The History of Encoders

Encoders are essential sensors in modern industrial control and automation systems. Their origins trace back to the 1940s, beginning as mechanical angular converters. With advancements in electronics, optics, communication, and MEMS, encoders have evolved into multifunctional platforms featuring nano-level precision, intelligent communication, and self-diagnostic capabilities.

1940s–1960s: Early Prototypes and the Mechanical Era

• In the 1940s, driven by military radar and aviation navigation technologies, German and British engineers developed brush-type rotary converters to measure angular displacement.
• In 1947, Bell Labs in the U.S. proposed the concept of converting mechanical angles into electrical pulse signals, a prototype of the encoder disk.
• By the early 1950s, the first mechanical encoders were introduced, using brush contact principles to trigger switch signals via rotating contacts.
• These encoders typically output Gray Code, used in early military rangefinders and analog computers.

Key features:

• Full mechanical contact, prone to wear and unstable signals
• Signal output was switch-based or analog voltage
• Very limited use, mainly in defense labs

1970s–1980s: Rise of Optical and Incremental Encoders

• In 1971, BEI Precision Instruments (USA) launched the first commercial optical incremental encoder, revolutionizing the industry.
• Grating discs made of plastic or glass featured etched stripes. Light passing through these stripes was detected by photodiodes, producing A/B pulse signals.
• In 1974, Germany’s Heidenhain added the Z-channel (zero pulse) for origin referencing.
• In 1976, Japan’s Koyo Electronics released industrial incremental encoders, expanding into CNC systems and promoting widespread use.

Innovations:

• Non-contact sensing improved lifespan and reliability
• Standard TTL and HTL output interfaces emerged
• Resolutions reached 1000–5000 PPR

1990s: Absolute Encoders and Digital Control Boom

• From 1989 to 1992, European manufacturers like Baumer and Heidenhain launched single-turn absolute encoders, using multi-track discs and photodetectors to generate parallel position data.
• In 1993, SICK Stegmann (Germany) developed multi-turn absolute encoders using gear counters or magnetic sensing to track rotations.
• SSI (Synchronous Serial Interface) became a serial communication standard promoted by Hubner (Germany).
• Programmable encoders were introduced, allowing users to set resolution and direction via software.

Technical breakthroughs:

• Encoders retained position after power loss (absolute value storage)
• Integrated ASIC chips enabled miniaturization and higher integration
• Enhanced reliability and noise immunity

2000s: Fieldbus, Ethernet, and System Integration

• Encoders adopted industrial fieldbus communication: CANopen (CiA 406), Profibus, DeviceNet, suitable for multi-node networks.
• Emerging industrial Ethernet protocols like EtherCAT (Beckhoff), Profinet (Siemens), and EtherNet/IP (Rockwell) became mainstream in high-speed control.
• In 2005, Japan’s Tamagawa released rotary encoders with SIL2-certified redundancy, used in elevators, robots, and railway systems.
• Encoders started integrating temperature compensation, digital filtering, and self-diagnostics, progressing toward intelligent sensors.

Key trends:

• Networked communication replacing traditional pulse wiring
• Multi-turn resolution extended beyond 30 bits
• Hot-plugging, online configuration, and remote updates introduced

2010s to Present: Smart Encoders, Micro Kits, and Wireless

• Smart encoders support Bluetooth, IO-Link, and industrial Wi-Fi, enabling two-way communication with PLCs or cloud platforms.
• Magnetic encoder kits emerged for collaborative robots (Cobots), AGVs, and drones, with diameters as small as Φ12 mm and weights under 10g.
• High-resolution magnetic linear encoders (e.g., Renishaw, RSF) serve semiconductor devices with sub-micron to nanometer precision.
• Hybrid sensors combining visual recognition and integrated IMUs are rising, offering full 6-DOF motion data.

Future Trends Outlook

1. Intelligence + Edge Computing: Encoders will feature built-in processors for data preprocessing, predictive maintenance, and edge AI.
2. Multi-dimensional Fusion Sensing: Integration with temperature, IMU, torque, and acceleration sensors for comprehensive motion detection.
3. Software-Defined Encoders (SD-E): Remote configuration of resolution, direction, communication protocols, and diagnostics.
4. Green Energy Design: Low power consumption, frictionless materials, and modular installation as emerging priorities.
5. Global Supply Chain Optimization: With a growing demand for key technology sovereignty, nations are enhancing local capabilities in gratings, custom chips, and communication protocols.

Conclusion

The evolution of encoders mirrors the broader transformation of industry—from analog to digital, centralized to intelligent, and closed to open systems. Originating from military applications, encoders have become ubiquitous in civilian industries. Understanding their history offers insight into their technical essence and prepares us to embrace the future of industrial sensing.