Product category:
Rotary Position, Tilt and Angular Sensors
News Release from: Renishaw | Subject: ML10 laser interferometer
Edited by the Engineeringtalk Editorial
Team on 11 January 2006
Costs cut at CNC water-jet cutting
machine maker
Renishaw's ML10 laser interferometer measurement system and QC10 ballbar reduces manufacturing costs and increases machine accuracy at Czech CNC water-jet cutting machine maker.
Renishaw's ML10 laser interferometer measurement system and QC10 ballbar has reduced manufacturing costs and increased machine accuracy at a Czech CNC water-jet cutting machine maker This has helped Prague manufacturer PTV grow sales of its machines and increase machine accuracy by a factor of four
Precision water cutting has advantages over traditional CNC machine tools in processing high specification metals, composites and other media.
Thin, flexible or sensitive materials, such as rubber, plastics and even paper, are especially difficult to machine using traditional methods.
In these cases, water cutting provides many of the advantages of laser cutting machines, but at a lower cost.
In the cutting process, the water is compressed to a pressure of over 4000bar, then directed through specially designed nozzles.
For certain materials and for high-speed grinding, water is mixed with natural garnet abrasive before cutting.
PTV makes one design of machine, but can vary the x and y dimensions over a large range, according to customer needs.
In effect, every machine is customised.
Engineers can adapt machine components both in initial construction in Prague and during installation at a user's site.
The machine was designed in 2002, originally with a magnetic linear encoder system and a MEFI CNC control.
Initially there were problems with maintaining the precise separation between encoder and read-head, particularly over distances greater than 6m.
There were also dynamic problems in achieving the required machine accuracy, due to the lightweight aluminium structures for the x-axis and y-axis.
MEFI suggested using a laser interferometer to identify the causes of these inaccuracies and PTV opted for the ML10.
Jan Kunert, CNC engineer, said: "We visited one of our customers, where a Renishaw engineer demonstrated the ML10 system".
"We realised that not only could we use it to identify the dynamic errors, but we could also use it to map errors during machine production".
"The system we bought is now used so extensively, both in the factory and during on-site installation, that we intend to buy another".
PTV removed the magnetic linear encoders from the original design, instead taking positional feedback from the rotary encoders integrated onto the drive motors.
These encoders had always been there, but had been thought to provide inaccurate feedback due to the variable distance and the resulting effects from the twisting of the ball-screw.
This is where the ML10 and Laser10 software proved its worth.
The system's laser optics are mounted onto the structure of the finished machine and readings taken at every 20mm of axis movement.
This is compared with the value provided by the machine's rotary encoder, which is at least always repeatable, to generate a compensation value for that position.
The positioning uncertainty on the original design could be up to 0.2mm per metre.
Accuracy is now always better than 0.05mm per metre.
The ML10 uses the stable wavelength of laser light to provide performance verification to ISO 230-6 and traceability of the measurements in line with ISO9001.
There are other machine characteristics that PTV checks and adjusts through the use of a 10min test with the QC10 ballbar.
During the test, the water cutting machine is instructed to describe a circular path in the x-y axis, with the ballbar coupled to the machine on magnetic mounts.
Any variation from the normal test circle radius is picked up by the ballbar's transducer and data fed back to a PC running Ballbar5 analysis software.
This provides exact error values for 21 machine characteristics.
Backlash and scale mismatch are two major sources of error but, provided with the exact values from the ballbar, engineers can adjust them immediately.
The company used to spend half a day on a machine attempting to find and remove errors.
Now it can be done in 30 to 40min. Request a free brochure from Renishaw ...
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