Revolute Joint
Joint with one revolute primitive
Libraries:
Simscape /
Multibody /
Joints
Description
The Revolute Joint block models a joint that has one rotational degree of freedom.
The joint constrains the motion of two arbitrary frames that connect to the base and follower frames of the joint to pure rotation about a common axis. The axis of rotation is aligned with the z-axis of the joint base frame. The base and follower frames have a common origin and z-axis, and the follower frame rotates about the z-axis, as shown in the image.
To specify the target of the initial state for a joint primitive, use the parameters under State Targets. The targets are specified in the base frame. You can also set the priority levels for the targets. If the joint is not able to satisfy all the state targets, the priority level determines which targets to satisfy first and how closely to satisfy them. For an example, see the Guiding Assembly section of How Multibody Assembly Works.
To model damping and the spring behavior for a joint primitive, use the parameters under Internal Mechanics. Use the Damping Coefficient parameter to model energy dissipation and the Spring Stiffness parameter to model energy storage. Joint springs attempt to displace the joint primitive from its equilibrium position, and joint dampers act as energy dissipation elements. The springs and dampers are strictly linear.
To specify the limits of a joint primitive, use the parameters under Limits. The lower and upper bounds define the width of the free region. The block applies a force to accelerate the joint position back to the free region when the position exceeds the bounds. The block uses a smoothed spring-damper method to compute the force. For more information about the smoothed spring-damper method, see the Description section of the Spatial Contact Force block.
The Force, Torque, and Motion parameters in the Actuation section control the motion of the joint primitives during simulation. For more information, see Specifying Joint Actuation Inputs. Additionally, the joint block has ports that output sensing data, such as position, velocity, acceleration, force, and torque, that you can use to perform analytical tasks on a model. For more information, see Sensing and Force and Torque Sensing.
To specify the joint mode configuration, use the Mode parameter. For more details, see Mode Configuration under the Ports and Parameters sections.
Faults
Using mode faults, you can change the joint modes during a simulation without modifying
the model design. The fault injection overrides the mode setting. For example, if a joint
has the Mode parameter set to Locked and the
Fault behavior parameter set to Disengaged, the
joint becomes disengaged.
To add a mode fault to a joint block, click on the joint block, in the Simscape Block tab, and the Faults
section, click Fault > Add Fault.
Alternatively, you can click the joint block, hover over the ellipsis to open the action
bar, and click the Add a fault on the block icon 
. You can add multiple faults to a joint block, but the
joint block can have only one active fault during a simulation.
As you add faults, in the Property Inspector, under the Fault section, specify the behavior and the trigger type of the fault. To
define the fault behavior, click the link next to the Fault
Behavior. This joint supports Locked,
Normal, or Disengaged mode. The joint blocks support
these trigger types: Always on, Timed,
Manual, and Conditional. For more details of these
trigger types, see Set Fault Triggers. To trigger a
conditional fault, you can use Simulink® signals, Simscape™ language blocks, and MATLAB® workspace variables. To set the active fault for a block, use the Fault Table.
For more details, see Access the Fault Table and Fault Dashboard.
To enable fault simulation, in the Simscape Block tab
and the Faults section, turn on the Fault Simulation button. The fault simulation is on when the button is green
and the status is on. The simulation logs the trigger
status data. To view the data, use the Simulation Data
Inspector. Also, you can see the fault status and a summary of the triggered faults
in the Fault Dashboard. To open the Fault Dashboard, in the Simscape
Block tab, click Faults > Fault
Dashboard.
To create and modify faults, you can also use Simscape and Simulink fault functions. For more details, see the function section of the Simulink Fault Controls and Simscape Faults Interface.
Examples
Single Pendulum in Simulink and Simscape Multibody
A single pendulum modeled using Simulink® input/output blocks and using Simscape™ Multibody™. The initial angle for the joint is defined by a MATLAB® variable. The annotations on the integrator block show the initial angle of the joint with respect to the world frame.
