Fail Safe is a scheme for acquiring the safety of operators even when a system or an element constituting the system fails, by fixing the state to a predetermined state on the safe side and limiting the effect of the failure, so that no labor disasters occur as a consequence of that failure. (From "Guidelines for achieving fail safe operation in the control mechanisms of metal working machines, etc.", Vol. 464 dated July 28, 1998.
In order to achieve fundamental safety of machines such as molds and injection molding machines, after first accepting the two facts of "1. Machines can fail" and "2. Operators can make mistakes", it is necessary during the stages of design, manufacturing, and modifications of machines in order to build a structure that ensures the safety of operators even if these occur by chance. For this purpose, although a "safety confirming system" is adopted, if the "safety confirming system" itself fails, since the safety of the operators is not acquired, and it is possible that a labor disaster occurs, it is necessary to have characteristics that even when the "safety confirming system" fails, always the equipment is on the safe side (stopping the machine in a state in which it does not cause labor disasters).
In order to achieve fail safe, it is necessary to carry out the design, manufacturing, and modifications of molds, injection molding machines, automatic machines, etc., while following the "fundamental rules for achieving fail safe" listed below.
 | 1） | As a rule, the following are the control mechanisms that are the target of implementing fail safe.
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| 2） | As a rule, the control mechanism should be designed to have "asymmetrical error characteristics". Asymmetrical error characteristics are the characteristics by which even when a system or a component constituting the system fails, the frequency of failures on the safe side is far greater than the frequency of failures on the danger side, or the characteristics of failing only on the safe side. | |||||||||||||||||||||||||||
| 3） | When adopting electronic control equipment such programmable controllers for the control mechanism, use only those having "asymmetrical error characteristics". | |||||||||||||||||||||||||||
| 4） | Danger or fault conditions are not mistakenly reported as safe by making safety information correspond to a high energy state, danger signals and fault signals correspond to a low energy state. | |||||||||||||||||||||||||||
| 5） | Safety information should be conveyed in an information conveying mode (unate information conveying) so that, unless safety information is input to the system, an operation permitting signal is not issued by mistake. | |||||||||||||||||||||||||||
| 6） | In order to acquire resistance to the maximum environmental noise that can be predicted, the safety information should be made to possess sufficient energy. |
A fail safe design philosophy is required during the design of molds that are opened and closed at a high speed during high cycle rates or of molds of large sizes.
This article was composed from notes taken from posts in misumi-techcentral.com
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