Patent Description:
Accelerometers function by detecting a displacement of a proof mass under inertial forces. Some accelerometers include a capacitive pick-off system. For example, electrically conductive material (e.g., a capacitor plate) may be deposited on the upper surface of the proof mass, and similar electrically conductive material may be deposited on the lower surface of the proof mass. An acceleration or force applied along the sensitive axis of the accelerometer causes the proof mass to deflect either upwardly or downwardly causing the distance (e.g., a capacitive gap) between the pick-off capacitance plates and upper and lower non-moving members to vary. This variance in the capacitive gap causes a change in the capacitance of the capacitive elements, which is representative of the displacement of the proof mass along the sensitive axis. The change in the capacitance may be used as a displacement signal, which may be applied to a servo system that includes one or more electromagnets (e.g., a force-rebalancing coil) to return the proof mass to a null or at-rest position. Document <CIT> discloses an electromagnetic accelerometer including a moving mass suspended to a peripheral frame and associated with stress gauges forming sensors for detecting the displacement of the moving mass which supports a coil, and a permanent magnet which is associated with a magnetic circuit formed by two pole pieces defining two air-gaps for channeling the magnetic field of the magnet. The moving mass includes a central recess having a surface at least equal to the surface of a free extremity of a first pole piece of the magnetic circuit and forming a shoulder for receiving the coil, the free extremity of the shoulder leading inside the air-gaps. Document <CIT> discloses accelerometers including a proof mass assembly and an accelerometer support.

In general, the disclosure is directed to devices, systems, and techniques for determining an acceleration of one or more devices. For example, an electromagnetic accelerometer may prevent a displacement of a proof mass by delivering an electrical current to a coil, causing a Lorentz force to prevent a displacement of the proof mass relative to one or more non-moving members. For example, a magnetic flux may form a loop between a pole piece, the coil, and a non-moving member. This magnetic flux and the electrical current flowing through the coil may cause a servo effect which prevents the displacement of the proof mass relative to one or more non-moving members. A relationship may exist between the magnitude of the electrical current and the acceleration of the proof mass along a sensing axis of the accelerometer such that processing circuitry can calculate the acceleration based on the magnitude of the electrical signal delivered to the coil.

The pole piece is rectangular in shape, and the coil is disposed around the pole piece such that the pole piece fits through a center of the coil. The coil is also rectangular in shape. As such, a magnitude of the magnetic field is constant in an area between a first side of the pole piece to the non-moving member. The rectangular pole piece includes four sides. A magnitude of the magnetic field at the first side of the pole piece may be substantially the same as a magnitude of the magnetic field at a first distance outward from the first side of the pole piece. It may be beneficial for the magnetic field between the pole piece and the non-moving member to be constant so that a movement of the coil relative to the pole piece does not affect the Lorentz force which prevents the displacement of the proof mass. That is, the accelerometer may more precisely determine the acceleration of the proof mass along the sensing axis when the magnetic field between the pole piece and the non-moving member is constant as compared with accelerometers in which the magnetic field between a pole piece and a non-moving member is variable.

According to the invention, an accelerometer system includes a proof mass and a pole piece, where the pole piece is connected to the proof mass. Additionally, the accelerometer system includes a coil disposed around the pole piece, where the coil is connected to the proof mass, and wherein the coil is rectangular in shape. Additionally, the accelerometer system comprises a non-moving member, wherein within a magnetic flux loop, a magnetic flux travels from the pole piece through the coil to the non-moving member, wherein the pole piece and non-moving member are configured such that the magnetic field in a first area extending away from a first side of first pole piece is uniform in magnitude, the magnetic field in a second area extending away from a second side of first pole piece is uniform in magnitude, the magnetic field in a third area extending away from a third side of first pole piece is uniform in magnitude, and the magnetic field in a fourth area extending away from a fourth side of first pole piece is uniform in magnitude. Additionally, the accelerometer system includes circuitry configured to deliver an electrical signal to the coil in order to maintain the proof mass at a null position, determine an electrical current value corresponding to the electrical signal, and identify, based on the electrical current value, an acceleration of the accelerometer system.

According to the invention, a method includes delivering, by circuitry of an accelerometer system, an electrical signal to a coil in order to maintain a proof mass at a null position. The accelerometer system includes the proof mass, a pole piece, where the pole piece is connected to the proof mass, the coil, wherein the coil is disposed around the pole piece, where the coil is connected to the proof mass, and where the coil is rectangular in shape, and a non-moving member, wherein within a magnetic flux loop, a magnetic flux travels from the pole piece through the coil to the non-moving member, wherein the pole piece and non-moving member are configured such that the magnetic field in a first area extending away from a first side of first pole piece is uniform in magnitude, the magnetic field in a second area extending away from a second side of first pole piece is uniform in magnitude, the magnetic field in a third area extending away from a third side of first pole piece is uniform in magnitude, and the magnetic field in a fourth area extending away from a fourth side of first pole piece is uniform in magnitude. Additionally, the accelerometer system includes the circuitry. The method further comprises determining, by the circuitry, an electrical current value corresponding to the electrical signal and identifying, by the circuitry based on the electrical current value, an acceleration of the accelerometer system.

According to the invention, an accelerometer system includes a coil disposed around a pole piece, where the coil is connected to a proof mass, and where the coil is rectangular in shape. Additionally, the accelerometer system includes circuitry configured to deliver an electrical signal to the coil in order to maintain the proof mass at a null position, determine an electrical current value corresponding to the electrical signal, and identify, based on the electrical current value, an acceleration of the accelerometer system.

Like reference characters denote like elements throughout the description and figures.

This disclosure is directed to devices, systems and techniques for determining an acceleration of an object using an accelerometer system. For example, the accelerometer system may be an electromagnetic accelerometer system configured to precisely measure acceleration values. The electromagnetic accelerometer system uses a combination of electrical signals and magnetic signals to determine the acceleration of the object. For example, the accelerometer system may include a magnetic pole piece, an electrical coil, a non-moving member, and a proof mass. A magnetic flux may travel from the pole piece, through the coil to the non-moving member, and back to the pole piece. An electrical current may flow through the coil. The accelerometer system may generate a Lorentz force based on the magnetic flux and the electrical current, the Lorentz force representing a servo effect which prevents a displacement of the proof mass.

