GB2395287A

GB2395287A - Weight measurement system

Info

Publication number: GB2395287A
Application number: GB0403427A
Authority: GB
Inventors: Matthew J Knox
Original assignee: Autoliv ASP Inc
Current assignee: Autoliv ASP Inc
Priority date: 2000-08-10
Filing date: 2001-08-07
Publication date: 2004-05-19
Anticipated expiration: 2021-08-07
Also published as: GB0403427D0; GB2395287B

Abstract

A weight measurement system for automatically calibrating weight sensors installed on a motor vehicle seat performs a calibrate operation whenever a valid weight measurement window is found. A valid weight measurement window is defined by the seat being empty, an associated door being open and an associated seat buckle being unlatched. The system operates in a factory install mode to establish a reference zero set value and in a diagnostic mode to establish a temporary zero set value that reflects drift of the weight sensors. The temporary zero set value is used by a weight management program to control occupant restraint devices.

Description

GB 2395287 A continuation (74) Agent and/or Address for Service: Urquhart-

Dykes & Lord Tower North Central, Merrion Way, LEEDS, LS2 SPA, United Kingdom

r 23 95287 WEIGHT MEASU.MF,NT SYSTEM, METHOD AND WF,IGlIT FNSOR BACKG1lOIJNI) 011 I.NVT.-'NTION l. Field of Invention

This invention relates to a system that measures weight in a seat of a motor vehicle, weight sensors or strain transducers used in the system and To the calibration ofthe weight sensors. In pa-ticr.lar, the invention relates to a method and system of calibrating weight sensors used in motor vehicles and to a transducer that can be used as a weight sensor in the system.

2. T)escription of Prior Art

Weight sensors are used in a motor vehicle seat to measure strain or stress as a result of weight in the seat. The amount of measured stress is processed with other information, such as in seat occupant positioning, to control primary and supplemental restraint systems, such as managed load no limiters, pre-tensioners and/or side and frontal air bags. Accurate weight in seat infonnation combined with supporting primary and supplemental restraints improves overall system decisions and performance ofthe system in protecting Occupants of the vehicle should a crash occur.

2.5 Current system installations use on-line assembly and field personnel

to calibrate the system. l-hese systens se data sampling, performance history data and a onc-tine zero set or reIerencc to achieve initial and

ongoing calibrations. The one-time calibration is usually performed at the time of initial installation in the vehicle. 'I'his type of calibration is unlikely to capture e a shift in zero set as a result of over stressing of the weight sensor during vehicle USC, aging of componont:s, and other dri ft causing factors that 5 occur throughout the lii'eLime of the vehicle. Atlas, such one-tine calibration systems will over time result in a shil-t in weight measurement readings that increase the system error rate as the vehicle ages.

Weight sensors used for sensing weight in the seat of a motor vehicle o have included pressure or bladder units, flexible membrane units, proximity sensor units or structural beam units that generate a change in an electrical characteristic such as resistance or capacitance. These units typically include an elastomerically deformable element upon which is mounted a plurality of strain gauge elements. l:ach oftle strain gauge elements has an i electrical characteristic, such as resistance, capacitance or inductee that varies as the elastomeric element deforms wider stress.

(conventional elastomeric beam transducers have generally been fondled with a bending process. Stress is distributed by such transducers in a o central region centered on a fore/aft axis, but offset Torn a lateral axis thereof: This has required the use of two strain gauge elements to capture positive and negative stress loads. Two strain gauges have complicated the system tasks of measuring weight, compensation, and calibration. 'I'his affects the complexity and cost of oysters hardware and software.

Thus, there is a need for a weight sensing system for a motor vehicle that has the capal.'ility of providing a calibration procedure and system that a)

improves accuracy of the system over the lifetime of the vehicle. There is also a need for a weight sensor that distributes stress in a central region that is centered about a fore/aft axis, but without. offset from a lateral axis thereof. SI JMMARY OF INVEN I ION

A strain transducer according to the invention includes a body having two lands with an elastoneic bean in juxtaposition with the two lands. The o mass of the elastomeric beam is less than the mass ol either of the lands.

The elastomeric beam has a r egion of minimum thickness and one or more regions of maximum thickness. An electrically resistive body is located on the elastomeric beam overlying the region of ninirnum thickness. First and second electrical contacts electrically contact spaced part locations of the s resistive body, whereby deformation of the elastomeric beam results in a change in electrical resistance of the elects ically resistive body between said first and second electrical contacts.

In some embodiments one or both of opposed sr.trlaces of the SO elastomeric beam are arcuate. In some embodiments. the electrically resistive body is a thick film resistor that is adhered to an arcuate surface of the elastomeric beam.

In another embodiment, the strain transducer includes a resistive body As disposed on an elastomeric beans with four equally spaced electrical contacts disposed thereon to delicate four electrical resistances of the body that are connected in a wheatsone bridge.

i]

A method according to the invention automatically calibrates a characteristic of a weight sensor installed to sense weight of a seat in a motor vehicle that has a door and a seat belt with a buckle associated with s the seat. The method determines if the seat is empty by metals of the weight sensor, a spatial detector or a pressure sensor or the like. Next, the method determines if a condition is present., where the condition is a member of the group consisting of the door being open and the seat belt being unbuckled.

If the seat is empty and tle condition is present, a set of values of the o characteristic that clef ne a calibrated zero set value are established. The calibrated zero set value is then presented for use as a zero set for in seat weight measurements. The determining step, the establishing step and the presenting step are repeated for as long as the vehicle is in use.

5 More particularly, tle nethocl retains a first set of the established values as a rel'erence set of values and a second set of values as a temporary set of values, if the second set of values exceeds a predetermined deviation from the reference set of values The temporary set of values den nes a modified zero set value reflecting drift of the weight sensors for the hi seat so weight. measurements.

In a particular ernbodineut, a plurality of weight sensors are installed to sense the weight of the seat and the sets of values are derived from measurements of the electrical resistance of the plurality of weight sensors.

t' According to one feature of the invention, the number of times a temporary set of values is established is limited during the time an open door condition is t'ound present.

