1. Servo Systems Servo is mechanism based on feedback control.
The controlled quantity is mechanical.
Jussi Suomela
HUT/Automation

2. Closed Loop Control Controller is the “Brain” Drive is the “Muscle”
Your Partner In Productivity
Controller is the “Brain”
Drive is the “Muscle”
Feedback Transducer is the “Eyes”
Motion
Command
Input
Mechanical
Motion
Output
Drive or
Amplifier
Controller
Feedback
Transducer

3. Servo systems are “Closed Loop” in design
Your Partner In Productivity
control
feedback
Uses feedback for automatic correction
High performance
control
Width of material must be very precisely controlled

4. Example - Closed Loop Control System
Speed Feedback
Movement
Load
Reducer
Encoder
Table
Motor Power
Ballscrew
AC/DC
Servo
Amp
IMC S
Class
Position Loop
Velocity Loop
0 to ±10V DC

5. Servo Control of an Electrical Motor
Three feedback lops
servocontroller
Jussi Suomela
HUT/Automation

6. Properties of Servo Systems
high maximum torque/force allows high (de)acceleration
high zero speed torque/force
high bandwidth provides accurate and fast control
robustness
Servo Systems are not servos
Jussi Suomela
HUT/Automation

7. How to design good Servo Systems?
Terminology:
Do not confuse “servos” with “servo motors”
DC motors (brushed or brushless) are also sometimes also referred to as “servo motors”
See:
“So when does a motor become a servo motor?
There are certain design criteria that are desired when building a servo motor, which enable the motor to more adequately handle the demands placed on a closed loop system.
First of all, servo systems need to rapidly respond to changes in speed and position, which require high acceleration and deceleration rates.
This calls for extremely high intermittent torque.

8. Intermittent Torque in Servos
Torque is related to current in the brushed servo motor.
So the designers need to keep in mind the ability of the motor to handle short bursts of very high current, which can be many times greater than the continuous current requirements.
Another key characteristic of the brushed servo motor is a high ratio of torque to inertia.
This ratio is an important factor in determining motor responsiveness.
Further, servo motors need to respond to small changes in the control signal.
So the design requires reaction to small voltage variations.

9. Hobby radio-controlled servos

10. Small Servos (servo-motors) for small robots
Positioning applications:

11. Three-wire interface of standard servos

12. PWM control of Servos

13. Pulse length controls the angle of the shaft rotation
Pulse between 0.6 ms and 2.0 ms

14. Speed Control PWM is not the same as the Servo PWM
Single pulse width
counterclockwise
center
clockwise

15. What to remember when you write software to control?
Writing software, take into account mechanical constraints

16. “Winch servo” and how to convert from standard servo

17. Pneumatic & Hydraulic Actuators
Large manipulators in industry frequently employ hydraulic drives,
since such drives provide a higher torque-to-weight ratio than electric motors
However, because of the maintenance problems associated with pressurized oil (including leaks), hydraulic motors are not used in smaller mobile robots
Pneumatic drives have been used as actuators in the past but are not currently popular
Air is compressible, resulting in nonlinear behavior of the actuator

18. Sources
Braunl
Jussi Suomela
Jussi Suomela
HUT/Automation