measuring the allocation of control in a 6 degree-of-freedom docking experiment
DESCRIPTION
Measuring the Allocation of Control in a 6 Degree-of-Freedom Docking Experiment. Introducing the M -metric. Maurice R. Masliah and Paul Milgram Ergonomics in Teleoperation and Control (ETC) Lab Department of Mechanical and Industrial Engineering - PowerPoint PPT PresentationTRANSCRIPT
Measuring the Allocation of Controlin a 6 Degree-of-Freedom Docking Experiment
Maurice R. Masliah and Paul Milgram
Ergonomics in Teleoperation and Control (ETC) LabDepartment of Mechanical and Industrial EngineeringUniversity of Toronto, Ontario, Canada, M5S 3G8http://etclab.rose.utoronto.ca{moman, milgram}@etclab.mie.utoronto.ca
Introducing the M-metric
(Images courtesy of Shumin Zhai and Ravin Balakrishnan)
Motivation
Overview
• Measures/definitions of performance metrics
• The M-metric
• Hypothesis for 6 DOF docking tasks
• 6 DOF docking experiment
• Results using the M-metric and discussion
• Shortcomings / Future Work of the M-metric
Start Position
Goal PositionA
Start Position
Goal Position
B
Start Position
Goal Position
E
Start Position
Goal Position
F
Start Position
Goal Position
G
Start Position
Goal Position
D
Start Position
Goal Position
C
Hypothetical Trajectories : 2 DOF
Measures/Definitions of Coordination
• time-on-target (“not very suitable” [Poulton ‘74])
• accuracy speed [Behbehani et al. ‘88]
• spatial or temporal invariance [Morrison & Newell ‘98]
• cross-correlations [Vereijken et al. ‘92, Zhai et al. ‘96]
• integrality [Jacob et al. ‘94]
• inefficiency [Zhai & Milgram ‘98]
Integrality vs. Inefficiency
• Integrality is a measure of simultaneity
(in the time domain)
• Inefficiency is a measure of distance traversed
(in the space domain)
Time
0
2
4
6
8
10
Am
ount
of M
ovem
ent
Amount of Movement Over Time
A
B
The M-metric
• Measures the allocation of control across DOFs
• “Control” = any movement which reduces error
• “Error” = the difference between the goal position and
the current position
• M-metric = (control simultaneity) × (control efficiency)
Err
or
Incr
eas
e
Err
or
Re
duct
ion
Time
DOF "X"DOF "Y"
Definition of Control Simultaneity
CHANGE IN
ERROR
Normalized Error
Reduction
Area under DOF curve = 1
Area of overlap, intersection between the DOFs.
Control Efficiency
Efficiency =the weighted average of the ratios of the length of the “optimal” trajectory for each DOF divided by the actual trajectory
StartPosition Goal
Position
a
bc
Efficiency =c
a + b
M-metric: Primary Features
• measures the allocation of control
• = simultaneity efficiency
• values between 0 and 1
• computed for any number of DOFs ( 2)• (also subsets of the total available DOFs)
• computed across DOFs encompassing different measurement units (cm, degrees)
Hypothesis for 6 DOF docking tasks
• Non-equal allocation of control across DOFs
• Novices • will allocate their control between translation and rotation
DOFs • will switch control back and forth
• As expertise develops:• will continue to allocate their control between translation
and rotation DOFs with improved control• will develop uniform allocation of control across all 6 DOFs
8 subjects total (between subjects design)
2 input devices :
216 docking trials per session
5 one hour sessions
Experimental Design
= 8640 total trials
Spaceball
Finger-ball
Results: Task Completion Times
Docking Performance over TimeIsotonic Position Device
Trial Number
0 200 400 600 800 1000
Tas
k C
ompl
etio
n T
ime
(sec
onds
)
0
5
10
15
20
25
30
35
40
Session Means
Docking Performance over TimeIsometric Rate Device
Trial Number
0 200 400 600 800 1000
Tas
k C
ompl
etio
n T
ime
(sec
onds
)
0
5
10
15
20
25
30
35
40
Session Means
Average M-metric Value for all Two-Way Comparisons
0.0
0.1
0.2
0.3
0.4
0.5
0.6
XY XZ YZXRX
XRYXRZ
YRXYRY
YRZZRX
ZRYZRZ
RXRY
RXRZ
RYRZ
M-m
etr
ic
Results: M-metric Scores 2-way Comparisons
within translation within rotationbetween translation & rotation
Results: M-metric Scores 3-way Comparisons
Average M-metric Value for all Three-Way Comparisons
0.0
0.1
0.2
0.3
0.4
0.5
0.6
XYZ
XYRX
XYRY
XYRZ
XZRX
XZRYXZRZ
YZRX
YZRYYZRZ
XRXRY
XRXRZ
XRYRZ
YRXRY
YRXRZ
YRYRZ
ZRXRY
ZRXRZ
ZRYRZ
RXRYRZ
M-m
etr
ic
within translation within rotationbetween translation & rotation
Results: M-metric Scores Over Time
within rotation
between translation & rotation
0
0.1
0.2
0.3
0.4
0.5
0.6
1 2 3 4 5
Session (Time)
M-m
etric
Isotonic Position Y-Z-RYIsometric Rate Y-Z-RYIsotonic Position RX-RY-RZIsometric Rate RX-RY-RZ
M-metric Summary
• new metric for measuring allocation of control
• tested in a longitudinal 6 DOF docking task
• subjects allocated allocated unequally control across all 6 dofs
• subjects controlled rotation & translation separately
• separation of control for the isometric device greater than for the isotonic device
Shortcomings / Future Work
• Need to define the “correct” path unequivocally• In docking, any trajectory which accomplishes the
docking goal is acceptable.
• Expand M-metric definition to include tracking, tracing, and target acquisition tasks.
• Next experiment : test M-metric on a dynamic 6 DOF tracking task
Conclusion:In a multi-degree of freedom continuous movement task:
• the M-metric provides a measure of how control is allocated across available DOFs
• it is possible to have two movements with equal performance scores, but with very different time-space trajectories
Acknowledgements
• Institute of Robotics and Intelligent Systems (IRIS)
• Natural Sciences and Engineering Research Council (NSERC)
• Shumin Zhai, IBM Almaden Research
• Ravin Balakrishnan, University of Toronto
Taxonomy of Manual Control TasksTime Domain
Externally Paced Self-Paced(Time Matching) (Time Minimizing)
Spac
e D
omai
n
D
istr
ibut
ed
Sin
gle
Loc
atio
n
L
ocat
ion
Target Acquisition ball catching instrument
playing at atempo
Target Docking menu
selection peg-in-hole
tasks
DynamicTracking target
gunnery driving at a
speed limit
Tracing drawing marking
menus
[Masliah ‘99]