© 2015 Fairchild Semiconductor Corporation www.fairchildsemi.com
FMT1000-series • Rev. 1.0 15
FMT1000-series — Motion Tracking Module With Output of Orientation, Inertial Motion Data and Magnetic Field
2 FMT1000-Series Architecture
This section discusses the FMT1000-series architecture
including the various configurations and the signal
processing pipeline.
2.1 FMT1000-Series Configurations
The FMT1000-series is fully-tested, self-contained
modules that can 3D output orientation data (Euler
angles (roll, pitch, and yaw), rotation matrix (DCM) and
quaternions), orientation and velocity increments (∆q
and ∆v) and sensors data (acceleration, rate of turn,
magnetic field). The FMT1000-series module is
available as an Inertial Measurement Unit (IMU),
Vertical Reference Unit (VRU) and Attitude and Heading
Reference System (AHRS). Depending on the product,
output options may be limited to sensors data and/or
unreferenced yaw.
All FMT1000-series feature the Fairchild FIS1100 (an
accelerometer/gyroscope combo-sensor), a
magnetometer, a high-accuracy crystal and a low-power
MCU. The MCU coordinates the synchronization and
timing of the various sensors, it applies calibration
models (e.g. temperature modules) and output settings
and runs the sensor fusion algorithm. The MCU also
generates output messages according to the proprietary
XBus communication protocol. The messages and the
data output are fully configurable, so that the FMT1000-
series limits the load, and thus power consumption, on
the application processor.
2.1.1 FMT1010 IMU
The FMT1010 module is an Inertial Measurement Unit
(IMU) that outputs 3D rate of turn, 3D acceleration and
3D magnetic field. The FMT1000-series also outputs
coning and sculling compensated orientation increments
and velocity increments (∆q and ∆v) from its
AttitudeEngineTM. Advantages over a gyroscope-
accelerometer combo-sensor are the inclusion of
synchronized magnetic field data, on-board signal
processing and the easy-to-use communication
protocol. Moreover, the testing and calibration
performed by Fairchild result in a robust and reliable
sensor module, that can be integrated within a short
time frame. The signal processing pipeline and the suite
of output options allow access to the highest possible
accuracy at any bandwidth, limiting the load on the
application processor.
2.1.2 FMT1020 VRU
The FMT1020 is a 3D vertical reference unit (VRU). Its
orientation algorithm (XKF3TM) outputs 3D orientation
data with respect to a gravity referenced frame: drift-free
roll, pitch and unreferenced yaw. In addition, it outputs
calibrated sensor data: 3D acceleration, 3D rate of turn
and 3D earth-magnetic field data. All modules of the
FMT1000-series are also capable of outputting data
generated by the strap down integration algorithm (the
AttitudeEngine outputting orientation and velocity
increments ∆q and ∆v). The 3D acceleration is also
available as so-called free acceleration which has
gravity subtracted. Although the yaw is unreferenced,
though still superior to gyroscope integration. With the
feature Active Heading Stabilization (AHS, see section
7.2) the drift in unreferenced yaw can be limited to 1 deg
after 60 minutes, even in magnetically disturbed
environments.
2.1.3 FMT1030 AHRS
The FMT1030 supports all features of the FMT1010 and
FMT1020, and in addition is a full gyro-enhanced
Attitude and Heading Reference System (AHRS). It
outputs drift-free roll, pitch and true/magnetic North
referenced yaw and sensors data: 3D acceleration, 3D
rate of turn, as well as 3D orientation and velocity
increments (∆q and ∆v), and 3D earth-magnetic field
data. Free acceleration is also available for the
FMT1030 AHRS.
2.2 Signal Processing Pipeline
The FMT1000-series is a self-contained module, so all
calculations and processes such as sampling, coning
and sculling compensation and the XKF3 sensor fusion
algorithm run on board.
2.2.1 Strap-down Integration
The optimized strap-down algorithm (AttitudeEngine)
performs high-speed dead-reckoning calculations at
1 kHz allowing accurate capture of high frequency
motions. This approach ensures a high bandwidth.
Orientation and velocity increments are calculated with
full coning and sculling compensation. At an output data
rate of up to 100 Hz, no information is lost, yet the
output data rate can be configured low enough for
systems with limited communication bandwidth. These
orientation and velocity increments are suitable for any
3D motion tracking algorithm. Increments are internally
time-synchronized with the magnetometer data.
2.2.2 XKF3TM Sensor Fusion Algorithm
XKF3 is a sensor fusion algorithm, based on Extended
Kalman Filter framework that uses 3D inertial sensor
data (orientation and velocity increments) and 3D
magnetometer, also known as „9D‟ to optimally estimate
3D orientation with respect to an Earth fixed frame.
XKF3 takes the orientation and velocity increments
together with the magnetic field updates and fuses this
to produce a stable orientation (roll, pitch and yaw) with
respect to the earth fixed frame.
The XKF3 sensor fusion algorithm can be processed
with filter profiles. These filter profiles contain predefined
filter parameter settings suitable for different user
application scenarios.
The following filter profiles are available:
General – suitable for most applications. Supported
by the FMT1030 module.
Dynamic – assumes that the motion is highly
dynamic. Supported by the FMT1030 module.
High_mag_dep – heading corrections rely on the
magnetic field measured. To be used when
magnetic field is homogeneous. Supported by the
FMT1030 module.