# Double-Acting Servo Valve Actuator (IL)

Double-acting servo cylinder with spring-centered spool in an isothermal liquid system

Since R2020a

Libraries:
Simscape / Fluids / Valve Actuators & Forces

## Description

The Double-Acting Servo Valve Actuator (IL) block models a double-acting servo cylinder arranged as a spring-centered spool. The spring neutral position is where the spool is located at the middle of the stroke. The motion of the piston when it is near full extension or full retraction is limited by one of four hard stop models. Fluid compressibility is optionally modeled in both piston chambers.

The physical signal output S reports the spool position.

### Hard Stop Model

To avoid mechanical damage to an actuator when it is fully extended or fully retracted, an actuator typically displays nonlinear behavior when the piston approaches these limits. The Double-Acting Servo Valve Actuator (IL) block models this behavior with a choice of four 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```.

• `Based on coefficient of restitution`

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 Spool stroke or piston initial displacement. Outside of this region, ${F}_{HardStop}=0.$

### Block Schematic

The Double-Acting Servo Actuator block comprises an Isothermal Liquid library block and two Simscape Foundation blocks:

## Ports

### Conserving

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Isothermal liquid conserving port associated with the liquid inlet of chamber A.

Isothermal liquid conserving port associated with the liquid inlet of chamber B.

### Output

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Physical signal associated with the spool position, in m. A position of zero indicates that the spool is at a neutral position in the middle of a stroke.

## Parameters

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### Cylinder

Cross-sectional area of the spool

Distance the spool travels in a stroke.

Spring rate of the centering springs.

Damping coefficient in the contact between the piston and the case.

### Hard Stop

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

Piston stiffness coefficient.

#### Dependencies

To enable this parameter, set Hard stop model to

• ```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```

Piston damping coefficient.

#### Dependencies

To enable this parameter, set Hard stop model to

• ```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```

Application range of the hard stop force model. Outside of this 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```.

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```.

Threshold relative speed between slider and stop before collision. When the slider hits the case with 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```.

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```.

### Effects and Initial Conditions

When the initial displacement of the spool is set to 0, the spool begins directly between chamber A and chamber B. A positive distance moves the spool away from chamber A, while a negative amount moves the spool toward chamber A.

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.

Pressure in actuator chamber A at the start of simulation.

#### Dependencies

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

Pressure in actuator chamber B at the start of simulation.

#### Dependencies

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

## Version History

Introduced in R2020a

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