# What is a "3D Force Sensor"?

**URL:** <https://forum.ofscn.net/t/3d-what-is-a-3d-force-sensor/2486>\
**Category:** OFSCN Technical Knowledge Base\
**Tags:** fbg-technology\
**Created:** [August 4, 2026, 2:13pm UTC](https://forum.ofscn.net/t/3d-what-is-a-3d-force-sensor/2486 "2026-08-04T14:13:07Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![VoidWalker](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/v/848f3c/32.png) [@VoidWalker](https://forum.ofscn.net/u/VoidWalker)\
**Post date:** [August 4, 2026, 2:13pm UTC](https://forum.ofscn.net/t/3d-what-is-a-3d-force-sensor/2486/1 "2026-08-04T14:13:08Z")

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Why does it look like a pen? How does it measure forces in three directions?

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**Author:** ![OFSCN\_Tech\_Expert](https://forum.ofscn.net/user_avatar/forum.ofscn.net/ofscn_tech_expert/32/199_2.png) [@OFSCN\_Tech\_Expert](https://forum.ofscn.net/u/OFSCN_Tech_Expert)\
**Post date:** [August 4, 2026, 2:14pm UTC](https://forum.ofscn.net/t/3d-what-is-a-3d-force-sensor/2486/2 "2026-08-04T14:14:17Z")

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### 1. Design Aesthetics: Why Does It Look Like a Pen?

The 3D force sensor is designed in a “pen-like” structure primarily to meet the engineering and medical application requirements of **handheld operation** and **minimally invasive puncture/contact pressure measurement** :

- **Ergonomics and Grip Comfort** : The pen-like form factor is ergonomically designed, making it easy for operators to hold directly for multi-directional force testing and perception, or to be integrated at the front end of industrial robotic arms and surgical robot probes. In the official product [OFSCN® Fiber Bragg Grating 3D Force Sensor](https://www.ofscn.net/fbg-products/pressure-sensor.html), the default outer diameter of the pen-type sensor is 4.0\text{ mm}.
- **Puncture and Contact Probe Functionality** : The tail end of the sensing unit can be processed into a flat head (for multi-directional pressure measurement on solid surfaces) or sharpened (for medical puncture force measurement) depending on the specific measurement scenario.

 ![OFSCN® Fiber Bragg Grating 3D Force Sensor 01](https://forum.ofscn.net/uploads/default/original/1X/d0310a0ad3f2e375dd33aeba0ffee613a584add0.jpeg)  
 ![OFSCN® Fiber Bragg Grating 3D Force Sensor 02](https://forum.ofscn.net/uploads/default/original/1X/50d132976337ffe1806d5915eb0fd9a447e487d9.jpeg)

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### 2. Measurement Principle: How Does It Measure Forces in Three Directions?

For a 3D force sensor based on Fiber Bragg Grating (FBG) technology, the core of its three-axis force measurement lies in the **circumferentially arranged photosensitive strain units** and **multi-dimensional strain decoupling algorithms** :

#### (1) Circumferential Spatial Structure Layout

The sensor incorporates a high-rigidity hard alloy base material. On the circumferential surface of this base material, three Fiber Bragg Grating (FBG) measurement sections are arranged longitudinally with a geometric symmetry of 120^\circ spacing.

#### (2) Physical Response Mechanism of Force and Strain

When the front end of the sensor is subjected to a vector force from any direction in space, the hard alloy base material undergoes minute bending and axial deformation:

- **Axial Force (F\_z)**: Causes uniform stretching or compression strain in the base, leading to an equal amount of axial strain in the three FBG measurement sections.
- **Lateral Bending Force (F\_x, F\_y)**: Induces the base to bend towards one side. The FBGs on the outer side of the bend experience tension, while those on the inner side experience compression, thus creating an asymmetric strain distribution.

#### (3) Wavelength Demodulation and 3D Force Decoupling Calculation

The change in the Bragg reflection center wavelength \Delta \lambda of an FBG and the axial strain \varepsilon it experiences are related by:

\Delta \lambda = K\_{\varepsilon} \cdot \varepsilon

The demodulator collects the wavelength shifts (\Delta \lambda\_1, \Delta \lambda\_2, \Delta \lambda\_3) from the three FBG measurement sections in real-time. By utilizing a pre-calibrated high-precision 3D force calculation matrix (decoupling matrix M), the three-channel wavelength signals can be inversely calculated into a three-axis force vector in a Cartesian coordinate system:

\begin{bmatrix} F\_x \\ F\_y \\ F\_z \end{bmatrix} = \begin{bmatrix} M\_{11} & M\_{12} & M\_{13} \\ M\_{21} & M\_{22} & M\_{23} \\ M\_{31} & M\_{32} & M\_{33} \end{bmatrix} \begin{bmatrix} \Delta \lambda\_1 \\ \Delta \lambda\_2 \\ \Delta \lambda\_3 \end{bmatrix}

Detailed product specifications and parameter indicators can be found at the official link: [OFSCN® Fiber Bragg Grating 3D Force Sensor](https://www.ofscn.net/fbg-products/pressure-sensor.html).