Motion-Parts and Motion-Points

Comparisons between the Motion-Part and Motion-Point

Motion-Parts are:

Parts that have their motion specified by a Motion-Dimension FB
A Joint constraint the Part to either Rotate or Slide

Motion-Points are:

Points that have their motion specified by a Motion-Path FB
A sketch-element constraints the Point to slide along its length

Motion-Point <

> Motion-Part

Constrained by a Sketch-Element <

> Constrained by a Joint

Motion-Path FB <

> Motion-Dimension FB

Motion-Parts

Motion Dimension FB

A Motion Dimension FB:

identifies a Part - that becomes a Motion-Part - we want to move with a specified motion
specifies the position of the Part relative to a different Part

Simple Rocker Example

Rocker

A Rocker is a Part joined to a kinematically-defined Part with a Pin-Joint that uses a Motion Dimension Function-Block to define its directional angle between Lines in the two Parts that radiate from the Pin-Joint.

Simple Slider Example

Slider

A Slider is a Part joined to a kinematically-defined Part with a Slide-Joint, that uses a Motion Dimension Function-Block to define the directional distance between Points at the end of the Lines used to define the Slide-Joint.

Motion-Points

Motion-Path FB

A Motion-Path FB is similar to a Motion-Dimension.

A Motion-Path FB

adds a Motion-Point to a sketch-element and identifies it as the Point we want to move with a specified motion
specifies the position of the Motion-Point along the sketch-element or sketch-loop

There are many application that can use a Motion-Path FB.  However, there are two useful 'Motion-Dyads'.

See Tutorial 16.

Simple Ram-R Example

Ram-R

The Ram-R is a similar to an RRR Dyad, but one of the Parts extends.

The Ram-R makes use of the Motion-Path FB. The Motion-Path FB adds a Motion-Point to a sketch-element (CAD-Line) in one Part.

The other Part is joined to the Motion-Point with a Pin-Joint.

motion-values are given to the Motion-Path FB by Motion FB.

The Red Arrow in the image shows the Motion-Path of the Motion-Point along the CAD-Line of one of the Parts.

Simple Ramp-P Example

Ram-P

The Ram-P is a similar to an RRP Dyad, but one of the Parts extends.

The Ram-P makes use of the Motion-Path FB. The Motion-Path FB adds a Motion-Point to a sketch-element (CAD-Line) in one Part.

The other Part is joined to the Motion-Point with a Pin-Joint.

motion-values are given to the Motion-Path FB by Motion FB.

The Red Arrow in the image shows the Motion-Path of a Point along the CAD-Line of one of the Parts.

tog_minus        Degrees-of-Freedom & Mobility of Motion-Parts

Gruebler Equation:

F = 3*(N-1) – 2*L- H

F = 3 * (2-1) – 2*1 –0

F = 3 – 2

F= 1

Degrees-of-Freedom = 1

Parts

N = 2.

There are two parts: the Part we wish to specify with a Motion Dimension FB and the kinematically-defined Part to which it is joined

Lower Pairs (Joints)

L = 1

There is one joint.

Higher Pairs (Cams or Gears)

H = 0

There are no Cams or Gear-Pairs

The Mobility - or Kutzbach Criterion - shows that a Motion Part has a Mobility of Zero.

Mobility = Degrees-of-Freedom – Motion Dimensions

Mobility = 1 – 1 = 0

Each Motion-Part has one Motion-Dimension that defines its Position.

tog_minus        How to Add

tog_minus        Rocker

KinChain-a1

1.Add a Part1s-red

The Part is a 'Free' Part.

The Part has three Degrees-of-Freedom

KinChain-1ab

2.Add a Pin-Joint between two Points2s

The Pin-Joint removes two Degrees-of-Freedom.

The Part now has one Degree-of-Freedom

KinChain-1ac

3.Add a Motion-Dimension FB3s

MD-32-FB-PINMDA-small This is the FB icon in the graphic-area for the Motion-Dimension FB when you add it to a Pin-Joint.

The Part has Zero (0) Mobility. Notice the Part-Outline and Pin-Joint are green

 

See Video to the Left.

