about 4 and 5 microns for cooking food in the oven (10).

Description

`~W~ ~3/~4328 2 1 1 5 ~ 8 0 P~ ;92/02357 Thi s invention relates to inf ra-red oYens ~nd primarily to comm~rcial o-rens which are compact in design and int~nded f or rapid cooking of a ~rariety o~
5 different food items.

In smaller commercial establishments, it is oten d~sirable to pro~ride f ood warmers f ~:r the diæplay of f ood whe~r~y individual or~2~s may b~o plac~d for lû :specific: it@ms: displayed. It h~s IlOW becom~ feasible to cook f ood i t~ms~ to order in such establishmeIlts uti}izing infra r~d ener~.
I~fra ;red~ erlergy isr partit:~larly sui~ed ~or smaller cler~ial establishments becau~3 the energy ; 15~ : prc)~uced i9 ~directional and production~does not i~lve ooking does not~re~uire h~ated air curr~nks whic~ may be~reIeased ~in~o :the: ambie~t atmospher~ as ~ith convec~ion oven~:and the li~Q. Whil~ mierowa~e ov~ns ~:~ are also useful in:such establi~hmen~s, microwa~e ov~ns 20 ~ have distin~t disadY~ntages r~lative to th~ inabil ty to brown bread or rolls and o char the exterior while cooking m~at~ Microwave oYens, howe~r, a~e compa~t and suitable for countertop use.
I~ U.S. Pa*ent No. 4,960,977~ assi~d to th~
as~ig~ee of thiB inYention, there wa~ d~scribed a .
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W~g3/043~8 P~T~VS~2/0235~ ' countertop-type infra-red radiation oven useful t for example, to cook pizza wherein the article to be cooked was di~posed upon a mesh turn~able. Infra-red emitters were disposed below snd above the item to be ooked and on two of its four sides. Accordingly, as the turntable rotated, all sides of the food product wexe expo~ed to radiation for cooking.
In the case of pizza, the sides, bottom, and top all may have differe~t cooking requir~ments. In the above-identified infra-red oven, the emitters wëre separately controlled. In addition, the top emitter was disposed in a movabl~ shroud which could be adjusted in height o~er the turntable as desired.
Shielding for the ov~n was no~ ne~essary because convection curre~ts were not involved in ~he cooking proce~s and only the dir~ctional radiation of the emitt~r used.
~ his type of oven was particularly suit~d to the use of etched foil emitters as con~rasted to the use of ~onve~tio~al ~uartz tubes, nichrome ~ire an~ the like.
~he foil emitters use a relatively low wattage, have a : rapid wanm-up a~d cool-down, and can be adjusted to the d~sired medium;range wavelength of cooking energy. In addit30n, a ~eramic: or other type shield is not necessary, ::
:~ In certain infra-re~ emitter~ such as that ;~ :described in U.S. Patent ~o. 3,B09~859, a refracto~y co~r is pro~ided o~er the wire he ting elements, which cover then is the source of infra-red energy to the product to be cooked. This type of de~ice then u~ilizes energy both to heat the refra~tory material and to then generate suffici ~t ener~y to direct the : same onto the product to be cooked.

,~ W093/04328 2 1 1 ~ ~ 8 0 P~T/U~9~/023~7 ~ , " . 3 It is also ~nown to provide con~eyor o~ens which utilize infra-red ener~y~ Such de~ices are described, for example, in U.S. Patents Nos. 4,245,613; 4,554,437;
and 4,615,014. Such ovens are normally multi-zo~e t~p~
oven~ and laxge type installations. In addition, as described in U.S. Patent No. 4,363,955, conventional thinking used sh~rtwave energy for food cooking such as infra-red energy in the wavelength of 1-2 microns as the preferred energy for cooking. In that l~tter identified patent, the conveyor o~en utilized was intended to brown rolls previously partially cooked.
To this end, i~fra-red radiating tubes were pro~ided across the path of travel of a con~eyor carrying the indi~idual rolls wi~h a plurality of tubes at the entrance emitting medium ra~ge microwaves, but the tubes interior to: the conveyor or tunnel oven bo~h above a~d below were :short wa~elength emitters.
As described in the above~identi~ied patent, No.
4,960,977, it has been diæ~oYered that medium wa~elength i~ra~red radiation i5 ~astly desirable for cooking food~as compared to ~he short ra~g0 spectrum of 1.0 to 2~5 microns. In this way, the cooking can occur at wavel~ngths in excess of that absorbed ~y wa~r of up to about~ for example, 4.20 to 4090 microns or higher.

