Brushless servo motor offers precise position, speed and torque control without compromising on power-to-weight ratio. It is also more compact and quieter.
Brushless motors eliminate brushes and commutator assembly. They time the power delivery to rotor windings with an electronic controller, making them a smart drive solution. This means greater efficiency, better performance, a longer lifetime, reduced noise and no ionizing sparks.
The Rotor
The rotor (rotating part) of a brushless servo motor consists of wire coils or permanent magnets that create a rotating magnetic field. The interaction of this field with the stationary stator causes the rotor to rotate. This rotation enables the motor to apply mechanical energy to a load or generate power.
There are many different rotor types used in BLDC motors. Some of them have a core made of magnetic steel with slots that are lined with copper wire windings or bars of aluminum. These coils or bars are connected at their ends by shorting rings to form a closed electrical circuit through which current can flow. Another type of rotor, called a squirrel cage rotor, consists of individual copper or aluminum bars brushless servo motor that are spaced apart along the length of the rotor and are electrically connected at their ends with copper or aluminum rings.
A rotor’s design and construction differ depending on the application and desired performance characteristics of a motor. For example, the rotor can be designed to use either trapezoidal or sinusoidal electronic commutation (the choice is usually dictated by economic constraints and motor precision requirements). Hall sensors or encoders are typically used as feedback devices on the rotor. They monitor the position, speed and load information of the motor in real time and provide this information to a controller. The servo control system then calculates and adjusts according to this feedback signal and controls the speed, torque and load of the motor.
The Stator
The stator is the stationary element of a brushless servo motor. It contains a stack of slotted laminations filled with copper wire that is wound in a pattern that compliments the magnet arrangement on the rotor. This winding determines the electrical characteristics of the motor. It also includes an insulation system to protect the copper wires from shorting against each other or the stator laminations when power is applied.
The copper wires within the stator are connected to form three separate phases, each with a distinct voltage waveform induced in it. These voltages are distributed to the rotor by means of sequential switching operations performed by the motor controller. These sequences are called commutation. The commutation process is a key aspect of the motor’s performance index and can be either trapezoidal or sinusoidal depending on the application.
Sensors monitor the position, speed and load of the motor in real time and feed the feedback signal to the motor controller. The controller uses the signal to calculate and adjust the current flow, enabling the motor to accurately perform the required motion tasks. The sensor information also informs the motor’s control loop, which determines what level of speed and torque to apply. The result is a high-performance, highly efficient electric motor with low noise vibration and excellent reliability. It also delivers greater torque with lower weight and power consumption than brushed DC motors.
The Bearings
The rotor is wedged between two bearings, making it the movable part of a brushless servo motor. It’s made of ultra-thin steel laminations that create a permanent magnet. The servo drive applies a field voltage to the rotor armature, increasing its power as it rotates faster. This increases the torque output of a servo motor, which can range from 27.5 Nm (243 lb-in) to higher.
To ensure that the servo motor has enough torque to meet your application needs, the rotor is supported by ball bearings fitted at both ends of the shaft. These bearings must be able to handle both radial and axial loads, as well as the heat generated by the rotor.
These rolling bearings also require a certain amount of lubricating grease to function correctly. Inadequate lubrication causes the bearings to overheat, leading to failure and damage. In addition, a poorly assembled side cover or bearing cover can prevent proper lubrication and lead to overheating.
The encoder, which is mounted to the motor, communicates with the servo drive and provides feedback that allows for highly accurate position, velocity, and speed control. A damaged encoder can cause error signals to be misinterpreted, leading to an unsatisfactory operation. It’s a good idea to replace the encoder every 20,000 to 30,000 hours. In most cases, it can be changed without demagnetizing the rotor, making the process simple.
The Feedback
Servo motors use closed-loop control systems and feedback devices to provide continuous feedback and real-time adjustments. This allows them to adapt to changing conditions quickly, and it contributes to their high performance, precision and reliability.
The feedback device on a brushless servo motor is often either an encoder or a resolver, both of which offer high resolutions that provide thousands (and sometimes brushless servo motor supplier millions) of counts per revolution. This means that they can measure the motor’s position precisely and compare it to a desired position, allowing the system to make adjustments in real-time.
Brushless DC motors use electronic commutation instead of the mechanical contact between brushes and a commutator, allowing them to operate at higher voltages with a much wider speed range. This makes them more powerful, quieter and requires less maintenance compared to traditional DC motors.
Servo motors are used in numerous applications due to their high torque-to-inertia ratio and precise positioning capabilities. They are especially popular in robotics, where their closed-loop feedback system enables continuous adjustment to ensure high performance and accuracy. They are also commonly used in industrial automation, where their ability to adjust to changing conditions and perform at high speeds is essential. Evaluate your application’s needs to determine which type of motor will provide the best fit.