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Check for Environmental Collisions with Manipulators

Generate a collision-free trajectory in a constrained workspace.

Define an environment

You can create a simple environment using collision primitives. For example, suppose the robot is in a workspace where the aim is to move objects from one table to another while avoiding a circular light fixture. These objects can be modeled as two boxes and a sphere. More complex environments can be created using collisionMesh objects.

% Create two platforms
platform1 = collisionBox(0.5,0.5,0.25);
platform1.Pose = trvec2tform([-0.5 0.4 0.2]);

platform2 = collisionBox(0.5,0.5,0.25);
platform2.Pose = trvec2tform([0.5 0.2 0.2]);

% Add a light fixture, modeled as a sphere
lightFixture = collisionSphere(0.1);
lightFixture.Pose = trvec2tform([.2 0 1]);

% Store in a cell array for collision-checking
worldCollisionArray = {platform1 platform2 lightFixture};

Visualize the environment using a helper function that iterates through the collision array.

exampleHelperVisualizeCollisionEnvironment(worldCollisionArray);

Add a manipulator robot

Add a Kinova manipulator to the environment at the origin. Load the provided robot model. Visualize the obstacles and show the robot in the same figure.

robot = loadrobot("kinovaGen3","DataFormat","column","Gravity",[0 0 -9.81]);
ax = exampleHelperVisualizeCollisionEnvironment(worldCollisionArray);
show(robot,homeConfiguration(robot),"Parent",ax);

Model the manipulator as an array of collision objects

Create an array of collision objects from the rigidBodyTree object. This approach uses an example helper, exampleHelperManipCollisionsFromVisuals, that extracts the meshes from the first visual in each rigidBody object. For an overview of other approaches, refer to Create Collision Objects for Manipulator Collision Checking.

% Generate an array of collision objects from the visuals of the associated tree
collisionArray = exampleHelperManipCollisionsFromVisuals(robot);

Generate a trajectory and check for collisions

Define a start and end pose as position and orientation. Use inverseKinematics to solve for the joint positions based on the desired poses. Inspect manually to verify that the configurations are valid.

startPose = trvec2tform([-0.5,0.5,0.4])*axang2tform([1 0 0 pi]);
endPose = trvec2tform([0.5,0.2,0.4])*axang2tform([1 0 0 pi]);

% Use a fixed random seed to ensure repeatable results
rng(0);
ik = inverseKinematics("RigidBodyTree",robot);
weights = ones(1,6);
startConfig = ik("EndEffector_Link",startPose,weights,robot.homeConfiguration);
endConfig = ik("EndEffector_Link",endPose,weights,robot.homeConfiguration);

% Show initial and final positions
show(robot,startConfig);
show(robot,endConfig);

Use a trapezoidal velocity profile to generate a smooth trajectory from the home position to the start position, and then to the end position. Use collision checking to see whether this results in any collisions.

q = trapveltraj([homeConfiguration(robot),startConfig,endConfig],200,"EndTime",2);

%Initialize outputs
isCollision = false(length(q),1); % Check whether each pose is in collision
selfCollisionPairIdx = cell(length(q),1); % Provide the bodies that are in collision
worldCollisionPairIdx = cell(length(q),1); % Provide the bodies that are in collision

for i = 1:length(q)
    [isCollision(i),selfCollisionPairIdx{i},worldCollisionPairIdx{i}] = exampleHelperManipCheckCollisions(robot,collisionArray,worldCollisionArray,q(:,i),false);
end
isTrajectoryInCollision = any(isCollision)
isTrajectoryInCollision = logical
   1

Inspect the Problem Cases

By inspecting the collisions, there are 2 collisions occurring. Visualize these configurations to investigate further.

problemIdx1 = find(isCollision,1);
problemIdx2 = find(isCollision,1,"last");

% Identify the problem rigid bodies
problemBodies1 = [selfCollisionPairIdx{problemIdx1} worldCollisionPairIdx{problemIdx1}*[1 0]'];
problemBodies2 = [selfCollisionPairIdx{problemIdx2} worldCollisionPairIdx{problemIdx2}*[1 0]'];

% Visualize the environment
ax = exampleHelperVisualizeCollisionEnvironment(worldCollisionArray);

% Add the robots & highlight the problem bodies
show(robot,q(:,problemIdx1),"Parent",ax,"PreservePlot",false);
exampleHelperHighlightCollisionBodies(robot,problemBodies1,ax);
show(robot,q(:,problemIdx2),"Parent"',ax);
exampleHelperHighlightCollisionBodies(robot,problemBodies2,ax);

Generate a Collision-Free Trajectory using Intermediate Waypoints

To avoid these collisions, add intermediate waypoints to ensure the robot navigates around the obstacle.

intermediatePose1 = trvec2tform([-.3 -.2 .6])*axang2tform([0 1 0 -pi/4]); % Out and around the sphere
intermediatePose2 = trvec2tform([0.2,0.2,0.6])*axang2tform([1 0 0 pi]); % Come in from above

intermediateConfig1 = ik("EndEffector_Link",intermediatePose1,weights,q(:,problemIdx1));
intermediateConfig2 = ik("EndEffector_Link",intermediatePose2,weights,q(:,problemIdx2));

% Show the new intermediate poses
ax = exampleHelperVisualizeCollisionEnvironment(worldCollisionArray);
show(robot,intermediateConfig1,"Parent",ax,"PreservePlot",false);
show(robot,intermediateConfig2,"Parent",ax);

Generate a new trajectory.

[q,qd,qdd,t] = trapveltraj([homeConfiguration(robot),intermediateConfig1,startConfig,intermediateConfig2,endConfig],200,"EndTime",2);

Verify that it is collision-free.

%Initialize outputs
isCollision = false(length(q),1); % Check whether each pose is in collision
collisionPairIdx = cell(length(q),1); % Provide the bodies that are in collision
for i = 1:length(q)
    [isCollision(i),collisionPairIdx{i}] = exampleHelperManipCheckCollisions(robot,collisionArray,worldCollisionArray,q(:,i),false);
end
isTrajectoryInCollision = any(isCollision)
isTrajectoryInCollision = logical
   0

Visualize the Generated Trajectory

Animate the result.

% Plot the environment
ax2 = exampleHelperVisualizeCollisionEnvironment(worldCollisionArray);

% Visualize the robot in its home configuration
show(robot,startConfig,"Parent",ax2);

% Update the axis size
axis equal

% Loop through the other positions
for i = 1:length(q)
    show(robot,q(:,i),"Parent",ax2,"PreservePlot",false);
    
    % Update the figure    
    drawnow
end

Plot the joint positions over time.

figure
plot(t,q)
xlabel("Time")
ylabel("Joint Position")