Off Axis Rotary User Manual
Contents
1. The following table shows an ideal set up for the offset calculation 1 Move the machine to the position where the interferometer and XR20 W are nominally closest Shown in the image below 2 Translate the linear axis so to maximise the signal strength 3 Manually record the machine rotary axis and linear axis positions and input them into Position 1 in the Calculate offset tab 4 Move the machine rotary axis to the other two positions re establish laser alignment and maximise the signal strength before recording the linear and rotary axis positions at each of them Then input the linear and rotary axis positions in the Offset calculation tab Positions 2 and 3 Note for the most accurate calculation of offset the two additonal positions should be as close to 180 apart as possible 5 Use the Calculate offset button to complete the offset calculation 6 Check the value produced is feasible for the hardware as set up an approximate check using a measuring tape and line of eye should be sufficient to highlight any gross errors Note If you are repeating a standard test with a known and standardised hardware setup then previously measured linear and angular positions can be inputted or recalled to calculate the offset M 9920 0307 02 13 RENISHAW 4 apply innovation 4 Generate the program On the Part program tab 1 Insert the program number in the Program ID fiel2. 1 arcsecond Ensure that angular misalignment E lt 0 025 or the TIR is lt 0 04 mm at a radius of 50 mm from the centre of rotation of the machine under test e Foran induced error to be less than 10 arcseconds ensure E lt 0 23 or the TIR is lt 0 4 mm at a radius of 50 mm from the centre of rotation of the machine under test The following drawing specifies the tolerance as a perpenidicularity which is more practical for hardware design required to achieve measurements within 1 arc second accuracy Note this does not consider any mathematical errors caused by the removal of the angular error in the linear axis only the result from the rotary axis part of the test aa AXIS HEAD MEN a MACHINE ROTATION AXIS MOUNTING BRACKET _ NO FITTINGS SHOWN 150 C XR2O W ROTATION AXIS WEASUREMENT BEAM M 9920 0307 02 19 RENISHAW 4 apply innovation It is equally important to consider the perpendicularity in both orientations as shown by the drawing below In some cases it may not be possible to achieve the mounting tolerance specified due to bracket geometry inaccuracies in bracket design or mounting setups As the error increases the induced error in the XR20 W measurement also increases The chart below shows the error from the XR20 W measurement that will be induced for a given parallelism tolerance Note depending upon the sign of this error the measurement may make an axis appear worse
3. from the beginning and gt gt from the end of the line leaving you with a line that will look like this RotaryAxisRollover gt true gt RotaryAxisRollover 4 Save the file and close the software for changes to take effect After restarting the software when the new custom controller is selected it will be in the 0 360 program generation format and no negative values will appear in targets or in the part programs M 9920 0307 02 24 RENISHAW amp apply innovation About Renishaw Renishaw is an established world leader in engineering technologies with a strong history of innovation in product development and manufacturing Since its formation in 1973 the company has supplied leading edge products that increase process productivity improve product quality and deliver cost effective automation solutions A worldwide network of subsidiary companies and distributors provides exceptional service and support for its customers Products include e Additive manufacturing vacuum casting and injection moulding technologies for design prototyping and production applications e Advanced material technologies with a variety of applications in multiple fields e Dental CAD CAM scanning and milling systems and supply of dental structures e Encoder systems for high accuracy linear angle and rotary position feedback e Fixturing for CMMs co ordinate measuring machines and gauging systems e Gauging systems for comparative measurement of
4. O R of the rotary axis This is required so that the machine control knows how far to move the linear axis for any given rotational move to avoid laser beam break Offset between centre of rotation for XR20 W and rotary axis This distance is automatically generated by the software from data collected using the setup procedure explained in the Offset calculation section M 9920 0307 02 4 RENISHAW amp apply innovation System components Off axis rotary software utilises standard XR20 W hardware and standard XL 80 hardware For details please consult the RotaryXL and LaserXL help To complete an Off axis rotary calibration the following equipment will be required e XL 80 laser system and LaserXL software e XR20 W rotary axis calibrator and RotaryXL software e Angular optics kit e Off axis rotary software In addition the XR20 W s axis of rotation must be mounted parallel to the axis of rotation under measurement Renishaw can provide the XR20 W 90 bracket to achieve this requirement or the user can design their own fixturing Design suggestions and specifications can be found in the mounting hardware section Safety A Warning This software generates CNC part programs that could cause a machine to collide or malfunction Generated part programs must be checked by experienced machine tool programmers before use All programs should be checked before running and performed at a low feed for the first time The
