Add collission geometry to prismatic joint

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Hey all,
I need to add collision meshes to my robot which has one prismatic degree of freedom.
Is there any possibility to add a colission Mesh to the Body that "expands" with the prismatic joint. If I add one to the corresponding body it cannot cover the whole arm when it is extended.
Any Ideas or workarounds are welcome, thanks in advance!!
Yours,
Lukas
  2 Comments
Lukas Schroth
Lukas Schroth on 2 May 2022
Hi Karsh,
Yes exactly, or another possibility to use colission checking in case of an prismatic joint.

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Answers (1)

Karsh Tharyani
Karsh Tharyani on 2 May 2022
Edited: Karsh Tharyani on 2 May 2022
Hi Lukas,
A rigid body, by definition, can't deform, hence it doesn't have a deformable collision geometry. A prismatic joint (specified via a "rigidBodyJoint") defines a constraint on the relative motion between two bodies, and doesn't actually hold a collision geometry.
You can add a collision geometry on a body, and self-collisions will be ignored between bodies on adjacent indices. Please refer to the following example which demonstrates planning for a rigid body tree with a prismatic and a revolute joint using "manipulatorRRT".
%% An example rigid body tree
rbt=twoJointRigidBodyTree("row");
body2=getBody(rbt,"body2");
prismaticjnt=rigidBodyJoint("j1","prismatic");
prismaticjnt.JointAxis=[1,0,0];
setFixedTransform(prismaticjnt,trvec2tform([0.5,0,0]));
replaceJoint(rbt,"body2",prismaticjnt);
addCollision(body2,"cylinder",[0.01,0.5],trvec2tform([0.25,0,0])*eul2tform([0,pi/2,0]));
body1=getBody(rbt,"body1");
addCollision(body1,"cylinder",[0.01,0.5],trvec2tform([0.25,0,0])*eul2tform([0,pi/2,0]));
show(rbt,"Collisions","on");
%% Add an obstacle to the environment
sphere=collisionSphere(0.1);
sphere.Pose=trvec2tform([0.7,0.7,0.1]);
env={sphere};
%% Plan between two joint configurations
planner=manipulatorRRT(rbt,env);
plannedpath=plan(planner,[0,0],[pi/2,-0.5]);
interpolatedPlan=interpolate(planner,plannedpath);
%% Visualize planned path
hold on;
show(env{1});
view([0,90])
for i = 1:size(interpolatedPlan,1)
show(rbt,interpolatedPlan(i,:),"Collisions","on","FastUpdate",true,"PreservePlot",false);
drawnow;
end
hold off;
I hope the above answers your query.
If you have a specific use case where deformable collision geometries are required, please don't hesitate to reach Technical Support and share your use case.
Best,
Karsh

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