Line following robot
BADI Year 3
John Errington MSc
Specifications
1.
Self-powered –
–
2.
3.
implies recharging or refuelling
Operating schedule
–
How long must it operate between recharges
–
What time is available for recharging
Outside dimensions and turning circle
–
Related to spaces it must travel through
4.
Nature of environment – clean, dirty, presence of contaminants, oil, swarf,
other moving objects, need for rerouting of track etc.
5.
Carrying capacity
6.
Max speed and braking,
7.
Max gradient and irregularity of floor
8.
The latter points determine the amount of motive power needed, and this
must be related to operating schedule
9.
Safety considerations
Engineering Design issues
1: line detection
• What kind of track options:
– Metal, optical: reflective, white or black?
• How will the track be detected?
• Will the detection scheme be on/off or
proportional? (prop’l is less reliable)
• How will stops, accel & decel zones, changes in
direction be signalled?
Engineering Design issues
2: motive power
• Electric, hydraulic, pneumatic
• Source(s) of energy:
– Fuel: petrol, diesel, paraffin, coal, LP gas, hydrogen
etc.
– Rechargeable batteries – what kind?
• Motors
– What type(s)? How many? How will they be
controlled?
– Final drive gear, belt, chain, direct
• Wheels, tracks, legs, other?
Line detection
• How many sensors are needed?
– One sensor
• can detect presence of line, but not direction of line loss
– Two sensors
• Can detect direction of line loss in simple situations, but
relies upon dithering to check for line
– Three sensors
• Can detect presence of line and direction of line loss
• Allows for other simple signals to indicate stops and
accel/decel zones.
3-sensor line detection
Sensor 0
Sensor 1 Sensor 2 Significance
0
0
0
No line
0
0
1
Off line to right
0
1
0
Line centered
0
1
1
Line slightly to right
1
0
0
Off line to left
1
0
1
1
1
0
1
1
1
Line slightly to left
Action req’d
3-sensor line detection: further
A more detailed appraisal shows that the
information available for decision-making
includes
– The current state of the line sensors
– The previous state of the line sensors
– Taking three sensors this implies 2^(3*2)
– giving 64 possible states.
Line detection:
State transition mapping
Then
Now
#
Sensor 0
Sensor 1
Sensor 2
Sensor 0
Sensor 1
Sensor 2
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
0
0
0
1
0
2
.
.
.
.
.
.
.
1
1
1
1
1
1
64
Significance
State transition diagram
• A simpler way to represent this information
involves
– assigning input values to all possible input
events, and
– state values to all possible end results
• A map is then produced showing the
change in output state that will result
following each input state
State transition diagram
• A std allows the conditions that cause
changes between states, and the
responses required to be shown on a
visual plan.
Partially completed state transition diagram
I1
1
5
I0
2
I0
6
3
I1
4
7
8
Analysis of S.T.D.
• An engineer can use the STD to design a
logic circuit that will produce the required
responses to the various input conditions
as shown on the map.
Partial state table and STD
Then
Now
#
Sensor 0
Sensor 1
Sensor 2
Sensor 0
Sensor 1
Sensor 2
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
0
0
0
1
0
2
.
.
.
.
.
.
.
1
1
1
1
1
1
64
1
I1
5
2
I0
I0
6
3
7
I1
4
8
Significance
Motor calculation
1.
Suppose the maximum speed required is 5 kph
2.
Suppose the maximum gradient in the factory is 1/100
Then in travelling up this gradient for 1 hour the robot
would rise by 5km / 100 = 50m
3.
Suppose the robot has a mass of 1000kg when fully
loaded
– its weight is = 1000kg *9.81 N
Size of motor
Force = 1000 * 9.81 Newtons
Work done in raising 9810N through 50m:
W = 9810 * 50 = 490500 J
(Work = force * distance)
Power is total work done (J) / time taken (sec)
Power (Watts) = 490500 / 60 * 60 = 135 Watts
Or since 1hp = 0.75kW
we need a 0.25 hp motor