CA1087389A - Distance measuring gauge using relative movement between diffraction gratings - Google Patents
Distance measuring gauge using relative movement between diffraction gratingsInfo
- Publication number
- CA1087389A CA1087389A CA249,931A CA249931A CA1087389A CA 1087389 A CA1087389 A CA 1087389A CA 249931 A CA249931 A CA 249931A CA 1087389 A CA1087389 A CA 1087389A
- Authority
- CA
- Canada
- Prior art keywords
- measuring
- gratings
- measuring member
- surface portions
- radiations
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 230000005855 radiation Effects 0.000 claims abstract description 17
- 230000005540 biological transmission Effects 0.000 claims abstract description 3
- 239000000463 material Substances 0.000 claims description 25
- 238000000034 method Methods 0.000 claims description 17
- 125000006850 spacer group Chemical group 0.000 claims description 9
- 239000000314 lubricant Substances 0.000 claims description 8
- 239000011248 coating agent Substances 0.000 claims description 6
- 238000000576 coating method Methods 0.000 claims description 6
- 230000005670 electromagnetic radiation Effects 0.000 claims description 4
- 230000000694 effects Effects 0.000 claims description 3
- 230000001050 lubricating effect Effects 0.000 claims description 3
- 229910052751 metal Inorganic materials 0.000 claims description 3
- 239000002184 metal Substances 0.000 claims description 3
- 239000007787 solid Substances 0.000 claims description 3
- 238000005530 etching Methods 0.000 claims description 2
- 239000007788 liquid Substances 0.000 claims 1
- 239000011521 glass Substances 0.000 description 14
- 230000008878 coupling Effects 0.000 description 8
- 238000010168 coupling process Methods 0.000 description 8
- 238000005859 coupling reaction Methods 0.000 description 8
- 238000004519 manufacturing process Methods 0.000 description 6
- 239000010408 film Substances 0.000 description 5
- 239000012530 fluid Substances 0.000 description 5
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 4
- 229910052804 chromium Inorganic materials 0.000 description 4
- 239000011651 chromium Substances 0.000 description 4
- 239000004568 cement Substances 0.000 description 3
- 238000013016 damping Methods 0.000 description 3
- 239000003921 oil Substances 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 238000005507 spraying Methods 0.000 description 3
- 239000012780 transparent material Substances 0.000 description 3
- 238000005259 measurement Methods 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 238000012552 review Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 241000518994 Conta Species 0.000 description 1
- 244000182067 Fraxinus ornus Species 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 230000003321 amplification Effects 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- ROUIDRHELGULJS-UHFFFAOYSA-N bis(selanylidene)tungsten Chemical compound [Se]=[W]=[Se] ROUIDRHELGULJS-UHFFFAOYSA-N 0.000 description 1
- 238000005422 blasting Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000000549 coloured material Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000002783 friction material Substances 0.000 description 1
- 239000003292 glue Substances 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 239000002648 laminated material Substances 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- CWQXQMHSOZUFJS-UHFFFAOYSA-N molybdenum disulfide Chemical compound S=[Mo]=S CWQXQMHSOZUFJS-UHFFFAOYSA-N 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 238000007639 printing Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000010979 ruby Substances 0.000 description 1
- 229910001750 ruby Inorganic materials 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- 210000003813 thumb Anatomy 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 238000001771 vacuum deposition Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B3/00—Measuring instruments characterised by the use of mechanical techniques
- G01B3/22—Feeler-pin gauges, e.g. dial gauges
- G01B3/24—Feeler-pin gauges, e.g. dial gauges with open yoke, i.e. calipers
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/36—Forming the light into pulses
- G01D5/38—Forming the light into pulses by diffraction gratings
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optical Transform (AREA)
- Length-Measuring Devices Using Wave Or Particle Radiation (AREA)
- Length Measuring Devices By Optical Means (AREA)
- Length Measuring Devices With Unspecified Measuring Means (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A hand held digital read-out measuring instrument in which interference fringes are generated by the transmission of radiations through gratings which move relative to one another according to a distance being measured and the fringes are counted to detect changes in the fringe pattern and generate a pulse output related to the distance, means being provided to control the rate of movement and to exert a substantially constant force on the movable elements.
A hand held digital read-out measuring instrument in which interference fringes are generated by the transmission of radiations through gratings which move relative to one another according to a distance being measured and the fringes are counted to detect changes in the fringe pattern and generate a pulse output related to the distance, means being provided to control the rate of movement and to exert a substantially constant force on the movable elements.
Description
.
\
This invention relates to measuring apparatus. The apparatus of the invention can be used, for example, to measure a dimension of an object or a distance by which an object moves.
The dimension or distance is measured by counting the number of fringes of an interference pattern that passes a given point during the movement of a grating with respect to another grating.
The history of the use of gratings in measuring apparatus is traced in a review article in the Journal of Physics E:Scientific Instruments for March 1972 Volume 5 No. 3 pages 193 - 198, publish~d by the Institute of Physics, London, England and entitled Gratings in MetrGlo~.
Known measuring apparatus-employing interference patterns are both bulky and expensive.
~ o some extent this is due to the difficulties experienced in manufacturing and copying accurate gratings having fine resolution characteristics. The difficulties experienced in making an accurate master grating, from which gratings to ~e used in measuring apparatus can be derived, are explained in the review article r~ferred to above. Partly as a result of these difficulties, it is the common practice in such known measuring apparatus to use gratings having a 10 micron period and to employ analog electronic division techniques to obtain a measuring resolution of 1 or 2 microns, as required.
~, One aspect of the present invention is concerned with the provisions of an improved method for making a master :, grating.
- 30 Another aspect of the present invention is concerned ,~ with the provision of a measuring apparatus that in at least one embodiment is small enough to be held in the 1~8738~
hand, that is self-contained and that can operate without connection to any additional apparatus or separate power supplies. It will be appreciated, however, that the invention is not limited to use with hand held apparatus, but that it can be applied to other measuring apparatus, for example bench mounted apparatus.
