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Permanent Magnet For Servo Motor
Date:2023-08-02
For the best performance from your servo motor, you need a permanent magnet that generates the most magnetic flux. That way, it can interact with the rotor’s field to produce torque. In PM motors, the interaction is known as “magnetic saliency” and it varies with different positions of the rotor relative to the stator field.
Unlike wound field DC motors, permanent magnet motors do not require an excitation current to create magnetic flux in the stator winding. This eliminates the need for field coils and reduces the size of the motor. This makes PM motors less expensive and more efficient than other DC designs. However, they must be operated with precise control system equipment to function properly. In addition, a permanent magnet motor can lose its magnetism if the temperature rises above its Curie temperature – at which point the magnets lose their magnetic attraction and become demagnetized.
A PM motor generates a back-emf voltage that can be used to create torque by directing the current through the motor. This can be done by boosting or opposing the magnetic field. Boosting the field will increase torque production, while opposing it will limit the field’s strength and reduce the back-emf voltage, freeing up that voltage to push the motor at higher speeds.
In a permanent magnet servo motor, the drive controls the motor current to match the speed of the rotor. It uses feedback for commutation, velocity and position information to calculate the correct currents to direct to the proper motor phases for optimum shaft rotation.
The drive also detects the rotor position by injecting high-frequency ac signals to the motor terminals. These signals are detected by the drive as changes in the impedance of the interior permanent magnet motor (IPM) terminals. The drive then determines the IPM motor’s offset angle, which is the distance between the high-frequency signal injection axis and the rotor’s magnetic pole axis.
IPM motor terminal impedance varies according to the injection angle, with its maximum at 90 electrical deg from the rotor’s main flux axis (d-axis). This difference in Impedance is known as magnetic saliency and is used to detect rotor position.
A common issue with permanent magnet motors is that they need to use rare-earth magnets like neodymium and samarium, which are environmentally taxing to mine and exhibit volatile prices in the market. This can increase the upfront cost of a PMACM, as well as the complexity and operating cost of its control systems. To address this, PM drives employ closed-loop feedback to track rotor position via sensors and adjust the input current to ensure continuous shaft rotation. The result is a high-performance servo motor that can offer superior performance, reliability and efficiency. This is especially true when coupled with a KEB spring-set brake.
Unlike wound field DC motors, permanent magnet motors do not require an excitation current to create magnetic flux in the stator winding. This eliminates the need for field coils and reduces the size of the motor. This makes PM motors less expensive and more efficient than other DC designs. However, they must be operated with precise control system equipment to function properly. In addition, a permanent magnet motor can lose its magnetism if the temperature rises above its Curie temperature – at which point the magnets lose their magnetic attraction and become demagnetized.
A PM motor generates a back-emf voltage that can be used to create torque by directing the current through the motor. This can be done by boosting or opposing the magnetic field. Boosting the field will increase torque production, while opposing it will limit the field’s strength and reduce the back-emf voltage, freeing up that voltage to push the motor at higher speeds.
In a permanent magnet servo motor, the drive controls the motor current to match the speed of the rotor. It uses feedback for commutation, velocity and position information to calculate the correct currents to direct to the proper motor phases for optimum shaft rotation.
The drive also detects the rotor position by injecting high-frequency ac signals to the motor terminals. These signals are detected by the drive as changes in the impedance of the interior permanent magnet motor (IPM) terminals. The drive then determines the IPM motor’s offset angle, which is the distance between the high-frequency signal injection axis and the rotor’s magnetic pole axis.
IPM motor terminal impedance varies according to the injection angle, with its maximum at 90 electrical deg from the rotor’s main flux axis (d-axis). This difference in Impedance is known as magnetic saliency and is used to detect rotor position.
A common issue with permanent magnet motors is that they need to use rare-earth magnets like neodymium and samarium, which are environmentally taxing to mine and exhibit volatile prices in the market. This can increase the upfront cost of a PMACM, as well as the complexity and operating cost of its control systems. To address this, PM drives employ closed-loop feedback to track rotor position via sensors and adjust the input current to ensure continuous shaft rotation. The result is a high-performance servo motor that can offer superior performance, reliability and efficiency. This is especially true when coupled with a KEB spring-set brake.