5. XR20 W rotary axis calibrator system is designed to be used for testing machine tools As such the user will need to prepare and run a part program which moves the machine as required DO NOT ROTATE THE SPINDLE It is assumed therefore that the user is thoroughly familiar with the operation of the machine tool and its controller and knows the location of all emergency stop switches Also if it is necessary to operate the machine with the guards or any safety feature removed or disabled it is the responsibility of the operator to ensure that alternative safety measures are taken in line with the machine manufacturer s operating instructions or relevant codes of practice Safety procedures should be in accordance with the user s risk assessment The XR20 W device works in conjunction with a Renishaw Laser System Before using the laser system please read the safety section of the Laser Measurement System Manual The XR20 W can reflect the laser beam from the laser around the room as it rotates Consideration should be given to other users working in the area If this equipment is used in a manner not specified by the manufacturer the protection provided by the equipment may be impaired M 9920 0307 02 5 RENISHAW amp apply innovation Getting started To complete a calibration of the rotary axis off axis it is necessary to perform a number of steps in sequence These can be summarised as follows Setting up 1 Set up hardware P
6. machined parts e High speed laser measurement and surveying systems for use in extreme environments e Laser and ballbar systems for performance measurement and calibration of machines e Medical devices for neurosurgical applications e Probe systems and software for job set up tool setting and inspection on CNC machine tools e Raman spectroscopy systems for non destructive material analysis e Sensor systems and software for measurement on CMMs e Styli for CMM and machine tool probe applications For worldwide contact details please visit our main website at www renishaw com contact RENISHAW HAS MADE CONSIDERABLE EFFORTS TO ENSURE THE CONTENT OF THIS DOCUMENT IS CORRECT AT THE DATE OF PUBLICATION BUT MAKES NO WARRANTIES OR REPRESENTATIONS REGARDING THE CONTENT RENISHAW EXCLUDES LIABILITY HOWSOEVER ARISING FOR ANY INACCURACIES IN THIS DOCUMENT 2013 2014 Renishaw plc All rights reserved Renishaw reserves the right to change specifications without notice RENISHAW and the probe symbol used in the RENISHAW logo are registered trade marks of Renishaw plc in the United Kingdom and other countries apply innovation and names and designations of other Renishaw products and technologies are trade marks of Renishaw plc or its subsidiaries All other brand names and product names used in this document are trade names trade marks or registered trade marks of their respective owners M 9920 0307 02 25
7. or better than in reality Effect of setup error on measurement errors 14 12 4 i 4 Induced measrurement error arc sec 1 10 100 1000 um error at 50 mm radius M 9920 0307 02 20 RENISHAW 4 apply innovation Design details of any bracket will depend upon the machine installation However as a design aid the basic features required by a bracket are provided in the drawing below 3 POSH Equi SPACED P MIO THRO 5 BS z be 7 bg zn 3 SS RE i a 28 Sy s E E e an ae By CUTOUT AS REQUIRED AS REQUIRED FILLET BUTRESS AS REQUIRED CLAMP TO 5TH AXIS CASTING DATUM A S THE MACHINE STH AXIS ROTATION NOTES a M 9920 0307 02 21 RENISHAW 4 apply innovation Appendix B Creating custom machine programs Machine tool builders often use specific code unique to enable functions for driving the axes Off axis rotary software uses a configurable XML file to define the codes generated for a given test setup The user is able to modify or create new controllers to suit their machine A Warning Editing the CNC controls in off axis rotary could cause unexpected machine movements Only experienced machine tool programmers should attempt such changes All programs should be checked before running and performed at a low feed for the first time e From the toolbar select Tools gt Edit CNC Controls File Edit CNC Controls A Warning Editing the file
8. the hardware Identify the rotary and linear axes to be moved then mount and align the hardware Setting up 2 Measure set up parameters P P the software Take measurements using the XR20 W and the laser to calculate the offset between the C O R for the rotary axis and C O R for the XR20 W Setting up 3 Generate NC program prog the software Use Off axis rotary to generate a part program for the machine Setting up 4 Capture rotary data p y the software Use RotaryXL and the XR20 W to measure the performance of the rotary axis Setting up 5 Capture angular data P g the software Use LaserXL and the XL 80 to measure the performance of the linear axis Setting up 6 Produce axis analysis the software Use Off axis software to remove any angular error in the linear axis Step 5 from the observed rotary axis results Step 4 This will give clean results for the rotary axis M 9920 0307 02 6 RENISHAW amp apply innovation Software installation This section explains how to install Off axis rotary software on your PC Before installing please check that the PC meets the minimum specification including the operating system To install the Off axis rotary software 1 Switch on your computer wait for it to boot up into Windows then insert the CD ROM disk into the CD drive The index should now run automatically If the index fails to autorun select Start gt Run from your computer s task bar to a
