Measuring and testing – Dynamometers – Responsive to force
Reexamination Certificate
2000-02-08
2003-04-15
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to force
C073S862627
Reexamination Certificate
active
06546817
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of diagnosing the state of a seat load measuring apparatus for measuring a load applied on a vehicle seat such as the weight of a passenger sitting thereon and thus detecting abnormalities.
BACKGROUND OF THE INVENTION
Automobiles are equipped with seat belt devices and airbag devices to secure safety for passengers in the automobiles. In recent years, there is a trend for controlling the operation of such safety devices according to the weight (body weight) of a passenger for improved performance of seat belt devices and airbag devices. For example, the amount of gas to be introduced into the airbag, an airbag inflating speed, or a pre-tension of the seat belt may be adjusted according to the weight of a passenger. For that purpose, some means are needed for measuring the weight of the passenger sitting on the seat. An example of such means includes a proposal of an apparatus for measuring the weight of a passenger by the following steps of arranging load sensors (strain gauges) at four corners of the bottom of a seat, obtaining loads on the respective corners, summing them to determine the seat weight including the weight of the passenger, and subtracting the seat weight when the passenger is not sitting thereon from the seat weight including the weight of the passenger.
A diagram of an example of such an apparatus is shown in FIG.
7
. In
FIG. 7
, numeral
21
designates strain gauges arranged at four corners of the bottom of a seat. A voltage is constantly applied to the respective strain gauges
21
from a power source
22
. As load is applied to the strain gauges
21
, the resistance values of resistor elements forming bridges are changed so that the balances among the bridges are also changed, whereby minimal voltages are generated from the strain gauges
21
. The minimal voltages are amplified by differential amplifiers
23
, respectively, and are outputted. The outputs of the four differential amplifiers
23
are then inputted into a multiplexer
24
, and selected one by one to be convened into digital signals by an A/D converter
25
. The digital signals are inputted into a micro processor unit (MPU)
26
. The MPU
26
reads the outputs of the amplifiers
23
one by one and multiplies each output by a conversion factor (sensitivity coefficient) to convert the outputs into load values. The load values are summed up to find the entire seat load. By using the seat load, the control of the seat belt device and/or the airbag device as mentioned above can be conducted by the MPU
26
or conducted by outputting the output to an external output circuit
29
.
Each strain gauge
21
has an offset voltage. The term “offset voltage” means voltage to be generated when the load is zero. Since each strain gauge
21
has its own value of offset voltage, it is necessary to compensate for the offset voltages in order to accurately measure the load. Since the load measured by the strain gauges
21
is the sum of the weight of the passenger and the weight of the seat, the weight of the seat as the dead load must be subtracted from the measured load in order to obtain the weight of the passenger. The MPU
26
has a function for this calculation (dead weight calibration). That is, when the MPU
26
receives a command from an external input circuit
28
in a state in which no passenger sits on the seat, the MPU
26
stores the loads detected by the strain gauges
21
as vacant loads in a memory
27
. In
FIG. 7
, the memory
27
includes four vacant load memory sections corresponding to the four strain gauges
21
, respectively, in which the vacant loads are stored. After that, loads given by subtracting the vacant loads from the loads computed from the outputs of the differential amplifiers
23
are taken as the loads detected by the strain gauges
21
. The sum of these loads is the load applied to the seat (e.g. the weight of the passenger) and is used for other control by the MPU
26
itself and/or is outputted to an external unit, if necessary.
Strictly speaking, since there are variations in the output voltages of the strain gauges
21
generated by the unit load for each of the strain gauges
21
, compensation for sensitivity (sensitivity calibration) may be necessary. Since the sensitivity of the strain gauges
21
may be varied according to a way of fixing the strain gauges, sensitivity calibration may also be necessary. In this case, sensitivity coefficients of the strain gauges are calculated from differences between the outputs of the differential amplifiers
23
when no load is applied on the seat and the outputs of the differential amplifiers
23
when a predetermined load is applied on the seat. For measuring load, the load is calculated by multiplying the outputs of the differential amplifiers
23
by the sensitivity coefficients and in this way, the sensitivity calibration can be achieved. It is suitable that the sensitivity coefficients are stored in the memory
27
.
As explained above, as long as commercially available metal strain gauges are used as the load sensors, the load applied on the seat can be accurately detected with a circuit construction as shown in FIG.
7
. However, there is a problem that a lot of man-hours and skills are required to attach the commercially available metal strain gauges to the seat portion. One example solution to this problem is a method in which ceramic strain gauges are formed integrally with circuits by using printing technique on a member which receives the seat load.
The aforementioned example is shown in FIGS.
8
(A),
8
(B). In FIGS.
8
(A),
8
(B), a seat
31
comprises a seat squab
31
a
, a seat back
31
b
, seat rails
31
c
, and seat legs
31
d
. The seat
31
is supported by deformable members
32
which are supported to a vehicle floor by brackets
33
. The deformable members
32
are made of steel. Integrally formed on the surface of each deformable member
32
are load sensors
35
,
36
and printed wirings
37
which are formed by a printing technique. As the load on the seat
31
is transmitted to the deformable members
32
via the seat legs
31
d
, the deformable members
32
are bent with brackets
33
as supports and with the seat legs
31
d
as power points and the deformation due to the bending is detected by the sensors
35
,
36
. The deformable members
32
are disposed at two positions on both sides of the seat
31
whereby load applied on a front portion and load applied on a rear portion of the seat
31
can be separately detected in combination with the load sensors
35
,
36
.
According to this method, the load sensors
35
,
36
and the printed wirings
37
are integrally formed by a printing technique, thereby facilitating the working steps. However, a load sensor manufactured by this method has defects in that the absolute values of the offset voltages and those variations are large and there are variations in the sensitivities as compared to the commercially available metal strain gauge which is manufactured by the use of fine processing technique such as lithography.
When the load sensors manufactured by the aforementioned method are used in an apparatus with the circuit construction as shown in
FIG. 7
, in extreme case, a problem may occur wherein the outputs of the differential amplifiers
23
are saturated due to the offset voltages of the load sensors. When the outputs of the differential amplifiers
23
are saturated, MPU
26
can no longer compensate to zero by using its dead weight calibrating function. Even when the outputs of the differential amplifiers
23
are not yet saturated, there is a problem that a weight heavier than a certain weight can not be measured due to the saturation of the amplifiers
23
when the offset values are shifted largely on one side (particularly, on the plus side of load) because this means that the measurable range is reduced. There is also a problem that it can not compensate for variations in the sensitivities of the respective load sensors because the circuit of
FIG. 7
is not provided with a s
Foley & Lardner
Noori Max
Takata Corporation
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