Patent GB-807220-A (GB)
Title: Improvements in or relating to control systems for positioning a driven element along a path
IPC: G05B19/37
Filed: 1956-05-18
Abstract: 807,220. Electric correspondence control. FARRAND OPTICAL CO. Inc. May 18, 1956 [Jan. 3, 1956], No. 15601/56. Class 40 (1). A machine, having means M1,. M2, Fig. 19, for driving an element 172 along a path, comprises means D1-D4, Fig. 1, for providing input data in terms of the path, means for translating the data into electrical signals to rotate a shaft 8, Figs. 15 to 18, means R3 for resolving the shaft movements into mutuallyperpendicular linear displacements, means R30, R40 for translating the displacements into other electrical signals and drives 184, 175, operated by the latter signals respectively, for operating the driven element, the speeds of the drives having relative values corresponding to the path. The machine may be a jig-borer or a planar-type milling machine having the tool 172, Fig. 19, rotating about a vertical axis on a compound slide 173, 178, and controlled by the card or tape inputs D1-D4 to cut a continuous contour on a workpiece 185. (Alternatively, the work may be moved or a spherical tool used for three-dimensional work.) The slide 178 is driven along the X axis by the motor M1 rotating the screw 184, thus moving a slider S2 along an " Inductosyn " (Registered Trade Mark) S1. Similarly, the motor M2 drives the slide 173 and moves a slider S4 over an Inductosyn S3. The slope data input D4 consists of angular data on a decimal basis having five groups of digits, the angle being that by which the shaft 8, Figs. 16 and 17, is to be rotated. The input is obtained from a punched card and a feeler brush which applies a potential of 24 volts to an appropriate column to operate a stepping switch. A coarse data element or resolver 37, Fig. 16 (such as is disclosed in Specification 801,517, [Group XXXV], has coils 34, 35 and a rotatable coil 36 which is driven to an angle determined by the sine of the sums of the angles established by the stepping switches which compute the 1 and 10 degree digits. The stepping switches for the 0.1 and 0.01 digits compute the sine and cosine of the sums of the angles and that value and the 1 degree value are computed for supply to quadrature windings 130, 131 of a fine data Inductosyn element 68, such as is disclosed in Specification 801,516, [Group XXXV]. The quadrature coils 34, 35 are selectively brought into circuit to allow for changing signs in cosine and sine values for angles greater than 90‹, 180‹ and 270‹. This computation of trigonometric functions for the sum of the angles called for by the digital information is described more particularly in Specification 807,219. The computation is based on the equation sin (a+b)=sin a cos b+cos+cos a sin b, each multiplication taking place by supplying a primary coil of a transformer with one cosine or sine value. Thus, the Inductosyn coils 130, 131 receive signals proportional to the two products, the voltages in lines 182 and 183 being taken on a similar side of the secondary windings so that a subtraction takes place to give cos (a+b). The error signal in the output circuit of the coarse data element 37 is employed in a servo system wherein the signal is amplified at 123 and supplied to a motor 124 which rotates the shaft 8 until the error is reduced to a small value, at which time a switch 125 brings the output circuit 126 of the fine data element into control so that its error signals determine the final adjustment of the shaft 8. (Such conversion of slope angle information to an angular shaft position is described in Specification 807,218.) The motor 124 drives the differential gear DG1 which also receives a drive from a shaft S6 of a curvature integrator. Similar differential gears DG4, DG2 and DG3 are provided in the output of the curvature motor M4, Fig. 15, and in the controls for the X and Y machine drives, Fig. 18. The output of the curvature motor M4 controls a ball integrator 215, the ball slide 214 of which drives a variable resistor 213, and the motor is controlled by digital information at D3, Fig. 1, which is converted into a voltage analogue through stepping switches. The rate of change of curvature data is set up in four columns on the card D2 and is fed to an octal-to-binary translator which supplies the resulting binary values to the binary gear ratio, Fig. 14, to drive its output shaft S9. The card data is transferred to stepping switches and the decoded information is transferred to holding circuits so releasing the steppers for further data. The shaft speeds are set by operating clutch coils such as 237, driving through differentials such as SG1. Condensers in the circuit provide for quick actuation of the clutches. A coil 313 can be energized to move a shaft S8 axially and engage reversing bevels such as 312, thus providing for negative and positive values of rate of change of curvature. The feed rate input D1 supplies a decimal digital input to an analogue feed rate converter, having a transformer and stepping switches, the voltage of the stepping switches being compared with that of a tachometer 276, Fig. 13, driven by the feed motor M3 and having a reference voltage fed from the input to the primary winding of the transformer. A servo generator 279 drives the motor M3 so that the voltage difference is substantially zero. (For D.C. operation, the transformer is replaced by resistors.) Means are provided to select any origin for the co-ordinates of the cutting path or to correct for tool radius. Thus, manual inputs Z2, Z3, Fig. 18, are connected to the differential gears DG2, DG3 which receive their programme inputs from shafts S11, S12, Fig. 17, connected to disc-ball cylinder X and Y integrators. The integrators integrate their inputs from ball slides 285, 286 with respect to the feed rate FR. The ball slides are connected to means R3 which resolves the instruction from shaft 8 into linear displacements at right angles to each other. The output shaft S13 from the differential gear DG2 is connected to the resolver R30, the quadrature windings of which and of the Inductosyn slider S2 are connected in circuit. The servomotor M1 is controlled by the fine error signal in line 308 which is always active, and medium and coarse error signals from lines 306, 307, all controlled by a switch SW2 similar to the switch 125, Fig. 16. The medium error signal is supplied to line 306 from a resolver R32 which is associated with a resolver R31, the resolvers serving as a synchro transmitter and receiver. The coarse error signal is supplied to line 307 from a transformer secondary winding 327, the primary winding 324 being connected to a slider 323 of a coarse data element 322 and the slider 325 of a receiver potentiometer 326. A reference voltage source 304 energizes windings 329 and 302 and the potentiometers 322, 326. The shaft S13 drives the resolver R31 through gears 330 and a shaft 331 drives the potentiometer 322. The motor shaft or screw 184 drives the resolver R32 through gears 352 and a shaft 332 drives the potentiometer 326. When the X and Y positioning has been accomplished by operating the inputs Z2, Z3 and by closing switches 401, 403, the switches are released and the slope curvature and rate of change of curvature information in shafts S11, S12 take command. The advance from one set of input data to another may be manual or automatic.