9. 20 W to the bracket using the fasteners and tooling supplied ensuring it is evenly seated and flush to the mating face NOTE The outer face of the bracket is also suitable for mounting the product however longer fasteners will be required in order to achieve this which are not supplied M 9920 0307 02 9 RENISHAW 4 apply innovation For occasions when the mounting bracket is not appropriate requirements for bracket design and manufacturer are available in Appendix A Mounting hardware design In some cases It may not be possible to achieve the mounting tolerance specified due to geometry inaccuracies in the bracket design or in the mounting setups As error between the parallelism of the measurement axis and XR20 W axis increases the induced error in the XR20 W measurement also increases The chart below shows the error from the XR20 W measurement that will be induced for a given parallelism tolerance Note depending upon the sign of this error the measurement may make an axis appear worse or better than in reality Effect of setup error on measurement errors Induced measrurement error arc sec 1 pi a 107 um error at 50 mm radius Mount the interferometer Details of optical configurations for different machine types can be found in the optical setup section Mount the magnetic base pillar interferometer onto the spindle machine bed as required for the type of machine under test For best measurement accura
10. CNCcontrols incorrectly could damage the file structure and prevent off axis rotary from running Please use extreme caution when editing the file It is recommended the user saves a copy of the original file before making edits e The file CNCcontrols xml will be opened in Notepad and should appear as shown below This file contains definitions for all of the controls supported by off axis rotary The XML is divided into a number of sections one for each of the controls For example the highlighted section shown on the image to the right indicates the section used to define Fanuc controls P NTT ell licks CNCcontrotsml Ne File Edit Format View Help o lt xml version 1 0 encoding utf 8 gt aC gt To produce an additional control definition or to customise an existing control it is best practice to copy and paste an existing section and then make modifications This way the original definition can always be reverted back to if required lt Control gt lt name gt Hei denhain lt name gt lt header format Heidenhain gt lt header gt lt xtras gt G90 lt extras gt lt offset gt lt offset gt comment l gt lt comment_1 gt lt comment_r gt lt comment_r gt M 9920 0307 02 22 RENISHAW 4 apply innovation Appendix C XML file structure lt control gt The XML file consists of a number of user defined parameters that allow the lt name gt Fanuc lt name gt lt E i 2 hea
11. apply innovation M 9920 0307 02 1 RENISHAW amp apply innovation Document information Disclaimer RENISHAW HAS MADE CONSIDERABLE EFFORTS TO ENSURE THE CONTENT OF THIS MANUAL IS CORRECT AT THE DATE OF PUBLICATION BUT MAKES NO WARRANTIES OR REPRESENTATIONS REGARDING THE CONTENT RENISHAW EXCLUDE LIABILITY HOWSOEVER ARISING FOR ANY INACCURACIES IN THIS DOCUMENT Renishaw reserve the right to make changes to this manual and to the product described herein without obligation to notify any person of such changes Copyright Copyright 2013 2014 Renishaw All rights reserved This help manual may not be copied or reproduced in whole or in part or transferred to any other media or language by any means without the written prior permission of Renishaw The publication of material within this document does not imply freedom from the patent rights of Renishaw plc Registered trademarks RENISHAW and the probe emblem used in the RENISHAW logo are registered trademarks of Renishaw plc in the UK and other countries apply innovation is a trademark of Renishaw plc Microsoft Windows Windows XP Vista Windows 7 Word DirectX and Internet Explorer are either registered trademarks or trademarks of Microsoft Corporation IBM is a registered trademark of International Business Machines Corporation The Bluetooth word mark and logos are registered trademarks owned by Bluetooth SIG Inc and any use of such marks by Ren
12. ccess the Run dialog box Click the Browse button and use Browse dialog box to access the Index htm file on the installation CD ROM disk Double click Index htm 2 Select Install Off axis software to start the software installation process 3 This wizard is a set of dialogues which automatically leads you step by step through the installation process Follow the instructions on each screen and click Next to go to the next stage Click Cancel to exit the installer To access the Off axis rotary software 1 To access Off axis rotary software select Start gt All Programs and then browse for the software M 9920 0307 02 7 RENISHAW amp apply innovation Setting up the hardware A Warning Before fixing XR20 W or the interferometer move the machine to the position at which the components will be closest together All setup and alignment should be performed at this position to avoid the potential for collisions when running the tests Mounting the XR20 W Details of optical configurations for different machine types can be found in the optical setup section It is important to ensure the axis under test is parallel with the axis of the XR20 W Parallelism of the axis under test and the XR20 W axis is controlled by two factors 1 The design and tolerance of any mounting bracket for the XR20 W A bespoke XR20 W 90 bracket is available to assist with mounting requirements associated with this type of measurement 2 The ali
