Four-bar Kinematic-Chains

Four-Part Kinematic-chains - which you may call a four-bar mechanism, four-bar linkage, or even four-bar - are the basis of the most frequently used mechanism in packaging machines.

This tutorial uses Pin-Joint and Slide-Joint elements. We combine the joints in different ways to configure the mechanism in different ways.

Objective of this Tutorial

To build kinematic-chains that have a total of four Parts and four Joints. These are often called four-bars.
To learn about Dyads.

Note:

The lengths of the Parts and kinematic-chains in the images and videos may be different to your model. I may edit the lengths of Parts if it is necessary to show a different kinematic configuration, or closure.

Try to add Parts that are approximately equal to the lengths of the Parts that are in the tutorial images. If necessary, edit the length of a Part - see Step 1.7: Edit the Length of the Crank.


Terminology: Reminder from Tutorial 1

Elements :

Elements are the objects we add to the model. They represent the objects in a machine.

Nearly always: the sequence of steps we use:

1. Add the element...
2....open the element's dialog-box...
3....edit the element's parameters in the element's dialog-box.

In addition to elements that you can see in the graphic-area (Parts, Pin-Joints, ...), there are elements you cannot see (Constraints, ...)

Plane :

the flat surface to which we add a new Mechanism-Editor. The 'Front-View' of each Mechanism-Editor perpendicular to its XY-Plane - NOT relative to the Global XYZ axes

Mechanism-Editor :

the workspace that includes the Mechanism-Plane , the graphic-area, the contextual -toolbars, and the Mechanism-Editor name-tab.

Part :

an element that becomes the moving, or fixed, rigid-bodies in the machine.

Joint :

Kinematic-Joints constrain the relative movement between two Parts.

Pin-Joint :

a Kinematic-Joint that constrains together two Points, with one Point in two different Parts.

Kinematic-Chain :

two or more Parts joined together with one or more Joints.

Kinematically-Defined :

Part or Kinematic-Chain that moves in a manner as specified by at least one Motion-Part. Parts that are kinematically-defined have Green Part-Outlines.

When a Part has a:

Green Part-Outline: the Part is a kinematically-defined Part. We also call it a 'Solved Part'.
Blue Part-Outline: the Part is not a kinematically-defined Part. We also call it an 'Unsolved Part'.

Our target is to make sure we have Green Part-Outlines, ALWAYS.

Motion-Part :

a Part, that is kinematically-defined, whose motion is precisely specified with a Motion-Dimension FB

Motion-Dimension FB :

a Function-Block(FB) that specifies the angular or linear position, velocity and acceleration of a Part as a function of the Master-Machine-Angle (there are exceptions)

Linear-Motion FB :

a Function-Block(FB) whose output is 0 – 360 (default). You can edit the initial value parameter to delay or advance the timing of a kinematic-chain.

Gearing FB :

a Function-Block(FB) with which you can apply parameters to the input motion-values in the form of a linear equation to give a different output.

Master-Machine-Angle :

the 'clock' that, when you cycle the machine, moves at a constant rate from 0 to 360, again and a again.

The positions of all kinematically-defined Parts are a function of Master-Machine-Angle. The Master-Machine-Angle (MMA) 'beats the drum' of the machine.

Rocker :

a Motion-Part that rotates with a specific motion relative to a different Part. It may index progressively, rotate continuously (as a Crank), or oscillate back-and-forth.

Terminology: Tutorial 2

Slide-Joint :

a Kinematic-Joint that constrains together two Lines, with one Line in two different Parts.

Slider :

a Motion-Part that slides with a specific motion relative to a different Part. It may index progressively, slide continuously (as a 'conveyor'), or oscillate back-and-forth.

Dyad :

a Dyad is a kinematic construction of:

2 Parts
3 Joints

Each Part in the Dyad is joined to different Parts and then they are joined together, to make three Joints in total.

Dyad Closure :

a different way to assemble the same Dyad.

Motion FB :

a Function-Block(FB) that links a Motion-name and motion-values in MotionDesigner to a kinematic-chain.

Crank-Rocker :

a kinematic-chain with one Motion-Part (the Crank) and one Dyad that has three Pin-Joints, and the output oscillate ('rocking') back-and-forth.

Crank-Slider :

a kinematic-chain with one Motion-Part (the Crank) and one Dyad that has two Pin-Joint and one Sliding-Joint, with the output reciprocating ('sliding') back and forth.

Mechanism names :

Scotch-Yoke, Whitworth Quick-Return are common names for some 'standard' mechanisms you may come across at different times in a machine.

Icon-AddMechanismEdit Kinematic-Chains

Tutorials and Reference Help Files for MechDesigner and MotionDesigner 14.2 + © Machine, Cam, Mechanism, and Motion Design Software by PSMotion Ltd