GB2350889A - Optical position target - Google Patents

Abstract

An optical positioning system is provided in which an optical positioning target is used to determine the mis-alignment of a light beam. The optical position target comprises a rotary member 1 with respectively a spoke slit 2 and a spiral slit 3. These slits 2, 3 allow a presented light beam to separately pass through in order to be detected by respective light sensors for each slit 2, 3. Thus, by rotation of the rotary member 1 a unique combination of angular presentations of that member 1 is provided at which a light beam striking the member 1 passes separately through each slit 2, 3. In such circumstances, this unique combination of angular positions of the member 1 enables a controller to determine the strike position of the light beam and so the mis-alignment of the light beam source from the optical target location. The slits may direct incident light along tunnels (figure 2,11,12) to detectors attached to the target.

Description

2350889 An Ornical Positioning Systemand an Optical Position Target

Therefo The present invention relates to an optical positioning system and more particularly to an optico positioning target for use with such a system particularly for alignment between components within a motor vehicle.

Location is a requirement in many areas of technology. Thus, for example, it may be necessary to accurately locate an emitter device relative to a sensor device such that breaking of a beam therebetween or variation in presented configuration can be utilised in order to control mechanisms or provide a warning alarm.

In particular it is known to provide within a vehicle an occupant detection system (ODS) which is arranged to selectively disable a passenger side air bag when not required or deployment would not be appropriate. Thus, for example, if a rear facing infant seat (RES) is fitted to a front passenger seat it will be understood that an inappropriate air bag deployment response could precipitate injury.

Some prior art occupant detection systems employ a transducer assembly in order to provide an occupant detection system. This transducer assembly radiates signal beams towards pre-defined locations on the passenger seat. In such circumstances, a distinct reflection pattern is developed based upon the reflection from the seat surface or passenger or objects placed upon the seat. The occupant detection system determines whether not it is appropriate to disable the passenger side air bag by reference to the reflections received. - Clearly, it is an essential requirement that there is accurate alignment between the elements of the occupant detection system. Unfortunately, within the manufacturing environment of a motor vehicle achieving such accurate alignment is difficult. Inherently, within any motor vehicle body there are build tolerances and in particular tolerance stack-up. Thus, specific variations in the locating points for the occupant detection system can adversely effect that system.

Typically, the mounting points for the occupant detection system will comprise cone lugs upon which a mounting plate for the system can be located. It is specific location of these lugs which is of paramount concern with regard to effective operation of the occupant detection system.

Normally, the respective components of the occupant detection system will be secured upon mounting plates which can be individually adjusted. However, such adjustment is a relatively skilled and time consuming activity. In such circumstAnces, it is important that the occupant detection system components are accurately located with the minimum of specific adjustment within a particular assembly.

Use of light beam sources to achieve optical positioning is well known. Thus, a laser beam source will typically be directed towards a position target such that the relative position between the two can be determined by a controller. Mounting a laser beam source within a vehicle upon the locating lugs for the occupant detection system is a relatively simple procedure. Thus, in order to determine accurately the position of the other side of the occupant detection system a target must either detect the degree of mis- alignment or reflect the beam back towards a sensor reciprocally coupled with the laser beam source.

With a position target, in which the degree of mis-alignment of the light beam is determined, it will be understood that the target in effect provides an area upon which the beam can strike. Thus, where the beam strikes that target area can be determined relative to the mounting lugs and so the degree of mis-alignment between the respective mounting lugs of the light beam source and the target identified by a controller. In such circumstances, when the actual occupant detection system components are installed that system's controller can take account of the mis-alignment between the respective mounting lugs and so provide a reliable response.

Clearly, with regard to the position target it is necessary that detection is as accurately determined as possible within the target area. Unfortunately, close packing of individual light detectors still leaves effectively dead areas between respective light detect elements due to the mounting packaging of those elements.

Furthermore, it will also be understood that individual light detector elements require separate wiring. Thus, even relatively small target areas will precipitate relatively complex connections with a large number of wires.