The weight measurement system of the invention includes a computer controller that performs flee method ofthe invention.

t' BRIEF DESCRIP ETON OF DIWINGS Other and further objects, advantages and features of the present invention will be understood by reference Lo the following specification in

conjunction faith the accompanying drawings, in which like reference 10 characters denote like elements of structure and: FIG. 1 is a per spective view of a strain transducer according to the invention; r) FIG. 2 is a side vices of Fig. 1; FIG. 3 is a plan view of the substrate that carries the strain gauge element of the FIG. 1 transducer and other circuit elements; 20 FIG. 4 is a schematic circuit diagram ofthe electrical components of FIG. 3;

FIG. 5 is a side view of an alternate enboclinent of a strain gauge element of the invention; FIG. 6 is a top view of another alternate ernbodiruent of a strain gauge element of the invention; r:

I7TG. 7 is a plan view of another alternate embodiment of a strain gauge element of the invention; 5 FIG. X is a plan view of another alternate embodiment of the strain gauge element of the invention; FIG. 9 is a cross-sectional view of a portion of the strain gauge elements of l:IGS. 6 and 7; FIG. 10 is a plan view of another alternate embodiment of the strain gauge element and of a circuit for obtaining resistance measurements t:herefi own; :s FIG. 1 1 is a plan view of another alternate embodiment of the strain gauge element and oi a circuit for obtaining resistance measurements therefi am; FIG. 12 is a perspective view of a portion of a motor vehicle with a o seat that contains a plurality of the FIG. I strain transducers; 1 l:G. 13 is a block diagram of a weight in seat measurement system for a motor vehicle that provides calibration according to the present invention; Al G. 14 is a block diagram ofthe memory of the FIG. 13 system;

FIG. 15 is a flow diagram ofthe calibration program ofthe FIG. 13 system; FIG. 16 is a flow diagram of the preinstall portion of the I:;TG. 15 5 program, FIG. 17 is a flow diagram ofthe set thermal and read sensors portion of the l IG. 15 program; oFIG 18 is a flow diagrain of the set factory reads portion of the I7ICI.

15 program; FIG. 19 is a flow diagram of the fault processing portion of the FIG. l 5 progran; 1 5 I;IG. 20 is a flow diagram of the diagnostic/active weight portion of the FIG. l 5 program; FIG. 21 is a flow diagram of the cualyze diagnostic reads portion of othe FIG. 15 program; FIG. 22 is a low diagrams of the update diagnostic cycle count portion :'ftle l IG. 15 program; and t,FIG. 23 is a table containing a legend of the ahlyreviations used in the flow diagrams of E1(,5. 16 through 22.

I)SCRlPTION 017 T)RF,FERRF,D EMBOOTMEiNT With reference to FIG:S. and 2, there is provided a strain transducer 20 according to the present invention. '1'ransducer 20 has an integral body 22 alla a strain gauge element 40. Integral body 22 includes a first land 24 and a second land 26 that are joined by an elastomeric beam 28 that deforms when stressed, but, due to its elasticity, returns to its original shape when the stress is removecl.

LO First land 24 has a bottom surface 25 that lies in a plane identified by line 30 in 11. 2. Second land 26 has a bottom surface 27 that lies in a plane identified by line 3 I. Planes 30 and 31 are substantially parallel.

Ilastomeric heaven 28 joins fust and second lands 24 and 26. Elastomeric beam 28 has a first surface 32 and a second opposed surface 34. First land Lr, 24 and second land 26 have masses that Ale each substantially larger than the mass of elastomeric bean 2. To this end, first and second surfaces 32 and 34 are shaped to produce a region 36 of minimum thickness and one or more r egions of naxium thickness at its ends 35 and 39. Preferably, first and second surfaces 32 and 34 see arcuate and, more preferably, are concave, to to produce a minimum thickness at region 36. Additionally, elastomeric beatn 28 has notches 37 and 38 on either side to further reduce its mass.

I-lowever, it will be appreciated by those skilled in the art that other shapes can provide beam 28 with a lower mass than lands 24 or 26. For, example, Fist surface 32 can be concave and second surt'ace can be of any shape, sucl, as a straight line, that produces a minimum thickness region.

AItcrnatively, first surface 32 may include a concave Hotels of a V or IJ

shape with second surface assuming any shape that yields a minimum thickness region at the apex of the V or U. Another example is shown in FIG. 5, in which lands 24 and 26 have large block shaped masses a elastomeric bran 28 has a narrow width. Anotller example is shown in FIG. I, 6, in which heaven 28 may simply have a smaller lateral cross-section than that of hymnals 24 or 26.

Mininlun1 thiclc,ess region 36 dctorns with a slight bend when transducer 20 is subjected to stress as represented by force arrows A and B o ilk FIG. 2. This deformation is sensed by strain gauge elcnerlt 40 with a resultant change in electrical characteristic as described below. Ior mounting purposes, first land 24 has a hole 21 and second land 26 has a hole 23. Strain transducer 2() Carl be any suitable alloy or polyncr that can be lorned such that elastomeric bean 28 is smaller than lands 24 and 26 and has a concentrated stress region needed for optimum performance and strength. (choice of notarial is dependent on the applied stress. For a low stress application, such as a low "g" or tilt sensor, the material could be a z o polymer, forncd, for example, by a pressure polymer molding process. I or a high stress application, such as a weight sensor in a motor vehicle, the natcrial could be an alloy, formed, for example, by a coining or stamping process. I-,lastomeric recovery after applied stress can lee enhance<! with higher glass content for the case of a polymer or by hardening/leat treating I, for the case of an alloy.

Strain gauge element 40 is carried on a substrate 41 and is centered on the geometric center of elastomeric beam 28 that is represented by an intersection 4( of fore/aft axis 42 with a lateral axis 44. Preferably, strain gauge element 40 has a flat geometry, such as is produced by thick film, thin 5 icily or etched foil on substrate 41. Substrate 41 is bonded to elastomeric beani 28 and first lanci 24. For example, the bonding process may use a balding or curing of the substrate to an enamel paint finish on elastomeric bean 28. Substrate 41 may suitably be a printed wiring board or films made of polyester, polyethylene, polyvinyl, polyimide, or any other material with dielectric properties stable enough to carry strain gauge element 40.

