HIGH FREQUENCY HEATING EQUIPMENT

Abstract: The equipment includes a DC power supply comprising a power generator (20), an electric power generator (22) and a rectifying means (23), an inverter power supply (24) which boosts the output voltage of the DC power supply and drives a magnetron (28), and an inverter controlling part for controlling the inverter power supply (24) according to the output of a generator output detecting means (31) for detecting the output of the DC power supply. A function of dielectric heating can be exhibited stably by controlling the operating state of the inverter power supply (24) through the use of the output of the DC power supply.

Description: TECHNICAL FIELD The present invention relates to an electronic range for heating foods, liquid, etc., a heat processing machine for heat processing wastes or a high-frequency heating apparatus for heating catalysts, etc., which are mounted on a mobile means such as a motor vehicle, a ship or the like. BACKGROUND OF THE INVENTION From EP-A-0 171 170 it is known a high-frequency heating apparatus which is mounted on a transport means for human beings, animals, etc., comprising a DC power source, an inverter power source which receives DC power from said DC power source, a magnetron which is actuated by output of said inverter power source, a DC output detecting means for detecting magnitude of output of said DC power source directly or indirectly, and a controller for controlling operation of said inverter power source. Conventionally, in substitution for the high-frequency heating apparatus of this kind represented by electronic ranges, a so-called electronic range for general home use adapted to employ a commercial power source has been used in combination with an AC dynamo for exclusive use having a predetermined frequency and a predetermined AC voltage. Fig. 13 is a view showing an arrangement of a prior art high-frequency heating apparatus. This is a drawing in which the high-heating apparatus is used in a sightseeing bus or the like. In Fig. 13, an engine 2 for generating transport power is provided in a car body 1 and the transport power is transmitted to tires 3 so as to transport passengers. A so-called electronic range 5 is mounted in such car body so as to perform microwave heating of a food 4. This electronic range 5 is constituted by a power source device 9 including a ferro-resonance type boosting transformer 6, a resonance capacitor 7 and a high-voltage diode 8, a magnetron 10 and an oven 11 and can be used by connecting a commercial power source for home use to terminals 12 and 13. Thus, in order to cause the electronic range 5 to exhibit normal functioning, it is essential to supply a predetermined voltage of, for example, 100 V to the terminals 12 and 13 at a predetermined frequency of, for example, 60 Hz. Therefore, conventionally, by using an AC voltage generator 16 provided with a power generator 14 for exclusive use and a dynamo 15 actuated by the power generator 14, a microwave heating apparatus having an arrangement as shown is achieved by this AC voltage generator 16 and the electronic range 5 for home use and has been used in the motor vehicle. On the other hand, due to great spread of motor vehicles in recent years, long-distance transport, long-distance drive or outdoor leisures such as yachting, camping, etc. have become popular and thus, a demand has increased for drinking and eating at locations having no commercial power source, for example, in a motor vehicle. Meanwhile, especially, in order to improve performance of catalysts for purifying exhaust gas of engines such as a diesel engine, need for use of microwave heating has arisen. Thus, necessity for the high-frequency heating apparatus usable easily especially at locations having no commercial power source has increased. However, based on the prior art described above, it was difficult to sufficiently meet increasing demand for use of high-frequency heating apparatuses at locations having no commercial power source. Namely, in the prior art, a special AC stabilizing power source capable of ensuring stability of frequency and voltage equivalent to those of the commercial power source is necessary and thus, a high precision AC stabilizing power source for exclusive use was absolutely necessary. This is because the ferro-resonance type transformer is employed in the power source device for driving the magnetron so as to stabilize operation and output of the magnetron through its resonance with the resonance capacitor. Therefore, the prior art high-frequency heating apparatus is very large, heavy and expensive due to the necessity of the AC stabilizing power source, ferro-resonance transformer, etc. and is difficult to handle due to its poor controllability. Especially, employment of the ferro-resonance type transformer means necessity of the AC stabilizing power source for exclusive use and thus, it was impossible to avoid the above mentioned inconveniences. Therefore, it was difficult to materialize at low cost, a high-frequency heating apparatus usable easily at locations where it is difficult to obtain a commercial power source, such as in a mobile space of a motor vehicle, a