Question on the "Plan a Reaching Trajectory With Multiple Kinematic Constraints" example

Hi,

I'm learning this Mathworks' example code:

Plan a Reaching Trajectory With Multiple Kinematic Constraints - MATLAB & Simulink - MathWorks Italia

In this part of the code:

the TargetPoint is set equal to [0, 0, 100] (from constraintAiming's Documentation, that correspond to the "iiwa_link_ee" [x y z] axis)

The question is: Why 100? What this value means?

Thank you in advance!

Paolo Rosettani.

[Yiping Liu]

This aiming constraint is useful to keep the cup posed straight up as the arm moves with the cup in gripper (not an ideal use case for AimingConstarint, but OK with the aiming point very far away, the cup might tilt slightly as you move) However, the aiming constraint seems not really necessary here, as the example is to plan a reaching trajectory to the cup (the cup is not yet in the gripper).

[Paolo Rosettani]

Hi Yiping,

Thank for your answer!

In the following figure there is my robot with:

    alignWithCup = constraintAiming(EndEffector);
    alignWithCup.TargetPoint = [0, 0, 1]; %[x y z]

Where the EndEffector is the selected one in yellow (with z-axis pointing up)

what happened here? (my cup is just 0.30 m from the base)

Thank you in advance.

[Paolo Rosettani]

Here you have the code if you want to try it.

you can find the IK constraints inside the "CinematicaInv.m" function.

[Yiping Liu]

Try

alignWithCup.TargetPoint = [0, 0, 100]

Answer 1

[Karsh Tharyani]

Hi Paolo,

The purpose of providing this constraint is to ensure that the "iiwa_link_ee" frame's (or "EndEffector" body's) z-axis is almost parallel to robot's base's z-axis (note that when "ReferenceBody" is ' ' it implies that the body is the base).

Since the target point is defined with respect to the base of the robot ("ReferenceBody"), and is way above the origin of the base body's frame along the z-axis, the two z-axes are almost parallel. You could keep it 1000 or any high number to obtain a similar effect.

I hope that answers your question.

Best,

Karsh

[Denizhan AKINCI]

What if we want to keep another joint's y axis paralel to the base's y axis ? The constraintOrientationTarget will be the joint and ref body will be the base right? Then the targetPoint will be [0 100 0] ? That's the logic we follow here ?