Referring to FIGS. 1 and 3, substrate 41 has a portion 41A that is clisposecl on elask,neric beam 28 and a second portion 41B that is disposed on first land 24. Strain gauge element 40 is disposed on substrate portion I, 41-. Strain gauge element 40 has a fore/alt resistance 48 defined by contacts CT1 and G4 and a lateral resistance 50 defined by contacts G2 and G3. Substrate portion 41B carTies a bridge circuit 54, a signal conditioner 56 and a number of electrical leads. Fore/aft resistance 48 is connected via leads 51 and 52 to bridge circuit 54. I;or example, bridge circuit 54 may be o a wheatstone bridge with fore/aft resistance 48 forming one leg thereof. A pair of leads 58 and (0 couple tile output of bridge 54 to signal conditioner 56. pair of leads 62 and 64 connect lateral resistance 50 to signal conditioner 56. A pair of leads 66 and 68 provide operating voltage to signal conditioner 56 and to bridge circuit 54. Signal conditioner 56 has a plurality :? i-, of output leads 70 for connection to tle system controller described lereinaller. All of the aforementioned leads may be carried on substrate 41.

Signal conditioner S6 includes circuitry for thermal compensation, transient 1 0

gauge element 4O, (also designated as resistor R1) and resistors R2, R3 arid R4. Contacts (l1, G2, G3 d G4 are coupled via connections 51, 62, 64 and 52 to circuit points designated as 1, 2, 3 and 4. Wheatstone bridge 54 also has circuit points 5 and 6 as well as circuit points 1 and 4. Circuit points I and 5 are coupled to receive operating voltage from the electrical system of a motor vehicle. Circuit points 1 through 4 are coupled to a weight measurement system for measurements of the resistance of strain gauge elcnent 40 for calibration as well as under various loading stresses o that occur during operation of the motor vehicle. Resistors R2, R3 and R4 are used for tcnpcratre compensation.

RcLening to IONIC,. 9, a strain gauge element 90 is shown constructed of a layer of resistive material 91 disposed on a layer of electrically insulat:irg material 92 that is disposed on a surface of elastomeric beans 20. '['his construction can be formed either with thick fihn fabrication techniques or with thin l'ilrm fabrication techniques. The inventors have discovered that a strain gauge element formed with this construction is extremely stable for high stress applications, such as sensing weight in :2 o seats of motor vehicles and can be used by itself without additional thermal compensation elenerlts.

Rei'errho to lIGS. 7, S and 10 strain gauge element 90 is shown with in three different resistive body shapes with a centrally located void 2r: 94 and contacts G1, G2, G3 and G4 disposed at edge locations similar as to strain gauge 40 of FIGS. 3 and 4. Strain gauge element 90 has been found to be so stable that it can be used as a -full bridge in stress as shown in 1- TC,. 10. 'this is in contrast to strain gauge 40 of FIGS. 3 and 4, which is used as one leg of a wheats toe bridge for measurements of resistance

Referring to I;IGS. 7, 8 and 10 strain gauge element 90 is shown with in three dittererrt resistive body shapes with a centrally located void 94 and contacts Gl, G2, G3 and G4 disposed at edge locations similar as to strain gauge 40 of l lGS. 3 and 4. Strain gauge element 90 has been found to be so 5 stable that it can be used as a full bridge in stress as shown in FIG. 10. This is in contrast to strain Gauge 40 of l IGS. 3 and 4, which is used as one leg of a wheatstone bridge for measurenerlts of resistance between contacts G1, G2, G3 and G4. In theory, a bridge is thermally Compensated, but in reality it is not because of dilfUrent thermal expansion characteristics and voltage drops of the various materials used in the strain gauge. Typically, the elements of a bridge are not completely equal due to different thermal expansions stresses, and the like. The interconnects, traces or wires all contribute to variation in response of the different "legs" of the bridge. This has required auxiliary thermal compensation.

The resistances between contacts G l, G2, G3 and G4 of resistive body 90 when corectecl as the legs of a bridge are very stable as they are located in tle same area, made of the same material and processed at the same time.

go Void 94 can be trUnned during or after fabrication to balance the resistances (-1-G2, Gl-G3, G2-G4 and G3-G4. Variations due to fabrication may also occur due to rotation of contacts Gl, G2, G3 and G4, of void.94 or of elenerlt 90 itself. IJsing the ovoid shape of 1l(. X or the round shape of Fl(-. 10 can minimize these variations that are most prevalent for the square A, shape of f;]G. 7.

it.,

Referring to FIG. 10, strain gauge element 90 is connected as a wheatsone bridge with resistive body resistances G1-G2, G1-G3, G2-G4 and G3-G4 forming the four legs of the bridge. A signal conditioner 56 is cormccted by leads 95, 96 97 and 98 to contacts G1, G2, G3 and G4, r: respectively. Leads 66 and 68 pi ovide operating power to signal conditioner 56 and to strain gauge element 90 via leads 95 and 96. Signal conditioner 56 has a plurality of output leads for connection to the system controller described hereinafter.

to Referring to FlCr. 1 1, an alternate strain gauge element 130 has a first resistive body 131 and a second resistive body 132 spaced apart from one another. Resistive bodies 131 and 132 are formed Title a construction of the type shown in FIG. 9. An electrical contact F2 is in contact with an edge of resistive body 131 and an edge of r csistive body 132. An electrical contact i-! 1 iS ir] contact. with an opposite edge of resistive body 131 and art electrical contact 1:3 is in contact with an opposite edge of resistive body 132.

With an electrical voltage applied across contacts F1 and F3, a resistance R1 of resistive body 131 is measured between contacts F1 and F2 20 and a resistance R2 is meastired between contacts F2 and F3. With R1 and R2 being substtntially equal for zero stress, flue voltage between contact F2 and Hitler contact F1 or F3 will be one halftlle voltage across contacts F1 and F3. l.)eviations frown this value are clue to stress.