yacht, etc. [DISCLOSURE OF THE INVENTION] Accordingly, objects of the present invention are to satisfy increasing demand for a high-frequency heating apparatus in which not only a high-voltage power can be easily supplied to a magnetron even if a DC power source mounted on a transport means of human beings, objects, animals, etc. and having poor accuracy in output stability is used but necessary stable dielectric heating function can be easily achieved even at locations where it is difficult to obtain a commercial power source and to improve reliability, improve safety and provide comfortable operational performance. To this end, a DC power source, an inverter power source for receiving DC power obtained from the DC power source, a magnetron which is actuated by output of the inverter power source, a DC output detecting means for detecting output of the DC power source directly or indirectly and an inverter controller for controlling operation of the inverter power source, characterized by an anode current detecting means for detecting anode current flowing through said magnetron, a reference signal generator, and an error amplifier for outputting difference between an output signal of said anode current detecting means and an output signal of said reference signal generator, wherein said controller is a pulse width modulation (PWM) control circuit for controlling operation of said inverter power source on the basis of an output signal of said error amplifier such that output of said reference signal generator is controlled in accordance with an output signal of said DC output detecting means. Thus, even if a power generator and a dynamo, which are poor in accuracy of output stability and inexpensive due to their simple constructions, are employed, required dielectric heating function can be stably achieved. [BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a whole block diagram of one embodiment of the present invention, Fig. 2 is a circuit diagram of the high-frequency heating apparatus, Figs. 3(a), 3(b) and 3(c) are operational waveform diagrams of an inverter of the high-frequency heating apparatus, Fig. 4 is an operational characteristic diagram of the inverter of the high-frequency heating apparatus, Fig. 5 is a circuit diagram showing a second embodiment of an inverter controller of the high-frequency heating apparatus, Fig. 6 is a characteristic diagram of the number of rotations of a dynamo and output voltage in the high-frequency heating apparatus, Fig. 7 is a characteristic diagram of the output voltage of the dynamo and high-frequency output in the high-frequency heating apparatus, Figs. 8(a) and 8(b) are characteristic diagrams of high-frequency heating output and heating period in the high-frequency heating apparatus, Fig. 9 is a whole block diagram of a third embodiment of the present invention, Fig. 10 is a sectional view of a body of a fourth embodiment of the present invention, Fig. 11 is a sectional view of a body of a fifth embodiment of the present invention, Fig. 12 is a sectional view of a body of a sixth embodiment of the present invention, and Fig. 13 is a view showing an arrangement of a high-frequency heating apparatus mounted on a motor vehicle. [BEST MODE FOR WORKING THE INVENTION] Hereinbelow, embodiments of the present invention are described together with the drawings. Fig. 1 is a block diagram showing a high-frequency heating apparatus of one embodiment of the present invention, which is applied to a motor vehicle. In the drawing, a rotating power of an engine 20 acting as a power generator is arranged to be transmitted to tires 21 but, at the same time, also to an AC dynamo 22. An output voltage of the dynamo 22 is supplied to a rectification means 23. A DC output of this rectification means acts as a power source for supplying electric power to an inverter power source 24. This inverter power source 24 is constituted by a switching circuit 25 including a switching transistor and a resonance capacitor and a boosting transformer 26 serving also as a resonance inductor. A high-voltage output of this inverter power source is arranged to be supplied to a magnetron 28 through a rectifier 27. Output electromagnetic wave of the magnetron is supplied to a food 30 in an oven 29 such that dielectric heating of the food 30 can be performed. Meanwhile, in order to stably control the number of rotations of the engine 20, it is necessary to perform sophisticated control of fuel supply and combustion state. In the case of the power generator 20 serving also as a transport power generator of the motor vehicle as in this embodiment, the number of rotations of the engine is forced to change greatly in accordance with the necessary number of rotations of the tires 21 corresponding to running speed of the motor vehicle. Therefore, output of the dynamo 22 changes greatly in accordance with the number of rotations of the power generator 20. In order to not only perform excellent dielectric heating of the food 30 in such greatly changing operational state of the power generator 20 but prevent deterioration of reliability due to application of abnormal overload to the dynamo 22, operational state of the