Erwin,

Thanks for this information and I'll take a look at iTasc.

Joe

On Thu, Oct 25, 2012 at 8:55 AM, Erwin Aertbelien <
Erwin [dot] Aertbelien [..] ...> wrote:

> On 10/25/2012 02:04 PM, Joe Hays wrote:
>
>> The question is general. As a perspective user, I'd like to be able to
>> have insight to the algorithms behind any library I am considering.
>> Educate the user and then let them decide if it fits for their
>> application or not. Today's needs may not be tomorrows needs. My $.02.
>>
>
> In theory, this sounds fine, in practice, it is good to know what we are
> talking about.
>
>
>
>> Having said that, my current needs are to see if KDL's inverse
>> kinematics can provide a redundant spacial serial manipulator's complete
>> joint trajectory (position, velocity and acceleration) when given a
>> trajectory of the end-effector in Cartesian space (6D in my case).
>>
>
> This is a not completely determined problem, and in order to solve the
> redundant kinematics, you have to implicitly or explicitly assume
> other optimisation criteria to solve it.
>
> As it is, KDL offers basic computational classes that can be used
> to solve the kinematics in this case.
> One way to solve this problem is to use one of the inverse velocity
> kinematic solvers ( chainiksolvervel_xxxx ) and to integrate
> the results to position.
> (i.e. "resolved motion rate control")
>
>
> Looking at the KDL API it appears that only the positions are returned
>> from the algorithm. Is this because of an API definition? Or, because of
>> the selected algorithm?
>>
>> I'd like to see if KDL can generate the needed joint position, velocity,
>> and acceleration inputs for a computed torque controller. I can always
>> differentiate the positions twice but that isn't necessarily the wisest
>> approach when other algorithms can provide them for you.
>>
> Oh... This makes the answer above only partially relevant.
> ( you see: it really depends on the use case...)
>
> For the moment, we do not have inverse acceleration kinematics in KDL,
> which is what you would do in these instances.
>
> There are inverse dynamics algorithm in KDL ( on of them implemented by
> Azamat, included in CC). But what you'll need, it probably depends on the
> exact computed torque control scheme that you choose.
>
> Note that starting from a fully specified Cartesian path is not always
> recommended. Often, to perform a robot task, only some contraints
> need to be specified, and not the whole Cartesian path of the end
> effector. Also, people want to have more control over how to optimize
> the redundant degrees of freedom.
> The iTasc framework ( http://www.orocos.org/wiki/**orocos/itasc-wiki<http://www.orocos.org/wik...) can solve for such specifications. (built on top of other parts of
> Orocos, such as RTT, KDL). Please note that this is tightly integrated
> with Orocos-RTT ( and rFSM, ...)
>
>
>
>> Joe
>>
>> On Thu, Oct 25, 2012 at 7:44 AM, Erwin Aertbelien
>> <Erwin.Aertbelien@mech.**kuleuven.be <Erwin [dot] Aertbelien [..] ...>
>> <mailto:Erwin.Aertbelien@mech.**kuleuven.be<Erwin [dot] Aertbelien [..] ...>>>
>> wrote:
>>
>> On 10/25/2012 01:39 PM, Joe Hays wrote:
>>
>> All,
>>
>> I'm new to Orocos and am considering use of KDL, however, I've
>> worked
>> through much of the documentation and have been unable to
>> determine the
>> algorithms used. For example, I'm trying to determine what inverse
>> kinematics algorithm is used.
>>
>> To what type of inverse kinematics are you referring ?
>>
>> Inverse velocity kinematics ?
>>
>> For what purpose do you want to use the kinematics ?
>>
>>
>>
>> Somewhere in the docs I saw it described
>>
>> as an "iterative" method. I'd like to know which one as they all
>> have
>> their strengths and weaknesses. There doesn't appear to be any
>> information on this topic in the group's listserv archive as well.
>>
>> Are there any resources available that can elaborate on the
>> algorithms
>> implemented in KDL? A list of papers or books would be best so
>> users can
>> clearly understand what the library is offering.
>>
>> Thanks,
>>
>> Joe
>>
>>
>>
>>
>>
>

On Thu, 25 Oct 2012, Erwin Aertbelien wrote:

[...]
>> I'd like to see if KDL can generate the needed joint position, velocity,
>> and acceleration inputs for a computed torque controller. I can always
>> differentiate the positions twice but that isn't necessarily the wisest
>> approach when other algorithms can provide them for you.
> Oh... This makes the answer above only partially relevant.
> ( you see: it really depends on the use case...)
>
> For the moment, we do not have inverse acceleration kinematics in KDL,
> which is what you would do in these instances.
>
> There are inverse dynamics algorithm in KDL ( on of them implemented by
> Azamat, included in CC).

And that one computes joint accelerations (as a byproduct).

Herman

> But what you'll need, it probably depends on
> the exact computed torque control scheme that you choose.
>
> Note that starting from a fully specified Cartesian path is not always
> recommended. Often, to perform a robot task, only some contraints
> need to be specified, and not the whole Cartesian path of the end
> effector. Also, people want to have more control over how to optimize
> the redundant degrees of freedom.
> The iTasc framework ( http://www.orocos.org/wiki/orocos/itasc-wiki ) can
> solve for such specifications. (built on top of other parts of Orocos,
> such as RTT, KDL). Please note that this is tightly integrated
> with Orocos-RTT ( and rFSM, ...)
>
>
>>
>> Joe
>>
>> On Thu, Oct 25, 2012 at 7:44 AM, Erwin Aertbelien
>> <Erwin [dot] Aertbelien [..] ...
>> <mailto:Erwin [dot] Aertbelien [..] ...>> wrote:
>>
>> On 10/25/2012 01:39 PM, Joe Hays wrote:
>>
>> All,
>>
>> I'm new to Orocos and am considering use of KDL, however, I've
>> worked
>> through much of the documentation and have been unable to
>> determine the
>> algorithms used. For example, I'm trying to determine what inverse
>> kinematics algorithm is used.
>>
>> To what type of inverse kinematics are you referring ?
>>
>> Inverse velocity kinematics ?
>>
>> For what purpose do you want to use the kinematics ?
>>
>>
>>
>> Somewhere in the docs I saw it described
>>
>> as an "iterative" method. I'd like to know which one as they all
>> have
>> their strengths and weaknesses. There doesn't appear to be any
>> information on this topic in the group's listserv archive as well.
>>
>> Are there any resources available that can elaborate on the
>> algorithms
>> implemented in KDL? A list of papers or books would be best so
>> users can
>> clearly understand what the library is offering.
>>
>> Thanks,
>>
>> Joe
>>
>>
>>
>>
>