2', It will be apparent to tlosc skilled in the art that strain gauge element 130 coull be a single resistive body with electrical contact F2 disposed centrally thereon to achieve strbst:ant:ially equal values of R1 and R2. Also,

contacts F1, F2 and F3 of FIG. 11 or contacts G1, G2, G3 and G4 of FIGS. 7 through 10 can alternatively be disposed entirely on the resistive body instead of straddling an edge thereof: 5 Refers ing to FIG. 12, a plurality of transducers 20 are shown in a weight sensing application for a motor vehicle 75 of which only a portion of a floor 77 and a portion of a seat 80 are shown. Seat 80 includes a seat cushion 82, a seat bucket 84 and a pair of seat tracks 86. Though seat bucket 84 is shown as having two side members, it also includes front and rear o members (not. shown) ar r anged with the side members to form a rectangular buclcet to support seat cushion 82. Seat tracks 86 are mounted on floor 77.

Transducers 20 anoint seat. bucket 84 to seat tracks 86. Although only two transducers 20 are shown in FIG. 12, preferably three or more :t transducers are used to obtain a reasonably accurate measurement of any weight in seat 80. I;or a buclcet type seat, preferably four transducers 20 ar used, two are located fore as shown in FIG. 12 and the other two (not shown) are located aft.

o Fore/aft axis 42 and lateral axis 44 are shown in FIG. 12 together with a mutually perpendicular vertical axis 43. Transducers 20 sense weight forces A and B as applied along vertical axis 43.

Relerring to FIG. 13, a weight measurement system 100 according to 2 the present invention includes a microprocessor 102, a memory 104, an input/output (I/O) port 106 Ad a device interface 108 that are all interconnected by a conpr.rter bus 110. Device interlace 108 is connected

with a motor vehicle ignition device 112, a spatial detector device 114, an optional weight tlueshold detector 116, an open door detector 1 18, a weight sensor syst:en 120, an air bag syst.en 122 and red and yellow alerts 124.

Microprocessor 102 under control of one or more programs stored in memory 104 processes data received frown vehicle ignition device 112, spatial detector l 14, optional weight threshold detector 116, open door detector 118 and weight sensor system 120 to control air bag system 122 and/or other vehicle occupant restraints.

In accordance with the present invention, a calibration program 150 is stored in Emory 104. Calibration program 150 is operative to control microprocessor 102 to calibrate the weight in seat measurement system at the time of installation as well as at any time throughout the motor vehicle :t 5 lily without the need for a visit to a service center.

Programs for weight neasuement system 100 including calibration program 150 may be loaded into memory 104 via I/O port 106 fiord a memory dislc device 105. I hat is, calibration program 150 is stored on nenory disk device 105 and loaded into memory 104 at a suitable time, such as the time of assembly.

Vehicle ignition device 112 provides an output signal that signifies whether the vehicle ignition is on or off. Spatial detector 114 provides an ? r) output signal that signifies if an occupant is in the seat. Weight threshold detector 116 provides an output signal that signifies if there is a weight in the seat that exceeds a threshold weight. For example, the threshold weight

may be 6 kilograms. If the weight of the seat is less than the threshold weight, the seat is considered empty. Open door detector 1 18 produces an output signal that signifies if the door is unlatched. Preferably, tile door is adjacent the scat being measured for weight. Weight sensor device 120 produces one or more output signals Flat signifies the amount of weight in a seat. Air l:,ag system 122 is a conventional air bag system that is controllable to release a frontal or a side bag.

lied and yellow alerts 124 provide a visual indication ofthc status of o weight measurerucnt system 100. For example, a yellow alert can signify that a calibration is underway and a red alert can signify that weight neasuremcnt system 100 has a fault.

Device controller 10X includes circuitry that can interface with analog 3. signals or digital signals produced by or used by devices 1 12 through 122 and convert such signals to a Corns usable by self-calibration system 100.

Thus, device interface 108 includes circuitry for analog to digital conversion, amplification, signal cleaning, level shifting and the like.

go Referringto FIG. 14,nemory 104 includescalibrationprograrn 150,a weight management program 152, a temporary zero set buffer 154, a reference zero set buffer l 56, a specified limits buffer 158, a zero shift deviation buffer 160 and a rnaxirnum acceptable zero shift limit buffer 162.

Memory 104 can suitably be a random access memory (RAM) or Nay be 25 divided into a RAM 104A and an erasable programmable read only ncmory l-PROM 104]3 as shown in RIG. 7. Buffers 154 through 160 are used by calibration prog)-an 150 as discussed below.

When vehicle 75 is not in use' calibration program 150 is in a sleep mode in which system 100 draws less power, thereby preventing excessive vehicle battery drain. When a wake up event occurs, calibration program 150 enters a factory install mode, a diagnostic mode or an active weight mode. The walce up event may, for example, be the opening of a vehicle door or the turning on of the vehicle ignition.

Once weight measurement system 100 has been calibrated by the JO factory install node, the diagnostic mode and active weight mode operate throughout the life time of motor vehicle 75 automatically talking weight sensor measurements for the purpose of recalibrating zero set or managing occupant restraint systems with weight management program 152. When in the factory install mode or the diagnostic mode, weight measurements Ace taken only if certain conditions are present. These conditions me empty seat, door open and seat belt unbuckled. These conditions assure a calibration window for taking measurements while the seat is unoccupied with either an occupant or an object.

JO Referring to FIG. 15, calibration program l 50 will now be described for the front r ight passenger seat of vehicle 75. It will be apparent to those skilled in the art that other seats in the vehicle can similarly be calibrated.

Calibration program 150 begins at step 164 with a determination of whistler weight neasurenent system 100 has been factory calibrated or a fault has 5 occurred. If not installed or if a fault has occurred, calibration program 150 enters a factory install sequence that begins with a preinstall routine 200.

I'reinstall routine 200 verifies that the seat is empty, the passenger door is

open and the seat belt buckle is unbuclded. If these conditions are met, a valid weight neasuroment window exists.

Calibration program 150 then enters a set thermal parameters and read s sensors routine 250 that evaluates the temperature conditions as sensed by thermal resistors R2, R3 and R4 of FIG. 4 and reads the resistance values of the weight sensors of the passenger seat. The next step 166 determines if system 100 is in or has entered the active weight node since tile weight neasurement window started.

