U.S. patent application number 09/770792 was filed with the patent office on 2002-07-25 for redundant rate sensor and method.
This patent application is currently assigned to BEI Technologies, Inc.. Invention is credited to Layton, Michael R..
Application Number | 20020097037 09/770792 |
Document ID | / |
Family ID | 25089683 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020097037 |
Kind Code |
A1 |
Layton, Michael R. |
July 25, 2002 |
Redundant rate sensor and method
Abstract
Redundant rate sensor and method in which inertial rate is
monitored with a plurality of vibratory sensing elements mounted in
a single enclosure, signals from the sensing elements are processed
to provide an independent rate output signal for each of the
sensing elements, and the independent rate output signals are
delivered to a connector which is accessible externally of the
enclosure.
Inventors: |
Layton, Michael R.;
(Clayton, CA) |
Correspondence
Address: |
Edward S. Wright
FLEHR HOHBACH TEST
ALBRITTON & HERBERT LLP
Four Embarcadero Center, Suite 3400
San Francisco
CA
94111
US
|
Assignee: |
BEI Technologies, Inc.
|
Family ID: |
25089683 |
Appl. No.: |
09/770792 |
Filed: |
January 25, 2001 |
Current U.S.
Class: |
324/76.49 |
Current CPC
Class: |
G01C 19/5783 20130101;
G01C 19/5607 20130101 |
Class at
Publication: |
324/76.49 |
International
Class: |
G01R 023/00 |
Claims
1. A redundant rate sensor, comprising an enclosure, a plurality of
vibratory rate sensing elements mounted in the enclosure, circuit
means within the enclosure for processing signals from each of the
sensing elements to provide an independent rate output signal for
each of the sensing elements, and an output connector connected to
the circuit means and accessible externally of the enclosure for
delivering the rate output signals for the sensing elements.
2. The redundant rate sensor of claim 1 wherein each of the
vibratory rate sensing elements is a tuning fork.
3. The redundant rate sensor of claim 2 wherein each of the tuning
forks is fabricated of quartz.
4. The redundant rate sensor of claim 1 wherein each of the sensing
elements is mounted on a common circuit board within the
enclosure.
5. The redundant rate sensor of claim 4 wherein the circuit means
is also mounted on the circuit board.
6. The redundant rate sensor of claim 5 including means within the
enclosure for exciting each of the sensing elements at a different
drive frequency.
7. The redundant rate sensor of claim 1 wherein each of the sensing
elements has a drive frequency and a pickup frequency which are
separated from each other by a predetermined amount, with the drive
and pickup frequencies for different sensing elements being
separated by different amounts.
8. The redundant rate sensor of claim 1 wherein the circuit means
includes a separate processing circuit for each of the sensing
elements.
9. In a method of sensing inertial rate, the steps of: monitoring
inertial rate with a plurality of vibratory sensing elements
mounted in a single enclosure, processing signals from the sensing
elements to provide an independent rate output signal for each of
the sensing elements, and delivering the independent rate output
signals to a connector which is accessible externally of the
enclosure.
10. The method of claim 8 wherein each of the sensing elements is
excited at a different drive frequency.
11. The method of claim 10 wherein each of the sensing elements is
operated at a drive frequency and a pickup frequency which are
separated from each other by a predetermined amount, with the drive
and pickup frequencies for different sensing elements being
separated by different amounts.
12. A redundant rate sensor, comprising an enclosure, first and
second vibratory rate sensing elements mounted in the enclosure
with the input axes of the two sensing elements perpendicular to
each other for sensing rotation about perpendicular axes, and a
third vibratory rate sensing element mounted in the package with
the input axis of the third sensing element parallel to the input
axis of the first sensing element to provide redundancy for the
first sensing element.
13. The redundant rate sensor of claim 12 wherein each of the
vibratory rate sensing elements is a tuning fork.
14. The redundant rate sensor of claim 13 wherein each of the
tuning forks is fabricated of quartz.
