Renishaw plc New Mills, Wotton-under-Edge, Gloucestershire GL12 8JR United Kingdom T +44 () 1453 524524 F +44 () 1453 52491 E uk@renishaw.com www.renishaw.com Why choose RENGAGE? Renishaw invented the touch-trigger probe for machine tools in the 197s. The success of this innovation, based on a kinematic resistive principle, has firmly established Renishaw as a world leader in the design, manufacture and support of dimensional measurement products. The basis of this design continues to play an invaluable role in part set-up, measurement and process control. Decades of continuous investment in development enables Renishaw to provide customers with exceptional products that are unmatched for technical excellence and performance. This document compares the technology of RENGAGE probes with that of conventional probe design and illustrates the superior performance capabilities based upon real world tests, and verified by machine tool builders. Rengage technology clearly delivers true three dimensional (3D) measurement performance and sub-micron repeatability. So for exceptional Performance Reliability Durability Why choose less?
Conventional probing......basic principles Kinematic resistive probes Three equally spaced rods rest on six tungsten carbide balls to provide six points of contact in a kinematic location. An electrical circuit runs through these contacts. The mechanism is spring loaded which (1). allows deflection when the probe stylus makes contact with the part, and, (2). allows the probe to re-seat to the same position within 1 µm 2σ when in free space i.e. not in contact. Under load of the spring, contact patches are created between the balls and the rods through which the electrical current flows. Upon making contact with (touching) a workpiece, the force translated through the stylus moves the balls and rods apart thus reducing the size of the contact patches and increasing their electrical resistance. When a defined threshold is reached the probe is triggered. Section view Spring Top view Rod and ball kinematic locations Resistance increases as area reduces Close up of kinematics Section through kinematics Current flows through kinematics Contact patch reduces as stylus force balances spring force Based on the above kinematic resistive principle the stages in trigger generation are shown below. Repeatable electrical triggering and mechanical reseating of the mechanism are critical to this process and fundamental to reliable metrology. All kinematics in contact Reactive force Mechanism pivots about these contacts Contacts separate Kinematics reseat to repeatable position Machine direction Machine direction Contact force
Conventional probing......basic principles Other types of probes Spherical seat or pivoting type probes are common alternative designs. Theory suggests that this methodology provides uniform trigger force in the XY plane. However the reality is very different because this is dependent upon the precision of the manufactured sphere/conical seat surface relationship and thus in practice trigger forces are highly variable. Trigger mechanism Stage 1 Stage 2 (trigger) Annular reference surface Reference ring Annular reference surface touches reference ring Stylus deflects trigger mechanism plunger Conical seat Spherical reference surface Spherical surface pivots within conical seat Further pivoting about contact point between reference surfaces The major drawbacks of this design are: 1. Free motion of the mechanism typically results in a significant stylus deflection before the probe triggers. 2. The stylus is not uniquely located because the sphere/conical seat relationship does not constrain all degrees of freedom. Performance characteristics - lobing Lobing is a characteristic of all probes. It is caused by bending of the stylus and movement of the probe mechanism before the probe registers contact witha surface. It is therefore dependent upon: Length and stiffness of the stylus Force required to trigger the probe Direction of contact with the surface Design of the probe mechanism All probes will therefore exhibit some lobing, which when plotted can resemble the irregular shape opposite. For two axis measurement, potential errors are relatively easy to calibrate out. In three axis measurement however, lobing errors are greater and more complex to compensate for, particularly with some conventional probes. These errors are significant and can adversely impact accuracy and repeatability in 3D measurement. Lobing plot (X-Y only) for conventional spherical seat type probe
RENGAGE innovation......and the elimination of error Innovatively engineered over years and patented by Renishaw, RENGAGE probes incorporate proven silicon strain gauge technology with ultra compact electronics and precision mechanical design to achieve unparalleled performance and capabilities. Suitable for a wide range of machine tool applications and able to address the 3D performance limitations of many alternative probe designs; Renishaw s MP25, OMP4 and RMP6 are the latest products to include this technology. Strain gauges are positioned on carefully designed webs, forming part of the probe s structure yet separate from the kinematic mechanism. The strain gauges are arranged to sense strains in all axes and their outputs are electronically combined using patented algorithms. On reaching a threshold in any direction a trigger signal is generated at forces that are much lower than those required to trigger conventional probes. The benefits in relation to a wide range of application issues are significant. Mechanism Structure Strain gauge - independent of mechanism Rengage probes still utilise Renishaw s kinematic mechanism to reseat the stylus. This system, proven over 3 years, guarantees a repeatable reseat and is fundamental to accurate metrology! As sensing is completely independent of the probe mechanism Rengage probes feature low force, highly repeatable, and consistent trigger characteristics that are not typically achievable with conventional probe designs. By using this technology it is possible to eliminate up to 9% of errors due to lobing, which, for two axis applications can eliminate the need for significant calibration, whilst for three axis applications and complex geometry it will be seen that Rengage probes are unique. Mechanism Structure Component miniaturisation and solid state technology are combined in a range of compact and ultra compact Rengage probes that provide innovative solutions toward the increasing trend for higher accuracy and smaller machine applications.
RENGAGE sets new standards......nothing else compares, we checked! To compare the 2D and 3D performance we tested a Renishaw OMP4 RENGAGE probe against a typical cross section of conventional probes from other brands. We also tested a Renishaw OMP6 kinematic resistive probe. Pole The tests, performed using 5 mm styli at a feed rate of 6 mm/min, were conducted on a popular machining centre typically used in normal production environments. equator Probing a 25 mm calibration sphere around its circumference at 5 increments in the X-Y plane and at increments in the Z plane provides data, which, when plotted, clearly illustrates lobing error. Meticulous care was taken during set-up to ensure reliable results. An in-house calibration programe performed prior to each probe test accurately established the sphere centre and importantly, enabled compensation for potential machine errors. First the probe (using active length correction) was positioned over the sphere and a nominal stylus radius input. The pole was then probed and Z position set. Measured values were taken about the equator and pole to establish positional error and true X, Y, Z positions. Five measured values were taken for each position and averaged following a check for excessive value variation. Pole Equator
RENGAGE sets new standards... The following plots show lobing error data from the best performing conventional probes from brands A, B and C and the Renishaw OMP6 probe. The results for brands A, B and C showed errors of up to approximately 6 μm. When compared to the data obtained using Renishaw s OMP4 RENGAGE probe the results are compelling. Brand A 6 5 4 Renishaw OMP6 6 5 4 3 3 2 2 1 1-1 -1-2 -3 Equator -2-3 Equator Brand B 6 5 Brand C 6 5 4 4 3 3 2 2 1 1-1 -1-2 -3 Equator -2-3 Equator
RENGAGE in a class of its own! This plot for the OMP4 featuring RENGAGE technology uses the same scale as the plots for the other probes tested (i.e. range = -1 to + 6 μm). Viewed against these other plots the results for the Rengage probe are clearly significantly different in two important ways. (1). the plots for each plane are contained within a very small area at the centre of the graph, and (2). the plots are almost overlaid. In other words the plots show that the lobing error is virtually eliminated and that this is consistent for each of the planes tested. Interestingly, the results for the Renishaw OMP6 probe indicate that although unable to match performance of the OMP4 with Rengage technology it still outperformed the other brands by a significant margin. Its accuracy was seen to be twice as good as the average result for the other conventional probes. Note: since errors for probes from Brand D were found to be above 6 μm this brand is not featured in the other plot results. Renishaw OMP4 Rengage probe Overall system radius error = < 4 µm irrespective of plane 6 5 4 3 2 1-1 -2-3 Equator Renishaw OMP4 RENGAGE probe, the smallest and most accurate spindle probe in the world! 7 6 5 Based on data from the best four of the five conventional probes tested the overall error is shown on the bar chart opposite. The average error at 4 µm is 1 times greater than with the Rengage probe. Lobing error (µm) 4 3 2 x 1 So in other words, 3D accuracy with Rengage probes is 1 times better! Since the machine tool used for the test was a typical production machine it is worth considering the possibilities when using Rengage technology in conjunction with high accuracy machines. Having a uni-directional repeatability of just.25 µm 2σ, Rengage technology is unequalled for accuracy in any plane! 1 Renishaw Renishaw kinematic Brand A Brand C Brand B XY lobing XYZ lobing Average
Unequalled accuracy and more! With the case for more accurate 3D capability established, consider the additional benefits offered by significantly reduced trigger forces. 1.5 Trigger forces compared (x,y axis) As shown by the graph (right), with RENGAGE technology, the force required to trigger is exceptionally low. Conventional probe designs cannot match this capability. Since the trigger is independent of the mechanism, stylus length can be significantly increased whilst maintaining the overall accuracy advantage, as illustrated below and right. Forces N 1.5 95% reduction With this performance enhancement, increasingly complex and challenging measurement tasks can be performed reliably and therefore with confidence. Repeatability Max. 2σ in any direction of 12 2D (XY) lobing Max. deviation from a ring gauge 3D (XYZ) lobing Max. deviation from a known sphere Stylus length 5 mm 1 mm 15 mm 2 mm.25 µm.35 µm.5 µm.7 µm ±.25 µm ±.25 µm ±.4 µm ±.5 µm ± 1. µm ± 1.75 µm ± 2.5 µm ± 3.5 µm Further, miniaturisation of the probe body made possible by the solid state technology means that the increasing trend towards smaller machines can be more easily accommodated. For example, at less than one quarter the size of a typical conventional probe, Renishaw s ultra compact OMP4 and MP25 probes are ideally suited in space restricted or physically awkward applications. Don t just take our word for it. Here s how customers value the opportunities, benefits and solutions offered by Rengage technology: Meeting current and future performance requirements for our products demands manufacture of ever smaller and more intricate parts that are consistently accurate to within 1 µm. Reliable set-up and measurement are therefore critical to this process and form the basis of our decision to use Rengage technology. The Renishaw OMP4 is the only product capable of reliably meeting our needs. Ian Crane, CEO, Flann Microwave, Bodmin, Cornwall, England. As aerospace stretch-forming specialists, there s hardly a part or a die in our shop without a parabolic, compound curved or cone shape. Rapid, precise measurement of machining work on these parts, whilst fixtured on the machine tool is essential to our lean manufacturing. The RMP6 Rengage probe provides the in-process performance needed for consistent, high-accuracy measurement of small hole diameters, contours and geometric tolerances. Gary Medlock, Triumph Fabrications, Shelbyville, Indiana, USA.
