Coordinate measurement relies on good software
March 5th 2008 07:46 pm By Web Development in India
Jon Hobden looks at the development of Coordinate Measuring Machines and the importance of finding the right CMM software for a given application
The advent of coordinate measuring technology in the 1960s made possible the reliable measurement in three dimensions of a group or cluster of dimensions, so that different features on a component could be checked in relation to each other in space. Whereas a cylinder in an engine block, for example, could be checked for length, diameter, cylindricity and so on, it was now possible to check that all cylinders in a block were in line and parallel, so that shaft failures could be reduced and designers given more freedom to create complex designs.
Mechanically, coordinate measuring machines (CMMs) were made to be ever more accurate and stable, granite tables used for thermal stability, probing and touch trigger systems refined for better measurement resolution and linear measuring scales made to more repeatable specifications and with better resolution to enable reading of the greater accuracies available.
As PC-based software became available in the late 1970s, coordinate systems were automated and programs made possible for a given part, making multiple measurements in a smaller amount of time.
Servo driven CNC machines were not just programmable but part programs could talk to other software.
CMMs were suddenly productive and suitable for a much wider range of applications.
But it was the introduction of error mapping that arguably made the largest contribution to mass availability of cost efficient CMMs.
Error mapping and the ability of software to predict positional differencies of the probing system, based upon temperatures measured at various points around the machine’s axes, meant that CMMS no longer had to be mechanically perfect.
This lead to cheaper materials being used, lighter construction, reduction in the mass of bridge and table structures and even less expensive manufacturing for items such as guideways, bearings and so on.
All this was possible without sacrificing accuracy or repeatability, since the software could make the necessary allowances and additional benefits were also apparent; lighter structures meant higher acceleration/deceleration values and higher speeds so that productivity was even further enhanced.
Today, it is the software - not the machine - that means the most to potential buyers of coordinate measuring machines.
Quality is important, of course; motors that break or bearings that fail result in downtime and must be considered.
However, the capability of the software and its robustness and integrity are key considerations for buyers.
Among the points to look for are: Simplicity of operation and user interface Ability to easily upgrade Amount of training required Part alignment functionality Number of clicks to program parts or components CAD interfaces and ability to export to and to ’speak’ to other softwares and languages Ability to work in ‘native’ CAD programs if required Ability to control the machine effectively; for instance to eliminate unnecessary distance when moving around the component and to optimise probe movements Ability to interpret scanned data into usable topographic information Above all, it is necessary to convince yourself that the CMM and software package is the best for your situation; while a given manufacturer’s machines may be excellent for turbine blades, the geometry of gears may present a different solution.
It is always advisable to take your parts to different manufacturers and to see what each can do with them.
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