13. cy ensure that the interferometer is mounted as rigidly as possible with the minimum number of extension bars M 9920 0307 02 10 RENISHAW 4 apply innovation Optical alignment 1 Nominally position the XL 80 XR20 W and interferometer as described in the previous section 2 Place the bubble level onto the laser and adjust the tripod to ensure it is level 3 Move the rotary and linear axes to the position where the XR20 W comes closest to the interferometer Far Position Close Position 4 If necessary adjust the positions of the components and the axes to ensure a collision cannot occur Align the laser to the linear axis across the full range of travel for the test setup 6 Hold a plane mirror against the face of the interferometer and rotate the interferometer so the beam returns into the output aperture of the laser Note the laser may go unstable at this point 7 Recheck the alignment across the linear axis and translate the XL 80 or interferometer to correct any misalignment caused during the previous step 8 Position the rotary axis at one extreme of rotary travel for the test to be run Move the linear axis so the interferometer is inline with the XR20 W and check full signal strength is achieved 10 Move the machine to the opposite extreme of travel for the test setup and repeat the two steps above O1 Co This completes the optical alignment procedure M 9920 0307 02 11 RENISHAW amp apply inn
14. d Note different program ID s Generate CNC part program should be used between rotary and linear programs Program ID Generate CNC Part Program Save CNC Part Program Program options 2 Select the appropriate program options e Check exclude comments to produce a G code only progam without comments scab lc aa a ata eae for rotary emor comection Exclude rotary ads Check the following box to exclude comments from part program Exclude comments I 3 Click the Generate CNC Part Program button 4 Once the program has been checked click the Save CNC Part Program to save the part program to disc Generation of the linear axis only program follows the same procedure as above but the user should ensure the exclude rotary axis tick box is checked at Step 2 5 Capture data 1 Use RotaryXL to perform the rotary axis measurement 2 Save the data from the rotary axis measurement with a descriptive title 3 Use Off axis rotary software to produce a RTA file for the linear axis measurment Step 1 Create and save RTA target file Note these targets must be used for the linear axis measurement Generate RTA File Save RTA File 4 Run LaserXL to capture the linear axis using angular optics and the RTA file generated in the previous step as follows Click File gt Open Browse to the RTA file then click Capture gt Start 5 Save the data from the linear axis measurement with a desc
15. der Tormat Tanuc gt lt header gt user to generate additional controllers or modify existing ones An example of lt extras gt G90 G64 lt extras gt ee i f i lt Oextras2 gt M184 lt extras2 gt a control definition is given in the image on the right lt offset gt G54 lt offset gt lt comment_1l gt lt comment_1 gt lt comment_r gt lt comment_r gt lt eob gt lt eo0b gt footer format Tanuc number gt S lt Tooter gt lt dwe 1 gt x lt dwel1 gt lt inch gt 620 lt inch gt lt metricso21 lt metric gt lt line _numbers enabled 0 gt lt 1ine_numbers gt lt inverse_timesl lt inverse_time gt lt End_Progr am 30 lt End_Progr am lt ProgramID_Prefix gt 1t lt ProgramID_Prefix gt lt ProgramID_Suffix gt amp gt lt ProgramID_Suffix gt lt Program_Fi le_Ext nc lt Program_Fi le_Ext gt lt control gt gt The following table describes the entries in the control definition and their purpose Name displayed in drop down menu in off axis rotary software Used to define file headers required by the control Allows the user to define addtionalG or M code required to allow the machine to run Allows the user to define addtionalG or M code required to allow the machine to run Used to call specify the active work offset Defines the opening delimiter for a comment Defines the closing delimiter for a comment Defines notation for end of block Used to define file footers required by the contr
