Arms, Legs, Wheels, Tracks and What Really Drives Them: Effectors and Actuators. By: J. Islam & Tiffany Stephenson

Transcription

1 Arms, Legs, Wheels, Tracks and What Really Drives Them: Effectors and Actuators By: J. Islam & Tiffany Stephenson

2 Components That Enable A Robots Actions Effector: Device that makes impact/influence on environment. i.e legs, wheels, arms, fingers Actuator: Enables effector to perform actions. i.e electric motors, hydraulic/pneumatic cylinders, chemically sensitive materials, etc -Actuator Drives Effector. Human Equivalent: Muscles plus tendons actuate arms and legs.

3 Active vs. Passive Actuation All actuators and effectors need a power source. Active- Power consumption. Passive Actuation- No power consumption. Uses potential energy effector to interact with environment. i.e. The Passive Walker. Has two legs and knees. Could walk self if places on downward slope.

4 Types of Actuators Hydraulics- Based on fluid pressure. (Pressure changes and actuator moves. Powerful and precise but large and dangerous) Pneumatics- Based on air pressure. (Pressure changes and actuator moves. Powerful and precise but large and dangerous) Chemically reactive materials- Respond to chemicals. Electric motors- Most common. (Affordable and simple). Uses electric current. Well suited for wheels.

5 Motors Direct Current (DC) Motors Simple, inexpensive, easy to find and use Variety of sizes and packaging Motor needs electrical power and voltage range to run. Low voltage means low power High voltage means high power (wear and tear occur faster) Need constant voltage in proper range.

6 Gears How to make DC motors useful to robots? Are properly designed so that the teeth of gear mesh together without being too tight or too loose. Different sized gears are used together to: Reverse the direction of a motor Increase or decrease the turning of a motor called torque. (The more current a motor uses, more torque it produces.)

7 Gears Cont. When counting gears and combining them, you can either power/gear up or power/gear down. i.e. 8 teeth and 24 teeth Gearing down-our 8 gear will power our 24 wheel. 8 gear will need to turn 3 times before allowing 24 gear to turn once fully. Gearing up- 24 gear will power 8 gear. With one full turn of our 24 gear the 8 will turn 3 times making this 3 times faster than previous gearing.

8 Gearing Down Gearing Up

9 Note: -When a small gear drives a large one, torque is increased and speed decreases. -When a large gear drives a small one, torque is decreased and the speed increases. -Backlash occurs when there is looseness present between meshing gears. This creates a sloppy movement between the gear mechanism without turning the entire gear.

10 Servo Motors (servos) Motors that can turn their shaft to a specific position. Made from DC motors by adding: Gear reduction Position sensor in motor to track turning and direction Electronic circuit that controls motor to tell directions much to turn.

11 Degrees of Freedom (DOF) DOF-way in which a robot moves or how it impacts the world to accomplish a task. (specify how robots move) Usually 6 DOF. Translation DOF- 3 of DOF that makes a robot move without turning. i.e Climbing up, diving down, moving straight. Rotational DOF- Remaining DOF that allow body to rotate. Roll, pitch, yaw (i.e. rolling from side to side and turning)

12 Degrees of Freedom Cont. Actuators determine which DOF is controlled and what it can do. Specific match determines if holonomic, nonholonomic, or redundant. Holonomic- robot/actuators control all DOF. i.e. helicopter has all 6 DOF and can be completely controlled. Nonholonomic- robot/actuators cannot control all DOF. i.e. cars control some DOF but face challenges like parallel parking. Redundant- can control more than 6 DOF. i.e. Can move shoulder up-down, side-to-side, and rotate. Open-close elbow, move wrist up-down, side-to-side and rotate again.

13 Chapter 4 Summary -Actuators, who enable a robot and effectors, which influence the environment work together to enable a robot to perform a given task. -Motors are the most common type of robot actuators, however, several others do exist. -Gears are used to decrease speed and increase motor power using simple gear size, speed, and torque relationships. -Servo motors have specific properties that compliment Direct Current motors & are useful in both robots & toys. -DOF specify how a robot can move. -The match btw. DOF and robot actuators determines if the robot will be holonomic or not or redundant, it has the most important impact on what the robot can do.

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