Design Requirements

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Theory

The main kinematic principle behind the device developed is the toggle position of a four bar linkage. The mechanism exploited the properties of a toggle point similar to an industrial four bar clamp shown in Figure XXXXXXXXX. in these devices, three of the four pin joints become aligned when moving the handle of the clamp to the closed position. This causes the jaws of the clamp to shut on an object and not release due to the high mechanical advantage (MA) at this location.

Figure XXXXXXXXXXXXXX: Four bar clamp in closed position with three pins aligned (http://www.directindustry.com/prod/emile-maurin/product-39388-754471.html)

The mechanical advantage can be understood from the following equation:

where r represents a radius from the input or output force relative to the instant center of rotation and ω represents the angular velocity of the input or output link. As the input link (handlebar) rotates the fourbar into a toggle position, the output link's angular velocity tends to zero. According to the above equation, this spikes the mechanical advantage at this point so that the joint "locks" once movement slightly beyond the toggle point is reached. This feature was utilized for holding and gripping the rope. 

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