CA1096653A - Servoed accelerometer utilizing rare earth magnets - Google Patents
Servoed accelerometer utilizing rare earth magnetsInfo
- Publication number
- CA1096653A CA1096653A CA308,107A CA308107A CA1096653A CA 1096653 A CA1096653 A CA 1096653A CA 308107 A CA308107 A CA 308107A CA 1096653 A CA1096653 A CA 1096653A
- Authority
- CA
- Canada
- Prior art keywords
- proof mass
- servoed
- accelerometer
- temperature
- restoring
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F7/00—Magnets
- H01F7/02—Permanent magnets [PM]
- H01F7/0205—Magnetic circuits with PM in general
- H01F7/021—Construction of PM
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P1/00—Details of instruments
- G01P1/006—Details of instruments used for thermal compensation
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P15/13—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by measuring the force required to restore a proofmass subjected to inertial forces to a null position
- G01P15/132—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by measuring the force required to restore a proofmass subjected to inertial forces to a null position with electromagnetic counterbalancing means
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Transmission And Conversion Of Sensor Element Output (AREA)
- Micromachines (AREA)
- Control Of Position Or Direction (AREA)
- Magnetic Bearings And Hydrostatic Bearings (AREA)
- Switches Operated By Changes In Physical Conditions (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The temperature stability of a servoed accelerometer having a proof mass, a detector means for measuring the deflection of the proof mass, and a restoring means including a coil cooperating with a permanent magnet to restore the proof mass to a null position, is significantly improved by utilizing permanent magnets composed of a material including the elements cobalt, gadolinium and samarium.
The temperature stability of a servoed accelerometer having a proof mass, a detector means for measuring the deflection of the proof mass, and a restoring means including a coil cooperating with a permanent magnet to restore the proof mass to a null position, is significantly improved by utilizing permanent magnets composed of a material including the elements cobalt, gadolinium and samarium.
Description
BACKGROUND OF_T~IE [NVENTION
1 The invention relates to acceleromel:ers and more particularly to servoed accelerometers utilizing permanent magnets as part of a restoring means.
In the prior art servoed accelerometers that utilize permanent magnets to provide a magnetic field that reacts with a restoring coil attached to a proof mass to restore the proof mass to a null position, variations in the flux of the permanent magnet due to the temperature changes could have a significant effect on the accuracy of the accelerometer. In closed loop instruments, such as servoed accelerometers, the feedback or the restoring force is generally proportional to the product of the current in the restoring coil and the amount of magnetic flux from the permanent magnet traversing the coil.
The current or voltage scale factor of this type of servoed instrument is typically inversely proportional to the amount of flux traversing the - coil. Unfortunately, the magnetic flux of most permanent magnets such as Alnico tends to change as a function of temperature. Since scale factor, the ratio of the restoring coil current to the acceleration force, typically represented as amperes per 9, tends to vary as a function of the magnetic flux output of the permanent magnets, it is necessary to provide some sort compensation for the temperature effects on the magnets. One such method of compensation is to calibrate the servoed accelerometer over temperature range and then to provide some means for measuring the temperature of the accelerometer during normal operations and to compensate the scale factor as the function of temperature. Another approach utilizes an internal compensation arrangement whereby the effects of temperature on the permanent magnet or magnets is opposed by other temperature effects on the accelerometer including changes in dimensions of the magnetic air gaps and changes in the resistance of various electrical components within the accelerometer.
.
1 However, in addition to adding to the cost and design co~plexity of the accelerometers, the compensating -techniques discussed above are often inadequate under conditions of rapid temperature change. This is due to the fact that under conditions of rapid temperature change, temperature gradients within the accelerometer tend to offset the compensating techniques. For example, the material forming the magnetic circuit may tend to increase in temperature much more rapidly than the permanent magnets thus affecting the magnetic gap at a different rate than the flux from the permanent magnets. As a result, the prior art temperature compensation techniques, in addition to being expensive and complex, also tend to lose their effectiveness in environments where the temperature is changing rapidly.
- SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a servoed accelerometer that includes a proof mass, a detector for measuring the deflection of the proof mass in response to acceleration, and a restoring means including a coil secured to the proof mass cooperating with a permanent magnet composed of a rare earth material having a flux output that is substantially invariant with temperature.