Accordingly the present invention provides a digilal read-out measuring instrument including a first measuring member, a second measuring member, the first measuring member being slidable relative to the second measuring member to effect a measuring cperation, a first measure-ment-providing member of an electromagnetic radiation-transmissive ma~terial having first and second surface portions at a given angle relative to one another/ a first diffraction grating on the first of the surface portions, the first diffraction grating being coupled through said first measurement-providing member to and movable in accordance with movements of the first measuring member, a second measurement-providing member of an electro-magnetic radiation-transmissive material having third and fourth surface portions at said given angle relative to one another, a second diffraction grating on the third of the surface portions, the second diffraction grating being fixed relative to the second measuring member and beinc so arranged in relation to the first diffraction grating that interference fringe patterns can be produced by q~. electromagnetic radiations passed successively thrGugh the two gratings, a source of electromagnetic radiations, means ; to detect radiations from the source, the source being so ~: 30 arranged that radiations emitted by the source are directed successively through the gratings and the detector means being arranged to detect the interference fringe pattern '~
`'; ~
resulting from the transmission of the radiations through the gratings and to provide a pulse output according to changes in the fringe pattern, a pulse counter connected to the output of the detector means, digital display means connected to the output of the counter, spacer means in the form of a non self-supporting coating on one of the first and third and one of the second and fourth surface portions to slidably space the first and third surface portions and the second and fourth surface portions apart respectively, and means for ccntrolling the speed of movement of the first measuring member.
A described embodiment has a plurality of features, apart from the use of an improved method of making a master grating referred to above, that contribute to a reduction in the bulk and the cost of the apparatus, thereby enabling, for example, a self-contained hand held apparatus to be made.
A further feature of a described embodiment is the use, in the counting of the fringes of an interference pattern, of an electrical circuit that is comparatively simple.
In a preferred embodiment of the invention, a circuit is used that requires only four pulses per cycle of the fringes to be generated and these pulses are generated from the signals obtained from two or more detectors using well G ~` known electronic techniquesr for example the techniques - ~ described in the specificiation of United Ringdom Patent No. 760,321.
In the preferred embodiment of the invention, in order - 30 to achieve a resolution of 1 micron, the period of the gratings used to generate the fringes is as small as 4 micro~s.
;\ ~
1~873B9 Yet a further feature of the des~ribed embodiments of the invention, which feature enables the contrast between the modulated signal output from the detectors and the unmodulated background noise to be as high as possible, is concerned with the provisicn of mounting means which enable the two gratings, which are to be moved relatively to one another, to be as close as possible to one another.
_ This requirement is particularly necessary with gratings having a period as small as 4 microns. In the preferred embodiment of the invention the spacing between the gratings is no more than 12 microns, although it is possible to operate the system with a spacing between the gratings of up to 20 microns.
In a particular embodiment of the invention to be described below in more detail, the invention is employed with a hand held micrometer and the embodiment to be described has the particular advantage over the conventional screw threaded instrument that measurements can be taken much more quickly. One reason for this is that the device to be described employs an instantaneous digital readout of the relative positions of the spindle of the instrument with reference to an anvil and has a spindle which can be slid directly to the position required, whereas it can take , .
as long as 20 seconds to move the spindle of a conventional instrument employing a screw to the fully open position.
A further feature of a described embodiment is the ; ~ use of a system which exerts a substantially constant - force to urge the spindle against the anvil, thereby ensuring that a force of the same value is consistently exerted upon an object being measured between the anvil and the spindle.
Yet another feature of an embodiment of the invention ~8`7~
is the provision of a damper system that controls the speed at which the spindle slides and thus the rate at which pulse signals are applied to a pulse counting circuit.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings wherein like parts are indicated by the same reference numerals and in which:
Fig. lA, Fig. lB and Fig. lC are a partly cut-away plan view, a longitudinal section on the line B-B of Fig.
lA, and a cross section on the line A-A of Fig. lB
respectively of a hand-held mi_rometer gauge, ~ig. 2A, Fig. 2B and Fig. 2C' are a side elevation, an end elevation and an exploded perspective view of a glass measu~ing block arrangement, Fig. 3 is a longitudinal section through a coupling unit used in the gauge, Fig. 4A and Fig. 4B are end and plan views respectively - of the glass measuring block arrangement showing an associated radiation emitter and receiver arrangment, Fig. 5 is a block schematic circuit diagram, Fig. 6A and Fig. 6B are a longitudinal section and a cross section on the line A-A of Fig. 6A of a grating and damper assembly, Fig. 7A, Fig. 7B and Fig. 7C are a diagrammatic cross-.:; -sectional view of the arrangement shown in Fig. 6A and 6B, t together with a mask system, a view on the line A-A of Fig. 7A and a view in the direction of the arrow B of the arrangement shown in Fig. 7A respectively and Fig. 8 is a flow chart illustrating the steps in the making of a master grating.
Referring now to the drawings, there is shown in Figs.
lA, lB and lC a hand-held measuring gauge having a spindle 1 (which constitutes the first of two "measuring members") which is arranged to slide towards and away from an anvil
\
This invention relates to measuring apparatus. The apparatus of the invention can be used, for example, to measure a dimension of an object or a distance by which an object moves.
The dimension or distance is measured by counting the number of fringes of an interference pattern that passes a given point during the movement of a grating with respect to another grating.
The history of the use of gratings in measuring apparatus is traced in a review article in the Journal of Physics E:Scientific Instruments for March 1972 Volume 5 No. 3 pages 193 - 198, publish~d by the Institute of Physics, London, England and entitled Gratings in MetrGlo~.
Known measuring apparatus-employing interference patterns are both bulky and expensive.
~ o some extent this is due to the difficulties experienced in manufacturing and copying accurate gratings having fine resolution characteristics. The difficulties experienced in making an accurate master grating, from which gratings to ~e used in measuring apparatus can be derived, are explained in the review article r~ferred to above. Partly as a result of these difficulties, it is the common practice in such known measuring apparatus to use gratings having a 10 micron period and to employ analog electronic division techniques to obtain a measuring resolution of 1 or 2 microns, as required.
~, One aspect of the present invention is concerned with the provisions of an improved method for making a master :, grating.
- 30 Another aspect of the present invention is concerned ,~ with the provision of a measuring apparatus that in at least one embodiment is small enough to be held in the 1~8738~
hand, that is self-contained and that can operate without connection to any additional apparatus or separate power supplies. It will be appreciated, however, that the invention is not limited to use with hand held apparatus, but that it can be applied to other measuring apparatus, for example bench mounted apparatus.
Accordingly the present invention provides a digilal read-out measuring instrument including a first measuring member, a second measuring member, the first measuring member being slidable relative to the second measuring member to effect a measuring cperation, a first measure-ment-providing member of an electromagnetic radiation-transmissive ma~terial having first and second surface portions at a given angle relative to one another/ a first diffraction grating on the first of the surface portions, the first diffraction grating being coupled through said first measurement-providing member to and movable in accordance with movements of the first measuring member, a second measurement-providing member of an electro-magnetic radiation-transmissive material having third and fourth surface portions at said given angle relative to one another, a second diffraction grating on the third of the surface portions, the second diffraction grating being fixed relative to the second measuring member and beinc so arranged in relation to the first diffraction grating that interference fringe patterns can be produced by q~. electromagnetic radiations passed successively thrGugh the two gratings, a source of electromagnetic radiations, means ; to detect radiations from the source, the source being so ~: 30 arranged that radiations emitted by the source are directed successively through the gratings and the detector means being arranged to detect the interference fringe pattern '~
`'; ~
resulting from the transmission of the radiations through the gratings and to provide a pulse output according to changes in the fringe pattern, a pulse counter connected to the output of the detector means, digital display means connected to the output of the counter, spacer means in the form of a non self-supporting coating on one of the first and third and one of the second and fourth surface portions to slidably space the first and third surface portions and the second and fourth surface portions apart respectively, and means for ccntrolling the speed of movement of the first measuring member.
