Verification of large CMMs - Artefacts and Methods. Eugen Trapet - Verification of... · Verification of large CMMs - Artefacts and Methods - Eugen Trapet, Spain ... - Quick review

Verification of large CMMs - Artefacts and Methods -

Eugen Trapet, Spain (Trapet Precision and ISM3D)

[email protected], www.trapet.de

Contents

- Quick review of ISO 10360-2

- Types of artefacts specifically useful for testing large CMMs

- Methods to extend the measurement range of artefacts

- Verifying corrections and maintaining corrections valid

- Conclusions

ISO 10360-2 - general rules

Measure 5 lengths in each of the specified lines of measurement

Measure these 5 lengths in each line 3 times

The maximum artefact length measured in each line must be >66% of the largest measurable length in the respective line

All lengths must be measured in a bi-directional way *)

The errors of all measured lengths must be smaller than the respective MPE

The repeatability must be smaller than the specified limit

*) if artefacts which allow bidirectional probing are not available, it is allowed to measure the errors due to bidirectional probing on separate artefacts and add them to the length measurement error (examples of non bidirectional standards of length: laser interferometers, ball beams)

ISO 10360-2 procedure in short

Measure 3 axis-parallel lines with zero-ram offset styli

Measure 4 corner-to-corner space diagonals with approximately zero ram axis offset styli

Measure 2 edge-to-edge plane diagonals in a plane parallel to the ram axis with ram axis offset styli (per default 150 mm offset)

On (large) CMMs where the longest axis is much longer than the other axes, it is recommended to measure additionally 2 corner-to-corner plane diagonals in a plane parallel to the ram axis and orthogonal to the longest axis, using styli which have no or little ram axis offset

Rules to deal with the uncertainty of the test

Use decision rules as stated in ISO 14253-1

Take into account artefact calibration uncertainty and drift

Take into account temperature influences as far as they are not attributed to the machine performance *)

Take into account alignment uncertainty and overlapping / joining uncertainty where needed

*) In case of a not-temperature-compensating CMM and when using steel artefacts no such influences need to be accounted for; on a CMM with object temperature compensation, normally the uncertainty of the CTE must be accounted for; on a CMM with no temperature compensation and when using low-CTE-artefacts account for: - thermometer uncertainty - temperature assessment uncertainty in situ - uncertainty of the CTE of the artefact

Suited artefacts for large CMMs

Gage blocks (normally up to 1 m length)

Step gages (normally up to 2 m length)

Ball beams and ball bars (normally up to 3 m, in some cases up to 5 m) *)

Disassemblable ball bars (up to 12 m) *)

Laser interferometer *)

If CTE of artefacts is < 0.000002 /K , then measure a 0.5 m gage block additionally (errors must be within specifications). On non-temperature-compensated CMMs: use “Virtual Steel” concept

*) additionally to be taken into account: bi-directional probing error, determined by the measurement of a sphere diameter or a gage block length in direction of the respective line of measurement

Step gages for the verification of CMMs according to ISO 10360-2 (2009)

Courtesy: KOBA

Ball beams for the verification of CMMs according to ISO 10360-2 (2009)

Here shown: ESCALON 2 m with precision joint on high accuracy CMM with 3 m maximum axis travel Courtesy: BIMAQ

3 different ways to large artefacts

1. Segmented ball beam:Calibrated bars between spheres; the sum of the length measurement errors of

the segments is very similar to length error of direct/total length: the difference

is only the cosine-error of the measured machine error, and not of the entire

measured length! The joining uncertainty per segment is <0.7 m. The

maximum length is >12 m, more than reached with any other artefact. The indi-

vidual elements can be calibrated on smaller reference measuring systems.

2. Overlapping by displacement of beam or by placing 2 or more beams in

series without precisely joining them and by adding the length measuring

error at the end of the prior position to the length measuring error at the begin-

ning of the following position.

3. Overlapping by precision joints between longer segments of several spheres

Each segment is calibrated individually. Segments can be used individually.

