Patent GB-864050-A (GB)
Title: Machine-tool or measuring machine equipped with a device causing the automatic stopping of at least one of its movable members in predetermined positions
IPC: G05B19/39
Filed: 1957-09-06
Abstract: 864,050. Photo-electric machine-tool control. SOC. GENEVOISE D' INSTRUMENTS DE PHYSIQUE. Sept. 6, 1957 [Feb. 11, 1957; Aug. 26, 1957], No. 28220/57. Class 40(3) [Also in Groups XIX and XXII] A machine tool or length measuring device includes two recording devices, one of which records the course position to which a mobile member of the machine is adjusted and the other of which records the required further adjustment, which is set up by means of a micrometer movable relative to a ruler mounted on the mobile member, which is necessary to bring the mobile member to the exact required position; means to repeat the recorded position of the mobile member for subsequent machining operations comprising, means controlled by the recording devices to move the micrometer to the position of exact adjustment originally set up thereon and to bring the mobile member, first at high speed and then at reduced speed into the position of course adjustment as originally set up, and means for causing further displacement of the mobile member under control of a photoelectric reading device sensitive to the relative positions of the micrometer and ruler, the photo-electric reading device causing the displacement of the mobile member to cease when it is in the exact required position. In performing a series of machining operations upon a first workpiece of a number of similar workpieces in a jig boring machine, an electric motor El is operated prior to each separate machining operation to move the work-table 1 into a position of coarse adjustment just short of the required exact position. An optical system projects on to a screen 20 on the machine frame 4 an image of a graduation mark on a scale 13 carried by the worktable. A pointer 21 carried by a rack 22 is manually displaced along the screen 20 by means of a vernier knob t by an amount corresponding to the fraction of a division of the scale 13 corresponding to the exact position required for the work-table. A handwheel 29 is then operated to further displace the table 1 until the graduation mark corresponding to the number of whole units of the scale 13 in the required setting is aligned with the pointer 21, the work-table 1 then being in the required exact position. The movements of the table 1 and of the knob t are transmitted by racks 44, 45 respectively, to an electric angle transmitter ET and an electric angle transmitter-receiver Et the outputs of which are delivered, respectively, to recording devices M, m. The recording device M comprises a shaft 49 carrying notched discs CM1, CM2..., co-operating with fingers FM1, FM2..., wherein the movement necessary to position the worktable 1 for each machining operation is recorded in terms of an angular displacement of a selected one of the discs CM1, CM2..., with respect to the shaft 49. Similarly the movement of the knob t to set up the required fraction of the scale 13 is recorded in terms of an angular displacement with respect to a shaft 80 of a selected one of notched discs Cm1, Cm2..., which cooperate with fingers Fml, Fm2... The displacements of the worktable 1 and pointer 21 necessary to bring the first workpiece into the various positions for the other several machining operations are similarly each recorded in terms of an angular displacement of a corresponding notched disc carried by the shafts 49, 80..To repeat the same machining operations on subsequent workpieces, selector switches SM, SM1, SM2, Sm, are set to cause a selected one finger of the series FM1, FM2, ... and one finger of a series Fml, Fm2, .. to engage the periphery of the corresponding notched disc for the particular operation to be performed. A motor Am is then started to rotate the shaft 80 of the recording device m. An electric angle transmitter-receiver Rm in the recording device drives an electric angle transmitter-receiver Et which in turn drives a rack 45 to move the pointer 21 over the scale 20. The selected finger Fm1, Fm2, .. , moves into the notch 81 in the corresponding disc and operates electric controls to switch off the motor Am so that the pointer 21 is adjusted, in accordance with the angular position of the corresponding disc Fml, Fm2,..., on the shaft 80, to the position it occupied for the same machining operation on the first workpiece. The motor El is then started to move the table 1 towards the required position. The transmitter ET is again driven by the table and this in turn rotates the recording device M. As the table approaches its required position the selected finger FM1, FM2, .., moves into a shallow portion 109 of the notch 48 in the corresponding disc and operates electric contacts which switch off the motor E1 and switch on a motor E2 which continues to move the table at a reduced speed. The finger FM1, FM2, .., then enters the deeper part of the notch 48 to operate electric contacts which bring into operation a photo-electric control device for automatically stopping the table in its exact position. The photo-electric control device comprises a photocell 47 which receives an image of that mark of the scale 13 which is also projected upon the screen 20. The image directed on to the photocell 47 is caused to oscillate across a slit 101 by means of a vibrating mirror 99, the arrangement being such that when the table 1 is in its exact position (when the pointer 21 is in alignment with the image of the mark 13 on the screen 20,) the oscillation of the image directed on to the photocell is symmetrical with respect to the slit 101, and equally spaced pulses are produced by the photocell. When the table 1 is not in its exact position, unequally spaced pulses are produced by the photocell 47, the degree of inequality reducing as the table 1 moves towards its exact position. At a predetermined low condition of unequal spacing of pulses, a relay RV is actuated to operate a gear box V to cause a very large reduction in the speed of travel of the table 1, and when the pulses become equally spaced a relay RE2 is actuated which switches off the motor E2, thereby the table is stopped in its exact position. Specification 686,274 is referred to.