# Single-Acting Rotary Actuator (IL)

Double-acting rotary actuator in an isothermal liquid system

Since R2020a

Libraries:
Simscape / Fluids / Isothermal Liquid / Actuators

## Description

The Single-Acting Rotary Actuator (IL) block models a rotary actuator that converts liquid pressure into mechanical torque in an isothermal liquid network. The motion of the piston when it is near full extension or full retraction is limited by one of four hard stop models.

Port A is the isothermal liquid conserving port associated with inlet of the liquid chamber. Ports R and C are the mechanical rotational conserving ports associated with the rotating shaft and the actuator casing, respectively. If Mechanical orientation is set to ```Pressure at A causes positive rotation of R relative to C```, the pressure in the liquid chamber causes a positive rotation of the shaft at port R relative to port C. When the shaft angle is calculated internally, the physical signal port q reports the angle. When the angle is set by a connection to a Simscape™ Multibody™ joint, it is received as a physical signal at port q.

### 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 neutral, or `0`, when the chamber volume is equal to the 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 Rotational Multibody Interface block connection to a Simscape Multibody joint.

### 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 Single-Acting Rotary Actuator (IL) block models this behavior with a choice of four 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```.

• `Based on coefficient of restitution`

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 Stroke or piston initial displacement. Outside of this region, ${F}_{HardStop}=0.$

### Block Schematics

The actuator block comprises three Foundation Library blocks:

Underlying Block Components

### Leakage

Laminar leakage is not accounted for in the Single-Acting Rotary Actuator (IL) block. To include leakage in your simulation, set the Cross-sectional geometry parameter to `Custom` and connect port A to port A of the Laminar Leakage (IL) block. Connect port B of the Laminar Leakage (IL) block to a Reservoir (IL) block.

## Ports

### Conserving

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Isothermal liquid conserving port associated with the actuator.

Mechanical rotational conserving port associated with the shaft angular velocity and torque.

Mechanical rotational conserving port associated with the actuator casing.

### Input

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Shaft angle, received as a physical signal from a Simscape Multibody block.

#### Dependencies

To expose this port, set Shaft rotation from chamber A to ```Provide input signal from Multibody joint```.

### Output

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Shaft angle, reported as a physical signal.

#### Dependencies

To expose this port, set Shaft rotation from chamber A to ```Calculate from angular velocity of port R relative to port C```.

## Parameters

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### Actuator

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.

Effective displacement of the actuator.

Shaft maximum travel between stops.

Volume of liquid when the piston displacement is `0`. This is the liquid volume when the piston is up against the actuator end cap.

Choice of environment pressure. Options include `Atmospheric pressure` and `Specified pressure`.

Pressure outside the actuator casing. This pressure acts against the pressures inside the actuator chambers. A value of zero corresponds to a vacuum.

#### Dependencies

To enable this parameter, set Environment pressure specification to ```Specified pressure```.

### Hard Stop

Model choice for the force on the piston at full extension or full retraction. See the Rotational Hard Stop block for more information.

Specifies the elastic property of colliding bodies for the Rotational Hard Stop block. The greater the value of the parameter, the more rigid the impact between the piston and the stop becomes. Lower values make contact softer and generally improve convergence and computational efficiency.

#### 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```

Specifies the dissipating property of colliding bodies for the Rotational Hard Stop block. 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.

#### 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```

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.

#### Dependencies

To enable this parameter, set Hard stop model to ```Stiffness and damping applied smoothly through transition region, damped rebound```.

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```.

Threshold relative speed between the 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```.

Minimum torque 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

Method for determining the shaft angle. The block can receive the angle from a Multibody block when set to ```Provide input signal from Multibody joint```, or calculates the angle internally, which is reported at port q.

The position of the actuator at the beginning of simulation. This value falls between `0` and the value of the Stroke in the positive orientation, and `0` and the negative value of the Stroke in the negative orientation.

#### Dependencies

To enable this parameter, set Shaft rotation from chamber A to ```Calculate from angular velocity of port R relative to port C```.

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

Pressure in actuator chamber A at the start of simulation.

#### Dependencies

To enable this parameter, select Fluid dynamic compressibility.

## Version History

Introduced in R2020a

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