It has b~en disco~ered that a lightweight and efficie~t conveyor lor tunnel oven can be pro~ided which is sufficiently compact to mount on a count~rtop. The oven of this in~ntion is also sufficien~ly ~ersatil~
to cook a wide variety of foods including pizza, fish :~ product~, chicken products, and bakery product~.

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~` 211~8~ P~T/US 9 2 / 0 23 5 7 4 03 Rac9d P~ O 1 7AUi~ 1993 The device of this invention utilizes a mesh conveyor belt which is preferably 18 inches wide and extends ~hrough a heatins chamber. The chamber mounts, above and below the belt, upper and lower heating elements which are etched foil heaters. ~he heaters ar0 disposed sufficiently close to the food items to effect rapid and efficient cooking. The heaters, however, are separately controlled. While these heating elem~nts normally disperse infra-red radiatian at a wavelength of about 3 ~o 6 microns, the waveLength desired can be provided by alkering the r~sistance on the heating element as i5 well known to those skilled in the art.
Accordingly, the etched foil heaters of this invention provide a controlled cooking en~ironment in a predetermined wavelength range utilizing heaters which minimize the wa~tage required. Etched foil heaters have a watt density of about 1.08 - 1.24 watts per square centimeter which is much lower than quartz tube heaters or similar types of heaters commonly used in cooking en~iro~ments.
The lower heater in the preferred embodiment is spaced only about 3.8 centimeters below thP conveyor belt, and the upp~x h~ater is spaced about 7.62 - 10.16 centime~ers aboYe the con~eyor belt.

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P~T/US 9 ~ / O Z 3 ~ ~
"~''3 2115580 03 ReG~d PCT/P~ 7 AUG 1993 In a preferred embodiment, the oven of this invention is only 42.19 centimeters high, 58.42 centimeters deep, and provides an opening for the conveyor belt at either side thereof which measures 7.77 centimeters high by 49.38 centimeters long. These J.atter dimensions are the food prod~ct clearance entering the de~ice.
It has ~urther been discovered that alternate embodiments of the device of this invention can be pro~ided. In one embodiment, the conveyor belt feed is continuous through the ov~n. In an altexnate ~ .

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.r~W093/0432g . 2 1 1 5 5 8 0 PCT/US92/02357 embodLment~ the conveyor belt is con~rolled so that it operates to move the product into the heating area, hold thP product therein fsr a prede$ermined period of time, and then move the product out so that khe proc~dure is a go-stop-go procedure~ In both instances, electro~ic controllers are pre~erred which control based on t~me only.
Etched foil heaters have the characteristic~ of rapid heating and cooling. To accommodate this characteristic, a timed cycling power input i~ utillzed in the preferred em~odiment. For ex~mple, full powex input may be interrupted for a period of 5-15 ~conds and then xeinitiated for 60-120 seconds. ~lso, a means to det~rmine if there is no cooking demand for a cooking cycle for a period of, for example, five minutes, ~ sensor could turn the power to khe unit off.
In addition, a means for determining the position of a food: product may be i~corporated ~y an electro-optical co~tr~l. This de~ice then could be u~ed to ; 20 ensu~e that the food product is po~itioned prop~xly between both the~top and ~ower heaters~ In this way~
: : use o: the heating elements can ~e contxolled to maximize cooking efficiency ~t a mi~Lmum of power re~uire~O
~ Accordingl~ t Ls an object of this invention to : provide a co~pact co~veyor oven whi~h may be utllized o~, for eæample,~a co~ntertop and which utilizes etched ~ foil i~fra-red el~ments~as hea~ sources for rapid and : ~efficient oooki~g. ~ l 3~ It is another object of this invention to provide alternstive embodLments of a ~co~pa~t conveyor oven : which either operate continuously or ~perate on an indexing go-stop-go procedure for coo~ing a wide WO 93io4328 P~/US /b variety of food products f:rom pizza ~o fish a~cl fowl products or bak~ary produc l:s .
It is yet another ob~e ::t o~ this in~rention to provide a compact con~reyor o~ren ha~rins~ a controll~r 5 controlling the heat requirements therein by ::ontrolling the power input to upper and to lower hea~ing elem0nts, s~parately, wherein the haating elemen~s are ~tched foil. elements to minimlze the wat~age requiremen~.
These and other objects will become readily apparent with ref erence to th2 drawings and ~ollowing de~cription wherein:

