Piezo Ring Actuator

Piezo Ring Actuator: The Ultimate Guide

Modern instrumentation, automation, and control require accurate piezo ring actuator with the ability to transform electrical signals into precise displacement.

To achieve this, you must know the vital aspects of piezo actuators, from design, specification, working principle to specific applications.

That’s exactly what you’re going to learn in this guide.

What is a Piezo Ring Actuator?

A piezo ring actuator is a type of stack actuator that assumes the shape of a ring.

It has a large aperture at the center of the ring with other connections on the outside such as connecting wires.

Figure 1 Piezo ring actuator

The piezo ring actuator is high-performance devices with polymer coatings that are compatible with the vacuum.

The piezo ring actuator matches perfectly to different ranges of driver modules and PiezoDrive amplifiers.

Figure 2 Piezo amplifier

Why should you opt for a piezo ring actuator?

Advantages of Piezo Ring Actuators

You should opt for the piezo ring actuator because of its numerous advantages.

Some of the advantages of using the piezo ring actuator include:

       i.          Easy Integration of the Ring

The shape of the piezo ring actuator makes it very easy to integrate with other devices. This makes the process of assembling devices with piezo ring actuators easy.

      ii.          Fast Reaction Time

Piezo ring actuators often react very fast in the delivery of enough power. The reaction time to produce enough power is very short.

    iii.          Small Size and Light Weight

Piezo ring actuators are very small in size and they are able to fit even in small devices. The lightweight also reduces the overall weight of the devices with piezo ring actuators.

    iv.          Low Energy Consumption

Piezo ring actuators depend on very low voltages to produce a significant amount of power.

      v.          Large Displacement

Despite the small size, the piezo ring actuator has produces huge displacement forces. You can use this force to power various applications.

    vi.          High Dynamic Drives

The drives available for use on a piezo ring actuator are very dynamic. They constantly change form in order to produce the energy you desire.

   vii.          Discreet Stack

The piezo ring actuator has a discreet stack that is capable of producing power at different voltages.

 viii.          Ability to Operate at Cryogenic Temperatures

You can operate the piezo ring actuator even at very low temperatures. The piezo ring actuator continues to produce power even at temperatures close to zero.

    ix.          No Magnetic Field

The piezo ring actuator does not produce an electric field and can operate well in a magnetic field.

      x.          Excellent Heat Dissipation Properties

The shape of the piezo ring actuator usually assists in removing the excess heat build on the ceramics.

Despite the numerous advantages, you are bound to find a few disadvantages of the piezo ring actuators.

Read about them in the next section.

Disadvantages of Piezo Ring Actuators

You may face a few challenges in the process of using a piezo ring actuator.

Some of the challenges or disadvantages of using the piezo ring include:

Figure 3 Piezo ring actuator

       i.          Not Suitable for Use in High Humidity Areas

The crystals of the piezo ring actuator are water-soluble. High humid areas will lead to absorption of moisture hence affecting the performance.

      ii.          Temperature Sensitivity

You can only operate the piezo ring actuator up to a certain temperature. Exceeding the temperature limit can lead to damages on the piezo ring actuator.

    iii.          Not Suitable for Drift Free Devices

You might need to install a position feedback system to monitor the drifting of the piezo ring actuator.

    iv.          Brittle Material

You have to be extra careful when using the ceramic piezo ring actuators. Ceramics are brittle and could break easily.

Well, despite the disadvantages, the piezo ring actuator is a very useful product.

In the next section, you are going to learn about the uses of the piezo ring actuator.

What are the Applications of Piezoelectric Ring Actuators?

For a fact, piezoelectricity has become popular in many industrial applications.

You can use the piezo ring actuator in devices that use low voltage to produce high mechanical effects.

Given the simple design, few moving parts, high reliability, and no lubrication operation status, the uses are limitless.

Some of the major uses of the piezoelectric ring actuators are as follows.

