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1、 i CONTENTS 1 About Servo System.2 1. What is “Servo System”.2 2. Positioning Mechanisms.3 3. Three Types of Control System.5 4. Configuration of the Servo System and Its Operation.7 2. About Servo Motor.11 1. Difference with Other Conventional Motor.11 2. Types and Features of Servo Motors.12 3. Co
2、nstruction of AC servo motor.13 3. About detector.19 1. Detector Classification According to Their Detection Method .19 2. Typical Detector .20 3. Features of Each Detector and Its Application. .22 4. About Servo Driver.23 1. Typical Servo Driver.23 5 About position Control.25 1 Two types of Positio
3、ning Systems.25 2. Speed Control and Torque Control.26 3. Response Frequency of Position Controllers.27 BASIC SERVO FUNDAMENTALS www.suc- 1 Servo Section 1 1 About Servo System.2 1. What is “Servo System”.2 2. Positioning Mechanisms.3 3. Three Types of Control System.5 4. Configuration of the Servo
4、System and Its Operation.7 www.suc- Servo Section 1 2 1 About Servo System 1. What is “Servo System” “Servo” derives from the Greek “Servus (servant).” The system is called “Servo System” as it responds faithfully to a command. It is a system to control mechanical instruments in compliance with vari
5、ation of position or speed target value (designated value, command value). www.suc- Servo Section 1 3 2. Positioning Mechanisms The servo system is not the only alternative to control positioning and feed speed of mechanical facilities. Beside simple mechanical devices, however, the servo system is
6、now the major control system to positioning and feed speed. Simple positioning Simple. Low cost. Available high speed operation. Flexible positioning by servo motor Precise. High speed. Easy to change target position and feed speed. No maintenance. High speed response Direct driving system Simple me
7、chanism. No backlash. No trouble bout gear life. Stopper Cylinder Clutch synchronous servo motor and induction type servo motor. Classification of servo motor Features of each servo motor Stepping motor DC servo motor Synchronous servo motor Induction type servo motor Capacity (watt) Less than 100 W
8、 Less than 500 W 100 to 2 kW 2 kW or up Advantages Compact and high output. Cheap. Smaller outside dimensions and large torque. Good operation efficiency. Good controllability. Cheap. High speed and high torque. Good operation efficiency. No maintenance required. High speed and high torque. No need
9、maintenance Durable. Large peak torque. Disadvantages Out-of-step and magnet noise at low speed operation Limit at rectification. Low reliability. Requires maintenance. Expensive. Bad operation efficiency with medium capacity models. Complicated control circuit. Expensive Servo motor DC servo motor
10、AC servo motor Stepping motor Synchronous servo (brushless DC servo) motor Induction type servo motor This is a AC servo motor www.suc- Servo Section 2 13 3. Construction of AC servo motor Features of AC servo motor compared with DC servo motor Permanent magnet is built-in the rotor.Rotating field t
11、ype Coils are provided on the statorStatic armature. In other word, electrical functions of rotor an stator are reversed. AC servo motor does not have the commutator and brushes which DC servo motor has. www.suc- Servo Section 2 14 Operation principle of AC servo motor Hall element Rotation angle ()
12、 240 0 120 360 480 H1 H2 H3 Rotation angle () 240 0 120 360 480 I1 I2 I3 Coiling magnetic current P1 P2 P1 P3 Switching order and stator field rotation Stator field www.suc- Servo Section 2 15 (1).Features of Servo motor Characteristics of servo motor N V Motor speed: N varies in proportion to impre
13、ssed voltage: V T I Motor torque: T varies in proportion to supplied current : I P N T output V I input Motor output power is nearly proportionate to product multiplied speed by torque, and product multiplied impressed voltage by current. Acceleration and deceleration time: t is in proportion to ine
14、rtia moment: J of the whole mechanism and arriving speed: N, and in inverse proportion to torque: T. Th I rms Operation limit of the motor is determined by temperature rise. Rising temperature is in proportion to square of effective value of current Motor rotation direction is determined by polarity
15、 of impressed voltage I N T T N J T deg Impressed voltage: V www.suc- Servo Section 2 16 (2) Comparison Between AC & DC Servo Ac servo DC servo Life 20, 000 h or up. Normally, 3,000 to 5,000 h Varies considerably due to load and environmental conditions. Maintenance No mechanical contact. (No brushe
16、s, commutators) Required periodical check and replacement of brushes. Sound noise Due to brush contacting noise. Electrical noise No noise as no brushes. Noise occurs due to actuation of brushes. Efficiency Excellent? Good cooling efficiency as heat radiates from stator. Rectification loss occurs. B
17、ad cooling efficiency due to rotor heat Against Overload Large thermal time constant. High speed and large torque. Small thermal time constant. Limited current due to brush flashover Response Characteristics Large power rate. (Small rotor inertia and large torque until high speed range.) Small power
18、 rate. (Large rotor inertia. Decrease torque at high speed range.) Cleanness Clean as no brush powder occurs Brush powder occurs. AC servomotor is more suitable for high speed, high response, and high acceleration/ deceleration control than DC servomotor. It also does not require maintenance. www.su
