Fall protection (machine component)
In mechanical engineering, fall protection is a technical safety device that offers protection against uncontrolled falling or sinking of assemblies due to the action of gravity.
Components can drop in an uncontrolled manner if the drive energy (air or hydraulic pressure or supply voltage) fails, the control is faulty or components fail (e.g. breakage of the piston rod of a cylinder, tear of a cable or loosening of fastening elements). Also, it can be triggered by improper removal of fasteners.
A fall protection system requires a certain overspeed in order to be effective and to bring the movement to a standstill.
history
Fall protection devices were common for conveyor baskets in mining . Here they consisted of solid wooden beams, into which steel claws dug themselves when the hauling rope tore, braked the cage and brought it to a standstill. Such a device is z. B. still in the old Elisabeth mine in Freiberg .
mechanical engineering
In mechanical engineering, attempts are made to prevent assemblies from falling down from the outset by relieving weight, using self-locking gears or clamping in the idle state. A fall can also be prevented by several redundant drive systems. As a support, components can be oversized with a safety factor and fastening elements such as nuts can be positively secured against unintentional loosening.
If this is not possible, there are various options:
- Spring-loaded clamping sleeves clamp slides or piston rods in the event of a drop in pressure in the hydraulics or pneumatics
- Valves on the hydraulic cylinder close and prevent a drop in spite of the pressure drop in the line
- Wedge mechanisms are triggered by the acceleration during a fall and prevent the fall by frictional engagement
- A rope or chain connects the falling component with a mechanism that, similar to a seat belt in a car, blocks when the vehicle is moving too fast
Lifting platforms
Mechanical safety devices, in which two pawls alternately engage in a rack, are often used on lifting platforms. This means that at most a fall of one tooth is possible, so that a high rate of fall cannot build up.
Winches
With cable winches, either self-locking worm gears or spring-loaded pawls are used to prevent the load from falling due to failure of the drive energy (in the simplest case, releasing the drive crank).
Elevators
Before adequate safety could be achieved through reliable materials and high safety factors in the load-bearing components, elevators were very unsafe. The first automatic fall protection for elevators was invented in 1853 by Elisha Graves Otis , who thus laid the foundation for his company, which still exists today.
Similar designs are still used today, especially in high-rise buildings. If the elevator car moves too fast, the brakes on the elevator car are first activated. If the speed is not reduced sufficiently, the car is brought to a standstill by means of the safety gear. This also works in the de-energized state, as this is only triggered mechanically.
There are three different types of safety gear: wedge, roller and sliding safety gear.