rus
Issue #5/2014
A.Medvedev, A.Grinkevitch, S.Markozov
Armament of Armored Force Vehicles Front Sections of Sighting Complexes Optimization
Armament of Armored Force Vehicles Front Sections of Sighting Complexes Optimization
In a effort to protect the tank optics which are the most vulnerable for current sniper’s weapon, the designers are looking for sighting-observation complexes compact front sections optimal variants. The article gives special attention to the design of the reflective parts of sight heads operating at high rotation angles of sight axes. The article is of interest for the specialists who are involved into the design of sighting complexes of armored force vehicles.
Теги: armored force vehicles cubical prism head mirror ir vision channel prism block reflection and refraction element бронетанковая техника головное зеркало отражающее-преломляющий элемент призма-куб призменный блок тепловизионный канал
Electrooptical devices on the armored force vehicles are the most vulnerable elements of the vehicle during the battle actions as well as during the direct skirmish with enemy. It is obvious that glass windows of the device front section, which overhang the armor protection, are the most unreliable components of optical and electrooptical devices. Experience of battle actions all around the world indicates that purposeful hardware kill of sighting optics by sniper and machine-gun fire became regular practice and effective method for fighting against armored vehicles.
Designers of armored force vehicles in the USSR strived to optimize all components of tanks fight efficiency and the Soviet tank school was characterized by the reasonable minimization of heads of sights and observation devices. Modern development of electrooptical sights of foreign tanks follows the same scenario – excessive growth of entrance windows and heads in order to reach the highest values of the range of vision of potential enemy military equipment. This aim, which is undoubtedly laudable, caused the strong conflict of tank optics with development trends of up-to-date sniper weapon and snipers skills.
Analyzing the peculiarities of finder systems of tank electrooptical units and design methods of counteraction against the exceeding "growth" of their heads, we will mention the following. In order to ensure the variation of vertical rocking angles of sight line, reflective or prism components are traditionally installed in front of the entrance pupil of optical devices in military equipment. As a rule, the head mirrors structurally connected with the gun by leverages are applied in case of small range of vertical angles variation, which is typical for the sights of tank guns.
Of course, application of the head mirror is very feasible practically; this is the simplest variant of head in order to change the position of sight line. But with the increase of elevation angles overall size of the head mirror grows due to the evidence of geometrical correlations and the sighting, for example, at zenith becomes basically impossible.
In case of large range of variation of vertical rocking angles of sight line (up to zenith which is typical for the sights of automatic guns of fighting vehicles of BMP type), prisms are traditionally installed in front of the entrance pupil of optical device. In order to avoid large dimensions at significant elevation angles prisms-cubes are applied (Fig. 1).
Rotation of the prism-cube in vertical plane provides sighting practically at any ranges which are possible with the frame of fighting vehicle and mechanical elements of optical device. In case if prism-cube is in the position a) (see Fig. 1) only one half of the prism functions. As the prism-cube rotates for sighting at zenith (see Fig. 1), in the position b) the second half of the prism is turned on, and upon the sighting at zenith both halves function [1].
The whole group of actions: from the increase of photodetector sensitivity to the use of not less efficient method – increase of the diameter of entrance pupil of nighttime sights – provides greater range of vision during the night time. However, the use of lenses with larger size of entrance pupil, which is required for the nighttime channels with electrooptical devices and for television and thermal imaging channels, causes the excessive increase of prism-cube dimensions. And for this reason, the stable and considerable growth of front sections of sighting complexes was observed in the proportion of natural development of fighting vehicles from one generation to another one. And in turn, it made the use of stabilization devices complicated and generated technical problems connected with the provision of resistance to impact loads.
Solving these problems, the specialists of the Design Bureau of OJSC "Rostov Optical Mechanical Plant" have developed different variants of the schemes for the minimization of front section of sighting complexes of armored force vehicles. They also considered multi-channel devices, equipped with the daytime visual and television channels with single and multiple magnifications, and nighttime electrooptical and thermal imaging channels.
In one of the solution variants of the thermal imaging-television device it was suggested to install small prism-cube above the visual channel and mirror – above the thermal imaging channel (Fig. 2). Reason for the substitution of prism-cube with mirror is based on the necessity to use optical parts made of ZnS. Technology of growth of this material, which serves as the basis for the parts functioning in the spectral range λ=0.4–14 μm, does not offer opportunity to obtain the workpiece for prism-cube with large dimensions. However, mirror in such scheme increases the head height (see Fig. 2). And although designers inclined the vertical axis of the channel for minimization of mirror dimensions, nevertheless its dimensions remained large.
