Introduction
In a previous blog post, the step-by-step process of creating a chain-driven telescoping arm within Ansys Motion in Mechanical was provided. Here, we will modify that model to include an inline spring to provide tight-side chain tension.
Modeling
The following steps illustrate how to update the reference model in order to add the inline spring connection.
Reference Model
The following image shows the reference model that has a continuous chain-drive:
Chain Modification
To interrupt the continuous chain, we simply suppress the links that will be replaced by the inline spring. Here, we choose to suppress 11 links in order to create a gap as close to 100 mm as possible. The links to be suppressed are highlighted in the image below:
After suppression, the resulting chain becomes, noting that the two free end links are connecting links:
Longitudinal Spring Connection
To create the inline spring, we add a Spring Connection from the Connections Ribbon in Mechanical. The Reference and Mobile faces are the pin holes in the opposing free end links as shown here:
The details of the Spring Connection are shown here, with Preload applied by entering the Free Length of the spring. Note that Preload is not required in the joint definition:
Spring Force Function Expression and Custom Result
In Ansys Motion, we define Function Expressions to either prescribe or retrieve a result from a kinetic or kinematic quantity. Thus, we will create a function that will retrieve the magnitude of the spring force. Then, we create a Custom Result for postprocessing the Function Expression value. The function that measures the magnitude of the force in the spring is FM (see the Motion Preprocessor Help for details), where the first entry is the Action Marker of the joint and the second entry is the Base Marker of the joint:
The details of the Custom Result for postprocessing are shown here:
Final Model and Spring Tension Result
Now that everything is in place, we solve the model, noting that a re-meshing will occur. The resulting motion is captured in this video:
Finally, the resulting spring tension is shown in the plot below:
Here we see that there is an initial jerk followed by a spring tension that ranges between 185-195 N due to the inherent sinusoidal nature of a spring.
Conclusion
In this article, we showed how direct it is to interrupt a continuous chain-drive with a tension spring in Ansys Motion. A spring is only one two of connection that is able to replace chain links: a physical part or a Bushing joint to name a few. Therefore, using Ansys Motion for multibody dynamics is not only accurate and robust, but also very straightforward and direct.
Going Further
- Replace the longitudinal spring joint with a bushing joint to implement a more general inline tensioner.
- Replace the longitudinal spring joint with a rigid or flexible part.
Downloadable Resources
