7/1/2009 | 3 MINUTE READ

Contact: Making More Accurate Measurements

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Here are some new developments for contact measuring.


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Done in One

So what do you do when you have exceedingly precise measurement tasks, when not only are you interested in measuring the contour of a workpiece, but the surface roughness as well? Chances are you do it with more than one pass and with more than one machine. But now there is an alternative, the HOMMEL nanoscan from Hommel Etamic America (www.hommel-etamic.com). Applications for the unit include common-rail fuel injectors, applications where, for example, chamfers on edges are in the range of 5 µm. Notably, the measure-ment process is performed in a single pass. That is, the accuracy of the system is such that the roughness and the contour can be measured with a resolution of 0.68 nm; the maximum stroke of the measurement device is 24 mm. What can make these measurement applications even more challenging on machined parts is that there can be edge burrs on the workpiece. But the system is able to determine whether there is a material build-up on the edge, which would indicate a burr, or a break, which is essentially the opposite of the burr.

The system makes use of a tactile stylus tip that runs across the surface of the workpiece. This is sent to a highly accurate laser interferometer system. The styli for the unit are quickly set into place, as they are located and fixed magnetically on the arm. An additional benefit of this approach is that should there be a collision, the stylus is knocked off of the arm, it doesn't break. Another interesting aspect of the styli is that each contains an RFID tag that is read by the system so that the appropriate measuring program is loaded into the machine control. Parts are fixtured on a CNC-controlled X-Y table.

Parameters measured by the nanoscan include roundness, run-out, Rzmax radial and axial, Ptmax, and bearing ratio.

Probe It

The Leitz LSP-X1 series of scanning probes has been launched by Hexagon Metrology (www.hexagonmetrology.com/us). The probe has an overall diameter of 30 mm, so when fitted into place on a measuring system—and it should be noted that it can be combined with a motorized head, such as the company's TESASTAR-M, which can be used to develop an analog scanning system with 2,952 positions—it has accessibility, even in tight spaces.

The LSP-X1 supports standard probing modes including single-point probing, self-centering, and continuous high-speed scanning for form and profile measurements.

The LSP-X1 comes in two styles, with the primary difference being the length of the styli. There is the LSP-X1s, which provides styli lengths from 20 to 115 mm, and the LSP-X1m, which ranges from 120 to 250 mm. The measurement range provided is ±2 mm; the resolution is <0.1 µm; the stiffness is 1.2 N/mm; and the return to zero is <0.002 mm.

The LSP-X1 has a modular design, so there can be automatic rack-based exchange of probes with other types of probes. There is also an option that permits just the styli to be changed.

Making It Modular

A coordinate measuring machine (CMM) with a modular design has been launched by Carl Zeiss Industrial Metrology (www.zeiss.com/imt). The ACCURA is capable of measuring cut, shaped, or molded parts, plastic or steel. There are software packages available for specific applications, such as HOLOS NT for free-form surface measurements and GEAR PRO for gears. What's more, there are various types of probes—contact and optical, which can be changed during a measurement operation—available to meet application needs.

The bridge-type machine has high-performance insulation on the bridge so that it helps assure temperature resistance such that the CMM can be used on the factory floor. The CMM is capable of operating at a temperature range of from 20 to 26°C. There is overall lightweight design (e.g., the bridge consists of aluminum and steel components) and air bearings deployed so that there are improved dynamics for the measuring routines. For example, there is a maximum vectorial travel speed of 800 mm/sec. with the Performance Package, which is 50% faster than Zeiss' previous generation CMM. (Because of this fast operation, there is a safety system that deploys laser scanners so that if there is movement detected within a specified safety zone, the speed is lowered within one second of detection.)

The CMM is available in four sizes. The smallest, which provides a measuring tolerance of 1.6 µm + L/333, has a measuring envelope of 900 x 1,400 x 800 mm (X, Y, Z). The largest in the line has a measuring range of 1,200 x 2400 x 1,000 mm.


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