Used angular method in base straightness measurements (like optical autocollimator);
Use the Wollaston method to determine “movement in space” measurements. For example, to characterise the movement of a machine table or working tool;
Used 3D method for rapid estimation of “movement in space”. Similarly to Wollaston method but the measurement is HPI-3d performs in the three axes at once.
The main parameters of those methods are described in the Lasertex Technical Data below.
|Straightness measurement (with angular optics)||0 – 15 m||0.01 µm (for 100 mm base)||± 0.2 %|
|Straightness measurement (with Wollaston optics)||0.3 – 9 m
Vertical range up to ± 30 mm
|0.01 µm||± 0.5 % x L µm|
|Straightness measurement (with 3D optics)||0 – 6 m||0.1 µm||± ( 10 + 10 * L ) µm|
In the picture you can see the application of the angular measurement method. You can use HPI-3D with the angular optics. The laser emitter outputs two polarised laser beams: Horizontal (H) and Vertical (V). It is possible because beam spliter inside IK1 is set at the Brewster angle. Both beams are directed into the measurement path but are parallel shifted by 1’’ or 2’’ distance (depending on the version).
During the measurement process you alter the distance between optical elements. As a result the frequency of both beams changes according to the Doppler Effect. Keep in mind, the laser head does notice a movement only if there is a rotation of IK1 versus RK1. For instance, when there is difference in lengths of beam paths. User the measured distance to obtain either the rotation angle (pitch or yaw of the machine) or the vertical movement of the optical component (IK1 or RK1).
The laser head with angular optics is insensitive to linear movements.
L – base length;
s – distance between beams on IK1 and RK1 elements;
x – distance measured by the Laser Head
α – angular rotation of RK1 element
h – difference in height between two measurement points
The Laser Head measures the parameter x. That is to say, the distance between beams s and the base length L must be set in the parameters of the HPI Software. Then the software can calculate the rotation angle α and the movement in the vertical direction h. Formula for the calculations:
Use the angular optics for the following type of measurements:
Measurement of pitch or yaw of a machine
Measurement of straightness of a machine bed
Measurement of small angles
Measurement of pitch or yaw of a machine and straightness of a machine bed
For the explanation of the first two applications see the picture. Move the RK1 prism assembly on a carriage over the measured guide rail. Meanwhile perform the measurements every 100 mm . The length of the carriage is usually 100mm to make it more convenient. In the same vein use formulas from previous chapter to calculate the angles (for pitch/yaw measurements) or the vertical translations (for straightness measurements).
It is worth to notice, that such straightness measurement method requires proper choice of measurement points. That is to say, choosing points denser than the carriage size results in excessive values of the straightness errors. But the shape of the error is proper.
If you choose points too sparse it may effect both the shape and the value of the error as shown in the figure below. In this special case the measured distance between beams will not change, because of too sparse measurement points the laser will not notice the change in the shape of the guide rail!
Measurement of small angles
The measurement of small angles allows very accurate measurements of small rotations. However the following two conditions should be met:
1. measured angle is within ±5 degrees
2. distance between RK1 and the laser head does not change more than a few centimeters.
The second limitation comes from the heterodyne effect present in the HPI-3D laser. This effect influences the angle according to (Δl is the change of distance between the laser and RK1 during measurements)