GB2088179A

GB2088179A - Microwave Heating Apparatus

Info

Publication number: GB2088179A
Application number: GB8134923A
Authority: GB
Original assignee: Sanyo Electric Co Ltd
Current assignee: Sanyo Electric Co Ltd
Priority date: 1980-11-20
Filing date: 1981-11-19
Publication date: 1982-06-03
Also published as: GB2088179B; NL186214C; DE3146045C2; NL8105244A; DE3146045A1

Abstract

Microwave heating apparatus comprises two heating portions, one heating portion having a ladder circuit portion 13 through which microwaves leak, whereby a material 40 being heated is heated by the leaked microwaves, the other heating portion 60 heating the material in response to the residual microwaves not consumed by the one heating portion. The other heating portion may directly heat the material being heated with the residual microwaves or may heat the material being heated by converting the residual microwaves to heat at 30, which is conveyed by a heat pipe 50. The heating apparatus may be used in an electrophotographic copier, the other heating portion drying the transfer sheet and the one heating portion fusing the image thereon; then a heat pipe connected to the other heating portion may pre-heat the transfer sheets before transfer of the image thereto. <IMAGE>

Description

SPECIFICATION Microwave Heating Apparatus Background of the Invention Field of the Invention The present invention generally relates to a microwave heating apparatus. More specifically, the present invention relates to an improved microwave heating apparatus for uniformly heating a sheet like material such as paper or the surface of any other material being heated.

Description of the Prior Art Heating a material being heated by the use of a microwave has been well-known. However, in heating such a thing as having a large surface area as compared with the volume, such as a sheet of paper, a conventional microwave heating apparatus involved a difficulty in heating effectively and uniformly a sheet like material being heated such as a sheet of paper in that a heating efficiency is small.

Therefore, the present inventors previously proposed an excellent microwave heating apparatus including a microstrip line having a ladder circuit portion and being capable of uniformly heating the sheet like material or the surface of a material having a thickness with a microwave leaked from the ladder circuit portion.

The previously proposed microwave heating apparatus is disclosed in United States Patent Application Serial No. , British Patent Application No.8124008, German Patent Application No. P 31 31 213.6 and Dutch Patent Application No. 81.03715 which were all assigned to the same assignee. Now one example of the previously proposed microwave heating apparatus will be briefly described with reference to Figure 1 for the purpose of facilitating the understanding of the present invention.

Figure 1 is a perspective view showing one example of a microwave heating apparatus which constitutes the background of the present invention. The example shown comprises a microstrip line 10, a coaxial line 20 for supplying a microwave to the microstrip line 10, and a dummy load 30. The microstrip line 10 comprises a dielectric base plate 11 made of ceramic such as aluminum, for example, and a center conductor 1 2 is formed on the surface of the dielectric base plate 11. The center conductor 12 is made of metal such as silver, for example, and a ladder circuit portion 1 3 is formed on a portion in the length direction thereof. The ladder circuit portion 13 includes a plurality of leaking openings or slits 14 disposed distributed in the length direction, i.e.

the microwave propagating direction. The microstrip line 10 further comprises a grounding conductor 1 5 of silver, for example, formed to be attached to the rear surface of the dielectric base plate 11. On the other hand, the coaxial line 20 comprises an inner conductor 21 and an outer conductor 22 and in the example shown in Figure 1 the inner conductor 21 is connected to the center conductor 1 2 of the microstrip line 10 and the outer conductor 22 is connected to the grounding conductor 1 5 of the microstrip line 10.

Meanwhile, since there is no polarity restriction between the inner conductor 21 and the outer conductor 22 of the coaxial line 20 and between the center conductor 12 of the microstrip line 10 and the grounding conductor 15, the center conductor 12 of the microstrip line 10 may be connected to the external conductor 22 of the coaxial line 20 and the grounding conductor 1 5 and the inner conductor 21 may be connected to each other.

A microwave oscillator including a magnetron or a gunn diode, although not shown, is provided as an input end, i.e. as a left side as viewed in Figure 1, of the coaxial line 20. A microwave from the microwave oscillator is supplied through the coaxial line 20 to the microstrip line 10. A dummy load 30 is connected to the end of the microstrip line 10 opposite to the input of the microwave. In the case of the proposed microwave heating apparatus, the dummy load 30 serves to absorb and consume the microwave not consumed by the ladder circuit portion 13, whereby the microwave oscillator is protected.

The Figure 1 microwave heating apparatus supplies a microwave to the microstrip line 10 upon energization of the microwave oscillator, not shown. A portion of the supplied microwave is leaked from the respective leaking slits 14 at the ladder circuit portion 13 formed on the center conductor 12. Accordingly, by placing a material being heated 40 such as a sheet of paper on the ladder circuit portion 13, the material being heated 40 is heated by the leaked microwave.

Since the microwave heating apparatus previously proposed and assigned to the present assignee, as described previously, employs a microstrip line having the ladder circuit portion formed, a compact and inexpensive microwave heating apparatus became available. However, the previously proposed microwave heating apparatus still further involved a problem to be solved set forth in the following. More specifically in the case of the Figure 1 apparatus there is a small amount of the microwave consumed by the microstrip line 10 and a major portion of the microwave was consumed by the dummy load 30. Accordingly, a considerable portion of the microwave supplied from the microwave oscillator does not contribute to the heating operation of the material being heated 40 and consumed wastefully.This is not preferred from the standpoint of effective utilization of the microwave and from the standpoint of saving energy.

Summary of the Invention Briefly described, the present invention comprises a microwave heating apparatus including first heating means having a first ladder circuit portion and for heating a material being heated with a microwave leaked through the first ladder circuit portion and second heating means for heating the material being heated by the use of the residual microwave not consumed by the first heating means. The second heating means can be utilized for preheating the same material being heated which is to be heated by the first heating means or can be utilized to heat a different material being heated which is to be heated by the first heating means.Therefore, according to the present invention, a microwave can be effectively utilized to heat a material being heated and hence a microwave oscillator of a lower output can be utilized or a microwave oscillator of an ordinary output can be utilized to heat a material being heated of a larger heat capacity. Accordingly, a microwave heating apparatus capable of saving energy is provided.

In a preferred embodiment of the present invention, the first and second heating means are utilized as heating means of an electrophotographic apparatus. As well known, an electrophotographic apparatus is structured to form an electrostatic image on a photosensitive material, to develop the electrostatic image as a toner image, to transfer the toner image to a transfer sheet, and to fix the toner image on the transfer sheet through thermal fusion thereof. The first heating means is utilized to perform the above described fixing through thermal fusion and the second heating means is used to heat and dry the transfer sheet before the transfer sheet is brought to the first heating means, i.e. the thermal fusion fixing portion.According to the above described preferred embodiment, an electrophotographic apparatus is provided in which the quality of the copied image can be improved without increasing power consumption.

More specifically, with a conventional electrophotographic apparatus, if and when a transfer sheet is wetted, a transfer efficiency of a toner to a transfer sheet is degraded, whereby the density of a copied image is decreased and the heat by the thermal fusion fixing means such as a heat roll is absorbed by a moisture in the transfer sheet, with the result that a disadvantage is involved that a toner image can not be well-fixed.

However, according to the preferred embodiment, a toner image is fixed by the first heating means and the residual microwave energy is utilized to heat and dry in advance a transfer sheet.

Accordingly, degradation of the density of a copied image can be prevented and a toner image can be assuredly fixed through thermal fusion with a less heat quantity.

The second heating means of the present invention may be structured in two major different ways. In one way, the second heating means is structured to heat a material being heated by converting into heat the residual microwave which was not consumed by the first heating means. In the other way, the second heating means is structured to heat directly a material being heated with the residual microwave.

According to the former approach, heat generating means is provided for generating Joule heat upon receipt of a microwave. On the other hand, according to the latter approach, the second heating means employs a ladder circuit portion of substantially the same structure as that of the first heating means.

Accordingly, a principal object of the present invention is to provide à microwave heating apparatus of a high microwave utilization efficiency and capable of saving energy.

One aspect of the present invention resides in a microwave heating apparatus comprising first heating means having a ladder circuit portion, and second heating means for heating the same or a different material being heated by the use of the residual microwave which was not consumed by the first heating means.

Another aspect of the present invention resides in an electrophotographic apparatus utilizing the above described first and second heating means.

A further aspect of the present invention resides in an electrophotographic apparatus adapted for fixing through thermal fusion of a toner image on a transfer sheet by means of the first heating means, heating and drying the transfer sheet with the residual energy before the transfer sheet is brought to the first heating means, thereby to improve the quality of a copied image.

Still a further aspect of the present invention resides in a microwave heating apparatus, wherein the second heating apparatus is adapted to heat a material being heated by converting to heat the residual microwave which was not consumed by the first heating means.

Still another aspect of the present invention resides in a microwave heating apparatus, wherein the second heating means is adapted for heating directly a material being heated with a residual microwave which was not consumed by the first heating means.

These objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

Brief Description of the Drawings Figure 1 is a perspective view showing one example of a microwave heating apparatus which constitutes the background of the invention; Figure 2 is a perspective view showing one embodiment of the present invention; Figure 3 is a sectional view of the Figure 2 embodiment taken along the line Ill-Ill in Figure 2; Figure 4 is a perspective view showing a modification of the Figure 2 embodiment; Figure 5 is a perspective view showing another modification of the Figure 2 embodiment; Figure 6 is a perspective view showing another example of the ladder circuit portion formed in a microstrip line which is utilizable in the present invention; Figure 7 is a bottom perspective view of the Figure 7 example; Figure 8 is a perspective view of a further embodiment of the present invention;; Figure 9 is a perspective view showing still a further embodiment of the present invention; Figures 1 OA and 1 OB are sectional views showing different examples of a short circuiting plate which is utilized in the embodiments shown in Figures 8 and 9; Figure 11 is a view showing a structure of one example of an electrophotographic apparatus in accordance with a preferred embodiment of the present invention; Figure 12 is a perspective view showing a major portion of the Figure 11 embodiment; and Figure 1 3 is a view showing a structure of another example of an electrophotographic apparatus in accordance with another preferred embodiment of the present invention.

Description of the Preferred Embodiments Figure 2 is a perspective view showing one embodiment of the present invention. Referring to Figure 2, the structure and connection of a microstrip line 10, a coaxial line 20 and a dummy load 30 are substantially the same as those of Figure 1 and therefore a detailed description of these will be omitted by incorporating the previous description in conjunction with Figure 1.

The Figure 2 embodiment comprises a second heating means utilizing heat generated by the dummy load 30. More specifically, the dummy load 30 is poupled to a heat pipe 50 serving as one example of a heat transmitting means, A heat dissipatipg member 60 is coupled to the output end of the heat pipe 50. Accordingly, the heat generated by the dummy load 30 is transmitted to the heat dissipating member 60 by means of the heat pipe 50. Meanwhile, the dummy load 30 is well-known as a resistive terminating load. The heat pipe 50 is also well-known in the article entitled "Applications of the Heat Pipe" appearing in the periodical Mechanical Engineering issued November 1968 in the United States, for example.Briefly described, the heat pipe 50 comprises an enclosed outer pipe 51 and a wick 52 formed inside the outer pipe 51 and made of a porous material serving as an organism for providing capillarity. The wick 52 is impregnated with an acting liquid such as water, alcohol, ammonium or the like. When one end of the heat pipe 50 of such structure is heated, the acting liquid is evaporated by absorbing the heat from the pipe wall, whereupon the vapor moves toward the other end of the heat pipe 50. The vapor is then cooled at the other end of the heat pipe 50 to be condensed to return to a liquid while simultaneously dissipating the heat. The liquid is then returned again to one end of the heat pipe 50 through the wick 52. Thus, the heat pipe 50 is structured as one example of the heat transmitting means.The heat dissipating member 60 may comprise a good heat transfer member of such as metal and is coupled to the other end of the heat pipe 50. Accordingly, the heat dissipating member 60 receives the heat generated by the dummy load 30 through the heat pipe 50, thereby to dissipate the heat therefrom. It is pointed out that the heat dissipating member 60 may comprise a number of fins for improving a dissipation effect or may be of any other shape.

In operation, a microwave from the microwave oscillator, not shown, is supplied through the coaxial line 20 to the microstrip line 10.

Accordingly, the microwave is leaked through the ladder circuit portion 13 of the microstrip line 10 and hence a material being heated 40 to be conveyed by a conveying means, not shown, for conveying the material being heated is heated by the leaked microwave. Not all of the microwave as supplied is consumed by the ladder circuit portion 13 and a portion of the supplied microwave, say approximately only two third of the microwave is consumed, while the microwave of the one third as not consumed is fed to the dummy load 30 coupled to the rear end of the microstrip line 10. The dummy load 30 thus receives the residual microwave energy not consumed, thereby to convert, the same to heat.

The heat generated by the dummy load 30 is transferred through the above described heat pipe 50 to the heat dissipating member 60. Therefore, it follows that according to the Figure 2 embodiment, the material being heated 40 is preheated with the heat dissipated from the heat dissipating member 60. However, the heat dissipated from the heat dissipating member 60 and then heated with the microwave from the ladder circuit portion 1 3 of the microstrip line 10.

