GB2276055A

GB2276055A - Speed measurement

Info

Publication number: GB2276055A
Application number: GB9305103A
Authority: GB
Inventors: Greville George Bloodworth; Peter Graham Long
Original assignee: YORK EQUIMED Ltd
Current assignee: YORK EQUIMED Ltd
Priority date: 1993-03-12
Filing date: 1993-03-12
Publication date: 1994-09-14
Anticipated expiration: 2013-03-12
Also published as: GB9305103D0; GB2276055B

Abstract

A speed measurement device comprises a transmitter 2 transmitting a microwave signal and mounted 22 on a moving body 20, and a receiver 4, mounted on the body, receiving reflections of the transmitted signal from the surroundings. The homodyned with the transmitted signal 6 is to provide a Doppler signal which is amplified 8 with a gain which increases with frequency. The resultant signal is digitally Fourier analysed 10, 12 (Fig. 4) to determine the frequency at which its amplitude-versus-frequency curve (Fig. 5A, 5B) drops suddenly. This frequency is used to determine the speed of the body 20. The speed is displayed on the device, transmitted to another part 30 of the moving body or transmitted by radio to a remote display unit. The display (Fig. 3) is in the form of LCD or LED bars, or may be a digital display. <IMAGE>

Description

SPEED MEASUREMENT This invention relates to speed measurement.

The Doppler effect has been used widely to measure the speed of moving objects. It depends upon aiming a beam of radiation towards the moving object, detecting the reflected radiation, and measuring the shift in frequency between the transmitted and received radiation waves. The frequency shift indicates the speed of the moving object.

Although Doppler-effect systems have been used mostly to measure the speed of a moving object relative to a stationary source of radiation, the same principal has been used to monitor the speed of a moving subject. In such cases, a radiation transmitter carried on the moving subject aims the radiation at a specific stationary object. and makes use of the Doppler-effect generally as described above.

In all cases of which we are aware, Doppler-effect speed measurement systems depend upon a high degree of directionality. For example, a stationary transmitter usually has to be aimed with some accuracy at a moving object, in order to measure its speed. Equally, a moving subject has to aim a radiation beam with some accuracy towards a stationary object (typically the ground or water surface).

Because of this relatively high degree of required directionality, Doppler-effect devices have not proved suitable for personal use - that is, in the form of a radiation transmitter to be carried by a person, to provide a Doppler-effect measurement of the person's speed. This is due to the inherent lack of accuracy in aiming a transmitter at a predetermined stationary object e.g the ground.

Preferred embodiments of the present invention aim to provide a Doppler-effect speed measurement system which is suitable for personal use, since it has, relative to the prior art a lower requirement of directionality.

According to one aspect of the present invention, there is provided a speed measurement system comprising: transmitting means for transmitting a signal at a predetermined frequency; receiving means for receiving a signal which comprises reflections of the transmitted signal from surroundings of the system; signal processing means for receiving the received signal and a portion of the transmitted signal and outputting a difference signal which represents the frequency difference therebetween and is gain-adjusted such that signal components of higher frequencies are boosted relative to signal components of lower frequencies; frequency analysing means for analysing the frequency components of the gain-adjusted difference signal;; detecting means for detecting a transition frequency or region of the gain-adjusted difference signal, below which frequency components have an average amplitude greater than that of frequency components above the transition frequency or region; and output means for providing an output signal which varies in dependence upon the transition frequency or region detected by the detected means to represent a speed at which the system is moving relative to its surroundings.

Preferably, said signal processing means comprises: comparing means for receiving as input signals the received signal and a portion of the transmitted signal and outputting a difference signal representing the frequency difference therebetween; and amplifying means for amplifying the difference signal output from the comparing means, the amplifying means having a gain that increases with the frequency of the difference signal.

Preferably, said frequency analysing means comprises sampling means for sampling the gain-adjusted difference signal; calculating means for calculating the amplitude of the sampled signal in each of a plurality of frequency bands; and storing means for storing the results of the calculations of said calculating means.

Preferably, said detecting means comprises means for scanning said results.

Preferably, said frequency analysing means and said detecting means are provided by a digital processor, a first memory means storing a program to control operation of the processor, and a second memory means serving as said storing means.

