6.3 DESIGN METHODS - DIMENSIONAL

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What follows is an assorted collection of independent design techniques.

These techniques can be used after the general mechanism type has been selected.

Learning these techniques before they are needed can help in the initial selection of mechanism types.

6.3.1 Two Position Design

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When we have an advance-return-ratio we can use the basic geometry of a linkage to specify dimensions.

For this approach we are given the extreme angular or position displacements.

We can then calculate the geometry of the mechanisms at the two extreme two positions.

If we are considering a slider crank mechanism we can find the extremes as shown below. A general relationship may be derived that can be used for subsequent design.

The next stage in design is to select, or constrain some values, and then through trial and error estimate a design.

Consider the following example,

A similar case arises when we are planning to design a crank-rocker mechanism for return time.

Consider the design problem below,

We can also use a closed form solution based on dyads.

Design a 4 bar mechanism to reach the points C and D below,

Consider the design problem below,