Difference between revisions of "Motor types"
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| + | Position, velocity and torque/force control applications mainly rely on two main categories of motors: servo motors and stepping motors. | ||
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Servo motor is a electromechanical mechanical actuator with feedback allowing precision closed loop motion control and monitoring. | Servo motor is a electromechanical mechanical actuator with feedback allowing precision closed loop motion control and monitoring. | ||
| + | |||
| + | Stepping motor is a low cost alternative to servo motors and can be operated without feedback device. | ||
==Construction== | ==Construction== | ||
Servo motor consists two main parts: | Servo motor consists two main parts: | ||
*Motor part - typically electromagnetic device that produces torque or force when driven with current | *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 | *Feedback device - typically electronic device that outputs measurement information such as shaft angle or velocity | ||
| + | Stepping motors can be used without any feedback device. | ||
==Shapes== | ==Shapes== | ||
| − | + | Motors and feedback devices come mainly in two shapes: | |
*Rotary | *Rotary | ||
*Linear | *Linear | ||
| − | Shape of motor doesn't change their electromechanical | + | Shape of motor doesn't change their electromechanical principle so both types of motors can be driven with same drives. |
==Motor technologies== | ==Motor technologies== | ||
List of electromagnetic motor part types. | List of electromagnetic motor part types. | ||
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===Brush DC=== | ===Brush DC=== | ||
Brush DC (direct current) motors typically have permanent magnet stator and rotor with mechanical commutator with brushes. | Brush DC (direct current) motors typically have permanent magnet stator and rotor with mechanical commutator with brushes. | ||
| − | === | + | ===Stepping motor=== |
| + | Stepper motors are high pole count permanent magnet brushless motors with 2 or 3 phase windings. High pole count enables position control without feedback devices but with several drawbacks such as risk of lost position. | ||
| + | |||
| + | ==Feedback device types== | ||
| + | ===Encoder=== | ||
| + | [[Quadrature]] encoders are nowadays the most common feedback device type in servo motors. Quadrature encoders are incremental sensors so they require position zeroing/homing to get absolute position feedback. | ||
| + | |||
| + | Another type of encoder is ''absolute encoder''. Absolute encoders typically output serial data of absolute position thus they may not need to be zeroed. The drawback of absolute sensors is higher price and lower compatibility & interchangeability. | ||
| + | ===Resolver/synchro=== | ||
| + | Resolver is an analog technology based on rotary transformer that can provide absolute position (single turn absolute, for multiturn absolute position zeroing is still needed). Resolvers are good for harsh conditions but don't provide as high precision as encoders. | ||
| + | ===Tachometer=== | ||
| + | Tachometer is a small DC generator that outputs DC voltage proportional to rotation speed. It can be used as velocity feedback device but not as position sensor. Tachometers are often seen in dual-loop configurations with position sensor. | ||
| + | ===Hall sensors=== | ||
| + | Hall sensors are found in AC & BLDC motors only. Halls provide commutation information (drive current phase angle) for drive. Modern drives such as all GD drives don't require Hall sensors but can utilize them to make faster power-up possible. Hall sensors are too low resolution for position or high performance velocity control. | ||
| + | ==Comparison== | ||
Comparison of motor technologies | Comparison of motor technologies | ||
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| Rated torque vs size || High || Low || Medium || Medium | | Rated torque vs size || High || Low || Medium || Medium | ||
|- | |- | ||
| − | | Dynamic performance || Low, | + | | Dynamic performance || Low, medium || Medium||High||Highest |
|- | |- | ||
| − | | Motion smoothness || | + | | Motion smoothness || Low to high||Medium||Medium||High |
|- | |- | ||
| Endurance || High || Medium || High || High | | Endurance || High || Medium || High || High | ||
| + | |- | ||
| + | | Energy efficiency || Low, medium || Medium || High || High | ||
|} | |} | ||
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[[Category:Hardware]] | [[Category:Hardware]] | ||
Revision as of 10:38, 18 April 2012
Position, velocity and torque/force control applications mainly rely on two main categories of motors: servo motors and stepping motors.
Servo motor is a electromechanical mechanical actuator with feedback allowing precision closed loop motion control and monitoring.
Stepping motor is a low cost alternative to servo motors and can be operated without feedback device.
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
Stepping motors can be used without any feedback device.
Shapes
Motors and feedback devices come mainly in two shapes:
- Rotary
- Linear
Shape of motor doesn't change their electromechanical principle 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.
Stepping motor
Stepper motors are high pole count permanent magnet brushless motors with 2 or 3 phase windings. High pole count enables position control without feedback devices but with several drawbacks such as risk of lost position.
Feedback device types
Encoder
Quadrature encoders are nowadays the most common feedback device type in servo motors. Quadrature encoders are incremental sensors so they require position zeroing/homing to get absolute position feedback.
Another type of encoder is absolute encoder. Absolute encoders typically output serial data of absolute position thus they may not need to be zeroed. The drawback of absolute sensors is higher price and lower compatibility & interchangeability.
Resolver/synchro
Resolver is an analog technology based on rotary transformer that can provide absolute position (single turn absolute, for multiturn absolute position zeroing is still needed). Resolvers are good for harsh conditions but don't provide as high precision as encoders.
Tachometer
Tachometer is a small DC generator that outputs DC voltage proportional to rotation speed. It can be used as velocity feedback device but not as position sensor. Tachometers are often seen in dual-loop configurations with position sensor.
Hall sensors
Hall sensors are found in AC & BLDC motors only. Halls provide commutation information (drive current phase angle) for drive. Modern drives such as all GD drives don't require Hall sensors but can utilize them to make faster power-up possible. Hall sensors are too low resolution for position or high performance velocity control.
Comparison
Comparison of motor technologies
| 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 | Low to high | Medium | Medium | High |
| Endurance | High | Medium | High | High |
| Energy efficiency | Low, medium | Medium | High | High |
