Patent GB-895048-A (GB)
Title: Control device for the setting in exact position of a movable member
IPC: G05D3/14
Filed: 1959-08-31
Abstract: 895,048. Automatic position control systems. SOC. GENEVOISE D'INSTRUMENTS DE PHYSIQUE. Aug. 31, 1959 [Sept. 24, 1958], No. 29683/59. Class 38 (4). [Also in Groups XXXVIII and XL (b)] In an automatic control system for positioning a movable member of a machine-tool, a dividing head or a measuring machine, a magnetostriction device, positioning the movable member is energized by an error voltage from a locating device to modify the position of the movable member in dependence on the value of the error voltage. As shown, Fig. 1, a movable member 1 is connected to a slide 2 by a magneto-strictive rod 3 responsive to the magnetic field of a solenoid 8. The movable member is approximately positioned by a lead-screw 5 so that a stroke 12 on a graticule 11, carried by the movable member, is projected on to a screen 15 by a microscope 13. The image of the stroke is swept across the screen by an oscillating prism 14 so that the current through a photo-cell 17, placed behind a slit 16 on the optical axis of the microscope, is reduced during the passage of the image across the slit. The current from the photo-cell 17 triggers an electronic device 18 generating short duration impulses i2 corresponding to the reduction in photo-cell current. The impulses trigger an electronic device 19 producing a rectangular waveform i3 having a flow duration, in one direction or the other, equal to the times between successive current reductions from the photo-cell, representative of the misalignment of the stroke 12 with the optical axis of the microscope 13. The current i3 of rectangular waveform is fed to an integrating circuit E, comprising a capacitor 22 and a resistor 21, so that the direct voltage across the capacitor represents in sign and magnitude the misalignment with the stroke 12 ; the solenoid 8 is connected across the capacitor and is energized to cause a change in the length of the magnetostrictive rod 3 tending to reduce the misalignment. In a modification, Fig. 4, the voltage across the capacitor 22 applies a bias to the grid of a cathode-follower 29 having the solenoid 8 connected as the cathode load. In a further modification, feed-back is applied to the grid of the transformer from the secondary of an impulse transformer having a primary in series with the solenoid 8. In another embodiment, Fig. 6, the apex of a totally reflecting triangular prism 35 is aligned with the optical axis of the microscope 13. Misalignment with the stroke 12 causes either the illumination of a photo-cell 35 or a photo-cell 36 to be reduced causing a bridge 38, having the photo-cells in adjacent arms, to be unbalanced and the resultant voltage through an amplifier 39 changes the energization of the solenoid 8 so as to tend to correct the misalignment. In a further embodiment, Fig. 7, an armature 42 carrying a coil 43 oscillates about a pivot 44. The slide 40 has magnetized or ferro-magnetic zones spaced at equal intervals along the upper face. The relative durations of successive half-cycles of the current signal induced in the coil 43 is representative of the misalignment of a zone with the perpendicular through the pivot. The current signal is shaped in the circuit 18 to control the pulse generator 19 feeding the integrating circuit 21, 22. In a modification, the transducer comprises a balanced inductance detecting alignment with raised lines on a magnetically permeable slide. In a further modification, a plate carrying a series of equallyspaced induction coils is secured to the slide and the movable member carries two pairs of induction coils, each coil having the same pitch as those on the plate but one pair of coils is shifted by half a pitch relative to the other pair of coils. A sinusoidal signal current is derived from the coils on the plate. In a further embodiment, the movable member and slide are connected to plates of a capacitor and the change in capacity with misalignment alters the tuning of a resonant circuit. The magnetostrictive device may comprise a single rod, as shown in Fig. 1, or comprise a rod inside a tube having the opposite magnetostrictive effect, the rod and tube being connected so that the changes in length are additive.