Re: regarding Constraints of my arm configuration

I have calculated the inverse kinematics for my 5 DOF robotic arm. I want to
know that is it necessary to calculate the differential kinematics and
dynamics for the same. I want to make it run through Orocos 0.20.


On 6/15/06, Erwin Aertbelien <[email protected]> wrote:
>
> This type of robot is not used for completely general robot tasks, but for
> task that only need 5 d.o.f. e.g. tasks with a rotation symmetric tool
> (like
> a grinding disk).
>
> Kinematics for this are not provided in Orocos.
>
> There are two problems to solve :
> (1) solving the inverse kinematics.
>         -For your type of robot there still exists a closed form
> solution.:
>                 - out of the specified orientation you can determine the
> POSITION of the
> intersection between axes 4 and 5.
>                 - This position determines the first three axes.
>                 - Once the first three axes are determined, you can
> determine the two last.
> (2) Specification :
>         you have to specify your task in 5 dof task space.
>         I know of two ways to do this :
>                 - using a 6 dof frame specification, and ignore a degree
> of freedom (e.g.
> rotation around X-axis).
>                 - using a 5-d.o.f. specification, like in Numerical
> Control (NC) milling
> machines :
>                         * position (3)
>                         * two direction cosinuses A and B,
>                    i.e. your 2 dof orientation can be specified with a
> normalized vector.
> The projection of this vector in some plane are A and B.
>         This choice of specification is important because it will
> determine your
> ability to cooperate with other components.
>
> Best regards,
> Erwin
>
>
> On Thursday 15 June 2006 07:28, H.S. Randhawa wrote:
> > I mailed yesterday regarding the configuration which is littlebit
> different
> > from Serial 321 configuration.
> > In this configuration the following spec. along with motor rotation are
> > there:
> >
> > LINK                 LENGTH           MOTOR (rotation angle)
> > Rotation axis(according to OROCOS)
> >                                                   [ Counter-Clockwise
> +ve ]
> >
> > BASE              3"                       0-180 Degree
> >       Z
> >
> > SHOULDER     4.75"                  0-180 Degree
> > X
> >
> > ELBOW           4.75"                  -150  to  +30 Degree
> > X
> >
> > WRIST            5.75"                  -90   to
> > 90                             parallel to Shoulder and elbow
> >
> > WRIST ROTATION -----             -90  to 90
> > Perpendicular to Wrist.
> >
> > GRIPPER                               opening 2" max.
> > Perpendicular to both wrist and wristRotation axes.
> >
> >
> >
> > The serial family has six *revolute* joints: a "wrist" with *three*
> > revolute joints with intersecting axes; an "arm" with *two* parallel
> axes;
> > and a "shoulder" with *one* revolute joint whose axis is orthogonal to
> the
> > axes of the "arm" set. but my arm is having three axes parallel (2nd,
> 3rd
> > and 4th) and more over  last three are  not intersecting  at a point.
> Only
> > 4th and 5th are intersecting. Sixth is at some offset of 2.2" from that
> > intersecting point.
> >
> > As this is not exactly a 6 DOF arm Its a 5 + gripper but still if we
> ignore
> > the last joint and want to move it through desire points, it should move
> > accordingly.
> > For some given point which is already in its workspace, Orocos is
> > calculating joint positions (radians) which are contradicting with motor
> > constraints so robot can't move to that point. eg  -ve value for base,
> or
> > some other value which is out of range for that particular joint motor.
> > How it can be resolved?
> >
> > Thanks
> > H.S.Randhawa
>
>
>
> Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm
>
>


-- 
H.S.Randhawa

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