Typical segment lengths are 1.5 m to 2 m.

errorlength


Here shown: ESCALON ball beam 2 .7m on CMM with 10 m x 2 m x 1 m axis travel, 4 times stitching in X-axis by simple shifting

Courtesy: LOMG


Here shown: ESCALON ball beam 2 .7m on CMM with 10 m x 2 m x 1 m axis travel, Diagonal placement and measurement with offset stylus

Courtesy: LOMG

Large solid carbon fibre ball beam (“3D-ball beam”), up to 5 m

Courtesy: TRIMEK

Large multi-sensor ball beam


2 x 1.4 m with precision joint = 2.9 m

3 x 2 m displacing and stitching of 1 bar on a 5 m holder = 6 m

Disassemblable ball beams for the verification of large CMMs

Here shown: Disassemblable ball bar of 5 m length Courtesy: HEXAGON


Courtesy: ZEISS, Daimler Benz


Courtesy: Metronom

Here shown: disassemblable ball bar of 8 m length


Laser ball bar for the verification of CMMs according to ISO 10360-2 (2009)

Courtesy: Caterpillar

Laser & Calibration Products

Division

22-Nov-2004

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Slide 20

Laser diagonal tests - laser set-up

ML10 laser, and linear optics aligned via a swivel

mirror to a machine body diagonal.

Courtesy: ETALON

The Laser Tracer

on the fly measurement

Laser Tracer hardware

Special features of the Laser Tracer concept

Machine performance verification according

to ISO 10360-2 and ISO 230-2 ff: axial and space-diagonal

displacement measurements

Courtesy: ETALON

Basic test measurement lines according to ISO 10360-2

Stylus-offset length measurement test lines according to ISO 10360-2

Specific case “Long CMM” according to ISO 10360-2

Stylus-offset length measurement test lines according to ISO 10360-2 in case of HAMs

X1

X2

Y1

Z2Z1

Y2

Duplex Alignmenttranslation and rotation;desirable: scale factor,pitch, yaw and rollharmonization

Duplex specific error “Twin-Coupling” is checked by ISO 10360-2 procedure

Z

YZ

YY

Z

XY

Z

XY

Z

X Y

Z

X Y

Z

Specific errors of large HAMs, cross-table machines and gantries where the coverage by the ISO standards is less good

Specific choices of the test lengths for HAMs operated in duplex mode

Overlapping or stitching concept to test CMMs larger than the standard

masure these spheres with arm No 2in CSY created with arm No 1;measure overlap of pos 2-3 completelywith arm No 2 (both ball beam positions)

measure these spheres with arm No 1;measure overlap of positions 1-2 completely with arm No 1 (both ball beam positions)

L5

L4

L1L2L3

measure these spheres with arm No 1;measure overlap of positions 1-2 completely with arm No 1 (both ball beam positions)

masure these spheres with arm No 2in CSY created with arm No 1;measure overlap of pos 2-3 completelywith arm No 2 (both ball beam positions)

L5

L5

L4

L4

L3

L3

L2

L1

L1

L2

due to the fact thatthe common measuringvolume of both arms isin the centre of the machine and is very limited, the short lengthswill always be in the centre of the machine too ISO 10360-2 prescribes for HAMs that eac h test length

consists of one side of the standard being measured by the first arm and the other side by the second arm

without stitching

stitching 2 bar positions

stitching 3 bar positions(... and so on ...)

Overlapping or stitching concept to test CMMs larger than the standard, specific considerations for HAMs

Probing Direction

Probing Direction

Position 1 Position 2

Requirement of standards with bi-directional length representation (“standards of size”)

Rules for “converting” one-directional or centre-to-centre artefact measurements into bi-directional measurements

Measure the 5 lengths in in a given line of measurement in a uni-directional or centre-to-centre way, each length 3 times

Measure the length of a gage block or equivalent standard of size 3 times in direction of the measurement line concerned

Add length measurement errors obtained on gage block to length measurement errors obtained for the 3 repetitions of each of the 5 lengths

-8,0

-6,0

-4,0

-2,0

0,0

2,0

4,0

6,0

8,0

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Measu

red

Err

or

[µ

m]

