Problems with robot simulation

asked 2022-03-10 00:26:20 -0500

PumpkinIcedTea gravatar image

updated 2022-03-10 00:27:00 -0500

Hi guys, I'm having some problems with robot simulation that I hope I can get some help on.

Firstly, an introduction. I'm trying to simulate a pick and place robot that grabs a box from a table, moves to another location, and puts the box down. I've managed to get the grabbing done with position controllers but now I face some issues which I have been unable to solve.

Problem 1 : The box vibrates up and down whenever it is in contact with the robot. This happened ever since I changed the max step size from the default value of 0.001 to 0.005. So my previous settings were :

RTF = Max Step Size * Max Frequency Update Rate = 0.001 * 1000Hz = 1

But I had to lower the max frequency update rate as my room (it has a lot of boxes) was getting too complicated and I couldn't get the simulation to run in real time, hence I decreased the max update rate but had to up the max step size as a result. So my settings are now as such :

RTF = Max Step Size * Max Frequency Update Rate = 0.005 * 200Hz = 1

But ever since I did this, although I achieved real time factor of 1, the box started to vibrate violently whenever its on the table or sitting on the robot. Eventually, it just veers off and falls off the table/robot entirely. I think this has something to do with the ERP parameter since its physics related and I changed the physics parameters when I modified the step size. But no matter what value I put for the ERP the box still keeps vibrating.

Problem 2: Box cannot keep up with the robot's rotation Ok so I understand that this may be hard to visualize so picture it like this. Imagine I have a flat plate with a box on top. I rotate the flat plate and the box should rotate right ? If I move the plate forwards, the box should also move forward with the plate right ? But no, the box can't seem to stay in contact with the plate. It just slips off. I tried varying the friction between the box and the plate, setting them to extremely high values as well as lowering the rotational and linear speed of the plate, but the box still "slips".

Problem 3: Robot sways back and forth when grabbing box. So for this one the problem is that when the robot extends its arm to grab the box, it gets pushed backward a little. I suspect this has something to do with Newton's Law that for a force applied in any direction an opposite force will be applied in the opposite direction. So when the robot extends its arms to pick the box up, it gets pushed backwards a little. And when it brings the box back to its body, it moves forward a little. I tried increasing the friction between ... (more)

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first thing I would check is whether the inertia tensors of the objects are correct (the visualized inertia boxes should roughly be the same size as the object itself). Then I would try playing around with surface contact parameters kd and kp -> have a look at the answers of this question link

rfn123 gravatar imagerfn123 ( 2022-03-10 04:35:19 -0500 )edit