Patent GB-869600-A (GB)
Title: Improvements relating to interpolator devices
Inventor: SPENCER ROLF EDMUND
IPC: G05B19/4105
Filed: 1956-08-04
Abstract: 869,600. Electric copying-machines. ELECTRIC & MUSICAL INDUSTRIES Ltd. July 31, 1957 [Aug. 4, 1956], No. 24085/56. Class 38 (6). [Also in Group XXXVI] An interpolating arrangement comprises means for providing two electrical signals which represent values of one co-ordinate at two spaced primary reference points, means for providing a further electrical signal which represents the value of said co-ordinate at a secondary reference point measured with reference to a particular point of the chord joining said primary reference points and expressed as a ratio of the length of said chord. and quadratic interpolating means responsive to said first two and said further electrical signals for producing one or more output signals which represent, or each of which represents, a value of said co-ordinate at an interpolated point on a quadratic curve defined by said interpolating means and passing through said primary and secondary reference points. Fig. 1 shows a group of primary, secondary, and primary reference points A, B, C of a curve ABC along which parametric interpolation as set forth in Specification 830,462 is required according to a quadratic law for the x and y components of the reference points with regard to time, represented as to A and C by signals from a tape reader and as to B by displacements #X and #Y in appropriate directions from the chordal midpoint, which may be recorded on the tape either directly or as fractions of the span voltages #X, #Y for each group of three reference points for suitable injection into the transformers of the interpolator circuit. The displacements may be expressed as #X=S #X-C #Y #Y=C #X+S #Y where #X, #Y are the respective span voltages between A, C in the appropriate co-ordinate   directions, and S = u/AC, C = v/AC, where v is   the perpendicular distance from point B to chord AC, and u is the chordal distance from B to the midpoint of AC. Values of S and C are recorded on the tape for successive secondary reference points separating corresponding pairs of primary reference points. Fig. 2 shows apparatus for controlling movements of the worktable 1 of a milling-machine in co-ordinates X, Y about the axis 6 of a fixed tool, as origin, wherein corresponding leadscrews 3, 10 are driven by servomotors 2, 9 to traverse the worktable and the sliders of X and Y co-ordinate potentiometers 15, 5 to develop follow-up voltages fed back to control amplifiers 12, 16 controlling the motors in opposition to X, Y control voltages derived from quadratic interpolating devices 13, 17 responsive to signals representing successive discrete values of x and y and of S and C recorded on punched tape 22 in binary decimal code; interpreted sequentially by tape reader 23 in response to synchronizing pulses from programme unit 25 controlled by master shaft 45 of the control mechanism rotated at constant speed by motor 46 determining the variations of the common parameter. The resultant signals are fed to the X stores 27, 28, 29; the Y stores 30, 31, 32; and the S and C stores incorporated within the signal synthesizing units 33, 34; all such stores being conditioned by pulses from unit 25 to receive only the pulses which are to be accommodated, and to respond to new values of the appropriate signals only at instants when not feeding out signals; as described with reference to Fig. 3. X-interpolator 13 comprises two quadratic networks 35, 36 of the kind described in Specification 796,994, each having interconnected transformers whose plural outputs are connected respectively to conjoined semi-circles of contacts traversed by a rotary contact 40 driven by shaft 45 and connected to the input of servo amplifier 12; the networks being operated alternately by switching unit 43 in synchronism with shaft 45, which connects the X-stores 27, 28, 29 cyclically in sequential pairs to the two inputs of 35, 36, whereby a continuous X-signal is derived from rotary contact 40. A similar rotary contact 42 is traversed by shaft 45 over another two conjoined semi-circles of contacts respectively connected tothe outputs of the quadratic networks 37, 38 of the Y-interpolator 17; operative similarly to the X interpolator in conjunction with Y-stores 30, 31, 32 and switching unit 44 synchronized with 43. Each quadratic network 35 and 36; 37 and 38 is supplied respectively with third X and Y signals derived from synthesizing circuits 33, 34 representing [S #X - C #Y] and [C #X+S #Y] to give the #x,#y information representing the displacement of the secondary reference point from the centre of a chord joining two corresponding primary reference points. In Fig. 3, binary codes representing decimal values S and C are respectively transmitted from tape reader 23 to 4-way terminal groups 47, 48 of which the latter are connected correspondingly to three identical independent relay operating units, of the kind described in