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.
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 for the new generation of hotel and office buildings. An operator in the car controlled a reversible, multispeed DC motor from inside the cab, at first by means of a shipper rope and later a dead man’s rheostat. A separate worker tending a steam engine was no longer required.
In 1892, Otis Electric Co., jointly owned by Otis Brothers and General Electric, was created for the purpose of designing and building elevator-specific electric motors for Otis Brothers and Company.
In the years that followed, Otis Brothers continued to acquire competing elevator manufacturers, and in 1898 they created a gigantic umbrella entity known as Otis Elevator Co., which is now well into its second century of operation.
From 1900 to the present, there have been numerous refinements in elevator technology, some incremental, some revolutionary. The trend has been to make vertical transportation safer, faster, more efficient, and more reliable. Three principle developments that revolutionized elevators in the twentieth century are:
■ The automatic elevator
■ The low-rise hydraulic elevator
■ The VFD, which enables use of AC induction motors to power elevators
We will discuss each of these.
At first elevators were operated by means of clumsy and not always reliable shipper ropes that passed through holes in the car floor and ceiling. (They are prohibited in the current ASME A17 Safety Code for Existing Elevators and Escalators.) Car and hoistway doors had to be opened and closed manually, and until the development of the door interlock, a door could be left open, sometimes resulting in fatal accidents.
The first automatic door mechanism was built and patented in 1887 by Alexander Miles, an African-American inventor in Duluth, Minnesota. The door opens and closes by means of a series of rollers and levers. After a car has stopped at a floor, a flexible belt extending the length of the shaft opens the shaft door. The car door also opens automatically. Both doors close before the car proceeds to the next stop.
Still, a human operator started and stopped the car by means of a controller inside the car, as shown in Figure 1-6.
FIGURE 1-6 Otis manual elevator controller. If for any reason the operator released the handle, it would return to the neutral position and the car would stop. (Wikipedia)
Rudimentary elevator automation first appeared in the 1920s. At the time there were no microprocessors or solid-state components, but digital logic could be accomplished by means of mechanical relays. These were cumbersome by today’s standards, and had some disadvantages. They were slower-acting, consumed more energy, were less reliable, and more costly. Still, they worked surprisingly well in elevator applications, and in contrast to today’s computer-controlled devices, there were never system-wide crashes.
The first relay version was complex and had few of the features we expect in fully automatic elevators. It was known as the selector. It had numerous mechanical parts including a magnetic tape attached to the top of the car. This tape, as the car traveled, caused mechanical gears to move in response. The gears controlled speed, position, and door operation. A human operator was still required, but car leveling and stopping were simplified.
In 1924 Otis introduced Signal Control, which was a fully automatic elevator system, still with mechanical relays. Throughout the 1940s and 50s, other manufacturers introduced enhanced relay-controlled automation, permitting the car to bypass floors when fully loaded.
Microprocessor-based controllers were introduced by Otis in 1979. The Elevonic 101 was a true motion controller, overseeing all aspects of elevator operation. Another Otis product, Elevonic 401, offered in 1981, was fully computerized.
All-in-one, microprocessor-based controllers, which are a product of China, are currently widely used. They are compact and consume far less energy than previous motion controllers. These units sense car position and door status and are capable of managing large group installations, with human intervention necessary only rarely in the event of sensor, termination, or wiring failure.
Software as a Service (SaaS) enables remote monitoring of group installations via web browser, and it will alert technicians and building managers of imminent or actual malfunctions. Remote monitoring systems are offered by Otis (REM), ThyssenKrupp (Vista), Schindler (Servitel), Kone (KRM) and Mitsubishi (ELE-FIRST).
We will discuss the inner workings of the contemporary motion controller in Chapter 9.
Speaking now of hydraulic elevators, we are no longer concerned with the water-powered affairs that were prominent in the late nineteenth century. The newer hydraulic elevators had some important differences. For one thing, the fluid that characterized them was not water, discarded after each cycle, but hydraulic oil, which, with an anti-foaming additive,