Patent GB-809649-A (GB)
Title: Improvements in or relating to positioning devices for machine tools, microscopes, measuring instruments and the like
IPC: G02B21/24
Filed: 1954-03-25
Abstract: 809,649. Boring &c. machine details. NEWELL ENGINEERING CO. Ltd., and TEMPLE, W. K. June 27, 1955 [March 25, 1954], No. 26501/53. Class 83 (3). In a machine tool, microscope, measuring instrument, &c., means for linearly or rotationally positioning a member 14 relatively to the fixed bed of the machine &c. comprises a magnetically graduated element 11 and a pick-up element 17, one of the elements being on the member 14 and the other on the bed, an electronic counter 19 to count the electrical impulses from the pick-up, and thus the units of movement of the member 14, and means operated by the counter at a given count to stop movement of the member 14. As illustrated in Fig. 1, impulses are obtained from a tape 11, of magnetic material or coated with magnetic material, having a series of magnetic modulations impressed uponit in a recording machine. The modulations, at intervals of 0.001 or 0.0005 inch on the tape, which is made slightly short and stretched to the standard length by a tensioning device 13, are fed to the counter 19, through an amplifying control-box 23, by the pick-up 17 upon relative movement between the pick-up and tape. Pick-ups may be mounted on the table 14 and cross-slide (not shown) of a jig boring machine and moved with the table &c. by rotation of a lead screw 15 which is driven by an electric motor 16, through a clutch and gear-box 22, allowing the movement to be slowed before the stopping-point is reached. This point is set by a series of selector switches 21 which correspond with Dekatron counting- tubes 20 in the counter, and when the tubes have counted up to the dimensions set by the switches, a thyratron tube is operated and stops the leadscrew drive. An initial impulse from the counter to the gear-box and clutch 22 through a relay amplifier 27, slows the drive, and a second impulse disengages the clutch, applies a brake in the reduction gear and stops the motor by a relay 28. The table may be positioned with an accuracy of 0.0001 inch by using a tape with modulations at intervals of 0.0005 and five pick-ups 17, 27, 37, 47, 57, Fig. 3, spaced at intervals of, say, 2 inches plus or minus 0.0001, the counter thus receiving an impulse from the pick-ups at movement intervals of 0.0001 inch. In this case the speed of movement should be reduced, before stopping, to a maximum of approximately 2 mils. per second. The pick-ups have circular magnetic cores with slits 35 close to the tape. Start, emergency stop and reverse switches 24, 54, 44 may be provided on the counter. The Specification refers to two publications for a suitable type of counter and a pick-up having a D.C. response which enables the counter to be counted back by returning the table. It is also stated that a cam shaft may set the switches 21 automatically, and enable the table and cross-slide to be moved automatically into a series of positions. The Provisional Specification refers also to the generation of the electric impulses by rotation of a lead screw which closes contacts repeatedly or operates mirrors illuminating a photo-sensitive cell. Alternatively, a linear scale may be scanned electronically, or two or more recordings may be made on the same tape, or several, e.g. five, tapes may be used. The part to be positioned may be moved manually, and the operator given an indication as to when to terminate the movement. Magnetic wire may also be used.