Note: Descriptions are shown in the official language in which they were submitted.
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ROTATIOI~ALLY ACTUATED POSITION SENSOR
Fie}d of the Invention
The present invention is related to position sensors and in particular to a
sensor that uses a bubble suspended in a fluid medium to deterrnine positions ina two-dimensional reference system.
Background of the Invention
A carpenter's level using a vial contAining a fluid and a suspended bubble
that is centered in the vial when the instrument is placed on a level surface iswell-kno~,vn. However, the basic carpenter's level is only useful for determining
whether the surface is level and not at what angle the surface may be inclined. In
recent years, the carpenter's level has been enhanced by incorporating electronic
l 5 level sensing devices in place of, or in addition to, the vial, fluid, and bubble.
One purpose of the improved carpenter's levels is to determine the inclination
angle of the surface. However, an inclination angle cannot be used to specify a
point in space, as the angle is expressed in terms of a single degree of freedom--
its rotation about one axis--while a point in space must be defmed in terms of at
least two degrees of freedom.
Other devices designated as orientation sensors work on the same
principal as the carpenter's level but employ different shaped containers for the
fluid and the bubble. These devices suffer from the same limitations of the
carpenter's level in that they only detect changes in a single degree of freedom.
In addition, these device reflect light off the bubble to determine the orientation
of the device so the light must transit the fluid twice, once to bounce off the
bubble, and again when reflected to a detector. Diffraction and refraction
problems introduced by the light's path and also by its reflection offthe bubblelead to inaccuracies in measurement unless the device is carefully mAnllfActuredand calibrated, making the production of such a device a complex and costly
process.
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There is a need for a device that combines the ability to define positions
in space in a two-dimensional coordinate system with simplicity of
manufacturing and long-lived accuracy.
Summary of the Invention
S Two curved surfaces are concentrically aligned to form a container which
is filled with a viscous, radiation-absorbent fluid and a bubble of a lighter-
weight, radiation-tr~n~mi~sive fluid that changes position within the container in
response to rotational movement of the container about two axis. The container
is placed between a radiation source and a radiation detector to form a positionsensor. A portion of electro-magnetic radiation from the radiation source is
transmitted through the bubble and activates a section of the radiation detectorwhile the remainder of the radiation is blocked by the fluid. Points in a two-
dimensional plane are equated to positions of the bubble within the container sothat the section of the radiation detector that is activated by the radiation
transmitted through the bubble corresponds to a point in the plane. By assigningposition coordinates to each section of the radiation detector, position sensingcil~;uilly is able to translate a signal from the activated section of the radiation
detector into position coordinates for the corresponding point.
The rotationally actuated position sensor is suitable for use in any
apparatus that relies on a two-dimensional coordinate system, such as
geographical tracking systems, and surveying equipment. The position sensor is
also applicable to computer-input devices that logically use a pair of coordinates
to address a point on a computer screen, and replaces the ball currently used ininput devices such as mice and trackballs so that the user is no longer
constrained to using the device on a surface. The position sensor also does not
become jammed as ball-controlled input devices currently do which causes great
user frustration.
A computer-input device or digital controller which uses the position
sensor can optionally include a control button that acts as a standard mouse
button or generates a third display attribute. The first and second display
attributes generated by the position sensor combine with the third display
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attribute generated by the control button to define the locator symbol in three
dimensions as it moves on the display. The third display attribute deterrnines the
size of the locator symbol so that the locator symbol appears to approach and
recede on the display as the its size is changed, thus simulating the movement of
a three-dimensional object on a standard two-~imensional display screen.
The rotationally actuated position sensor addresses the limitations found
in the prior art devices. The electronic components are long-lived, the radiation
source is replaceable, and, when made of high-impact plastics, the sensor is
virtually indestructible. Furthermore, the sensor is simple and inexpensive to
manufacture as it incorporates common materials, off-the-shelf components, and
it does not incur the diffraction and refraction problems inherent in the prior art.
Finally, its degree of accuracy is high, will not degrade over time, and can be
calibrated to the specific application in which the sensor is employed.
Brief Description of the Drawin.~.~
15 Figure la is a perspective view of an embodiment of a position sensor.
Figure lb is a cross-section view of the position sensor shown in Figure I a
taken along line 1-1.
Figure 2 is a functional diagram of the position sensor.
Figure 3a is a cross-section view of a hemispherical-shaped container in the
position sensor.
Figure 3b is a cross-section view of a dome-shaped embodiment of the
container.
Figure 4 is the cross-section view of Figure 3b with the addition of a
radiation detector.~5 Figure 5 is the cross-section view of Figure 3a showing a plurality of
dimples.
Figure 6a is an alternate embodiment of position sensor shown in Figure 4.
Figure 6b is another alternate embodiment of position sensor shown in
Figure 4.
... .... . ... ... . ....
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Figure 7 is a perspective view of an embodiment of a rotationally actuated
three-dimensional digital controller incorporating the position
sensor.
Figure 8 is a block diagram of one embodiment of the digital controller.
Description of the Embodiments
In the following detailed description of the embodiments, reference is
made to the accompanying drawings which form a part hereof, and in which is
shown by way of illustration specific embodiments in which the invention may
be practiced. These embodiments are described in sufficient detail to enable
those skilled in the art to practice the invention, and it is to be understood that
other embodiments may be utilized and that structural, logical and electrical
changes may be made without departing from the scope of the present
inventions. The following detailed description is, therefore, not to be taken in a
limiting sense, and the scope of the present inventions is defined only by the
appended claims.
Numbering in the Figures is usually done with the hundreds digits
corresponding to the figure number, with the exception that identical
components which appear in multiple figures are identified by the same
reference numbers.
Figures 1 a and I b show two views of an embodiment of a rotationally
actuated position sensor 100. Figure 1 a is a perspective view and Figure 1 b is a
cross-section view taken along line 1-1 of Figure la. The position sensor
comprises a curved container 102 filled with a viscous fluid 104 and a lighter-
weight fluid forming a bubble 106. As the sensor 100 is rotated around either a
first axis 120 or second axis 122, the lighter bubble 106 moves within the
viscous fluid 104 in reaction to gravity acting on the viscous fluid 104 and in
accordance with the principals of fluid dynamics. The rotation of the sensor 100around a third axis 124 does not cause the bubble to move within the container
102.
The viscosity of the viscous fluid 104 is sufficient to prevent the bubble
106 from disintegrating while allowing it freedom to move within the viscous
T
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fluid 104. In one embodiment, the viscous fluid 104 is a light-weight oil and the
bubble 106 contains nitrogen gas. The weight of the oil is dependent on the sizeof the container 102 and the desired velocity of the bubble 106. The substitution
of other fluids and/or gases with these and other required qualities as discussed
5 later will be a~l,a t;r~t to those skilled in the art.
The container 102 is positioned between a radiation source 108 and a
radiation detector 110. Position sensing circuitry 112 is coupled to the radiation
detector 110 to translate signals generated by the radiation detector 110 into
position coordinates. The position sensing circuitry 112 is further coupled to al 0 read-out device (not shown), such as a digital numeric display or a computer,
that presents the position coordinates to a user in a desired format. The radiation
source 108, the radiation detector 110 and the position sensing circuitry 112 are
further electrically coupled to a power supply such as a battery or an AC sourcewhich is not shown.
As shown in Figure 2, the viscous fluid 104 is substantially opaque to the
wavelength of radiation emitted by the radiation source 108 but the lighter-
weight fluid forming the bubble 106 is substantially transparent to the same
wavelength so that a portion, or beam, 202 of the radiation passes through the
bubble 106 and activates a section of the radiation detector 110 while the
20 remainder of the radiation 204 is substantially blocked by the viscous fluid 104.
