GB2350890A - Optical position target - Google Patents

Abstract

An optical positioning system is provided in which an optical position target is used to determine the mis-alignment of a light beam presented to the target. The optical position target comprises a rotator member 1 incorporating a plurality of light detectors 2. These detectors 2 are arranged to have distinct orbits of rotation as the rotator member 1 is rotated. Thus, when a light beam strikes the rotator member 1 there is an indicative combination of rotator member 1 angular position and specific detector 2 activated which is utilised by a controller to determine the degree of mis-alignment between the beam source and the target. Thus, the controller can allow calibration correction of a sensor system, such as an occupant detection system (ODS) in a motor vehicle.

Description

2350890 An Optical Ppsiltioning System and an Optical Position Target

Therefo The present invention relates to an optical positioning system and more particularly to an optical 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, 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 pLssenger 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 positioning target for a light beam source to determine specific location of that target relative to the light beam source, the target comprising a rotator member and a plurality of light detectors distributed about one surface of that rotator member such that each light detector has an orbit of rotation with the rotator member which does not coincide with orbits of rotation of other light detectors whereby a light beam incident upon the target will be detected by light detectors only at a specific angular positions of the rotator member.

Also in accordance with the present invention there is provide an optical positioning system comprising a light beam source and an optical positioning target comprising a rotator member and a plurality of light detectors distributed about one surface of that rotator member such that each light detector has an orbit of rotation with the rotator member which does not coincide with orbits of rotation of other light detectors whereby a light beam incident upon the target will be detected by light detectors only at a specific angular positions of the rotator member, a controller coupled to the target being arranged to determine which light detectors have detected a light beam and the angular position of the rotator member at which detection is made in order to determine the relative position of the target to the light beam source.

Typically, the light detectors will be arranged in radial spokes from a central region of the rotator member. Normally, these spokes will originate at the centre 10 and extend substantially to the peripheral edge of the rotator member.

1 It will be understood that the light detectors are normally photodiode devices. Thus, in the central region it is difficult to pack these devices sufficiently close for full area detection so a degree of accuracy and tolerance fan off is generally present in this region of the rotator member.

Typically, the light detectors in the central region will be juxtaposed in a close packed relationship.

Preferably, the light detectors will be arranged in a cross configuration centred on the central region.

Normally, the rotator member will be rotated by a stepping motor which can 20 provide relatively accurate signals to the controller of angular position.

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; Figure 2 is a schematic cross-section of the target depicted in Figure 1 in the direction X-X Figure 3 is a flow diagram indicating the process of light incidence signal determination by a controller; and, Figure 4 is a flow diagram illustrating data processing in order to determine relative position between a light beam source and an optical position target.

Relative positioning between two locations is a requirement in a wide of technologies. The present invention will be described with regard to the requirenents 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 5Omm in ODS sensor alignment between the mounting position and the expected reflection area. However, it will be understood that this degree of deviation or mis-alignment is also dependent upon the distance separating these locations.

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 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-calibration of the system controller.

The ODS mounting bracket is fitted to the car chassis at a defined angle with respect to 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 mis-alignment 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 beam 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 rotator member 1 incorporates a plurality of light detectors 2 arranged to radial from a central region 3. The rotator member 1 can rotate under the control of a stepping motor such that each detector 2 has a unique orbit of rotation. In such circumstances, it will be understood that by a combination of the specific detector 2 and the angular position of the rotator member 1 that determination of the position of beam strike upon that member 1 can accurately determined. Thus, the degree of mis-alignment of that position of beam strike can be established from that expected for perfect relative location between the light beam source and target.

Typically, as illustrated in figure 1, the light detectors 2 will be arranged into a cross formation that radiates outwards from the central region 3 towards a peripheral edge 4 of the rotator member 1. Thus, it will be understood that each detector 2 upon its respective wing of the cross formation will be at a distinct radial displacement from the central region 3 and more particularly an axis of rotation X-X of the rotator member 1. In such circumstances, as the rotator member 1 is turned about the axis X-X, each detector 2 sweeps its orbit of rotation in order to determine whether a light beam is incident upon the detector 2 at any angular position.

