The Mechanical Handling and Storing of Material

THE AUTOMATIC WEIGHING OF MATERIAL 719 cams a and G are on one shaft, and this is driven by bevel wheels from one of the conveyor terminals. Each of the ten pawls is one-tenth of the pitch of the teeth of the ratchet wheel in advance of the next' to its left. The maximum slip is therefore one-tenth of a tooth. In the latest machines a conical clutch is used instead of the ratchet wheel and pawls; this improvement eliminates all loss of motion and ensures still greater accuracy. In the machines already built the cycle occurs every five seconds, and is as follows : The steelyard is free for about three seconds, during which time it assumes the position proportional to the load upon that section of the conveyor which is supported by the weighing machine. It is then gripped by the action of the first cam, the second cam immediately allowing the measuring quadrant to move forward until it touches the steelyard, where it remains until pushed back by the further motion of its cam ; the first cam then releases the steelyard. The weight is recorded by the backward motion of the measuring gauge. There are thus four motions—gripping, measuring, recording, and releasing—which occupy somewhat less than half the time of the whole cycle. It will be readily understood that when the steelyard is at its lowest position it must touch the measuring gauge at its stationary position, as there can be no motion of the latter if the steelyard indicates no load. It has, however, proved impracticable to allow the steelyard to touch the gauge at the lowest position, for two reasons:— Firstly, it is difficult to adjust the steelyard so accurately that it touches the gauge and yet exercises no pressure upon it. Secondly, the vibration of the conveyor gearing, etc., sets up oscillations in the steel- yard which would allow the gauge to occasion- ally gather a few pounds and so introduce an error. This difficulty has been overcome by balancing the steelyard at a point somewhere above zero, and then subtracting a correspond- ing amount of weight each time a weighing takes Fig 1033 Registering Device as used with place. the “Blake-Denison” Weighing Machine. Thus, for instance, if the steelyard is so balanced as to remain in a position corresponding to | cwt., when there is no load on the conveyor, the measuring gauge will register on its return stroke i- cwt. each time. But if a device is introduced for deducting i cwt. from the register each time, the motions cancel each other, and the register remains unaltered. The device referred to consists of a set of wheels, two of which gear with a pinion carried upon an arm of the wheel driving the counter (see Fig. 1033). If the two bevel wheels move an equal amount, but in opposite directions, the result will be - that the pinion is merely revolving upon its axis. But if one of the wheels moves more than the other, the pinion will be driven forward or backward accordingly, and will carry the registering wheel with it. To the spindle of one of these bevel wheels is attached a ratchet wheel having a suitable number of teeth—where the lever is balanced at | cwt. the number would be forty—while a lever and pawl operated from the camshaft drives the ratchet wheel one tooth every cycle, deducting a corresponding amount from the register. The other bevel wheel is driven from the measuring gauge. The counter or register thus operated records the quantity of material passed over the conveyor during a given period. The measuring gauge or quadrant consists of a vulcanite plate securely fastened to a light steel frame. The frame encloses a finely divided steel ratchet wheel, and carries a set of ten pawls of different lengths engaging