Patent GB-740826-A (GB)
Title: Improvements in or relating to planimeters and like mechanical integrating apparatus
Inventor: FULLER JOHN RODNEY DYSON
IPC: G01B5/26
Filed: 1953-02-16
Abstract: 740,826. Planimeters. BRISTOL AEROPLANE CO., Ltd. Feb. 16, 1954 [Feb. 16, 1953], No. 4297/53. Class 106 (1). A planimeter is constructed with the measuring- wheel running upon a surface formed by a part of the apparatus, which surface is rotated and displaced proportionately to the parallel displacement of the tracing point. Two forms of the apparatus are described ; both measure moments of area as well as area itself. The first form, Fig. 1, comprises a frame 1 supported horizontally and somewhat above table level by means of rollers 2, 3 and 17, the roller 17 running on the table whilst the rollers 2 and 3 run along a straight guide-bar 4 secured between supports 5. One arm 15 of a lever 16, pivoted at P to the frame 1, carries the area measuring wheel 11 which engages the face of a disc 10 fast with the roller 2. A tracing rod 30 is adjustably secured to the other arm 23 of lever 16 by means of a toggle clamp 29 and bears a tracer 36 of transparent material marked with a circle and tracing point T. The parts are so arranged that, when the line PT is parallel to the guide bar 4, the measuring wheel 11 lies in a plane parallel to a line through P and the centre O of the disc 10. As the tracing point T is moved round the perimeter of an area under measurement, the movement of the carriage 1 to and fro on the guide bar 4 rotates the disc 10 proportionately, the disc driving the measuring wheel 11. Simultaneous rocking of the lever 16 by the tracing arm 30 varies the position of the measuring wheel on the disc and consequently the transmission ratio between them. With the parts arranged as stated, it is shown that the resulting rotation of the measuring wheel is proportional to the area traced by the point T. For simultaneously measuring moments of area, a second measuring wheel 12 is carried by a second lever 21 pivoted at 22 to the frame 1. The lever 21 bears a follower roller 25 adapted to bear against an interchangeable cam 24 attached by screws 27 to the lever 16. The cam is shaped according to whether the first or a higher moment of area is required and appropriately modifies the transmission ratio between the disc 10 and wheel 12 in relation to the angular position of the tracing arm 30 and lever 16. The second and preferred form, Fig. 4, differs from that of Fig. 1 mainly in that the tracing arm is not carried by the lever 16 carrying the area measuring wheel 11 but by an arm 23a pivoted at P1 to an outwardly extending portion of the frame 1, an arm 23b and a link 52 connecting the lever 16 and arm 23a so that they move equally. Moreover, the interchangeable moment cams are provided with a notch 57 for hooking over one or other of two studs 54, 54a on the lever 16, and with an abutment face 58 adapted to bear against a stud 55 on the lever under the action of a spring 61 and shackle 60 provided to secure the cam in position. The lever 21 carrying the moment wheel 12 terminates in a fork, one branch carrying the cam follower roller 25 and the other a roller 162 engaging an inner edge of the cam under the action of a spring 65. The main pivots of the apparatus are fitted with ball bearings.