how to input position velocity acceleration multibody simscape

In this picture i want to find torque of robot arm,I have position velocity and acceleration value data to input in simscape multibody (below picture blue circle input).

Diagram input position velocity and acceleration (below picture)

i have problem motion of robot arm isn't true and torque value is over torque . how i can solve this problem ? sorry if my english isn't good and Thank for ur answer help me pls. (i do it long time TT)

Answer 1

[Steve Miller]

Hi - if you share the model, we can give a better suggestion.

Your method of prescribing motion should work, though it is not the best way. When you use the du/dt block, you can run into numerical issues. We normally recommend either:

1. Inputting the acceleration and integrating to get the velocity and position OR
2. Inputting the position and letting Simscape calculate a consistent set of first and second derivatives for the motion. This will put a slight lag in your results, but if you make the filter constant very small the results should be quite close.

If you are not getting the answers you expect, first try one of these methods. You could also try reducing the maximum step size and tolerances and see if this improves the behavior of your model.

--Steve

[Arka]

Hi Steve, I want to ask you a follow up question. If I have a signal that I have measured (acceleration in XYZ directions), is it practical to use the integration of the signal as velocity and position inputs for my Simulink-PS converter block?? Will the noise in my signal create a problem during the integration ??

Secondly is there any other way(apart from actuating the joint using a motion or force) that I can use to impart this acceleration input to my multibody model? I just need to excite my body with the acceleration signal. Looking forward to hearing from you.

The problem is that I only have the acceleration measured and not the velocity and position.