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Confusion in block diagram of open loop and close loop control system?
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I am studying Modern Control Systems, 11th edition, by Dorf and Bishop.
On page 221 it first shows in fig4.7 open loop control system(the writer names it as open loop) and on page 222 close loop control system is shown in fig 4.9
Snapshots of both images are attached
I wonder why the writer is calling fig4.7 as open loop despite the fact that it contains feedback path with gain block Kb
control control-system
asked 12 hours ago
abtjabtj
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$begingroup$
I am studying Modern Control Systems, 11th edition, by Dorf and Bishop.
On page 221 it first shows in fig4.7 open loop control system(the writer names it as open loop) and on page 222 close loop control system is shown in fig 4.9
Snapshots of both images are attached
I wonder why the writer is calling fig4.7 as open loop despite the fact that it contains feedback path with gain block Kb
control control-system
asked 12 hours ago
abtjabtj
584 bronze badges
New contributor
abtj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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There is something off about how the author draws the "back electromotive force" coming off the speed, but I'm pretty sure it's open loop since it doesn't use a direct measurement of what it is controlling in the feedback loop. The second one uses a tach which provides a measured speed, the first one does not.
$endgroup$
– Ron Beyer
11 hours ago
add a comment
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$begingroup$
I am studying Modern Control Systems, 11th edition, by Dorf and Bishop.
On page 221 it first shows in fig4.7 open loop control system(the writer names it as open loop) and on page 222 close loop control system is shown in fig 4.9
Snapshots of both images are attached
I wonder why the writer is calling fig4.7 as open loop despite the fact that it contains feedback path with gain block Kb
control control-system
asked 12 hours ago
abtjabtj
584 bronze badges
New contributor
abtj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
I am studying Modern Control Systems, 11th edition, by Dorf and Bishop.
On page 221 it first shows in fig4.7 open loop control system(the writer names it as open loop) and on page 222 close loop control system is shown in fig 4.9
Snapshots of both images are attached
I wonder why the writer is calling fig4.7 as open loop despite the fact that it contains feedback path with gain block Kb
control control-system
control control-system
asked 12 hours ago
abtjabtj
584 bronze badges
New contributor
abtj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 12 hours ago
abtjabtj
584 bronze badges
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abtj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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edited 12 hours ago
abtj
asked 12 hours ago
abtjabtj
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New contributor
abtj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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asked 12 hours ago
abtjabtj
584 bronze badges
asked 12 hours ago
abtjabtj
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584 bronze badges
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abtj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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$begingroup$
There is something off about how the author draws the "back electromotive force" coming off the speed, but I'm pretty sure it's open loop since it doesn't use a direct measurement of what it is controlling in the feedback loop. The second one uses a tach which provides a measured speed, the first one does not.
$endgroup$
– Ron Beyer
11 hours ago
add a comment
|
$begingroup$
There is something off about how the author draws the "back electromotive force" coming off the speed, but I'm pretty sure it's open loop since it doesn't use a direct measurement of what it is controlling in the feedback loop. The second one uses a tach which provides a measured speed, the first one does not.
$endgroup$
– Ron Beyer
11 hours ago
$begingroup$
There is something off about how the author draws the "back electromotive force" coming off the speed, but I'm pretty sure it's open loop since it doesn't use a direct measurement of what it is controlling in the feedback loop. The second one uses a tach which provides a measured speed, the first one does not.
$endgroup$
– Ron Beyer
11 hours ago
$begingroup$
There is something off about how the author draws the "back electromotive force" coming off the speed, but I'm pretty sure it's open loop since it doesn't use a direct measurement of what it is controlling in the feedback loop. The second one uses a tach which provides a measured speed, the first one does not.
$endgroup$
– Ron Beyer
11 hours ago
add a comment
|
3 Answers
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This system:
Actually uses the Motor's back EMF as a feedback signal, it does not use the speed information directly.
