Rotation estimation device, rotation estimation method, recording medium stored with rotation estimation program, trajectory prediction device, trajectory prediction method, recording medium stored with trajectory prediction program, and ball-returning robot

A trajectory prediction method, comprising:

• employing a rotation estimation method to acquire state information including a measured position and a measured velocity of an incoming ball and to compute an estimated rotational velocity of the ball, the rotation estimation method comprising:
• solving an aerodynamic model based on the measured position and the measured velocity of the ball at a first time point and based on a provisional rotational velocity so as to perform processing to find a predicted position and a predicted velocity of the ball at a second time point different from the first time point for a plurality of the provisional rotational velocities, and so as to compute, as the estimated rotational velocity, either the provisional rotational velocity minimizing a difference between the predicted position at the second time point and the measured position at the second time point or a predicted rotational velocity at the second time point corresponding to the provisional rotational velocity minimizing the difference,
• wherein the estimated rotational velocity is output to a trajectory prediction section of a trajectory prediction device, and
• wherein (i) if a number of acquisitions of measured positions and measured velocities is a predetermined threshold value or greater, the measured positions and the measured velocities of the acquired time series are corrected by using a quadratic function that approximates the measured positions and the measured velocities of the acquired time series, and
• (ii) if a number of acquisitions of measured positions and measured velocities is below the predetermined threshold value, the measured positions and the measured velocities of the acquired time series are corrected by using a linear function that approximates the measured positions and the measured velocities of the acquired time series;
• and
• solving an aerodynamic model based on the measured position, the measured velocity, and the estimated rotational velocity at a given time point so as to predict a trajectory of the ball from the given time point onward, wherein the trajectory of the ball is output to a control device of a ball-returning robot.

A non-transitory recording medium storing a trajectory prediction program that is executable by a computer to perform processing, the processing comprising:

• executing a rotation estimation program so as to acquire state information including a measured position and a measured velocity of an incoming ball and to compute an estimated rotational velocity of the ball, execution of the rotation estimation program comprising:
• solving an aerodynamic model based on the measured position and the measured velocity of the ball at a first time point and based on a provisional rotational velocity so as to perform processing to find a predicted position and a predicted velocity of the ball at a second time point different from the first time point for a plurality of the provisional rotational velocities, and so as to compute, as the estimated rotational velocity, either the provisional rotational velocity minimizing a difference between the predicted position at the second time point and the measured position at the second time point or a predicted rotational velocity at the second time point corresponding to the provisional rotational velocity minimizing the difference,
• wherein the estimated rotational velocity is output to a trajectory prediction section of a trajectory prediction device, and
• wherein (i) if a number of acquisitions of measured positions and measured velocities is a predetermined threshold value or greater, the measured positions and the measured velocities of the acquired time series are corrected by using a quadratic function that approximates the measured positions and the measured velocities of the acquired time series, and
• (ii) if a number of acquisitions of measured positions and measured velocities is below the predetermined threshold value, the measured positions and the measured velocities of the acquired time series are corrected by using a linear function that approximates the measured positions and the measured velocities of the acquired time series;
• and
• solving an aerodynamic model based on the measured position, the measured velocity, and the estimated rotational velocity at a given time point so as to predict a trajectory of the ball from the given time point onward, wherein the trajectory of the ball is output to a control device of a ball-returning robot.