Rangefinder With Sighting Device

A rangefinder (1) with a sighting device (8,9), the rangefinder (1) comprising a transmitter (4) for emitting a beam, a measuring beam for re-emitting or scattering the measuring beam from the measuring target. A receiving optical system (5), a receiver (6) connected after the receiving optical system (5) for converting the light beam into an electrical measurement signal, and a receiver (6) for comparing the measurement signal with a reference The signals are compared with a signal processing device (7) in order to determine therefrom the distance to the measurement target and to make the results available to the user. The aiming device (8,9) includes a photoelectric image acquisition system (9) connected to an electronic display device, and an analysis and processing unit (7) used to form a difference in the collected images. The photoelectric image acquisition system (9) of the aiming device and the electronic display device are arranged in a common housing, which is equipped with a separate imaging objective lens (9) for the photoelectric image acquisition system (9). 8).

It is characterized in that the image acquisition system (9) includes an optoelectronic semiconductor device preferably based on a C-MOS structure and a rangefinder with a aiming device. Method for detecting measuring points on measuring targets whose distances are to be determined.

Distance meters of the following type are well known from the prior art. They have ranges from tens of meters and are often constructed as handheld instruments. They are used primarily in building surveying or interior construction, for example for the three-dimensional measurement of spaces. Other areas of application for distance meters are geodetic and industrial surveying. The basic principle of distance measurement by known instruments is based on analyzing and processing the time changes in the characteristic parameters of the electromagnetic beam emitted by the instrument and re-emitted by the aimed target. The rangefinder is equipped for this purpose with a transmitter for emitting an intensity-modulated beam. In order to facilitate the targeting of the measuring point, in the case of hand-held instruments this mainly involves light beams in the visible wavelength range. The beam is re-emitted or scattered by the aimed measuring point and recorded by a receiver built into the instrument. The distance to the measurement target is derived from the time delay of the received modulated beam relative to the beam emitted by the transmitter.

Visible beams used in handheld instruments in internal spaces are usually Laserbeams that are clearly identifiable to the naked eye at the measurement target. However, if the measurement target is strongly illuminated, it will be difficult for the naked eye to distinguish the measurement point from the background. This is especially the case in outdoor applications where the measurement target is repeatedly exposed to very strong sunlight, and the naked eye can often only detect the measured target with difficulty or not at all before emitting light. measuring point. To eliminate this problem, the user of the rangefinder sometimes uses spectacles equipped with filters, which only allow the passage of the measuring beam reflected by the measuring target. The supplemental specialized glasses are easily breakable, are often not readily available, and often feel annoying and cumbersome to the user. As an alternative to solving this problem, it is also known to use sighting telescopes for known Rangefindersthat can be retrofitted to the instrument. At this point, these sighting telescopes should help the user of the rangefinder identify the measurement points on the measurement target to be measured. Sighting telescopes additionally equipped with special filters, which are adjusted to the light at the measuring point, have also been disclosed. Aiming a telescope is laborious and expensive. In particular, a sighting telescope or similar optical sighting aid must always be aligned with the laser beam. Such instruments are therefore very sensitive to shocks. In order to cope with this disadvantage and not to unnecessarily increase the weight of the rangefinder, the sighting telescope is often constructed as a separate part, which has to be mounted on the rangefinder and calibrated only when necessary. A single aiming telescope is afraid of damage. Users often do not take it with them, or it is simply lost. It must be calibrated with the laser beam only after installation. This is to eliminate these shortcomings of the prior art rangefinders. The distance meter should be modified in such a way that in unfavorable light conditions, especially on strongly illuminated measuring targets, the measuring point on the aimed measuring target can be simply and uniquely identified. The described solution should be simple and cost-effective to implement. The instrument should be compact and handheld and allow flexible use.

These tasks are solved by a handheld rangefinder with a sighting device, which is characterized in that the image acquisition system (9) includes an optoelectronic semiconductor component, preferably based on a C-MOS structure. A method for detecting a measurement point on a measurement target whose distance is to be determined includes the method steps described in independent method claim 8. Preferred embodiment variants and/or advantageous developments of the apparatus and method are the subject matter of the associated device or method claims respectively.

