US444640A - Electric elevator - Google Patents
Electric elevator Download PDFInfo
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- US444640A US444640A US444640DA US444640A US 444640 A US444640 A US 444640A US 444640D A US444640D A US 444640DA US 444640 A US444640 A US 444640A
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- switch
- shifter
- detent
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- 230000033001 locomotion Effects 0.000 description 15
- 238000010276 construction Methods 0.000 description 8
- 208000027418 Wounds and injury Diseases 0.000 description 5
- 230000006378 damage Effects 0.000 description 4
- 208000014674 injury Diseases 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 238000013021 overheating Methods 0.000 description 2
- 208000002177 Cataract Diseases 0.000 description 1
- 241001246312 Otis Species 0.000 description 1
- 241001225883 Prosopis kuntzei Species 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000003292 diminished effect Effects 0.000 description 1
- 230000003467 diminishing effect Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 230000003028 elevating effect Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B66—HOISTING; LIFTING; HAULING
- B66B—ELEVATORS; ESCALATORS OR MOVING WALKWAYS
- B66B1/00—Control systems of elevators in general
- B66B1/02—Control systems without regulation, i.e. without retroactive action
- B66B1/06—Control systems without regulation, i.e. without retroactive action electric
Definitions
- Our invention relates to that class of elevators in which electricity is employed as the motive power for moving the cage; and our invention has for its obj eet to insure certainty in the operation of the motor and to prevent injury to the apparatus liable to result from excessive currents or from arresting or unduly reducing the speed of the armature from any cause, or from the heating of the parts.
- Our invention consists in means fully set forth hereinafter whereby the circuit is broken automatically without injury to any part of the apparatus should the controlling de vices be improperly adjusted, or in case of excessive currents being sent over the main line, and whereby the armature is out out of circuit in case its movement is unduly diminished, or if the cage or counter-weight exceeds the limit of its motion, and means are provided for indicating the fact to the operator should the bearings or resistance become overheated, or should the controlling device be improperly adjusted.
- Figure 1 is an elevation showing part of the operating-electromotor and part of an elevator apparatus.
- Fig. 2 is a plan view.
- Fig. 3 is a view illustrating a modification.
- Fig. a is a view showing portions of the apparatus with the parts in a different position from that shown in Fig. 1.
- Fig. 5 is aview illustrating a modification.
- the electromotor A may be of any of the usual or suitable constructions, and, as shown, is provided with a field-magnet 12 and revolving armature 13, as in the wellknown Eickmeyer motor, in which the fieldmagnet has a surrounding casing of iron in the magnetic circuit, and in connection with the motor we'use a current-controller, preferably in the form of a resistance device 13, which also may be of any suit-able construction, but is, as shown in dotted lines, provided with a switch or cut-out -10, so connected with the conductors and arranged in respect to the resistance-terminals 41 i2 and connected with the properly-wound armature that the movement of the switch from its mid-position (shown in Fig. 1) to one side will close the circuit through the resistance and will gradually cut out the resistance and impart motion to the armature in one direction, while the movement to the other side will gradually cut out the resistance and impart movement to the armature in the other direction.
- a current-controller preferably in the form of a
- Different means may be employed for bringing the shifter and the parts connected therewith to the mid-position, and the shifter may be of different constructions, varying with the character of the apparatus.
- the shifter is in the form of a bar 3, sliding horizontally in bearings on the base 0, and the winding-drum D is geared with the armatureshaft through the medium of the worm 47 on said shaft and worm-wheel 48 upon the shaft 7 of the drum D.
- the ordinaryshifting-rope may be employed to move the shifter 3 but we prefer to use the double traveling-rope device shown in Fig. 1.
- This consists of two ropes or cables m, passing over elevated guide-pulleys 50 and around guide-pulleys '51 51, carried by a lever 52, connected with the shifter, the opposite ends of each rope being connected to a lever 53 upon the carat opposite sides of its shaft 54, which passes through the carand is there provided with an operating-handle 55.
- These parts are so arranged that the handle 55 will be in its mid-position when theshifter is in its mid-positiomso that the operator in the car can thereby know at all times the actual position of the shifting device.
