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constraintDistanceBounds

Constrain body within distance bounds of reference body

Description

The constraintDistanceBounds object describes a constraint on the distance of one body (the end effector) relative to another body (the reference body) within the same rigidBodyTree. This constraint is satisfied if the distance, d, of the end effector origin relative to the reference body origin frame is within the specified bounds.

Creation

Description

example

distConst = constraintDistanceBounds(endeffector) returns a distance bounds constraint object, distConst, that represents a constraint on distance between the specified endeffector and the reference body specified by the ReferenceBody property.

distConst = constraintDistanceBounds(endeffector,Name=Value) specifies properties using one or more name-value arguments.

Properties

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Name of the end effector, specified as a string scalar or character vector. When using this constraint with a generalizedInverseKinematics solver, the name must match a body specified in the associated RigidBodyTree robot model.

Example: "left_palm"

Data Types: char | string

Name of the reference body frame, specified as a character vector or string scalar. The default '' indicates that the constraint is relative to the base of the robot model. When using this constraint with a generalizedInverseKinematics solver, the name must match a body specified in the associated RigidBodyTree robot model.

Example: "base"

Lower and upper distance bounds imposed on the end effector from the reference body, specified as a two-element row vector of the form [minimum maximum].

Example: [1 3]

Weight of the constraint, specified as a numeric scalar. This weight is used with the Weights property of all the constraints specified in generalizedInverseKinematics solver to properly balance each constraint.

Example: 2

Examples

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Create a constraintDistanceBounds object and observe its effect on an inverse kinematics solution.

Load Robot and Set Up Solver

Load a Universal UR5e robot into the workspace, and create a generalized inverse kinematics solver.

rng default;
robot = loadrobot("universalUR5e",DataFormat="column");
gik = generalizedInverseKinematics("RigidBodyTree",robot);

Set the constraint inputs distance for a distance bounds constraint, and position for the target constraint.

gik.ConstraintInputs = {'distance','position'};
gik.SolverParameters.MaxIterations = 100;

Create Distance Bounds Constraint

Create Distance Bounds constraint to constrain the origin of the end effector body, tool0, relative to the origin of the reference frame, base.

constrDist = constraintDistanceBounds("tool0",ReferenceBody="base");

Set the minimum distance between two bodies to 0.25 meters, and the maximum distance to 0.5 meters. This constraint prevents the inverse kinematics solver from solving for a configuration that violates the bounds.

minDist = 0.25;
maxDist = 0.5;
constrDist.Bounds = [minDist maxDist];

Constrain the first wrist link, wrist_1_link, to a target position to add some complexity.

forearmTgt = constraintPositionTarget('wrist_1_link');
forearmTgt.TargetPosition = [0.0 0.25 0.25];

Visualize Constraint

Run the solver through three random configurations, using the constraints, and then display the solver status. Each iteration, the solver finds a solution where the distance of the end effector is either equal to or within the specified bounds. Visualize the bounds by using the exampleHelperVisualizeBounds helper function to plot the distance bounds as two transparent spheres.

for i = 1:3
    figure
    q0 = randomConfiguration(robot); % Initial guess for solver
    [q,solutionInfo] = gik(q0,constrDist,forearmTgt);
    show(robot,q);
    view(90,0)
    hold on
    exampleHelperVisualizeBounds(minDist,maxDist)
    hold off
    eeDist = norm(tform2trvec(getTransform(robot,q,"tool0")));
    display(["Solver Status: ",solutionInfo.Status])
    display(["End Effector Distance: ",num2str(eeDist)])
end

Figure contains an axes object. The axes object contains 30 objects of type patch, line, surface. These objects represent base_link, base, base_link_inertia, shoulder_link, upper_arm_link, forearm_link, wrist_1_link, wrist_2_link, wrist_3_link, flange, tool0, base_link_inertia_mesh, shoulder_link_mesh, upper_arm_link_mesh, forearm_link_mesh, wrist_1_link_mesh, wrist_2_link_mesh, wrist_3_link_mesh.

  1x2 string array

    "Solver Status: "    "success"
  1x2 string array

    "End Effector Distance: "    "0.48425"

Figure contains an axes object. The axes object contains 30 objects of type patch, line, surface. These objects represent base_link, base, base_link_inertia, shoulder_link, upper_arm_link, forearm_link, wrist_1_link, wrist_2_link, wrist_3_link, flange, tool0, base_link_inertia_mesh, shoulder_link_mesh, upper_arm_link_mesh, forearm_link_mesh, wrist_1_link_mesh, wrist_2_link_mesh, wrist_3_link_mesh.

  1x2 string array

    "Solver Status: "    "success"
  1x2 string array

    "End Effector Distance: "    "0.29671"

Figure contains an axes object. The axes object contains 30 objects of type patch, line, surface. These objects represent base_link, base, base_link_inertia, shoulder_link, upper_arm_link, forearm_link, wrist_1_link, wrist_2_link, wrist_3_link, flange, tool0, base_link_inertia_mesh, shoulder_link_mesh, upper_arm_link_mesh, forearm_link_mesh, wrist_1_link_mesh, wrist_2_link_mesh, wrist_3_link_mesh.

  1x2 string array

    "Solver Status: "    "success"
  1x2 string array

    "End Effector Distance: "    "0.48713"

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2022a