Two axis accelerometer

• US 5,142,485 A
• Filed: 07/16/1990
• Issued: 08/25/1992
• Est. Priority Date: 05/17/1990
• Status: Expired due to Fees

• Current Assignee: State of Israel--Ministry of Defence Armament Development Authority Rafael
• Original Assignee: State of Israel--Ministry of Defence Armament Development Authority Rafael
• Inventors: Bar-Avi, Patrick, Rosenberg, Jehuda
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): PIPALA, EDWARD J
• Application Number:
  US07/553,244
• Time in Patent Office: 771 Days
• Field of Search: 74/5 F, 74/5.22, 74/5.34, 74/5.6 A, 73/488, 73/493, 73/495, 73/504, 73/510, 73/514, 364/566, 364/550, 364/559, 364/453
• US Class Current: 702/141
• CPC Class Codes: G01C 19/42 for indicating rate of turn; for integrating rate of turn
• CPC Class Codes: G01P 15/093 by photoelectric pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: Y10T 74/1293 Flexure hinges for gyros

Abstract

A new two-axis accelerometer comprising a rotating body linked to the motor rotor via a flexure zone. In a first type the rotating mass is concentrated and the flexure zone permits the rotating mass to perform a transversal parallel shift. In a second type the rotating body is an inertia rotor and the flexure zone is an extension of the rotor shaft that embodies a flexible portion. In either type the rotating body/flexure zone combination has two degrees of flexing freedom with two different flexure coefficients in two mutually perpendicular directions both normal to the electric motor shaft. The accelerometer further comprises a deflector shaft coaxial with the rotor shaft and extending beyond the rotating body and associated with electro-optical measuring means and processor means for measuring linear acceleration components in said two mutually perpendicular directions. In one of its aspects the two axis accelerometer in accordance with the invention measures only two perpendicular components of the acceleration of a body to which it is attached. By another aspect the two axis accelerometer according to the invention is a multisensor being at one and the same time a two-axis angular rate gyroscope and a two axis accelerometer. By yet another aspect of the invention there is provided a multisensor inertial measurement unit (MIMU) serving for the simultaneous measurement of three angular velocity and three linear acceleration components.

Claims

1. A two-axis accelerometer for measuring linear acceleration in two mutually perpendicular directions designated herein as axis 2 and axis 3 comprising an electric motor with rotor and rotor shaft that is normal to said axis 2 and axis 3, which electric motor drives a rotating body that is distinct from the motor rotor and linked to the latter via a flexure zone to form a rotating body/flexure zone combination, which combination is selected from the group consisting of type (i) and type (ii) combinations, said type (i) combination comprising a concentrated mass in combination with a flexure zone of a kind that permits the rotating body to perform a transversal parallel shift, and said type (ii) combination comprising an inertia rotor in combination with an extension of the electric motor shaft that embodies an asymmetric flexible portion constituting said flexure zone;

which type (i) and type (ii) combinations each have two degrees to flexing freedom with two different flexure coefficients in two mutually perpendicular directions both normal to the electric motor rotor shaft;

there being provided a deflector shaft coaxial with the rotor shaft and extending beyond the rotating body in a direction away from the electric motor, and in association with said deflector shaft electro-optical measuring means and processor means for measuring linear acceleration components in said two mutually perpendicular directions.

2. An accelerometer according to claim 1 referred to herein as type (i), wherein the rotating body has a concentrated mass and said flexure zone is a kind that permits the rotating body to perform a transversal parallel shift, the performance of the deflector shaft is expressed by the algorithmic expression

3. An accelerometer according to claim 2, wherein the flexure zone consists of a plurality of peripherically arranged flexure rods.

4. An accelerometer according to claim 1 referred to herein as type (ii) wherein the rotating body is an inertia rotor keyed on an extension of the electric motor rotor shaft that embodies a flexible portion constituting said flexure zone, the performance of the deflector shaft is expressed by the algorithmic expression

5. An accelerometer according to claim 4, wherein the inertia rotor is asymmetric.

6. An accelerometer according to claim 1 designed as a multisensor adapted to measure at one and the same time both linear acceleration components and angular velocities in said axes 2 and 3.

