Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
2003-02-04
2004-12-21
Gregory, Bernarr E. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C250S201600
Reexamination Certificate
active
06833909
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is based on a device for optical distance measurement as generically defined by the preamble to the independent claim.
Optical distance measuring devices per se have long been known and by now are also sold commercially. These devices emit a modulated beam of light, which is aimed at the surface of a desired target object whose distance from the device is to be ascertained. The light reflected or scattered by the target area aimed at is partly detected again by the device and used to ascertain the distance sought.
The range of use of such distance measuring devices generally encompasses distances in the range from a few centimeters to several hundred meters.
Depending on the distances and the reflectivity of the target object, different demands are made of the light source, the quality of the measuring beam, and the detector.
The optical distance measuring devices known from the prior art can be divided in principle into two categories, depending on the disposition of the transmission and reception channels necessarily present in the device. First, there are devices in which the emission channel is disposed at a certain spacing from the reception channel, so that the respective optical axes extend parallel to one another. Second, there are monoaxial measuring devices, in which the reception channel extends coaxially to the emission channel.
The biaxial measuring systems have the advantage of not requiring complicated beam splitting for selecting the returning measurement signal, so that optical crosstalk from the emission channel directly into the reception channel can for instance better suppressed.
On the other hand, in biaxial distance measuring devices there is the disadvantage among others that for the range of relatively short measurement distances, parallax can cause detection problems:
The projection of the target object onto the detector surface of the measurement receiver integrated with the device, which projection, for long target distances, is still unequivocally located on the detector wanders increasingly away from the optical axis of the receiving branch as the measuring distance becomes shorter and furthermore undergoes a variation in the beam cross section in the plane of the detector.
This means that unless further provisions are made in the device for the near range of detection, that is, for a short distance between the target object and the measuring device, the measurement signal can tend toward zero.
From German Patent Disclosure DE 43 16 348 A1, a device for distance measurement is known with a visible measuring beam generated by a semiconductor laser; its receiver contains an optical waveguide with an optoelectronic converter downstream of it. The light entry face into the fiber of the waveguide is disposed in the projection plane of the receiving lens element of this device for great object distances and from this position can be shifted transversely to the optical axis.
In this way, in the device of DE 43 16 348 A1, the measuring beams, which for short object distances strike the receiving lens element more and more obliquely, can be directed, via the tracking of the optical fibers, onto the light-sensitive surface of the detector, for a detector that is not three-dimensionally variable.
The requisite electronic triggering of the tracking and the use of additional and in particular also moving parts in the distance measuring device disclosed in DE 43 16 348 A1 mean a not inconsiderable expenditure, which increases the complexity and thus the costs and vulnerability of such a system.
Alternatively, DE 43 16 348 A1, for solving the parallax problem in biaxial measuring devices, proposes that the optical waveguide entry face be stationary, and by optical deflection means in the peripheral region of the receiving lens element to assure that the measuring light beams can still strike the detector even as the distance from the object is decreasing. Among other things, it is proposed that a deflection mirror be used for this purpose, which deflects the measuring beams, entering the measuring device from a short object distance, onto the detector. For solving the same object, the same reference also proposes the use of a prism, which is placed in the peripheral region of the receiving lens.
The necessary additional components must be considered a disadvantage in solving the problem in the above way. Moreover, a negative interaction of these additional components with the beam path of the measuring beams from a great distance cannot always be precluded, so that for this reason as well, signal impairments can occur that restrict the usable measurement range of the distance measuring device.
SUMMARY OF THE INVENTION
The device for optical distance measurement of the invention having the characteristics of the independent claim has the advantage over the prior art of being able to dispense with additional optical elements for correcting the parallax problem, and nevertheless of making a measurement signal on the detector possible that is also sufficient for the near range.
The shape of the light-sensitive, active face of the detector of the invention is selected such that even in the near range, a signal of adequate amplitude is available at the detector surface.
This makes it easily and reliably possible to expand the measurement range accessible to this measuring device.
Compared to the devices for optical distance measurement known from the prior art, the device of the invention has the advantage that the distance covered by the optical beam is not affected by the means for overcoming the parallax problem, so that these means have no negative effects on the distance measurement.
Moreover, no calibration of additional and in particular moving components in the measuring device is needed.
Advantageous versions of the device of the invention will become apparent from the characteristics recited in the dependent claims.
Advantageously, the size of the light-sensitive face of the detector of the receiver unit is selected to be so great that a still-adequate signal strikes the detector even in the near range. Because the measuring beam returning from the target object, for a decreasing object distance, migrates laterally in the common plane of the optical axis of the emitter unit and the optical axis of the receiver unit, the detector will advantageously assume a form that is elongated in that direction. In this way, the dependency of the direction of the returning measurement signal on the distance of the measuring device from the target object is taken into account by the concrete shape, according to the invention, of the effective, active detector face.
The shape according to the invention of the effective detector face furthermore makes it possible to take into account the dependency of the intensity of the returning measurement signal on the distance of the measuring device from the target object. Because the square law is fundamental to the change in intensity as a function of the distance traveled, the returning measurement signal for the near range is markedly larger than for target objects that are located far away from the measuring device.
The length of the effective detector face perpendicular to the common plane of the optical axes of the emitter unit and receiver unit can therefore decrease to the extent that the light signal, because of the shorter distance, increases in the near range. This has the advantage that because of the length of the detector, enough light from the near range will still strike the detector, yet because its active, light-sensitive face is becoming smaller in this direction, the detector cannot be oversteered by the light from the near range. A displacement of the detector out of the focus of the receiving lens along the optical receiving axis for adapting the signal intensity striking the detector is thus no longer necessary in the device of the invention.
The embodiment of the detector face according to the invention thus also has the advantage that the ratio of useful light to ext
Flinspach Gunter
Schmidt Dierk
Stierle Joerg
Wolf Peter
Andrea Brian
Gregory Bernarr E.
Robert & Bosch GmbH
Striker Michael J.
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