In some cases, the accelerometer system is configured to measure the acceleration of the object in real-time or near real-time, such that processing circuitry may analyze the acceleration of the object over a period of time to determine a positional displacement of the object during the period of time. For example, the accelerometer system may be a part of an inertial navigation system (INS) for tracking a position of an object based, at least in part, on an acceleration of the object. Additionally, the accelerometer system may be located on or within the object such that the accelerometer system accelerates with the object. As such, when the object accelerates, the acceleration system (including the proof mass) accelerates with the object. Since acceleration over time is a derivative of velocity over time, and velocity over time is a derivative of position over time, processing circuitry may, in some cases, be configured to determine the position displacement of the object by performing a double integral of the acceleration of the object over the period of time. Determining a position of an object using the accelerometer system located on the object - and not using a navigation system external to the object (e.g., a global navigation satellite system (GNSS)) - may be referred to as "dead reckoning.

In order to more accurately track the position of the object using the INS, it may be beneficial to improve a quality of acceleration values determined by the accelerometer system. For example, the accelerometer system may be configured to determine an acceleration along a sensing axis which is perpendicular to a plane of the proof mass. When the accelerometer system is accelerating according to a vector which includes a component parallel to the sensing axis and at least one component perpendicular to the sensing axis, the accelerometer system my precisely determine that magnitude of the component that is parallel to the sensing axis.

Forces which are perpendicular to the sensing axis of the accelerometer system may be referred to herein as "sideways" forces. The accelerometer system may prevent sideways forces form adversely impacting a precision in which the accelerometer system measures acceleration. A pole piece is located within a center of a coil. The coil is rectangular in shape with a rectangular-shaped opening in its center, and a cross-section of the pole piece is rectangular such that the pole piece fits through the rectangular-shaped opening of the coil. In some examples, there may be a gap between the pole piece and the coil on each side of the pole piece. The pole piece includes a first side, a second side, a third side, and fourth side, since the cross-section of the pole piece is rectangular. Sideways forces (e.g., vibration forces) may temporarily cause the coil to move with respect to the pole such that the coil moves closer to the first side of the pole piece and farther from the second side of the pole piece, for example.

Due to the pole piece being rectangular in shape, a magnetic field on each of the four sides of the pole piece remains constant moving away from the pole piece. In this way, movements of the coil relative to the pole piece might not affect a magnitude of a Lorentz force produced by the accelerometer system. For example, even if the coil were to move sideways relative to the pole piece, a magnitude of the magnetic field flowing across the coil from the pole piece will remain constant. The Lorentz force represents a cross product of the magnetic field across the coil and an electrical current flowing through the coil. Consequently, due to the fact that the magnetic field across the coil remains constant even when the coil moves sideways relative to the pole piece, sideways movements of the coil might not affect a magnitude of the Lorentz force.

<FIG> is a block diagram illustrating an accelerometer system <NUM>, in accordance with one or more techniques of this disclosure. As illustrated in <FIG>, accelerometer system <NUM> includes processing circuitry <NUM>, proof mass <NUM>, first pole piece 106A, second pole piece 106B (collectively, "pole pieces <NUM>"), first non-moving member 108A, second non-moving member 108B (collectively, "non-moving members <NUM>"), first coil 110A, second coil 110B (collectively, "coils <NUM>"), first sensor 112A, and second sensor 112B (collectively, "sensors <NUM>").

Accelerometer system <NUM> is configured to determine an acceleration associated with an object (not illustrated in <FIG>) based on a magnitude of one or more electrical signals delivered to coils <NUM>, the electrical signals preventing proof mass <NUM> from displacing from a null position. For example, first sensor 112A may be configured to generate a first sense signal which indicates a size of a gap between proof mass <NUM> and first non-moving member 108A and second sensor 112B may be configured to generate a second sense signal which indicates a size of a gap between proof mass <NUM> and second non-moving member 108B. Processing circuitry <NUM> may generate a first electrical signal for delivery to first coil 110A based on the first sense signal and generate a second electrical signal for delivery to second coil 110B based on the second sense signal. The first electrical signal and the second electrical signal may induce one or more Lorentz forces which prevent the displacement of proof mass <NUM> from a null position.

A Lorentz force represents a force caused by an interaction of an electric fields and a magnetic field. For example, a Lorentz force may be defined by a cross-product of an electrical field and a magnetic field, where the direction of the Lorentz force depends on the direction of the electrical field and the direction of the magnetic field, and where the magnitude of the Lorentz force depends on the magnitude of the electrical field and the magnitude of the magnetic field.

Processing circuitry <NUM> may include one or more processors that are configured to implement functionality and/or process instructions for execution within accelerometer system <NUM>. For example, processing circuitry <NUM> may be capable of processing instructions stored in a memory. Processing circuitry <NUM> may include, for example, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or equivalent discrete or integrated logic circuitry, or a combination of any of the foregoing devices or circuitry. Accordingly, processing circuitry <NUM> may include any suitable structure, whether in hardware, software, firmware, or any combination thereof, to perform the functions ascribed herein to processing circuitry <NUM>.

A memory (not illustrated in <FIG>) may be configured to store information within accelerometer system <NUM> during operation. The memory may include a computer-readable storage medium or computer-readable storage device. In some examples, the memory includes one or more of a short-term memory or a long-term memory. The memory may include, for example, random access memories (RAM), dynamic random access memories (DRAM), static random access memories (SRAM), magnetic discs, optical discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable memories (EEPROM). In some examples, the memory is used to store program instructions for execution by processing circuitry <NUM>.

Processing circuitry <NUM> may generate the first electrical signal and the second electrical signal as a part of a one or more negative feedback loops which maintain proof mass <NUM> in the null position. Processing circuitry <NUM>, first coil 110A, and first sensor 112A represent components of a first negative feedback loop. The first negative feedback loop may maintain a width of the gap between proof mass <NUM> and first non-moving member 108A at a first null width. For example, first sensor 112A may generate the first sense signal which indicates a capacitance value. The capacitance value is correlated with the width of the gap between proof mass <NUM> and first non-moving member 108A and delivers the first sense signal to processing circuitry <NUM>. Processing circuitry <NUM> may generate the first electrical signal based on the first sense signal and deliver the first electrical signal to first coil 110A in order to maintain the capacitance value of the first sense signal at a first null capacitance value. By generating the first electrical signal in order to maintain the capacitance value of the first sense signal at the first null capacitance value, processing circuitry <NUM> maintains a width of the gap between the proof mass <NUM> and the first non-moving member 108A at the first null width.

Processing circuitry <NUM>, second coil 110B, and second sensor 112B represent components of a second negative feedback loop. The second negative feedback loop may maintain a width of the gap between proof mass <NUM> and second non-moving member 108B at a second null width. For example, second sensor 112B may generate the second sense signal which indicates a second capacitance value. The capacitance value is correlated with the width of the gap between proof mass <NUM> and second non-moving member 108B and delivers the second sense signal to processing circuitry <NUM>. Processing circuitry <NUM> may generate the second electrical signal based on the second sense signal and deliver the second electrical signal to second coil 110B in order to maintain the capacitance value of the second sense signal at a second null capacitance value. By generating the second electrical signal in order to maintain the second capacitance value of the second sense signal at the second null capacitance value, processing circuitry <NUM> maintains a width of the gap between the proof mass <NUM> and the second non-moving member 108B at the second null width.

Additionally, by maintaining the width of the gap between the proof mass <NUM> and the first non-moving member 108A at the first null width and maintaining the width of the gap between the proof mass <NUM> and the second non-moving member 108B at the second null width, processing circuitry <NUM> may maintain a position of proof mass <NUM> at a null position relative to non-moving members <NUM>.

When an acceleration of accelerometer system <NUM> along a sense axis changes, the resulting acceleration force applied to proof mass <NUM> may change. Consequently, processing circuitry <NUM> may change change a magnitude of the first electrical signal delivered to first coil 110A and the second electrical signal delivered to second coil 110B in order to prevent a displacement of proof mass <NUM> relative to non-moving members <NUM>. In one example, the acceleration along the sense axis may increase from a first acceleration value to a second acceleration value. The processing circuitry <NUM> may change the magnitude of the first electrical signal and change the magnitude of the second electrical signal in order to account for the change in acceleration so that proof mass <NUM> remains in the null position relative to non-moving members <NUM>. Processing circuitry <NUM> may determine the acceleration of accelerometer system <NUM> along the sense axis based on the magnitude of the first electrical signal delivered to first coil 110A and the magnitude of the second electrical signal delivered to second coil 110B.

In some examples, the magnitude of the first electrical signal delivered to first coil 110A is proportional to the acceleration along the sense axis. In some examples, the magnitude of the second electrical signal delivered to second coil 110B is proportional to the acceleration along the sense axis. As such, an increase in the magnitude of the first electrical signal may correspond to an increase in the acceleration along the sense axis and an increase in the magnitude of the second electrical signal may correspond to an increase in the acceleration along the sense axis. Alternatively, a decrease in the magnitude of the first electrical signal may correspond to a decrease in the acceleration along the sense axis and a decrease in the magnitude of the second electrical signal may correspond to a decrease in the acceleration along the sense axis.

Accelerometer system <NUM> may include a first magnetic flux loop and a second magnetic flux loop. The first magnetic flux loop may include first pole piece 106A, first non-moving member 108A, and first coil 110A. Within the first magnetic flux loop, a first magnetic flux may travel from first pole piece 106A through first coil 110A to first non-moving member 108A. The first magnetic flux then travels through first non-moving member 108A back to first pole piece 106A. In some examples, first pole piece 106A may include a first magnet which generates the first magnetic flux. The second magnetic flux loop may include second pole piece 106B, second non-moving member 108B, and second coil 110B. Within the second magnetic flux loop, a second magnetic flux may travel from second pole piece 106B through second coil 110B to second non-moving member 108B. The second magnetic flux then travels through second non-moving member 108B back to second pole piece 106B. In some examples, second pole piece 106B may include a second magnet which generates the second magnetic flux.

Accelerometer system <NUM> may represent a servo system which counter-balances acceleration along the sense axis with Lorentz forces parallel to the sense axis. For example, if accelerometer system <NUM> accelerates along the sense axis, the acceleration may apply an acceleration force to the proof mass <NUM>, where the acceleration force is applied to proof mass <NUM> in an opposite direction of the acceleration of accelerometer system <NUM>. Processing circuitry <NUM> delivers the first electrical signal to first coil 110A and delivers the second electrical signal to second coil 110B in order to generate one or more Lorentz forces which counter-balance the acceleration force resulting form the acceleration along the sense axis. That is, the one or more Lorentz forces are applied to proof mass <NUM> in an opposite direction to the acceleration force, such that proof mass <NUM> is not displaced from a null position by the acceleration force. The magnitude of the acceleration force changes based on the magnitude of the acceleration along the sense axis. As such, to prevent the displacement of proof mass <NUM> from the null position, processing circuitry <NUM> changes the magnitude of the first electrical signal delivered to first coil 110A and the magnitude of the second electrical signal delivered to second coil 110B in order to change the magnitude of the one or more Lorentz forces which counter-balance the acceleration signal.