A described embodiment has a plurality of features, apart from the use of an improved method of making a master grating referred to above, that contribute to a reduction in the bulk and the cost of the apparatus, thereby enabling, for example, a self-contained hand held apparatus to be made.
A further feature of a described embodiment is the use, in the counting of the fringes of an interference pattern, of an electrical circuit that is comparatively simple.
In a preferred embodiment of the invention, a circuit is used that requires only four pulses per cycle of the fringes to be generated and these pulses are generated from the signals obtained from two or more detectors using well G ~` known electronic techniquesr for example the techniques - ~ described in the specificiation of United Ringdom Patent No. 760,321.
In the preferred embodiment of the invention, in order - 30 to achieve a resolution of 1 micron, the period of the gratings used to generate the fringes is as small as 4 micro~s.
;\ ~
1~873B9 Yet a further feature of the des~ribed embodiments of the invention, which feature enables the contrast between the modulated signal output from the detectors and the unmodulated background noise to be as high as possible, is concerned with the provisicn of mounting means which enable the two gratings, which are to be moved relatively to one another, to be as close as possible to one another.
_ This requirement is particularly necessary with gratings having a period as small as 4 microns. In the preferred embodiment of the invention the spacing between the gratings is no more than 12 microns, although it is possible to operate the system with a spacing between the gratings of up to 20 microns.
In a particular embodiment of the invention to be described below in more detail, the invention is employed with a hand held micrometer and the embodiment to be described has the particular advantage over the conventional screw threaded instrument that measurements can be taken much more quickly. One reason for this is that the device to be described employs an instantaneous digital readout of the relative positions of the spindle of the instrument with reference to an anvil and has a spindle which can be slid directly to the position required, whereas it can take , .
as long as 20 seconds to move the spindle of a conventional instrument employing a screw to the fully open position.
A further feature of a described embodiment is the ; ~ use of a system which exerts a substantially constant - force to urge the spindle against the anvil, thereby ensuring that a force of the same value is consistently exerted upon an object being measured between the anvil and the spindle.
Yet another feature of an embodiment of the invention ~8`7~
is the provision of a damper system that controls the speed at which the spindle slides and thus the rate at which pulse signals are applied to a pulse counting circuit.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings wherein like parts are indicated by the same reference numerals and in which:
Fig. lA, Fig. lB and Fig. lC are a partly cut-away plan view, a longitudinal section on the line B-B of Fig.
lA, and a cross section on the line A-A of Fig. lB
respectively of a hand-held mi_rometer gauge, ~ig. 2A, Fig. 2B and Fig. 2C' are a side elevation, an end elevation and an exploded perspective view of a glass measu~ing block arrangement, Fig. 3 is a longitudinal section through a coupling unit used in the gauge, Fig. 4A and Fig. 4B are end and plan views respectively - of the glass measuring block arrangement showing an associated radiation emitter and receiver arrangment, Fig. 5 is a block schematic circuit diagram, Fig. 6A and Fig. 6B are a longitudinal section and a cross section on the line A-A of Fig. 6A of a grating and damper assembly, Fig. 7A, Fig. 7B and Fig. 7C are a diagrammatic cross-.:; -sectional view of the arrangement shown in Fig. 6A and 6B, t together with a mask system, a view on the line A-A of Fig. 7A and a view in the direction of the arrow B of the arrangement shown in Fig. 7A respectively and Fig. 8 is a flow chart illustrating the steps in the making of a master grating.
Referring now to the drawings, there is shown in Figs.
lA, lB and lC a hand-held measuring gauge having a spindle 1 (which constitutes the first of two "measuring members") which is arranged to slide towards and away from an anvil
2 (which constitutes the second of the two "measuring members") located on a jaw frame 3. The anvil 2 and the adjacent end of the spindle 1 form jaws, in a similar manner to the jaws of known micrometer screw gauges.
~ - The gauge has a main frame 4 from which a bearing holde: 5 extends around the ~pindle 1. The jaw frame 3, which extends around the bearing holder 5 is attached to the f~ame 4 by means of glue and a key 6. The bearing holde~ 5 carries a bearing 7 which provides a bearing surface for the spindle.l. A second bearing surface 8 for the spindle 1 is located in the main frame 4. A first part of an arm 9 is connected between the spindle 1 and a sliding button 10. m e said first part of the arm 9 extends through a slot 11 in a case 12. A second part of the arm 9 is connected between the spindle 1 and a damper assembly 13. A "flexator" coil spring 14 is connected between a location pin 15 on the spindle 1 and a location pin 16 on the frame 4. There may be more than one such , . "flexator" spring. A "flexator" spring is a tension coil spring arranged so that it operates in a flexing mode. In ; this manner a substantially constant force is exerted between the pins 15 and 16 in ~rder to urge the spi.ndle 1 ,:~
~, towards the anvil 2. The force will be exerted upon the spindle 1 even when the spindle 1 is positioned against the arlvil 2. Other means can, of course, be used to urge the spindle 1 towards the anvil 2.
The damper 13 includes a piston 17 within a body 18.
The damper body 18 is attached to the arm 9 and the piston 17 is coupled, via a flexible rod 19, to an end cap 20.
m e end cap 20 is attached by a screw 21 to the main frame 10~738~ `
4. The damper assembly further includes sealed bellows 22 and is filled with a. viscous fluid.
When the body 18 moves relatively to the piston 17, which slides within it, a re.straining or drag force is exerl:ed between the piston 17 and the b.ody 18 due to the presence of the viscous fluid, thereby limiting the speed at which the spindle 1 is able to slide in the bearings 7 and 8. me spindle 1 is urged to move towards the anvi.l 2 by the "flexator" spring 14, which has a rate which is apprcximately zero. To open the jaws, the spindle 1 is caused to slide in the bearings 7 and 8 by an operator sliding the button 10, which i.s coupled via the first part of the arm 9 to the spindle 1, along the casing 12.
