Fig. 2.

Representative time series of the racket (dashed black) and ball (solid gray) trajectories over five cycles (from k − 2 to k + 2). In the model the ball apex during cycle k, b_apex,k, is evaluated in order to determine the desired racket velocity at the next impact, i.e. ṙ_des,k+1 (black solid line). The height error HE is the signed difference between b_apex and the target height.