Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
2001-05-30
2003-01-21
Tarcza, Thomas H. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C356S004010
Reexamination Certificate
active
06509958
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for the detection of the distance between a measuring device comprising a transmitter and a receiver and an object, in which a modulated light signal is emitted along a transmission channel by the transmitter in the direction of the object, the light signal reflected at the object is received by the receiver via a reception channel and is converted into a reflection signal, and the distance between the measuring device and the object is determined from the light transit time of the received light signal. The invention is further directed to a distance measuring device having a transmitter emitting at least one light signal along a transmission channel and having a receiver for the reception of the light signal reflected at an object via a reception channel and for the generation of a corresponding reflection signal, with the measuring device comprising a measuring unit for the measurement of the light transit time of the received light signal and an evaluation unit for the determination of the distance between the measuring device and the object from the light transit time measured.
A method and a distance measuring device of this kind are known wherein a light pulse is emitted in the direction of the object by the measuring device to determine the distance between the measuring device and the object, with a counter being started simultaneously with the emission of the light pulse. When the light pulse reflected by the object is incident to the receiver, the counter is stopped if the output signal of the receiver generated by the light signal incident to the receiver exceeds a certain threshold value. The distance between the measuring device and the object can then be calculated from the number of count impulses, which corresponds directly to the light transit time of the light signal received and from the propagation speed of the light signal.
This method and the measuring device working with this method have proven their value in practice. In particular when a very high measuring accuracy is required, however, the problem can occur with the known method that the firing point for the transmission diode usually used does not coincide exactly with the actual time of the emission of the transmission pulse due, for example, to a changing response behavior of the transmission diode due to age. As the counter used is started simultaneously with the firing of the laser diode, a certain measurement inaccuracy can be present in the measurement of the light transit time in this way. The light transit time determined furthermore also depends on the choice of the threshold value for the output signal of the receiver, since the light pulses emitted and received usually have oblique flanks and therefore a higher threshold value results in a later stopping of the counter.
SUMMARY OF THE INVENTION
It is an object of the present invention to further develop a method and a measuring device of the kind initially mentioned such that an increased measurement accuracy is achieved.
Starting from the method of the kind initially mentioned, the object relating to the method is satisfied in accordance with the invention in that, in addition to the light signal reflected at the object, at least a part of the light signal emitted is received as a reference light signal by a receiver without reflection at the object and is converted into a reference signal; and in that the phase shift between the reflection signal and the reference signal is determined to find the light transit time, with an optical separation being present between the transmission channel and the reception channel.
The part of the object relating to the measuring device is satisfied in accordance with the invention starting from a distance measuring device of the kind initially mentioned in that a receiver is provided at a pre-set distance to the transmitter, in particular in direct proximity thereto, with which at least a part of the light signal emitted can be received directly as a reference light signal, that is, without reflection at the object, and can be converted into a reference signal; in that the phase shift between the reflection signal and the reference signal can be determined by the evaluation unit for the determination of the light transit time; and in that an optical separation is present between the transmission channel and the reception channel in the region of the transmitter and the receiver.
In accordance with the invention, it is thus not the firing point of the transmission element which is used as the starting point for the measurement, but the light signal emitted is received twice, once after reflection at the object and once without reflection at the object, so that two reception signals are present for the determination of the light transit time whose phase shift is determined. If a delay should occur between the firing of the transmission element and the actual emission of the light pulse generated thereby, then this is automatically compensated by embodiments of the invention since, for the determination of the light transit time, the transmission light signal delayed in this case is used as the reference for the determination of the light transit time. The receiver generating the reference signal is preferably arranged in direct proximity to the transmitter, since in this way the reference signal generated by the receiver can be used directly as the temporal reference value. If a greater pre-set distance is present between the transmitter and the receiver, then a corresponding offset value can be taken into account in the determination of the phase shift.
It is excluded by the optical separation provided in accordance with the invention between the transmission channel and the reception channel in the region of the transmitter and the receiver that stray light from the transmission channel can enter into the reception channel and result in a dazzling of the reception unit. Cross-talk between the transmission channel and the reception channel can thus be completely avoided in accordance with embodiments of the invention.
The term “light signal” is used in the meaning of generally optical signals in connection with this application. Light signals in the visible light range and/or in the infrared range and/or in the UV range can preferably be used.
In accordance with an advantageous embodiment of the invention, pulse-like light signals are used. Depending on the application, single pulses or impulse packages or also absolutely any forms of signal can be used.
In accordance with a further advantageous embodiment of the invention, the same receiver is used to receive the reflected light signal and the reference light signal. This has the advantage that the reference light signal and the light signal reflected at the object are received and converted into a corresponding output signal by one and the same receiver. Differences which can be present in the use of different receivers, for example due to aging, temperature errors or production tolerances, are excluded in this way. Preferably, a part of the light signal emitted by the transmitter is guided directly to the receiver as the reference light signal. If the transmitter and the receiver are optically uncoupled from one another, then this can be done, for example, by a light guide which guides a part of the light signal emitted by the transmitter to the receiver. The amount of the light signal guided to the receiver can be set exactly in this way, which is in particular important because the sensitivity of the sensor is usually very high in order to receive light signals which are reflected by objects which are arranged far away or by dark object surfaces. The part of the emitted light signal guided to the receiver as the reference light signal is therefore preferably attenuated. If the same receiver is used for the reflected light signal and the reference light signal, it is furthermore of advantage if the reference light signal is guided to the receiver via such a light guide which int
Andrea Brian
Sick AG
Tarcza Thomas H.
Townsend & Townsend & Crew LLP
LandOfFree
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