Method and apparatus for stabilizing high-dynamics devices

A method and apparatus for stabilizing relatively high-dynamics devices (e.g. a sight) mounted on a low-dynamics support such as a tank. Movement of the low-dynamics support is determined by means of an inertial central sensor block that may comprise a strapdown set of gyros or gyros and accelerometers. Stabilization is achieved by a two-step process in which the individual high-dynamics devices are stabilized with respect to the support by means of large bandwidth control loops. The much slower support movement is applied to a superposed loop of appropriately smaller band-width. Compensation thereby takes place by specifying a reference value for the control loops of the higher-dynamics devices.

BACKGROUND 
1. Field of the Invention 
The present invention relates to the stabilization of a higher-dynamics 
device mounted on a low-dynamics support such as a tank, ship or the like. 
More particularly the invention pertains to such stabilization in which 
movements of the low-dynamics support are detected by a central sensor 
block. 
2. Description of the Prior Art 
U.S. Pat. Ser. No. 4,632,012 of Feige et al., for "Fire Control System for 
Moving Weapon Carriers", property of the assignee herein, teaches a fire 
control and navigation system for movable weapon supports such as combat 
tanks. That system utilizes a single central strapdown sensor block for 
both primary stabilization of, for example, a sighting or visual device 
and secondary stabilization of a weapon. 
The sensor block for the system includes a pair of double-axis, dry, 
dynamically tuned gyros and three single-axis accelerometers, the outputs 
of which are processed in digital format. This known system enables one to 
achieve exact firing control as well as dynamic weapon point 
stabilization. 
In order to utilize the advantages of such a strapdown fire control and 
navigation system it is necessary to stabilize not only the weapon but 
also the line of sight by means of a central set of sensors. Thus, in a 
gunner's sighting device, for example, a relatively small deflecting 
mirror having substantially higher dynamics than its support (the tank) 
also requires stabilization. 
By employing the approach of the Feige et al., patent, one would fit gyro 
measuring devices and accelerometers at the deflecting mirror. This would 
entail redesign of the inertial sensors and the digital data processing 
for the high bandwidth of the deflecting mirror. This approach thus 
imposes stringent requirements on both the dynamics of the sensor block as 
a whole and system bandwidth. 
SUMMARY AND OBJECTS OF THE INVENTION 
It is, therefore, an object of the invention to provide a method and 
apparatus for stabilizing the position in space of devices having 
relatively high dynamics that are mounted on low-dynamics supports. 
Another object of the invention is to achieve the above object in a 
technically simple manner in a flexible system that permits adaptation to 
the type, number and individual dynamics of the individual devices. 
It is yet another object of the invention to achieve the above objects in a 
system in which common inertial sensors are fitted to the support. 
The present invention achieves the above and additional objects by 
providing, in a first aspect, a method for stabilizing relatively high 
dynamics devices mounted to a low dynamics support whose movement is 
controlled by a central sensor block comprising an inertial set of sensors 
engaged thereto. The method includes the step of providing, as the central 
sensor block, a set of gyros responsive to rotations about at least three 
independent axes. The bandwidths of the gyros are selected solely in 
accordance with the dynamics of the support. A closed control loop is 
provided whose bandwidth is selected in accordance with the dynamics of 
the device. 
Thereafter, the setting of the device with respect to the support is 
determined along at least two axes by means of angle pickups. This is 
followed by applying the setting to the central loop so that the changes 
in setting determined by the central sensor block are superimposed as 
reference values upon the control loop. 
In another aspect, the inertial sensor block includes not only a set of 
gyros, as above, but also a sufficient number of accelerometers to measure 
acceleration along three independent axes, such as is available in a 
strapdown system or analytical platform. Such a system can provide data 
concerning the position, speed, acceleration, setting, and change of 
setting relative to a navigation coordinate system related to the earth. 
The foregoing features and advantages of this invention will become 
apparent from the detailed description that follows. This written 
description is accompanied by a set of drawing figures. Numerals of the 
drawing figures and the accompanying text point to the features of the 
invention, like numerals referring to like features throughout both the 
written description and the illustrations.

DETAILED DESCRIPTION 
FIG. 1 is a top perspective view of a combat tank 1 equipped with a number 
of high dynamics sensor devices requiring stabilization. 
The tank 1, including a turret 2, functions as a relatively low-dynamics 
support. A number of devices requiring stabilization are mounted to the 
turret 2 including a gun 4 that functions as the main tank weapon, a 
(commander's) periscope 5 and a (gunner's) sighting device 6. A central 
sensor block 3, mounted as a complete unit in the turret 2, measures the 
comparatively slow turret movements relative to a navigation co-ordinate 
system that is fixed with respect to the earth. 
