Why use a Motion-Path Function-Block?

Motion-Path FB

MechDesigner adds a Motion-Point to a sketch-element* - this is the 'source Motion-Point'.

The motion-values at the input-connector to the Motion-Path FB specify the motion for the source Motion-Point along the sketch-element.

Applications of a Motion-Path FB and Motion-Point include: Robot Path, Chain or Belt Path, Ram-R dyad and Ram-P dyads.

* The sketch-element can be a:

sketch-element : a single sketch-element such as a Line, Arc, Circle, Blend-Curve.
sketch-path : sketch-elements, with end-Points merged, but as an 'open loop'.
sketch-loop : sketch-elements, with end-Points merged, and in an endless 'closed loop'.

The sketch-loop may be 'crossed (8)' or 'not-crossed (0)'.

Motion-Path FB dialog-box parameters:

Add more Motion-Points to the same Motion-Path
Move the Base-Value of the source Motion-Point along the sketch-element from its start-Point.
Edit the Range with which the Motion-Points move along the sketch-elements in a Machine-Cycle.
Display the displacement (linear dimension or normalized to 0–360) of the Motion-Point as it moves along the sketch-loop.

Motion-Path FB

Add Motion-Path FB

Kinematics FB toolbar > Motion-Path FB [right of Graphic-Area >>]


Add menu > Add Motion-Path FB


Motion-Path dialog-box


STEP 1: Add the Motion-Path Function-Block to the graphic-area

1.Click Add menu [toolbar] > Add Motion-Path FB

The Command-Manager opens ; you need to select a sketch-element.

2.Click a sketch-element, sketch-path or sketch-loop, in the graphic-area
3.Click OK-tiny-13-17 in the Command-Manager


STEP 2: Open the Motion-Path Function-Block dialog-box :

1.Double-click a Motion-Path FB in the graphic-area

- or -

See Motion-Path Function-Block dialog-box to review all parameters.

Its behaviour is a function of the data-type at its input-connector and if they are Rotary or Linear units.

Data-Type @input-connector:

If you connect a wire from a Linear-Motion FB to a Motion-Path FB, the Motion-Point will move along the complete Path in one machine cycle at constant velocity.
If you connect a Motion FB to a Motion-Path FB, then you must use the Linear or Rotary check box [do not use the Motion check-box] in the Motion FB dialog-box - see below.

Data-Type at the input-connector of a Motion-Path FB

When you connect a wire from the output of a Motion FB to the input of a Motion-Path FB, then the Motion FB dialog-box : Output Data Type : Linear or Rotary check-box is important.

Motion FB > Output Data Type:

Motion FB > Output Data-Type : Linear check-box

The Motion-Point moves along the sketch-path by the same distance[mm] as the range of the actual motion that you link to the Motion FB.

Current Position of the Motion-Point along sketch-path = Current motion-value at at input-connector to Motion-Path FB [+Base-Value, set in Motion-Path dialog-box]

Motion FB > Output Data-Type : Rotary check-box

The Motion-Point moves the full length of the sketch-path when the motion-value at the input-connector have a range of 360.

Current Position of the Motion-Point along Path = Current motion-value at input-connector * Total Length of the sketch-path / 360

Make the motion have a range of 0 – 360 to move the Point along the Path by '1 Path Length'. [Similar to rotating a Rocker by one rotation, 360º]

If the sketch-path is 'Open', and you want to move the Motion-Point between the ends of the sketch-path, it is best to make the range of the motion from 0.001 to 359.999'. This prevents the Motion-Point 'flicking' for an instant from the start-Point to the end-Point [or end-Point to the start-Point] of the sketch-path when the motion-value is <0 [or >360] and should never be <0 [or >360].

Compare : Motion-Path FB and Motion-Dimension FB

A Motion-Path FB / Motion-Point can be compared with a Motion-Dimension FB / Motion-Part.


Motion-Path FB <

> Motion-Dimension FB

Motion Element:

Motion-Point <

> Motion-Part


Sketch-Element/Sketch-Path/Sketch-Loop <

> Joint


Motion-Values at its input-connector <

>Motion-Values at its input-connector


Motion of a Motion-Point constrained by a sketch-element <

> Motion of a Motion-Part constrained by a joint


You need to add a sketch-element in a Part. You can configure the sketch-elements as a sketch-loop, or as an open series of merged sketch-elements. The Path Length is the total length of the merged sketch-elements.

It is best to drag, as you add each sketch-element to the sketch-path, from the end-Point of a sketch-element and in the positive direction of the motion.


Do not add sketch-elements to a Motion-Point. You should add sketch-elements to a Part that you join to the Motion-Point with a Pin-Joint.

It is best not to do Add Auto-Profiles with a kinematic-chain when you have a Motion-Path.

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