The embodiment is adapted such that the same material being heated 40 is preheated with the heat dissipated from the heat dissipating member 60. However, the heat dissipating member 60 may be utilized otherwise as desired and may be disposed to heat a separate material being heated for other purposes. The above described microstrip line 10 constitutes a first heating means and the heat dissipating member 60 and the associated components constitutes a second heating means.

Meanwhile, according to the Figure 2 embodiment, the second heating means is constituted such that heat is transferred by the use of the heat pipe 50. However, it is pointed out that the second heating means can be implemented without utilizing such heat pipe 50.

Figure 4 is a perspective view showing a modification of the Figure 2 embodiment.

Referring to Figure 4, the residual microwave not consumed by the microstrip line 10 is guided to the position of the heat dissipating member 60 by means of the coaxial line or other microwave transmitting line 70 and the dummy load 30 is provided at the rear end of the coaxial line 70, whereby the heat generated by the dummy load 30 is directly fed to the heat dissipating member 60. The Figure 4 embodiment brings about an advantage that heat loss is decreased as compared with a case where the heat pipe is employed.

Figure 5 is a perspective view showing another modification of the Figure 2 embodiment. The Figure 5 embodiment employs a microstrip line 1 0' in place of the heat dissipating member 60 of the Figure 4 embodiment. The microstrip line 10' may be of substantially the same structure as that of the microstrip line 10 constituting the first heating means and hence a more detailed description will be omitted.

Figures 6 and 7 are perspective views showing another example of the microstrip line for use in the present invention, wherein Figure 6 is an upper perspective view and Figure 7 is a bottom perspective view. The embodiment shown has a ladder circuit portion 13' formed on a grounding conductor 1 5 of the microstrip line 10 and the center conductor 12 formed with a constant width as in the case of an ordinary microstrip line.

By thus forming the leakage slits 14' and thus the ladder circuit portion 13' on a portion or the hole of the grounding conductor 15, any particular structure or means for achieving impedance matching with the coaxial line 20 can be substantially dispensed with. Furthermore, the example shown in Figures 6 and 7 provides an increased electric field component of a microwave being leaked from the slits 14' of a ladder circuit portion 13' as compared with a case where a ladder circuit portion is formed in the center conductor. As a result, the microwave power of the former required for providing the same heating energy may be approximately one tenth as compared with the latter. Meanwhile, since the details of such microstrip line has been fully disclosed in the previously referenced patent applications, the same is incorporated herein by reference thereto.

Figure 8 is a perspective view showing another embodiment of the present invention. The embodiment shown employs a waveguide for constituting a ladder circuit portion. More specifically, a microwave from a microwave oscillator 80 energized by a direct current power supply 81 is supplied to à waveguide 100 forming a first ladder circuit portion 101 through a waveguide 82 and a uniguide 90 coupled to the waveguide 82. The microwave supplied to the waveguide 100 is leaked in part from the leakage slits 102 constituting the ladder circuit portion 101, whereby the material being heated 40 is heated.In the absence of the material being heated 40 such as a paper sheet on the ladder circuit portion 101, the residual microwave which was not consumed by the ladder circuit portion 101 is reflected by the short circuiting plate 103 coupled to the rear end of the waveguide 100, whereby the same passes again through the waveguide 100 in the opposite direction. A portion of the microwave thus reflected is again leaked at the ladder circuit portion 101 and the residual microwave not consumed is then supplied through a branch guide 91 of the uniguide 90 to a waveguide 100' constituting a second heating means. The waveguide 100' is formed with a second ladder circuit portion 101' formed with a plurality of leakage slits 102'. A dummy load (a resistive terminating load) 104 is coupled to the rear end of the waveguide 100'.

Accordingly, the residual microwave reflected from the short circuiting plate 103 constituting the reflecting means is leaked from the second ladder circuit portion 101', whereby a material being heated 40', if placed thereon, is directly heated with the leaked microwave.

More specifically, the Figure 8 embodiment is adapted such that in the presence of a material being heated 40 on the ladder circuit 101 no reflected wave exists in the waveguide 100 through adjustment of the reflecting plate 103 so that only a traveling wave exits in the waveguide 100. By thus setting, in the absence of a material being heated 40 on the ladder circuit 100 a reflected wave from the short circuiting plate 103 passes through the waveguide 100 in the opposite direction. The material being heated 40' is heated by the second ladder circuit portion 101' with the above described reflected wave.

Therefore, according to the Figure 8 embodiment it follows that only a traveling wave exists in the waveguide 100 and thus on the ladder circuit portion when the material being heated 40 is to be heated and thus a portion of a larger energy intensity travels in succession. Therefore, uneven heating of the material being heated 40 can be effectively prevented as compared with a case where a standing wave exists in the waveguide 100 and thus on the ladder circuit portion 101.

