What Is a Piezo Actuator?
A piezo actuator is an actuator that uses a phenomenon known as the piezoelectric (Piezo) effect.
The piezoelectric (piezo) effect refers to a physical phenomenon in which mechanical energy applied to a piezoelectric material solid, such as quartz or ceramics, generates electrical energy. Since this phenomenon is reversible, a linear displacement is obtained in the piezoelectric material when an opposite electrical signal is input, and this reverse piezoelectric effect is used in many cases in Piezo actuators.
Piezo actuators are characterized by low power consumption, small size, high speed, and no magnetic field.
Uses of Piezo Actuators
Piezo actuators are used in internal positioning mechanisms for HDD drives and semiconductor lithography equipment, ink pumps for inkjet printers, switches for smartphones, and energy harvesting (environmental power generation). Especially in recent years, tactile feedback technology unique to Piezo actuators has been used in many cases as switches for smartphones and in-vehicle car navigation systems.
One of the advantages of utilizing Piezo actuators is the ability to create seamless designs. Piezo actuators are also beginning to be used for energy harvesting (environmental power generation), where mechanical energy such as vibration from the environment is used to generate electricity. Energy harvesting refers to the conversion of energy from the environment into electricity.
Principle of Piezo Actuators
The principle of operation of a piezo actuator is based on the physical phenomenon of mechanical micro-deformation (vibration) of a piezoelectric crystal solid when an electric field is applied to a piezoelectric element such as ceramics, and this phenomenon is used in the actuator mechanism.
This physical phenomenon is the opposite of the piezoelectric (Piezo) effect and is called the inverse piezoelectric effect because it converts electrical energy into mechanical energy. The structure of a piezo actuator, at its simplest, consists of a piezoelectric material sandwiched between electrodes and wiring, and because of its simplicity, it has excellent durability and high reliability.
Currently, ferroelectric ceramic crystals such as barium titanate are widely used as piezoelectric materials.
Types of Piezo Actuators
Typical types of Piezo actuators include stacked, bimorph, and tube types.
1. Multilayer Piezo Actuator
This actuator consists of alternating layers of piezo sensors and electrodes, and can easily obtain precise micro displacement. It is also used for precision positioning due to its high generated stress and good response.
2. Bimorph Piezo Actuator
Two longitudinally extensible piezoelectric elements are joined together, and when one is extended, the other is deflected. When a deflection force is applied, electrical energy is generated. For this reason, there are many examples of use as acoustic sensors and flexure sensors.
3. Tube-Type Piezo Actuator
This actuator expands and contracts radially and axially when voltage is applied to the inner and outer electrodes.
Other Information on Piezo Actuators
1. Hysteresis Correction
Piezo actuators are simple in structure, highly reliable, and excel in minute, compact, high-speed operation, but their greatest drawback is that they have hysteresis error. Ideally, there should be a perfectly proportional relationship between the applied voltage and the stroke of the actuator, but in reality, there is a hysteresis variation of up to 15% in the stroke value when the voltage increases or decreases. To compensate for this, products with position detection mechanisms and ASIC feedback compensation functions are also used.
2. Load Considerations
Ferroelectric ceramics are very resistant to loads in the expected operating direction, but unexpected loads such as shear stress, unbalanced loads, and rotational moments may cause the laminate crystals to fracture because of the ceramic crystals. It is important to pay close attention to the manufacturer’s precautions for use and take care not to misuse the product.