Joint Actuator (SimMechanics)

Apply force/torque or motion to a joint primitive

Library

Sensors & Actuators

Description

A joint between two bodies represents relative degrees of freedom (DoFs) between the bodies. The Joint Actuator block actuates a Joint block connected between two Bodies with one of these signals:

A generalized force:

Force for translational motion along a prismatic joint primitive
Torque for rotational motion about a revolute joint primitive

A motion:

Translational motion for a prismatic joint primitive, in terms of linear position, velocity, and acceleration. The velocity signal must be the derivative of the position signal, and the acceleration the derivative of the velocity.
Rotational motion for a revolute joint primitive, in terms of angular position, velocity, and acceleration. The angular velocity signal must be the derivative of the angle signal, and the angular acceleration the derivative of the angular velocity.

The generalized force or the motion is a function of time specified by a Simulink input signal. This signal can be any Simulink signal, including a signal feedback from a Sensor block.

The Joint Actuator applies the actuation signal along/about the joint axis in the reference coordinate system (CS) specified for that joint primitive in the Joint's dialog box. The Joint connects a base and a follower Body. The base-follower sequence determines the sense of the actuation signal.

The inport is the Simulink input signal. The output is the Connector Port you connect to the Joint block you want to actuate. A Joint Actuator block actuates one joint primitive at a time:

A primitive Joint (Prismatic or Revolute) has only one primitive within the Joint to actuate.
A composite Joint has multiple joint primitives within, and you must choose which of those primitives to actuate with the Joint Actuator.

You cannot connect a Joint Actuator to a Spherical or spherical primitive.

Dialog Box and Parameters

The dialog box has one active area, Actuation.

Actuation

Connected to primitive: In the pull-down menu, choose the joint primitive within the Joint that you want to actuate with the Joint Actuator. A primitive Joint block has only one joint primitive.; You cannot connect a Joint Actuator to a spherical primitive.; If the Joint Actuator is not connected to a Joint block, this menu shows only Unknown.

Here is a Joint Actuator connected to a Prismatic that connects two Bodies:

You must add an Actuator port (Connector Port) to the Joint block to connect the Joint Actuator to it. The base (B)-follower (F) Body sequence on the two sides of the Joint determines the sense of the Joint Actuator data.

Using the radio buttons, you can toggle between the two types of actuation, Generalized forces and Motion.

Generalized Forces

This option interprets the actuation signal as a force or a torque between the Bodies connected by the Joint block you are actuating.

Apply torque (revolute only): In the pull-down menu, choose units for the actuation torque. The default is N-m (Newton-meters). This choice is valid only if you connect this Actuator block to a revolute primitive.; The Simulink input is a 1-component signal.
Apply force (prismatic only): In the pull-down menu, choose units for the actuation force. The default is N (Newtons). This choice is valid only if you connect this Actuator block to a prismatic primitive.; The Simulink input is a 1-component signal.

Motion

This option interprets the actuation signal as a motion of the joint primitive to which you connect the Joint Actuator.

Apply translational motion (prismatic only): In the pull-down menus, choose units for the linear actuation Position, Velocity, and Acceleration. The defaults are m (meters), m/s (meters/second), and m/s² (meters/second²), respectively.; The Simulink input is a bundled 3-component signal with components in the order shown in the dialog box.
Apply rotational motion (revolute only): In the pull-down menus, choose units for the angular actuation Angle, Angular Velocity, and Angular Acceleration. The defaults are deg (degrees), deg/s (degrees/second), and deg/s² (degrees/second²), respectively.; The Simulink input is a bundled 3-component signal with components in the order shown in the dialog box.

See Creating Joints.

In Simulink, see the Signal Routing Library and the Sources Library.

In-Plane Joint Initial Condition Actuator