Robotics

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# Robotics - PowerPoint PPT Presentation

Robotics. Actuators. Motors. Sensors. NXT-G logic. Lab: Measurements Homework: Task moodle assignment! Mechanics readings. Prepare summary. Postings. Next class: Closer look at programming and build &amp; program robot with bumper (use of touch sensor). Recap. Build: attention to detail.

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### Robotics

Actuators. Motors. Sensors. NXT-G logic.

Lab: Measurements

Homework: Task moodle assignment! Mechanics readings. Prepare summary. Postings. Next class: Closer look at programming and build & program robot with bumper (use of touch sensor)

Recap
• Build: attention to detail.
• Review construction: parts used for attaching, stability.
• Refine & experiment
• Challenge to do the exact job
• My process: took 4-5 iterations. Added sound block. Changed from rotations to degrees.
• 360 degrees in a rotation (of the motor), not the wheel.
• NOTE: more power means faster, not more distance if you are specifying rotations or degrees

Inserted to be sure when turning move over

9 rotations too many

Gentle curve

Steering
• Steering can accept an input value: -100 to 100.
• When we get to variables, can set a variable with a number and use data wires to set exact steering
Joints
• Robots have joints (think of joints of the body) that connect links
• A robot joint [generally] provides 1 degree of freedom (d.o.f.)
• [Note: a Carnegie Mellon robot travels around on a ball: work of Ralph Hollis. More later or report in posting]
• Rotational versus linear motions
Preview
• Kinematics
• Each joint is set to specific position, where is endpoint?
• move my shoulder, move my elbow, move my wrist, raise my finger, where is tip of finger?
• Inverse Kinematics
• What to set each joint in order to have the endpoint at a given point (orientation)
• how much do I move each joint in order to have the tip of my finger touch my nose?
Actuators
• One type of actuator is a motor: motors make the robot [a joint of the robot] move
• Many types of motors
• Stepper motor allows for precise positioning
• DC or AC Servo motor allows for feedback … for precise positioning
• “is it there yet?”
• Hydraulic or pneumatic pistons
• May or may not involve gears/gearing

Extra credit: report on advantages/disadvantages of specific type of motor, other types of actuator.

Sensors
• Machine (electro-mechanical) device that detects something about external world
• Generates a signal back to the program
• Refer to
• Programmable, sensory robots as robots that
• can be programmed
• Programming can involve/use sensory input
Sensors
• Contact, touch, switch
• Proximity
• Light
• Light level
• Vision systems: BIG topic
• Sound
• Sound signal (range)
• Speech systems: BIG topic
Sensors (& joints)
• Locality of sensing
• Where is ‘the robot’ when the ultrasonic sensor (proximity) says <20 cm??
• In positioning and movement, need to provide clearance for ALL the robot + any payload.
Calibration
• Process to set (define) relationship between strength (size) of thing being measured and the measurement scale
• REQUIRED for most sensors
• May be required EACH TIME sensor is used (in specific environment)
• This will be the case for the light sensor
Strain gauge
• Category of touch, but…
• Detects some amount of force (strain, push back)
• Physical force deforms material that produces change in resistance (electrical quantity). This electrical quantity is what is measured.
• Common in industrial robotics
• The Lego touch sensor is NOT a strain gauge. It is off or on
• States are off, pressed, [just] released
• Bump = pressed and released
• Good tutorial on www.societyofrobots.com
Logic
• Event driven programming in high[er] level language such as Flash ActionScript: specify event and handler and the system does everything else.
• var mytimer:Timer: new Timer(1000)mytimer.addEventListener(TimerEvent.TIMER, moveball);
• In other places, need to specify testing explicitly. In NXT-G, need to put in wait blocks and other blocks, perhaps use switch blocks and loop blocks.
• NOTE: Flash & other languages generate the code that does the checking and re-checking…
NXT-G wait until
• Next class will do move until bump sensor. Here Wait until certain NXT button pressed
• unlimited motors movewait until button pressedbrake motors block
Preview: NXT-G logic
• Logic block: takes 1 or 2 inputs and performs
• AND, OR, XOR, NOT
• What do you do with result?
• Input to looping block
• Input to switch block
• Input to …
NXT-G
• Arithmetic blocks
• Comparison blocks
• Variables
• Input from sensors AND motors and calculations and (Bluetooth) messages
NXT-G Looping
• Loop block: block can contain other blocks
• Looping forever, sensor, count, logic, time
• System inserts the appropriate block
Preview: NXT-G switch
• Switch block can have sensor or value to control
• Think of this as IF/ELSE
Preview: NXT-G
• Set up two (or more) sequences of blocks.
• NXT-G generates coding.
• This may produce essentially the same as periodic checks along one thread.
General comment
• Program may set up to check for sequence/set of events over and over
• Duty cycle
• Event loop
• Can give the program too much to do.
• Think of sentry doing guard duty, adding checkpoints.
Mechanics 101

Very, very loose definitions

Torque used for defining the power of the motor. Torque = force * distance. Motor can apply that force at that distance.

Velocity is speed in a direction—a vector as opposed to a scalar quantity. Acceleration refers to changes in velocity. Robots need acceleration to start and to overcome gravity and friction. For wheels, velocity = circumference * rpm. Revolutions Per Minute depend on torque from motor AND friction from wheels against specific surface

Gears/gearing is to put the torque where you want it.

Work load of robot is the robot itself plus the payload (what it needs to carry)

Considerations for robots
• Want motor that is powerful enough to do the job
• Do the job most of the time
• Not too powerful, because powerful generally means expensive and heavy
• Robot may need to carry itself + tooling + parts
• Payload refers that to that which pays for the job.
Lab: challenges
• Measurements: measure & record distance traveled and time taken
• 180 degrees, 1 rotation, 5 rotations at power levels 25, 50, 75.
• 1 second, 5 seconds [time taken should be close to inputs]

Prepare neat tables to show.

• Navigate field with obstacles (fixed = static)
• Go around obstacle (chair or stool). You decide route. Time it. Prepare report to show.
Suggestion
• You can use the wait until block with the NXT buttons. This gives you time to make the measurements
Homework

Read statics, dynamics and gear sections of

http://www.societyofrobots.com/mechanics_dynamics.shtml

Or