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Single-Acting Actuator (TL)

Linear actuator with piston motion controlled by one thermal liquid chamber

Library

Thermal Liquid/Actuators

Description

The Single-Acting Actuator (TL) block models a linear actuator with piston motion controlled by a single thermal liquid chamber. The actuator generates force in the extension and retraction strokes, but the actuation force depends on the gauge pressure at a single chamber.

The figure shows the key components of the actuator model. Port A represents the thermal liquid chamber inlet. Port R represents the translating actuator piston and port C the actuator case. Port H represents the thermal interface between the thermal liquid chamber and the environment.

Single-Acting Actuator Schematic

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 positive gauge pressure at port A yields a positive piston translation relative to the actuator case. The direction of motion reverses for a negative mechanical orientation.

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.

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

Composite Component Diagram

Parameters

Actuator Tab

Mechanical orientation

Orientation of the actuator piston relative to the direction of 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 default setting is Positive.

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

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 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 Positive and at minus the piston stroke if Mechanical Orientation is set to Negative.

Dead volume

Fluid volume remaining in the actuator chamber at a zero piston displacement. The block uses this volume to account for mass and energy storage in the chamber when the piston is at position zero. The dead volume must be greater than zero. 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 chamber. 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 1 mm..

Initial Conditions Tab

Piston initial 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 Positive. It must be between zero and minus the piston stroke if the Mechanical orientation parameter is set to Negative. The default value is 0 m.

Initial liquid temperature

Temperature in actuator chamber A 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

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

Ports

  • A — Thermal liquid conserving port representing chamber A

  • C — Translational conserving port representing the actuator casing

  • R — Translational conserving port representing the actuator piston

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

  • P — Physical signal output port for the piston position data

Introduced in R2016a

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