ROBO!!!!! <3 Flashcards
R
Input/Reference signal
U
Manipulated variable
Causes the plant to behave a certain way
Y
System output
G
Plant/System
USED FOR…..
When is Open Loop Control Used?
- C and G have known transfer functions - System if fully identified
- C and G are linear and time invariant
C
Controller
Generates the actuation signal that drives the process
Reasons to not use Open Loop
- To make the output of the system more consistent
- Voltage can vary over time…drop when load is too much/messes with system
- Improve Open loop by using a higher voltage source with less internal resistance. Also thicker wires for less resistance. i.e. over sizing controller and plant
Closed-loop Control
Used to provide more precise control of outputs
Feeds back a signal that is proportional to the output
Reduces the effect of variation (non-linearity) in plant characteristics on the output system
Correcting signal
- Output from the combination of the input and feedback value
- Bigger difference in expected and actual output leads to a greater value in correction
Summing Junction/Comparator
Circle with plus and minus
Combines R and Y
E
Error i.e. difference between expected and actual output
Model-reference control
The accuracy of the predicted output determines the changes needed to adjust the feedback signal
Benefits of Closed-loop Systems
- More precise control - decreasing sensitivity to variation and disturbances in the system
- Input tracking allows for a faster dynamic response
- Drives the PLANT harder so gets the most out of it’s functionality?
Cross-over distortion
Don’t know what it is. But it can be rectified by using a feedback loop with…high forward path gain
Presents it’self in both the frequency and time domain
Saturation Distortion
When a voltage is input, the output rises linearly and after a certain point the output falls of and settles to a certain level
Can be rectified by using a feedback loop with high forward path gain
Outputs in freq domain at harmonics start to present themselves
Transient Response
Concerned with how changing the load on a circuit effects the voltage being given in the system
Adding load –> decrease in voltage before it levels off again
Removing load –> increase in voltage before it levels off again
High gain
May cause the performance of the system to be unstable
Might present itself in oscillations in the output
Assumptions for Laplace Analysis
Assume the systems under inspection are linear
Analysing properties of transfer function
If you replace s by j.omega, you can see how the frequency determines the functionality of the plant (through it’s transfer function)
Open-loop control
Transfer functions are (approximately) liner and time invariant despite changes in operating conditions.
So the gains don’t change much due to disturbances (temperature, power-supply voltage, loading etc.)
In these conditions the input (R) and output (Y) have an approximately constant and repeatable relationship
