OpenIGTLink/Protocol/JHUBRP

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JHU BRP Robot protocol description


System Diagram

MRI Robot System Diagram2.png

Workflow

  1. Scanner: Scout image acquisition with the landmark close to the prostate
  2. Navigation soft and scanner: Calculate Z-frame position, scan a slice through the Z-frame
  3. Repeat previous step if the Z-frame is not visible enough to register the robot
  4. Scanner: 3D volume acquisition of the prostate
  5. Navigation soft: Select (or import) the targets, show needle path, allow modification
  6. Navigation soft: Calculate the target and path, send it to the robot
  7. Robot: Execute command
  8. [Optional] Navigation soft: send current robot coordinates to the Real Time scanner IO for needle tracking, display image
  9. Navigation soft: Display robot position and status
  10. Scanner: Confirm robot location before biopsy
  11. Manual: Insert biopsy needle
  12. [Optional] Navigation soft: show Real time images of the needle insertion
  13. Manual: Fire biopsy gun

Open IGT Link Protocol

Some commands / queries are expecting parameters in the Body section which follows the Header Structure. The parameter can be:

  • 8 bit Byte
  • 32 bit Integer
  • 32 bit Float

For example the Position and Orientation parameters in SET_Z_FRAME command will be the following. 

 Bytes (Body)
 58      62      66      70      74      78      82
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |   X   |   Y   |   Z   |  Ox   |  Oy   |  Oz   |  
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Set Workphase (Slicer -> Robot)

There are no parameters for this commands.

START_UP

Slicer: Send "START_UP" Workphase command
Robot: Initialize robot and respond with status message

PLANNING

Robot: Do nothing, respond with status

CALIBRATION

Robot: Do nothing, respond with status. Waiting for SET_Z_FRAME command (Z-Frame transformation).

TARGETING

Robot: Fail if Z-Frame was not set. Respond with status. Waiting for targets (MOVE command).

MANUAL

Robot: Engage breaks, responds with status.
Slicer sends "GetCoordinate" query periodically to update the display.

EMERGENCY

Robot: Responds with status


Command / Query (Slicer -> Robot)

Command: INITIALIZE

Parameters: none
Robot: Initialize, set the encoders, remember this position as "HOME". Respond with status.

Command: SET_Z_FRAME

Parameters (24 byte total):

  • Vector of three 32 bit floats: position X, Y, Z
  • Vector of three 32 bit floats: orientation

Robot: Store Z-frame position and orientation (global RAS coordinate system) - respond with status.

Command: MOVE_TO

Parameters (24 byte total):

  • Vector of three 32 bit floats: position X, Y, Z
  • Vector of three 32 bit floats: orientation

Robot: Go to this coordinate - position, orientation (later: speed?) (global RAS coordinate system). Respond with status.

Command: INSERT

Parameters (4 byte): 32 bit float
Robot: Insert the needle to this depth - float (in mm)

Command: BIOPSY

Parameters: none
Robot: Take biopsy (Retract Cannula)

Command: HOME

Parameters: none
Robot: Go to Home (collapses the robot to remove/replace needle)

Command: STOP

Parameters: none
Robot: Stop moving

Command: E_STOP

Parameters: none
Robot: Emergency Stop (stop + purges the air lines)

Command: SET_JOINT

Parameters: a set of 32bit floats. The number of floats is BODY_SIZE/4.
Robot: Set Joint Positions - float[max.16] - move joint here

Command: SET_VELOCITY

Parameters: a set of 32bit floats. The number of floats is BODY_SIZE/4.
Robot: Set Joint Velocities - float[max.16] - move joint with this speed

Command: SET_AIR_PRESSURE

Parameters: TBD
Robot: sets the air pressure / voltage output

Command: LOCK

Parameters: none
Robot: Engage brakes - all of them

Command: UNLOCK

Parameters: none
Robot: Unlock - disengage all the brakes so the robot can be moved manually

Command: LOCK_AXIS

Parameters: one or more 32bit integers (BODY_SIZE/4)
Robot: Engage brakes on a give axis

Command: UNLOCK_AXIS

Parameters: one or more 32bit integers (BODY_SIZE/4)
Robot: Unlock - disengage the brakes on a give axis, so it can be moved manually

Command: LIMIT_VELOCITY

Parameters: one 32 bit float
Robot: Set entire robot velocity limit in Robot Coords. - float (like 10 mm/s)

Query: GET_COORDINATE

Parameters: none
Robot: Respond with current coordinate (position and orientation in global RAS coordinate system)

Query: GET_STATUS

Parameters: none
Robot: Respond with status (see the packet description below)

Query: GET_BIOPSY

Parameters: none
Robot: Respond with Actual Insertion Depth

Query: GET_NR_JOINT

Parameters: none
Robot: Get Number of Joints - integer, see the description below

Query: GET_JOINT

Parameters: one or more 32bit integers (BODY_SIZE/4)
Robot: Get Actual Joint Positions

Query: GET_VELOCITY

Parameters: one or more 32bit integers (BODY_SIZE/4)
Robot: Get Actual Joint Velocities

Query: GET_AIR_PRESSURE

Parameters: one or more 32bit integers (BODY_SIZE/4)
Robot: Get Actual Air Pressures

Query: GET_JOINT_TRACK

Parameters: one or more 32bit integers (BODY_SIZE/4)
Robot: Get Actual Joint Tracking Errors

Query: GET_BRAKE

Parameters: none
Robot: Get Brakes status

Query: GET_MOVING

Parameters: none
Robot: Get Joint Moving status


Responses sent by the robot (Robot -> Slicer)

Status: STATUS

Response from Robot: Robot done moving, Error message, Emergency stop
See OpenIGTLink/Protocol#STATUS for description.

Status: BRAKES

Response from Robot: Brake status - boolean[max.16] - true(locked)/false(loose) for each joint
Structure: a number of bytes, defied by BODY_SIZE. 0 means false, 1 means true.

Status: DONE_MOVING

Response from Robot: Done moving/joint - boolean[max.16] - true/false for each joint Structure: a number of bytes, defied by BODY_SIZE. 0 means false, 1 means true.

Response: COORDINATES

Response from Robot: Actual coordinates and insertion depth - 6DOF in global RAS coordinate system
Structure (28 byte total):

  • Vector of three 32 bit floats: position X, Y, Z
  • Vector of three 32 bit floats: orientation
  • One 32 bit float: current insertion depth

Response: JOINTS

Response from Robot: Number of Joints - integer
Structure: one 32 bit integer (4 bytes total)

Response: JOINT_POS

Response from Robot: Actual joint positions - float[max.16] (joint positions in mm)
Structure: a set of 32bit floats. The number of floats is BODY_SIZE/4.

Response: JOINT_VEL

Response from Robot: Actual joint velocities - float[max.16] (joint velocities in mm/s)
Structure: a set of 32bit floats. The number of floats is BODY_SIZE/4.

Response: JOINT_TRACK

Response from Robot: Actual joint tracking error - float[max.16] - "actual joint position" - "set joint position"
Structure: a set of 32bit floats. The number of floats is BODY_SIZE/4.

Response: AIR_PRESSURE

Response from Robot: Actual air pressures - float[max.32] - two per joint! (PSI for each valve)
Structure: a set of 32bit floats. The number of floats is BODY_SIZE/4.

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