16. gnment of the bracket with respect to the axis under test XR20 W 90 bracket installation Renishaw accessory A Renishaw solution to the mounting requirements during off axis testing is available It features a precision machined 90 bracket held to manufacturing tolerances suitable for off axis use Mounting to the machine can be achieved by the magnetic mounting system included with the kit or via direct mounting to the machine through fixturing holes in the bracket The bracket is also useful for solving on axis mounting difficulties on trunion type machines as shown below M 9920 0307 02 8 RENISHAW 4 apply innovation 1 Determine the most suitable method of attaching the bracket to the machine under test Attach the three off magnet assemblies to the base of the bracket or source required fasteners and T nuts to suit the machine if required 2 Locate bracket only onto the machine With the bracket secured to the machine align the red ball on the outer diameter of the XR20 W with the matching red ball on the bracket 3 To ensure alignment of the bracket is correct it is best to use a dial type indicator DTI to measure and minimise the run out of the mounting face against the linear axis as shown below To minimise the test errors relating to the misalignment ensure that the DTI reading is less than 60um across the bracket from A B and down the face of the bracket B C 4 Attach the XR
17. ishaw is under license All other brand names and product names used in this manual are trade names service marks trademarks or registered trademarks of their respective owners M 9920 0307 02 2 RENISHAW amp apply innovation Introduction About off axis rotary Traditionally rotary axis calibration has required that the XR20 W is mounted on the centre of the machine s rotational axis This can lead to difficulties on machines where access to the Centre Of Rotation C O R is limited resulting in complex brackets and alignment procedures being required to calibrate the axis This problem is often encountered on machine configurations such as trunnion and swivel head A solution to this is to mount the XR20 W Off axis so that it is not mounted on the C O R and perform a test which synchronises linear and rotary moves so that the laser beam alignment is maintained throughout a test This can significantly simplify the mounting hardware and set up requirements This manual explains the use of Off axis rotary software to enable this solution to be used Off axis rotary software allows the user to e Easily calculate the offset distance between the C O R of the XR20 W and the C O R of the rotary axis required to generate a test part program e Generate a test part program which synchronises rotary axis and linear axis moves to maintain laser beam alignment e Remove any contributory linear axis angular error from
18. ol Specifies the notation for a dwell Specifies notation to call operation in imperial Specifies notation to call operation in metric Flag set to produce line numbers on part program output Flag to define feedrate mode Defines to notation for the end of program Defines notation applied before the program ID Defines notation applied after the program ID Defines the file extension for saved programs M 9920 0307 02 23 RENISHAW 4 apply innovation Appendix D Enabling 0 360 rollover function Some controllers cannot handle negative targets Their range of positions is 0 360 An example highlighting the requirement for this function is shown below Partial arc range 0 120 Over run 5 On this type of machine the software will output an initial over run position of 5 when for certain types of machine this over run position should be 355 There is no method of determining this requirement from the RTA test file An additional control field has been added to the CncControls xml file that will allow the part program generator to cater for machines with the above requirement Method 1 The recommended method to enable the 0 360 rollover function is by creating a custom CNC control by following the Creating custom machine programs section 2 At the bottom of the new custom CNC control the following line will be present lt lt RotaryAxisRollover gt true lt RotaryAxisRollover gt gt 3 Remove lt lt
19. onvention The user does not need to provide any input for sign convention on the rotary aspect for the process RotaryXL automatically sets the sign convention during the over run move However the user must manually set the sign convention during the angular measurement on the linear axis The sign of the angular error will depend upon the configuration of the angular optics For the angular measurement setup the retroreflector should always be mounted to the moving linear axis with the interferometer mounted to the stationary component If the XR20 W is replaced by the retroreflector then the rule is straightforward Retroreflector Interferometer Move the rotary axis in the positive direction Set sign of angular error positive If the XR20 W is replaced by the interferometer the rule is reversed In the example below the interferometer has replaced the XR20 W which was mounted to the machine spindle Retroreflector Interferometer Move the rotary axis in the positive direction Set the angular error negative M 9920 0307 02 18 RENISHAW amp apply innovation Appendix A M ounting hardware design To ensure accurate measurement it is essential that the XR20 W is mounted to the machine so that the axis of the device and rotary axis are parallel The requirements for off axis rotary measurement are the same as for a traditional on centre measurement in that the objectives are e Foran induced error to be less than