Lorentz forces are forces which arise from an interaction between an electrical field and a magnetic field. As discussed above, accelerometer system <NUM> includes a first magnetic flux loop and a second magnetic flux loop. The first magnetic flux loop includes a passage of a first magnetic flux from the pole piece 106A to first non-moving member 108A through first coil 110A. The first electrical signal flows through first coil 110A. The first magnetic flux and the first electrical signal may cause a first Lorentz force to be applied to proof mass <NUM> in an opposite direction of the acceleration force applied to proof mass <NUM> due to the acceleration along the sense axis. Additionally, the second magnetic flux loop includes a passage of a second magnetic flux from the second pole piece 106B to second non-moving member 108B through second coil 110B. The second electrical signal flows through second coil 110B. The second magnetic flux and the second electrical signal may cause a second Lorentz force to be applied to proof mass <NUM> in an opposite direction of the acceleration force applied to proof mass <NUM> due to the acceleration along the sense axis.

In some examples, pole pieces <NUM> may be square in shape, and coils <NUM> may be square in shape such that respective openings of coils <NUM> are configured to receive pole pieces <NUM>. For example, first coil 110A may include a first opening which receives first pole piece 106A which includes a square-shaped cross-section. Second coil 110B may include a second opening which receives second pole piece 106B which includes a square-shaped cross-section. As discussed above, accelerometer system <NUM> includes a first magnetic flux loop and a second magnetic flux loop. As a part of the first magnetic flux loop, a first magnetic flux may flow out each side of the four sides of first pole piece 106A.

Since the cross-section of first pole piece 106A is rectangular, the magnetic field in a first area extending away from a first side of first pole piece 106A may be uniform in magnitude, the magnetic field in a second area extending away from a second side of first pole piece 106A may be uniform in magnitude, the magnetic field in a third area extending away from a third side of first pole piece 106A may be uniform in magnitude, and the magnetic field in a fourth area extending away from a fourth side of first pole piece 106A may be uniform in magnitude. The first area extends from the first side of first pole piece 106A to first non-moving member 208A, meaning that the magnetic field in a space between the first side of first pole piece 106A and first non-moving member 208A is uniform. The second area extends from the second side of first pole piece 106A to first non-moving member 208A, meaning that the magnetic field in a space between the second side of first pole piece 106A and first non-moving member 208A is uniform. The third area extends from the third side of first pole piece 106A to first non-moving member 208A, meaning that the magnetic field in a space between the third side of first pole piece 106A and first non-moving member 208A is uniform. The fourth area extends from the fourth side of first pole piece 106A to first non-moving member 208A, meaning that the magnetic field in a space between the fourth side of first pole piece 106A and first non-moving member 208A is uniform.

Since the cross-section of second pole piece 106B is rectangular, the magnetic field in a first area extending away from a first side of second pole piece 106B may be uniform in magnitude, the magnetic field in a second area extending away from a second side of second pole piece 106B may be uniform in magnitude, the magnetic field in a third area extending away from a third side of second pole piece 106B may be uniform in magnitude, and the magnetic field in a fourth area extending away from a fourth side of second pole piece 106B may be uniform in magnitude. The first area extends from the first side of second pole piece 106B to second non-moving member 208B, meaning that the magnetic field in a space between the first side of second pole piece 106B and second non-moving member 208B is uniform. The second area extends from the second side of second pole piece 106B to second non-moving member 208B, meaning that the magnetic field in a space between the second side of second pole piece 106B and second non-moving member 208B is uniform. The third area extends from the third side of second pole piece 106B to second non-moving member 208B, meaning that the magnetic field in a space between the third side of second pole piece 106B and second non-moving member 208B is uniform. The fourth area extends from the fourth side of second pole piece 106B to second non-moving member 208B, meaning that the magnetic field in a space between the fourth side of second pole piece 106B and second non-moving member 208B is uniform.

Sideways movements may displace a coil relative to the respective pole piece. These sideways movements may cause, for example, first coil 110A to move sideways relative to first pole piece 106A. In some examples, first coil 110A passes through a first area which extends from the first side of first pole piece 106A to first non-moving member 208A, a second area which extends from the second side of first pole piece 106A to first non-moving member 208A, a third area which extends from the third side of first pole piece 106A to first non-moving member 208A, and a fourth area which extends from the fourth side of first pole piece 106A to first non-moving member 208A. In some examples, a sideways movement of coil 110A causes coil 110A to move closer to pole piece 106A in the first area and move away from pole piece 106A in the second area. In at least some such examples, the magnetic field across first coil 110A does not change since the magnetic field in the first area is uniform and the magnetic field in the second area is uniform.

<FIG> is a conceptual diagram illustrating a side cutaway view of an accelerometer system <NUM>, in accordance with one or more techniques of this disclosure. As seen in <FIG>, accelerometer system <NUM> includes proof mass assembly <NUM>, first pole piece 206A, second pole piece 206B (collectively, "pole pieces <NUM>"), first non-moving member 208A, second non-moving member 208B (collectively, "non-moving members <NUM>"), first coil 210A, second coil 210B (collectively, "coils <NUM>"), first magnet 220A, and second magnet 220B (collectively, "magnets <NUM>"). Proof mass assembly <NUM> includes proof mass <NUM>, first capacitive plate 205A, and second capacitive plate 205B (collectively, "capacitive plates <NUM>"). In the example of <FIG>, accelerometer system <NUM> further includes center raised pads 222A-222B (collectively, "center raised pads <NUM>"), outer raised pads 224A-224D (collectively, "outer raised pads <NUM>"), first band 226A, second band 226B (collectively, "bands <NUM>"), first capacitive gap <NUM>, and second capacitive gap <NUM>. In the example of <FIG>, accelerometer system <NUM> may include accelerometer supports 214A-214B (collectively, "accelerometer supports <NUM>"), which may be formed by a combination of pole pieces <NUM>, non-moving members <NUM>, and magnets <NUM>. Accelerometer system <NUM> may be an example of accelerometer system <NUM> of <FIG>. Proof mass <NUM> may be an example of proof mass <NUM> of <FIG>. Pole pieces <NUM> may be an example of pole pieces <NUM> of <FIG>. Non-moving members <NUM> may be an example of non-moving members <NUM> of <FIG>. Coils <NUM> may be an example of coils <NUM> of <FIG>.

