Double-Acting Actuator Model

Aim :- Develop a double-acting actuator model using Simscape Multibody and Simscape components.

Objective :- The mechanical system of the cylinder needs to be built using Simscape Multibody library components/blocks, and the hydraulic system needs to be modeled using Simscape library physical components.

Theory :-

The following Cylindrical Model Schematic shows the three different configurations of the piston

Half Retracted, Fully Retracted, Fully Extended

How the Double Acting Hydraulic actuator works -

Unlike single-acting actuators, double-acting actuators use air pressure to both open and close the valve.

This is the most popular style of the pneumatic valve actuator. Double-acting actuators are selected for their lower cost and superior longevity since the absence of mechanical springs in most models eliminates the least durable component in the actuator. It is not uncommon for a high-quality double-acting actuator to cycle millions of times before failing.

Double-acting hydraulic cylinders have a Cylindrical housing and one piston. When hydraulic oil is supplied to its cap end port, hydraulic pressure force will be applied over the piston and the end cylinder will be extended. During the extension of the piston hydraulic oil at the rod, the end side will be pushed out and directed towards the reservoir.

For the returning stroke, the hydraulic direction is reversed with the help of the direction control valve. During the returning stroke hydraulic oil is supplied to the rod end side and hence piston is retracted. During the retracting of the piston cap end, oil is directed towards the reservoir. hence the double-acting hydraulic actuator operated in both the directions

The extra port also allows more control of the piston during retraction and ensures it always returns back to its starting point

When to use double-acting Actuator

Double-acting actuators are ideal for high cycle applications and/or applications where the valve failing to the closed (or open) position when power is lost does not present a critical issue. Double-acting actuators are the most popular choice for their lower cost and superior longevity. Double-acting actuators are also more compact than single-acting actuators and may be the only option in small form factor applications.

Double Acting with Failsafe

Gemini Valve now offers an industry-first double-acting pneumatic actuator with failsafe. This actuator combines the durability of a double-acting actuator with the failsafe normally only offered by spring-return models. The actuator operates in a double-acting configuration until power or air pressure is lost and the springs engage automatically to return the valve to the normal position.

Difference Between Double Acting Hydraulic actuator and Single acting Hydraulic actuator

When determining what type of valve you need for a specific application, it’s important to know which kind of valve actuator your project requires.

In an automated valve assembly, the actuator is the component that causes the valve to open or close. Valve actuators can be triggered by electricity, hydraulic pressure or air (pneumatic) pressure. Although single-acting hydraulic and electric actuators do exist, the term single-acting is most commonly used to describe pneumatic actuators.

What is a Single Acting Actuator?

Commonly referred to as spring-return actuators, a single-acting pneumatic actuator uses air to open the valve and a mechanical spring (or springs) to close the valve. The actuator can also be configured inversely so that air closes the valve and the spring is used to open the valve; this is called a normally-open configuration.

The most common reason single-acting actuators are chosen is for their reliable fail-safe design. This means that if power or air pressure is lost, the valve will quickly move to the normal position. This is useful in applications where serious consequences may occur if the valve remains open (or closed) when power and/or air pressure is lost.

Three drawbacks to single-acting actuators are:

• The inclusion of mechanical springs in the design adds additional cost to the valve assembly. Cost difference depends on the size and style of the valve.
• The springs are susceptible to fatigue and will usually be the first component in the actuator to fail. Therefore, single-acting actuators are generally considered to be less durable than double-acting actuators.
• The spring-modules give the actuator a larger form factor that may not be compact enough to fit into some applications.

Single-acting actuators are common in low to moderate cycle applications where the valve failing in the wrong position could present a serious safety hazard and/or cause damage to nearby equipment. If power or air pressure is lost, single-acting actuators ensure that the valve will fail to the normal position. For this reason, single-acting actuators are the best choice when the simplicity and reliability of a safety system are of the utmost concern.

Model :

We build the required model as follows:

We use a valve input, a mechanical model subsystem, a physical model subsystem along with a translational multibody interface to build the model. The valve acts as the input to the entire system.

Hydraulic system :(Physical model)

For the physical model subsystem, we use a hydraulic pressure source, pressure relief valve, 4-way directional key, translational hydro-mechanical converters along with a mechanical translational reference. The valve position acts as the input to the hydraulic system.

As we know we need constant hydraulic pressure for Double acting hydraulic actuator we used the Hydraulic pressure source block which supplies constant pressure of 4⋅e7">4⋅e74⋅e7 Pascal.

Hydraulic fluid is used -

Pressure Relief Valve -

4 Way Directional valve -

Translational Hydro-Mechanical Converter(Chamber A) -

This block converts the hydraulic energy to mechanical actuation

Translational Hydro-Mechanical Converter(Chamber B) -

Stroke length-

Mechanical Model :

The mechanical model is built using the multibody interfaces in the library to build various multibody elements such as follows:

Cylinder -

Bottom cap -

Head cap -

Cylinder Body-

This hole cylinder assembly is connected to the base port of the prismatic joint

Piston head -

Rod -

This is our assembly connected to the follower port of the prismatic joint

Prismatic joint -

it shows the prismatic motion of the piston with the base cylinder

Valve Input -

Using the wave generator we create the valve input as shown above, which acts as the input to the entire system.

Position of Rod (or Actuation)

Here we observe that the valve position follows the input signal accurately and the rod position is that of a saw tooth wave as expected. Hence the model functions precisely to give desired results.