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Dept. of Electrical and Computer Engineering

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1 Dept. of Electrical and Computer Engineering
ECE5320 Mechatronics Assignment#01:Literature Survey on Sensors an Actuators Topic: Piezoelectric Bimorph Actuator Prepared by: Vipin Varghese Dept. of Electrical and Computer Engineering Utah State University Tel: (435) 3/8/2007 ECE 5320 Mechatronics

2 Outline Reference list. To probe further.
Basic definition of bimorph actuators. Basic definition of Piezoelectric Bimorph Actuators. Bimorph Actuator Configuration. Design of Bimorph Actuators. Structure Techniques. Major applications. Basic Working Principle. Characteristics of PZT Bimorph. A typical sample configuration in application: Weaving Machine High Dynamic Pressure Regulator Major specifications. Advantages and Limitations Where to buy. 3/8/2007 ECE 5320 Mechatronics

3 Reference List
3/8/2007 ECE 5320 Mechatronics

4 To explore further: (survival pointers of web references
3/8/2007 ECE 5320 Mechatronics

5 What are Bimorph Actuators?
A bimorph actuator is composed of two thin panels of ceramic elements bonded together with a flexible metallic panel as it's central electrode. By wiring these two elements in such a way as to make one elongate and the other contract by applying voltage, inflection deviation occurs conforming to the waveform of the applied voltage. Bimorphs are operated in d31 mode. Courtesy : 3/8/2007 ECE 5320 Mechatronics

6 What are Piezoelectric Bimorph Actuators?
It can be described as a sandwich-type actuator in which two layers of a piezoelectric material are laminated onto one surface of a supporting beam or plate. The two piezoelectric layers are generally poled in the same direction, typically in the direction normal to the supporting beam/plate. When opposing electric fields are applied to the two piezoelectric layers, their corresponding dimensional changes are of the opposite character, which gives rise to bending of the beam. 3/8/2007 ECE 5320 Mechatronics

7 PZT Bimorph Actuator Configuration
Two Electrode Bimorph (Serial Bimorph): Here one of the two ceramic plates is always operated opposite to the direction of polarization. To avoid depolarization, the maximum electric field is limited to few hundred volts per millimeter. These type of actuator is widely used in accelerometers and force sensors. Three Electrode Bimorph (Parallel Bimorph): Here the two piezoelectric plates are of the same polarization directions and the actuator is driven by applying electrical field between surface electrodes and the bonding layer Courtesy: /unrestricted/etd.pdf 3/8/2007 ECE 5320 Mechatronics

8 Design of PZT Bimorph Actuators
Cantilever Design: As can be seen from the figure, the cantilever design results in an uniform upward and downward motion. This design can be used in applications involving high speed micro fans for cooling or nano-precision positioning. S-Beam Design: In this design, there exists different motions at different areas of the actuator upon proper voltage. This kind of design can be used in applications like bimorph mirrors where depending on the voltage applied, the deflection changes at various points leading to optical changes accurately. 3/8/2007 ECE 5320 Mechatronics

9 Bimorph Structure Techniques
Apart from bimorph techniques in PZT actuator ,other forms are also employed such as: 3/8/2007 ECE 5320 Mechatronics

10 Major Applications Nano-positioning.
Needle control in textile weaving. Braille machines. Accelerometers. Opening/closing valves. Small volume pumping. Switching applications-touch switches. Cooling devices. Robotics. Fiber optical switches. High dynamic pressure regulator. Hearing Aids. Generators 3/8/2007 ECE 5320 Mechatronics

11 Basic Working Principle
Two PZT thin films are stacked co-axially on both sides of a thin elastic bronze piece, and an outer ring and an inner ring are separately installed and are firmly fixed on outer and inner diameter of the elastic piece by two ring covers. 3/8/2007 ECE 5320 Mechatronics

12 Basic Working Principle (cont.)
When a proper excitation voltage is applied on it, the upper PZT thin film expands vertically and contracts horizontally, the lower PZT contracts vertically and expands horizontally. This establishes the bimorph bending, the effect of which produces the deformation. 3/8/2007 ECE 5320 Mechatronics

13 Characteristics of PZT Bimorph
No load displacement: The displacement caused when no load is applied. Elastic Load displacement: The displacement caused when an elastic load is applied. Static Load displacement: The displacement caused when an static load is applied. Blocked Load displacement: The displacement caused when an static load is applied. 3/8/2007 ECE 5320 Mechatronics