Accelerometer system <NUM> may be configured to sense an acceleration along sense axis <NUM>. For example, accelerometer system <NUM> may be configured to sense an acceleration along sense axis <NUM> in a first direction <NUM>. In some cases, accelerometer system <NUM> precisely determines a magnitude of the acceleration along the sense axis <NUM> in the first direction <NUM> in real time or near-real time such that processing circuitry (not illustrated in <FIG>) may track a position of accelerometer system <NUM> using dead reckoning. As seen in <FIG>, proof mass assembly <NUM> is suspended between first non-moving member 208A and second non-moving member 208B by center raised pads <NUM> and outer raised pads <NUM>. In some examples, the processing circuitry may receive a first sense signal indicative of a width of first capacitive gap <NUM> and receive a second sense signal indicative of a width of second capacitive gap <NUM>. In turn, the processing circuitry may deliver a first electrical signal to first coil 210A and deliver a second electrical signal to second coil 210B in order to prevent a displacement of proof mass <NUM> in response to an acceleration of accelerometer system <NUM> along sense axis <NUM>. The magnitude of the first electrical signal and the magnitude of the second electrical signal may be correlated with the magnitude of the acceleration.

Non-moving members <NUM> may be attached to (e.g., clamped) center raised pads <NUM> and outer raised pads <NUM>, securing proof mass assembly <NUM> between first non-moving member 208A and second non-moving member 208B. The term "non-moving member" may refer to a member representing a reference position by which a position of proof mass assembly <NUM> may be compared. In other words, the position of proof mass assembly <NUM> may represent a position of proof mass assembly <NUM> relative to non-moving members <NUM>. In some examples, non-moving members <NUM> include dual metal materials, which may be part of a magnetic flux loop. In some examples, non-moving members <NUM> may be similar to stators of a variable capacitor.

Coils <NUM> may, in some cases, conduct electricity such that electrical signals flow through coils <NUM>. For example, a first electrical signal may flow through a path of first coil 210A and a second electrical signal may flow through a path of second coil 210B. The path of first coil 210A may form a square path and the path of second coil 210B may form a square path. Since <FIG> represents a cutaway view of accelerometer system <NUM>, the square path of first coil 210A and the square path of second coil 210B is not illustrated in <FIG>. Coils <NUM> extend fully around an outer surface of pole pieces <NUM> such that the first electrical signal flows around the outer surface of pole piece 206A through first coil 210A and the second electrical signal flows around the outer surface of pole piece 206B through second coil 210B.

Bands <NUM> are a metal pieces which fasten first non-moving member 208A to second non-moving member 208B. In some examples, bands <NUM> may be attached to (e.g., bonded with epoxy) non-moving members <NUM>, when non-moving members <NUM> are attached to proof mass assembly <NUM> by center raised pads <NUM> and outer raised pads <NUM>. Accelerometer system <NUM> includes first capacitive gap <NUM> and second capacitive gap <NUM>. First capacitive gap <NUM> represents a gap between first capacitive plate 205A and first non-moving member 208A, second capacitive gap <NUM> represents a gap between second capacitive plate 205B and second non-moving member 208B. First capacitive plate 205A may generate a first sense signal which indicates a first capacitance value. The first capacitance value is correlated with a width of first capacitive gap <NUM>. Second capacitive plate 205B may generate a second sense signal which indicates a second capacitance value. The second capacitance value is correlated with a width of second capacitive gap <NUM>. In this way, first capacitive plate 205A may represent first sensor 112A of <FIG> and second capacitive plate 205B may represent second sensor 112B of <FIG>. Processing circuitry (not illustrating in <FIG>) may receive the first sense signal and the second signal and control electrical signals delivered to coils <NUM> based on the first sense signal and the second sense signal.

A null width of first capacitive gap <NUM> may, in some examples, be defined by a width of outer raised pads <NUM> and center raised pads <NUM>. In some examples, the null width of first capacitive gap <NUM> is within a range from <NUM> inches to <NUM> inches. A null width of second capacitive gap <NUM> may, in some examples, be defined by a width of outer raised pads <NUM> and center raised pads <NUM>. In some examples, the null width of second capacitive gap <NUM> is within a range from <NUM> inches to <NUM> inches. When the width of first capacitive gap <NUM> is at the null width of first capacitive gap <NUM> and the width of second capacitive gap <NUM> is at the null width of second capacitive gap <NUM>, proof mass <NUM> may be located at a null position. That is, proof mass <NUM> may be located at the null position such that the processing circuitry is configured to determine the acceleration along sense axis <NUM> based on the first electrical signal delivered to first coil 210A and the second electrical signal delivered to second coil 210B.

In some examples, first capacitive gap <NUM> may have a first capacitance value. The processing circuitry may detect the first capacitance value of first capacitive gap <NUM>, which in a closed-loop differential capacitance configuration can be detected and used by the processing circuitry to determine the acceleration of accelerometer system <NUM>. Additionally, second capacitive gap <NUM> may have a second capacitance value. The processing circuitry may detect the second capacitance value of second capacitive gap <NUM>, which in a closed-loop differential capacitance configuration can be detected and used by the processing circuitry to determine the acceleration of accelerometer system <NUM>. In some examples, an increase in a width of first capacitive gap <NUM> and a decrease in a width of second capacitive gap <NUM> may be indicative of an acceleration of accelerometer system <NUM> in first direction 211A. Conversely, an increase in the width of second capacitive gap <NUM> and a decrease in the width of first capacitive gap <NUM> may be indicative of an acceleration of accelerometer system <NUM> in the second direction 211B. The processing circuitry may deliver the first electrical signal to first coil 210A and deliver the second electrical signal to second coil 210B in order to counter-balance a displacement of proof mass <NUM> from the null position. The magnitude of the first electrical signal and the magnitude of the second electrical signal may be correlated with the magnitude of the acceleration along sense axis <NUM>.