The same principle also applies to the Figure 9 embodiment to be described subsequently.

Figure 9 is a perspective view showing another embodiment of the present invention and employs a microstrip line in place of the waveguide of the Figure 8 embodiment. More specifically, a microwave from the microwave oscillator 80 is supplied through a coaxial line, a uniguide 90 and a coaxial line 20 to a microstrip line 10. As in the case of the Figure 8 embodiment, the microwave is reflected from the short-circuiting plate 103. A portion of the reflected microwave is again leaked from the first ladder circuit portion and then the residual microwave is supplied through a branch guide 91 of the uniguide 90 to a second microstrip line 10'.

The microstrip line 10' comprises a second ladder circuit portion 13" formed with a plurality of leakage slits 14". A resistive load or a dummy load 30' is coupled to the rear end of the microstrip line 10'. The second microstrip line 10' constituting the second heating means may be of the same structure and the same operation as those of the microstrip line 10 constituting the first heating means and hence a more detailed description thereof will be omitted.

Figures 1 OA and 1 OB are sectional views showing different examples of the short circuiting plate 103. Figure 1 OA shows a short-circuiting plate of a so-called box type and Figure 1 OB shows a short circuiting plate of a so-called choke type. As seen from Figures 1 OA and lOB, preferably the short-circuiting plate 103 is provided to be displaceable in the arrow direction.

By displacing the position of the short-circuiting plate 103, the phase of the reflecting wave can be arbitrarily adjusted. Accordingly, a reflected wave from the first heating means, i.e. from the first ladder circuit portion 101 or 13 can be effectively cancelled. Therefore, no standing wave is caused in the ladder circuit portion 101 or 13 and hence a portion of strong energy moves in succession.

By thus adjusting the position of the shortcircuiting plate 103, the material being heated can be uniformly or evenly heated. It is needless to say that a short-circuiting plate of a so-called screw type may also be employed.

Figure 11 is a view showing an electrophotographic apparatus in accordance with a preferred embodiment of the present invention. The electrophotographic apparatus 200 shown comprises a housing 201. A photosensitive drum 202 is rotatably provided in the housing 201 and is formed with a photosensitive layer of such as selenium on the surface thereof in a well-known manner. A charging corotron 203 is provided in the vicinity of the photosensitive drum 202 for uniformly changing the electric charge on the surface of the drum 202. An optical means 204 is provided above the photosensitive drum 202. The optical means 204 comprises a light source 205 and a short focus point lense alley 206 including a condensing light conductor of a number of closely disposed bar lenses.An original copy carriage 229 is provided on the top the housing 201 so as to be movable to and from in the arrow direction by means of rollers 230 and 231. The original copy carriage 229 is made of a transparent material so that the image of the original copy placed on the original copy carriage 229 illuminated by the light beam from the light source 205 is focussed on the photosensitive drum 202 through the short focus point lense array 206. Thus an electrostatic image is formed on the surface of the photosensitive drum 202.

The electrostatic image formed on the photosensitive drum 202 is developed by means of a developing means 207 as a toner image, i.e.

a visible image. The developing means 207 comprises a toner box 209 for stirring a toner 208 and a magnetic brush 210. The magnetic brush 210 serves to supply the toner to the photosensitive drum 202 while the drum 202 is rotated, with the toner 208 kept on the outer surface of a sleeve by means of a magnetic force.

The toner image thus developed by the developing means 207 is transferred to a transfer sheet 212 by means of a transferring means 211.

More specifically, the transferring means 211 comprises a corotron of a corona discharge type and generates an electric charge of the polarity opposite to that of the toner, whereby the toner 208 is attracted such that the toner is adhered onto the transfer sheet 212 passing above the means 211. The transfer sheet 212 is stacked in a sheet container 214 and is fed by means of a sheet supplying means 213 including a sheet supplying roller 215 and a sheet supplying roller pair 216 and 217.

A conveying roller 219 is provided in the vicinity of the photosensitive drum 202 for conveying the transfer sheet 212 through cooperation with the photosensitive drum 202 and a separator 21 8 is provided at the subsequent stage thereof for separating the transfer sheet adhered onto the surface of the photosensitive drum 202. The transfer sheet 212 thus fed is further conveyed in the arrow direction with a conveying roller pair 220 and 221 and is then delivered by a paper delivering roller pair 223 and 224. The transfer sheet thus delivered by the delivering roller pair 223 and 224 is then stacked in succession in a tray 225.A heating means 222 is provided between the photosensitive drum 202 and the paper delivering roller pair 223 and 224 and below a transfer sheet 212 for heating the toner image formed on transfer sheet 212 for thermally fusing the same to fix the same. The heating means 222 will be described in more detail.

