an outside water wheel.
The principle components were a brake wheel, two fixed and two free pulleys, two endless belts, and a belt shifter. A crossed belt permitted the direction of car motion to be reversed, as needed in any elevator.
FIGURE 1-2 William Strutt (1756–1830) (Wikipedia)
A pinion gear was attached to one end of the main shaft, and its teeth meshed with those of a spur gear attached to the hoisting pulley shaft.
This was the first in a long series of working elevators that spanned the nineteenth century. Strutt’s Teagle, as it was known, was complex in the sense that it had a lot of ropes, belts, and pulleys, but simple in that these things worked smoothly together to deliver the power to where it was needed so that the car could deliver workers throughout Strutt’s five-story textile mill.
By the 1840s, two trends in vertical transportation merged. Increasingly, elevators were optimized to carry freight exclusively or to transport only workers, residents of tall buildings, and hotel guests from ground level to the growing number of floors in taller buildings that began to crowd the cities. Also, of necessity there was greater emphasis on safety.
Previously, lower-powered lifting machines had their share of accidents, sometimes resulting in well-publicized fatalities. This was true not only in elevators, but throughout the world of increasingly mechanized, more powerful and faster machinery that characterized the new industrial age. Accidents took two forms. In one, the suspension rope and associated rigging that raised and lowered the car in a traction elevator failed, causing the car, which was slowed only a little by the air column below, to free fall to the bottom of the shaft. The inevitable result was severe injury, often fatal. The other type of accident involved the absence of reliable door interlocks, which would prevent a door from opening when the car was moving and/or prevent the car from moving when the doors were not closed and locked.
Without these interlocks, an occupant of the building could step through an open door assuming that the car was at the landing, and fall to the bottom of the shaft. Another equally great hazard was that an occupant of the car could be crushed between the car floor and the top of the door opening at any floor while the car was ascending. We shall see how mid-nineteenth century advances in elevator technology confronted these hazards and greatly reduced the number of injuries resulting from them.
Before midcentury, freight elevators were typically designed in-house to meet the needs of the many industrial facilities that were appearing, especially in England and eastern U.S. Then, beginning around 1845, industries and commercial operations such as hotels and office buildings began to look to certain emerging elevator manufacturers to meet these needs. Henry Waterman in New York City was a freight and passenger elevator manufacturer. One of his early machines, built in Manhattan for Croton Flour Mills, was operated from within the car so that an outside attendant was not required. Car motion was initiated by moving a simple iron lever, rather than tugging on the shipper rope. For passengers, the trip became smoother and more user-friendly. The control lever moved an attached chain that passed through openings in the car roof and floor, then engaged devices at the top of the shaft. The mechanism consisted of a friction clutch driven by a conventional power shaft, eliminating the need for pulleys and a belt shifter as in Strutt’s Teagle.
The operator caused the car to ascend by pulling the handle, which released the brake and engaged the clutch. Upward travel continued as long as the operator maintained pressure on the handle. The clutch disengaged and the brake was applied when the operator released the handle. To descend, the operator applied an intermediate amount of pressure on the handle, releasing the brake, and the car would descend, its speed regulated by the brake.
The innovation in Waterman’s elevator was that it was controlled from within the car by means of what we would call a joystick, rather than the bothersome shipper rope that is prohibited today.
By 1850, George H. Fox and Co., a Boston firm, was building freight elevators that were safer and more efficient. Fox replaced meshing spur gears with a worm gear attached to the winding shaft. This arrangement is superior because it is self-locking. The worm can turn the gear, but the gear cannot turn the worm. Consequently, a separate brake was not required for the hoist, which would hold its position when the driving belt was disengaged. This arrangement meant less chance of a car and occupants falling to the bottom of the elevator shaft due to mechanical failure in the drive system.
Safety was further enhanced by other innovations by Fox and Co. One was the replacement in 1852 of traditional hemp rope by stronger and more wear-resistant steel wire rope. The other innovation was a safety brake, which could stop the car from free falling in the event of rope failure. This brake, however, was not automatic and depended upon quick action by an alert operator.
Falling cars were still a severe hazard, but after 1850 new developments in elevator technology greatly reduced the number of occurrences.
In the mid-nineteenth century, William Adams and Co. manufactured freight elevators in Boston. In 1859, one of their freight platforms in a group installation dropped to the bottom of its shaft. An engineer for the firm, inspecting the damage, found that it was not as severe as might be anticipated. He concluded that the hoistway, as built, happened to be relatively airtight, and as a result, the air as it was compressed below the falling platform acted as a cushion and slowed its fall. This suggested a way to mitigate these disasters, and in fact the idea was patented and hardware developed and marketed.
Elisha Graves Otis Invents Safeties
Another very active key figure in the evolving elevator industry in mid-nineteenth century America was Elisha Graves Otis (1811–1861). His Improved Elevator of 1854 incorporated an automatic safety mechanism, which in the event of rope failure as shown in Figure 1-3, would activate automatically.
All elevators, of course, had guide rails, which were necessary to prevent the suspended car from swinging from side to side, striking the hoistway walls. The Otis Improved Elevator was a variation on existing rack-and-pinion drives, in which the rack was attached to the guide rails. In the new design, the teeth curved upward rather than extending perpendicular from the rack. The brake, relocated below the cross beam at the top of the platform or car, consisted of safety dogs connected to a spring and the hoisting rope. Because the rope, as long as it remained intact, supported the freight platform or passenger car, the spring remained compressed and held the safety dogs away from the rack and the elevator functioned as expected. In the event of a break in the rope or if for any reason it lost tension, the safety dogs would engage the upward angled rack teeth, preventing the car or platform from falling.
Otis was an accomplished mechanic and very inventive builder of elevators, always sensitive to safety issues. However, on the financial side his business failed to prosper despite the success of his Improved Elevator with its advanced safety mechanism. Beginning around 1860, nearly all traction elevators incorporated his braking system in one form or another.
FIGURE 1-3 Elisha Graves Otis cuts the hoisting rope, demonstrating his new safeties, still used, that prevent an elevator car from free falling. (Wikipedia)
Just three months after receiving his patent, Elisha Otis died of natural causes. His business flourished under the ownership of his sons, who reconstituted the firm as N.P. Otis and Brother. The company
