In the field of industrial automation and precision control, servo motors, as the core executing components, directly determine the accuracy and dynamic response capability of the system based on their performance. ButIncremental encoderAs the "perception organ" of the servo system, real-time feedback of rotor position and velocity information has become a key technical support for achieving closed-loop control.

1、 The working principle and core advantages of incremental encoders

Incremental encoders convert mechanical rotation angles into electrical pulse signals by detecting periodic changes in grating disks or magnetic stripes. Its core output includes three sets of signals:

A/B phase pulse: Two orthogonal pulses with a phase difference of 90 °, used to calculate displacement and rotation direction (distinguishing clockwise/counterclockwise by judging the rising/falling edge order);

Z-phase zero position signal: Each rotation outputs a pulse as the absolute reference point for the mechanical origin, solving the problem of position loss in incremental encoders after power failure.

Compared to absolute encoders, incremental encoders have three significant advantages:

High cost-effectiveness: simple structure, no need for complex encoding disks, price is only 1/3~1/2 of the same precision absolute encoder;

Strong anti-interference ability: The magnetic incremental encoder can work stably in harsh environments such as strong electromagnetic interference, oil pollution, dust, etc;

Fast dynamic response: Low delay in pulse signal transmission, suitable for high-speed motion control scenarios.

2、 Position control: from pulse counting to nanometer level accuracy

The incremental encoder achieves position closed-loop control through pulse counting, and its core process is as follows:

Pulse acquisition: The encoder rotates by one resolution unit (such as a 1024 line encoder outputting 1024 pulses per revolution), and the controller records the number of pulses through the high-speed counting port;

Position conversion: According to the formula position=pulse number/resolution, convert the pulse number into actual angle or linear displacement (combined with gear ratio or screw lead);

Error compensation: Accumulate errors through regular calibration of Z-phase zero position signals, combined with feedforward control algorithms to eliminate nonlinear factors such as mechanical clearance and elastic deformation.

Typical application cases:

CNC machine feed system: using a 17 bit incremental encoder (with a resolution of 131072 pulses/revolution), combined with a grating ruler to achieve micrometer level positioning accuracy, meeting the requirements of precision machining;

Robot joint control: By using 4x technology (including the rising and falling edges of A/B phase pulses), the encoder resolution is increased to 4096 pulses per revolution, achieving sub radian level control of joint angles;

Semiconductor equipment: In wafer transfer robots, incremental encoders are combined with linear motors to achieve a repeat positioning accuracy of ± 0.1 μ m through pulse counting.

3、 Speed measurement: technological evolution from frequency method to MT method

Incremental encoders achieve speed measurement through the temporal characteristics of pulse signals, and mainstream methods include:

1. Frequency method (M method)

Principle: Count the number of pulses within a fixed time window and calculate the speed using the formula speed=number of pulses/(resolution x time window).

Features:

High speed measurement accuracy (such as at 1000rpm, the 1024 line encoder can capture 17 pulses every 10ms with an error of only 0.6%);

At low speeds, the error is significant (for example, at 10rpm, there are only 0.17 pulses within 10ms, and the counting period needs to be extended or frequency doubling techniques need to be used).

Optimization plan:

Hardware Frequency Doubling: By using FPGA or dedicated chips to achieve 4x and 16x frequencies, low-speed resolution can be improved;

Software filtering: using sliding average algorithm to suppress pulse jitter.

2. Periodic method (T method)

Principle: Measure the time interval between adjacent pulses and calculate the speed using the formula speed=1/(resolution x time interval).

Features:

Low speed measurement accuracy is high (for example, at 1rpm, the pulse interval of the 1024 line encoder can reach 60ms, and the measurement error can be controlled within 0.1%);

The error increases at high speeds (such as when the pulse interval is only 0.6ms at 1000rpm, limited by clock accuracy).

Optimization plan:

High frequency clock interpolation: using clocks above 100MHz to segment pulse intervals and improve high-speed measurement accuracy;

Multi pulse synchronous measurement: simultaneously capture multiple pulse cycles, take the average to reduce random errors.

3. Mixed method (MT method)

Principle: Combining frequency method and period method, count the number of pulses within a fixed time (M method), while measuring the number of high-frequency clock pulses (T method). Calculate the speed by using the formula speed=high-frequency clock frequency x pulse number/(resolution x high-frequency clock count).

Features:

Full speed domain accuracy balance (such as errors less than 0.01% within the range of 1rpm to 10000rpm);

The algorithm has high complexity and requires dedicated hardware support.

Typical application scenarios:

Elevator traction machine: The MT method is used to measure the motor speed, achieving a speed control accuracy of 0.01m/s to ensure elevator comfort;

New energy vehicle main drive motor: achieved low-speed crawling control of 0.1rpm through redundant design of incremental encoder and rotary transformer, combined with MT method;

Wind turbine pitch control system: In the wide speed range of 0.1rpm to 15rpm, the MT method ensures a blade angle control accuracy of ± 0.1 °.

4、 Technical Challenges and Development Trends

Although incremental encoders have advantages in cost and reliability, their reliance on external counters and the need to reset to zero after power outages still limit their application expansion. There are two major trends in current technological development:

Intelligent integration: Integrating the encoder and driver design, implementing hardware based pulse counting, speed calculation, and error compensation through built-in DSP chips, reducing controller load;

Multi sensor fusion: By combining incremental encoders with absolute encoders and current sensors, a multimodal feedback system is constructed to enhance the system's fault tolerance (such as switching to current loop control when the encoder fails).

　

　 Incremental encoderWith its high cost-effectiveness and reliability, it occupies a dominant position in the field of servo motor position control and speed measurement. With the increasing demand for equipment accuracy and intelligence in Industry 4.0, incremental encoders are constantly breaking through performance boundaries through technological innovation, providing more accurate motion control solutions for intelligent manufacturing.