US3580363A

US3580363A - Hydraulic gimbal lock

Info

Publication number: US3580363A
Application number: US878116A
Authority: US
Inventors: Moshe L Plawner; Vincent R Vento; Abraham Gordon
Original assignee: US Air Force
Current assignee: US Air Force
Priority date: 1969-11-19
Filing date: 1969-11-19
Publication date: 1971-05-25
Anticipated expiration: 1988-05-25

Abstract

An improved lock is disclosed, as applied to the elevation gimbal of a large telescope installation. Hydraulic pressure is employed firmly and simultaneously to force a number of contact members against a stationary surface of circular configuration and forming part of the fork gimbal or yoke pedestal. The hydraulic pressure is made effective by the use of a bellows system in which each bellows carries a contact head positioned a short distance from the stationary surface and the bellows are equally spaced from one another. A solenoid having a movable core and controlled from a position near the eyepiece of the telescope is employed to operate a miniature hydraulic pump which feeds oil under pressure simultaneously to each of the bellows. The latter elongate and press firmly against the stationary surface and at the same time, the motor which drives the gimbal to which the telescope is attached, can be declutched so that instant braking is effected. There is no overrun and the telescope remains strictly in line with the star being sighted when the control is operated.

Description

United States Patent 72] Inventors Moshe L. Plawner Wayne; Vincent R. Vento, Morris Plains; Abraham Gordon, Teaneck, NJ. [2]] Appl. No. 878,116 [22] Filed Nov. 19, 1969 [45] Patented May 25, 1971 [73] Assignee The United States of America as represented by the Secretary of the United States Air Force [54] HYDRAULIC GIMBAL LOCK 8 Claims, 7 Drawing Figs.

[52] U.S. Cl 188/74, 350/83 [51] 1nt.Cl F16d 51/00 [50] Field of Search 350/82, 83, 85; 188/74, 184 356/(Inquired) [5 6] References Cited UNITED STATES PATENTS 2,326,552 8/1943 Morse 350/83 3,338,350 8/1967 Schilling ABSTRACT: An improved lock is disclosed, as applied to the elevation gimbal of a large telescope installation. Hydraulic pressure is employed firmly and simultaneously to force a number of contact members against a stationary surface of circular configuration and forming part of the fork gimbal or yoke pedestal. The hydraulic pressure is made effective by the use of a bellows system in which each bellows carries a contact head positioned a short distance from the stationary surface and the bellows are equally spaced from one another. A solenoid having a movable core and controlled from a position near the eyepiece of the telescope is employed to operate a miniature hydraulic pump which feeds oil under pressure simultaneously to each of the bellows. The latter elongate and press firmly against the stationary surface and at the same time, the motor which drives the gimbal to which the telescope is attached, can be declutched so that instant braking is effected. There is no overrun and the telescope remains strictly in line with the star being sighted when the control is operated.

PATENTEU HAY25 IHYI SHEET 1 [IF 3 SHEET 2 OF 3 PATENTED HAY25 l9?! HYDRAULIC GIMBAL LOCK BACKGROUND OF THE INVENTION Large telescope installations are employed for sighting distant stars, tracking satellites, also for observing the travel of space vehicles and the operation of propulsion rockets, etc. Many of these telescopes are housed in observatories and most of them are operated by electric motors through pushbutton control, operated by the observer at the eyepiece position. The telescope proper is usually fixedly mounted on at least one four-sided gimbal carried on trunnions and the gimbal is swingable between the legs of an upright fork structure or yoke. The latter is provided with a heavy central column, swingable or rotatable in a vertical bearing. For convenience the last-mentioned structure will be termed a fork gimbal to distinguish it from the quadrilateral gimbal on which the telescope proper is mounted. Both gimbals are quite massive and usually have square cross sections of wide and thick dimensionswith a hollow interior so as to reduce the weight as much as possible. The telescope is fixedlymounted on the quadrilateral gimbal and the latter is adapted to swing within the space between the two opposite legs of the yoke or fork structure. Thus, the telescope can be swung in the vertical direction with its gimbal and in the horizontal or azimuth direction by the turning movement of the fork gimbal in its bearing.

