Patent GB-595204-A (GB)
Title: Improvements in or relating to copying machines
IPC: B24B17/04
Filed: 1945-03-23
Abstract: 595,204. Copying by milling. KAPELLA, Ltd., and COOKE, E. A. March 23, 1945, No. 7354. [Class 83 (iii)] [Also in Groups XXIII, XXXVIII and XL] Milling turbine blades.-In a copying machine, wherein a tracer and cutter co-operate respectively with a rotary pattern and work piece, the tracer comprises a pivoted straight edge or beam bearing tangentially against the pattern and controlling mechanism for moving the work relatively to the cutter in accordance with pivoting and translational movements of the beam caused by the pressure of the pattern thereon, One form of machine comprises a base A, Fig. 1, having a transversely movable slide B carrying a longitudinally movable slide C on which are mounted rotary work and pattern tables F<1>, O<1> respectively. The slides are mounted on roller guides B<1>, C<1> as described in Specifications 570,189 and 572,144 and are adjusted by hand wheels B<3>, C<3> or by pairs of reversely moving electric motors D, D<1>, and E, E<1>. The work and pattern tables are connected by a flexible band H<4> or gearing and are rotatable synchronously by a worm-gear H<2> and handle H<1> on the slide C. The cutter, such as a grinding wheel K, is driven by an electric motor K<2> and is adjusted by a manuallyoperated shaft K<3> to bring its operative edge into the primary plane P-P of the machine. Photo-electric cell control. The tracer head M is fixed to the base A and is provided with a cruciform member M<1>, Fig. 2, slidable on a guide M2 and carrying the pivoted tracer beam M<8> which is normally maintained parallel to the primary plane P-P by springs M<6>. The member M is biassed towards the front of the machine by a spring M<9> and the beam M<8> carries a mirror or prism N to deflect a beam of light N<6> on to either of two photo-electric cells N<1>, N<2> or on to a separating shield N<5>, the cells &c. being movable with the member M<1>. A flexible band R<1> has one end attached to the member M<1> and the other end connected through a spring R<3> to the machine base and passes over a roller R<2> rotatably mounted by tapes R<4> on the base. A mirror or prism R on the roller R<2> deflects a beam of light S<6> on to one or other of photo-electric cells S<1>, S<2> or a shield S<5> and the outputs from the cells N<1>, N<2>, S<1>, S<2> are passed to thermionic amplifiers 0<1>, O<2>, Fig. 1, and then to the motors E, E<1>, D, D<1>. Operation. The cutter K is adjusted with its operative edge in the plane P-P and the slide C is adjusted by hand-wheels B<3>, C3 so that a pattern V on table G<1> makes contact with the tracer beam M<8> in said plane and in line with the fulcrum of the beam so that the latter will be undeflected. With the cutter rotating in contact with a work-piece W on table F<1>, the tables F<1>, G<1> are rotated.by handle H<1> and movement of the pattern against the beam Me causes the point of contact therewith to pass out of alignment with the fulcrum, thereby oscillating the mirror N and energising one or other of the cells N<1>, N<2> to cause one of the motors E, E to be actuated and move the slide C, together with the tables F<1>, G<1> along the coordinate x. Simultaneously, the member M<1> will be displaced along guide M<2> by the pattern to oscillate mirror R and energize one of cells S<1>, S<2>, thus actuating one of the motors D, D<1> to move slide B and carry the work and pattern away from the cutter and tracer respectively along co-ordinate y. This tends to restore mirrors N, R to normal position parallel to plane P-P, and the movements of slides B, C are stopped unless the operative portion of the pattern continues to displace the mirrors as the tables are rotated by the handle H<1>. Balanced coil control. In a modification, the photo-electric cells are dispensed with and the beam M<8> and roller R<2> carry armatures which are oscillated by the pattern to upset the balance of coils in balanced bridge circuits, e.g. as described in Specifications 541,628, [Group XXXV], and 556,607, [Group XXXVI], the outputs from the bridges being amplified and used to control the motors or the roller R<2> may be dispensed with and its armature mounted directly on member M<1>. In an embodiment of this type of control, applied to a machine as described in Specifications 570,189, the tracer beam M<8>, Fig. 14, is secured to an inclined arm M<6> pivoted by means of spring ligaments on a member M<2> so that it may oscillate about its longitudinal axis M<10>. An armature L is secured to the arm M<6> and cooperates with balanced coils I<1>, I<2>, which control circuits for the x co-ordinate motion of the work and pattern. The member M<2> is pivoted by ligaments M4 to a frame M<5> and carries a button T<6>, Fig. 13, normally pressed against an arm T<4> pivoted on the frame M<5> by ligaments M<3>. An armature T<3> secured to arm T<4> coacts with balanced coils T\ T<2>, which control circuits for the y co-ordinate motion of the work and pattern. Pressure of the pattern on the beam M<8> will thus rock the arm M‹ for giving x co-ordinate motion and will also displace the member M<2> to allow a leaf-spring T<7> to rock arm T<4> to give the y co-ordinate motion. The ligaments M<3> give a yielding overload mounting to the member M<1> and a spring T<8> maintains the members M<1>, M<2> in contact, whilst a spring T<9> holds member M<2> yieldingly against the frame M<5>. The A.C. voltage controlled by the coils I<1>, I<2>, T<1>, T<2> is proportional to the angular or translational displacements of the beam M<8> and after passing through thermionic valve amplifiers is fed to the field circuits of the motors whose power is just sufficient to accelerate the work and pattern slides from rest. The circuit for the amplifiers is described in detail in the Specification. For setting the tracer beam M<8> in the zero position, the pattern is replaced by a plug of known radius concentric with the pattern spindle, the carriage C is displaced by an amount equal to the radius of the plug, and the tracer head M is then adjusted on its support until the contact of the beam with the plug gives a signal from the amplifiers of predetermined strength as read by a meter. The compound slides B, C may be replaced by anti-friction bearing and guiding devices as described in Specification 588,986 and instead of using thermionic amplifiers, the outputs from the photo-electric cells or balanced coils may be applied to the grid circuits of gas-discharge tubes of the type known under the Registered Trade Mark " Thyratron ". Alternatively, the displacements of the beam M<8> may vary the strain and therefore the electrical resistance of a detector of the " wire strain gauge " type, and the outputs from the amplifiers may control electromagnetic couplings of the eddy current type. In another modification the slides B, C, may be operated from electric motors operating differential worm gearing, wherein worms driven by two motors gear with opposite sides of a single worm wheel mounted on the slide, variations in the motor speeds controlled by tracer displacements causing the axis of the worm-wheel, and consequently the slide, to be fed. The worms may be connected to their respective motors through electromagnetic couplings. The pattern and work supports F<1> G<1>, may be rotated by a motor instead of by hand, the gearing from the motor being capable of giving complete rotation or oscillatory motion to the supports, and the movements of the slides B, C may be recorded by a pen or indicator for comparison with a master curve corresponding to the pattern. A microscope mounted on the base A with its axis in the plane P-P may be used for setting the tables and cutter in zero positions. The amplified currents from the cells or coils may be used to control the pressure of fluid in cylinders which effect movement of the tool and work supports in one or both of the x and y directions. The Provisional Specification also refers to Specification 588,963, [Group XXXIV].