Comparison of iPad Pro® s LiDAR and TrueDepth Capabilities with ... - MDPI

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Article

Comparison of iPad Pro?¡¯s LiDAR and TrueDepth Capabilities

with an Industrial 3D Scanning Solution

Maximilian Vogt 1, * , Adrian Rips 2 and Claus Emmelmann 3

1

2

3

*









Fraunhofer Research Institution for Additive Manufacturing Technologies IAPT, 21029 Hamburg, Germany

School of Mechanical Engineering, Hamburg University of Technology TUHH, 21073 Hamburg, Germany;

adrian.rips@tuhh.de

Institute of Laser and System Technologies, Hamburg University of Technology TUHH,

21073 Hamburg, Germany; c.emmelmann@tuhh.de

Correspondence: maximilian.vogt@iapt.fraunhofer.de

Abstract: Today¡¯s smart devices come equipped with powerful hard- and software-enabling professional use cases. The latest hardware by Apple utilizes LiDAR and TrueDepth, which offer the

capability of 3D scanning. Devices equipped with these camera systems allow manufacturers to

obtain 3D data from their customers at low costs, which potentially enables time-efficient mass

customization and product differentiation strategies. However, the utilization is limited by the

scanning accuracy. To determine the potential application of LiDAR and TrueDepth as a 3D scanning

solution, in this paper an evaluation was performed. For this purpose, different Lego bricks were

scanned with the technologies and an industrial 3D scanner. The results were compared according to

shape and position tolerances. Even though the industrial 3D scanner consistently delivered more

accurate results, the accuracy of the smart device technologies may already be sufficient, depending

on the application.

Citation: Vogt, M.; Rips, A.;

Emmelmann, C. Comparison of iPad

Keywords: 3D scanning; reverse engineering; iPad Pro; TrueDepth Camera; LiDAR

?

Pro ¡¯s LiDAR and TrueDepth

Capabilities with an Industrial 3D

Scanning Solution. Technologies 2021,

9, 25.

1. Introduction

technologies9020025

To ensure the future competitiveness of manufacturing companies, it is necessary to

face constantly changing customer requirements and market turbulence. Consequently, a

shortening of the product development cycle is constantly pursued in order to adapt to the

dynamic market efficiently and quickly [1]. Manufacturers today tend to adopt product

differentiation strategies and more customer-centric approaches to remain competitive.

Hence, mass customization and product diversification are one of the most commonly

implemented business models. As part of the digital transformation and Industry 4.0, these

objectives are being realized. Additive manufacturing technologies offer high potential for

individualization at low cost in a short period of time [2]. Cost-effective and high-quality

mass customization requires technological resources such as reverse engineering and 3D

scanning. Currently, smartphones and tablets can be utilized as 3D scanners as well [3].

This lowers the entry barrier for both private users and industrial users to digitize objects.

While the customer only needs to be provided with the hardware, the manufacturer can

realize the product design by means of reverse engineering (RE). This means that the basic

scanning can be performed by customers themselves so that the manufacturer can offer

them a product tailored to their needs. An example for this is the business model of the

company HEXR, which produces custom-fit bike helmets with additive manufacturing. In

order to scan the shape of the customers¡¯ heads, a smartphone application and a fitting cap

are needed. The application uses the standard smartphone camera and the random texture

of the fitting cap to model the shape of the head [4]. However, with LiDAR and TrueDepth

technologies included in the newest devices by Apple, even more enhanced possibilities to

digitize real objects are offered.

Academic Editor: Manoj Gupta

Received: 14 February 2021

Accepted: 3 April 2021

Published: 7 April 2021

Publisher¡¯s Note: MDPI stays neutral

with regard to jurisdictional claims in

published maps and institutional affiliations.

Copyright: ? 2021 by the authors.

Licensee MDPI, Basel, Switzerland.

This article is an open access article

distributed under the terms and

conditions of the Creative Commons

Attribution (CC BY) license (https://

licenses/by/

4.0/).

Technologies 2021, 9, 25.



Technologies 2021, 9, 25

2 of 13

Ref. [5] defines the processes of designing, manufacturing, assembling and maintaining products and systems as engineering and divides it into two different types. While

forward engineering implies the process of the approach from a highly abstracted idea to

the physical implementation of a system, RE refers to already existing objects. Thereby, an

existing part, subassembly or product without drawings and documentations is duplicated.

Furthermore, RE is a process to obtain a 3-dimensional computer model from an existing

object through measurements without consideration of functionalities. This process is

also known as Computer Aided Reverse Engineering (CARE), which involves the steps

of data collection, mesh construction and surface fitting [6]. For data collection, different

hardware can be used, whereas mesh construction and surface fitting focus mainly on

software solutions. The hardware is divided into noncontact and contact-based methods,

which can be used for data acquisition [7].

When the highest scan accuracy is required, coordinate measuring machines (CMM)

can be used. These are based on the principle of contact by measuring the surface to

be tested with a probe. Due to the high precision manufacturing processes and built-in

reference standards, CMMs provide the highest accuracy in inspection processes [6]. In

addition, the results are independent of the reflection rate of a surface. Limited operating

space is a point of emphasis because the object needs to be accessed and touched by the

probe. The amount of contact points determines the accuracy. Therefore, the process can

get time-consuming by inspecting complex structures as well as unknown shapes [6¨C8].

An alternative to this procedure is the noncontact method, in which no physical

contact to the surface is needed. Noncontact methods are subdivided into different scan

technologies including photogrammetry, structured light and Time of Flight (ToF). Those

techniques are used by a variety of scanning systems with different capabilities and limitations [7,9]. Based on the field of application, it is important to select a suitable scanner

that meets the requirements. Besides a relatively short processing time, noncontact 3D

scanners cost much less compared to a CMM [8]. In addition, a high point cloud density of

some 3D scanners can be used to measure complex and deep features with high accuracy.

Thereby, the point density is defined by the quantity of emitted points and the obtained

measured values. As a result, a higher point density provides more measured values for

the same scan area [10]. Portable scanners are also becoming increasingly interesting for

the manufacturing industry.

The scanning method Structured Light is based on the principle of triangulation, while

incident laser lines are projected onto the object to be scanned. A common industrial 3D

scanner is the Artec Space Spider, which uses structured light as scan technology. The Artec

Space Spider uses a blue LED with a narrow wavelength, which allows better filtering of

interference from ambient light [11]. From the narrowband of laser stripes with known

angular width, many points of the stripe are reflected by the surface. These points are

detected by a charge-coupled device (CCD) sensor and transformed to 3D coordinates via

the triangulation principle [8]. In total, the Artec Space Spider uses three cameras at various

angles and depths. In the center of the device, an RGB camera is installed surrounded by

LED flash light to capture textures without the need for special light setup. Thereby the

Artec Space Spider is advertised with a pinpoint accuracy of 0.05 mm and 3D resolution of

0.1 mm [11].

Recent developments of commercial devices such as smartphones and tablets have

shown that in addition to photogrammetry, scanning is also feasible with LiDAR (light

detection and ranging) and TrueDepth. LiDAR includes ToF measurements, which determine the time it takes for an object, particle or wave to travel a distance. Therefore, LiDAR

emits a pulse or modulated light signal and measures the time difference in the returning

wavefront [12]. TrueDepth uses vertical-cavity surface-emitting laser (VCSEL) technology

and consists of a traditional camera, an infrared camera, a proximity sensor and a dot

projector as well as a flood illuminator. The system is named and patented by Apple. The

dot projector emits more than 30,000 points of infrared light, which are reflected on the

surfaces. Consequently, the infrared camera picks up these light dots again and the pattern

Technologies 2021, 9, x FOR PEER REVIEW

Technologies 2021, 9, 25

3 of 15

3 of 13

surfaces. Consequently, the infrared camera picks up these light dots again and the pattern

is analyzed

by software

to create

a depth

map.Using

Usingthis

thisdepth

depthmap,

map,aa mathematical

mathematical

is analyzed

by software

to create

a depth

map.

model is generated by machine learning algorithms [9,13¨C15].

In iOS,

iOS, the

theoperating

operating

system

of Apple¡¯s

smartphones

and tablets,

TrueDepth

is

system

of Apple¡¯s

smartphones

and tablets,

TrueDepth

is mainly

mainly

for 3D

face authentication

and recognition,

while enables

LiDAR enables

new feaused forused

3D face

authentication

and recognition,

while LiDAR

new features

for

tures

for Augmented

Reality

by accelerating

plane detection.

scan objects,

it is therefore

Augmented

Reality by

accelerating

plane detection.

To scanTo

objects,

it is therefore

necessary to install

an additional

application.

Heges

is such

an iOS

that exploits

necessary

to install

an additional

application.

Heges

is such

an application

iOS application

that exTrueDepth

and LiDAR.

The authors

of [16] of

evaluated

different

smartphone

applications,

ploits

TrueDepth

and LiDAR.

The authors

[16] evaluated

different

smartphone

applishowingshowing

that Heges

one has

of the

resolutions

(0.5 mm).

application

can be

cations,

thathas

Heges

onefinest

of the3D

finest

3D resolutions

(0.5The

mm).

The application

usedbetoused

scanto

objects

and export

STL and

polygon

(PLY) files,

while

colors

can

also

can

scan objects

and scans

exportasscans

as STL

and polygon

(PLY)

files,

while

colors

be captured.

In contrast

other applications,

Heges is also

notislimited

to limited

scan faces

only.

can

also be captured.

In to

contrast

to other applications,

Heges

also not

to scan

In addition,

screen sharing

function

facilitates

a one-time

allows

faces

only. Ina addition,

a screen

sharing

functionscanning,

facilitatesand

scanning,

and payment

a one-time

payunlimited

export

of

these

scan

files

[16].

Apple

itself

does

not

specify

the

accuracy

of the

ment allows unlimited export of these scan files [16]. Apple itself does not specify

respectiveoftechnologies

or technologies

hardware. or hardware.

accuracy

the respective

While the

the hardware

hardwareand

andthe

thesoftware

softwareofof

the

device

determine

scan

accuracy

While

the

device

determine

thethe

scan

accuracy

ininternally,there

thereare

arealso

alsoexternal

externalfactors

factorsinfluencing

influencingscan

scanquality.

quality.AAliterature

literature research

research has

has

ternally,

shown that

that factors

factors are

are reflectance,

reflectance, shape

shape and

and color

color of

of the

the object

shown

object as

as well

well as

as surface

surface texture

texture

and

ambient

lightning.

In

addition,

the

distance

between

object

and

scanner,

and ambient lightning. In addition, the distance between object and scanner, scanning

scanning

strategy and

and scanning

scanning movements

During post-processing,

post-processing,

strategy

movements influences

influences scan

scan quality

quality [7¨C9,17].

[7¨C9,17]. During

the

meshing

and

surface

fitting

have

also

shown

influences

[17].

Depending

on the

the scan

the meshing and surface fitting have also shown influences [17]. Depending on

scan

accuracy,

different

fields

of

applications

can

be

exploited.

accuracy, different fields of applications can be exploited.

To determine

determine the

the potential

potential use

use of

of LiDAR

LiDAR and

and TrueDepth

TrueDepth included

in the

the recent

recent iPad

iPad

To

included in

Pro

and

iPhone

12

Pro

lineup

as

a

3D

scanner,

this

study

was

conducted.

For

the

evaluation,

Pro and iPhone 12 Pro lineup as a 3D scanner, this study was conducted. For the evaluaan iPad

Pro (2020)

[3] was

usedused

and and

waswas

compared

to the

industrial

Artec

Space

Spider

tion,

an iPad

Pro (2020)

[3] was

compared

to the

industrial

Artec

Space

SpiHandheld

3D

Scanner

[11].

Therefore,

different

Lego

bricks

were

scanned

and

compared

der Handheld 3D Scanner [11]. Therefore, different Lego bricks were scanned and comvia the software GOM Inspect. The aim of this study was to determine the scan accuracy of

pared via the software GOM Inspect. The aim of this study was to determine the scan

LiDAR and TrueDepth as 3D scanning technique.

accuracy of LiDAR and TrueDepth as 3D scanning technique.

2. Materials and Methods

2. Materials and Methods

The procedure of this study is shown in Figure 1 and can be divided into three steps:

The procedure of this study is shown in Figure 1 and can be divided into three steps:

(1) Scanning

?(2) (1)

Scanning

Measurement

?(3) (2)

Measurement

Comparison

?

(3) Comparison

Real Lego Brick

Measurement

3D Scanning

Industrial 3D-Scanner

Artec Space Spider

Blue-Light Technology

Scanned

Data 1

Heges Application

iPad Pro 2020

TrueDepth LiDAR

Scanned

Data 2

Keyence VHX-5000

Reference

CAD Model

Scanned

Data 3

Comparison

Artec

Studio

MeshLab

GOM

Inspect

Figure 1. Schematic illustration of the procedure to evaluate the accuracy of TrueDepth and light detection and ranging

Figure 1. Schematic illustration of the procedure to evaluate the accuracy of TrueDepth and light detection and ranging

(LiDAR) using an iPad Pro (2020) in comparison to an industrial 3D scanning system.

(LiDAR) using an iPad Pro (2020) in comparison to an industrial 3D scanning system.

Technologies 2021, 9, 25

4 of 13

2.1. Scanning

The first step is to scan an object. Thereby, it is important to control the factors that

influence the scan quality and only modify the factors that should be4 of

analyzed.

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of

thewith

object

permm

minute

Lighting

conditions:

scanner

placed

identically

insettings

the same

environment

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settings

(resolution

etc.):

same

?

Scanning

angle:

constant

65¡ã

?

Scanning

angle:

constant

with

65¡ã

???? Scanning

angle:

constant

with

65¡ã

?

Scanning

speed:

one

rotation

of

the

object

persame

minute

Lighting

conditions:

scanner

placed

identically

in the

same environment

Lighting

conditions:

scanner

placed

identically

in

the

environment

?

Scanning

angle:

constant

with

65¡ã

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angle:

constant

with

65¡ã

?

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angle:

constant

with

65¡ã

speed:

one

rotation

of

the

object

per

minute

?

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movements:

no

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of

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devices

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speed:

one

rotation

of

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object

per

minute

?

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conditions:

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placed

identically

in

the

same

environment

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conditions:

scanner

placed

identically

in

the

same

environment

???

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conditions:

scanner

identically

in

same

environment

???? Relative

movements:

no

movement

of

thethe

scanning

devices

Hence

Lego

produced

within

aobject

tolerance

of

10

?m,

suitable for the following

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speed:

oneplaced

rotation

of

the

per

minute

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speed:bricks,

one

rotation

of

the

object

per

minute

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conditions:

scanner

placed

identically

inthe

the

sameare

environment

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conditions:

scanner

placed

identically

in

same

environment

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conditions:

scanner

placed

identically

in

same

environment

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movements:

no

movement

of

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scanning

devices

Post-processing

(point

spline,

surface

model,):

same

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movements:

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movement

of

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devices

?

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speed:

one

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of

the

object

per

minute

???

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speed:

one

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of

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per

minute

?

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speed:

one

rotation

of

the

object

per

minute

?

Post-processing

(point

cloud,

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model,):

same

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movements:

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devices

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movements:

no

movement

of

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research

due

to

high

manufacturing

accuracy

and

differences

in shape and color [18].

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speed:

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ofsettings

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per

minutesame

??

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speed:

one

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of

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permodel,):

minute

?? Scanning

speed:

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rotation

of

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per

minute

Post-processing

(point

cloud,

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surface

model,):

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settings

(resolution

same

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(point

cloud,

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same

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movements:

no

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of

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devices

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movements:

no

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devices

???According

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no

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????? movements:

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settings

(resolution

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same

settings

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(point

cloud,

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model,):

same

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(point

cloud,

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model,):

same

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movements:

no

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of

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devices

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movements:

no

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to

the

shape

tolerances¡ªstraightness,

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movements:

no

movement

of

the

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devices

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settings

(resolution

etc.):

same

settings

?

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settings

(resolution

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same

settings

Hence

bricks,

produced

within

asurface

tolerance

ofsettings

10 ?m,

are suitable

for the follow?? Lego

Post-processing

(point

cloud,

spline,

surface

model,):

same

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(point

cloud,

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surface

model,):

same

???

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(point

cloud,

spline,

model,):

same

?

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settings

(resolution

etc.):

same

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settings

(resolution

etc.):

same

settings

Hence

Lego

bricks,

produced

within

a

tolerance

of

10

?m,

are

suitable

for

the follow?

Post-processing

(point

cloud,

spline,

surface

model,):

same

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(point

cloud,

spline,

surface

model,):

same

?

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(point

cloud,

spline,

surface

model,):

same

bricks

were

selected

for

the(resolution

examination

as

in of

Table

1. Besides

the

shape,

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Hence

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bricks,

produced

within

ashown

tolerance

10

?m,

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suitable

for

the followresearch

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to

high

manufacturing

accuracy

and

in

shape

color

[18].

?? Lego

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settings

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a tolerance

ofdifferences

10 ?m,

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settings

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same

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settings

(resolution

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ing

research

due

to

high

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accuracy

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differences

in

shape

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color

[18].

?

Software

settings

(resolution

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settings

?willSoftware

settings

(resolution

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same

settings

Hence

Lego

bricks,

produced

within

a

tolerance

10

?m,

are

suitable

for

the

follow?

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settings

(resolution

etc.):

same

settings

Hence

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bricks,

produced

within

a

tolerance

of

10

?m,

are

suitable

for

the

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evaluated

by

comparing

a

profile

of

a

surface,

profile

of

a

line

and

the

position

of

research

due

to

high

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accuracy

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differences

in

shape

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color

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the

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tolerances¡ªstraightness,

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ing research

to

high

manufacturing

accuracy

and

differences

in

shape

and

color

[18].

Hence

Lego

bricks,

produced

within

aa tolerance

of

10

?m,

are

suitable

for

the

followHence

Lego

bricks,

produced

within

tolerance

of

10

?m,

are

suitable

for

the

followHence

bricks,

produced

within

aa tolerance

of

10

?m,

are

suitable

for

the

followAccording

to

the

shape

tolerances¡ªstraightness,

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ingLego

research

due

to

highproduced

manufacturing

accuracy

and

differences

in

shape

and

color

[18].

ing

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due

to

high

manufacturing

accuracy

and

differences

in

shape

and

color

[18].

Hence

Lego

bricks,

produced

within

a

tolerance

of

10

?m,

are

suitable

for

the

followHence

Lego

bricks,

produced

within

tolerance

of

10

?m,

are

suitable

for

the

followHence

Lego

bricks,

within

a

tolerance

of

10

?m,

are

suitable

for

the

followAccording

to

the

shape

tolerances¡ªstraightness,

flatness,

roundness

and

cylindricity¡ª

bricks

were

selected

for

the

examination

as

shown

in

Table

1.

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the

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profile

According

to

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tolerances¡ªstraightness,

flatness,

roundness

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features

in

relation

to

the

real

object.

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the

colors

white,

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green,

ing

research

due

to

high

manufacturing

accuracy

and

differences

in

shape

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color

[18].

ing

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due

to

high

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accuracy

and

differences

in

shape

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color

[18].

ing

research

to

high

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differences

in1.shape

and

color

[18].

bricks

were

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examination

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shown

in

Table

Besides

the

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According

to

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the

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ing

research

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differences

inshape

shape

and

color

[18].

ing

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due

to

high

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accuracy

and

differences

and

color

[18].

ing

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due

to

high

manufacturing

accuracy

differences

in

and

color

[18].

bricks

were

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for

examination

as

shown

in

Table

1.shape

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the

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evaluated

by

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athe

profile

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line

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position

ofthe

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the

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as

in

Table

1.and

Besides

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black

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the

investigation

color

impact.

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to

the

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flatness,

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According

to

the

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cylindricity¡ª

According

to

the

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be

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by

comparing

a

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of

a

surface,

profile

of

a

line

and

the

position

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bricks

were

selected

for

the

examination

as

shown

in

Table

1.

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the

shape,

the

profile

bricks

were

selected

for

the

examination

as

shown

in

Table

1.

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the

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profile

According

to

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to

theevaluated

shape

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According

to

the

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will

be

by

comparing

a

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of

a

surface,

profile

of

a

line

and

the

position

of

features

in

relation

to

the

real

object.

Additionally,

the

colors

white,

orange,

red,

green,

will be evaluated

by

comparing

a

profile

of

a

surface,

profile

of

a

line

and

the

position

of

bricks

were

selected

for

the

examination

as

shown

in

Table

1.

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the

shape,

the

profile

bricks

were

selected

for

the

examination

as

shown

in

Table

1.

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the

shape,

the

profile

bricks

were

selected

for

the

examination

as

shown

in

Table

1.

Besides

the

shape,

the

profile

features

in

relation

to

the

real

object.

Additionally,

the

colors

white,

orange,

red,

green,

will

be

evaluated

by

comparing

a

profile

of

a

surface,

profile

of

a

line

and

the

position

of

will

be

evaluated

by

comparing

a

profile

of

a

surface,

profile

of

a

line

and

the

position

of

bricks

were

selected

for

the

examination

as

shown

in

Table

1.

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the

shape,

the

profile

bricks

were

selected

for

the

examination

as

shown

in

Table

1.

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the

shape,

the

profile

bricks

were

selected

for

the

examination

as

shown

in

Table

1.

Besides

the

shape,

the

profile

features

in

relation

to

the

real

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the

colors

white,

orange,

red,

green,

black

andin

turquoise

were

chosen

for

the

investigation

of

color

impact.

features

relation

to

the

real

object.

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the

colors

white,

orange,

red,

green,

Table 1. Overview ofwill

thebe

used

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bricks

for

the

inspection

of

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characteristics

and

tolerances

[19].

will

be

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by

comparing

aa profile

of

aaprofile

surface,

profile

of

aathe

line

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the

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of

will

be

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by

comparing

profile

of

surface,

profile

of

line

and

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position

of

evaluated

by

comparing

aa profile

of

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aa colors

line

and

position

black

and

were

chosen

the

investigation

of

colororange,

impact.

features

inturquoise

relation

the

real

object.

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the

white,

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features

in

relation

to

the real

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colorsof

white,

will

be

evaluated

byto

comparing

profile

ofthe

surface,

profile

of

linered,

andgreen,

theof

position

of

will

evaluated

by

comparing

profile

of

surface,

line

and

position

of

will

be

evaluated

by

comparing

aafor

profile

of

aaprofile

surface,

profile

of

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line

and

the

position

of

black

and

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were

chosen

for

the

investigation

of

color

impact.

blackbeand

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were

chosen

for

the

investigation

of

colorof

impact.

features

in

relation

the

real

object.

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the

colors

white,

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features

in

relation

to

the chosen

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object.

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the

colors

white,

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green,

features

in

relation

to

the

real

object.

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the

colors

white,

orange,

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green,

black

and

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were

chosen

for

the

investigation

of

color

impact.

black

and

turquoise

were

for

the

investigation

of

color

impact.

features

in

relation

to

the

real

object.

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the

colors

white,

orange,

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green,

in

relation

to

the

real

object.

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the

colors

white,

orange,

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green,

features

in

relation

to

the

real

object.

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the

colors

white,

orange,

red,

green,

Table 1.Evaluation

Overview offeatures

the

used

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bricks

for

the

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of

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[19].

of Scanned

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Shape

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According

toimpact.

DIN

EN

ISO

1101 [19].

and

turquoise

were

chosen

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investigation

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color

impact.

black

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chosen

forinspection

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of color

Table 1. Overview

of black

the

used

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the

ofthe

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black

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color

impact.

black

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chosen

forofthe

the

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color

impact.

and

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investigation

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ofLego

the

used

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bricks

for

the

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geometric

characteristics

and

tolerances

[19].

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ofblack

the used

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[19].

