The collagens constitute an important population of proteins providing the structural support in vertebrate tissues. A collagen is mainly based on a series of tripeptides of the type GX 1 X 2 (G = Glycine, X 1 and X 2 being any residues). The nine amino acids occurring with significant frequencies in the X 1 and X 2 residue sites and G form the reduced protein alphabetQ = {A,D,E,G,K,L,P,Q,R,S} (A = Alanine, D = Aspartic acid, E = Glutamic acid, K = Lysine, L = Leucine, P = Proline, Q = Glutamine, R = Arginine, S = Serine). Surprisingly, the method based on the autocorrelation functionw (X) i w analysing the probability that an amino acid w in Q occurs any i residues X after an amino acid w in Q (calledi -motif w(X) i w ), identifies six types of modulo 3 periodicities in collagens: three basic types 0, 1 and 2 modulo 3 and three combined types 0,1, 0,2 and 1,2 modulo 3. Furthermore, the classification of these 100 i-motifs according to the types of periodicities shows several strong relations between four sub-sets of Q {G}, {A,D,P,S}, {E,L} and {K,Q,R}. Then, these relations allow the construction of a simple automaton for the generation of model collagen sequences. Indeed, this automaton can simulate the six types of periodicities and it retrieves the types of periodicities for almost all i-motifs. Finally, the autocorrelation function based on the sub-set {K,Q,R} identifies segments of 18 amino acids in collagens which may correspond to the exons (segments of genes of 54 nucleotides) coding for those collagens.