3 dimensional machine tool positioning accuracy: laser vector measurement vs. linear measurement. - laser linear measurement device

by：UMeasure     2019-12-02

The increasing demand for machining parts precision is due to the fact that it drives economic growth by reducing assembly, warranty and ownership costs.
Traditionally, the manufacturer ensures that the accuracy of the part is linear (one-dimensional)
Calibration of machine tools used to manufacture them.
However, linear calibration is not enough to ensure the accuracy of 3D parts. ASME B5. 54 and ISO230-
The performance measurement standards of six kinds of volumetric machine tools are introduced.
Because of the cost, the machine is not required
In two or three days of production, manufacturers have been reluctant to adopt volume calibration.
However, laser vector technology developed by Optodyne for 3D volume calibration and compensation
The use of laser Doppler calibration equipment has become increasingly popular as it reduces the time factor from two to three days to two or three hours.
Relying on linear calibration
The only possible error for the dimensional measurement of the motion axis is assumed to be the screw and thermal expansion error.
However, this ignores non-linear errors, Flatness errors, angle errors, and errors caused by non-linear errors
Rigid body motion.
In fact, there are many large non-
Rigid body positioning error due to changes in weight and weight, etc.
Using Taylor's linear expansion theory to push this to the extreme, two slope terms can be added in the vertical direction.
Asa results for 3-
Shaft machine, there are 45 errors.
Of course, not all of these
The rigid body error term is important.
Because the positioning accuracy of the machine tool is very complicated, it is simplified under various assumptions.
For example, a rigid body hypothesis proposes six errors--
One displacement error, two Flatness errors and three angle errors--
In the X, Y, and Z axes. For a 3-
The machine of the shaft has 18 errors plus 3 square errors, with a total of 21 errors.
Therefore, in order to obtain higher positioning accuracy, angle, flatness and Flatness errors must be measured and compensated.
Using laser vector technology, determining 3D volumetric accuracy requires only four measurements of body-to-direction displacement.
The diagonal displacement error of the body is very sensitive to all Volume error components, so the volume accuracy is effectively tested.
Laser vector technology measures all three displacement errors, three vertical Flatness errors and three horizontal Flatness errors with only four devices.
The working volume of a typical VMC includes eight body diagonal lines, defined by starting from an angle of the base plane and moving to the opposite angle of the top plane.
These body diagonal lines are defined by the movement of the positive or negative axis.
In addition to the opposite direction, the last four body diagonal lines are the same as the first four diagonal lines.
Therefore, there are only four diagonal directions of the body moving forward and reverse (bidirectional)
There are only four settings.
For each setting, the motion of the machine spindle along each diagonal is measured by performing the X, Y and Z parts of the rotation stroke first.
For three displacement errors, three vertical Flatness errors and three horizontal Flatness errors, the readings are performed and recorded at each intermediate step.
Two main systems for linear displacement and volume calibration of laser calibration machine tools and CMMs include dual-aperture laser interference systems and single-aperture interference systems.
Both systems use laser and optical systems, but they differ in the way data is collected and analyzed.
The dual-aperture laser interference system is based on the dual-aperture laser interference system.
As shown in the figure, there are two beams of laser, the output beam and the return beam, they are parallel but the displacement is about 1"1.
These two beams of light require a large optical system.
Also, alignment is critical because three elements must be aligned
Increased installation time.
The laser head of the double aperture laser interferometer is large and heavy, and requires a heavy tripod to support it. [
Figure 1 slightly]The single-
The aperture optical difference laser system is based on laser measurement.
Very compact laser head (2" x 2" x8. 5")
And completed the stable circuit, electronic
Optics and photosdetectors.
As shown in the figure.
The output beam has the same aperture as the return beam.
A small reverse reflection or flat
Can be used as a target mirror;
Therefore, the laser system is very compact and widely used.
Ability to use a tablet
The Mirror as the target is very important for laser vector technology.
Since there are only two elements that need to be aligned, alignment is not as difficult as a dual-aperture laser interferometer.
In addition, the system is very compact and can be installed on the machine tool, providing higher accuracy, and there is no need to remove the cover or remove the machine tool.
There are significant differences between dual-aperture and single-aperture interference systems.
For example, the single aperture interference system uses only two optical elements, one laser head and one reflection pole, making calibration and setting easier and faster.
Because the optical system is much smaller, the whole system will be installed in a huge briefcase, making it easier to install and transport.
The single aperture interference system is the only one that can use the flat mirror as the target, which is the time-
Laser-saving vector technology for 3D volume calibration.
Regular volume calibration and compensation increases productivity and cost effectiveness, and shortens cycle times, improves part quality, reduces number of repairs, and reduces warranty costs.
With more and more quality control procedures requiring calibration, the ability to utilize volume calibration and compensation will inevitably lead to a more competitive and profitable manufacturing process. Optodyne Inc. ,www. rsleads. com/308tp-
200 or 200 circle FAQ questions: when following ASME b5. 54-
1992 and ISO 230-
6 calibration standard, is there a situation where the machine tool can get good results even if its volume performance is poor?
A: ASME b5. 54-
1992 and ISO 230-
The 6 standards have been in use for a long time, and their efficacy has been verified over the years through the empirical physical cutting test.
In theory, the only case where the volume performance may be poor and still shows good results is when there is a linear displacement error in X, Y and z, and 18 other angles, the error of flatness and straightness is 0.
However, this is very unlikely because of ASME b5. 54-
1992 and ISO 230-
6 in 3D space, at least 10 measurement points are required along the diagonal of the body between the two corners.
While the error of all 10 points may be exactly the same and offset each other, it is a hypothetical situation where there is little chance of copying in real life.
Question: Will linear displacement errors vary when using sequential step sizes and traditional linear techniques?
A: the traditional linear displacement technology only measures one side, and does not consider the pitch angle, yaw angle and angle error.
This step can measure all four edges.
The measurement is average and the result is a displacement error through the center of the volume, which is essentially more accurate.
For example, pitch angle, yaw angle, and roll angle errors affect all measurements, including linear displacement measured by conventional laser interferometer.
So along the X-
When measured at different Y and Z positions, the axes are different.
This is because different Abbe deviates from different positions, as well as pitch angle, yaw angle and roll angle movement.
That's why b5.
54 all linear displacement measurements in standard states must be along three orthogonal lines (
Parallel to 3 axis)
Through the center of the work volume.
The advantage of laser vector technology is that the measurement contains the positioning error caused by the angle error and is expressed as the average linear error along the center line of the working volume.
This is important because most machine tools cannot compensate for the angle error.
If the angle error cannot be compensated, the best way is
The surrounding is to compensate for the average linear error.
Of course, due to Abbe offset and angle error, the displacement error and straight line error measured on one side of the working volume will be different from the displacement error and straight line error measured on the other side of the edge.
This is why the laser vector technology measures four errors and the average error.
Question: using laser vector technology, will the measurement be inaccurate if the mirror is misplaced?
A: No, because the error is a constant.
Any misplacement of Planemirrior results in an error proportional to the distance from the reflection point to the new point on the reflection point multiplied by the misplacement angle.
This error can be very large in some cases.
But this error is a constant (
The distance is a constant, and the dislocation angle is a constant).
If the mirror image is not aligned, the error is constant and calculated automatically by the device.
However, if someone is concerned about this, it will take only a few minutes to re-align the mirror to the right position.
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