Prepared by: Vikranth Ceakala Dept. of Electrical and Computer Engineering Utah State University

1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Stepper Motors Prepared by: Vikranth Ceakala Dept. of Electrical and Computer Engineering Utah State University 3/9/2007

2. Outline • Reference list • To probe further • Actuator– • Major applications • Basic working principle • Stepper motors in reality • Useful animations • Phase sequence • Advantages • Limitations ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. Reference list • Bishop, Robert H; The Mechatronics Handbook, CRC Press 2002 • http://www.casde.iitb.ac.in/Mechatronics • http://hibp.ecse.rpi.edu ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. To explore further (survival pointers of web references etc) • http://www.howstuffworks.com/ ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. Major Applications Computer Peripherals • Floppy disc position controller • Carriage drive for printers • Paper feed mechanism in printers • Optical Scanner ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. Major Applications(continued.) • 3-dimensional positioning in plotters. • Air-fuel mixture adjustment in carburetors of automobiles. • ATM Machines ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

7. Major Applications(continued.) • Film Drive • Many other applications where precise positioning of parts is required. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. Basic working principle • Magnetism - Physical motion produced by magnetic attraction and/or repulsion. • Like poles attract and opposite poles repel ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. Basic working principle • Stepper motor is a digital motor. • A pulse signal or a sequence of pulse signals are used to turn a stepper motor. • The smallest unit of movement in a stepper motor is called a step. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. Basic working principle • A stepper motor consists of stator and rotor. • The stator is a series of electromagnets arranged to form a circle. • A rotor is usually a permanent magnet. • The rotor can be moved by changing polarities of the stator in a sequence. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. Basic working principle Full Stepper Motor • This is achieved by energizing two coils at a time. • Next pair of coils are energized just as the rotor aligns with one of the stator poles. • In this example there are 4 steps. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Basic working principle Half Stepper Motor • This is achieved by energizing two coils first and then only one coil and repeating the sequence. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Basic working principle Half Stepper Motor (continued) • A half stepping motor has double the number of steps of a full stepper motor. • The half stepper differs from a full stepper motor, in that, the second phase is turned on even before the first phase is turned off. • Thus we will have overlapping of two different phases. • During the overlapped phase stage also called the half step the rotor is in between two full step positions. • For this reason a half stepper motor has twice the resolution of a full stepper motor. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Stepper motors in reality • Examples in previous slides showed the rotor as having only 10 poles. In reality a stepper motor’s rotor has as many as 100 poles. • A rotor with multiple poles is achieved by mounting a single magnet in line with the rotor axis and staggering the teeth. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. Stepper motors in reality • In reality even the stators have many teeth. • These teeth are arranged such that they have a phase difference of 90 degrees between two phases. • A stepper motor might not use a permanent magnet. • Instead it might use a rotor which is made up of iron laminates. • This is also called a switched reluctance motor. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. Animation showing the working of a half stepper motor ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Animation showing a full stepper motor ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. Phase sequence Figure shows the phase sequences for a full-step motor and a half step motor for a 4 phase stepper motor. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Advantages • Long life - no wear and tear due to the absence of brushes • Can operate in an open loop configuration. • Inexpensive compared to other motion control systems. • Good torque at low speeds. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. Limitations • Excessive vibration when full stepping • Motors suffers from counter electro motive force (emf) when switching between phases. • This gives rise to current even after the motor is switched off. This may damage or affect the performance of the motor. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

21. Thank You Vikranth Ceakala ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators