Joint Initial Condition Actuator (SimMechanics)

Apply initial position and velocity to a joint primitive before starting simulation

Library

Sensors & Actuators

Description

The Joint Initial Condition Actuator block supplies a joint primitive in a Joint block with initial value data. The initial values are the position and velocity of that joint primitive and fully specify the initial state of motion (initial kinematic state) of that primitive.

When you build your machine, the geometric configuration implicitly specifies the initial positions/angles of bodies relative to one another and to World. The Ground, Body, and Joint layout process, however, only specifies initial coordinates (degrees of freedom), not their corresponding velocities. Starting a simulation in this state implicitly sets all initial velocities to zero. You can set the full initial kinematic state, both positions and velocities, of all joint primitives by using the Joint Initial Condition Actuator block.

You can set initial position and velocity for two primitive types:

Translational initial conditions for a prismatic primitive, in terms of linear position and velocity
Rotational initial conditions for a revolute primitive, in terms of angular position and velocity

This block actuates one joint primitive at a time.

The Joint Initial Condition Actuator applies the initial state 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 output is the Connector Port you connect to the Joint block you want to actuate. You set the initial linear or angular position and velocity in the block's dialog box, so there is no inport or input signal.

You cannot connect a Joint Initial Condition 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 primitives within the Joint that you want to actuate with the Joint Initial Condition Actuator. A primitive Joint block has only one joint primitive.; You cannot connect a Joint Initial Condition Actuator to a spherical primitive.; If the Joint Initial Condition Actuator is not connected to a Joint block, this menu shows only Unknown.

Here is a Joint Initial Condition Actuator connected to a Prismatic, which connects two Bodies:

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

Initial position: In this field, set the initial linear or angular position, depending on whether this Actuator is connected to a prismatic or revolute primitive. The default is 0.0.; In the pull-down menu, choose the units for the initial position, linear or angular. The default for linear units is m (meters); for angular units, the default is deg (degrees).
Initial velocity: In this field, set the initial linear or angular velocity, depending on whether this Actuator is connected to a prismatic or revolute primitive. The default is 0.0.; In the pull-down menu, choose the units for the initial velocity, linear or angular. The default for linear units is m/s (meters/second); for angular units, the default is deg/s (degrees/second).

See Using JICA Blocks for setting general initial conditions (positions and velocities) of DoFs in a machine.

See Creating Joints.

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

Joint Actuator Joint Sensor