While great effort is made to balance the quadrilateral gimbal carrying the telescope about its bearing in an attempt to make it swingable by hand, at the larger installations it has been found more practical to motor drive both gimbals under the control of the observer. However, it has been found that notwithstanding the care taken by the latter, either to power drive or hand operate the gimbals in order to quickly give the telescope the proper orientation, the gimbals tend to overrun and sometimes to underrun the proper position so that a back and forth shifting movement may become necessary. Even microservomechanism and slow gearing are not always sufficient to prevent the occurrence of an undesired movement of the heavy parts which have considerable momentum even when being moved slowly. Sometimes a fast fix on a star becomes an absolute necessity in which the parts must be moved rapidly and in that case the problem of wobble about the proper position could become aggravated. Various attempts have been made to devise fast stoppage of the moving parts on command and perhaps the most recent was the use of a mechanical wedge which was jammed between two machined surfaces of the gimbals. In addition to the difficulty of quickly removing the wedge, the lock operated erratically and occasionally jammed in the locked position. This is particularly so if the support on which the telescope is mounted is subject to vibration from an extraneous source such as a rocket in the propulsion stage. Moreover, the wedge form of lock becomes almost impossible when it is necessary to quickly unlock the trunnions and orient the telescope on a second star in which the switching operation, including the unlock and subsequent lock action, must be kept within a matter of a few seconds.

SUMMARY OF THE INVENTION An object of the invention is to provide a telescope mount 'part of the mount.

Another object is toprovide a device or structure which is applicable to telescopes employing heavy swingable mounts and which will prevent even the slightest overrun beyond the desired predetermined swinging movement.

Still another object is to provide an improved device or structure for locking the elevation gimbal and the yoke gimbal together at the exact point of the termination of the desired movement between them.

A more specific object is to provide an improved lock for securing the gimbals of a large telescope together in order to prevent unauthorized use.

A more general object is to provide in a telescope mount a provision for remotely locking, unlocking and relocking two sets of gimbals to each other in the minimum of time with a high degree of accuracy and in which the lock is to uncouple from the mating gimbal in such a manner that the motion of the gimbals is unaffected by the presence of the lock.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view of a typical telescope and mounting of the larger type and to which the improved lock structure is applied as an accessory. The lock structure is shown in section.

FIG. 2 represents a section of the lock structure taken on line 2-2 in FIG. 1 and looking in the direction of the arrow.

FIG. 3 is an end view of the lock structure, taken at about line 2-2 in FIG. 1 and showing the lock members in an unlocked position, i.e., the elevation or quadrilateral gimbal is free to swing, either by power or by hand. The figure is drawn to about twice the size of FIG. 1.

FIG. 4 is a view similar to FIG. 3 but in which the lock members have made contact with a stationary ring surface attached to the yoke or fork gimbal.

FIG. 5 depicts a section taken along line 5-5 in FIG. 3.

FIG. 6 is an enlarged schematic view of a single unit of the lock mechanism and showing the placement of the pivot points of the lock.

FIG. 7 shows a circuit controllable from the eyepiece switchboard for energizing an improved two-part solenoid which operates the pump.

DESCRIPTION OF THE PREFERRED EMBODIMENT The drawing to the left of FIG. 1 shows a typical large telescope of the so-called two gimbal" type and to which the improved locking assembly or accessory shown to the right of FIG. 1 is particularly useful. Reference character I designated in general the fork or yoke gimbal of a large telescope mount. This gimbal is provided with a pair of oppositely positioned legs 2 joined together by a large casting 3 which fits around a shaft 4. The casting 3 has generally a rectangular cross section and is hollow over at least some portion thereof in order to reduce the weight as much as possible. The casting is keyed to the shaft 4 as indicated at 5. The shaft 4 rests upon, and is secured to, a heavy metal plate 6, the lower surface of which formspart of the race of a ball bearing 7 of which the other race portion is contained in a large and fairly heavy baseplate 8. A driving shaft 9 extends upwardly through an opening in the base plate and is connected to the circular plate 6. This shaft carries at the lower end a large gear 10 which meshes with a small gear 11, the latter being carried on a shaft 12 which mechanically connects with a motor 13. The shaft 9, gears 10, 11, the motor shaft the motor 13 are contained in a well 14 formed in a concrete floor, the plate 8 being sufficiently large to extend over the well and is secured to the floor.

