In the relentless pursuit of precision, reliability, and efficiency within high-end industrial and automation equipment, engineers constantly seek advanced sensing solutions. Among these, the Absolute Ring Hollow Encoder stands out as a critical component, primarily utilized for accurately measuring rotational angles, positions, and speeds.
At its core, this encoder provides a unique, one-to-one digital code corresponding to a specific position within a full 360° rotation. The most significant advantage? Upon power-up, it instantly communicates its absolute position to the system without requiring a "homing" or "referencing" sequence to a mechanical origin. This "power-on-and-know" capability is a game-changer for complex machinery.
An absolute hollow type ring encoder (often called a hollow-shaft absolute ring encoder or absolute magnetic ring encoder) is a position feedback device designed to measure rotational angle or position directly on a rotating shaft or ring, with an absolute position output rather than incremental pulses.
Let's explore the diverse applications where these encoders are indispensable:
Used for: Spindle orientation, tool changer mechanisms, and rotary tables (e.g., 4th and 5th axes).
Function: Ensures the spindle stops at precise angles for tool changes and controls the accurate indexing of rotary tables for complex surface machining.
Used in: Each joint of the robot (the "shoulder," "elbow," "wrist," etc.), for joint angle detection in articulated arms or rotary axes.
Function: Provides real-time absolute angle feedback for each joint, forming a closed-loop control system that ensures the robot's end-effector moves to pre-programmed positions with high precision and repeatability.
Used in: Measurement equipment, semiconductor manufacturing equipment (e.g., lithography machines), and precision assembly lines.
Function: Achieves extremely high-precision angular positioning and indexing, such as rotating by fixed, minute angles.
Used for: Pitch and azimuth axes of military radar and satellite communication antennas.
Function: Accurately feeds back the antenna's pointing angle, enabling precise target tracking and locking.
Used in: Rotary gantry of CT scanners, robotic arms of radiotherapy equipment (Gamma Knife, CyberKnife), and for compact, high-precision rotary motion sensing.
Function: Ensures absolute positional accuracy for imaging and treatment, which is paramount for patient safety.
Used as: An integral part at the rear of many high-performance servo motors, directly connected to the motor shaft, providing integrated position feedback without mechanical couplers.
Function: Provides high-resolution absolute position feedback to the servo drive, enabling precise torque, speed, and position control.
Wind Turbines & Rotating Platforms: Shaft angle measurement even after power loss.
The absolute ring hollow encoder's operation is elegantly simple yet highly effective:
The hollow ring is mounted directly onto a shaft, bearing, or rotor (no coupling needed).
A stator or readhead (sensor head) is fixed on the stationary part, reading the absolute position of the ring.
The encoder ring has coded tracks (optical or magnetic) corresponding to absolute angular positions.
Output is digital absolute position data (e.g., SSI, BiSS-C, Tamagawa, Panasonic, MODBUS).
Once powered on, it immediately provides the exact angular position — no homing or reference run needed.
For details, please check the video: https://youtu.be/IAC7Gk6mKbY
Compared to traditional incremental encoders and other absolute encoder structures, absolute ring hollow encoders offer significant advantages:
| Feature | Advantage |
|---|---|
| Hollow structure | Enables direct mounting around shafts or through cables, pipes, or rotary joints — saves space and simplifies design. |
| Absolute position | Reports true position immediately at power-up — no need for calibration or homing. |
| Compact & lightweight | Ideal for compact robotic joints or integrated drives. |
| No mechanical coupling | Reduces backlash, misalignment issues, and mechanical wear. |
| High accuracy & resolution | Optical types offer up to arcsecond-level precision; magnetic types are robust with micrometer-level accuracy. |
| Robust against vibration/dust | Especially magnetic versions — suitable for harsh industrial environments. |
| Maintenance-free | Non-contact design means no wear over time. |
| High Rigidity and Stability | The ring structure is typically mounted securely to the equipment via flanges or screws, forming a robust mechanical unit. This design offers excellent vibration and shock resistance, maintaining long-term measurement stability. |
| Strong Anti-Interference Capability | Outputs digital or serial data, less susceptible to electrical noise than pulse signals, ensuring greater reliability in complex industrial environments. |
An absolute hollow type ring encoder is ideal for modern compact motion systems needing:
Direct-on-shaft installation.
Reliable absolute angular data.
Low profile and non-contact measurement.
Robust performance in dynamic or harsh environments.
It's especially popular in robot joints, direct-drive motors, and integrated servo systems, where traditional shaft-type encoders are too bulky or need extra couplings.
As a solo manufacturer of absolute ring encoders in China, Hopo Tech provides a comprehensive selection of ring sizes to meet diverse customer needs. Our outer diameters range from 82mm to 450mm, offering resolutions up to 2 arc seconds. Hopo Tech's specifications compete directly with leading global brands like RLS and Heidenhain, but at a significantly more competitive pricing, making high-precision automation more accessible.
Contact us to learn how our advanced solutions can elevate your machinery.