It is an object of the present invention to provide an optical positioning system and an optical positioning target which can accurately determine specific location of that target relative to a light beam source.

In accordance with the present invention there is provided an optical position target for a light beam source to determine specific location of that target relative to the beam source, the target comprising a rotary member having an aperture surface including a spoke slit and a spiral slit radiating towards the edge of that rotary member whereby a light beam instant upon the rotary member will separately pass through each of said spoke slit and spiral slit at a substantially unique pair of angular positions of said rotary member.

Also in accordance with the present invention there is provided an optical positioning system comprising a light beam source and an optical positioning target comprising a rotary member having an aperture surface including a spoke slit and a spiral slit both radiating towards the edge of that rotary member whereby a light beam from the light beam source instant upon the rotary member will separately pass through each of said spoke slit and said spiral slit at a substantially unique pair of angular positions of said rotary member, the light beam passing through each of said spoke slit and said spiral slit being detected by light detection means in order that a respective light incident signal is provided to a controller and the controller determines the respective angular positions of the rotary member when such light incident signals are provided in order that the relative position of the target to the light beam source is determined and indicated.

Typically, the light detection means will comprise opposed reflective surfaces with one of said surfaces being the aperture surface, material between the reflective surfaces having a reflective index to present the light in a light tunnel between the respective reflective surfaces and a light detector being associated with the rotary member to determine light passing through the respective spoke slit or the spiral slit and so provide the light incident signal to the controller.

The spoke slit and the spiral slit may originate at the centre of the rotary member and radiate outwards to the peripheral edge of the rotary member.

The rotary member may be rotated by a stepping motor providing signals to the controller indicative of angular position of the rotary member.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which:- Figure 1 is a schematic plan view of an optical position target; and, Figure 2 is a schematic cross-section of the target depicted in Figure 1 in the direction X-X.

Relative positioning between two locations is a requirement in a wide of technologies. The present invention will be described with regard to the requirements of an occupant detection system within a motor vehicle. The occupant detection system (ODS) senses whether a rear facing infant seat (RES) has been installed on the passenger seat or not. Dependent upon this determination the passenger air bag is disabled by a controller device. By such means, protection of infants placed in a rearward facing infant seat is achieved by avoiding the force of an air bag deployment during a motor vehicle collision.

Typically, an occupant detection system includes a sensor utilising eight infra red beams. These infra red beams are directed towards a passenger seat. The infra red beams are reflected by the seat surface or passenger or rearward facing infant seat to provide distinct distance patterns indicative of seat occupancy.

The present invention relates to accurately locating the occupant detector system sensor relative to a vehicle seat. Typically, the ODS sensor is fastened to a bracket mounting which in turn is secured about a top rail of a vehicle windscreen. To ensure constant alignment of this bracket there are two cone-shaped studs incorporated into a foot plate of the ODS sensor assembly. Alignment of the infra red emitter and receiver array within the ODS sensor housing is accurately determined during manufacture. However, there are sources of error relating to correct alignment of the ODS sensor device with respect to the vehicle passenger compartment or seat. In such circumstances, a principle source of error with regard to ODS sensor alignment is the inherent tolerance band with regard to mounting the bracket within a motor vehicle chassis. It has been found that tolerance stack-up between vehicle chassis manufacture, seat shift and other inaccuracies within forming the motor vehicle body shell can give an approximate deviation of plus or minus 50mm in ODS sensor alignment dependent upon the projected distance between the mountin location and the reflective surface.

Such deviations in alignment can be accommodated provided the ODS sensor controller is aware of such deviation. Alternatively, the ODS sensor mounting within the vehicle can itself be adjusted until an acceptable tolerance deviation is provided. Such mounting bracket adjustment will be conducted as the vehicle is 5 manufactured and so should be a simple procedure.

The present invention provides an optical position target and a system for using such a target which either provides information for mis- alignment correction or allows auto correction by a controller.

