Hello,
I need to know best way to calculate minimum force that needed to move an object.
See image below for details.
Thanks !
Hello,
I need to know best way to calculate minimum force that needed to move an object.
See image below for details.
Thanks !
Hello,
I think thid case is general problem for machine design and moving system engineer.
Any help or sharing on thid case will be very appreciate.
Thanks
If you know the materials and finishes, you can probably find a good value to use for friction coefficient. Box will move when applied force is greater than static friction force.
For horizontal sliding: friction force = weight * coefficient
Hi Ray & Roland
Thanks for your suggestion.
Here I also attached the 3D models.
Hope you can create motion study from those model.
Regards,
AZ
Hope is good. Keep hope alive.
I hope Ray and Roland won't mind me re-posting their excellent replies, with some added emphasis so that hopefully you can pick out the most important parts:
If you know the materials and finishes, you can probably find a good value to use for friction coefficient. Box will move when applied force is greater than static friction force.
Ahmad, I only know of two ways to answer your question. One requires you to ascertain the coefficient of static friction, which is usually hard to come by. That would allow you to calculate the force require to get the box moving. The other method requires you to go out to the shop with a box and some sort of force gauge and do a little testing. This method is probably the easiest to accomplish and will give you the most accurate answer.
I hope this advice helps you solve your problem.
Hi Ahmad,
The accuracy of what you get out of the motion simulation depends on what you put in. Friction is a tricky thing to find good numbers for specific combinations of materials/surface finishes. Motion can account for the friction between bodies and give you a good feel for the force needed to push the body, but it is only as good as the friction coefficient.
If you still want set up the model, it is very straight forward. The simplest is to suppress any mates between the box and other components and then define 2 contacts. One between the box and whatever it slides on and the other between the actuator rod and the box. Specify the friction materials and it will populate an approximate friction value. I would not bother with defining Friction for the contact between the box and the actuator rod. Then enforce a movement on the actuator rod (using a linear motor to extend it a certain distance over a certain is best) and it should push the box when you solve it. For flat on flat type contacts, the facetted contact should be good enough. For anything other than flat faces, use precise contact.
To obtain the force needed to push the box, select the linear motor and plot the applied force in the relevant direction.
Note that the force needed to push the box may be heavily dependant on time if it is a high speed operation due to inertia.
Hope this helps you out.
Cheers,
Ian
Hi Ian,
Below is the result ( without gravity ) :
Click above image to see animation.
Why the value ( newton ) negatif ?
Thanks
Message was edited by: Ahmad Zulker
Hi Ian,
Below is result when gravity added :
Click image to see animation !
Thanks,
AZ
Message was edited by: Ahmad Zulker
Hi Ahmad,
If you are plotting force in say the x axis direction, this is just the sign convention meaning the actuator is experiencing a force acting in the -x direction.
Remember, the box will experience and equal and opposite force, so be wary of signs with respect to what you are measuring force on.
Plot Magnitude if you are not concerned with direction.
Ian
Hi Ian,
Please clarify me...
1. I need force = 108 N to move the box ( without gravity )
2. I need froce = 368 N to move the box ( with gravity )
Is that correct ?
Another question is, Why the box move down through anothe body when I applied gravity ?
Look at my second animation.
Thanks Ian
Hi Ahmad,
It looks like you have bad material properties. The bodies should not penetrate that much.Without gravity the only effect should be the actuator overcoming the inertia to move the box.
Change materials to steel for all the contacts.
The box falls through the bottom due to a small thickness. What happens is that it is penetrating too far and there is no obvious direction to apply a force to push the box back out of the surface, so if falls through. Increasing material stiffness properties should help this, but if it does not, then set your maximum time step an order of magnitude lower.
There are other threads on the forum for recommendations on contact properties. Just remember that the contact properties are a means of approximating body stiffness to give more realistic force responses compared to having infinitely stiff bodies hit each other.
Cheers,
Ian
Hi Ian,
>Change materials to steel for all the contacts.
Yes, it solved .
When I ran two study with and without gravity, I got result below :
Why the result without gravity bigger than with gravity ?
If I apply gravity, it should mean increase friction, or maybe I am doing something wrong ?
Thanks !
Hi Ahmad,
In all honesty, I would not try to focus on the forces at the initial collision. Focus on the long term force (steady state solution) needed to move the box.
There is a lot of complexity in modeling the true transition from static to sliding and the frictional changes that occur during that phase. I don't know what your application is, but the motion solver uses coulomb friction which is a simplified friction model that models sliding friction very well, but makes an approximation for the friction behavior when shifting from static to dynamic friction.
The other reason to ignore the initial peak forces is because we are approximating the material characteristics. Unless you have a good idea of the linear stiffness of the parts in question (usually obtained from experiment or FEA analysis) it is only going to give you a ball park figure. So there is little value in chasing down ways to more accurately capture the initial contact event which is really what the issue is here.
If you still want to refine the model, then increase the number of frames per second to several hundred. This not only smooths out the results, but automatically reduces the maxium time step to 1/number of frames so you get more accurate results.
Cheers,
Ian
Hi Ian, Roland and others
Thanks for all your response on this thread. Thats help me a lot to find minimum force that needed to move an object.
So the conclusion on how to find it is below :
The accuracy of what you get out of the motion simulation depends on what you put in. Friction is a tricky thing to find good numbers for specific combinations of materials/surface finishes. Motion can account for the friction between bodies and give you a good feel for the force needed to push the body, but it is only as good as the friction coefficient.
If you still want set up the model, it is very straight forward. The simplest is to suppress any mates between the box and other components and then define 2 contacts. One between the box and whatever it slides on and the other between the actuator rod and the box. Specify the friction materials and it will populate an approximate friction value. I would not bother with defining Friction for the contact between the box and the actuator rod. Then enforce a movement on the actuator rod (using a linear motor to extend it a certain distance over a certain is best) and it should push the box when you solve it. For flat on flat type contacts, the facetted contact should be good enough. For anything other than flat faces, use precise contact.
To obtain the force needed to push the box, select the linear motor and plot the applied force in the relevant direction.
Note that the force needed to push the box may be heavily dependant on time if it is a high speed operation due to inertia.
Hope this helps you out.
Cheers,
Ian
Hi Ahmad,
The accuracy of what you get out of the motion simulation depends on what you put in. Friction is a tricky thing to find good numbers for specific combinations of materials/surface finishes. Motion can account for the friction between bodies and give you a good feel for the force needed to push the body, but it is only as good as the friction coefficient.
If you still want set up the model, it is very straight forward. The simplest is to suppress any mates between the box and other components and then define 2 contacts. One between the box and whatever it slides on and the other between the actuator rod and the box. Specify the friction materials and it will populate an approximate friction value. I would not bother with defining Friction for the contact between the box and the actuator rod. Then enforce a movement on the actuator rod (using a linear motor to extend it a certain distance over a certain is best) and it should push the box when you solve it. For flat on flat type contacts, the facetted contact should be good enough. For anything other than flat faces, use precise contact.
To obtain the force needed to push the box, select the linear motor and plot the applied force in the relevant direction.
Note that the force needed to push the box may be heavily dependant on time if it is a high speed operation due to inertia.
Hope this helps you out.
Cheers,
Ian