19、c- Servo Section 2 17 (3) Torque number of rotation characteristics AC servo motor Number of rotation Rated number of rotation Instantaneous max. number of rotation Continuous operation zone Rated torque Torque Instantaneous max. torque Short time operation zone www.suc- 18 Servo Section 3 3. About
20、detector.19 1. Detector Classification According to Their Detection Method .19 2. Typical Detector .20 3. Features of Each Detector and Its Application. .22 4. About Servo Driver.23 1. Typical Servo Driver.23 www.suc- Servo Section 3 19 3. About detector 1. Detector Classification According to Their
21、 Detection Method Detectors installed on servo motors are classified into three categories according to their detection method. Now, detectors are intended to carry out signal treatment of encoders and resolvers outputs, and function as both speed an position detectors. Classification of detectors D
22、etection method Linear type Rotary type Detector Speed Position Use seed generated power Induction type speed detector. DC tacho generator. Permanent magnet type Other excited type AC tacho-generated Brushless DC tacho- generator Permanent magnet type Drag cup type Use pulse or phase equivalent to p
23、osition and angle Photo type Magnetic type Electro-magnetic induction type Contact type Linear encoder Rotary encoder Magnet scale Rotary magnet scale Linear inductsyn Rotary inductsyn Sunchro Resolver Brush type Brushless type Contact type linear encoder Contact type rotary encoder www.suc- Servo S
24、ection 3 20 2. Typical Detector Rotary encoder, and resolver are examples of present day detectors for AC servo (1) Rotary Encoder Increment rotary encoder Basic principle of rotary encoder Incremental rotary encoder The above figure shows detection system. A beam of light is directed at the rotatio
25、n disc, which is installed on the fixed disc and the rotation disc installed on the input shaft. As the slits on both discs pass in rotation, this beam shuts off and on. This pulse is converted into electric signal by the photo diode. Both A and B slits on the fixed disc have phase difference of 90.
26、 Thus, smoothed waveform output has two short waves having 90 phase difference. Counting this pulse output makes it possible to detect rotation angle. The outputs of both A and B enable detection of rotation direction when they pass through the direction judgement circuit, and are used to add or ded
27、uct measuring value. In addition, some rotary encoders have a slit per rotation to get zero position standard signal. Incremental type rotary encoder has simple construction and is cheap so that only a few output lines are required. On the contrary, it may accumulate differences generated by electri
28、cal noise at signal transportation. When power is OFF, the display disappears and does not store its data so that a separate counter is required. www.suc- Servo Section 3 21 (2) Resolver The resolver is a rotation angle detection sensor to detect mechanical rotation angle as rotor electro-magnetic i
29、nduction voltage. Two stator coils are arranged to have a 90 angle to each other around the rotor coil. While AC voltage is charged with a rated frequency to the rotor coil, the rotor coil generates induction voltage waveform output relative to angle variation with the rotor. Features of the resolve
30、r compared with the photo type rotary encoder are as follows: 1) Durable against environmental conditions like vibration, shock, and electrical noise as simple construction, no semiconductors are used. 2) Durable against power fluctuation and ambient temperature variation as no semiconductors are us
31、ed. 3) Number of division per rotation can be selected by preparing an external circuit. 4) Complicated convert circuit from excitation voltage to digital, and increase peripheral circuit. KE sin(t + ) E sin t K cos t E sin t KE sin(t + ) Construction of synchronous resolver www.suc- Servo Section 3
32、 22 3. Features of Each Detector and Its Application. Each detector has constructional, functional features and need required conditions to use it in compliance with those features. Item Photo type encoder Magnetic type encoder Resolver Features Simple processing circuit. Durable against electrical
33、noise as it is digital signal. Easy to get high resolution. Weak against vibration and shock. Not suitable for high temperature operation. Simple processing circuit. Durable against electrical noise as it is digital signal. Relatively strong against vibration and shock. Not suitable for high tempera
34、ture operation. Rugged Strong against vibration and shock. Available high temperature operation. Adjustable resolution change by processing circuit. Complex processing circuit. Speed Detection By F/V converter Usable as digital data By F/V converter. Usable as digital data Uses phase variation by ph
35、ase change at a rated interval as speed data. Position Detection Use incremental pulse. Easy to apply zero position pulse. Use incremental pulse. Easy to apply zero position pulse. Two pole resolver has the same function as absolute encoder. Incremental data is available by processing circuit Magnet
36、 pole sensor Available by adding slit for magnetic pole sensor on rotation disc. Available by adding track for magnetic pole sensor on magnetic drum. Available by using same pole of motor or two pole resolver www.suc- Servo Section 4 23 4. About Servo Driver 1. Typical Servo Driver Let us become fam
37、iliarized with the circuit and operation of PWM transistor driver which is one of major drivers for servo motors. Transistor PWM An example of main circuit Operation M Comparator M Command Standard triangle Tr3 Tr4 Transistor servo main circuit www.suc- 24 Servo Section 5 5 About position Control.25 1 Two types of Positioning Systems.