Weighing scales – Computer – Electrical
Reexamination Certificate
2002-03-07
2004-02-10
Martin, David (Department: 2841)
Weighing scales
Computer
Electrical
C177S144000, C177S185000, C177S199000, C177S200000, C701S045000, C180S273000
Reexamination Certificate
active
06689960
ABSTRACT:
BACKGROUND
The present invention relates to a seat weight measuring apparatus for measuring the weight of a seat in the passenger car (the seat weight referred to in this application includes the weight of a passenger or of an object as well as the weight of the seat itself, when a passenger is sitting thereon or an object is placed thereon).
As devices having the responsibility to ensure safety of occupants, the passenger car is equipped with seat belts or airbags. In recent years, attempts have been made to control the action of these safety devices depending on the weight (body weight) of the occupant in order to improve the performance of these systems. For example, the values such as the amount of gas for deploying the air bag, the deployment speed thereof, or the pretension of the seatbelt are adjusted depending on the body weight of the occupant.
In order to perform such control, it is necessary to measure the weight of the occupant sitting on the seat. As an example of methods for measuring the weight of the occupant, there is proposed a system which involves arranging load sensors (e.g., strain gauges) at four corners of the seat at the bottom of the seat, obtaining loads exerted on each corner, summing these values to obtain the weight of the seat including the weight of the occupant, and calculating the weight of the occupant from the difference between the seat weights with and without an occupant sitting thereon.
FIG. 8
shows an example of such seat weight measuring apparatus. In
FIG. 8
, the seat
1
includes a seat cushion
1
a
, a seatback
1
b,
a seat rail
1
c,
and a seat leg
1
d
is supported by the displacing member
2
, which in turn is secured on the floor via a bracket
3
. The displacing member
2
is formed of steel, and is formed with load sensors
5
,
6
and a printed wiring
7
integrally on the surface thereof by a printing technology. When the load of the seat
1
is transmitted to the displacing member
2
via the seat leg
1
d,
the displacing member
2
is bent by a force exerted by the seat leg
1
d
working as a power point while being supported by a bracket
3
as fulcrum, and the displacement thereof is detected by the load sensors
5
,
6
. Though only two load sensors are shown in
FIG. 8
, the seat
1
is actually provided with seat legs
1
d
at four corners thereof, and thus four load sensors are provided to obtain the seat weight from the summation of the outputs of these four sensors.
FIG. 9
shows an example of the measuring circuit in such seat load measuring apparatus. In
FIG. 9
, the reference numeral
11
designates strain gauges provided at four corners on the bottom of the seat, and a constant voltage is exerted on each strain gauge
11
by a power supply unit
12
. When the resistance value of the resistance element that constitutes a bridge varies due to exertion of load onto the strain gauge
11
, the balance of the bridge varies, and slight voltage is generated at the strain gauge
11
. The generated voltage is amplified by the differential amplifier
13
and supplied therefrom.
Actually, the outputs of these four differential amplifiers are supplied to a multiplexer
14
, selected sequentially to be converted into digital values at an A/D converter
15
, and supplied to a mechanism for processing the values, typically a microprocessor unit (MPU)
16
. MPU
16
reads the outputs of respective amplifiers
13
sequentially, multiplies them by a conversion factor (factor of sensitivity) respectively to obtain load values, and sums them up to obtain an total seat load. The seat load is then utilized to control the aforementioned seatbelts or airbags in the MPU
16
or by supplying the outputs to the external output circuit
19
as required.
Each strain gauge
11
has an offset voltage. The offset voltage is a voltage generated when the load is zero, and since the value of the offset voltage varies among the strain gauges
11
, the offset voltages have to be compensated in order to measure the load accurately. In addition, since the value measured by the strain gauge
11
is a sum of the weights of the occupant and of the seat itself, the weight of the seat itself have to be deducted in order to obtain the weight of the occupant. The MPU
16
has a feature to perform such adjustment (tare adjustment). In other words, when a command signal is supplied from the external input signal circuit
18
with no occupant sitting on the seat, the MPU
16
stores the weight values detected at the respective strain gauges
11
in a memory
17
as unoccupied loads.
In the figure, since four strain gauges
11
are provided, four unoccupied load memories corresponding thereto are provided in the memory
17
, in which the unoccupied loads are stored respectively. Thereafter, the value obtained by deducting the unoccupied load from the weight calculated from the output of each differential amplifier
13
is taken as a load detected by each strain gauge
11
. The value obtained by summing these values is used by the MPU
16
for other controls as a load exerted onto the seat (for example, the weight of the occupant), and are supplied to external equipment as required.
As described above, when the seat weight is detected by four load sensors, in normal conditions each load sensor should be able to detect a maximum load of about 60 kgf even with the tare weight of the seat taken into account. On the other hand, in case of automobile collision accident or the like, an excessive load such as 100 kgf or more may be exerted onto these load sensors, which may result in breakage of the load sensors. Therefore, a mechanism for protecting the load sensor from excessive loads is practically provided though it is not shown in the figure. For example, there is provided a mechanism that mechanically prevents excessive deformation of the displacement member
2
even when a total load that may exceed 60 kgf for each sensor acts on the displacement member as shown in FIG.
8
.
The seat weight measuring apparatus having such a construction has a recognized disadvantage because while there exists no problem when the loads acting on the respective load sensors are uniform, a problem is encountered that when there are extreme differences among the loads acting on the respective load sensors. In these circumstances, an accurate load cannot be measured. For example, assuming that the sum of the weight of the seat and of a person sitting on the seat is 100 kg, when the load is exerted uniformly on each load sensor, the load exerted on each load sensor will be 25 kgf. However, when the person sits on the seat with the seatback reclined, there may be the case where a load of −20 kgf is exerted onto each of the front two load sensors (that is, a load in the upper direction is exerted), and a load as much as 70 kgf is exerted onto each of the rear two load sensors.
In this case, since the load is mechanically blocked when a load of more than 60 kgf is exerted on one sensor as described above, the value detected by the rear load sensor will be 60 kgf at the maximum. As a consequent, the sum of the values from four load sensors will be (−20 kgf)×2+(60 kgf)×2=80 kgf, and thus the wrong measured value is supplied.
Even when the seat is vacant, if the seat is deformed, the tare weight (a weight exerted when no person is seated) sensed by each load sensor may vary as much as ±40 kgf. In the sensor having a tare output of ±40 kgf, the output may be saturated only with exertion of a load as little as 20 kgf (for example, a load exerted by an occupant), and thus an accurate output cannot be obtained yet. In certain circumstances, this problem may lead to an incorrect determination of whether an occupant is a child or an adult.
Even when an occupant is sitting in a normal posture, and the load exerted on each of the four legs is uniform, if the vehicle travels on a road having rough surface, a load in excess of the weight of the occupant is generated and thus the mechanical blockage provided to protect the load sensor from an e
Foley & Lardner
Martin David
Takata Corporation
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