20. ovation Setting up the software Off axis rotary software allows the user to generate the part programs for both rotary and linear tests needed to complete the off axis testing process The rotary test part program will synchronise the rotary and linear position moves so that the beam is not broken in between moves The steps to produce a part program are as follows Produce an RTA file to describe the test setup using RotaryXL Define the CNC control parameters Calculate the offset between the XR20 W and the rotary axis centre s of rotation Generate the program Capture data Produce axis analysis Our OUN 1 Produce test setup Using RotaryXL define the test setup and trigger settings for the axis under test and save the RTA file Full details of how to acheive this are given in the RotaryXL help file 1 In the test setup tab of Off axis rotary software use Load RTA file from RotaryXL button to import the file All the test settings should now appear in RotaryXL test Test template settings window Load RTAfile from RotaryXL 2 Select the rotary axis to be tested and the linear axis to be synchronised Note fois selection these values will be automatically populated by the software based on the values TT f Rotary j Linear stored in the RTA file but should be checked before generating the part program L 3 Enter a suitable dwell and move time Note the move time is the time taken in second
21. riptive title M 9920 0307 02 14 6 Produce axis analysis In Off axis rotary software select the error correction tab 1 Select the Rotary button and browse to the location of the rotary axis measurement data file 2 Select the Linear button and browse to the location of the linear axis measurement data file 3 Select the Create error corrected file button Note A third RTA file will be produced with the name of the original rotary measurement file but with CLEANED as a suffix 4 Select Analyse error corrected file to open the analysis of the cleaned data file for the rotary axis M 9920 0307 02 15 RENISHAW amp apply innovation Step 2 Select and parse data files Rotary Select RTA File gt Linear Seed RTA Ries Create emor comected file Step 3 nalyze Analyze eror comected file RENISHAW 4 apply innovation General information This sections includes additional information regarding off axis rotary measurement a NS SNS M 9920 0307 02 16 RENISHAW amp apply innovation Optical set ups The optical setup will depend upon the machine type being tested The following table shows the optical configurations for the most common machine applications ft Off axis setup Angular measurement setup Head machine type 1 fis a E E T E E D Table machine type 1 Table machine type 2 M 9920 0307 02 17 RENISHAW 4 apply innovation Sign c
22. s for each angular step to be completed It may be necessary to consider a Part program user settings move of 90 to determine a practical value for the move time an i up Owell time A Seconds Move time 10 Seconds 2 Define the CNC parameters On the CNC control tab in the software 1 Select the appropriate CNC control NC control selection 2 Select the appropriate measurement mode Measurement mode Metric a Inch 3 Offset calculation The offset is the distance between the centre of rotation C O R for the rotary axis and the C O R of the XR20 W It is essential this is calculated correctly so that the machine program correctly synchronises moves of the rotary and linear axes A Warning Incorrect offset calculation could result in a machine crash M 9920 0307 02 12 RENISHAW amp apply innovation The process of calculating the offset relies on moving the machine to three positions and ensuring laser optics alignment at each of these Where possible the most accurate calculation of offset is achieved using the two positions parallel to the linear axis travel and a third approximately at mid travel between these The order of the positions is not important for the following process but it is essential to capture data at all three positions Take care when recording positions from the machine control to ensure all values are taken with the same work offset applied as will be used when the program is run
23. the observed rotary axis results to give clean results for the rotary axis RotaryXL software is used to capture the angular positioning error of the rotary axis and is covered in the RotaryXL manual LaserXL software is used to capture the angular error of the linear axis and is covered in the LaserXL manual Principles of operation The principle of operation is to use synchronised moves of machine linear and rotary axes As shown above for each rotary axis move there is a corresponding linear axis movement Note that even for identical angular axis movements the linear axis movement intervals will be unequal to ensure that the interferometer and the XR20 W maintain alignment M 9920 0307 02 3 RENISHAW amp apply innovation Because one of the optics is fixed to the moving linear axis the observed angular axis data will also include error terms from the linear axis for example the angular error shown below Angular error in linear axis For this reason additional and separate angular measurements should also be taken along the linear axis at the same stop positions as used during the initial synchronised moves The two error files can then be combined to remove the effect of the linear axis angular errors and leave a true representation of the rotary axis rotational accuracy In order to create a program with synchronised moves it is necessary to know the distance between the C O R of the XR20 W and the C
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