Patent GB-795284-A (GB)
Title: Improvements relating to the control of devices for dividing material
Inventor: CRAXTON ROBERT TREVOR
IPC: B27L5/08
Filed: 1955-06-07
Abstract: 795,284. Cutting wood. BRITISH THOMSONHOUSTON CO., Ltd. June 6, 1956 [June 7, 1955], No. 16373/55. Class 145. Apparatus for dividing material 1, such as veneer, into a number of set lengths which are free from defects randomly disposed in the material is controlled by means which include a roll 6 bearing on the material so as to rotate an apertured disc D between a light source and a photo-electric cell connected to a lengthmeasuring counter and a, number of signal storage elements 9 and signal transfer elements B1-B8 movable relatively to each other at a rate corresponding to the feed of the material. When a defect appears in the material at a watched position W, the operator presses a button PB and a charge or signal is applied by an element B to one of the storage elements and re-applied from the storage elements at appropriate times through other transfer elements to preselector devices S1-S4 so that a guillotine (which, in the absence of defects in the material is controlled solely by the counter to cut off the longest of the set lengths) will operate as the counter measures shorter set lengths to divide off the greatest possible set length commensurate with the amount of good material available before the defect and will operate again just after the defect passes to divide off a short scrap length containing the defect. The storage and transfer elements may comprise, respectively, a magnetic tape and a recording head and several spaced reproducing heads or, as shown, a commutator device 7 having segments 8 connected through capacitors 9 to earth and engaged by spaced brushes B1-B8. It is stated that the signal produced by operation of the pushbutton PB could, in some applications be produced automatically. The brushes B1-B8, taken in order in the direction of rotation of the commutator 7, are the signal application brush B1, four length selecting brushes B2-B5, a cancellation brush B6, the operative brush B7 and the earthed discharging brush B8. The arc traversed by any segment in passing from the brush B1 to the operating brush B7 corresponds to the distance between the guillotine and the watched position W and the arcs between the brushes B2-B6 and the brush B7 correspond to the five set lengths to be cut. The signal from the push button PB may be applied through the brush B2, corresponding to the greatest set length, and the brush B1 may then be omitted. The brushes B2-B5 are each coupled to the grid of a thyratron T1 in each of the four preselectors S1-S4 and the anode of the thyratron is connected to the operating coil of a preselector relay PR, and, through a capacitor C, to the anode of an extinguishing valve V which has its grid connected to the grid of the thyratron in the next preselector or, in the case of the last preselector S4, to the cancellation brush B6. In each preselector, the relay PR has contests connected to a selector relay SR which establishes a setting of the selector circuit to determine at which measured set length the counter will cause the guillotine to operate, other than the longest length, since the normal setting of the counter when all the SR relays are de-energized corresponds to the longest set length. Each relay SR has a holding circuit through contacts SR-2, TR-2 and is also connected to contacts, such as STR-1, of a common selection transferring relay STR which is connected to contacts TR-1 of a triggering relay TR. The relay TR is connected to the anode of a triggering thyratron T in series with contacts of the relay STR and the grid of the thyratron T is connected to the operating brush B7. When a defect is observed at the watched position W and the operator presses the push button PB, relay contacts RL 1-1 close and apply a charge to one of the segments 8 through the brush B1. When this charged segment reaches the next brush B2, corresponding to the longest set length, a signal is applied to the thyratron T1 in the preselector S1 and the thyratron energizes the relay PR so that the contacts PR-1 close. When the charged segment reaches the brush B3, corresponding to the second longest set length, the thyratron T1 in the preselector S2 is rendered conductive and the corresponding relay PR is energized. At the same time, the signal is applied to the extinguishing valve V in the first preselector and the drop in anode potential of the first thyratron through the now conductive valve V renders the former non-conductive and the first relay PR is de-energized. Similar actions take place as the segment passes the brushes B4 and B5 and the relay PR in preselector S4 remains energized until the segment reaches the cancellation brush B6, at which time the length of material between the defect and the guillotine has reduced to the shortest set length. If, after the active segment has passed the brush B6, the guillotine operates, either by action of the counter itself (to cut a longest set length) or because a preceding active segment, representing a defect, has reached the operating brush B7, the former active segment will reach the brush B7 and operate the guillotine again, to cut out a portion containing the defect, before the counter can measure the shortest set length. On initiation of an operation of the guillotine, the triggering thyratron is rendered conductive by the signal applied to its grid and the triggering relay TR closes its contacts TR-1 so that the transfer relay STR opens its contacts TR-2 in the holding circuit for the SR relay in any preselector that may be energized at the time. If no preselectors are energized, the counter can measure up to the longest set length, but, if a defect is approaching at a distance between two of the set lengths, the relay PR in the preselector indicating this fact will be picked up. The circuit for the corresponding selector relay SR will then be established through the nowclosed contacts of this relay and the relay STR and the guillotine will operate to cut the lower of these two set lengths. The selection transfer relay STR, which is shunted by a half-wave rectifier Rf to introduce a degree of time lag, also opens its contacts STR-5 to render the thyratron T non-conductive and consequently de-energize the relays TR and STR. Each preselector is restored to its initial position when the next preselector is activated so that information regarding the position of more than one defect approaching the guillotine can be stored in them and if two or more relays SR are energized when the transfer relay STR operates, the counter will initiate a subsequent operation when it has measured the lowest of the set lengths for which the selector may then be set. Any charged segment will be finally discharged when it reaches the brush B8. If a defect extends for a substantial distance, it can be cut out by the operator registering both its leading edge and trailing edge.