6.2 DESIGN METHODS - SYNTHESIS

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This stage is somewhat inexact and should involve a few questions about the application.

- Is there a starting/ending position?

- What is the starting ending position?

- Are there dimensional limits?

- How much power must be transmitted?

- Is the mechanism function generating, prescribed path or body guidance?

- How fast is the mechanism?

- Does the motion need to be smooth?

- How many degrees of freedom does the motion require?

- Is the input/output motion type known? (i.e. rotation, linear, other)

- Are inertial effects desired?

- Can the mechanisms be planar/3D?

- How much error is permissible? Is accuracy needed at all points?

- Does the mechanisms appear to have multiple modes of motion?

There are a number of excellent books that can be used to find suitable matches. These can often be modified to suit your needs. This technique is often known as `cookbook'.

Chironis & Sclater, Mechanisms and Mechanical Devices Sourcebook, McGraw-Hill, 1995

Jones, F.D., Ingenious Mechanisms for designers and inventors, Industrial Press Inc., Volumes 1-4, 1930.

6.2.1 Mechanism Typing

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This method helps systematically generate mechanism types.

We begin by considering the Gruebler/Kutzbach equation rewritten,

After the # of degrees of freedom for the application are determined we can then use the equation to generate alternatives.

1. Examine # dof in the application.

2. Pick a # of links in the mechanism.

3. List values of B, T, Q, P, etc. that satisfy the equation.

4. Sketch mechanisms based on the list of B, T, Q, P, etc.

5. Sketch a suitable mechanism and then do detailed design.

6. If the design isn't satisfactory choose a new mechanism.

Consider the problem below and find possible solutions.