Elevator Suspension Methods
For the proper functioning of an elevator, the elevator cabin must be suspended in the elevator shaft and move up or down to facilitate the transportation of passengers and cargo. Naturally, the elevator installation system differs from that of a regular hoist. In regular hoists, the load is lifted by a steel rope directly attached to it, and a motor at the top winds the steel rope around a pulley, pulling the load upward. However, in this system, the load experiences jolts during the ascent, and advanced speed and smooth movement control are impossible.
In contrast, the operation of an elevator is entirely different. The elevator movement must be secure, without jolts, and ensure the safety of passengers and cargo inside the cabin. Therefore, an elevator must be installed with a precise and efficient movement system to ensure the cabin is suspended in the shaft and moves smoothly. This movement system cannot rely solely on a single steel rope but requires additional elements such as counterweights and various pulleys. These counterweights and pulleys must be arranged according to a specific system to maintain the speed, stability, and safety of the elevator cabin and the elevator itself for a long period after installation. This system is referred to as the Elevator Roping System. These aspects are thoroughly covered in practical elevator installation training classes.
Elevator suspension systems come in various types as described below:
- 1:1 suspension system
- 2:1 suspension system
- 3:1 suspension system
- 4:1 suspension system
Concept of 1:1 and 2:1 Suspension Systems
In elevator suspension systems, the numbers 1, 2, 3, etc., refer to the speed ratio between the elevator cabin and the counterweight frame. If the suspension system is designed so that the speed of the elevator cabin and the speed of the elevator motor are identical, this is known as a 1:1 suspension system. If the suspension system is designed so that the elevator motor moves at twice the speed of the elevator cabin, it is known as a 2:1 suspension system. In the above diagram, suspension systems a, b, c, and d, are 1:1 suspension systems, and suspension systems e, f, and g are 2:1 suspension systems.
During elevator installation, the procedure follows to set up a 1:1 or 2:1 suspension system: In a 1:1 system, both ends of the wire ropes are attached to the elevator cabin and the counterweight frame, as clearly shown in the diagram above. In a 2:1 suspension system, however, both ends of the wire ropes, after passing over the gearbox pulley of the elevator motor and the pulleys on the elevator cabin and counterweight frame, go to the shaft ceiling in the machine room and are then attached to the yoke structure.
1:1 Suspension System
The 1:1 suspension system is Iran’s most well-known and widely used elevator suspension system. As previously mentioned, in this system, the speed of the elevator cabin and the speed of the counterweight frame are equal. This suspension system is suitable for most elevators. In the diagram above, suspension systems a, b, c, and d, are of the 1:1 type.
2:1 Suspension System
The 2:1 suspension system, represented by suspension systems e, f, and g in the diagram above, causes the elevator motor to move at twice the speed of the elevator cabin. Advantages of this suspension system include increased elevator power and better, more reliable movement.
3:1 and 4:1 Suspension Systems
This type of suspension system, as shown in the diagram with systems h and i, causes the elevator motor to move at three or four times the speed of the cabin. This significantly increases the elevator’s power and provides better speed and stability in movement. Consequently, these two types of suspension systems are used in freight or high-capacity elevators.
Double Wrap
In high-speed elevators, especially heavy-duty elevators, to prevent friction and increase the lifespan of the wire ropes and pulleys, double wrapping the wire rope around the pulley is used (Double Wrap). Although the pulling force significantly increases in double wrapping the wire rope, using this method complicates the entire wire rope system and the elevator’s driving force. In this case, the width of the traction pulley must be increased due to the doubling of the number of grooves for the wire ropes, and the amount of bends in the wire rope also increases, which causes more wear on the wire ropes.
Without using a speed-reducing gearbox, the speed of the wire rope will be equal to the peripheral speed of the traction pulley and the rotation speed of the motor (rpm). In new elevators or gearless elevators that use smaller pulleys, the rotational speed is less compared to geared models.
Considering that the minimum diameter of the wire rope pulley should not be less than 40 times the diameter of the wire rope, the diameter of the traction pulley can be considered up to this extent.
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