MXPA98001567A - Emit thermal radiation detection device - Google Patents

Abstract

An emitted thermal radiation detection device is configured to detect objects in vehicle visual blind spots, a low cost differential detector is used that is sensitive to temperature changes, the optical has two different display fields in the detector and switch between the two display fields to provide a blind spot display field and a reference display field, the presence of a vehicle in the blind spot display field results in a temperature difference between the two display fields; The resulting detection output is compared to the predetermined minimum levels and then used to provide an indication, either visual or audible, various modalities of the optical and the switching of the display fields are provided.

Description

THERMAL RADIATION DETECTION DEVICE ISSUED FIELD OF LR INVENTION The present invention relates to a device for detecting emitted thermal radiation and refers particularly to the use of said device for detecting objects in a blind spot.

BACKGROUND OF THE INVENTION THE PROBLEM OF DETECTING The presence of a vehicle approaching from behind in the blind spot of a vehicle is well known. For example, the Patent of E.U.A. No. 5,122,796 issued on June 16, 1992 to George Beggs et al. And assigned to Auto-Sense Ltd., describes an active system utilizing an optical-optical transmitter and receiver. The emitter operates in an infrared region of short wavelength avoiding interference from long-wavelength thermal or infrared radiation sources emitted as hot objects. A bandpass filter is used to limit the detector to the pass band of the emitter. To add devices in automotive applications, it is desirable to operate power sources independent of the vehicle's main power system. Active devices such as the Beggs transmitter / detector system and others have a relatively high power consumption and a connection to the vehicle's electrical system may be necessary. Passive detector systems have been proposed. For example, the inventor of The present is a co-inventor of an international patent application of PCT / CA95 / 0013t filed on March 10, 1995, which proposes the use of a thermal radiation detector of the type found in motion detectors. of security system for a passive blind spot detector. This type of emitted thermal radiation detector requires a change in temperature to provide a supply. As in the case of the motion detector application, the proposed detector is based on the movement of the heat generating object through the detector's visualization field to generate a output signal. However, this type of detector is insensitive to permanently stationary objects. Therefore, a vehicle approaching from the back, which remains in the blind spot, if it remains in a fixedly fixed position, can not be detected and can be taken care of by the vehicle operator. The PCT application published under WO 86/03916 describes a radiation detector having a wide and narrow viewing field. However, this document does not conceive any way of detecting an infrared object or other radiant object in a blind spot of a vehicle. The description of VoL research. 338, N9, 076, 10 Dunio, 1992, Emsworth, GB describes a method for detecting an object in a blind spot of a vehicle by comparing the temperature in the blind spot with the road temperature. However, this is subject to temperature variations of the road and may give a false reading under certain circumstances.

BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to provide an improved device for detecting emitted thermal radiation. According to an aspect of the invention, there is provided a device for detecting thermal radiation emitted to detect objects in a blind spot comprising: detection means for generating an output signal that responds to emitted thermal radiation; means for defining first and second fields of visualization in relation to detection means; means for switching the detected display field to generate a combined output signal; and means for deriving an indication of a nearby object from the combined output signal. According to another aspect of the present invention, there is provided a thermal radiation detection device emitted to detect objects in a blind spot comprising: a detector that responds to changes in the thermal radiation emitted received to generate a supply signal; optics to define first and second fields of view in relation to the detector; a trigger to switch the detected field of view to generate a combined output signal; a signal generator to provide a square wave of predetermined frequency to operate the trigger; a high-pass filter connected to the detector to filter the combined output signal; a demodulator connected to the high pass filter and the signal generator to carry an object event signal; and an annunciator for comparing the object event signal to predetermined min levels and providing an indication of the presence of an object in the blind spot. An advantage of the present invention is the ability to detect a relatively stationary object at a blind spot. Another advantage of the present invention is the insensitivity relative to variations in surface temperatures common to the display fields.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be further understood from the following description with reference to the drawings in which: Figure 1 illustrates a thermal radiation detection device issued in accordance with a preferred embodiment of the present invention; Figure 2 illustrates the operation of the emitted thermal radiation detection device of Figure 1 mounted on a front vehicle to detect, at its visual blind spot, the presence of a vehicle approaching from the rear; Figure 3 schematically illustrates a composite Fresnel lens used in the emitted thermal radiation detection device of Figure 1; The figure schematically illustrates a circuit for deriving an indication of the presence of a vehicle approaching from the rear for use with the detector of Figure 1 in accordance with a preferred embodiment of the present invention; Figures 5a, 5b and 5c graphically illustrate typical signals in various stages of the circuit of Figure 4; Figure 6 illustrates a second mode of the thermal radiation detector emitted; Figure 7 illustrates a third mode of the thermal radiation detector emitted; and Figure 8 illustrates a fourth mode of the thermal radiation detector emitted.

