Introduction
A common application of multibody dynamics simulation is the insertion of one body into another. One such use case is the insertion of an electrical connector into a header in which the two bodies are initially misaligned. The initial misalignment requires motion in all 6 degrees of freedom (DOF) to achieve complete insertion. In this article, we will provide a method in Ansys Workbench Motion that utilizes a manually defined SixMotion joint to achieve the insertion of a tapered key into a base with tapered pocket.
Example Model
To illustrate the procedure for implementing a SixMotion joint, we will use an example model in which we would like to insert a rigid male keyed part (top body) into a rigid base with female pocket (bottom body) that is fixed to ground.
The image above shows the assembly in an exploded state. To begin, the key part is brought closer to the base and offset so that transverse, and potentially rotational, motion is required for insertion. The following image shows the y-direction (left image) and the x-direction (right image) skewed initial position of the key body.
Finally, five copies of the key body are created and placed in the same initial position of the key. These copies are dummy bodies each of which are used to impart one of the 6 DOF onto the key. The five dummy bodies are named dummy1, dummy2, ..., dummy5.
6-DOF Motion Model
To implement the SixMotion joint, we need to establish a kinematic chain from key to base (to ground). The following model establishes that chain.
Kinematic Chain and Joint Connections
The kinematic chain that we would like to create is as follows:
- dummy1 -> key: Translational Body-Body in Z-direction
- Vertical motion will be prescribed using Joint Load Properties and a Function Expression on this joint.
- dummy1 -> dummy2: Translational Body-Body in Y-direction
- dummy2 -> dummy3: Translational Body-Body in X-direction
- dummy3 -> dummy4: Revolute Body-Body about Z-axis
- dummy4 -> dummy5: Revolute Body-Body about Y-axis
- dummy5 -> base: Revolute Body-Body about X-axis
- base -> ground: Fixed
Note: It is required to align the X-axis of the reference coordinate system for each translational joint and the Z-axis for revolute joints to appropriate the global directions as described above.
For joints 1-5, we select the coplanar top face for the corresponding body as the Geometry Selection:
Similarly, the dummy->base joint is scoped as shown here:
Contact and Contact Properties
Since the key and base pocket are misaligned, a frictional contact is defined so that the surfaces can move relative to each other:
The coefficient of friction is specified using a Contact Friction Properties object, in which we use the defaults for this example:
Design Variable
The initial distance between the planar faces of the key and base is 0.22 in. However, in Motion, the default solver length units are in mm. Therefore, we create a Design Variable object that allows us to vary the travel distance parametrically. Thus, we compute the travel distance in mm using a Workbench parameter expression to control the design variable that will be used in the Function Expression that drives the joint load (discussed below):
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Function Expressions
In order to drive the motion and retrieve reaction forces or resulting travel distances/rotations, Motion uses Function Expressions with respect to Action and Base Markers for joints among other possibilities. (See the Motion Preprocessor Manual for further details.)
For this example, we have defined many Function Expressions, one of which (the top in the list) drive motion, whereas the others record results. Here, we will only explain the motion driver Function Expression; the others can be investigated by looking at the downloadable example model archive.
The travel distance function expression is a Step function that ramps from 0 to the final position over 1 second. The definition of the Step function is shown here, where the Design Variable is denoted as argument p1:
The details of the Step function can be found in the Motion Theory Manual.
Joint Load Properties
Finally, we prescribe the vertical translation using a Joint Load Properties object, the details of which are
Results
The resulting motion after running the model as described above is shown in this animation:
Notice that the key rotations and translates in order to be fully-seated. Additionally, may Results Objects have been created to interrogate the characteristics of the motion. Refer to the model archive for details.
3-DOF Motion Model (No Rotations)
Now, suppose that we only want to allow for translations of the key, we only have to make a few simple modifications to the 6-DOF model, described in the sequel.
Geometry Adjustments
Since rotations are no longer allowed, the kinematic chain is simplified. Thus, we suppress bodies dummy3, dummy4, and dummy5.
Connection Updates
The revolute joints are no longer used, and the last translational joint is changed from dummy2->dummy3 to dummy2->base:
Results
All other things being equal, the insertion with only translations is shown in this video:
Conclusion
In conclusion, by creating an appropriate kinematic chain, Ansys Motion can easily simulate general 3D motion of body that is required to simulate self-alignment in an insertion application.
Downloadable Content
Ansys 2025 R2 Workbench Model Archive
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