Patent GB-640256-A (GB)
Abstract: 640,256. Target-tracking apparatus. AKTIE-BOLAGET BOFORS. March 17, 1947, No. 7369. Convention date, July 25, 1941. [Class 92 (ii)] A gun fire-control system or a targettracking apparatus comprises a first instrument (not shown) by which the position of a target is measured continuously in a given system of co-ordinates -polar co-ordinates for example-this instrument being controlled by elements 23, 24, 25, of a second instrument using a different system of co-ordinates e.g. rectangular. The elements 23, 24, 25 shown are threaded on roller-carrying shafts 20, 21, 22, which rotate at a speed determined by the radial positions of their rollers 17, 18, 19, with respect to continuously rotating discs 14, 15, 16 with which they frictionally engage, and the whole apparatus is so designed and manipulated that the axial positions x, y, z, of the elements continuously correspond to the position of the moving target. The first instrument receives this x, y, z data, converts it into polar co-ordinates, uses the information in known manner to position a sighting instrument on the target and feeds back certain data to the second instrument as explained below. The radial positions of the rollers 17, 18, 19, are varied when desired, to vary the speed of movement of the elements 23, 24, 25 by three control knobs 29. 30. 31, which are used one by each of the three users of the first instrument when errors are detected in the azimuth, elevation and range data of their sighting instrument. These knobs when actuated rotate discs 32, 33, 34, engaged by friction rollers, as shown, whose radial positions are set by shafts leading from the first instrument and correspond to certain trigonometrical functions of the target position. These discs and rollers, cooperate with a further disc and roller device 46, differentials 41, 45, and 54, and screw and nut mechanisms 56, 60,43, to position the rollers 17, 18, 19 on their discs. The Specification gives the mathematical considerations which determine the manner in which the various friction rollers must be positioned and how the various parts of the mechanism must be arranged. Operation. If the target is being correctly tracked no adjustments are necessary. If however the range observer (for example) notes a range error, he adjusts the knob 31 to rotate disc 34, thus rotating a roller 69 through an angle proportional to cos p, this being proportional to the radial position of the roller where P is the angle of elevation of the target. Roller 69 rotates the disc 46 upon which there is a roller 48 whose radial displacement corresponds to cos α where α is the azimuth angle ; roller 48 thus rotates by a amount proportional to cos P cos a and this is fed to the nut 56 to position the roller 17. The displacement is shown to be equal to x<SP>1</SP>, with the result that the element 23 will now move at a corrected new speed. The same movement of the knob 31 also repositions the roller 18 by an amount proportional to cos # sin a, and the roller 19 by sin #. The corrected x, y, z speeds apply a correct change of range to the sighting instrument without affecting the azimuthal and elevational positions thereof. The other knobs function in a similar manner. Shafts 79, 80, 81 associated with the shafts 20, 21, 22 are used for " trapping " a target. Specification 418,670 is referred to.