Renishaw plc · LSE:RSW
Renishaw — Technical Presentation (August 2018)
28 slides from Renishaw's technical presentation, Aug 20, 2018
Slide 1: Laser diagonal testing
Laser diagonal testing H-5650-2056-01-B 20/08/2018 1
Slide 2: Introduction
Introduction • This presentation explains how Renishaw laser calibration systems can be used to check machine positioning performance along machine diagonals, in accordance with the B5.54 and ISO 230-6 standards. • It also explains the strengths and weaknesses of this method of machine performance e
Slide 3: Laser diagonal tests - B5.54 and ISO 230-6
Laser diagonal tests - B5.54 and ISO 230-6 • Laser diagonal tests for machining centres are described in both ASME B5.54 (2005) and ISO 230-6 (2002) standards. • In these tests, a laser interferometer is used to measure the linear positioning accuracy of the machine as it 6 face diagonals* 4 body di
Slide 4: Diagonal measurement equipment and software
Diagonal measurement equipment and software • A laser mounting plate is available from Renishaw which allows the XL-80 laser, swivel mirror, beam steerer and linear measurement optics to be mounted directly on the machine to simplify alignment. • XCal-View software includes diagonal measurement anal
Slide 5: Test set-up
Test set-up • The XL-80 laser can be mounted directly to the machine using the mounting plate. • The laser beam is aligned to the face or body diagonal using the swivel mirror and laser beam steerer. • The figure shows the laser system aligned to a machine body diagonal. • Mounting the laser on the
Slide 6: Data collection
Data collection • A number of equi-spaced target positions are defined along each body diagonal. • The machine is programmed to move along the Equi-spaced diagonal from one target position to the next. target positions along a body • The laser measures the linear positioning error at diagonal each t
Slide 7: Data analysis - stage
Data analysis - stage 1 • The data gathered for each diagonal is analysed separately in accordance with ISO 230-6 to give a bi-directional systematic positioning error E, and a reversal error B for each diagonal, as follows; – The mean forward (Xi↑) and mean reverse (Xi↓) positioning errors are calc
Slide 8: Data analysis - graphical representation
Data analysis - stage 1 - graphical representation B = 3.7µm E = 7.4 µm E = The bi-directional systematic positioning error of the diagonal B = The reversal error of the diagonal 11/09/2018 8
Slide 9: Data analysis - body diagonals
Data analysis - body diagonals - stage 2 • In the case of body diagonal measurement, the previous analysis will yield four values for the systematic positioning error (E1,E2, E3, E4) and four values for the reversal error (B1,B2, B3, B4), one for each diagonal. • The worst case results for E and B a
Slide 10: Data analysis - body diagonals - final report
Data analysis - body diagonals - final report 11/09/2018 10
Slide 11: Data analysis - face diagonals
Data analysis - face diagonals - stage 2 • In the case of face diagonal measurement, the previous analysis will yield two values for the systematic positioning error (E1(ab),E2(ab)) and two values for the reversal error (B1(ab),B2(ab)), on each face, where (ab) represents the plane of test (XY, YZ o
Slide 12: Data analysis - face diagonals - final report
Data analysis - face diagonals - final report 11/09/2018 12
Slide 13: Squareness analysis
Squareness analysis • ISO 230-1 2012 (in section 10.3.2.6) states that it is also possible to calculate the non-squareness between axes using face diagonals*. Considering a test in the XY plane as an example: • If X and Y are the programmed travel lengths along the X and Y axes, then the squareness
Slide 14: Squareness analysis
Squareness analysis • The accuracy of the squareness result is improved if: • The machine’s axes are of similar lengths (improves sensitivity and accuracy). – The graph shows effect of ±1 ppm and ±5 ppm shifts in laser reading on the accuracy of squareness results for various aspect ratio machines.
