THE STRAPDOWN INERTIAL SENSOR MODEL


In addition to the GPS output, the Tapestry system can generate high rate Strapdown Inertial Measurement Unit (IMU) data comprised of Δν (incremental velocity) andΔθ (incremental attitude) using our proprietary multi-function I/O card (MFIO). The card will generate the data in one of our predefined binary formats in addition to a complete simulation of the hardware clock and handshaking signals.  TAPESTRY, with the Multi-Function Input/Output [MFIO] feature card installed, will model the Electrical and Data Protocol for STRAPDOWN Inertial Measurement Units implemented Digitally via SDLC / ± RS422 and in Analog via a D2A.

The digital output characteristics:

  • Scaled and Interleaved, Autopilot and Inertial Data [Δv and Δθ] at 0 - 1.2 KHz
  • SDLC / ± RS422 Transparent Mode, CRC, 0-BIT Insert.
  • Source/Slave 1 MHz Data Clock.
  • DB25 on MFIO Tang.

The analog output characteristics:

  • Rate Gyro Triad, 0-5 VDC, 50W. Programmable scale factor and offset.
  • Accelerometer Triad, 0-5 VDC, 50W. Programmable scale factor and offset.
  • 16 bit D2A / 100 Hz update.
  • DB25 on MFIO Tang.

In all configurations:

  • Per-axis error models.
  • Case-to-body axis modeling.
  • Adaptation parameter modeling.
  • Truth data access for analysis support.

 


The supported formats, LSB’s, and electrical interfaces include:

  • Honeywell HG-1700 (SDLC)
  • Rockwell Collins GNP-10, GIC-100, IMU-202
  • Boeing DQS
  • Litton LN-200 (SDLC)

For the SDLC systems, the full CRC is generated along with the navigation, autopilot, data interleaving, zero bit insertion, etc.  The user may define and configure the following model elements for the system: 


  • IMU Case-to-BODY axis alignment

  • Accelerometer Bias, Scale Factor, White and Correlated noise.

  • Gyro Bias, Scale Factor, White noise and Random walk.

Our PCI multifunction I/O card (MFIO) resides within the computer system expansion bus using high speed dual ported RAM. This interface, combined with a 5-element ring buffer, virtually eliminates timing error between the generated RF and IMU data outputs. The differential data interface is via a DB25 connector on the feature card.

The six-degree-of-freedom vehicle motion generator included with the Tapestry system, constructs the Dn and Dq data automatically reflecting the simulated dynamics of the host vehicle. This data is synchronized with the GPS RF signal and output to the feature card by the run time executive. A 1-PPS reflecting the epoch timing of the synchronized RF and IMU outputs is provided. The IMU electrical interface can be derived from either and internal or external clock.


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