14 Characteristics of PZT Bimorph (cont)
3/8/2007 ECE 5320 Mechatronics

15 Sample configuration in application: Weaving
The internal 3D design of the module used in SITEX ® M - Textile machine used for circular knitting ,with PZT Bimorph Actuator is shown below. Courtesy: 3/8/2007 ECE 5320 Mechatronics

16 Sample configuration in application: Weaving
SITEX M - Textile machine module : The picture shows the actual module used in the textile weaving machine. Each of these modules uses the PZT bimorph actuator configuration shown in the earlier slide. SITEX M Circular knitting machines : The figure shows the Circular knitting machine with each module in place to control the needles in the proper direction by use of PZT bimorph actuator. Courtesy: 3/8/2007 ECE 5320 Mechatronics

17 High - dynamic pressure regulator
The figure shows the pressure regulator constructed using PZT bimorph actuator. Depending upon the flap position and the applied voltage to the actuator bending (displacement) takes place. Courtesy: 3/8/2007 ECE 5320 Mechatronics

18 Major specifications For bimorph actuator specifications, we need to take into account the following parameters: Performance Characteristics: Maximum Displacement (mm/V) Blocked Force (N) Maximum Voltage (volts) Stiffness (N/mm) Resonance Frequency (Hz) Capacitance (F) Compliance Response Time (ms) 3/8/2007 ECE 5320 Mechatronics

19 Major specifications (cont)
Physical Specifications Length (mm) Diameter/Height (mm) Thickness (mm) Mass (g) 3/8/2007 ECE 5320 Mechatronics

20 Major specifications (cont)
h = thickness Lt = total length L = free length w = width z = deflection. 3/8/2007 ECE 5320 Mechatronics

21 Major specifications(cont)
For a parallel PZT bimorph actuator the specification can be given as: Maximum Displacement = Bending = Resonant Frequency = 3/8/2007 ECE 5320 Mechatronics

22 Major specifications(cont)
Charge Output = Capacitance = Voltage Output = Blocking Force (stiffness) = 3/8/2007 ECE 5320 Mechatronics

23 Major specifications (cont)
Here the constants for each of the formula has been calculated with respect to a specific piezoelectric substance been used. There are other factors to be considered too along with this specifications like: Young’s Modulus Operating Temperature Storage Temperature Mechanical quality factor,etc. 3/8/2007 ECE 5320 Mechatronics

24 Advantages Unlimited Resolution : A bimorph piezoelectric actuator can produce extremely fine position changes down to the sub nanometer range. The smallest changes in operating voltage are converted into smooth movements. Motion is not influenced by stiction/friction or threshold voltages. Large Force Generation: Piezoelectric bimorph actuators can generate a force of several 10,000 N. It can also bear loads up to several tons and position within a range of more than 100 μm with sub-nanometer resolution. No Magnetic Fields: Piezoelectric bimorph actuators are especially well-suited for applications where magnetic fields cannot be tolerated. Low Power Consumption: The piezoelectric effect directly converts electrical energy into motion, absorbing electrical energy during movement only. Static operation, even holding heavy loads, does not consume power. 3/8/2007 ECE 5320 Mechatronics

25 Advantages (cont) No Wear and Tear: A piezoelectric actuator has neither gears nor rotating shafts. Its displacement is based on pure solid-state effects and exhibits no wear and tear. Vacuum and Clean-Room Compatible: Bimorph PZT actuators employ ceramic elements that do not need any lubricants and exhibit no wear or abrasion. This makes them clean-room compatible and ideally suited for ultra-high-vacuum applications. Operation at Cryogenic Temperatures: The piezoelectric effect is based on electric fields and functions down to almost zero Kelvin, albeit at reduced specifications. 3/8/2007 ECE 5320 Mechatronics

26 Limitations There are three major limitations to the bimorph piezoelectric actuator. The shaping of the electrodes and laminate. The bandwidth. Blocking force. The Shaping of the electrodes and laminate can be in several forms C-shape Bar, rectangular Disk Each shape will have a different response time and force when a specific voltage is applied. 3/8/2007 ECE 5320 Mechatronics

27 Limitations (cont) Shaping can also effect bandwidth.
A larger laminar area will cause the bandwidth to drop. As the bandwidth drops the response time also drops. This could either be an advantage or a disadvantage depending on the plant. Blocking force is also determined by the deflection and compliance of the two laminar surfaces. This ends up being inversely proportional to the length which indicates longer the lamina the less force it is able to exert. 3/8/2007 ECE 5320 Mechatronics

28 Where to Buy? There are many companies around which supply these kind of actuators depending upon design and demand. Some of the companies and the links (Click the logo) are: FUJI & CO PIEZO SYSTEMS,INC 3/8/2007 ECE 5320 Mechatronics

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