Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1998-06-05
2001-03-20
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S227140
Reexamination Certificate
active
06204499
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to motion sensors. More particularly, the present invention relates to sensing rotation and angular position in a body, even if the body is not rotating.
2. Background of the Invention
There are many applications where it is desirable to measure absolute angle or inclination. Examples include guidance and navigation systems, construction tools and equipment, and rollover protection devices for vehicles.
Various techniques have been implemented in the past to measure angle, including bubble-based inclinometers (based on the concept of a standard carpenter's level), pendulums, and accelerometers. Each of these technologies is capable of measuring angle. Undesirably, however, these technologies also produce output when subjected to linear acceleration. The automotive rollover application is a particularly good example because deployment of air bags and other safety measures is controlled in part by a rollover indication. It is highly undesirable for the sensor to indicate that the vehicle is rolling over when in fact it is accelerating or going around a corner (producing centrifugal acceleration) as such indication could trigger application of the vehicle's airbags.
Various techniques have been implemented or proposed in the past to avoid the problems due to linear acceleration. Each has its own disadvantage. Mechanical gyroscopes are capable of responding to rotation while rejecting linear acceleration. However, they are subject to drift problems and can be quite cumbersome, expensive, and fragile. Fiber optic gyros solve many of these problems, but respond to angular velocity, rather than absolute angle. Sensors which respond to angular velocity are useful in many applications, but when absolute angle is needed, such as detecting an unstable roll angle in a vehicle, a measure of the absolute angle is desired.
Other techniques such as tuning fork assemblies (see “Detection of Incipient Rollovers Grows in Importance”, Automotive Engineering, September 1997, pp. 94-96 (“Automotive Engineering”)) and Faraday-effect devices (see U.S. Pat. No. 3,940,983, “Faraday effect fluid flow and direction indicator”, to Greene (“Greene”)) can be constructed at relatively low cost, but also provide angular velocity information, rather than absolute angle information.
Some conventional devices used multiple fluids in a cylindrical or spherical container (see U.S. Pat. No. 4,779,353, “Tool for measuring inclination and rotation”, to Lopes, et al. (“Lopes”) and U.S. Pat. No. 5,416,977, “Pitcb Sensor System”, to Striffler (“Striffler”)). Although theoretically providing absolute angle information, the devices are susceptible to failure (i.e., provide erroneous results) if there is mixing between the fluids or if the boundary layer between the fluids changes. Other devices exist which use fluids that move in response to angular velocity. Each has properties similar to the above described techniques. (see U.S. Pat. No. 4,361,040, “Integrating Angular Accelerometer”, Taplin, et al. (“Taplin”), and U.S. Pat. No. 4,163,325 “Verticality Sensors”, to Hughes (“Hughes”)).
To provide an estimate of absolute angle, hybrid sensor approaches have been proposed and implemented. One common technique used in automotive rollover applications is to combine an accelerometer (or other gravitationally-sensitive device) with an angular rate sensor (see Automotive Engineering). Static angle measurements are made whenever the vehicle appears to not be undergoing acceleration (e.g., when the measured acceleration is 1.0 G, the acceleration due to gravity). Based on this reference static angle, the output from the angular rate sensor is integrated to produce an estimate of absolute angle. Although this approach can be accurate when the vehicle is relatively stable, and when any rotation is high in angular velocity, it is prone to significant errors in integration. The integration problem is more acute where integration needs to be performed for a significant amount of time (a second is often significant). In this case, if there is even a small offset in the output of the angular rate sensor, the integration will have a cumulative error which grows larger with time.
Thus, it would be preferable to have a sensor which provides no cumulative angle measurement error, and which can measure absolute angle regardless of the linear acceleration experienced by the device.
SUMMARY OF THE INVENTION
The present invention is directed to a rotation sensor for, measuring rotation and angular position in a body, even if the body is not rotating. Preferably the rotation sensor is constructed of a fluid-filled container. As the container is rotated, the fluid tends to remain stationary. However, when the container is subjected to gravity or linear (non-rotational) accelerations, the fluid tends to move with the cylinder. Using the apparatus and method of the present invention, the relative motion of the container with respect to the fluid is measured.
In a preferred embodiment, the container is a cylinder. A set of one or more freely rotating vanes is rotatably disposed within the cylinder. The vanes are mounted on a shaft and are free to move with the fluid. As the cylinder is rotated, therefore, the rotating vanes tend to remain stationary with respect to the fluid, and hence rotate with respect to the cylinder.
Another preferred embodiment of the present invention can be used to detect rotational velocity. In this preferred embodiment a flexible cantilever is fixably attached at one end to the cylinder. The larger the angular rate of the cylinder, the larger the deflection of the cantilever.
The position of the cantilever or of the rotating vane(s) provides an output indicating the rotation of the cylinder. Several embodiments are described for using the position of the cantilever or rotating vane(s) to produce an output indicative of the rotation of the cylinder.
One embodiment uses an LED or other light source to shine on the vane or cantilever. One or more photodetectors are used to receive the light. The light source and photodetector(s) are arranged such that the position of the cantilever or vane modulates the amount of light received by each photodetector. This embodiment requires that the fluid be transparent with respect to the lights.
Another embodiment uses two or more electrodes and measures the electrical impedance between the electrodes. The electrodes are positioned such that the position of the cantilever or vane modulates the impedance between the electrodes. This embodiment requires that the fluid not be a perfect conductor of electricity.
In another embodiment, a cam is fixed to the vane or cantilever. The position of the cam modulates the light transmission or electrical impedance between two points to produce an output indicative of the rotation angle of the cylinder.
Another embodiment uses an optical fiber attached to the vane or cantilever. The optical fiber is positioned so that as the cantilever or vane moves, the amount of light through the fiber changes, or the direction of the light shining through the fiber changes. The change in the amount of light through the fiber or the direction that the light travels through the fiber is indicative of the rotation angle of the cylinder.
The output of the means for measuring the rotation of the cylinder may be passed through mathematical filtering to correct for the non-idealities of the device. These non-idealities are caused because the fluid begins to move to some extent with the cylinder. Causes of this fluid movement include friction along the inside surface of the cylinder, relative motion of the cantilever or vanes through the fluid, and because the measuring device may not deflect linearly with rotation. This mathematical filtering is implemented by creating an inverse model of these non-idealities.
These and other objects of the present invention are described in greater detail in the detailed description of the invention, the appended drawings and the attached claims.
REFERENCES:
pat
Lee John R.
Pittman Shaw
Simula Inc.
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