Main Content

Double-Acting Actuator (TL)

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

  • Library:
  • Simscape / Fluids / Thermal Liquid / Actuators

  • Double-Acting Actuator (TL) block

Description

The Double-Acting Actuator (TL) block models 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:

Composite Component Diagram

Ports

  • A — Thermal liquid conserving port representing actuator chamber A

  • B — Thermal liquid conserving port representing actuator chamber B

  • C — Mechanical conserving port representing the actuator case

  • R — Mechanical conserving port representing the actuator piston

  • HA — Thermal conserving port representing the thermal interface between chamber A and the environment

  • HB — Thermal conserving port representing the thermal interface between chamber B and the environment

  • p — Physical signal input port for the piston position data. To expose this port, set Piston displacement from chamber A cap to Provide input signal from Multibody joint.

  • p — Physical signal output port for the piston position data. To expose this port, set Piston displacement from chamber A cap to Calculate from velocity of port R relative to port C.

Parameters

Actuator Tab

Mechanical orientation

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.

The mechanical orientation affects the placement of the actuator hard stops. One hard stop is always at position zero. The second hard stop is at the piston stroke distance if the mechanical orientation is positive and at minus the piston stroke distance if the mechanical orientation is negative.

Piston cross-sectional area at A

Area normal to the direction of flow in actuator chamber A. The block uses this area to calculate the hydraulic force due to the fluid pressure in chamber A. The piston cross-sectional area must be greater than zero. The default value is 0.01 m^2.

Piston cross-sectional area at B

Area normal to the direction of flow in actuator chamber B. The block uses this area to calculate the hydraulic force due to the fluid pressure in chamber B. The piston cross-sectional area must be greater than zero. The default value is 0.01 m^2.

Piston stroke

Maximum distance the actuator piston can travel. The piston stroke must be greater than zero. The default value is 0.1 m.

Hard stops limit piston motion to the length of the piston stroke. One hard stop is located at position zero. The second hard stop is at the piston stroke distance if Mechanical Orientation is set to Pressure at A causes positive displacement of R relative to C and at minus the piston stroke if Mechanical Orientation is set to Pressure at A causes negative displacement of R relative to C.

Dead volume at A

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. The default value is 1e-5 m^3.

Dead volume at B

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. The default value is 1e-5 m^3.

Environment pressure specification

Choice of environment pressure. Options include Atmospheric pressure and Specified pressure. Selecting Specified pressure exposes an additional parameter, Environment pressure.

Environment pressure

Pressure outside the actuator casing. This pressure acts against the pressures inside the actuator chambers. A value of zero corresponds to a vacuum. The default value is 0.101325 MPa. This parameter is visible only when Environment pressure specification is set to Specified pressure.

Hard Stop Tab

Hard-stop stiffness coefficient

Spring coefficient of the actuator hard stops. The spring coefficient accounts for the restorative portion of the hard-stop contact force. Increase the coefficient value to model harder contact. The default value is 1e10 N/m.

Hard-stop damping coefficient

Damping coefficient of the actuator hard stops. The damping coefficient accounts for the dissipative portion of the hard-stop contact force. Increase the coefficient value to reduce bounce upon contact. The default value is 150 N/(m/s).

Hard stop model

Modeling approach for hard stops. Options include:

  • Stiffness and damping applied smoothly through transition region (default) — Scale the magnitude of the contact force from zero to its full value over a specified transition length. The scaling is polynomial in nature. The polynomial scaling function is numerically smooth and it produces no zero crossings of any kind.

  • Full stiffness and damping applied at bounds, undamped rebound — Apply the full value of the calculated contact force when the hard-stop location is breached. The contact force is a mix of spring and damping forces during penetration and a spring force—without a damping component—during rebound. No smoothing is applied.

  • Full stiffness and damping applied at bounds, damped rebound — Apply the full value of the calculated contact force when the hard-stop location is breached. The contact force is a mix of spring and damping forces during both penetration and rebound. No smoothing is applied. This is the hard-stop model used in previous releases.

Transition region

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 specified here. It is at its full value when the distance to the hard stop is zero. The default value is 1mm.

Initial Conditions Tab

Piston displacement from chamber A cap

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. The default value is Calculate from velocity of port R relative to port C.

Initial piston displacement

Piston position at the start of simulation. This value must be between zero and the piston stroke if the Mechanical orientation parameter is set to Pressure at A causes positive displacement of R relative to C. It must be between zero and minus the piston stroke if the Mechanical orientation parameter is set to Pressure at A causes negative displacement of R relative to C. The default value is 0 m. To enable this parameter, set Piston displacement from chamber A cap to Calculate from velocity of port R relative to port C.

Initial liquid temperature at A

Temperature in actuator chamber A at the start of simulation. The default value is 293.15 K.

Initial liquid temperature at B

Temperature in actuator chamber B at the start of simulation. The default value is 293.15 K.

Fluid dynamic compressibility

Option to model effects due to fluid dynamic compressibility. Select On to enable fluid dynamic compressibility and Off to disable it.

Initial liquid pressure in chamber A

Pressure in actuator chamber A at the start of simulation. The default value is 0.101325 MPa.

Initial liquid pressure in chamber B

Pressure in actuator chamber B at the start of simulation. The default value is 0.101325 MPa.

Extended Capabilities

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

Introduced in R2016a