Works in the Experimental Design Bureau of OJSC "ROMZ" in this area resulted in the creation of complex multi-purpose anti-aircraft sight TKN-4GA-03 with daytime single-multiple and thermal imaging sighting-observation channels on the basis of known anti-aircraft sight TKN-4GA. This device was designed thanks to the original solution of the scheme of sight front section, in which instead of mirror the reflective-refractive prism unit is installed above the thermal imaging channel (Fig. 3).
It should be noted that the capability of various spatial location of individual prisms, which the unit consists of, occurs upon the use of prism-cube unit in front of the entrance pupil of optical device. Location of individual prisms of the unit in front of the entrance pupil does not influence on the image formation by lens.
The only thing that must be kept is the equality of angles, at which the faces of prisms-cubes composing the unit are positioned, in order to exclude the double imaging. Particularly this factor led to the ultimate variant of the solution of head reflector for any type of the head of tank sighting device.
As an alternative, reflective-refractive element of the head can consist of five prisms: two prisms-cubes and one prism of АР-90° type located in one unit (Fig. 3). Size of prism side is ~26 mm, length – 78 mm. Large, main prism-cube of the device TKN-4GA is shown with thin lines (see Fig. 3) for comparison.
Due to the decrease of the total volume of glass, the weight of the whole unit turned out to be smaller than the weight of large prism-cube by three times upon the equal diameter of lens entrance pupil.
In order to make every prism element of the unit, optical workpiece with the thickness of not more than 20 mm is required and it allows making such unit at the reasonable price even with the use of the material ZnS. With such construction of the main reflective-refractive element any sight angles can be achieved. In case if independent stabilization of the head is assumed, all prisms should be analogous – in the variant of three small prisms-cubes (Fig. 4). Axis of rocking of the prism-cube unit passes through the geometrical center of the unit and at small rocking angles only one half of every prism-cube will function. As the unit rotates for the sighting at zenith, the second half of every prism-cube is turned on, and upon the sighting at zenith both halves function. In case if such unit is located in front of the entrance pupil of sighting channel lens, the form of round pupil will have other appearance (Fig. 5). And the area of pupil does not change, lens light-gathering power is retained providing the initial energy ratios.
Weight of the prism-cube unit Mun will decrease in the proportion to the amount of used small prisms-cubes (relatively to the variant of use of one prism-cube) and correspond to the ratio:
Мбл = ( 1,0 –: 1,2 ) Mб.пр. / N,
where Ml.pr. refers to the weight of large prism-cube in the variant of its use.
The weight of one large prism-cube proper which is shown for the comparison in Figure 2 with the side of 74 mm will be 1.6 kg if it was made for ZnS thermal imaging-television channel. However, understanding the impossibility to create such optical workpiece from ZnS, we will draw your attention to the fact that the side of small prism-cube does not exceed 30 mm and therefore its production can be performed technologically.
This solution at any angular positions of the unit ensured the complete propagation of beams on the whole diameter of the lens entrance pupil practically without loss due to vignetting.
Since such reflective-refractive element in the form of the prism unit has considerably lower dimensions than one large prism-cube, protective glass in the form of one plate made of the material ZnS can be used and it will simplify the device head and make it smaller. And the loss connected with the light transmission in such unit will be considerably lower than in the variant with one large prism.
Such head has quite unusual appearance because the reflective-refractive element in the form of the prism unit us installed seemingly other way round in relation to the traditional position of the mirror in regular head with the regular reflective mirror. Besides, with the increase of rocking angle the vertical size of the head is not increased but vice versa, decreased. Single channel with the regular small cube TKN-4GA is shown in Figure 6 for the comparison with the reflective-refractive element.
Thus, any sighting system using the considered reflective-refractive element instead of mirror will ensure any maximum rocking angles, up to 90°. And the system will work with the entrance pupil having large dimensions, vertical dimensions of such head will be decreased by not more than ~1.5 times in comparison with the mirror variant. At the same time, the weight of the prism unit will be decreased also in comparison with one prism in the variant of its making from the materials which are transparent in the visible and IR spectrum bands. Herewith, only one plate made of the material ZnS can be applied in the capacity of protective glass (Fig. 6).
Such structural solution ensures the complete propagation of beams on the whole diameter of the lens entrance pupil practically without the loss connected with vignetting at any angular positions of the prism unit.