Each of the legs 2 near the top is provided with openings which carry ball bearings 15 and the latter rotatably support a shaft 16. Each shaft extends inwardly into the space between the legs 2 and are fixedly mounted in a pair of heavy anchoring devices 17 which are bolted or otherwise secured to the upper or elevation gimbal 18. The latter has a quadrilateral shape (not shown) and a square cross section of wide and thick dimensions and is cast with a hollow space which extends around the four lengths of the gimbal. These lengths are spaced a considerable distance apart and within this space there are a number of struts or braces extending inwardly (not shown) which support a large circular metal casting 19 closed at the bottom but open at the top. A metal frustum of a cone 20, forming a shield, extends upwardly from the open or upper edge of the casting 19, the latter serving as a lower support for a number of struts or rods 21 forming a framework which supports at the top a disc member 22. This member has a central opening for receiving a metal cylinder 23 which contains a condensing lens (not shown) of any-suitable and well-known type. The distance between the lens at the top and the gimbal 18 could be quite considerable in the case of a large telescope installation. Within the circular casting 19 there are wellknown supports (not shown) for locating a large reflecting lens 23' which focuses the rays onto the deflecting mirror 24 and these rays then enter the lens system of the eyepiece at the observer station. The observer in looking through the eyepiece under focus can direct the small condensing lens at the top of the framework onto the star, satellite or any other object assuming that he has been able to swing the elevating gimbal about its shaft 16, and also the fork gimbal 1 about its vertical bearing. The manner in which this is accomplished will be described in greater detail hereinafter. To the right of the observers station or eyepiece there is a platform having a number of pushbuttons 26, as will also be explained hereinafter, for controlling the movement of the two gimbals and also for other purposes. The right-hand shaft 16 carries a disc 27 and a corresponding disc or plate 28 is mounted on the heavy plate 6, these discs having angular markings thereon so that the observer would know the angular displacement of the gimbals as they are swung in their respective directions. In order to swing the gimbal 18 so as to elevate or depress the telescope, there is loosely carried on the left-hand shaft 16, a large gear 29 which meshes with a small gear 30. The latter is connected either directly to the motor 31 through a shaft 32 or through a suitable form of declutching mechanism which can be remotely controlled by an electrical impulse as explained hereinafter. This declutching mechanism is indicated simply as a small rectangle 33. The motor 31 is suspended from the lower surface of the gimbal 18 in any suitable manner, and circuits (not shown) are connected between each of the

motors

31 and 13 to the push button group 26 located on a keyboard in easy reach of the observer.

IMPROVED LOCK STRUCTURE The lock structure assembly constituting our invention takes the form of an accessory generally designated at 33'. However, the structure of the accessory about to be described could be concealed within the telescope mount itself and not project beyond one of the legs of the fork gimbal. There is a hub member 34 of round configuration having a flange 35 which is bolted to one of the legs of the fork gimbal and in line with an extension of shaft 16. A web 36 of substantial thickness extends radially outward from the hub member 34 and this web carries an overhanging ring member 37 which is also of considerable thickness. The member 37 has an inside peripheral surface 38 which is preferably ground to a perfectly round configuration. The ring surface 38 maintains a rigid position in space but moves with the fork gimbal. Within the hub member 34, there is a cylinder 39 of substantial thickness which runs free of the hub member and is attached to the shaft by a holding nut 40. The cylinder is supported peripherally on ball bearings 41 and is driven by the shaft 16. Thus, as the elevation gimbal 18 swings on its shafts 16 the cylinder 39 turns freely in the same amount within the surrounding metal housing. The cylinder has an extended portion 42 of smaller diameter than the main portion and is closed at the remote end as indicated at 43. This cylindrical portion contains a piston 44 having a piston rod 45 which is extended to the left (as seen in FIG. 1) to form the core of two adjacently posi tioned but separately operated

