JPS6170428A - Measuring device for resolution of interferometer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Background of the Invention Interferometric measurements have a resolution of distance measurement to the length of the nearest fringe or half wavelength of the light being used, and in some instruments the distance of six fringes can be measured by a quarter of a minute. No. 1.

It is also possible to divide the 8-minute IK. However, such resolution requires a comparator circuit that is difficult to maintain balance.

The inventors have found a method of 5 which yields a much finer resolution for interferometric distance measurements π.

This finer resolution arrangement is also faster, more accurate, and easier to maintain than conventional crude equipment.

SUMMARY OF THE INVENTION This decomposition device generates two detection signals of a voltage that changes to form two sinusoidal waves in a rectangular manner when interference fringes occur from changes in the optical heat length between a reference beam and a measurement beam. This invention relates to a laser interferometer having an optical system that allows

A pair of AD converters each receive the varying voltage signals and convert each signal into digital values that subdivide each sinusoidal fringe cycle into a plurality of increments. An amplifier down counter, fed with a meaningful value from each block, counts the fringes corresponding to the change in optical path length. A computer that has access to the fringe count output from the counter and the digital increment value from the 7F sacred treasure determines the distance measurement value based on the number of fringe f caused by the change in optical path length from the needle planting value, and also calculates the digital increment/minute value. From the value to the optical path length
A distance measurement based on the final value of (,=i) at the incremental value of any subdivided fringe cycle after the conversion is determined.

DETAILED DESCRIPTION FIGS. 1-3 illustrate a typical and commonly known interferometric detection system in which interference fringes produce two rectangular sinusoidal waves. Interferometrically recombined reference and measurement beam 1
1 is imaged on -4 by a series of detectors from lens L2ff. Beam splitter 13 splits this light between a pair of polarizing beam splitters 14 and 15, one beam splitter including a quarter wave plate 16 to square the signal. Polarizing beam splitters 14 and 15 polarize each beam perpendicularly to each other to six pairs of detectors D1.2 and D.
In step 3.4, complementary beams are divided into π such that a phase difference of 180° is produced. When the signals from the six pairs of detectors are inverted and added as shown in FIGS. 2 and 3, they each produce a pure sine wave with no DC offset. Each of the sinusoids 19 and 19 is a changing voltage signal that traces the wave cycle for the six-fringe T transition as the optical path length increases between the reference and measurement beams. When applied to the X and Y plates of the oscilloscope.

The two rectangular sine waves form a sajous figure as shown in Figure 4, and the six stripes move around each other (fit 1).
The 1L pressure draws a circle centered on the intersection of the XY axes.

Counting and resolution in such devices is conventionally accomplished with a comparator that performs an electronic count each time the signal passes through zero or crosses the X or Y axis. This allows eight counts to be made for each wavelength of J'jlrll in the direction of the measurement beam. Signals can also be added and removed to make counts whenever X=Y or X=-Y and Vr to vcB counts can be made per wavelength of motion.

However, keeping such a series of comparators balanced is cumbersome, especially as more comparators are added to increase resolution.

The inventor has developed two variable voltages 1 that generate a rectangular sine wave.
51 that 9 and 9 are digitally subdivided into incremental values yielding even finer resolution. As shown in FIG. 5, in the present invention rectangular signals 19 and 20
is supplied to 7 ranoshu A-D converters 21 and 22. Converters 21 and 22 convert each sinusoidal fringe cycle into converter 2.
Multiple increment values vc depending on bit tolerance of 1 and 22
71j divide. For example, in a 6-pint transducer, each sinusoidal fringe cycle is divided into 64 increments. Further, finer decomposition is possible with an 8-bit or more converter.

6-stripe 1 degree angle 0 point or a meaningful value such as axis crossing value or up-down and fringe count 25
K%, this counter counts the fringes that occur when the optical path length is doubled between the reference beam and the measurement beam, and determines from the rectangular relationship whether the count is increasing or decreasing. The fringe count power from counter 25 thus corresponds to the distance change in the optical path length of the measurement beam as represented by the total fringe meter flVC. This is more efficient than trying to count all the subdivided increments of each set represented by the digital outputs of the transducers 21 and 22, and is more efficient than trying to count all the subdivided increments of each set represented by the digital outputs of the transducers 21 and 22. requires relatively slow movement in the direction of the measurement beam optical path.