Each section of the radiation detector 110 is assigned a pair of position
coordinate values that define a point on a flat plane in a cartesian reference
system. In an alternate embodiment, each pair of coordinate values defines a
point in terms of spherical coordinates, such as altitude and azimuth, so that the
25 sensor 100 can be used to deterrnine positions on a curved plane. The position of
the bubble 106 in the container 102 deterrnines which section of the radiation
detector 110 is activated by the beam 202 and thus what coordinate values are
transmitted by the position sensing circuitry 112 to the read-out device.
The position coordinates are relative to an origin point within the
30 container 102. In one embodiment, the origin point is fixed within the container
102; in an alternate embodiment, the location of the origin point in the container
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102 is defined by the position sensing circuitry 112. In a further alternate
embodiment, the origin point is a previous position of the bubble 106 and the
position sensing circuitry 112 transmits the difference in position coordinates
between the base position and a new position of the bubble 106 as it moves
5 within the container 102.
The sensitivity of the radiation detector 110 to the wavelength of the light
emitted by the radiation source 108 determines the percentage of the radiation
that the viscous fluid 104 must absorb (the "opaqueness" of the fluid). The
required opaqueness can be an inherent property of the fluid chosen, or the
10 viscous fluid 104 can be "dyed" to absorb the emitted wavelength. In one
embodiment, the radiation emitted from the radiation source 108 is visible lightand the viscous fluid 104 is a light-weight oil infused with a substance such asgraphite that absorbs visible light. The use of alternate pigments to dye the
viscous fluid 104 to the required opaqueness will be apparent to those skilled in
15 the art.
Figures 3a and 3b show cross sectional views of two embodiments of the
container 102 of the position sensor. In both figures, the container 102 is formed
from two curved surfaces 320 and 330, and the bubble 106 touches both surfaces
320 and 330. Each surface 320 and 330 is forrned of continuous, smooth arcs so
20 each surface has a single convex side 322 and 332 and a single concave side 324
and 334. The surfaces have similar curvatures and are substantially
concentrically aligned so that the concave side 324 of one surface, referred to as
the outer surface 320, is substantially equidistant from the convex side 332 of the
other surface, referred to as the inner surface 330. The curvatures of the surfaces
25 320 and 330 determines the shape of the container 102 so that if the degrees of
curvature are substantially 180~, a hemispherical container is formed as shown in
Figure 3a, and if less than 180~, a dome-shaped container is formed as shown in
Figure 3b. The use of surfaces with other degrees of curvature, including 360~ to
form a container in the shape of a complete sphere, will be apparent to those
30 skilled in the art. Furthermore, the use of curved segments from surfaces of
three-dimensional objects other than regular spheres, such as oblate spheroids or
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elliptic paraboloids, will also be ap,~,~elll to those skilled in the art. The choice
of surface curvature determines whether the velocity of the bubble 106 is
constant throughout the container 102 and also determines the range of bubble
movement when the container 102 is rotated.
The surfaces 320 and 330 are formed of a thin material that is
substantially transparent to the wavelength emitted by the radiation source 108.In one embodiment, a sheet of acrylic is heat-pressed to the desired curvature to
form at least one of the surfaces; in another embodiment, liquid urethane plastic
is poured into a mold with the desired curvature. Both these alternate
embodiments provide surfaces substantially transparent to visible light. The useof alternate materials and m~nllf~cturing methods for making the container 102
will be ~palelll to those skilled in the art.
The tr~n~mi~ion of position coordinates caused by slight, accidental
movements of the bubble 106 within the container 102 reduce the accuracy of
the sensor 100. In one further alternate embodiment the viscosity of the viscousfluid 104 provides a damping effect so that minor vibrations do not cause the
bubble 106 to move. In still another alternate embodiment, the construction of
the container 102 combines with the position sensing circuitry 112 to filter outunintentional movements. The curvature of the container 102 causes the bubble
106 to return to a neutral location within the container when the sensor 100 is at
rest. A dimple 310 is formed in the concave side 324 of the outer surface 320 atthe neutral location. During manipulation of the sensor 100 by a user, the bubble
106 moves away from the dimple 310. If the user continues to move the sensor
100 so that the bubble 106 moves back toward the dimple 310, the bubble 106
transits the dimple 310 without stopping because of the inertia imparted by the
user. However, if the bubble 106 moves toward the dimple 310 because the user
is no longer moving the sensor 100 or because of minor vibrations, the bubble
106 lodges in the dimple 310 and the position sensing c;hcuiL~y 112 registers the
position change as only "noise." The sensor 100 can have more than one neutral
position depending on its shape and application, and thus have more than one
dimple 310 as shown in Figure 5. The dimples 310 are small enough in size so
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as to not significantly interfere with the radiation tr~n~mi.~ion through the
bubble 106.