A cleaning means 226 is provided in the vicinity of the photosensitive drum 202 for removing the toner remaining on the photosensitive drum 202 after the toner image on the transfer sheet 212 is transferred as described above. The cleaning 226 comprises a blade 227 for removing the remaining toner through contact thereof with the surface of the photosensitive drum 202. An electric charge removing corotron 228 is provided in the vicinity of the photosensitive drum 202 and between the cleaning means 226 and the electric charge corotron 203. The electric charge removing corotron 228 is adapted to generate an electric charge of the polarity opposite to that of the charging corotron 203 for removing the remaining electric charge on the photosensitive charge 202.Meanwhile, such electrophotographic apparatus 200 is wellknown, apart from the heating means 222 constituting one of the features of the embodiment shown, and hence a more detailed description thereof will be omitted.

Figure 12 is a perspective view showing one example of the heating means 222 which constitutes one of the features of the embodiment. The heating means 222 comprises waveguides 100 and 100'. The two waveguides 100 and 100' are coupled to a converter coupler 107 to each other. The waveguide 100 is formed with a first ladder circuit portion 101 including a plurality of leakage slits 102 and the waveguide 100' is formed with a second ladder circuit portion 101' including a plurality 6f leakage slits 102'. The waveguide 100 receives the microwave from the microwave oscillator 80 through the waveguide 105 and the converter coupler 106. A portion of the microwave thus supplied is leaked at the first ladder circuit portion 1 01, so that the transfer sheet 212 being conveyed and the toner adhered thereto are heated.Accordingly, the toner image is thermally fused and fixed onto the transfer sheet 212. The residual microwave not consumed by the first waveguide 100 is then supplied through the converter coupler 107 to the second waveguide 100'. The second waveguide 100' is disposed upstream of the waveguide 100 in terms of the conveying path of the transfer sheet. Accordingly, the microwave leaked from the second ladder circuit portion 101', serves to heat and dry the transfer sheet before the toner image transferred onto the same is fused to be fixed by means of the first ladder circuit portion 101. Accordingly, the transfer sheet 212 has been dehydrated when the same is brought to the first ladder circuit portion 101, i.e. to the thermal fusion fixing means and therefore the heat absorbing amount of the transfer sheet itself has become extremely small.

Therefore, the microwave from the thermal fusion fixing means, i.e. the first ladder circuit portion is iittle used for the transfer sheet 212 itself and thus almost all of the microwave from the first ladder circuit portion 101 can be utilized for fusing the toner image. As a result, even if the transfer sheet as stacked in the sheet container 214 contains a considerable amount of moisture, thermal fusion and fixing of the toner image can be assuredly achieved.

The embodiment now in description is also adapted such that the transfer sheet stacked in the sheet container 214 is in advance heated and dried. More specifically, the heat generated by the resistive terminating load, i.e. the dummy load 104 coupled to the rear end of the second waveguide 100' is transmitted through the heat pipe 50' to the sheet container 214. The other end of the heat pipe 50' is disposed in a zigzag fashion in the sheet container made of a good heat conductor such as metal, as shown in Figure 12, so that the maximum quantity of heat is supplied to the sheet container 214. Accordingly, the sheet container 214 per se is heated, whereby the transfer sheets stocked in a stacked manner is heated and dried.

According to the preferred embodiment shown in Figures 11 and 12 the transfer sheet is preheated before the same is brought to the position of the first heating means. In the above described embodiment two means, i.e. the second ladder circuit portion and the heat pipe 50' are employed as the preheating means.

Accordingly both of these constitute the second heating means. More specifically, the second heating means may be constituted as including at least one of the waveguide 100' and the heat pipe 50' in cooperation with the sheet container 214.

In the foregoing the embodiment was described by taking an example of the waveguides 100 and 100' as the heating means 222. However, it is clear that these waveguides 100 and 100' may be replaced by the microstrip lines 10 and 10' of the same structure as described in conjunction with Figure 9.