inverter power source 24, i.e. electric power conversion amount is required to be controlled in accordance with electric power generating capability in one form or another. To this end, a voltage detecting means (generated electric power output detecting means) 31 for detecting generated electric power of the dynamo 22 as output voltage of the rectification means 23 and an inverter controller 32 for controlling the switching circuit 25 of the inverter power source 24 in response to a signal of this voltage detecting means 31 are provided such that the inverter power source 24 is operated in accordance with magnitude of generated electric power output. By such arrangement, however large variation range of the number of rotations of the power generator 20 may be, deterioration of reliability due to overload state does not occur and proper microwave heating of the food 30 can be achieved. Fig. 2 is a circuit diagram showing a further detailed structure of the above mentioned embodiment of the present invention of Fig. 1. Numerals identical with those of Fig. 1 denote the corresponding constituent elements and detailed description thereof is abbreviated. An output of the dynamo 22 is rectified by the rectification circuit 23 constituted by diodes 33, 34 and 35 and a capacitor 36 so as to be converted into a DC voltage. This DC voltage is supplied to the inverter power source 24 constituted by an inductor 37, a by-pass condenser 38, a resonance capacitor 39, a boosting transformer 40, a transistor (IGBT) 41, a diode 42, etc. An output of the inverter power source 24 is supplied, as outputs of two secondary windings of the boosting transformer 40, to the magnetron 28. The output of the high-voltage secondary winding is converted into a high-voltage DC by the high-voltage rectification circuit 27 constituted by a capacitor 43 and diodes 44 and 45 and then, is supplied to the magnetron 28. On the other hand, the output of the low-voltage secondary winding is directly supplied to a cathode of the magnetron 28. The inverter controller 32 mainly includes an inverter control circuit 48 which detects a collector voltage of the IGBT 41 as a synchronous signal by resistors 46 and 47 so as to control an energization period Ton of the IGBT 41 synchronously with resonance state of a resonance circuit constituted by the resonance capacitor 39 and the boosting transformer 40. Figs. 3(a), 3(b) and 3(c) are wave-form diagrams of a collector voltage Vce, a collector current Icd and a gate voltage Vg of the IGBT 41 and illustrate operational state of the inverter referred to above. Namely, the inverter control circuit 48 detects a point P of intersection between Vce and its power source voltage Vcc and outputs the gate voltage Vg after a predetermined period Td (referred to as "synchronous oscillation control"). Then, the inverter control circuit 48 controls the pulse width Ton of the gate voltage such that a desired electromagnetic wave output of the magnetron 28 is obtained. Meanwhile, reference numeral 49 denotes a power source circuit. A terminal voltage of a resistor 50 is fed, as an anode current detecting signal of the magnetron 28, back to the inverter control circuit 48. The period Ton is controlled by this feedback signal such that the electromagnetic wave output of the magnetron 28 is controlled to an arbitrary set value. Magnitude of the generated electric power output of the dynamo 22 is detected, as a DC output voltage of the rectification circuit 23, by resistors 51 and 52 so as to be supplied to the inverter control circuit 48. In response to this detection signal, the inverter control circuit 48 is capable of controlling operational state of the inverter 24. Thus, even if operational state of the power generator 20 varies greatly, deterioration of reliability due to generation of overload state in the dynamo 22 does not occur and proper electromagnetic wave heating can be performed by the magnetron 28. Namely, when the number of rotations of the power generator 22 has dropped extraordinarily, output of the dynamo drops. Hence, the period Ton of the IGBT 41 is reduced such that output voltage of the dynamo falls within a range enabling stable operation of the inverter power source 24, whereby consumed electric power of the inverter power source is so controlled as to conform to magnitude of output of the dynamo. Relation between Ton and Po is shown in Fig. 4 and Po changes in proportion to square of Ton. This is because electric power supplied to the magnetron 28 is substantially proportional to square of Icd by operation of the inverter shown in Fig. 3. On the contrary, in the case where output of the dynamo is too large, Po becomes too large when Ton is as it is, with the result that the IGBT 41, etc. may be thermally fractured due to not only excessive increase of heating output but excessive increase of loss of the inverter power source 24. Accordingly, also in this case, Ton is controlled to a small value such that high reliability and proper heating output are achieved. Fig. 5 is a circuit diagramm showing a more detailed configuration of the present invention of Figs. 1 and 2 referred to above. In Fig. 5, numerals identical with