Preferably, said transmitter and receiver are arranged to transmit and receive signals in the frequency range 1 to 30 GHz.

A system as above may further comprise a display means arranged to receive said output signal and display a current speed of the system relative to its surroundings.

Said display means may be adapted to be worn by a user. It may comprise a series of elements each having two display modes, and adapted to change between said modes as said output signal passes threshold values respective to the element.

Said elements may comprise LEp or LCD elements, and the higher the speed represented by said output signal, the more of said elements change mode.

According to another aspect of the present invention, there is provided a method of measuring the speed of a subject, comprising the steps of: carrying on or adjacent the subject a speed measurement system according to any of the preceding claims; operating said transmitting means to transmit said signal of predetermined frequency in a direction which is generally forward or rearward of a direction of motion of the subject:: operating said receiving means to receive a signal which comprises reflections of the transmitted signal from surroundings of the system; operating said signal processing means to receive the received signal and said portion of the transmitted signal and output said gain-adjusted difference signal; operating said frequency analysing means to analyse the frequency components of the gain-adjusted difference signal; operating said detecting means to detect said transition frequency or region of the gain-adjusted difference signal; and operating said output means to provide said output signal to represent the speed at which the system is moving relative to its surroundings.

Said subject may be a person - for example, a rider or a horse rider.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: Figure 1 is a circuit diagram of one example of the speed measurement system embodying the present invention; Figure 2 illustrates a horse rider equipped with such a system; Figure 3 illustrates one example of a display unit that may be used with the system of Figure 1; Figure 4 illustrates a digital embodiment of parts 10 to 14 of the system of Figure 1; and Figures 5A and 5B are frequency spectrum diagrams.

The speed measurement system 1 of Figure 1 comprises a transmitter 2, receiver 4, mixer 6, amplifier 8, frequency analyzer 10, detector 12, output driver 14 and display unit 16.

The transmitter 2 is arranged to transmit electromagnetic signals in the microwave range - of the order of 1010 Hz. The receiver 4 is arranged to receive a received signal which comprises reflections of the signal transmitted by the transmitter 2, after reflection by the surroundings of the system 1.

The mixer 6 mixes a small proportion of the signal transmitted by the transmitter 2 with the signal received by the receiver 4, and produces a difference signal which represents the difference in frequency between the transmitted and received signals. Such "Doppler effect" frequency differences are caused by the speed of the system 1 relative to its surroundings.

The amplifier 8 amplifies the difference signal received from the mixer 6 with a nonlinear gain. The gain of the amplifier 8 increases with frequency - for example, at a rate of approximately 40 decibels per decade. Thus, the signal components of higher frequency are amplified more than the signal components of lower frequency.

The frequency analyzer 10 receives the gain-adjusted difference signal from the amplifier 8, and analyses its frequency components. The detector 12 detects a transition frequency or transition region in the analyzed signal, at which there is a significant change in amplitude between lower and higher frequencies. The frequency or (mean frequency) at which this transition occurs represents the speed of the system 1 relative to its surroundings, and the detector 12 outputs a signal relative to the transition frequency. This signal is amplified by the output driver 14, and fed at a suitable level to the display unit 18, which provides an appropriate speed display.

The reason for the non-linear gain of the amplifier 8 is as follows. The microwave signal from the transmitter 2 is reflected by various stationary objects surrounding the system 1, and these reflect the transmitted signal back to the receiver 4 from a variety of directions. The receiver 4 picks up reflections from objects both close and quite far away. The relative speed of the system 1 with respect to the furthest objects will be faster than for nearer objects because the angle subtended between the direction of travel and the path to the object increases with proximity. The received frequency is proportional to the cosine of this subtended angle. Therefore, reflections from the horizon may be directly proportional to forward speed but very weak, and reflections from the ground near the subject have low speed components but are relative strong.By amplifying the difference signals so that the higher frequencies present are increased more than the lower ones, the power spectrum may be obtained within an approximately flat amplitude response up to the maximum frequency available. At this frequency, a sharp cut-off occurs which corresponds to the forward velocity of the sensor, towards objects in the line of motion.

Examples of waveforms from the frequency analyzer 10 are shown in Figures 5A and SB. These represent results obtained in practical experiments.

