Thanks in advance! (We are following Nortons book) Design of a mechanism Goals:

Question

Thanks in advance! (We are following Nortons book)

Design of a mechanism Goals: Your objective is to design a planar, mechanism (made only of solid linkages) that would convert a rotary motion supplied by a motor to straight-line motion as shown in the figure. Your goal to achieve this in the smallest rectangular package with minimum material area used (i,e. minimize total material area + area of the rectangular package) such that mechanism should be within the rectangular of( 12 inch times 15 inch) as shown in figure during whole journey output. You must use a bar mechanisms to achieve the closest approximation to the Straight line shown below Specifications : Your Mechanism should meet the following specifications Mechanism must be made of linkages only. Mechanism size must be minimized and fit in a rectangular package in permissible area. Linear output must have a travel of 5 inches (Refers to diagram above). Output speed must approach but not exceed 10 in/s. Output acceleration must approach but no exceed 55 in/s2.

Explanation / Answer

It is impossible for me to give the exact solution as this is a graphical construction...stil I will try to help....

I will construct an four bar mechanism to approximate this straight loine

1. First choose the pivots....one in the pivot location which will be driven by the motor...second one anywhere convenient...preferably in the upper half....

2.Now construct 3 chebyshev accuracy points on the given straight line.....If you do not know what are chebyshev accuracy points the just choose three points on the line at almost equal gaps...

3. Choose a crank of any length connected to the motor pivot....the length should not be too large or too small.....

4. Now we have to design the coupler (which will be triangular here) and the follower such that the coupler points pass through the 3 points on the straight line as the crank rotates....This is exactly a path generation problem....

5. It is very difficult to explain this method here....So I just suggest you to study path generation methods...These are done by a concept called inversion where we imagine the coupler to be fixed and move the pivots and the follower .....This will give the follower length and hence the whole four bar mechanism....

Hope this helps....If you have any other queries regarding this problem do comment...I will surely reply....

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