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Interpreting the angle values for each hand segment

DWQA Questions › Category: KINARM End-Point Lab › Interpreting the angle values for each hand segment

Yokhesh Krishnasamy Tamilselvam asked 3 years ago

Hi, I am using KINARM end point robot. I would like to obtain the elbow joint angles as the participant uses the KINARM. I found out that arm has been divided into segments and their angles are provided in global coordinates. I was not sure how to interpret these values. How are these angles measured ? Is there a motion capture in KINARM that gets the arm movement and give out the angles for each segment? The reason i am asking this question is that there are more than one arm movement that can be done to get to a target. How does the KINARM capture the arm segment angles? For instance, if i am performing the same task twice, Would the KINARM provide different angle values if i reach the same target location in both the instances with varying joint movements? The first time i can get to target just by moving my elbow joint and the second time, i can get to the target by moving my shoulder joint. In this case, the angle for each segment would be different in each instance. Can the KINARM capture these differences and provide the corresponding angle data for each segment? My second question is that how can we extract the joint angles from the angle values provided for each arm segment? Basically, i need the angle values for the elbow and shoulder joint as the participant performs the task. Please let me know. Thank you, Yokhesh

3 Answers

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Duncan McLean Staff answered 3 years ago

Hello Yokhesh, When using the End-Point robot we do not capture any of the subject's joint angles, that can only be done with an Exo-skeleton robot. The segment angles stored in data files are all for the robot's joints. I know of one group that tried to put motion capture together with an End-Point robot. This can be tricky because of the VR stand obscuring the view of the arms. Duncan

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Duncan McLean Staff answered 3 years ago

Hi Yorkesh,

In Dexterit-E Explorer, in the list of available kinematics there is a line that says "Derived channels". Everything below that line are values we calculate when the file is loaded, everything above that line is data saved in the exam file.

Shoulder and elbow angles for Exoskeleton data (again, for End-Point robots this does not make sense) are:

Right_ShoAng = Right_L1Ang;
Right_ElbAng = Right_L2Ang - Right_L1Ang;

Left_ShoAng = pi - Left_L1Ang;
Left_ElbAng = -1* (Left_L2Ang - Left_L1Ang);

This definition matches the shoulder and elbow angles that are available in a running task as part of the KINdata_bus. That is to say, these are outer shoulder and outer elbow angles. Running this task will show you exactly what these angles mean:

https://kinarm.com/download/robot-data-visualization-demo/

All the best,
Duncan

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Yokhesh Krishnasamy Tamilselvam answered 3 years ago

Hi Duncan, Thanks for the response. I am able to see the parameters indicating the elbow and shoulder angle values in the Dexterit explorer under derived channels. But, when i extract them and open the same zip file in MATLAB for processing, i am not able to find the elbow and shoulder angle values. I am able to find other values like force, torque, position values in MATLAB. But, i am just not able to find the elbow and shoulder angle values in MATLAB after extracting the same zip file. Why is it i can see these values only in Dexterit explorer and not in MATLAB? In fact, i am opening the exact same file in both dexterit explorer and MATLAB. Please let me know. Regards, Yokhesh

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