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Views: 0 Author: Site Editor Publish Time: 2025-08-12 Origin: Site
In modern motion control, robotics, aerospace, and automotive systems, precision feedback devices are indispensable. Among them, the resolver stands out as one of the most reliable and durable sensors for detecting angular position, velocity, and direction of rotating machinery. Unlike optical encoders, which may suffer from dust, vibration, or extreme temperatures, resolvers thrive in harsh environments while still providing accurate feedback.
When the resolver’s primary winding is energized with an AC reference signal, the rotor couples this excitation into the secondary windings. Depending on the rotor’s angular position, the induced voltages in the secondary windings vary as sinusoidal functions of the angle.
Cosine Output (Vcos): Represents the cosine of the shaft angle multiplied by the excitation voltage.
Sine Output (Vsin): Represents the sine of the shaft angle multiplied by the excitation voltage.
Mathematically, these can be expressed as:
Vcos = Vref × cos(θ)
Vsin = Vref × sin(θ)
Where Vref is the excitation voltage applied to the primary winding, and θ is the rotor angle.
These two signals form an orthogonal pair, meaning that regardless of the shaft position, the vector sum of their magnitudes remains constant. This property makes resolvers inherently resistant to electrical noise and scaling errors.
The performance of a resolver is directly linked to the characteristics of its output voltages. These voltages are influenced by several design and operating parameters that together determine how accurately the resolver can translate mechanical position into electrical signals. Below are the key factors that define resolver voltage behavior:
Resolvers require an AC reference signal, commonly referred to as the excitation voltage. This signal energizes the primary winding and induces secondary voltages in the sine and cosine windings.
Typical values: 2–15 V RMS at frequencies between 2–20 kHz.
Stability matters: The amplitude and frequency of the excitation directly influence output accuracy. Any fluctuation in the excitation source may lead to scaling errors in the sine and cosine signals.
System design consideration: In high-precision systems, the excitation is often supplied by a dedicated driver circuit designed to minimize distortion and maintain consistency across a wide temperature range.
The transformation ratio (TR) is the ratio of the secondary voltage (output) to the primary voltage (excitation). In most resolvers, TR values fall between 0.2 and 1.
A higher transformation ratio increases the signal amplitude, which can improve resolution and noise immunity.
Conversely, a lower ratio reduces the burden on the signal processing electronics but may require more sensitive amplifiers to achieve the same accuracy.
Designers must balance TR selection based on the requirements of the downstream resolver-to-digital converter (RDC) or control electronics.
Resolvers do not operate in isolation—their performance depends on the load presented by the connected electronics. Typically, this load is the input impedance of an RDC.
Proper impedance matching ensures the resolver delivers maximum signal strength without distortion.
A mismatched load may cause amplitude reduction, waveform distortion, or phase shift, all of which degrade angular accuracy.
High-end RDCs are designed with optimized input stages that minimize loading effects, ensuring consistent resolver output behavior.
Resolvers are manufactured to different accuracy classes, which define their electrical and mechanical tolerances.
Precision-grade resolvers feature low harmonic distortion in the sine and cosine outputs, enabling high angular resolution.
Industrial-grade resolvers may tolerate slightly higher error but are more rugged and cost-effective.
Selecting the right accuracy class depends on the intended application: aerospace and robotics demand high precision, while automotive or heavy machinery may prioritize robustness over absolute accuracy.
One of the key advantages of resolvers over purely digital encoders is their robustness against noise.
The resolver’s sinusoidal voltage outputs vary smoothly with rotor position, making them less susceptible to electromagnetic interference (EMI) and electrical noise from nearby motors or switching circuits.
This makes resolvers ideal for use in harsh industrial environments, aerospace systems, and electric vehicles, where digital encoders might struggle with signal corruption.
Additionally, the analog nature of the signals allows for effective filtering and signal conditioning to further improve reliability.
The sine and cosine voltages produced by a resolver cannot be directly used by most control systems. Instead, they are processed by resolver-to-digital converters (RDCs). These devices:
Excite the resolver’s primary winding with a stable reference signal.
Measure the induced sine and cosine voltages.
Use mathematical algorithms (such as the arctangent function) to compute the exact rotor angle.
Provide digital outputs for position and velocity, which can be used by servo drives, controllers, or monitoring systems.
Modern RDCs can achieve very high resolution, often up to 16–18 bits, ensuring smooth motion control even in demanding applications like robotics or aerospace navigation.
Understanding resolver output and voltage gives insights into why resolvers remain relevant even in the era of digital encoders:
High Reliability in Harsh Environments
Oil, dust, humidity, or extreme heat has little effect on resolver operation.
Aerospace and military systems rely heavily on them due to this durability.
Infinite Resolution
Unlike digital encoders that have discrete steps, resolver outputs are analog signals, theoretically allowing infinite resolution when paired with high-quality electronics.
Cost Efficiency with Recycled Materials
Because resolvers do not require delicate optics or electronics at the sensing head, they are often more economical over long-term usage, especially in heavy-duty applications.
Robust Signal Transmission
Resolver voltages maintain integrity over long cable runs, unlike some digital sensors that suffer from signal degradation.
Because of their rugged construction and dependable voltage-based outputs, resolvers are used in a wide range of industries:
Automotive: Electric power steering (EPS), hybrid/electric drivetrains, and motor position sensing.
Aerospace: Flight control actuators, landing gear systems, and engine control.
Robotics: Servo motors for precise movement and safety-critical tasks.
Industrial Machinery: CNC machines, packaging equipment, and heavy-duty motors.
Renewable Energy: Wind turbine pitch control and solar tracking systems.
In each of these applications, accurate interpretation of resolver voltages ensures smooth and safe operation.
While resolvers offer many advantages, engineers should also account for:
Signal Conditioning Requirements: The sine and cosine outputs require careful amplification and filtering.
Excitation Stability: Fluctuations in excitation voltage or frequency can degrade accuracy.
Integration with Modern Electronics: Although RDCs are widely available, designing them into systems requires expertise in analog and digital signal processing.
Nonetheless, with proper design and calibration, these challenges are easily managed.
As industries move toward electrification, automation, and sustainability, the role of resolvers remains strong. Although optical and magnetic encoders are increasingly common, resolvers still dominate in high-reliability sectors.
Emerging designs integrate resolvers with modern RDCs in compact modules, making them easier to adopt in next-generation electric vehicles, collaborative robots, and aerospace systems. Additionally, innovations in resolver materials and winding techniques are improving signal quality, reducing voltage harmonics, and enhancing overall efficiency.
Resolvers remain one of the most dependable solutions for position and velocity sensing. Their output voltages, derived from sine and cosine functions of the rotor angle, provide continuous, noise-immune, and highly accurate feedback even in the harshest operating conditions. By understanding how resolver voltage is generated, transmitted, and processed, engineers can design systems that maximize performance, reliability, and longevity.
If you are exploring reliable resolver solutions for your applications, NINGBO START MOTOR TECHNOLOGY Limited is a trusted partner with expertise in high-quality motion control components. Their products are engineered for precision and durability, making them a solid choice for industries that demand long-lasting performance. To learn more or explore suitable resolver options, we recommend reaching out to NINGBO START MOTOR TECHNOLOGY Limited for further information and professional support.
