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manipulatorCollisionBodyValidator

Validate states for collision bodies of rigid body tree

    Description

    The manipulatorCollisionBodyValidator object performs state and motion validity checks for a rigid body tree robot model. To check if the collision bodies collide either with other bodies (self-collisions) or the environment, use the isStateValid object function. To check if a motion between two states is valid, use the isMotionValid object function.

    Creation

    Description

    manipSV = manipulatorCollisionBodyValidator creates a state validator with default values for a manipulatorStateSpace object.

    example

    manipSV = manipulatorCollisionBodyValidator(ss) creates a state validator for a manipulatorStateSpace object that represents a robot model state space and contains collision bodies for rigid body elements. Specify ss as a manipulatorStateSpace object.

    manipSV = manipulatorCollisionBodyValidator(ss,Name=Value) specifies Properties as name-value arguments

    Properties

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    Distance resolution for motion validation, specified as a positive scalar. The validation distance determines the number of interpolated states between states specified to the isMotionValid object function. The object function validates each interpolated state by checking for collisions with the robot and the environment.

    Data Types: double

    Ignore self collisions toggle, specified as a logical. If this property is set to true, the isMotionValid object function skips checking between bodies for collisions and only compares the bodies to the environment. Not checking for self-collisions can improve the speed of the planning phase, but your state space should contain joint limits that ensure self-collisions are not possible.

    Data Types: logical

    Collision objects in the robot environment, specified as a cell array of collision objects of these types:

    box = collisionBox(0.1,0.1,0.5); % XYZ Lengths
    box.Pose = trvec2tform([0.2 0.2 0.5]); % XYZ Position
    sphere = collisionSphere(0.25); % Radius
    sphere.Pose = trvec2tform([-0.2 -0.2 0.5]); % XYZ Position
    env = {box sphere};
    manipSS = manipulatorCollisionBodyValidator(ss,Environment=env);

    Data Types: logical

    Manipulator state space, specified as a manipulatorStateSpace object, which is a subclass of nav.StateSpace (Navigation Toolbox).

    Object Functions

    isStateValidCheck if state is valid
    isMotionValidCheck if path between states is valid

    Examples

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    Generate states to form a path, validate motion between states, and check for self-collisions and environmental collisions with objects in your world. The manipulatorStateSpace object represents the joint configuration space of your rigid body tree robot model, and can sample states, calculate distances, and enforce state bounds. The manipulatorCollisionBodyValidator object validates the state and motion based on the collision bodies in your robot model and any obstacles in your environment.

    Load Robot Model

    Use the loadrobot function to access predefined robot models. This example uses the Quanser QArm™ robot and joint configurations are specified as row vectors.

    robot = loadrobot("quanserQArm",DataFormat="row");
    figure(Visible="on")
    show(robot);
    xlim([-0.5 0.5])
    ylim([-0.5 0.5])
    zlim([-0.25 0.75])
    hold on

    Figure contains an axes object. The axes object contains 16 objects of type patch, line. These objects represent world, base_link, YAW, BICEP, FOREARM, END-EFFECTOR, base_link_mesh, YAW_mesh, BICEP_mesh, FOREARM_mesh, END-EFFECTOR_mesh.

    Configure State Space and State Validation

    Create the state space and state validator from the robot model.

    ss = manipulatorStateSpace(robot);
    sv = manipulatorCollisionBodyValidator(ss);

    Set the validation distance to 0.05, which is based on the distance normal between two states. You can configure the validator to ignore self collisions to improve the speed of validation, but must consider whether your robot model has the proper joint limit settings set to ensure it does not collide with itself.

    sv.ValidationDistance = 0.05;
    sv.IgnoreSelfCollision = true;

    Place collision objects in the robot environment. Set the Environment property of the collision validator object using a cell array of objects.

    box = collisionBox(0.1,0.1,0.5); % XYZ Lengths
    box.Pose = trvec2tform([0.2 0.2 0.5]); % XYZ Position
    sphere = collisionSphere(0.25); % Radius
    sphere.Pose = trvec2tform([-0.2 -0.2 0.5]); % XYZ Position
    env = {box sphere};
    sv.Environment = env;

    Visualize the environment.

    for i = 1:length(env)
        show(env{i})
    end
    view(60,10)

    Figure contains an axes object. The axes object contains 18 objects of type patch, line. These objects represent world, base_link, YAW, BICEP, FOREARM, END-EFFECTOR, base_link_mesh, YAW_mesh, BICEP_mesh, FOREARM_mesh, END-EFFECTOR_mesh.

    Plan Path

    Start with the home configuration as the first point on the path.

    rng(0); % Repeatable results
    start = homeConfiguration(robot);
    path = start;
    idx = 1;

    Plan a path using these steps, in a loop:

    • Sample a nearby goal configuration, using the Gaussian distribution, by specifying the standard deviation for each joint angle.

    • Check if the sampled goal state is valid.

    • If the sampled goal state is valid, check if the motion between states is valid and, if so, add it to the path.

    for i = 2:25
        goal = sampleGaussian(ss,start,0.25*ones(4,1));
        validState = isStateValid(sv,goal);
        
        if validState % If state is valid, check motion between states.
            [validMotion,~] = isMotionValid(sv,path(idx,:),goal);
    
            if validMotion % If motion is valid, add to path.
                path = [path; goal];
                idx = idx + 1;
            end
        end
    end

    Visualize Path

    After generating the path of valid motions, visualize the robot motion. Because you sampled random states near the home configuration, you should see the arm move around that initial configuration.

    To visualize the path of the end effector in 3-D, get the transformation, relative to the base world frame at each point. Store the points as an xyz translation vector. Plot the path of the end effector.

    eePose = nan(3,size(path,1));
    
    for i = 1:size(path,1)
        show(robot,path(i,:),PreservePlot=false);
        eePos(i,:) = tform2trvec(getTransform(robot,path(i,:),"END-EFFECTOR")); % XYZ translation vector
        plot3(eePos(:,1),eePos(:,2),eePos(:,3),"-b",LineWidth=2)
        drawnow
    end

    Figure contains an axes object. The axes object contains 28 objects of type patch, line. These objects represent world, base_link, YAW, BICEP, FOREARM, END-EFFECTOR, base_link_mesh, YAW_mesh, BICEP_mesh, FOREARM_mesh, END-EFFECTOR_mesh.

    Introduced in R2021b