Title of Invention

"A DEVICE USEFUL FOR THE ENHANCEMENT OF RESOLUTION OF AN AUTOCOLLIMATOR "

Abstract A device useful for the enhancement of resolution of an autocollimator which comprises a plane reflecting surface (E) mounted perpendicularly on to a rotatable surface (B), characterized in that a second plane reflecting surface (F) being fixed in the same plane as the first reflecting surface (E) but independent of the said rotary table (B) so as to enable multiple internal reelections of an autocollimator incident beam (A), a detector-reflector (D) being fixed so as to enable retro reflection of the inter-reflected autocollimator incident beam (A), a detector-reflector (D) being fixed so as to enable retro reflection of the inter-reflected autocollimator incident beam (A) from the plane reflecting surfaces (E) and (F).
Full Text The present invention relates to a device useful for the enhancement of resolution of an autocollimator. The device of the present invention is mainly useful for increasing the resolution of autocollimators by increasing their measurement capabilities for small angle measurements and calibration of indexing tables.
Presently in industry and in research establishments there exists a large number of low resolution autocollimators having resolution of 1 to 0.1 sec of arc. Systems presently available for calibration of angular gauges and rotary table, autocollimator of 0.01 sec of arc to 0.005 sec of arc resolution constitute the main part of these measurement set-ups. All these autocollimators also need calibration facilities for their own recalibrations. Realization of such facilities based on interferometric techniques such as inteferometric measurement of angles have been carried out by Malacara (D) and Harris O. as reported in Applied optics 9(1970) S 1639-1633. Another arrangement has been described as Winkelmessungen mit Laser Interferometers by E. Debler in PTB Bericht-PTB-me-8, Oct. 1975 Braunschweig, Germany, such interferometer devices are costing prohibitantly high.
Using the resolution enhancement technique, a low resolution autocollimator say of 0.1 sec of arc can be used as that of 0.01 sec of arc or even as 0.005 sec of arc resolution instrument. The user agencies of these techniques will include precision laboratories, automobile industries, gear manufacturing and precision engineering industries etc.
The multiplicative reflection approach in combination with autocollimators for generating different standard equal divisions of a circle has been discussed in reference JOSA 51(1961)859-862 which describes an arrangement of mirrors and polygon to deviate a light beam to form a complete circle through alternate reflections. Figure. 1 shows such an arrangement where an autocollimator (1) with the support of an optical cube (2) and plane mirrors (3), (4), (5) and (6) and the rotary table (7) constitute a set up of dividing the 360 deg. Into 4 equal parts. It is to be noted that with rotation of optical bcube (2) by an angle a., the reading in the autocollimator (1) will change by an mount of 2a x 2x.4, i.e. 16α. An autocollimator with several plane mirrors have been used for dividing the 360°C circleinto

integer standard angles. The autocollimator magnification is enhanced in such arrangements .However, the drawback is because of their regular cyclic character, the set up is more complicated in their system component requirements and adjustments.
It is found that there is no equipment and or device available for increasing the resolution of existing autocollimators or enhancing the resolution of low resolution, and low cost autocollimators.
The main objective of the present invention is to provide a device useful for the enhancement of resolution of an autocollimator.
Another objective of the present invention is to provide incorporation of the device of the present invention to a low resolution autocollimator thereby removing the drawback of low resolution and enabling the said autocollimators to function as high resolution autocollimators.
Yet another object of the present invention is to provide a device capable of enhancing autocollimator resolutions economically.
In the drawing accompanying this specification, fig. 2. represents the schematic diagram of the device of the present invention wherein, (A) is an autocollimator whose resolution is to be enhanced by a given integer factor n, (B) is a rotatable surface such as a circular rotating table; (E)and (F), are two plane reflecting surfaces and (D) is reflector-detector. The plane reflecting surface (E) is fixed on the turn table (B) and is fixed in such a manner that is parallel to reflecting surface (E). Reflecting surface (F) remains fixed irrespective of rotation of the rotary table (B). Reflecting - detecting surface (D) is also mounted independent of(B)but is fixed in such a manner as to enable the incident beam to reflect back to the autocollimator (A). The reflecting surfaces (E) and (F) are so adjusted that reflected light is observed in the Autocollimator (A) after known number of reflections 'n' from the surface (E). A tilt/rotation of the rotary table (B) by a small angle q will be deflected in the autocollimator as 2nq hence the resolution enhancement factor obtained is n.

