Sensors and actuators form the backbone of modern instrumentation systems in the process and manufacturing industries. Sensors serve as input devices for machine eyes and ears, while actuators are output devices that move objects. An actuator is essentially a mechanical or electromechanical device that responds to controlled stimuli to produce motion.

In a typical control system, sensors provide information to the microcontroller and activate actuators based on this information. This series of operations is the foundation of all industrial control, instrumentation, and automation systems. The mechanism can be better understood through the following diagram:

Figure 1: Simple Control System

A typical actuator requires two types of signals: 1) control signal and 2) power signal. The control signal tells the actuator when and to what extent motion is generated, while the power signal is used to keep the device powered on. According to the type of power supply, actuators can be divided into three categories:

Hydraulic

Pneumatic

electromechanical

Hydraulic and pneumatic actuators are mechanical devices, while electromechanical actuators use electrical energy. There are many different types of electromechanical actuators, but in this article, we will focus on KEMET's multi-layer piezoelectric actuators.

What is a piezoelectric actuator?

Before discussing piezoelectric actuators, it is important to understand the concept of piezoelectricity. The ability of certain materials to generate voltage in response to mechanical stress is called piezoelectricity. Applying mechanical stress to piezoelectric materials will generate voltage at the output end of the material. On the contrary, applying an input voltage to piezoelectric materials can cause mechanical motion at the output end, such as sound, vibration, or displacement. The piezoelectric phenomenon is shown in the following figure:

Figure 2: Piezoelectric phenomenon

By utilizing the piezoelectric principle, various types of electrical and electronic devices, including sensors and actuators, can be constructed. According to its structure, there are two types of piezoelectric actuators: 1) single-layer actuators and 2) multi-layer actuators.

Comparison of single-layer and multi-layer piezoelectric actuators

As the name suggests, single-layer piezoelectric actuators are made of a single piezoelectric element, while multi-layer piezoelectric actuators are composed of stacked layers of piezoelectric materials. The following figure shows two types of actuators:

Figure 3: Single layer and multi-layer piezoelectric actuators

Multi stage piezoelectric actuators provide a wider range of forces and displacements under the same applied voltage. This is because the stacking of piezoelectric elements produces a multiplication effect. A single-layer piezoelectric actuator produces a displacement of 1 μ m at 1kV. In contrast, multi-layer piezoelectric actuators produce a displacement of 100 μ m at 100V. Therefore, multi-stage piezoelectric actuators generate 10 times the force at 100 times the voltage. These numbers demonstrate that the performance difference between these two types of actuators is significant. The low operating voltage with high force extends the functionality of piezoelectric actuators, making them suitable for a wider range of control applications. The ceramic material used in KEMET's multi-stage piezoelectric actuator is PZT (lead zirconate titanate).

How do piezoelectric actuators compare to electromagnetic actuators?

There are two main techniques for constructing electromechanical actuators: 1) electromagnetics and 2) piezoelectricity. Piezoelectric actuators outperform electromagnetic actuators in terms of force output, accuracy, response time, efficiency, control, and size. The following figure shows a comparison of these two actuator technologies:

Figure 4: Comparison of electromagnetic and piezoelectric actuators

It can be clearly seen from the comparison that piezoelectric actuators have excellent performance in terms of force, accuracy, response time, control, and size. The only area where these actuators lag behind electromagnetic actuators is displacement. The displacement generated by electromagnetic actuators is in the range of a few millimeters, while the displacement generated by piezoelectric actuators is in the order of a few micrometers. However, with the advancement of multi-stage piezoelectric actuator technology, it is expected that displacement response will become better over time.

How can KEMET piezoelectric actuators be better?

A closer look at KEMET piezoelectric actuators reveals some key structural changes compared to traditional piezoelectric actuators. The main difference lies in the position and structure of the electrodes. Traditional piezoelectric actuators have partial internal electrodes, while KEMET piezoelectric actuators have complete internal electrodes. Some internal electrodes have a lower ability to withstand mechanical stress, making them prone to breakage or fracture. On the contrary, all internal electrodes exhibit high reliability, durability, and efficient performance. The difference in electrode structure between traditional and KEMET piezoelectric actuators is shown in the following figure:

Figure 5: Comparison between KEMET and traditional piezoelectric actuators

KEMET piezoelectric actuator products

KEMET offers a variety of multi-stage piezoelectric actuators, covering a wide range of industrial and commercial applications. KEMET's multi-stage piezoelectric actuators are divided into two categories:

Resin coated actuator

Metal shell actuator

The resin coated actuator is a standard type actuator with a thin white coating. There are two product series in this category, namely AE and AER. The AE series consists of standard actuators with rectangular shapes, while the AER series consists of annular resin coated actuators.

The category of metal casing types consists of three product series, namely ASB, Asli, and AHB These are high-performance actuators with higher thermal ratings. The ASL series offers a thermal rating of up to 150 ° C The AHB series offers a thermal rating of 85 ° C with higher displacement.

Figure 7: Construction of metal type piezoelectric actuator

Application of multi-stage piezoelectric actuators

Multi stage piezoelectric actuators can be used for a wide range of applications. Some of the main applications of these high-performance actuators include:

Precision machining and position control system (XY stage, part feeder, knitting machine)

Semiconductor assembly and manufacturing (mass flow controllers, stepper motors, and nanoprinters)

Optical instruments (lens positioning, autofocus microscope)

Instrumentation (vibration control, control valves, testing instruments)

conclusion

Mechanical and electromechanical actuators are important components of all types of instruments and control systems. Piezoelectric actuator is an electromechanical actuator that converts electrical energy into mechanical motion. Compared with single-layer and traditional piezoelectric actuators, KEMET multi-stage piezoelectric actuators have many advantages. They have excellent precision, response time, efficiency, and control characteristics. Therefore, they are highly suitable for applications that require high precision, accuracy, and efficiency. So don't wait any longer.

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