Scovill Mfg. Co. v. Satler
| Decision Date | 27 August 1927 |
| Docket Number | No. 1850.,1850. |
| Citation | 21 F.2d 630 |
| Court | U.S. District Court — District of Connecticut |
| Parties | SCOVILL MFG. CO. v. SATLER. |
James Q. Rice, M. C. Massie, and H. M. Humason, all of New York City, for plaintiff.
Robert Starr Allyn and Philip S. McLean, both of New York City, and Arthur L. Shipman, of Hartford, Conn., for defendant.
On an application filed August 10, 1916, patent No. 1,258,423 was issued to Fritz Lowenstein on March 5, 1918. By mesne assignment the plaintiff corporation acquired title on November 15, 1924. The application of the patent in suit is a division of an earlier application serial No. 569,325, filed by Lowenstein on June 28, 1910. The bill charges infringement, and the defendant pleads invalidity and noninfringement.
The invention of the patent in suit relates to variable condensers adapted for use in radio or wireless work. Broadly defined, a condenser comprises a plurality of surfaces insulated from each other, which afford an area on which an electrical charge is stored. The invention of the patent in suit is more particularly directed to that type of electrical condenser which comprises a set of stationary spaced metal plates and a series of movable spaced metal plates; the latter being adapted to be interspersed to a greater or less degree between the stationary plates to effect changes in the capacity of the condenser.
In the most commonly known variable electrical condensers of the type mentioned, both sets of plates are semicircular; the stationary plates being separated from each other a uniform distance, while the movable plates, which are mounted on a rotatable shaft, are also separated a uniform distance from each other in absolute parallelism. The layers of air between juxtaposed surfaces of the plates constitute the insulating medium or dielectric of the condenser. The dielectric prevents an electrical charge which is collected on the juxtaposed surfaces from jumping across and thus short-circuiting and rendering the condenser useless. The ability of a condenser to store electrical charges is known as capacity, which is measured in micro-microfarads, which in turn is one-millionth of a millionth of a farad; the farad being a very large unit. The capacity of a condenser depends directly on its area, so that area and capacity are equivalents in speaking of condensers.
In the condenser just described, the change in area of the movable plates active between the stationary plates is always the same for equal angular movements of the shaft, with the result that for a given angular movement of the shaft there will be the same increase or decrease of capacity throughout the range of movement of the movable plates, no matter where that movement may be made. The movable plates turn through an angle of 180°. In other words, this variable condenser is so designed that equal angular movements or displacements of the movable plates within the working range of the instrument produce unequal percentage variations in capacity.
The main object of the invention described in the patent in suit is to so design the instrument, for a purpose hereinafter described, that a given angular displacement of the movable plates produces substantially the same percentage change in capacity at any point within the range of the instrument. The condenser described in the patent in suit includes, preferably, a set of semicircular stationary condenser plates 14, supported in parallel relation by rods 15, which depend from a cover plate and are clamped thereto by nuts 16 and 17. The stationary condenser plates are uniformly spaced apart by collars 18. The parallel movable condenser plates 21a are secured to a central vertical shaft 22, which is supported at its lower end on a pivot 23 and is held at its upper end in a bearing 24 in the cover plate. Spacing collars 25 are provided to maintain the plates 21a the proper distance apart, and they are securely clamped in position between nuts 26 and 27. The relative positions of the fixed or stationary plates and the movable plates are such that, when the central shaft is turned, the movable plates enter the spaces between the fixed plates. The movable plates, with the exception of five at the top of the set which are of equal size and a little more than semicircular, are cut off at angles which are progressively greater from the top downward. As a result, the edges of the movable set of plates are arranged in stoplike fashion, so that the movable plates enter successively between the stationary plates as the shaft is turned. The proportioning of the plates and their arrangement is such that the capacity of the condenser is variable, following substantially the law of geometrical progression or in accordance with a logarithmic law fully set forth in the specification of the patent in suit. It is due to such proportioning and arrangement of the plates that a given angular displacement of the movable plates produces substantially the same percentage changes in capacity at any point within the range of the instrument and that the change in capacity is much more gradual than in a condenser where both sets of plates are semicircular.
For the purpose of understanding the invention described and claimed in the patent in suit, it is sufficient to note that the band of frequencies assigned to various radio broadcasting stations in the United States is from 500 kilocycles to 1500 kilocycles, and that the difference between the frequencies of successive stations in the United States is assumed to be 10 kilocycles so as to prevent the sendings of the various broadcasting stations from interfering with each other. Broadly speaking, the condenser is used to separate the frequency of one station from another in tuning, and it is obvious that the frequency on which one broadcasting station operates should not be so near to the frequency of another station that the condenser cannot separate one from the other. Considering now the action of a semicircular plate condenser, it is to be noted that the changes in the amounts of capacity required for a given change of frequency when tuning in that range of the condenser which covers the high frequencies and short wave lengths are much less than when tuning in that range of the condenser which covers the long wave lengths and low frequencies. If it is assumed that the movable plates are fully within the stationary plates, the condenser is then in condition to give the greatest amount of capacity. Then it may be assumed that we are tuning for a frequency of, say, 500 kilocycles, which is the longest wave length and lowest frequency of the band used in the United States. If now we decide to pass from a station operating on a frequency of 500 kilocycles to a station operating on 510 kilocycles, the amount of capacity required will call for a movement of about 7° of the movable plates of this condenser; that is to say, they must move out about 7° from the stationary plates. Assuming that we are tuned for this station at 510 kilocycles, and we now desire to tune for a station at 520 kilocycles, we will not get the required capacity if we move another 7°. As a matter of fact, the turn required will be 6.6°. If after tuning for this station at 520 kilocycles we desire to tune for one at 530 kilocycles, the movement of the movable plates will again be less than the preceding movement. It will be 6.2°. Skipping the intermediate stations in passing from a station at a frequency of 500 kilocycles to one having a frequency of 600 kilocycles, in order to tune for this station, the movable plates of the semicircular plate condenser would have to be moved about 55°. In other words, in tuning for the first ten stations between 500 and 600 kilocycles, 55° of the possible 180° of turn of the movable plates will have been consumed, leaving only 125° for the remaining stations. When we operate this condenser at the other end of its range — that is, the range covering the short wave lengths and high frequencies — so much of the area of the movable plates has been withdrawn from the stationary plates that only very minute movements of the movable plates can be made to give the required changes in capacity, and this operation becomes increasingly difficult and consequently increasingly ineffective. As a matter of fact, there are only 3° left of the area of the movable plates to be divided among the last ten stations; that is, the stations between 1,400 and 1,500 kilocycles. While the operation of the semicircular plate condenser in the range of short wave lengths and high frequencies is not impossible, it requires such minute movements that its operation is extremely difficult.
The condenser described and claimed in the patent in suit differs from the semicircular plate condenser, because minute movements of the movable condenser plates are not required when tuning in that range of the condenser which covers the short wave lengths and high frequencies, and for the additional reason that it introduces or subtracts the plate area or capacity more evenly throughout its range. This mode of operation and result is obtained by redistributing the plate area of the old semicircular condenser in such a manner that a given angular displacement of the movable plates produces substantially the same percentage change in capacity at any point within the range of the instrument, or throughout the working tuning range.
The plaintiff relies on claims 1, 2, 3, and 4, which read as follows:
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