Double-Acting Actuator (IL)

R2026b

Linear conversion of pressure differential to actuation in an isothermal liquid system

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Double-Acting Actuator (IL) block

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Libraries:
Simscape / Fluids / Isothermal Liquid / Actuators

Description

The Double-Acting Actuator (IL) block represents the linear conversion of a pressure differential between two chambers to piston motion. The piston actuation is controlled by the pressure differential acting on the piston plate that separates the chambers. 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.

Ports A and B are isothermal liquid inlets. Port C represents the actuator casing, while piston velocity is returned at port R. When the piston position is calculated internally, it is reported at port p, and when the position is set by a connection to a Simscape™ Multibody™ joint, it is received as a physical signal at port p.

You can define the piston displacement direction with the Mechanical orientation parameter. If the mechanical orientation is set to Pressure at A causes positive displacement of R relative to C, the piston extends when the pressure differential p_A – p_B is positive. If Mechanical orientation is set to Pressure at A causes negative displacement of R relative to C, the piston retracts for a positive pressure difference between the liquid and gas chambers.

Displacement

The piston displacement is measured as the position at port R relative to port C. The Mechanical orientation identifies the direction of piston displacement. The piston displacement is neutral, or 0, when the chamber A volume is equal to the chamber dead volume. When displacement is received as an input, ensure that the derivative of the position is equal to the piston velocity. This is automatically the case when the input is received from a Translational Multibody Interface block connection to a Simscape Multibody joint.

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 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 Piston stroke or piston initial displacement. Outside of this region, $$F_{HardStop}=0.$$

For more information about these settings, see the Translational Hard Stop block page.

Cushion

The block can model cushioning toward the extremes of the piston stroke. Select Cylinder end cushioning to slow the piston motion as it approaches the maximum extension, defined by the Piston stroke parameter. For more information on the functionality of a cylinder cushion, see the Cylinder Cushion (IL) block.

Friction

The block can model friction against piston motion. When you select Cylinder friction, the resulting friction is a combination of the Stribeck, Coulomb, and viscous effects. The block measures the pressure difference between the chamber pressure and the environment pressure. For more information on the friction model and its limitations, see the Cylinder Friction (IL) block.

Numerically-Smoothed Area and Pressure

You can maintain numerical robustness in your simulation by adjusting the Smoothing factor parameter. If the Smoothing factor parameter is nonzero, the block smooths the cushion A and B orifice areas and the check valve pressure ranges. The orifice area is smoothly saturated between the cushion A and cushion B Leakage area between plunger and cushion sleeve and Cushion plunger cross-sectional area parameters while the valve pressure is saturated between the cushion A and cushion B Check valve cracking pressure differential and Check valve maximum pressure differential parameters. For more information, see Numerical Smoothing.

Block Schematic

The Double-Acting Actuator (IL) block comprises four Simscape Foundation blocks:

• Translational Mechanical Converter (IL)

• Translational Hard Stop

• Ideal Translational Motion Sensor

• Infinite Flow Resistance (IL), if you select Same fluid on both sides.

and two Isothermal Liquid library blocks:

• Cylinder Cushion (IL)

• Cylinder Friction (IL)

This figure shows how the components connect to model the actuator block if you select Cylinder A end cushioning, Cylinder B end cushioning, Cylinder friction effect, and Same fluid on both sides.

Momentum Balance

The momentum conservation equation for the actuator is

$$\text{F= }\epsilon (S_A{p}_A-S_B{p}_B-S_{Rod}{p}_{env})$$

where:

• F is the force the liquid exerts on the converter interface. This force expression does not account for the force contributions due to the hard stop, cylinder cushions, or cylinder friction subcomponents. To see those force contributions to the converter interface, see the documentation pages for those subcomponents.

• ε depends on the Mechanical orientation of the converter. If Mechanical orientation is Pressure at A causes positive displacement of R relative to C, ε = 1. If Mechanical orientation is Pressure at A causes negative displacement of R relative to C, ε = -1.

• S_Rod is the rod cross-sectional area where$$S_{Rod}=S_A-S_B$$.

• S_A is the value of the Piston cross-sectional area in chamber A parameter.

