From the ptc.com website
Suggested Technique on Defining [MDX] Slot Follower Connections
Introduction
A
Slot Follower is a point-curve constraint between two bodies. One of the bodies has a 3D curve (
the slot) bound to it and the second body has a point (
the follower) bound to it. The follower point follows the slot in all three dimensions.
You can use an open or closed curve to define the slot. The
Slot Follower constrains the follower point to the interior of the defining curve. If you want the slot curve to be shorter than the size defined by the default endpoints, you can define slot endpoints.
If you have a license for Mechanism Dynamics Option [MDO], you can simulate the impact force when the
Slot Follower hits the end of the slot by defining a coefficient of restitution.
This suggested technique describes the procedure to define
Slot Follower connections when used in conjunction to regular [MDX] joints.
The Model
Download Example Files for this Technique: apm11043_INITIAL.zip
This technique suggests some tips and methods on modeling and animating tracks (
Figure 1.).
Figure 1.
The track-like motion will be attained using the
Slot Follower connection and some additional [MDX] joints to restrain unwanted motion.
The geometry model consists mainly of the following (
Figure 2.):
slot_curve.prt (that will define the shape of the entire track) and multiple
track_segment.prt parts that fit perfectly in the full-enclosed chain.
Figure 2.
The
slot_curve.prt component is going to be the "Ground Body" and its placement at Pro/ENGINEER's 'Default' location (
Figure 3).
Figure 3.
Modeling Strategy
As mentioned in the introduction, the
Slot Follower is a point-curve constraint between two bodies. One of the bodies has a 3D curve (
the slot) bound to it and the second body has a point (
the follower) bound to it. The follower point follows the slot in all three dimensions.
Based on this assumption, the main instinct would be to connect each track segment with
Slot-Follower connections. It won't be sufficient to simply define a point (point of
track_segment.prt) on curve (curve from
slot_curve.prt) constraint to define the motion.
The lead
track_segment.prt needs to be constrained within the plane of motion such that to not tip over (
Figure 4). This will be attained using regular [MDX] joints.
Figure 4.
This technique will describe how you can attain this motion and apply the
Slot Follower connection in addition to [MDX] joints in order to deliver the 'true' track movement. The steps will be:
I.) Define [MDX] Constraints to Avoid
track_segment.prt's Tip-Over.
II.) Define the
Slot-Follower Connection to Constrain
track_segment.prt to the curve from
slot_curve.prt.
II.) Connect Additional
track_segment.prt Components to Complete the Track.
III.) Verify and Animate Motion.
I.) Define [MDX] Constraints to Avoid track_segment.prt
's Tip-Over.
The plan is to define the proper [MDX] joints to the first
track_segment.prt component. Then once this first part will be connected to the slot curve via a
Slot-Follower connection and it won't tip over. All the other components -properly connected to it- will follow and not tip over as well.
Let's list all the [MDX] joints that are possibilities to constrain
track_segment.prt as to avoid the motion presented in
Figure 4.
Slider and
Planar joints come as options.
Slider joint is not a choice as the motion is forced along a straight edge/axis and we want to follow the path depicted by the slot curve. Series of
Slider joints is out of the question.
Planar it's a valid option but it will cause
track_segment.prt to 'float' in-plane. But... when using the
Slot-Follower connection point-to-curve constrain should work.
Start by creating a new assembly
>File >New, and select 'Assembly' as the file type. Name the file
track, and place the slot_curve.prt as 'Ground Body' by constraining it to Pro/ENGINEER's 'Default' location.
Assemble
track_segment.prt component and use a
Planar [MDX] joint. Use as geometrical references the selection listed in
Figure 5. [/list]
Figure 5.
II.) Define the
Slot-Follower Connection to Constrain
track_segment.prt to the curve from
slot_curve.prt.
Our next step is to define the
Slot-Follower connection in order to constrain the
track_segment.prt to follow the path of
slot_curve.prt.
First, while with
track.asm still in session, access
>Applications >Mechanism and dynamically move (using
>Drag) the track segment. Notice how the component moves freely in the plane of constraint. After completing this substep, create a
Slot-Follower connection using the following selection of menupicks (
Figure 6.):
Figure 6.
Once in the
Slot-Follower definition window follow the steps from
Figure 7 (
a.,
b., and
c.) in order to create a
Slot Follower between
track_segment.prt and the curve(s) from
slot_curve.prt.
Figure 7a.
Figure 7b.
Figure 7c.
Couple of things you should be aware of before selecting the curves or points:
The follower point must be on a different body from the slot curve
You can select a datum point or a vertex.
Assembly-level datum points cannot be used for follower points
Your datum point must belong to a single body [/list]Also, you can select any of these types of curves to define the slot:
Planar or non-planar curves
Edges
Datum curves (Open or Closed). [/list]The selected curves must be continuous, but do not have to be G1 or G2 continuous. [MDX] automatically smooths multiple curves to ensure G2 curve results. A curve is G1 continuous if the direction, but not necessarily the magnitude, of its first derivative varies smoothly everywhere on the curve. A curve is G2 continuous if the direction of its second derivative varies smoothly everywhere on the curve.
Please select the geometrical references following the steps from
Figure 7 and the input from
Figure 8:
Figure 8.
Complete this
Slot Follower connection and dynamically move (using
>Drag) the track segment. Notice how the component moves freely in the plane of constraint but following the slot curve.
II.) Connect Additional track_segment.prt
Components to Complete the Track.
Additional
track_segment.prt components can be added to the track and linked to the first
track_segment.prt component.
The
Planar joint constrains the tip-over movement for the first
track_segment.prt component. Therefore, any additional component connected to it will follow the same motion excluding the need for additional
Planar joints. Any
track_segment.prt's need just to be connected to the first
track_segment.prt and point-on-curve constrain (using the
Slot-Follower connection). This connection can be a
Pin or a
Cylinder joint.
While
track.asm is still in session, assemble (
>Insert >Component >Assemble) a new
track_segment.prt using a
Pin joint (
Figure 9a. and
b.):
Figure 9a.
Figure 9b.
Using the same selection of menupicks from
Figure 6 and
7 (
a.,
b., and
c.), define a new
Slot Follower connection for the second
track_segment.prt (
Figure 10).
Figure 10.
Or, you can assemble them using Cylinder joints:
While
track.asm is still in session, assemble (
>Insert >Component >Assemble) a new
track_segment.prt using a
Cylinder joint (
Figure 11):
Figure 11.
After completing this connection define the
Slot-Follower connection as in previous steps.
This procedure:
Pin (or
Cylinder joint) +
Slot Follower connection needs to be defined for the remaining
track_segment.prt components (
Figure 12.).
Figure 12.
III.) Verify and Animate Motion.
In the postprocessing stage (when creating MPEG/JPEG files) the slot curve can be placed on a layer and excluded from display. Also it is recommended for each step completed to use the dynamic drag capability from [MDX]. Ultimately the motion will end up as in animation below:
Animation 1.
Edited by: prouser1
