Whether you’re looking for a permanent magnet motor review or you are simply interested in finding out more about this type of motor, you’re in the right place. In this article, you’ll learn about the types of motors available, how to choose a motor for your needs, and how to maintain your motor.
Servomotors
Servomotors and permanent magnet motors are a type of electrical motor used in industrial applications such as blowers and pumps. While they offer advantages over induction motors, they can have disadvantages. Fortunately, the benefits of a servomotor can sometimes outweigh the drawbacks. Understanding the difference between these types of motors can help you choose the right system for your application.
A servomotor is a small-diameter, high-torque, closed-loop electrical motor with no brushes or fan. It is typically designed for direct drive applications. Its torque density is higher than that of an induction motor. It can also have a higher ingress protection rating.
A permanent magnet synchronous motor (PM synchronous motor) is an electric motor with no contact loss between the brush and slip ring. It also has no excitation loss on the rotor. It has a sinusoidally distributed stator winding. This allows it to produce sinusoidal back EMF waveforms. It can be rated to constant torque to 2,000:1 with an encoder.
An AC servomotor is used in applications requiring rapid response. Its small diameter and high torque density make it ideal for fast start-up and stop cycles. Its high resistance ensures that it will provide accurate control. It can be used in a variety of applications, including glass manufacture.
A line start induction motor can help solve applications that have no speed feedback. However, induction motor systems are better for applications that need high power and constant velocity. Alternatively, PMDC motors can be used in these applications. They also use dynamic braking, reducing the mechanical brake size.
A d-q model is one of the most common types of motors. The d-axis inductance is measured when the flux passes between the magnetic poles. When the rotor is rotating, the difference in inductance at the motor’s terminals is known as saliency. It is an important dynamic figure of merit.
The SMB series of brushless servomotors are designed to provide rugged performance. They incorporate high-energy permanent magnet technology to reduce energy consumption and increase torque. They also feature Salient Pole technology.
The Kollmorgen Goldline series of servomotors has a wide selection of sizes and voltages. It also offers co-engineered modifications. Its application specialists can help develop custom mechanical designs. They can also help you minimize costs associated with shorter lead times.
Hybrid stepper motors
Compared to servomotors and variable reluctance motors, hybrid stepper motors offer advantages in terms of torque and position control. They are used in a variety of applications, including industrial automation, medical automation, and aerospace. These motors have a compact design, high-torque output at low speeds, and are able to perform precise motions in small volume.
The basic design of a hybrid stepper motor involves two rotor halves with a permanent magnet sandwiched between them. The magnet attracts the teeth on the rotor and induces axial polarity. The magnet material must be strong enough to deliver the required torque.
The magnetic field strength is proportional to the amount of turns in the windings. The number of poles in the rotor is also a factor. The more poles, the weaker the magnetic force. The number of phases in a hybrid stepper is an important aspect of the design. The higher the number of phases, the smaller the step angle.
In addition to the number of phases, the number of stator poles can be an important component of a hybrid stepper’s performance. A 0.9deg step motor has eight poles, while a 1.8deg step motor has two poles.
A hybrid stepper’s rotor consists of 80 laminations of silicon steel. Each lamination is insulated with thin insulation to reduce energy loss. This type of construction enhances the reliability of the system. Traditionally, laminations were bonded with adhesives. However, innovative manufacturing processes now die-punch laminations to make interlocking them easy.
The magnet materials used in a hybrid stepper have special properties. Neodymium-iron-boron (NiB) magnets are highly magnetic and have good strength over a wide temperature range. They are also available in different shapes and sizes.
Another feature of a hybrid stepper is that it is a 3-D device. The rotor’s teeth are precision ground, typically. This provides high torque without requiring the use of velocity feedback devices.
These types of hybrid stepper motors are a popular choice in factory automation and office automation, where they can deliver accurate position control. They are also well suited for robotics applications, where they can offer high-torque, direct motions.
Variable reluctance type of stepper motors
Unlike other motors, variable reluctance stepper motors are very simple to operate. They have a very small rotor mass and respond quickly. This makes them ideal for applications where torque and speed are important.
Variable reluctance type of stepper motors are used in a number of applications, including advanced clocks, printing machines, and industrial machinery. They are also designed for use in open-loop control systems.
They are generally composed of a stationary part (stator) and a moving part (rotor). The stator consists of a core of magnetic material and poles which are energized to create a magnetic field. The rotor has a single permanent magnet or variable reluctance iron core. The rotor is magnetized along the axis of the stator to form a strong magnetic field.
In a three-phase machine, the stator windings are connected in a delta or star configuration. When a switching circuit is applied to the windings, they are excited to create a magnetic field that aligns the rotor to the magnetic field. In addition, a number of poles are formed on the rotor, which attract the magnetic field.
A number of pulses are applied to the stator to rotate the rotor. The direction of the rotation is determined by the sequence of the pulses. The resulting magnetic field rotates at synchronous speed. This is the main reason why stepper motors are ideal for cost-sensitive applications.
In addition to being simple to operate, variable reluctance type of steppermotors have a high torque to inertia ratio. This allows them to perform very low-speed synchronous rotation. However, they are not able to achieve a very high speed because of mechanical resonance of the motor load combination.
The motors are typically capable of producing a few grams of torque when running. When the step rate is ramped up, the torque increases until it reaches maximum torque for starting and stopping. Once the step rate has decreased, the torque decreases as well. It is therefore recommended that a gearbox is included to increase the torque.
During the operation, the rotor rotates in quarter-tooth steps. This provides a very small area between the rotor and stator gears, which results in a very small loss of magnetic force.
Magnetic saliency
Besides the torque, another very important factor for flux weakening control in PMSM servo systems is the magnetic saliency of the permanent magnet motor. The saliency ratio is a measure of the variation in the inductance of the rotor terminal as it is influenced by the poles. The saliency ratio is also measured in relation to the armature reaction fluxes.
The d-axis inductance increases with the increase in the width of the magnet. Similarly, the q-axis inductance decreases with the increase in the thickness of the magnet.
The magnetic saliency of the FSCW PMSM is investigated through theoretical and simulation studies. Two 10 poles and 12 slots PMSM models are constructed and the d- and q-axes inductances are calculated. The results show that the FSCW IPMSM has a relatively low saliency ratio.
This saliency ratio can be increased by reducing the quadrature inductance value. The FEA also calculates the influence of air-gap length on the saliency ratio. The maximum saliency ratio is obtained when the air-gap length is about 0.3 mm. The results match well with the TC and FEA results when the thickness is about 4 mm.
The FEA results also indicate that the inductance difference between the Lq and Ld is lower when the FSCW IPMSM is rated at a low load angle. It would have been better if the generator was a ferrite generator instead of an amorphous generator.
The d-axis inductance tends to increase more when the concentration windings are applied. It is difficult to calculate the inductance of a d-axis in a ferrite machine. Moreover, the d-axis permeance is also reduced with saturation. The q-axis inductance is almost the same level as the d-axis inductance.
The d- and q-axes armature reaction fluxes are illustrated in Fig. 4. It is observed that the maximum saliency ratio is achieved at 90 electrical degrees from the main flux axis. The d- and q-axes are obstructed by the flux barriers, but they do not disturb the direct flux. The saliency ratio is therefore higher at the d-axis than at the q-axis.
The motor is fitted with a stator that includes angularly spaced teeth inward toward the rotor. The electrically conductive coils are wound around some of the teeth.