• S_B is the value of the Piston cross-sectional area in chamber B parameter.

• p_A is the pressure inside chamber A.

• p_B is the pressure inside chamber B.

• p_env is the environment pressure.

Examples

Hydraulic Actuator with Dual Counterbalance Valves

An actuator controlled by a 4-way directional valve and loaded with an overriding load, requiring the use of counterbalance valves to prevent the load from creeping when the directional valve is in the neutral position. In the neutral position, the directional valve connects ports A and B to the reservoir while blocking the pressure port P. The counterbalance valves block flow from returning to the reservoir, thus holding the actuator in place.

• Open Model

Drill-Ream Actuator

An actuator that drives a machine tool working unit performing a sequence of three technological operations: coarse drilling, fine drilling, and reaming. One of three pressure-compensated flow control valves controls the actuator speed as metering out return flow from the cylinder. Directional valves that are activated by a control unit perform the selection of an appropriate flow control.

• Open Model

Troubleshoot Actuator Block Models

Troubleshoot problems in a model that contains actuator blocks and cannot converge during simulation. Blocks that interface with the mechanical domain, like actuators, can cause solver problems. These problems arise because the mechanical domain can introduce variables that cause a high differential index, which the solver cannot always overcome. A high differential index occurs when there are not sufficient degrees of freedom in the model. This behavior can cause issues where a model makes physical sense, but generates errors when the solver cannot converge.

• Open Script

Ports

Input

p — Piston position input, m

physical signal

Physical signal input port associated with the piston position that you specify using a Simscape Multibody block.

Dependencies

To expose this port, set Piston displacement from chamber A cap to Provide input signal from Multibody joint.

Programmatic Use

Port: p_in

Output

p — Piston position output, m

physical signal

Physical signal port associated with the piston position.

Dependencies

To expose this port, set Piston displacement from chamber A cap to Calculate from velocity of port R relative to port C.

Programmatic Use

Port: p_out

Conserving

A — Inlet to chamber A

isothermal liquid

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

Programmatic Use

Port: A

B — Inlet to chamber B

isothermal liquid

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

Programmatic Use

Port: B

C — Actuator casing

mechanical translational

Mechanical translational conserving port associated with the case.

Programmatic Use

Port: C

R — Actuator piston

mechanical translational

Mechanical translational conserving port associated with the piston.

Programmatic Use

Port: R

Parameters

Actuator

Same fluid on both sides — Option to model same fluid in both chambers

on (default) | off

Whether to model the same fluid in both actuator chambers. If you select this parameter, the actuator propagates fluid properties through both chambers. Clear this parameter to model each chamber as a different fluid, where each chamber is connected to an isolated fluid network.

Programmatic Use

Parameter:	single_fluid
Values:	"true" | "false"

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

Sets the 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 liquid at port A is expanding. This corresponds to rod extension.

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

Programmatic Use

Parameter:	mech_orientation
Values:	"foundation.enum.MechOrientationTranslational.Positive" | "foundation.enum.MechOrientationTranslational.Negative"

Piston cross-sectional area in chamber A — Chamber A piston area

0.01 m^2 (default) | positive scalar

Cross-sectional area of the piston rod on the chamber A side.

Programmatic Use

Parameter: piston_area_A

Piston cross-sectional area in chamber B — Chamber B piston area

0.01 m^2 (default) | positive scalar

Cross-sectional area of the piston rod on the chamber B side.

Programmatic Use

Parameter: piston_area_B

Piston stroke — Maximum piston travel distance

0.1 m (default) | positive scalar

Maximum piston travel distance.

Programmatic Use

Parameter: stroke

Dead volume in chamber A — Chamber A minimum volume without hardstop penetration

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

Volume of liquid when the piston displacement is 0 in chamber A. This is the liquid volume when the piston is up against the actuator end cap.

Programmatic Use

Parameter: dead_volume_A

Dead volume in chamber B — Chamber B minimum volume without hardstop penetration

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

Volume of liquid when the piston displacement is 0 in chamber B. This is the liquid volume when the piston is up against the actuator end cap.