There is a transmitter for emitting the light beam, a receiving optical system for the measurement light beam that is re-emitted or scattered by the measurement target, and a receiver connected after the receiving optical system for converting the light beam into an electrical measurement signal. , and a signal processing device for comparing the measurement signal with a reference signal in order to determine the distance of the measurement target therefrom and make the results available to the user. The aiming device includes an optoelectronic image acquisition system connected to an electronic display device, and an analysis and processing unit for forming a difference value on the acquired image. The optoelectronic image acquisition system and the electronic display device of the aiming device are arranged in a common housing, which is equipped with a separate imaging objective lens for the optoelectronic image acquisition system. The sighting device of the rangefinder equipped with an electro-optical image acquisition system takes advantage of the much higher light sensitivity of this system compared to the naked eye. This creates the prerequisite for generating measuring points on the measuring target even under unfavorable light conditions. In addition, the aiming device also has an analysis and processing unit for forming a difference between the signals or data provided by the photoelectric image acquisition system, and has an electronic display device, which realizes, if necessary, the signal or data. After data processing, the image of the measurement target captured by the image acquisition system is displayed to the user. The user thus has the possibility to check directly whether the distance meter actually illuminates the measuring target whose distance is to be measured. Optical aids such as special glasses or special aiming binoculars that are easily broken and easily lost or forgotten can thus be eliminated. Alignment of the aiming telescope is thus rendered unnecessary. Software can be used to select image segments that are displayed to the user in lieu of calibration. The optoelectronic image acquisition system and the electronic display device of the aiming device are arranged in a common housing, which is equipped with a separate imaging objective lens for the optoelectronic image acquisition system. The components for distance measurement and those of the sighting device with electronic display are arranged separately from each other and can operate independently of each other. This results in greater flexibility in the overall rangefinder concept. Preferred optoelectronic image acquisition systems are digital cameras, which are available as integrated semiconductor devices, especially in C-MOS structures, in very compact designs. Digital cameras equipped with optoelectronic semiconductors with 3 megapixels and more were very cheap during this period. The high resolution of digital cameras allows very precise targeting of measurement targets. It is also possible to utilize the high resolution of the digital camera in conjunction with the evaluation unit to implement an electronic zoom function. This has the advantage that the user can first have a rough orientation and, when aiming precisely at the measurement target, can use the zoom to bring the measuring range in front of him in order to then position the measuring point exactly in the measuring environment. In an advantageous variant, in order to improve the signal-to-noise ratio, an optoelectronic image acquisition system is used, in particular a monochromatic digital camera having an optoelectronic semiconductor component which is sensitive to monochromatic light. A bandpass filter, which is transparent in the wavelength range of the rangefinder beam, is inserted in front of the photosensitive acquisition surface of the digital camera.

In an alternative implementation variant, a color camera is used with a color camera chip which is designed to capture the three primary colors. The color camera chip already has filters for the red, green and blue spectral segments. If, for example, a Laserbeam in the red wavelength range is used to illuminate the measurement target and only the red part of the image provided by the color camera is used for evaluation, the signal-to-noise ratio of the laser measurement point recorded in the image relative to the ambient beam is thus significantly improved. The aiming device can also be integrated into a separate instrument. This involves, for example, a handheld or laptop computer with an integrated camera. The processing of the signal or data provided by the camera is implemented in the computer. Output the image through a computer monitor or screen. The computer and the rangefinder can be connected to each other in order to synchronize the beam source, such as a laser, and the image acquisition. The communication connection is preferably realized through a wireless communication connection, for example according to the Bluetooth standard. With this equipment the computer can be used as the aiming device. This variant is particularly suitable as a possible retrofit for an existing rangefinder.

