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can be performed concurrently or sequentially.
Information from different sensors can be obtained
simultaneously. Concurrency of mechanical actuator
and electronic operation execution is especially
important for optimal real time robot design.
At phase zero (time interval T
0
) the registers of
nods are charged with data from the main program.
This program can be hold in ROM of central unit or
loaded using wireless connection from user data
base. This zero phase is not necessary to enclose in
the autonomous mobile outdoor robot real time
characteristic estimation.
Phase one (time interval T
1
) – the environment
estimation and building the route map:
- T
11
the robot start point estimation using GPS
(t
1gp
), data acquisition by video camera module at
start position (t
1vi
, data acquisition from digital
compass (t
1cm
) and data acquisition from infrared
optical short range distance meter (t
1sd
) and infrared
optical long range distance meter (t
1ld
), start point
coordinate estimation (t
1cu
) using CU.
Data acquisition from GPS, digital compass and
distance sensors can be executed simultaneously in
time t
1vi
required to complete data acquisition by
video camera module. Then start point coordinate
estimation in time T
11
is t
1vi
and t
1cu
determined
- T
12
is a sum of times required to turn camera in
horizontal (t
1th
) and vertical (t
1tv
) directions to search
for the first nearest object, using servomotors and
image acquisition time getting information about
recognized objects t
1vi.
This process repeats as much
times N
1tm
as needed to investigate view sector for
the object. T
12
is N
1tm
,t
1th
, t
1tv
and t
1vi
determined.
At the optimal conditions N
1tm
=1
- T
1
route map calculation (t
1cum
) by central unit
using main algorithm and data from GPS, digital
compass, video camera module and distance sensors.
Phase two (time interval T
2
) - robot turning to
the required direction actuating both left (t
2trl
) and
right (t
2trr
) motors. Motors are actuated
simultaneously, it can be accepted that their
operation time is equal T
2
= t
2trl
= t
2trr
Phase three (time interval T
3
) – robot movement
by calculated route map to the first, second, or N
st
objects, actuating motor drivers, distance encoders,
video camera module and compass:
- image acquisition by video camera module (t
3vi
)
- driving and steering (t
3ds
) to the object reading
data from distance l encoders
and required direction
α from compass. T
3
is N
st
,t
3ds
, t
3vi
determined.
Phase four (time interval T
4
) –investigation of
object parameters using video camera module (t
4vi
)
and central unit program (t
4cuo
). T
4
is t
4vi
and t
4cuo
determined.
Phase five (time interval T
5
) – obstacle
avoidance: obstacle determination using video
camera (t
5vi
), avoidance decision taking by CU
(t
5cuob
) (jump over or go around), obstacle avoidance
realization (t
5rob
). T
5
is t
5vi
, t
5cuob,
t
5rob
determined.
For the robot real time characteristics’
investigation, it is suitable to select some application
specific limited route map and time interval T
1
for
the calculation and select it as the deadline.
A deadline can be determined for each execution
phase. When sequence of all of the phases can be
determined in WCET
i
(worst-case execution time) -
the robot can be determined as hard RTS.
T
1
= T
1
+ T
2
+ T
4
+ T
5
=∑
i
5
WCET
i
= D
h
To compare and estimate different robot
realization structures using (1) it is necessary to
select the same numbers of N
1tm
and N
st
.
For sophisticated autonomous mobile robot
timelines with task completion slack time, start time
and soft deadlines utility accrual UA approach can
be used. The Utility (U) depends on the activity’s
completion time for phases T
i
and particular cycles
t
k
. These soft time constraints are subject to
optimality criteria such as completing all time-
constrained activities as close as possible to their
optimal completion time — so as to yield maximal
collective utility. Time/utility functions is a
generalization of the deadline constraint, specifies
the utility to the system resulting from the
completion of activity as a function of its completion
time.
Activity ji utility (U) calculation is useful to
compare the realization time t
ji
and some soft
deadline d
s
(Figure 1.).
Figure 1: Activity j realization with deadline d
s.
This soft deadline depends on environment
where is acting the autonomous mobile robot. While
developing our research robot physical model the d
s
usually was equal to image processing delay (Baums
et al., 2011).
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