Brushless servo drives are automatic instruments that monitor the performance of any mechanism based on the continuous feedback that it receives. Basically, it is a closed loop mechanism that sends rectification signals if the performance of the machine / instrument is deviating from the commanded data. Now, the instrument that really monitors the performance is called the servo drive. It is just an electronic amplifier that gets linked to a servo mechanism to monitor its performance. Servo drives can be brushed or brushless. While brushed motors provide exchange via physical contacts, brushless motors provide electronic exchange without physical contact, with the help of sinusoidal or the trapezoidal drives. These trapezoidal drives can energize two motor windings simultaneously before proceeding to the next pair of windings. Sinusoidal servo drives, on the other hand, can provide do this to three motor windings simultaneously with the sinusoidal signals.
Brushless motors work quite like AC motors where the rotor movement is caused by a dynamic magnet field. Brushless motors are known to have predicable linear characteristics. Brushless servo drives are AC or DC types. It is basically the way the motor is powered gives it the name AC or DC.
Read more about ac servo drives.
Torque developed by brushless servo drives depends on the control technology used. Type of control is determined by the feedback scheme exercised. DC motors use Hall sensors for feedback, whereas AC motors use resolver or encoder for feedback. Speed accuracy is very high in fact with the more popular brushless drive, almost close to 0%. This is due to the presence of a digital encoder and the drive controller regulation of position. High torque to inertia ratios provides high acceleration and deceleration rates with dynamic response. Controller bandwidth is almost 8 times higher than the Brush DC drive. The Brushless DC motors have good thermal characteristics too. Motor efficiencies range anywhere around 90-96 % and controller efficiency around 97% giving overall efficiencies far superior than brush DC systems.
The benefits of brushless servo drives are:
- Very precise average speed control over a very wide speed range
- High dynamic response ensuring precise instantaneous speed control
- Constant power factor meaning lowest possible input current
- Smaller in size than the brush type
- No regular motor maintenance is needed
- Feedback device (encoder) is fitted internally and thereby less subject to errors
- Higher overall efficiency
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