Safety devices
La seguridad del sistema es un elemento clave en los ascensores. Para maximizar la seguridad se emplean varios dispositivos específicos:.
Electromechanical door interlock
In access to the floors, which makes it impossible to open all the access doors except that of the floor on which the car is stopped.
All the locks, one on each landing, have a strap or an arm with a wheel, which when pressed allows the door to be unlocked, and only when it is mechanically locked by the double-claw hook, the electrical contact of the interlock is closed, allowing power to reach the coils of the contactors, and the movement of the elevator is allowed. There are two types of mechanisms that allow the exterior doors to be opened when the car reaches the floor. In old elevators there is an element called an electroleva, which is responsible for pressing the strap on the door of the destination floor. This electrocam is retractable, that is, it travels with the car retracted so as not to press the straps of each floor it passes through (which would allow the opening of each of the doors and the stop of the elevator), so only when the maneuvering control indicates by means of an electrical signal that the car is at the relevant stop, the electrocam expands and activates the strap of the corresponding door. The reverse process occurs when the elevator is required from another location: the electrolever retracts before departure and only expands upon reaching it. In modern elevators there are other types of mechanisms. If the exterior doors are automatic, that is, they open by themselves, one of the cabin leaves has a retractable skate installed that opens the exterior door at the same time as opening the interior of the cabin. If the exterior doors are manual or semi-automatic (they are opened by the person who is going to enter the elevator and they close by themselves), the car doors incorporate a skate that pushes the lock pulley or interlock lever to allow the exterior door to be opened.
Breakage or unbalance parachutes of traction cables (a. electrodynamic)
There are instantaneous and also progressive, for high and medium speed elevators. It consists of a system of levers whose movement activates some wedges or rollers that are located in a box next to the guides (wedge box). When the cabin falls or exceeds the nominal speed, the guides are bitten by the wedges or rollers and the cabin stops.
Speed limiter (electrodynamic a.) (speed governor)
It is made up of two pulleys: one installed in the machine room and another aligned vertically with the first at the bottom of the shaft. A steel cable passes through both, the ends of which are linked, one to a fixed point on the cabin frame, and the other to a system of levers whose end is located at the top of the frame. The cable accompanies the cabin at all times and is absolutely independent of the traction cables, that is, it does not intervene in the support of the cabin and the counterweight. The cable is suddenly stopped in the upper pulley of the limiter when the speed of said pulley (and therefore that of the cabin) exceeds 25% of the nominal speed. The limiter cable activates the system of levers, called the parachute. It also incorporates an electrical contact both in the cabin wedging mechanism and in the upper pulley that cuts the main series to prevent the engine from continuing to operate once the cabin has been "nailed" to the guides by the wedging mechanism. This mechanism was patented by Rubén Lorenzo Curiel") in 1853.
End of career
They interrupt the power supply when the car passes the extremes of ascent or descent.
Mechanical travel safety devices
The car of an electric elevator can never be crushed against the ceiling of the shaft since shortly after passing the limit of the upward stroke, the counterweight already rests on the spring of the shaft and the tractor pulley that moves the cables loses traction.
The same thing happens in a hydraulic elevator, but due to the size of the piston. A few centimeters after the cabin passes the upper limit switch, the piston rod cannot extend further since it stops inside the piston and at the guide stops.
Emergency stop device
It interrupts the maneuver, cuts off the power to the tractor group and applies the brake. It allows the elevator to be stopped, rendering the cabin and floor controls ineffective. Normally you lower the cab to the lowest stop. If we refer to STOP or STOP, normally you should allow the car to stop at the next stop both up and down. This emergency system can also be called "Rescata-matic". In old elevators, pressing the STOP button produced an instantaneous stop of the cabin, and the traveler could become trapped between two floors without the possibility of exit. In current models, this button no longer exists on the cabin panels, leaving only the alarm button as an emergency device in the hands of the user.
Alarm bell
For passengers to use in case of emergency. In current elevators it is connected to a telephone line from which you can request assistance in case you get trapped.
• - Operation: When a power failure occurs, the emergency lighting inside the cabin is automatically turned on, the electronic alarm remains operational due to its own battery power supply. When the supply is restored, the emergency lighting goes off and the equipment automatically starts recharging.
emergency light
Illuminates the cabin in case normal lighting is interrupted.
There must be a backup source, with automatic recharging, that is capable of powering at least one one-watt lamp for one hour, in the event of interruption of the normal lighting supply current. Emergency lighting must be switched on automatically as soon as the normal lighting supply fails.
Load weighing system
A device called a load weigher is usually installed in modern elevators. The function of this element is to prevent the elevator from moving more weight than the maximum allowed, thus avoiding excessive wear of the tractor group and the brakes. There are several types of weighing systems and currently all of them are digital, so they have a fairly high accuracy.
In older elevators to which a load weighing system is to be adapted, a mechanism is usually used that consists of sensors that are adapted to the traction cables and a control unit that collects the information given by the sensors. This control unit is in turn connected to the elevator control box, so the control panel knows at all times if the elevator has more weight than allowed.
In new elevators, the system is similar, but the sensors are placed between the floor of the cabin and the chassis, allowing even greater accuracy.
The control panels have 3 different states as far as the load weigher is concerned:
• - Normal: The cabin has less weight than the maximum allowed, so all systems will function normally.
• - Complete: The elevator has reached the maximum permitted weight, so the control panel will allow the cabin to make the programmed trip, but will not allow anyone else to enter the cabin until one of the passengers or cargo gets off. In the case of elevators with selective maneuver (the elevator picks up passengers as they go up or down), it will not stop on any floor until the state of the load weigher returns to normal, that is, until a person or load leaves the cabin.
• - Excess load: The elevator will not allow any travel until a person or package leaves the cabin. In this case there is usually a light and sound indication that indicates the state of excess charge. The doors will not close and the elevator will not move until it returns to normal status.