solenoids

46, 47. The separation of these solenoids are indicated by the line 47' and the purpose of separating them will be explained hereinafter. It is apparent that when either of the

solenoids

46, 47 or both are electrically energized, the core within the solenoid which represents the extension of the piston rod 45 will move the piston 44 to the right. The maximum travel of the piston is such that a small space is still left between the end of the piston and the end 43 of the cylinder. The cylinder portion 42 is provided with four quadrantally arranged segments 48, which extend outwardly edgewise from the cylinder to which they are secured. These segments are substantially pie-shaped with a round outer periphery and terminate at each end in flat, smooth edges, the adjacently positioned edges constituting pairs and positioned at right angles to one another so that the assembly of these segments present four grooves 48 having parallel sides and extending radially outward from the center of the segment assembly.

Projecting from each side of the segmental surfaces, as seen in FIG. 1, and formed integrally therewith there is a pair of projections or lugs 49 which have flat surfaces and are separated from the segmental surfaces by a space indicated at 50. Thus, the projections or lugs 49 extend on both sides of the segmental member assembly, each corresponding projection on opposite sides of the segment member being in line with one another to constitute a pair and in effect extend the grooves 48' beyond the perimeter of the segment assembly. There is an aperture in each of the projections, the aperture in one projection being in line'with the aperture in the companion projection. These apertures receive a pin 52 as seen more clearly in FIG. 1, and the purpose of which will be explained hereinafter. Each lock member 53 has a shape similar to that shown in enlarged diagram FIG. 6 and is provided with an aperture to loosely receive the pin 52. The shape of the lock member is characterized by a curved surface 54 having the approximate curvature of the surface 38 formed on the overhanging member 37. The sides or

edges

55, 56 of the member are parallel and the edge 55 is longer than the edge 56. These two edges are closed by the rounded portion 57 and a longer portion 58. The longer edge portion extends at an angle of about 50 with respect to a reference horizontal line and is so illustrated in the figure. Thus, each lock member takes on the general appearance of a triangle with the pivot pin 52 located near the narrow end of the member. The thickness of the lock member is such as to be readily slidable between each pair of projections 49. The size of the aperture is such as to permit the member to turn or swing easily on the pin 52 with the pointed end resting on the periphery of the segmental assembly 48. When mounted in position, the uppermost surface is positioned somewhat above the lugs 49 as can be seen in FIG. 2. There is a small gap between the upper surface 54 of each lock member and the surface 38 of the overhanging metal portion 37 (FIG. 2). A second aperture 58' is provided in the lock member, this aperture being positioned near the curved surface 54 and the short edge 56; the purpose of this aperture will be explained hereinafter. Directly over the grooves 48 and at each side of the segmental assembly, there is a plate 59 (FIG. 5) of rectangular shape except having the inner comers cut off. These plates are screwed as indicated at 60 to the outer surfaces of the projections 49. Thus, a squareshaped compartment 61 is formed (FIG. 5) of which the vertical sides are constituted of the inside edges of the lugs 49 and the top and bottom sides are constituted of the plate 59. Each compartment is closed at the inner end by a disc 62 of metal in any suitable manner and fastened to the wall of the compartment 61. Within each compartment there is positioned a bellows device 63 of any suitable type having a diametrical size as to fit slidably but not loosely within the compartment 61. The outer end of each bellows is preferably provided with a rounded head member 65 of solid metal and the overall length of the bellows including the solid head is such that when the inner ends of the bellows rest upon the metal disc 62 the solid head member will just contact the angular surface of the lock member as can be seen in FIG. 6. The disc 62 has an opening therein (not shown) in the center which communicates with the interior of the bellows and also by a suitable conduit system (not shown) with the interior of the cylinder portion 41. it is apparent that when oil is introduced in the space between the piston 44 and the end 43 of the cylinder and assuming that one or both of the

