Inertial unit

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Specifications

The Inertial unit is made of:

  • a 3-axis gyrometers with an angular speed of ~500°/s,
  • a 3-axis accelerometer with an acceleration of ~2g.

Location

The Inertial unit is located in the torso with its own processor.

Position relative to the Torso frame.

Device X(m) Y(m) Z(m)
Accelerometer -0.008 0.00606 0.027
Gyrometer -0.008 0.006 0.029

Output data

The output data enables an estimation of the torso speed and attitude (Yaw, Pitch, Roll).

Compute Torso Angle Algorithm

An SoftBank Robotics algorithm computing the torso Angle from accelerometers and gyrometers is programming inside the inertial board.

This algorithm used the good proprieties of each sensor: accelerometer is the only absolute reference and give the good torso angle in static mode. When some motion is detected, the output angle is computed with gyrometers which have a good behavior in dynamic. However, integration of gyrometers creates a bias of the compute angle, so in dynamic mode, a fusion of compute angle from accelerometer and gyrometer is done to reduce this bias.

https://developers.softbankrobotics.com/sites/default/files/repository/51_html_nao/_images/hardware_inertial_unit_landmark.png

Definition of AngleX and AngleY. [x, y, z] is the reference frame attached to torso.

Accessing value using ALMemory key name

https://developers.softbankrobotics.com/sites/default/files/repository/51_html_nao/_images/hardware_inertialunit.png