Patent GB-869013-A (GB)
Title: Method and apparatus for numerical control of machine tools
IPC: G05B19/4103
Filed: 1957-05-31
Abstract: 869,013. Electric copying machines. GIDDINGS & LEWIS MACHINE TOOL CO. May 31, 1957 [June 5, 1956], No. 4515/59. Divided out of 869,012. Class 38 (6). [Also in Group XXII] A planer type skin milling machine, Fig. 1 (not shown) (see Group XXII) having five possible movement axes is controlled by phasemodulated pulse signals recorded on a multichannel magnetic tape. The magnetic tape is automatically recorded by a director computing system in accordance with distance, direction and time information supplied on a manuallyprepared binary coded punched paper tape. Provision is also made for additional codes to effect acceleration limiting, axis selection and a large number of on/off switching functions. Punched tape preparation.-Tool movement is divided into a series of increments, depending upon the accuracy of finish required. The corresponding distance to be moved along each axis to effect one increment is computed and, in decimal form is typed axis by axis in sequence into a paper tape punching machine, Figs. 2, 7, 8, 9 (not shown) where each decimal number is recorded as a six-digit binary code group, together with code groups defining a selected one out of nine possible machining time periods, the direction of movement along each axis, and if required, a choice of special codes for acceleration limiting as in Specification 869,012 and for stopping and starting the system. These latter codes are prefixed " X " and are discussed in Specification 869,014. The instructions for each axis follow each other in series. Punched tape translation.-The punched tape is read at 120 by finger-operated contacts, Figs. 4, 5, 10 (not shown) which control a bank of relays 121 through a decoding diode matrix. There is one relay for each decimal number 0 to 9, and eight auxiliary relays for directional and special codes. These relays in turn control four output lines 122, Fig. 11 (not shown), through a further diode matrix so as to represent the decimal numbers (i.e. distance and time), the direction of movement, and certain other codes (excluding the " X " codes), in a four-place binary code in which the four places represent respectively the decimal numbers 5, 2, 1, 1. For this purpose, the direction of motion and other codes are allocated arbitrary decimal numbers. The " X " codes, are, by the " X " relay separately switched as in Specification 869,014. Magnetic store.-The four code lines 5, 2, 1A, 1B are connected to a magnetic storage system 125. This provides, Figs. 12A, 12B, 12C (not shown), each of the four code lines with a sequence of six magnetic core shift registers (one for each of the five axis distance signals and one for the time information). The tape reader 120 also supplies a series of shift pulses so that the information in one " block," i.e. the time information and the five distances recorded in sequence, are advanced into the registers. The original decimal information; (prior to the tape punching, re-coding &c.) uses a fixed number of digits for each number, with zeros used as fillers where necessary. Each of the registers has the appropriate number of magnetic cores so that a given number of shift pulses transfer the whole information into the appropriate places in the register. Provision is made to omit certain registers if three axis instead of five axis operation is required as in Specification 869,014. When filled, each of the four lines of shift registers dumps its contents into a corresponding magnetic core storage register so that the shift registers become available for receiving the next block of punched tape information. The four lines of storage registers are mainly duplicated so that " distance " information can be switched from one of the pair to the other each time the storage register is interrogated. The direction, time and acceleration limiting codes are not, however, required repeatedly and so their parts of the storage registers are not duplicated. The digits in the registers are stored in decimal rank, i.e. a programmed distance of 100 inches along some axis would energize the last core along the " 1B " line (the 1A line is the auxiliary line for numbers like 4, i.e. 2+1A+1B) in the part of register appropriate to the axis in question. A distance of 10 inches would energize the next core along, and so on down to 0.001 inch. Similarly distances of 200 inches down to 0.002 inch are stored in sequence along the cores of the " 2 " line. Dimensions outside the capability of the machine are obviously omitted, so that for each of the five axes, twenty-three cores store the relevant distance information. Corresponding cores for each axis are connected in parallel to the appropriate one of twenty-three outputs of a complex frequency-divider chain 129 (see below). The nine time codes selectively control nine gates 126 which connect a 16 kc/s. command clock 128 to nine alternative input points along this frequency-divider chain 129, Figs. 14A, 14B, 14C (not shown). If for example the longest machining time, 200 seconds, has been programmed, the complete divider chain will be in operation and will divide by 3.2 x 10<SP>6</SP> so that a final transfer pulse will emerge on line 130 after 200 seconds to initiate the reading of the next block of instructions. The alternative input points provide progressively less division down to a ¢-second control period. The twenty-three output lines are provided at intermediate points along the chain such that if any one output pulse represents 0.000125 inch of movement, then the numbers of pulses appearing at each of the twenty-three output lines during a selected time period will represent 200 inches, 100 inches, 50 inches, 20 inches, 10 inches, 10 inches &c. following in decimal rank the 5-2-1-1 weighting down to 0.0005 inch. If a short time period is selected then, of course, the large distance outputs are inoperative. These twenty-three output lines are connected to interrogating coils on the twenty-three corresponding magnetic cores for each axis in the store, i.e. the train of pulses from the 200-inch output line interrogates each of the five 200-inch stores &c. If a particular core contains a digit then the appropriate pulse train is passed to the output circuit 131 where all the outputs for a particular axis are added. (Due to delay lines in the frequency divider, none of the trains of pulses coincide in time.) Hence during the selected time period five trains of incremental pulses are produced, one for each axis, the numbers of pulses in each train being proportional to the distance to be moved. Phase modulator and magnetic tape recorder.- The incremental (command) pulse trains control the phase modulation of master pulse trains in a decoder 132, as follows. Only one axis will be described as all five are identical. Master pulses from a clock 134, Figs. 22A, 22B (not shown), are applied together with the command pulses to a gate so that one master pulse is passed for each command pulse. These selected pulses are then delayed by half a master pulse period to space them from other master pulses used subsequently. The delayed pulses are then either added to a train of master pulsesif movement in one direction is required; or used to control a gate so that corresponding pulses are omitted from the train of master pulses-if movement in the opposite direction is required. The required action is determined by gates controlled, Fig. 25 (not shown); by the direction codes in the magnetic store 125. The modulated master pulse train is then frequencydivided by 800 so that each pulse added or subtracted is the equivalent of a phase-change of 360/800 degrees, and this divided train is recorded at 98 on one of six magnetic tracks, Fig. 24 (not shown). An unmodulated reference train is also recorded. Magnetic tape play-back and machine tool servo-system.-The tape is played back on a multi-channel machine, Fig. 40 (not shown). The output of the reference channel synchronizes a local oscillator, the output of which is split into 3 phases to energize the stators of 3-phase selsyns, the rotors of which are driven by the five-controlled tool and bed-plate movements. The phase of the rotor, voltage is compared with the phase of the appropriate recorded signal, and a servo-motor is energized to move the tool &c. and rotor to eliminate the error. Specification 869,015 also is referred to.