Resolver/Transformer, also known as a synchronous resolver, is an electromagnetic sensor whose operating principle and function hold significant importance in industrial automation and servo control systems.
I. Working Principle of the Resolver
The resolver operates based on the principle of electromagnetic induction: a changing magnetic flux induces an electromotive force in a conductor. Its core function involves transferring electrical energy and converting angular position information through the interaction between a rotating magnetic field and both stationary and rotating windings.
1. Basic Structure
A rotary transformer primarily consists of two parts: the stator and the rotor:
- Stator: The stator winding serves as the primary side of the transformer, receiving excitation voltage. Excitation frequencies typically use standard values such as 400Hz, 3000Hz, and 5000Hz. The stator winding is fixed to the stationary part, generating a rotating magnetic field through alternating current.
- Rotor: The rotor winding serves as the secondary side of the transformer, receiving induced voltage through electromagnetic coupling. Composed of wire coils, the rotor winding traverses varying magnetic flux within the rotating magnetic field as its angular position changes. This induces varying magnitudes of electromotive force within the wires.
Additionally, rotary transformers incorporate auxiliary components such as support systems and induction systems to ensure stable operation and precise measurement.
2. Operating Process
The operating process of a rotary transformer can be summarized in the following steps:
- Excitation Process: Connecting the power source to the stator windings generates an alternating current, creating a rotating magnetic field. This rotating magnetic field forms the foundation for the rotary transformer's operation.
- Induction Process: As the rotor rotates, the conductors within the rotor windings traverse varying magnetic flux within the rotating magnetic field. According to the law of electromagnetic induction, these changing magnetic flux lines induce an electromotive force (EMF) in the rotor windings.
- Magnetic Coupling and Power Transfer: Due to magnetic coupling between the stator and rotor windings, the induced electromotive force in the rotor windings is coupled to the stator windings. Through different wiring configurations, objectives such as power transfer and current transformation can be achieved.
3. Output Characteristics
The output voltage of a rotary transformer maintains a specific functional relationship with the rotor's angular position. This relationship typically takes the form of a sine, cosine, or linear function. The exact form depends on the rotary transformer's design parameters and wiring configuration. For instance, in certain high-precision detection systems, the output voltage may follow a sinusoidal or cosine function relative to the rotor angle; whereas in some linear measurement systems, a linear relationship may be maintained.
II. Functions of Rotary Transformers
Rotary transformers find extensive applications in industrial automation and servo control systems, with their primary functions summarized as follows:
1. Angular Position Measurement
The most fundamental function of a rotary transformer is to measure the angular displacement of a rotating shaft. By detecting the magnitude and direction of the induced electromotive force in the rotor windings, the rotor's rotational angle can be calculated. This measurement method offers high precision, reliability, and non-contact operation, making it particularly suitable for applications requiring precise angular position control.
2. Angular Velocity Measurement
Beyond position measurement, rotary transformers can measure the angular velocity of rotating objects. By continuously monitoring the rate of change in the induced electromotive force within the rotor windings, the angular velocity can be calculated. This measurement method is crucial for implementing speed feedback and closed-loop control in motion control systems.
3. Coordinate Conversion and Function Calculation
Rotary transformers can also function as computational elements for coordinate conversion and function calculation. In certain complex control systems, angular position information must be converted into other coordinate formats or undergo specific function operations. The unique output characteristics of rotary transformers facilitate the implementation of these functions.
4. Applications in Servo Systems
Within servo control systems, rotary transformers play a vital role as both angle signal generators and detectors. They convert the rotational angle of a motor into an electrical signal for transmission to the control system while simultaneously receiving command signals from the control system to adjust the motor's rotational angle. This closed-loop control method significantly enhances the precision and stability of servo systems.
5. High-Precision Detection Systems
Rotary transformers are an ideal choice for systems requiring high-precision detection. Their high accuracy, reliability, and non-contact operation make them widely used in aerospace, precision machinery, and other fields. For instance, in aircraft autopilot systems, rotary transformers enable precise measurement of the aircraft's attitude and heading; in precision machine tools, they achieve high-accuracy position control and machining precision.