• Amplifiers
• Optical systems
• Microscopy
• Hydraulic systems such as valves
• Nanopositioning
• Precision machining
• Automotive systems
• Tunable lasers
• High-speed switching
• Instruments and measurement systems
• Accurate pumping and dosing systems
• Ultrasonic measurement technology

Characteristics of Best Piezoelectric Ring Actuator

Whenever you are looking for a good piezoelectric ring actuator, there are certain factors to look at.

You will match these characteristics with the application that you desire.

The main characteristics that you need to look at include:

Figure 4 Piezoelectric ring actuators

· Range of Piezo Electric Ring Actuator

You will choose a piezo ring actuator with a range that will match the voltage you will apply.

For example, the voltage range of the piezo ring actuator can range between -30 V to + 150 V.

In case you are using a unipolar voltage (0V to 150V), you will reduce the specific range by 0.75.

You can reduce the travel range by restraining on the endplates. You can do this by bonding the actuator to a stiff base.

The effect will be more significant in actuators with a smaller length less than twice the outside diameter.

·Length of Piezo Actuator

Specify the length of the piezo ring actuator that you need in millimeters.

The length of the piezo ring actuator will affect all the other characteristics of the piezo ring actuator.

Implying that an increase in length will have a significant effect on the range, stiffness, and blocking force among others.

·Inner Diameter and Outer Diameter

In a piezo ring actuator, the inner diameter is often smaller than the outer diameter.

For instance, you can have piezo ring actuators with an inner diameter of 4.5 mm and the outer diameter of 8mm.

· Capacitance

The capacitance of the piezo ring actuator is the small-signal capacitance which you will measure at room temperature.

The effective capacitance will increase with an increase in the load you apply due to hysteresis.

At full range operations, the effective capacitance will be twice the capacitance of the small signal.

Note that the capacitance will also increase with an increase in temperature.

In case you increase the temperature by about 50 degrees Celsius, the effective capacitance will double.

·       Precision

The precision of the piezo ring actuator should be as high as possible.

The greater the precision, the higher the amount of force that the piezo ring actuator will produce.

·       Blocking Force

This is the force that the piezo ring actuator will apply to take it back to the original length.

Without the blocking force, it would be impossible to generate enough force from the piezo ring actuators.

When you intentionally block the actuator from moving, it will produce maximum force.

Implying, the higher the blocking force, the higher the energy that the piezo ring actuator will produce.

·       Stiffness

To understand this better, assume the piezo ring actuator as a mass system and spring.

The stiffness of the piezo ring actuator depends on:

1. Elasticity module of the ceramic material
2. The cross-sectional area of the piezo ring actuator

• Length of the active material

1. Other non-linear parameters

A typical piezo ring actuator should have a stiffness of between 1 and 2000 newtons per micrometer.

·       Piezoelectric Ring Resonance

The resonance frequency is the frequency with which ceramic elements vibrate readily and converts the electrical energy to mechanical energy.

The higher the resonance frequency of a piezo ring actuator, the higher the mechanical energy it produces.

You should consider going for a piezo ring actuator with higher piezoelectric resonance.

·       Voltage Range

Depending on the voltage range, you can choose between the monolithic sintered or classical high voltage piezo ring actuators.

Monolithic piezo ring actuators are low voltage actuators that operate at voltages up to 130V. This because they have a very small thickness ranging between 20 to 100 micrometers.

On the other hand, the classical high voltage actuators have a greater thickness between 0.5 to 1mm.

It can operate at voltages of up to 1000 V.

·       Free Stroke Displacement

The amount of displacement that a piezo ring actuator can produce depends on the load you will apply.

Apart from that, it will change with the changes in the stroke that you will be applying.

For example, when the force is constant in an active piezo ring actuator, you will observe maximum stroke.

In such a case the amount of displacement of the piezo ring is very low. At a maximum stroke, the amount of displacement from the piezo ring actuator is also at a maximum.

·       Coupling Factor

The coupling factor indicates the effectiveness with which the piezo ring actuator converts electrical energy to mechanical energy.