those of Figs. 1 and 2 denote corresponding constituent element and, therefore, detailed description thereof is abbreviated. In Fig. 5, the inverter controller 32 is constituted by a pulse width modulation (PWM) control circuit 53 for controlling Ton, which has a function of synchronous oscillation control as described in Fig. 3, a differential amplifier 55 for applying to the PWM control circuit 53, a difference signal between an anode current detection signal of the magnetron 28 and a signal of a reference signal generator 54 and a heating control circuit 56 for controlling, on the basis of a signal of the generated electric power output detecting means 31 for detecting magnitude of outputted electric power of the dynamo 22, a reference signal of the reference signal generator 54 to its corresponding value. This heating control circuit 56 can be easily formed by using, for example, a microcomputer and is adapted to perform overall adjustments of magnitude of electromagnetic wave output of the magnetron in accordance with a predetermined program as described below. When the number N of rotations of the dynamo 22 changes in accordance with change of operational state of the power generator 20, detection voltage Vo of the generated electric power output detecting means 31 changes as shown in Fig. 6 and fixed interrelation exists between N and Vo. Therefore, by detecting Vo in place of N, the arrangement of Fig. 5 in which the signal detecting circuit is greatly simplified can be employed. Fig. 7 shows one example showing how the heating control circuit 56 controls the output Po of the magnetron 28 with respect to Vo detected as the output signal of the dynamo. As Vo drops through a, b and c, Po is controlled low to A, B and C. Then, in an area in which Vo is smaller than c, Po is controlled to zero substantially or a state in which the inverter is operated at such a low input electric power that Po assumes zero substantially. Thus, the inverter power source 24 is operated at the excessively small Vo such that occurrence of inconveniences such as fracture of the IGBT 41 and failure of the dynamo 22 is prevented. Then, even if Vo rises again, Po is prohibited from being outputted again until Vo rises to d. This is designed to prevent reduction of service life of the magnetron 28 or deterioration of reliability of the inverter power source 24 due to repetition of intermittent turning on of the output Po of the magnetron 28 in an operational state of the power generator 20 in which Vo assumes a value close to c. Thus, the heating control circuit 56 is arranged to control the reference voltage generator 54 such that Po is as shown in Fig. 7 in response to change of Vo. The heating control circuit 56 is arranged to adjust a heating period tc of the food 30, etc. in response to change of the output Po of the magnetron 28 as in Fig. 8(a) or 8(b). Fig. 8(a) shows a case in which the heating period tc is increased proportionally as Po changes through A, B and C and operation of the inverter power source 24 is stopped substantially when Po is not more than C. On the other hand, Fig. 8(b) shows an embodiment in which an area of change of Po is divided into two regions between A and B and between B and C such that different fixed heating periods tc are allocated to the regions, respectively. Practically, by correcting the heating periods tc in such an arrangement, sufficient heating correction control in response to change of Po can be performed. Meanwhile, Fig. 9 shows a third embodiment including a battery 57, a transmission cable 58, the rectification means 23, the inverter power source 24, the rectifier 27, the magnetron 28 and the oven 29. Numerals identical with those referred to above are operated in a similar manner and detailed description thereof is abbreviated. By the above described arrangement, the transmission cable 58 transmits to the inverter power source 24 through the rectification means 23, whole electric power received from the battery 57. This DC power is converted to a high-voltage power by the inverter power source 24 and is rectified by the rectifier 27 so as to be applied to the magnetron 28. By the above mentioned high-voltage power, the magnetron 28 irradiates microwave into the oven 29 so as to heat the article 30 to be heated. By employing the above mentioned arrangement, electric power is stably obtained from the battery 57. Meanwhile, since the transmission cable 58 does not supply electric power except for the inverter power source 24, voltage drop due to the transmission cable can be minimized. Moreover, Fig. 10 shows a fourth embodiment of the present invention. In Fig. 10, numeral 135 denotes a heating chamber for accommodating an article to be heated, numeral 136 denotes a first member which is provided on the bottom face of the heating chamber and is worked concavely at its substantially central portion and numeral 137 denotes a cylindrical second member which is assembled with an outer periphery of the concave portion of the first member. These first and second members are assembled through threaded engagement. Numeral 138 denotes.a magnetron for generating microwave supplied to the heating chamber, numeral 