Control Module (Kybern)

Current bugs or problems

• Response oscillates too much. When running in fixed-distance-to-target mode limit cycles may occur. Need to redesign control law to take into account delays and latencies in the network.

How to execute this module

• Log in to Nomad20
• Make sure robotd is running as root in the background. If not, then run the daemon as follows:
  1. Log in as root
  2. cd to /Nomad200/Nomad_robot/robot-linux???
  3. run robotd &
• cd to /home/hhg_19/demo
• If running full demo (see comments) make sure robot is under a landmark.
• run kybern <float> <float> <float>. The actual parameters are calculated by the calibration program. Parameters change with the camera configuration.
• Typical Parameters (check with calibration program): -2.9 1.0 0.0

Revision history

1. April, 1995: First version finished.
2. April, 1995: Added landmark relocalization.
3. July, 1995: Improved process model.
4. July, 1995: Improved target tracking by using a better model for the angular error predictor.
5. Switch to new Nomad class which uses binary port to connect to the robot daemon (instead of the ascii port).
6. January, 1996: Linux version implemented.
7. January, 1996: Changed the communication protocol with the planner to match the new planner version.
8. September, 1997: Controller rewritten (renamed Kybern). Socket connections improved, Clock class incoporated (clean timing and synchronization mechanism), State and State_History class incorporated (data history spread uniformly in time, intersample acces by linear interpolation), running mode selected automatically depending on the supporting modules being run (see comments).
9. October 15, 1997: Added dead-zone to control laws to remove limit cycles and oscillations.

Ideas for improvement

• Incorporate trajectory tracking capability.
• Add local collision avoidance.
• Merge control and planning in a single module.
• Redesign regulator to take better account of the communication delays and latencies.

Other comments

• landmark.map file should be in the same directory as Kybern.
• parameters.ctrl contains constants used by the controller, and should also be in the same directory. The (typical) contents are:

  HISTORY_SCOPE	4.0	Retain a data history of this duration (in seconds).
  SP_D	65.0	Stay at this distance from target in fixed-distance-to-target mode.
  KVR	1	You do not want to modify this.
  TWAIT	3.0	Wait this many secs after loosing track before going to search mode.
  TDELAYT	0.0	Target measurement delay.
  TDELAYL	0.0	Landmark measurement ADDITIONAL delay (communication latency)
  MAX_X_ERR	24.0
  MAX_Y_ERR	24.0
  Maximum allowable relocalization shifts (stupidity test).
  STATE_CONV_ERR	3.0	Controller dead-zone.
  NOMAD_RADIUS	8.875	The robot radius.
  KTU	0.20	Turret loop gain.
  KTH	0.20	Steering loop gain.
  KR	0.15	Radial translation loop gain.

• The controller will attempt to establish connections with other modules. At least the target server module should be up and running. The operation mode will be chosen as follows:
  1. No planner: Vision servo demo, observer tries to stay at SP_D inches from the target. Absolute positions are available if the landmark server is on.
  2. Planner running, no landmark server: Full demo running at dead reckoning. Errors will build up, but demo will run for a while with luck. User should provide initial localization.
  3. Landmark and planner running. Full demo, make sure the input arguments of the program (camera configuration) is the correct one. Observer should start under a landmark (any).
• The controller will accept connections once the target is first seen (i.e., once execution enters the main control loop).