In Southey’s Common-Place Book: Original Memoranda, Etc. (London 1876) we find this all-too-brief mention of a spanking machine:
“Pocock, the schoolmaster, by S. Michael’s churchyard, has a machine to punish the boys, which they call the royal patent self-acting ferule.”
Sadly, no image of this machine seems to have survived. One wonders: would a careful and tedious search of ancient British patent records turn up an engineering drawing?