Single-Acting Actuator (G)

Single-acting linear actuator in a gas network

Since R2023b

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Libraries:
Simscape / Fluids / Gas / Actuators

Description

The Single-Acting Actuator (G) block models a linear actuator with a piston controlled by a single gas chamber. The actuator generates force in the extension and retraction strokes, but the actuation force depends on the gauge pressure at a single chamber.

The figure shows the key components of an actuator. Port A represents the gas chamber inlet. Port R represents the translating actuator piston, and port C represents the actuator case. Port H represents the thermal interface between the gas chamber and the environment.

Displacement

The block measures the piston displacement as the position at port R relative to port C. The Mechanical orientation parameter identifies the direction of piston displacement. The piston displacement is neutral, or 0, when the chamber volume is equal to the value of the Dead volume parameter. When the Piston displacement parameter is Provide input signal from Multibody joint, you input the piston displacement using port p. You can ensure that the derivative of the position signal is equal to the piston velocity by using a Translational Multibody Interface block to provide the piston displacement.

The direction of the piston motion depends on the Mechanical orientation parameter. If the mechanical orientation is positive, then the piston translation is positive in relation to the actuator case when the gauge pressure at port A is positive. The direction of motion reverses when the mechanical orientation is negative.

Hard Stop

A set of hard stops limit the piston range of motion. The block uses an implementation of the Translational Hard Stop block, which treats hard stops like spring-damper systems. The spring stiffness coefficient controls the restorative component of the hard-stop contact force and the damping coefficient the dissipative component.

The hard stops are located at the distal ends of the piston stroke. If the mechanical orientation is positive, then the lower hard stop is at x = 0, and the upper hard stop is at x = +stroke. If the mechanical orientation is negative, then the lower hard stop is at x = -stroke, and the upper hard stop is at x = 0.

Block Composite

This block is a composite component based on these Simscape™ Foundation blocks:

• Translational Mechanical Converter (G)

• Translational Hard Stop

• Ideal Translational Motion Sensor

Ports

Input

p — Multibody piston position input, m

physical signal

Physical signal input associated with the piston position, in m. Connect this port to a Simscape Multibody™ network using a Translational Multibody Interface block.

Dependencies

To enable this port, set Piston displacement to Provide input signal from Multibody joint.

Output

p — Piston position, m

physical signal

Physical signal output associated with the piston position, in m.

Dependencies

To enable this port, set Piston displacement to Calculate from velocity of port R relative to port C.

Conserving

A — Liquid port

gas

Gas conserving port associated with chamber A.

C — Actuator casing

translational mechanical

Translational mechanical conserving port associated with the actuator casing.

R — Actuator piston

translational mechanical

Translational mechanical conserving port associated with the actuator piston.

H — Heat transfer

thermal

Thermal conserving port associated with the thermal mass of the gas volume.

Parameters

Actuator

Mechanical orientation — Piston displacement direction

Pressure at A causes positive displacement of R relative to C (default) | Pressure at A causes negative displacement of R relative to C

Piston displacement direction. When you set this parameter to:

• Pressure at A causes positive displacement of R relative to C, the piston displacement is positive when the volume of gas at port A is expanding. This motion corresponds to rod extension.

• Pressure at A causes negative displacement of R relative to C, the piston displacement is negative when the volume of gas at port A is expanding. This motion corresponds to rod contraction.

Piston cross-sectional area — Cross-sectional area of piston rod

0.01 m^2 (default) | positive scalar

Cross-sectional area of the piston rod.

Piston stroke — Maximum piston travel distance

0.1 m (default) | positive scalar

Maximum piston travel distance.

Dead volume — Fluid volume at full piston retraction

1e-5 m^3 (default) | positive scalar

Volume of gas when the piston displacement is 0. This parameter is the gas volume when the piston is against the actuator end cap.

Cross-sectional area at port A — Area at port A

0.01 m^2 (default) | positive scalar

Cross-sectional area of port A.

