Roll angle determination

Abstract: The invention relates to an arrangement for determining the roll angle position of a rotating projectile, shell, missile or the like with the aid of polarised electromagnetic radiation, comprising a transmitter (Fig. 3) arranged to emit a position-determining polarised radiation in the direction towards the projectile and a receiver arranged in the projectile (Fig. 4) in order to receive the transmitted radiation. The emitted radiation consists of two components, on the one hand a component in the long-wave band (LF) and on the other hand a component in the microwave band. The microwave component comprises a pulse train in which the pulses are intended to indicate when the long-wave component is situated in a certain phase position, for example to indicate the sinusoidal long-wave component's zero cross-overs with a positive-going derivative. This takes place in such a way that a synchronising pulse is emitted by the long-wave transmitter to the microwave transmitter which transmits a short series of microwave pulses (13) as an indication to the projectile.

Description: The present invention relates to an arrangement for determining the roll position of a rotating projectile, shell, missile or the like with the aid of polarised electromagnetic radiation. The arrangement comprises a transmitter arranged to emit a position-determining polarised radiation in the direction towards the projectile and a receiver arranged in the projectile in order to receive the transmitted radiation. The emitted polarised radiation consists of two components, on the one hand a first radiation component of a longer wavelength and on the other hand a second radiation component of a shorter wavelength, this second radiation component transmitting phase position information. The invention is applicable to all types of projectiles, missiles or the like which are fired from a barrel or launch tube and which rotate in their trajectory. The invention can be used in particular in so-called terminal-stage-guided ammunition, i. e. projectiles which are fired in a conventional manner in a ballistic trajectory to the immediate vicinity of the target, where they receive a command for necessary correction. Due to the fact that the projectile rotates in its trajectory, its roll position must be determined when the command is executed. In the absence of members for determining the roll position, an error otherwise occurs in the course of correction. It is already known from Swedish Patent Application 8801831-2 to determine the roll angle position with the aid of polarised electromagnetic radiation, comprising a transmitter arranged to emit a polarised radiation in the direction towards the projectile and a polarisation-sensitive receiver arranged in the projectile. By having the emitted polarised radiation consist of at least two mutually phase-locked radiation components with a wavelength ratio of 2:1 and/or multiples thereof, which are superposed and form an asymmetrical curve shape, the roll position of the projectile can be unambiguously determined. The abovementioned arrangement presupposes that a transmitter is placed in connection with the launching position of the projectile and that the projectile is provided with a rearward-directed receiving antenna in order to receive the transmitted radiation. The arrangement furthermore presupposes that two mutually phase-locked radiation components with different frequencies are transmitted. This means that both the transmitter and the receiver are of a relatively complicated construction. It is also already known from EP 0,345,836 to determine the roll angle position by giving the one carrier wave a sinusoidal amplitude modulation in order to continuously to transmit information on the phase position. It emerges from the description that such a system has advantages on the account of simpler construction of the receiving part in the projectile. However, it emerges that two antennas of known relative orientation are required in the receiver. The aim of the present invention is to provide an alternative to the arrangement described above for roll angle determination, in which, instead of a continuous transmission of the phase position a transmission of phase information takes place only at certain points in time when the signal passes through zero with a positive-going or alternatively negative-going derivative. According to the invention the second radiation component is transmitted in the form of a pulse train in which the pulses indicate the first radiation component's zero cross-oven with a positive-going derivative, or alternatively with a negative-going derivative. The two radiation components are then detected in the shell and are applied to a microprocessor system for evaluation. The advantage of transmitting the information on the phase position only when the first radiation component passes zero with a certain derivative sign is that such a system is more interference-proof. The risk of detection is less, since it is more difficult to calculate, from the short pulses, the frequency which is being used for the transmission and in this way to disrupt the transmission. It suffices to transmit the information on a single occasion when the shell is at the start of its trajectory. If the processor of the receiver has received the information only once, it can then keep track of the roll position of the shell by counting dips in the envelope of the received signal. Alternatively, the information on the phase position can be transmitted exactly at the time when correction of the trajectory is to be carried out. In order to improve the interference security through redundancy, the information can preferably be repeated on a number of occasions during the passage of the shell in the trajectory. A further advantage of the invention is that only one antenna need be used in the long-wave receiver for the detection. This of course represents a simplification, and both an antenna and an amplifier can be omitted in the long-wave receiver. An embodiment of the invention is shown diagrammatically in the attached drawings, in which Figure 1 is a view of the projectile and the equipment required for determining the roll angle position of the projectile, Figure 2 shows the curve shape of the radiation components, Figure 3 shows the construction of the transmitter in a block diagram, and Figure 4 shows the construction of the receiver. In order to give a projectile, shell or the like an improved stability in its trajectory, it is already known to give it a rotation upon firing. In-built electronics in the shell intended for tactical purposes in this case lose the references to the roll position angle. Figure 1 shows an outline diagram of how a roll angle reference can be unambiguously determined. A transmitter is positioned on the gun or in its immediate vicinity, which transmitter comprises two sets of transmission equipment, one for the long-wave band and one for the microwave band, these transmitting polarised electromagnetic radiation towards the shell 1. The long-wave transmitter 2 transmits via an antenna 3 a vertically polarised (VP), sinusoidal radiowave in the long-wave band (LF) and a microwave transmitter 4 transmits via the antenna 5 a directed circularly polarised wave (CP) towards the shell 1 on the microwave band ( V). The transmitter 2 sends synchronising codes to the transmitter 4 via connection 6. The long-wave band (LF) comprises the frequency range of 30-300 kHz and the mediumwave band (MF) comprises the frequency range of 300-3000 kHz. The frequency of the sinusoidal long-wave component thus lies in the LF range or lowest decile of the MF range, while the frequency of the microwave component exceeds 1 GHz. In the shell there are two receivers, on the one hand a receiver 7 which detects the magnetic field H LV of the long-wave signal, with the aid of a loop antenna 8, and a receiver 9 which detects the microwave signal from an antenna 10 situated in the rear of the shell. The two detected signals are applied to a microprocessor system 11 for evaluation. The transmitted long-wave signal 12 has a harmonic sinusoidal form, see Figure 2a. After each zero cross-over with a positive-going derivative, a synchronising pulse is sent from the long-wave transmitter 2 via the connection 6 to the microwave transmitter 4, which thus initiates transmission of the microwave radiation in the form of a pulse train 13, see Figure 2b. The antenna 8 in the shell for receiving the long-wave radiation is aligned with the aid of a reference point 14 in the shell. When the antenna 8 is oriented parallel to the antenna 3 of the long-wave transmitter, a signal 15 is obtained, and when the shell has turned 180°, a signal 16 is obtained, see Figure 2c. In Figure 2d, the received signal is shown relative to the orientation of the shell. Since the time between the nodes on the rotation envelope corresponds to half a turn of the shell, the microprocessor, knowing the speed of rotation, can calculate in a known manner the actual roll angle position of the shell. In Figure 3, a block diagram shows how the transmitter is constructed. The transmitter comprises a generator 17 which generates one of the two signals which are required for determining the position, namely the long-wave signal. The other position-determining signal is emitted by the microwave transmitter 18. The signals are amplified in amplifier 19 for the long-wave signal and amplifier 20 for the microwave signal, and the two signals are transmitted by antennae 3 and 4, respectively. An arrangement 21, which detects the derivative and the zero cross-overs of the long-wave signal, gives a signal to a microprocessor 22 and the microwave transmitter 18 when the long-wave signal is situated in the predetermined position. In response to this signal, the microwave transmitter 18 transmits the unique signal which indicates that the long-wave signal is situated in a certain phase position. Figure 4 shows the construction of the receiver. The receiver comprises two antennae, a long-wave antenna 8 and a microwave antenna 10. The long-wave signal is incoming at a receiver 7 which amplifies the signal to levels which pass through an A/D converter 23. A microprocessor 11 reads the A/D converter and preserves these values in a register. The microwave signal is converted by the microwave receiver 9 to digital signals which are collected in a buffer 24. The main task of the microprocessor is to evaluate the long-wave signal and calculate the actual rotation position starting from earlier data. When information is incoming on the microwave channel, interrupt is requested. If the information contains a derivative indication, the information is updated upwards/downwards, and if it contains a command, the latter is decoded and executed. As already mentioned, the time between each node in the long-wave signal corresponds to half a turn of the shell. In order to be able to determine unambiguously the actual roll angle position, the speed of rotation must be calculated. This can be calculated with knowledge of the time between the nodes of the rotation envelope. The momentary angle of rotation is calculated such that the time from the latest node gives a value which lies between 0° and 180°. The upward/downward information then gives an offset of 0° (up) or 180° (down). This combination then gives an unambiguous value for the instantaneous angular position.

