How Do PMT High-Precision Angle Encoders Ensure Measurement Accuracy in Portable CMMs?
Have you ever wondered how CNC machines achieve precise cutting, how industrial robots move with the flexibility of a human hand, or how precision metrology equipment such as portable CMMs delivers accurate measurements? Behind this precise and coordinated performance is the angle encoder. Installed at critical points within the equipment, this compact component plays a decisive role in positioning accuracy. That is why high-precision, highly stable angle encoders are indispensable sensors for automated industrial processing and inspection.
This article answers common questions about angle encoders. Whether you are evaluating an angle encoder or exploring how portable CMMs are applied in real-world environments, we hope this guide provides useful reference.
What Is an Angle Encoder?
An angle encoder, also known as a rotary encoder for angular position measurement, is a precision sensing device that converts the angular displacement or angular position of a rotating shaft into electrical signals or digital position data that a system can read. It is typically installed near the rotating shaft and turns with it, following these steps to obtain the final position information:
- Physical Sensing: During rotation, components inside the encoder, such as the grating disc and index grating, generate periodic changes in physical signals;
- Signal Conversion: The receiver (or sensing element) converts these physical signals into electrical signals;
- Signal Processing: The processor calculates the electrical signals to determine the corresponding shaft angle;
- System Application: The controller, such as a PLC, CNC system, or servo drive, combines the angle data with other structural parameters of the equipment. In a portable CMM, the system uses the angle feedback from each joint encoder together with the machine’s kinematic model and calibration parameters to calculate the three-dimensional coordinates of the probe tip.
What Types of Angle Encoders Are Available, and Where Are They Used?
Based on their output signal type, angle encoders can be divided into incremental and absolute encoders. Each type has its own characteristics and application focus.
Incremental encoders have mature manufacturing processes, high resolution, and fast response, offering strong overall performance and stability. They are widely used in servo motors for CNC machines, conveyor systems on automated production lines, portable CMMs, and other industrial production and inspection equipment.
Absolute encoders are more commonly used in CNC rotary tables, industrial robots, elevators, and other equipment. By assigning a unique code to each position, they allow the system to immediately determine the precise mechanical position whenever powered on, avoiding the need to return to the zero position after position information is lost.
How to Read the Performance Parameters of an Angle Encoder
When selecting an angle encoder, it is essential to understand its performance parameters. Electrical parameters are generally among the most important factors to evaluate:
First is accuracy. This parameter determines how accurately the encoder reports position data and directly affects whether the equipment can meet its final machining and inspection requirements. For equipment with demanding positioning requirements, such as portable CMMs, accuracy is typically the first consideration during selection.
Repeatability is also critical. Simply put, it indicates whether repeated measurements of the same position produce consistent results. This value directly reflects the stability of the encoder.
Resolution refers to the smallest angular change that the encoder can detect. A smaller value means finer angular sensing. However, higher resolution is not necessarily better: if accuracy cannot keep pace, highly resolved data may still be unreliable. The two parameters need to be evaluated together.
Finally, consider signal output frequency and communication interface. The angle encoder connects to the controller through its interface, so the encoder must be compatible with the controller to ensure normal operation of the complete equipment.
Beyond electrical parameters, mechanical specifications and actual production-site conditions should also be considered when evaluating overall encoder performance.
What Challenges Arise in Angle Encoder R&D?
The biggest challenge in angle encoder development is finding the right balance among high accuracy, high stability, and cost control. Higher accuracy places stricter demands on assembly concentricity and interference resistance, increasing manufacturing complexity and cost. In multi-joint serial equipment such as portable CMMs, even a small error in a single encoder can be progressively amplified as it propagates through multiple axes, placing greater demands on overall system stability.
This is why encoder development cannot focus solely on laboratory data. R&D must not only overcome the encoder’s own accuracy and manufacturing challenges, but also account for complex industrial-site conditions and the budget constraints of equipment procurement.
What Is the Current Market Trend for Angle Encoders?
As automation continues to expand across industries, the angle encoder market is expected to grow at an estimated rate of about 7.1% from 2024 to 2035. Optical encoders, with their excellent resolution, accuracy, and stability, serve a wide range of applications. Their share is rising particularly in precision-intensive segments such as robotics and aerospace, where demand for high accuracy is especially strong.
