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Double-Acting Actuator (H-G)

(Not recommended) Linear actuator with opposing isothermal liquid and gas chambers

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The Hydraulics (Isothermal) library will be removed in a future release. Use the Isothermal Liquid library instead. (since R2020a)

For more information on updating your models, see Upgrading Hydraulic Models to Use Isothermal Liquid Blocks.

  • Double-Acting Actuator (H-G) block

Libraries:
Simscape / Fluids / Hydraulics (Isothermal) / Valves / Valve Actuators

Description

The Double-Acting Actuator (H-G) block represents a linear actuator with opposing chambers of isothermal liquid and gas. The chambers can be individually pressurized to power the actuator in both the extension and retraction strokes. A piston between the chambers converts the pressure difference across them into actuation force.

The figure maps the conserving ports of the block to the actuator parts. Ports A and B are the inlets of the isothermal liquid and gas chambers. Ports R and C are the translating piston and case. The gas chamber can exchange heat with the environment and is fitted for this purpose with port H. The isothermal liquid, being of constant temperature, exchanges heat neither with the environment nor with the gas across the piston.

The sign of the piston displacement relative to the case depends on the mechanical orientation of the actuator. Use the Mechanical orientation parameter to specify this setting. If the mechanical orientation is positive, the piston displacement is positive when the pressure is highest in the isothermal liquid chamber (port A). If the mechanical orientation is negative, the piston displacement (under the same pressure conditions) is negative.

Use port P to output the instantaneous piston position. The position measurement can be absolute or relative. Configure the Piston position display parameter to switch the measurement type if needed:

  • From piston initial distance from port A — The measurement is absolute. The first reading is the value specified in the Piston initial distance from port A. If that value is 10 in, the first reading is also 10 in.

  • From zero — The measurement is relative to the initial piston position. The first reading, as it corresponds to the initial piston position, is zero.

Hard stops limit the motion of the piston to the length of the case. The stops are modeled as spring-dampers, with spring and damping coefficients to capture material compliance. One is located at the bottom of the piston stroke and the other at the top:

  • If the Mechanical orientation setting is Positive, the bottom stop is at zero, and the top stop is at a distance equal to the piston stroke.

  • If the Mechanical orientation setting is Negative, the top stop is at zero, and the bottom stop is at a distance equal to the piston stroke.

The block is a composite component built from Simscape™ Foundation blocks. For more information on how the Double-Acting Actuator (H-G) block works, see the reference pages of the constituent blocks:

Ports

Output

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Piston position measurement. The measurement can be absolute or relative to the initial piston position. Use the Piston position display parameter to specify the measurement type.

Conserving

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Hydraulic (isothermal liquid) conserving port associated with the inlet to chamber A.

Gas conserving port associated with the inlet to chamber B.

Mechanical translational conserving port representing the piston rod. The piston is capable of translational motion relative to the casing.

Mechanical translational conserving port associated with the case.

Thermal conserving port associated with the surface of the gas chamber through which heat exchange with the surroundings can occur. The thermal processes at this port determine the temperature in the gas chamber and therefore at port B.

Parameters

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Hydraulic Side

Orientation of the actuator piston relative to the direction of fluid flow. A positive orientation causes the piston to move in the positive direction relative to the actuator casing in response to a positive flow rate through port A. The mechanical orientation affects the placement of the piston hard stops. See the block description for more information on the hard stop placement.

Area normal to the direction of flow in the body of the hydraulic chamber. The block uses this area to calculate the hydraulic force due to the fluid pressure in the hydraulic chamber. This parameter must be greater than zero.

Total distance of travel available to the piston, from one hard stop to the other. The hard stops limit the piston motion so that the piston is confined to stroke of the piston. See the block description for more information on the locations of the hard stops.

Reference against which to measure the piston position. This setting reflects in the output of port P. Use the default setting, From piston initial distance from port A, to output the absolute piston position; the first position reading is then the value of the Piston initial distance from port A parameter. Use the alternative setting, From zero, to output the piston position relative to the specified initial value; the first position reading is then zero.

Distance of the piston from the hard stop closest to the hydraulic inlet at the start of simulation. Use this parameter to change the starting position of the piston. This parameter affects the placement of the piston hard stops. For more information on the hard stop placement, see the block description.

Option to model the effects of dynamic compressibility inside the hydraulic chamber. The hydraulic fluid is treated as compressible if this parameter is set to On and as incompressible if it is set to Off. The block ignores the dependence of the hydraulic fluid density on pressure and temperature if Off is selected.

Hydraulic fluid volume remaining in the hydraulic chamber when the piston is pressed against the hard stop closest to the hydraulic inlet. The dead volume enables the block to capture the internal states of the hydraulic fluid volume—its pressure and temperature—when this volume is at a minimum. This parameter must be greater than zero.

Dependencies

This parameter is enabled when the Compressibility parameter is set to On.

Ratio of the specific heat of the gas entrained in the hydraulic fluid at constant pressure to that at constant volume. The block uses this parameter in the calculations of density for the hydraulic fluid.

Dependencies

This parameter is enabled when the Compressibility parameter is set to On.

Pressure inside the hydraulic chamber at simulation time zero relative to absolute zero. This parameter helps set the initial states of the hydraulic fluid volume.

Dependencies

This parameter is enabled when the Compressibility parameter is set to On.

Gas Side

Area normal to the direction of flow in the body of the gas chamber. The block uses this area to calculate the pneumatic force due to the fluid pressure in the gas chamber. This parameter must be greater than zero.

Area normal to the direction of flow at the entrance to the gas chamber. The cross-sectional area at the entrance can differ from that in the body of the chamber. Set the two cross-sectional areas to different values to model the effects of a sudden area change at the inlet. This parameter must be greater than zero.

Gas volume remaining in the gas chamber when the piston is pressed against the hard stop closest to the gas inlet. The dead volume enables the block to capture the internal states of the gas volume—its pressure and temperature—when this volume is at a minimum. This parameter must be greater than zero.

Pressure inside the gas chamber at simulation time zero relative to absolute zero. This parameter helps set the initial state of the gas volume.

Option to set the environment pressure of the gas chamber to the typical value of one earth atmosphere or to a custom value. Selecting Specified pressure exposes an additional parameter, Environment pressure, that you use to specify a custom pressure.

Pressure outside the gas chamber relative to absolute zero. This pressure acts against the pressure inside the gas chamber. A pressure of zero corresponds to a perfect vacuum.

Dependencies

This parameter is enabled when the Environment pressure specification is set to Specified pressure.

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.

Extended Capabilities

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

Version History

Introduced in R2016b

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See Also

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