addBody

Add body to robot

Syntax

addBody(robot,body,parentname)

Description

addBody(robot,body,parentname) adds a rigid body to the robot object and is attached to the rigid body parent specified by parentname. The body property defines how this body moves relative to the parent body.

Examples

Attach Rigid Body and Joint to Rigid Body Tree

Add a rigid body and corresponding joint to a rigid body tree. Each rigidBody object contains a rigidBodyJoint object and must be added to the rigidBodyTree using addBody.

Create a rigid body tree.

rbtree = rigidBodyTree;

Create a rigid body with a unique name.

body1 = rigidBody('b1');

Create a revolute joint. By default, the rigidBody object comes with a fixed joint. Replace the joint by assigning a new rigidBodyJoint object to the body1.Joint property.

jnt1 = rigidBodyJoint('jnt1','revolute');
body1.Joint = jnt1;

Add the rigid body to the tree. Specify the body name that you are attaching the rigid body to. Because this is the first body, use the base name of the tree.

basename = rbtree.BaseName;
addBody(rbtree,body1,basename)

Use showdetails on the tree to confirm the rigid body and joint were added properly.

showdetails(rbtree)

--------------------
Robot: (1 bodies)

 Idx    Body Name   Joint Name   Joint Type    Parent Name(Idx)   Children Name(s)
 ---    ---------   ----------   ----------    ----------------   ----------------
   1           b1         jnt1     revolute             base(0)   
--------------------

Build Manipulator Robot Using Denavit-Hartenberg Parameters

Use the Denavit-Hartenberg (DH) parameters of the Puma560® robot to build a robot. Each rigid body is added one at a time, with the child-to-parent transform specified by the joint object.

The DH parameters define the geometry of the robot with relation to how each rigid body is attached to its parent. For convenience, setup the parameters for the Puma560 robot in a matrix [1]. The Puma robot is a serial chain manipulator. The DH parameters are relative to the previous row in the matrix, corresponding to the previous joint attachment.

dhparams = [0   	pi/2	0   	0;
            0.4318	0       0       0
            0.0203	-pi/2	0.15005	0;
            0   	pi/2	0.4318	0;
            0       -pi/2	0   	0;
            0       0       0       0];

Create a rigid body tree object to build the robot.

robot = rigidBodyTree;

Create the first rigid body and add it to the robot. To add a rigid body:

1. Create a rigidBody object and give it a unique name.

2. Create a rigidBodyJoint object and give it a unique name.

3. Use setFixedTransform to specify the body-to-body transformation using DH parameters. The last element of the DH parameters, theta, is ignored because the angle is dependent on the joint position.

4. Call addBody to attach the first body joint to the base frame of the robot.

body1 = rigidBody('body1');
jnt1 = rigidBodyJoint('jnt1','revolute');

setFixedTransform(jnt1,dhparams(1,:),'dh');
body1.Joint = jnt1;

addBody(robot,body1,'base')

Create and add other rigid bodies to the robot. Specify the previous body name when calling addBody to attach it. Each fixed transform is relative to the previous joint coordinate frame.

body2 = rigidBody('body2');
jnt2 = rigidBodyJoint('jnt2','revolute');
body3 = rigidBody('body3');
jnt3 = rigidBodyJoint('jnt3','revolute');
body4 = rigidBody('body4');
jnt4 = rigidBodyJoint('jnt4','revolute');
body5 = rigidBody('body5');
jnt5 = rigidBodyJoint('jnt5','revolute');
body6 = rigidBody('body6');
jnt6 = rigidBodyJoint('jnt6','revolute');

setFixedTransform(jnt2,dhparams(2,:),'dh');
setFixedTransform(jnt3,dhparams(3,:),'dh');
setFixedTransform(jnt4,dhparams(4,:),'dh');
setFixedTransform(jnt5,dhparams(5,:),'dh');
setFixedTransform(jnt6,dhparams(6,:),'dh');

body2.Joint = jnt2;
body3.Joint = jnt3;
body4.Joint = jnt4;
body5.Joint = jnt5;
body6.Joint = jnt6;

addBody(robot,body2,'body1')
addBody(robot,body3,'body2')
addBody(robot,body4,'body3')
addBody(robot,body5,'body4')
addBody(robot,body6,'body5')

Verify that your robot was built properly by using the showdetails or show function. showdetails lists all the bodies in the MATLAB® command window. show displays the robot with a given configuration (home by default). Calls to axis modify the axis limits and hide the axis labels.

showdetails(robot)

--------------------
Robot: (6 bodies)

 Idx    Body Name   Joint Name   Joint Type    Parent Name(Idx)   Children Name(s)
 ---    ---------   ----------   ----------    ----------------   ----------------
   1        body1         jnt1     revolute             base(0)   body2(2)  
   2        body2         jnt2     revolute            body1(1)   body3(3)  
   3        body3         jnt3     revolute            body2(2)   body4(4)  
   4        body4         jnt4     revolute            body3(3)   body5(5)  
   5        body5         jnt5     revolute            body4(4)   body6(6)  
   6        body6         jnt6     revolute            body5(5)   
--------------------

show(robot);
axis([-0.5,0.5,-0.5,0.5,-0.5,0.5])
axis off

References

[1] Corke, P. I., and B. Armstrong-Helouvry. “A Search for Consensus among Model Parameters Reported for the PUMA 560 Robot.” Proceedings of the 1994 IEEE International Conference on Robotics and Automation, IEEE Computer. Soc. Press, 1994, pp. 1608–13. DOI.org (Crossref), doi:10.1109/ROBOT.1994.351360.

Modify a Robot Rigid Body Tree Model

Make changes to an existing rigidBodyTree object. You can get replace joints, bodies and subtrees in the rigid body tree.

Load an ABB IRB-120T manipulator from the Robotics System Toolbox™ loadrobot. It is specified as a rigidBodyTree object.

manipulator = loadrobot("abbIrb120T");

View the robot with show and read the details of the robot using showdetails.

show(manipulator);

showdetails(manipulator)

--------------------
Robot: (8 bodies)

 Idx     Body Name            Joint Name            Joint Type     Parent Name(Idx)   Children Name(s)
 ---     ---------            ----------            ----------     ----------------   ----------------
   1          base        base_link-base                 fixed         base_link(0)   
   2        link_1               joint_1              revolute         base_link(0)   link_2(3)  
   3        link_2               joint_2              revolute            link_1(2)   link_3(4)  
   4        link_3               joint_3              revolute            link_2(3)   link_4(5)  
   5        link_4               joint_4              revolute            link_3(4)   link_5(6)  
   6        link_5               joint_5              revolute            link_4(5)   link_6(7)  
   7        link_6               joint_6              revolute            link_5(6)   tool0(8)  
   8         tool0          joint6-tool0                 fixed            link_6(7)   
--------------------

Get a specific body to inspect the properties. The only child of the link_3 body is the link_4 body. You can copy a specific body as well.

body3 = getBody(manipulator,"link_3");
childBody = body3.Children{1}

childBody = 
  rigidBody with properties:

            Name: 'link_4'
           Joint: [1x1 rigidBodyJoint]
            Mass: 1.3280
    CenterOfMass: [0.2247 1.5000e-04 4.1000e-04]
         Inertia: [0.0028 0.0711 0.0723 1.3052e-05 -1.3878e-04 -6.6037e-05]
          Parent: [1x1 rigidBody]
        Children: {[1x1 rigidBody]}
         Visuals: {'Mesh Filename link_4.stl'}
      Collisions: {'Mesh Filename link_4.stl'}

body3Copy = copy(body3);

Replace the joint on the link_3 body. You must create a new Joint object and use replaceJoint to ensure the downstream body geometry is unaffected. Call setFixedTransform if necessary to define a transform between the bodies instead of with the default identity matrices.

newJoint = rigidBodyJoint("prismatic");
replaceJoint(manipulator,"link_3",newJoint);

showdetails(manipulator)

--------------------
Robot: (8 bodies)

 Idx     Body Name            Joint Name            Joint Type     Parent Name(Idx)   Children Name(s)
 ---     ---------            ----------            ----------     ----------------   ----------------
   1          base        base_link-base                 fixed         base_link(0)   
   2        link_1               joint_1              revolute         base_link(0)   link_2(3)  
   3        link_2               joint_2              revolute            link_1(2)   link_3(4)  
   4        link_3             prismatic                 fixed            link_2(3)   link_4(5)  
   5        link_4               joint_4              revolute            link_3(4)   link_5(6)  
   6        link_5               joint_5              revolute            link_4(5)   link_6(7)  
   7        link_6               joint_6              revolute            link_5(6)   tool0(8)  
   8         tool0          joint6-tool0                 fixed            link_6(7)   
--------------------

Remove an entire body and get the resulting subtree using removeBody. The removed body is included in the subtree.

subtree = removeBody(manipulator,"link_4")

subtree = 
  rigidBodyTree with properties:

     NumBodies: 4
        Bodies: {[1x1 rigidBody]  [1x1 rigidBody]  [1x1 rigidBody]  [1x1 rigidBody]}
          Base: [1x1 rigidBody]
     BodyNames: {'link_4'  'link_5'  'link_6'  'tool0'}
      BaseName: 'link_3'
       Gravity: [0 0 0]
    DataFormat: 'struct'

show(subtree);

Remove the modified link_3 body. Add the original copied link_3 body to the link_2 body, followed by the returned subtree. The robot model remains the same. See a detailed comparison through showdetails.

removeBody(manipulator,"link_3");
addBody(manipulator,body3Copy,"link_2")
addSubtree(manipulator,"link_3",subtree)

showdetails(manipulator)

--------------------
Robot: (8 bodies)

 Idx     Body Name            Joint Name            Joint Type     Parent Name(Idx)   Children Name(s)
 ---     ---------            ----------            ----------     ----------------   ----------------
   1          base        base_link-base                 fixed         base_link(0)   
   2        link_1               joint_1              revolute         base_link(0)   link_2(3)  
   3        link_2               joint_2              revolute            link_1(2)   link_3(4)  
   4        link_3               joint_3              revolute            link_2(3)   link_4(5)  
   5        link_4               joint_4              revolute            link_3(4)   link_5(6)  
   6        link_5               joint_5              revolute            link_4(5)   link_6(7)  
   7        link_6               joint_6              revolute            link_5(6)   tool0(8)  
   8         tool0          joint6-tool0                 fixed            link_6(7)   
--------------------

Input Arguments

robot — Robot model

rigidBodyTree object

Robot model, specified as a rigidBodyTree object.

body — Rigid body

rigidBody object

Rigid body, specified as a rigidBody object.

parentname — Parent body name

string scalar | character vector

Parent body name, specified as a string scalar or character vector. This parent body must already exist in the robot model. The new body is attached to this parent body.

Data Types: char | string

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

When creating the rigidBodyTree object, use the syntax that specifies the MaxNumBodies as an upper bound for adding bodies to the robot model. You must also specify the DataFormat property as a name-value pair. For example:

robot = rigidBodyTree("MaxNumBodies",15,"DataFormat","row")

To minimize data usage, limit the upper bound to a number close to the expected number of bodies in the model. All data formats are supported for code generation. To use the dynamics functions, the data format must be set to "row" or "column".

The show and showdetails functions do not support code generation.

Version History

Introduced in R2016b