Effectors and Actuators

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Effectors and Actuators

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Lecture 16: (20/11/09) Sensing self-motion Key points: Why robots need self-sensing Sensors for proprioception in biological systems – PowerPoint PPT presentation

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Title: Effectors and Actuators

1
Lecture 16 (20/11/09)
Sensing self-motion

Key points
Why robots need self-sensing
Sensors for proprioception
in biological systems
in robot systems
Position sensing
Velocity and acceleration sensing
Force sensing
Vision based proprioception

Michael Herrmann
michael.herrmann_at_ed.ac.uk, phone 0131 6 517177,
Informatics Forum 1.42
2
Why robots need self-sensing

For a robot to act successfully in the real world
it needs to be able to perceive the world and its
relation to the world.
The state of the robot is not entirely up to the
robot itself, but also reflects external events.
Thus, information about the body is an
important source of information about the world
Another use of proprioceptive information is
stabilization and smoothing of planned movements
against perturbations
In particular, to control its own actions, it
needs information about the position and movement
of its body and parts.
Our body contains at least as many sensors for
our own movement as it does for signals from the
world.

3
Proprioception Detecting our own movements

To control our limbs we need feedbackKinesthesia
Muscle spindles
where length
how fast rate of stretch
Golgi tendon organ
how hard force

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Proprioception Detecting our own movements

To control our limbs we need feedback on where
they are.
Muscle spindles
Golgi tendon organ
Pressure sensors in skin

Pacinian corpuscle transient pressure response
6
Proprioception (cont.)

To detect the motion of our whole body have
vestibular system based on statocyst
Statolith (calcium nodule) affected by gravity
(or inertia during motion) causes deflection of
hair cells that activate neurons

7
Describing movement of body

Requires
Three translation components
Three rotatory components

Vestibular System
Utricle and Saccule detect linear acceleration.

Semicircular canals detect rotary acceleration in
three orthogonal axes

Fast vestibular-ocular reflex for eye
stabilisation

9
Robert J. Peterka (2009) Comparison of human and
humanoid robot control of upright stance. Journal
of Physiology Paris 103, 149158
10
Using proprioceptive information
Control
Efference copy
Proprioception
Exteroception
body surface
11
For a robot

Need to sense motor/joint positions with e.g.
Potentiometer (current measures position)
Optical encoder (counts axis turning)?
Servo motor (with position feedback)?

12
For a robot

Velocity by position change over time or other
direct measurement Tachometer
E.g. using principal of dc motor in reverse
voltage output proportional to rotation speed
(Why not use input to estimate output?)?
Acceleration could use velocity over time, but
more commonly, sense movement or force created
when known mass accelerates, i.e. similar to
statocyst

13
Gyroscope uses conservation of angular momentum
Accelerometer measures displacement of weight
due to inertia

There are many alternative forms of these
devices, allowing high accuracy and
miniaturisation (e.g. ceramic piezo gyros)

14
Inertial Navigation System (INS)

Three accelerometers for linear axes
Three gyroscopes for rotational axes (or to
stabilise platform for accelerometers)
By integrating over time can track exact spatial
position
Viable in real time with fast computers
But potential for cumulative error

15
For a robot

To sense force e.g.
Strain gauge resistance change with deformation
Piezoelectric charge created by deformation of
quartz crystal (n.b. this is transient)

16
For a robot

Various other sensors may be used to measure the
robots position and movement, e.g.
Tilt sensors
Compass
GPS
May use external measures e.g. camera tracking of
limb or robot position

17
Some issues for sensors

What range, resolution and accuracy are required?
How easy to calibrate?
What speed (i.e. what delay is acceptable) and
what frequency of sampling?
How many sensors? Positioned where?
Is information used locally or centrally?
Does it need to be combined?

18
Haptic perception combines muscle touch sense
19
Vision as proprioception?

An important function of vision is direct control
of motor actions
Test standing on one leg with eyes closed or
standing up ...

20
The swinging room - Lee and Lishman (1975)
21
Optical flow
22
Optical flow Heading focus of expansion
provided that it can discount flow caused by eye
movements
23
Optical flow Flow on retina forward
translation eye rotation
Flow-fields if looking at x while moving towards
Bruce et al (op. cit) Fig 13.6
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From optical flow to time to contact
P distance of image from centre of flow
X distance of object from eye V velocity of
approach
Y velocity of P on retina
t P/Y X/V rate of image expansion
time to contact
Lee (1980) suggested visual system can detect t
directly and use to avoid collisions e.g. correct
braking.
26
Using expansion as a cue to avoid collision is a
common principle in animals, and has been used on
robots

E.g. robot controller based on neural processing
in locust Blanchard et. al. (2000)?

27
Proprioceptive control
28
Proprioceptive control
29
Summary

Have discussed a variety of natural and
artificial sensors for self motion
Have hardly discussed how the transduced signal
should be processed to use in control for a task.
E.g. knowing about muscle and touch sensors
doesnt explain how to manipulate objects

30
Dimensions of robotics

Defining goals Tasks or models
Reaching goals programming or learning
Reason or emotions
Evaluation of performance
Energy consumption
Social issues
Dynamical systems for control
Design principles

31
1. Biorobotics

Robots as models of animal behaviour
Proof of (functional) principle
Bio-inspired robotics
Biomorphic engineering
Service robots
Prosthetics
Human-robot interaction

32
2. Programming vs. Learning
O. Lebeltel, 1996
33
2. Programming vs. Learning
O. Lebeltel, 1996
34
Programming and Learning for control

Action languages (R. Reiter)
Middleware concepts
Machine learning algorithms
Objective functions
Self-organisation of behaviour
Evolution and development
Reinforcement learning
Neural networks
Artificial emotions, consciousness

Methods from
Comp. Sc.
Engineering
Math
Physics
Biology
Psychology

35
The uncanny valley (Masahiro Mori, 1970)?

Repliee Q1 and Geminoid
(H. Ishiguro, U Osaka, 2005, 2007)

36
3. Emotion vs. Reason

Emotions for robots
Interaction with humans
Internal evaluation
Centralised supervision
Kansei (emotion) engineering
Reason for robots cf. 2. and previous lectures

37
4. Performance Competition vs. Measurement

DARPA Grand Challenge
RoboCup Robot Soccer Rescue
Climbing, underwater, fire fighting, ...
RunBot Fastest robot on two legs
Service limits, running costs, monitoring and
support, flexibility, upgradability

38
5. Energy consumption

Super-human efficiency in certain tasks
Inspiration from biology Passive dynamics in
walking, energy re-use by springs, locking
mechanisms for posture maintenance, modularity,
hibernation
Development of enduring batteries
Alternative energies Solar robots
Fly-eating robot (UWE, 2004)

39
6. Social robots