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workspaceGoalRegion

Define workspace region of end-effector goal poses

Description

The workspaceGoalRegion object defines a region for valid end-effector goal poses. To sample poses within the bounds of the goal region, use the sample object function. You can also visualize the bounds you define using the show object function.

The object is typically used with rapidly exploring random tree (RRT) planners like the manipulatorRRT object. The sample generates alternative goal states to increase the likelihood of finding valid paths.

Image of workspace goal region showing an XYZ reference frame, an offset pose, an XYZ bounding box, and Euler angle rotations. The offset pose, bounding box, and angle rotations are all relative to the original reference frame pose.

The key elements of the goal region are defined as object properties:

  • ReferencePose — Pose of the reference frame in the world frame. The bounds and offset pose are relative to this frame.

  • EndEffectorOffsetPose — Offset pose applied to any pose sampled in the reference frame. Use this offset if the end effector needs to be positioned differently based on grasping or other geometric restrictions.

  • Bounds — Bounds of the region as a 6-by-2 matrix with the minimum and maximum values for the XYZ-position and ZYX Euler angle orientation, in respective column vectors.

Creation

Description

example

goalRegion = workspaceGoalRegion(EndEffectorName) creates a default workspace goal region object for the specified end-effector name. Sets the EndEffectorName property.

goalRegion = workspaceGoalRegion(EndEffectorName,Name,Value) sets additional properties on the object using name-value pairs. For example, workSpaceGoalRegion("endEffector","Bounds",limits) creates a workspace goal region with the Bounds property specified as a matrix.

Properties

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Name of the end effector, specified as a string scalar.

Example: "eeTool"

Data Types: string

Pose of the reference frame, specified as a 4-by-4 homogeneous transformation matrix. The Bounds property defines the limits of the goal region relative to this reference frame.

Example: trvect2tform([1 2 3])

Data Types: double

End-effector offset pose applied to poses sampled in the reference frame, specified as a 4-by-4 homogeneous transformation matrix. This offset is applied to all poses sampled. Use this offset if the end effector needs to be positioned differently based on grasping or other geometric restrictions.

Example: trvect2tform([0.5 1 0])

Example: eul2tform([pi/2 0 -pi/4])

Data Types: double

Position and orientation bounds on pose samples, specified as a 6-by-2 matrix with the minimum and maximum values in column vectors.

wgr.Bounds = [ minX  maxX;
               minY  maxY;
               minZ  maxZ;
               minEulZ  maxEulZ;
               minEulY  maxEulY;
               minEulX  maxEulX ];

The first three rows are the XYZ-position bounds. The last three rows are the orientation bounds, which are specified as intrinsic ZYX Euler angles. Orientation is based on the right-hand rule, with counterclockwise rotations about the respective axes being positive and measured in radians. During sampling, a pose is uniformly sampled within each of these bounds to obtain a sample pose in the reference frame.

Data Types: double

Object Functions

sampleSample end-effector poses in world frame
showVisualize workspace bounds, reference frame, and offset frame

Examples

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Specify a goal region in your workspace and plan a path within those bounds. The workspaceGoalRegion object defines the bounds on the XYZ-position and ZYX Euler orientation of the robot end effector. The manipulatorRRT object plans a path based on that goal region and samples random poses within the bounds.

Load an existing robot model as a rigidBodyTree object.

robot = loadrobot("kinovaGen3", "DataFormat", "row");
ax = show(robot);

Figure contains an axes. The axes contains 25 objects of type patch, line. These objects represent base_link, Shoulder_Link, HalfArm1_Link, HalfArm2_Link, ForeArm_Link, Wrist1_Link, Wrist2_Link, Bracelet_Link, EndEffector_Link, Shoulder_Link_mesh, HalfArm1_Link_mesh, HalfArm2_Link_mesh, ForeArm_Link_mesh, Wrist1_Link_mesh, Wrist2_Link_mesh, Bracelet_Link_mesh, base_link_mesh.

Create Path Planner

Create a rapidly-exploring random tree (RRT) path planner for the robot. This example uses an empty environment, but this workflow also works well with cluttered environments. You can add collision objects to the environment like the collisionBox or collisionMesh object.

planner = manipulatorRRT(robot,{});

Define Goal Region

Create a workspace goal region using the end-effector body name of the robot.

Define the goal region parameters for your workspace. The goal region includes a reference pose, XYZ-position bounds, and orientation limits on the ZYX Euler angles. This example specifies bounds on the XY-plane in meters and allows rotation about the Z-axis in radians.

goalRegion = workspaceGoalRegion(robot.BodyNames{end}); 
goalRegion.ReferencePose = trvec2tform([0.5 0.5 0.2]);
goalRegion.Bounds(1, :) = [-0.2 0.2];    % X Bounds
goalRegion.Bounds(2, :) = [-0.2 0.2];    % Y Bounds
goalRegion.Bounds(4, :) = [-pi/2 pi/2];  % Rotation about the Z-axis

You can also apply a fixed offset to all poses sampled within the region. This offset can account for grasping tools or variations in dimensions within your workspace. For this example, apply a fixed transformation that places the end effector 5 cm above the workspace.

goalRegion.EndEffectorOffsetPose = trvec2tform([0 0 0.05]);
hold on
show(goalRegion);

Figure contains an axes. The axes contains 35 objects of type line, patch. These objects represent base_link, Shoulder_Link, HalfArm1_Link, HalfArm2_Link, ForeArm_Link, Wrist1_Link, Wrist2_Link, Bracelet_Link, EndEffector_Link, Shoulder_Link_mesh, HalfArm1_Link_mesh, HalfArm2_Link_mesh, ForeArm_Link_mesh, Wrist1_Link_mesh, Wrist2_Link_mesh, Bracelet_Link_mesh, base_link_mesh.

Plan Path To Goal Region

Plan a path to the goal region from the robot's home configuration. Due to the randomness in the RRT algorithm, this example sets the rng seed to ensure repeatable results.

rng(0)
path = plan(planner,homeConfiguration(robot),goalRegion);

Show the robot executing the path. To visualize a more realistic path, interpolate points between path configurations.

interpConfigurations = interpolate(planner,path,5);

for i = 1 : size(interpConfigurations)
    show(robot,interpConfigurations(i,:),"PreservePlot",false);
    set(ax,'ZLim',[-0.05 0.75],'YLim',[-0.05 1],'XLim',[-0.05 1],...
        'CameraViewAngle',5)
  
    drawnow
end
hold off

Figure contains an axes. The axes contains 35 objects of type line, patch. These objects represent base_link, Shoulder_Link, HalfArm1_Link, HalfArm2_Link, ForeArm_Link, Wrist1_Link, Wrist2_Link, Bracelet_Link, EndEffector_Link, Shoulder_Link_mesh, HalfArm1_Link_mesh, HalfArm2_Link_mesh, ForeArm_Link_mesh, Wrist1_Link_mesh, Wrist2_Link_mesh, Bracelet_Link_mesh, base_link_mesh.

Adjust End-effector Pose

Notice that the robot arm approaches the workspace from the bottom. To flip the orientation of the final position, add a pi rotation to the Y-axis for the reference pose.

goalRegion.EndEffectorOffsetPose = ... 
    goalRegion.EndEffectorOffsetPose*eul2tform([0 pi 0],"ZYX");

Replan the path and visualize the robot motion again. The robot now approaches from the top.

hold on
show(goalRegion);
path = plan(planner,homeConfiguration(robot),goalRegion);

interpConfigurations = interpolate(planner,path,5);

for i = 1 : size(interpConfigurations)
    show(robot, interpConfigurations(i, :),"PreservePlot",false);
    set(ax,'ZLim',[-0.05 0.75],'YLim',[-0.05 1],'XLim',[-0.05 1])
    drawnow;
end
hold off

Figure contains an axes. The axes contains 45 objects of type line, patch. These objects represent base_link, Shoulder_Link, HalfArm1_Link, HalfArm2_Link, ForeArm_Link, Wrist1_Link, Wrist2_Link, Bracelet_Link, EndEffector_Link, Shoulder_Link_mesh, HalfArm1_Link_mesh, HalfArm2_Link_mesh, ForeArm_Link_mesh, Wrist1_Link_mesh, Wrist2_Link_mesh, Bracelet_Link_mesh, base_link_mesh.

References

Berenson, Dmitry, Siddhartha S. Srinivasa, Dave Ferguson, Alvaro Collet, and James J. Kuffner. "Manipulation Planning with Workspace Goal Regions." In 2009 IEEE International Conference on Robotics and Automation (ICRA), 618–24. Kobe, Japan: Institute of Electrical and Electronics Engineers, 2009. https://doi.org/10.1109/ROBOT.2009.5152401.

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