It should be noted that upon the introduction of permissible vignetting the dimensions of the prism unit can be decreased and it will offer opportunity to locate additional channels, for example, radiating tract of laser rangefinder. Reception path of rangefinder can be combined with one of the active sight channels. The principle of combination of reception path with the daytime visual channel, which is practically worked through, is one of the variants of the structural solution. Single-pupil rangefinder, in which transmitting and detecting channels have one exit (entrance) window, can serve as the alternative to such solution. This solution is based on the use of well-known property of laser radiation – linear polarization.
Thus, as a result of the activities of designers, the thermal imaging-television device which retained the dimensions of the entrance pupils of standard sight TKN-4GA was designed. And the most important, as consequence, overall dimensions of the head remained the same and this fact ensures the interchangeability of the object upon the installation to standard turret. Rotation angles of the sight line by the elevation within the range of – 10° to 70° remained unchanged at the expense of the unique technical solution which was implemented for the first time in the objects of the armament of armored force vehicles.
Structurally basic variant of the sight TKN-4GA-03 consists of 2 channels: thermal imaging multiple channel and daytime single-multiple channel. Appearance of the sight is given in Figure 7 and technical characteristics are specified in the table. Switching of magnifications of the daytime channel is performed by the mechanical lever. Common ballistic mechanism with the system of sighting and range-finding scales and system of angle rings is located in the single-multiple sighting-observation daytime channel.
Output of the visual data to the small-sized viewing device of ocular type (within the field of view of standard right ocular) is provided in the thermal imaging sight channel with the help of micro-monitor located inside of the sight frame. Operation information in the form of scales for the required set of armament (for example, 2А72, PKTM, KPVT) is formed electronically with the introduction within the sight field of view.
Control panel of the thermal imaging channel of the sight TKN-4GA-03 is executed in the form of buttons for regulation of image quality (mode, contrast, brightness) and engage switch and located on the sight frame.
Application of the thermal imaging channel in the sight TKN-4GA-03 allows observation and if needed – twenty-four-hour sight shooting at ground and air targets at dawn, during the daytime, in the twilight and at the nighttime (including under adverse conditions of smoke, fog, dust, snowfall, rain, camouflage using leaves etc.).
The sight ensures the increase of parameters of vision range and sight shooting of the object by 2-2.5 times in relation to the stock-produced item despite the level of ambient illumination, time of the day, seasonal and weather conditions, peculiarities of local combat situation, using only the passive operation mode.
It is obvious that suggested variant of the multi-purpose structural execution of modernized sight TKN-4GA-03, which has daytime single-multiple and thermal imaging channels and maintains the capability of shooting at zenith rotation angles and operational interchangeability with the standard sight, indicates the significant improvement of tactical, technical and performance characteristics of application objects including BTR-82A and makes step towards the next stage of improvement of the object combat efficiency. ■
Designers of armored force vehicles in the USSR strived to optimize all components of tanks fight efficiency and the Soviet tank school was characterized by the reasonable minimization of heads of sights and observation devices. Modern development of electrooptical sights of foreign tanks follows the same scenario – excessive growth of entrance windows and heads in order to reach the highest values of the range of vision of potential enemy military equipment. This aim, which is undoubtedly laudable, caused the strong conflict of tank optics with development trends of up-to-date sniper weapon and snipers skills.
Analyzing the peculiarities of finder systems of tank electrooptical units and design methods of counteraction against the exceeding "growth" of their heads, we will mention the following. In order to ensure the variation of vertical rocking angles of sight line, reflective or prism components are traditionally installed in front of the entrance pupil of optical devices in military equipment. As a rule, the head mirrors structurally connected with the gun by leverages are applied in case of small range of vertical angles variation, which is typical for the sights of tank guns.
Of course, application of the head mirror is very feasible practically; this is the simplest variant of head in order to change the position of sight line. But with the increase of elevation angles overall size of the head mirror grows due to the evidence of geometrical correlations and the sighting, for example, at zenith becomes basically impossible.
In case of large range of variation of vertical rocking angles of sight line (up to zenith which is typical for the sights of automatic guns of fighting vehicles of BMP type), prisms are traditionally installed in front of the entrance pupil of optical device. In order to avoid large dimensions at significant elevation angles prisms-cubes are applied (Fig. 1).
