GB2087188A

GB2087188A - Range finder

Info

Publication number: GB2087188A
Application number: GB8132958A
Authority: GB
Original assignee: Diehl GmbH and Co
Current assignee: Diehl Verwaltungs Stiftung
Priority date: 1980-11-03
Filing date: 1981-11-02
Publication date: 1982-05-19
Also published as: DE3041272A1; FR2493529B3; GB2087188B; FR2493529A1

Abstract

An electronic range finder for ascertaining the distance of a target, wherein a transmitter (2, 2') radiates an optical or acoustic transmission impulse sequence which, after reflection at the target, arrives at a reception amplifier (8) the amplification factor of which is raised in a time-dependent manner during the transmission impulse interval. Each transmission impulse switches a further impulse sequence onto an impulse counter (5) the impulse frequency of which sequence is higher than the frequency of the transmission impulse sequence. The counter state is conducted to an evaluation circuit, e.g. a display unit (11) A control circuit (6, 7) forms, from the counter state, a control quantity which embraces the square of the counter state and possibly a correction for the input voltage dependency of the amplification factor of the amplifier (8). The control quantity controls the amplification of the amplifier (8). The amplifier (8) stops, upon the receipt of an impulse, the counter (5), and upon the occurrence of a transmission impulse, the counter (5) is reset. An impulse transit-time measurement for a wide range of target distances is possible even if short transmission impulses and long transmission impulse intervals are employed. Application to proximity fuses is mentioned. <IMAGE>

Description

SPECIFICATION An electronic range finder The invention relates to an electronic range finder, for ascertaining the distance of a target, in which range finder a transmitter radiates an optical or acoustic transmission impulse sequence which, after reflection at the target, arrives at a reception amplifier, the amplification factor of which is raised in a time-dependent manner during the transmission impulse interval.

In the case of range finders which detect the transit time of a transmission impulse to and from the target, the reflected signals received lie in a wide dynamic range. By virtue of the square-law relationship, the intensity of the reflected signals decreases with the square at the distance traversed by the signals, so that when the measuring range of the range finder is designed forthefactor 100, the reception amplifier has to process reflected signals with a dynamic range of at least 104.

An adjustment of the reception amplifier by the reception signals would be possible if the keying ratio (pause to pulse ratio) were low. Usually the keying ratio in the case of impulse transit-time range finders is, however, high, so that, by virtue of necessary control time constants, an adjustment in practice is not possible.

In United States Patent No. 3725925 it is mentioned that the reception amplifier can timewise be so controlled that the amplification factor thereof is raised during the transmission impulse interval.

An object of the invention is to provide a range finder, of the kind described, which makes possible the measurement of impulse transit-time over a wide range of distances using short transmission impulses and long pauses between the transmission impulses.

According to the present invention, there is provided a range finder of the kind described which is characterised in that each transmission impulse switches onto an impulse counter a further impulse sequence the impulse recurrence frequency of which is higher than the frequency of the transmission impulse sequence; in that the counter state is conducted to an evaluation circuit; in that a control circuit forms, from the counter state, a control quantity or value which embraces the square of the counter state (with or without a correction for any input voltage dependency of the amplification factor); in that the control quantity or value is converted into a control voltage which controls the amplification of the reception amplifier; in that the reception amplifier stops the impulse counter upon the reception of a reflected impulse; and in that upon the occurrence of a transmission impulse the impulse counter is or has been reset.

In operation, the impulse counter is switched on simultaneously with the radiation of a transmission impulse. In the course of the run-up of the counter, the amplification factor of the amplifier is increased proportionally to the square of the respective counter state: if the dependency of the amplification factor upon the input voltage is non-linear, this non-linearity is also taken into account by means of a suitable correction or correction value as the amplification factor is increased.

When a reflected impulse arrives, the amplifier is set at that instant to an amplification factor which ensures the necessary amplification of the reflected impulse. Upon receipt of the reflected impulse, the counter is stopped. The counter final value is a measure of the distance covered by the impulse to and from the target.

The impulse recurrence or repetition frequency of the impulse sequence stepping-on the counter can be so selected that the counter steps-on per unit of the target distance, for example each 1 decimetre, by "1". The counter final state is evaluated in the evaluation circuit.

