Patent GB-695635-A (GB)
Title: Improvements in or relating to weighing scales
IPC: G01G23/34
Filed: 1950-05-09
Abstract: 695,635. Optical projection apparatus. HOBART MANUFACTURING CO. May 9, 1950 [May 11, 1949], No. 11507/50. Class 97 (i). [Also in Groups XI, XVIII and XIX] Weighing apparatus comprises a chart being weight indications which is actuated by the weighing mechanism and of which an image is projected optically on to a screen, there being provided, in addition to a main projection light source, a reserve source which is automatically substituted if the main source fails. In the form shown in Fig. 1 the projection lamp 200, and a spare lamp 230, are carried in an inner housing 202 closed top and bottom, by gauze ends mounted behind louvres 234 formed in the upper part of the main casing. Condenser lenses are mounted in the side walls of this inner casing and the emergent light is used for the projection system mounted on the plate 70 by which projection is effected on to screens visible to customer and salesman through windows 81, 80. The lamp 200 is carried in a holder pivoted at 207. It has two filaments, one of which is normally aligned with the condensers. If that fails a relay in the supply circuit energizes the other and also a solenoid 222 which pulls the lampholder, against a spring, to align the second filament with the condensers. In the unloaded position of the scale pan a resistance is brought into the lamp circuit by a switch actuated by the lever system supporting the pan. The system includes a rearwardly extending arm 44 coupled to counterbalance spring and scale mechanism by means shown in greater detail in Fig. 3 and, in elevations from a perpendicular direction, in Fig. 2. The upper end of the spring 88 is fixed and the lower end is secured to a C-shaped member 96 which supports a bearing 97 for the end 45 of the lever 44. The central portion 131 of an H-shaped frame 130 carries a pin 132 extending down through a hole in the arm 44, its lower end being sumpported at the free end of a bimetallic strip 135 secured beneath the arm. The lower limbs of the frame 130 carry inwardly projecting flexible rods 141 engaged in recesses in the side of the arm 44. The upper limbs of the frame 130 support between them a spindle carrying rollers 121. Each of a pair of flexible tapes 120 is secured at one end to the fixed frame 116, passes over one of the rollers 121 and is, secured . to a plate 106 supported for vertical movement in rollers 111. A vertical rod 105 is secured at its lower end to the plate 106 and is supported between rollers 102, 103 at its upper end to which is secured the chart 100. The chart 100 carries, at one edge, a weight scale. This is projected by a light beam 300, Fig. 15, formed by the condenser. 210 at one side of the lamp housing and reflected by a mirror 301 through the chart and by a prism 302 through the projection lens 303. The beam is divided by a semi-reflecting mirror 315 and after subsequent reflections, as shown, the parts fall on screens 330, 340, at 300a, 300b. The chart 100 also carries a number of vertical scales of prices for the measured weights, each scale corresponding to a particular unit price. Another optical system is arranged to select one scale for projection by transverse movement of a carriage 152 (Fig. 15), effected by rotation of a shaft 160 (Fig. 1), which drives the carriage through a cord drive. The carriage has two limbs disposed on the two sides of the chart 100. One limb carries a condensing lens 373, a negative collimating lens 377 and a prism 375. This system receives, by reflection from mirrors 371, 372 a light beam 370 which is part of the beam from the condenser 209. The beam passing through the chart passes through the projecting lens 380 and is reflected by a prism 383 and divided by a semireflecting mirror 385, the two parts after subsequent reflections, as shown, falling on the screens 330, 340 at 370a, 370b. The carriage 152 also carries a scale of prices per unit weight and the price corresponding to the column projected from the chart 100 is projected by a lens 356. The scale is illuminated by part 350 of the beam from the condenser 209 reflected by mirrors 351, 352 and passing through a condenser 355. After reflection by a prism 360, and subsequent reflection, as shown, it falls on a semi-reflecting mirror 363, part of the beam then falling on the screen 330 at 350a and part being reflected on to a separate screen 365. Various baffle plates, such aa 390 and 391, and others, not shown, are provided to prevent overlapping of the various light beams incident on the screens. To take account of the movement of the optical system on the carriage 152, and to ensure a constant width of the beam 370a incident on the screen 330 a device as shown in Fig. 23 is inserted in the reflected beam from the mirror 385. This beam passes between two blades 423, 424 upstanding from a pivoted base 420. The latter is engaged by a bent wire 431 which also rests between the teeth of a worm 430 on the shaft 160 so that the member 420 is rotated as the shaft 160 is rotated to adjust the carriage 152. Some of the mirrors, such as 315, are adjustably mounted to align the images on the screens. Such mounting comprises a body portion 319, Fig. 8, slotted to provide a resilient upper portion 317 to which the mirror is secured and which is adjustable by a screw 321. Each of the projection lens assemblies 303, 356, 380 comprises two lenses 306 (Fig. 9) mounted eccentrically in a tubular housing 305, being spaced therein by tubular spacers 307 and a diaphragm 308. It is secured in a body 304 having a split clamping portion 310. A hexagonal portion 311 permits rotation of the housing. For easy selection of the correct unit price the scale 150 carries a line extending diagonally along its length, Fig. 20, showing the scale as projected on the screen 365. The projected line 405b thus appears to rise and fall past a scale 400, graduated to give an approximate measure of the projected scale reading while the individual graduations thereof may be passing too fast to be read. The numbers such as 346b, adjacent individual graduations of the scale 150 indicate the size of each division. This size may change at some point along the scale, a corresponding change occurring in the scale 400.