In another advantageous implementation variant, the sighting device is integrated into the rangefinder. For this purpose, the rangefinder has, for example, a digital camera with a viewfinder objective near the emission window for its light beam, for example a Laserbeam. The image forming difference analysis and processing device is connected. A display or the like for displaying images captured by a digital camera is arranged on the instrument housing. This integrated implementation variant is particularly simple to operate and does not require additional equipment. In the method according to the invention for detecting a measuring point on a measuring target, the distance of which is to be determined, the measuring target is illuminated by means of a distance meter with a light beam, preferably with a laser beam in the visible spectrum. The measurement points generated on the measurement target are captured by an optoelectronic image acquisition system, fed to an evaluation unit that forms the difference values ​​of the captured images, and the results are displayed on an electronic display device. Aiming is already achieved directly with the measuring beam of a rangefinder or with a measuring laser. Errors are thus reliably avoided and additional parallax correction can be dispensed with. The use of optoelectronic image acquisition systems takes advantage of the extremely high light sensitivity of such systems. It is preferred to use a digital camera with an integrated semiconductor camera chip, especially a digital camera based on a C-MOS structure. C-MOS devices have smaller power consumption. They are therefore particularly suitable for portable instruments with batteries or accumulators. During this period digital cameras were available cheaply and already had very high resolution. Typically this is a higher resolution than it is necessary for identifying measurement points on a display device, screen, monitor, or the like. Due to the high sensitivity of digital cameras, it is often possible to work with only a single image in good lighting conditions, that is, in low-light environments and at short distances. In a simple variant of the invention, under favorable light conditions, a mark of the type of crosshatch in the telescope can also be superimposed on the display device. The electronic detection of the measuring point can now be cancelled. Only occasionally it is necessary to fine-tune the size of the superimposed marks. In this case, a rough distance measurement can be used to determine and, in particular, automatically correct the parallax that occurs due to the deflection of the laser beam relative to the camera optics.

In order to reliably locate the measurement point, a photoelectric image acquisition system is used to capture at least one image without an incident light beam and at least one image with an incident light beam from the measurement target. In the evaluation unit, a difference image in which the measuring point is electronically detected is determined from the electronically converted image. On the measurement target image shown on the electronic display device, the position of the detected measurement point is highlighted by a superimposed mark or the like.

If the lighting conditions are severe, for example because the measuring point is over-illuminated by the measuring object, as may be the case with strong sunlight, the measuring point is identified by averaging many images. For this purpose, a plurality of images of the measurement target, which are briefly successive in time, with and without the incident light beam, are acquired. Since the image segments may be displaced by small movements and vibrations, an image with a Lasermeasuring point and an image without a laser measuring point are always acquired directly next to each other and a difference image is determined from these. The difference images are averaged. This measure has a favorable effect on the signal-to-noise ratio, since undesired noise is filtered out during averaging.

In order to improve the signal-to-noise ratio, it proves to be advantageous if the beam power is increased simultaneously during the acquisition of the measurement target with the incident light beam, in particular by a factor of about 2 to about 20 times. In pulsed operation, higher powers are also allowed to be emitted for short periods of time, whereas for continuous operation of such Laser-equipped instruments, the average laser power is limited to a certain power in accordance with safety standards.

In an alternative approach, a monochromatic image acquisition system is used to improve the signal-to-noise ratio, preferably a monochromatic camera with an optoelectronic semiconductor component, in particular based on C-MOS, to capture the measurement target. In this case, the beam that is re-radiated or scattered by the measurement object is guided at least temporarily through a bandpass filter that is transparent in the wavelength range of the incident beam. Another possibility for improving the signal-to-noise ratio is to use a color camera for capturing the measurement target. In this case, it is preferable to further process only the portion of the image corresponding to the wavelength band of the incident light beam.

It is also possible to use an existing rangefinder and detect the light beam originating from the measurement target by means of a camera, which is arranged in a separate instrument, preferably in a palmtop or laptop computer. The computer enables further processing of the collected signals or data. The screen or display of the computer is used as a display device. For this purpose, the computer and the rangefinder are connected to each other in order to synchronize the beam source, such as a Laser, and the image acquisition. The communication connection is preferably realized through a wireless communication connection, for example according to the Bluetooth standard. This equipment allows the computer to be used as a targeting device. It is also possible to carry out the method according to the invention with a specially designed distance measuring device. At this time, the image acquisition of the measurement target is achieved with the help of an optoelectronic image acquisition system, preferably a digital camera integrated into the rangefinder. The collected signals are analyzed and processed using an analysis and processing unit arranged in the instrument. The acquired and processed signals or data are then displayed on an electronic display device, such as a display or the like arranged on a rangefinder.

The invention will be described in detail below on the basis of an embodiment schematically shown in the drawing.

Figure 1 shows a view of a rangefinder according to the invention;

Figure 1

Figure 2 shows a flow chart illustrating the method of the invention;

Figure 2

FIG. 1 shows a schematic illustration of an embodiment of a rangefinder, generally designated with reference numeral 1 .