As may also be seen more clearly with reference to ., Figs. 2A, 2B and 2C, the gauge includes a glass block 23 - which carries an optical grating 24 on a surface 25, (constituting a..first surface portion), the surface 25 being adjacent to a surface 26 (constituting a third surface portion) of a second glass block 27 which is fixed to the frame 4. The surface 26 carries a second optical grating 28 and the block 23 is arranged to slide adjacent '~ the block 27, the block 23 being coupled via a coupling unit 29 to the spindle 1. The sliding block 23 has a ', . bevel:Led face via which the block is urged against the back or reference -block 27 and a glass base block 30 by a leaf spring 31 (Fig. lC), which is retained by two location pins : (not shown) against an arm 32. This ensures that intimate - contact is maintained between the block 23 (which constitutes the first of two measurement-providing members) and the .~ 30 blocks 27 and 30 (which together constitute the second ofthe two measurement-providing members). I~e arm 32 transfers the reaction force of the spring 31 via a ball arrangement ~08~
33 to a strip ~f low friction material 34, which is attached to an extension of the main frame 4. The arm 32 is connected to the spindle 1 in such a way that it is free to rotate about the spinc.le with a minimum amount of orthcgonal movement. This is achieved, as may more clearly be seen by reference to Fig. 3, by employing a bearing member 35 which passes through a hole in the arm 32, is attached to the end of the spindle 1, and provides one end of the coupling unit 29.
The coupling unit 29, as may be more clearly seen from Fig. 3, includes a pin 36 having a conical portion at one end which is inserted into a conical socket 37 in a member 38, the member 38 being coupled, as indicated~ to the sliding glass block 23. At its other end, the pin 36 has a conical portion which locates in a conical socket 39 ` in the bearing member 35. The conical sockets 37 and 39 define included angles which are greater than those of the conical end portions of the pin 36. The members 35 and 38 ' u' are coupled together flexibly by means of a coil spring 40 which is under tension and which holds the pin 36 in place between the sockets 37 and 39. It will be seen that the coupling unit 29 is so designed that, while it constrains the sliding block 23 to move directly in accordance with ` the movement of the spindle 1 along its longitudinal axis, it allows a degree of linear and rotational movement of the block 23 in other directions, thereby enabling wear and ~ ._ .
variations due to manufactuxing tolerances to be taken up.
The coupling unit 29 is thus a universal coupling which permits 5 degrees of freedom.
The construction and disposition of the glass blocks 23, 27 and 30 will now be described in more detail, par-ticularly with reference to Figs. 2A, 2B and 2C. It will ~ f ~ :
be appreciated that, although transparent glass blocks are used, other combinations of mechanically stable transparent materials, or transparent and reflective materials could be used.
The material for the blocks 23, 27 and 30 is first selected and then machined and/or polished to provide smooth rectangular surfaces. The gratings 24 and 28 are line and space gratings and are printed on the surfaces 25 and 26 using standard photo-mechanical techniques and emploxing optically opaque thin films. In the preferred embodiment the period of the gratings is chosen to be 4 microns. Other periods could, of course, be used. me ;~ gratings 24 and 28 are produced by coating the surfaces 25 ~. ' .
and 26 of the blocks 23 and 27 in a vacuum with a chromium fil~. A film of photo-resist material is then applied to the c~lromium film. The film of photo-resist material is ...
then exposed by means of ultra-violet light to an image of a master grating. The parts of the resist material which have been exposed to ultra-violet light are more soluble -~ 20 in a "ldeveloper" than are the unexposed parts, with the , .
~,; result that, u~on the development of the coating, the areas of the layers of chromium that are not required are exposed.
e exposed areas of chromium are then etched away and an image of the original master srating is obtained. Similar techniques are well known in the manufacture of printed circuits.
A method of making a master grating will be described below with reference to Fig. 8.
m e lines of the gratings 24 and 28 are produced on the surfaces 25 and 26 in such a way that they are substan-tially perpendicular to the longitudinal edges of the surfaces 25 and 26 respectively.
1~8'7;38~ `
In assembling the blocks, it is important that the base block 30 be fixed accurately to the back or reference block 27 and that its face 41 and the face 26 of the reference block 27 should both be flat. It is also important that, when the glass blocks 23, 27 and 30 are assembled together as a unit, the slider block 23 should fit accurately into the angle between the base block 30 and the reference block 27. This is most conveniently achieved by ensuring that the face 42 (constituting a second surface portion~ of the sli~ing block 23 and the . .
face ~3 of the base block 30 to which it is adjacent are perpendicular to the surface 25 of the sliding block 2:
which carries the grating 24. The surface 25 of the sliding block 23 is, of course, arranged to be flat.
It is not necessary for the gratings 24 and 28 to :-l extend to the longitudinal edges of the blocks 23 and 27 . r and, in order to prov~de low friction sliding surfaces and to space the gratings thereby reducing the possibility of the gratings becoming wor~ during use, the surfaces 25 and 26 of the blocks 23 and 27 are provided with spacer rails 44 and 45 respectively along the edges of the blocks. The rails 44 and 45 are suitably between 1 and 10 microns thick.
In the preferred embodiment the rails are 4 microns thick.
Thin spacer layers 46 (constit~ting a fourth surface portion) and 47 on the surfaces 43 and 42 of the blocks 30 and 23 respectively space the blocks 30 and 23 and provide low friction sliding surfaces. In the particular embodiment, the spacer rails 44 and 45 and the surfaces 46 and 47 are of PTFE applied by a spraying process. Other solid lubricant materials, for example molybdenum disulphide, tungsten diselenide or carbon may be used. These materials can be applied either by spraying or by a vacuum deposition process.
~87389 In order to improve the adhesion of the sprayed on rails 44 and 45 and the layers 46 and 47, it is advanta-geous to roughen the surfaces of the glass blocks locally, for example by etching or shot blasting, before the lubricant material is applied Other methods of spacing and lubricating the blocks - can be used. For example an oil film can be used between the surfaces 25 and 26 to provide lubrication and the spacing between the blocks can be obtained by using vacuum deposited metal spacer rails. Alternatively the block 23 can be maintained between two films of oil of approximately . . , ~` equal thickness which are constrained by the block 27 and ~ an additional similar block or the other side of the block f:,', 23.
To assemble the blocks 23, 27 and 30 as a single unit they are arranged in a jig in ~hich they are aligned as ~', required. m e angle between the gratings 24 and 28 is adjusted by tilting the base block 30 until fringes of the re~uired period are generated between the two gratings.