Figure 1 is a perspective ~iew of an embod~nent of 15 the o~Ten of thi~ invention.
Figur~ 2 is a sid~ view thereof.
Figure :3 is a top ~iew of the c~en o this inv~ntion. ~
Figure 4 is a side ~riew of the o~ren of this ~: , in~e~tion~showing the two heating el~m~nts.
Fig~re: S is an :alternative embodimsnt of this invention:in~ol~ing stacked o~e~s.
Fig~re 6A is a schematic of the control cir~uit for an embodiment o~ t~Ls~ inve~tion using an inde~i~g : 25 ~: belt ~eed~for~a gOStQp-go me~ns o travel thxough the o~en of t~is~in~e~tion.
igure~ ~ ~6B: is a: ~Tiew similar to Figu:re 6a o~ly showir~g the~ ~control circuit for ~ conti~uou~ bE~lt feed in an e~od:LllLent of this i~vention.
~:~; 30 ~ Pigure 7A is a schematic s~owing the ! control circuits : for the h~ating elements in a three-pha~e elem~nt hookup. ~ ~

PC,7/lJ~ 92/o~5~ `

2115S80 ~3 Rec'd P~TJP~O 11 l AUG ~993 Figure 7B is a view simîlar to Figure 7a showing the c~rcuit for a single-phase element hookup.
Figure ~ is a graph showing a typical fluctuation in the surface temperature and wavelength over time for a heating circuit in a device o~ this invention.
Figure 9 is a graph depicting surface temperature against time illustrating a typical heat up and cool down mode of operation of ~he device of this invention.

Detailed Description of the Invention With attention to the drawings and to Figures 1-3, in particular, the device of this invention 10 in its preferred construction is modular. Accordingly, a housing 12 preferably mounts a top heater module 14, a bottom heater module 16, and a control panel 18. Both modules and the control panel preferably are slidably mounted within the housing 12 and, therefore, can be easily removed for cleaning, testing, or repair. As shown in Figure 2, the housing has an opening 20 for a conveyor belt (not shown) to carry food through the hous.ing 12. In the preferred embodiment of this invention, the opening 20 is 7.77 centimeter~ by 49.38 centimeters in diameter. This has been found to be adequate for most food products. In addition, the overall housing depth is preferred to be 58.42 . ~ :

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~r ~ 2115580 PCT~ 9 2 / 02~i57 7a ~3 R~'d P~T/P~O 1 1 AUG ~993-centimeters with the height 42.19 centimeters, the dimensions shown of the embodiment in the view of Figure 2. This unit then will accommodate a conveyor beLt with a width of 45.72 centimeters, and meets a desired specification that it~be no more than 60.96 centimeters deep. It then can be comfortably mounted on a restaurant counter, or food processing area, or similar location.
The housing 12 includes lateral extensions 22 and 24 for supporti.ng the conveyor bslt. A conveyor belt support frame member ~: :

