Light Curtain Bypass Logic for Selective Machine Shutdown
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Solution Overview
Problem
Existing safety sensor systems in danger zones often unnecessarily shut down machines when non-safety-critical objects, like workpieces, are detected, leading to increased costs due to the need for additional muting sensors and complex fail-safe units.
Innovation Solution
A safety sensor system with a bridging unit that uses simultaneous monitoring of object presence signals from two independent signal sources to differentiate between safety-critical and non-safety-critical objects, avoiding unnecessary shutdowns by generating a bridging signal only when both signals confirm the presence of a permissible object within a specific time interval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If muting sensors and fail-safe units are added to differentiate between safety-critical and non-safety-critical objects, then machine shutdown accuracy is improved, but system cost and complexity increase significantly
Solution Approach 1:
The protective field is divided into multiple sub-regions (first protective field and second protective field) with different safety requirements. The first sub-region contains the hazardous area requiring safety monitoring, while the second sub-region allows permissible objects without shutdown. This segmentation enables differentiated safety responses without additional muting sensors.
Solution Approach 2:
The patent introduces a spatial dimension to object evaluation by defining different protective field regions. Instead of using additional sensors to differentiate objects, the system uses the spatial position within the protective field as an additional dimension for decision-making. Objects in the first sub-region trigger shutdown, while objects in the second sub-region do not, eliminating the need for complex object identification.
2Reliability
If muting sensors are deployed at both input and output of the danger zone, then reliability of object classification is improved, but the number of sensors and system cost double
Solution Approach 1:
The protective field is segmented into multiple sub-regions with different safety functions. The first sub-region monitors for safety-critical objects requiring shutdown, while the second sub-region permits permissible objects. This segmentation provides reliable object classification using only the existing light curtain sensors without requiring additional muting sensors at input and output.
Solution Approach 2:
The existing light curtain sensors are made multi-functional by evaluating them differently based on their spatial position. The same sensors serve both safety monitoring functions: detecting hazardous objects in the first sub-region and permitting permissible objects in the second sub-region, eliminating the need for separate muting sensor systems.
3Reliability
If the light curtain shuts down the machine upon detecting any object in the danger zone, then safety function is ensured, but machine availability decreases due to unnecessary shutdowns
Solution Approach 1:
The protective field is divided into a first sub-region with hazardous area requiring shutdown on object detection, and a second sub-region where permissible objects do not trigger shutdown. This segmentation maintains safety by ensuring the hazardous area is protected while improving availability by allowing permissible objects in the second sub-region without unnecessary machine shutdowns.
Solution Approach 2:
Different safety responses are applied to different spatial locations within the protective field. The first sub-region maintains strict safety monitoring with shutdown function, while the second sub-region has relaxed monitoring that permits permissible objects. This local differentiation ensures safety where needed while maximizing machine availability where permissible.
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
This approach enhances the availability of work equipment by preventing unnecessary shutdowns while maintaining safety standards, even with unreliable signal sources, and reduces design and operational costs by simplifying the safety sensor system.
Implementation Method 1
A safety sensor (1) with a sensor unit having at least one light-emitting transmitter (4) and a light-receiving receiver (6)
Implementation Method 2
at least one light-emitting transmitter (4) and a light-receiving receiver (6) for monitoring a protective field (8)
Data Source
Figure 1~2
Figure 3
AI summary
The sensor i.e. light curtain (1), has a sensor unit with a transmitter and a receiver for monitoring a protection field. An evaluation unit generates a stop command for a machine or system as a safety function during detection of an object in the protection field. An external or internal bypass unit is arranged for bypassing the safety function of the sensor, when an object existing signal is registered within an interval of two independent signal sources. One of the signal sources is automatically integrated in the safety sensor.