139 denotes a waveguide, numeral 140 denotes a stirrer for stirring microwave supplied to the heating chamber, numeral 141 denotes a partition plate, numeral 142 denotes a door, numeral 143 denotes an operating panel, numeral 144 denotes a body, numeral 145 denotes an electronic range driving power source actuated by a power source of a motor vehicle and numeral 146 denotes a container in which a fluid food is accommodated. By the above described arrangement, the container accommodating the fluid food is placed on the concave portion of the first member. By rotating the second member in this state, depth of the concave portion can be varied to a proper value corresponding to the container. Since the container is stored and fixed in the concave space, spill of the fluid food can be prevented. Meanwhile, the bottom face of the heating chamber is preliminarily subjected to proper spinning such that depth of the concave portion defined by the first and second members enables accommodation of not less than a half of the container. In order to rotate the second member conveniently, it is preferable that a finger hole for rotation be formed on an upper face of the second member. Furthermore, since each member is made of nonmetallic, the article to be heated is placed above the bottom face of the heating chamber made of metallic material. Thus, even if the article to be heated is small in thickness, upper and lower surfaces of the article to be heated can be heated effectively. Then, description is given with reference to Fig. 11. In Fig. 11, members identical with those of Fig. 10 are designated by identical numerals. In Fig. 11, numeral 148 denotes a heating chamber for accommodating an article to be heated and numeral 149 denotes a member which is detachably mounted on a side wall of the heating chamber 148. The member 149 is made of nonmetallic material having low loss of microwave and is formed with a hole 150 of a predetermined shape into which a container stored on a bottom face of the heating chamber is inserted so as to be supported. By the above described arrangement, a container 146 in which a fluid food is accommodated is inserted into the predetermined hole of the member 149 so as to be supported by the member 149. Movement of this member 149 is restrained by four sides of the heating chamber, which include the door 142. Therefore, the container 146 is supported and fixed in space of the heating chamber by the member 149. Thus, vibrations of the motor vehicle are transmitted to the container in a more damped state. Meanwhile, when not in use, this member 149 is placed on the bottom face of the heating chamber so as to be stored. When this member 149 is stored on the bottom face of the heating chamber or is used by being taken out, the hole for inserting the container thereinto can be used to full extent. As described with reference to Fig. 10, when the member 149 is stored on the bottom face of the heating chamber, heating of the article to be heated can be promoted effectively from its upper and lower surfaces even if the article to be heated is small in thickness. Also in Fig. 12, members identical with those of Fig. 10 are designated by identical numerals. In Fig. 12, numeral 151 denotes a heating chamber for accommodating an article to be heated, numeral 152 denotes an electromagnet which is provided adjacent to a bottom face of the heating chamber and numeral 153 denotes a container having a bottom face provided with magnetic material 154. By the above mentioned arrangement, when the electromagnet is actuated after the container 153 containing a fluid food has been accommodated, the magnetic material provided on the bottom face of the container is attracted by magnetic field produced by the electromagnet such that the container 153 is attracted and fixed to the bottom face of the heating chamber. Meanwhile, actuation of the electromagnet is controlled by employing control associated with opening and closing states of the door 142, manual control using an independent operating key, automatic control based on driving state of the motor vehicle, etc. individually or in combination. [INDUSTRIAL APPLICABILITY] As described above, in accordance with the present invention, it is so arranged that output of the dynamo actuated by the power generator is rectified into DC power and this DC power is supplied to the magnetron by the inverter power source. When operational state of the inverter power source is arranged to be controlled in accordance with magnitude of generated electric power output by the generated electric power output detecting means and the inverter controller, high-voltage power can be easily supplied to the magnetron even if the power generator, the dynamo and the battery, which are simple in structure, inexpensive and have poor accuracy in output stability, are used. Furthermore, even at a location where it is difficult to employ a commercial power source, required stable dielectric heating function can be achieved and thus, increasing demand for utilization of high-frequency heating apparatuses can be satisfied. Since especially, the arrangement in which DC power converted from output of the dynamo is