Patent SE-7508513-L (SE)
Inventor: READAL G J
IPC: G05B15/02
Filed: 1975-07-25
Abstract: 1516341 Automatic control USS ENGS & CONSULTANTS Inc 29 July 1975 [29 July 1974] 31648/75 Heading G3N [Also in Division G4] The invention concerns a system for tracking features, such as welds, in a metal strip through a continuous processing line. A processing line to which the invention may be applied is shown in Fig. 1: the processing section for galvanizing the strip comprises an annealing furnace 10, a molten zinc bath 12 and an arrangement of "air knives" 14 which wipe off excess zinc; the pressure at the knives determines the coating thickness. Either side of the processing section is an entry section in which rolls of strip are welded end to end and an exit section where they are separated by a flying shear 22 either into new rolls 24 or into individual sheets. Since the strip must be stopped to permit welding or cutting loops 6' are formed between the sections in deep pits 6. To permit tracking it is necessary to know the lengths of the loops: pulse generators PG1, PG2, PG3 produces pulses per unit length of strip passing into and out of each loop. A counter ELC-1 counts up PG1 pulses and down PG2 pulses to determine the length in the first loop. Since errors may accumulate loop sensing switches or photo-detectors Si, S 2  are provided to detect when the loop reaches predetermined lengths; logic then forces the counter to a value representing the predetermined length to correct any error. The tracking system comprises a plurality of banks of counters Fig. 2. When a weld is made a start signal is generated either automatically or by a manual switch, the logic selects an empty entry section counter ENC and begins to increment it from the PG1 pulses; the start signal also selects a corresponding process section counter UPC and loads it with a value equal to sum of the current length of the entry loop from counter ELC-1 and a fixed value representing the distance from the welder to a reference point in the process section such as the position of the zinc bath; the counter UPC is then decremented by the PG2 pulses; the value in counter UPC is also subject to correction by the loop sensing switches the corrected value being transferred to a counter CPC. When the weld is made to join in the new roll of strip data may be fed into the logic to determine for instance the thickness of coating to be applied; when the count in counter CPC reaches zero the weld is then at the zinc bath and the logic acts on the previously stored data to adjust the air knives accordingly. The tracking is now taken over by new counters ZPC, UXC, CXC acting in the same manner as ENC, UPC, CPC respectively and the others are released for tracking further welds, &c. The apparatus of Fig. 2 may track simultaneously up to five welds or other features or points on the strip. Product data is also tracked from the zinc bath by means of a set of memory cells Fig. 3. The memory cells each correspond to fixed point in the line and their number is equal to the length of the line and some way beyond the shear 22 into the output roll or stack. The information in each cell is shifted from one cell to the next in synchronism with the advance of the strip and in response the pulses from the pulse generators. Data about the air knives, the measured thickness of coating and the shear 22 are inserted into the cells corresponding to their positions. The data from the last exit section memory cell may be recorded for the purposes of production reporting. The air knives in the processing section are controlled by a rectro-active system as described in Specification 1516342.