Patent GB-1475728-A (GB)
Title: Removing unwanted material from the surfaces of a series of workpieces
IPC: G05D5/03
Filed: 1974-06-07
Abstract: 1475728 Automatic control NUOVO PIGNONE SpA 7 June 1974 [12 June 1973] 25496/74 Heading G3N A machine for shearing the pile of a textile material, e.g. cloth, to a desired height comprises a cloth thickness detector 5, Figs. 2 and 3, at a distance L upstream of a shearing cylinder 8 and comb 9 which define a shearing gap which is sensed by a detector 10, Fig. 2, to give an output signal S'. A measured thickness signal S from detector 5 is processed in control apparatus of Fig. 2 as described below and is fed to an adder 12 together with the gap size signal S' and a desired pile height signal from a device 11. The resulting output of the adder 12 is applied to a regulator 13 which controls a D.C. motor 14 coupled to move the comb 9 and thus adjust the shearing gap as a function of the measured thickness of the cloth and the desired pile height. The length of cloth L is notionally divided into for example four equal parts L/4 and the signal processing apparatus averages the measured thicknesses for a part, stores the average value and presents it to the adder 12 to adjust the gap at the time when the respective part is to pass therethrough. The signal S is first changed from analogue to digital by an A/D converter 16. An adder/divider unit 17, controlled by clockpulses from a programmer 20 having a period <SP>L</SP>/ 32  equal to the time required for the cloth to advance toward the shearer 8 by a distance <SP>L</SP>/32, samples the digital signals and forms the arithmetic mean of eight consecutive samples each <SP>L</SP>/4 period, i.e. for each part <SP>L</SP>/4 of the cloth. The mean value is applied via a gate 18 to a buffer store 19 which holds it and delivers during each <SP>L</SP>/ 4  period the mean value from the preceding <SP>L</SP>/4 period. Shift registers 23 to 26 are stepped in synchronism with the cloth progress by clockpulses from the rpogrammer 20 and which have a repetition period <SP>L</SP>/4. Thus the mean value of the first part will be in SR26 when that cloth part is about to enter the shearer. The, with a  micro-switch 30 at position 28, this value will be fed to a second buffer store 31 and from thence via a D/A converter 32 to the adder 12 to control the shearing gap as described above. A similar procedure pertains for the remaining parts. Should a sewing join in the cloth length be sensed by detector 5, a trigger unit 15 sends a pulse via a delay unit 34 and which causes the comb 9 to be lowered to widen the shearing gap just as the join is about to pass therethrough. Lowering of the comb closes switch 30 to position 29 and connects the preceding register 25 content to the store 31. Since the join produces an excessively large mean thickness value for that part e.g. the second part, the pulse from 15 is also received by an auxiliary shift register 35 which acts to close the gate 18 and block the signals B in respect of the second part, from passing to the buffer store 19. When the store 19 is next clocked it will still contain the preceding value  A and this is passed to register 23 and is subsequently used to control the shearing of the second part also, the "erroneous" signal B being cancelled. In the described embodiment the mean value signal C in respect of the third part is also cancelled when it reaches SR24 and is replaced by signal D. This is effected by the pulse from 15 which after passing via shift registers 35, 36, 37 opens the gate 21 to pass signal D into SR24, so that SR23 and SR24 both contain signal D. Thus the shear gap will be the same for the third and fourth parts following  the join.