- a toothed sector 20, pivoted to the frame of the machine, is connected with the shifter 3 and gears 'with'a pinion upon the'shaft 4, that carries the resistance-switch or cut-out 40, so that when the shifter 3 is moved by the manipulation of'the handle 55 or other device the'switch 40'will also be moved to an extent proportioned to the movement of the handle.
- any suitable means may be employed for carrying the shifter, when not otherwise controlled, to its mid-position shown in Fig. 1.
- springs 11 are confined between shoulders 43 upon the shifter and bearings 44 upon the frame, so that one of said springs will be compressed when the shifter is moved in either direction from its central position.
- that spring 11 which is compressed will immediately upon the release of the handle move the shifter to its central position, cut out the entire current, and arrest the machine.
- the detent 16 is in the form of an L-shaped pawl, one arm of which has a projection 10, that enters a V-shaped notch 18 in the shifter whenever the latter is at the limit of its movement in either direction, while the other arm of the detent enters the groove of a sleeve of a ball-governor G upon a prolongation of the armature-shaft.
- the weight of the car is counterbalanced by a weight L, connected with the cable Wound on the drum in a direction the reverse of the cage-cables, as usual.
- the parts arearranged so that neither the cage nor the counterweight will on proper operation of the apparatus touch the floor; but should eitherbe brought against the floor, thereby arresting the revolution of the armature and governor, the detent 10 will be withdrawn and the switch will assume automatically its. position to break the circuit.
- a solenoid 28, electro-magnet, or other electromotor connected with the detent 16 and proportioned soas to be operated only by a current in excess of the normal current, to thereby lift the detent and release the shifter, which assumes at once its mid-position, thereby preventing the armature from being driven atan excessive speed or from overheating.
- thermostat 17 in connection with each. of such parts, and in a circuit inciudinga switch connected to be operated by-said thermostat we
- a switch or circuit-breaker I so arranged as to break the circuit when the switch is in its normal position or in proper position at the limit of either movement, but so as to complete the circuit and sound the alarm when the shifter is at any other point of its movement.
- a flexible contact piece or brush 9 which is on the circuit and extends between the plates or is otherwise out of contact with them when the shifter is in mid-position, and which is opposite and out of contact with the outer end of one of the plates 56 when the shifter is in either extreme position, but otherwise, when the shifteris at intermediate points, is in contact with one of the plates and completes the circuit, causing the indicator to be operated to indicate to the operator the fact that the switch or shifter has not been moved to a proper extent It will be evident that this arrangement may be reversed, so that the indicator is operated when the shifter is in a central position only, as shown in Fig. 5, the circuit being broken when the shifter moves to either side.
- the shifter S in the form of a bar and controlled by springs to carry it to a mid-position, it may be in the form of a disk.
- the shifterdisk 3, Fig. 3 may be mounted upon the end of the shaft 4: of the resistance device, and a cord ⁇ V, passing between guide-pulleys 47, is attached to the edge of the disk and carries a weight that normally brings the disk to the mid-position shown, at the same time turning the shaft a and the switch 40, attached thereto.
- the detent 16 bears upon the edge of the disk, and, if desired, the hand shifting-rope so may extend around the disk in a groove thereof.
- the switch or circuit-breaker of the ther mostat may control a circuit (dotted lines Z) b, Fig. 1) through the solenoid or its equivalent 28, so as to lift the detent and shift the main switch i0 upon the heating of the parts, and any suitable form of current-controller maybe substituted for the resistance device 13.
- pendulums may be used.
- a dash pot or cataract of the usual construction consisting of a cylinder '71, piston 72, piston rod 73, and circuiting-channel 70.
- the motion of the bar either way from the center lifts the piston until the bolt 7% is pushed back by the inclined cam by the pin on the bolt traveling on the inclined face of the cam.
- the piston returns now to its bottom position, and the toe '76 in its downpath strikes the detent-bolt 77 and releases the shifter-bar 3, which then returns to the center and opens the circuit, shutting off the current.
- the bolt 7/ holds the bar so that the operator can let go the lever in the car without the necessity of bearing upon it until the motor gets its proper speed.