Claims: Arrangement for determining the roll angle position of a rotating projectile, shell, missile or the like with the aid of polarised electromagnetic radiation, comprising a transmitter arranged to emit a position-determining polarised radiation in the direction towards the projectile and a receiver arranged in the projectile in order to receive the transmitted radiation, the emitted polarised radiation consisting of two components, on the one hand a first radiation component (12) of a longer wavelength and on the other hand a second radiation component (13) of a shorter wavelength, this second radiation component comprising a pulse train (13) in which the pulses indicate that the first radiation component is situated in a certain phase position, characterised in that the pulses in the microwave component (13) indicate the sinusoidal long-wave component's zero cross-overs with a positive-going derivative, or alternatively with a negative-going derivative. Arrangement according to Patent Claim 1, characterised in that the transmitter comprises a first generator (17) and an antenna (3) for transmitting the first radiation component, a second generator (18) and an antenna (4) for transmitting the second radiation component, and an arrangement (21) for detecting when the first radiation component passes zero with a certain derivative sign and which emits a signal to the second generator (18) when the first radiation component passes said zero with a certain sign, said second generator (18) emitting a pulse in order to indicate said passing of zero. Arrangement according to Patent Claim 2, characterised in that the receiver in the projectile comprises a receiver part (7, 8) for receiving the first radiation component, a receiver part (9, 10) for receiving the second radiation component. and a microprocessor (11) for evaluating the first radiation component. Arrangement according to Patent Claim 3. characterised in that the receiver part (7. 8) for receiving the first radiation component comprises an antenna(8) which is aligned with the aid of a reference point (14) in the projectile.

Inventors: HANSEN AKE, HANSEN, AKE, Hansén, Ake
Applicants: BOFORS AB
Application year: 1991
Main classification: F41G7
IPC codes: F41G7, F41F3, F42B15, G06F19