Double-Acting Actuator (TL)

Linear actuator with piston motion controlled by two opposing thermal liquid chambers

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Libraries:
Simscape / Fluids / Thermal Liquid / Actuators

Description

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

The figure shows the key components of the actuator model. Ports A and B represent the thermal liquid chamber inlets. Port R represents the translating actuator piston and port C 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 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 considered 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.

The direction of the piston motion depends on the mechanical orientation setting in the block dialog box. If the mechanical orientation is positive, then a higher pressure at port A yields a positive piston translation relative to the actuator case. The direction of motion reverses for a negative mechanical orientation.

Hard Stop

A set of hard stops limit the piston range of motion. The hard stops are treated as 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 at x = +stroke. If the mechanical orientation is negative, then the lower hard stop is at x = -stroke and the upper hard stop at x = 0.

Block Composite

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

• Translational Mechanical Converter (TL)

• Translational Hard Stop

• Ideal Translational Motion Sensor

Composite Component Diagram

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

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.

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.

Conserving

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 representing the actuator piston.

C — Actuator casing

mechanical translational

Mechanical translational conserving port representing the actuator casing.

HA — Chamber A heat flow

thermal

Thermal conserving port associated chamber A.

HB — Chamber B heat flow

thermal

Thermal conserving port associated with chamber B.

Parameters

Actuator

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.

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 is the liquid volume when the piston is up 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 is the liquid volume when the piston is up 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 — 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.

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

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

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.

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 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.

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.

Initial Conditions

Piston displacement — 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.

Initial piston displacement — Piston position at start of simulation

0 m (default) | scalar

Piston position at the start of the simulation.

Dependencies

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

Fluid dynamic compressibility — Whether to model fluid compressibility

on (default) | off

Whether to model any change in fluid density due to fluid compressibility. When you select Fluid compressibility, 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.

Initial liquid temperature in chamber A — Starting liquid temperature in chamber A

293.15 K (default)

Initial temperature of the liquid volume in the actuator.

Initial liquid temperature in chamber B — Starting liquid temperature in chamber B

293.15 K (default)

Initial temperature of the liquid volume in the actuator.

Initial liquid pressure in chamber A — Starting liquid pressure in chamber A for compressible fluids

0.101325 MPa (default) | positive scalar

Starting liquid pressure for compressible fluids.

Dependencies

To enable this parameter, select Fluid dynamic compressibility.

Initial liquid pressure in chamber B — Starting liquid pressure in chamber B for compressible fluids

0.101325 MPa (default) | positive scalar

Starting liquid pressure for compressible fluids.

Dependencies

To enable this parameter, select Fluid dynamic compressibility.

Extended Capabilities

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

Version History

Introduced in R2016a

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.