1) If not, step 168 determines if the sensor reads are valid by checking the current status -,f the buckle, passenger door and seat. If valid, step 170 determines if system 100 has been factory installed. If not, calibration program 150 enters an adjust sensor gain and set factory reads routine 300 5 that records the reference zero set values 156 in 12E'ROM 1 04L3. If routine 300 is conpleted without a fault, calibration program 150 retunes to start. 11 a fault occurs during either routine 250 or routine 300, calibration program 150 enters a fault processing routine 350. An example of a fault is the weight sensor reads being outside of specified limits 158 during routine 250 2 or being outside zero shift limits 160 during routine 300. Fault processing routine 350 processes the faults and then calibration program 150 returns to start. Once calibration program 150 has completed a factory install mode, it 5 subsequently operates in diagnostic mode or weight measurement mode unless weight sensors 20 are subject to a high stress ( a high g event), passenger seat 80 is removed or one or more of weight sensors 20 have to be IS

replaced. When a wake up event occurs subsequent to a factory install mode, step 164 will detennine that factory install has occurred. Step 172 deternies if a high g event has occurred. If so, calibration program lSO enters fault processing routine 350. If not, calibration program enters a 5 diagnostic/active weight test routine 400. Routine 400 determines if a valid weight measureneut window exists. if not, routine 400 sets a flagthat signifies that active weight node is on and that the most recently recorded temporary Zero set values are to be used. Whether routine 400 determines a valid weight measurement window exists or that active weight mode is to be o set, calibration program 150 proceeds to set thermal parameters mid read sensors routine 250.

Routine 250 first sets the thermal parameters. If the active weight node flag has been set, routine 250 ends. Step 166 will determine active r) weight node. Weiglt nanageneut program 152 then operates to take weight measurenents that control decisions for operation of the passenger restraints during operation of vehicle 75. When a set of measurements have been recorded, step 174 resets system alerts l 24 Abed cycle counters. While vehicle 75 is being operated, calibration program]50 repeats the sequence 20 of step 172, routines 400 and 250, step 166, program 152 and step 174.

lf diagnostic/active weight routine 400 determines that a valid weight measurement window is present, routine 250 sets the thermal parameters and reads the current resistance values of weight sensors 20. If these current 25 values are not within acceptable limits I SO, calibration program lSO pr oceeds to fault processing routine 350. If the current resistance values are within the acceptable limits, step l 66 will detennine that the active weight 1',

flag has not been set. Step 168 verifies whether the weight measurement window is still valid. If so, step l 70 will determine that factory install is completed. Calibration program l 50 then enters an analyze diagnostic reads routine 450. Analyze diagnostic reads routine 450 compares the current weight sensor reads with reference zero set values 156. If the comparison results in a deviation greater than zero shift value 16(), temporary zero set values 154 are updated to the current weight sensor reads. If not, temporary zero set valuesl54 are not changed. (calibration program lSO then enters an update diagnostic cycle count r outine 50(). Routine 500 assures that a l 0 limited number of consecutive diagnostic sequences will be pertorned for a continuous open door condition.

I f step 1 6X determines that weight measurement window is not valid for either tle factory install mode or the diagnostic mode, step 176 :t determines if factory install is corrplete. If not, calibration program enters fault processing routine 350. If so, calibration program 150 enters change open door count routine 500.

llelening to FIGS. 16 though 22, abbreviations used in these figures to are defined by tle legend that appeals in FIG. 23. With reference to FIG. 16, preinstall routine 200 for the factory install node begins at step 202 with a reset of all counters and cycles. The cycles are minimally set to allow three consecutive cycles. In the event during one of these cycles, a fault cor r ects itself, the event will be recorded and the cycle counter reset, thereby :: resulting in normal operation ofthe factory install node. Step 203 resets a high g flag that may have been set by the occurrence of a high g event. As noted in the description of FIG. 15, step 172 will prevent initiation of the

TO

diagnostic or the active weight modes while the high g flag is set. This requires that vehicle 75 be brought to a service center for inspection, any necessary repair and a factory install mode.

r) Step 204 resets any alerts 124 that may have been set. Step 206 records tle activity of steps 202 through 206 to provide a history. Other steps identified as record in FIGS. 16 th ough 22 pet form a similar function and will lee ignored in die description that follows. Step 208 sets yellow

alert 124 that indicates system 100 is undergoing, a systems checlc. In the i o event of a non-recoverable fault, yellow alert 124 is turned off and r ed alert 124 is tuned on. Upon a successful systems clock (Iactory installation or calibration), yellow alert 124 is reset.

Steps 21(), 211, 21, and 213 validates the presence of an acceptable is weight sensor or cell 20 at the rear right, rear left, Font right and front left locations, respectively of seat 80. If a weight sensor is absent or out of an acceptable resistance range, the condition triggers a r eport 214 identi tying the detected fault. Other steps identified as report in FIGS. 16 through 22 perform a similar function and will be ignored in the description Flat

so follows. In this case, report 214 is followed by a fault being recorded and a julep to fault processing routine 350.

If steps 210 through 213 determine that all weiglt sensors 20 are present and acceptable, steps 216, 220 and 224 deter mine if certain conditions are present that ciefine a valid weight measurement window.

These conditions are an unbuckled seat belt, an open passenger door and an empty seat determined by steps 216, 220 and 224, respectively. A latched

seat buckle can possibly affect the accuracy of seat weight measurements.

An open passenger door can signify that there is a brief window of opportunity to calibrate. An empty seat validates the window of opportunity. A latched seat buckle or a closed passenger door will not result in innediate fault. Instead, the condition is reported via a monitor (not shown), to give the operator an opportunity to correct the fault. For example, the service personnel may have inadvertently left the seat belt latched or the passenger door closed. Thus, steps 218 and 222 determine if cycle counters have a value of less than 2. If so, tle fault is comn1tnicated :to to the operator via a monitor. If the fault condition is not removed before the cycle count equals 2, the fault is recorded and cahbration program 150 enters fault processing routine 350.