III. Types and Characteristics of Rotary Transformers
Rotary transformers can be categorized into various types based on their structure and operating principles, each possessing unique characteristics and application scenarios.
1. Two-Pole and Four-Pole Rotary Transformers
- Two-Pole Rotary Transformer: Features one pair of magnetic poles on both the stator and rotor. This relatively simple structure offers limited precision, suitable for general-accuracy measurement and control systems.
- Four-Pole Rotary Transformer: Features two pairs of magnetic poles on both the stator and rotor. This structure provides higher precision and stability, making it ideal for high-accuracy detection systems and servo control systems.
2. Variable Reluctance Resolver
The Variable Reluctance Resolver (VRR) is a specialized type of resolver that operates based on the reluctance effect rather than traditional electromagnetic induction. A VRR typically consists of a stator winding and one or more rotors equipped with salient poles or slots made of reluctive materials (such as ferromagnetic materials).
Working Principle
When an alternating current is applied to the stationary winding, it generates an alternating magnetic field around it. As the rotor rotates, the magnetic reluctance material on the rotor periodically alters the magnetic reluctance of the magnetic path. This change in reluctance causes variations in magnetic flux, inducing an electromotive force (EMF) in the stationary winding or an additional detection winding that is proportional to the rotor's position. By measuring this induced electromotive force, the angular position of the rotor can be calculated.
Features
- High Accuracy: Due to their unique structure and operating principle, magnetic resistance rotary transformers typically offer high angular measurement precision, making them suitable for control systems requiring high-accuracy position feedback.
- High Reliability: With no sliding contact components, magnetic resistance rotary transformers exhibit high reliability, minimizing failures caused by wear or poor contact.
- Strong Environmental Adaptability: Resistive rotary transformers operate across a wide temperature range and exhibit robust resistance to electromagnetic interference, making them suitable for diverse harsh environments.
- Rich Output Signals: Beyond fundamental angular position data, resistive rotary transformers can provide signals related to speed, acceleration, and other parameters, delivering multi-dimensional feedback to control systems.
IV. Application Examples of Rotary Transformers
1. Servo Motor Control
In servo motor control systems, rotary transformers function as position sensors, continuously monitoring the rotor's position and feeding this information back to the controller. The controller adjusts the motor's control strategy based on this position feedback signal to achieve precise position control, speed control, and torque control. The high precision and stability of rotary transformers are crucial for enhancing the overall performance of servo systems.
2. Robot Joint Control
Rotary transformers are extensively used in industrial robots and precision robotic arms for joint position detection and control. By installing rotary transformers at joints, real-time rotational angle data is captured, enabling precise control over the robot's motion trajectory. This control method significantly improves robotic working accuracy and minimizes cumulative error.
3. Aerospace Applications
In aerospace applications, rotary transformers are extensively employed in aircraft attitude control and navigation systems due to their high precision and reliability. For instance, within aircraft autopilot systems, rotary transformers measure critical parameters such as pitch, roll, and yaw angles, providing accurate positional feedback to flight control systems. They also play vital roles in spacecraft attitude adjustment and stabilization control.
4. Precision Measuring Instruments
In precision measuring instruments such as optical devices, measuring microscopes, and laser processing equipment, rotary transformers are frequently employed as angular measurement components. Their high precision and stability ensure accurate measurement results, enhancing the instruments' measurement accuracy and reliability.
V. Summary
As a vital electromagnetic sensor, the rotary transformer finds extensive applications across industrial automation, servo control, aerospace, and precision measurement fields. Their operating principle is based on electromagnetic induction and the magnetoresistance effect, converting and transmitting angular information by measuring the relative position between the rotor and stator. Rotary transformers offer advantages including high precision, reliability, non-contact operation, and strong environmental adaptability, providing dependable solutions for systems requiring precise position control. With ongoing technological advancements, rotary transformers will play increasingly vital roles across more fields, driving the continuous advancement of industrial automation and intelligent processes.