Patent GB-1349563-A (GB)
Title: Control systems for gear cutting machines
IPC: B23Q15/12
Filed: 1971-03-17
Abstract: 1349563 Gear-hobbing machines WERKZEUGMASCHINENKOMBINAT "7 OKTOBER" BERLIN VEB 17 March 1971 7087/71 Headings B3K and B3B [Also in Division C3] An adaptive control system for a gear cutting machine with steplessly controllable feed and milling spindle drive for controlling feed and cutting speed comprises a measuring device for the actual cutting torque associated with a controller which is connected to a computer by which a desired cutting torque is determined and to a speed control device for the feed drive, which latter device receives for the control of the feed an actuating variable which is produced in the controller by comparison of the actual cutting torque with the desired cutting torque, and which control system detects the wear on the tool by means of a measuring device or devices for the cutting temperature and/or vibration of the tool, the said measuring device or devices being connected by way of a comparator, in which the measured actual values for the wear are compared with predetermined desired values, to a further controller to which computers are connected by which a desired milling cutter rotational speed is computed, a speed control device being provided for the milling spindle drive, which latter device for the purpose of controlling the cutting speed, receives an actuating variable from the further controller. As shown, a spur gear hobbing machine has a milling spindle drive 1 connected by gearing 2, 4 to a hob 3 and workpiece 5 and a feed drive 7 for the hob slide 6, a shift drive 9 being provided for a tangential slide 8 on which the hob is mounted. The drive 7 is controlled by a thyristor rectifier speed regulating device 16 in turn supplied with the output of a controller 12 receiving an actual cutting torque signal M FI  from a sensing device 11 connected to the milling spindle 10 and receiving a desired cutting torque signal M FS  from an optimum adjuster 14 fed by a computer 13, the latter receiving a signal m @ . from a central input unit 15 in which are adjusted the following desired working parameters representing technological or geometrical data for the gear cutting operation:-a normal modulus m n , an axial feed per workpiece rotation S a , the number of teeth of the workpiece Z w , a minimum axial feed per workpiece rotation S amin  for the initiation of the shift step through path W s , a milling cutter speed n F , a milling cutter diameter d F , a tool life T, a type of milling cutter FA and the machinability B of the material. The computer 13 calculates a maximum cutting torque which is adjusted by member 14 in accordance with an optimum previously determined from the desired quantity output of the cutting process, the quality of the machining and the manufacturing costs for machining the workpiece in question. Sensing devices 19, 20 respectively detect the cutting edge temperature v I  and vibrations f I  associated with the hob slide 6, these actual valve signals being fed to a comparator 21 also receiving corresponding desired valve signals v s  and f s . The output of comparator 21 supplies a controller 22 for the thyristor speed regulating device 26 of the milling spindle drive 1, the controller 22 also receiving a desired milling speed signal n FS  supplied by an optimum adjuster 25 receiving the output of a computer 24 determining the maximum milling cutter speed n Fmax  in turn supplied with a maximum cutting speed signal V max  calculated by a computer 23. The computers 23, 24 receive the parameters d F , T, FA, B and m n  and comprise circuits including operational amplifiers, a servo system, resistor-diode networks, potentiometers and switches, Fig. 2 (not shown). The optimum set in the adjuster 25 is dependent on the same parameters as those used by the adjuster 14. In a typical gear cutting operation the following steps occur:-(1) Prior to engagement of members 3, 5, the drives 1, 7 are controlled by members 22...26 and 12, 13, 14, 16 to attain their respective desired speed values, with suitable limitation in the initial switch-on period. (2) Engagement of members 3, 5 causes increase in the output of sensor 11 until, at a predetermined value, a switching, amplifier 18 initiates the comparison-control action of members 12, 22, whereby the feed is varied to maintain M FI  equal to M FS  and the cutting speed is varied to maintain the signals v I  and f I  at the desired values. (3) If wear on the tool cutting edge causes a continuous increase of the signal M FI , so that a minimum feed S amin  is not maintained, a controller 17 passes a switch pulse to the shift drive 9 whereby the latter operates, after the machining operation has been completed, to displace the slide 8 through the predetermined path W s  in order to provide new cutting edges for the next workpiece and so obtain uniform wear on the hob 3. The operation of computers 23, 24 during a typical cutting operation is also described. The aforementioned operation may be preceded by a "first cut" operation, in which switches 28, 29 are changed over to control the drive 7 at a constant feed calculated by a computer 27 fed with signals S a , Z w  and n F  and to control the drive 1 at a speed determined by the signal n F .