In the preferred embodiment a fringe period of about 12 millimetres is chosen. An anaerobic or ultra-violet light curing cement is then introduced by capillary or other action between the surface 26 of the back or reference block 27 and the face 41 of the base block 30 which is ` in contact with a part of the surface 26 and the cement is cured, thereby holding the two blocks together at the co~rect angle. It will be appreciated that other types of cement or other methods of securing the blocks together can be used.
The arrangement of the glass blocks 23, 27 and 30 and radiation transmitting and detecting devices will now be described, particularly with reference to Figs. 4A and 4B
1~8~7389 which show a source o radiations, in the form of a lamp 48, arranged to direct a beam of radiations via a lens 49, the sliding block 23, the gratings 24 and 28, the reference block 27 and a lens arrangement 50, to an a^ray of ph~to-sensitive devices 51 and 52. The photo-sensitive devices 51 and 52 are spaced ~n a perpendicular direction to the fringe pattern generated by the passage of radiations from the source 48 through the gratings 24 and 28. lrhe devices 51 and 52 det:ect movements in the fringe pattexn due to relative longitudinal movement between t-he ~locks 23 and 27 and the consequent movement between tke ; gratings 24 and 28. In the particular embodiment beiny described the devices 51 and 52 are silicon photo transistors and are spaced apart by ~ne quarter of the period of the fringe pattern, so that on relative movement between the gratings 24 and 28, output signals are obtained from the photo-transistors 51 and 52 which are approximately sinu-soidal and have a xelative phase difference of approximately 90 . In the particular embodiment being described, the lamp 48 is an infra-red light emitting diode, and the beam of radiation from the lamp 48 is deflected by means of mirrors 53 and 54 in order to enable the width of the instrument to be reduced while maintaining the path of the radiations. It is, of course, possible to use other sources of radiation and other radiation detectors. A further photo-sensitive device 55, which in the particular embodiment is a photo-transistor, i5 used to monitor the output from the lamp 48 and thus give a signal which is used to adjust a circuit and compensate for variations in voltage from the power supply or due to ageing of the lamp.
Reference will now be made to Fig. 5, which shows the output 'rom ~he photo-transistors 51 and 52 applied to - ~2 -"
10~37389 respective amplifiers 56 and 57 whose outp4ts are then squared during amplification in further respective circuits 58 and 59. The outputs from the circuits 58 and 59 are maintained symmetrical about a voltage level which is adjusted in accordance with changes in a d.c. output signal from the reference photo-detector 55. Ideally, the outputs from the amplifiers 5~ and 59 are square waves in quadrature. The outputs from the amplifiers 58 and 59 are both applied to a detector 60, which provides a pulse - 10 output for every amplitude transition of both square waves, and a phase detector 61. A pulse is obtained from the detector 60 for every quarter of a cycle of the fringe ~, pattern. In the preferred em~iodiment being described with ;. i a 4 micron period grating, this corresponds to a spindle movement of 1 micron. The movement would be 2 microns for an 8 micron period grating. The pulse output from the detector 60 is applied to an up-down counter 62, to which the output from the phase detector 61 is also applied.
The phase detector 61 determines the direction of movement of the fringe pattern from the inputs applied to it and sets the up-down count mode of the counter 62 accordingly. The ~ output from the counter 62 is fed to a digital display 63 from which the exact position of the end of the spindle 1 relative to the anvil 2 can b~ read out.
The housing 12 includes a power pack 64, which may suitably be rechargeable batteries, electric circuit elements 65, a switch 66, which controls the supply of power to the circuit arrangement, and the digital display device 63.
In operation, the electric circuits are energised and the counter 62 is set to zero upon the operation of the switch 65. The spindle 1 is then withdrawn from the anvil 2 by sliding the thumb operated button 10 along the slot 11 in the case 12 against the force exerted by the ;' approximately zero rate, spring 14 and the damper 13.
An object to be measured is introduced between the anvil 2 and the spindle 1, the sliding button 10 is released, and the spindle 1 is allowed to return under the influ~nce of the spring 14, towards the anvil 2 until it meets the object which is located against the anvil 2.
The spring 14 then exerts a c~osure force, which is approximately constant over the full operating range of the instrument, due to the zero rate spring 14. The speed of return of the spindle 1 is controlled by the damper 13. The movement of the spindle 1 is indicated during i,ts movement continuously on the display 63 as a result of the interrogation of the fringe pattern produced by radiations from the source 37 passing through the gratings 24 and 28 by the photo-transistors 51 and 52, in the way described above; the counter 62 counting up when , the movement of the spindle is in one direction and down when it is in the other direction. The display can easily be read when the object is between the anvil 2 and the spindle 1, or the display can be set to zero by operating the switch 66 when the spindle 1 is on the object to be measured, and then by removing the o~ject and allowing the counter to count back until the closed position of the spindle is reached, a negative indication of the object size can be read from the display. There is thus provided a facility that enables measurement to be made when the display cannot conveniently be read in situ.
In another embodiment in which oil or other fluid is used to space the gratings and provide damping it is particularly convenient to use a circular section grating 1~ -1~87389 assembly.
A particular ~orm of such a circular section assembly will now be described with reerence to Figs. 6A, 6B, 7A, 7B an~ 7C in which there is shown a rod 67 of transparent material, for example glass, which slides, with a small clearance, in a tube 68 of transparent material. When the arranc~ement is assembled in a gauge, the rod 67 is attached at one end 69 via a coupling joint (not shown) such as that shown at 29 in Fig. lB to a spindle of a measuring instru-ment and the tube 68 is attached to the main frame of the instrl1ment. A transparent viscous damping fluid is conta ned between t~e rod 67 and the tube 68 and within a bellows unit 70, which serves to seal the assembly. The viscous fluid operates as a damping medium, as the rod 67 moves through the tube 68 in accordance with the movement of the spindle of the measuring instrument. Gratings 71 and 72 are printed on the outside of the rod 67 and the inside of the tube 68 respectively. During the printing of the gratings, the relative angles between the two gratings are so controlled that, on assembly, the fringe pattern between the *wo gratings has a required period.
` ~ It would, of course, be possible to print the grating 72 on the outside of the tube 68, although such an arrangement would not be preferred.
As shown particularly in Fig. 6A, light from a lamp 73 is collimated by a lens 74 and passed through one side of the tube 68 and the two gratings 71 and 72. The transparent rod is so chosen that it acts as a lens, which then focusses the light, modulated by the interference fringe pattern resulting from the effect of the gratings 71 and 72, on to a detector array indicated at 75. The array 75 includes a pair of photo-transistors 76 and 77, 1(~87389 .
which are indieated more clearly in Fig. 7B.