Figure SA illustrates the case of the system 1 moving at a speed of approximately 15 mph relative to its surroundings. The transmitter was pointed in a generally forward direction, but with no great accuracy of directionality. It can be seen that there is a distinct transition frequency or region fl in the frequency spectrum of the gain-adjusted difference signal.

The transition occurs in the region of 450 Hz, indicating a Doppler shift frequency of around 30 Hz for each mile per hour. Figure SB shows a similar frequency spectrum for a forward speed of approximately 25 mph.

Here, the frequency transition f2 occurs in the region of 750 Hz.

Figure 2 illustrates how a speed measurement system such as that of Figure 1 may be used by a horse rider 20. A combined transmitter/receiver 22 is mounted on the rider's helmet 24, to point in a generally forward direction. The unit 22 is connected to a signal processing unit 26 worn by the rider 20 on a belt 28. The signal processing unit 26 is in turn connected to a display unit 30 which is worn on the rider's wrist. An example of the display unit 30 is shown in Figure 3.

In use, microwave radiation is transmitted to the surroundings from the transmitting/receiving unit 22. and reflections from the rider's surroundings are received in the unit 22. Mixing of the transmitted and received signals may conveniently be effected by allowing a small amount of the transmitted signal to illuminate the receiver. The mixed signal is then fed to the signal processing unit 26, where gain adjustment. frequency analysis detection and output driving are carried out. as described above with reference to Figure 1.

The speed measurement output signal is fed to the display unit 30.

In the example shown in Figure 3, the display unit 30 has a wrist strap 34 and comprises a series of LED (Light-Emitting-Diode) or LCD (Liquid Crystal Display) segments 32. Each segment represents a speed increment of approximately 3 mph. Thus, if three segments are illuminated or energised, the forward speed is approximately 9 mph. Such a display 30 may be convenient where it is desired to represent speed only in an approximate manner. Alternatively, a full digit (or alternative) display may be employed, to give a more accurate reading.

Preferably, the frequency analysis and detection is carried out by digital processing, and real-time fast Fourier transform techniques may be employed.

For example, a digital signal processing unit may sample the gain-adjusted difference signal at frequent intervals and calculate the signal amplitude in each of a large number of frequency bands. The values of the signal amplitudes are stored in a results table, through which a processor scans regularly, starting at a high-frequency location until the first occurrence of a number exceeding a preset threshold is reached. This location corresponds to the highest significant frequency detected and therefore is proportional to the forward speed of the subject. The address number associated with this frequency is loaded into a digital filter which smooths out rapid variations in sampling, which may be caused by vibration of the transmitter and/or receiver, or major changes and reflections due to approaching objects.The display unit 16 may be illuminated. and may be updated about 3 or 4 times per second.

Figure 4 shows one possible realisation of the frequency analyzer 10, detector 12 and output driver 14. This comprises an analog-to-digital converter 11 which receives the output signal from the amplifier, and provides a digital output to a digital processor 13, which is programmed by means of an electrically erasable programmable read only memory (EEPROM) 15 and is provided with a random access memory (RAM) 17 for processing data.

The output of the processor 13 passes to a digital-to-analog converter 19, the output of which passes to the display 16.

A particular advantage of the illustrated embodiment of the invention is that the transmitter/receiver (which may be combined as a single unit) need not be directed at the ground, as is generally the case with previously proposed systems. On the contrary, it is preferred that the transmitter/receiver unit is pointed generally towards the horizon, in order that the reflections may be obtained from a variety of different objects. Advantage is taken of the fact that these objects will provide Doppler shift frequencies over a wide range, up to a maximum frequency corresponding to a dead-ahead object. It is the termination of the spectrum of frequencies that enables the maximum frequency of the spectrum, and therefore the dead-ahead speed, to be calculated. Also, it is relatively easy to filter out spurious frequencies caused by other moving objects, since they will provide a Doppler shift frequency in a very narrow band which, generally, will be outside the relatively wide spectrum that is detected by the frequency analysing and detector unit. Thus. single or very narrow band frequencies outside the continuous spectrum of interest may be ignored by the processing unit.

It will be appreciated that. although the transmitter/receiver unit may usually be pointed in a generally forward direction, it may work also by being oriented in a generally rearward direction. since a similar Doppler effect will be created, due to the speed of the subject relative to its surroundings.

