GB2062819A - Mounting of gun sights - Google Patents

Abstract

On the body 7 of a tank are mounted a gun 5 which pivots about axis 1 and a sight 8 which pivots about an axis 2. To ensure that the sight 8 is aligned with the gun 5 for all angles of elevation the sight 8 and gun 5 are joined by a link 13. Adjustments must be made to ensure that the axes 1, 2, 3 and 4 lie at the corners of a parallelogram. This is done by setting the gun at mid-range and adjusting turnbuckle 13A until the sight is aligned with it. The gun is then lowered to a given elevation and the error in the elevation of the sight is noted. The gun is then raised to another elevation and the error in the elevation of the sight again noted. From the two error values the adjustment required to the distance between axes 2 and 3 and the distance between axes 3 and 4 can be calculated. A special adjusting mechanism (Fig. 2: not shown) is used to carry out these adjustments. <IMAGE>

Description

SPECIFICATION Improvements relating to gun sights This invention relates to apparatus comprising a gun and a sight fitted to the gun. It also relates to a method of adjusting the sight so that it is aligned with the gun at all elevational angles of the gun.

The invention arose through the need to fit a new sight to a gun belonging to an existing tank.

Owing to the construction of the tank it was necessary for the sight to be located at a position spaced from the gun whilst ensuring that the movement of the sight accurately followed the movement of the gun. In the existing tank the position of the pivotal axis of the gun was not accurately known and this made it difficult to construct a satisfactory mechanical linkage to ensure that the elevation of the sight was the same as the elevation of the gun for all positions of adjustment.

According to the invention there is provided apparatus comprising a gun pivotted about a first axis on a support, a sight pivotted about a second axis on the support, a link pivotted about a third axis to the sight and about a fourth axis to the gun, means for adjusting a first distance between the first and second or the third and fourth axes and for adjusting independently a second distance between the first and fourth or the second and third axes.

When employing the invention as defined in the immediately preceding paragraph it is necessary to ensure that the four axes are located at the corners of a parallelogram. This can be done by a trial and error process involving adjusting the first and second distances until the sight is found to be aligned with the gun at all angles of elevation. This can be tested either by test firings of the gun or by using an instrument such as a clinometer for measuring angles of inclination.

During trials it was found to be very difficult, time consuming, and accordingly expensive to find the correct position of adjustment. The inventor devised a way of overcoming this difficulty involving the steps of: a) setting the gun at a given elevation angle; b) adjusting the said first and second distances until the sight is at the same elevation angle as the gun as indicated by an inclination sensing instrument; c) lowering the gun to a lower elevation angle and noting the corresponding elevation of the sight as indicated by an inclination sensing instrument; d) before or after step c) above, raising the gun to a higher elevation angle and noting the corresponding elevtion of the sight as indicated by an inclination sensing instrument;; e) deriving from the noted values at least the approximate amounts by which the said distances need be adjusted for the sight to be aligned with the gun at all angles of elevation of the gun; and f) adjusting the said distances accordingly.

By employing these measures it has been found possible to adjust the aparatus of the invention in a small fraction of the time which would otherwise be necessary.

It will be noted that, under step e) above it is only necessary to use a relatively easily derived approximation of the adjustments required. Further accuracy can be achieved simply by repeating steps c)tof).

One way in which the invention may be performed will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic diagram depicting part of a turret of a tank in which the invention is employed, an outer body of the tank being shown in cross-section.

Figure 2 is a detail, again very schematic, of an adjusting device employed in the apparatus of Figure 1, and Figure 3 is an even more diagrammatic form of Figure 1.

Referring to Fig. 1 the four axes of the invention are shown respectively at 1,2,3 and 4. These axes are all parallel to each other and at right angles to the plane of the drawing. The axis 1 is the axis of rotation of a gun 5 which is attached to pivot pins, one of which is shown at 1 A. The pins 1 A fit in journals defined by lugs (one of which is shown at 6) forming part of an armoured body 7 of the tank.

A telescopic sight 8 comprises an eye-piece 9 and reflectors 10 enabling an observer, depicted .schematically at 1 to view a target through a window 12 in the body 7. The sight 8 is pivotted on a shaft 2A about the axis 2, the shaft 2A rotating in a bearing fixed in relation to the body 7.

A link 13 fits on the pivots relative to shafts 3A and 4A which are associated with the axes 3 and 4 and are fixed relative to the sight and gun respectively. This link 13 is formed in two parts joined by a turnbuckle 1 3A having opposite threads as shown so that the length of the link can be increased or decreased by turning the turnbuckle in the appropriate direction.

The connection between the link 1 3 and the sight 8 is an adjustable pivot connection and is shown in greater detail in Figure 2. Referring to Figure 2, attached, e.g. by welding, to the outer casing of the sight 8 is a guide 14 having a groove 1 4A machined along it, this groove being parallel to the line joining axes 2 and 3. The groove 1 4A terminates short of one end of the guide 14 to leave an end wall 1 4B. Reference 1 4C depicts side rails which define the parallel edges of the groove.

The groove 1 4A receives a slide 1 5. This slide has threaded bore (not shown) receiving a threaded shaft 1 6 which bears in the end wall 1 4B and can be turned by manipulating an adjusting member 1 7.

Such turning drives the slide 15 along the groove 14A, the distance of movement being indicated by graduations on the member 17 and an index mark on the wall 14B. The groove 14 is slightly undercut and the slide 1 5 is correspondingly dovetailed to hold the slide in the groove.

The slide 1 5 is similar in construction to the guide 14 having an undercut groove 15A, and end wall 1 5B and side walls 1 5C. The groove 1 5A is perpendicular to the groove 1 4A and receives a second slide 18 driven by a threaded shaft 19 and an adjusting member 20. The member 20 has graduations which co-operate with an associated index mark on the wall 14C.

The second slide 18 is fixed to the pivot pin 3 to which the link 13 is attached.

The sight is adjusted as follows. First the gun 5 is elevated to a reference angle of 120 mils, i.e.

0.12 radians relative to the horizontal as measured by a clinometer. This angle is chosen because it is the middle of the elevational range of this particular gun. It will be understood that different angles would be chosen for different guns. The turnbuckle 1 3A is then adjusted until the elevation of the sight is also 120 mils, again as measured by a clinometer.

The gun is now lowered until the angle of the sight reaches a chosen value S close to the lower limit of the range. Let us say, for example, that S1 is minus 40 mils (the negative sign indicating that the angle is below the horizontal). The angle G1 of the gun is then noted and suppose that this is minus 38 mils. An error value E, is then calculated according to the equation E1=G1--S1 i.e. plus 2 mils.

The gun is now elevated until the sight achieves an angle S2 which is above the reference angle of 120 mils by an amount equal to the amount by which G2 was below the reference angle. In other words S2 equals 280 mils. The gun clinometer reading G2 is then noted and let us suppose that this is 281.5 mils. An error value E2 is then calculated according to the equation E2=G2-S i e 125 mils.

For angles S1 and S2 given by way of example in the foregoing it can be shown that the amount X by which the distance x between points 2 and 3 must be lengthened, in order to make the linkage 2,3,4,5 a parallelogram, are given by the equations: X -- E1/5 + E2 equation I Y -7 (E1 + E2 equation Therefore, for the figures of E1 and E2 given in the foregoing X= +43 mils.

Y = -5 mils.

Accordingly the adjustor 1 7 is turned clockwise by 43 divisions and the adjustor 20 is turned anticlockwise by 5 divisions. The sight should then be approximately correctly adjusted. However, to eliminate inaccuracy due to the approximations made in deriving equations I and 11 the gun 5 may be lowered again until S1 equals40 mils and the process of adjustment be repeated.

Equations I and II above are calculated as follows, with reference to Fig. 3 where points 1,2,3 and 4 correspond to the axes 1,2,3 and 4 of Fig. 1 and the dimensions x and y are Cartesian co-ordinates of the point 3 relative to the point 2, these co-ordinates being those which can be adjusted using members 1 7 and 20 respectively. Point 31 is the position to which point 3 must be adjusted to make the linkage a parallelogram The requirement for tracking is: S=G for all 0 when -40 mils < G < 280 mils This is achieved by making the linkage a parallelogram: i.e., by making z = a, and X2 + Y2 = b2.

We shall write x=b +X y =b sin ( -0) + Y z=a +Z where X, Y, Z are the required shortenings of the 3 lengths x y and z.

By applying Pythagoras' Theorem to a triangle with hypotenuse z: z2 = (a - b cos A + x cos D + y sin D)2 +(bsinA+xsinDycosD)2 = a2+b2+x2+y2 -- 2ab cos A + 2ax cos D + 2ay sin D - 2bx cos (A-D) +2by sin (A-D) Now transform from x,y,z and X,Y,Z, and linearise by neglecting squares and products of X, Y, Z, A--D, #--#.

a2 - 2aZ a2 + b2 + b2 + 26X -2ab cos D + 2ab sin D sin (A-D) +2absin (-0)sin D + 2aYsin D --2b2--2bX.

