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Geared Five-Bar Mechanisms

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Geared Five-Bar Mechanisms

Geared Five-bar mechanisms are usually built with:

•	One Gear-Pair

•

One Dyad

Applications

Geared five-bar mechanisms are very interesting...to some people. They can give:

•	Complex Coupler Curves

•	Complex Function Generators

Geared Five-bar Mechanism Configurations

There are four ways to edit 'Geared Five-bar Mechanisms':

1.	Gear-Pair: Use fixed or orbiting gear centres

2.	Dyad: use one of the five dyads:RRR, RRP, RPR, RPP, or PRP.

3.	Gear Mesh: Use an external or internal gear-mesh

4.	Basic Design: Edit the number of teeth on each gear.

Typical Geared Five-bar Mechanism Configurations

Complex Coupler Curves

QST14-IGS-1

Gear-Pair: 1:1, Fixed-Centres, Internal Mesh

Dyad: RRR Dyad

Application: Coupler Curve

In a Geared Five-bar, three Parts are the

•	Base-Part, Input Crank, and Geared-Rocker

The other two Parts are joined as a Dyad. Typically, the Dyad is an RRR Dyad.

STEP 1:

Add a Simple Gear-Pair - Option 1

QST14-IGS-2

Step 1 is complete.

STEP 2:

Add an RRR Dyad

To remind you:

2.a.	Add two Parts

Step 2.a is complete.

QST14-IGS-3

2.b.	Add three Joints between the Parts that are the Gear Pairs.

Step 2.b is complete.

Geared Five-Bar Mechanisms can give unusual motions and complex coupler curves.

QST14-IGS-4

You may want to be more flexible with the design

STEP 3:

Edit the Part used for Gear 2

As an alternative to the R (Pin-Joint) at the end of the Part used for Gear 2, add a Point (with a Line) in the Part.

Use the new Point for one of the Pin-Joints in the RRR Dyad. You can edit the phase of the Gear 2 relative to Gear 1.

The design parameter options are:

1.	Gear Ratio between Gear 1 and 2 (Number-of-Teeth), Module to give centre distance

2.	Phase between the Gears

3.	Length of Gear 'Cranks'

4.	Length of Dyad Parts

5.	Position of Coupler Point

Geared-FiveBar-Ep5

STEP 4:

Change the number-of-teeth with the Gear-Pair dialog-box - for example 60:40.

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.

STEP 5:

Add a Gearing FB; make the Gear ratio = 2

STEP 6:

Connect the wire between the Linear-Motion FB, Gearing FB and the Motion-Dimension FB

STEP 7:

Connect the Output from the Motion-Dimension FB to the X input of the Graph FB

Geared-Fivebar-Simple-1

Here is an 'interesting' Coupler Curve.

In these Coupler Curves we are plotting the motion of the middle joint of the RRR Dyad.

You can add a Point to one of the Parts to give even more complex Coupler Curves.

Geared Five-Bars as Complex Function Generators

Geared-FiveBar-Ep1

Gear-Pair: 1:1, Orbiting-Centres, Internal Mesh

Dyad: RRR Dyad

Application: Function-Generation

Typically, you can get interesting 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 1:

Add an Epicyclic Gear-Pair

STEP 2:

Make the gear ratio 1:1 (for example 50:50 Gear Teeth)

Geared-FiveBar-Ep2

Step 2 is complete.

STEP 3:

Add an RRR Dyad

between the end the Geared Rocker and the Line in the Base-Part

Step 3 is complete.

Geared-FiveBar-Ep3

STEP 4:

Measure the angular position of the output Part over a Machine Cycle with a Measurement FB

STEP 5:

Add a Graph FB

STEP 6:

Connect the Measurement FB to an input of the Graph FB

Step 6 is complete.

Add a Design-Set to give a quick way to edit the Part lengths.

Geared-FiveBar-Ep4

This Graph shows the Output Shaft Rotation as a Function of the Input, Constant Speed, Shaft Rotation.

Notes about Mechanism Synthesis

It is typical that an output to input relationship is given. Then a mechanism is found to repeats the function.

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. However, it is far more easy to synthesise a mechanism for a function. I will not suggest how you do.

Geared-FiveBar-Ep5

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.

STEP 7:

Change the Gear ratio - for example 60:40.

In this case, it takes two rotations of the input crank to complete the function at the output shaft

STEP 4:

Add a Gearing FB; make the Gear ratio 2

STEP 5:

Connect the wire between the Linear-Motion FB, Gearing FB and the Motion-Dimension FB

STEP 6:

Connect the Output from the Motion-Dimension FB to the X input of the Graph FB

Geared-FiveBar-Ep6

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.

Geared Five-Bars: Pin-Joints and Slide-Joints

Geared-Fiveba-SG-Slide1

Gear-Pair: 1:1, Fixed-Centres, Internal Mesh

Dyad: RPR Dyad

Application: Coupler Curve

Geared-FiveBa-SG-Slide2

Gear-Pair, 2:1 Fixed-Centres with an RPR Dyad

Application: Coupler Curve

•	The Gear-Pair ratio changed to 60:40

•	The Crank must rotate twice for the mechanism to repeat a machine cycle.

•	To plot the complete Coupler Curve you should add a Gearing FB before the Motion-Dimension FB and make the Gearing Ratio parameter equal to 2.

Geared-Fiveba-SG-RRP1

Gear-Pair 1:1, Fixed-Centres, RRP Dyad.

Application: Coupler Curve

Geared-Fiveba-EG-RPR1

Gear-Pair 1: 1, Orbiting-Centre, RPR Dyad

Application: Function-Generation

Geared-Fiveba-EG-RPR1-graph

The motion of the output Rocker as a function of the input-rocker.

It has a reasonable dwell.

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