Reliable optical transit time method for determining distance values

Abstract

In a method and an optical time-of-flight sensor for determining distance values d, di by an optical time-of-flight method, an illumination light 40 is emitted which is modulated with a modulation frequency f and a modulation phase q. Reflected light 42 is acquired as an output signal Rx and evaluated by acquisition of a phase shift δ between the illumination light 40 and the reflected light 42, so that an output signal d, di with at least one distance value d is generated. Distance values d, di are determined for a sequence of successive frames, with a plurality of acquisitions being made in each frame in the form of micro-frames μF1-μF8 with different modulation phases φ. A sequence of modulation phases φ1-φ4 of the micro-frames μF1-μF8 is specified for each frame. In order to achieve a particularly high reliability of the data supplied, the order of the modulation phases φ1-φ4 changes. A self-calibration and self-verification take place in an initialization step (60). The subsequent data acquisition takes place in frame acquisition steps 62 with acquisition of signals and calculation and output of the distance values for each pixel for subsequent processing (68). Each step (62) in the acquisition of a frame is divided into a setup step (64) and a subsequent acquisition of signals in micro-frames μF1-μF8. In setup step (64), the central processing unit MCU calculates (pseudo-)random numbers and uses these to determine the order of the micro-frames μF1-μF8, i.e. the respective modulation frequencies f and phase angles φ. Optical time-of-flight methods, in which the acquisition and signal evaluation are carried out with a variable order of modulation phases, are thus particularly suitable for safety-related applications, e.g. as optical area monitoring systems for industrial production facilities.

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