It can also indicate the effectiveness by which the piezo ring actuator converts the mechanical energy to electrical energy.

For efficient energy conversion, the direction of the application of electrodes should be as high as possible.

Are we getting somewhere?

Well, let us look at the step by step process of mounting a piezo ring actuator.

How to Mount a Piezo Ring Actuator?

Mounting a piezo ring actuator is a simple process.

All you need to do is to make sure that you follow all the rules accordingly to avoid any functional issues.

Any wrong move in the mounting process will lead to a change in the functionality of the whole system.

Figure 5 Piezoelectric ring actuator

Step One: Prepare the Mounting Area of the Piezo Ring Actuator

You need to grind the top and the bottom of the piezo ring actuator.

Apart from that, you will grind the surface where you will place the piezo ring actuators.

How?

Using a grinder, carefully polish the upper and the bottom surfaces of the piezo ring actuators.

Make sure that the grinding is perpendicular to the direction of expansion.

Why should you grind the surface and the ring actuators?

Grinding will assist you to obtain a parallel and flat mounting surface.

Step Two: Actual Mounting

You can either mount the piezo ring actuator by gluing or mechanical clamping.

Using a mechanical clamp or glue, stick the ring actuators to the mounting surface.

In case you are gluing the piezo ring actuators, you can use the epoxy glue.

Apply very thin layers of glue between the substrates and the CMA.

Apply the force on the full surface of the ring actuator for a better distribution of load.

The glue or mechanical clamp will ensure that the ring actuators remain in one position.

Make sure that you do not expose the ring actuators to:

1. Significant tensile loads
2. Unequally distributed loads

• Off-axis loads

1. Bending moments
2. Torque
3. Tilting and shearing forces

• Mechanical clamping or gluing on the sides of the ring actuators.

You should also avoid short-circuiting the piezo ring actuator by:

1. Adding Kapton foil to the metallic surfaces
2. Placing inactive ceramic plates between the metal plates and the CMA.

With that in mind, let’s proceed to the next section and look at the different types of piezo ring actuators.

What are the common types of Piezo Ring Actuators?

You have the freedom of choosing from the wide range of piezo ring actuators available in the market.

Your choice will depend on your application requirements.

Figure 6 Piezo ring actuators

Let us have a look at some of the types of piezoelectric ring actuators available for you.

a)     Multilayer Piezo Stack Ring Actuator

This type of ring actuator has more than one layer of ring actuators.

You can either choose a multilayer piezo ring actuator with horizontal or vertical ring mounting.

The rings are of different sizes from the outer ring with the greatest diameter to the inner ringer with a smaller diameter. The height of the rings remains the same from the outer ring all the way to the inner ring.

Apart from that, you can choose to have multiple rings with one layer vertically on top of another. In this case, the height of the piezo ring actuator will change according to the number of piezo ring actuators.

b)     Laminated Piezo Ring Actuator

This type of piezo ring actuator has a cover or a laminate around the piezo ring actuator.

You will find piezo ring actuators with stainless steel casings or laminates.

The main function of the cover or laminate is to protect the inner delicate parts of the piezo ring actuator.

The laminate or casing does not in any way affect the performance of the piezo ring actuator.

c)     Bare Ring Actuators without Preload

The piezo ring actuator does not have a laminate or a casing and can work without a preload.

Implying that the tensile strength of the piezo ring actuator is relatively high.

In this case, the piezo ring actuator will not depolarize mechanically during the process of operation.

Apart from that, you will not have to worry about the generation of tensile stress.

d)     Ring Actuators with Preload

This is a ring actuator with a preload to increase the tensile strength of the piezo ring actuator.

The preload usually increases the tensile strength of the piezo ring actuator by 5 to 10 MPa.

You should, however, make sure that the preload is as low as possible.

A preload of 15MPa is sufficient enough to take care of the dynamic forces.

I bet you may be asking how a piezo ring actuator works.