In order to reduce the variations of the accelerometer scale factor with temperature the restoring means is provided with a magnet composed of cobalt and samarium wherein the samarium is doped with a predetermined percentage of gadolinium ranging from 20 to 55 percent.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross section of a servoed accelerometer; and Fig. 2 is a block diagram of a servoed accelerometer sensor circuit.
DETAILED DESCRIPTION OF THE INVENTION
In Fig. 1, is illustrated in somewhat simplified form a servoed accelerometer of the type more fully disclosed in Jacobs, U.S. Patent 3 3,702,073, assigned to the assignee of this application. Surrounding the
1 The invention relates to acceleromel:ers and more particularly to servoed accelerometers utilizing permanent magnets as part of a restoring means.
In the prior art servoed accelerometers that utilize permanent magnets to provide a magnetic field that reacts with a restoring coil attached to a proof mass to restore the proof mass to a null position, variations in the flux of the permanent magnet due to the temperature changes could have a significant effect on the accuracy of the accelerometer. In closed loop instruments, such as servoed accelerometers, the feedback or the restoring force is generally proportional to the product of the current in the restoring coil and the amount of magnetic flux from the permanent magnet traversing the coil.
The current or voltage scale factor of this type of servoed instrument is typically inversely proportional to the amount of flux traversing the - coil. Unfortunately, the magnetic flux of most permanent magnets such as Alnico tends to change as a function of temperature. Since scale factor, the ratio of the restoring coil current to the acceleration force, typically represented as amperes per 9, tends to vary as a function of the magnetic flux output of the permanent magnets, it is necessary to provide some sort compensation for the temperature effects on the magnets. One such method of compensation is to calibrate the servoed accelerometer over temperature range and then to provide some means for measuring the temperature of the accelerometer during normal operations and to compensate the scale factor as the function of temperature. Another approach utilizes an internal compensation arrangement whereby the effects of temperature on the permanent magnet or magnets is opposed by other temperature effects on the accelerometer including changes in dimensions of the magnetic air gaps and changes in the resistance of various electrical components within the accelerometer.
.
1 However, in addition to adding to the cost and design co~plexity of the accelerometers, the compensating -techniques discussed above are often inadequate under conditions of rapid temperature change. This is due to the fact that under conditions of rapid temperature change, temperature gradients within the accelerometer tend to offset the compensating techniques. For example, the material forming the magnetic circuit may tend to increase in temperature much more rapidly than the permanent magnets thus affecting the magnetic gap at a different rate than the flux from the permanent magnets. As a result, the prior art temperature compensation techniques, in addition to being expensive and complex, also tend to lose their effectiveness in environments where the temperature is changing rapidly.
- SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a servoed accelerometer that includes a proof mass, a detector for measuring the deflection of the proof mass in response to acceleration, and a restoring means including a coil secured to the proof mass cooperating with a permanent magnet composed of a rare earth material having a flux output that is substantially invariant with temperature.
In order to reduce the variations of the accelerometer scale factor with temperature the restoring means is provided with a magnet composed of cobalt and samarium wherein the samarium is doped with a predetermined percentage of gadolinium ranging from 20 to 55 percent.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross section of a servoed accelerometer; and Fig. 2 is a block diagram of a servoed accelerometer sensor circuit.
DETAILED DESCRIPTION OF THE INVENTION
In Fig. 1, is illustrated in somewhat simplified form a servoed accelerometer of the type more fully disclosed in Jacobs, U.S. Patent 3 3,702,073, assigned to the assignee of this application. Surrounding the
- 2 -1 accelerometer and forming a housing is an excitation ring 10 composed of an upper half 12 and a lower half 14 that serves also as a magnetic circuit. Secured to the excitation rings 12 and 14 are a pair of permanent magnets 16 and 18. Attached to one end of each of the magnets 16 and 18 are pole pieces 20 and 22 which are usually configured out of soft iron and served to direct the magnetic field produced by the permanent magnet 16 and 18 in the desired directions. Suspended between the interior portions of the excitation rings is a proof mass 24 supported by a flexure 25. Attached either side of the proof mass are a pair of coil retaining bobbins 26 and 28 and wound around the bobbins 26 and 28 are a pair of restoring coils 30 and 32. Located opposite each side of the proof mass 24 on the interior portions of the excitation rings 12 and 14 are electrodes 34 and 36. The proof mass 24 in combination with the electrodes 34 and 36 form a pair of capacitors that are used as a - detector. By measuring the difference in capacitance, the deflection of the proof mass from a predetermined or null position between the excitation rings is determined which in turn generates a restoring force that provides a measure of acceleration. The excitation rings 12 and 24 are spaced apart by a support ring 38.
