Elevator Troubleshooting & Repair. David Herres

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СКАЧАТЬ the magnetic field to achieve the required alignment.

      Since Sprague was working for Edison, the improved motor design at this point belonged to Edison. Sprague evidently saw the writing on the wall, and shortly thereafter tendered his resignation.

      While Edison continued to refine his incandescent light bulbs and DC power generation and distribution system, Sprague, after eleven months working in Edison’s large organization, formed the Sprague Electric Railway and Motor Company. His lifelong project was to move rail traffic by means of electric motors. In this he was very successful and was renowned among electricians and transportation workers as “the father of electric traction.” He came to define these words to include vertical as well as horizontal traction. His elevator work was a relatively brief interlude, but its impact was enormous. After completing some difficult early streetcar and railway projects, he turned his attention in 1889 to elevator design and construction.

      Sprague, together with his old friend Ed Johnson and elevator manufacturer Charles Pratt, rented a factory building and in 1892 formed Sprague Electric Elevator Company. Ed Johnson was the legal and financial specialist. Sprague provided electrical expertise, and Pratt was the mechanical engineer. Together they planned to offer two very different types of elevators. For low-rise buildings, a conventional drum-type elevator would be reconfigured with a reversible, adjustable-speed electric motor replacing the steam engine.

      For high-rise applications, a faster machine would consist of a large, threaded-steel shaft placed horizontally and powered through a gearbox by an electric motor. A large nut would move along the turning shaft, driving a cable pulley. The contraption actually worked, and in fact dominated the industry until shortly before the turn of the century.

      After constructing a small prototype in their new Manhattan facility, the firm secured a contract to install a similar elevator in the Grand Hotel in New York City.

      There were problems in this installation. The control system, which had been satisfactory in Sprague’s electric trolleys, did not provide the smooth performance required in an elevator.

      Sprague’s electrical expertise was severely challenged. First, he built an improved resistance network, known as the grid, for the controller. This smoothed out the elevator motion, but the resistance network and controller mechanism heated and contacts had to be replaced.

      The elevator was put back in operation, but after a few days at an upper floor the ascending car suddenly dropped, its speed doubling, coming to a stop after striking the bumpers at the bottom level.

      Fortunately, there were no injuries. The cause was determined to be a defective motor that ran the reversing lever in the controller. The sudden reversal damaged the safeties, permitting the car to drop.

      Soon redesigned safeties and controls were in place and the elevator resumed normal operation. This did not solve the network problem. Eventually, the firm built and installed a new controller with heavier contacts, but the problem persisted. Sprague favored a cast iron grid, which turned out to work on a long-term basis. The Grand Hotel signed off on the project and Sprague Electric Elevator Company moved on to another project, the Postal Telegraph Building. This was to be located close by on Broadway and be far bigger and faster than the Grand Hotel installation. There would be four local and two express elevators, rising 14 stories above street level.

      The immense screw and traveling nut mechanisms resulted in heavy loading and increased friction, which Sprague intended to mitigate by incorporating captive steel balls within the nuts.

      After mishaps and delays, the Postal Telegraph Building installation performed flawlessly in tests and was placed in operation. It was a prestigious project, and the Postal Telegraph Company Building Committee was well satisfied. But unfortunately, the country was enduring a severe financial depression. New building had halted, and orders were not coming in. Sprague, never one to let up, had some ideas for improving elevator safety and efficiency, and the business slowdown allowed time to work on them. One innovation was the self-centering “dead man’s control,” which stopped the car if for any reason the control was released by the operator. Another innovation was an automatic elevator that incorporated door interlocks and floor alignment. Sprague stuck with the screw and nut design, rather than going with an improved traction drive, which together with his electric motor became the wave of the future. The business climate improved and by 1895 new orders soared and the company moved to a larger facility across the Hudson River, in New Jersey.

      In 1898, Sprague decided to return to his first love, railroad electrification. He sold the elevator business to Otis for $1,000,000, retaining royalty rights to two thirds of foreign business and rights to lease back plant and equipment for five years. With that transaction Sprague became much less of a presence in the elevator world, in which Otis was now the most prominent player.

The Otis Story

      Elisha Graves Otis (1811–1861), a skilled builder and mechanic, in 1850 found his way to Albany, New York, where he was employed to manage a bedstead factory. Relocating in nearby Bergen, New Jersey, in 1851 and then in Yonkers, New York, he organized and managed successive bedstead facilities, and in the Yonkers factory he built a freight elevator. Soon, he established an independent company, which by 1853 was building and installing freight hoists in nearby manufacturing facilities.

      In early 1854, as we have seen, one of the defining events in elevator history occurred. At an exhibition in New York’s Crystal Palace, Otis ascended in one of his fully-loaded open freight hoists, and in the presence of astonished onlookers, cut the hoisting rope. Rather than crashing to the floor, a frequent cause of fatal elevator accidents, the platform dropped a short distance and then stopped.

      Otis had demonstrated the effectiveness of his great invention. Safeties, as they were (and still are) called, in response to breakage or loss of tension in the rope, automatically, which is to say without human intervention, gripped racks attached to guides, bringing the car or platform to a stop. These safeties, in one form or another, were universally adopted in the elevator industry and have saved many lives.

      Otis, in 1855, established the Union Elevator Works. The firm sold a gradually increasing number of hoists in the years that followed. They were powered by water or steam engines, which were optionally furnished, and always with the new safeties.

      Elisha Otis was a great mechanic and inventor, if not always successful financially. Following his death in 1861, his sons, Norton and Charles Otis, took over the firm, renaming it N.P. Otis and Brother. As inventors and builders, their skills equaled Elisha’s, and financially they succeeded where their father had been challenged.

      After the American Civil War, in 1867, Norton and Charles again renamed the firm Otis Brothers and Company. In the years that followed, the organization, by means of intense research and development and aggressive marketing, became the preeminent powerhouse that it is today. By the end of the nineteenth century, through a series of mergers, stock acquisitions, and purchases, Otis absorbed its major competitors.

Electrification

      First Edison, and then Tesla and Westinghouse had built electrical distribution systems capable of supplying power where needed. Clearly, the electric motor was the wave of the future. At first, elevators moved from steam engine to electric power merely by substituting an electric motor for the connection to mill shafting or the steam engine. This arrangement worked reasonably well, but Otis Brothers and Company between 1887 and 1889 realized further advantages in fully integrating the motor into the elevator mechanism. This development occurred at a time when new, taller buildings were proliferating in New York City and other urban areas. Otis began selling passenger elevators СКАЧАТЬ