SimMechanics

Body Actuator

Apply force/torque to a body

Library

Sensors & Actuators

Description

The Body Actuator block actuates a Body block with a generalized force signal, representing a force/torque applied to the body:

• Force for translational motion
• Torque for rotational motion

The generalized force 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 Body Actuator applies the actuation signal in the reference coordinate system (CS) specified in the block dialog box.

The inport is the Simulink input signal. The output is the Connector Port you connect to the Body block you want to actuate.

You should carefully distinguish the Body Actuator from the Driver blocks:

• The Body Actuator block applies generalized forces to one body in a specified reference CS.
• The Driver blocks drive relative degrees of freedom between pairs of bodies.

Other Ways to Actuate Bodies

The Body Actuator block actuates a Body with force/torque signals only. To actuate a Body with motion signals or initial conditions, or to drive the relative degrees of freedom between a pair of Bodies, see Actuating a Joint and Joint Actuator Example: Body Driver.

The mech_body_driver model from the Demos library shows how to drive the relative DoFs between a pair of bodies. To actuate one body alone, use this model and replace the second Body block with a Ground block. To set body initial conditions, replace the second Body block with a Ground block and the Joint Actuators with Joint Initial Condition Actuators.

Dialog Box and Parameters

The dialog box has one active area, Actuation.

Actuation

Actuating body at coordinate system

This field is not active. You choose the Body CS at which to apply the actuation by connecting it to the Body Actuator.

Using reference coordinate system

In the pull-down menu, choose the coordinate system (CS) in which the actuating force/torque is interpreted: either the Local (Body CS) to which the Actuator is connected or the default Absolute (World).

Here is a Body Actuator connected to a Body:

You must connect the Body Actuator to the Body at one of that Body's attached Body CSs, at the corresponding Body CS Port. The actuation signal acts on the Body at that Body CS's origin.

Generalized Forces

You can apply a force, a torque, or both generalized forces to a body.

If you apply both, you need to bundle the torque and force vectors into a 6-component signal, in the order shown in the dialog box.

Apply torque

Select the check box if part or all of the actuating signal is a rotational torque. The default is unselected. The Simulink torque input is a 3-component bundled signal.

In the pull-down menu, choose units for the actuating torque. The default is N-m (Newton-meters).

Apply force

Select the check box if part or all of the actuating signal is a translational force. The default is selected. The Simulink force input is a 3-component bundled signal.

In the pull-down menu, choose units for the actuating force. The default is N (Newtons).

See Also

Body, Body Sensor, Driver Actuator, Joint Actuator, Joint Initial Condition Actuator

See Actuating a Joint and Joint Actuator Example: Body Driver.

See Creating Bodies and Grounds and Creating Constraints and Drivers.

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

Body

Body Sensor