Problem with ikine()

[Jaskeerat Singh]

Hello everyone

I , Jaskeerat Singh , is an undergraduate student at the Indian Institute of Technology, Kanpur (IIT Kanpur, India). This summers , I am doing a summer project at my institute in which I am working with the toolbox developed by you.

I am having problem with using the function ikine().

Given below is the code I wrote:

l1=Link('d',0,'a',1,'alpha',pi/2);

l2=Link('d',0,'a',1,'alpha',pi/2);

l3=Link('d',0,'a',1,'alpha',pi/2);

l4=Link('d',0,'a',1,'alpha',pi/2);

l5=Link('d',0,'a',1,'alpha',pi/2);

l6=Link('d',0,'a',1,'alpha',pi/2);

bot=SerialLink([l1 l2 l3 l4 l5 l6],'name','jas');

Q1=[1 1 1 1 1 1];

T1=bot.fkine(q1);

Q2=bot.ikine(T1);

The errors I get are:-

Warning: Initial joint angles results in near-singular configuration, this may slow convergence 

> In SerialLink.ikine at 152 

Warning: solution diverging at step 3, try reducing alpha 

> In SerialLink.ikine at 257 

Warning: solution diverging at step 6, try reducing alpha 

> In SerialLink.ikine at 257 

Warning: solution diverging at step 10, try reducing alpha 

> In SerialLink.ikine at 257 

Warning: solution diverging at step 16, try reducing alpha 

> In SerialLink.ikine at 257 

Warning: solution diverging at step 21, try reducing alpha 

> In SerialLink.ikine at 257 

Warning: solution diverging at step 30, try reducing alpha 

> In SerialLink.ikine at 257 

Warning: solution diverging at step 33, try reducing alpha 

> In SerialLink.ikine at 257 

Warning: solution diverging at step 37, try reducing alpha 

> In SerialLink.ikine at 257 

Warning: solution diverging at step 43, try reducing alpha 

> In SerialLink.ikine at 257 

Warning: solution diverging at step 45, try reducing alpha 

> In SerialLink.ikine at 257 

Warning: solution diverging at step 64, try reducing alpha 

> In SerialLink.ikine at 257 

Warning: solution diverging at step 79, try reducing alpha 

> In SerialLink.ikine at 257 

Error using tr2angvec (line 48)

matrix not orthonormal rotation matrix

Error in SerialLink/ikine (line 187)

            [th,n] = tr2angvec(Rq'*t2r(T));

I am attaching a screen shot of the errors.

Please help me , as I cannot move further in my project without solving this error.

Hoping for your response.

Jaskeerat Singh

IIT Kanpur

India

[Arthur]

Hello Jaskeerat Singh,

I was not also able to get a solution without a better initial guess.

try a better guess like [.6 .6 .6 .6 .6 .6]

then i am getting 

ikine(bot, T1,'pinv' ,q1*0.6, 'verbose')

Warning: Initial joint angles results in near-singular configuration, this may slow convergence 

> In SerialLink.ikine at 139 

Warning: solution diverging, try reducing alpha 

> In SerialLink.ikine at 230 

15 iterations

ans =

    1.0002    1.0000    1.0003    0.9997    1.0000    0.9998

ikine tries to find the solution iteratively, but there is no guarantee to find a solution.

Arthur

[Jaskeerat Singh]

Thank you Arthur for taking out time to comment.

 

But when I tried the following command:- 

ikine(bot, T1,'pinv' ,q1*0.6, 'verbose')

It gave me errors shown below:

Warning: Initial joint angles results in near-singular configuration, this may slow

convergence 

> In SerialLink.ikine at 152 

Error using tr2angvec (line 48)

matrix not orthonormal rotation matrix

Error in SerialLink/ikine (line 187)

            [th,n] = tr2angvec(Rq'*t2r(T));

What should I do now ?

[Arthur]

Hello,

I am using the ikine version from the Robotics Toolbox 9.8. I think you are using the Robotics Toolbox 9.9.

Just copy ikine.m from RT9.8 into rvctools\robot\@SerialLink from RT9.9 and try again.

Arthur