EducationIntroduction to Variable Reluctance Resolvers: How They Work and Why They Matter

Introduction to Variable Reluctance Resolvers: How They Work and Why They Matter

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Variable reluctance resolvers (VRRs) are a type of electromagnetic sensor that can measure the position and speed of rotating machinery with high accuracy and precision. They are widely used in various industrial applications such as robotics, aerospace, automotive, and manufacturing. In this article, we will provide an introduction to VRRs, discuss how they work, and explain why they are important.

What are Variable Reluctance Resolvers

Variable reluctance resolvers are a type of rotary position sensor that uses changes in the magnetic reluctance of a magnetic circuit to measure the angle of a rotating shaft. A VRR consists of a rotor and a stator. The rotor has a ferromagnetic core with teeth, while the stator contains windings and a ferromagnetic core without teeth. When the rotor rotates, it changes the magnetic reluctance between the rotor and stator cores, inducing a voltage in the stator windings that is proportional to the rotor angle.

How do Variable Reluctance Resolvers Work

VRRs work on the principle of magnetic reluctance, which is the resistance of a magnetic circuit to the flow of magnetic flux. When a magnetic circuit is not aligned, or when there is a gap between two ferromagnetic materials, the magnetic reluctance is higher, and the flux density is lower. On the other hand, when the two materials are aligned, the magnetic reluctance is lower, and the flux density is higher. In VRRs, the rotor has teeth that create air gaps with the stator core. As the rotor rotates, the number of teeth that align with the stator increases, reducing the magnetic reluctance and increasing the flux density. This change in flux density induces a voltage in the stator windings that can be used to determine the rotor angle.

Why are Variable Reluctance Resolvers Important

Variable reluctance resolvers are important because they provide a highly accurate and reliable method of measuring the position and speed of rotating machinery. They are resistant to environmental factors such as temperature, humidity, and vibration, making them ideal for use in harsh industrial environments. VRRs also have a fast response time, making them suitable for high-speed applications. In addition, they are relatively simple and inexpensive to manufacture, making them an attractive option for a wide range of applications.

Understanding the Design and Construction of Variable Reluctance Resolvers

The design of VRRs is based on the principle of magnetic reluctance, which is the resistance of a magnetic circuit to the flow of magnetic flux. In VRRs, the magnetic circuit is formed by a rotor and a stator. The rotor has a ferromagnetic core with teeth, while the stator contains windings and a ferromagnetic core without teeth. When the rotor rotates, it changes the magnetic reluctance between the rotor and stator cores, inducing a voltage in the stator windings that is proportional to the rotor angle.

Construction of Variable Reluctance Resolvers

The construction of VRRs involves several key components and features that make them work. These include:

1. Rotor – The rotor is the rotating part of the VRR that has a ferromagnetic core with teeth. The teeth create air gaps with the stator core, which change the magnetic reluctance as the rotor rotates.
2. Stator – The stator is the stationary part of the VRR that contains windings and a ferromagnetic core without teeth. The windings are wound around the stator core and are connected to an external circuit that can measure the induced voltage.
3. Bearings – The bearings support the rotor and allow it to rotate smoothly. They are typically made of materials that can withstand high temperatures, vibrations, and other environmental factors.
4. Signal Conditioning Circuitry – The signal conditioning circuitry processes the voltage signal induced in the stator windings and converts it into a format that can be used to determine the position and speed of the rotor.
5. Housing – The housing encloses the VRR and protects it from environmental factors such as dust, moisture, and temperature changes. It also provides a mounting surface for the VRR.

Comparison of Variable Reluctance Resolvers with Other Sensor Technologies

Variable reluctance resolvers (VRRs) are a type of electromagnetic sensor that are commonly used in various industrial applications to measure the position and speed of rotating machinery. However, there are other sensor technologies available that can also perform similar tasks. In this article, we will compare VRRs with other sensor technologies, discussing their similarities, differences, and relative advantages and disadvantages.

Types of Sensor Technologies

Before we begin our comparison, it is important to understand the various types of sensor technologies that are commonly used in industrial applications. These include:

1. Magnetic encoders – These are sensors that use a magnetized rotor and a stator with magnetic sensors to detect the position of the rotor.
2. Optical encoders – These are sensors that use light and a patterned disc to detect the position of the disc.
3. Resolvers – These are sensors that use two windings to detect the position of a rotor by measuring the voltage difference between the windings.
4. Hall effect sensors – These are sensors that use a magnetic field to detect changes in position or speed.

Comparison of Variable Reluctance Resolvers with Other Sensor Technologies

Now, let’s compare VRRs with other sensor technologies:

1. Magnetic Encoders – Like VRRs, magnetic encoders use a rotating magnet to detect position and speed. However, they typically have higher resolution and accuracy than VRRs, making them more suitable for precise applications.
2. Optical Encoders – Optical encoders offer higher accuracy and resolution than VRRs, but they are more sensitive to environmental factors such as dust and moisture.
3. Resolvers – Resolvers are similar to VRRs in that they both use a rotor and a stator to detect position and speed. However, resolvers are typically more expensive and complex than VRRs, making them less suitable for some applications.
4. Hall Effect Sensors – Hall effect sensors are less accurate than VRRs or other types of encoders, but they are typically more affordable and easier to use. They are also less sensitive to environmental factors, making them suitable for harsh industrial environments.

When it comes to measuring the position and speed of rotating machinery, two common sensor technologies that are often compared are incremental encoders and resolvers. Incremental encoders use a rotating disc with evenly spaced slots or marks and a stationary sensor to detect changes in position or speed. They offer high resolution and accuracy, but they do not provide absolute position feedback. On the other hand, resolvers use a rotating rotor and stator with two windings to detect position and speed. They offer absolute position feedback and are resistant to electromagnetic interference, making them suitable for harsh industrial environments. However, they are typically more expensive and complex than incremental encoders. Ultimately, the choice between incremental encoders and resolvers will depend on the specific requirements of the application, including resolution, accuracy, and environmental factors.

Now that we have compared VRRs with other sensor technologies, let’s discuss their advantages and disadvantages:

• VRRs are resistant to environmental factors such as temperature, humidity, and vibration, making them ideal for use in harsh industrial environments.
• They have a fast response time, making them suitable for high-speed applications.
• They are relatively simple and inexpensive to manufacture, making them an attractive option for a wide range of applications.

• VRRs have lower resolution and accuracy compared to some other sensor technologies, making them less suitable for precise applications.
• They are sensitive to electromagnetic interference, which can affect their performance.
Electronics and Telecommunications engineer with Electro-energetics Master degree graduation. Lightning designer experienced engineer. Currently working in IT industry.