F.2.1 Principle
The principle of the length error assessment using concatenated lengths is to use two calibrated test lengths, traceable to the metre, to demonstrate compliance of the articulated arm CMM to the stated maximum permissible error of the combined length measurement provided by the manufacturer. The manufacturer may choose to provide specifications for the maximum permissible error of unidirectional length measurement, Euni,mpeE, the maximum permissible error of bidirectional length measurement, Epi,MPE, Or both.
F.2.2 Measuring equipment
The measuring equipment, which includes one or more calibrated test length, has the characteristics described in 6.4.2.
F.2.3 Procedure
As shown in Figure F.1, place a first calibrated test length so that the first end of the artefact lies within a spherical envelope covering 60 % to 100 % of the measuring range.
<a ~ 6 7 >> >
Key
1 first calibrated test length, E11, E12, E13 2 first end of first calibrated test length 3 second end of first calibrated test length 4 centre of articulated arm CMM
5 spheres about centre 6 60% of measuring range 7 100% of measuring range
Figure F.1 — View showing first calibrated test length
Measure the first calibrated test length three times using the elbow position indicated in Table 3. The same sequence of elbow positions is used for all three repeats.
As shown in Figure F.2, place a second calibrated test length so that the distance between the second end of the first calibrated test length and the first end of the second calibrated test length is not greater than 12 mm. Align the second test length to have the same nominal direction as the first test length.
The distance between the first end of the first calibrated test length and the second end seat of the second calibrated test length shall be at least 66 % of the measuring range. The second end of the second calibrated test length shall lie within a spherical envelope covering 60 % to 100 % of the measuring range.
10
11
Key
first calibrated test length, E11, E12, E13 first end of first calibrated test length second end of first calibrated test length second calibrated test length, E11, E12, E13 first end of second calibrated test length second end of second calibrated test length centre of articulated arm CMM
spheres about centre
Oo ON AD ƠI fF WN KF
66 % of measuring range 10 60% of measuring range 11 100 % of measuring range
Figure F.2 — View showing relative positions of first and second calibrated test lengths Measure the second calibrated test length three times using the elbow position indicated in Table 3.
The same sequence of elbow positions is used for all three repeats.
This procedure is required for each position indicated in Table 2 that requires concatenation.
F.2.4 Derivation of test results
Following the procedure of 6.4, the first test length is measured three times and the calibrated test length subtracted from each of the three measured values to obtain three signed length errors E41, E12, and E13. In these expressions, the first subscript represents the number of the test length (first or second), and the second subscript indicates the number of the repetition (first, second, or third). The errors £14, Ej2, and E13 may represent Eni, Epi, or both, according to the manufacturer’s specifications.
The second test length is likewise measured three times and the calibrated test length subtracted from each to obtain three signed length errors E21, E22, and E23.
Three concatenated length errors are calculated using Foi = F141 + E21, Ec2 = F12 + E22, and Ec3 = E143 + E23. Each of the concatenated length errors may be a unidirectional length measurement error, Eyni, a bidirectional length measurement error, Fpj, or both Eyni and Epi according to the manufacturer’s specifications. Note that the three repetitions are matched. The first repetition of the first test length is added to the first repetition of the second test length, and so forth.
NOTE1 The measurement errors for the first calibrated reference length and the second calibrated reference length are reported with the sign (+ or -) of the error. The sign is retained in subsequent additions to get the three concatenated length errors.
NOTE2 The concatenation method of this annex typically overestimates the error that would have occurred with a single calibrated test length spanning 66 % of the measuring range. The intermediate nest position provides an additional source of error because of non-repeatability of the measurement system.
F.2.5 Test value uncertainty
For the three measurements of the first calibrated test length, calculate three corresponding signed length errors.
The evaluation of the test value uncertainties is to be carried out for each test position of the calibrated test length.
The test value uncertainty associated with the concatenation method depends on the calibrated test lengths used in the procedure. If a different calibrated test length artefact is used on stage 2 of the concatenation than on stage 1 then the test value uncertainty includes the RSS (root-sum-of-squares) of the two uncertainties. If the calibrated test length used is stage 2 of the concatenation method is the same artefact as stage 1 then the test value uncertainty includes the arithmetic sum of the uncertainties associated with each calibrated test length measurement. The uncertainty contribution from the action of staging itself, i.e. misalignment of the artefacts relative to the line between the start and end nests, is evaluated for each stage of the measurements:
u(E) | is the standard uncertainty of length measurement error;
us1(E) is the standard uncertainty of length measurement error for the first test length;
Us2(E) is the standard uncertainty of length measurement error for the second test length.
The general measurement uncertainty contributors are:
u(E) = ye (e,4))+u" (=„)+ u^ (e,)+u? (Eatign ) + u^ (Eee) + u^ (Eariee )
where
u(Ecal) is the calibration standard uncertainty;
u(Eq) is the standard uncertainty due to CTE;
u(et) is the standard uncertainty due to temperature during measurement;
u(Ealign) is the standard uncertainty due to alignment (in the concatenation method, the mis- alignment is that of the calibrated test length relative to the line between the starting nest and the ending nest of the measurement procedure);
u[Efix) is the standard uncertainty due to fixturing;
u(Earift) is the standard uncertainty attributed to changes in the calibrated test lengths.
NOTE The standard uncertainty due to CTE, u(€q), and temperature, u{(et), are zero for either of two cases:
(1) no artefact temperature compensation is used or (2) artefact temperature compensation is provided as part of the articulated arm test system. The standard uncertainty due to CTE, u(€,), and temperature, u(€), are not zero when temperature compensation, which is not part of the articulated arm test system, is applied by the operator.
The expanded uncertainties (k = 2) for the two artefact stages are
U s4 (E) — 2 lu (=ôm ) + ut (Ê„ ) + ut (e, ) + ut (ign + ut (Êz„: ) + ut (Eann )
_ 2 2 2 2 2 2
Uso (E) = 2 lu (ea) Tu; (£„ +; G +; (atign + Up (nxt +; (anit
The test value uncertainty associated with the concatenated test length is
_ if the first calibrated test length is the same as the second calibrat-
U(E)=Usi(E)+Us2(E) ca test length, and
2 2 if the first calibrated test length is different than the second cali-
U(E) = \U§i (E) +Ùs; (E) brated test length.
Annex G (informative)
Optional probing articulated size and forms errors
G.1 General
A method for determining articulated location errors is described in 6.3. By mutual agreement, two additional errors may be calculated using the data collected in the test procedure of 6.3:
probing articulated size error, Psize.sph.5x5:Art:Tact.AArm, and probing articulated form error, Porm.
Sph.5x5:Art:Tact.AArm: