Polarization Filter for Laser Distance Meter Dynamic Range

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Solution Overview

Problem

Hand-held laser distance meters face challenges in achieving a large usable dynamic range due to the need to detect weak light pulses from distant, non-reflective surfaces and strong light pulses from close, reflective surfaces, leading to overloading and reduced measurement accuracy.

Innovation Solution

Incorporating a polarization filter arranged along the reception axis, which partially shadows light from nearby reflective surfaces while allowing polarized light from distant surfaces to reach the photoreceiver, enhancing the dynamic range by suppressing strong light signals and increasing sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the photoreceiver is designed to be highly sensitive to detect weak light pulses from distant surfaces, then the detection capability for weak signals is improved, but the receiver becomes overloaded by strong light signals from close reflective surfaces

Engineering Contradiction:

Improvedetection capability for weak light signalsVSAvoidoverloading from strong light signals

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies local quality by implementing a polarization filter that selectively affects different portions of the light signal based on their polarization state. The filter is positioned to shadow only the direct reflected light from close reflective surfaces while allowing scattered light from distant surfaces to pass through, creating different optical paths with different polarization characteristics for near and far objects

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The polarization filter acts as an intermediary element between the photoreceiver and the incoming light signals. It mediates the conflict between weak and strong signals by selectively blocking polarized light from reflective surfaces while transmitting unpolarized or differently polarized light from scattered surfaces, enabling the receiver to handle both signal types without overload

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If the photoreceiver area is reduced to handle strong reflected signals, then the dynamic range is increased, but the reception of weak scattered light signals is diminished

Engineering Contradiction:

Improvedynamic range for different reflection conditionsVSAvoidreception of weak scattered light signals

Core Design Contradiction:

Adaptability or versatilityVSIllumination intensity

Solution Approach 1:

The polarization filter creates local quality differentiation in the optical path by allowing full light transmission for scattered signals while blocking polarized reflected signals. This enables the photoreceiver to maintain full area for detecting weak scattered light while the filter locally suppresses strong reflected signals that would cause overload

Inventive Principle:

Principle #3Local quality

3Stability of the object's composition

If the laser diode emits polarized light to improve beam coherence, then the beam quality is improved, but reflected components from close surfaces cause extensive interference and overloading

Engineering Contradiction:

Improvebeam coherence and qualityVSAvoidinterference from reflected polarized components

Core Design Contradiction:

Stability of the object's compositionVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful polarized reflected light into a beneficial filtering mechanism. By using a polarization filter oriented perpendicular to the laser's polarization direction, the system selectively blocks the harmful polarized reflected components while allowing the useful unpolarized scattered light to pass, turning the polarization property from a source of interference into a tool for signal discrimination

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 solution increases the measurable range and allows accurate measurements near reflective surfaces by optimizing the photoreceiver's sensitivity and reducing overloading, thereby improving the device's performance across varying distances and surface types.

Implementation Method 1

a polarization filter (10) inside the reception beam bundle (9), by which, with respect to a polarization direction, the light from measurement objects in the near field is shadowed

Methodology Applied

Scientific EffectPolarization: Polarisation

Implementation Method 2

receiving optics with a photoreceiver (7) for receiving parts of the light beam (4) that is backscattered in a reception beam bundle (9) from a measurement object (8)

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Implementation Method 3

an electric radiation source (3) in form of a laser diode for generating a modulated, linearly polarized, bundled and visible light beam (4)

Methodology Applied

Scientific EffectLaser: Laser

Data Source

PatentUS8068215B2Laser distance meter

Publication Date: 2011.11.29 HILTI AG

AI summary

An electro-optic laser distance meter (1, 1′) has a hand-held housing (2), an electric radiation source (3) for generating a bundled light beam (4), and receiving optics (5) with a photoreceiver (7) for receiving parts of the light beam (4) that is backscattered in a reception beam bundle (9) from a measurement object (8), with the photoreceiver (7) being arranged along the reception axis (E) in the focal point (6), extending in a plane transverse to the reception axis (E), and being partially shadowed inside the reception beam bundle (9) by a polarization filter (10, 10′, 10″, 10′″).