1. 1 CMPUT 412 Actuation Csaba Szepesvári University of Alberta TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: AA A A A A A

2. 2 Defining sensors and actuators Environment actions Sensations (and reward) Controller = agent Sensors Actuators

3. 3 Actuation Why? How? The process of sensing Characterizing sensors Some sensors

4. 4 Actions  Effectors, actuators  Motors  Wheels  Wheeled locomotion

5. 5 Actions for Moving Things  What moves?  Robot moves  locomotion  Objects move  manipulation

6. 6 What Makes an Action Possible?  Effector = device on a robot that has an effect (impact or influence) on the environment e.g. leg, wheel, arm, finger  Actuator = Mechanism that enables the effector to work e.g. electrical motors, hydraulic or pneumatic cylinders

7. 7 Types of Actuation  Passive actuation Utilizes potential energy Examples  Nature: flying squirrels  Robots: walking  Active actuation External energy transformed into motion Tad McGeer’s passive walking robot

8. 8 Active Actuation: How?  Electromagnetism Electric motors  Pressure Hydraulics (fluid pressure) Pneumatics (air pressure)  Materials Photo-reactive materials Chemically reactive materials Thermally reactive materials Pizeoelectric materials (crystals) Incomplete! Direction of motion: -Rotation -Linear

9. 9 Direct Current (DC) Motors  Advantages: Simple, inexpensive, easy to use, easy to find  Input: Voltage “Right range” -> current drawn ~ work work = force * distance  Power out ~ torque * v rot Free running/stalled: p=0  Speed: 3K-9K rpm (50-150rps)  Problem: Speed high, force low shaft Power wires

10. 10 Operation: Brushed DC Motor

11. 11 Gearing: The Challenge  Purpose: Change the torque output of motors  Wheels: torque out ~ torque in /radius why?  Can decrease torque!  Problem: How to increase torque?  Solution: Gears

12. 12 Gearing  Const ´ power ~ torque * v rot  v rot,2 = v rot,1 /3 ===  torque 2 = torque 1 * 3 3:1 gear reduction Input (1) Output (2)

13. 13 More Gearing  How to achieve 9:1 gear reduction? Use larger gears Use multiple gears  Issues: Loosiness btw meshing gears  Backlash No loosiness  increased friction  energy waste  Solution: “Gearbox” 9:1 gear reduction with ganged gears input output

14. 14 Servo Motors  Purpose: Instead of continuously rotating, move to a given position  Servo (Motors)  Components DC Motor Gear reduction Position sensor Controller  Input signal: pulse-width modulated  Position control vs. torque control

15. 15 NXT Motor Motor Wheel encoder Gears Place for main shaft

16. 16 NXT Motor: Servo Function Target RPM (% of max RPM) No load, no servo, 9V No load, no servo, 7.2V 11.5 Ncm load, no servo, 9V NXT 11.5 Ncm load, servo, 9V 11.5 Ncm, load, servo, 7.2V Source: http://www.philohome.com/nxtmotor/nxtmotor.htm

17. 17 Moving the Robots Degrees of Freedom Controllable Degrees of Freedom

18. 18 Moving the Robot  “Degrees of Freedom”: How many variables are needed to describe the configuration of the system in space? Rigid body in 3D  6DOF 1DOF in 2D

19. 19 Joints Hinge: 1DOF Saddle: 2DOF Ball and socket: 3DOF Plane: 1DOF

20. 20 Explosion of the DOF

21. 21 Controllable Degrees of Freedom  Controllable vs. uncontrollable DOF  Can cars get to anywhere?

22. 22 Classification of Systems  TDOF = CDOF  Holonomic e.g. helicopter  TDOF > CDOF  Nonholonomic e.g. car  CDOF > TDOF  Redundant e.g. human arm without hand 7DOF  3 shoulder (ball&socket joint)  1 elbow  3 wrist

23. 23 Summary  Effectors & actuators enable robots to produce movement: manipulation or locomotion  Actuators: many types, motors most common  Gears: change speed, torque  Servo motors: Complement DC motors  DOF != CDOF