Quality Innovations: Easier Error Compensation

January 28, 2009
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When Automated Precision Inc. noticed a need for a shorter and simpler calibration process for machine tools, the company set about finding a solution-a solution that has already proven to be popular.

API’s Volumetric Error Compensation uses a laser tracker and its Active Target laser tracking to precisely calibrate machines in a matter of hours. Source: Automated Precision Inc.


When Automated Precision Inc. (API, Rockville, MD) noticed a need for a shorter and simpler calibration process for machine tools, the company set about finding a solution-a solution that has already proven to be popular.

Dave Maxham, marketing director at Automated Precision Inc., explains that the company’s Volumetric Error Compensation (VEC) technology, released in the fourth quarter of last year, can be used on a variety of machine tools for calibration.

As the machine tolerances change over time, the machines need to be regularly calibrated, Maxham says.

Traditional methods of machine tool calibration often take several days to perform as they measure each axis of travel one at a time, he explains. When a machine has three axes to measure, the typical solutions have been measuring each one of those axes, a process that might take four or five days for calibration. These techniques require multiple setups of a laser interferometer to map the machine, a time consuming process that is subject to thermal drift as the machine stands idle. After this data is collected, it often takes hours to process and determine the compensation factors for each of the machine tool’s 21 error parameters.

With API’s error compensation technology, its Active Target system and T3 laser tracker, operators can measure all of these error parameters, within the machine’s working volume, at a much faster rate.

“Our system can calibrate a large six-axis machine tool in half a day to a day,” Maxham says.

The Active Target constantly moves 300 to 400 points within that volume, then uses mathematics to build a model to map the locations of errors. It then automatically builds compensation tables and downloads them directly to the machine controller.

“What we’re doing is taking essentially a mathematical approach to this problem, rather than the typical mechanical approach,” he says.

By transferring data to the controller, manufacturers can realize tremendous timesavings. “Typically, it may take hours upon hours to compile all of your measurement data,” Maxham says.

Thus, in addition to saving tens of thousands of dollars in downtime, manufacturers can avoid producing parts that are not in spec.

The VEC technology can be applied to almost any type of machine from computer numerical control (CNC) machines to rotary blades, Maxham says. All machine tools need this type of calibration periodically, but it often is so time consuming that operators tend to put it off and learn to work around the machine’s tolerances, he says. This technology makes it a far easier and faster process.

API offers this technology as a service.

“We will bring in all the equipment that’s necessary; we come in and do any error compensation for them,” Maxham says. “They really don’t need to buy any equipment.”

Cost is completely dependent on the machine itself, Maxham says, and whether the company is using a machine the size of a desk or one that is 15 feet tall. The reason for this is the complexity of the machines, making the VEC technology more cost effective with the larger, more complex machines, Maxham says.

“I think its sweet spot is going to be for larger, more complex machines, the ones that are going to be down for a week to calibrate,” Maxham says.

Technology Contact

For more information, contact:
    Automated Precision Inc.
    15000 John Hopkins Dr., Rockville, MD 20850
    (240) 268-0400
    dave.maxham@apisensor.com
    www.apisensor.com


Specifications

  • API’s Volumetric Error Compensation uses a laser tracker and its Active Target to precisely calibrate machines in a few hours.

  • Using a single setup, the tracker performs continuous measurements to map the machine tool as it moves throughout the machine’s entire working volume. The VEC software then processes the data in minutes.

  • This software has the ability to simulate the entire machine tool path, graphically display the volumetric error, calculate compensation tables and upload them directly to the controller.

  • Test results have confirmed a four-fold improvement in machine tool accuracy in less time using the VEC process vs. traditional calibration methods.
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