Operation of the servoed accelerometer shown in Fig. 1 is illustrated by the circuit shown in Fig. 2. Deflection of the proof mass 24 in response to acceleration is measured by the difference in capacitance of the capacitors defined by the proof mass 24 and electrodes 34 and 36. Signals indicating the diFference in capacitance are transmitted over lines 40 and 42 to a servoed amplifier 44. In order to restore the proof mass 24 to a null position where the capacitances 34 and 36 are equal, the servoed ampliFier generates a signal or a current on line 46 to the coils 30 and 32. The magnetic field generated by the current flowing through the coils 20 and 32 will cooperate with the
Operation of the servoed accelerometer shown in Fig. 1 is illustrated by the circuit shown in Fig. 2. Deflection of the proof mass 24 in response to acceleration is measured by the difference in capacitance of the capacitors defined by the proof mass 24 and electrodes 34 and 36. Signals indicating the diFference in capacitance are transmitted over lines 40 and 42 to a servoed amplifier 44. In order to restore the proof mass 24 to a null position where the capacitances 34 and 36 are equal, the servoed ampliFier generates a signal or a current on line 46 to the coils 30 and 32. The magnetic field generated by the current flowing through the coils 20 and 32 will cooperate with the
3 magnetic fields produced by the permanent magnets 16 and 18 to restore the proof mass to the null position. The amount of current flowing through . . : , . - . .:
1 line 46 will then be directly proportional to the force required to restore the pendulum 24 to the null position. The resulting current from coil 30 will then flow through a line 48 and through a scaling resistor 50 to ground. The resulting voltage across resistor 50, as measured on terminals 52 and 54, provides a measure of the acceleration force being measured. The servoed amplifier ~4 is also provided with a power supply over terminals 56 and 58.
Since the amount of force required to restore the proof mass 24 to the null position is directly proportional to the amount of current flowing through line 48, the scale factor or ratio between signal output and the amount of force being measured is directly proportional to the value of the resistor 50. However, due to the fact that the permanent magnet 16 and 18, which in the prior art were usually configured out of material such as Alnico 9, tended to vary their flux output as a function of temperature, the scale factor or output of the accelerometer would also tend to vary with temperature. To prevent variations in the scale factor due to changes in the flux output of the permanent magnets 16 and 18, certain rare earth magnets can be used to provide a substantially constant flux output over a wide temperature. In particular it has been discovered that magnets composed of cobalt and samarium doped with gadolinium in the relation Co5 (GdxSml_x) provide particular useful temperature flux characteristics. The doping range represented by X equal from .2n to .55 provides the preferred composition of the magnets.
.
1 line 46 will then be directly proportional to the force required to restore the pendulum 24 to the null position. The resulting current from coil 30 will then flow through a line 48 and through a scaling resistor 50 to ground. The resulting voltage across resistor 50, as measured on terminals 52 and 54, provides a measure of the acceleration force being measured. The servoed amplifier ~4 is also provided with a power supply over terminals 56 and 58.
Since the amount of force required to restore the proof mass 24 to the null position is directly proportional to the amount of current flowing through line 48, the scale factor or ratio between signal output and the amount of force being measured is directly proportional to the value of the resistor 50. However, due to the fact that the permanent magnet 16 and 18, which in the prior art were usually configured out of material such as Alnico 9, tended to vary their flux output as a function of temperature, the scale factor or output of the accelerometer would also tend to vary with temperature. To prevent variations in the scale factor due to changes in the flux output of the permanent magnets 16 and 18, certain rare earth magnets can be used to provide a substantially constant flux output over a wide temperature. In particular it has been discovered that magnets composed of cobalt and samarium doped with gadolinium in the relation Co5 (GdxSml_x) provide particular useful temperature flux characteristics. The doping range represented by X equal from .2n to .55 provides the preferred composition of the magnets.
.
