GB2378597A

GB2378597A - Object Detection Device

Info

Publication number: GB2378597A
Application number: GB0119134A
Authority: GB
Inventors: Adrian George Garrod
Original assignee: Roke Manor Research Ltd
Current assignee: Roke Manor Research Ltd
Priority date: 2001-08-06
Filing date: 2001-08-06
Publication date: 2003-02-12
Also published as: WO2003014765A1; GB0119134D0

Abstract

An object detection device comprises at least two sensors (1 and 2), each adapted to transmit and receive signals, and a processor (3) to control operation of the sensors. A timing control signal from the processor switches the sensors between transmit/receive mode and receive only mode. A first sensor operates in transmit/receive mode, the first sensor transmitting at a first pulse repetition frequency and receiving reflections of the transmitted signal, reflected off an object; wherein the reflections are mixed with a reference signal to produce an intermediate frequency (IF) signal and analysed to derive a direct range measurement. The other sensor operates in receive only mode to produce an indirect range measurement and the receiver pulse generator operates at a second pulse repetition frequency. The operation is repeated for each other sensor operating in transmit/receive mode such that a set of direct and indirect measurements are obtained, whereby a linear distance from the object is derived from the direct and indirect range measurements. The device is particularly applicable to use as a parking aid.

Description

OBJECT DETECTION DEVICE This invention relates to an object detection device, particularly to assist a driver when parking a vehicle.

Many different types of parking aid have been proposed. For example, US 6,215, 415 describes a system in which three sensors, capable of both transmitting and receiving, are positioned closely adjacent one another and emit signals at three different frequencies. The reflection of each emitted signal off an object is received by their respective receivers and evaluated by a processor to determine the distance of the vehicle from the object. This information is then provided to the driver in the form of an audible or visual warning.

Another example is described in EP-1 043 213 in which multiple sensors are positioned around the vehicle and emit signals orthogonal to one another, reflections of which are received by the respective sensor which emitted them. The signals are processed and used to control the vehicle speed as it approaches an obstacle. However, in these prior art systems, the individual sensors do not operate in a co-operative way to provide an estimate of the closest object to the rear of the vehicle.

In accordance with a first aspect of the present invention, an object detection device comprises at least two sensors, each sensor being adapted to transmit and receive signals; and a processor to control operation of the sensors; wherein a timing control signal from the processor switches the sensors between transmit/receive mode and receive only mode; wherein a first sensor operates in transmit/receive mode, the first sensor transmitting at a first pulse repetition frequency and receiving reflections of the transmitted signal, reflected off an object; wherein the reflections are mixed with a reference signal to produce an intermediate frequency (IF) signal and analysed to derive a direct range measurement; wherein the or each other sensor operates in receive only mode to produce an indirect range measurement; wherein the receiver pulse generator operates at a second pulse repetition frequency; and wherein the operation is repeated for the or each other sensor operating in transmit/receive mode such that a set of direct and indirect measurements are obtained; whereby a linear distance from the object is derived from the direct and indirect range measurements.

The present invention provides an object detection device which is able to use sensors in an arrangement which maintains the simplicity of processing of individual

sensors making direct measurements, but enables a receiver at a remote location to be used to make indirect measurements. The combined effect gives a linear distance from an object, without complex processing being required.

Preferably, the sensors are pulse radar sensors.

For use in motor vehicles, this has the benefit over ultrasonic sensors that no cutout in the bumper is required, which would'spoil'the car's styling.

Typically, the sensors operate at frequencies in the range 2 to 100 GHz.

In accordance with a second aspect of the present invention, a vehicle parking zn aid comprises an object detection device according to the first aspect.

An example of an object detection device according to the present invention will now be described with reference to the accompanying drawings in which :- Figure 1 illustrates a general arrangement of the system; Figure 2 illustrates in more detail, a sensor in the system of Fig. 1 ; and, Figure 3 illustrates potential errors in range estimates for prior art systems and how the present invention overcomes these.

For simplicity, in this example, the system of the present invention comprises a first sensor 1 and a second sensor 2 connected to a central unit 3. However, commonly the system would comprise multiple sensors. The central unit 3 provides phase and time synchronising signals to each sensor during operation and receives range data from the sensors which it then processes. An advantage of this system is that the synchronising signals have a low frequency (of the order of MHz) which is related to the pulse repetition frequency (PRF) and are easy to distribute compared to synchronising the actual transmission between sensors.

The sensor itself is shown in more detail in Fig. 2. The sensor comprises a microcontroller 4 which controls a first pulse generator 5 which acts as a transmitter so that a signal for transmission is output through a directional coupler 6 via an antenna 7.

The transmitted signal reflected off an object is received by the antenna 7 and input to a low noise amplifier (LNA) 8 via the directional coupler 6. The output of the LNA is mixed in a mixer 9 with a signal from a second pulse generator 10 to produce an intermediate frequency (IF) signal which is amplified in the IF amplifier 11 and analysed by the microcontroller 4. The transmitter pulse generator and receiver pulse generator outputs differ only by a small amount with respect to their pulse repetition

frequencies. The IF signal incorporates a time expansion factor related to the b difference in PRF frequencies. This simplifies the processing of the IF signal. A substantially stable frequency difference is maintained between the frequencies of the first and second pulse generators.

In one example, the pulse generators operate at 5.8GHz, with a pulse repetition frequency of 3.6MHz, an IF of 70KHz, and the frequency difference is maintained at 43Hz. A benefit of using this sampling technique is that the scaling factor on the IF is significantly less than on the RF, so standard signal processing techniques can be used for processing of the received reflected signals. For this example the synchronising signals between sensors could be the PRF signal at 3.6 MHz and the difference frequency at 43 Hz.

With a single sensor only the radial distance from the sensor to the object can be determined. For a parking aid the linear distance from the rear of the vehicle to the object is required, hence multiple sensors are required. Using direct measurements from one or more sensors allows an obstacle's position to be calculated by triangulation (intersection of circles). An example of a technique for obtaining direct measurements is given in US-A-4, 521, 778.

However, a possible error mechanism which arises in systems using only direct measurements for an extended target is illustrated in Fig. 3a. Using indirect measurements as proposed in the present invention, allows this situation to be detected and corrected as shown in Fig. 3b. Obtaining indirect measurements provides further information placing obstacles on ellipses and so improving the accuracy of the position estimate. For some object positions, an object will not record a direct measurement for one of the sensors but will provide an indirect measurement, hence the position can still be calculated.

Claims

1. An object detection device, the device comprising at least two sensors, each sensor being adapted to transmit and receive signals; and a processor to control operation of the sensors; wherein a timing control signal from the processor switches the sensors between transmit/receive mode and receive only mode; wherein a first sensor operates in transmit/receive mode, the first sensor transmitting at a first pulse repetition frequency and receiving reflections of the transmitted signal, reflected off an object; wherein the reflections are mixed with a reference signal to produce an intermediate frequency (IF) signal and analysed to derive a direct range measurement ; wherein the or each other sensor operates in receive only mode to produce an indirect range measurement; wherein the receiver pulse generator operates at a second pulse repetition frequency; and wherein the operation is repeated for the or each other sensor operating in transmit/receive mode such that a set of direct and indirect measurements are obtained; whereby a linear distance from the object is derived from the direct and indirect range measurements.

2. A device according to claim 1, wherein the sensors are pulse radar sensors.

3. A device according to claim 1 or claim 2, wherein the sensors operate at frequencies in the range 2 to 100 GHz.

4. A vehicle parking aid comprising an object detection device according to any preceding claim.