TOF Camera Multipath Error Correction via External Object Arrangement

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Time of flight (TOF) cameras face inaccuracies in distance measurement due to the multipath phenomenon, where external objects cause erroneous large distance measurement values, leading to incorrect determination of monitored objects' presence in the monitoring area, especially at distant positions.

Innovation Solution

An object monitoring system that calculates the arrangement and reflectivity of external objects to estimate the shift in distance measurement values caused by these objects, and corrects the determination based on this estimation to accurately assess the presence of monitored objects within the monitoring area.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If TOF camera uses phase difference method for distance measurement, then measurement coverage and response speed are improved, but multipath reflection causes erroneous large distance measurement values

Engineering Contradiction:

Improveresponse speedVSAvoiddistance measurement accuracy

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent introduces an intermediary calculation process that computes the expected distance measurement value based on the arrangement of external objects. This intermediary calculation acts as a mediator between the raw TOF measurement and the final monitoring determination, allowing the system to compensate for multipath reflection effects without changing the fundamental TOF measurement method.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system implements feedback by using the calculated arrangement of external objects to estimate and correct the shift amount in distance measurement values. The corrected distance measurement value is then fed back into the monitoring determination process, creating a closed-loop system that continuously compensates for multipath effects.

Inventive Principle:

Principle #23Feedback

2Adaptability or versatility

If external objects are present in the vicinity of monitoring area, then environmental complexity is increased, but multipath effect causes erroneous determination of monitored object presence

Engineering Contradiction:

Improvemonitoring area coverageVSAvoidobject presence determination accuracy

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The system performs preliminary action by calculating the arrangement of external objects and estimating the shift amount before making the final determination about monitored object presence. This preliminary calculation of external object arrangements allows the system to pre-compensate for multipath effects in the monitoring area.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the parameter used for distance measurement interpretation by introducing a corrected distance measurement value that accounts for external object arrangements. Instead of using the raw distance measurement value directly, the system adjusts this parameter based on the calculated shift amount caused by external objects.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If distance measurement value is used directly for monitoring determination, then system complexity is minimized, but measurement errors from multipath lead to incorrect monitoring results

Engineering Contradiction:

Improvesystem structureVSAvoiddistance measurement accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system replaces the direct mechanical use of raw distance measurement values with a computational correction mechanism. Instead of relying solely on the physical TOF measurement process, the system substitutes a computational model that calculates and corrects for external object effects, achieving higher precision without adding physical components.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 system provides accurate object monitoring by accounting for the multipath effect, ensuring that monitored objects are correctly identified as present or absent, even in areas influenced by external objects, thereby enhancing the reliability of the monitoring process.

Implementation Method 1

Many TOF cameras use a phase difference method in which a target space is irradiated with reference light which is intensity-modulated over predefined cycles, and the distance measurement value of the target space is output based on a phase difference between the irradiated measurement light and the light reflected from the target space.

Methodology Applied

Scientific EffectPhase difference method:

Implementation Method 2

TOF (time of flight) cameras which output a distance based on the tine of flight of light as distance measuring devices

Methodology Applied

Scientific EffectTime of flight: Time of Flight

Implementation Method 3

the phenomenon (so-called 'multipath') wherein distance measurement values are erroneously large when certain distance measurement points are strongly influenced by reference light which has been multi-reflected via other objects

Methodology Applied

Scientific EffectMultipath reflection: Reflection

Data Source

PatentUS11454721B2Object monitoring system including distance measuring device

Publication Date: 2022.09.27 FANUC LTD

AI summary

An object monitoring system includes means for calculating an arrangement of an external object in a target space based on a distance measurement value of the external object, and estimating a shift amount of the distance measurement value caused by the external object in accordance with the calculated arrangement, and means for correcting, based on the estimated shift amount, determination of whether or not a monitored object is present in a monitoring area set in the target space.