Programmatic Use

Parameter: dead_volume_B

Environment pressure specification — Reference environment pressure

Atmospheric pressure (default) | Specified pressure

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

Programmatic Use

Parameter:	pressure_spec
Values:	"foundation.enum.pressure_spec.atmospheric" | "foundation.enum.pressure_spec.specified"

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.

Programmatic Use

Parameter: environment_pressure

Hard Stop

Hard stop model — Select the 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

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

Programmatic Use

Parameter:	hardstop_model
Values:	"simscape.enum.hardstop.smooth" | "simscape.enum.hardstop.fullundamped" | "simscape.enum.hardstop.fulldamped" | "simscape.enum.hardstop.modechart"

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

• 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

Programmatic Use

Parameter: stiff_coeff

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

• 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

Programmatic Use

Parameter: damping_coeff

Transition region — Application range of hard stop force model

0.1 mm (default) | positive scalar

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.

Programmatic Use

Parameter: transition

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.

Programmatic Use

Parameter: coeff_rest

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

0.001 m/s (default) | nonnegative scalar

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.

Programmatic Use

Parameter: v_tol

Static contact release force threshold — 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.

Programmatic Use

Parameter: f_tol

Converter Cushion A

Cylinder A end cushioning — Whether to model piston slow-down at maximum extension

off (default) | on

Whether to model piston slow-down at the maximum extension. See the Cylinder Cushion (IL) block for more information.

Programmatic Use

Parameter:	cushion_A_spec
Values:	"true" | "false"

Cushion plunger cross-sectional area — Cylinder cushion plunger area

1e-4 m^2 (default) | positive scalar

Area of the plunger inside the actuator cushion element.

Dependencies

To enable this parameter, select Cylinder A end cushioning.

Programmatic Use

Parameter: area_plunger_A

Cushion plunger length — Length of cushion plunger

1e-3 m (default) | positive scalar

Length of the cushion plunger.

Dependencies

To enable this parameter, select Cylinder A end cushioning.

Programmatic Use

Parameter: length_plunger_A

Cushion orifice area — Area of orifice between cushion chambers

1e-6 m^2 (default) | positive scalar

Area of the orifice between the cushion chambers.

Dependencies

To enable this parameter, select Cylinder A end cushioning.

Programmatic Use

Parameter: area_cushion_orifice_A

Leakage area between plunger and cushion sleeve — Gap between cushion plunger and sleeve

1e-7 m^2 (default) | positive scalar

Gap area between the cushion plunger and sleeve. This value contributes to numerical stability by maintaining continuity in the flow.

Dependencies

To enable this parameter, select Cylinder A end cushioning.

Programmatic Use

Parameter: area_leak_plunger_A

Check valve cracking pressure differential — Cushion threshold pressure

0.01 MPa (default) | positive scalar

Pressure beyond which the valve operation triggers. When the pressure difference between port A and P_env meets or exceeds the value of this parameter, the cushion valve begins to open.

Dependencies

To enable this parameter, select Cylinder A end cushioning.

Programmatic Use

Parameter: p_crack_differential_A

Check valve maximum pressure differential — Maximum cushion differential pressure

0.1 MPa (default) | positive scalar

Maximum cushion valve differential pressure. This parameter provides an upper limit to the pressure so that system pressures remain realistic.

Dependencies

To enable this parameter, select Cylinder A end cushioning.

Programmatic Use

Parameter: press_max_differential_A

Check valve maximum area — Area of fully opened cushion valve

1e-4 m^2 (default) | positive scalar

Cross-sectional area of the cushion valve in the fully open position.

Dependencies

To enable this parameter, select Cylinder A end cushioning.

Programmatic Use

Parameter: check_valve_area_max_A

Check valve leakage area — Cushion valve gap area in fully closed position

1e-10 m^2 (default) | positive scalar

Sum of all gaps when the cushion check valve is in the fully closed position. Any area smaller than this value saturates to the specified leakage area. This value contributes to numerical stability by maintaining continuity in the flow.

Dependencies

To enable this parameter, select Cylinder A end cushioning.

Programmatic Use

Parameter: check_valve_area_leak_A

Converter Cushion B

Cylinder B end cushioning — Whether to model piston slow-down at maximum extension

off (default) | on

Whether to model piston slow-down at the maximum extension. See the Cylinder Cushion (IL) block for more information.

