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New User - Creating mechanical mechanism model to investigate forces?

Posted 10 years ago

Hello,

I am a new user working to learn System Modeler. I've been modeling simple mechanisms to see if I can obtain outputs that match my expectations.

I'm now stuck on a pretty basic issue. I created a model of a rectangular body with mass that swings on a pivot. A prismatic joint connected to the rectangular mass represents a hydraulic cylinder. A pictorial depiction of the simple mechanism is shown below: enter image description here

The rectangular mass's rotation is now driven by a combiTimeTable with an Accelerate Rotational Source. For now, let's say that the resulting motion profiles (acceleration, velocity, and position) of the rectangular mass are exactly what we want. With this simple model, I'm looking to determine the hydraulic cylinder force profile (over the simulation time span) that would accelerate and decelerate the rectangular mass through the motion prescribed by the combiTimeTable. Right now, when I plot the prismatic joint's force (f), it's value is zero over the entire model time span. Understanding that System Modeler is acausal, I was hoping that I could find the force through a prismatic joint by defining the motion of a driven, connected part. If this can be done, I'm making a mistake somewhere along the line.

If anyone can lend me hand with this, the help will be greatly appreciated. I've attached the model and the combiTimeTable file to this post. Thanks.

Dave

Attachments:
POSTED BY: Dave F
5 Replies
Posted 10 years ago

Johan, I finally had a moment to break away from the chaos as work to play with System Modeler. Yes, I see now how you were driving the model in your earlier post.

You and your co-worked were a huge help. Thank you! The last model you posted perfectly nails what I was trying to accomplish. I would never have found the inverse block constraint on my own.

Once again, you got me past a roadblock. Thank you!

-dave

POSTED BY: Dave F
Posted 10 years ago

Dave, In my previous answer I changed the model to only follow a linear position change, so it's not the same profile and not the same model as yours. Hopefully it makes sense when you download the model.

A co-worker suggested using an inverse block constraint. This constraint can be used to find the force needed to get the wanted acceleration.

Model with inverse block constraint

Running this model results in the following:

inverseModeling Prismatic SystemModeler

More material about learning to use the inverse block constraint can be found in this example. That example can be downloaded and played with. Also attaching the model I the pasted the diagram from.

Attachments:
POSTED BY: Johan Rhodin
Posted 10 years ago
POSTED BY: Dave F
Posted 10 years ago
Attachments:
POSTED BY: Johan Rhodin
Posted 10 years ago
POSTED BY: Johan Rhodin
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