7. A multisensor according to claim 6 fitted with a first deflector assembly at one end dedicated to measuring linear acceleration, and with a second deflector assembly at the opposite end dedicated to measuring angular velocities.

8. A multisensor according to claim 7, wherein the deflector assembly dedicated to measuring linear acceleration is type (i).

9. A multisensor according to claim 7, wherein the deflector assembly dedicated to measuring linear acceleration is type (ii).

10. A multisensor according to claim 6, comprising one single deflector assembly type (ii) with one single inertia rotor, designed for measuring both the linear acceleration components and the angular rate in said axes 2 and 3.

11. A multisensor according to claim 10, wherein both the inertia rotor and flexure shaft are asymmetric and the performance of the deflector shaft is governed by the following algorithmic expressions:

space="preserve" listing-type="equation">θ

.sub.2 =-α

.sub.1 ω

.sub.3 +α

.sub.2 a.sub.2 cos (2nt)-α

.sub.3 a.sub.3 sin (2nt)

space="preserve" listing-type="equation">θ

.sub.3 =α

.sub.1 ω

.sub.2 +α

.sub.2 a.sub.3 cos (2nt)+α

.sub.3 a.sub.2 sin (2nt)

where α

₁, α

₂ and α

₃ are constants depending on the rotary inertia properties, a₂ and a₃ are the acceleration components at the two mutually perpendicular axes 2 and 3, ω

₂ and ω

₃ are the angular velocities in the axes 2 and 3, n is the motor speed, and θ

₂, θ

₃ are the angular deflections of the inertia rotor in axes 2 and 3; and

said processor means are designed to resolve these algorithmic expressions.

12. A multisensor according to claim 10, wherein the inertia rotor is symmetric and the flexure shaft is asymmetric, the performance of the deflector shaft is expressed by the algorithmic expressions:

space="preserve" listing-type="equation">θ

.sub.2 =-α

.sub.1 ω

.sub.3 +α

.sub.2 a.sub.2 +(α

.sub.3 ω

.sub.3 +α

.sub.4 a.sub.2) cos (2nt)-(α

.sub.3 ω

.sub.2 +α

.sub.4 a.sub.3) sin (2nt)

space="preserve" listing-type="equation">θ

.sub.3 =α

.sub.1 ω

.sub.2 -α

.sub.2 a.sub.3 +(α

.sub.3 ω

.sub.2 +α

.sub.4 a.sub.3) cos (2nt)+(α

.sub.3 ω

.sub.3 +α

.sub.4 a.sub.2) sin (2nt)

where α

₁, α

₂, α

₃ and α

₄ are constants depending on the rotary inertia properties, the flexure shaft constants and the position of the rotor center of mass and a₂, a₃, ω

₂, ω

₃, n and θ

₂, θ

₃ are as in claim 10 and said processor means are designed to resolve these algorithmic expressions.

13. A multisensor inertial measurement unit comprising three sensors that are "degenerated" multisensors according to claim 6 which sense indiscriminantly linear accelerations and angular rates.

14. A multisensor inertial measurement unit comprising three sensors that are "degenerated" multisensors according to claim 7 which sense indiscriminantly linear accelerations and angular rates.

15. A multisensor inertial measurement unit comprising three sensors that are "degenerated" multisensors according to claim 8 which sense indiscriminantly linear accelerations and angular rates.

16. A multisensor inertial measurement unit comprising three sensors that are "degenerated" multisensors according to claim 9 which sense indiscriminantly linear accelerations and angular rates.

17. A multisensor inertial measurement unit comprising three sensors that are "degenerated" multisensors according to claim 10 which sense indiscriminantly linear accelerations and angular rates.

18. A multisensor inertial measurement unit comprising three sensors that are "degenerated" multisensors according to claim 11 which sense indiscriminantly linear accelerations and angular rates.

19. A multisensor inertial measurement unit comprising three sensors that are "degenerated" multisensors according to claim 12 which sense indiscriminantly linear accelerations and angular rates.