System Quality

Int J Adv Manuf Technol (****) **:**** ****

DOI *0.1007/s00170-008-1794-9

ORIGINAL ARTICLE

Influence of roughness on surface scanning by means

of a laser stripe system

Eduardo Cuesta & J. Carlos Rico & Pedro Fern ndez &

David Blanco & Gonzalo Vali o

Received: 6 May 2008 / Accepted: 6 October 2008 / Published online: 31 October 2008

# Springer-Verlag London Limited 2008

Abstract This work deals with the determination of the of process time and cost is achieved compared with other

parameters that have influence in the scanning of parts with traditional contact-type methods.

different surface roughness. A commercial laser stripe The 3D noncontact scanning techniques have suffered an

system has been used for capturing points on a part surface evolution from research works in an initial stage to a wide

by means of triangulation techniques. The parameters number of industrial applications today [1, 2]. Since the

which can be affected by the roughness surface are first accuracy of noncontact scanning systems has greatly

analyzed in order to establish the optimal conditions for the improved, these type of scanning technologies are currently

scanning tests. This way, gauges with different roughness applied not only to reverse engineering but also to the

grades and manufactured by different processing technolo- inspection of complex and large geometries that are

gies have been tested. Since the roughness gauges were flat, difficult to inspect by traditional methods. Moreover, all

the set of points captured onto a plane as well as their these applications take advantage of the portability that the

spatial dispersion with regard to the best-fit plane have been systems offer to be mounted onto measuring articulated

used as indicators of quality of the scanning process. The arms, coordinate measuring machines (CMM), and other

results of the tests provide some recommendations about customized manipulators or industrial robots.

the methodology and working conditions for scanning each Despite the above advantages, the commercial scanners

type of surface. based on triangulation are less accurate than the traditional

contact-type methods. Moreover, there are still limited

Keywords Scanning . Laser stripe . Surface roughness research focused on describing and solving problems like

those derived from variations in surface reflectance and

shape, from the material, from the color, or from the

speckle noise caused by the rough surfaces [3 6]. Curless

1 Introduction

and Levoy [4] found that these errors can be reduced or

In recent years, noncontact scanning techniques based on eliminated by analyzing the time evolution of the reflected

laser systems have started to be used. Although not very light imaged onto the sensor of the digitizing system.

extended yet, the main advantage of these techniques is a Dorsch et al. [5] also verified the error introduced by

high speed for point acquisition that allows for capturing speckle noise in the distance measurements by laser

thousands of points per second. An extraordinary reduction triangulation. Others, like Forest and Salvi [6], proposed

the use of digital filtering techniques in order to reduce the

speckle noise when different surfaces with different optical

E. Cuesta : J. C. Rico : P. Fern ndez : D. Blanco : G. Vali o properties and different noise levels are scanned.

Department of Manufacturing Engineering, University of Oviedo,

Other researchers studied the influence of reflection

Campus de Gij n,

errors and scattering of the laser light during the scan [7].

33203 Gij n, Asturias, Spain

This way, they measured spheres with different reflectivity,

e-mail: ********@******.**

color, and roughness and used sensors with different

E. Cuesta

detectors: simple position-sensitive diodes and charge-

e-mail: *********@*****.***

Int J Adv Manuf Technol (2009) 43:1157 1166

1158

observed. Moreover, works made in this field are still

coupled device (CCD) arrays as well as diode arrays.

limited, mainly by using commercial scanning systems.

Measurements carried out showed a strong dependency of

Most research use experimental systems, making practical

the measurement uncertainty on the orientation of the surface

application of results difficult.

and the scattering characteristics of the objects to be

In the present work, a commercial laser scanning system

measured. They proposed the use of more than one detector

has been used for analyzing the influence of the surface

to find the best signal to be used to give the distance from

roughness in the scanning quality. Gauges with different

the object. By taking into account the errors caused by

roughness and made by different manufacturing processes

scattering, some authors like Wang et al. [8] proposed an

have been tested. Since the roughness gauges were flat, the

optical technique for measuring the surface roughness of a

set of points captured onto a plane as well as their spatial

flat surface based on a direct correlation between the

dispersion with regard to the best-fit plane have been used

roughness and a characteristic value of laser scattering.

as indicators of quality of the scanning process.