From a back EMF viewpoint, this is a closed system (the back EMF is directly controlled).
From a motor speed viewpoint, this is an open system (the speed is not directly controlled).
However, this system:
does use the speed of the motor as a feedback signal so the speed is directly controlled.
There is still the back EMF feedback but that does not control the motor speed directly (assuming "sane" choices for $K_b$ and $K_t$)
answered 11 hours ago
BimpelrekkieBimpelrekkie
59.2k2 gold badges61 silver badges135 bronze badges
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The back EMF is an inherent characteristic that is a factor in determining the motor's torque vs. speed curve. Without feedback, the motor speed is not indeterminate. It varies as load change as determined by the slope of the torque vs. speed curve. The back EMF gives the motor a certain amount of built-in feedback, but the effect is limited. The gain can not be adjusted.
answered 11 hours ago
Charles CowieCharles Cowie
24.2k1 gold badge18 silver badges44 bronze badges
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$begingroup$
Your first diagram shows the behavior of the motor alone. The feedback (back EMF) shown does exist, but it does nothing to stablize the motor speed against load changes. For a given voltage in, and a fixed load torque (bearing friction, load friction, air resistance, etc) you can set the motor speed by varying the input voltage. Some systems do this quite handily - electric fans, for instance. However, if you vary ("disturb") the load torque, the motor speed will change. This is not an issue for some applications (electric drills, electric golf carts, etc). For these applications, the operator supplies the feedback when the output speed needs to be constant.
Because there is no built-in stabilizing loop, these systems are called "open loop", although if you include the effects of a human operator this description is not accurate.
When you add external control paths, as shown in your second figure, the effects of the added tachometer allow the system to maintain speed without operator intervention, and these are called closed-loop systems.
answered 10 hours ago
WhatRoughBeastWhatRoughBeast
51k2 gold badges29 silver badges78 bronze badges
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
This system:
Actually uses the Motor's back EMF as a feedback signal, it does not use the speed information directly.
From a back EMF viewpoint, this is a closed system (the back EMF is directly controlled).
From a motor speed viewpoint, this is an open system (the speed is not directly controlled).
However, this system:
does use the speed of the motor as a feedback signal so the speed is directly controlled.
There is still the back EMF feedback but that does not control the motor speed directly (assuming "sane" choices for $K_b$ and $K_t$)
answered 11 hours ago
BimpelrekkieBimpelrekkie
59.2k2 gold badges61 silver badges135 bronze badges
$endgroup$
add a comment
|
$begingroup$
This system:
Actually uses the Motor's back EMF as a feedback signal, it does not use the speed information directly.
From a back EMF viewpoint, this is a closed system (the back EMF is directly controlled).
From a motor speed viewpoint, this is an open system (the speed is not directly controlled).
However, this system:
does use the speed of the motor as a feedback signal so the speed is directly controlled.
There is still the back EMF feedback but that does not control the motor speed directly (assuming "sane" choices for $K_b$ and $K_t$)
answered 11 hours ago
BimpelrekkieBimpelrekkie
59.2k2 gold badges61 silver badges135 bronze badges
$endgroup$
add a comment
|
$begingroup$
This system:
Actually uses the Motor's back EMF as a feedback signal, it does not use the speed information directly.
From a back EMF viewpoint, this is a closed system (the back EMF is directly controlled).
From a motor speed viewpoint, this is an open system (the speed is not directly controlled).
However, this system:
does use the speed of the motor as a feedback signal so the speed is directly controlled.
There is still the back EMF feedback but that does not control the motor speed directly (assuming "sane" choices for $K_b$ and $K_t$)
answered 11 hours ago
BimpelrekkieBimpelrekkie
59.2k2 gold badges61 silver badges135 bronze badges
$endgroup$
This system:
Actually uses the Motor's back EMF as a feedback signal, it does not use the speed information directly.
From a back EMF viewpoint, this is a closed system (the back EMF is directly controlled).