The ODS mounting bracket is fitted to the car chassis at a defined angle with respect tb a seat squab. By measuring the lateral off set of a light beam spot directed towards the vehicle passenger compartment, it will be understood that, slight angular deviations caused by distortion or wrong positioning of the bracket within the vehicle chassis can be determined. Thus, these measurements give a direct indication of bracket misalignment in terms of the amount of off set of the area covered by the ODS sensor when installed.

Typically, the light beam will be provided by a laser temporarily mounted - upon the ODS mounting bracket using a suitable foot plate. Furthermore, in order to ease assembly and operation, the laser beam will be autonomously powered by a rechargeable battery. The laser beam required to produce the light beam spot directed to the vehicle floor can be relatively weak due to the short distance involved. In such circumstances, class I or class II lasers can be used.

Clearly, an optical target must be mounted at the position upon the vehicle floor that it is expected the laser beam will strike. However, as indicated previously, it is impractical to provide a passive target in which a large number of light detectors are located next to each other in order to indicate light strike position. Thus, according to the present invention an optical position target as illustrated in Figures 1 and 2 is used.

A laser beam cannot spread over the target area. Thus, it is not necessary to provide light detection over the full target area all of the time. In accordance with the present invention, a rotary member 1 incorporates a spoke slit 2 and a spiral slit 3. The respective slits 2, 3 originate from the centre of the rotary member and radiate outwards towards a peripheral edge 4 of the member 1.

The rotary member 1 comprises a sandwich of optically active material on which the slits 2, 3 are etched or otherwise form in reflective surfaces 5, 6, 7. In such cirdumstances, light passing through the slits 2, 3 engages the respective reflective surfaces 5, 6, 7 in order to become incident upon light detectors 8, 9 for each respective slit 2, 3.

The rotary member 1 rotates about an axis 10 such that any light beam spot presented to the rotary member has a unique combination of angular positions where the light beam spot passes through respective slits 2, 3. Thus, by using a stepping motor or similar device to rotate the rotary member 1, it will be appreciated that, the angular positions of the light beam spot passing through respective slits 2, 3 can be indicated to a controller device as a control signal for each of such incidents. The controller can then determine the point of light beam strike upon the rotary member 1 relative to typically the axis 10. In such circumstances, the mis-alignment between the mounting location of the light beam source and the axis 10 can be determined. By such means, and using the ODS system as an example, it will be understood that the degree of mis-alignment between the mounting bracket (ODS sensor/receiver) and the target location with the vehicle chassis can be determined. Normally, only one determination of misalignment is required as indicated previously alignment between the infra red sensors and receivers of the ODS sensor assembly will be very accurately determined during their manufacture.

Once the degree of mis-alignment is determined it will be appreciated that the mounting bracket for the ODS sensor assembly can be adjusted until greater alignment is achieved or the controller for the ODS system can calibrate itself to accommodate such mis-alignment in normal use.

As indicated in Figure 2 respective light detectors 8, 9 will be provided for each slit 2, 3. The reflective surfaces 5, 6, 7 providing respective light tunnels within which the laser beam passing through the slits 2, 3 is directed towards the detectors 8, 9. In order to achieve appropriate light coupling between the incident laser beam and the respective tunnels 11, 12 it will be understood that careful consideration must be made with regard to the width of the respective slits 2, 3 and with regard to the reflective index of the material from which the rotary member 1 and in particular the tunnels 11, 12 are made. Clearly, the narrower the slits 2, 3 the more accurate the determination of laser striking upon the rotary member 1. However, a greater angle of refraction is then required in order to couple the incident laser beam into their respective tunnels 11, 12. In any event, it is only necessary that sufficient light is coupled into the tunnel 11, 12 in order to activate the light detectors 8, 9 respectively in order to indicate to the controller those angular positions of the rotary member indicated by the stepping motor at which laser beam incidence is determined. In such circumstances, the intensity of light presented to the respective detectors 8, 11 can be low provided background light can be kept to a minimum. The light detectors 8, 9 will provide light incident signals to the controller once light intensity of a particular level is determined.