FIG. 2 is a block diagram of device stabilization apparatus for utilization 
with a combat tank system in accordance with FIG. 1. As shown, the central 
sensor block 3 (e.g. a strapdown set) supplies the support (turret 2) 
setting and setting change data via a data line 12 to a junction point 13 
of a closed control loop 10 that serves to stabilize one of the devices 
(4, 5 or 6) mounted in the turret 2. The support setting data supplied at 
the junction point 13 serve as an infraposed guide quantity or reference 
value in the control loop 10. The (relative) setting data of the control 
loop 10 (actual data) are supplied by angle pickups such as resolvers 14. 
The reference value that determines the setting of the support is 
superposed and supplied to one or more device control elements 15 at the 
junction point 13. 
The operation of the invention is advantageously illustrated with reference 
to an example in which a mechanically rigid support is presumed. An 
armored combat vehicle or tank is assumed to be the support. Accordingly, 
the movably fitted devices include, for example, the gunner's main 
telescopic sight 6, the commander's periscope 5, and the main tank weapon 
4. Stabilization is required for the lines of sight of the gunner's and 
commander's sighting devices 6 and 5, respectively, as well as for the 
setting of the weapon 4. In accordance with prior stabilization methods, a 
pair of single-axis rate gyros with associated control systems is required 
per device. As such, stabilization (with respect to bearing and elevation) 
occurs separately for each device. Thus, the gyros and the control systems 
of the stabilized devices must, in each instance, exhibit a sufficiently 
wide bandwidth to detect fully and to stabilize the movements of those 
devices in space. For example, a known combat tank currently requires six 
single-axis rate gyros. This solution becomes particularly costly when 
several devices must be stabilized on a common support as a set of gyros 
is required for each device. 
In contrast and as an improvement thereto (c.f. the system set forth in the 
above-mentioned patent, the method of this invention permits the mounting 
of a central sensor block at a protected position that is fixed in 
relation to the vehicle while, at the same time, permitting a simple 
method of stabilization of the higher-dynamics devices. A technical 
distinction exists between two cases, each set forth below. 
FIRST CASE 
The central sensor block consists of a single set of gyros. In this 
arrangement, the set of gyros includes a sufficient number of gyros to 
measure quantities with respect to three independent measurement axes. 
Thus, for example, when double-axis gyros are utilized, at least two are 
required, whereas, in the case of single-axis gyros, at least three gyros 
are necessary. In this case, the devices may only be stabilized with 
respect to inertial space. This is similar to the above-described prior 
art systems for combat tanks. However, only a single set of gyros is 
necessary for the stabilization of all of the high dynamics devices. 
SECOND CASE 
The inertial sensor block includes not only a set of gyros as in the prior 
case, but also a sufficient number of accelerometers to measure along 
three independent axes. Such a set of sensors is available, for example, 
in a strap-down system or analytical platform. That type of a system may 
provide data concerning the position, speed, acceleration, setting (and 
change of setting) of the support relative to a navigation co-ordinate 
system with respect to earth. Thus, in this case, device stabilization may 
be undertaken in relation to a navigation co-ordinate system with respect 
to the earth. 
In both of the above-referenced cases, the inertial sensor block senses 
movements of the turret co-ordinate system. The outputs of the sensor 
block are utilized as reference values by the individual device 
stabilization control systems. Each device (e.g. weapon, visual device, 
sighting device or the like) is provided with its own control system 
having a device-specific bandwidth. The settings of the devices relative 
to the support (turret of the combat tank) are determined by angle 
pickups, the outputs of which control setting mechanisms (at the devices) 
by means of high bandwidth closed control loops. Accordingly, changes of 
setting and turret movements are utilized as guide quantities by the 
device control loops. 
The inventors have found that the angles of disturbance that occur in a 
comparatively massive support (e.g. tank turret) decrease rapidly with 
increasing frequency. Indeed, to stabilize a tank's gun in accordance with 
the above-referenced patent requires a bandwidth that is approximately 
three times greater than the measured bandwidths of the angles of 
disturbance at the tank turret. The stabilization of line-of-sight devices 
can require regulating systems and sensors having bandwidths that are 
approximately fifteen times greater. The above findings are reasonable as 
a tank turret which weighs several tons moves with relatively great 
inertia. A lighter gun exhibits higher dynamics, and the relatively light 
deflecting mirrors of optical sighting devices (telescopic sight of the 
gunner, periscope of the commander) exhibit very high dynamics. The 
invention takes advantage of the foregoing by means of a two-step process 
wherein the individual high-dynamics devices are stabilized with the 
required large bandwidth with respect to the support and the lesser 
movement of the support determined and compensated by means of a 
superposed control loop of smaller bandwidth. 
