Otis Elevator Co. v. Kaestner & Hecht Co.

234 F. 926, 1916 U.S. Dist. LEXIS 1523
CourtDistrict Court, N.D. Illinois
DecidedJune 9, 1916
DocketNos. 30294, 30295, and 30306
StatusPublished

This text of 234 F. 926 (Otis Elevator Co. v. Kaestner & Hecht Co.) is published on Counsel Stack Legal Research, covering District Court, N.D. Illinois primary law. Counsel Stack provides free access to over 12 million legal documents including statutes, case law, regulations, and constitutions.

Bluebook
Otis Elevator Co. v. Kaestner & Hecht Co., 234 F. 926, 1916 U.S. Dist. LEXIS 1523 (N.D. Ill. 1916).

Opinion

SANBORN, District Judge.

Infringement suits on patents for control of elevator operation. The first suit was brought in January, 1911, on patent to Frank E. Herdman, No. 548,830, issued October 29, 1895; the second was brought in January, 1911, on the patent to August Sundh, No. 861,197, issued July 23, 1907; and the last brought in February, 1911, on the patent Issued to Frank J. Sprague, March 20, 1906, No. 815,756.

[1] Suit No. 30,295, on Sundh Patent. I adopt the description of counsel for defendant in their brief in the Sundh suit, as preliminary to a consideration of these three cases:

“It will better conduce to an understanding of the purpose and means of the Sundh patent and of the prior art references if certain characteristics of motors are first understood. An electric motor is composed of two main parts, its armature and its field magnet. The field magnet is a fixed structure magnetized by coils thereon, and these coils are known as the field winding. In elevator practico this field winding is in a shunt or branch circuit, and the motor is known as a shunt wound motor. The armature of the motor is the revolvable member and carries a number of turns of wire, which lie in the magnetic field produced by the field magnet. It is a law of electromagnetism that whenever a wire is moved through a magnetic field in the proper direction an electric current tends to be generated in that wire, and will bo generated if that wire is connected in a closed circuit. The converse is equally true, namely, that when a wire lies in a magnetic field, and a current is sent through the wire from an outside source, the wire tends to move through the magnetic field. Therefore we have such a structure having a fixed field magnet and a revolvable armature, with wires properly located thereon and connected to an outside circuit. We fiavo a structure that will act as a motor if current is supplied to the wires of the armature from an outside source, and will act as a generator if the armature is rotated by an outside force and the wires upon it are closed through an outside circuit. In other [928]*928words, the same structure is a dynamo generator or a motor, according to whether the armature is driven by an outside force or whether current is supplied to the armature from an outside source.
“In either casfe, as the armature is revolving it generates a voltage, or electromotive force, or pressure, and it is therefore to that extent a generator, even when it is acting as a motor. When it is acting as a generator, this voltage or electromotive force or pressure determines the output of current from the armature. When the structure is acting as a motor — that is, when it is being driven by the current supplied to it from an outside source — the pressure or voltage' or electromotive force that is generated by the rotation of the armature is opposed or counter to the electromotive force applied to the armature from the outside source. In this case the current flowing through the armature is determined by the difference between the electromotive force applied from the outside force and the counter-electromotive force generated by the motor.
“The electromotive force generated by a dynamo and the counter-electromotive force generated by a motor vary with two factors, the rate of movement of the armature and the strength of the field of the field magnet. When a motor is at rest, therefore, it has no counter-electromotive force, and if the full electromotive force of the outside force were applied to it, it would take a very large current; compared to that which it would take if it had developed speed and therefore the counter-electromotive force to oppose the applied electromotive force. It is for this reason that in starting a motor from rest it is customary to include a considerable external resistance in series with the armature, so as to cut down the current flowing through it, which resistance is removed gradually as the speed of the motor increases and its counter-electromotive force develops.
“To reverse the motor it is necessary either to reverse the current in the field winding or to reverse the electromotive force applied to the armature. Such a reversal of one or other of these currents causes the armature to rotate in the opposite direction. Suppose, now, that the motor is revolving at a high speed in one direction and its counter-electromotive force is high, and is preventing any but a normal current from passing through the armature. If we should accidentally reverse the connections to the motor, we would find that what was before a counter-electromotive force, protecting the motor, becomes an electromotive force assisting that of the outside force, and therefore tending to send an enormous current through the armature. The electromotive force is no longer counter to that of the applied electromotive force, because the electromotive force generated by the rotation of the armature is in the same direction as before, whereas the applied electromotive force is in an opposite direction. It has, therefore, long been recognized that in automatic control systems, such as that employed in elevator practice, a means should be provided for preventing reversal of the connections of the motor to the outside source, except at a time when the motor is at rest or of a low enough speed so that it will not develop so high an electromotive force as to cause a dangerous flow of current through the motor.
“Since the reversal of the motor requires the disconnection of one of its elements and its subsequent connection in a reverse direction, and since the electromotive force across the armature terminals at the moment of disconnection is a measure of the speed of the motor, Sundh (and the prior pat-entees) made use of this principle by providing a protective magnet so connected that it would be energized when the electromotive force generated by the armature is high at the time that it is disconnected from the circuit and employed this protective magnet to prevent the operation of the mechanism to reverse the motor.”

In the operation of the patent in suit the operator m.ay energize the operating circuit for either up or down by turning his lever right or left. The current will then pass from its source of supply through one or the other of two reversing coils, and pull up its switch to establish an electrical connection for the armature through its rheostat, and thence through the contacts controlled by a protective magnet, to [929]*929the ground. This magnet is not energized, except when both reversing switches are open. The same movement of the operating arm sends a current through the contacts established by the operating current in the reversing coil, through the armature, its rheostat, and back to the ground. Suppose the car is now going up and the operator wishes to go down. He turns his lever to the right and into engagement with a contact for downward motion. If now the reverse current should be allowed to be turned into the armature, which is still going at high speed, it would have an electromotive force assisting that applied to it, and there would be an abnormal rush of current through the motor. This brings us to the device that Sundh adds to remove this defect. Moving the arm off the contact for up motion de-energizes one of the reversing coils, which thereupon drops its core, closing a contact of a circuit through the protective coil, which, when sufficiently energized, lifts its core, and breaks the operating circuit.

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Bluebook (online)
234 F. 926, 1916 U.S. Dist. LEXIS 1523, Counsel Stack Legal Research, https://law.counselstack.com/opinion/otis-elevator-co-v-kaestner-hecht-co-ilnd-1916.