The bubble 106 exists due to the property of fluids to forrn a curved
surface, or a "meniscus," where the fluid comes in contact with a container. In a
5 further alternate embodiment, the viscous fluid 104 chosen has a meniscus that is
highly reflective to the wavelength of the radiation from the radiation source
108. The reflective quality of the meniscus reduces diffusion of radiation
through the viscous fluid 104 in the areas where the viscous fluid 104 is thinnest
and is less opaque to the radiation.
The size of the areas where the bubble 106 is in contact with the surfaces
320 and 330 determines the diameter of the beam 202 of radiation transmitted
through the bubble 106. The size of these areas is determined by the size of thebubble 106 and the distance between the inner and outer surfaces 330 and 320.
The size of the bubble 106 is determined by the type and amount of the lighter-
15 weight fluid introduced into the container 102 and the viscosity of the viscous
fluid 104.
In the radiation detector 110 as shown in Figure 4, each section of the
radiation detector 110 is a radiation responsive grid element 402 sensitive to the
wavelengths of radiation emitted by the radiation source 108. For visible light,20 each grid element 402 can be a sensor such as a silicon pin photodiode, part
number BPV23NFL, from Telefunken of Germany. Many other photodiodes or
other types of sensors from various manufacturers are also suitable. The
minimum size of the grid elements 402 is determined by the diameter of the
beam 202 transmitted through the bubble 106. The number of grid elements 402
25 and the shape of the radiation detector 110 depend upon the specific application
using the sensor 100. Figure 4 also shows a portion of the radiation detector 110
and illustrates a grid configuration where the grid elements 402 are abutted edge
to edge to form a sensor array. Such a sensor array is manufactured by affixing
the grid elements 402 to a silicon base or onto a flexible sheet made of a material
30 such as Mylar~ which can be stretched to fit over the container 102. Alternate
,.............. .~. . .
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manufacturing methods and materials suitable to construct a radiation detector of
an al)p,~ pliate size and shape will be apparellt to those skilled in the art.
In an alternate embodiment, more than one sensor is activated by the
beam 202 of radiation transmitted through the bubble 106. The position sensing
S circuitry 112 interpolates the signals from all the activated sensors to a single
coordinate pair using well-known algorithms similar to those currently in use intouch pad input devices such as the Glide Point from Cirque. In a further
embodiment in which the position sensor 100 has a plurality of dimples 310 as
shown in Figure 5, the radiation detector 110 has a corresponding plurality of
10 radiation responsive grid elements 402.
Figure 4 further illustrates the radiation detector 110 as having a
curvature substantially similar to that of the outer surface 320 and affixed to the
convex side 322 of the outer surface 320 of the container 102. In an alternate
embodiment shown in Figure 6a, the curvature of the radiation detector 110 is
15 also substantially similar to that of the outer surface 320 but is spaced apart from
the outer surface 320. In still another embodiment shown in Figure 6b, the
radiation detector 110 is a flat plane positioned adjacent to the outer surface 320.
Other locations for the radiation detector 110 will be apparent to those skilled in
the art. In such cases, the individual grid elements 402 are mapped to desired
20 coordinate pairs based on their position relative to the bubble 106 and the
radiation source 108.
The radiation source 108is positioned to substantially evenly illl]min~te
the radiation detector 110. In one embodiment, the radiation source 108is
positioned below the concave side 334 of the inner surface 330 of the container
25 102 as shown in Figures la and lb. In an alternate embodiment shown in Figure4, the radiation source 108is positioned within a cavity bounded by the concave
side 334 of the inner surface 330. The radiation can directly illnmin~te the
container 102 or be routed through a diffuser designed to more evenly distributethe radiation. In still another embodiment, the radiation source 108 comprises a30 plurality of light pipes, one for each radiation responsive grid element 402.
. ,, ~ . , . . . .. , . , ., , . . ,,, . , ~ .. . .
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A particular use for the position sensor of the present invention in a
digital controller for a computer system is described with reference to Figures 7
and 8. In particular, Figure 7 is a perspective view of a rotationally actuated
three-dimensional digital controller 700. The embodiment of the digital
S controller 700 shown in Figure 7 comprises a housing 702, a rotationally
actuated position sensor 704, and three control buttons 706, 708 and 770. The
position sensor 704 is of the type disclosed above. In one embodiment, the
housing 702 comprises elongated octagonal-shaped top and bottom surfaces and
eight rectangular sides. In a further embodiment, the housing 702 is
egonomically shaped to be comfortable in different-sized hands. The top and
bottom surfaces are spaced apart so that a cavity is formed in between them thatis bounded by the sides. First and second control buttons 706 and 708 are
disposed directly opposite one another on two of the sides. A third control
button 710 is mounted on a side mutually perpendicular to the sides having the
first and second control buttons 706 and 708. The position sensor 704 is
disposed on the top surface of the digital controller 700. In an alternate
embodiment, the position sensor 704 is disposed on the bottom surface, and in
yet another alternate embodiment, the position sensor 704 is sized to fit whollywithin the cavity of the digital controller 700.
The position sensor 704 generates first and second display attributes in
response to a user rotating the digital controller 700 about an axis 712 (shown by
arc 714) and/or an axis 716 (shown by arc 718). The first, second and third
control buttons 706, 708 and 710 generate signals when pressed by a user. The
first and second control buttons 706 and 708 each separately generate a third
display attribute while the third control button 710 generates a command, such as
"execute program'', to the output device 720. In a further alternate embodiment~the digital controller 700 has a single button with functions corresponding to
control button 710. In still another alternate embodiment, the digital controller
700 has no buttons and is used only to generate the first and second display
attributes while commands are generated through a standard keyboard or similar
input device. Use of more or fewer buttons with the same or different functions,
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and different locations for the buttons, as well as the inclusion of triggers, keys,
or other user-operated functions will be apparent to those skilled in the art.
The digital controller 700 is communicatively coupled to a read-out or
output device 720 having a display screen 722. The first and second display
5 attributes generated by the digital controller 700 defines a position for a locator
symbol 724 on the display screen 722 while the third display attribute
determines a size for the locator symbol 724. In one embodiment, a first
transceiver (806 in Figure 8) coupled to the digital controller 700 broadcasts
electro-magnetic signals representing the display attributes to a second,
10 corresponding transceiver 726 coupled to the output device 720. Such
transceivers are common, industry-standard components used in wireless
computer input devices. That the electro-magnetic signals can be frequency
modulated pulses, or infrared light, or other portions of the electro-magnetic
spectrum will be appalcll~ to those skilled in the art, as will alternatively
15 coupling the digital controller 700 to the output device 720 through copper wire,
fiber optic cabling, or similar hard-wired connections.
In one embodiment, the output device 720 is a computer having a central
processing unit (CPU) coupled to a computer monitor or screen equivalent to
display screen 722. The CPU executes application software that supports a
20 simulated three-dimensional display using the locator symbol 724, which may be
a cursor, a graphics tool, a game character, or the like. Standard pointing device
driver software supplies the first and second display attributes to the application
software along with information on the state of the control buttons 706 and 708.The application software translates the state of the control button 706 and 708
25 into the third display attribute to create the appropriate sized locator symbol 724
and to position it on the display screen 722 in the location specified by the first
and second display attributes. Any currently available driver software that
supports the second and/or third buttons on a standard mouse pointing device canbe used in conjunction with the three-dimensional digital controller 700 without30 modification. The same driver software can be used with the alternate
embodiment of the digital controller 700 which have only control button 710 or
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no control buttons, or alternate driver software that supports only a single button
mouse can be substituted.