Feng et al. [9] have analyzed and characterized the

The results of the tests provide some recommendations

digitizing errors of a commercial laser scanner. The

about the methodology and working conditions for scan-

objectives have been to identify the primary scanning

ning each type of surface.

process parameters that contribute to the digitizing errors

and to establish an empirical relationship to accurately

predict the digitizing errors for typical laser scanning

operations. In particular, the authors analyzed the effect of

2 Characteristics of laser stripe systems

the scan depth and the projected or view angle on the

process precision. Likewise, they proposed a bilinear model

A laser stripe system (LC-50 by Metris ) has been used in

to estimate and correct the effects of these two parameters.

this work. Similar to the traditional inspection and scanning

Godin et al. [10] also related the scan depth with changes in

process using contact-type measuring devices, a relative

measurement distance by the laser scanning system on

movement between the laser system and the surface is

marble surfaces (translucent material). Similarly, they have

necessary to carry out the scanning process. This movement

noted that the noise observed in the measurement was

consists not only of linear displacements but also of

strongly related to the surface finish.

orientation changes either of the laser head or the surface.

The triangulation sensors convert the change of a spot

Hence, the laser system used in this work has been installed

position on the detector into an object displacement on the

onto the motorized head of a CMM (Global Image by

assumption of perfect spot point. However, there is a light

Brown and Sharpe). This way, three possible linear

intensity distribution (LID) on the detector. Kim et al. [11]

displacements (X, Y, Z) are available in combination with

reduced errors of optical systems based on triangulation by

two rotations (A, B) of the machine head (PH10MQ). Since

means of algorithms capable of compensating LID captured

the head orientation changes are discrete (7.5 ), 720

by the system sensor. On the other hand, authors like Lee

feasible orientations of the laser system can be adopted

and Chang [12] developed a laser digitizing sensor with four

with regard to the scanning surface.

position-sensitive device detectors in order to overcome the

In laser scanning sensors, an incident laser beam of

defects of the triangulation principles. By means of these

known width is projected onto a part and the stripe

four detectors, they established the error data between the

generated on the surface is detected by a CCD camera.

displacement and inclination angle of the measured surface

By means of image-processing techniques and the triangu-

in order to improve the measurement accuracy.

lation principle, 3D coordinates of the surface points are

Other works analyzed the influence of temperature on

acquired. Figure 1 shows the main parameters of this type

the positioning errors of both the machine and the

of laser system. Some of these parameters are imposed by

measuring laser device mounted on the machine head. For

the system manufacturer:

example, Harris and Spence [13] proposed an algorithm for

Depth of field: range of distance from the laser source

compensating the pose position and angle of a laser

within which CCD can acquire points on the scanned

digitizer mounted on a CMM. To implement the integrated

surface

error compensation, the scan plane coordinates and the

Scan width: width of the laser beam measured in the

CMM axis scale positions were recorded simultaneously in

half position of the depth of field

real time and compensated for pose (position and angle)

Field of view: region within which CCD can acquire

obtained by image processing. They obtained a 65% to

points on the scanned surface. It is defined by the depth

90% improvement in the accuracy of the data.

of field and the scan width

As a result of the aforementioned research, a high

Standoff distance: distance from the laser source to the

number of variables and factors that influence the charac-

reference surface located in the half zone of the field of

terization of typical errors in laser scan systems can be

Int J Adv Manuf Technol (2009) 43:115*-****-****

Fig. 1 Parameters of the scan-

ning laser system

view. This distance controls the laser beam to be coincides with the maximum power of the laser beam

intensity (1 mW). In other sensors also based on

focused on the reference surface

triangulation techniques the laser light intensity is

Triangulation angle: angle between the incident and the

reflected laser beam when they are focused on the replaced by the exposure time. In both cases, several

reference surface experiments show their influence on the scanning quality.