- the timing arrangement is set to unlock after the proper speed is acquired, in which case the detent 10 holds the bar. It, then, the movement of the armature should stop or be unduly reduced, or if the current through the magnet 28 should become too strong, the detent 10 would be released.
- the bolt 77 of the timing device is intended to hold in case the detent fails or from any circumstances is drawn out of operation; but it releases the bar before damage can result from an excessive current, or in case the detent is in inoperative condition to release the bar, so that it will be under the control of the detent.
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- Engineering & Computer Science (AREA)
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- Types And Forms Of Lifts (AREA)
Description
(No Model.) 3 SheetsSheet l.
N. P. OTIS 8B R. 0. SMITH. ELECTRIC ELEVATOR.
No. 444,640. Patented Jan 13, 1891.
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UNITED STATES PATENT OFFICE.
NORTON P. OTIS AXD RUDOLPH 0. SMITH, OF YONKERS, NE YORK.
ELECTRIC ELEVATOR.
SPECIFICATION forming part of Letters Patent No. 444,640, dated January 18, 1891.
Application filed January 31, 1890. Serial No, 333,770. (No model.)
To all whom it may concern:
Be it known that we, NORTON P. OTIS and RUDOLPH 0. SMITH, citizens of the United States, residing at Yonkers, \Yestchester county, State of New York, have invented certain new and useful Improvements in Electrical Elevator Apparatus, of which the following is a specification.
Our invention relates to that class of elevators in which electricity is employed as the motive power for moving the cage; and our invention has for its obj eet to insure certainty in the operation of the motor and to prevent injury to the apparatus liable to result from excessive currents or from arresting or unduly reducing the speed of the armature from any cause, or from the heating of the parts.
In consequence of the fact that unskilled help is generally employed for operating the controlling devices of elevator-motors accidents are liable to occur from improper manipulation of said devices, and this is especially the case when electromotors are employed,inasmuch as any overloading or obstruction to the movement of the car or platform, and consequent diminution or cessation of the speed of the armature of the motor, prolongedfor anyconsiderablc time, will cause the armature or other parts to be overheated or burned out, the undue reduction of the speed of the armature, as is well known, diminishing the counter electro-motive force so that the current soon exceeds the capacity of the armature-coils to carry the currents without danger. It a fusible conductor or safetyf use is employed, the same is apt to be burned out in case of the failure of the armature to maintain its proper speed, causing delay and annoyance, while when resistance-coils are employed, if the attendant should so adjust the parts that the current passes through but a portion of the resistance, the coils may become overheated, and if the parts are not soon properly adjusted are injured or burned out.
Our invention consists in means fully set forth hereinafter whereby the circuit is broken automatically without injury to any part of the apparatus should the controlling de vices be improperly adjusted, or in case of excessive currents being sent over the main line, and whereby the armature is out out of circuit in case its movement is unduly diminished, or if the cage or counter-weight exceeds the limit of its motion, and means are provided for indicating the fact to the operator should the bearings or resistance become overheated, or should the controlling device be improperly adjusted.
On reference to the accompanying drawings, Figure 1 is an elevation showing part of the operating-electromotor and part of an elevator apparatus. Fig. 2 is a plan view. Fig. 3 is a view illustrating a modification. Fig. a is a view showing portions of the apparatus with the parts in a different position from that shown in Fig. 1. Fig. 5 is aview illustrating a modification.
The electromotor A may be of any of the usual or suitable constructions, and, as shown, is provided with a field-magnet 12 and revolving armature 13, as in the wellknown Eickmeyer motor, in which the fieldmagnet has a surrounding casing of iron in the magnetic circuit, and in connection with the motor we'use a current-controller, preferably in the form of a resistance device 13, which also may be of any suit-able construction, but is, as shown in dotted lines, provided with a switch or cut-out -10, so connected with the conductors and arranged in respect to the resistance-terminals 41 i2 and connected with the properly-wound armature that the movement of the switch from its mid-position (shown in Fig. 1) to one side will close the circuit through the resistance and will gradually cut out the resistance and impart motion to the armature in one direction, while the movement to the other side will gradually cut out the resistance and impart movement to the armature in the other direction.
We combine with the electromotor and the resistance device a shifter device constructed and connected to be operated in any suitable manner from the cage or platform so as to throw the switch to any desired position, and in connection with these parts we employ means whereby the shifter is automatically.
restored to its normal position, carrying the switch to its mid-position and throwing open the circuit of the motor whenever the operator fails to properly adjust the switch, or in case the motor moves at an improper speed,
or should an excessive current be thrown on the mainline.
Different means may be employed for bringing the shifter and the parts connected therewith to the mid-position, and the shifter may be of different constructions, varying with the character of the apparatus.
In the construction shown in Fig. 1 the shifter is in the form of a bar 3, sliding horizontally in bearings on the base 0, and the winding-drum D is geared with the armatureshaft through the medium of the worm 47 on said shaft and worm-wheel 48 upon the shaft 7 of the drum D. The ordinaryshifting-rope may be employed to move the shifter 3 but we prefer to use the double traveling-rope device shown in Fig. 1. This consists of two ropes or cables m, passing over elevated guide-pulleys 50 and around guide-pulleys '51 51, carried by a lever 52, connected with the shifter, the opposite ends of each rope being connected to a lever 53 upon the carat opposite sides of its shaft 54, which passes through the carand is there provided with an operating-handle 55. These parts are so arranged that the handle 55 will be in its mid-position when theshifter is in its mid-positiomso that the operator in the car can thereby know at all times the actual position of the shifting device.
A toothed sector 20, pivoted to the frame of the machine, is connected with the shifter 3 and gears 'with'a pinion upon the'shaft 4, that carries the resistance-switch or cut-out 40, so that when the shifter 3 is moved by the manipulation of'the handle 55 or other device the'switch 40'will also be moved to an extent proportioned to the movement of the handle.
Any suitable means may be employed for carrying the shifter, when not otherwise controlled, to its mid-position shown in Fig. 1. Thus springs 11 are confined between shoulders 43 upon the shifter and bearings 44 upon the frame, so that one of said springs will be compressed when the shifter is moved in either direction from its central position. As a result of this construction, should the attendant move the shifter so as to carry the cut-out 40 to .such aposition as to cutout only a part of the resistance on either side, that spring 11 which is compressed will immediately upon the release of the handle move the shifter to its central position, cut out the entire current, and arrest the machine.
In order that the shifter and the switch 40 may be maintained in position when the resistance has been properly cut out to either side, and to avoid the necessity when the engine is running properly of the operator maintaining continuous hold upon the handle 55, we combine with the shifter a detent, and a governor operating the latter, to hold the shifter in place so long as the motor moves at thetproper speed. 'Such detent may be con-. structed in various ways, and the governor may be a governor of any of the usual forms connected with the armature-shaft or other part of the machine in any way so 'as to be driven thereby. Thus the detent 16 is in the form of an L-shaped pawl, one arm of which has a projection 10, that enters a V-shaped notch 18 in the shifter whenever the latter is at the limit of its movement in either direction, while the other arm of the detent enters the groove of a sleeve of a ball-governor G upon a prolongation of the armature-shaft.
The above-described parts are so adjusted and proportioned that when the armature is revolving at the proper rate of speed the shifter will be held by the detent; but should the cage be overloaded or the armature for any other reason be obstructed in its movement, so as no longer to be operating under proper conditions, or the count-er electro-motive force falls below a condition of safety, then the change in the position of the'governorwill shift the pawl and release the shifter, which will at once assume its mid-position, shifting the switch and arresting the inotion of the machine. As the notches and the projection 10 have beveled or inclined faces, the operator can at any time shift the switch by exerting sufficient force to move the shifter and lift the project-ion outof the'notch.
In the construction shown in Fig. 1 the weight of the car is counterbalanced by a weight L, connected with the cable Wound on the drum in a direction the reverse of the cage-cables, as usual. The partsarearranged so that neither the cage nor the counterweight will on proper operation of the apparatus touch the floor; but should eitherbe brought against the floor, thereby arresting the revolution of the armature and governor, the detent 10 will be withdrawn and the switch will assume automatically its. position to break the circuit.
