t1 = 1; t2 = 2; Umax = 1.95; u[t_] := 0.05 + Umax + Umax Limit[ArcTan[(-t - t1)/x]/\[Pi], x -> 0] + Umax Limit[ArcTan[(t - t2)/x]/\[Pi], x -> 0] Plot[{u[t], 0}, {t, -15, 15}]