Angle of the field of view : angle of the laser beam When laser intensity is too high, a distortion of the spot size

appears on the scanned surface causing positioning errors

of the acquired points (saturated points). Different experi-

Other parameters of the laser system may be controlled

ments have proven that there exists a percentage value of

by the user and they have also been analyzed in this work:

the maximum laser intensity above which the CCD sensor

View angle : angle between the incident laser beam starts to acquire saturated points. For a white spherical

and the surface normal of a point being measured surface, this value was found to be 23% of full power. The

Laser light intensity laser system used in this work applies a filter that can

Stripe interval: distance between laser stripes remove the saturated points as well as improve the

Point interval: distance between points within each dispersion range of the acquired points. Figure 2 illustrates

stripe the positive effect of this filter on the dispersion range. The

Illumination use of any external polarizing filter has not been considered

to maintain the original features of the sensor invariable.

2.1 View angle

2.3 Point and stripe intervals

The head orientation determines the view angle and then

The intervals of the points on a single laser stripe and

the zones of the scanned surface that can or cannot be

between two consecutive laser stripes affect the total

acquired depending on its greater or smaller inclination.

The highest number of points acquired is reached when the

laser beam is perpendicular to the surface. As head

direction moves away from the surface normal direction,

the number of points captured is reduced. This way, a limit

orientation (limit view angle) for which laser head does not

acquire points may be defined. Consequently, scanning

tests are recommended to be carried out with a perpendic-

ular laser head orientation.

2.2 Laser light intensity

For the laser system used in this work, the light intensity

scale varies from 0% to 100% where the highest value Fig. 2 Filtering influence on point cloud dispersion range

Int J Adv Manuf Technol (2009) 43:1157 1166

1160

number of acquired points and therefore the detail level of light stripe captured by CCD in the absence of external

the scanned surface (Fig. 3a). These parameters represent light sources, whereas Fig. 4c shows the same laser light

the resolution level of the laser scanning system and both projection when the surface scanned is illuminated with the

have influence on the point acquisition speed. In particular, halogen light. In consequence, scanning tests are recom-

the maximum resolution of the LC-50 Metris system is mended to be carried out in absence of external light.

10 m measured in the motion direction of the sensor

(minimum diameter that can be recognized by the CCD

camera) and 100 m between points of a stripe line. For 3 Conditions for the experiments

example, in Fig. 3b, a point interval of 0.2 mm produces

198,500 points in 11 s with a high scanning quality. According to the results of the tests described in the

Otherwise, when the interval is 2 mm, the number of previous section and in order to analyze the influence of the

acquired points decreases to 2,170 points and the scanning surface roughness in the scanning quality, the configurable

time is lower than 1 s. However, the scanning quality is parameters of the laser system were adjusted as follows:

substantially poorer. In consequence, scanning tests are

All tests were carried out with the laser device

recommended to be carried out with a high-resolution

orientation perpendicular to the scanned surface.

number of points.

Since the reference surface was located in the half zone

of the field of view, the position of the surface to be

2.4 Illumination

scanned was also adjusted to be coincident with the

reference one.

Other tests have demonstrated the influence of illumination

In order to avoid light registration different to that from

on the scanning process. Since the commercial illumination

the laser source, all tests were carried out in the absence

sources commonly used emit light in a wide spectrum of

of ambient illumination.

frequencies, a part of the energy emitted by these light

Both points and stripe intervals were adjusted to

sources may be in the range of wavelengths of the laser

0.1 mm. The density of points acquired (0.1

system ( =635 650 nm). Moreover, they are in the

0.1 mm) was sufficient to appreciate the effects of

theoretical range of wavelengths accepted by the CCD

roughness on the scanned surface.