solenoids

46, 47 are energized and the piston is caused to move to the right as seen in FIG. 1, the oil is placed under pressure and is forced through the conduit system simultaneously into each of the bellows 63. Thus, the oil under pressure will cause these bellows to elongate outwardly within the compartment 61 causing the edge 58 of the lock member to move outwardly since the disc 62 will prevent movement of the bellows inwardly. The head member 65 will press against the surface 48 and will cause the lock member to rotate about its pin 52 until the curved surface 54 makes firm contact with the inside surface 38 of the locking ring surface. This condition is shown in H0. 4. It will be noted in this respect that the pivot pin 52 is located eccentrically with respect to the lock member 53 so that an outward pressure exerted on the surface 38 by the head of each of the bellows provides an enormous leverage in the pressing force available between the head 65' and the surface 38. Since all of the bellows receive the same oil pressure the solid head members 65 will exercise equal forces on all of the lock members 53 which serve to swing each member about its pin 52. The long curved surface 54 provides an enormous length of contact at each of the four positions about the segmental assembly 48, each position being represented by two lock members actuated by the end 65 of the individual bellows. Due to the rigidity of the ring member 37, these pressures are distributed almost equally about the entire cylindrical body of the member. This force reacts through the shaft 16 on the elevation gimbal l8 and stops the latter immediately at the farthest position of the piston when the

solenoids

46, 47, or either one of them, are energized.

The energization of the solenoids is preferably controlled by one or more of the keys 26 located at theobservers post. A suitable form of electrical circuit that may be employed for this purpose is illustrated in FIG. 7 and will be described hereinafter. When it is desired to swing the elevation gimbal to a new position of the telescope, the solenoids are first deenergized and the lock members 53 are caused to withdraw from the surface 38 by means of a return spring 67 which loosely fits into an aperture 58' in the lock member and is bent to clear the outer surfaces of the lugs or projections 49. The other end of the spring is frictionally held under a small triangularly shaped plate 68, riveted or otherwise secured to the outside surfaces of the segmental assembly. These springs must assert sufficient force to swing each lock member about its pin and thus return the member to its original position. The oil passes through the conduits (not shown) under spring pressure to the space within the cylinder so as to move the piston to its original or left-hand position. The elevation gimbal is then allowed to freely swing on its axis and driven, if desired, by the motor 31 until a fix has been made at the lens 23 on the desired star at which time the observer simply presses the stop button at the keyboard and an abrupt stoppage against further movement of the gimbal is again effected. On the energization of the

solenoids

46, 47 in the manner described, it may be desirable to provide a declutching mechanism between the gear 30 and the motor 31 which may be of any suitable and well-known type, such as to disconnect the motor 31 upon the energization of the

solenoids

46, 47. The declutching effect may also be exercised by a suitable push button 26. It will be noted that the stop or braking effect exercised hydraulically by the bellows 63 is independent of any horizontal movement of the fork gimbal 1 since the abrupt stoppage of movement reacts only on the shafts 16 of the elevation gimbal and not on the shaft 4 of the fork gimbal. Thus, the overhanging metal portion 37, and particularly the inner surface 38, constitutes a locking ring which is effective regardless of the position of the fork gimbal.

A suitable circuit that may be employed for energizing the

solenoids

46, 47 and controlled by push button is shown in FIG. 7. One end of the solenoid 47 is connected to a switch 69 and the latter is also connected to one end of the solenoid 46. The other end of the solenoid is connected by a conductor to one end of a resistance 70. The opposite end of the resistance is connected to the right-hand end of the solenoid 47 and also to one pole of a battery 71. The other side of the battery is connected both to the left-hand end of the solenoid 47 and also to the switch 69. A switch 72 is connected across the resistance 70 so as to short out the latter when desired. The battery 71 may have a voltage of about 40 direct current. To move the bellows 63 outwardly, and to apply the maximum force by the core on the piston 44, it is necessary to close both

