I tried to simulate such a model on the basis of a standing model of AMMR1.1:
with applying 20lbs load on the two hands, a standing man push the loads upward. the man’s shoulder flexion/extension angles from 88 to 92 degrees, shoulder abduction angles from -2 to 2 degrees. No more movement.
I created a text file to input the angles of shoulder abduction, shoulder flexion, and shoulder external rotation in 3 columns, with the first column of time data.
Please have a look at my model.
When I run the kinematic analysis, two waring messages appeared “Arm/Interface.any : GHMeasure : Close to singular position : Orientation close to Gimbal Lock, i.e., first and third axis of rotation being parallel”.
Finally, the Kinematic analysis failed in time step 5.
My questions are:
(1) Was I correct to apply the loads to the hands as external loads in the Mannequin file?
(2) How to deal with the problems happened to the kinematic analysis? Was it because of my data? or anything else?
Thanks in advance for your generous help!
I almost solved the model. But I still got this warning message:
GHMeasure : Close to singular position : Orientation close to Gimbal Lock, i.e., first and third axis of rotation being parallel
I can still complete the inverse dynamic analysis finally. Do I have to solve this GHMeasure problem?
For the output, I want to find the activity and force loaded on the neck muscles: sternocleidomastoid. But I found the activity of this muscle was very very small, 1.66e-016 (*100%), and Sternocleidomastoid.Fm was at most 3.68e-014 (Newton).
These values are too small. How can I modify the model to achieve my goal to analyze the external loading of Sternocleidomastoid muscle in the neck?
By the way, I applied the loads of 44.5 Newtons to each hand. The model will push/pull the loads upward/downward, with shoulder flexion (88 to 92 degrees), shoulder abduction (-2 to 2 degrees), Elbow flexion (90 degrees).
I want to analyze the loading for theses muscles: Sternocleidomastoid (on the neck), and upper trapezius muscles on the shoulder-arm part.
How to achieve my goal of analysis?
To your first questions: yes the loads are correctly applied via the mannequin file, it is the right way to do it.
About the gimbal lock i am not going to try a long explanation (you can surely find a better one in wikipwdia), but it is a singularity in the rotational measure that appears for a certain position. So this is due to the motion you input, and guess you solved it by changing slightly the motion.
If the warning about the gimbal lock being close still appears, it is not really a problem as long as the lock does not actually occurs. So you can leave it like this if the simulation runs.
And concerning the neck i think most of them are simply not loaded by this particular load case. You would need the have some load applied to the head or the neck more directly to see a more obvious activation of those muscles.
Best regards, Sylvain.