Sistemas de paro hombre muerto: interruptores de validación

manuales Cuando una máquina necesita funcionar en un modo especial, a veces es necesario

desactivar total o parcialmente los dispositivos de protección. En tales condiciones, los

Sistemas de paro hombre muerto o interruptores habilitadores manuales, en conjunto

con

otras medidas de seguridad, sirven para proteger al operario ante situaciones

peligrosas.

Estos interruptores sirven para habilitar las señales de mando de otras unidades de

control (por ejemplo de movimientos peligrosos). Las señales de control de

movimientos peligrosos no deben activarse sólo con el interruptor habilitador. Si el

operador suelta el

pulsador, o, en el caso de la versión de 3 posiciones, lo pulsa más allá del punto de

activación, la señal de ‘en marcha’ se interrumpe mediante la apertura forzada de un

contacto NC.

El uso prolongado de estos dispositivos presenta inconvenientes ergonómicos.

http://en.wikipedia.org/wiki/Dead_man's_switch

A dead man's switch (for other names, see alternative names) is a switch that is

automatically operated in case the human operator becomes incapacitated, such as

through death or loss of consciousness.

The switch usually stops a machine, and is a form of fail-safe. They are commonly used

in locomotives, aircraft refuelling, freight elevators, lawn mowers, tractors, personal

watercraft, outboard motors, chainsaws, snowblowers, tread machines, snowmobiles,

and many medical imaging devices.

The Special Weapons Emergency Separation System is an application of a dead man's

switch in the field of nuclear weapons.

A dead man's switch may also be used to activate a harmful device, such as a bomb or

IED. The user holds down a switch of some sort in their hand which arms the device.

When the switch is released, the device will activate, so that if the user is killed while

holding the switch, the switch will be released and the bomb will detonate.

Types Handle

Pneumatically or electrically linked dead-man's controls, still used today, involve

relatively simple modifications of the controller handle, the device that regulates

traction power. The main requirement is that the train's emergency brakes are applied if

pressure is not maintained on the controller.

Typically, the controller handle is a horizontal bar, rotated to apply the required power

for the train. Attached to the bottom of the handle is a rod which, when pushed down,

contacts a solenoid or switch inside the control housing. The handle springs up if

pressure is removed, releasing the rod's contact with the internal switch, instantly

cutting power and applying the brakes.

Though there are ways that this type of dead-man's control could conceivably fail, they

have proven highly reliable.

On some earlier equipment, pressure was not maintained on the entire controller, but on

a large button protruding from the controller handle. This button also had to be pressed

continuously, typically with the palm of the hand so that the button was flush with the

top of the handle. Another method used, particularly with some lever-type controllers,

which are pushed or pulled rather than rotated, requires that the handle on the lever be

turned through 90 degrees and held in that position while the train is in operation.

Some dead-man's controls require the motorman to hold it in the mid-position rather

than apply full pressure (see pilot valve).

In modern New York City Subway trains, for example, the dead man's switch is

incorporated into the train's speed control. On the R142A car, the train operator must

continually hold the lever in place. This was depicted in the movie and book The Taking

of Pelham 123, in which a group of men hijack a New York City subway train for

ransom, but need to override the dead man's switch in order to escape.

Every lawn mower sold in the US since 1982 has an "operator-presence" device, which

by law must stop the blades within 3 seconds after the user lets go of the controls.[2]

Touch sensor

On the Nottingham Express Transit vehicles, the tram's speed controller is fitted with a

capacitive touch sensor to detect the driver’s hand. If the hand is removed for more than

a short period of time, the track brakes are activated. Gloves, if worn, have to be finger-

less for the touch sensor to operate. A back up dead-man's switch button is provided on

the side of the controller for use in the case of a failed touch sensor or if it is too cold to

remove gloves.

Pedal

A pedal can be used instead of a handle. In the Waterfall train disaster, it appeared that

the driver slumped on his seat, keeping the pedal depressed when he died suddenly of a

heart attack. In the movie Silver Streak, a man hijacks the train and keeps it running by

placing a heavy toolbox on the pedal.