From a motor speed viewpoint, this is an open system (the speed is not directly controlled).
However, this system:
does use the speed of the motor as a feedback signal so the speed is directly controlled.
There is still the back EMF feedback but that does not control the motor speed directly (assuming "sane" choices for $K_b$ and $K_t$)
answered 11 hours ago
BimpelrekkieBimpelrekkie
59.2k2 gold badges61 silver badges135 bronze badges
answered 11 hours ago
BimpelrekkieBimpelrekkie
59.2k2 gold badges61 silver badges135 bronze badges
answered 11 hours ago
BimpelrekkieBimpelrekkie
59.2k2 gold badges61 silver badges135 bronze badges
answered 11 hours ago
BimpelrekkieBimpelrekkie
59.2k2 gold badges61 silver badges135 bronze badges
59.2k2 gold badges61 silver badges135 bronze badges
add a comment
|
add a comment
|
$begingroup$
The back EMF is an inherent characteristic that is a factor in determining the motor's torque vs. speed curve. Without feedback, the motor speed is not indeterminate. It varies as load change as determined by the slope of the torque vs. speed curve. The back EMF gives the motor a certain amount of built-in feedback, but the effect is limited. The gain can not be adjusted.
answered 11 hours ago
Charles CowieCharles Cowie
24.2k1 gold badge18 silver badges44 bronze badges
$endgroup$
add a comment
|
$begingroup$
The back EMF is an inherent characteristic that is a factor in determining the motor's torque vs. speed curve. Without feedback, the motor speed is not indeterminate. It varies as load change as determined by the slope of the torque vs. speed curve. The back EMF gives the motor a certain amount of built-in feedback, but the effect is limited. The gain can not be adjusted.
answered 11 hours ago
Charles CowieCharles Cowie
24.2k1 gold badge18 silver badges44 bronze badges
$endgroup$
add a comment
|
$begingroup$
The back EMF is an inherent characteristic that is a factor in determining the motor's torque vs. speed curve. Without feedback, the motor speed is not indeterminate. It varies as load change as determined by the slope of the torque vs. speed curve. The back EMF gives the motor a certain amount of built-in feedback, but the effect is limited. The gain can not be adjusted.
answered 11 hours ago
Charles CowieCharles Cowie
24.2k1 gold badge18 silver badges44 bronze badges
$endgroup$
The back EMF is an inherent characteristic that is a factor in determining the motor's torque vs. speed curve. Without feedback, the motor speed is not indeterminate. It varies as load change as determined by the slope of the torque vs. speed curve. The back EMF gives the motor a certain amount of built-in feedback, but the effect is limited. The gain can not be adjusted.
answered 11 hours ago
Charles CowieCharles Cowie
24.2k1 gold badge18 silver badges44 bronze badges
answered 11 hours ago
Charles CowieCharles Cowie
24.2k1 gold badge18 silver badges44 bronze badges
answered 11 hours ago
Charles CowieCharles Cowie
24.2k1 gold badge18 silver badges44 bronze badges
answered 11 hours ago
Charles CowieCharles Cowie
24.2k1 gold badge18 silver badges44 bronze badges
24.2k1 gold badge18 silver badges44 bronze badges
add a comment
|
add a comment
|
$begingroup$
Your first diagram shows the behavior of the motor alone. The feedback (back EMF) shown does exist, but it does nothing to stablize the motor speed against load changes. For a given voltage in, and a fixed load torque (bearing friction, load friction, air resistance, etc) you can set the motor speed by varying the input voltage. Some systems do this quite handily - electric fans, for instance. However, if you vary ("disturb") the load torque, the motor speed will change. This is not an issue for some applications (electric drills, electric golf carts, etc). For these applications, the operator supplies the feedback when the output speed needs to be constant.
Because there is no built-in stabilizing loop, these systems are called "open loop", although if you include the effects of a human operator this description is not accurate.
