Motion control systems_lec - This is Serrvo Control Methods

© 2024 Nguyễn Duy Ánh, ndanhcdt@hcmut.edu.vn
Motion control systems
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Servo Control Methods

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Servo system

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Servo system
❖ Definition of a Servo System:
➢ A servo system is a closed-loop control system that uses feedback to regulate the
motion and position of a motor.
❖ Key Components:
➢ Controller: Processes the feedback signal and determines the appropriate
response.
➢ Motor: Executes the control actions to adjust position, speed, or torque.
➢ Sensor: Provides feedback to the controller about the system's performance, such
as position or speed.

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Servo system

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AC servo
Motor Driver
Servo system

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DC Motor Driver
Servo system

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DC Servo Driver
Servo system

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BLDC Motor Driver
Servo system

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Servo system

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Stepper Motor Driver
Servo system

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Stepper Motor Driver
Servo system

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Incremental Encoder
Pseudo-absolute method
Servo system

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Absolute Encoder
Analog signals
Digital signals
Servo system

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Encoders can be optical, magnetic
Servo system

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Types of Servo Control Systems

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Types of Servo Control Systems

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How to measure the feedback value?
• Open loop
– no feedback system
• Current control
– no special feedback
• Speed control
– feedback devices for DC motors: Encoder, DCTacho,
Hall-sensor
• Position control
– feedback devices: Encoder, Hall-Sensor

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Analog encoder speed control loop
• Speed control loop with encoder feedback
- Amplification (gain) depends on parameters PID
- Applies also to Hall Sensor feedback with EC motors (6 IMP)
• Current control loop
- Subordinate control loop, enhances system dynamics
- Power amplifier (MOSFET)
power
amplifier
motor
encoder
current
speed
feedback
current
command
set value
speed
 
current-
feedback
speed
amplifier (PID)
+
-
+
-
R
E
C

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Digital control loop
• Digital parameters (profile, position, amplification)
• DSP: digital signal processor
• Firmware: software of the controller
power
amplifier
motor
encoder
position feedback
current
command
set value
speed
current feedback
position
decoder
DSP
set value
position
speed feedback
path
generator

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Applications of Servo Systems

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Choice of Servo Control Method
Selecting the appropriate control method for a servo motor depends on various factors:
❖ Application Requirements: The specific task determines whether position, speed, or torque control is
needed.
For example, precision tasks like CNC machining require position control, while consistent speed applications
like conveyor systems benefit from speed control.
❖ Load Characteristics:
Understanding the load’s nature, including its inertia and variability, helps determine the best control method.
High-inertia loads may require torque control to manage force effectively.
❖ Environmental Conditions:
The operating environment, such as temperature, humidity, and exposure to dust or chemicals, can influence
the choice of control method. Harsh conditions may necessitate more robust control systems.
❖ System Dynamics:
The dynamic behavior of the system, including response time and stability, impacts the control method choice.
Fast-response systems may benefit from speed control, while stable systems with varying loads might require
torque control.
❖ Cost and Complexity:
Consideration of budget and system complexity is crucial. Position control systems may be more expensive
and complex due to the need for precise feedback devices like encoders.

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Position, Speed, and
Torque Control Methods

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Torque, Speed, and Position Control
Torque, speed, and position control are vital aspects of motor
control that directly impact the motor’s performance and
efficiency. Precise control over these parameters enables
optimized operation, improved energy efficiency, and enhanced
system responsiveness.

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Servo Motor Torque Control
How to measure torque
of a servo motor?
1. Torque is directly
proportional to the current
and can be derived from it
by knowing shaft speed and
motor efficiency => Indirect
measurement of torque
2. For a precise and accurate
shaft output torque
measurement, a reaction
torque sensor is used =>
Direct measurement of
torque

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Torque Control by Analog Voltage
Torque Control Diagram

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Field Oriented Control (FOC)

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Quadrature or
Torque current
Direct or Flux current

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Quadrature current Iq
Direct current Id

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Direct Torque Control (DTC)

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Servo Motor Speed Control
Speed Control by Analog Voltage
Speed Control Diagram

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Scalar control of motor
Scalar control (frequency control) is a
control technique of a brushless
AC motor, which is to keep the
voltage/frequency ratio (V/Hz) constant
throughout the full operating speed
range, with control only the magnitude
and frequency of the supply voltage. Voltage variation of the motor power during scalar
control
Scalar control without speed sensor
Scalar control with speed sensor

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Vector control of motor
Vector control is a control method of brushless AC electric motors, which allows
independently and practically inertialess adjusting the rotation speed and torque on
the motor shaft.
General functional diagram of vector control
Among vector control, the most widely used are field oriented control and direct
torque control.

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Characteristics of the main control methods of AC motors
Note:
1.Open loop
2.Closed loop
3.In steady state

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Servo Motor Position Control
Position Control Using a Pulse Signal
Position Control Diagram

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Servo Motor Position Control

Motion control systems_lec - This is Serrvo Control Methods

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