15. A redundant rate sensor, comprising an enclosure, first and
second vibratory rate sensing elements mounted in the enclosure
with the input axes of the two sensing elements perpendicular to
each other, and a third vibratory rate sensing element mounted in
the package with the input axis of the third sensing element at a
non-orthogonal angle relative to the input axes of the first and
second sensing elements to provide redundancy for the first and
second sensing elements.
16. The redundant rate sensor of claim 15 wherein each of the
vibratory rate sensing elements is a tuning fork.
17. The redundant rate sensor of claim 16 wherein each of the
tuning forks is fabricated of quartz.
18. The redundant rate sensor of claim 15 wherein the axis of the
third sensing element is at an angle of 45.degree. relative to the
input axes of the first and second sensing elements.
19. A redundant rate sensor, comprising an enclosure, three
vibratory rate sensing elements mounted in the enclosure with the
input axes of the three sensing elements perpendicular to each
other for sensing rotation about perpendicular axes, and a fourth
vibratory rate sensing element mounted in the package to provide
redundancy for at least one of the three sensing elements.
20. The redundant rate sensor of claim 19 wherein the input axis of
the fourth sensing element is parallel to the input axis of one of
the three sensing elements.
21. The redundant rate sensor of claim 19 wherein the input axis of
the fourth sensing element is oriented at a non-orthogonal angle
relative to the input axes of at least two of the three sensing
elements.
Description
[0001] This invention pertains generally to inertial rate sensors
and, more particularly, to a rate sensor with built-in redundancy
for use in an automobile stability control system.
[0002] In automobile stability control systems and other
applications where safety is critical, redundancy is sometimes
employed for greater reliability. That is presently being done on a
somewhat limited basis in automobile braking systems, using two
complete, stand-alone devices, with the outputs of the two devices
being compared for a suitable match by the braking system. This
provides a system which is more tolerant of sensor faults than
systems which have only one sensor.
[0003] Redundancy itself is not a new concept in applications where
high reliability is required, and examples of prior art redundant
systems are found in U.S. Pat. Nos. 3,551,776, 3,663,879,
3,813,990, 3,881,670 and 4,105,900. In these systems, the outputs
of a plurality of separate identical sensors (typically three) are
compared by a control system which is an integral part of the
redundant system to verify that the primary sensor is
functional.
[0004] The use of multiple stand-alone sensors to achieve
redundancy has certain disadvantages. Each sensor requires a
separate mounting location, a separate mounting procedure, and
separate cabling which must be routed to the particular mounting
location. In applications such as automobiles where cost is
critical, the added cost of additional sensors, multiple mounting
locations, additional installation procedures, and additional
cabling is generally prohibitive.
[0005] It is in general an object of the invention to provide a new
and improved rate sensor and method with built-in redundancy.
[0006] Another object of the invention is to provide a rate sensor
and method of the above character which are particularly suitable
for use in automobile stability control systems.
[0007] Another object of the invention is to provide a rate sensor
and method of the above character which overcome the limitations
and disadvantages of the redundant sensors heretofore provided.
[0008] These and other objects are achieved in accordance with the
invention by providing a redundant rate sensor and method in which
inertial rate is monitored with a plurality of vibratory sensing
elements mounted in a single enclosure, signals from the sensing
elements are processed to provide an independent rate output signal
for each of the sensing elements, and the independent rate output
signals are delivered to a connector which is accessible externally
of the enclosure.
[0009] FIG. 1 is an exploded isometric view of one embodiment of a
redundant rate sensor incorporating the invention.
[0010] FIG. 2 is a simplified block diagram of the redundant rate
sensor in the embodiment of FIG. 1.
[0011] FIGS. 3-6 illustrate additional embodiments of redundant
rate sensors incorporating the invention.
[0012] As illustrated in FIG. 1, the rate sensor has a relatively
flat, generally rectangular housing 11 consisting of an upper
section 12 and a lower section 13, with flexible rubber mounts 14
at the corners of the housing for providing mechanical isolation
between the sensor and the structure on which it mounted.