Frequently asked questions Q. Since Rengage probe technology is so advanced, is it a lot more expensive than other probes? A. No. The price premium over a Renishaw conventional probe system is about 2%, yet the numerous benefits will in many cases help provide faster payback. Furthermore, Rengage probes can be used to undertake work that is not possible with a conventional probe. Q. Given the sensitivity of the strain gauge sensing, will machine vibrations adversely affect Rengage probe performance and generate false triggers? A. No. Filtering circuitry establishes whether strains seen at the gauges are the result of vibration or a real deflection of the stylus. Q. Is a probe with Rengage technology more delicate than a conventional probe? A. No. It is equally as robust as all other Renishaw probes. Q. Does Renishaw still produce its conventional probes, and why is this if the Rengage probe technology is superior? A. Yes. Renishaw conventional probes have defined the standard and continue to fulfil a valuable role for many applications. This is why Renishaw continues to maintain its position as market leader in the design, manufacture and support of these products. Q. How long has Rengage technology been available in machine tool probes, and is it field proven? A. Renishaw developed strain gauge technology for use in its MP7 probe in 1996. Further developments saw the technology miniaturised and launched in 26 in the ultra compact OMP4. This product received multiple industry awards including the Queens Award for Enterprise 29. Put simply, Rengage technology is tried, tested, patented and acknowledged. Q. Can existing Renishaw probe systems be upgraded to utilise probes with Rengage technology? A. Yes, currently the OMP4 and RMP6 probe models are backward compatible with existing receivers. Contact your Renishaw representative for details. Q. Which probes feature Rengage technology and what are their applications? A. Only Renishaw probes feature Rengage technology. See below for details. Q. What are the main advantages and benefits of Rengage technology? A. See overleaf. Probe Transmission type OMP4 Optical RMP6 Radio Application (All high accuracy and repeatability) Small - medium machining centres Medium - large machining centres MP25 Hard wired Grinding machines * If styli length is increased, performance will be affected. Size 5 mm (1.97 in) x Ø 4 mm (1.57 in) 76 mm (2.99 in) x Ø 63 mm (2.48 in) 4.7 mm (1.6 in) x Ø 25 mm (.98 in) Max. stylus length 2 mm (7.87 in)* 3 mm (11.81 in)* 1 mm (3.94 in)
Renishaw plc New Mills, Wotton-under-Edge, Gloucestershire GL12 8JR United Kingdom T +44 () 1453 524524 F +44 () 1453 52491 E uk@renishaw.com www.renishaw.com Advantages Unbeatable 3D accuracy and repeatability, enables reliable on-machine gauging/measurement Improved accuracy with long styli, means awkward parts can be probed more easily Unmatched performance for delicate work helps eliminate surface and form damage Compact design enables better access in restricted spaces and small machines Robust in the harshest environment means reliable measurement and long service life Key benefits Reduced set-up and calibration time leaves more time for machining Improved process control and quality Reduced rework, concessions and scrap Increased automation and reduced operator intervention Increased payback and profits Greater competitive edge and business opportunity More than just doing the job, with RENGAGE probes you can work smarter, more profitably and with confidence. More information For further details on the products mentioned in this flyer, please visit: www.renishaw.com/mtp 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. 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. H-2-3537-1-A Renishaw plc 211 Issued June 211