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ofOverview

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Bricks

bythe

Shape

According

to DIN

ENtolerances

ISO

1101

TableGeometric

1.

the used

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forTolerances

the inspection

of geometric

characteristics

and

tolerances

[19].

Table

1. Overview

of

the usedofLego

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for

inspection

of geometric

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[19].

Element

Evaluation

of of

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According

totolerances

DINand

ENtolerances

ISO 1101Control

SymbolTable

Tolerance

Type

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Summary

Table

1.

Overview

the

used

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inspection

of

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characteristics

Table

1.

Overview

of

the

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for

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of

geometric

characteristics

and

[19].

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1.

Overview

of

the

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[19].

1ISO

1. Overview

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1 Control

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DIN

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1101[19].

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of

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According

to Number

DIN

EN

ISO

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SymbolTable

Geometric

Characteristic

Tolerance

Type

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Element

Summary

Characteristic

Number

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1. of

Overview

the

used

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1. Overview

of

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of Brick

geometric

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[19].

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1.

the

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characteristics

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1 Control

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Type

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Number

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According

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ENtolerances

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According

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ISO

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1

1

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Element

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Type

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Element

Number

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Summary

Evaluation

of

Scanned

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Bricks

Shape

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According

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1101

1ISO

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Evaluation

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1101

11 Summary

1Number

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Geometric

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Element

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Summary

Symbol Symbol

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Type

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Element

Number

Control

Symbol

Geometric

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Type

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Element

Number 11 Control

Summary

Straightness

4,181,139/44,237

11Number

Symbol

Geometric

Characteristic

Tolerance

Type

LegoBrick

Brick

Element

ControlSummary

Summary

Symbol Symbol

Geometric

Characteristic

ToleranceTolerance

Type

Lego Brick

Element

Number

Control Summary

Geometric

Characteristic

Type

Lego

Element

Number

Control

Straightness

4,181,139/44,237

Straightness

4,181,139/44,237

Straightness

4,181,139/44,237

Straightness

4,181,139/44,237

Straightness

4,181,139/44,237

Straightness

4,181,139/44,237

Straightness

4,181,139/44,237

Straightness

4,181,139/44,237

Straightness

4,181,139/44,237

Straightness

4,181,139/44,237

Straightness

4,181,139/44,237

Straightness

4,181,139/44,237

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300,123/3001

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1

1

Technologies 2021, 9, 25

Technologies 2021, 9, x FOR PEER REVIEW

5 of 15

5 of 13

control

influencing

factors,

following

setup

chosen:

one object

was placed

ToTo

control

influencing

factors,

the the

following

setup

was was

chosen:

one object

was placed

onon

a rotary

table

with

anan

irregular

surface

texture,

which

increases

the the

object

tracking

duedue to

a rotary

table

with

irregular

surface

texture,

which

increases

object

tracking

tothe

thehigh-contrast

high-contrast color

color design.

design. Radially

Radially the

the scanning

scanningdevices

deviceswere

werestationary-mounted

stationary-mounted with

with

a constant

distance

300mm

mmtotothe

themiddle

middle of

of the table

scana constant

distance

ofof

300

table(object).

(object).To

Tocontrol

controlthe

the

scanning

ning

speed,

table,

includingthe

theirregular

irregularsurface

surface texture

texture and

speed,

thethe

table,

including

and the

the object,

object,was

wasrotated

rotated one

one

full

rotationper

perminute.

minute.One

One scanner

scanner was

minute

scanning

thethe

object

full

rotation

wasactivated

activatedfor

forone

one

minute

scanning

object in

? . After

in360

360¡ã.

After aa scan,

scan, the

the process

process was

was repeated

repeated analogously

analogously with

with the

the next

next scanning

scanning technology

technology

the object

next object

was placed.

This ensured

thatplacement

the placement

ofLego

the Lego

beforebefore

the next

was placed.

This ensured

that the

of the

brick was

brick

was

always

the

same

for

each

scan

technology

and

each

scanning

session.

In each

total, object

always the same for each scan technology and each scanning session. In total,

each

wasbyscanned

by technology

each scan technology

times.sensors

All three

sensors

were

wasobject

scanned

each scan

three times.three

All three

were

aligned

so that a

aligned

so

that

a

scan

angle

of

65¡ã

was

set

with

respect

to

the

surface.