It is to be found particularly convenient to use radiation in the form of electromagnetic waves in the microwave frequency range - e.g. 1 - 30 GHz.

However, radiation of other frequencies may be utilised (including ultrasonics).

Although the illustrated embodiment of the invention shows a speed measurement system applied to a horse rider, embodiments of the invention may have various other applications. For example, a system may be used simply to measure the speed of a human being, walking or running. A system may be carried on or adjacent a human being, and/or on or adjacent the body of an animal (or other ridden object). to measure its speed. It could be secured directly to the body of an animal (or other ridden object) to measure its speed. It may be provided with a telemetry link to provide a speed reading to a remote monitoring station. It may have other sports applications - e.g.

for skiers and cyclists; and other non-sports applications - e.g. it may be applied to robotic devices, to measure their speed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims. abstract and drawings), and/or all of the steps of any method or process so disclosed. may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims. abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS:

1. A speed measurement system comprising: transmitting means for transmitting a signal at a predetermined frequency; receiving means for receiving a signal which comprises reflections of the transmitted signal from surroundings of the system; signal processing means for receiving the received signal and a portion of the transmitted signal and outputting a difference signal which represents the frequency difference therebetween and is gain-adjusted such that signal components of higher frequencies are boosted relative to signal components of lower frequencies; frequency analysing means for analysing the frequency components of the gain-adjusted difference signal:: detecting means for detecting a transition frequency or region of the gain-adjusted difference signal below which frequency components have an average amplitude greater than that of frequency components above the transition frequency or region: and output means for providing an output signal which varies in dependence upon the transition frequency or region detected by the detected means to represent a speed at which the system is moving relative to its surroundings.

2. A system according to claim 1. wherein said signal processing means comprises: comparing means for receiving as input signals the received signal and a portion of the transmitted signal and outputting a difference signal representing the frequency difference therebetween; and amplifying means for amplifying the difference signal output from the comparing means, the amplifying means having a gain that increases with the frequency of the difference signal.

3. A system according to claim 1 or 2, wherein said frequency analysing means comprises sampling means for sampling the gain-adjusted difference signal; calculating means for calculating the amplitude of the sampled signal in each of a plurality of frequency bands: and storing means for storing the results of the calculations of said calculating means.

4. A system according to claim 3, wherein said detecting means comprises means for scanning said results.

5. A system according to claims 3 and 4, wherein said frequency analysing means and said detecting means are provided by a digital processor.

a first memory means storing a program to control operation of the processor.

and a second memory means serving as said storing means.

6. A system according to any of the preceding claims, wherein said transmitter and receiver are arranged to transmit and receive signals in the frequency range 1 to 30 GHz.

7. A system according to any of the preceding claims, further comprising a display means arranged to receive said output signal and display a current speed of the system relative to its surroundings.

8. A system according to claim 7, wherein said display means is adapted to be worn by a user.

9. A system according to claim 7 or 8, wherein said display means comprises a series of elements each having two display modes, and adapted to change between said modes as said output signal passes threshold values respective to the element.

10. A system according to claim 9, wherein said elements comprise LED or LCD elements, and the higher the speed represented by said output signal the more of said elements change mode.

11. A speed measurement system substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

12. A speed measurement system substantially as hereinbefore described with reference to Figures 1 to 5 of the accompanying drawings.

13. A method of measuring the speed of a subject, comprising the steps of: carrying on or adjacent the subject a speed measurement system according to any of the preceding claims: operating said transmitting means to transmit said signal of predetermined frequency in a direction which is generally forward or rearward of a direction of motion of the subject; operating said receiving means to receive a signal which comprises reflections of the transmitted signal from surroundings of the system; operating said signal processing means to receive the received signal and said portion of the transmitted signal and output said gain-adjusted difference signal; operating said frequency analysing means to analyse the frequency components of the gain-adjusted difference signal; ; operating said detecting means to detect said transition frequency or region of the gain-adjusted difference signal: and operating said output means to provide said output signal to represent the speed at which the system is moving relative to its surroundings.

14. A method according to claim 13 wherein said subject is a person.

15. A method according to claim 14. wherein said person is a rider.

16. A method according to claim l 15. wherein said person is riding a horse.