Fifty Years of CMM History leading up to a Measuring Revolution
The coordinate measuring machine first appeared at the International Machine Tool exhibition in Paris in 1959 exhibited by the British company Ferranti having delivered the world’s first commercially available general purpose computer in 1951.
The CMM quickly evolved with a plethora of CMM manufacturers from European Countries, USA and Japan entering the field in the mid 1960’s; the uptake of coordinate measuring machines by manufacturing companies rapidly gathered pace after the introduction of the Touch Trigger Probe by Renishaw in the early 1970’s.
The touch-trigger probe, invented by Sir David McMurtry, the co-founder of Renishaw, solved a specific inspection requirement for the Olympus engines used on the supersonic Concorde aircraft. This innovative product led to a revolution in three-dimensional co-ordinate measurement, enabling the automatic and accurate measurement of machined components and finished assemblies.
A typical CMM is composed of three orthogonal axes, X, Y and Z operating in a three-dimensional coordinate system. Each axis has a scale system that indicates the position of that axis. The machine will read the input from the touch probe, as directed by the operator or computer program. The machine then utilises the X,Y,Z coordinates of each of these discrete points to determine size and position with micrometre precision.
The touch probe allows for the automatic generation of measured point on the component surface while simultaneously and automatically recording the XYZ position in space of the point taken. This simple patented device has revolutionized the inspection of manufactured parts throughout manufacturing and has played a critical role in the globalization of manufacturing in past decades.
Renishaw dramatically increased the performance capabilities of the CMM even further with the introduction of the motorized probe head in the early 1980’s and the coordinate measuring machine as we know it today was born. Further advancements by Renishaw have included the introduction of compact and affordable scanning probes, automatic probe change racks allowing CMM automation and automatic probe stylus changing.
Few, if any, companies can match the innovation levels achieved by Renishaw and their absolute focus on advancement of the industry they serve. Typically they invest 18% of annual sales in engineering and R & D. 2010 turnover was approximately $500 million.
What is remarkable is that during the past 3 decades of Renishaw innovation the core technology behind the Co-ordinate Measuring Machine has remained static. For sure the CMM mechanical structure has been improved by making it lighter with improved repeatability. The development of miniaturized digital CNC controller technology has been effectively applied to the CMM structure providing a more accurate motion path along a defined vector along with the CMM’s ability to perform circular motion paths rather than just straight line moves together with the ability to operate the CMM structure at higher speeds and acceleration levels. All of these improvements to the CMM have been incremental and more based upon technological advancements from outside the industry than internally generated innovation.
One innovation that has occurred has been the construction of the CMM structure from new high technology alloys materials, moving away from the original granite and steel designs. These alloys provide a lighter, stiffer structure while at the same time improving reaction to, and dispersion of, temperature changes and actually result in less deformation of the CMM structure than that experienced by the slowly reacting granite structures. Integrated with the alloy structures are measuring scales, typically from Renishaw, that are located in sub-straits mounted to the CMM structure. The measuring scales are free and in-dependant of any CMM structural movements increasing dramatically CMM accuracy even in non-perfect environments. Granite structures are also less predictable due to the inconsistent material properties of the natural product and have their scales rigidly mounted. In addition, with the introduction of low-cost PC computation, geometric error compensation has been harnessed allowing the accuracy of a CMM to be improved considerably beyond what is achievable by using a mechanical accuracy only structure and at the same time reducing CMM purchase costs. Today the operation of advanced jet airliners is totally reliant upon ‘fly by wire’ computer based technology; so then are modern Co-ordinate Measuring Machines whereby the actual position of the recorded probe data points, from the measuring sensor, are derived from the real-time software running in the background and calculating the actual probe position rather than just providing its assumed position.
The increasing use of scanning probes on CMM machines demands a stiffer structure due to the scanning acceleration forces involved. COORD3 has pioneered the introduction of Silicon Carbide for the Z ram of Coordinate Measuring Machines which is lighter and stiffer and significantly outperforms granite.
“Traditional” CMM companies, many with CMM designs dating back 20 years or more, are still manufacturing using the original materials adopted by the CMM industry before computerised finite element analysis modelling arrived allowed dynamic structural behaviours to be understood and designs to be improved based upon the modelled data. Many of these companies sell tradition; in reality they are supplying outdated and archaic design concepts and obsolete for today’s modern manufacturing environment. Much of their resistance to change comes from their investment in internal house granite production facilities which the newer CMM designs render obsolete.
Small start-up companies based in the emerging markets of China and India also produce granite structures; granite blocks are in cheap and plentiful supply and require only a minimum effort to produce a CMM frame design and have a fast time to market minimizing investments. (In fact more investment is made in cover design and tooling for product aesthetics than in the rest of the CMM structure combined). This scenario was also followed by CMM builders of the 1980’s and 90’s in both Europe and USA resulting in a large CMM supplier base. The majority of these suppliers have now been consumed by economics pressures leaving a huge installed base of obsolete machines behind. It’s inevitable that a consolidation of the ‘new world’ CMM builders in China and India will also occur in the coming future.
Another Measuring Innovation from Renishaw
After more that 10 years in development and the investment of many tens of millions of dollars in Research & Development expenditure Renishaw has introduced the largest single step-change ever seen in the CMM industry. Renishaw has introduced 5 Axis Measuring Technology to market whereby the CMM structure role in the measurement process is dramatically reduced and ‘dumbed down’ resulting in huge improvements in CMM measurement productivity and with improved metrology.
5 Axis is disruptive technology to the traditional CMM supply base even though the benefits to the end-user are overwhelming. OEM resistance to Renishaw 5 axis is due in main to the fact that to access this new technology requires utilisation of a Renishaw CMM controller. Most OEM’s see the CMM motion controller as part of their domain (even though most purchase in and ‘badge’ their motion controller) and as a consequence have taken a stance not to offer this new revolutionary technology to its customers. The complexity of driving a continuous motion head with third-order polynomial interpolation algorithms with fully integrated touch probe and scanning capabilities left Renishaw no option but to seamlessly integrate all probing functions with the much simpler 3 axis CMM motion in order to deliver a seamless, risk free, next generation solution to market. In addition new international standards on CMM interoperability between brands driven by end user demands insists that all CMM probe calibration and data mapping is completed and stored at a CMM controller level allowing the application software packages to be ‘plug and play’ and the CMM metrology integrity to be independent of these application software packages.
A CMM Measuring Philosophy Change for Customers
Introduced integral with 5 Axis technology are new CMM feature based measuring routines including ‘Head Touches’ whereby the complete geometry of a part feature is inspected within the 5 Axis Head completely eliminating the CMM structure from having in role in the measuring function. Not only do ‘Head Touches’ triple CMM productivity they also dramatically improved the accuracy of measured data by eliminating the CMM structure errors from the measuring activity. Other unique measuring routines introduced with 5 Axis CMM Scanning allow the collection of thousands of data-points per second and only require a single linear axis motion of the CMM.
COORD3 is embracing the benefits offered by 5 Axis Technology and is one of only a few CMM supplier 100% focused on delivering 5 axis products to customers utilising the full complement of Renishaw Technology Components.