Each orbit is distinct from all the orbits of other detectors 2. Thus, accuracy of the target is largely determined by the number of detector 2 and the width of increment or spread of these detectors 2 outwards from the central region 3. It will be understood too wide a spread of detectors 2 may mean that a narrow light beam will str& between two orbits without detection whilst a narrow spacing may mean that a single light beam may activate two detectors 2 by partial overlap with each orbit. Specific choice must therefore be made as to close spacing for accuracy and potential for multiple detector 2 activation.

Normally, the target and light beam will be controlled by a controller. Thus, the light beam which is usually in the form of a laser, is projected towards the target whilst that target is rotated. The controller then gathers information as to the specific detector 2 struck by the light beam and the angular position of the rotary member 1 at which such strike took place. The controller will then, either from a look up table or by algorithmic determination, calculate the degree of misalignment between the light beam source and the target.

In order to achieve best results in accordance with the present invention generally each incremental radial displacement of adjacent detectors 2 win be as illustrated in figure 1 will be accompanied with a 90 degree spacing upon the member 1. By such means it will be understood that potential for multiple detector 2 activation is reduced as there is approximately a four increment displacement between adjacent detectors upon the same wing or spar of the cross formation illustrated in figure 1. Thus, a normal light beam will not have sufficient width to overlap two detectors 2 in the same spar and so a differential can be made by angular position between two detectors 2 if they are activated. It will also be understood that spacing of the detectors as described will enable wiring of the respective detectors 2 to be rendered easier by the greater spacing between adjacent detectors 2.

With the configuration of the rotator member 1 as depicted in figure 1 and 2, with the exception of the light detectors 2 in the central region 3, there is no combination of adjacent detectors 2 stuck by an incident light beam. Thus, it will be possi61e to provide relatively simple control of the light beam source and target. For example, if there are thirty light detectors outside of the central region 3 then in an eight bit data byte word, five bits can be dedicated to those detectors 2 and a sixth for the detectors in the central region 3. The remaining two data bits can then be defined as a zero position flag and a data available flag to a controller coupled to the target. Thus, after each stepper motor jump, it will be understood that a data word as defined above can be transmitted to the controller. It will also be understood that usually significantly less than eight bits of date are required to control and define stepper motor motion (direction, half/full step, steplno step and pre-set). In such circumstances, only one data byte need be exchanged for effective control.

In order to determine light beam strike location, it will be understood that, the data byte will be converted by the controller into a distance from the origin or axis of rotation of the rotator member 1. This distance or radius of strike is associated with the angular position of strike in terms of the current stepping motor angle, normally defined by the number of steps. Clearly, a complete interrogation process for the target must be performed before full analysis upon the acquired data is performed otherwise there is a possibility of spurious results being provided. It will also be understood that as the interrogation process is relatively simple and so quick. The target could be interrogated several times before final determination is made. Furthermore, where the target is interrogated several times, the results of each interrogation may be combined by any desired manner of statistical analysis including averaging, standard deviation and median valuations.

Those skilled in the art will also understand that typically the data words used will include a check conducted by the controller to determine whether impossible combinations have been received. Clearly, if such a combination is received, it will be ignored and an error message flagged.

The control regime in accordance with the present invention will normally be implemented in an algorithm built into a computer as a controller device. Furthermore, generally as the stepping motor will only conduct one hundred steps per second then execution of the control algorithm will be substantially time independent with a typical speed computer processor.

Figures 3 and 4 illustrate basic flow diagrams of data acquisition and data evaluation operation respectively. These diagrams are relatively straight forward to understand. Thus, in figure 3 illustrating data acquisition, essentially an iterative regime of stepping motor motion is described where variables X, Y and Z are incrementing integers and B a response signal from the light detectors. The data acquisition and data evaluation algorithms are normally operated sequentially and so the variables, X, Y and Z are absolutely independent between each operation algorithm. Thus, each one can be implemented as separate procedures.