When you add external control paths, as shown in your second figure, the effects of the added tachometer allow the system to maintain speed without operator intervention, and these are called closed-loop systems.
answered 10 hours ago
WhatRoughBeastWhatRoughBeast
51k2 gold badges29 silver badges78 bronze badges
$endgroup$
add a comment
|
$begingroup$
Your first diagram shows the behavior of the motor alone. The feedback (back EMF) shown does exist, but it does nothing to stablize the motor speed against load changes. For a given voltage in, and a fixed load torque (bearing friction, load friction, air resistance, etc) you can set the motor speed by varying the input voltage. Some systems do this quite handily - electric fans, for instance. However, if you vary ("disturb") the load torque, the motor speed will change. This is not an issue for some applications (electric drills, electric golf carts, etc). For these applications, the operator supplies the feedback when the output speed needs to be constant.
Because there is no built-in stabilizing loop, these systems are called "open loop", although if you include the effects of a human operator this description is not accurate.
When you add external control paths, as shown in your second figure, the effects of the added tachometer allow the system to maintain speed without operator intervention, and these are called closed-loop systems.
answered 10 hours ago
WhatRoughBeastWhatRoughBeast
51k2 gold badges29 silver badges78 bronze badges
$endgroup$
add a comment
|
$begingroup$
Your first diagram shows the behavior of the motor alone. The feedback (back EMF) shown does exist, but it does nothing to stablize the motor speed against load changes. For a given voltage in, and a fixed load torque (bearing friction, load friction, air resistance, etc) you can set the motor speed by varying the input voltage. Some systems do this quite handily - electric fans, for instance. However, if you vary ("disturb") the load torque, the motor speed will change. This is not an issue for some applications (electric drills, electric golf carts, etc). For these applications, the operator supplies the feedback when the output speed needs to be constant.
Because there is no built-in stabilizing loop, these systems are called "open loop", although if you include the effects of a human operator this description is not accurate.
When you add external control paths, as shown in your second figure, the effects of the added tachometer allow the system to maintain speed without operator intervention, and these are called closed-loop systems.
answered 10 hours ago
WhatRoughBeastWhatRoughBeast
51k2 gold badges29 silver badges78 bronze badges
$endgroup$
Your first diagram shows the behavior of the motor alone. The feedback (back EMF) shown does exist, but it does nothing to stablize the motor speed against load changes. For a given voltage in, and a fixed load torque (bearing friction, load friction, air resistance, etc) you can set the motor speed by varying the input voltage. Some systems do this quite handily - electric fans, for instance. However, if you vary ("disturb") the load torque, the motor speed will change. This is not an issue for some applications (electric drills, electric golf carts, etc). For these applications, the operator supplies the feedback when the output speed needs to be constant.
Because there is no built-in stabilizing loop, these systems are called "open loop", although if you include the effects of a human operator this description is not accurate.
When you add external control paths, as shown in your second figure, the effects of the added tachometer allow the system to maintain speed without operator intervention, and these are called closed-loop systems.
answered 10 hours ago
WhatRoughBeastWhatRoughBeast
51k2 gold badges29 silver badges78 bronze badges
answered 10 hours ago
WhatRoughBeastWhatRoughBeast
51k2 gold badges29 silver badges78 bronze badges
answered 10 hours ago
WhatRoughBeastWhatRoughBeast
51k2 gold badges29 silver badges78 bronze badges
answered 10 hours ago
WhatRoughBeastWhatRoughBeast
51k2 gold badges29 silver badges78 bronze badges
51k2 gold badges29 silver badges78 bronze badges
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add a comment
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abtj is a new contributor. Be nice, and check out our Code of Conduct.
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$begingroup$
There is something off about how the author draws the "back electromotive force" coming off the speed, but I'm pretty sure it's open loop since it doesn't use a direct measurement of what it is controlling in the feedback loop. The second one uses a tach which provides a measured speed, the first one does not.
$endgroup$
– Ron Beyer
11 hours ago