Programmatic Use

Parameter:	cushion_B_spec
Values:	"true" | "false"

Cushion plunger cross-sectional area — Cylinder cushion plunger area

1e-4 m^2 (default) | positive scalar

Area of the plunger inside the actuator cushion element.

Dependencies

To enable this parameter, select Cylinder B end cushioning.

Programmatic Use

Parameter: area_plunger_B

Cushion plunger length — Length of cushion plunger

1e-3 m (default) | positive scalar

Length of the cushion plunger.

Dependencies

To enable this parameter, select Cylinder B end cushioning.

Programmatic Use

Parameter: length_plunger_B

Cushion orifice area — Area of orifice between cushion chambers

1e-6 m^2 (default) | positive scalar

Area of the orifice between the cushion chambers.

Dependencies

To enable this parameter, select Cylinder B end cushioning.

Programmatic Use

Parameter: area_cushion_orifice_B

Leakage area between plunger and cushion sleeve — Gap between cushion plunger and sleeve

1e-7 m^2 (default) | positive scalar

Gap area between the cushion plunger and sleeve. This value contributes to numerical stability by maintaining continuity in the flow.

Dependencies

To enable this parameter, select Cylinder B end cushioning.

Programmatic Use

Parameter: area_leak_plunger_B

Check valve cracking pressure differential — Cushion threshold pressure

0.01 MPa (default) | positive scalar

Pressure beyond which the valve operation triggers. When the pressure difference between port A and P_env meets or exceeds the value of this parameter, the cushion valve begins to open.

Dependencies

To enable this parameter, select Cylinder B end cushioning.

Programmatic Use

Parameter: p_crack_differential_B

Check valve maximum pressure differential — Maximum cushion differential pressure

0.1 MPa (default) | positive scalar

Maximum cushion valve differential pressure. This parameter provides an upper limit to the pressure so that system pressures remain realistic.

Dependencies

To enable this parameter, select Cylinder B end cushioning.

Programmatic Use

Parameter: press_max_differential_B

Check valve maximum area — Area of fully opened cushion valve

1e-4 m^2 (default) | positive scalar

Cross-sectional area of the cushion valve in the fully open position.

Dependencies

To enable this parameter, select Cylinder B end cushioning.

Programmatic Use

Parameter: check_valve_area_max_B

Check valve leakage area — Cushion valve gap area in fully closed position

1e-10 m^2 (default) | positive scalar

Sum of all gaps when the cushion check valve is in the fully closed position. Any area smaller than this value saturates to the specified leakage area. This value contributes to numerical stability by maintaining continuity in the flow.

Dependencies

To enable this parameter, select Cylinder B end cushioning.

Programmatic Use

Parameter: check_valve_area_leak_B

Smoothing factor — Numerical smoothing factor

0.01 (default) | positive scalar

Continuous smoothing factor that introduces a layer of gradual change to the flow response when the variable orifice and check valve are in near-open or near-closed positions. Set this value to a nonzero value less than one to increase the stability of your simulation in these regimes.

Dependencies

To enable this parameter, select Cylinder B end cushioning.

Programmatic Use

Parameter: smoothing_factor_A

Friction

Cylinder friction effect — Whether to model friction against piston motion

off (default) | on

Whether to model friction against piston motion. The block accounts for Coulomb, Stribeck, and viscous friction. See the Cylinder Friction (IL) block for more information.

Programmatic Use

Parameter:	friction_spec
Values:	"true" | "false"

Breakaway to Coulomb friction force ratio — Ratio of breakaway force to Coulomb friction force

1.2 (default) | positive scalar

Ratio of the breakaway force to the Coulomb friction force.

Dependencies

To enable this parameter, select Cylinder friction.

Programmatic Use

Parameter: breakaway_Coulomb_ratio

Breakaway friction velocity — Threshold for motion

0.1 m/s (default) | positive scalar

Threshold velocity for the motion against the friction force to begin.

Dependencies

To enable this parameter, select Cylinder friction.

Programmatic Use

Parameter: breakaway_velocity

Preload force — Initial force on cylinder

20 N (default) | scalar

Force on the cylinder when it is in the neutral position.

