Robotics Flashcards Preview

R, B & M > Robotics > Flashcards

Flashcards in Robotics Deck (33)
Loading flashcards...
1

Classifications of robots

1. Manual handling devices - device with multi degrees of freedom actuated by an operator
2. Fixed sequence - device that performs successive stages of a task according to a predetermined and fixed program
3. Variable sequence - performs the successive stages of a task according to a predetermined but programmable method
4. playback robot - human operator performs the task manually by leading the robot, motions recorded for later playback , robots repeats the motions according to the recorded information
5. Numerical control - operator supplies robot with motion programme rather than teaching it the task manually
6. Intelligent robot- ability to understand its environment and successfully complete a task despite changes in the surrounding condition

2

Robot mechanical subsystems

1. mechanical subsystem composed of rigid bodies
2. a sensing subsystem
3. an actuation subsystem
4. a controller
5. an information processing subsystem

3

Wrist DoF

Roll - rotation about the X-axis of global coordinate system

Pitch - rotation about the Y-axis of global coordinate system

Yaw - rotation about the Z-axis of global coordinate system

4

Proximity sensors

Inductive sensor - sense existence of a metallic object due to a change in inductance

Capacitative - sense existence of gas, liquid or metals that cause a change in capacitance

Hal effective - work based on interaction between voltage of semiconductor material and magnetic fields

Sonic, ultrasonic & optical - work based on the reflection or modification in an emitted signal by objects

5

End effector considerations

1. shape & size of grasped object
2. uniformity or tolerance of handled objects
3. are surfaces smooth, what is the coefficient of friction
4. what is the spacing of objects
5. how will they be oriented and presented
6. what placement and spacing dimensions can be modified
7. what are placement tolerances
8. what are grasping forces or pressure limits
9. are complementary tools needed
10. is compliance necessary for assembling parts
11. special environmental considerations

6

Cleanroom design guidelines

1. minimise number of moving parts
2. place all moving parts below the substrate
3. enclose and seal the robot interior and evacuate generated particles
4. use internal robot cabling only
5. apply coating or treatment to external robot surfaces
6. use cleanroom approved lubricants
7. use stainless steel screws and washers
8. minimise the contact surface of end-effectors
9. brushless motors
10. direct-drive trains to eliminate belts

7

Transformation of kinetic geometry

- determination of the trajectory in cartesian coordinate space
- transformation of the cartesian trajectory into equivalent joint coordinate space
- generation of motor torque commands to realise trajectory

8

Euler angles

precession = inverse Cos(r33)

nutation = inverse Tan(r31/r32)

spin angle = inverse Tan (r13/r23)

9

CCD camera principle

- photons of light striking the individual semiconductor elements in an array creates a charge on each element
- individual charges are coupled sequentially to the output, where they are amplified, converted to a digital value and stored in a frame buffer

10

Contour tracing algorithm

- random search algorithm used to find a boundary
- if pixels ahead are different, go ahead
- if both pixels 0, turn right
- if both pixels 1, turn left

11

General functions required of mobile robot systems

- environmental perception
- environmental modelling
- navigation
- task planning
- interaction
- safety monotoring

12

Environmental perception methods

- bumper switch
- ultrasonic sensor
- laser sensor
- CCD stereo camera

13

SCARA configuration

- two horizontal revolute joints
- widely used for assembly
- prismatic joint provides compliant vertical motion

14

Closed kinematic chain

- parallel linkages
- active and passive joints
- passive joints coordinates are functions of active joints and robot geometry

15

Electric actuated robots

- cleaner, quieter and more precise than hydraulic and pneumatic
- effective at high speeds so high gear ratio is needed

16

Typical robot joint actuation

- first axis direct motor drive
- second axis band drive
- third axis belt drive
- fourth axis linear ball-screw drive

17

Hydraulic advantages & disadvantages

ADV
- superior at high load carrying
- high power-to-weight ratios
- actuator control through solenoid or servo valve

DIS
- power supply is bulky
- fast & accurate servos are constly
-leak & maintenance limit their use

18

AC construction

- single phase or three phase
- coils on outside, magnets in the middle
- no. of windings and frequency of power fed to coils make the speed of the motor
- windings on outside can be cooled better
- best in constant speed applications

19

Permanent magnet DC

- coils on rotor, magnets on outside
- low inductance, low friction
- lots of electrical noise due to brush sparks, brushes can wear out and get clogged with dirt
- torque and speed can be controlled
- high gyroscopic effect due to coils on rotor

20

Stepper motors

- capable of precise incremental shaft motion
- low rotational mass so they can stop accurately, similar construction to AC & DC
- cant handle sudden changes in loads

21

Transmission types

Direct drive: high torque, low speed, eliminate free play & smooth torque transmission

Band drives: up to 10:1 drive ratios. actuator mass moved away from joint

Belt drives: up to 100:1 with multiple stages, tension controlled by idlers

Gear drives: spur or helical, sealed reliable and low paintenance

Harmonic: elastic geared ring, no backlash, lightweight, high gear ratios

22

Types of end-effector

PASSIVE & PREHENSILE
- parallel axis, typically pneumatic actuated, must be synchronised, close around jaw centre
-parallel/rotary jaws, not parallel, jaw centre changes
- four-bar linkage, rotary motion converted into parallel jaw motion, changing jaw centre
- chuck style jaws for cylindrical parts, very strong grip

23

Active end-effectors

- aim to mimic human hand, allow 3 dimensional grasping, can grasp irregular objects
- control is difficult as there are variations in contact area, fingers continually making/breaking contact

24

Remote Compliance Centre device (RCC)

- allows force/deflection properties of end effector to be tailored to suit a task
- allows an assembly robot to account for positioning errors
- can reduce damage, lower contact forces vie lower horizontal and rotational stiffness'

25

Payload considerations

- payload is the weight or mass of the end effector
- acceleration forces and moments are considered part of the load
- force calculations for payloads must be determined at all critical locations

26

6 human grasping modes

- spherical
- cylindrical
- hook
- lateral
- palmar
- tip

27

Link offset D

displacement along the Zi-1 axis to go from the link i-1 to the link i perpendicular

28

Joint angle Theta

rotation about Zi-1 required to align Xi-1 with Xi
positive rotation is clockwise looking in direction of Zi-1

29

Link length Ai

length of the perpendicular i.e. displacement required in the Xi direction to bring the origin frame {i-1} coincident with that of frame {i}

30

Link twist alpha(i)

rotation required about Xi to make Zi-1 coincident with Zi ( positive rotation is clockwise looking in the direction of Xi)