Motor types
Servo motor is a electromechanical mechanical actuator with feedback allowing precision closed loop motion control and monitoring.
Contents
Construction
Servo motor consists two main parts:
- Motor part - typically electromagnetic device that produces torque or force when driven with current
- Feedback device - typically electronic device that outputs measurement information such as shaft angle or velocity
Shapes
Servo motors and feedback devices come mainly in two shapes:
- Rotary
- Linear
Shape of motor doesn't change their electromechanical princible so both types of motors can be driven with same drives.
Motor technologies
List of electromagnetic motor part types.
AC
Typical AC (alternating current) servo motor is a 3 phase permanent magnet syncronous machine. This type of motors are driven by 3 wires each driving one phase coil. In ideal case 3 phase AC servo is driven by sinusoidal current waveforms that are synchronized to the permanent magnet rotor.
BLDC
BLDC (brushless DC) is very similar to AC motor with only expection that it is desgined to be driven by trapezoidal current waveforms instead of sinusoidal. BLDC motors can always be driven with same drives regardless of current waveform matching.
Brush DC
Brush DC (direct current) motors typically have permanent magnet stator and rotor with mechanical commutator with brushes.
Comparison
| Stepping motor | DC servo | BLDC servo | AC servo | |
|---|---|---|---|---|
| Closed loop | No | Yes | Yes | Yes |
| Torque control | No, inpractical | Yes | Yes | Yes |
| Velocity control | Yes | Yes | Yes | Yes |
| Position control | Yes | Yes | Yes | Yes |
| Available speed range | Low, Medium | Medium | High | Highest |
| Rated torque vs size | High | Low | Medium | Medium |
| Dynamic performance | Low, Medium | Medium | High | Highest |
| Motion smoothness | Very low to high | Medium | Medium | High to very high |
| Endurance | High | Medium | High | High |
Feedback device types
Quadrature encoder
Resolver/synchro
Tachometer
Hall sensors
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