Trying to simulate Schunk SVH fingers

asked 2020-06-05 04:03:04 -0500

CharlieMAC gravatar image

Hello Everone,

I´m trying to simulate the dynamics of the Schunk SVH Hand using OpenModelica, but considering the motors and all the mechanical components, which can be seen without opening the hand. Unfortunately, I´m not very convinced about the results of the current signals.

In the controller_user.yaml file from the ROS driver, there´s a quite detailed explanation for every single value of the config file, but there are a couple of things I´m not quite sure. First, the tick to rad conversion. This is a value that is used to convert the encoder ticks into usable radian values. How should I use this value in a simulation? Should I ignore it? Since the angular sensors in OpenModelica only output values in degrees or radians, I´m not sure what to do.

The second issue is the feedback scaling of the internal current controllers, with a value of 0.405. Multiplying the measured signal by this value has no apparent influence on the magnitude of the current signal. Actually, I get really small current values (micro Amps), which are not consistent with reality.

The third issue is the value of the derivative gain for the position controller. This value ranges from 100 to 2000, which is extremely high and produces unstable response on both the position and the current signals. If I reduce this value to 0.4 or fewer, the output is more consistent. Does this value contain units that I´m ignoring here?

Last but not least. Is there a filter connected to the H-Bridge in order to output continuous DC voltage to the motors?

Thanks in advance!


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Just some expectation management: you're asking some pretty in-depth questions about a relatively old piece of hw. Most users are happy the ROS driver exists, exactly so they don't have to bother themselves with the kinds of details you're asking questions about.

I'm not implying you won't get any answers, but it could take a while before someone who happens to know these kinds of things about the SVH visits ROS Answers, finds your question and then posts an answer.

gvdhoorn gravatar image gvdhoorn  ( 2020-06-05 04:27:05 -0500 )edit