Length [mm]

Example: Results from verification of large high accuracy CMM with ESCALON ball beam (without stitching)

Metrological Properties "Length Measurement Errors" Page

in defined Lines of Measurement" and "Probing Errors" 4 of

(Verification according to ISO 10360-2) 10

Measurement line 1 (parallel to the X-axis)

The following deviations from the calibrated lengths were measured:

Measured Lengths Uncert. max.perm. deviations measured

Meas 1 Meas 2 Meas 3 (k=2) MPEE E

[mm] [mm] [mm] [µm] [µm] [µm] [µm] [µm]

149,912 149,914 149,915 2,34 11,05 3,14 5,14 6,14

2699,614 2699,617 2699,618 4,74 28,90 25,68 26,68 28,68

5249,275 5249,273 5249,272 7,26 46,74 23,83 21,83 20,83

7798,913 7798,913 7798,913 9,11 64,59 -0,35 -0,35 -0,35

10348,580 10348,580 10348,580 10,64 82,44 4,46 4,46 4,46

[mm]

149,909

2699,589

5249,251

7798,913

10348,576

0

01.10.07

01/00/00

Calibrated

Lengths

-100,0

-80,0

-60,0

-40,0

-20,0

0,0

20,0

40,0

60,0

80,0

100,0

0 2000 4000 6000 8000 10000 12000

Me

as

ure

d E

rro

r[µ

m]

Length (mm)

Example: Results from verification of very large CMM with ESCALON ball beam with 4 position stitching

Example: Results from verification of very large CMM with disassemblable ball bar

Metrological Properties "Length Measurement Errors" Page

in defined Lines of Measurement" and "Probing Errors" 4 of

(Verification according to ISO 10360-2) 10

Measurement line 2 (parallel to the Y-axis)

The following deviations from the calibrated lengths were measured:

Measured Lengths Uncert. max.perm. deviations measured

Meas 1 Meas 2 Meas 3 (k=2) MPEE E

[mm] [mm] [mm] [µm] [µm] [µm] [µm] [µm]

499,5028 499,5028 499,5028 1,00 44,99 -21,70 -21,70 -21,70

998,9676 998,9676 998,9676 1,41 54,98 -11,63 -11,63 -11,63

1997,7789 1997,7789 1997,7789 2,00 74,96 15,84 15,84 15,84

3496,5888 3496,5888 3496,5888 2,65 100,00 32,38 32,38 32,38

4995,3157 4995,3157 4995,3157 3,16 100,00 33,68 33,68 33,68

[mm]

499,5245

998,9792

1997,7631

3496,5564

4995,2820

Calibrated

Lengths

0

01.10.07

01/00/00

-150,0

-100,0

-50,0

0,0

50,0

100,0

150,0

0 1000 2000 3000 4000 5000 6000

Me

as

ure

d E

rro

r [µ

m]

.

Length [mm]

Laser tracker verification with overlapping ball beam

Calibration certificat of disassemblable ball bar

Interim checking large CMMs

Courtesy photograph on right: UNIMETRIK Periodic checking large CMM in ISM3D

Interim checking large CMMs, Here: disassemblable tetrahedron 2m

Courtesy: METRONOM/AIMESS

Interim checking of large CMMs, Here: “Virtual Tetrahedron”

Courtesy: BalTec

Conclusions

The ISO 10360-2 (2009) provides rules for the verification of large CMMs, including duplex machines. One important rule is that the artefact (reference system) must have at least 66% of the length of the maximum machine travel. Artefacts suited for the standardized procedures are commercially available as well are accredited laboratories to calibrate them. One may choose between different concepts of reaching the required length: - stitching smaller artefacts mathematically to one bigger artefact (with and without auxiliary devices to place the artefact in the subsequent positions) - using precision-connections to assemble several artefacts to create one bigger artefract - using segmented artefacts where each individual length is separately calibrated and joined on a stable holder

Verification of large CMMs - Artefacts and Methods. Eugen Trapet - Verification of... · Verification of large CMMs - Artefacts and Methods - Eugen Trapet, Spain ... - Quick review

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