PaXini Tactile Sensor Technical Documentation

Written By Jerry Huang

PaXini PX-6AX GEN3 Technical Documentation

1. System Overview

The PaXini PX-6AX GEN3 series is a family of multidimensional tactile sensing modules designed to provide spatially distributed, triaxial force measurements for robotic manipulation and contact-rich interaction.

Each module integrates sensing, signal processing, force reconstruction algorithms, and digital communication into a compact unit, enabling direct integration into learning-based robotic systems.

The sensor outputs time-synchronized force fields, rather than single-point force values, making it suitable for tactile perception, manipulation learning, and multimodal data collection. 

2. Sensing Principle

2.1 Physical Architecture

PX-6AX GEN3 adopts a semi-flexible, multi-layer structure:

  • Elastic deformation layer

    Deforms under contact and transmits force information.

  • Rigid sensing layer

    Hosts Hall-effect sensors that detect magnetic field changes.

  • Embedded magnetic elements

    Translate mechanical deformation into measurable magnetic displacement.

Force-induced deformation changes the relative position of magnetic sensing points, which are then reconstructed into triaxial force vectors (Fx, Fy, Fz) via onboard algorithms.

This architecture enables:

  • Measurement of normal and tangential forces

  • High durability under repeated contact

  • Stable sensing under real-world conditions

2.2 Magnetic Interference Mitigation

To ensure signal integrity, PX-6AX GEN3 includes anti-stray-field compensation algorithms that suppress interference from:

  • External magnetic fields

  • Strong lighting conditions

  • Environmental electromagnetic noise

This is critical for long-duration data collection and deployment in non-laboratory environments.

3. Sensor Output Model

3.1 Distributed Force Representation

At each sampling step, the sensor reports:

  • Per-cell triaxial force vectors

    \mathbf{f}_i = (F_{x,i}, F_{y,i}, F_{z,i})

  • Aggregated resultant forces

    \mathbf{F} = \sum_i \mathbf{f}_i

Force units:

  • Resolution: 0.1 N per LSB

  • Normal force (Fz): 0–25 N

  • Tangential force (Fx, Fy): ±10 N

Example:

A reported Fz value of 10 corresponds to 1.0 N normal force. 

3.2 Spatial Resolution

  • Spatial resolution: 1 mm

  • Minimum detectable force: 0.1 N

  • Accuracy: 1% FS

Depending on the module variant, sensing arrays range from 9 to 239 measurement points, enabling high-density tactile perception at fingertips, finger pads, or palms.

4. Coordinate System

Each sensor defines a local global coordinate frame anchored at a fixed reference point on the sensor housing.

  • All sensing points are expressed in this frame

  • Triaxial force axes are consistent across modules

  • Sensing point positions are fixed and known

This explicit geometric grounding allows tactile data to be:

  • Aligned with robot kinematics

  • Fused with vision and proprioception

  • Used directly as structured learning observations

5. Hardware Variants

The PX-6AX GEN3 family includes Elite, Core, and Omega variants, differing in:

  • Physical dimensions

  • Number of sensing points

  • Maximum current consumption

All variants share:

  • Identical sensing principles

  • Consistent force scaling

  • Unified communication semantics

This enables cross-device dataset consistency.

6. Electrical Characteristics

  • Operating voltage: 3–5 V DC

  • Logic level: 3.3 V

  • Maximum current:

    • Elite: up to 150 mA

    • Core: up to 350 mA

    • Omega: up to 700 mA

Sensors are designed for embedded integration and can be powered from standard robotic control boards.

7. Communication Interfaces

7.1 Supported Protocols

PX-6AX GEN3 supports multiple digital interfaces:

Protocol

Characteristics

Use Case

SPI

High throughput, deterministic timing

Real-time learning and control

UART

High baud rate (921600)

Embedded systems, debugging

I²C

≤200 kHz

Low-speed integration

Protocol selection occurs only at power-on, based on pin configuration. 

7.2 Addressing and Module Identification

  • Device address = module index + 1

  • Multiple sensors can be daisy-chained

  • Chip-select pins encode module role (DP / IP / CP / Palm)

This enables scalable deployment on multi-fingered robotic hands.

8. Register Map and Data Access

8.1 Address Spaces

The sensor exposes two main register regions:

User Configuration Area (0x79)

  • Calibration trigger

  • Control flags

  • Write-limited (non-contiguous writes only)

Application Area (0x7B)

  • Read-only force data

  • Continuous streaming supported

  • Per-cell force values stored sequentially

8.2 Force Data Layout

Force data is stored as:

[Fx1, Fy1, Fz1, Fx2, Fy2, Fz2, ...]

Each value:

  • 1 byte

  • Little-endian

  • Scaled at 0.1 N per unit

This layout is optimized for:

  • DMA transfer

  • Real-time streaming

  • Efficient tensor conversion

9. Data Acquisition Workflow

9.1 Calibration

  • Calibration must be performed under no-load conditions

  • Triggered via configuration register

  • Zero-offset applied internally

Proper calibration is required before any data collection session.

9.2 Streaming and Logging

The host software supports:

  • Real-time force visualization

  • Continuous data logging

  • Timestamp-aligned recording

This enables direct ingestion into:

  • Dataset pipelines

  • Learning frameworks

  • Offline analysis tools

10. Learning-Oriented Data Semantics

From a learning system perspective, PX-6AX GEN3 provides:

  • Contact localization (where touch occurs)

  • Force magnitude and direction

  • Shear and slip indicators

  • Temporal evolution of contact

These signals are critical for:

  • Grasp stability detection

  • Slip prediction

  • Contact-aware control policies

  • Failure and recovery modeling

11. Safety and Operating Limits

The sensor is designed for:

  • Touching

  • Gripping

  • Squeezing

  • Sliding contact

It is not intended for:

  • Piercing or cutting contact

  • Exposure to fire or corrosive liquids

  • Strong magnetic fields

  • Medical, military, or aviation systems

Safe load:

  • 200% rated load

  • 300% impact overload

12. Maintenance and Reliability

  • Service life: >10 million contact cycles

  • Elastomer surface can be cleaned with:

    • Adhesive tape

    • Lint-free cloth

    • Mild alcohol (low concentration)

Organic solvents and aggressive chemicals must be avoided.

13. Intended Integration Scenarios

PX-6AX GEN3 is intended for:

  • Learning-based robotic manipulation

  • Tactile-enhanced imitation learning

  • Reinforcement learning with contact feedback

  • Multimodal dataset creation (vision + touch + proprioception)

It is explicitly designed to be a data source, not just a sensor.

14. Summary

The PaXini PX-6AX GEN3 series provides dense, spatially grounded, triaxial tactile data through a robust, digitally accessible interface.

By exposing tactile perception in a form suitable for learning systems and dataset pipelines, PX-6AX GEN3 enables robots to reason about contact—not as an event, but as a measurable, learnable signal.

Jerry Huang
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