To prevent injury from the transmission of excessive currents to the motor, we place in the main circuit a solenoid 28, electro-magnet, or other electromotor connected with the detent 16 and proportioned soas to be operated only by a current in excess of the normal current, to thereby lift the detent and release the shifter, which assumes at once its mid-position, thereby preventing the armature from being driven atan excessive speed or from overheating.
thermostat 17 in connection with each. of such parts, and in a circuit inciudinga switch connected to be operated by-said thermostat we In order to fur-' IIO position, as the parts would burn out if the switch were left partly turned, we combine with the switch and with the alarm-bell or indicator and circuit, including the latter, a switch or circuit-breaker I, so arranged as to break the circuit when the switch is in its normal position or in proper position at the limit of either movement, but so as to complete the circuit and sound the alarm when the shifter is at any other point of its movement. Thus in the circuit a, including the bell or other indicator 30, are two separated plates 56 56, mounted upon but insulated from the shifter, or otherwise controlled. by the change of position of the switch, and supported above the plates is a flexible contact piece or brush 9, which is on the circuit and extends between the plates or is otherwise out of contact with them when the shifter is in mid-position, and which is opposite and out of contact with the outer end of one of the plates 56 when the shifter is in either extreme position, but otherwise, when the shifteris at intermediate points, is in contact with one of the plates and completes the circuit, causing the indicator to be operated to indicate to the operator the fact that the switch or shifter has not been moved to a proper extent It will be evident that this arrangement may be reversed, so that the indicator is operated when the shifter is in a central position only, as shown in Fig. 5, the circuit being broken when the shifter moves to either side.
Although in Fig. l we have shown the shifter S in the form of a bar and controlled by springs to carry it to a mid-position, it may be in the form of a disk. Thus the shifterdisk 3, Fig. 3, may be mounted upon the end of the shaft 4: of the resistance device, and a cord \V, passing between guide-pulleys 47, is attached to the edge of the disk and carries a weight that normally brings the disk to the mid-position shown, at the same time turning the shaft a and the switch 40, attached thereto. In this case the detent 16 bears upon the edge of the disk, and, if desired, the hand shifting-rope so may extend around the disk in a groove thereof.
The switch or circuit-breaker of the ther mostat may control a circuit (dotted lines Z) b, Fig. 1) through the solenoid or its equivalent 28, so as to lift the detent and shift the main switch i0 upon the heating of the parts, and any suitable form of current-controller maybe substituted for the resistance device 13.
In order to further insure againstthe switch being left for an excessive time in any position where the current would be on without turning the armature at the proper speed, we use a time arrangement, which is set to release the shifter-bar after a given limited time, such that no overheating of the resistance and other parts can take place. This is practicable in elevators, as the length of a trip scarcely ever exceeds a few minutes. We do not confine ourselves to any of the wellknown timing arrangements. Clocks, fans,
pendulums, may be used. We have shown a dash pot or cataract of the usual construction, consisting of a cylinder '71, piston 72, piston rod 73, and circuiting-channel 70. The motion of the bar either way from the center lifts the piston until the bolt 7% is pushed back by the inclined cam by the pin on the bolt traveling on the inclined face of the cam. The piston returns now to its bottom position, and the toe '76 in its downpath strikes the detent-bolt 77 and releases the shifter-bar 3, which then returns to the center and opens the circuit, shutting off the current.
In consequence of the incline of the notches in the bar the operator can, by the application of sufficient force, shift the bar at any time when the bolts are in the notches, which is the normal condition, the said belts or detents coming into operation after a limited time and in certain contingencies described. Thus, assuming that the operator has shifted the bar to the position shown in Fig. i, and that all the detents are in the notches, which is the normal condition immediately after shifting the bar, if under these circumstances the detent 10 was withdrawn, the timing-bolt 7 7 would still prevent an immediate return of the bar and the cutting off of the current by the switch .40. In anyevent the bolt 7/ holds the bar so that the operator can let go the lever in the car without the necessity of bearing upon it until the motor gets its proper speed. The timing arrangement is set to unlock after the proper speed is acquired, in which case the detent 10 holds the bar. It, then, the movement of the armature should stop or be unduly reduced, or if the current through the magnet 28 should become too strong, the detent 10 would be released.