The range finder may have a digital display unit connected subsequent to the impulse counter to offer a readable display.

If the range finder is arranged in a proximity fuze, the counter state is compared with a stored desired value and, in the event of conformity, the ignition or detonation is triggered.

Further advantageous developments of the invention will become apparent from the following description of a exemplary embodiment shown diagrammatically in the accompanying drawings.

In the drawings: Figure 1 shows a circuit diagram of a range finder with a display unit as evaluation circuit; Figure 2 shows another evaluation circuit for the range finder; and Figure 3 shows an impulse diagram.

A generator 1 produces a transmission impulse sequence, in which respect the impulse duration is short, for example lies in the nano-second (ns)range, and the impulse intervals are long, for example lie in the second (s)-range. Such an impulse sequence is shown in Figure 3a. Connected subsequent to the generator 1 is a transmission amplifer 2 which acts on an opto-electronic transmission component part 2'. Instead of the opto-electronic transmision component part, an electroacoustic transmission component part working in the ultra-sonic range can be provided.

The output of the generator 1 is connected to a gate circuit 3, which lies between a further impulse generator 4 and a digital counter 5. The generator 4 produces an impulse sequence the frequency of which is considerably higher than that of the transmission impulse sequence (see Figure 3b). Upon the occurrence of a transmission impulse, this closes the gate circuit 3 in such a way that the generator 4 is connected to the counter 5 so that the counter 5 receives timing impulses from the generator.

Connected subsequent to the counter 5 is a control circuit which comprises a programmable fixed-store module (PROM) 6. Such a module is known, for example, under the type designation CDP 1833 C of Messrs. Hughes. Connected subsequent to the PROM 6 is a digital/analogue converter 7 of the control circuit, the analogue output of which converter 7 is connected to that input of a reception amplifier 8 by means of which the amplification factor can be adjusted or controlled. At the input of the reception amplifier 8 there is connected a reception component 9 which corresponds to the transmission component 3.

The output of the reception amplifier is so connected by way of an impulse shaper stage 10 to the gate circuit 3 that an output impulse of the impulse shaper stage 10 opens the gate circuit 3 and thus interrupts the connection between the generator 4 and the counter 5.

In the case of the exemplary embodiment shown in Figure 1, an evaluation circuit, in the form of a digital display unit 11, is connected subsequent to the counter 5.

The programmable fixed-store module 6 is so programmed that it forms, from the respective counter state, a control quantity or value which is proportional to the square of the counter state.

Moreover, as a result of the programming facility afforded by the module 6, a correction or correction value can be provided to compensate for any dependency of the amplification factor of the amplifier 8 upon the reception voltage from the component 9. This dependency can be perceived from the data sheets of such a reception amplifier 8 (for example TBA 400 Siemens; MC 3340 Motorola). The control quantity which the module 6 produces is a digital quantity or value. This is converted, in the converter 7, into a corresponding analogue control voltage value.

Thus, during the running of the counter 5 (see Figure 3d), i.e. during the travel of the transmission impulse from the transmission component 2' to the target and back to the reception component 9, the amplification factor of the reception amplifier 8 is continually raised. In the case of fairly great distances between the range finder and the target, the reflected or incoming impulse is thus received when the amplifier 8 is set to a higher amplification factor than in the case when the target is at shorter distances, in which respect the square-law decreases of the intensity of the impulse with its distance traversed is taken into account.

In order to achieve the simpiest possible construction of the display unit 11, the frequency of the generator 4 is so arranged that 0.5-impulses are counted per smallest unit of display (dm, m) for each unit travelled by the transmitted impulse taking into account the speed of the signai impulse (the speed of sound or the speed of light) so that the counter steps on by 1 unit per unit of target distance. In the case of acoustic impulses there emerges, taking into account the speed of sound of 330 m/s and if decimetres are to be displayed as lowest units, an impulse repetition frequency of about 1.66 kHz for the generator 4. For light impulses there emerges, taking into account the speed of light of 3.1 or mis, if metres are to be displayed as the lowest units, a frequency of 150 MHz.