Slide 15: Squareness analysis
Squareness analysis • Accuracy of the squareness result is also improved if: • The diagonals start and finish at identical X, Y or Z co-ordinates as shown opposite. This ensures that the effects of other machine errors are eliminated. • Backlash is eliminated by moving in the same direction before e
Slide 16: Strengths and weaknesses
Strengths and weaknesses The following section describes some of the strengths and weaknesses of laser diagonal measurements 11/09/2018 16
Slide 17: Strengths and weaknesses
Strengths and weaknesses • ISO 230-6 2002 states: “Diagonal displacement tests allow estimation of the volumetric performance of a machine tool. Complete testing of the volumetric performance of a machine tool is a difficult and time-consuming process. Diagonal displacement tests reduce the time and
Slide 18: Strengths and weaknesses
Strengths and weaknesses • The strength of body diagonal testing is that this simple, quick Machine error Sensitivity test is sensitive to a wide range of different machine errors Linear displacement errors Yes using minimal equipment. Reversal errors Yes • However, this wide range of sensitivity is
Slide 19: Weaknesses
Weaknesses • This technical paper demonstrated the following: • Estimates of volumetric machine performance, which are based on diagonal tests alone, are unreliable. • The results of a diagonal test, in isolation, cannot be used as a reliable machine comparison index. • The reasons for this are summ
Slide 20: Laser diagonal tests - 2D example
Laser diagonal tests - 2D example • The weakness of the diagonal test is most easily understood by considering a simple 2D example first. • Consider a perfect 1 metre square planar machine. The travel of the 1.000000 m X and Y axes are both exactly 1 metre, and the machine contains no other position
Slide 21: Laser diagonal tests - 2D example
Laser diagonal tests - 2D example • Now imagine that the machine is distorted such that the X axis over- travels by 25 µm/metre, and the Y axis under-travels by 25 µm/metre. (Linear positioning errors of this magnitude are common in machines due to inaccuracies in the feedback system e.g encoder ten
Slide 22: Laser diagonal tests - 2D example
Laser diagonal tests - 2D example • Diagonal lengths of perfect machine Perfect machine Distorted machine = 1.4142136 m • Diagonal lengths of distorted machine = 1.4142136 m 1.000000 m 0.999975 m • The diagonal lengths are all the same (within 0.001 µm) • Both the perfect and the distorted machine s
Slide 23: Laser diagonal tests - 2D example
Laser diagonal tests - 2D example • It might be thought that this is a very special case, which only occurs on a 2D machine if the error in the X axis motion is exactly equal and opposite to the error in the Y axis motion. • This is not the case! • If any axis (or axes) shows an over-travel error wh
Slide 24: Laser diagonal tests - 3D example
Laser diagonal tests - 3D example • The table shows the simulated Error Machine A Machine B Machine C performance of three nominally identical machine tools with cubic 1 m3 volumes. X axis linear error (µm/m) 50 50 100 • Each machine has a different Y axis linear error (µm/m) 50 0 -50 combination of
Slide 25: Laser diagonal tests - 3D example
Laser diagonal tests - 3D example • Note the complete lack of correlation between Error Machine A Machine B Machine C the volumetric accuracy of these machines and their diagonal test results. Diagonal test result Ed (µm) 0 29 14 • Machine A has the worst volumetric accuracy, Volumetric accuracy* (µ
Slide 26: Machine comparison
Machine comparison • Because of this limitation ASME B5.54* now recommends the following tests to quickly estimate the performance of a three axis machine: • Recommended minimum test set 1. Contouring 2. Linear positioning 3. Diagonal 4. Precision performance test accuracy and displacement tests con
Slide 27: Conclusions
Conclusions 11/09/2018 RENISHAW& 27 apply innovation”
Slide 28: Conclusions
Conclusions • Laser diagonal tests can be used to measure the diagonal systematic deviation of positioning and reversal errors in accordance with B5.54 and ISO 230-6 standards. • Renishaw can provide suitable mounting hardware and software to simplify the process. • Laser diagonal tests are sensitiv