Patent GB-568800-A (GB)
Title: Improvements in or relating to apparatus for measuring or indicating the roughnessesor undulations of a surface
IPC: G01B7/34
Filed: 1943-05-13
Abstract: 568,800. Telephone instruments. KAPELLA, Ltd., and REASON, R. E. May 13, 1943, No. 7665. [Class 40 (iv)] [Also in Group XIX] In apparatus for gauging surface roughness of the type in which movement of a feeler member normal to the test-surface varies an air-gap, a magnetic or electric coupling is varied to control a measuring or indicating strument. In Fig. 1, a bracket A<2> is adjusted vertically by rack - and - pinion until the foot C<1> of an arm C pivoted at A <5> to the bracket contacts the testpiece B with the arm C substantially horizontal. A rod E<6> is traversed through guides C<4> at one of a number of speeds in the manner described in Specification 539,273, whereby a feeler E is drawn over the testpiece. The feeler is secured to a U-shaped magnetic core E<1> pivoted by leaf springs E<4>, E <5> to the rod E<6>. Vertical movement of the feeler E varies the air gaps between the taps of the core E<1> and a polished reference surface D built up of a stock of laminations of magnetic material and secured to the arm C. To compensate for endeffect and errors in permeability, one of the laminations may have an appropriately deformed edge D<3> (Figs. 2, 3, not shown). Coils E<7>, E<8> may be carried by the core E<1> or by the end of the rod E<6>, and are incorporated in an amplifying circuit. In Fig. 4, the core is divided into two parts F<1>, F<2> carried by the end of the rod E<6>, and the feeler, mounted on leaf springs, carries a light armature F, whereby four air gaps F<5>, F<6>, E<9>, E<10> are formed, the total reluctance of the electric circuit varying with movement of the feeler. In Fig. 5 (not shown), the feeler moves a plate forming with the reference surface a condenser, the capacity of which is accordingly varied. In Fig. 6, the feeler carries two condenser plates H, H<1> co-operating with opposite faces D<2>, D<3> of the reference plate D. One air gap increases as the other decreases and the condensers so formed are connected up differentially. For measuring the roughness of a small bore, the feeler E, Fig. 8, projects from the casing C longitudinally on a lever J pivoted at J<1> and carrying a condenser plate J<3>. The traversing tube E<6> carries a condenser plate J<4> co-operating with the other surface of the plate D, whereby irregularities in the traversing movement causing movement of the plate J<4> will be cancelled out by a correcting movement of the plate J<3>. In this Figure, the traversing movement is effected by cam, lever and.spring mechanism K in the bracket A<2>, the pivot A being replaced by two spaced pivot pins K<5>. The condenser arrangement of Fig. 8 may have a magnetic equivalent (Fig. 9, not shown). The roughness of a surface of revolution is measured by the apparatus shown in Fig. 10. The test-piece is mounted on a support L<2> adjusted to a central position by two screws L<3> and oppositely arranged springs L<4> on a vertical rotatable spindle L. The feeler O' is adjustable along an arm O<3> carried on leaf springs by an arm O<1> pivoted to the base. Movement of the feeler alters the air gaps between two cores O<5>, O<6> and a reference member M of magnetic material with a smooth cylindrical surface carried by the spindle L. A corresponding condenser arrangement is described (Fig. 12, not shown). Circuits of the type described in Specifications 539,271, 539,272, 539,274, [Group XXXVIII], may be employed for converting the capacitances or reluctances into indications of the surface roughness. As an alternative to magnetic or electrostatic coupling, the feeler may carry a coil to induce eddy currents in member D, Fig. 15, the eddy current losses induced by the movement of the feeler being applied through a resonant circuit to the measuring instrument T<1>. Specification 552,675 also is referred to.