Optics: measuring and testing – Angle measuring or angular axial alignment – Automatic following or aligning while indicating measurement
Reexamination Certificate
1999-08-24
2001-04-17
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Angle measuring or angular axial alignment
Automatic following or aligning while indicating measurement
C356S141300, C356S141500, C359S199200
Reexamination Certificate
active
06219133
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a spatial optical transmission device and method of spatial optical transmission in which information is transmitted by light passing through space.
BACKGROUND ART
The transmission of information by light passing through space has been implemented for example by IrDA (Infrared Data Association). In particular, the divergent type of transmission method, in which light is transmitted in a divergent beam, does not require optical axis collinearity, and allows the provision of transmitter and receiver to be simple.
With such a divergent type of transmitter, for information to be transmitted optically through space, a large light output is required even for close range operation (not exceeding 1 m), and if the transmission distance is 10 m or so, a light output of at least 500 mW is required.
As the information transfer rate increases, this requires broad band transmission and a high frequency, and to detect light modulated at a high frequency requires the receiving area of the receiving optics to be small, and the electrical capacitance of the element to be small. For example, when transmitting information in the 1-GHz waveband, if a photodiode is used as the photodetector, light-receiving area must be not more than 0.1 mm
2
. As a result, for broad band optical transmission, because the light-receiving area is small, a larger light output is required.
On the other hand, in the beam type of transmission method in which the light is transmitted along a straight line, the light output can be less than for the divergent type, but the alignment of the optical axis is difficult. In particular, if the positions of the transmitter and receiver move, a mechanism for following the light beam is required. As the mechanism for following the light beam, for example, Japanese Patent Application Laid-Open No. 8-181654, discloses that an optical axis is adjusted by detecting a target to which the light beam is directed on the basis of image information obtained by using a lens and a charge-coupled device (CCD).
However, not only does such a CCD have a high power consumption, but it is not practical for the transmitter to be combined with a complex element such as a CCD, and moreover, the analysis of the image information, the detection of the target, and control of the direction of the light beam require a complicated algorithm.
The present invention solves the above-mentioned problems, and provides a beam type of spatial optical transmission device and method of spatial optical transmission such that the light beam can be tracked with simple control.
DISCLOSURE OF THE INVENTION
(1) A spatial optical transmission device of the present invention comprises:
a transmitter which has a plurality of tracking beam transmitters of a divergent type for emitting light at a wide angle, a data beam transmitter of a beam type for emitting light at a narrow angle, an error information beam receiver, and an optical axis control section; and
a receiver which has a tracking beam receiver, a data beam receiver, an error information generation section, and an error beam transmitter of a divergent type;
wherein the tracking beam transmitters emit light beams toward a coordinate plane that has a plurality of coordinate axes and has a fixed relative positional relation with the tracking beam transmitters; the optical axes of at least two of the light beams emitted from the tracking beam transmitters are placed at different positions on each coordinate axis; and adjacent light beams among the light beams partially overlap on one of the coordinate axes, the optical intensity of each of the adjacent light beams showing uneven distribution;
wherein the tracking beam receiver is positioned in the coordinate plane, receives the light beams from the tracking beam transmitters, and detects the intensity of each of light beams thereof;
wherein the error information generation section calculates positional difference between the tracking beam receiver and a datum point of the coordinate plane based on the detected intensity of the light beams, and generates error information;
wherein the error information beam transmitter transmits the error information to the error information beam receiver; and
wherein the optical axis control section controls the optical axes of the light beams from the tracking beam transmitters based on the error information so that the tracking beam receiver is positioned at the datum point in the coordinate plane, and also controls the optical axis of the light beam from the data beam transmitter to correspond with the data beam receiver.
According to the present invention, a beam of light is transmitted from the tracking beam transmitter to the tracking beam receiver. This beam of light is of the divergent type, so that even if the optical axis is displaced somewhat, the light can be received by the tracking beam receiver.
In the present invention, a coordinate plane including a plurality of coordinate axes is established. This coordinate plane has a fixed positional relation with the tracking beam transmitter, and the optical axes of a plurality of light beams are placed at different positions on each coordinate axis, and adjacent light beams partially overlap. Further, the optical intensity of each light beam from the tracking beam transmitter shows uneven distribution along the coordinate axis. Therefore, by comparing the intensities of a plurality of light beams partially overlapping along the coordinate axis, the position of the tracking beam receiver in the coordinate plane can be detected.
The error information generation section, based on the light intensities indicating the position of the tracking beam receiver, calculates the positional difference between a previously determined datum point and the position of the tracking beam receiver. The error information beam transmitter transmits the error information to the error information beam receiver of the transmitter.
In the transmitter, based on the error information, the optical axis of the light beam from the tracking beam transmitter is controlled, and at the same time the optical axis of the light beam from the data beam transmitter is controlled.
With the above control carried out, the optical axis of the light beam from the data beam transmitter can be aligned with the data beam receiver. According to the present invention, since the tracking beam receiver only detects optical intensities, a large amount of electrical power is not required, and the algorithm for calculating the error information is not complex. In this way, with simple control, the light beam from a data beam transmitter can be tracked.
(2) In the above spatial optical transmission device, the intensity of each of the light beams emitted from the tracking beam transmitters may be distributed such that the intensity decreases further from the optical axis.
(3) In the above spatial optical transmission device, the light beams from the tracking beam transmitters may be emitted sequentially one at a time. In this way, the intensity of each beam can be detected.
(4) In particular, the error information may be generated after signals based on all of the light beams emitted one at a time have been sequentially sampled and latched.
(5) In the above spatial optical transmission device, the error information generation section, based on the detected intensity of the light beams, may generate an intensity signal for each of the tracking beam transmitters, calculate the difference in the intensity signal for light beams whose optical axes are positioned on the same coordinate axis, and generate coordinate error information for each coordinate axis; and the error information may comprise all of the coordinate error information.
By this means, the positional difference between the tracking beam receiver and the datum point can be calculated.
(6) The above spatial optical transmission device may further comprise at least one lens through which the light beams from the tracking beam transmitters and the data beam transmitter pass; and th
Kawase Takeo
Kitamura Shojiro
Buczinski Stephen C.
Oliff & Berridge PLC.
Seiko Epson Corporation
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