Essentially the rotary member 1 comprises a disc which is able to rotate and consists of a material which guides optical light as described previously. The light beam is allowed to enter the disc through the slits 2, 3 in order to allow respective light detection i.e. photo transistors to determine those respective angular presentations of the rotary member 1 which are consistent with the laser beam light entering the member 1 through the slits 2, 3.

The process of data acquisition is relatively simple. The stepping motor which rotates the rotary member 1 will progressively increment such rotation until one of the light detectors 8, 9 determines incident laser beam light passing through its respective slit 2, 3. This angular position of the rotary member win be noted by the controller. The stepping motor then further increments rotation of the rotary member 1 until the other light detector 8, 9 determines incident laser light passing through the other respective slit 2, 3 and the angular presentation of the member 1 noted by the controller. Thus, by this unique combination of angular presentations of the rotary member 1 noted by the controller, the position of striking by the laser beam upon the rotary member 1 as an optical position target can be determined either from a look-up table stored in an appropriate memory device or through an algorithm comparing such angular positions of the rotary member 1 at which laser light passes through respective slits 2, 3 in order to proved an indication of strike position upon that member 1.

An optical positioning system using the optical position target described above would comprise, in addition to appropriate controller means, the following items.

a. a light beam source such as a laser secured upon an appropriate foot plate for a typical mounting above a target area; and, b. an optical position target as described with regard to Figures 1 and 2 secured upon a mounting mechanism reciprocal with the target area.

Thus, the laser source will present a laser light beam towards the target area and the optical position target will operate in order to determine the point of that beam striking the target. Typically, the axis of rotation 10 of the target will be consistent with the perfect strike position for the laser beam. Furthermore, the mounting for the target will incorporate a stepping motor or similar device in order to provide rotation to the rotary member 1 of the position target and the rotation shaft of this stepping motor will be either consistent with the axis 10 or through appropriate belt drive or similar mechanisms to provide rotation of the rotary member 1 about the axis 10.

In accordance with the optical positioning system of the present invention the unique angular presentations of the rotary member 1 at which a light beam strikes a member 1 through respective slits 2, 3 will be determined. Thus, any light beam striking the target within the geometry of the rotary member or more particularly the slits 2, 3 will be determined and so the degree of mis-alignment between perfect striking at the axis 10 by the laser beam from the upper mounting determined. By such means, the actual mounting of the light source can be adjusted until perfect or better alignment is achieved with the axis 10 or a controller device becomes calibrated by cognisance with regard to the degree of mis-alignment.

As indicated previously the present optical position target and optical positioning system can be used with regard to rapid determination of mis alignment between a radiating source and a reflectiVe surface for use with regard to safety features such as an ODS system within a motor vehicle. However, it will be also understood that the present optical position target and optical positioning system could be used with regard to other situations where alignment between positional locations is required. Thus, the system could be used with regard to theodolite surveying, security beam installation or other situations where alignment is required either as a one off determination or as an on-going consideration with regard to movement between the respective locations of emission and target.

Clearly, the rate of rotation of the rotary member 1 should be such that accurate determination of the respective light incident positions for the slits 2, 3 can be determined. Thus, as indicated previously typically the rotary member 1 will be rotated by the stepping motor having 1.80 steps and at a rate consistent with light detector response times. An example of a suitable stepping motor is supplied by RS Components Limited under stock number 191-8340 and described as a 1.80 step angle stepping motor, whilst the light detectors 8, 9 for example, may be 3mi Honeywell Silicon transistors (SDP 8475) also supplied by RS Components. Typically, in order to achieve the necessary refraction angle the materials from which the rotary member 1 is formed will be a lead glass.

The slits 2, 3 may be open channels or more normally simply sections in the respective tunnel 11, 12 layers of the rotary member 1 below etched apertures in the respective reflective layers 5, 6, 7. It will. be understood that the reflective layers 5, 6, 7 most importantly must be reflective inwards of their respective tunnels 11, 12. Furthermore, it is preferable that the upper surface, as depicted in Figures 1 and 2 as reflective layer 5, is non-reflective as presented to the laser beam in order to avoid potentially dangerous light beam scatter.

