Angle sensor

Details Angle sensor Angle sensor

2001-05-01

2002-09-17

Fulton, Christopher W. (Department: 2859)

Geometrical instruments

Indicator of direction of force traversing natural media

Level or plumb, terrestrial gravitation responsive

C033S366160

Reexamination Certificate

active

06449858

ABSTRACT:

The present invention relates to improvements in angle sensors.
In U.S. Pat. No. 5,794,355 a container is formed by a pair of concentrically aligned hemispherical surfaces. The container is filled with a viscous fluid and a bubble of a lighter-weight fluid and placed between a radiation source and a radiation detector. The bubble changes position within the container when the sensor is moved, transmitting a beam of radiation from the radiation source through the bubble to activate a section of the radiation detector while the remainder of the radiation is blocked by the fluid. Two-axis angle sensing is achieved by the use of a radiation detector comprising a two-dimensional array of grid elements (eg photodiodes).
The arrangement of U.S. Pat. No. 5,794,355 suffers a number of problems. Firstly, in order to achieve a measurement range of n measurement units the two-dimensional radiation detector must have n*n grid elements. As n increases the radiation detector can become large and expensive. Secondly, random measurement errors in the signal from the radiation detector can be large.
An alternative method of achieving two-axis angle sensing is suggested in U.S. Pat. No. 5,218,771 at column 4 lines 15-19. This suggests using two angular motion detectors, mounted with their respective central axes oriented perpendicular to each other. However the arrangement of U.S. Pat. No. 5,218,771 still suffers from the problem of random measurement error.
In accordance with a first aspect of the present invention there is provided a two-axis angle sensor comprising
a first bubble chamber containing two fluids of different characteristics such that a bubble is formed in the chamber;
a first bubble detector for generating a signal indicative of the orientation of the first bubble chamber with respect to a first detector axis by sensing the position of the bubble in the first bubble chamber;
a second bubble chamber containing two fluids of different characteristics such that a bubble is formed in the chamber;
a second bubble detector for generating a signal indicative of the orientation of the second bubble chamber with respect to a second detector axis by sensing the position of the bubble in the second bubble chamber, and
a processor for calculating the angle of the sensor with respect to first and second measurement axes by combining the signals from the first and second bubble detectors in accordance with a predetermined algorithm, wherein the measurement axes are angularly offset from the detector axes.
Instead of aligning the bubble detectors and bubble chambers with the measurement axes and taking direct independent readings from the bubble detectors, we offset the bubble detectors and bubble chambers from the measurement axes and combine the signals from the bubble detectors. We have recognised that if the detector signals suffer from random errors with a gaussian distribution then the error associated with one bubble detector will tend to cancel out the error associated with the other bubble detector. Thus the combined measurement will be more accurate than a single independent measurement.
The bubble chambers and bubble detectors can then be provided in a sensor housing which is aligned with the measurement axes. Thus for example the sensor housing may comprise a joystick which is shaped to be gripped by the hand such that the “forward/reverse pitch” direction is aligned with one measurement axis and the “left/right roll” direction is aligned with the other measurement axis. Alternatively the sensor may be a “mouse” type computer input device which is gripped by the hand but not constrained to be used on a surface. In this case the sensor housing will be shaped to be gripped by one or more hands such that the “forward/reverse” direction is aligned with one measurement axis and the “left/right roll” direction is aligned with the other measurement axis. One or more buttons may also be provided in a position to ensure that the sensor housing is gripped in the preferred orientation. In a further alternative the sensor may be mounted in a vehicle or aeroplane with one of the measurement axes aligned with the direction of forward movement.
A variety of algorithms may be used, depending on the outputs of the detectors. In a preferred example the predetermined algorithm comprises:
summing a pair of values derived from the bubble detector signals to calculate the angle of the sensor with respect to the first measurement axis; and
subtracting a pair of values derived from the bubble detector signals to calculate. the angle of the sensor with respect to the second measurement axis.
The precise form of the algorithm will depend on the angular relationship of the axes. These axes may be offset from each other by any desired angle. However in a preferred example the detector axes are arranged substantially at right angles to each other, and the measurement axes are arranged substantially at 45 degrees to the detector axes. This enables the bubble detector signals to be simply added or subtracted without requiring either signal to be scaled up or down with respect to the other signal before addition or subtraction.
A further problem with the arrangement of U.S. Pat. No. 5,794,355 is that some radiation may be transmitted through the viscous fluid making it difficult to detect the bubble. U.S. Pat. No. 5,794,355 addresses this problem by adding a dye to the viscous fluid to absorb the radiation. In addition there is no design freedom in the positioning of the radiation detector—ie. it must be positioned directly behind the container on the opposite side to the radiation source.
In U.S. Pat. No. 5,218,771 the materials forming the bubble and the liquid are chosen so that the interface surface between them is highly reflective. Thus the detector detects light reflected from the surface of the bubble. A problem with this arrangement is that there is no design freedom in the positioning of the radiation detector—ie. it must be positioned to receive the reflected light from the bubble.
In accordance with a second aspect of the present invention there is provided an angle sensor comprising
a bubble chamber containing two fluids of different characteristics such that a bubble is formed in the chamber;
a radiation source for illuminating the bubble with radiation whereby the radiation is refracted by the bubble; and
a radiation detector positioned to detect the refracted radiation from the bubble and generate a signal indicative of the angle of the bubble chamber.
In contrast to the conventional approach we detect refracted radiation from the bubble. As a result it is not necessary to dye the fluid. Furthermore we can accommodate different arrangements for the radiation source and radiation detector by selecting appropriate refractive indices for the bubble chamber and the two fluids. This is not possible in prior art systems which detect reflected or transmitted light since the angle of reflection or transmission is fixed regardless of the refractive indices.
In a preferred arrangement an interface is positioned to receive the refracted radiation from the bubble and deliver the refracted radiation to the radiation detector. This increases the amount of refracted radiation falling on the detector, thus improving the measurement accuracy.
A number of different interfaces may be provided. For instance the interface may comprise a light guide such as a fibre-optic cable. In one arrangement the interface comprises one or more lenses positioned between the bubble chamber and the radiation detector for focusing the refracted radiation onto the radiation detector. Alternatively the interface may comprise a radiation transmissive projection in the bubble chamber. The projection typically has a face arranged at an angle such that refracted radiation from the bubble passes through the face, and radiation from other directions is internally reflected by the face back into the bubble chamber.
In order to absorb radiation which has not been refracted by the bubble, the bubble chamber preferably has a radiation absorbent

Affiliated with

Also associated with

Rating

Angle sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Angle sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Angle sensor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2865097