Hang in there, as we will be talking about it in the next section.

What is the Piezo Ring Actuator Working Principle?

Generally, a piezo ring actuator will produce linear displacement when you apply an electric field.

How does that happen?

Let us take you through a step by step process on how this can happen.

First, you need to have the piezo ring actuator and a source of power.

You also need to know the voltage range of the piezo ring actuator to avoid using low or excess power.

After that, you will connect the piezo ring actuator to the power source and power it on.

The main thing that usually happens is the piezo effect.

As the power flows from the source, through the connecting wires to the piezo ring actuator.

The piezoelectric materials will deform or change in shape once in contact with the electric current.

The deformation of the piezoelectric materials leads to the production of a mechanical force.

The mechanical force that it produces is capable of producing subsequent displacement.

The amount of mechanical force that it produces depends on the actuators’ cross-sectional area.

You will be able to perform specific functions depending on the amount of energy the piezo ring actuator produces.

How can you manufacture a piezoelectric ring actuator?

Piezoelectric Ring Actuator Construction

Here, you are going to go through the step by step process of constructing a piezo ring actuator.

The type of piezo ring actuator that you will construct will depend on the final application.

It can also be bare, laminated, single layer or multilayer.

Figure 7 Piezo actuator assembly: Photo courtesy: Tech briefs

In this section, we are going to look at the basics of making a multilayer piezo ring actuator.

Step One: Gathering all the Components for Construction

You will collect all the parts you need to include in the piezo ring actuator.

This includes ceramic materials, connecting wires, stainless steel cover, glue among other things.

Step Two: Shaping the Ceramic Materials to Make a Complete Ring

You need to know the size of the actuator that you need by measuring.

Using a cutting tool, you will shape the ceramic materials and make a ring.

Make as many rings as possible depending on the number of layers you need.

Step Three: Connecting the Multiple Layers

In this case, you will connect all the layers of the piezo ring actuator together using glue.

Do not apply too much pressure on the ceramics as they are weak and can break.

You should also apply the pressure uniformly on top of the layers.

After that, you can connect the multiple layers to the connecting wires.

The connecting wires will be the path through which the electric current will flow through.

You can also include a stainless steel casing to protect the inner delicate ceramic materials.

Step Four: Finishing and Testing

At this point, you will connect the piezo ring actuator to any of the compatible devices.

Connect it to an electric source and then test how it works.

In case of any hitches, you need to repeat the process again and rectify the faulty areas.

Lastly, let us compare between square and circular shaped piezo ring actuators.

What is the Comparison of Shaped Piezo Ring Actuator vs. Circular Shaped Piezo Ring Actuator?

Piezo ring actuators may come in two different shapes.

Figure 8 Round and square piezoelectric actuator

In this section, we are going to compare the efficiency of the two different shapes.

Let us begin with:

·       Circular Shaped Piezo Ring Actuator

The ring piezo allows the equal and uniform distribution of load across the entire surface.

Since it does not have sharp corners, it is immune to stress build-up.

Immunity to stress build-up allows you to make piezo ring actuators with very thin layers.

The circular design allows the round piezo ring actuator to have longer strokes.

This increases the amount of energy it produces.

·       Square Shaped Piezo Ring Actuator

On the other hand, the piezo ring actuator with a square outer dimension may have stress concentration at the corners.

The sharp corners may also have cracks that can lead to more stress on the piezo ring actuator.

This may lead to the malfunctioning of the square piezo ring actuator.

To avoid frequent cracks, you need to make them thicker thus increasing the weight of the ring actuator.

The design does not allow the piezo ring actuator to have longer strokes.

It can, therefore, produce less energy.

Conclusion

Very well, we have come to the end of the guide hoping that you are a piezo ring actuator expert.

You should not be experiencing any challenges when you are purchasing a piezo ring actuator.

In fact, you can call your supplier and order a custom piezo ring actuator with confidence.

Remember to negotiate a good deal using the necessary terms for the piezo ring actuator.