replaceJoint

Replace joint on body

Syntax

replaceJoint(robot,bodyname,joint)

Description

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

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 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

robot — Robot model

rigidBodyTree object

Robot model, specified as a rigidBodyTree object.

bodyname — Body name

string scalar | character vector

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

joint — Replacement joint

rigidBodyJoint object

Replacement joint, specified as a rigidBodyJoint object.

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