# Double-Acting Actuator (G-IL)

Linear actuator with isothermal liquid and gas chambers

• Library:
• Simscape / Fluids / Fluid Network Interfaces / Actuators

## Description

The Double-Acting Actuator (G-IL) block models an isothermal liquid chamber and a gas chamber separated by a piston plate. The piston actuation is controlled by the pressure differential between the chambers. The motion of the piston when it is near full extension or full retraction is limited by one of three hard stop models.

Port A is the isothermal liquid inlet and port B is the gas inlet. Connect elements for heat transfer between the gas chamber and the environment to port H. Port C acts as a mechanical translational reference for the actuator casing, while piston velocity is returned at port R and piston position at port P.

You can define the piston displacement direction with the Mechanical orientation parameter. If the mechanical orientation is set to `Fluid pressure moves R away from C`, the piston extends when the pressure differential pApB is positive. If Mechanical orientation is set to ```Fluid pressure moves R towards C```, the piston retracts for a positive pressure difference between the liquid and gas chambers.

### Hard Stop Model

To avoid mechanical damage to the piston when it is fully extended or fully retracted, an actuator typically displays nonlinear behavior when the piston approaches these limits. The Double-Acting Actuator (G-IL) block models this behavior with a choice of three hard stop models, which model the material compliance through a spring-damper system. The hard stop models are:

• ```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```.

The hard stop force is modeled when the piston is at its upper or lower bound. The boundary region is within the Transition region of the Piston stroke or piston initial displacement. Outside of this region, ${F}_{HardStop}=0.$

### Block Schematic

The Double-Acting Actuator (G-IL) block is a composite of four Simscape Foundation blocks:

## Ports

### Conserving

expand all

Inlet port to the liquid chamber.

Inlet port to the gas chamber.

Mechanical translational conserving port associated with the reference velocity of the actuator casing.

Mechanical translational conserving port associated with the rod velocity.

Heat transfer to or from the gas chamber.

### Output

expand all

Piston position in m, returned as a physical signal.

## Parameters

expand all

### Configuration

Piston displacement direction. ```Fluid pressure moves R away from C``` corresponds to actuator rod extension when the pressure difference between chambers A and B is positive. `Fluid pressure moves R towards C` corresponds to actuator rod retraction when the pressure difference between chambers A and B is positive. Pressure is always expressed as a positive value.

Maximum piston travel distance.

Initial piston offset.

Piston stiffness coefficient.

Piston damping coefficient for motion near the piston ends.

Model choice for the force on the piston at full extension or full retraction. See the Translational Hard Stop block for more information.

Application range of the hard stop force model. Outside of the range of the piston maximum extension and piston maximum retraction, the Hard stop model is not applied and 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```.

### Isothermal Liquid Side

Cross-sectional area of the piston rod in chamber A.

Open volume in the fluid chamber when the piston is fully retracted.

Whether to model any change in fluid density due to fluid compressibility. When Fluid compressibility is set to `On`, changes due to the mass flow rate into the block are calculated in addition to density changes due to changes in pressure. In the Isothermal Liquid Library, all blocks calculate density as a function of pressure.

Initial liquid pressure for compressible fluids.

#### Dependencies

To enable this parameter, set Fluid dynamic compressibility to `On`.

Environment reference pressure. The ```Atmospheric pressure``` option sets the environmental pressure to 0.101325 MPa.

User-defined environmental pressure.

#### Dependencies

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

### Gas Side

Cross-sectional area of the piston rod in chamber B.

Cross-sectional area at port B.

Open volume in the gas chamber when the piston is fully retracted.

Initial pressure in the gas chamber.

Initial temperature in the gas chamber.

Environment reference pressure. The ```Atmospheric pressure``` option sets the environmental pressure to 0.101325 MPa.

User-defined environmental pressure.

#### Dependencies

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