The pedal can also have a vigilance function built in, where drivers must release and re-

press the pedal in response to an audible signal. This prevents it from being defeated by

the above circumstances, and is a standard feature on British DSD systems.[3]

Some types of locomotive are fitted with a three-position pedal, which must normally

be kept in the mid-position. This also eliminates the possibility of accidentally defeating

it, although it may still be possible to deliberately do so. Adding a vigilance function to

this type of pedal results in a very safe system. However, isolation devices are still

provided in case of equipment failure, so a deliberate override is still possible. These

isolation devices usually have tamper-evident seals fitted for that reason.

Seat switches

On modern tractors, the switch is beneath the seat, and will cut the engine if the operator

gets off the tractor while the transmission is engaged or the power take-off is spinning.

Key switches

On recreational vehicles, such as boats with outboard motors, snowmobiles, jet skis and

waverunners, the user has the ignition key attached to his wrist or waist by a leash. The

key will be removed from the ignition switch if the rider falls off the vehicle, thus

turning off the engine or setting the throttle position to "idle". Some exercise treadmills

also have this feature, to stop the treadmill if the user falls. The dead man switch on a

treadmill usually consists of an external magnet controlling the circuitry that provides

power to the treadmill belt.

Altimeter switches

Strategic Air Command developed a dead man's switch for its nuclear bombers, known

as Special Weapons Emergency Separation System (SWESS), that ensured the nuclear

payload detonated in the event of the crew becoming incapacitated through enemy

action. The purpose of this device, unlike other examples mentioned above, was to fail-

deadly rather than fail-safe. Once armed, the system would detonate the onboard nuclear

weapons if the aircraft's altitude dropped below a predetermined level.[4]

Se basa en un sistema de doble etapa, que consiste en la secuencia de actuación que os describo a continuación: Secuencia pisado pedal: A los 30 segundos de haber pisado el pedal se enciende una luz en el panel. Si no se desactiva, después de 2,5 segundos suena un aviso acústico de alta intensidad. Si pasados 2,5 segundos el maquinista no lo desactiva, se abre el lazo del freno provocando el frenado de emergencia del tren. Secuencia de pedal no pisado. A los 2,5 segundos de no haber pisado el pedal, se enciende una luz azul en el panel. Si no se desactiva 2,5 segundos después suena un aviso acústico de alta intensidad. 2,5 segundos más tarde, si el maquinista no lo desactiva, se abre el lazo de freno, provocando el frenado de emergencia que detendrá el convoy

Esta tarde por correo electrónico, ha llegado una pregunta relacionada con la seguridad en los trenes. Me han pedido que explique que es el hombre muerto, y eso es lo que voy a intentar a continuación. Para empezar os diré que se trata de un sistema de seguridad instalado los trenes. Se le denomina de diversas formas: hombre muerto, pedal de hombre de conducción de cualquier tren. Se trata habitualmente de un pedal ubicado en la parte inferior de la consola de conducción y tiene como misión, la activación del sistema de frenado en el supuesto que el conductor se desmaye y/o pierda la conciencia. Asegura por tanto, que el

maquinista está en condiciones de conducir el tren mientras éste se encuentra en marcha. Al tratarse de un pedal, podéis pensar que nada más Con solo ponerle un peso engañamos el sistema. Nada más lejos de la realidad. Veamos como funciona Se basa en un sistema de doble etapa, que consiste en la secuencia de actuación que os describo a continuación: Secuencia pisado pedal: A los 30 segundos de haber pisado el pedal se enciende una luz en el panel. Si no se desactiva, después de 2,5 segundos suena un aviso acústico de alta intensidad. Si pasados 2,5 segundos el maquinista no lo desactiva, se abre el lazo del freno provocando el frenado de emergencia del tren. Secuencia de pedal no pisado. A los 2,5 segundos de no haber pisado el pedal, se enciende una luz azul en el panel. Si no se desactiva 2,5 segundos después suena un aviso acústico de alta intensidad. 2,5 clasifi cación que se marca en la UNE-58408-1991. Carretillas de manutención.