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- 2115!~80 PCTI~J~ 92/02357 8 0~ ~ec9d P~T/PT~ l 7 AUG 199 is mounted in each lateral extension 22 and 24 for supporting the conve~or bel~ (not shown). Lateral support members 28 are provided for this purpose.
The upstream lateral support 22 further moun~s a c~nveyor belt sprocket drive shaft 30 for the conveyor belt and a similar shaft 32 is provided downstream at extension 24. A conventional thumbscrew-type tensioning means 34 is pro~ided on sprock~t 32 to re~ulate the tension in the bel~. With attention to Figure 4, the con~eyor belt 36 is shown in phantom ther~in.
Top and bottom heating elemen~s respectively 38 and 40 are provided in housing 12 above and below the upper flight of the conveyor belt 36~ These elements are preferably etched foil heaters obtainable, for example, from Thermal Circuits, Inc., of Salem, Massachusetts. Thé heaters ~ypically operate in the 3 6 micron wavelength range for optimum cooking and have a watt density of about 1.08 - 1.24 watts per square centime~er. This is a much lower watt density than quartz tube heaters that radiate in a wide wavelength range. As noted above, the wavelength can be further defined by adding resis~ance as would be ob~iou~ to those skilled in the art. As will be sub~aquently described, each heating element 38 and 40 will be separately controlled.

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8a 03 R~c~d P~T/P~O 1 7 AUG 1993 With atten~ion to Figure 3, there is also provided an illumination means for interior lighting at four locations 42 at, respectively, the entranc0s and exits to the housing 12 upstream and downstream of the cooking area.
In addition, an optical indicator 44 may be provided upstream of the housing 12 whereby when the cooking cycle for one food item has been completed and ' : ~ ~
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~ W093/043Z8 2 1 ~ 5 5 8 0 PCT/US92/02357 a~other food item is not entering th~ housing 12, the indicators 44 will so advise the controller, and the controller in turn will shut down ~he heating elements 38 and 40. Electro-~ptical controllers are available, for example, from Microswitch Di~ision of Honeywell, Inc., Freepor~, Illinois.
The control panel 18, is part o a control module ~not shown) which rests upon a tray behind the control panel 18. The controller contains, a3 w~ll be o~ious to those skilled in the art, all major o~en control element~. El~ctronically programmable controls suitable for use in this in~ention can be obtained frvm United Electric Controls, Inc. of Wa~ertown, Maine or co~ve~tional controllers, as will be obvious to ~hofie skill~d in ~he art, may be used to contxol belt peed, top hea~ and ~tom h~at. In the pref~rred em~od ~ent~
: the Gontrol is by tLme only ra~her than temperature.
With a~tention to Figure 5, ~y using a mounting collar 46~ a~plurality of units lO can be sta~ked as 0 desiredO ~The collar 46 is merely a con~entional ~ flange-type~col:~ar:~adapted to rest on th~ upper surfa~e : of housing 12 and receive the lower surf~ce of the next higher unit to~e s~acked. Obviously, ~he ~upport legs 48 will be removed fr~m the stacked units.
: ~ also ::shown in the Figures, ~he housing 12 pro~ided a~plurali~y of ~ents 50. Internal:fa~ may be ~;~ provided as dQsired. In the preferred embodLme~t, with :~ refere~ce to ~igure ~4, ventilation fans $2 shown :~ schematically are provided above the heating element ~ 30 : 3~, ~
:~ The de~ice of this i~vention then is a ~ompact conveyor ov~n which utilizes upper and lower heating elements which are e~ched foil heater~. ~he top heater 38 is di~po~ed about 3-4 in~hes above the upper flight , , ~~ 2il5~80 PCT/US 9~ / 023 ~7 03 Rec'd PCT/~T~ 1 7 ~UG ~993 of ~he conveyor belt, and the lcwer heater 4~ is d.isposed below the upper flight o~ the conveyor belt, a distance of about 3.8 centimet~rs. The interior of h~using 12 is further construc~ed of aluminum coating steel to reflect the infra-red radiation generated.
As shown in Figure 9, etched foil heaters inherently achieve a very rapid change in temperature, both in the heating up phase, and in cool down. As shown in Figure 9, the heat up phase of ahout six minut~s is satisfackory to produce a temperature above 337.8 degrees C and a wavelength of about 4.5. Cool down occurs similarly rapidly. Accordingly, i~ may be desixable ~o provide an interrupted power input whereby for a period of 5 ~o 15 seconds, power is cu~ off, and reinitiated for 60 to 120 seconds. For example, in Figure 8, ~he result causes a fluctuating wavelength of from about 4.5 up ~o about 5 microns and a temperature variation of abou~ 304.4 to about 371.1 degrees C. The controller above-: : identified can be so p~ogrammed if desired.
It has been dlscovered as noted above, that a cooking wavelengkh 4-5 microns i~ optimal a~ compared to short wavelen~ths in the~1-2 micron range. It is intended, wi~hin ~he scope of this invention, to encompass any con~entional controller for regulating the generated heat to a wavelength within the desired range.
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211~58~ P~TIIJS 9 2 / 0 23 5 7 lOa 03 Rgc'd P~TIPT0 l 7 AUG '993 With attention to Figures 7A and 7B, there are depicted therein a schemati~ in a preferred version of the heater element hookup of the device of this invention. These schematics are intended to be illustrative, however, and not limitative. Figure 7A is a tnree-phase element hookup while Figure 7B is a single-ph~se element hookup. H-l, signifies the : ~ !

