Switch dead man

Fail-Safe Devices Fail-safe devices are safety devices designed to prevent exposure to hazards. They also prevent injury or damage when a system or machine fails. Examples of fail-safe devices are automatic fire doors, air brakes on truck trailers, a dead-man switch on powered hand tools, and safety cans with a spring-closing lid for flammable liquids. 

The next priority in the sequence is to provide safety devices, or features that prevent people from being exposed to a hazard. Safety devices are automatic and require no action on the part of a person. Safety devices do not ehminate hazards. Examples of safety devices are interlocks, dead-man switches, guards, fences, automatic fire doors, some types of fire sprinklers, and automatic air brakes that activate when there is a break in an air line. A significant problem with many safety devices is that people intentionally disable them and fail to reinstall or activate them after service or maintenance. 

These complex systems were investigated in a European "TE)E" project for mobile medical manipulator systems, in which the author was concerned with safety issues ( 10). The TIDE project specified an international bus structure for a collection of sub-systems, (powered wheelchairs, manipulator and environmental controller). It also highlighted the particular problems for medical manipulators in this role. For the wheelchair and other systems a Dead Mans Switch ( DMS) has been recommended whereby for any prime mover to continue to act, a switch has to be positively held in an on-position. The moment that the DMS is released the power is removed from the local prime mover power relays. However, such a severe stop would be disadvantageous for the smooth control of a manipulator, so instead it is proposed for die manipulator to have a DMS linked to a zero velocity command, fed into the normal control system. This has the disadvantage that the DMS is now reliant upon the integrity of the control system, but is probably the best overall compromise. 

Does each portable power tool have a constant pressure switch (dead man switch) that will shut off the power when pressure is released ... 

Luggage carts in airports and lawn mowers in which the hand brake must be held down at all times. If it is released, the cart will stop (i.e., dead man s switch). 

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