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How can i lock the movement of a translational joint in one direction?

Hello,

I am working on a motion simulation in MotionView and have the following question:

Can I lock the movement of a translational joint in the -x direction, for example, and only allow movement in the +x direction? Do I need a general constraint for this, and if so, what should the expression look like?

I haven't been working with MotionView for very long, so I'm not yet very familiar with the expression builder. I hope someone can help me with this.

Thanks.

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MotionView/MotionSolve

Accepted answers

GTT Adam

Hi @FabianUhlig,

If the "counter holder" is meant to exert an opposite force until a certain limit is reached, then that can be modeled with a force that acts like a stiff spring until a limit is reached. I created another example to demonstrate this:

Here, we have the hay bale represented by a spring. The piston is moved by an applied force, the hay bale is compressed, and the counter force is applied until a limit of 1000N is reached.

The counter force is calculated like a spring force, F=Kx, where x is the deflection of the counter block from its initial position and K is a stiff spring constant.

Using an IF function, the counter spring force will saturate at a set limit, stop generating any additional force, and break away. The IF function is detailed below:

IF(EXPR1: EXPR2, EXPR3, EXPR4)

If the value of EXPR1 is less than zero, the IF function evaluates to EXPR2.
If the value of EXPR1 is equal to zero, the IF function evaluates to EXPR3.
If the value of EXPR1 is greater than zero, the IF function evaluates to EXPR4.

As you can see in the plot, when the counter force (green) 1000N limit is reached, the counter force flatlines and the assembly breaks away to the left.

mvms_2025_1_square_baler_rev00.mdl

Hope this helps!

Adam Reid

All comments

GTT Adam

Hi @FabianUhlig,

To prevent movement in one direction, it is common to create a Force that is defined with an expression that uses the IMPACT function. This method will replicate a Contact and prevent the movement when the displacement between two markers reaches a certain value.

Hope this helps!

Adam Reid

GTT Adam

Hi @FabianUhlig,

To demonstrate this, I whipped up this model to showcase how the IMPACT function can work. In this example, a sphere moves on a translational joint from the right to the left. A Force using the IMPACT function stops the sphere from moving too far right and another from moving too far left.

The green and red cylinders are purely for visual purposes. The 'contact' that looks like is happening is achieved purely with the limit Forces applied.

Please find the model used below:

mvms_2025_1_impact_demo_rev00.mdl

Hope this helps!

Adam Reid

FabianUhlig

Hi @GTT Adam,

Thanks for the tip about the IMPACT function, but I still can't quite find a solution to my problem.

I would describe my problem, broken down to the sphere in your minimal example, as follows: A force in the positive x direction acts on the sphere all the time. Another force counteracts this force in a sinusoidal manner, overcoming it and shifting the sphere to the left. When the variable force decreases, the sphere remains in its new position.
I have tried to implement this in a simple way by adjusting the limit rh marker to the sphere rh, but I am still not getting anywhere.

Best regards,

Fabian

Orestis_YB

Hello @FabianUhlig,

I guess you are using just forces (in case you are using motion entity IMPACT or BISTOP functions won't work). You said that when sin force overcomes the constant force the body should move to the left, while when sin is reduced the body should stay in the new position. Is this something similar to a ratchet effect that you are trying to simulate? @GTT Adam in the above example used two IMPACT forces to simulate fix limits (where green meets the red part of the cylinder).

Best regards,
Orestes

GTT Adam

Hi @FabianUhlig,

Another option you could use is a sequential simulation in which a fixed joint is activated using Templex. Please use the following example for setting up this type of sequential simulation that creates joints using non-coincident markers:

https://help.altair.com/hwsolvers/ms/topics/solvers/ms/understand_seq_sim_intro_t.htm

Hope this helps!

Adam Reid

FabianUhlig

Hi @Orestis_YB and @GTT Adam

Yes it is some kind of ratchet effect. It is a coupled simulation with EDEM and MotionView of a square baler. I want to simulate the pressing process. New material is fed into the press channel and a press piston presses the material against a counterholder. The counterholder generates a counterforce and is then moved to the left by the movement of the piston as soon as the counterforce is overcome. Then the piston moves back to the right and new material is fed into the channel and the process starts again. The pressed material and the counterholder remain in their position.

I also thought about something simple like measuring the force acting on the counterholder and appling a similar force to it, to limit the movement. So if the measured force is less then the specified counter force, the applied force is -measured force. If it is more then the applied force is -specified force.

Is this possible and how can i use the measured force as an input variable?

Best regards,
Fabian

GTT Adam

Hi @FabianUhlig,

Here, we have the hay bale represented by a spring. The piston is moved by an applied force, the hay bale is compressed, and the counter force is applied until a limit of 1000N is reached.

The counter force is calculated like a spring force, F=Kx, where x is the deflection of the counter block from its initial position and K is a stiff spring constant.

Using an IF function, the counter spring force will saturate at a set limit, stop generating any additional force, and break away. The IF function is detailed below:

IF(EXPR1: EXPR2, EXPR3, EXPR4)

If the value of EXPR1 is less than zero, the IF function evaluates to EXPR2.
If the value of EXPR1 is equal to zero, the IF function evaluates to EXPR3.
If the value of EXPR1 is greater than zero, the IF function evaluates to EXPR4.

As you can see in the plot, when the counter force (green) 1000N limit is reached, the counter force flatlines and the assembly breaks away to the left.

mvms_2025_1_square_baler_rev00.mdl

Hope this helps!

Adam Reid

GTT Adam

mvms_2025_1_square_baler_rev00.mdl

Model failed to attach, please find it above.

FabianUhlig

Hi @GTT Adam,

Thank you for your effort and patience with my problem.
I think I could do it exactly as in your example.
I saw that you tried to measure the input_force directly at the joint and then use it for the IfStatement. That would be exactly the solution I need. But why didn't it work there, and how could I make it work? Or is it not possible to measure and adjust the counterforce at the same time?

Thanks and best regards,

Fabian