In order to be able to understand the main instrument part of the invention, the rangefinder 1 is shown without a covering casing, in particular a Laserrangefinder. Several openings are arranged in the end plate 2 of the rangefinder. One of the openings is an exit window 4 for the measurement beam of a laser arranged on the carrier plate 3, which laser is not shown in detail in the illustration. The receiving lens 5 for the measuring beam re-emitted or scattered by the measuring object occupies the far largest part of the end plate 2 . The photovoltaic unit 6 is mounted on the carrier plate 3 behind the receiving lens 5 . Said photovoltaic unit 6 is of conventional construction and includes a reference section, various optical elements such as beam splitters, mirrors and the like, at least one photodetector, signal converters, filters and the like. The acquired and converted measurement signals are transmitted to a central signal processing device, which includes a storage unit and a microprocessor and is represented at 7 in Figure 1 . To this extent, the distance measuring device 1 described corresponds to the known instruments provided by the applicant. An imaging objective lens 8 is additionally arranged on the end plate 2, and an image acquisition system, especially a camera 9 with a photoelectric pickup chip, is arranged behind the imaging objective lens 8. The ingestion chip is, for example, a semiconductor device based on a C-MOS structure. The capture chip can be designed for monochrome or color imaging.

Figure 2 shows the sequence of a method for detecting a measuring point on a measuring target whose distance is to be determined. When the rangefinder is switched on, the aiming procedure is also started in the signal acquisition unit. This is represented by the start position 10 in the flow chart. After the first rough aiming of the measurement target, the Laseris briefly switched off in step 11. After this, an image of the measuring target without laser irradiation is captured and stored using the camera 12 . In a further step 13, the laser is switched back on and a further image 14 of the measurement target with the measurement points illuminated by the laser from now on is recorded and stored. In the query program 15, a query is made as to whether the number i of recorded images is smaller than a preferably definable maximum number N. If the specifiable maximum number N has not yet been reached, further images of the measurement target are acquired and stored. In this case, an image with a laser measurement point and an image without a laser measurement point are always captured, and a difference is formed therefrom. Erroneous measurements, which can occur through displacements of the targeted image segments due to vibrations and movements, are thus prevented. When the maximum number N is reached, the acquired difference images are averaged in a further step 16 in order to improve the signal-to-noise ratio. In an evaluation step 17 , the resulting averaged difference image is evaluated to see whether a measurement point can be detected on it. This can be achieved, for example, by threshold analysis of the difference signal brightness. If the analysis shows that a measuring point on the measuring target cannot yet be detected, the maximum number N of images to be acquired is increased. This is represented in step 18 by the programming technology assignment N=N+1. Here, the assignment N=N+1 does not mean that exactly 1 image must be raised. This only means that the maximum number N should be increased by a fixed value or even by an enternable value. If a measurement point on the measurement target is detected in the difference image, display 19 of the measurement target image is achieved on a monitor, screen or the like. The position of the measuring point is highlighted by preferably electronically superimposed markings. This completes the aiming process and enables measurement of the distance to the target.

The embodiment of the rangefinder shown in Figure 1 has a camera integrated into the instrument. However, the invention is not limited to such an instrument. For example, the camera described can also be integrated into a laptop or handheld computer. For this purpose, the computer and the rangefinder are connected to each other in order to synchronize the Laserand image acquisition. The communication connection is preferably realized via a wireless communication connection, for example according to the Bluetooth standard. This equipment allows the computer to be used as a targeting device. The method for detecting the measuring points is then executed by the computer. The display of the measurement target image and the detected measurement points is realized through the computer monitor or screen. The capacity of computers is realized by taking in multiple images and by determining distance information to generate, for example, electronic models of building facades. The electronic model generated by the computer then allows many other measurements to be performed in the office using models of objects on the building facade. This is advantageous if, for example, a support is to be erected on a building facade or to carry out measurements on areas of the object that would otherwise only be inaccessible.

ERDI TECH LTD is a company specializing in overall solutions for Laserranging. To learn more about laser ranging, please visit www.erdicn.com.

Read More

• Intelligent Laser Distance Meter
• ERDI TECH LTD's Advanced Target Acquisition Method and Device for Laser Rangefinders with False Alarm Rates
• ERDI TECH LTD Precision Laser Range Finder
• Introduction To Laser Positioning Ultrasonic Rangefinder
• Laser Rangefinder Solutions for Industrial and Military Distance Measurement