Adaptive Transmit Light Control for ToF Camera Safety
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Solution Overview
Problem
Time-of-Flight (ToF) camera distance measurement accuracy is limited by maximum permissible light energy due to eye and skin safety standards, restricting exposure time and performance.
Innovation Solution
An apparatus with a controller that determines and controls the maximum transmit light time based on transmitted light power/energy, using a shunt resistor or photodiode to monitor and modulate the light source, ensuring safe operation while maximizing measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the exposure time is extended to improve measurement accuracy, then the distance measurement accuracy is improved, but the transmitted light energy exceeds safety limits causing eye and skin damage
Solution Approach 1:
The patent applies dynamics by making the light transmission parameters adaptive rather than fixed. The controller dynamically adjusts the duty cycle and exposure time based on real-time monitoring of transmitted light energy, allowing the system to operate at optimal accuracy levels while continuously maintaining safety constraints. This resolves the contradiction by enabling extended exposure times when safe and limiting them when approaching safety thresholds.
Solution Approach 2:
The patent changes the operational parameters (duty cycle, exposure time, light power) adaptively based on monitored conditions. By continuously adjusting these parameters within safe boundaries, the system maximizes measurement accuracy without exceeding eye and skin safety limits. The controller modifies transmission parameters in real-time to optimize the balance between accuracy and safety.
2Object-affected harmful factors
If the transmitted light energy is reduced to maintain safety standards, then eye and skin safety is maintained, but the distance measurement accuracy deteriorates
Solution Approach 1:
The patent implements feedback by using a monitoring circuit to continuously measure the actual transmitted light energy and feed this information back to the controller. The controller uses this feedback to adjust the duty cycle and exposure time, optimizing measurement accuracy while ensuring safety constraints are never violated. This closed-loop control resolves the contradiction by adapting light transmission to the maximum safe level rather than using conservative fixed limits.
Solution Approach 2:
The system transitions from static safety limits to dynamic adaptive control. The controller continuously monitors transmitted energy and adjusts operational parameters in real-time, allowing the system to operate at the boundary of safety limits when conditions permit, thereby maximizing measurement accuracy without compromising safety.
3Object-affected harmful factors
If a predetermined maximum exposure time is enforced to ensure safety, then eye and skin safety is guaranteed, but the performance and measurement accuracy of the ToF camera are limited
Solution Approach 1:
The patent replaces fixed predetermined exposure time limits with dynamic adaptive control. The controller adjusts the exposure time and duty cycle based on real-time monitoring of transmitted light energy, allowing the system to extend exposure times beyond traditional predetermined limits when safety conditions permit, thereby improving measurement accuracy and overall camera performance.
Solution Approach 2:
The system changes from using fixed operational parameters to adaptive parameter control. By continuously monitoring transmitted energy and adjusting exposure time, duty cycle, and light power accordingly, the system optimizes performance within safety boundaries rather than being constrained by conservative fixed limits.
4Duration of action of moving object
If advanced modulation schemes are used to allow longer exposure times, then the average light energy is reduced below maximum permissible values, but the system complexity increases
Solution Approach 1:
The patent employs periodic modulation of the light source through duty cycle control, where the light is transmitted in periodic pulses rather than continuously. This periodic action allows longer effective exposure times while keeping the average light energy below safety thresholds. The controller adjusts the duty cycle to optimize the balance between exposure duration and average power, improving performance without requiring complex modulation schemes.
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 allows for increased performance by reducing the 'guardband' between actual light power/energy and safety thresholds, enhancing measurement accuracy while maintaining eye and skin safety without exceeding safety limits.
Implementation Method 1
The shunt resistor 150 is configured to measure its voltage drop to determine a current through the light source 120. The current is proportional to the transmit light output power/energy
Implementation Method 2
rather than the light transmitted by the light source 120 being determined by a voltage drop across the shunt resistor 150, transmitted and/or reflected light is measured with a photodiode 250
Implementation Method 3
The light source 120 may comprise a Light Emitting Diode (LED), a laser, and/or any other suitable light source. The modulation switch 130 is configured to modulate the transmitted light by turning the light source 120 on and off
Data Source
AI summary
An apparatus, having a transmitted light power/energy monitor configured to monitor transmitted power/energy of light transmitted by a light source, and a controller configured to determine and control a maximum transmit light time based on the transmitted light power/energy and a transmit light power/energy threshold based on time.