MEMS accelerometer systems
A MEMS accelerometer system can include a proof mass device having a proof mass configured to move from an initial position in response to an input acceleration, a transducer operatively connected to the proof mass device to output a transducer signal correlating to a movement and/or position of the proof mass, a driver operatively connected to the proof mass device and configured to drive the proof mass, and a controller operatively connected to the driver to control the driver. The controller is operatively connected to the transducer to receive the transducer signal and output a drive signal to the driver to drive the proof mass toward an initial position. The system can include an observer module operatively connected to the controller to receive the drive signal. The observer module can be operatively connected to the transducer to receive the transducer signal. The observer module can be configured to deterministically estimate the input acceleration based on the transducer signal and the drive signal based on a deterministic model. The observer module can be configured to output an estimated input acceleration signal.
1 . A MEMS accelerometer system, comprising:
a proof mass device having a proof mass configured to move from an initial position in response to an input acceleration;
a transducer operatively connected to the proof mass device to output a transducer signal correlating to a movement and/or position of the proof mass;
a driver operatively connected to the proof mass device and configured to drive the proof mass;
a controller operatively connected to the driver to control the driver, wherein the controller is operatively connected to the transducer to receive the transducer signal and output a drive signal to the driver to drive the proof mass toward an initial position;
an observer module operatively connected to the controller to receive the drive signal, wherein the observer module is operatively connected to the transducer to receive the transducer signal, wherein the observer module is configured to deterministically estimate the input acceleration based on the transducer signal and the drive signal based on a deterministic model, wherein the observer module is configured to output an estimated input acceleration signal.
2 . The system of claim 1 , wherein the observer module is not connected to the input of the controller such that the estimated input acceleration signal is not used to control the driver or the position of the proof mass.
3 . The system of claim 2 , wherein the observer module is configured to receive a temperature signal from a temperature sensor, wherein the observer module is configured to estimate the input acceleration further based on the temperature reading.
4 . The system of claim 3 , wherein the observer module includes a displacement calculator module, a drive acceleration calculator module, and an observer dynamics module.
5 . The system of claim 4 , wherein the displacement calculator module is configured to receive the transducer signal and the temperature signal, and to output a calculated displacement signal.
6 . The system of claim 5 , wherein the drive acceleration calculator module is configured to receive the driver signal, the temperature signal, the calculated displacement signal, and a reference signal, and to output a calculated restorative acceleration signal that estimates the restorative acceleration required to drive the proof mass to the initial position.
7 . The system of claim 6 , wherein the observer dynamics module is operatively connected to the drive acceleration calculator module and the displacement calculator module, wherein the observer dynamics module is configured to calculate the estimated input acceleration based on the calculated restorative acceleration signal and calculated displacement signal.
8 . The system of claim 7 , wherein the observer module includes a low pass filter operatively connected to the observer dynamics module to receive the estimated input acceleration signal to filter noise from the estimated input acceleration signal and to output a filtered estimated input acceleration signal.
9 . The system of claim 8 , wherein the observer module is configured to generate an estimate of the proof-mass displacement {circumflex over (x)} 1 t , the proof-mass speed {circumflex over (x)} 2 t , and the input acceleration â in t , in accordance with the below relationships:
[
x
^
.
1
t
x
^
.
2
t
x
^
.
3
t
]
=
[
-
K
1
a
12
0
a
21
-
K
2
a
22
+
L
L
-
a
21
-
a
22
-
L
-
L
]
[
x
^
1
t
x
^
2
t
x
^
3
t
]
+
[
0
K
1
1
K
2
-
1
0
]
[
a
d
cal
t
x
1
cal
t
]
a
^
in
t
=
-
L
x
^
2
t
-
L
x
^
3
t
wherein K 1 , K 2 and L are observer gains, and wherein a 12 , a 21 , a 22 are constant parameters in a proof-mass second order linear dynamical model from the total applied acceleration to proof-mass displacement as shown in the relationship below:
[
x
.
1
t
x
.
2
t
]
=
[
0
a
12
a
21
a
22
]
[
x
1
t
x
2
t
]
+
[
0
1
]
a
d
t
-
[
0
1
]
a
in
t
+
[
0
1
]
w
x
.
y
=
x
1
t
+
w
y
where w x and w y denote unknown in general disturbances and/or uncertainties (e.g. measurement noise).
10 . The system of claim 9 , further comprising a device or system operatively connected to the low pass filter to receive the filtered input acceleration signal and either use, record, transmit, or display the data as required.