Step 224 tests the weight of the Ninety seat as a son of the output its values of the individual weight sensors 20. If the stein is within a deviation of X% from the aforementioned threshold value, tile seat is considered empty and the calibration will proceed. Step 230 establishes that the weight measurements to be talcen or read will be factory set or permanent reads.

That is, Clay will constitute reference zero set values 156. On the other 20 Land, if step 224 determines that the seat is not empty, step 226 assigns a temporary zero set. Step 22X checks to see if- the cycle count is less than 2.

If so, step 224 will validate an empty seat due to the temporary zero set by step 226. This will allow the factory calibration to proceed. This feature allows the system to adapt to varying assembly/installation processes, 25 thereby providing flexibility and contr-1 ofthe process with minimal attendant involvement.

It will be appreciated by those skilled in the art that other conditions, such as interior spatial sensing, in seat proximity/usage sensors can also be used to validate empty seat.

Referring to FIG. 17, set thermal parameters and read sensors r outine 250 begins at step 252. Step 252 is entered 1rorn step 230 of factory preinstall routine 200 or fiom diagnostic/active weight test routine 400. Step 252 initiates the first of four weight sensor reads with the Iront right sensor.

Step 960 resets the buffers containing previous reads for the sensors but does o not reset temporary zero set values 154. Step 262 sets thermal compensation parameters for the sensor reads by measuring the resistance values of resistors R2, R3 aid R4. Step 264 determines if the active weight node flag is set. This flag will not be set during either a factory install or diagnostic calibration. Step 268 reads the resistance between sensor contacts G 1 d G2 and step 270 reads the resistance between sensor contacts G l a Id G3. Step 272 cualyzes the relationship between the grid pairs Gl, (G2 and Gl, G3. I his relationship: must be within a specified tolerance in order for the calibration ? O process to proceed. If within the specified tolerance, step 274 reads the resistance between sensor contacts (T4 and G2 and step 276 reads the resistance between sensor contacts G4 rued G3. Step 278 compares the relationship between the grid pairs (T4, G2 and G4, G3. If within the specified tolerance, step 28() compares the relationship between sensor ?. S contacts Gl, G2, G3, G4 and CT4, G2, G4, G3.

If steps 272, 278 or 280 detennne their respective comparisons as outside the specified tolerance, a fault condition is recorded and calibration program 150 proceeds lo fault processing routine 350. If the fault condition persists after consecutive attempts to clear it, calibration program 150 will 5 fault the sensor. Examples of faults include a degraded resist element or interconnect or an environmental condition, such as moisttue.

If all grid relationships are within the specified tolerance, step 282 reads the resistance between sensor contacts Gl and (4. Step 284 then JO analyzes the resistance between sensor contacts Gl arid (r2 with respect to a stored calculated Gl, G4 empty seat signature. During factory install mode, if within a specified tolerance range, the G1, G4 value is recorded as reference zero set value 156. However, tle original calculated stored value is always maintained and used as a default in tle event factory installs are i.5 needed in the future.

Step 288 then determines if all reads are done. For this ease, only the front right sensor has been read so step 288 determines other r cad is needed. Step 254 determines if the front. right sensor has been read. If not, O steps 262 throtigh 284 are repeated for the front right sensor. If so, step 25G determines if the rear left sensor has been read and so on until step 288 determines that all sensors have been read.

If step 264 determines that tle active weight: flag is set, step 286 verifies that all sensors are present. If not, a fault is recorded and fault processing routine 350 is entered. If step 286 determines that all sensors are present, step 288 determines that there are no sensors to be read.

With reference to FIG.15, at this point in a factory install mode, steps 166, 168 and 170 are performed anti gain adjust and set factory reads routine 300 is entered. Referring to FIG. 18, gain adjust and factory set routine 300 5 begins at steps 302 and 304 with reading the values measured and stored by set thermal and read sensors routine 250 and calculating a gain factor for each sensor. Step 306 averages all of the sensor reads of contacts Cil, G4 and determines a zero shift (deviation frotn the specified zero shift). If this deviation exceeds a tolerance limit of x, step 310 resets install. For example, :i t: x may minimally be about 3 kilograms Step 312 then reset the tenporaTy reset (if set at step 226 of Fly. 1G) and fault processing routine 350 is entered. If step 30S; determines that the zero shift is within the tolerance limit, step 314 sets the reference zero set values i 56. Calibration program 150 then returns to start.

Refening to FIG. 19, fault processing routine 350 begins at step 352 with setting yellow alert 124. SLOP 354 determines if factory install is complete. Fault processing routine 350 allows three cycles to occur before setting a system fault that requites operator intervention. Tlus, cycle 20 counters 356, 360,364 and 366 test for cycle greater than two. Il so, the fault has occurred for the third cycle. If the fault occurred during factory install mode, factory install is not complete. Step 356 determines it the cycle count is greater than 2. If not, factory preinstall routine is re-enered at step 206 (FIG 9). II- the cycle count is greater than 2, step 368 resets install.

25 Step 370 sets a red alert and step 372 records the conclition, faults tle system and returns calibration program 150 to slant.

gr'

If step 354 determines that factory install is complete, step 358 determines if the current node is diagnostic. If so, step 360 determines if the cycle count is greater than 2. If so, steps 368,370 and 372 are performed. If not, calibration program 150 returns to strut. Il step 358 r' determines that the current mode is not diagnostic, step 362 determines if the current mode is active weight. If so, step 364 determines if the cycle count is greater thail 2. If so, steps 368 and 370 are performed. If not, calibration program 150 returns to start. If step 362 determines that the cur r ent mode is not active weight, step 366 determines if the cycle count is greater than two :t o for faults other than install, diagnostic or active weight. If so steps 368, 370 and 372 are performed. lfnot, calibration program 150 returns to start.

Refcning to FIG. 20, diagnostic/active weight node routine 400 begins at step 402 deteninig if tle passenger door is open. If so, step 403 5 determines if a diagnostic cycle count is less than one. If so, step 404 determines if the seat is empty. If so, step 405 determines if the seat buckle is latched. If not, a valid weight measurement window exists and step 406 sets yellow alert 124. Step 408 sets a diagnostic mode flag and calibration program 150 enters set thermal and read sensors routine 250.

