9a robotic systems sensors
TRANSCRIPT
-
7/29/2019 9a Robotic Systems Sensors
1/26
Robotic Systems(9a)
Dr Richard Crowder
School of Electronics and Computer Science
-
7/29/2019 9a Robotic Systems Sensors
2/26
Robot Sensors Global objective: Acquire knowledge and resolve uncertainty about the
position or quality of an object and/or its environment.
Application
Robot parameters for the internal control loops
Locating objects
Correcting for errors between the world and the robots model
Detecting and avoiding failures
Detecting and avoiding collisions
Monitoring interactions (force control)
Monitoring the environment for changes (temperature)
Inspection
Guidance
-
7/29/2019 9a Robotic Systems Sensors
3/26
Sensing within a Gripper
Slip sensorTouchsensor
-
7/29/2019 9a Robotic Systems Sensors
4/26
Tactile sensing to control a gripper
-
7/29/2019 9a Robotic Systems Sensors
5/26
Sensing process
TransducerSignal
conditioningADC orsimilar
Datareduction& analysis
Modelanalysis
PhysicalQuantity
ElectricalSignal
Linearised &lifiedsignal
Digitalsignal
Model
Perception
Depending on the sensor and application, not all steps are required
-
7/29/2019 9a Robotic Systems Sensors
6/26
Hierarchy Perception analysis of the model to infer
State of the world
Consequence of actions
Collisions
Model formation of a geometric model Data compression
Sensor fusion
Feedback to actuators
Measurement physical model
Conversion of electrical signals to physical quantities
Physical
Interface
Signal conditioning
transducers
-
7/29/2019 9a Robotic Systems Sensors
7/26
Types
Internal to the robot
Joint position: Encoders, Resolvers
Safety: Joint limit switches
External to the robot
Tactile, Force and Slip
Vision
Chemical (pheromones)
.
-
7/29/2019 9a Robotic Systems Sensors
8/26
Tactile Sensing
Tactile
The detection and determination of the spatial distribution offorces over an defined area.
Touch
Single point sensing (can be binary touch or no-touch)
Force
Measurement of forces along the principle axes
Slip
Measurement of the loads velocity relative to the sensor
-
7/29/2019 9a Robotic Systems Sensors
9/26
Typical Characteristics
Sensor surface must be compliant and durable
Spatial resolution should be approximately 1mm
Sensor should be stable, monotonic, and repeatable
Sensors require as low hysteresis as possible
Response time typically 1-10ms
A sensitivity of 0.01N, and a dynamic range of 1000 : 1
A typical array should have 50 - 200 individual elements.
Harmon, L. D. 1982. Automated tactile sensing. Int. J. Robotics Research 1(2):331.
-
7/29/2019 9a Robotic Systems Sensors
10/26
Sensing Technologies
Strain gauges
=
GFR
R
G
Where GF is the gauge factor (typically 2)and is the strain
http://en.wikipedia.org/wiki/Image:Strain_gauge.svg -
7/29/2019 9a Robotic Systems Sensors
11/26
Resistive foam
0 0.2 0.4 0.6 0.8 1
0.5
1
Applied Force
Sensor
Resistance
Protective Surface
Conductive Foam
Dot and Ring
on substrate
-
7/29/2019 9a Robotic Systems Sensors
12/26
Piezoelectric
PVDF Polyvinylidene Fluoride
Top and bottom surfaces
Coated with aluminium
Chargeamplifier
Long chain molecules
Orientated during manufacture
-
7/29/2019 9a Robotic Systems Sensors
13/26
Optical
Optical receiver
Optical source
Deformable tube
Spring steel
Reflective surface
Combined optical receiver
and source
-
7/29/2019 9a Robotic Systems Sensors
14/26
Photelastic
Receiver
fibre
Sourcefibre
Photoelastic
material
Analyser
Polariser
-
7/29/2019 9a Robotic Systems Sensors
15/26
Tactile technology summary
SENSOR ADVANTAGE DISADVANTAGEMechanical Arrays Simple Complex to manufacture
Poor spatial resolution
Resistive (including FSR) Wide dynamic rangeDurable
Good overload tolerance
HysteresisLimited spatial resolution
Capacitive Wide dynamic rangeRobust
Susceptible to EMITemperature sensitiveLimitation in spatial resolution