[0013] A pair of vibratory rate sensing elements in the form of
quartz tuning forks 16, 17 are mounted on opposite sides of a
printed circuit board 18 within the housing, with the input axes
19, 21 of the tuning forks parallel to each other. Circuitry for
processing signals from the tuning forks is included in integrated
circuits 22, 23 which are mounted on the circuit board next to the
tuning forks, with a separate integrated circuit being provided for
each of the tuning forks. These circuits provide independent rate
output signals for each of the sensing elements.
[0014] A connector assembly 24 is mounted on the housing, with its
pins accessible externally of the housing. Connections to the
integrated circuits are made through the connector pins. Those
connections typically include power and calibration connections as
well as the output signals for the two sensors.
[0015] This system provides two independent rate output signals,
one for each sensor. These outputs are substantially identical in
every respect, and they are compared to ensure proper operation of
the system. This comparison is generally done by the electronic
control unit of the braking system or by signal processors
elsewhere in the automobile, and no added benefit is achieved by
including that capability within the sensor package.
[0016] Other elements such as power conditioning circuitry which
serve both channels of the rate sensor can be included within the
housing.
[0017] As illustrated in FIG. 2, sensing elements 16, 17 are in the
form of double ended tuning forks. Each of these tuning forks is
fabricated of single crystal quartz material, and has an H-shaped
configuration, with drive tines 26 at one end and pick-up tines 27
at the other. Each pair of tines is disposed symmetrically about
the input axis 19, 21 of the tuning fork.
[0018] The drive tines are driven to oscillate at the natural
frequency of the tuning fork and in the plane of the tuning fork.
To prevent any unwanted cross-coupling between the two sensing
elements and the associated circuitry, different drive frequencies
are used for the two tuning forks. The drive frequencies are
typically separated by about 1 KHz. When the tuning fork is
subjected to rotation about its longitudinal axis, the Coriolis
force causes the tines to deflect out of the plane of the fork,
stimulating the pickup mode of oscillation. The drive and pickup
signals are coupled to the tines in a conventional manner by the
use of electrodes (not shown), with the drive signals stimulating
mechanical vibration of the tines via the piezoelectric effect and
the pickup signals being in the form of electric charge generated
by the inverse piezoelectric effect in response to strain produced
by the Coriolis force.
[0019] With some tuning forks, the pickup frequency is separated
from the drive frequency, and error signals can occur as a result
of rotational inputs at the separation frequency, typically during
vibration of the unit. To increase the likelihood of detecting such
errors, different frequency separations can be used for different
sensing elements within a unit. Thus, for example, one sensor in a
unit might have a separation of about 340 Hz between its drive and
pickup frequencies, and the other sensor might have a separation of
about 280 Hz. These values are not critical, and any suitable
separations can be used.
[0020] With a redundant sensor and different frequency separations
for the sensors in it, the likelihood of undetected vibration
induced errors is greatly reduced because it is highly unlikely
that equal vibration induced errors will occur at the separation
frequencies of both sensors simultaneously.
[0021] Although the sensing elements are illustrated as being
double ended tuning forks, other types of vibratory sensing
elements, including single ended tuning forks, can be utilized, if
desired.
[0022] In each channel of the rate sensor, the pickup signals from
the tuning fork pass through a charge amplifier 28, to a
preamplifier 29, and then to a demodulator 31. The signals from the
demodulator pass through a low pass filter 32 and then to an output
amplifier 33, with the rate output signal appearing as a baseband
signal at the output of the output amplifier.
[0023] Excitation signals are applied to the drive tines by a drive
circuit 34 which can, for example, be of the type shown in Ser. No.
09/663,742, filed Sep. 15, 2000, the disclosure of which is
incorporated herein by reference.
[0024] The outputs of the output amplifiers 33 in the two channels
are connected to separate pins of output connector 24, and
operating power is also supplied to the two channels through the
connector and a power conditioning circuit 36 within the housing.
Redundant (separate) power conditioning circuits may be used as an
option for increased reliability.
[0025] In situations where additional redundancy is desired,
additional sensing elements and processing circuits can be included
within the unit. This may require a modest increase in the size of
the housing, but that size package will still be much smaller than
three individual, stand-alone units.