The variables A and D represent angle and distance (radius) values respectively representative of where the light beam strikes the target. The other variables X, Y, Z and B, are all temporary in order to count the number of acquisition/evaluation loops or define an address within the two arrays, one for the 5 acquired data and one for the evaluated data.

As indicated previously, the data received by the controller in the present optical positioning system is tested for plausibility. This test involves determining whether there are any two distance (D) or angle (A) values that are more than three millimetres apart or have a spacing greater than 90 degrees apart. It will be understood that three millimetres is typically the spacing of detectors in the target 1 and, as indicated previously, 90 degrees is the rotation of the rotatator member 1 between detectors 2 having adjacent orbits of rotation for detection of light beam strike. Essentially this is a simple test based upon the clear premise that the light beam cannot strike the target i.e. rotator member 1 at two different locations and has a finite width.

In order to achieve greater accuracy, it is normal to conduct a final averaging procedure. Thus, interpolate points that he on the edge between two detectors 2 can yield a value for the radius (D) and angle (A) as misalignment or deviation from the centre or axis of rotation X-X. These averaged results will provide polar co-ordinates that can be easily converted into Cartesian co-ordinates to give a clearer perception of the degree of mis-alignment or deviation.

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 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.

As indicated previously the present optical position target and optical positioning system can be used with regard to rapid determination of misalignment 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 allgnment 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.

13- Clearly, the rate of rotation of the rotator member 1 should be such that accurate determination by the light detectors 2 can be achieved. 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 L80 step angle stepping motor, whilst the light detectors 2 for example, may be 3mm Honeywell Silicon transistors (SDP 8475) also supplied by RS Components.

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 seat is appropriately located within the vehicle such that this ODS sensor assembly can determine occupancy as required.

Claims (10)

1. -14CLAIMS

   An optical positioning target for a light beam source to determine specific location of that target relative to the light beam source, the target comprising a rotator member and a plurality of light detectors distributed about one surface of that rotator member such that each light detector has an orbit of rotation with the rotator member which does not coincide with orbits of rotation of other light detectors whereby a light beam incident upon the target will be detected by light detectors only at a specific angular positions of the rotator member.
2. 2. An optical positioning system comprising a light beam source and an optial positioning target comprising a rotator member and a plurality of light detectors distributed about one surface of that rotator member such that each light detector has an orbit of rotation with the rotator member which does not coincide with orbits of rotation of other light detectors whereby a light beam incident upon the target will be detected by light detectors only at a specific angular positions of the rotator member, a controller coupled to the target being arranged to determine which light detectors have detected a light beam and the angular positions of the rotator member at which detection is made in order to determine the relative position of the target to the light beam source.
3. 3. An optical position target as claimed in claim 1 wherein the light detectors are arranged in radial spokes from a central region of the rotator member.
4. 4. An optical position target as claimed in claim 3 wherein the radial spokes substantially originate at a centre of the rotator member and radiate substantially to a peripheral edge of the rotator member.
5. 5. An optical position target as claimed in any of claims 1, 3 or 4 wherein the fight detectors are photodiode devices.
6. 6. An optical position target as claimed in any of claims 1, 3, 4 or 5 wherein the rotator member has a central region in which the light detectors are in a substantially juxtaposed relationship whilst other light detectors are incrementally spaced or spread to have orbits of rotation which provide a desired degree of receptivity to an incident light beam to enable determination of the location of that light beam strike upon the rotator member.
7. 7. An optical position target as claimed in any of claims 1, 3, 4, 5 or 6 wherein the light detectors are arranged in a cross configuration.
8. 8. An optical position target as claimed in any of claims 1, 3, 4, 5, 6 or 7 wherein the rotator member is associated with a stepping motor arranged to rotate that rotator member in order to move each light detector through its orbit of rotation.
9. 9. An optical position target substantially as hereinbefore described with respect to figures 1 and 2.
10. 10. An optical positioning system substantially as hereinbefore described with regard to the accompanying drawings.