B. Demonstrating closed-loop control to track a predetermined path
A closed-loop feedback control system utilizes a negative feedback loop with a sensor to measure the output and
compare the measured output, represented by Y(s), with the reference input, represented by R(s), to generate an
error signal, represented by Ea(s), that drives the controller. If we can utilize the error signal appropriately, then we
will achieve our tracking objective, that is, minimize E(s)=Y(s)-R(s), in the presence of external disturbances and plant
uncertainties and parameter changes. This is the key objective of closed-loop feedback controller design. The IR sensor
can used to distinguish between colors based on differences in IR reflectivity to track a prescribed path marked on the
ground. It can also measure the distance to obstacles allowing us to miss obstacles or track a prescribed path through
an obstructed area. With the introduction of the sensor, we have additional unwanted sensor noise, represented by
N(s). The main benefits of closed-loop control include (i) increased robustness of the closed-loop performance to
changes in the parameters of the plant, (ii) improved external disturbance rejection, measurement noise attenuation,
and reduction of the steady-state error of the system, and (iii) ready control and adjustment of the transient response
of the system by skillful design of the controller. However, these advantages come with cost. The main cost of closed-
loop feedback control is additional complexity that means higher monetary costs and greater likelihood of component
failures. Since the benefits far outweigh the disadvantages, we find closed-loop feedback control is widely employed
in modern control systems. The key to closed-loop feedback control is the use of the tracking error signal to improve
the transient response (settling time, percent overshoot, etc.) as well as reduce steady-state errors tracking errors.
Note: Control concepts described in detail in Modern Control Systems, by R. C. Dorf & R. H. Bishop, 13th Ed., Pearson
Education, Inc., 2017.
Figure 2 Closed-loop control of the rover with IR sensor feedback.
Plant
Rover vehicle
Sensor
Infrared (IR) range finder
Actuator
DC servo motors
Performance
Command following in the presence of disturbances
Design objectives
Tune the control system by adjusting PID gain constants & track the predetermined
path
Reference inputs
Predetermined path with obstacles
Y(s)
Plant
Controller
G
c
(s)
G(s)
Actuator
Balancing Robot
T
d
(s)
R(s)=0
Sensor
H(s)
-
N(s)
E
a
(s)
Desired angle
from vertical
Actual angle
from vertical
Rover Vehicle Assembly
81
Summary of Contents for 41427
Page 1: ...RobotBuilder sGuide for NI myRIO 41427 POWERED BY...
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Page 26: ...Step 12 Step 14 Step 16 Step 11 Step 13 Step 15 24 Subassembly Construction Instructions...
Page 27: ...Step 18 Step 17 Finished Assembly Subassembly Construction Instructions 25...
Page 29: ...Step 6 Finished Assembly Step 5 Subassembly Construction Instructions 27...
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Page 57: ...Step 1 0 Step 1 1 Rover Vehicle Assembly 55...
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Page 117: ...Finished assembly should look like this BalancingArmAssembly 115 Balancing Arm Assembly 115...
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Page 143: ...Partial assembly should look like this Self Balancing Robot Assembly 141...
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Page 153: ...Finished assembly should look like this Self Balancing Robot Assembly 151...