[0026] In other embodiments, two degrees of freedom of rate sensing
output can be provided, with redundancy about one or more axes. In
those embodiments, three or more sensing elements are mounted in a
single package, with at least one of the elements oriented with its
axis perpendicular to the axes of the others in order to sense
rotation about a second axis. Redundancy of output is provided by a
plurality of sensing elements aligned along one or both of the axes
in this device.
[0027] Thus, for example, in the embodiment illustrated in FIG. 3,
sensing elements 38, 39 are aligned along mutually perpendicular
axes 41, 42, with redundancy being provided for each of them by
sensing elements 43, 44. As in the embodiment of FIG. 1, a separate
processing circuit provides an independent rate output signal for
each of the sensing elements in these embodiments.
[0028] In another embodiment, one redundant sensing element is
shared among two or more orthogonally mounted sensors. In this
embodiment, the input axis of the redundant sensing element is
positioned at an angle to the input axes of the other sensing
elements so that it detects a component of rotation about the input
axes of the other elements.
[0029] For example, in the embodiment illustrated in FIG. 4, two
non-redundant rate sensing elements 46, 47, which are mounted with
their axes 48, 49 perpendicular to each other, are both provided
with a redundant signal from a sensing element 51 which has its
input axis 52 oriented at an angle of 45.degree. with respect to
the axes of the two non-redundant elements. The sensing element
oriented at 45.degree. degrees to the two principal sensing axes
can be used as a check on the performance of the primary sensing
elements by comparing its output to the appropriate vector sum of
the other two outputs. Here again, separate processing circuits
provide an independent rate output signal for each of the sensing
elements.
[0030] In the embodiment of FIG. 5, three sensing elements 54, 56,
57 have their input axes 58, 59, 61 perpendicular to each other,
and a fourth sensing element 62 has its input axis 63 parallel to
the input axis of sensing element 54 to provide redundancy for that
sensing element.
[0031] In the embodiment of FIG. 6, three sensing elements 64, 66,
67 have their input axes 68, 69, 71 perpendicular to each other,
and a fourth sensing element 72 has its input axis 73 at a
non-orthogonal angle relative to the input axes of at least two of
the other three sensing elements. With this arrangement, the fourth
sensing element provides redundancy for the two or three sensing
elements to which its axis is not perpendicular.
[0032] The invention has a number of important features and
advantages. With two sensing channels sharing a common printed
circuit board, power conditioning circuitry, a single housing and
common mechanical isolators, the overall cost of the two channels
of rate output is substantially less than that of two separate rate
sensor units. Moreover, with redundant sensors in a single package,
only one mounting location, one set of connecting cables, one set
of mounting bolts, and one installation procedure are required.
[0033] Moreover, with redundant sensors, a reduced level of
accuracy can be tolerated in the redundant channel because that
channel is only used for verifying that the output of the primary
channel is valid. That tends to increase sensor yield during
manufacture since not all of the rate sensing elements are required
to meet the more stringent performance requirements of the primary
channel. It also tends to improve the performance of the primary
channel since the sensing elements with the best performance can be
used in it. The net effect is to provide increased performance at
reduced cost with the added reliability of redundancy.
[0034] The algorithm used to process the redundant outputs could
consist, for example, of combining two redundant outputs as both
sum and difference signals. The sum signal would be used as the
primary output for vehicle stability control or other purposes,
while the difference signal could be used to establish the validity
of the output. A sensing element which performs much better than
its specified requirement could be matched with one which is
somewhat worse than that requirement. The sum of these two,
effectively an average, could still be within the original
specification error limit. If, however, the difference signal were
to exceed a predetermined value, the system would detect a fault,
and no erroneous braking actions would be performed.
[0035] It is apparent from the foregoing that a new and improved
redundant rate sensor and method have been provided. While only
certain presently preferred embodiments have been described in
detail, as will be apparent to those familiar with the art, certain
changes and modifications can be made without departing from the
scope of the invention as defined by the following claims.
* * * * *