In order to obtain quadrature signals from the photo-transistors 76 and 77, it is convenient to use a mask 78, as shown in Fig. 7. The rod ~7 acts as a cylindrical lens and the mask 78 is required in order to select the fraction of th2 fringe pattern which is to be focussed on to the respective photo-transistor. Thus an aperture 79 in the mask 78 defines the light that is to be focussed on to the detector 76, whilst an apertur~e 80 in the mask 78 defines the light that is to be focus~ed onto the other detector 77.
A method of making a master grating will now be described with reference to Fig. 8. ~he method employs adaptations of techniques used in the manufacture of solid state semiconductor eircuits. A description of the kncwn techniques is given on pages 193 - 205 of a book entitled "Dividing, Ruling and Mask-Making" by D.F. Horne, published by Adam Hilger, London 1974.
The first step in the method, indieated by block 81 in Fig. 8, is the making of a master. In the particular method, a Rubylith master is employed. A Rubylith master is a plasties laminate material eonstituted by a base of translueent white material and a strippable coating of ruby coloured material. The master represents a small section of a grating which is 100 times the size of the required grating. In the particular method a pattern is eut in the Rubylith material by means of a programme eontrolled co-ordinate eontrolled eutting machine, generally known as a co-ordinatograph. The master comprises a sheet of Rubylith material which is 35 cm long and 4 cm wide.
100 lines, each extending in the direction of the length of the material, are eut aeross its width with a 400 micron spaeing between the lines.
The master is then photographed with a high degree of accuracy and reduced in size by a factor of 10, as indicated by block 82. The negative which is so produced is col~nonly referred to as a reticle plate.
'~e reticle plate is then placed, as indicated by block 83, in a known step and repeat camera, for example of the type described on pages 200 - 205 of the book by D.F. E[orne referred to ~bove, and photographically reduced in size by a further factor of 10 on to a part of a final master plate, which may be a photographic plate or a photo-resist coated chromium plate. The relative positions of the reticle plate and the final master plate in the s~ep and repeat camera are then changed so that an image of the reticle plate is obtained at a very accurate interval along the master plate from the first image and an im~ge of the reticle plate is again photographically produ~ed on an adjacent part of the final master plate reduced by a factor of 10. The process is repeated until a photographic image is produced on the final master plate of a grating of the required length. The image is then developed, as indicated by block 84, and the grating on the final master grating can then be used in the making of line and space gratings on glass blocks, as described with refer~n~e to Figs. 2A, 2B and 2C.
Although the invention has been described with reference to particular embodiments, it will be understood that variations and modifications can be made within the scope of the invention claimed.
For example the sliding spindle 1 could be caused to slide in the bearings 7 and 8 by the rotation of an a.ssociated knob or wheel, even though the spindle itself does not rotate.
,'' :
It will also be appreciated that other faces of the glass block 23, for example,the bevelled'surface, than those referred to can have a coating of lubricating material applied to it.
It will also be understocd that the spacer rails 44 and 45 on the surfaces 25 and 26 of the blocks 23 and 27 could be replaced by a continuous rail on one of the surfaces and a series of separate regions of lubricant material, for example dots, on the other surface. Further-more, the lubricant material on one of the surfaces need not be the same as the lubricant material with which it co-operates on the other surface.
In order to give good adhesion between the surfaces 25, 26 and the lubricant material, the lubricant material is applied in particulate form, for example by spraying or vacuum,deposition and not by causing a preformed body to ' adhere to either of the surfaces.
:
, 20 .
.
~ 30 , ':
: '
~ - The gauge has a main frame 4 from which a bearing holde: 5 extends around the ~pindle 1. The jaw frame 3, which extends around the bearing holder 5 is attached to the f~ame 4 by means of glue and a key 6. The bearing holde~ 5 carries a bearing 7 which provides a bearing surface for the spindle.l. A second bearing surface 8 for the spindle 1 is located in the main frame 4. A first part of an arm 9 is connected between the spindle 1 and a sliding button 10. m e said first part of the arm 9 extends through a slot 11 in a case 12. A second part of the arm 9 is connected between the spindle 1 and a damper assembly 13. A "flexator" coil spring 14 is connected between a location pin 15 on the spindle 1 and a location pin 16 on the frame 4. There may be more than one such , . "flexator" spring. A "flexator" spring is a tension coil spring arranged so that it operates in a flexing mode. In ; this manner a substantially constant force is exerted between the pins 15 and 16 in ~rder to urge the spi.ndle 1 ,:~
~, towards the anvil 2. The force will be exerted upon the spindle 1 even when the spindle 1 is positioned against the arlvil 2. Other means can, of course, be used to urge the spindle 1 towards the anvil 2.
The damper 13 includes a piston 17 within a body 18.
The damper body 18 is attached to the arm 9 and the piston 17 is coupled, via a flexible rod 19, to an end cap 20.
m e end cap 20 is attached by a screw 21 to the main frame 10~738~ `
4. The damper assembly further includes sealed bellows 22 and is filled with a. viscous fluid.
When the body 18 moves relatively to the piston 17, which slides within it, a re.straining or drag force is exerl:ed between the piston 17 and the b.ody 18 due to the presence of the viscous fluid, thereby limiting the speed at which the spindle 1 is able to slide in the bearings 7 and 8. me spindle 1 is urged to move towards the anvi.l 2 by the "flexator" spring 14, which has a rate which is apprcximately zero. To open the jaws, the spindle 1 is caused to slide in the bearings 7 and 8 by an operator sliding the button 10, which i.s coupled via the first part of the arm 9 to the spindle 1, along the casing 12.
As may also be seen more clearly with reference to ., Figs. 2A, 2B and 2C, the gauge includes a glass block 23 - which carries an optical grating 24 on a surface 25, (constituting a..first surface portion), the surface 25 being adjacent to a surface 26 (constituting a third surface portion) of a second glass block 27 which is fixed to the frame 4. The surface 26 carries a second optical grating 28 and the block 23 is arranged to slide adjacent '~ the block 27, the block 23 being coupled via a coupling unit 29 to the spindle 1. The sliding block 23 has a ', . bevel:Led face via which the block is urged against the back or reference -block 27 and a glass base block 30 by a leaf spring 31 (Fig. lC), which is retained by two location pins : (not shown) against an arm 32. This ensures that intimate - contact is maintained between the block 23 (which constitutes the first of two measurement-providing members) and the .~ 30 blocks 27 and 30 (which together constitute the second ofthe two measurement-providing members). I~e arm 32 transfers the reaction force of the spring 31 via a ball arrangement ~08~
33 to a strip ~f low friction material 34, which is attached to an extension of the main frame 4. The arm 32 is connected to the spindle 1 in such a way that it is free to rotate about the spinc.le with a minimum amount of orthcgonal movement. This is achieved, as may more clearly be seen by reference to Fig. 3, by employing a bearing member 35 which passes through a hole in the arm 32, is attached to the end of the spindle 1, and provides one end of the coupling unit 29.
