Fiber Optic Rotary Encoder Helps Guide Aerial Tramways
- Sunday, 01 October 2006
In situations where human travel is necessary but where the geography is too steep or treacherous, aerial tramways often are used as a convenient alternative. Ski resorts, mountaineering centers, even archeological sites and cities with a diverse geography have tapped tramways as a method of transportation. When FREY AG (Stans, Switzerland) began constructing new aerial tramway systems, it turned to Micronor’s (Newbury Park, CA) fiber optic MR314 ZapFree™ high resolution hollow shaft rotary encoder to be part of the tramway’s positioning and cable systems.
Aerial tramways differ from gondola lifts, which have smaller cabins, carry lighter loads, have several “cars,” and rely on a circulating looped cable. An aerial tramway is composed of one or two fixed track cables, a loop of cable called a haulage rope, and two passenger cabins (some have only one). The fixed cables provide support for the cabins. The haulage rope, by means of a grip, is connected to the wheel mechanism in the control tower that rolls on the cables. The haulage rope is usually driven by an electric motor, and, being connected to the cabins, moves them along the span of the tramway. The entire system uses a “jig-back” system, where the weight of the down-coming cabin helps to pull the other cabin upwards.
The passive rotary encoder is used by FREY AG as part of the aerial tramway’s complex safety system, and is immune to lightning and other explosive atmospheric conditions that could potentially disrupt function (the unit has no integral electronics within the encoder housing). Specifically, the encoder is used to determine both the position of the cabins on the system as well as to determine the pull of cable, with two encoders per cabin. Signals are relayed among the cabins, towers, and control rooms.
Three recently installed FREY AG aerial tramway projects use the encoder, two in Switzerland and one in Spain. Several other FREY systems using the encoder are under construction or in the testing stage in Switzerland, Slovenia, and Poland. In the United States, FREY AG and Micronor are taking part in the construction of the $40 million Portland (OR) Aerial Tramway, of which the encoder is integral. As part of the city’s plan to lessen automobile traffic, the 3,400-foot tram system will ferry passengers (80 per cabin) from downtown Portland’s South Waterfront District to the summit of Marquam Hill in approximately three minutes. Aerial tramways can carry anywhere from 40 to 100 people. The systems are now being seen as viable alternatives in overpopulated cities where geography or the urban landscape prohibits conventional transportation networks such as additional roads, subway lines, or trains. Aerial tramways are also used as an escape route at launch sites; pads 39A and 39B at Cape Canaveral are fitted with such systems.
The safety-relevant monitoring systems, which in previous systems had been implanted in electronic boards and relay technology, are today implemented in programmable safety control systems. While Micronor designed the MR314 for environments where hazards to encoder function are obvious (such as in heavy industry or EMI/RFI environments), FREY systems deal with corroding agents that are more surreptitious and long term. The company’s aerial tramways run in a wide range of geographical environments, from the moisture-laden conditions of the Colombian cloud forests, to the thin, cold air of the Swiss Alps, to the dry, hot air of Saudi Arabia’s western mountains, to the saline environment of South Africa’s coastal ranges. Each region presented a unique set of conditions for an encoder function that is exposed to the elements 24 hours a day and year-round. Several tramways also run in urban settings, whose man-made microenvironments present yet another set of conditions pertaining to operation. FREY does not restrict its use of the encoder to aerial tramways; the unit is also being used in the company’s inclined railway systems.