Image analysis – Applications
Reexamination Certificate
1999-06-09
2002-04-30
Couso, Yon J. (Department: 2723)
Image analysis
Applications
C348S169000
Reexamination Certificate
active
06381340
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of multi-sensor tracking devices, and more particularly to a method of calculating relative phases between channels of a multi-sensor tracking device.
2. Description of the Relevant Art
Multi-sensor tracking devices are well known in the art and are used to orient moving components of a system employing the device with respect to a known position. Multi-sensor tracking devices have application in, for example, virtual reality systems. More particularly, tracking devices may be employed in a headset of a virtual reality system to generate orientation signals relating an instant position of the tracking device, and thus the headset, relative to a predetermined point in space.
FIG. 1
is a block diagram of a typical multi-sensor tracking device
12
used to track angular motion. Tracking device
12
shown in
FIG. 1
includes three signal channels
14
A-
14
C, respectively, coupled to a digital signal processor
16
. Channels
14
A-
14
C include motion sensors
20
A-
20
C, respectively, analog signal processing circuits
22
A-
22
C, respectively, and analog to digital converters
24
A-
24
C, respectively.
Although not shown in
FIG. 1
, each sensor
20
A-
20
C is physically mounted within tracking device
12
such that a sensitive axis thereof substantially aligns with one of the orthogonal axes of the tracking device
12
. More particularly, sensitive axis of sensor
20
A is substantially aligned with the azimuth axis, sensitive axis of sensor
20
B is substantially aligned with the elevation axis, and sensitive axis of sensor
20
C is substantially aligned with the roll axis.
In theory, each sensor is sensitive to motion with respect to a single axis of the tracking device
12
, but insensitive to motion with respect to the remaining axes. Thus, if tracking device
12
shown in
FIG. 1
is subjected to simultaneous movement with respect to all three of its orthogonal axes, each motion sensor simultaneously generates an analog signal the magnitude of which is linear to the component of movement with respect to its corresponding axis. These signals may be proportional to the angular position, angular velocity, or angular acceleration about the given axis
Analog signals generated by motion sensors
20
A-
20
C are provided as inputs to analog signal processing circuits
22
A-
22
C, respectively. Analog signal processing circuits
22
A-
22
C provide one or more functions. In particular, analog signal processing circuits
22
A-
22
C may operate to amplify the sensor analog signal inputted thereto. Additionally, analog signal processing circuits
22
A-
22
C may operate to filter random pattern or fixed pattern noise components of the analog sensor signal inputted thereto. The processed analog signals are then provided to analog to digital converters
24
A-
24
C for conversion. Digital signal processor
16
coordinates function of the analog to digital converters
24
A-
24
C. More particularly, digital signal processor
16
generates a sample signal which is simultaneously received by each of the analog to digital circuits
24
A-
24
C. In response thereto, internal sample and hold circuits within the analog to digital converter circuits
24
A-
24
C, sample and hold the analog signals outputted by analog signal processing circuits
22
A-
22
C. The held sampled analog signals are subsequently transformed into digital format by analog to digital converters
24
A-
24
C and forwarded to digital signal processor
16
. At this point the relative phases of the three channels are locked, and remain precisely defined throughout the processing within the digital signal processor.
Digital signal processor
16
operates in accordance with well known algorithms to generate an orientation signal as a function of the three digital signals outputted by the channels
14
A-
14
C in general, and the analog to digital converters
24
A-
24
C in particular. For example, digital signal processor may accumulate digital channel signals representing angular velocity in order to generate orientation signals relating current position of the tracking device
12
to a known start point.
It is important to note that the algorithms employed within digital signal processor
16
may operate to combine data from the three separate channels with the presumption that the channel signals are synchronous. However, this is not always the case. Manufacturing tolerances dictate that corresponding elements within the channels
14
A-
14
C are less than physically identical. These physical differences between components may cause relative signal delay between channels. Additionally differences between analog signal processing circuits
22
A and
22
B may cause a greater signal transmission time through signal processing circuit
22
A when compared to signal processing time through circuit
22
B. Thus, analog signal processing circuits
22
A and
22
B may generate analog signal outputs at different times (i.e., out of sync.) not withstanding sensor signal inputs provided at the same instant of time. The overall relative time delay, also referred to as relative phase, between signals outputted by channels
14
A-
14
C, may impair accuracy of the subsequently generated orientation signals.
SUMMARY OF THE INVENTION
The present invention relates to a method for calculating relative phases between channels of a multi-sensor tracking device. The calculated phases can be subsequently used by an internal digital signal processor to generate a more accurate orientation signal. The multi-sensor tracking device comprises a plurality of channels each one of which includes at least one sensor for sensing movement with respect to a corresponding axis. To calculate at least one relative phase between channels, the tracking device is subjected to a known movement constrained with respect to one of the orthogonal axes thereof. As the tracking device moves, a plurality of first signals generated by a first channel is recorded. Concurrently, a plurality of second signals generated by a second channel are likewise recorded. Thereafter, a relative phase between the first and second channels is calculated as a function of the recorded plurality of first signals and recorded plurality of second signals. It is this relative phase which may be used to compensate for relative time lags between signals propagating through the first and second channels in subsequent real time application of the tracking device.
REFERENCES:
patent: 4675820 (1987-06-01), Smith et al.
patent: 5307289 (1994-04-01), Harris
patent: 5414643 (1995-05-01), Blackman et al.
patent: 5421187 (1995-06-01), Morgan
patent: 5537118 (1996-07-01), Appriou
patent: 6176837 (2001-01-01), Foxlin
Patent Abstracts of Japan, Publication No. 59069808, Apr. 20, 1984.
Foxlin, “Intertial Head-Tracker Sensor Fusion by a Complementary Separate-Bias Kalman Filter,” Proceedings of VRAIS, Mar. 1996, pp. 185-194.
International Search Report, Application No. PCT/US99/14477, mailed Oct. 19, 1999.
Couso Yon J.
DigiLens Inc.
Skjerven Morrill & MacPherson LLP
LandOfFree
Method for calculating relative phases between signal... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for calculating relative phases between signal..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for calculating relative phases between signal... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2876530