Buffering latches 23 and 24 receive the entire series of numbers from converters 21 and 22 and synchronize this series to the access rate of computer 30. Preferably, the combination processor 30 is a relatively fast microprocessor with a wide data bus and access rates in the kilohertz frequency range. converters 21 and 2
2 is Megaher, 714ft')FfAeh'W
Buffering latches 23 and N are preferred to hold data at intervals suitable for transferring to computer 30 Vc. Latches 23 and 24 can be ophthalmic latches that receive data from a 6-bit converter and can be increased in size by 5+17 to accommodate larger converters.

The computer 30 also has an up/down counter 25
Receives the fringe meter θ output from and determines the rough distance from it. Although the subdivided t1j fine resolution of each fringe cycle is computed as a result of the optical path length change, this information is not available until the optical path length change is complete and the length of the measurement beam is at its maximum value. It has no meaning until it stabilizes at a distance of (.).Then the -jr portion of any fringe that occurs over the entire fringe count is determined by the computer 31 and shown on the display 31K.

There are several ways in which the fine resolution of distance moved can be determined from the subdivided digital increments produced by computer 30 or transducers 21 and 22. Since the phase angle is directly proportional to the distance, 9In the present invention, the phase angle at which incremental position within the fringe cycle? computer 3 to also determine
Should I program 0? What is this?
This can be easily done with an elevation tangent table that also shows the phase angle of the viewing area.

For example, point A of the Nori-Sajous figure in FIG. 4 has pressures X and Yol that are tangential to the phase angle that is proportional to the distance increment within the fringe cycle. The constant pressures in X and Y at point B have a tangential relationship to different phase angles for different distance increments. Therefore, using the digital increments 21 and n and the computer 30, one fringe representing many half-wavelengths of motion with fine distance resolution can be rewritten into many 11 fractional values for much more accurate distance determination. Can be divided. As an improvement over conventional arrangements 'π, the resolution is increased by a factor of ten, allowing the apparatus of the present invention to resolve distances up to 1/100,000th of an inch.

[Brief explanation of the drawing]

Figure 1 shows a radial meter detection system that produces two detection signals of voltage that vary to form rectangular sinusoids when radial fringes result from changes in the optical path length between the reference and measurement beams. Figure 2 schematically shows a commonly known arrangement #2 of the device. Figures 2 and 3 show the portion of the apparatus shown in Figure 1 that processes signals from six pairs of detectors. FIG. 4 is a diagram of a Lissajous figure showing the decomposition points established by the apparatus of the invention. FIG. 5 is a schematic diagram of a preferred embodiment of the molecule 3' of the present invention.
...Fluctuating pressure 21.22...A-D converter 23, 24...Buffering latch 25...Up/down counter 30...Computer 31...Display D,, D2. D3. D4...Detector. (5 other people)

Claims (1)

[Claims] 1. When interference fringes arise from a change in the optical path length between the reference beam and the measurement beam, two detection signals of voltages that vary to produce two rectangular sinusoids are produced. A laser interferometer resolution device having an optical system (a) adapted to receive each of said varying voltage signals and convert each signal into digital values subdividing each sinusoidal fringe cycle into a plurality of incremental values; (b) an up-down counter supplied with a meaningful value from each of said converters for counting fringes corresponding to said change in optical path length; and (c) said fringes. Determine from the count a distance measurement value based on the number of fringes resulting from the change in the optical path length, and from the digital increment value the final value of the signal at any subdivided fringe cycle increment after the change in the optical path length. a computer having access to the fringe count output from the counter and the digital increments from the transducer to determine the fine resolution of the distance measurements based on resolution measuring device. 2. A laser interferometer as claimed in claim 1, including a pair of buffering latches adapted to receive said digital increments from said converter and to synchronize access of said computer to said digital increments. Resolution measuring device. 3. The resolution measuring device for a laser interferometer according to claim 1, wherein the computer determines the fine resolution by determining the phase angle of the final value of the signal. 4. The resolution of a laser interferometer as claimed in claim 3, including a pair of buffering latches adapted to receive digital increments from said converter and to synchronize said computer's access to said digital increments. measuring device.