Rotation of the prism-cube in vertical plane provides sighting practically at any ranges which are possible with the frame of fighting vehicle and mechanical elements of optical device. In case if prism-cube is in the position a) (see Fig. 1) only one half of the prism functions. As the prism-cube rotates for sighting at zenith (see Fig. 1), in the position b) the second half of the prism is turned on, and upon the sighting at zenith both halves function [1].
The whole group of actions: from the increase of photodetector sensitivity to the use of not less efficient method – increase of the diameter of entrance pupil of nighttime sights – provides greater range of vision during the night time. However, the use of lenses with larger size of entrance pupil, which is required for the nighttime channels with electrooptical devices and for television and thermal imaging channels, causes the excessive increase of prism-cube dimensions. And for this reason, the stable and considerable growth of front sections of sighting complexes was observed in the proportion of natural development of fighting vehicles from one generation to another one. And in turn, it made the use of stabilization devices complicated and generated technical problems connected with the provision of resistance to impact loads.
Solving these problems, the specialists of the Design Bureau of OJSC "Rostov Optical Mechanical Plant" have developed different variants of the schemes for the minimization of front section of sighting complexes of armored force vehicles. They also considered multi-channel devices, equipped with the daytime visual and television channels with single and multiple magnifications, and nighttime electrooptical and thermal imaging channels.
In one of the solution variants of the thermal imaging-television device it was suggested to install small prism-cube above the visual channel and mirror – above the thermal imaging channel (Fig. 2). Reason for the substitution of prism-cube with mirror is based on the necessity to use optical parts made of ZnS. Technology of growth of this material, which serves as the basis for the parts functioning in the spectral range λ=0.4–14 μm, does not offer opportunity to obtain the workpiece for prism-cube with large dimensions. However, mirror in such scheme increases the head height (see Fig. 2). And although designers inclined the vertical axis of the channel for minimization of mirror dimensions, nevertheless its dimensions remained large.
Works in the Experimental Design Bureau of OJSC "ROMZ" in this area resulted in the creation of complex multi-purpose anti-aircraft sight TKN-4GA-03 with daytime single-multiple and thermal imaging sighting-observation channels on the basis of known anti-aircraft sight TKN-4GA. This device was designed thanks to the original solution of the scheme of sight front section, in which instead of mirror the reflective-refractive prism unit is installed above the thermal imaging channel (Fig. 3).
It should be noted that the capability of various spatial location of individual prisms, which the unit consists of, occurs upon the use of prism-cube unit in front of the entrance pupil of optical device. Location of individual prisms of the unit in front of the entrance pupil does not influence on the image formation by lens.
The only thing that must be kept is the equality of angles, at which the faces of prisms-cubes composing the unit are positioned, in order to exclude the double imaging. Particularly this factor led to the ultimate variant of the solution of head reflector for any type of the head of tank sighting device.
As an alternative, reflective-refractive element of the head can consist of five prisms: two prisms-cubes and one prism of АР-90° type located in one unit (Fig. 3). Size of prism side is ~26 mm, length – 78 mm. Large, main prism-cube of the device TKN-4GA is shown with thin lines (see Fig. 3) for comparison.
Due to the decrease of the total volume of glass, the weight of the whole unit turned out to be smaller than the weight of large prism-cube by three times upon the equal diameter of lens entrance pupil.
In order to make every prism element of the unit, optical workpiece with the thickness of not more than 20 mm is required and it allows making such unit at the reasonable price even with the use of the material ZnS. With such construction of the main reflective-refractive element any sight angles can be achieved. In case if independent stabilization of the head is assumed, all prisms should be analogous – in the variant of three small prisms-cubes (Fig. 4). Axis of rocking of the prism-cube unit passes through the geometrical center of the unit and at small rocking angles only one half of every prism-cube will function. As the unit rotates for the sighting at zenith, the second half of every prism-cube is turned on, and upon the sighting at zenith both halves function. In case if such unit is located in front of the entrance pupil of sighting channel lens, the form of round pupil will have other appearance (Fig. 5). And the area of pupil does not change, lens light-gathering power is retained providing the initial energy ratios.
Weight of the prism-cube unit Mun will decrease in the proportion to the amount of used small prisms-cubes (relatively to the variant of use of one prism-cube) and correspond to the ratio:
Мбл = ( 1,0 –: 1,2 ) Mб.пр. / N,
where Ml.pr. refers to the weight of large prism-cube in the variant of its use.
The weight of one large prism-cube proper which is shown for the comparison in Figure 2 with the side of 74 mm will be 1.6 kg if it was made for ZnS thermal imaging-television channel. However, understanding the impossibility to create such optical workpiece from ZnS, we will draw your attention to the fact that the side of small prism-cube does not exceed 30 mm and therefore its production can be performed technologically.
