Light Barrier Device With PLL Modulation Coding
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Solution Overview
Problem
Light barrier arrangements face interference from stray light, which can simulate a free monitoring area despite the presence of objects, due to reflections from mirror-reflective objects and overlapping light beams from adjacent systems, compromising detection reliability.
Innovation Solution
A light barrier arrangement with multiple beam axes and a digital phase-locked loop (PLL) for each beam axis, using transmission modulation coding on light beams to distinguish between intended and stray light sources, and a redundant evaluation unit with multiple digital processors for fail-safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If simple light beams are used without modulation, then the device complexity is reduced, but the immunity to interference from stray light and adjacent light barrier arrangements deteriorates
Solution Approach 1:
The patent applies periodic action by modulating the light beams with a transmission modulation that varies over time. The evaluation unit uses a PLL (phase-locked loop) to detect this periodic modulation, allowing the system to distinguish between intended light beams and interfering stray light. This temporal coding enables reliable differentiation without requiring complex spatial filtering or multiple light sources.
2Measurement precision
If no coding is applied to light beams, then the ease of operation is improved, but the ability to differentiate from interfering light sources deteriorates
Solution Approach 1:
The patent applies parameter changes by encoding information in the transmission modulation parameters (frequency, phase, or amplitude variations) of the light beams. The evaluation unit detects these parameter changes through the PLL, enabling precise identification of intended beams versus interfering sources. This coding approach maintains operational simplicity while significantly improving measurement precision through parameter-based differentiation.
3Reliability
If adjacent light barrier arrangements operate without coordinated modulation, then the system simplicity is maintained, but false detection of clear areas deteriorates
Solution Approach 1:
The patent applies feedback through the PLL mechanism, which continuously adjusts to track the transmission modulation of intended light beams. This feedback loop enables the evaluation unit to dynamically distinguish between expected modulated signals and interfering unmodulated or differently modulated light, preventing false detection of clear areas while maintaining system reliability without requiring complex coordinated control between adjacent arrangements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides high immunity to interference and ensures reliable object detection by accurately identifying transmission modulations and distinguishing between stray and intended light sources, enhancing functional reliability and safety in surveillance applications.
Implementation Method 1
at least one transmitter (4) emitting light beams (3)
Implementation Method 2
an associated receiver (6) which forms a beam axis with the transmitter (4). If the monitored area is clear, the light beams (3) are directed to the receiver (6)
Data Source
Figure 1
Figure 2~3
Figure 4a)~4b)
AI summary
The invention relates to a light barrier arrangement for detecting objects in a monitoring area, comprising at least one light beam emitting a transmitter (4) and an associated receiver (6) that forms a beam axis with the transmitter (4). When the monitoring area is clear, the light beams (3) are directed onto the receiver (6). If an object enters the monitoring area, the path of the light beams (3) is at least partially interrupted. An evaluation unit (9) generates an object detection signal based on the received signals from the receiver (6). The light beams (3) are encoded in the form of a transmission modulation, for example, a brightness modulation. The evaluation unit (9) includes a PLL (14) in which the encoding of the light beams (3) is determined.