The coupling unit 29, as may be more clearly seen from Fig. 3, includes a pin 36 having a conical portion at one end which is inserted into a conical socket 37 in a member 38, the member 38 being coupled, as indicated~ to the sliding glass block 23. At its other end, the pin 36 has a conical portion which locates in a conical socket 39 ` in the bearing member 35. The conical sockets 37 and 39 define included angles which are greater than those of the conical end portions of the pin 36. The members 35 and 38 ' u' are coupled together flexibly by means of a coil spring 40 which is under tension and which holds the pin 36 in place between the sockets 37 and 39. It will be seen that the coupling unit 29 is so designed that, while it constrains the sliding block 23 to move directly in accordance with ` the movement of the spindle 1 along its longitudinal axis, it allows a degree of linear and rotational movement of the block 23 in other directions, thereby enabling wear and ~ ._ .
variations due to manufactuxing tolerances to be taken up.
The coupling unit 29 is thus a universal coupling which permits 5 degrees of freedom.
The construction and disposition of the glass blocks 23, 27 and 30 will now be described in more detail, par-ticularly with reference to Figs. 2A, 2B and 2C. It will ~ f ~ :
be appreciated that, although transparent glass blocks are used, other combinations of mechanically stable transparent materials, or transparent and reflective materials could be used.
The material for the blocks 23, 27 and 30 is first selected and then machined and/or polished to provide smooth rectangular surfaces. The gratings 24 and 28 are line and space gratings and are printed on the surfaces 25 and 26 using standard photo-mechanical techniques and emploxing optically opaque thin films. In the preferred embodiment the period of the gratings is chosen to be 4 microns. Other periods could, of course, be used. me ;~ gratings 24 and 28 are produced by coating the surfaces 25 ~. ' .
and 26 of the blocks 23 and 27 in a vacuum with a chromium fil~. A film of photo-resist material is then applied to the c~lromium film. The film of photo-resist material is ...
then exposed by means of ultra-violet light to an image of a master grating. The parts of the resist material which have been exposed to ultra-violet light are more soluble -~ 20 in a "ldeveloper" than are the unexposed parts, with the , .
~,; result that, u~on the development of the coating, the areas of the layers of chromium that are not required are exposed.
e exposed areas of chromium are then etched away and an image of the original master srating is obtained. Similar techniques are well known in the manufacture of printed circuits.
A method of making a master grating will be described below with reference to Fig. 8.
m e lines of the gratings 24 and 28 are produced on the surfaces 25 and 26 in such a way that they are substan-tially perpendicular to the longitudinal edges of the surfaces 25 and 26 respectively.
1~8'7;38~ `
In assembling the blocks, it is important that the base block 30 be fixed accurately to the back or reference block 27 and that its face 41 and the face 26 of the reference block 27 should both be flat. It is also important that, when the glass blocks 23, 27 and 30 are assembled together as a unit, the slider block 23 should fit accurately into the angle between the base block 30 and the reference block 27. This is most conveniently achieved by ensuring that the face 42 (constituting a second surface portion~ of the sli~ing block 23 and the . .
face ~3 of the base block 30 to which it is adjacent are perpendicular to the surface 25 of the sliding block 2:
which carries the grating 24. The surface 25 of the sliding block 23 is, of course, arranged to be flat.
It is not necessary for the gratings 24 and 28 to :-l extend to the longitudinal edges of the blocks 23 and 27 . r and, in order to prov~de low friction sliding surfaces and to space the gratings thereby reducing the possibility of the gratings becoming wor~ during use, the surfaces 25 and 26 of the blocks 23 and 27 are provided with spacer rails 44 and 45 respectively along the edges of the blocks. The rails 44 and 45 are suitably between 1 and 10 microns thick.
In the preferred embodiment the rails are 4 microns thick.
Thin spacer layers 46 (constit~ting a fourth surface portion) and 47 on the surfaces 43 and 42 of the blocks 30 and 23 respectively space the blocks 30 and 23 and provide low friction sliding surfaces. In the particular embodiment, the spacer rails 44 and 45 and the surfaces 46 and 47 are of PTFE applied by a spraying process. Other solid lubricant materials, for example molybdenum disulphide, tungsten diselenide or carbon may be used. These materials can be applied either by spraying or by a vacuum deposition process.
~87389 In order to improve the adhesion of the sprayed on rails 44 and 45 and the layers 46 and 47, it is advanta-geous to roughen the surfaces of the glass blocks locally, for example by etching or shot blasting, before the lubricant material is applied Other methods of spacing and lubricating the blocks - can be used. For example an oil film can be used between the surfaces 25 and 26 to provide lubrication and the spacing between the blocks can be obtained by using vacuum deposited metal spacer rails. Alternatively the block 23 can be maintained between two films of oil of approximately . . , ~` equal thickness which are constrained by the block 27 and ~ an additional similar block or the other side of the block f:,', 23.
To assemble the blocks 23, 27 and 30 as a single unit they are arranged in a jig in ~hich they are aligned as ~', required. m e angle between the gratings 24 and 28 is adjusted by tilting the base block 30 until fringes of the re~uired period are generated between the two gratings.
In the preferred embodiment a fringe period of about 12 millimetres is chosen. An anaerobic or ultra-violet light curing cement is then introduced by capillary or other action between the surface 26 of the back or reference block 27 and the face 41 of the base block 30 which is ` in contact with a part of the surface 26 and the cement is cured, thereby holding the two blocks together at the co~rect angle. It will be appreciated that other types of cement or other methods of securing the blocks together can be used.
The arrangement of the glass blocks 23, 27 and 30 and radiation transmitting and detecting devices will now be described, particularly with reference to Figs. 4A and 4B
1~8~7389 which show a source o radiations, in the form of a lamp 48, arranged to direct a beam of radiations via a lens 49, the sliding block 23, the gratings 24 and 28, the reference block 27 and a lens arrangement 50, to an a^ray of ph~to-sensitive devices 51 and 52. The photo-sensitive devices 51 and 52 are spaced ~n a perpendicular direction to the fringe pattern generated by the passage of radiations from the source 48 through the gratings 24 and 28. lrhe devices 51 and 52 det:ect movements in the fringe pattexn due to relative longitudinal movement between t-he ~locks 23 and 27 and the consequent movement between tke ; gratings 24 and 28. In the particular embodiment beiny described the devices 51 and 52 are silicon photo transistors and are spaced apart by ~ne quarter of the period of the fringe pattern, so that on relative movement between the gratings 24 and 28, output signals are obtained from the photo-transistors 51 and 52 which are approximately sinu-soidal and have a xelative phase difference of approximately 90 . In the particular embodiment being described, the lamp 48 is an infra-red light emitting diode, and the beam of radiation from the lamp 48 is deflected by means of mirrors 53 and 54 in order to enable the width of the instrument to be reduced while maintaining the path of the radiations. It is, of course, possible to use other sources of radiation and other radiation detectors. A further photo-sensitive device 55, which in the particular embodiment is a photo-transistor, i5 used to monitor the output from the lamp 48 and thus give a signal which is used to adjust a circuit and compensate for variations in voltage from the power supply or due to ageing of the lamp.