If the passenger door is not open, the count is less than 1, the seat is not empty or the buckle is latched, step 410 retains the current temporary zero set values] 54 and step 412 sets an active weight mode i:lag. Step 414 determines if the passenger door is closed. If not, calibration program 150 25 enters the set thermal and r cad sensors routine 250. If so, step 415 resets the diagnostic cycle count and calibration program 150 enters the set thermal and read sensors routine 250.

The diagnostic mode cycle count assures that for a continuously open passenger door, a diagnostic mode is performed a limited number of tinges, which for the illustrated embodiment is only once.

Referring to FIG. 21, analyze diagnostic reads routine 450 begins at step 452 Title a comparison of the diagnostic sensor reads with the reference zero set values 156. Step 454 determines if there is a zero shift that is less than zero shift deviation 160 of x. If so, the temporary zero set values 154 established by a previous diagnostic cycle will be retained. Step 176 <if l;lG.

16 then determines if factory install is complete. If so, calibration program 150 proceeds to change diagnostic cycle count routine 500.

If step 454 determines that the zero shift is greater than x, step 456 t5 compares the diagnostic sensor reads with the reference zero set values 156.

Step 458 determines if the zero shift is greater than act acceptable nnaximum zero shift 162 [choose a different alphabetic character for the drawings. If the zero shift exceeds acceptable limit 162, calibration program t50 enters fault processing routine 350. If step 458 determines that ibe zero shift is not ?. o greater than acceptable naximun limit 162, step 460 sets a new temporary set of values 154. These values will be used by weight nanagement program l 52 until changed by a subsequent diagnostic mode.

Referring to FIG. 22, change diagnostic cycle count routine 500 ? r) begins at step 502 with a determination of whether the passenger door its open. I f not, step 508 resets the diagnostic cycle count and calibration program 150 enters weight n.magement program 152. I f so, the diagnostic / I

cycle count is incremented at step S()4. Step 5()6 detennines it the passenger door is closed. If so, step 508 resets the diagnostic cycle COtMlt. If the passenger door is not closed (i.e., still operl), calibration progarn 150 then enters weight management program 152.

The present invention having been flus described with particular reference to the presented forms thereof, it will be obvious that various changes and modifications may be nade therein without departing from the spirit and scope ofthe present invention as defined in rho appended claims.

A) E)

Claims

C Q - S

l. method of automatically cahbrating a characteristic of a wc islet sensor installed to' sense wciglt of a scat in a not-'r vclicle that has a door and a seat belt with a bucicle associated with the scat, said method cc'nprising: I

(a) determining that the seat is empty and that a condition is present, where the condition is a member of LhC group consisting ol the door being open and the seat belt being unbuckled; (b) if step (a) deternincs that the seat is empty and that said condition is present, establishing a set of values of said characteristic that define a zero set value; <d (c) presenting the set of values that define a:.ero set value for m seat weight measurements.
2. The method of claim ', farther comprising: (d) repeating steps (a), (h) cl (c) so long as the seat is installed in the motor vehicles 3 Lee method of claim A, further comprising: (e) retaining a first set ol values est.ablishecl by a first performance of step (b) as a reference set of values 4 Tle method of claim 3, further comprising: (f) retaining a second set of values as a tennporary set of values, if the second set of values (i) is established by step (b) after tile reference set ol values is established and (ii) exceeds a predetermined deviation firm the reicrence set of values; and so

wherein step (c) presents the temporary set of values as defining a modified zero set value for said in seat weight neasurernents.

s' The method of claim if, wherein the temporary set of values is one of a plurality of the temporary sets of values established by separate performances of step (b), and wherein step (c) presents the most recently established one of the temporary sets of values for tle in seat weight measurements. . The method of claim 5, wherein the weight sensor is one of a plurality of weight sensors installed k' sense said weight of the seat, and wherein the sets of values established by step (b) -e derived fiord measurements ol'said characteristic of each of said plurality of weight sensors. 7 The method of claim, further comprising: (g) limiting the number oftimes steps (a) though (h) are performed during the time the open door condition is found present.

8. 'lithe method of claim I, I'ur-ther comprising: (d) if step (a) determines that either the scat is not empty.,r the condition is not present, establishing the set of values; 3\

(e) if the seat is still empty or the condition is still not present, rejecting the set of values; (f) repeating steps (d) and (e) ul:'to rtimes, where n is an integer greater than one; (g) if the seat is found empty and the condition found present before step (c) is perforncd an nth time, retaining the set of values established by step (d); and (h) performing step (c) with the retained set of values.

lo The method of claim I, furtler comprising: (d) comparing the set of values Fitly a specified set of values to produce a deviation; (c) if the deviation exceeds a specified deviation, rejecting the set of values; (f) repeating steps (d) d (e) up to n times, where n is an integer greater than one; (g) i f the deviation is Soured to be less Clean tle specified deviation before step (c) is performed an nth tinge, retaining the set of values established by step (d); and 3,

(h) perfornn ing step (e) with the r etained set of values.

tl. The method of claim A, wherein said characteristic is an electrical characteristic. tz The method of claim In, wherein said electrical characteristic is resistance. t3. Ill he method ol claim at, wherein the weight sensor includes an electrical resistance element that has three or more electrical contacts, wherein said set of values is deternined h om neasurenents of the resistance values between the three or more terminals.

to. A seat weight measurement system for a seat in a motor vehicle, the motor vehicle having door and a seat belt with a buckle, said system corrprising: a weight sensor installed in said seat, said weight sensor having a characteristic that varies with the weight of said seat; one or nature detectors that detect if-the seat its empty, if the door i; open and the seat belt is unbuckled; a computer controller for automatically calibrating said weight sensor by perlorning tle steps of:

(a) determining that the seat is empty and that a condition is present, where the condition is a member of the group consisting of the door being open and the seat belt being unbuckled; (b) if step (a) determines that the seat is empty and that said condition is present, establishing a set of values of said characteristic that define a zero set value; an (c) presenting the set of values that dcf no a zero set value for in seat weight measurements.

The seat weight measurement system of claim 4, wherein the computer controller performs the l-irther step of: (d) repeating steps (a), (b) and (c) so long as the seat is installed in the motor vehicle.