As described above, the size of the radiation detector (110 of Figure 1 b)
within the position sensor 704 is dependent on the number of sensors it containsas well as the desired range of motion. In one embodiment, rotation of the
digital controller 700 in an arc of 90~ around axis 716 moves the locator symbol724 from one side of the display screen 722 to the other side. Similarly, rotation
of the digital controller 700 in an arc of 90~ around axis 712 moves the locatorsymbol 724 from the top of the display screen 722 to the bottom. Thus, the size
10 of radiation detector in this embodiment is no larger than necessary to track the
bubble as it moves along these two arcs. The device driver software is also usedto modify the relationship between the movement of the symbol and the
movement of the bubble in a manner similar to that used by standard mouse
driver software to determine how far the mouse must move in order to move a
cursor a fixed distance on the screen. In order to increase the speed of symbol
movement, the device driver maps an arc of much less than 90~ to the movement
of the symbol 724 from top to bottom and/or from side to side of the display
screen 722.
Other determining factors for the size and shape of the radiation detector
20 include: the size and shape of the container (102 of Figure Ia) and the size and
shape of the digital controller 700. As described above, the radiation detector
may be affixed to and have a substantially similar curvature as that of the
container, or may be separate from the container and be curved or flat. The
amount of the container covered by the radiation detector depends on the how
the device driver maps the arcs of rotation of the digital controller 700 to themovement of the locator symbol 724. Additional sizes and shapes for the
radiation detector other than those described above will be apparent to those
skilled in the art.
The position sensor 704 of the digital controller 700 operates as
30 described above, wherein the movement of the bubble in the container controls the movement of the locator symbol 724. In one embodiment, the screen
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coordinates are relative to an origin point on the display screen 722 and a bubble
position within the container is defined as a base position representing the origin
point. The position coordinate values that are assigned to the sections of the
radiation detector are relative to the base position and thus to the origin point on
the screen. In one alternate embodiment, the base position is fixed; in another
alternate embodiment, the location of the base position is defined by the position
sensing circuitry of the position sensor 704. In a further alternate embodiment,the base position is a previous position of the bubble 206 and the first and second
attributes are equated to the difference between the position coordinate values of
the base position and those of a new position of the bubble as the bubble moves
within the container.
In addition to having a base position equated to the previous position of
the bubble, another alternate embodiment also designates a neutral position
within the container to which the bubble returns when the digital controller 700is at rest. Movement of the bubble to the neutral position from the base position
does not change the screen coordinates of the locator symbol 724. This feature is
analogous to the "return to zero" found in most computer joysticks and permits
the user to put down the digital controller 700 without changing the position ofthe locator symbol 724.
Figure 8 is a block diagram of still another alternate embodiment of the
digital controller 700. The position sensor 704 and the first control button 706are electrically coupled to a switching circuitry 804 which is further coupled to a
battery 802. The switching circuitry 704 controls distribution of power to the
digital controller 700 in response to a user action. In one embodiment the
switching circuitry 804 comprises timer circuitry and the user action is moving
or not moving the controller. Power is distributed to the controller when the
controller is in use, and not distributed to the controller 700 when it is not in use
and a time-out period has elapsed. The time-out period can be selectable by the
user or pre-set by the manufacturer of the digital controller 700. In an alternate
embodiment, the switching circuitry 804 comprises capacitive coupling
manufactured as part of the housing 702 so that while a user is touching the
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14
housing (the user action), power is distributed to the controller 700. Figure 8
a]so shows the first transceiver 806 electrically coupled to the position sensor704 and the first button 706 so that the first transceiver 806 broadcasts the
display attributes to the second transceiver 726.
It is to be understood that the above description is intended to be
illustrative, and not restrictive. Many other embodiments will be apparent to
those of skill in the art upon reviewing the above description. The scope of theinvention should, therefore, be determined with reference to the appended
claims, along with the full scope of equivalents to which such claims are entitled.