switches

69 and 72, in which case battery voltage at full strength is applied to each of the

solenoids

46, 47. However, after the solid tip 65 has caused the lock members to contact the locking surface 38, and it is desired that this locking effect should extend over long periods of time in order to discourage any unauthorized movement of the elevation gimbal 18, it may be desirable to cut the voltage applied to the solenoid 46 but apply full voltage only to the solenoid 47. In this case, the switch 72 is opened, which in effect inserts the resistance in the circuit which contains the solenoid 46. The resistance 70 is sufficiently high that when the battery 71 is assumed to be 40 volts DC, the voltage applied to the solenoid 46 is reduced by dropping 45.5 volts across the resistance. The net effect is to reduce the dissipated wattage from approximately 40 watts to 4 watts and sufficient energy will still be applied to the

solenoids

46, 47 to firmly hold the lock members 53 tightly against the locking surface. This may save using an excessive amount of power if it isdesired that the locking effect should extend over long periods of time to prevent any unauthorized movement of the elevation gimbal.

One advantage, of this hydraulic lock over all other locks, including the use of the wedges between machine parts, is that it is capable of withstanding the environment, such as vibration, etc., without slippage of the lock. Moreover, the presence of the lock does not apply any strain about the elevation axis of the telescope mount. Finally, the hydraulic system is effective, regardless of the relative positions of the fork gimbal and the elevation gimbal. It is also apparent that since the oil pressure is obtained from the centrally located piston 44, this pressure is applied to all of the bellows 63 simultaneously and in equal amounts. Thus, the force exercised by the lock members 53 against the locking surface 38 is equally distributed about the surface of the locking ring to provide the optimum locking effect and thus prevent even the slightest tendency for the elevation gimbal l8to overrun its proper position, as determined by the observer.

We claim:

1. In a telescope mounting including a pair of gimbals swivelly connected together for permitting the telescope to be moved in the vertical and horizontal directions, the vertical moving gimbal being supported on oppositely positioned shafts journaled on a horizontally moving gimbal, and. brake means attached to said extended shaft for applying a braking effect to the swinging movement of the gimbal which positions the telescope in the vertical direction said brake means comprises a cylinder secured to the periphery of the cylinder and extending radially outward, the edge portions of the plate sections being spaced from one another to form outwardly extending slots which have parallel sides and the slots being arranged at right angles to one another, expandable elements in said slots, said elements terminating in solid heads at their outer ends, said elements being responsive to hydraulic pressure in order to expand, a pair of lock members swingably mounted on pivots on opposite sides of each slot, said members having tapered edges which bear against the head of said expandable elements, the lower end of the member bearing against the periphery of the multisection plate member, a stationary ring member surrounding said expansible elements, and means for causing each cxpansible element to elongate and swing the lock members about their respective pivots to make contact with the stationary ring member when hydraulic v pressure is applied to each element whereby a braking action is effected on the elevation moving gimbal through said cylinder and shaft extension to prevent overrun of one gimbal with respect to the other gimbal.

2. In a telescope mounting according to claim 2 and in which said elements consist of bellow members closed at the head end and in communication at the other end with the hydraulic pressure developed within said cylinder.

3. In a telescope mounting according to claim 2 and in which the hydraulic pressure is developed by a solenoid and piston structure contained within said cylinder and controllable from the eyepiece position.

4. In a telescopic mounting according to claim 2 and in which said last mentioned means includes a cylinder, a piston within the cylinder and a solenoid in the cylinder having a core connected to said piston, said solenoid being electrically controllable from the observers position, oil in the cylinder at the position of the piston which upon the compression stroke of the piston forces the oil into the expansible members which serve to press the lock members against said locking surface.

5. In a telescope mounting according to claim 1, said means for causing each expansible element to elongate being constituted of a solenoid in said cylinder, a core in said solenoid and connected to a piston located at one end of the cylinder, the piston end of the cylinder being in communication with said expansible elements, oil in said cylinder so that when the solenoid is activated, the piston moves to place the oil under pressure which is forced into the expansible elements, a stationary ring surrounding the expansible elements and secured to the horizontally moving gimbal, said expansible elements upon receiving the oil under pressure expands and contacts the stationary ring wherebya powerful braking action is obtained and the gimbal which moves the telescope in the vertical direction is brought to a complete stop to prevent overrun.

