Distance meter comprising SPAD arrangement for consideration of multiple targets
A distance meter for the high-accuracy single-point distance measurement to a target point by means of an oriented emitted beam, wherein the receiver has an optoelectronic sensor based on an arrangement of microcells for acquiring the received beam. The receiver and a computer unit are configured in this case for deriving a set of runtimes with respect to different cross-sectional components of the received beam acquired using subregions of the receiver, and therefore, for example, an evaluation is enabled as to whether the received beam has parts of the emitted beam reflected on a single target or a multiple target in its lateral extension.
1. A distance meter for detecting signal corruption in a reception signal of a receiver caused by the reception signal being generated by a mixture of reflection components from different targets within a received beam and taking into account the signal corruption when measuring a distance to a target object by the received beam, the distance meter comprising:
a transmitter, which is configured to generate an oriented emitted beam, which defines a target axis, for a single-point measurement to the target object;
the receiver for detecting the received beam to generate the reception signal, the received beam being the emitted beam returning from the target object and the reception signal being generated by a mixture of reflection components from different targets within the received beam, wherein the receiver has a multi-pixel photon counter (MPPC), which comprises hundreds or thousands of microcells and is configured to add currents of the microcells on the MPPC and to subsequently convert the added currents into a voltage signal, which asymptotically approaches a maximum limiting voltage with increasing received radiation; and
a computer unit, which is configured to derive a distance to the target object by a time measurement based on a threshold value method or a signal sampling method applied to the reception signal, wherein:
the MPPC and the computer unit are configured such that different individually readable subregions of the MPPC are definable, wherein the different subregions correspond to different cross-sectional components of the received beam impinging on the MPPC and a corresponding MPPC subregion output signal can be generated for each of the subregions, and
the receiver and the computer unit are configured to use the MPPC subregion output signals to derive and compare runtimes with respect to the different cross-sectional components of the received beam, and, based thereof, to evaluate whether there is a signal corruption of the reception signal in that the received beam impinging on the receiver has in its cross section parts associated with different target distances.
2. The distance meter according to claim 1 , wherein the computer unit is configured, based on the cross-sectional components of the received beam acquired using the individually readable subregions of the receiver, to carry out an evaluation of surfaces of the target object irradiated using the emitted beam.
3. The distance meter according to claim 2 , wherein the receiver and the computer unit are configured to take the evaluation into consideration in the derivation of the distance to the target object, and wherein, based on the evaluation:
the distance to the target object derived from the received beam is identified as incorrect, or
distance measurement data which are acquired using the individually readable subregions of the receiver are weighted differently, or
a further set of adapted individually readable subregions of the receiver is defined for the target object.
4. The distance meter according to claim 1 , wherein the receiver and the computer unit are configured such that a defined cross-sectional component of the emitted beam is associated with respective individually readable subregions of the receiver.
5. The distance meter according to claim 4 , wherein the receiver and the computer unit are configured:
to derive raw distance data respectively associated with the individually readable subregions of the receiver,
to carry out an unfolding algorithm for deriving a set of fine distances, based on the raw distance data, especially wherein one fine distance is derived for each individually readable subregion of the set of individually readable subregions, and
to associate fine distances with defined target directions in relation to the target axis.
6. The distance meter according to claim 5 , wherein the computer unit is configured to carry out an automated preprogrammed measurement procedure having the following steps:
deriving the raw distance data,
deriving the set of fine distances, and
associating fine distances with defined target directions.
7. The distance meter according to claim 5 , wherein the derivation of the set of fine distances is based on at least one of the following:
a lookup table, which enables a correlation between a raw distance and a beam diameter of the emitted beam imaged on the receiver, and
a function, which outputs a beam diameter of the emitted beam imaged on the receiver based on the raw distances as function parameters.
8. The distance meter according to claim 1 , wherein the MPPC is configured such that it has at least one of the following properties:
a photosensitivity for wavelengths between 300 nm and 1100 nm wherein the MPPC is based on a silicon receiver,
a photosensitivity for wavelengths between 700 nm and 2000 nm wherein the MPPC is based on an InGaAs receiver,
an overbreak operating mode, or
a linear operating mode.
9. The distance meter according to claim 1 , wherein the receiver is configured such that:
the MPPC is configured such that the microcells are readable individually or in microcell groups and thus individually readable subregions of the receiver are definable, or
the receiver has multiple MPPCs, wherein the multiple MPPCs are configured such that individually readable subregions of the receiver are each definable such that they are based on microcells of a single MPPC or on microcells of a combination of MPPCs of the multiple MPPCs.
10. The distance meter according to claim 1 , wherein the transmitter is configured to provide the emitted beam as pulsed laser measurement radiation.
11. The distance meter according to claim 1 , wherein the receiver is configured by means of a filter mask having different filters with respect to transmission behavior, such that the MPPC surface has regions having spectral photosensitivity different from one another.
12. The distance meter according to claim 11 , wherein the computer unit is configured, based on the regions having spectral photosensitivity different from one another, to take into consideration diffraction effects of the speckle field when carrying out the evaluation.
13. The distance meter according to claim 1 , wherein the distance meter has a fiber coupling and is configured such that returning parts of the emitted beam are distributed by means of light mixing uniformly onto the MPPC.
14. The distance meter according to claim 1 , wherein the distance meter has a receiving circuit, which is configured for processing the reception signal and to provide at least one of the following:
a waveform digitization of the reception signal having sub-picosecond-accurate time resolution,
a time measuring circuit having a time-digital converter, and
a phase measurement of the reception signal with respect to an emitted signal provided by the emitted beam.