It will be seen from the above that the bolt 77 of the timing device is intended to hold in case the detent fails or from any circumstances is drawn out of operation; but it releases the bar before damage can result from an excessive current, or in case the detent is in inoperative condition to release the bar, so that it will be under the control of the detent.
Without limiting ourselves to the precise construction and arrangement of parts shown, we claim-- 1. The combination, with the electremotor of an elevator, of a current-controlling device constructed to both reverse and vary the current and provided with a switch, means for automatically turning the switch to its normal position with the current cut-off, and means for operatin g said switch from the cage to carry it from its normal position in either direction, substantially as set forth.
2. The combination, in an elevating apparatus, of an electroinotor, a controller provided with a switch, a shifter connected with said controller and with the cage to be operated therefrom, automatic means for carrying the shifter to one position, a detent for holding the shifter in another position, and a governor connected with said detent and driven from a moving part of the apparatus, substantially as set forth.
3. The combination, with the cage-and electromotor of an elevator, of a controller provided with a switch, a shifter connected to be operated from the cage and also connected to said switch, means for carrying the controller to one position, a detent engaging with bearings upon the controller to hold it in another position in either direction, and a governor driven from the armature and connected with said detent, the parts being arranged to release the shifter when the spced of the armature is reduced, substantially as set forth.
4. The combination, with the shifter connected to be operated from the cage and with the switch,- of an alarm upon the cage and a circuit-breaker carried by the shifter to complete the circuit including thealarm when the position of the shifter is changed from one position to the other, substantially as described.
5. The combination of the switch controlling the current to the motor of an elevator, a circuit-indicator, and a circuit-breaker connected to move with said switch and in circuit with said indicator, substantially as described.
6. The combination, with the cage and electromotor, of a resistance controlling the current to the motor, the switch or cut-out of said resistance, a shifter connected to be operated from the cage and with said switch, automatic means for carrying the shifter to its mid-position, and a detent and governor controlling the same for holding the shifter in its extreme positions, substantially as set forth.
7. The combination, with the motor and cage of an elevator, of a regulating-switch controlling the circuit to the motor through a series of resistances, a detent controlling the switch, and an electrical governor for the detent, arranged in the main circuit and connected with the detent to'release the switch when the main current becomes excessive'to allow the switch to return to'its normal position, substantially asset forth.
' 8. The combination, with an electromotor, a switch controlling the current through the same, means for moving the switch to one position, and a detent for holding it at the limit of its movement in either direction, of a timing device for releasing the detent, substantially as set forth.
9. The combination, with the switch and with the shifting devices connected with the elevator-cage, of a detent for holding the switch, constructedto yield under the action of the shifting device, substantially as described.
10. The combination, with an elevator-cage and electromotor connected to operate the cage, of a switch controlling the circuits to operate the motor in either direction, devices for carrying the switch to its normal position, a detent for locking the switch in its operating position, and automatic means for operating the detent, substantially as set forth.
11. The combination, with the :cage and shifter-bar and connections for moving it from the cage, of a switch and a lever connected withsaid bar and having a rack engaging a pinion on the switch-shaft, substantially as set forth. Q
12. The combination,with the cage, motor, switch, and yielding detent for holding the switch in one position, of a spring for shifting the switch, substantially as set forth.
In testimony whereof we have signed our names to this specification in the presence of two subscribing witnesses.
NORTON P. OTIS. RUDOLPH 0. SMITH. Witnesses:
Enwn. K. ANDERTON, HUGO A. HENKEL.
Publications (1)
| Publication Number | Publication Date |
|---|---|
| US444640A true US444640A (en) | 1891-01-13 |
Family
ID=2513533
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US444640D Expired - Lifetime US444640A (en) | Electric elevator |
Country Status (1)
| Country | Link |
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| US (1) | US444640A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2678416A (en) * | 1951-02-01 | 1954-05-11 | Gen Motors Corp | Motor control |
-
0
- US US444640D patent/US444640A/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2678416A (en) * | 1951-02-01 | 1954-05-11 | Gen Motors Corp | Motor control |
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