How to accurately link a parallel configuration with dummy?

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gloria7@scuthahaha
Posts: 4
Joined: 15 Oct 2017, 10:01

How to accurately link a parallel configuration with dummy?

Post by gloria7@scuthahaha » 20 Mar 2018, 16:50

Hello:

I'm figuring out a parallel configuration as a shoulder part of a robotic arm. And I read that the v-rep contain the inverse kinematics modules, just export the STL model into the v-rep scene and fix the physical structure and assembly tree correctly, then add the dummy into the end of the tree and you can get the model works well.
But things didn't work as I put the inverse tip-target into my model, and the model link is :https://drive.google.com/open?id=1rsK4A ... tMI83okiLi.
There are 3 questions:
1, As my model is a 3-DoF configuration, only the under part of gear can moving passively and other joint should run as the restraint of the model, but as I run the simulation, it works only to the gear part and other joint didn't run.
2, How to assemble the parallel configuration? I choose to make the upper platform under the gear3 chain and use tip-target to restraint the model but it didn't works well.
3, My system is macOS so I cannot use the vortex or video record tools in 3.5.0 version, is there any resolution to solve it?(but it actually not essential for I can use other applications to record the scene: >)

Thank you,
Gloria

coppelia
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Posts: 6497
Joined: 14 Dec 2012, 00:25

Re: How to accurately link a parallel configuration with dummy?

Post by coppelia » 21 Mar 2018, 11:36

Hello Gloria,

the link you provided is not public...

Cheers

gloria7@scuthahaha
Posts: 4
Joined: 15 Oct 2017, 10:01

Re: How to accurately link a parallel configuration with dummy?

Post by gloria7@scuthahaha » 22 Mar 2018, 07:28

Hello:

sorry , I didn't check the link. And the model link is https://drive.google.com/drive/folders/ ... sp=sharing,hope this link can work well.

cheers,
Gloria

coppelia
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Posts: 6497
Joined: 14 Dec 2012, 00:25

Re: How to accurately link a parallel configuration with dummy?

Post by coppelia » 26 Mar 2018, 07:44

You have to decide what kind of simulation you want to achieve: kinematic or dynamic. Be aware of the differences. Basically, with kinematics you'll achieve precise and exact calculation, while with dynamics, things will be slower, more wobbly and less precise, since things are resolved differently and by the physics engine (i.e. masses and inertias need to be taken into account, etc.).
I'd really go with a kinematics simulation. Have a look at this tutorial, and also the demo model Models/robots/non-mobile/ABB IRB 360.ttm for example.

Currently your model appears to be a kinematic model, but there are a few dynamically enabled parts which doesn't make sense.

Cheers

gloria7@scuthahaha
Posts: 4
Joined: 15 Oct 2017, 10:01

Re: How to accurately link a parallel configuration with dummy?

Post by gloria7@scuthahaha » 12 Apr 2018, 14:13

Hi, coppelia:

your resolution is very useful and I have solved the question of kinematic model I think.But there is an other question that as I reference to the model of irb360 in vrep, I read the control code of it and migrated it to my model. I didn't understand the usage of

Code: Select all

sim.rmlMoveToJointPositions(fkDrivingJoints,-1,currentAngVel,currentAngAccel,maxAngVel,maxAngAccel,maxAngJerk,{-80*math.pi/180,0*math.pi/180,0*math.pi/180},targetAngVel)
therefore, my model perform like this:
https://drive.google.com/open?id=1UDUz2 ... 4hsCoFi9HR
like the control code has effect on dummy but not my joint? And the inverse kinematic of my model still don't works.That's confused me so much.
Hope you can give me some instructions, many thanks.


Yours,
Gloria

coppelia
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Posts: 6497
Joined: 14 Dec 2012, 00:25

Re: How to accurately link a parallel configuration with dummy?

Post by coppelia » 16 Apr 2018, 06:32

So you have decided for a kinematic simulation. Now you need to decide whether you want IK, FK, or both.

With your mechanism, IK alone would be the simplest to implement (simply 3 kinematic branches that close at the end-effector or upper platform). FK is more complex since you will need a branched kinematic, a Y-type tree where the tree base comes from the bottom, and the two tree branches close at the bottom.
IK/FK is even more complex.
I highly recommend that you have a close look at how the demo model Models/robots/non-mobile/ABB IRB 360.ttm was made.

Cheers

gloria7@scuthahaha
Posts: 4
Joined: 15 Oct 2017, 10:01

Re: How to accurately link a parallel configuration with dummy?

Post by gloria7@scuthahaha » 17 Apr 2018, 09:28

Hi Coppelia:
Yes, I want to develop a kinematic simulation. Thanks for your reply so I decided to do the inverse solution first. But the question is that when I start the simulation ,it will report the error that :
Lua runtime error: [string "CHILD SCRIPT target1"]:38: Object not tagged for explicit handling. (sim.handleIkGroup)
stack traceback:
[C]: in function 'handleIkGroup'
[string "CHILD SCRIPT target1"]:38: in function <[string "CHILD SCRIPT target1"]:15>
So I think the question is my ik-tip group I set was wrong. (but I have already look at the model of irb360 and learn the link method of it)And my supervisor suggest me to write the Jacobin matrix by myself and do the inverse kinematic model on my own. So is there any example to write the inverse kinematic script?

Yours,
Gloria

coppelia
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Posts: 6497
Joined: 14 Dec 2012, 00:25

Re: How to accurately link a parallel configuration with dummy?

Post by coppelia » 17 Apr 2018, 17:19

Did you check out this tutorial?

Cheers

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