Accordingly the present invention provides a device useful for the enhancement of resolution of an autocollimator which comprises a plane reflecting surface (E) mounted perpendicularly on to a rotatable surface (B), characterized in that a second plane reflecting surface (F) being fixed in the same plane as the first reflecting surface (E) but independent of the said rotary table (B) so as to enable multiple internal reflections of an autocollimator incident beam (A), a detector-reflector (D) being fixed so as to enable retro reflection of the inter-reflected autocollimator incident beam (A), a detector-reflector (D) being fixed so as to enable retro reflection of the inter-reflected autocollimator incident beam (A) from the plane reflecting surfaces (E) and (F).
In a feature of the present invention the plane reflecting surfaces (E) and (F) used may be such as mirrors, front or back polished surfaces of metallic and non-metallic materials.
In another feature of the present invention the rotatable surface used may be such as capable of rotation by means such as manual, prime movers.
In yet another feature of the present invention the incident beam may be such as white light beam, infr-red beam, laser beam and light emitting diode (LED).
Still another feature of the present invention is the reflector-detector used may be such as a plane reflecting surfaces, an autocollimator.
Accordingly, the present invention provides an autocollimator incorporating the device of the present invention which comprises of an autocollimator incorporated with the device as described above.
In an embodiment of the device of the present invention, an autocollimator whose resolution is to be enhanced is field on a stand. A plane mirror fixed on a rigid rotary table with the reflecting surface of the mirror perpendicular to that of the table. Another plane mirror resting on a stand independent of the rotary table so that both the reflecting surfaces face each other in near parallel position at any convenient separation from each other and in almost symmetric position to the centre of the rotary table. The autocollimator and the mirror.
strips are set in a position such that the light beam coming out of the autocollimator experiences multiple reflections after falling on one of the plane mirrors on one end and emerging out at the other end. A reflector-detector placed independently of the rotary table receives this emergent beam. In case the reflector-detector is a plane reflecting surface such as a plane mirror, the plane mirror sends back the optical beam to retrace its path to be detected by the emanating autocollimator which will now show the enhanced angular deviation. In this case the enhancement factor of the angle of rotation given to plane mirror resting on the rotary table is the total number of reflections taking place from this rotatable mirror in forth and back direction.
In case, the reflector-detector is an autocollimator, the emergent beam coming from the near parallel plane mirrors is received by this autocollimator rather than reflected back into the multiple reflection zone once again. Enhancement of rotated angle of the plane mirror resting on the turn table do takes place in this case too. But the multiplication factor is equal to the number of the reflections taking places from the rotatable mirror rather than the double of this number which was the case when the reflector-detector was reflector.
The basic principle used in the device of the present invention is one of the reflectors principle namely a reflected ray is deviated by double the angle of mirror rotation. This double rotation in the reflected beam is employed in specific multiple manner to achieve a practical resolution enhancement set-up.
The angle multiplication factor is 'n' where n is the number of reflections from the plane mirror resting on the rotary table. Thus the number of reflections taking place from the moving mirror are important in deciding the resolution enhancement factor and not the total number of reflectors by which the beam is being reflected in the set-up. In other words, the number of reflection from the stationary mirrors do not contribute in the angular enhancement of the angle by which the rotary table is rotated.