Specification 796,993 in the first of which the presence of a positive digital pulse on line P, due to a sensing of binary pulse 1 plus the corresponding negative conditioning pulse applied to normally positive terminal 51 opens rectifiers M10, M12 so that relay RLD is energized and contact RLD1 changes over, so that on termination of the pulses RLD holds from the positive D.C. energization of 51 over rectifier M11 and contact RLD1 to negative D.C. Sensing of a subsequent binary pulse " 0 " applies no positive pulse to P1 but the negative pulse on terminal 51 de-energizes relay RLD by closing rectifier M11. The remaining relays RLA, RLB, RLC and associated rectifiers and contacts are so arranged that the coding of a binary digit presented at terminals 48 together with a conditioning pulse at 51 is represented by corresponding states of relays BLA-RLD and their contacts, unique for each binary coded digit, while contacts RLA2, RLA3, RLB2, RLB3, RLB4, RLC2, RLC3, RLD2 are connected in the form of a " decoding tree " to the decade tappings of autotransformer T 1  energized by an A.C. signal representing #X derived as stated below, so that switching in accordance with the binary coding develops a corresponding analogue signal in series with transformers T 3  and T 6 . Relays RLA-RLD control similarly a second decoding contact arrangement shown as block 54 connected to a decade tapped autotransformer T 2  energized by an A.C. signal representing #Y to derive a corresponding analogue signal energizing transformer T 5. Blocks 49, 50 represent relay arrangements similar to that of BLARLD, responsive respectively to conditioning pulses on terminals 52, 53 and to second and third binary digit codings at 48, so that corresponding decoding trees denoted by blocks 49a, 50a, associated with autotransformer T 1  apply a second digit analogue signal in series with the primary of transformer T 3  and the secondary of transformer T 4  having 10 to 1 reduction ratios, and a third digit analogue signal in series with the primary of transformer T 4 . Since the digital signal at input 48 represents C when conditioning signals are applied to 51, 52, 53, the combined analogue signal on lead 58 represents C #X while that on lead 55 of decoding block 54 similarly represents C #Y. Terminals 47 also receive signals from tape reader 23, and block 56 represents 3 sets of relays and decoding trees similar to those described, associated with decade autotransformers T 1 , T 2  and conditioned to be operated in response to the binary coded successive digits of factor S; block 56b representing the decoding trees associated with T 2  but operated by the relays of block 56. Leads 57, 59 of blocks 56, 56b derive analogue signals of S #X and S #Y, respectively, for connection in series with secondary of transformer T 5  and the primary of transformer T 6  in such sense that the output terminals 60, 61 derive analogue signals S #X - C #Y=#x; C #X+S #Y=#y; respectively. Two complete arrangements, as shown in Fig. 3, are utilized alternately as the synthesizing means 33, 34 (Fig. 2). In Fig. 4, showing in detail the structure of interpolators 13, 17 (Fig. 2), there are provided stores 27, 28, 29 for successive primary values of X and 30, 31, 32 for successive primary values of Y; each accommodating the coded equivalents of five decimal characters with respective inputs 63, 64; each store having a group of 5 conditioning input terminals corresponding to the decimal characters, denoted by 65, 66, 67, 68, 69, 70 receiving signals sequentially from the programme unit (Fig. 5), and being generally similar to those for successive values of S, C (Fig. 3). Three successive x values are stored in 27, 28, 29 which are coupled to bus-bars 71, 72, 73 connected to successive contacts as shown on the banks of uniselectors 74, 75 whose rotary contacts 74a, 74b are operated by stepping unit 76 and 75a, 75b by stepping unit 77 in response to alternate signals from commutator switch 78 driven by shaft 45. Contacts 74a, 74b energize the ends of linearly-tapped transformer T 7  and contacts 75a, 75b energize those of similar transformer T 8  ; the intermediate taps of each being connected in series with the respective windings of two similar separate transformers 79, 80, the turns ratios of whose windings with regard to the control winding of each range are quadratically related to the order of each winding referred to the centre, as set forth in Specification 796,994. The latter windings are connected to opposed semi-circular banks of contacts 39a, 39b making up circle 39 scanned by rotary make-before-break contact 40 driven by shaft 45, while windings 79 are coupled to transformer winding 81 energized by S #X - C #Y signals from synthesizing unit 33, and windings 80 are coupled to a transformer winding 82 energized by S #X-C #Y signals from unit 34. A similarly operative arrangement of switching uniselectors 87, 88 and y interpolation transformers 37, 38 co-operates in similar manner with juxtaposed semi-circul