IMPROVEMENTS IN OR RELATING TO PHOTOELECTRIC DEVICES FOR THE AUTOMATIC POSITIONING OF CARRIAGES OR TURNTABLES OF MACHINE TOOLS

1,201,487. Digital positioning apparatus. FEINMESS DRESDEN VEB. 4 Oct., 1967, No. 45128/67. Addition to 1,175,992. Heading G4H. [Also in Division G1] In the apparatus of the parent Specification, for stopping a machine tool carriage or turntable at positions determined by photoelectrically sensed marks, each mark carrier is provided with a coded indication of its identity which is sensed and compared with a command signal. Coincidence between the sensed and command signals initiates the slowing down of the carriage or turntable. The code may be in the form of cams sensed by feelers, electrically conductive or magnetic marks sensed by suitable pick-ups or reflective and non-reflective areas sensed by photo-diodes. The code is four or five digit binary. The marks on the mark carrier are sensed by three photo diodes so staggered that their output pulses after differentiation give pulses which occur a distance a/2 on either side of the rest position of the carriage or table, the distance a/2 being equal to the distance travelled by the carriage or table in stopping from its slowest speed.