Trailblazer shape sensing development platform

Trailblazer is an entry-level solution for shape sensing. It enables the reconstruction and display of the entire shape of a thin, flexible optical fiber.

By discretizing the entire fiber in thousands of 150 ┬Ám long segments Trailblazer is able to extract for every location along a fiber the strain, twist and bending direction that are derived to compute 3D coordinates and provide information on the location of the fiber in space relative to its origin. Trailblazer is a self-contained unit delivered along with a 3D shape sensor and visualization software.

The patented technology implemented in Trailblazer finds its origins at NASA and is unique as a generic shape sensing instrument available in the market place.

Unlike alternative shape sensing technologies, Trailblazer supports tortuous paths, 6 degrees of freedom, twist and more than 50cm sensing length.

Trailblazer development platform features

  • Monitors a single 3D shape sensor
  • Minimum 60 frames per second refresh rate
  • Maximum 30ms hardware latency
  • Desktop unit can be used in laboratory environment
  • Connects to any TSSC shape sensor
  • Displays shape in real time on a screen or streams via Ethernet
  • Shape measurements are automatically compensated for changes in temperature

What Trailblazer can measure

  • 3D shape
  • Twist
  • Bending direction and bending radius
  • Strain
  • Temperature
  • Force (haptic feedback)
  • Pressure

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Background on Fiber Bragg Gratings

Fiber Optic Sensing (FOS) technology is based on the use of 80m glass fiber that has been continuously inscribed with Fiber Bragg Gratings (FBG). They are the unique optical sensing element that turns ordinary telecom grade optical fiber into a powerful and robust sensing tool. These sensors act as embedded mirrors inside the fiber that reflect a specific wavelength.

When an FBG fiber is bonded to a material and interrogated with light, the FBGs will reflect different wavelengths as the fiber is strained. The optical equivalent of a foil strain gauge or thermocouple, an FBG is a sensor inscribed into the core of the optical fiber by periodically modulating the refractive index of the core, as shown below.

The Fiber Bragg Grating is formed in the core by a series of refractive index modulations. A single grating is composed of thousands of modulations, but only a handful are shown for clarity.

The resulting grating structure acts as a wavelength selective mirror for light propagating through the fiber. Most wavelengths of light will travel through the grating uninterrupted.

However, constructive interference occurs at one specific wavelength and light is partially reflected back down the fiber. This phenomenon is illustrated in Figure 3, where a broad spectrum light beam is passed through the fiber.

The working principle of a Fiber Bragg Grating

The wavelength which an FBG will reflect is called the Bragg wavelength. The effective refractive index of the core and the grating period both depend on mechanical strain  and temperature. Thus, the reflected FBG wavelength can be used to determine strain or temperature at that location along the fiber. Optical transduction involves monitoring the reflected FBG wavelength and correlating that information to either strain or temperature.

Mechanical strain and temperature are the two quantities that the The Shape Sensing Company technology measures directly. A critical objective behind fiber optic strain sensing is eliminating the thermal strain component, such that the final strain is only the mechanical and load-induced strain in order to derive shape.

One approach is to remove the average strain measured before the load application and after the load removal. This type of baseline correction can be used effectively if the temperature change is small and gradual. These conditions are usually met in short duration loading within a contained space and in room temperature.  The Shape Sensing Company has developed more elaborate techniques for temperature compensation.