Measuring and testing – Instrument proving or calibrating – Speed – velocity – or acceleration
Reexamination Certificate
2002-05-31
2004-09-21
Williams, Hezron (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Speed, velocity, or acceleration
C073S504020, C073S504160
Reexamination Certificate
active
06792792
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates in general to angular rate sensors and in particular to an apparatus and a method for performing a diagnostic test upon an angular rate sensor.
Angular rate sensors are widely used in many commercial applications, such as, for example, attitude control systems for automobiles, a gyroscope for a navigation system included in a moving object or a hand-shake compensating system for video cameras. Angular rate sensors measure the rate of rotation of a body about its three principle axes. The rotational movement is typically referred to as yaw, pitch and roll which are related to vertical, transverse and longitudinal axes, respectively.
A simplified angular rate sensor element
10
is illustrated in
FIGS. 1 and 2
as a tuning fork. Such sensors typically include a pair of vibrating elements, that are shown as tines
11
and
12
in FIG.
1
. The lower ends of the tines
11
and
12
are connected by an output shaft
3
. The tines
11
and
12
, which function as proof masses, are driven in opposite directions in the plane of the drawing by electrostatic drive motors
14
and
15
. The tines
11
and
12
vibrate in the directions shown by the small arrows labeled
16
and
17
. when an angular rate, illustrated by the circular arrow
18
, is applied to the sensor element
10
about an axis
19
in the plane of the sensor element
10
, the tines
11
and
12
are caused to oscillate out of the plane by a Coriolis force due to Coriolis effect, as shown in
FIG. 2
by the small arrows labeled
20
and
21
. The resulting out-of plane oscillation motion amplitude, which is proportional to the input angular rate, is detected and measured by capacitive or electrostatic pickoff plates
22
that are located adjacent to the upper ends of the tines
11
and
12
. While a simplified sensor element
10
has been shown in
FIGS. 1 and 2
, it will be appreciated that angular rate sensors typically include one, two, four or any plurality of tuning forks in a unitary system.
The size of angular rate sensors has been reduced by the development of resonant Micro Electro Mechanical System (MEMS) angular rate sensors that feature micromachined mechanical components and integrated support electronics. Thus, MEMS includes the concept of integration of microelectronics and micromachining. These devices can be fabricated from various materials, such as, for example, silicon, quartz and ceramics. Examples of successful MEMS devices include inkjet printer cartridges, accelerometers that deploy car airbags and miniature robots.
A schematic diagram for a typical MEMS angular rate sensor
23
is illustrated in FIG.
3
. Components shown in
FIG. 3
that are similar to components shown in
FIGS. 1 and 2
have the same numerical identifiers. Additional capacitive or electrostatic pickoff plates
24
and
25
have been added to measure amplitude and frequency of the oscillation of the tines
11
and
12
within the plane of the sense element
10
. The information obtained from pickoff plates
24
and
25
is fed back through the lines labeled
28
and
29
to a closed loop sense element drive circuit
30
. While the lines
28
and
29
are shown as single wires, it will be appreciated that the circuit has been simplified for clarity and that multiple wires or traces may actually be used. The sense element drive circuit
26
is conventional and typically includes an oscillator with automatic gain and frequency control (not shown) that receives the feedback from the pickoff plates
24
and
25
to assure that the linear motion is provided to sense element
10
. Sense element drive signals are supplied to the electrostatic drive motors
14
and
15
by the output lines
28
A and
29
A.
Analog data from the Coriolis force pickoff plates
22
is supplied through the lines labeled
32
and
34
to an open loop signal conditioning circuit
36
. While the lines
32
and
34
are as single wires, it will appreciated that the drive circuit has been simplified for clarity and that multiple wires or traces may actually be used. The signal conditioning circuit
36
generates an output signal that is proportional to the angular rate on an output line
38
. The output signal may be either an analog or a digital signal. The output line
38
is connected to an input port of a microprocessor (not shown).
A block diagram
40
for typical signal conditioning circuit
36
is illustrated in FIG.
4
. Additionally, the sense element
10
is shown in block form. Thus, an input angular rate &ohgr;
in
is applied to a proof mass, m, or the tines
11
and
12
in the illustrative example, in block
42
. The proof mass m responds to the angular rate &ohgr;
in
with an input force F
in
that is applied to the sense elements, or the Coriolis force pickoff plates
22
, in block
44
. The in input force F
in
is converted to voltage, V, in block
46
and supplied to the signal conditioning circuit
36
. The voltage V is amplified and any offset is cancelled in block
48
. The amplified signal is filtered in block
50
and then converted to a digital signal by a quantizer in block
52
. Alternately, the output of the filter in block
50
can be directly used as an analog signal, in which case the quantizer in block
52
is omitted from FIG.
4
.
It is known to test angular rate sensors as illustrated in FIG.
5
. In
FIG. 5
, the output of the filter block
50
is supplied directly as an analog signal to an analog input pin
53
of an Electronic Control Unit (ECU)
54
. The ECU
54
has a test output pin
55
that is connected to a test signal generator
56
. The test signal generator
56
generates an analog test signal when the ECU output pin
55
changes state, such as, for example, goes from zero voltage to a high value, which is typically five volts. The analog test signal is injected at point
57
to the input of the signal conditioning circuit
36
. The resulting analog output signal is converted to a digital output signal by an analog to digital converter
58
within the ECU
54
. The digital output signal is supplied to a comparator
59
that compares the output signal value to an expected value that corresponds to the test signal. If the output signal value is different from the expected value, an error flag is set to indicate that the signal conditioning circuit is malfunctioning. Alternately, the difference between the output signal and the expected value are compared to a predetermined threshold. If the difference exceeds the threshold, the error flag is set. While the test signal generator
56
is shown in
FIG. 5
as a separate component, it will be appreciated that the circuit can be included in the ECU
54
(not shown).
The above test exercises all components of the angular rate sensor but the MEMS element. Accordingly, it would be desirable to provide an angular rate sensor that includes a functional test of the sense element
10
.
SUMMARY OF THE INVENTION
This invention relates to an apparatus and a method for performing a diagnostic test upon a angular rate sensor.
The present invention contemplates a device for measuring a angular rate comprising a sensor element with a first feedback control device connected to the sensor element, the first feedback control device operative to resonate the sensor element. The device also includes a second feedback control device connected to the sensor element, the second feedback control device operative to sense the presence of a secondary mode signal generated by the sensor element in response to a Coriolis force and to generate a null signal that cancels said secondary mode signal. The second feedback control device also generates an output signal that is proportional to the null signal.
The angular rate measuring device further includes a test device connected to the second feedback control device, the test device being operative to inject a test signal into the second feedback loop such that the test signal is passed through the sense element. Accordingly, the output signal will be proportional to the test signal. The test device is
Fayyaz Nashmiya
Kelsey-Hayes Company
MacMillan Sobanski & Todd LLC
Williams Hezron
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