sensor and, therefore, they will introduce a percentage of

Roughness gauges of Rugotest type (TESA ) were

energy in the image captured that do not come from the

tested, classified into roughness grades from N1 to N11

laser light emission. This way, data reading and interpreta-

(ISO/R468 and ISO2632-1.2) and related to different

tion are modified and consequently they will affect the

processes: turning, planing, milling, electrical-discharge

calculation of accuracy. As an example, Fig. 4a shows the

machining (EDM), reaming, lapping, shot-blasting, shap-

theoretical emission spectrum for a light source of halogen

ing, and grinding. Other roughness gauges manufactured by

type. It stands out the range of wavelengths in which the

forming processes like deep-drawing, extrusion, or rolling

halogen light spectrum overlaps the laser light spectrum

were also tested.

used in the work. Figure 4b shows the aspect of the laser

Fig. 3 a Point and stripe inter-

vals for the LC-50 Metris laser

system. b Influence of point and

stripe intervals on scanning

quality

Int J Adv Manuf Technol (2009) 43:115*-****-****

further analysis. The process of trimming the original point

cloud to obtain this region was carried out in several stages.

First, as can be seen in Fig. 5a, a rigid mask with a window

was set over the roughness gauges, which provided a

scanning area of 14 7 mm. In order to avoid the capture of

points outside the window, the mask was painted in bright

black color. This mask also had attached three white

spheres which were scanned simultaneously to the rough-

ness gauge. The centers of these spheres were used to create

a reference coordinate system for aligning the control

rectangle (Fig. 5b). Then, by using this control rectangle,

the point cloud was trimmed. This control rectangle was

slightly smaller than the mask window. Therefore, the

scanned points close to the window borders were eliminat-

ed and, consequently, feasible disturbing effect on the point

cloud captured was avoided.

4 Experiments

Two types of tests were carried out. First, the influence of

laser intensity on roughness and the manufacturing process

of each gauge were analyzed. The objective of these tests

was to determine an optimum value of laser intensity for

scanning each gauge by considering different roughness

and processes. The second type of tests analyzed the quality

of the points captured in the scanning. Taking into account

that the roughness gauges were flat, the flatness of the

points captured to a plane could be used as a measure of

quality.

4.1 Influence of laser intensity

Once the point and the stripe intervals were fixed and the

dimensions of the control rectangle defined, the maximum

number of points that the system could capture was known.

However, low values of laser intensity led to a lack in the

capture of points since their images on the CCD were weak

Fig. 4 a c Influence of a halogen light source on an image captured

and, therefore, they were discarded by the system. On the

by a CCD

other hand, too high values of laser intensity caused

saturation on the CCD. This means that the point images

Roughness grade N represents a range of values for the were bigger than they were when using appropriate laser

parameter Ra. All of the roughness gauges were verified by intensity and, consequently, the system mixed the adjacent

using a roughness tester (Rugotest T10 from TESA) in points into only one point so that the number of points

order to determine an accuracy measure. Apart from Ra, captured was lower.

other parameters such as Rq, Rt, Rz, Rsm, etc. were For example, for a roughness gauge N10 made by

measured as well as the primary (P), roughness (R), and planing, Fig. 6 shows the relation between the laser

waviness (W) profiles. intensity and the number of points captured. Two interest-

In order to compare the number of points digitized on ing points stand out in this graph: the minimum intensity

each roughness gauge, the point clouds obtained must be of necessary to capture points and the intensity where the

the same dimensions. For this reason, a control rectangle number of points captured is maximum, which was called

optimum intensity. In this case, the first point corresponds to

was defined, so that all the points outside this region were

eliminated whereas the points inside were considered for 16% of maximum laser intensity to capture the initial

Int J Adv Manuf Technol (2009) 43:1157 1166

1162

Fig. 5 a Black mask with a

window of 14 7 mm set on a

roughness gauge to be scanned.

