Double-Acting Actuator (TL)

Double-acting linear actuator in a thermal liquid network

Libraries:
Simscape / Fluids / Thermal Liquid / Actuators

Description

The Double-Acting Actuator (TL) block models a linear actuator with a piston controlled by two opposing thermal liquid chambers. The actuator generates force in the extension and retraction strokes. The generated force depends on the pressure difference between the two chambers.

The figure shows the key components of the actuator. Ports A and B represent the thermal liquid chamber inlets. Port R represents the translating actuator piston and port C represents the actuator case. Ports HA and HB represent the thermal interfaces between each chamber and the environment. The moving piston is adiabatic.

Double-Acting Actuator Schematic

Displacement

The block measures the piston displacement as the position at port R relative to port C. The Mechanical orientation parameter identifies the direction of piston displacement. The piston displacement is neutral, or 0, when the chamber A volume is equal to the value of the Dead volume in chamber A parameter. When the Piston displacement from chamber A cap parameter is Provide input signal from Multibody joint, you input the piston displacement using port p. You can ensure that the derivative of the position signal is equal to the piston velocity by using a Translational Multibody Interface block to provide the piston displacement.

The direction of the piston motion depends on the Mechanical orientation parameter. If the mechanical orientation is positive, then the piston translation is positive in relation to the actuator case when the gauge pressure at port A is positive. The direction of motion reverses when the mechanical orientation is negative.

Hard Stop

A set of hard stops limit the piston range of motion. The block uses an implementation of the Translational Hard Stop block, which treats hard stops like spring-damper systems. The spring stiffness coefficient controls the restorative component of the hard-stop contact force and the damping coefficient the dissipative component.

The hard stops are located at the distal ends of the piston stroke. If the mechanical orientation is positive, then the lower hard stop is at x = 0, and the upper hard stop is at x = +stroke. If the mechanical orientation is negative, then the lower hard stop is at x = -stroke, and the upper hard stop is at x = 0.

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 (TL) 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 (TL) block.

Block Composite

This block is a composite component based on these Simscape™ Foundation blocks:

Diagram of elements that make up the block.

If you select Cylinder friction, Cylinder A end cushioning, or Cylinder B end cushioning, the block composite also includes the Cylinder Friction (TL) block or two Cylinder Cushion (TL) blocks.

Diagram of elements that make up the block with friction and cushion.

Examples

Reciprocal Actuator with Differential Cylinders

A double-acting actuator with differential cylinders. The pump output is connected to cylinder B of the actuator while cylinder A of the actuator can be connected to either the pump or the reservoir through the 3-way directional valve. When cylinder A is connected to the pump, pressures at both cylinders become equal. Because of the larger effective piston area in cylinder A, the interface force in cylinder A is larger than that of in cylinder B which causes the piston to extend. When cylinder A is connected to the reservoir, the piston starts to retract. The 3-way directional valve is controlled by a sinusoidal signal to achieve repeating reciprocal motion in the actuator.

Open Model

Ports

Input

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p — Piston position input, m
physical signal

Physical signal input associated with the piston position, in m. Connect this port to a Simscape Multibody™ network using a Translational Multibody Interface block.

Dependencies

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

Output

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p — Piston position, m
physical signal

Physical signal port associated with the piston position.

Dependencies

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

Conserving

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A — Chamber A inlet
thermal liquid

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

B — Chamber B inlet
thermal liquid

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

R — Actuator piston
mechanical translational

Mechanical translational conserving port associated with the actuator piston.

C — Actuator casing
mechanical translational

Mechanical translational conserving port associated with the actuator casing.

HA — Chamber A heat flow
thermal

Thermal conserving port associated with chamber A.

HB — Chamber B heat flow
thermal

Thermal conserving port associated with chamber B.

Parameters

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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.

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`

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 motion 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 motion corresponds to rod contraction.

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.

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.

Piston stroke — Maximum piston travel distance
`0.1 m` (default) | positive scalar

Maximum piston travel distance.

Dead volume in chamber A — Chamber A fluid volume at full piston retraction
`1e-5 m^3` (default) | positive scalar

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

Dead volume in chamber B — Chamber B fluid volume at full piston retraction
`1e-5 m^3` (default) | positive scalar

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

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.

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.

Hard Stop

Hard stop model — 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`

Hard stop model to use when the piston is at full extension or full extraction. See the Translational Hard Stop block for more information.

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 one of these settings:

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

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 one of these settings:

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

Transition region — Application range of hard stop force model
`0.1` `mm` (default) | positive scalar

Application range of the hard stop force model. The block does not apply the hard stop model when the maximum extension or retraction of the piston is outside of this range. In this situation, 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.

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.

Static contact speed threshold — Threshold relative speed between slider and stop before collision
`0.001 m/s` (default) | nonnegative scalar

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

Static contact release force 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.

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 (TL) block for more information.

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.

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.

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.

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.

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.

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.

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.

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.

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 A end cushioning.

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 (TL) block for more information.