supplied to the magnetron by the inverter power source can provide high controllability of supplied electric power, control of operational state, corresponding to output of the dynamo, namely, control of electric power can be performed easily. Since the dynamo and the power generator are stable, reliable operation and excellent dielectric heating function can be achieved simultaneously. Meanwhile, when in the arrangement in which DC power is obtained by rectifying output of the dynamo actuated by the power generator for transporting human beings or baggages, operational state of the inverter power source is adapted to be controlled in accordance with output of the dynamo by the generated electric power output detecting means and the inverter controller, the dielectric heating apparatus for the transport apparatus can be easily achieved by using the dynamo acting also as the power generator, having low accuracy in output stability and having a simple structure and required dielectric heating function can be obtained stably. Furthermore, if the inverter controller is arranged to substantially stops operation of the inverter (an operational state of low input electric power in which electromagnetic wave output assumes zero substantially is included) when output of the dynamo is not more than a predetermined value, generation of overload state of the power generator and the dynamo in terms of electric power and abnormal operation or fracture of the inverter can be prevented positively and a high-frequency heating apparatus having high reliability can be provided. In addition, by using a battery as the DC power source, an electric power generator such as the dynamo is made unnecessary and high-frequency heating can be performed freely even at a location having no mobile means. Meanwhile, when it is so arranged that the transmission line for transmitting electric power from the battery to the inverter power source is not branched to others, voltage drop due to the transmission line is minimized and electric power can be stably transmitted to the inverter power source. Furthermore, erroneous operation of other devices due to switching noises of the inverter power source can be prevented. Meanwhile, by employing the arrangement in which the apparatus body and the operating portion are provided detachably, the body can be mounted in even a compact vehicle. Moreover, the high-frequency heating apparatus for vehicles can be achieved which can be operated at a location easiest to operate during running and the body can be installed at a location suitable for its installation. Thus, the high-frequency heating apparatus can be mounted in a vehicle which is not so large as a leisure vehicle. In the arrangement in which changes of gravity applied to this apparatus are detected by the acceleration detecting means, the centrifugal force detecting means or the angular velocity detecting means, the unstable states in environments of use of this apparatus, such as accelerated or decelerated running state of the mobile means or curved running state at a fixed velocity can be detected and safe environments of use of the apparatus can be clarified to the users.

Claims: A high-frequency heating apparatus which is mounted on a transport means for human beings, animals, etc., comprising: a DC power source (22, 23; 57; 59; 76; 112); an inverter power source (24; 61; 79; 122) which receives DC power from said DC power source (22, 23; 57; 59; 76; 112); a magnetron (28; 62; 80; 104) which is actuated by output of said inverter power source (24; 61; 79; 122); a DC output detecting means (31) for detecting magnitude of output of said DC power source directly or indirectly; and a controller (32) for controlling operation of said inverter power source; characterized by an anode current detecting means (50) for detecting anode current flowing through said magnetron; a reference signal generator (54); and an error amplifier (55) for outputting difference between an output signal of said anode current detecting means (50) and an output signal of said reference signal generator (54); wherein said controller is a pulse width modulation (PWM) control circuit (53) for controlling operation of said inverter power source on the basis of an output signal of said error amplifier (55) such that output of said reference signal generator (54) is controlled in accordance with an output signal of said DC output detecting means (31). A high-frequency heating apparatus as claimed in Claim 1, wherein said DC power source (22, 23) is constituted by a dynamo (22) and a rectification means (23) for rectifying output of said dynamo (22). A high-frequency heating apparatus as claimed in Claim 1, wherein said DC power source (57; 112) is constituted by a battery. A high-frequency heating apparatus as claimed in Claim 1, 2 or 3, wherein a feeder line from said DC power source (22, 23; 57; 59) to said inverter power source (24; 61) does not have a branch line.

Inventors: BESSYO DAISUKE, MAEHARA NAOYOSHI, MATSUMOTO TAKAHIRO, NAKABAYASHI YUJI, BESSYO, DAISUKE, MAEHARA, NAOYOSHI, MATSUMOTO, TAKAHIRO, NAKABAYASHI, YUJI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: H05B6
IPC codes: H05B6