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Mechatronics Brushless Motors. Mechatronics A servosystem is capable of transforming any mathematical function into a mechanical movement  it can replace.

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Presentation on theme: "Mechatronics Brushless Motors. Mechatronics A servosystem is capable of transforming any mathematical function into a mechanical movement  it can replace."— Presentation transcript:

1 Mechatronics Brushless Motors

2 Mechatronics A servosystem is capable of transforming any mathematical function into a mechanical movement  it can replace mechanical elements, such as cams and cam shafts, indexing gears, differentials, etc. A servosystem consists of a servomotor with its control unit. Servosystems can be used for: Positioning; the position, linear or angular, follows a predetermined position function. Speed control; the motor speed follows a predetermined speed function. Torque control; the torque of the motor follows a predetermined acceleration function. Hybrid control; the system alternates between different kinds of control

3 Mechatronics The servomotor, which is a permanently magnetized brushless AC motor, is a relatively new type of motor. 24 slots 2 rotor poles

4 Mechatronics

5 Electro-Magnetic Flux Distribution 21 slots 8 rotor poles

6 Mechatronics Brushless Solution Pros&Cons: Velocity (no sparks at the commutator) Efficiency (Torque/Inertia) Weight Dimensions Thermical Dissipation Acoustic Noise Maintenance MTBF Disadvantages: Cost

7 Mechatronics 1. BL-Servo with MP Cold Only the stator is warm. Warm 2. DC-Servo with MP Rotor and commutator are warm 3. AC-Servo (ASM squirrel cage) Heiß Both rotor and stator are warm Warm Thermical Behaviour

8 Mechatronics Two brushless motors types exist (they differ in stator windings, permanent magnets lay-down, statoric field wave shape): AC brushless: with sinusoidal field (fcem) DC brushless: with trapezoidal field (fcem)

9 Mechatronics Permanent Magnets (PM) types: Ferrite Ferrite: low cost, low Kt, torque loss: 0.2%/K, demagnetization temperature: 150C Samarium Cobalt (Sm 2 Co 17 ) Samarium Cobalt (Sm 2 Co 17 ): high cost, high Kt, torque loss: 0.04%/K, demagnetization temperature: >150C (example: Danaher HD series, Rockwell MPG series) Neodimium Iron Boron (NdFeB) Neodimium Iron Boron (NdFeB): medium cost, higher Kt, torque loss: 0.09%/K, demagnetization temperature: >150C (example: Danaher HR series, Rockwell H, Y, 1326, MPL series)

10 Mechatronics M agnetism NdFeB (vs. SmCo) higher energy content worse thermical reversibility lower Curie temperature lower cost corrosion (not present with SmCo) bigger resistance in , that in turn limits eddy currents 400 300 200 E [kJ/m 3 ] 1860 1880 1900 1920 1940 1960 1980 2000 100 0 Year Steel Al Ni Co Sm Co Nd Fe B Ferrite

11 Mechatronics 8,3Sm 2 Co 17 density [g/cm^3] 7,4 Curie Temp. [°C] Br temp. coeff. [% 1/°C] Nd Fe B 825 315 -0,03 (20°C ÷ 200°C) -0,1 (20°C ÷ 150°C) SmCo vs. NdFeB Temperature that causes para-magnetic behaviour (i.e. weak magnetisation) Campo coercitivo JHc [kA/m] 500 1000 1500 2000 2500 50 100 150 200 250 300 350 400 Max Energetic Product (B*H)max [kJ/m^3] SECo 5 qualità speciali SECo 5 Sm 2 Co 17 NdFeB (Field that can demagnetize the magnet)

12 Mechatronics The permanent magnets lay-out on the rotor surface depends on: AC or DC brushless, Kt, Cogging Torque (coppia di impuntamento).

13 Mechatronics



16 Servo System Electrical Scheme

17 Mechatronics

18 PTC Resistor Positive Thermal Coefficient resistor, used as a sensor inside the motor, in order to stop the driver/controller in case of too-high temperature (before to burn the motor)

19 Mechatronics Servo Motor Shapes and Air Cooling

20 Mechatronics

21 Direct Drive Solution Problem: Motor shaft elastical torsion (i.e. its flexibility): resonance frequency limited band-width low gains in the control loop poor kinematic performances

22 Mechatronics Direct Drive Solution (cont’d) Possible Solutions: Digital FiltersDigital Filters (only for constant resonance frequencies) High Stiffness MotorsHigh Stiffness Motors (a high inertia would not solve the problem) Torque MotorsTorque Motors (Motori Coppia) with: – low velocity – high stiffness – they don’t need gearboxes (i.e. they are direct-drive)

23 Mechatronics Once solved the resonance frequency problem, the control loop gains can be increased and thus a good accuracy in the position sensor becomes mandatory: Resolver Resolver: 6 arc min = 0.1 degrees SinCos Encoder SinCos Encoder: 0.01 arc sec = 2.8E-6 degrees or 1nm for linear encoders (righe ottiche) Direct Drive Solution (cont’d)

24 Mechatronics Position Sensors used in the Brushless Motors

25 Mechatronics Resolver  Characteristics:  linearity: 0. 1 - 0.5%  resolution: 0. 1 - 0.5°  sensitivity: 5 - 10mV/° (Vref =20V)  frequency: 20KHz

26 Mechatronics Resolver (cont’d)

27 Mechatronics Resolver (cont’d)  Pro  absolute in one turn  low cost  robust  Cons  sinusoidal 20KHz reference voltage  non-linear output  brushes in some (old) versions  It has been the standard position sensor on brushless motors

28 Mechatronics Encoder

29 Encoder (cont’d)

30 Mechatronics Encoder (cont’d)

31 Mechatronics Encoder (cont’d)  Encoder types:  Absolute  Battery Back Up  One-Turn Absolute  Multi-Turn  Incremental  SinCos (resolver output, encoder design, precise as an encoder) e.g.: Stegmann mounted on Rockwell MPL motors

32 Mechatronics Degree of Protection IPXY (e.g.: IP65) Digit 1 (X): Solid Objects Protection 0Non Protected 1Protected against solid objects > than 50 mm 2Protected against solid objects > than 12 mm 3Protected against solid objects > than 2.5 mm 4Protected against solid objects > than 1 mm 5Dust Protected 6Dust Tight Digit 2 (Y): Water Protection 0Non Protected 1Protected against dripping water 2 Protected against dripping water when tilted to worse case opening 3Protected against spraying water 4Protected against splashing water 5Protected against water jets 6Protected against heavy seas 7Protected against the effects of immersion 8Protected against submersion

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