Magnetic Wide dynamic rangeRobust
Poor spatial resolutionSusceptible to EMI
Optical (intrinsic and extrinsic) Intrinsically safeVery high resolution possible
Electronics can be complex
Piezoelectric Wide dynamic rangeGood mechanical properties
Pyroelectric effectDynamic response onlyCharge amplifier
-
7/29/2019 9a Robotic Systems Sensors
16/26
Tactile sensing to control a gripper
-
7/29/2019 9a Robotic Systems Sensors
17/26
Sensor Functionality
Sensor Location Parameter
Tactile array sensor Outer surface of thefinger tip
Pressure distribution,local shape
Fingertip, force torquesensors
Finger tip structure Contact force andtorque vectors
Finger joint anglesensor
Finger joint or at amotor
Finger tip position,contact location
Actuator effort"
sensor
Motor or joint Motor torque
Dynamic tactile sensor Outer surface of thefinger tip
Vibration, stress,changes, slip
-
7/29/2019 9a Robotic Systems Sensors
18/26
Touch sensors in manipulation
-
7/29/2019 9a Robotic Systems Sensors
19/26
Object recognition using tactile sensing
The key is to break the sensing down into a number of primitive steps:surface properties, structural properties andfunctional properties.One approach to the problem could be:
Approach: The end effector moves to grip the object; the points of
contact will give an initial indication of shape. Shape: Movement of the fingers over the object, using a compliant
frame with no specific gaol.
Texture: derived from the mean and standard deviation of thesensor values.
Hardness: Force is applied and the resultant localiseddisplacements are measured.
Thermal: Used to distinguish between metal and other materials.
-
7/29/2019 9a Robotic Systems Sensors
20/26
Problem with tactile arrays
The resolution is poor, tens of taxels against thousands of pixels.
The background of a tactile image is clear - no object no force.
A tactile sensor suffers from considerable cross talk, while equivalent to visual
blurring it cannot be easily solved in the same manner.
Applied force
-
7/29/2019 9a Robotic Systems Sensors
21/26
Slip Sensing
Tactile array image
Touch data (photo elastic sensor)
Special purpose sensor
Spring loaded Roller,Connected to aposition sensor
-
7/29/2019 9a Robotic Systems Sensors
22/26
Tactile sensors - applications
Industrial automation is clearly the area of greatestopportunity in robotics. Such operations as assembly, pick-and-place, grinding, and inspection will becomeincreasingly more automated in the next 10 years. Touchsensing, now extremely primitive, can be expected to evolveinto a highly developed technology in the near future.(Harmon 1982, p. 30)
However this is not been the case the key drivers was notconventional industrial applications.
-
7/29/2019 9a Robotic Systems Sensors
23/26
Future growth areas
Surgery and Medicine
Very rapid take-up Restore taction in MIS
Disposable equipment Laparoscopy improvements
Soft tissue discrimination Hardness/softness sensing
Health Care and Service RoboticsDemographic projections Personal space manipulation
Enormous demand imminent Mobility aids
Cost reduction essential Automated household tools
Haptic exploration, dexterity Safety
Adaptation, customization Reliability
Low costs User acceptance
-
7/29/2019 9a Robotic Systems Sensors
24/26
Force Control and Measurement
Force control
Active
The system will respond to sensory information Passive
inherently correct, reliance on springs or compliantsystems
-
7/29/2019 9a Robotic Systems Sensors
25/26
Remote Centre Compliance - RCC
TheRCCsystem is a passive system, and relies on a springand link structure.
The system can correct for minor error in position, both
rotational and translational.
The design relies on the RCC and the object withstandingthe applied forces
-
7/29/2019 9a Robotic Systems Sensors
26/26
RCC
Translation Rotation