Kinematics-Tree

KT-Rocker1

The elements that define a Rocker are:

Dowel

Pin-Joint

Part

Part

MD-32-FB-PINMDA-small

Mot-Dim Rocker

tog_minus        Slider

KinChain-a1

1.Add a Part1s-red

The Part is a 'Free' Part.

It has a blue Part-Outline

A 'Free' has three Degrees-of-Freedom

SlidingJoint1

2.Add a Slide-Joint between two Lines2s

The Slide-Joint removes two Degrees-of-Freedom.

The Part has one Degree-of-Freedom

Notice the Arrowhead at the 'Origin' of the Line in the kinematically-defined Part 1GS . It points in the Positive direction of the dimension.

SliderMotDim

3.Add a Motion-Dimension FB.

Add Motion-Dimension FB is available in the Kinematic-FB toolbar.

MD-32-FB-SLIMDA-small This is the FB icon in the graphic-area of the Motion-Dimension FB when you add it to a Slide-Joint.

The Part has Zero Mobility. Notice the Part-Outline and the Slide-Joint are green

 

See Video to the Left.

Kinematics-Tree

KY-Slider1

The elements that define a Slider are:

Slide-Joint1

Slide-Joint

Part

Part

MD-32-FB-SLIMDA-small

Mot-Dim Slider

tog_minus        How to Add

tog_minus        Ram-R

KinChain-RamR0

1.Add a Part1s-red

The Part is a Free Part.

The Part has three Degrees-of-Freedom

KinChain-RamR1

2.Add a Pin-Joint between two Points

The Pin-Joint removes two Degrees-of-Freedom.

The Part now has one Degree-of-Freedom

KinChain-RamR2

3.Add a Motion-Path FB

Select the CAD-Line.

The Motion-Path FB adds a Motion-Point1s-red at the start of the sketch-element to which you add the Motion-Path FB. The Motion-Point is coincident with the Origin at the start of the CAD-Line.

The Part is a still a Free-Part

KinChain-RampR3

4.Edit the Motion-Path FB

The Ram-P does not usually work when the Motion-Point1s-red is at the Origin of the CAD-Line.

Note: If the Motion-Point is at the Origin of the CAD-Line in the first Part, then the second Part would need to have a length exactly the same as the distance between the two Pin-Joints in the Base-Part. This is kinematically impossible.

 

KinChain-RamR3

5.Add a Part and Pin-Joint

This Part is a Free-Part

 

KinChain-Ramr4

6.Add a Pin-Joint between the new Part and the Motion-Point1s-red

The kinematic-chain is now kinematically-defined chain.

It is a Ram-R

tog_minus        Ram-P

KinChain-RamR0

1.Add a Part1s-red

The Part is a 'Free' Part.

It has a blue Part-Outline

A 'Free' has three Degrees-of-Freedom

KinChain-RamR1

2.Add a Pin-Joint between two Points

The Pin-Joint removes two Degrees-of-Freedom.

The Part now has one Degree-of-Freedom

KinChain-RamR2

3.Add a Motion-Path FB

Select the CAD-Line.

The Motion-Path FB adds a Motion-Point1s-red at the start of the sketch-element to which you add the Motion-Path FB. The Motion-Point is coincident with the Origin at the start of the CAD-Line.

The Part is a still a Free-Part

KinChain-RampR3

4.Edit the Motion-Path FB

The Ram-P does not usually work when the Motion-Point1s-red is at the Origin of the CAD-Line.

Why? It becomes clear later.

KinChain-RamP1

5.Add a Part and Slide-Joint
6.Add a short Line1s-red to the Sliding-Part

KinChain-RamP2

7.Add a Pin-Joint1s-red between the short-line in new Part and the Motion-Point1s-red

The kinematic-chain is now kinematically-defined chain.

It is a Ram-R

Note: If the Motion-Point is at the Origin of the CAD-Line in the first Part, then the second Part would need to have a length that is exactly the same as the distance between the two Pin-Joints in the Base-Part. This is kinematically impossible.

Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd