Geared Five-bar mechanisms are built with:
• | One Gear-Pair |
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• | One Dyad - two Parts, three Joints. |
Gruebler Equation: F = 3*(N–1) – 2*L- H F = 3 * (5–1) – 2*5 – 1 F = 12 – 10 – 1 F= 1 Degrees-of-Freedom = 1 |
Parts N = 5. Lower Pairs (Joints) L = 5 Higher Pairs (Cams or Gears) H = 1 There is one Gear-Pair |
A Geared Five-Bar mechanism has one Motion-Dimension that defines its Position. The Mobility - or Kutzbach Criterion - shows that a Motion-Part has a Mobility of Zero. Mobility = Motion Dimensions – Degrees-of-Freedom Mobility = 1 – 1 = 0 |
Geared Five-bar mechanisms are often used:
• | To give complex Coupler Curves |
• | As complex Function Generators |
The Coupler Curves and the Functions can be more complex than available from Four-bar mechanisms.
When you assemble a Geared Five-bar Mechanism, you can edit the:
1. | Gear-Pair: - Fixed Gear Centre or Orbiting Gear Centre |
2. | Dyad: - R-R-R, R-R-P, RPR, RPP, or PRP |
3. | Gear Mesh - External Mesh or Internal Mesh |
4. | Ratio of Gear-Teeth |
5. | Lengths of the Part |
In a Geared Five-bar, three Parts are the
The other two Parts are joined as a Dyad. Frequently, the Dyad is an R-R-R Dyad.
Step 1 is complete. |
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To remind you:
Step 2.a is complete.
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Step 2.b is complete.
Geared Five-Bar Mechanisms can give unusual motions and complex coupler curves. |
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You may want to be more flexible with the design
As an alternative to the R (Pin-Joint) at the end of the Part used for Gear 2 Use the new Point for one of the Pin-Joints in the R-R-R Dyad The design parameter options are:
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You can change the gear ratio to give more complex coupler curves.
In this case, it takes two rotations of the input crank to complete the function at the output shaft To plot the complete Trace-Point ,you must rotate the input crank two times faster.
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Here is an interesting Coupler Curve.
In these Coupler Curves we are plotting the Point of the Pin-Joint. You can add a Point to one of the Parts to give even more complex Coupler Curves. |
Typically, you can get interesting output motions from a Geared Five-bar that has a Gear-Pair with an Orbiting Centre. The output motion is a function of the input constant speed motion and is therefore called a Function-Generator.
Step 2 is complete. |
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Step 3 is complete. |
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Step 6 is complete. Add a Design-Set to give a quick way to edit the Part lengths.
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This Graph shows the Output Shaft Rotation as a Function of the Input, Constant Speed, Shaft Rotation. Notes about Mechanism Synthesis Typically, the output motion is given as a function of the input. Then a mechanism is found that has an output Part that moves with the necessary function when the input Part moves. Four-bar mechanism Function-Generators are limited. For example, it is not easy to synthesise a mechanism that oscillates the output shaft more than one time in a machine cycle. It is clear from this graph that more complex functions are possible with Geared Five-bar mechanisms. |
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Change the Gear Ratio to give more interesting Function Generation You can change the gear ratio of the Gear-Pair to give more complex function generation.
In this case, it takes two rotations of the input crank to complete the function at the output shaft
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The Graph will show the Y-axis for two rotations of the crank to give the complete Function-Generation for the 60:40 gearing ratio. |
Gear-Pair, 1:1, Fixed-Centres, RPR Dyad. Application: Coupler Curve
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Gear-Pair, 2:1 Fixed-Centres with an RPR Dyad Application: Coupler Curve
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Gear-Pair, Fixed-Centres, R-R-P Dyad. Application: Coupler Curve |
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Gear-Pair, Orbiting-Centre, RPR Dyad Application: Function-Generation |
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The 'Function' at the output Rocker. It has a reasonable dwell. |