Environment pressure specification — Reference environment pressure

Atmospheric pressure (default) | Specified pressure

Environment reference pressure. When you select Atmospheric pressure, the block assumes a pressure of 0.101325 MPa.

Environment pressure — User-defined environmental pressure

0.101325 MPa (default) | positive scalar

User-defined environmental pressure.

Dependencies

To enable this parameter, set Environment pressure specification to Specified pressure.

Hard Stop

Hard stop model — Hard stop model

Stiffness and damping applied smoothly through transition region, damped rebound (default) | Full stiffness and damping applied at bounds, undamped rebound | Full stiffness and damping applied at bounds, damped rebound | Based on coefficient of restitution

Hard stop model to use when the piston is at full extension or full extraction. See the Translational Hard Stop block for more information.

Hard-stop stiffness coefficient — Stiffness coefficient

1e10 N/m (default) | positive scalar

Piston stiffness coefficient.

Dependencies

To enable this parameter, set Hard stop model to one of these settings:

• Stiffness and damping applied smoothly through transition region, damped rebound

• Full stiffness and damping applied at bounds, undamped rebound

• Full stiffness and damping applied at bounds, damped rebound

Hard-stop damping coefficient — Damping coefficient

150 N*s/m (default) | positive scalar

Piston damping coefficient.

Dependencies

To enable this parameter, set Hard stop model to one of these settings:

• Stiffness and damping applied smoothly through transition region, damped rebound

• Full stiffness and damping applied at bounds, undamped rebound

• Full stiffness and damping applied at bounds, damped rebound

Transition region — Application range of hard stop force model

0.1 mm (default) | positive scalar

Application range of the hard stop force model. The block does not apply the hard stop model when the maximum extension or retraction of the piston is outside of this range. In this situation, there is no additional force on the piston.

Dependencies

To enable this parameter, set Hard stop model to Stiffness and damping applied smoothly through transition region, damped rebound.

Coefficient of restitution — Ratio of final-to-initial relative speed between slider and stop after collision

0.7 (default) | unitless value between 0 and 1

Ratio of the final to the initial relative speed between the slider and the stop after the slider bounces.

Dependencies

To enable this parameter, set Hard stop model to Based on coefficient of restitution.

Static contact speed threshold — Threshold relative speed between slider and stop before collision

0.001 m/s (default) | nonnegative scalar

Threshold relative speed between the slider and stop before collision. When the slider hits the case with a speed less than the value of the Static contact speed threshold parameter, they stay in contact. Otherwise, the slider bounces. To avoid modeling static contact between the slider and the case, set this parameter to 0.

Dependencies

To enable this parameter, set Hard stop model to Based on coefficient of restitution.

Static contact release force threshold — Force needed to transition from contact mode to free mode

0.001 N (default) | positive scalar

Minimum force needed to release the slider from a static contact mode.

Dependencies

To enable this parameter, set Hard stop model to Based on coefficient of restitution.

Initial Conditions

Piston displacement — Method for determining piston position

Calculate from velocity of port R relative to port C (default) | Provide input signal from Multibody joint

Method for determining the piston position. The block can receive the position from a Multibody block when set to Provide input signal from Multibody joint, or can calculate the position internally and report the position at port p. The position is between 0 and the value of the Piston stroke parameter when the mechanical orientation is positive and between 0 and the negative value of the Piston stroke parameter when the mechanical orientation is negative.

Initial piston displacement — Piston position at start of simulation

0 m (default) | scalar

Piston position at the start of the simulation.

Dependencies

To enable this parameter, set Piston displacement to Calculate from velocity of port R relative to port C.

Initial gas pressure — Starting gas pressure

0.101325 MPa (default) | positive scalar

Initial pressure of the gas volume in the actuator.

Initial gas temperature — Starting gas temperature

293.15 K (default) | scalar

Initial temperature of the gas volume in the actuator.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2023b