Foods and beverages: apparatus – Electric – radiant or vibrational treating means
Reexamination Certificate
2000-10-11
2001-06-19
Simone, Timothy F. (Department: 1761)
Foods and beverages: apparatus
Electric, radiant or vibrational treating means
C099S358000, C099S44300R, C099S483000, C099SDIG014, C219S707000, C219S771000, C219S780000
Reexamination Certificate
active
06247395
ABSTRACT:
BACKGROUND ART
This invention relates to a high-frequency thawing apparatus for supplying a high-frequency power to a pair of opposing electrodes to thaw an article such as a frozen food carried in between the electrodes by dielectric heating.
Japanese Examined Patent Publication Nos. 51-15100 and 55-46152, for example, propose a high-frequency thawing apparatus in which a group of frozen articles to be thawed (hereinafter, merely referred to as “article”) are serially carried on a conveyor and introduced into an electric field generated by application of a high frequency to a pair of opposing electrodes while passing therebetween, thereby being thawed one after another.
The conventional thawing apparatuses has such an arrangement that a signal of a high frequency from a high frequency generating circuit is power-amplified by a transformer and the amplified voltage is supplied to one of the pair of electrodes (namely, the high-voltage electrode) for high-voltage application to generate a high frequency electric field between the high-voltage electrode and the other one of the electrodes which is connected to the ground (namely, ground electrode). The article interposed between the high-voltage electrode and the ground electrode is heated by dielectric loss.
Generally, the dielectric constant of the article rises as the thawing is carried on. Namely, the dielectric heating causes an impedance change on time-basis. Accordingly, it is necessary to vary a high-frequency power to be supplied to the article as the thawed state of the article, which is a load in the high-frequency power generating circuit, varies (namely, a matching control of the high-frequency power is necessary). Particularly, since the dielectric constant greatly differs between ice and water, the following problem occurs in the case where the article is expected to be heated up to a temperature around 0° C. after thawing. The amount of water that has been contained in the article in a super-cooled state changes as the article is heated and, accordingly, the above matching control of the high-frequency power supply in the high-frequency thawing apparatus is extremely difficult. It has been practically impossible to uniformly heat a plurality of frozen articles while serially conveyed by using a pair of electrodes or a single power generating device.
In the case where a thick block of article is thawed by heat with use of the thus constructed conventional thawing apparatus, a portion of the article adjoining the high-voltage electrode is apt to be more heated than a portion opposite and away from the high-voltage electrode. Thus, heated state differs portion by portion of the article, thereby making it difficult to uniformly thaw the article.
Further, in the case of transporting the article on the conveyor, it is required to finalize thawing of the article by dielectric heating before the instant article completely passes the space in between the pair of electrodes. This requires to set the high-frequency power at a relatively high level. Consequently, there is a possibility that conspicuous is a so-called “edge effect” due to the electric field generation in which an edge of the article is apt to be more heated than the other part of the article, thereby resulting in a non-uniform thawed state between inner part and outer part of the article.
DISCLOSURE OF THE INVENTION
This invention has been invented to solve the above problems residing in the prior art. It is an object of this invention to provide a high-frequency thawing apparatus in which a group of articles are sequentially transported on a conveyor to thaw the articles one after another. The apparatus is provided with a plurality of pairs of electrodes arrayed in a thawing chamber which also functions as an electromagnetic shield to uniformly thaw the article with heat in accordance with a change of the dielectric constant of the article.
According to an aspect of this invention, a high-frequency thawing apparatus comprises: a conveyor unit for transporting an article to be thawed in a predetermined direction; a thawing chamber in which at least part of the conveyor unit over which the article is to be transported is encased; a plurality of opposing pairs of electrodes, each electrode pair arrayed side by side in the transport direction of the conveyor unit apart at a certain interval in the thawing chamber; a plurality of high-frequency power generating circuits provided in correspondence to the plurality of electrode pairs to generate a high-frequency field in between each pair of the electrodes; and a plurality of impedance matching circuits provided between the respective high-frequency power generating circuits and conductors (sic), each impedance matching circuit including a conductor with an inductance different to each other.
In the above arrangement, the length of at least one of the conductors provided downstream from the other conductor with respect to the transport direction of the conveyor unit may be longer than that of the other conductor.
Three pairs of the opposing electrodes may be provided, and the respective conductors corresponding to the three pairs of electrodes may have different lengths to one another.
Alternatively, three pairs of the opposing electrodes may be provided, and the length of the conductor corresponding to the most downstream-located electrode pair with respect to the transport direction of the conveyor unit may be set longer than that of the other two conductors.
Further, the opposing electrode pairs may be arranged such that the distance between the corresponding electrodes of the adjacent electrode pairs is longer than that between the opposing electrode pair.
The high-frequency thawing apparatus may further comprise a plurality of elevating units each adapted for moving at least one of the corresponding electrode pair up and down.
The transport speed of the conveyor unit may be set variable.
Further, each of the high-frequency power supply devices (sic) may be intermittently driven.
The intermittent driving may be so controlled as to change at least one of a drive period and a pause period for each of the high-frequency power generating circuits.
Also, a circuit on a load side where a high-frequency power is to be supplied including the opposing electrode pair may have a balance circuitry configuration.
Alternatively, a circuit on a load side where a high-frequency power is to be supplied including the opposing electrode pair may have an unbalance circuitry configuration.
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Jordan and Hamburg LLP
Simone Timothy F.
Yamamoto Vinita Co., Ltd.
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