The following examples are given by way of illustrations of the device of the present invention and therefore should not be construed to limit the scope of the present invention.
EXAMPLE - 1
The experimental schematic diagram is shown in figure 2. The autocollimator (A) whose resolution was to be enhanced was manual autocollimator of 0.2 sec of arc. resolution. (A) has been fixed on rigid stand inclined to a rotary table (B). (B) was a rigid indexing table with rough and fine rotating provisions to the order of fraction of a second of arc. The plane mirror (E) and (F) were rectangular strips of 30mm x 400mm size each cut from a plane looking mirror (E) and (F) were fixed with their reflecting surfaces facing each other in near parallel position and almost symmetrical tot the centre of the rotary table (B). Mirror (E) has been fixed on (B) while (F) has been fixed independent of (B). Autocollimator (A) was adjusted at an inclined angle so that light beam coming out of it gets reflected alternately from (E) and (F). The number of reflections from (E) or (F) are easily countable and can be changed by changing the inclination angle of (A) and (E). A plane mirror (D) was adjusted also independent of the rotary table (B) so that the light beam has been received by the autocollimator (A) after retracing its path through multiple reflections from (E) and (F). The number of reflections form (E) taking place in forth and back travel of the light beam were adjusted to be 8. A laser interferometer with its angular optics has been mounted on (B) to note the angular change given to (B). The readings were taken of the autocollimator (A) for a rotation of 2 sec of arc to (B). The autocollimator (A) has been found to give a mean value of 15 sec of arc which is 8 time the given 2 second of rotation and is acceptable with in experimental limits.
EXAMPLE - 2
The experimental schematic diagram is shown in figure 2. The autocollimator (A) whose resolution was to be enhanced was manual autocollimator of 0.2 sec of arc. resolution (A) has been fixed on rigid stand inclined to a rotary table (B). (B) was a rigid indexing table with rough and fine rotating provisions to the order of fraction of a second of arc. The plane

mirrors (E) and (F) were rectangular strips of 30mm x 400mm size each cut from a plane looking mirror (E) and (F), were fixed with their reflecting surfaces facing each other in near parallel position and almost symmetrical tot her centre of the rotary table (B). Mirror (E) has been fixed on (B) while (F) has been fixed independent of (B). (A) was adjusted at an inclined angle so that light beam coming out of it gets reflected alternately from (E) and (F). The number of reflections form (E) and (F) are easily countable and can be changed by changing the inclination angle of (A) and (E).
A plane mirror (D) was adjusted also independent of the rotary table (B) so that the light beam bas been received by the autocollimator (A) after retracing its path through multiple reflections from (E) and (F). The number of reflections from (E) taking place in forth and back travel of the light beam were adjusted to be 10. A laser interferometer with its angular optics has been mounted on (B) to note the angular change given to (B). The autocollimator (A) has been found to give a mean value of 21 sec of arc which is 20 time the given 2 second of rotation and is acceptable within experimental limits.
EXAMPLE - 3
The experimental schematic diagram is shown in figure 2. The autocollimator (A) whose resolution was to be enhanced was a manual autocollimator of 0.2 sec of arc. resolution. (A) has been fixed on rigid stand inclined to rotary table (B). (B) was a rigid indexing table with rough and fine rotating positions to the order of fraction of second of arc. The plane mirror (E) and (F) were rectangular strips of 330mm x 400mm size each cut from a plane looking mirror (E) and (F) were fixed with their reflecting surfaces facing each other in near parallel position and almost symmetrical to their centre of the rotary table (B). Mirror (E) has been fixed on (B) while (F) has been fixed independent of (B). Autocollimator (A) was adjusted at an inclined angle so that light beam coming out of it gets reflected alternately from (E) and (F). The number of reflections from (E) or (F) are easily countable and can be changed by changing the inclination angle of (A) and (E). A plane mirror (D) was adjusted also

