Patent GB-1300036-A (GB)
Title: Feedrate control system
IPC: G05B19/416
Filed: 1971-04-19
Abstract: 1300036 Numerically controlled machine tools BENDIX CORP 19 April 1971 [30 March 1970] 25169/71 Heading G3N In a numerical control system of a contouring type milling machine wherein the motion of a single output member is controllable along three axis XYZ which may be mutually perpendicular, a feedrate controller 22, Fig.1, computes the sum of the squares of the X, Y, Z components of the resultant motion command pulses i.e. (X<SP>2</SP> + Y<SP>2</SP> + Z<SP>2</SP>) and the sum is compared therein with the square of the desired resultant feedrate (FR)<SP>2</SP> commanded on tape 10. Servo motors 26, 28, 30 produce one increment of motion of their driven members for each pulse received the pulse rate being sufficiently high to ensure smooth continuous motion. On the basis of the above comparison if the controller 14 is not producing pulses at the proper rate to achieve the desired commanded feed rate then a difference value is produced and a pulse generator (94), Fig.2, in the feedrate controller is caused to apply "add" signals to the controller 14 increasing simultaneously the rates of all the command pulse trains output therefrom. When the difference value passes through zero an inhibit signal is produced which blocks output from the "add" pulse generator. This process continues in a see-saw manner so as to maintain an average command pulse rate just sufficient to produce output motion at the resultant vector rate called for by the tape. A manual override of the command feedrate signal FR may be provided. As shown Fig.2, the X Y and Z motion commands on lines 16, 18, 20 are loaded into command registers 50, 52, 54 respectively, of controller 14. Each time an add pulse is received on line 38 from the feedrate controller 22 the contents of all the command registers are simultaneously added by respective adders 62, 64, 66 to respective sum registers 56, 58, 60. Each time an overflow occurs from a sum register an output pulse is fed on its output line 32, 34 or 36 to a respective servo. The command feedrate from the tape on a line 24 is loaded into a feedrate register 70 of controller 22. The contents of register 70 are repeatedly added via an adder 72 to a sum register 74, overflows therefrom on line 76 constituting a pulse train having a rate proportional to the feedrate number magnitude. The add commands for adder 72 are produced by a variable frequency generator 78. The pulses on line 76 are squared in a circuit 82 comprising a pulse/digital converter, Fig. 3, similar to the squaring circuits 84, 86, 88. If the contents of counter 100 are termed "N" each time a pulse is received on line 76 the subtractor 102 performs computation (2N-1) and the integral of the numbers out of subtractor 102 to 92 will have the value N<SP>2</SP>. The command pulses on lines 32, 34, 36 are similarly squared and fed to a summer 90. When the integral of the numbers provided by circuit 82 exceeds that provided by summer 90, a comparator 92 produces a signal causing pulse generator 94 to feed add commands signals on line 38. These add signals increase the rate of command pulses produced by controller 14 until the comparator output is reduced to zero inhibiting the signal to the pulse generator, so terminating the add signals.