Magnets <NUM> are magnets for providing a magnetic field to drive magnetic circuits of magnets <NUM>, pole pieces <NUM>, coils <NUM>, and non-moving members <NUM>. In some examples, magnets <NUM> may be made of Alnico, samarium-cobalt, neodymium-iron-boron, or other such materials. In some examples, magnets <NUM> may receive the forces and/or strains transmitted from non-moving members <NUM> caused by the construction of accelerometer system <NUM>. In some examples, magnets <NUM> may be part of a zero gauge configuration of accelerometer system <NUM>.

Pole pieces <NUM> are magnetic structure that enables the magnetic field of magnets <NUM> to be focused and drive the magnetic circuit of magnets <NUM>, pole pieces <NUM>, coils <NUM>, and non-moving members <NUM>. For example, pole pieces <NUM> may be magnetic structures that enable the magnetic field of the magnet to turn a corner and flow through coils <NUM>. In these examples, by allowing the magnetic field of magnets <NUM> to go through coils <NUM>, the magnetic field of magnets <NUM> may enter non-moving members <NUM> and flow around to the opposite side of the magnet through non-moving members <NUM>, and flow back through the magnet to the pole piece completing the magnetic circuit. For example, a first magnetic circuit may represent a magnetic flux loop in which a first magnetic flux passes from first magnet 220A to first pole piece 206A. The first magnetic flux travels from first pole piece 206A to first non-moving member 208A through first coil 210A. Then, the first magnetic flux travels through first non-moving member 208A back to first magnet 220A in order to complete the first magnetic circuit. A second magnetic circuit may represent a magnetic flux loop in which a second magnetic flux passes from second magnet 220B to second pole piece 206B. The second magnetic flux travels from second pole piece 206B to second non-moving member 208B through second coil 210B. Then, the second magnetic flux travels through second non-moving member 208B back to second magnet 220B in order to complete the second magnetic circuit.

In some examples, pole pieces <NUM> may be part of a zero gauge configuration of accelerometer system <NUM>. In some examples, pole pieces <NUM> may be made from a permeable material such as invar, Mu Metal, Permalloy, or other such material.

In some examples, accelerometer system <NUM> may include coils <NUM> attached on each side of the proof mass. In some examples, accelerometer system <NUM> may include processing circuitry (not illustrated in <FIG>) configured to deliver a first electrical signal and a second electrical signal to coils <NUM> in order to position proof mass <NUM> at the null position. In some examples, when accelerometer system <NUM> accelerates along sense axis <NUM>, the processing circuitry may increase an electrical current magnitude of the first electrical signal and increase an electrical current magnitude of the second electrical signal to maintain the proof mass <NUM> at the null position. In this example, the electrical current magnitude of the first electrical signal and the electrical current magnitude of the second electrical signal are proportional to the magnitude of the acceleration along the sense axis <NUM>.

Preventing proof mass <NUM> from displacing form the null position may be referred to herein as the "servo effect. " In some examples, the processing circuitry may cause one or more Lorentz forces to counter-balance an acceleration force applied to proof mass <NUM> such that proof mass <NUM> does not move from the null position. This means that the processing circuitry is configured to adjust the one or more Lorentz forces in real time or near-real time such that the one or more Lorentz forces counter-balance the acceleration force applied to proof mass <NUM> at any given time, thus constantly maintaining the proof mass <NUM> at the null position. The electrical signals required to induce the one or more Lorentz forces may be generated by the processing circuitry based on the first sense signal received from first capacitive plate 205A and the second sense signal received from the second capacitive plate 205B.

Coils <NUM> may be mounted on either side of proof mass <NUM> of proof mass assembly <NUM>. In some examples, processing circuitry may modify the current in coils <NUM> to servo proof mass <NUM> to maintain the null position. Any acceleration of accelerometer system <NUM> will momentarily move the proof mass of proof mass assembly <NUM> out of the plane of the null position and the increase in current required to maintain proof mass <NUM> in the null position is proportional to the magnitude of the acceleration of accelerometer system <NUM> along sense axis <NUM>.

Although <FIG> illustrates accelerometer system <NUM> with a capacitive plate and a coil on both sides of proof mass assembly <NUM> to form a combined capacitive pick-off system, it is understood that accelerometer system <NUM> may function with a capacitor plate and a coil on only one side of proof mass assembly <NUM>. Similarly, although <FIG> illustrates accelerometer system <NUM> with a non-moving member on both sides of proof mass assembly <NUM> to form the combined capacitive pick-off system, it is understood that accelerometer system <NUM> may function a non-moving member and a capacitor plate on the same side of proof mass assembly <NUM>.

<FIG> is a conceptual diagram illustrating a top cutaway view of an accelerometer system <NUM>, in accordance with one or more techniques of this disclosure. As seen in <FIG>, accelerometer system <NUM> includes proof mass <NUM>, capacitive plate <NUM>, pole piece <NUM>, non-moving member <NUM>, coil <NUM>, and bands 326A-326D (collectively, "bands <NUM>"). Accelerometer system <NUM> may be an example of accelerometer system <NUM> of <FIG>. Proof mass <NUM> may be an example of proof mass <NUM> of <FIG>. Capacitive plate <NUM> may be an example of first capacitive plate 205A of <FIG>. Pole piece <NUM> may be an example of first pole piece 206A of <FIG>. Non-moving member <NUM> may be an example of first non-moving member 208A of <FIG>. Coil <NUM> may be an example of first coil 210A of <FIG>. In some examples, sense axis <NUM> of accelerometer system <NUM> extends into and out from the page of <FIG>. That is, accelerometer system <NUM> may sense an acceleration into the page of <FIG> and sense an acceleration out of the page of <FIG>. In some examples, plane <NUM> represents a cut-out plane which defines the side cutaway view of <FIG>.

