simscape.multibody.Joint Class

Namespace: simscape.multibody
Superclasses: simscape.multibody.Component

Abstract base class for joints

Since R2022a

Description

simscape.multibody.Joint is the abstract base class for joints, such as prismatic joints and revolute joints. To create a joint, use the object of a subclass, such as simscape.multibody.PrismaticJoint or simscape.multibody.RevoluteJoint.

An object of a joint has two frame connectors called B and F that correspond to the base and follower frames of the object. The connectors link two arbitrary objects together in a simscape.multibody.Multibody object. After being linked, the object connected to the follower frame is able to move in certain ways relative to the object connected to the base frame.

The Joint class has a DegreesOfFreedom property that indicates how many degrees of freedom are between the base and follower frames of a joint object. The value of the DegreesOfFreedom property is the sum of the degrees of freedom of all the joint primitives contained in the joint object.

See the More About section for more information about the Joint class.

Class Attributes

Abstract	true
ConstructOnLoad	true
RestrictsSubclassing	true

For information on class attributes, see Class Attributes.

Properties

DegreesOfFreedom — Degrees of freedom of joint object

positive integer

Degrees of freedom between the base and follower frames of a joint object, returned as a positive integer. The value is the sum of the degrees of freedom of all the joint primitives contained in the joint object.

Attributes:

GetAccess	public
SetAccess	Restricts access
Transient	true
NonCopyable	true

More About

Joint Type

The simscape.multibody.Joint class has 17 subclasses that each corresponds to a particular type of joint. A joint object contains zero or more joint primitives arranged in a particular sequence from the base frame to follower frame of the object. For example, the figure shows the joint primitives of a simscape.multibody.PlanarJoint object.

A joint object has an associated kinematic map that maps a set of joint variables, such as rotations and translations, to a prescribed transformation between the base and follower frames. The table summarizes the joint primitives and degrees of freedom for different types of joint objects:

Joint Type	Degrees of Freedom	Primitives	Primitive Names
simscape.multibody.WeldJoint	0	None	None
simscape.multibody.RevoluteJoint	1	1 simscape.multibody.RevolutePrimitive	Rz
simscape.multibody.PrismaticJoint	1	1 simscape.multibody.PrismaticPrimitive	Pz
simscape.multibody.LeadScrewJoint	1	1 simscape.multibody.LeadScrewPrimitive	LSz
simscape.multibody.CylindricalJoint	2	1 simscape.multibody.RevolutePrimitive	Rz
		1 simscape.multibody.PrismaticPrimitive	Pz
simscape.multibody.PinSlotJoint	2	1 simscape.multibody.PrismaticPrimitive	Px
		2 simscape.multibody.RevolutePrimitive	Rz
simscape.multibody.UniversalJoint	2	2 simscape.multibody.RevolutePrimitive	Rx
			Ry
simscape.multibody.RectangularJoint	2	2 simscape.multibody.PrismaticPrimitive	Px
			Py
simscape.multibody.ConstantVelocityJoint	2	1 simscape.multibody.ConstantVelocityPrimitive	CV
simscape.multibody.GimbalJoint	3	3 simscape.multibody.RevolutePrimitive	Rx
			Ry
			Rz
simscape.multibody.PlanarJoint	3	2 simscape.multibody.PrismaticPrimitive	Px
			Py
		1 simscape.multibody.RevolutePrimitive	Rz
simscape.multibody.CartesianJoint	3	3 simscape.multibody.PrismaticPrimitive	Px
			Py
			Pz
simscape.multibody.SphericalJoint	3	1 simscape.multibody.SphericalPrimitive	S
simscape.multibody.BearingJoint	4	1 simscape.multibody.PrismaticPrimitive	Pz
		3 simscape.multibody.RevolutePrimitive	Rx
			Ry
			Rz
simscape.multibody.TelescopingJoint	4	1 simscape.multibody.SphericalPrimitive	S
		1 simscape.multibody.PrismaticPrimitive	Pz
simscape.multibody.BushingJoint	6	3 simscape.multibody.PrismaticPrimitive	Px
			Py
			Pz
		3 simscape.multibody.RevolutePrimitive	Rx
			Ry
			Rz
simscape.multibody.SixDofJoint	6	3 simscape.multibody.PrismaticPrimitive	Px
			Py
			Pz
		1 simscape.multibody.SphericalPrimitive	S

State Parameters

The state parameters of a joint object include position and velocity. The position can be a translation or rotation, and the velocity is the derivative of the position. It is often necessary to specify a simscape.multibody.Multibody object in a particular state for an analysis. For example, you may need to set a multibody system in a certain configuration or simulate the system from a particular initial condition. To specify the configuration or initial condition of a Multibody object, use a simscape.op.OperatingPoint object to set the targets and the priority level of the targets for the state parameters of some or all the joint objects. See Examples for how to specify the state parameters for a revolute joint object.

If a Multibody object has a tree-like structure, the state parameters of all the joint objects can always achieve the specified targets. If a Multibody object has a kinematic loop, the state targets of joint objects might be incompatible with each other. In this case, the computeState method of simscape.multibody.CompiledMultibody class makes compromises to achieve a physically possible state when computing the state of the Multibody object.

Version History

Introduced in R2022a