By employing the teachings of the invention, it is possible, by employing a 
conventional set of inertial sensors (e.g. strapdown system) on the 
support and angle pickups, or rotational speed pickups, such as 
tachogenerators, and angle measuring devices, such as resolvers, 
respectively at the devices, to stabilize the high-dynamics devices. In 
this regard, it is highly significant that the bandwidth of the set of 
inertial sensors need only be sufficiently large to permit accurately 
known movements of the low-dynamics support. This bandwidth is, in 
general, markedly smaller than those of the devices to be stabilized. When 
an analytical platform is employed for the set of inertial sensors, the 
platform invariably supplies the position and the setting of the support 
and quantities derived therefrom for additional functions, such as those 
utilized by a central firing control. The number of devices which may be 
stabilized and their bandwidths are in principle, unlimited. The method 
permits an optimum modular construction and is suitable for varying types 
of vehicles (regardless of the number of devices to be stabilized). For 
example, the gunner's sighting device requires the greatest stability in a 
combat tank. Therefore, the control systems and angle pickups for that 
device exhibit the greatest bandwidth. The other devices to be stabilized 
(e.g. commander's periscope, weapons) can then be equipped with control 
systems whose bandwidths are individually coordinated with the dynamics of 
those devices. In contrast to prior stabilization methods, especially 
those for use with combat tanks, the following advantages are achieved: 
(First Case) 
(a) Inertial sensors of the central sensor block (analytical platform) may 
be located at a protected unexposed position; 
(b) Size and weight restrictions of the central sensor block are not 
applicable; 
(c) The central sensor block is of standardized form, readily accessible 
and easily maintained; 
(d) An arbitrary number of devices may be simultaneously stabilized by the 
inertial sensor block; 
(e) The central sensor block, or more precisely, the electronics system 
(17) associated with it, can be constructed in digital technology, and 
requires only sufficient processing speed to correctly describe the 
movements of the support. At the same time, the device control systems may 
be constructed as rapid analog control systems, permitting a low cost 
solution by employing standard systems in the central sensor block; 
(f) A set of high-quality gyros may be employed in the inertial sensor 
block. A higher degree of system reliability and availability is achieved 
since strapdown gyros have a markedly greater service life than the rate 
gyros which are customarily employed for armored weapons stabilization; 
and 
(g) Navigation quality strapdown gyros exhibit lower drift (by a number of 
orders of magnitude) than conventional rate gyros. Accordingly, high 
accuracy of navigation data is obtained. 
(Second Case) 
When an inertial sensor block with accelerometers (e.g. strapdown system) 
is employed, additional advantages are achieved: 
(h) The earth's rotation is taken into consideration and compensated during 
stabilization as stabilization is undertaken with respect to a coordinate 
system that is fixed with respect to earth. As a result, the observation 
and monitoring of portions of terrain by optical sighting systems are 
enhanced; 
(i) The speed of the support can be compensated, resulting in a drift-free 
image (even during travel) when an observation or sighting device, for 
example, is stabilized in accordance with the invention; 
(j) Three-axis stabilization may be accomplished without additional 
inertial sensors. As a result, image rotation about the support tilt axis 
is prevented, permitting steady image presentation on viewing devices; 
(k) The vertical sensor formerly required to compensate tilt angle is 
dispensed with, as its function is carried out by the central sensor 
block. 
As the invention is based upon the application of an inertial central 
sensor system including accelerometers, data are provided with respect to 
the location, setting and movement of the support. As a result, additional 
useful functions may be performed in an armored vehicle. As the central 
sensor block (analytical platform) supplies the position of the vehicle 
with respect to a navigation system that is fixed in relation to the 
earth, the vehicle's orientation in unknown terrain, poor visibility or 
other difficult environmental conditions is facilitated. Moreover, the 
strapdown system supplies data concerning the speed and angular velocity 
of the turret for improved firing control as, for example, correction of 
the muzzle velocity of the projectile of the gun 4. All data are made 
available via the data bus 12. Furthermore, with the aid of range-finding 
measurements from the armored vehicle to the target, point stabilization 
dynamic aiming-off allowance computations can be performed with accuracy. 
While this invention has been described with reference to its presently 
preferred embodiment, it is by no means limited thereto. Rather, its scope 
is limited only insofar as defined by the set of claims which follows and 
it includes all equivalents thereof.