1. al he seat weight measurement system of claim is, wherein the computer controller performs the further step of.

(e) retaining a first: set of values established by a first performance of step (b) as a reference set of values.

lo. The seat. weight. measurement system of claim it, wherein the computer controller performs the l:i.rther step of:

(1) retaining a second set of values as a temporary set of values, if the second set of values (i) is established by step (b) after the reference set of values is established and (ii) excceds a predetermined deviation Tom the reference set of values; and wherein step (c) presents the temporary set of values as defining a modified zero set value for said in scat weight measurements.

18. The scat weight measurement system of claim In, wherein the temporary set of values is ogle of a plurality ofthe temporary sets of values established by separate perforinLlces of step (b), and wherein step (c) presents the most recently established cane of the tcnporary sets of values for the in seat weight measurements.

In lithe scat weight measurement system of claim In, wherein the temporary set of values is one of a plurality of the temporary sets of values established by separate performances of step (b), and wherein step (c) presents the most recently established one of the temporary sets of values for the in seat weight measurements.

0 T he seat weight measurement system of claim i', wherein the computer controller performs the further step of: (g) Ihniting the number oftimes steps (a) though (h) are performed during the tinge the open door condition is found present.

as

it\. The seat weight measurement system of claim '4, wlercin the computer conLro]]er pcrfoms the further steps of (d) if step (a) determines that either the seat is not empty or the condition is not present, establishing the set of values; (e) if the seat is still empty or the condition is still not present, rejecting the set of values; (I-') repeating steps (d) and (e) Up to n times, where n is an integer greater than tine; (g) if the scat is found empty and the condition found present before step (c) is perforn:ed.u nth time, retaining the set of values established by step (d); and (h) perl'orming step (c) with the retained set of values.

I'he scat weight ncasurement system ol'claim +, wherein the computer controller pcrfonns the furThcr steps of: (d) comparing the set of values with a specified set of values to produce a deviation; (c) if the deviation exceeds a specified deviation, rejecting the set of values; 3L

(f) repeating steps (d) and (e) up to n times, where n is an integer greater than one; (g) if the deviation is found to be less than the specified deviation before step (e) is perfonned an nth time, retaining the set of values established by step (d); and (h) performing step (c) With the retained set of values.

t3. T}1C seat weight measurement system of claim to, wherein said characteristic is an electrical characteristic.

ah 'I'he seat weight neasurenent system of claim at, wherein said electrical characteristic is resistance.

as. The seat weight measurement system of claim '4, wherein the \veight sensor includes an electrical resistance element that has three or snore electrical contacts, wherein said set of values is determined from measneme.s of tle resistance values between the three or more terninals.

2t A menory medium for controlling a computer controller of a seat weight neasureme't: system i'or a motor vehicle having a seat, a door and a seat belt Title a brclcle, said Sensory medium comprising: means for controlling the computer controller to perform the steps of:

(a) determining that the seat its empty and that a condition is prc sent, where the condition is a member ofthe group consisting of the door being open and the seat belt being unbuckled; (b) if step (a) determines that the seat is empty and that said condition is present, establishing a set olvalues of said characteristic that define a zero set value; and (c) presenting the set of values that define a zero set value for in seat weight. measurements.

I. The nenory medium of claim in, further comprising: means for controlling the computer controller to perform the further step of: (d) repeating steps (a), (b) arid (c) so long as the seat is installed in the motor vehicle.

28. The memory medium of clahn 27, further comprising: means for controlling the computer controller to perform the further step of: (e) retaining a first set of values established by a first performance olstep (b) as a reference set of values.

in The memory medium of claim a, further comprising: means for controlling the computer controller to pe:rforn the further step of: (f) retaining a second set of values as a tenporary set of values, if the second set of values (i) is established by step (b) after the reference set of values is establislecl and (ii) exceeds a predetermined deviation frown the reference set of values; and wherein step (c) presents the temporary set of values as deigning a modified zero set value for said in seat weight neasurements.
3. The memory medium oLclairn 35, wherein said electrical characteristic is rcsistancc.

39 rl'he memory nediun of claim 35, wherein t}c weight. sensor includes an electrical resistance elcmcut that has three or more electrical contacts,

wherein said set of values is determined from mesur ements of tic r csistance v alues between the three or more tcrnials

3 Al he menor-y medhn of claim 9, wherein the temporary set of values is one of a plurality of the tenporuy sets of values established by separate pertornances ol step (b), and wherein step (c) presents the most recently established one of the tenporay sets at values for the in seat weight measurements. 3. The menory medium of claim 30, wherein the weight sensor is one of a plurality of weight sensors installed to sense said weight of the seat, and wherein the sets of values established by step (b) are derived fiom measurements of said characteristic of each of said plurality of weight sensors. 32. The memory medinnl oiclaim 3t, t.rrther comprising:

means for controlling the computer controller to perform the t.'urther step of: (g) limiting the number of times steps (a) tlrough (h) are performed during the time the open door condition is found present.

s3. Tle rmernory medium of claim tL, f'uther comprising: means for controlling the computer controller to perf'orn the h.rthcr steps of: (d) if step (a) determines that either the seat is not sanity or the condition is not present, establishing the set of values; (e) if the seat is still empty or the condition is still not present, rejecting the set of values; (f) repeating steps (d) and (e) up to n times, where n is an integer greater than one; (g) lathe scat is found empty and the condition found present before step (e) is performed an nth time, retaining the set of'values established by step (d); and (h) perf'orrning step (c) with the retained set of values.

34. 'I'he memory rnediun of claim ZG, further comprising: go

means for controlling the computer controllc to perform the further steps of (d) comparing the set of values with a specified set of values to produce a deviation; (e) if the deviation cxcccds a specified deviation, rejecting the set of values; (f) repeating stalls (d) and (c) up to n times, where n is an integer greater than one; (g) if the dcviaton is l'o. rld to be less than tile specil'ied deviation bel'ore step (c) is perfonned an nt}1 time, retaining tile set of values established by step (d); and (h) perfor Ming step (c) with the retained set. of values.

35. The memory rnediurn of claim 32, herein said characteristic is an electrical characteristic.