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Tracking

The API supports a few different representations of glove tracking data:

  • Fingertip positions / rotations
  • Percentage bent of the fingers
  • Raw exoskeleton data

Coordinate system

We use the following coordinate system: Tracking-coordinate-system When the wrist rotation is 0, 0, 0, the following is true:

  • The X-Axis runs parallel with the stretched fingers, running roughly from the wrist joint to the middle finger MCP joint.

  • The Y-Axis runs along the MCP joints. For right hands, the positive direction is from pinky MCP to index finger MCP. For left hands, the positive direction is from index MCP to the index finger MCP.

  • The Z-Axis points 'up' from the hand palm. The positive direction is from the palm of the hand to the back of the hand.

  • Our left- and right hands share the same 'forward' and 'upward' directions. The difference in positive y-direction between left- and right hands means that finger flexion also shares the same positive / negative direction between the hands.

Origin of the glove (0,0,0)

The 0.4 will have a dot just above the version number printed. For the 0.3 this is the same point but not visual on the prototype. In prototype 0.2, this has been a screw near the thumb base.

Fingertip positions, rotations

get_fingertips_pos_rot() gets the position (vec3) and rotation (quaternion) of each fingertip. The red point indicates this tip.

Fingertip and rotation

This can be adjusted by changing FINGERTIP_OFFSET and FINGERTIP_OFFSET_ROT variable for the respective exoskeleton type within SG_API.exo_dimensions, which hold the offsets with respect to the final exoskeleton position/rotation. TODO: make this a user function.

TODO: Fingertip distances

Percentage bent

Percentage bent can be retrieved with the function get_percentage_bents(). This returns flexion_perc_bents and abduction_perc_bents. Each is an array with as length of the number of fingers.

  • flexion_perc_bents:

    • All fingers: 0 (open) to 10000 (closed)

  • abduction_perc_bents:

    • Thumb:
      • 0 → thumb is in plane with the palm
      • 10000 → thumb is not aligned with handpalm, but radially extended maximally
    • Fingers:
      • 0 → splay to the left
      • 10000 → splay to the right
      • 5000 → in the middle

How percentage bent is calculated

The percentage bent calculations uses the orientations of the fingertips to determine how bent the fingers are.

Percentage bent

The orientations of these arrows are used. We calculate these by adding up the exoskeleton flexion angles for flexion percentage bent, and use the single abduction sensor for abduction percentage bent. This is then normalized between 0 and 10000 normalized based on a pre-set open and closed finger value. The left hand on the image would give 0, the middle around 7000 and the right one around 4000 in default settings. We use this algorithm because it is independent of different hand sizes.

Adjusting the min/max bent settings:

flex_angles and abd_angles can be obtained from SG_main.get_raw_percentage_bent_angles(). These are the raw angles the percentage bent calculations are based on, and is β in the image.

The min/max ranges of these angles were determined experimentally. These can be changed by overwriting the default values with SG_main.set_percentage_bent_vars().

TODO: Gripper open close

This function will map the movement of the index and thumb to a gripper open (0) and gripper closed (10000) value.

Raw exoskeleton data

Exo positions rotations

get_exo_joints_poss_rots() returns the positions (vec3) and rotations (quaternion) of each joint in the exoskeleton with respect to the hub origin. These are indexible like [finger_nr][exo_joint_nr]. The image shows the position locations, and the orientation when multiplying the quaternion with [1,0,0].

exo_angles

For flexion joints, the position is the center of each joint. For the first joint (splay), it is on the axis of the splay rotation, with the z of the first flexion joint.

Exo angles

get_exo_angles_rad() and get_exo_angles_deg() give the raw exoskeleton angles. These can be indexed with angles[finger_nr][angle_nr]. angle_nr 0 is the splay angle (around z), the rest are flexion angles.

The flexion angle definitions are:

  • When an angle is set to 0, the linkages connected to that joint form a straight line.
  • When the next link bends towards the handpalm, the angle is positive.
  • When the next link bends away from the handpalm, the angle is negative.

The following image defines the angles in a common configuration.

exo_angles

Tracking specs

40 (5 fingers x 8 sensors) rotary hall effect sensors enable robust tracking of all five fingers, providing millimeter level precision at the fingertips and along each phalanx. Data can be retrieved from software in the following formats: fingertip position/rotations, exoskeleton rotations/positions, and percentage bents.

alt text

For further tracking possibilities and tracking definitions see the docs.

Tracking error Error
Average absolute deviation per joint: 0,42 degrees
Max deviation measured in a joint: 3,0 degrees
Exo fingertip open finger: up to 3 mm
Exo fingertip near closed hand up to 7 mm

Notes:

  • When using our robot hand mapper algorithm, this compensates for the tracking error resulting in pinch perfect accuracy.
  • Above values are for aligned exoskeleton linkages in a jig. The exoskeleton can bend sideways which allows for ergonomics of, for example, the ring finger and pinky. This can cause additional deviations in position.
  • These values are for a 0.4 prototype. Tolerances improved for 0.5 (version since January 2026), which may result in more accurate tracking.

For further tracking possibilities, measurement conditions and tracking definitions see the docs.

Appendix: Spec measurement conditions

The R1 hub, normally strapped around the hand, was screwed to a jig. Four fingers of the exoskeleton were fixed on the jig with the attachments that normally connect them to the glove. This placed all links in the exoskeleton in fixed angles. alt text This was done at 4 increasingly steep angles (155 degrees, 129 degrees respectively, 100 degrees, and 62 degrees). The experiment was repeated 2 times. The more collapsed the exoskeleton, the lower the error was, due to at what rotation the encoders are calibrated. The errors listed in the table for semi open hand are flexion joint angles: 155 degrees and 129 degrees respectively, and near closed hand flexion joint angles: 100 degrees and 62 degrees respectively.

A single 0.4 prototype was used for evaluation. The 0.5 prototype (current version) has better tolerances and may have improved tracking.