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-- W093/04328 2 1 1 ~ 5 8 0 PCT/~S92/02357 schematic for the top heater 38 and H-2 simil~rly identi~ies the lower heater 40. The separate controllers, CR-1 and CR-2 are reflected in the panel 18.
5Figures 6A and 6~ show, respectively, schema~ics for the indexing belt eed and a continuous ~elt feed.
In the indexing belt f eed, th~3 belt ad~rances the f ood product into housing 12 and stops with the product located between heating elements 38 and 40. This 1 Omovem~3nt would be identif ied by optical sensors 4 4 and the controller signalled accordingly. In the preferred em~odiment of this invention, the control i5 by tLme rather than temperature and, theref ore, af ter a predetermined period of time, the belt dri~re would ~hen 15index the food out of the housing 12 and onto extension 24 whereupon the belt would stop while the food product is reme)ved and another f ood product placed at the er~tranc~, o~ the ~ belt portion in e:~etension 22.
In the continuous belt f eed, ~he belt will run ~0continuously at a ~peed to be determi ned at the control panel 18 whereby residence tiIr.e within the hc~using 12 wherein ~he heatiny elements ar~3 dispensing inf ra~red radiation at a predetermined wa~elength or within a predetermined waYelens~th range, ~he produc:t will be ~5 cooked.
As with Figures ~ 7A and 7B, Figures ~A and 6B are in~ended to be illu~trative and not l~mitati~Te of this in~rention . Accordingly, a dif ~rent type of control s::ircuit or control function is intended to be witHin 30the scop~ of this invention.
The invention may be em~odied in o~her specified forms without departing from the spirit or ~ssential :~characteristics thereto. The present embodLments are therefore to be considered in all respects as WO93/~4328 ` ~ ` PCT/U~92/02357 ~
211558~ 12 illustrati~re and not restrictive, the s ::ope of the invention being indicated by the appended claims rather than by the f oregoing description, and all charlges which may cc~me within the me~ning and range of 5 e~ui~alency of the lai.ms are th~refore in~ended to bé
embrac~d therein.