Sothatthe counter beginsto count afresh from zero from the transmission of each impulse, the counter is reset to its zero value in the time between the arrival of the incoming reflected impulse and the transmission of the next impulse. The decaying flank of the reflected impulse after the impulse shaper stage 10 can be used for resetting the counter. In this case the display, which has continued to be counter up till then, can be maintained by means of an intermediate store, e.g. until the occurrence of the next reflected impulse.

If or when the rising flank of the transmission impulse at the output of the generator 1 is used for the resetting of the counter 5, then the decaying flank of the transmission impulse is utilised for the closing of the gate circuit 3.

The circuit in accordance with Figure 2 can be used instead of the display unit 11 if an ignition procedure is to be triggered at a specific target range instead of the target range being indicated. In this embodiment the evaluation circuit comprises a comparison stage 12 to which the counter 5 and a desired-value transmitter 13 are connected. Connected subsequent to the comparison stage 12 is an ignition circuit 14. In the event of the counter state conforming with the desired value set in the transmitter 13, the comparison stage 12 triggers the ignition circuit 14.

Shown in Figure 3a is a transmission impulse sequence, in which respect the transmission pulse interval amounts to about 2 seconds. If one makes a start from the fact that the impulse repetition frequency of the generator 4 (Figure 3b) amounts to 1.65 kHz, then, in the case of one reflected impulse which has returned after 1 second (Figure 3c 1), 1650 timing impulses will have passed into the counter 5 (see Figure 3d 1). Accordingly, the display of the display unit reads "165.0 m". This display is equal to the distance of the range finder from the target, because the acoustic impulse has travelled in 1 second from the transmitter to the target and back at a speed of 330 metres per second so that 1 timing impulse has been counted for each 2 decimetres travelled by the transmission impulse.

In Figure3cl, d1,the conditions for an approaching target are shown. In Figure 3c2 and 3d2, the conditions for a target which is moving away are shown. The upper limit of the detectable range in the case of an acoustic impulse and the said transmission impulse spacing amounts theoretically to 330m.

Upon the use of light impulses, the conditions change according to the speed of light and the then-selected impulse repetition frequency of the generator 4.

The embodiment described has the advantage that, by virtue of the digital counting, a timetemperature drift does not occur in practice.

Claims

1. An electronic range finder for ascertaining the distance of a target, in which a transmitter radiates an optical or acoustic transmission impulsesequ- ence which, after reflection at the target, arrives at a reception amplifier the amplification factor of which is raised in a time-dependent manner during the transmission impulse interval, characterised in that each transmission impulse switches onto an impulse counter, a further impulse sequence the impulse frequency of which is higher than the frequency of the transmission impulse sequence; in that a control circuit forms, from the counter state, a control quantity which embraces the square of the counter state, with or without a correction for any input voltage dependency of the amplification factor; in that the control quantity, converted into a control voltage, controls the amplification of the reception amplifier; in that the reception amplifier stops the impulse counter upon the receipt of a reflected impulse; and in that upon the occurrence of a transmission impulse the impulse counter is or has been reset.

2. A range finder as claimed in claim 1, characterised in that the impulse repetition frequency of the further impuse sequence is so selected that the impulse counter steps-on by "1" per unit of the target distance.

3. A range finder as claimed in claim 1 or 2, characterised in that the evaluation circuit comprises a display unit.

4. A range finder as claimed in claim 1 or 2, characterised in that the evaluation circuit comprises a comparison stage, a desired-value setter and an ignition circuit.

5. A range finder as claimed in any one of the preceding claims, characterised in that the control circuit comprises a programmable fixed-store module and by a digital/analogue converter.

6. A range finder as clamed in any one of the preceding claims, characterised in that provided between a generator for the production of the further impulse sequence and the impulse counter there is a gate circuit which is controlled, on the one hand, by the transmission impulse and, on the other hand, by the reception impulse.

7. A range finder as claimed in any one of the preceding claims arranged so that a trailing flank of an impulse derived from a reflected impulse can be used to reset the counter before transmission of a subsequent transmission impulse.

8. A range finder as claimed in any one of the preceding claims arranged so that a rising flank of a transmission impulse can be used to reset the counter and a decaying flank of said impulse can be used to switch said further impulse sequence onto the counter.

9. A range finder substantially as hereinbefore described with reference to Figure 1 or Figure 1 as modified by Figure 2 of the accompanying drawings.