Patent GB-958004-A (GB)
Title: Measuring machine or precision machine tool
IPC: G01B5/00
Filed: 1962-09-18
Abstract: 958,004. Machine tool details. SOC. GENEVOISE D'INSTRUMENTS DE PHYSIQUE. Sept. 18, 1962 [Sept. 30, 1961], No. 35423/62. Headings B3B and B3C. [Also in Division G1] A measuring machine or a machine tool, comprising a movable tool, feeler or workpiece holder 8, and a device 12 for linear measurement of the positions occupied by said movable holder along its path, said device including a linear reference element 11 serving as a standard, at least two temperature detectors 21, 23, 24 to provide information concerning the temperature of a tool, feeler or workpiece and of the standard, a differential device 48-50, means 31 to adjust said differential device in accordance with the information provided by said temperature detectors and the coefficients of thermal expansion of said tool, feeler or workpiece and said standard, said differential device including a member 54 adapted to be displaced in accordance with said adjustments, the amount of displacement being a function of the temperatures and coefficients of expansion of both the tool, feeler or workpiece and standard, and indicating means 14 controlled by displacement of said member of the differential device to indicate the real values of the movements of said movable holder, reduced to a reference temperature even when the temperature of the tool, feeler or workpiece and of the standard differ therefrom. In a jig-boring machine, the drill 5 is carried on a slide 4 adjustable on a vertically movable beam 2. The work-table 7 is traversed by a screw 11 rotated by a handwheel 12 carrying graduations 13. The graduations co-operate with an index mark 14 on a drum adjusted angularly as the slide moves by a cam 20 and levers 19, 17, 15a to compensate for lead-screw irregularities. The temperature of the workpiece 8 is measured by a thermo-couple 21 and indicated on a dial 22. The mean temperature of the screw 11 which represents the standard, is measured by thermocouples 23, 24 and is indicated on a dial 25. The table 7 carries two slides 27, 28 adjustable by pinions 31 rotated by graduated knobs and set according to the readings on the dials 22, 25. The slide 27 carries a member 41 which is adjusted angularly by a graduated knob according to the coefficient of expansion of the work. A surface 47 on the slide 28 represents the coefficient of expansion of the screw 11. The upper surface of the member 41 and the surface 47 are engaged by rods 48, 49 which are toothed to engage a toothed member 54 mounted on an elongated bar 56 pivoted at 57 and carrying the cam 20. In operation, the differential movement of the rods 48, 49 and the member 54 cause a setting of the bar 56 to modify the position of the index mark 14. Slight inaccuracies due to longitudinal movement of the bar 56 may be compensated by mounting the cam 20 on a parallelogram linkage. In a modification, graduations on a scale attached to the slide to measure its movement are projected by way of a mirror 66, Fig. 14, on to a screen 67 carrying an index mark 68. Inaccuracies in the scale are compensated by a bar 70 which is mounted and adjusted by means 48, 49 as previously described. The bar 70 is contacted by a feeler 72 which controls tilting movements of the mirror. In an automatic device, the angular adjustment of the bar 75, Fig. 16, carrying the cam 74 (corresponding to the bar 56 and the cam 20 of the first embodiment), is effected by a motor 77 driving worm gear 79, a shaft 81 and a sector gear 83. A transformer 86 has a primary winding 88 fed by the two thermo-couples 89, 90 detecting the temperature of the lead-screw 11. A thermo-couple 94 detects the temperature of the work and feeds the primary winding 93 of a transformer 87. (Alternatively, thermistors could be used.) Switches 92, 96 are adjusted according to the coefficients of thermal expansion of the screw and the work. A potentiometer 98 is adjusted by the shaft 81 to control a generator 84. One phase of the motor 77 is thus controlled by the generator 84 and the other by the Wheatstone bridge circuit 85 through an amplifier 97. In a further modification, the cam 74 is replaced by a rotary cam 102, Fig. 17, and movement of the table is represented by a slider 105 varying the ratio of a transformer 103. In a measuring machine, the tool is replaced by a feeler and the temperature of the room may be measured instead of that of the screw since no heat is generated as in a machining operation.