Against this backdrop of rapid market growth, PMT has established a distinctive competitive advantage through its self-developed core technologies.
What Are the Advantages of PMT Angle Encoders?
From its early days, PMT recognized the market trend and committed to an independently controlled technology development path. The company developed its own angle encoders, overcoming a series of technical challenges and ultimately launching the incremental RA-1 angle encoder, which entered in-house production and sales in 2018. The encoder incorporates advanced optical technologies, manufacturing processes, and algorithms:
- Algorithm: The RA-1 uses a proprietary high-order interpolation technology. Without compromising output resolution, it achieves absolute positioning accuracy of 1 arcsecond. This high accuracy helps control accumulated errors more effectively when multiple axes are connected in series.
- Assembly: A combination of mechanical and electrical alignment processes is used. The high concentricity between the main shaft and grating disc helps eliminate eccentricity-related errors at the assembly stage.
- Output Performance: PMT angle encoders support incremental output up to 500 kHz. Pulse integrity is maintained even at high interpolation levels, providing fast signal response and low closed-loop latency. Within the specified response-frequency range, the encoder maintains stable counting without pulse loss, making it suitable for precision low-speed rotary closed-loop control. Compared with encoders in the same domestic category, it offers a higher frequency limit and stronger acquisition compatibility.
- Signal Compatibility: The encoder supports multiple output signals, including TTL, RS-422, BISS-C, SSI, and CAN. Custom protocols can also be developed for special requirements, reducing compatibility concerns when connecting to different equipment.
- Structural Design: The encoder adopts a split design that can be customized according to the customer’s actual installation space and dimensional requirements, rather than being limited to one or two fixed specifications.
Together, these capabilities give PMT’s incremental angle encoder strong overall performance, maintaining high industry-level standards in resolution, accuracy, and stability.
How Is the PMT Angle Encoder Applied in Equipment?
Every joint of the PMT portable CMM is equipped with a self-developed RA-1 angle encoder. By providing real-time feedback on the rotation angle of each joint, the encoder enables accurate calculation and control of the probe’s spatial coordinates and serves as a critical component in maintaining equipment accuracy.
In real-world use, operators often rely on portable CMMs for continuous, high-frequency point collection directly on the shop floor. Such demanding environments place high requirements on angle encoders: measurements at individual points must be sufficiently accurate, while accuracy must remain stable during prolonged, repeated rotation across multiple angles without drift.
Thanks to its high-order interpolation algorithm and high-concentricity assembly process, PMT’s angle encoder keeps the angular error of each joint within a very small range, supporting high-precision portable CMM measurement results. Maximum single-point measurement accuracy can reach 0.012 mm, while maximum length measurement accuracy can reach 0.022 mm. At the same time, multiple signal output interfaces allow the encoder to work smoothly with the complete machine control system, reducing additional losses during signal transmission.
With the precise and stable performance of its angle encoders, PMT portable CMMs combine highly stable core-component design with standardized calibration and maintenance to support long-term measurement stability. If factory service is required, the calibration cycle for PMT portable CMMs is as short as three working days.
What Are the Advantages of PMT Portable CMMs?
In addition to the self-developed RA-1 angle encoder, PMT portable CMMs offer a range of other strengths:
- The complete system is designed, assembled, and accuracy-calibrated according to applicable standards for precision metrology equipment. The products comply with applicable ISO requirements and have completed CE conformity assessment.
- Structurally, PMT uses a globally pioneering external decoupling and internal balancing design. This provides stronger structural support, smoother arm movement, and greater comfort during extended handheld operation.
- The arm uses aerospace-grade carbon fiber, offering strong thermal resistance while better controlling torsional and bending deformation.
- The system supports multiple contact and non-contact probe options. For complex surfaces or difficult-to-reach areas, the two approaches can be combined to provide comprehensive coverage across measurement scenarios.
- Data transmission uses a dedicated 5 GHz Wi-Fi module and a dedicated USB interface, enabling stable and smooth on-site data transfer.
- The operating temperature range is 5°C to 45°C, with normal operation at 0–95% humidity. The system also has an IP54 dust- and water-resistance rating, making it well suited to workshop environments.
With its independently developed high-precision angle encoder and comprehensive equipment-level advantages, PMT portable CMMs deliver high accuracy, high stability, and strong adaptability, supporting reliable measurement performance in precision manufacturing and quality control.