Dependencies

To enable this parameter, select Cylinder friction effect.

Programmatic Use

Parameter: preload_force

Coulomb friction force coefficient — Coulomb friction force coefficient

1e-6 N/Pa (default) | positive scalar

Coulomb force coefficient of friction.

Dependencies

To enable this parameter, select Cylinder friction effect.

Programmatic Use

Parameter: Coulomb_coeff

Viscous friction coefficient — Viscous friction coefficient

100 N/(m/s) (default) | positive scalar

Viscous friction coefficient.

Dependencies

To enable this parameter, select Cylinder friction effect.

Programmatic Use

Parameter: viscous_coeff

Initial Conditions

Piston displacement from chamber A cap — 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 calculates the position internally and reports the position at port p. The position is between 0 and the Piston stroke when the mechanical orientation is positive and 0 and –Piston stroke when the mechanical orientation is negative.

Programmatic Use

Parameter:	displacement_spec
Values:	"foundation.enum.DisplacementSpec.Calculate" | "foundation.enum.DisplacementSpec.InputSignal"

Initial piston displacement from chamber A cap — Piston position measured from chamber A cap at start of simulation

0 m (default) | scalar

Piston position with respect to the chamber A cap at the start of the simulation.

Dependencies

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

Programmatic Use

Parameter: x0

Enable dynamic compressibility — Whether to model fluid compressibility

on (default) | off

Whether to model the dynamic compressibility of the liquid. Dynamic compressibility affects the transient response of the system at small timescales. If you select this parameter, the pressure responds dynamically based on the accumulation of fluid mass in the volume. If you clear this parameter, the volume does not accumulate mass and the pressure response is instantaneous. Clearing this setting can improve simulation performance, but may have a negative effect on the simulation robustness. Only clear this setting for small fluid volumes or models with long simulation times.

Programmatic Use

Parameter:	dynamic_compressibility
Values:	"true" | "false"

Initial liquid pressure in chamber A — Starting liquid pressure in chamber A

0.101325 MPa (default) | positive scalar

Starting liquid pressure for compressible fluids.

Dependencies

To enable this parameter, select Enable dynamic compressibility.

Programmatic Use

Parameter: p0_A

Initial liquid pressure in chamber B — Starting liquid pressure in chamber B

0.101325 MPa (default) | positive scalar

Starting liquid pressure for compressible fluids.

Dependencies

To enable this parameter, select Enable dynamic compressibility.

Programmatic Use

Parameter: p0_B

Nominal liquid pressure in chamber A — Pressure at nominal operating conditions in chamber A

0.101325 MPa (default) | scalar

Liquid pressure at nominal operating conditions in chamber A. The block uses this value to calculate the nominal density to use in the mass conservation equation when dynamic compressibility is disabled.

Dependencies

To enable this parameter, clear the Enable dynamic compressibility checkbox.

Programmatic Use

Parameter: p_nominal_A

Nominal liquid pressure in chamber B — Pressure at nominal operating conditions in chamber B

0.101325 MPa (default) | scalar

Liquid pressure at nominal operating conditions in chamber B. The block uses this value to calculate the nominal density to use in the mass conservation equation when dynamic compressibility is disabled.

Dependencies

To enable this parameter, clear the Enable dynamic compressibility checkbox.

Programmatic Use

Parameter: p_nominal_B

Extended Capabilities

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

Version History

Introduced in R2020a

R2026b: Internal leakage parameter will be removed

The Internal leakage parameter will be removed in a future release. If you select Internal leakage, the block generates an error. To model an actuator that models leakage, replace the Double-Acting Actuator (IL) block with this network:

R2026a: Internal leakage parameter will be removed in a future release

The Internal leakage parameter will be removed in a future release and the block will no longer model leakage. If you select Internal leakage, the block will issue a warning.

R2024a: Model different fluids on each side of the actuator

Clear the new Same fluid on both sides parameter to block the propagation of fluid properties and model each chamber as a different fluid connected to its own isolated fluid network.

R2023a: New hard stop parameterization option

The block has a new option for the Hard stop model parameter. This option, called Based on coefficient of restitution, models the hard stop by using a mode chart.