b Control rectangle for trimming

the point cloud captured

points. As it can be seen in Fig. 6, there is a lack of points Figure 7 shows similar graphs but now when considering

inside the control rectangle for the point cloud obtained with the same manufacturing process for different roughness

this laser intensity. The optimum intensity for this roughness values. All graphs are qualitatively similar, showing an

gauge was 22%. The highest number of points was captured optimum value of the laser intensity and a slight decrease

for this laser intensity and the control rectangle was plenty of (even stabilization) of the number of points captured after

points in its whole extension. Laser intensities over the this value.

optimum intensity cause saturation in the CCD sensor so that Frequently, the shape of a curve makes it difficult to

determine the optimum intensity so that an interval of

the number of points captured is reduced.

optimum intensities must be defined. In this interval, the

The behavior showed in this graph was very similar to

the rest of surfaces analyzed in this work which consisted in number of points captured slightly increases or even

several samples of different roughness obtained by different remains constant. For example, in Fig. 7 for planning

manufacturing processes (Figs. 6, 7, and 8). gauges, there exists a very clear optimum laser intensity for

Fig. 6 Relation between laser

intensity and number of points

captured for a roughness gauge

N10 manufactured by planing

Int J Adv Manuf Technol (2009) 43:115*-****-****

Fig. 9 Intervals of optimum laser intensity for different roughness

Fig. 7 Relation between laser intensity and number of points captured

gauges manufactured by planing

for different roughness gauges manufactured by planing

cases, the light reflectivity effect is predominant over the

ISO N6 curve, whereas the optimum value is ambiguous for roughness characteristics of the surface.

ISO N11 roughness gauge and therefore an interval of Figure 11 summarizes the optimum laser intensity for all

optimum intensities must be defined. In some manufactur- the processes analyzed in this work considering their

ing processes, the interval of optimum intensities is very characteristic range of roughness. Table 1 gathers the

narrow or even is reduced to a point which coincides with optimum value for each process as well as the width of

the optimum intensity, such as the case of EDM, as it can the optimum laser intensities interval, as recommended for

be seen in Fig. 8. The interval of optimum laser intensities use in practice.

for other processes is very wide and sometimes it exceeds

the maximum laser intensity of the system, as it happens for 4.2 Quality of points captured

flat grinding (Fig. 8).

Figure 9 shows the optimum intensities and the The flatness of all roughness samples was measured by

associated intervals of optimum intensity for the process means of a contact CMM. In all cases, flatness resulted

considered before. It can be observed that a higher significantly lower (more than 50%) than the one obtained

roughness requires a higher value of optimum laser by laser scanning. In fact, the high dispersion on the

intensity. Furthermore, the size of the optimum intensity location of the captured points into the rectangle control

interval also enlarges when roughness increases for the (Fig. 5b) was used as a measurement of the laser scanning

same machining process. These behavior is common for all quality. For flatness measurement of each point cloud

machining processes with medium high roughness such as captured by laser, best-fit techniques (RMS) were applied to

determine a best-fit plane. The flatness value was defined as

milling, planning, EDM, shot-blasting, or shaping (left

curve of Fig. 10). However, the opposite behavior was the interval between two parallel planes in which the set of

points are included and located closer to the best-fit plane.

observed for finishing process with low roughness such as

flat grinding (right curve of Fig. 10) or lapping. In these last By filtering the most distant points, it was possible to assure

Fig. 8 Laser intensity used for scanning gauges with identical Fig. 10 Values of optimum intensity and intervals for roughness

roughness manufactured by EDM and flat grinding surfaces (EDM) and burnished surfaces (flat grinding)

Int J Adv Manuf Technol (2009) 43:1157 1166

1164

As an example, 0.019 mm was obtained by contact as

the flatness value for a shot-blasting gauge. When using

laser scanning, the flatness was 0.172 mm and it was

improved down to 0.094 mm (54% lower) by filtering only

2% of the points captured. A similar test was applied to a

milling gauge with 0.053 mm of flatness measured by

contact. The flatness obtained by laser scanning was

improved from 0.315 to 0.190 mm (60% lower) also by

filtering 2% of points. Similar effects were observed for

other processes and roughness regardless of laser intensity

used in the scanning process. Although the accuracy

achieved was always lower than that obtained by contact

inspection, it could be suitable for some applications such

as reverse engineering.

