Arcminaxis™: Revolutionizing Position Sensing in Robotics

Introduction

In the evolving world of robotics, achieving motion control with high accuracy is key. The precision and reliability of a robot's movements depend heavily on the quality of its position-sensing technology. Arcminaxis™, a groundbreaking technology from Melexis, addresses these challenges with a revolutionary approach to magnetic encoding.

What is Arcminaxis™?

Arcminaxis™ is a cutting-edge, high-resolution position-sensing technology designed to meet the growing demand for affordable, high-precision solutions in robotic joints. It combines multi-axis sensing capabilities with Vernier technology, resulting in a compact and easy-to-integrate solution.

Acrminaxis™ products, like the MLX90384, come with a magnet, sensor and operating software.

How Does it Work?

Traditional magnetic encoders often rely on measuring a single component of the magnetic field in several separate locations, which can introduce errors and limitations. Arcminaxis™ takes a different approach by using two sensing areas to measure two pairs of orthogonal magnetic field components — axial and tangential. This multi-axis sensing, combined with a unique dual-track magnet design (featuring a Master and Nonius track), eliminates the need for precise sensor placement, accommodates larger magnet poles, and significantly enhances accuracy and overall precision.

• Multi-axis Sensing: Arcminaxis™ utilizes two orthogonal components – axial and tangential - in each of the two sensing areas. This approach eliminates the need for precise sensor placement allowing for more airgap between the magnet and sensor, as well as accommodating larger magnet poles, and increasing design flexibility.
• Dual-Track Magnet Design: The encoder incorporates a two-track magnet system, featuring a Master track and a Nonius track. This design, coupled with multi-axis sensing, enables accurate 360° measurement and enhances overall precision.

Advanced Signal Processing

Arcminaxis™ applies sophisticated signal processing techniques to ensure high accuracy:

• Nonius Angle Reconstitution: Leveraging the four distinct signals and advanced algorithms, the system effectively mitigates crosstalk from the Master track, enabling precise extraction of the Nonius angle.
• Amplitude and Phase Correction: The system corrects amplitude and phase mismatches in the Master signals, minimizing harmonic errors.
• Fine Angle Reconstruction: The fine angle is derived from the Master track signals and the restored Nonius angle, contributing to precise position determination.
• Harmonic Correction and Linearization: After another correction step, we are able to minimize harmonic errors deriving from mechanical misalignments (e.g. eccentricity) and residual magnetic crosstalk. Finally, a Look-Up Table (LUT) compensates for non-linearity caused by magnet imperfections.

The optimal coefficients to apply the correction mentioned above are found via an automatic calibration routine which can be initiated when the system is set in motion at constant speed (at least one full rotation is required). This ensures peak performance and minimizes setup time

Performance and Benefits

• Exceptional Accuracy and Resolution:
  With up to 18 bits of resolution over the full 360° range it enables robots to perform tasks with greater consistency and repeatability.
  
  It should be noted that the resolution is more valuable than accuracy in many robotic applications. In fact, a key aspect of these applications is the repeatability of motions that are taught to robots. The high resolution ensures that the same positions are reached every time and therefore high repeatability is guaranteed.
• Compact and Easy-to-Integrate Design:
  • Large assembly tolerances: The sensor can be positioned with a tolerance of ±0.5mm in all three directions, axial, tangential and radial.
  • The nominal air gap of 1.5mm allows for mounting and operating the sensor and magnet inside a robotic joint at safe distance, without the danger of a “head crash” which can destroy the encoder in other systems.
• Pitch independent:
  1 sensor module accommodates various magnets (size, number of pole pairs).

• Integrated calibration routine:
  As previously described, a smart algorithm enables 360° measurement and enhances overall precision.
• Cost-Effectiveness:
  Despite its advanced capabilities, Arcminaxis™ offers a cost-effective solution compared to other high-accuracy position sensing technologies.
• High-Speed SPI Interface:
  The MLX90384 is operated via a versatile high-speed SPI interface of 6MHz, allowing a versatile command structure for retrieving angle, speed and turn-count, reading errors and even calibrating the system in situ.

Use Cases and Applications

Robotics: It can enable more precise and agile movements for different robotic joints, such as those in the example below:

Conclusion

Arcminaxis™ is a breakthrough in high-resolution position sensing, poised to reshape the robotics and the automation landscape. Its exceptional accuracy, resolution, and seamless integration empower engineers to achieve unprecedented levels of precision, efficiency, and reliability in motion control, opening doors to a new era of possibilities.