This solution at any angular positions of the unit ensured the complete propagation of beams on the whole diameter of the lens entrance pupil practically without loss due to vignetting.
Since such reflective-refractive element in the form of the prism unit has considerably lower dimensions than one large prism-cube, protective glass in the form of one plate made of the material ZnS can be used and it will simplify the device head and make it smaller. And the loss connected with the light transmission in such unit will be considerably lower than in the variant with one large prism.
Such head has quite unusual appearance because the reflective-refractive element in the form of the prism unit us installed seemingly other way round in relation to the traditional position of the mirror in regular head with the regular reflective mirror. Besides, with the increase of rocking angle the vertical size of the head is not increased but vice versa, decreased. Single channel with the regular small cube TKN-4GA is shown in Figure 6 for the comparison with the reflective-refractive element.
Thus, any sighting system using the considered reflective-refractive element instead of mirror will ensure any maximum rocking angles, up to 90°. And the system will work with the entrance pupil having large dimensions, vertical dimensions of such head will be decreased by not more than ~1.5 times in comparison with the mirror variant. At the same time, the weight of the prism unit will be decreased also in comparison with one prism in the variant of its making from the materials which are transparent in the visible and IR spectrum bands. Herewith, only one plate made of the material ZnS can be applied in the capacity of protective glass (Fig. 6).
Such structural solution ensures the complete propagation of beams on the whole diameter of the lens entrance pupil practically without the loss connected with vignetting at any angular positions of the prism unit.
It should be noted that upon the introduction of permissible vignetting the dimensions of the prism unit can be decreased and it will offer opportunity to locate additional channels, for example, radiating tract of laser rangefinder. Reception path of rangefinder can be combined with one of the active sight channels. The principle of combination of reception path with the daytime visual channel, which is practically worked through, is one of the variants of the structural solution. Single-pupil rangefinder, in which transmitting and detecting channels have one exit (entrance) window, can serve as the alternative to such solution. This solution is based on the use of well-known property of laser radiation – linear polarization.
Thus, as a result of the activities of designers, the thermal imaging-television device which retained the dimensions of the entrance pupils of standard sight TKN-4GA was designed. And the most important, as consequence, overall dimensions of the head remained the same and this fact ensures the interchangeability of the object upon the installation to standard turret. Rotation angles of the sight line by the elevation within the range of – 10° to 70° remained unchanged at the expense of the unique technical solution which was implemented for the first time in the objects of the armament of armored force vehicles.
Structurally basic variant of the sight TKN-4GA-03 consists of 2 channels: thermal imaging multiple channel and daytime single-multiple channel. Appearance of the sight is given in Figure 7 and technical characteristics are specified in the table. Switching of magnifications of the daytime channel is performed by the mechanical lever. Common ballistic mechanism with the system of sighting and range-finding scales and system of angle rings is located in the single-multiple sighting-observation daytime channel.
Output of the visual data to the small-sized viewing device of ocular type (within the field of view of standard right ocular) is provided in the thermal imaging sight channel with the help of micro-monitor located inside of the sight frame. Operation information in the form of scales for the required set of armament (for example, 2А72, PKTM, KPVT) is formed electronically with the introduction within the sight field of view.
Control panel of the thermal imaging channel of the sight TKN-4GA-03 is executed in the form of buttons for regulation of image quality (mode, contrast, brightness) and engage switch and located on the sight frame.
Application of the thermal imaging channel in the sight TKN-4GA-03 allows observation and if needed – twenty-four-hour sight shooting at ground and air targets at dawn, during the daytime, in the twilight and at the nighttime (including under adverse conditions of smoke, fog, dust, snowfall, rain, camouflage using leaves etc.).
The sight ensures the increase of parameters of vision range and sight shooting of the object by 2-2.5 times in relation to the stock-produced item despite the level of ambient illumination, time of the day, seasonal and weather conditions, peculiarities of local combat situation, using only the passive operation mode.
It is obvious that suggested variant of the multi-purpose structural execution of modernized sight TKN-4GA-03, which has daytime single-multiple and thermal imaging channels and maintains the capability of shooting at zenith rotation angles and operational interchangeability with the standard sight, indicates the significant improvement of tactical, technical and performance characteristics of application objects including BTR-82A and makes step towards the next stage of improvement of the object combat efficiency. ■
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