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Double-Acting Servo Valve Actuator (IL)

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

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  • Simscape / Fluids / Valve Actuators & Forces

  • Double-Acting Servo Valve Actuator (IL) block

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 three hard stop models. Fluid compressibility is optionally modeled in both piston chambers.

The physical signal output P 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 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 Spool stroke or piston initial displacement. Outside of this region, FHardStop=0.

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

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 of the spool position, in m, specified as a physical signal. 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

Specifies the elasticity for the hard stop model. The greater the value of the parameter, the more rigid the impact between the rod and the stop becomes. Lower values result in softer contact and generally improve simulation efficiency and convergence.

Specifies dissipating property of colliding bodies for the hard stop model. At zero damping, the impact is elastic. The greater the value of the parameter, the greater the energy dissipation during piston-stop interaction. Damping affects slider motion as long as the slider is in contact with the stop, including the period when slider is pulled back from the contact. Set this parameter to a nonzero value to improve the efficiency and convergence of your simulation.

Modeling approach for hard stops.

  • Stiffness and damping applied smoothly through transition region, damped rebound — Specify a transition region in which the torque is scaled from zero. At the end of the transition region, the full stiffness and damping are applied. This model has damping applied on the rebound, but it is limited to the value of the stiffness torque. Damping can reduce or eliminate the torque provided by the stiffness, but never exceed it. All equations are smooth and produce no zero crossings.

  • Full stiffness and damping applied at bounds, undamped rebound — This model has full stiffness and damping applied with impact at the upper and lower bounds and no damping on the rebound. The equations produce no zero crossings when velocity changes sign, but there is a position-based zero crossing at the bounds. Having no damping on rebound helps to push the slider past this position quickly. This model has nonlinear equations.

  • Full stiffness and damping applied at bounds, damped rebound — This model has full stiffness and damping applied with impact at the upper and lower bounds and damping applied on the rebound. The equations are switched linear, but produce position-based zero crossings. Use this hard stop model if simscape.findNonlinearBlocks indicates that this is the block that prevents the whole network from being switched linear.

Distance below which scaling is applied to the hard-stop force. The contact force is zero when the distance to the hard stop is equal to the value of this parameter. The contact force is at its full value when the distance to the hard stop is zero.

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.

Introduced in R2020a