Responsive to an acceleration of accelerometer system <NUM> along sense axis <NUM>, processing circuitry (not illustrated in <FIG>) of accelerometer system <NUM> may deliver electrical signal <NUM> to coil <NUM>. As seen in <FIG>, electrical signal <NUM> travels through the path of coil <NUM> in the clockwise direction. Additionally, a magnetic flux <NUM> propagates outwards from pole piece <NUM> to non-moving member <NUM> through coil <NUM>. Coil <NUM> includes four sides. As seen in <FIG>, for each of the four sides of coil <NUM>, electrical signal <NUM> flows in a direction that is perpendicular to the direction of magnetic flux <NUM>. The electrical signal <NUM> flowing perpendicular to the direction of magnetic flux <NUM> may induce a Lorentz force directed outwards form the page of <FIG>. This Lorentz force may counteract an acceleration force applied to proof mass <NUM> directed into the page of <FIG>. The direction of the Lorentz force (e.g., into the page or outwards from the page) induced by electrical signal <NUM> may depend on the direction of electrical signal <NUM> within coil <NUM>. For example, when electrical signal <NUM> flows through coil <NUM> in the clockwise direction, the resulting Lorentz force is directed outwards from the page. Alternatively, when electrical signal <NUM> flows through coil <NUM> in the counterclockwise direction, the resulting Lorentz force is directed into the page.

<FIG> is a conceptual diagram illustrating an electrical signal which travels through a coil <NUM> and a magnetic flux emitted by a pole piece <NUM>, in accordance with one or more techniques of this disclosure. As seen in <FIG>, electrical signal 442A-442D (collectively, "electrical signal <NUM>") travels through coil <NUM> in a clockwise direction. Coil <NUM> includes a first side 452A, a second side 452B, a third side 452C, and a fourth side 452D (collectively, "sides <NUM>"). Coil <NUM> may be a part of an accelerometer system which senses an acceleration along a sense axis <NUM>, which extends outward from the page of <FIG> and into the page of <FIG>. Magnetic flux 454A may travel from pole piece <NUM> through side 452A of coil <NUM>, magnetic flux 454B may travel from pole piece <NUM> through side 452B of coil <NUM>, magnetic flux 454C may travel from pole piece <NUM> through side 452C of coil <NUM>, and magnetic flux 454D may travel from pole piece <NUM> through side 452D of coil <NUM>. Pole piece <NUM> may be an example of any one or more of pole pieces <NUM> of <FIG>, pole pieces <NUM> of <FIG>, and pole piece <NUM> of <FIG>. Coil <NUM> may be an example of any one or more of coils <NUM> of <FIG>, coils <NUM> of <FIG>, and coil <NUM> of <FIG>.

Processing circuitry (not illustrated in <FIG>) may deliver the electrical signal <NUM> to coil <NUM> such that electrical signal <NUM> travels around the path of coil <NUM> in a clockwise direction. Magnetic flux 454A-454D (collectively, "magnetic flux <NUM>"), travels outwards from pole piece <NUM> such that magnetic flux <NUM> is normal to electrical signal <NUM>. As seen in <FIG>, electrical signal 442A is perpendicular to magnetic flux 454A, electrical signal 442B is perpendicular to magnetic flux 454B, electrical signal 442C is perpendicular to magnetic flux 454C, and electrical signal 442D is perpendicular to magnetic flux 454D. As such, electrical signal <NUM> is perpendicular to magnetic flux <NUM> at each of sides 452A-452D of coil <NUM>, inducing a Lorentz force outward from the page of <FIG>, where the Lorentz force is parallel to sense axis <NUM>. In an example where electrical signal <NUM> travels around the path of coil <NUM> in a counterclockwise direction, this may induce a Lorentz force into the page of <FIG>.

As seen in <FIG>, a cross-section of pole piece <NUM> is square in shape, and a cross-section of coil <NUM> is square in shape with a square-shaped opening, such that pole piece <NUM> fits in the square-shaped opening of coil <NUM>. The square shape of the cross-section of pole piece <NUM> may be beneficial for precisely measuring an acceleration along sense axis <NUM>. For example, by emitting magnetic flux <NUM> from the straight edges of the pole piece which has a square cross-section, magnetic flux 454A is uniform in density. That is, a magnitude of a magnetic field is substantially the same at any point within magnetic flux 454A, a magnitude of a magnetic field is substantially the same at any point within magnetic flux 454B, a magnitude of a magnetic field is substantially the same at any point within magnetic flux 454C, and a magnitude of a magnetic field is substantially the same at any point within magnetic flux 454D.

A Lorentz force represents a cross-product of an electrical field and a magnetic field perpendicular to the electrical field. As such, a magnitude of the Lorentz force depends on both of the magnitude of the electrical field and a magnitude of the magnetic field. It may be beneficial for the magnitude of the electrical field represented by magnetic flux <NUM> to be uniform, so that sideways movements of coil <NUM> relative to pole piece <NUM> do not affect a magnitude of the Lorentz force representing the cross-product of electrical signal <NUM> and magnetic flux <NUM>. In one or more examples where a cross-section of a pole piece is circular and without straight edges, the magnetic field emitted by the pole piece would not be uniform extending outwards form the pole piece. For example, a strength of the magnetic field would decrease moving away from the circular pole piece. This means that a movement of a coil disposed around the circular pole piece may affect a magnitude of the resulting Lorentz force, thus affecting a measured acceleration. As such, the accelerometer system <NUM> which includes a pole piece having a cross-section in the shape of a polygon (e.g., a square, a rectangular, a triangle, or another polygon) may determine an acceleration more precisely than an accelerometer system <NUM> which includes a pole piece having a cross-section with one or more rounded edges.

One or more techniques described herein may allow accelerometer system <NUM> to precisely determine an acceleration along sense axis <NUM>, under conditions in which accelerometer system <NUM> vibrates according to a vector which is not parallel to sense axis <NUM>. For example, vibrations along an axis which is not parallel to sense axis <NUM> may cause coil <NUM> to move "sideways" relative to pole piece <NUM>. These sideways movements may cause the coil <NUM> to move relative to pole piece <NUM> such that coil <NUM> crosses through to a different part of the magnetic flux <NUM> than as compared with prior to the sideways movement of coil <NUM>. Since a magnitude of the magnetic field of magnetic flux <NUM> is uniform in the areas of magnetic flux <NUM> illustrated in <FIG>, sideways movements of coil <NUM> relative to pole piece <NUM> might not affect a magnitude of the Lorentz force produced by electrical signal <NUM> and magnetic flux <NUM>.

