In a drag-link quick-return mechanism where the shortest link is fixed, what is the sum of the lengths of the shortest and longest links _______________?
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Answer: C. less than sum of other two
Explanation
For a drag-link mechanism, the sum of shortest and longest link lengths must be smaller. This Grashof condition ensures that the shortest link can fully rotate relative to adjacent links. Violating this specific length inequality prevents the mechanism from achieving continuous dual-crank rotation. A drag-link mechanism is a four-bar linkage where both input and output cranks can rotate completely. Grashof's criterion states that the sum of shortest and longest links must be less than others. This mechanism is commonly used to convert continuous rotation into non-uniform continuous rotation.
Quick-return mechanisms in shaping machines utilize drag-link principles to optimize cutting stroke speeds. Rotary motion converters in industrial machinery rely on proper link sizing for smooth operation. Kinematic synthesis requires strict adherence to these length rules to avoid mechanical locking. Option A describes a different Grashof condition associated with rocker-rocker linkage configurations. Option B violates the fundamental Grashof inequality required for continuous crank-crank rotation. Option D is incorrect because strict mathematical relationships govern four-bar linkage mobility.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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