System and method of controlling tethered self-propelled platforms

A method of controlling tethered self-propelled platforms, the method comprising:

• providing a platform leader and a platform follower connected to the leader with a linear tether to define a first heading line of the leader and a first coordinate frame of the follower, the tether being a linear structure and having a length that is telescopically adjustable to allow linear movement between the leader and follower, each of the leader and the follower being pivotally moveable relative to the tether, defining a leader angle and a follower angle, respectively;
• determining the leader angle, the follower angle, and the length of the tether relative to the first coordinate frame of the follower;
• estimating a current position of the leader based on at least one of the leader angle, the follower angle, and the length of the tether, the current position of the leader being the current location and the current orientation of the leader relative to the first coordinate frame of the follower;
• estimating a predicted position of the leader based on the current position, a current speed, and a current yaw rate of the leader relative to the first coordinate frame of the follower, the predicted position of the leader defining a predicted heading line of the leader;
• determining a trajectory of the follower from the first coordinate frame to a point on the predicted heading line defining a second coordinate frame of the follower, the trajectory being based on a desired distance to the point on the predicted heading line and a desired change in yaw angle of the follower, wherein the desired distance is a distance least traveled from the first coordinate frame to the point on the predicted heading line, and wherein the change in yaw angle of the follower is defined by the first heading line of the leader and the desired distance;
• determining a desired speed of the follower along the trajectory based on the desired distance from the first coordinate frame of the follower to the point on the predicted heading line;
• determining a desired yaw rate of the follower along the trajectory based on the desired change in yaw angle of the follower;
• and
• moving the follower along the trajectory to the second coordinate frame based on the desired speed, the desired distance and the desired yaw rate of the follower.

A system for controlling tethered self-propelled platforms, the method comprising:

• a leader controller disposed on a platform leader and a follower controller disposed on a platform follower, the platform follower being connected to the platform leader with a linear tether to define a first heading line of the leader and a first coordinate frame of the follower, the tether being a structure and having a length that is telescopically adjustable to allow linear movement between the leader and follower, each of the leader and the follower being pivotally moveable relative to the tether, defining a leader angle and a follower angle, respectively;
• a sensor disposed on the follower and in communication with the controller for sensing a current position, a current speed, and a current yaw rate of the leader relative to the first coordinate frame of the follower;
• wherein the controller is programmed to estimate a predicted position of the leader based on the current position, the current speed and the current yaw rate of the leader to define a predicted heading line of the leader;
• wherein the controller is programmed to determine a trajectory of the follower from the first coordinate frame to a point on the predicted heading line defining a second coordinate frame of the follower, the trajectory being based on a desired distance to the point on the predicted heading line and a desired change in yaw angle of the follower, wherein the desired distance is a distance least traveled from the first coordinate frame to the point on the predicted heading line, and wherein the change in yaw angle of the follower is defined by the first heading line of the leader and the desired distance;
• wherein the controller is programmed to determine a desired speed of the follower along the trajectory based on the desired distance from the first coordinate frame of the follower to the point on the predicted heading line;
• wherein the controller is programmed to determine a desired yaw rate of the follower along the trajectory based on the desired change in yaw angle of the follower;
• and
• an actuator disposed on the follower and in communication with the controller for moving the follower along the trajectory to the second coordinate frame based on the desired speed, the desired distance and the desired yaw rate of the follower.