6. In a telescope mounting according to claim 1, a locking gimbal for maintaining the telescope at a desired position in elevation, said gimbal including a bearing structure for receiving a shaft on which the telescope can move in the vertical direction, said structure also including a metal ring which is secured to the gimbal that moves in the horizontal direction and having an interior peripheral surface which constitutes a locking surface, a plurality of lock members for maintaining the telescope and its bearing structure fixed with respect to the horizontally movable gimbal, and means for hydraulically pressing the lock members against the locking surface when the telescope is pointed at the precise altitude of the target star.

7. In a telescope mounting according to claim 3 and having spring means operable on the withdrawal of the hydraulic pressure for removing the lock members out of contact with the locking ring so as to permit the telescope to be moved in elevation.

8. ,In a telescope mounting according to claim 3 and in which said ring includes a casting which surrounds at least one end of said cylinder and is connected to the gimbal which moves in the horizontal direction, said casting having a radially extending web which carries an annular member of substantial thickness and extends in the horizontal direction, the inside surface of said annular member presenting a cylindrical surface against which said lock can contact when hydraulic pressure is applied to the expansible element.

Claims

1. In a telescope mounting including a pair of gimbals swivelly connected together for permitting the telescope to be moved in the vertical and horizontal directions, the vertical moving gimbal being supported on oppositely positioned shafts journaled on a horizontally moving gimbal, and brake means attached to said extended shaft for applying a braking effect to the swinging movement of the gimbal which positions the telescope in the vertical direction said brake means comprises a cylinder secured to the periphery of the cylinder and extending radially outward, the edge portions of the plate sections being spaced from one another to form outwardly extending slots which have parallel sides and the slots being arranged at right angles to one another, expandable elements in said slots, said elements terminating in solid heads at their outer ends, said elements being responsive to hydraulic pressure in order to expand, a pair of lock members swingably mounted on pivots on opposite sides of each slot, said members having tapered edges which bear against the head of said expandable elements, the lower end of the member bearing against the periphery of the multisection plate member, a stationary ring member surrounding said expansible elements, and means for causing each expansible element to elongate and swing the lock members about their respective pivots to make contact with the stationary ring member when hydraulic pressure is applied to each element whereby a braking action is effected on the elevation moving gimbal through said cylinder and shaft extension to prevent overrun of one gimbal with respect to the other gimbal.

4. In a telescopic mounting according to claim 2 and in which said last mentioned means includes a cylinder, a piston within the cylinder and a solenoid in the cylinder having a core connected to said piston, said solenoid being electrically controllable from the observer''s position, oil in The cylinder at the position of the piston which upon the compression stroke of the piston forces the oil into the expansible members which serve to press the lock members against said locking surface.

5. In a telescope mounting according to claim 1, said means for causing each expansible element to elongate being constituted of a solenoid in said cylinder, a core in said solenoid and connected to a piston located at one end of the cylinder, the piston end of the cylinder being in communication with said expansible elements, oil in said cylinder so that when the solenoid is activated, the piston moves to place the oil under pressure which is forced into the expansible elements, a stationary ring surrounding the expansible elements and secured to the horizontally moving gimbal, said expansible elements upon receiving the oil under pressure expands and contacts the stationary ring whereby a powerful braking action is obtained and the gimbal which moves the telescope in the vertical direction is brought to a complete stop to prevent overrun.

8. In a telescope mounting according to claim 3 and in which said ring includes a casting which surrounds at least one end of said cylinder and is connected to the gimbal which moves in the horizontal direction, said casting having a radially extending web which carries an annular member of substantial thickness and extends in the horizontal direction, the inside surface of said annular member presenting a cylindrical surface against which said lock can contact when hydraulic pressure is applied to the expansible element.