OVERVIEW Referring to Figure 1, a blind spot detector according to one embodiment of the present invention is illustrated. The blind spot detector includes a thermal radiation detector 10, a Fresnel lens 12 in separate relation to the thermal radiation detector 10 emitted and a shutter 14 disposed between the thermal radiation detector 10 emitted and the Fresnel lens 12. Fresnel lens 12 includes four lens elements, 16, 18 and 20 defining display fields for the detector 10 corresponding to the blind spot and lens element 22 defining a field of view for the detector 10 directed towards a reference point in the road behind the vehicle. The obturator 14 is operated between a first position 24 and is biased towards that position by the return spring 26 and a second position 28 and is attracted towards the second position by an electromagnet 30. In the first position 24, the obturator blocks the fields The lens elements 16, 18 and 20 corresponding to the blind spot of the vehicle and allows the field of view of the lens element 22 corresponding to the reference point on the road to fall on the detector 10. In the second position 28 on The energizing electromagnet 30 the shutter blocks the field of view of the lens element 22 and allows the visualization fields of the lens elements 16, 18 and 20 corresponding to the blind spot of the vehicle to fall on the detector 10. Since the detector 10 It is sensitive to changes in temperature to switch between fields of view of a reference point in the way behind the vehicle to the point c vehicle, will provide The difference if there is a vehicle present within the blind spot. Referring to Figure 2, a vehicle 32 has a blind spot detector 34 mounted in accordance with the present invention and travels along a road in a lane 36. A second vehicle 38 follows the first vehicle in an adjacent lane 40. The blind spot detector 34 establishes viewing fields 42, 44 and 46 within the blind spot of the vehicle and is generally directed to a carriage 40 and a reference viewing field 48 directed from the rear of the vehicle 32 in the rail 36. Display fields 42, 44, 46 and 48 correspond to the Fresnel lens elements 16, 18, 20 and 22, respectively. The emitted thermal radiation detector 10, for the 8-14 mi scale, is preferably a single element pyroelectric detector such as Hamamatsu P4736. As an alternative, a pyroelectric detector that has two detector elements, for example, a Hynman LAH958 can be used with one of the covered detection elements. Alternatively, a semi-personal device can be used. Said devices are generally manufactured with a large resistor, e.g., 100 GOhm, parallel to the sensing elements. A lower value of this resistor provides a wider effective bandwidth with an exchange of less sensitivity at lower frequencies. For the present embodiment, in which a lower frequency cutoff of about 10 Hz is desired, a resistor value of approximately 100 MOhm would be appropriate. These types of pyroelectric detectors are sensitive to changes in temperature and not to absolute temperature, so the detector should see a change in temperature to generate an output signal. This change in temperature will occur when a heat generating object such as a running vehicle is detected in one of the detector's display fields. The change in temperature between one of the display fields of the blind point and the reference display field is achieved in the preferred mode by means of a shutter mechanism. The shutter is driven at a constant speed of 10 Hertz. The operating speed must be slow enough to be within the bandpass of the pyroelectric detector using and must be fast enough to provide sufficient warning time for a vehicle entering the blind spot. The response of the pyrodetector limits the maximum shutter speed to less than 50 Hertz while the vehicle detection requirement limits the lowest speed of approximately 2 Hertz. At this lowest speed there is a measurement of the blind spot display field every 500 milliseconds. Assuming that a vehicle approaches a relative speed of 20 km / h (5.6 meters / seconds), this gives a change in distance between samples of 2.3 meters. Therefore, if the maximum detection scale of the unit is 10 meters, an approaching vehicle will be detected between 10 and 7.6 meters. The reference field of reference 40 is directed from behind the vehicle in an area that is not in the blind spot of a driver and in which a vehicle would not normally be located. The switching between the reference display field 48 and the blind spot viewing fields 42, 44 and 46 provides the necessary change in temperature for the detector where the heat generating objects such as a running vehicle is present within those Fields of visualization. Referring to Figure 3, a Fresnel lens is illustrated in accordance with the preferred embodiment of the present invention. The Fresnel lens includes lens elements 16, 18 and 20 directed toward the blind spot of the vehicle and the Lens element 22 directed towards the road behind the vehicle. The elements of Lens 16, 18 and 20 are offset from one another to provide different fields of visualization, as illustrated in Figure 2. The Fresnel lens 12 also includes an opaque mask of thermal radiation emitted around the Lens areas. . The lens elements 16, 18 and 20 of the blind spot have a total area equal to the viewing lenses 22 of the path. This ensures that the emitted thermal radiation collected by the three blind spot lenses in an empty path will be equivalent to those collected by the road lens 22 only. This is true as long as the road temperature is consistently constant throughout the road and the blind spot visualization fields.

Referring to Figure 4, a circuit is illustrated schematically to drive the shutter mechanism and to derive from the detector an indication of the presence of a vehicle within the blind spot. In accordance with one embodiment of the present invention, the circuit includes a detector circuit 52 that provides input to an amplifier circuit 54 that provides input to a demodulator circuit 56 that provides input to an annunciator circuit 58. The demodulator circuit 56 is driven by a 10 Hertz square wave generator 60 which also drives the electromagnet of the shutter 30. The output of the detector is capacitively coupled through the capacitor C1 to the amplifier circuit 52 provided with two amplification stages 62 and 64. The amplifier circuit 54 acts as a high-pass filter with a cutoff frequency of approximately 10 Hertz. The output of the amplifier circuit 54 is applied as input to the demodulator circuit 56. The demodulator circuit 56 is operated at a frequency of 10 Hertz by applying the output of the square-wave generator 60 of 10 Hertz to switches within the modulator circuit. The annunciator circuit 58 having comparators 66 and 68 compares the output of the demodulator circuit 56 to minimum values to determine the presence of a vehicle in the blind spot and in response provides a signal output in the form of a pulse signal to an LED D3. Referring to Figures 5a, 5b and 5c, the outputs of the detector 50, the amplifier 54 and the demodulator 56 are illustrated graphically with the minimum values applied by the annunciator circuit 58 superimposed thereon. Figure 5a illustrates graphically a typical starting signal output from the pyroelectric detector 10. This signal contains a response from a car in the blind spot between 0.5 to 1.8 seconds superimposed on the signal caused by variations in the temperature of the road. The background signal caused by the variations in the path is a predominantly lower frequency, so that the high-pass filter will separate a signal from the car of the background signal. The applicator circuit 54 operates as a high-pass filter with a cut-off frequency of 10 Hertz and produces a output signal from the input signal of 5a as shown in Figure 5b. The signal of Figure 5b is then demodulated by switching the polarity synchronously with the obturator to produce a detection signal as illustrated in Figure 5c. The annunciator circuit 58 then compares the signal with minimum values to determine the presence of a vehicle in the blind spot. Figures 6, 7 and 8 illustrate alternative embodiments of the thermal radiation detector emitted. In the preferred embodiment of Figure 1, the reference display field of the road surface and the blind spot display fields are defined by the Fresnel lens elements 16, 18, 20 and 22, respectively, the selection of the field of view being determined by the shutter 14. It is possible to provide various arrangements of mechanical shutter eg vibrating tubes or rotating blades. An LCD using as a shutter can work with emitted thermal radiation, but it requires further investigation. It is also possible to change the display field of the detector 10 by other means as described below. Referring to Figure 6, an individual Fresnel lens 80 is provided and is supported on one side by a vibrating device 82. The vibrating device 82 can be electrochemical or piezoelectric in nature. By applying the pulse signal to the vibrating device 82, the Fresnel Lens 80 is oscillated between two positions, which correspond to a reference display field and a blind spot visualization field. Since the detector 10 is sensitive to the change in temperature, the change in the display fields results in a output signal that is generated with the presence of a vehicle in the blind spot. The operation of the rest of the detector is described with respect to the preferred embodiment. As it is well known, the optical elements, lenses and optical elements, mirrors, can be interchanged. Therefore, the Fresnel lens of Figure 6 can be replaced by a concave mirror. Figure 7 illustrates said arrangement in a third embodiment of the present invention. In the third embodiment, the Fresnel Lens 80, of Figure 6 is replaced by a concave mirror 86. The mirror 86 is mounted in a manner similar to the Fresnel lens and during operation vibrates between two display fields. The fourth embodiment of Figure 8 uses fixed optics 88, ie a lens or a mirror but imparts movement relative to the detector to define two fields of view. Although the embodiments of Fig. 6 to 8 have been described using the square wave generator of the preferred embodiment of Fig. 1, other waveforms are possible. The modalities of Figures 6 to 8 define visualization fields based on relative position and would be able to perform continuous movement between positions if the detector had sufficient bandwidth. For example, either an MCT detector (HgCdTe) or a pyroelectric with a rel- atively low parallel resistor (approximately 1 MOhm) would have sufficient bandwidth. Therefore, a sawtooth waveform could be used to drive the vibrator device 82 to cause the display field to sweep an area within the blind spot. For example, the visualization field could be swept from a relatively close position to a significantly distant position within the blind point, thus combining a reference visualization field and a blind point visualization field in a continuous scrutineer. In addition, a phase discriminator could be added to quantify the relative position of the vehicle indication and different colored LEDs could be used to display the relative position.

For example, red, yellow and green, corresponding to close, intermediate and distant positions of the vehicle in the blind spot. Although the embodiments of the present invention are described in the context of detecting vehicles approaching from behind in the posterior visual blind spot of the front vehicle, other applications of the present invention are contemplated. For example, the present invention can be used on the front of a school bus to detect children that can not be visibly detected by the driver. The present invention can also be used to detect people and vehicles in the blind spot directly behind large trucks, to warn the driver before driving in reverse. Numerous modifications, variations and adaptations can be made to the preferred embodiments of the invention described above without departing from the scope of the invention, which is defined in the claims.

Claims (30)

NOVELTY OF THE INVENTION CLAIMS

1. - A device for detecting thermal radiation emitted to detect objects in a blind spot comprising: detection means for generating an output signal in response to emitted thermal radiation; means for defining first and second fields of visualization in relation to the detection means; characterized in that the first display field comprises the blind spot and the second display field comprises a reference display field, means for switching the display fields and for generating a combination exit signal; and means for deriving an indication of a nearby object from the combination output signal, whereby the switching between the first and second display fields generates a difference in thermal radiation emitted in the detector means when the next object is in the first display field.

2. A device according to claim 1, further characterized in that the detection means comprise a differential emitted thermal radiation detector.

3. A device according to claim 2, further characterized in that said means for defining first and second fields of visualization comprise optics having first and second optical elements.

4. A device according to claim 3, further characterized in that said first and second optical elements are Fresnel lenses.

5. - A device according to claim 3, further characterized in that said first and second optical elements are concave mirrors.

6. A device according to claim 2, further characterized in that said means for defining the first and second fields of visualization comprise optics having a single optical element capable of moving between a first position and a second position corresponding to the first and second respective visualization fields.

7. A device according to claim 6, further characterized in that the optical element is a Fresnel lens.

8. A device according to claim 6, further characterized in that the optical element is a concave mirror.

9. A device according to claim 6, further characterized in that the optical element is a plane mirror and the optic further comprises a fixed optical element.

10. A device according to claim 9, further characterized in that the fixed optical element is a Fresnel lens.

11. A device according to claim 9, further characterized in that the fixed optical element is a concave mirror.

12. A device according to claim 3, further characterized in that said means for switching comprises a shutter operable between a first and second corresponding positions to allow the first and second respective display fields to be detected.

13. A device according to claim 12, further characterized in that the shutter includes an opaque panel pivotally disposed between the detector and the optics, a spring that deflects the panel to the first position and an electromagnet to attract the panel to the second. position.

14. A device according to claim 12, further characterized in that the obturator includes an elastic tube disposed between the detector and the optic and an electromagnet for causing the tube to vibrate at a predetermined sequence.

15. A device according to claim 12, further characterized in that the shutter includes a rotating blade disposed between the detector and optics.

16. A device according to claim 6, further characterized in that said computing means comprises a vibrator to effect movement of the optics between the first and second corresponding positions to allow the first and second respective fields of visualization to be detected.

17. A device according to claim 16, further characterized in that the vibrator is a piezoelectric device.

18. A device according to claim 16, further characterized in that the vibrator is an electromechanical device.

19. A device according to claim 1, further characterized in that the detection means comprise a first and second proportional detectors and said first and second fields of visualization respectively relate to them.

20. A device according to claim 19, further characterized in that the switching means comprise an electrical switch for switching between the outputs of the first and second detectors.

21. A device according to claim 1, further characterized in that said means for deriving an indication include a high pass filter.

22. A device according to claim 21, further characterized in that the derivation means include an amplifier.

23. - A device according to claim 22, further characterized in that the derivation means include a demodulator operable at a predetermined frequency corresponding to the operating frequency of the switching means.

24. A device according to claim 23, further characterized in that the derivation means includes an annunciator.

25. A device according to claim 3, further characterized in that the switching means include a square wave generator of predetermined frequency.

26. A device according to claim 6, further characterized in that the switching means include a square wave generator of predetermined frequency. 27.- A device according to claim 6, further characterized in that the switching means include a waveform generator of sawtooth shape of predetermined frequency. 28. A device for detecting thermal radiation emitted in accordance with claim 1, further characterized in that it comprises (a) said detection means comprising a detector that responds to changes in thermal radiation emitted received to generate an output signal; (b) optics for defining the first and second fields of view in relation to the detector; (c) a shutter for switching the display fields to generate a combination output signal; (d> a signal generator for providing a square wave of predetermined frequency for operating the shutter; (e) bypass means comprising: (i) a high pass filter connected to the detector for filtering the combination output signal; (ii) a demodulator connected to the high-pass filter and the signal generator to derive an object event signal, and (iii) an annunciator to compare the object event signal to predetermined minimum values and provide an indication of the presence of an object in the blind point, so that the switching between the first and second fields of visualization generates a difference in thermal radiation emitted in the detector means when the next object is the first visualization field. with Claim 1, further characterized in that the total radiation collected in the first and second non-object display fields in the blind spot is approximately A device according to claim 4, further characterized in that the total area of the Fresnel lens of the first optical element is approximately the same as the total area of the Fresnel lens of the second optical element.