With regard to the exemplary ODS system, it will be appreciated that once mis-alignment has been determined, the light beam source and optical position target are removed and the specific ODS sensor assembly secured typically to the mounting bracket used for the light beam source whilst a scat is appropriately located within the vehicle such that this ODS sensor assembly can determine occupancy as required.

As illustrated typically the spoke split and the spiral slit 3 will be continuous from the origin axis 10 to the peripheral edge 4. However, it will be appreciated that these slits 2, 3 could be composite or broken if required in order to limit those areas of the rotary disc I as the optical position target which are sensitive to light 5 beam strike.

Typically, the optical target comprising the rotary member I will as illustrated comprise two layers with respective light detectors 8, 9. However, where necessary, it will be appreciated that more layers with respective Slits and light detectors may be provided in order to facilitate three or more combinations of 10 angular presentations of the rotary member indicative of light beam strike position I upon the optical position target. Clearly, with greater rotary member 1 depth further consideration must be made of the refractive index of the materials from which the rotary member 1 is made.

With regard to an ODS arrangement within a motor vehicle, it will be understood that, once the degree of deviation or mis-alignment between the mounting point and the target area is known, by using the present optical positioning system, then the controller of the ODS system can be configured for calibrated correction or the emitter/receiver mounting adjusted for best performance. Clearly, once specific relative location between the light beam source and the target is determined by the present system then these components are removed to allow installation of the ODS system.

In practice, normally the ODS sensor mounting will be used by a 'dummy' sensor incorporating'a laser to provide a light beam for projection towards the target for relative mis-alignment determination. Typically, a relatively low power class II laser diode will be used (670gm, 0.8mW). This laser will generate a narrow beam to provide good strike definition in the target. In order to achieve 13- independent operation, the laser will have its own rechargeable electrical battery supply and microswtches to control operation of the laser. Thus, when the light beam source is mounted upon the existing plate for the ODS sensor, a microswitch is tripped to activate the light beam. Similarly, the optical position target as described above is operated by activation of microswitches and the responses of the light detectors 2 and stepping motor passed to the controller through cabling or other transmission coupling.

1

Claims (7)

- 14CLAIMS

1. An optical positioning system in which an optical position target for a light beam source comprises a rotary member having an aperture surface including a spoke slit and a spiral slit both radiating towards the edge of that rotary member whereby a light beam incident upon the rotary member will separately pass through each of said spoke slit and said spiral slit at a substantially unique combination of angular positions of said rotary member, the light beam passing through each of said spoke slit and said spiral slit being detected by light detection means in order that a respective light incidence signal is provided to a controller and the controller determines by these respective angular positions of the rotary member 1 at which such light incidence signals are provided the relative position of the target to the source of light beam.

2. An optical position target for a light beam source to determine the specific location of that target relative to the light beam source, the target comprising a rotary member having an aperture surface including a spoke slit and a spiral slit both radiating towards the edge of that rotary member whereby a light beam incident upon the rotary member will separately pass through each of said spoke slit and said spiral slit as a substantially unique combination of angular positions of that said rotary member to be detected by light detection means.

3. An optical positioning target as claimed in claim 2 in which the light detection means comprises opposed reflective surfaces with one of said surfaces being the aperture surface, material between the respective opposed reflective surfaces having a refractive index to couple the light beam into a light tunnel between the respective opposed reflective surfaces and a respective light detector being associated with the rotary member to determine light passing through the respective spoke slit or the spiral slit and so provide light incidence signals.

4. An optical positioning target as claimed in Claim 2 or Claim 3 wherein the spoke slit or spiral slit originate at the centre of the rotary member and radiate outwards to the peripheral edge of the rotary member.

5. A positioning system as claimed in Claim 1 wherein the rotary member is rotated by a stepping motor providing an angular presentation or position signal to the controller.

6. A positioning system substantially as hereinbefore described with reference to the accompanying drawings.

7. An optical position target substantially as hereinbefore described with reference to the accompanying drawings.