Another relevant effect detected during the experiments

was that the scanning system used in this work modified the

Z position of the point cloud and its best-fit plane when

using different laser intensities. This effect was more

significant when using laser intensities below the optimum

value, that is, with incomplete point clouds.

For the case of a gauge made by shot-blasting, Fig. 13

shows how the location of Z coordinate varies with the

intensity. In the graph, the reference corresponds to the

Fig. 11 Suggested values of optimum laser intensity for different

optimum intensity for each sample. When higher laser

roughness gauges obtained by different processes

intensity was used, the point clouds appeared in a lower

position than that corresponding to the optimum intensity.

a better flatness value. Several levels of filtering were On the contrary, when using laser intensity lower then the

applied in order to analyze the flatness improvement. optimum, the point clouds appeared in a higher position.

Figure 12 shows the variation of the measured flatness Another complementary effect observed was that the

with regards to the proportion of filtered points. It can be samples of highest roughness (N11) were more sensitive to

observed that the most important deviation of flatness is this Z displacement than other roughness grades (N6).

caused by a reduced number of points (less than 5%) and, An easy way to eliminate this effect is to use the same

by filtering them, dispersion of the rest of the points laser intensity for scanning the whole part. When more than

decreased to 50% with regards to the best-fit plane. one laser intensity will be required, it will be better to work

Table 1 Recommended values and intervals for optimum laser intensity (% of full power)

Roughness ISO N

Processes 1 2 3 4 5 6 7 8 9 10 11

100*-****-**** 100*-**-**-**-** 46 14 52 14

Flat grinding 2 2

0 0 0 0 0 0

87-13-971*-***** 100**-**-**-**-** 32 8 38 8

Cylindrical grinding 6 5 4 2 2

35 5 29 2 19 6

Lapping 0 0 0

13 *-**-*-**-*-**-*-** 2 30 4

Horizontal milling 2 3 1 2

0 0

19 *-**-*-**-*-**-*-** 14 30 14

Vertical milling 2 2 2

0 0 0

19 *-**-*-**-*-**-*-** 8

EDM 1 2

0 0 0

14 *-**-*-**-*-**-*-** 6 29 8

Planing 0 0 0 0 0 0

19 *-**-*-**-*-**-*-** 3 25 10

Shot-blasting (sharp grain) 1 1 3 2 3

0

16 *-**-*-**-*-**-*-** 6 44 12

Shot-blasting (spherical grain) 1 1 1 2 4

0

19 2 16 2 17 2

Shaping hand filing (crossed) 0 0 0

13 1 13 1 5 1

Shaping hand filing (straight) 0 0 0

24 2 16 3

Sheet metal extrusion 0 0

22 1 19 1

Sheet metal deep-drawing 1 1

19 1 16 3

Sheet metal rolling 1 0

Int J Adv Manuf Technol (2009) 43:115*-****-****

Fig. 12 Variation of measured

flatness for two different rough-

ness gauges, with regard to the

proportion of filtered points

with laser intensities greater than the optimum value to in Fig. 11 as recommended values to use in practice.

moderate (Fig. 13) this undesired effect. Table 1 also gathers the recommended intervals of optimum

laser intensities when a unique value of optimum intensity

cannot be determined.