independent of the rotary table (B) so that the light beam has been received by the autocollimator (A) after retracing its path through multiple reflections from (E) and (F).
The number of reflections from (E) taking place in forth and back travel of the light beam were adjusted to be 12. A laser interferometer with its angular optics has been mounted on (B) to note the angular change given to (B). The readings were taken of the autocollimator (A) for a rotation of 2 sec of arc to (B). The autocollimator (A) has been found to give a mean value of we sec of arc which is 24 times the 2 second of rotation and is within experimental acceptable limits.
EXAMPLE - 4
The experimental schematic diagram is shown if figure 2. The autocollimator (A) whose resolution was to be enhanced was manual autocollimator of 0.2 sec of arc. resolution. (A) has been fixed on rigid stand inclined to rotrary table (B). (B) was rigid indexing table with rough and fine rotating provision to the order of fraction of second of arc. The plane mirrors (E) and (F) were fixed with their reflecting surfaces facing each other in near parallel position and almost symmetrical to the centre of the rotary table (B). Mirror (E) has been fixed on (B) while (F) has been fixed independent of (B). Autocollimator (A) was adjusted at a inclined angle so that light beam coming out of it gets reflected alternately form (E) and (F). The number of reflections for (E) and (F) are easily countable and can be changed by changing the inclination angle of (A) and (E).
In this case with reflector- detector was an autocollimator as detector i.e. another autocollimator with a resolution of 2 sec of arc has been used for detecting the change in angle position of the emergent collimated beam coming from the autocollimator(A) after multireflections from mirrors (E) and (F). The number of reflections taking place from mirror (E) were 5. A laser interferometer with its angular optics has been mounted on (B) to note the angular change given to (B). The readings were taken of the autocollimator (D) for a rotation of 2 sec of arc to (B). The values have been found to be in the ration of 1:5.

From the above four examples it is clear that the device of the present invention successfully enhances the resolution of low resolution autocollimators.
The main advantages of the present invention are as follows:
1. A simple and low cost device useful for enhancing the resolution of low resolution/low
cost autocollimators.
2. The device provides flexibility resolution enhancement by varying the number of reflections.
Wide range of resolution enhancement factor can be generated by mere change of the angle
between the autocollimator axis and the plane of the plane mirror i.e. its incidence angle.
3. The device provides a standard enhancement factor for changing resolution and it can never
be a fractional number , the stated fact is built -in in the principle of invention, so it its very
much suited to the standard set-ups for the calibration applications.


We Claim:
1. A device useful for the enhancement of resolution of an autocollimator which
comprises a plane reflecting surface (E) mounted perpendicularly on to a
rotatable surface (B), characterized in that a second plane reflecting surface (F)
being fixed in the same plane as the first reflecting surface (E) but independent
of the said rotary table (B) so as to enable multiple internal reflections of an
autocollimator incident beam (A), a detector-reflector (D) being fixed so as to
enable retro reflection of the inter-reflected autocollimator incident beam (A), a
detector-reflector (D) being fixed so as to enable retro reflection of the inter-
reflected autocollimator incident beam (A) from the plane reflecting surfaces (E)
and (F),
2. A device as claimed in claim 1 wherein the reflector detector used is selected
from a plane reflecting surface, autocollimator.
3. A device useful for the enhancement of resolution of an autocollimator
substantially as herein described with reference to the examples and figure2 of
the drawings accompanying this specification.

Documents:

3156-del-1998-abstract.pdf

3156-del-1998-claims.pdf

3156-del-1998-correspondence-others.pdf

3156-del-1998-correspondence-po.pdf

3156-del-1998-description (complete).pdf

3156-del-1998-drawings.pdf

3156-del-1998-form-1.pdf

3156-del-1998-form-19.pdf

3156-del-1998-form-2.pdf


Patent Number 215718
Indian Patent Application Number 3156/DEL/1998
PG Journal Number 12/2008
Publication Date 21-Mar-2008
Grant Date 03-Mar-2008
Date of Filing 28-Oct-1998
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI - 100001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 PARVINDER PAL SINGH NATIONAL PHYSICAL LABORATORY NEW DELHI
2 LAKHAN SINGH TANWAR NATIONAL PHYSICAL LABORATORY NEW DELHI, INDIA.
PCT International Classification Number G02B 17/06
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA