replaceJoint

Replace joint on body

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Syntax

replaceJoint(robot,bodyname,joint)

Description

example

replaceJoint(robot,bodyname,joint) replaces the joint on the specified body in the robot model if the body is a part of the robot model. This method is the only way to change joints in a robot model. You cannot directly assign the Joint property of a rigid body.

Examples

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Open Live Script

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

Load example robots as rigidBodyTree objects.

load exampleRobots.mat

View the details of the Puma robot using showdetails.

showdetails(puma1)
--------------------
Robot: (6 bodies)

 Idx    Body Name   Joint Name   Joint Type    Parent Name(Idx)   Children Name(s)
 ---    ---------   ----------   ----------    ----------------   ----------------
   1           L1         jnt1     revolute             base(0)   L2(2)  
   2           L2         jnt2     revolute               L1(1)   L3(3)  
   3           L3         jnt3     revolute               L2(2)   L4(4)  
   4           L4         jnt4     revolute               L3(3)   L5(5)  
   5           L5         jnt5     revolute               L4(4)   L6(6)  
   6           L6         jnt6     revolute               L5(5)   
--------------------

Get a specific body to inspect the properties. The only child of the L3 body is the L4 body. You can copy a specific body as well.

body3 = getBody(puma1,'L3');
childBody = body3.Children{1}
childBody = 
  rigidBody with properties:

            Name: 'L4'
           Joint: [1x1 rigidBodyJoint]
            Mass: 1
    CenterOfMass: [0 0 0]
         Inertia: [1 1 1 0 0 0]
          Parent: [1x1 rigidBody]
        Children: {[1x1 rigidBody]}
         Visuals: {}
      Collisions: {}


body3Copy = copy(body3);

Replace the joint on the L3 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(puma1,'L3',newJoint);

showdetails(puma1)
--------------------
Robot: (6 bodies)

 Idx    Body Name       Joint Name       Joint Type    Parent Name(Idx)   Children Name(s)
 ---    ---------       ----------       ----------    ----------------   ----------------
   1           L1             jnt1         revolute             base(0)   L2(2)  
   2           L2             jnt2         revolute               L1(1)   L3(3)  
   3           L3        prismatic            fixed               L2(2)   L4(4)  
   4           L4             jnt4         revolute               L3(3)   L5(5)  
   5           L5             jnt5         revolute               L4(4)   L6(6)  
   6           L6             jnt6         revolute               L5(5)   
--------------------

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

subtree = removeBody(puma1,'L4')
subtree = 
  rigidBodyTree with properties:

     NumBodies: 3
        Bodies: {[1x1 rigidBody]  [1x1 rigidBody]  [1x1 rigidBody]}
          Base: [1x1 rigidBody]
     BodyNames: {'L4'  'L5'  'L6'}
      BaseName: 'L3'
       Gravity: [0 0 0]
    DataFormat: 'struct'

Remove the modified L3 body. Add the original copied L3 body to the L2 body, followed by the returned subtree. The robot model remains the same. See a detailed comparison through showdetails.

removeBody(puma1,'L3');
addBody(puma1,body3Copy,'L2')
addSubtree(puma1,'L3',subtree)

showdetails(puma1)
--------------------
Robot: (6 bodies)

 Idx    Body Name   Joint Name   Joint Type    Parent Name(Idx)   Children Name(s)
 ---    ---------   ----------   ----------    ----------------   ----------------
   1           L1         jnt1     revolute             base(0)   L2(2)  
   2           L2         jnt2     revolute               L1(1)   L3(3)  
   3           L3         jnt3     revolute               L2(2)   L4(4)  
   4           L4         jnt4     revolute               L3(3)   L5(5)  
   5           L5         jnt5     revolute               L4(4)   L6(6)  
   6           L6         jnt6     revolute               L5(5)   
--------------------

Input Arguments

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Robot model, specified as a rigidBodyTree object.

Body name, specified as a string scalar or character vector. This body must be on the robot model specified in robot.

Data Types: char | string

Replacement joint, specified as a rigidBodyJoint object.

See Also

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Introduced in R2016b

Robotics System Toolbox Documentation

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