Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1999-01-19
2002-02-26
Williams, Hezron (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C702S153000
Reexamination Certificate
active
06351118
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to magnetic trackers for tracking the orientation and position of a helmet used by vehicle operators in such vehicles as tanks, planes, etc. Trackers are well known in the present area of technology and the operation of a tracker is described in references U.S. Pat. No. 4,287,809, U.S. Pat. No. 4,945,305, and U.S. Pat. No. 3,868,565.
FIG. 1
shows a block diagram of a tracker. A receiver
12
is mounted on a helmet
13
. The receiver
12
is what receives the electromagnetic information of the magnetic field in the operator area. The receiver
12
is typically attached to the operator's helmet
13
so as the helmet
13
moves, the receiver
12
will receive the information required to determine the helmet
13
position and orientation. An example of a receiver
12
would be three inductive coils which is well known in this area of technology. Three coils, one coil each to represent one axis of the triad axes in the helmet coordinate frame, exist to sense the electromagnetic field vectors to be transmitted by a transmitter
11
.
Once the components of the magnetic field are obtained, it is necessary to perform calculations on the data. As a result, the data is sent from the receiver
12
to pre-amplifiers
22
,
23
,
24
via cable
21
. The reason for three preamplifiers
22
,
23
,
24
is to accommodate for the x, y, and z signals of the helmet movements and to amplify the signals for processing. The output of the pre-amplifiers
22
,
23
,
24
are sent to a multiplexer
25
to combine the three signals. The output of the multiplexer
25
is sent to a central processing unit (CPU)
32
. The CPU
32
performs calculations on the data to obtain and accurate mapping of the operator area. Filters, such as bandpass filters, can be used at any point of the system to filter out unwanted signals. Amplifiers, such as a variable gain amplifier, can also be used at any stage of the system to amplify the signals. Furthermore, it is well known that A/D converters are also required for the CPU
32
to process the data. The figure has been simplified only to show the essence of the operation and structure of currently existing trackers.
A selector switch
47
is used to control the transmission of signals to the transmitter
11
by selecting which signal will be sent. The signals are sent through amplifiers
60
,
61
, and
62
so that the signals have sufficient power for energizing the transmitter
11
. The transmitter
11
transmits a magnetic field in the operator area back to the helmet
13
. Orientation and position information is sent back to the vehicle systems via an interface so that the vehicle operates accordingly with the information. One such example would be to control the instrumentation of an aircraft.
A driver is used to supply energy to the transmitter
11
to a desired level. As is presently known, inductive coils have been used in a transmitter. A typical drive system uses three or six inductive coils driven sequentially at a fixed repetition rate. During each drive period of each coil, the coil is driven for several periods at the excitation frequency. The large coil excitation levels required are generated by placing a capacitor in series with each transmitter coil so that a high-Q series-resonant network is obtained at the excitation frequency. This resonant network is driven by a sine voltage from a drive amplifier. A high accuracy current sensing resistor provides feedback so that the coil current is driven to the desired level. In previous designs, a separate amplifier and current sensing resistor were used with each coil network. When a sine drive is applied to a network, several excitation cycles elapse before the current stabilizes, as the stored energy increases in the resonant network. It would be desirable to have a driver that does not require several excitation cycles to elapse. Further, it would be desirable to have a non-complex driver with a quicker response.
SUMMARY OF THE INVENTION
A helmet tracker including a transmitter to transmit information regarding the orientation and position of the helmet, a receiver for receiving the information, and a processor for processing the information to determine the position and orientation of the helmet. An apparatus is connected to the transmitter to attain a faster response time for the transmitter to transmit the information.
REFERENCES:
patent: 4870554 (1989-09-01), Smith
patent: 5347289 (1994-09-01), Elhardt
Ackerman John F.
Lange Erik H.
Anderson Henry S.
Bremer Dennis C.
Honeywell Inc.
Williams Hezron
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