Patent GB-966878-A (GB)
Title: Method and apparatus for automatically adjusting a machine part
IPC: G05B19/39
Filed: 1961-04-07
Abstract: 966,878. Machine-tool control systems. DIXI S.A. April 7, 1961 [April 12, 1960], No. 12540/61. Heading G4H. [Also in Division G3] The input to the system is from punched cards or selector switches 45, Fig. 1 and the machine element is driven to a commanded position by a first, coarse-positioning, operation using the servo-loops shown in Fig. 1, and by a second, fine-positioning, operation as follows: A magnified image of a scale carried by the machine element and having lines 65, Fig. 3 spaced 1 mm apart is projected on to a picture tube together with an image of a reference scale having a line spacing corresponding to 1/ 100  mm. The output of the picture tube resulting from one scan of the images includes a train of pulses from the reference scale, and the repetition frequency of these pulses is multiplied by ten before the pulses are applied to a gate which is closed by a large pulse resulting from a line 65 being scanned. The number of pulses passed by the gate thus represents the fine position of the machine element in units of 1/ 1,000  mm, this number being registered in a counter and compared with the fine digits of the command signal to provide an error signal for controlling the final adjustment of the machine element. The fine positioning is performed in three stages. The counter has three decades corresponding to 1/ 10, 1/ 100  and 1/ 1000  mm. The count registered by the 1/ 10  decade is compared with the corresponding command digit, and a "forward" or "back" control signal produced. Measuring and adjusting operations are performed in alternate half cycles of the A.C. mains so that the counter is frequently brought up-to-date with the machine element position. As soon as the 1/ 10  mm error is zero, control is transferred to the 1/ 100  mm decade, and in turn to the 1/ 1000  mm decade. As shown in Fig. 3, the reference scale has two portions 67, 68 each corresponding to different ranges of 0. 5 mm. Each portion 67, 68 is extended by 0. 3 mm at each end so as to provide 300 pulses for the counter when a line 65 lies on the zero of the scale portion. Only outputs 3-8 of the 1/ 10  mm decade are utilized, and the 1/ 10  mm command digit determines which of portion 67, 68 is scanned. Coarse-positioning operation: The wipers of commutators 35, Fig. 1 are automatically positioned on the selected segments 0-IX. In addition, a commutator 33 driven by the 1/ 10  mm selector energizes one of segments 37 of the commutator 35 in the mm channel over an associated lead 38, 39 or 40, and cam 47 rotates the segments 36 of this commutator over linkage 50 so that the final position taken up by brush 34 corresponds to the cam of the mm and 1/ 10  mm commands. Brush 34 of commutator 35 in the cm channel is positioned in accordance with the sum of all three commands by means of segments 37 and leads 38-40 connected to commutator 33 of the mm channel. The position of the machine element 1 transmitted through gears 10, 11 is compared with the commanded position by commutators 12. Commutator 12 of the cm channel energizes relay 16 or 17 controlling hydraulic valve 3 until the gap between segments 14, 15 reaches brush 29, whereupon control is transferred to the mm channel and thence to the fine-positioning apparatus as the commanded position is approached.