Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2002-02-14
2004-04-13
La, Anh (Department: 2636)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S539130, C340S010100, C340S003510, C340S505000
Reexamination Certificate
active
06720876
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to tracking the position of one or more untethered objects.
2. Related Art
The ability to track the location and/or orientation of an object (sometimes referred to herein either singly or collectively as the “position” of the object) can be desirable for a variety of purposes. A number of different position tracking systems exist. The operation of such position tracking systems is typically tailored in accordance with the characteristics of the particular application or applications for which the system is intended to be used, thus producing a position tracking system having particular characteristics.
Position tracking systems can be “tethered” or “untethered.” In a tethered position tracking system, the object being tracked is either mounted on, attached to, or connected by another physical object (such as a wire) to a part of the tracking apparatus that is fixed with respect to the space (“tracking space”) within which the position of the object is to be tracked. In an untethered position tracking system, there is no such physical mounting, attachment or connection. Typically, a tethered position tracking system restricts the movement of the tracked object with respect to the tracking space more than does an untethered system. Therefore, a tethered position tracking system may be undesirable or unusable for applications in which unfettered movement of the object is desired or necessary, such as applications in which the position of an object is to be tracked within a relatively large scale tracking space. Untethered position tracking systems, on the other hand, may not be as accurate as tethered position tracking systems, as a consequence of the less direct connection between the object being tracked and the tracking apparatus. Thus, untethered position tracking systems may be undesirable or unusable for applications in which a high degree of accuracy is required. Such applications tend to be, in general, applications in which the position of the object is to be tracked within a relatively small tracking space.
For example, the Global Positioning System (GPS), a satellite navigation system developed by the United States Department of Defense, is an untethered position tracking system used to track objects on a global (i.e., very large) scale. Multiple transmitters are positioned at fixed and known positions relative to the Earth. The transmitters emit signals that can be received by a receiver that is typically positioned on or near the surface of the Earth. The receiver receives signals from multiple transmitters. The duration of time required for each signal to travel from the corresponding transmitter to the receiver can be ascertained and used to determine the position of the receiver.
Because GPS transmitters must produce a signal that is strong enough to be detected globally, GPS transmitters require a relatively large amount of power. It is often not feasible, therefore, to implement a GPS transmitter having sufficient power that is small enough to be constructed as part of an object to be tracked. Consequently, as described above, a GPS tracking system is implemented so that the receiver, rather than the transmitter, is constructed as part of an object to be tracked. Further, the size of a physical device that embodies a receiver typically cannot be reduced beyond a certain point (i.e., there must be a minimum area devoted to receiving the incoming signal), even for very low power position tracking signals. Thus, a GPS tracking system is generally not well-suited to tracking the position of small objects.
Depending upon the characteristics of the hardware used in, and the geometry of, a particular implementation, a GPS tracking system can provide an estimate of the location of an object within approximately 20-30 meters in each direction. Thus, a GPS tracking system is useful in tracking an object within a relatively large scale tracking space (e.g., tracking the global position of an object), where such accuracy is acceptable.
A Polhemus tracking system is an example of a position tracking system that can be used for position-tracking in small tracking spaces. A Polhemus tracking system makes use of magnetic sensing to enable tracking. In a Polhemus tracking system, a magnetic field generator (transmitter) creates a magnetic field in the tracking space. A magnetic sensor (receiver) that is attached to an object being tracked includes a set of coils that are positioned at a known location and orientation with respect to the object. The magnetic field induces a current in the coils. The magnetic sensor is connected to a computer which can ascertain the magnitude and direction of the currents induced in the coils, and determine the location and orientation of the magnetic sensor (and, thus, the object) from those currents. The sensing electronics and the required computational capacity are each sufficiently complex that the magnetic sensor and computer can not typically be constructed together in an apparatus that is sufficiently small to be attached to the (typically small) object being tracked. Thus, Polhemus tracking systems are constructed as tethered systems in which the magnetic sensor is connected to the computer by a wire.
Similar to a GPS tracking system, the transmitter (magnetic field generator) of a Polhemus tracking system requires a relatively large amount of power, necessitating that the transmitter be embodied by a relatively large physical device. Since an object to be tracked is typically small, it is generally not feasible or desirable to implement a Polhemus tracking system so that a transmitter is attached to the object, rather than a receiver. Further, as indicated above, the size of a physical device that embodies a receiver typically cannot be reduced beyond a certain point. Thus, a Polhemus tracking system may not be capable of use in tracking the position of very small objects.
A Polhemus tracking system can enable accurate determination of the position of an object. However, since the object is tethered to the computer which performs the computations necessary to determine the position, a Polhemus tracking system can track the position of an object only within a relatively small tracking space. Further, since the objects are tethered, the number of objects that can feasibly be tracked is rather small, since, as the number of objects increases, the tethering wires become increasingly likely to become entangled.
Another example of a small scale position tracking system is a computer mouse that includes three receivers, fixed in position at known locations external to the mouse, that are adapted to receive ultrasound signals emitted by a transmitter that is attached to the mouse. The location of the transmitter (and, thus, the mouse) at the time a signal is emitted can be determined from the duration of time required for the signal to reach each receiver. The mouse is tethered to a computer to enable power to be supplied to the mouse, and to enable communication between the mouse and a computer with which the mouse is used.
This position tracking system also suffers from some limitations. The system is only adapted to track a single object. The system is also only adapted for use in tracking an object within a very small tracking space, e.g., a range of about a yard from the receivers. Finally, the object is tethered, thus limiting the range of motion of the object.
There are a variety of situations in which it is desirable to track the position of an object that is part of a computer interface. Such objects can be referred to as “active objects” and that term is sometimes used herein for that purpose. Further, herein, “computer interface” is used broadly to describe any point of interaction between a system including a computational device and a user of that system. For example, a glove worn by a user of a virtual reality system can be an active object. Or, a set of computer-controlled toy vehicles can be active objects. The chess pieces in a computerized chess game
Interval Research Corporation
La Anh
Van Pelt & Yi LLP
LandOfFree
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