This simplifies to ZXcosD+YsinD + b sin D {sin(A-D) + sin (#-#)] ButA-D±O=G-S=E So the correction equation is --X cos D-Y sin D+Z = b sin D sin E The alignment procedure: i) adjusts z to make E=O when G=Go = 120 mils, so D=D0 = 1444.2 mils.

ii) measures E=E, when G=G7 = -40 mils, so D=D1 = 1284.2 mils.

iii) measures E=E2, when G=G2 = 280 mils, so D=D2 = 1604.2 mils iv) solve for X and Y the simultaneous linear equations --XcosDO--Ysin Do+Z=O --XcosD1-YsinD1 + Z = b sin D1 sinE1 --X cos D2 -- Y sin D2 + Z = b sin D2 sin E2 v) shortens andy by X and Y vi) repeats (i) to (v) as necessary.

Elimination of Z gives the pair of equations X (cos D0 -- cos D1) +Y (sin D0 -- sin D1) =bsinD1 sinE1 X (cos Do -- cos D2) - Y (sin Do --sin D2) = b sin D2 sin E2 The particular numerical values quoted previously lead to the equations: -- 0.1647 X --0.0237 Y =0.1355 E1 0.1673X+0.0042Y=0.1401 E2 working in mm and mils.

By Gaussian elimination: X + 0.1432Y = --0.8181 E1 X + 0.0253Y= 0.8375 E2 0.1 178 Y = --0.8181 E1-.0.8375E2 y = --6.94 E1 --7.11 E2 X= 0.18E1+1.02E2 again working in mm and mils.

More approximately: x=E1/5 + E2 y=--7 (E1 + E2)

Claims (14)

1. Apparatus comprising a gun pivotted about a first axis on a support, a sight pivotted about a second axis on the support, a link pivotted above a third axis to the sight and about a fourth axis to the gun, means for adjusting a first distance between the first and second or the third and fourth axes and for adjusting independently a second distance between the first and fourth or the second and third axes.

2. Apparatus according to claim 1 in which the means for adjusting includes a length adjusting device for adjusting the effective length of the link.

3. Apparatus according to claim 2 in which the actual length of the link is adjustable.

4. Apparatus according to claim 1,2 or 3 in which the means for adjusting includes an adjustable pivot connection by which one of the members, namely the gun, the support structure, the sight, or the link is connected to another of the said members, this pivot connection having two adjusting mechanisms which can be manipulated to adjust the position of the appropriate axis independently in two orthogonal directions.

5. Apparatus according to claim 4 in which the adjustable pivot connection includes a bearing rigidly attached to one of said members, a shaft which rotates in the bearing and is attached to another of the said members, a first slide by which the shaft and bearing can be slidably adjusted in one direction, and a second slide by which the shaft and bearing can be slideably adjusted in another direction.

6. Apparatus according to claim 5 in which the first slide runs in a track formed in the second slide, which second slide runs in a second track formed in a body which is fixed relative to one of said members.

7. Apparatus according to claim 5 or 6 including screw adjusting mechanism for adjusting said slides.

8. Apparatus according to any preceding claim including guages for indicating the amount of adjustment of the said first and second distances.

9. Apparatus according to claim 1 substantially as described with reference to the accompanying drawings and substantially as illustrated therein.

10. A method of adjusting a gun sight in an apparatus constructed in accordance with claim 1 comprising: a) setting the gun at a given elevation angle, b) adjusting the said first and second distances until the sight is at the same elevation angle as the gun as indicated by an inclination sensing instrument; c) lowering the gun to a lower elevation angle and noting the corresponding elevation of the sight as indicated by an inclination sensing instrument; d) before or after step c) above, raising the gun to a higher elevation angle and noting the corresponding elevation of the sight as indicated by an inclination sensing instrument; e) deriving from the noted values at least the approximate amounts by which the said distances need to be adjusted for the sight to be aligned with the gun at all angles of elevation; and f) adjusting the said distances accordingly.

11. A method according to claim 8 in which steps c), d), e) and f) are repeated.

12. A method according to claim 10 or 11 in which the step b) is effected using a relatively course adjusting mechanism and step f) is effected using relatively fine adjusting mechanisms.

13. A method according to claim 12 in which step b) is effected by adjusting the actual length of the said link.

14. A method according to claim 10 and substantially as described with reference to the accompanying drawings.