Patent GB-926524-A (GB)
Title: Improvements relating to programmed machine tool control systems
Inventor: MYNALL DENNIS JAMES
IPC: G11B20/16
Filed: 1959-10-23
Abstract: 926,524. Programmed control of machine tools. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Oct. 24, 1960 [Oct. 23, 1959], No. 36022/59. Class 38 (6). A programmed control system for controlling a machine tool in at least two directions of movement and employing recorded digital programme data comprises in respect of each of said directions a sequence of binary position numbers, the sequences of numbers relating to the respective direction of movement being interlaced and processed in common equipment before being effective to control the machine tool movement. As described, programme data is recorded on a magnetic tape T, Fig. 2, in the form of successive " packets " P, the data within each packet being in serial binary-coded form, with each successive triplet of binary digits recorded in parallel in three channels A, B, C, to form a " group " a fourth channel D having a parity digit for each successive position in the channels A, B, C, the parity digit being such as to give an even total of binary ones for synchronization positions and an odd total for data positions. Each packet P comprises nine significant blocks of 24 digit groups comprising in order: (1) a one-group 3-digit number ZS for synchronization, (2) a threegroup 9-digit number INS representing an instruction such as stopping the tape, damping the machine, turning on coolant, &c., (3) a fourgroup 11-digit number ZPN representing the Z position, the 12th place being occupied by a sign digit S, (4) a one-group 3-digit number XS for synchronization, (5) a three-group 9-digit number XC representing an X correction factor and its sign digit, (6) a four-group 11-digit X position number XPN and associated sign digit S (7)-(9) Y data similar to the X data (4)-(6). The even parity groups ZS, XS, YS are called start groups. The X and Y correction factors XC, YC are to prevent cutting errors which would otherwise be introduced due to the radius of the cutter. The pulses of each digit group on the tape T are read out in turn into a temporary store TS comprising bi-stable transistor flip-flop circuits tsa-tsd which are connected to a logical circuit GN arranged to provide a clock signal output on a lead pc if the inputs to the circuits tsa-tsd have an odd parity, i.e. are derived from a data group on the tape and to provide an output on one of leads epx, epy, epz in response to a synchronization group XS, YS, ZS respectively. The pulses read from the tape are also applied to an " or " gate Gc which is connected to blocking oscillator BLO (Fig. 4, not shown), the output of which is applied to condition gates Gpc, Gep1-3 which produce the outputs from the logical circuit GN. The output from the blocking oscillator BLO is also connected to read out the data from the flip-flops tsa-tsc over lines ta-tc to a serializer DS in the form of a three-digit magnetic core shift register circuit (Fig. 6, not shown). The pulses pc and epx-epz are applied to a central control circuit CC (Fig. 5, not shown) which provides outputs used as stepping or shift pulses in various shift registers and also provides digit timing pulses and certain reset and transfer signals. The serialized data from DS is applied to a distributer DR (Fig. 6) comprising gates controlled by the control circuit CC to route the serialized data to its correct destination. The nine instruction digits are sent to an instruction staticizer IS, the X, Y and Z positional numbers together with the correction factor sign digits are sent to a combining unit CU and the correction factors are sent to a multiplier M. The multiplier M is as described and claimed in Specification 926,525. Combining unit CU, Fig. 9.-The combining unit CU is arranged to effect algebraic addition of the digital position correction computed by the multiplier M and the relevant position numbers as read from the recording tape and serialized. A switch SW is closed if the cutter is oversize and opened if the cutter is undersize relatively to its nominal radius to control, as appropriate, addition or subtraction of the output of the multiplier M on a lead rc to or from the positional number on a lead pn. For addition, the data on lead rc is passed through an add/subtract control circuit ASC, comprising magnetic cores 11-14, without inversion to an adder ACU. For subtraction, digit pulses are applied to a winding i on a core 11, the data on lead rc is inverted in the circuit ASC, the true difference being obtained by inserting a binary " 1 " in the lowest order. The correction digits so obtained are applied to a terminal it1 of an adder ACU where they are added to the position number digits on a terminal it2. If a roughing cut is required, the switch SW is closed and switching connections in the multiplier M are set in dependence on the thickness of excess material required. The output of the combining unit CU is applied to a position staticizer PS, a circuit CD being provided to convert the pure binary output from the adder ACU to reflected binary, the pure binary number applied serially to one input of an adder comprising cores 24, 25 (least significant digit first) and also to a second input of the adder with a delay of one digit period, all carries being ignored. The reflected binary number thus obtained, representing the corrected position is transferred to a register SR from which it may be applied in parallel to ten digit stores PSN1-PSN10 comprising bi-stable transistor circuits. The outputs of the digits stores PSN1-PSN10 are connected to a digital/ analogue converter DA which converts the digital input to a voltage magnitude for feeding to the controlling servomechanisms. The servomechanisms employ position-sensing devices constituted by rotary resolver synchros, or may be as described in Specification 872,152. The converter DA may be as described in Specification 821,187 or 895,605. The output of the converter DA is passed to one or another of servo-mechanisms XSM, YSM, ZSM depending on the state of relays RLx-RLz which are controlled by the central control circuit CC. Each servo-mechanism is driven by an error signal obtained as a pulse of magnitude proportional to the error from a circuit (Fig. 10, not shown) comprising transformers and a rectifier bridge. The central control circuit may include an error checking circuit which gives an alarm indication if the recording on the tape is faulty or if faults arise in the reading of the recorded data or in the timing of the sequence of processing operations occurring within the period of a packet of information. This error detecting circuit comprises a mono-stable flip-flop set to its unstable state at the beginning of an operation but prevented from reverting to its stable state by a series of pulses. Specifications 926,527, 926,528 and 926,529 also are referred to.