<FIG> is a conceptual diagram illustrating a magnetic field strength throughout a cross-section of accelerometer system <NUM>, in accordance with one or more techniques of this disclosure. Accelerometer system <NUM> includes non-moving members 508A-508B (collectively, "non-moving members <NUM>"), coils 510A-510B (collectively, "coils <NUM>"), and bands <NUM>-526B (collectively, "bands <NUM>"). Accelerometer system <NUM> may be an example of accelerometer system <NUM> of <FIG>. Non-moving members <NUM> may be an example of non-moving members <NUM> of <FIG>. Coils <NUM> may be an example of coils <NUM> of <FIG>. Bands <NUM> may be an example of bands <NUM> of <FIG>. <FIG> illustrates the strength of the magnetic field based on shade darkness. Darker shades represent stronger magnetic fields and lighter shades represent weaker magnetic fields.

Gap 560A represents a gap between non-moving member 508A and a first side of magnet 520A, which includes a corresponding pole piece. Gap 560B represents a gap between non-moving member 508A and a second side of magnet 520A. Gap 560C represents a gap between non-moving member 508B and a first side of magnet 520B, which includes a corresponding pole piece. Gap 560D represents a gap between non-moving member 508B and a second side of magnet 520B. As seen in <FIG>, the shade within gaps 560A-560D is substantially uniform. This means that a movement of coil 510A within gaps 560A and 560B or a movement of coil 510B within gaps 560C and 560D will not change a strength of the magnetic field across coil 510A or a strength of the magnetic field across coil 510B, respectively. The magnetic field uniformity of gaps <NUM> is due to the face that magnet 520A and the corresponding pole piece are square in shape and magnet 520B and the corresponding pole piece are square in shape.

<FIG> is a conceptual diagram illustrating a perspective view of an accelerometer <NUM>, in accordance with one or more techniques of this disclosure. The accelerometer <NUM> may, in some cases, represent the accelerometer shown in the cutaway views of any of <FIG>. As seen in <FIG>, non-moving member 608A and 608B are fastened together using bands 626A-626C, as well as a fourth band which is not illustrated in <FIG>. Magnets 620A and 620B are located at a center of accelerometer <NUM>. Coil 610A is disposed around magnet 620A and Coil 610B is disposed around magnet 620B. Non-moving members <NUM> may be an example of non-moving member <NUM> of <FIG>. Coils <NUM> may be an example of coils <NUM> of <FIG>. Magnets <NUM> may be an example of magnets <NUM> of <FIG>.

<FIG> is a flow diagram illustrating an example operation for determining an acceleration using an electromagnetic accelerometer, in accordance with one or more techniques of this disclosure. <FIG> is described with respect to accelerometer system <NUM>, of <FIG>. However, the techniques of <FIG> may be performed by different components of accelerometer system <NUM> or by additional or alternative devices.

Processing circuitry <NUM> may receive, from first sensor 112A, a first capacitance signal which indicates a capacitance value (<NUM>). In some examples, first sensor 112A may represent a first capacitive plate (e.g., first capacitive plate 205A of <FIG>) located on a first side of proof mass <NUM>. Processing circuitry <NUM> may generate, based on the capacitance signal, an electrical signal to include an electrical current value which maintains proof mass <NUM> at a null position (<NUM>). Processing circuitry <NUM> may deliver the electrical signal to first coil 110A (<NUM>). In some examples, processing circuitry <NUM> may deliver the electrical signal to first coil 110A such that first coil 110A applies a Lorentz force to proof mass <NUM>, counteracting an acceleration force applied to proof mass <NUM>.

Processing circuitry <NUM> may determine an electrical current value corresponding to the electrical signal (<NUM>). Subsequently, processing circuitry <NUM> may identify, based on the electrical current value, the acceleration of accelerometer system <NUM> based on the electrical current value (<NUM>). In other words, the strength of the electrical signal required to maintain proof mass <NUM> in a null position is correlated with the acceleration of accelerometer system <NUM> along a sense axis.

Instructions may be executed by one or more processors within the accelerometer or communicatively coupled to the accelerometer. The one or more processors may, for example, include one or more DSPs, general purpose microprocessors, application specific integrated circuits ASICs, FPGAs, or other equivalent integrated or discrete logic circuitry. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for performing the techniques described herein.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses that include integrated circuits (ICs) or sets of ICs (e.g., chip sets). Rather, various units may be combined or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

Claim 1:
An accelerometer system (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising:
a proof mass (<NUM>, <NUM>, <NUM>);
a pole piece (<NUM>, <NUM>, <NUM>, <NUM>), wherein the pole piece is connected to the proof mass;
a coil (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, 610a, 610b) disposed around the pole piece, wherein the coil is connected to the proof mass, wherein the coil is rectangular in shape, and wherein a cross-section of the pole piece is rectangular such that the pole piece fits through a rectangular-shaped opening of the coil;
a non-moving member (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, 608a, 608b), wherein within a magnetic flux loop, a magnetic flux travels from the pole piece through the coil to the non-moving member, wherein the pole piece and non-moving member are configured such that the magnetic field in a first area extending away from a first side of first pole piece is uniform in magnitude, the magnetic field in a second area extending away from a second side of first pole piece is uniform in magnitude, the magnetic field in a third area extending away from a third side of first pole piece is uniform in magnitude, and the magnetic field in a fourth area extending away from a fourth side of first pole piece is uniform in magnitude; and
circuitry configured to:
deliver an electrical signal (<NUM>, <NUM>, 442a, 442b, 442c, 442d) to the coil in order to maintain the proof mass at a null position (<NUM>);
determine an electrical current value (<NUM>) corresponding to the electrical signal (<NUM>, <NUM>, 442a, 442b, 442c, 442d, <NUM>); and
identify, based on the electrical current value (<NUM>), an acceleration of the accelerometer system.