For

TrueDepth,

?

scan angle of 65 was set with respect to the surface. For TrueDepth, the iPad wasthe

laid flat

iPad

laid flaton

onaits

display

on a stand,

it is asensor.

front-facing

sensor. In

on was

its display

stand,

because

it is a because

front-facing

In addition,

theaddition,

device had to

the

had

to? .be rotated 180¡ã.

bedevice

rotated

180

ToTo

ensure

thethe

same

post-processing,

the automatic

meshing

in Artec

StudioStudio

15 was15 was

ensure

same

post-processing,

the automatic

meshing

in Artec

used every time. For the scans with Heges, the files were exported as stereolithography

used every time. For the scans with Heges, the files were exported as stereolithography

files (*.STL) and cleaned in MeshLab the same way.

files (*.STL) and cleaned in MeshLab the same way.

2.2.

Measurement

2.2.

Measurement

The digital microscope Keyence VHX-5000 was used to obtain the actual geometry

The digital microscope Keyence VHX-5000 was used to obtain the actual geometry of

of an object using the optical metrology with 200¡Á magnification. Based on those measan object using the optical metrology with 200¡Á magnification. Based on those measureurements, the bricks were reconstructed in Autodesk Inventor 2020 and saved as inventor

ments, the bricks were reconstructed in Autodesk Inventor 2020 and saved as inventor part

part files (*.ipt). The scanned meshes and designed components were imported in GOM

files (*.ipt). The scanned meshes and designed components were imported in GOM Inspect

Inspect Suite 2020. This Software offers a wide range of inspection tools with high accuSuite 2020. This Software offers a wide range of inspection tools with high accuracy and a

racy and a low standard deviation, as tests performed by [21] showed.

low standard deviation, as tests performed by [21] showed.

2.3. Comparison

2.3. Comparison

The generated meshes were examined for deviations in mm as absolute values as

The generated meshes were examined for deviations in mm as absolute values as

shown in Figure 2. While the color influence was investigated by a flatness test (a), shape

shown in Figure 2. While the color influence was investigated by a flatness test (a), shape

tolerances were examined with inspection tools from GOM Inspect (b). In this analysis no

tolerances were examined with inspection tools from GOM Inspect (b). In this analysis no

relation between features was considered. To compare the size, form and orientation of

relation between features was considered. To compare the size, form and orientation of

scanned surfaces based on datum references, a target-actual comparison was established

scanned

surfaces

based on

datum

references,

a target-actual

comparison was

(c).

(c).

Therefore,

the scanned

Lego

bricks

were aligned

with the reconstructed

one established

in GOM

Therefore,

the

scanned

Lego

bricks

were

aligned

with

the

reconstructed

one

in

GOM

Inspect.

Inspect. Then, the deviation between the scanned mesh to the constructed part was deterThen,For

thethe

deviation

between

the

scanned

meshsurface

to the constructed

mined.

profile of

a line the

edge

of a curved

was used. part was determined.

For the profile of a line the edge of a curved surface was used.

(a)

(b)

(c)

Figure

with

GOM

Inspect

Suite

2020:

(a) flatness

test by

scanned

Lego Lego

brick with

Artec

Figure2.2.Examination

Examinationofofdeviation

deviation

with

GOM

Inspect

Suite

2020:

(a) flatness

testa by

a scanned

brickthe

with

the Artec

Space

influence

thethe

scan

quality

scanned;

(b) form

tolerance

analysis

of a Lego

brick scanned

by the by the

SpaceSpider

Spiderwhether

whethercolors

colors

influence

scan

quality

scanned;

(b) form

tolerance

analysis

of a Lego

brick scanned

TrueDepth

comparison

of aofLego

brick

scanned

by the

camera

for thefor

examination

of

TrueDepthcamera;

camera;(c)

(c)target-actual

target-actual

comparison

a Lego

brick

scanned

byTrueDepth

the TrueDepth

camera

the examination

of

scan accuracy of a profile on a surface.

scan accuracy of a profile on a surface.

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