A dynamic analysis of a four-bar mechanism shows that it has many critical speeds where the response of the system is large compared to the response at neighboring speeds. Some of these critical speeds are limiting critical speeds. The lowest of these limiting speeds cannot be exceeded because stresses in one of the links would become greater than the safe working stress. This paper examines methods for computing critical speeds and suggests a method whereby the first limiting critical speed of a mechanism can be adjusted either continuously or discretely so that speeds above the first limiting critical speed can be achieved without the mechanism ever experiencing undue duress.

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