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Claims (18)

Claims

1. A compact, countertop type conveyor oven comprising: a housing defining a cooking chamber having an inlet and an outlet;
a conveyor belt extending through the chamber and through the inlet and outlet and drive means therefor; support arms mounted on said housing at the inlet and outlet for supporting that portion of said conveyor belt extending therefrom; top and bottom infra-red heating elements mounted within said chamber a predetermined distance above and below the upper flight of that portion of the conveyor belt disposed in said chamber each element contained in a plane disposed parallel to the upper flight and spaced a predetermined distance therefrom, said elements substantially covering that portion of the flight disposed within said chamber, said elements being etched foil heaters; and control means coupled to said oven for controlling the speed of travel of the conveyor belt through said chamber and the wavelength of the infra-red radiation generated and time of exposure thereto within the chamber to control the range of the wavelength generated between about 4-5 microns by interrupting the operation of said heaters.

2. The oven of claim 1 wherein the heaters have the capacity of about 1.08 - 1.24 watts power per square centimeter of surface area.

3. The oven of claim 1 wherein the conveyor belt is only about 45.72 centimeters wide.

4. The oven of claim 3 wherein the upper heater element is dispose about 7.62 - 10.16 centimeters above the plane containing the upper flight of said conveyor belt.

5. The oven of claim 4 wherein the lower heater element is disposed about 3.8 centimeters below the plane containing the upper flight of said conveyor.

6. The oven of claim 1 wherein said control means in sequence advances said belt into said chamber, stops for a predetermined period of time and then advances said belt again through said chamber so that a food product thereon is indexed into the chamber for a predetermined period of time to cook it and then advanced through the outlet so that it can be replaced in the chamber with another food product to be cooked.

7. The oven of claim 1 wherein said control means advances said belt continuously at a predetermined speed proportional to the residence time of an incremental portion of said conveyor belt within the cooking chamber.

8. The oven of claim 1 wherein the depth of said oven in the direction of said parallel planes is no more than about 60.96 centimeters.

9. The oven of claim 8 wherein the inlet and outlets have rectangular dimensions of about 7.7 by 49.4 centimeters.

10. The oven of claim 1 further comprising optical indicator means for indicating when a food product is disposed on said conveyor at the inlet to said chamber.

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11. Method for cooking food in a compact, countertop type conveyor oven comprising: providing a housing defining a cooking chamber having an inlet and an outlet; a conveyor belt extending through the chamber and through the inlet and outlet and drive means therefor; support arms mounted on said housing at the inlet and outlet for supporting that portion of said conveyor belt extending therefrom; top and bottom infra-red heating elements mounted within said chamber above and below the upper flight of that portion of the conveyor belt disposed in said chamber each element contained in a plane disposed parallel to the upper flight and spaced a predetermined distance therefrom, said elements substantially covering that portion of the flight disposed within said chamber, said elements being etched foil heaters; and control means coupled to said oven for controlling the speed of travel of the conveyor belt through said chamber and the wavelength of the infra-red radiation generated and time of exposure thereto within the chamber; and passing food to be cooked through said oven on said conveyor while subjecting said food to infra-red radiation generated by said foil heaters at a wavelength between about 4-5 microns while maintaining a surface temperature of less than about 371° C in said heaters by interrupting the operation of said heaters.

12. The method of claim 11 wherein the heaters have a capacity of about 1.08 - 1.24 watts power per square centimeter of surface area.

13. The method of claim 11 wherein the conveyor belt provided is only about 45.72 centimeters wide.

14. The method of claim 11 wherein said control means in sequence advances said belt into said chamber, stops for a predetermined period of time and then advances said belt again through said chamber so that the food product thereon is indexed into the chamber for a 14b predetermined period of time to cook it and then advance through the outlet so that it can be replaced in the chamber with another food product to be cooked.

15. The method of claim 11 wherein said control means advances said belt continuously at a predetermined speed proportional to the residence time of an incremental portion of said conveyor belt within the cooking chamber.

16. The method of claim 11 wherein the depth of said oven n the direction of said parallel planes is no more than about 60.96 centimeters.

17. The method of claim 16 wherein the inlet and outlets have rectangular dimensions of about 7.62 by 49.53 centimeters.

18. The method of claim 11 further comprising providing an optical indicator means for indicating when a food product is disposed on said conveyor at the inlet to said chamber.