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Summary of PID control for Mechanical Engineering Experiment II Course, Department of Mechanical Engineering, Khon Kaen University, Thailand.
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PID CONTROLMechanical Engineering Experiment II
Department of Mechanical EngineeringFaculty of EngineeringKhon Kaen University
Khon Kaen, THAILAND
NUMPON MAHAYOTSANUN
IDEAL SYSTEM Ideal SystemSetpoint Desired Output
Desired output not equal to setpoint
Desired output too slow
Desired output oscillates
Not quite ideal because...
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CLOSED LOOP CONTROL
SystemSetpoint Desired OutputController
Desired output is measured and processed by a controller
The controller compares the desired output to the setpoint level to determine a new control input for the system
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PID CONTROL
Proportional term Proportional gain (tuning parameter) Error (setpoint – output) time or instantaneous time Integral term Integral gain (tuning parameter) Dummy integration variable Derivative term Derivative gain (tuning parameter)
Proportional Term (P)
- Directly make changes to the current error- Multiply the error by a constant Kp- High proportional gain yields large change in output- Too high proportional gain yields unstable system- Too small proportional gain yields less re-sponsive controller
Integral Term (I)
- Sum the error over time- Give the accumulated offset that should have been corrected previously- Multiply the accumilated error by a constant Ki- Accelerate the controller output towards setpoint- Eliminate the residual steady-state error pro-duced by the proportional term
Derivative Term (D)
- Calculate the slope of the error over time- Multiply the rate of change of the error by a constant Kd- Reduce the magnitude of the overshoot produced by the integral term- Is sensitive to noise in the error term
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PID CONTROL
Why using PID control?
Proportional term shows “PRESENT”Integral term shows “PAST”
Derivative term shows “FUTURE”
So
“PRESENT” + “PAST” + “FUTURE”
P Characteristics
Larger value yields faster response
Too large value yields instability and oscialla-tions
I Characteristics
Larger value eliminates steady-state erros quickly
Too large value yields overshooting
D Characteristics
Larger value reduces overshoot but gives slow reponse and is sensitive to noise
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FEEDBACK RESPONSE
Parameters
Overshoot- Maximum error between input and output- Percent overshoot = (Maximum overshoot / Desired value) x 100%
Time delay (Td)- Initial time response until 50% of the output
Rise time (Tr)- Time response between 10% to 90% of the output
Settle time (Ts)- Initial time until the oscillation is within 5%
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PID CONTROL LABORATORYObjectives
1. To understand how a closed loop system works2. To understand how a PID controller works3. To understand the behaviors of each term (P, I, and D)4. To understand the relationship among the terms (P + I, P + D, I + D, P + I + D)
Tasks
Week 1You are required to design a closed loop system (PID) to control the po-sition of the given servo motor.
Week 2You are required to carry out an experiment of your closed loop sys-tem design. The laboratory report must be written and submitted to [email protected] before week 3.
Week 3You are required to take the laboratory oral exam and your laboratory report will be commented.
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LABORATORY EQUIPMENTS
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LABORATORY EQUIPMENTS
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LABORATORY EQUIPMENTS
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LABORATORY EQUIPMENTS
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LABORATORY EQUIPMENTS
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LABORATORY EQUIPMENTS
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LABORATORY EQUIPMENTS
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REFERENCES
1. PID Controller. Wikipedia.
2. CONTROL SYSTEMS, ROBOTICS, AND AUTOMATION - Vol. II - PID Control - Araki M.
3. http://www.mstarlabs.com/docs/tn031.html
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