Claims (2)
1. A servoed accelerometer comprising:
a proof mass responsive to an acceleration Force;
detector means for measuring the deflection of said proof mass from a predetermined null position; and restoring means including at least one coil secured to said proof mass, a source of electrical current responsive to said detector means and at least one permanent magnet cooperating with said coil for restoring said proof mass to said null position wherein said magnet is composed of Co5(GdxSx-1) wherein X ranges from .20 to .55.
a proof mass responsive to an acceleration Force;
detector means for measuring the deflection of said proof mass from a predetermined null position; and restoring means including at least one coil secured to said proof mass, a source of electrical current responsive to said detector means and at least one permanent magnet cooperating with said coil for restoring said proof mass to said null position wherein said magnet is composed of Co5(GdxSx-1) wherein X ranges from .20 to .55.
2. The accelerometer of Claim 1 wherein said restoring means includes two of said permanent magnets wherein each magnet has approximately the same value of X.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US84301377A | 1977-10-17 | 1977-10-17 | |
| US843,013 | 1977-10-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1096653A true CA1096653A (en) | 1981-03-03 |
Family
ID=25288833
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA308,107A Expired CA1096653A (en) | 1977-10-17 | 1978-07-25 | Servoed accelerometer utilizing rare earth magnets |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5459182A (en) |
| AU (1) | AU3825078A (en) |
| CA (1) | CA1096653A (en) |
| DE (1) | DE2833915A1 (en) |
| FR (1) | FR2406202A1 (en) |
| GB (1) | GB2006439B (en) |
| IT (1) | IT1106152B (en) |
| SE (1) | SE7810693L (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4245263A (en) * | 1979-05-14 | 1981-01-13 | Honeywell Information Systems Inc. | Write precompensation and write encoding for FM and MFM recording |
| US4250757A (en) * | 1979-11-05 | 1981-02-17 | Sundstrand Data Control, Inc. | Movable element with position sensing means for transducers |
| FR2558263B1 (en) * | 1984-01-12 | 1986-04-25 | Commissariat Energie Atomique | DIRECTIVE ACCELEROMETER AND METHOD FOR MANUFACTURING IT WITH MICROLITHOGRAPHY |
| JPS6117959A (en) * | 1984-07-05 | 1986-01-25 | Japan Aviation Electronics Ind Ltd | Accelerometer |
| FR2594957B1 (en) * | 1986-02-21 | 1989-06-16 | Schilling Franz | ACCELEROMETER TO SIX DEGREES OF FREEDOM WITH ELECTROMAGNETIC SUSPENSION |
| US5060039A (en) * | 1988-01-13 | 1991-10-22 | The Charles Stark Draper Laboratory, Inc. | Permanent magnet force rebalance micro accelerometer |
| FR2637984B1 (en) * | 1988-10-19 | 1991-01-11 | Sagem | PENDULUM ACCELEROMETER WITH ELECTROSTATIC DETECTION |
| US4933515A (en) * | 1989-03-09 | 1990-06-12 | Automotive Systems Laboratory, Inc. | Accelerometer with dual-magnet sensing mass |
| US10161956B2 (en) * | 2016-04-25 | 2018-12-25 | Honeywell International Inc. | Reducing bias in an accelerometer via a pole piece |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3702073A (en) * | 1969-02-28 | 1972-11-07 | Sundstrand Data Control | Accelerometer |
-
1978
- 1978-07-21 AU AU38250/78A patent/AU3825078A/en active Pending
- 1978-07-25 CA CA308,107A patent/CA1096653A/en not_active Expired
- 1978-08-02 JP JP9371378A patent/JPS5459182A/en active Pending
- 1978-08-02 DE DE19782833915 patent/DE2833915A1/en not_active Withdrawn
- 1978-08-18 FR FR7824185A patent/FR2406202A1/en not_active Withdrawn
- 1978-10-13 IT IT51491/78A patent/IT1106152B/en active
- 1978-10-13 SE SE7810693A patent/SE7810693L/en unknown
- 1978-10-17 GB GB7840883A patent/GB2006439B/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| IT1106152B (en) | 1985-11-11 |
| GB2006439A (en) | 1979-05-02 |
| SE7810693L (en) | 1979-04-18 |
| FR2406202A1 (en) | 1979-05-11 |
| JPS5459182A (en) | 1979-05-12 |
| GB2006439B (en) | 1982-01-20 |
| DE2833915A1 (en) | 1979-04-19 |
| IT7851491A0 (en) | 1978-10-13 |
| AU3825078A (en) | 1980-01-24 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |