1. Assignment#01: Literature Survey on Sensors and Actuators ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Comb Drive Prepared by: Michael Tait Dept. of Electrical and Computer Engineering Utah State University 3/9/2012

2. 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-2 Outline –Reference list –To probe further –Definition –Operation –Equations –Structure –Limitations –And many more relevant issues in applications (such as, how to choose, cost information, where to buy etc.)

3. 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-3 Reference list http://en.wikipedia.org/wiki/Comb_drive http://ecourses.ou.edu/cgi- bin/ebook.cgi?doc=&topic=mz&chap_sec=05.0http://ecourses.ou.edu/cgi- bin/ebook.cgi?doc=&topic=mz&chap_sec=05.0 http://mems.sandia.gov/about/actuators.html

4. 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-4 To explore further (survival pointers of web references etc) http://en.wikipedia.org/wiki/Comb_drive Many scholarly articles are available on the web, however, they are very in depth (search Comb Drive on Google and view the PDFs)

5. 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-5 Definition Comb drives are linear motors that utilize electrostatic forces that act between two metal combs www.globalspec.com

6. Definition Comb drives built on normal sized “human” scales are extremely inefficient They are built very small to maintain efficiency, on microscopic or nano-scale devices 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-6 ecourses.ou.edu

7. Definition As the size of a comb drive is very small, they are manufactured generally in two ways: –bulk micromachining –surface micromachining a silicon wafer substrate 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-7 www.crossfiber.com

8. Operation Uses electrostatic forces A voltage is applied between the static and moving combs causing them to be drawn together The combs must be arranged so that the teeth never touch (otherwise the voltage potential between them would be zero, see the image on the next slide) 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-8

9. Operation The electric potential on the surface of a comb drive 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-9 www.comsol.no

10. Operation The force developed by the actuator is proportional to the change in capacitance between the two combs The force also depends on the number of comb teeth and the gap between the teeth Typically the teeth are arranged so that they can slide past one another until each tooth occupies the slot in the opposite comb 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-10

11. Useful Equations The energy in a capacitor: E = ½*C*V^2 The force derived by differentiating the energy in the direction of the force: F = ½*(∂C/∂dx drive )*V^2 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-11

12. Useful Equations Parallel plate capacitance: C = ε*A/d Force equation: F = ½*(n*t*ε 0 *ε r *V^2)/d 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-12

13. Equation Definitions F = ½*(n*t*ε 0 *ε r *V^2)/d V = applied electric potential ε r = relative permittivity of dielectric ε 0 = permittivity of free space n = number of pairs of electrodes t = thickness in the out of plane direction of electrodes d = gap between electrodes 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-13

14. Structure Rows of interlocking teeth Teeth half fixed, half moveable assembly Electrically isolated Electrostatic attraction/repulsion Typically 10 μm long 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-14

15. Application Comb drive use locations: –Gyroscopes –Microengines –Resonators 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-15 mems.sandia.gov Typical Comb Drive Resonator

16. Application The force output for a comb drive is typically less than 50 μN Remains a popular actuator because: –Linear response –Highly predictive behavior 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-16

17. Limitations As mentioned above, a comb drive can only be used in very small implementations as the efficiency is very poor in large arrangements The force created by a comb drive is very small and may be too small for some implementations The drive is very sensitive to surrounding electrostatic potential and must be shielded against unwanted potentials 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-17

18. Cost and Availability As a comb drive is very small and must be manufactured on silicon wafers, I was unable to find one for sale commercially It appears that the comb drive is relatively new as it is a nanotechnology and there isn’t a lot of information available regarding the actuator 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-18

19. Cost and Availability Many scholarly articles refer to comb drives (especially at Sandia National Laboratories) leading one to believe they are still very much in development 5/13/2015 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Slide-19