In general, the interval size of optimum laser intensities

5 Conclusions

changes with roughness for any machining process. For

machining processes of medium high roughness grades

The influence of laser intensity in the scanning of gauges

manufactured by different processes and having different (ISO N5 to ISO N12), the interval gets wider as roughness

roughness grades has been analyzed in this work. Initial increases, whereas, for machining processes of lower

experiments have been carried out to establish the best roughness grades, the effect is the contrary (Fig. 10).

conditions for this analysis and to avoid external influences Gauges with a burnished finishing (grinding and lapping)

such as the optimal orientation of the laser device, the depth show reflectivity problems and, then, high laser intensity is

of field value, the illumination, and the number of points required for acquiring an adequate number of points. Even

and stripe intervals. in these cases and for samples with very low roughness

Tests have demonstrated that there exists a value of grades (ISO N1 to ISO N3), the interval of optimum

optimum laser intensity which corresponds to the maximum intensity grows significantly so that an optimum intensity

number of points captured (from Figs. 6, 7, and 8). value cannot be determined (Fig. 11). Consequently,

The insights that represent these optimum values or reflecting materials are not suitable for laser scanning

intervals for each process and for each roughness are shown whereas rough materials (e.g., EDM gauges) are.

Since all roughness gauges tested were flat, the position

of points captured to a plane was used as a quality

measurement of the points captured in the scanning. It

seemed initially that there was a high dispersion of the

points captured, but it was finally demonstrated that it was

caused by a low number of points, less than 5% in all cases.

By filtering these points, an improvement of 50% of

flatness was achieved.

Another effect detected during the experiments was that

the scanning system used in this work modified the Z

position of the point cloud and its best-fit plane when using

different laser intensities. This effect was more significant

when using laser intensities below the optimum value, that

is, with incomplete point clouds (Fig. 13). The displace-

ment in Z coordinate was more important as roughness

Fig. 13 Variation of Z position of the point cloud captured by the LC-

grade increases except for finishing processes.

50 Metris laser system with regard to laser intensity

Int J Adv Manuf Technol (2009) 43:1157 1166

1166

4. Curless B, Levoy M (1995) Better optical triangulation through

Taking this into consideration, it is recommend to scan all

space time analysis. In: Proceedings of the 5th International

the surfaces of the part by using a unique value of intensity.

Conference on Computer Vision, Boston, MA, USA, pp 20 23

When this cannot be possible, similar intensities must be used 5. Dorsch RG, H usler G, Herrmann JM (1994) Laser triangulation:

preferably above the optimum laser intensity (saturation zone). fundamental uncertainty in distance measurement. Appl Opt 33

(7):1306 1314

In general, it could be said that finishing processes show

6. Forest J, Salvi J (2004) Laser stripe peak detector for 3D scanners.

an opposite behavior to the machining and sheet-metal-

A FIR filter approach. In: Proceedings of the Pattern Recognition,

forming processes as was shown in Figs. 8 and 10. 17th International Conference on Pattern Recognition (ICPR 04),

Cambridge, UK, 3, pp 646 649.

Finally, it is important to emphasize that the results

7. H ser D, Rothe H (1998) Robust averaging of signals for

obtained in this work can be applied to other systems based

triangulation sensors. Meas Sci Technol 9(7):1017 1023

on triangulation replacing the intensity variable by the doi:10.1088/0957-0233/9/7/002

exposure time. The qualitative results will be similar but the 8. Wang SH, Tay CJ, Quan C, Shang HM, Zhou ZF (2000) Laser

quantitative ones will depend on each sensor and on its integrated measurement of surface roughness and micro-displace-

ment. Meas Sci Technol 11(5):454 458 doi:10.1088/0957-0233/

constructive characteristics.

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9. Feng H-Y, Liu Y, Xi F (2001) Analysis of digitizing errors of a

Acknowledgements This work is part of the results obtained in a laser scanning system. Precis Eng 25(3):185 191 doi:10.1016/

research project supported by the Spanish Education and Science S0141-6359(00)00071-4

Ministry (MEC-04-DPI2004-03517) and FEDER. 10. Godin G, Beraldin J-A, Rioux M, Levoy M, Cournoyer L (2001)

An assessment of laser range measurement on marble surfaces. In:

Proceedings of the 5th Conference on Optical 3D Measurement

Techniques, Vienna, Austria, pp 49 56

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