Figure 13 is a view showing another preferred embodiment of the present invention. Referring to the embodiment shown, the housing 201 of the electrophotographic apparatus 200 may be the same as that described in conjunction with Figure 11 and therefore a detailed description thereof will be omitted. A transfer sheet storing case 232 is provided at the lower portion of the housing 201 for supporting the housing 201 through a supporting member 235. The transfer sheet storing case 232 is formed with a plurality of sucking apertures 236 and a plurality of evacuating apertures 237. The transfer sheet storing case 232 comprises shelves 233 and 234 provided in the case 232 for storing the transfer sheets 212 in a stacked manner. Accordingly, the transfer sheets can be stored in the case 232 and can be taken out therefrom by opening a door, not shown, of the same.The supporting member 235 is detachably mounted to the storing case 232 by means of a suitable fixing means, not shown.

In the embodiment shown the heating apparatus 222 comprises the microstrip line 10, the detail of which may be seen with reference to Figures 2 or 4 and 5. The microstrip line 10 comprises a ladder circuit portion 13 and receives a microwave from the microwave oscillator 80 energized with the direct current power supply 81 through the waveguide 82 and the coaxial cable 20. The residual microwave not consumed at the microstrip line 10 and thus at the ladder circuit portion 1 3 is supplied to the resistive terminating load 30" through the microwave transmitting means such as a coaxial cable 70. More specifically, the transfer sheet 212 is heated with a microwave leaked from the ladder circuit portion 13.The residual microwave through the coaxial line 70 is converted to heat at the resistive terminating load, i.e. the dummy load 30" and the heat thus generated heats the transfer sheet storing space in the transfer sheet storing case 232. Accordingly, the transfer sheet 212 stocked in a stacked manner on the shelves 233 and 234 are dried with the heat generated by the resistive terminating load 30". Therefore, as in the case of the previously described Figure 11 embodiment, the electric resistance value of the transfer sheet is increased. Accordingly, the electric charge of the toner is prevented from being neutralized with the electric charge of the transferring corotron 211 through the transfer sheet 212 and therefore the toner can maintain a large quantity of electric charge whereby the toner is more strongly attracted by the transferring means 211.

Accordingly, the advantage is brought about that a transferring efficiency of a toner image is enhanced, as in the case of the Figure 11 embodiment in which the sheet container 214 is heated. The heat absorbing amount of the transfer sheet 212 is also decreased and as a result another advantage is brought about that a toner image can be thermally fused and fixed assuredly with a less amount of energy as in the case of the previously described embodiments.

In the above described preferred embodiments, the present invention was employed as a heating means for an electrophotographic apparatus.

However, the inventive microwave heating apparatus can be utilized for the purpose of uniformly heating throughout a sheet-like material or for uniformly heating the surface of a material having a given thickness, with any desired modifications made as necessary, as is needless to say. By way of one example, the present invention could be advantageously utilized in an apparatus for thermal adhesion or for a rubber curing process.

In addition, even in the case where the transfer sheet is stored in a roll state, the sheet may be heated with the second heating means in the same manner. Furthermore, the above described embodiments may be combined as desired and as necessary.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims

1. A microwave heating apparatus, comprising: microwave supplying means for supplying a microwave, a first heating means receiving the microwave from said microwave supplying means and including a first ladder circuit portion allowing for leakage of a portion of the microwave therefrom for heating a material being heated with the leaked microwave, and second heating means operatively coupled to said first heating means for heating said material being heated with the residual microwave not consumed by said first heating means.

2. A microwave heating apparatus in accordance with Claim 1, wherein said second heating means comprises heat generating means for generating heat upon receipt of said residual microwave.

3. A microwave heating apparatus in accordance with Claim 2, wherein said second heating means comprises microwave transferring means for receiving said residual microwave, and heat generating means for generating heat upon receipt of the microwave from said microwave transferring means.

4. A microwave heating apparatus in accordance with Claim 2, wherein said second heating means comprises heat generating means for generating heat upon receipt of said residual microwave, heat conducting means for conducting the heat generated by said heat generating means, and heat dissipating means for dissipating the heat conducted by said heat conducting means.

5. A microwave heating apparatus in accordance with Claim 4, wherein said heat conducting means comprises a heat pipe coupled to said heat generating means.

6. A microwave heating apparatus in accordance with Claim 5, wherein said heat dissipating means comprises a good heat conductive material coupled to said heat pipe.

7. A microwave heating apparatus in accordance with Claim 3, wherein said heat generating means comprises a resistive terminating load coupled to said microwave transferring means.

8. A microwave heating apparatus in accordance with Claim 4, wherein said heat generating means comprises a resistive terminating load coupled to said first heating means.

9. A microwave heating apparatus in accordance with Claim 1, wherein said second heating means comprises heating means receiving said residual microwave and including a second ladder circuit portion for allowing for leakage of the microwave from said second ladder circuit portion for heating said material being heated with the leaked microwave.

