Centralizing maps on the ring of strictly upper triangular matrices

We describe all linear maps \(f:N_r\rightarrow N_r\) satisfying \([f(A),A]\in Z(N_r)\) for every \(A\in N_r\) where \(N_r\) denotes the algebra of \(r\times r\) strictly upper triangular matrices with entries in a field \(F\) with center \(Z(N_r)\).