Step 10.2: The Whitworth Quick Return Kinematic-Chain

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Step 10.2: The Whitworth Quick Return Kinematic-Chain

A 'Whitworth' kinematic-chain – or a Quick-Return kinematic-chain

A 'Whitworth Quick Return' changes rotary movement to a back-and-forth movement. The Part moves faster in one direction than the other.  

This kinematic-chain has:

1.A Motion-Part – a Crank

2.Two Dyads – an RPR and an R-R-P Dyad

The video shows the Whitworth Quick-Return kinematic-chain.

Input: A Crank – the Motion-Part

Output: It slides quickly in one direction and slowly in the other direction. This is the Quick-Return Part.

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STEP 1: Add the Input Part – a Crank

The CrankRed-14-1b is the input Part to the mechanism. See Tutorial 1, or

1.Mechanism-Editor: Kinematic elements > Add Part , Drag to add a Part

2.Part-Editor: Edit the Base-Part, Add a Horizontal Line , Exit the Part-Editor

3.Mechanism-Editor: Kinematic elements > Add Pin-Joint : Join the Part to the Base-Part with Pin-Joint

4.Mechanism-Editor: Add a Motion-Dimension FB to give the Angle of the Part relative to the Line

5.Mechanism-Editor: Add a Linear-Motion FB and connect it to the Motion-Dimension FB

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STEP 2: Add Dyad 1

Add the first Dyad

Remember: A Dyad ALWAYS has two Parts and three Joints.

Dyad 1: Part 2 and Joint 3

1.Part-Editor: Edit the Base-Part, Add a vertical line, from the start-Point of the Horizontal Line, Exit the Part-Editor.

2.Mechanism-Editor: Kinematic elements > Add PartRed-14-2 | Drag to add Part

3.Mechanism-Editor: Kinematic elements > Add Pin-JointRed-14-3 :

a.Click the start-Point of PartRed-14-2

b.Click the end-Point at the bottom of the vertical Line in the Base-Part

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Dyad 1: Part 1 and Joint 1

Add a PartRed-14-4 and join it to the end of the CrankRed-14-1b.

1.Mechanism-Editor: Kinematic elements > Add Part | Drag to add a new PartRed-14-4

2.Mechanism-Editor: Kinematic elements > Add Pin-Joint

a.Click the end-Point of the CrankRed-14-2

b.Click the start-point of new PartRed-14-4

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Dyad 1: Joint 2

Use Add Slide-Joint and select the Lines along the centre of the two Added-Parts with the Blue Part-Outlines.

1.Mechanism-Editor: Kinematic elements > Add Slide-JointRed-14-8  

a.Click the CAD-LineRed-14-6 along PartRed-14-4 - see above

b.Click the CAD-LineRed-14-7 along PartRed-14-2 - see above

A Slide-Joint completes the new R-P-R Dyad.

The Parts become Green Parts to indicate they kinematically-defined.

This is the basic Whitworth Quick Return kinematic-chain. The output Part moves quickly in as the Crank (input) rotates from (counter clockwise) from 240 to 330 degrees, and more slowly as the crank rotates from 330 to 240 degrees.

The length of the Crank and the distance between the Pin-Joints in the Base-Part give the 'Return Ratio'.

Return Ratio =

Crank Angle Range(Degrees) for one direction one

Crank Angle Range (degrees) for direction two

Experiment with the length of the Crank.

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Add Dyad 2 - a Dyad ALWAYS has two Parts and three Joints

1.Part-Editor: Edit the Base-Part, Add Horizontal Line Exit the Part-Editor

2.Mechanism-Editor: Kinematic elements > Add Part | Drag to add PartRed-14-1b

3.Mechanism-Editor: Kinematic elements > Add Slide-JointRed-14-2.

a.Click the CAD-Line in partRed-14-1b

b.Click the new Horizontal Line in the Base-Part

4.Mechanism-Editor: Kinematic elements > Add Part | Drag to add PartRed-14-3,

5.Mechanism-Editor: Kinematic elements > Add Pin-JointRed-14-4

a.Click start-Point of PartRed-14-3

b.Click end-Point of long Part (see Dyad 1 )

6.Mechanism-Editor: Kinematic elements > Add Pin-JointRed-14-5

a.Click the start-Point of partRed-14-1b

b.Click the end-Point of PartRed-14-3

This is the kinematics-chain for a Whitworth Quick-Return.

It has a:

Rocker (this is the Crank)

R-P-R Dyad: Pin-Joint, Slide-Joint, Pin-Joint

R-R-P Dyad: Pin-Joint, Pin-Joint, Slide-Joint

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