10. A microwave heating apparatus in accordance with Claim 9, wherein said first heating means includes a first microwave transferring path for receiving the microwave from said microwave supplying means and said first ladder circuit portion has a plurality of leakage slits provided associated with said first microwave transferring path, and which further comprises a unidirectional path inserted between said microwave supplying means and said first microwave transferring path, reflecting means for reflecting in the opposite direction through said first microwave transferring path said residual microwave that has passed through said first microwave transferring path, and directional coupling means coupled to the output of said unidirectional path for supplying the microwave from said microwave supplying means to said first microwave transferring path and the microwave reflected from said reflecting means to said second heating means, said second heating means receiving the microwave reflected from said directional coupling means.

11. A microwave heating apparatus in accordance with Claim 10, wherein said second heating means comprises a second microwave transferring path for transferring said reflected microwave, and a second ladder circuit portion provided associated with said second microwave transferring path.

1 2. A microwave heating apparatus in accordance with Claim 11, wherein said second microwave transferring path includes a waveguide and said second ladder circuit portion has a plurality of leakage slits formed on said waveguide.

1 3. A microwave heating apparatus in accordance with Claim 11, wherein said second microwave transferring path includes a microstrip line, and said microstrip line comprises a dielectric plate, a center conductor formed on said dielectric plate, and at least one grounding conductor formed on said dielectric plate, and said second ladder circuit portion has a plurality of leakage slits formed on any one of said center conductor and said at least one of the grounding conductor.

14. A microwave heating apparatus in accordance with Claim 10, wherein said reflecting means is provided at the position for offsetting the reflected wave caused by said first ladder circuit portion.

1 5. A microwave heating apparatus in accordance with Claim 14, wherein said reflecting means comprises a shortcircuiting plate coupled to the rear end of said second microwave transferring path to be displaceable.

1 6. A microwave heating apparatus in accordance with any one of the preceding Claims 1 to 15, wherein said first heating means and said second heating means are provided in an electrophotographic apparatus, said electrophotographic apparatus comprising means for forming an electrostatic image on a photosensitive member, means for developing said electrostatic image as a toner image, means for transferring said toner image onto a transfer sheet, and fixing means for thermally fusing said toner image for fixing the same onto said transfer sheet, said fixing means including said first heating means, said first heating means heating said transfer sheet as said material being heated.

1 7. A microwave heating apparatus in accordance with Claim 16, wherein said electrophotographic apparatus comprises sheet supplying means for supplying said transfer sheet to said first heating means, said second heating means heating said transfer sheet before said transfer sheet is brought to said first heating means by means of said sheet supplying means.

1 8. A microwave heating apparatus in accordance with Claim 17, wherein said sheet supplying means comprises sheet storing means for storing said transfer sheet, said second heating means heating said transfer sheet being stored in said sheet storing means for drying the same.

1 9. A microwave heating apparatus in accordance with Claim 18, wherein said sheet storing means comprises a sheet container made of a good heat conductive material, and said second heating means comprises means for conducting the heat to said sheet container.

20. A microwave heating apparatus in accordance with Claim 18, wherein said sheet storing means comprises means for defining the space for storing said transfer sheets, and said second heating means comprises means for dissipating the heat in said storing space.

21. A microwave heating apparatus in accordance with Claim 17, wherein said sheet supplying means comprises sheet storing means for storing said transfer sheets, said second heating means being disposed between said sheet storing means and said first heating means.

22. A microwave heating apparatus in accordance with Claim 1, wherein said first heating means comprises a waveguide, and said first ladder circuit portion comprises a plurality of leakage slits formed on said waveguide.

23. A microwave heating apparatus in accordance with Claim 1, wherein said first heating means comprises a microstrip line said microstrip line including a dielectric plate, a center conductor formed on said dielectric plate, and at least one grounding conductor formed on said dielectric plate, said first ladder circuit portion comprising a plurality of leakage slits formed on any of said center conductor and said at least one grounding conductor

24. A microwave heating apparatus substantially as herein described with reference to Figures 2 and 3, optionally modified as described with reference to Figure 4 or Figure 5, Figures 6 and 7, Figure 8 or Figure 9 each with either Figure 1 OA or Figure lOB, Figures 11 and 12, or Figure 13, of the accompanying drawings.

25. Electrophotographic apparatus including a microwave heating apparatus as claimed in any one of the preceding claims for thermally fusing a toner image on a transfer sheet.