Reference will now be made to Fig. 5, which shows the output 'rom ~he photo-transistors 51 and 52 applied to - ~2 -"
10~37389 respective amplifiers 56 and 57 whose outp4ts are then squared during amplification in further respective circuits 58 and 59. The outputs from the circuits 58 and 59 are maintained symmetrical about a voltage level which is adjusted in accordance with changes in a d.c. output signal from the reference photo-detector 55. Ideally, the outputs from the amplifiers 5~ and 59 are square waves in quadrature. The outputs from the amplifiers 58 and 59 are both applied to a detector 60, which provides a pulse - 10 output for every amplitude transition of both square waves, and a phase detector 61. A pulse is obtained from the detector 60 for every quarter of a cycle of the fringe ~, pattern. In the preferred em~iodiment being described with ;. i a 4 micron period grating, this corresponds to a spindle movement of 1 micron. The movement would be 2 microns for an 8 micron period grating. The pulse output from the detector 60 is applied to an up-down counter 62, to which the output from the phase detector 61 is also applied.
The phase detector 61 determines the direction of movement of the fringe pattern from the inputs applied to it and sets the up-down count mode of the counter 62 accordingly. The ~ output from the counter 62 is fed to a digital display 63 from which the exact position of the end of the spindle 1 relative to the anvil 2 can b~ read out.
The housing 12 includes a power pack 64, which may suitably be rechargeable batteries, electric circuit elements 65, a switch 66, which controls the supply of power to the circuit arrangement, and the digital display device 63.
In operation, the electric circuits are energised and the counter 62 is set to zero upon the operation of the switch 65. The spindle 1 is then withdrawn from the anvil 2 by sliding the thumb operated button 10 along the slot 11 in the case 12 against the force exerted by the ;' approximately zero rate, spring 14 and the damper 13.
An object to be measured is introduced between the anvil 2 and the spindle 1, the sliding button 10 is released, and the spindle 1 is allowed to return under the influ~nce of the spring 14, towards the anvil 2 until it meets the object which is located against the anvil 2.
The spring 14 then exerts a c~osure force, which is approximately constant over the full operating range of the instrument, due to the zero rate spring 14. The speed of return of the spindle 1 is controlled by the damper 13. The movement of the spindle 1 is indicated during i,ts movement continuously on the display 63 as a result of the interrogation of the fringe pattern produced by radiations from the source 37 passing through the gratings 24 and 28 by the photo-transistors 51 and 52, in the way described above; the counter 62 counting up when , the movement of the spindle is in one direction and down when it is in the other direction. The display can easily be read when the object is between the anvil 2 and the spindle 1, or the display can be set to zero by operating the switch 66 when the spindle 1 is on the object to be measured, and then by removing the o~ject and allowing the counter to count back until the closed position of the spindle is reached, a negative indication of the object size can be read from the display. There is thus provided a facility that enables measurement to be made when the display cannot conveniently be read in situ.
In another embodiment in which oil or other fluid is used to space the gratings and provide damping it is particularly convenient to use a circular section grating 1~ -1~87389 assembly.
A particular ~orm of such a circular section assembly will now be described with reerence to Figs. 6A, 6B, 7A, 7B an~ 7C in which there is shown a rod 67 of transparent material, for example glass, which slides, with a small clearance, in a tube 68 of transparent material. When the arranc~ement is assembled in a gauge, the rod 67 is attached at one end 69 via a coupling joint (not shown) such as that shown at 29 in Fig. lB to a spindle of a measuring instru-ment and the tube 68 is attached to the main frame of the instrl1ment. A transparent viscous damping fluid is conta ned between t~e rod 67 and the tube 68 and within a bellows unit 70, which serves to seal the assembly. The viscous fluid operates as a damping medium, as the rod 67 moves through the tube 68 in accordance with the movement of the spindle of the measuring instrument. Gratings 71 and 72 are printed on the outside of the rod 67 and the inside of the tube 68 respectively. During the printing of the gratings, the relative angles between the two gratings are so controlled that, on assembly, the fringe pattern between the *wo gratings has a required period.
` ~ It would, of course, be possible to print the grating 72 on the outside of the tube 68, although such an arrangement would not be preferred.
As shown particularly in Fig. 6A, light from a lamp 73 is collimated by a lens 74 and passed through one side of the tube 68 and the two gratings 71 and 72. The transparent rod is so chosen that it acts as a lens, which then focusses the light, modulated by the interference fringe pattern resulting from the effect of the gratings 71 and 72, on to a detector array indicated at 75. The array 75 includes a pair of photo-transistors 76 and 77, 1(~87389 .
which are indieated more clearly in Fig. 7B.
In order to obtain quadrature signals from the photo-transistors 76 and 77, it is convenient to use a mask 78, as shown in Fig. 7. The rod ~7 acts as a cylindrical lens and the mask 78 is required in order to select the fraction of th2 fringe pattern which is to be focussed on to the respective photo-transistor. Thus an aperture 79 in the mask 78 defines the light that is to be focussed on to the detector 76, whilst an apertur~e 80 in the mask 78 defines the light that is to be focus~ed onto the other detector 77.
A method of making a master grating will now be described with reference to Fig. 8. ~he method employs adaptations of techniques used in the manufacture of solid state semiconductor eircuits. A description of the kncwn techniques is given on pages 193 - 205 of a book entitled "Dividing, Ruling and Mask-Making" by D.F. Horne, published by Adam Hilger, London 1974.
The first step in the method, indieated by block 81 in Fig. 8, is the making of a master. In the particular method, a Rubylith master is employed. A Rubylith master is a plasties laminate material eonstituted by a base of translueent white material and a strippable coating of ruby coloured material. The master represents a small section of a grating which is 100 times the size of the required grating. In the particular method a pattern is eut in the Rubylith material by means of a programme eontrolled co-ordinate eontrolled eutting machine, generally known as a co-ordinatograph. The master comprises a sheet of Rubylith material which is 35 cm long and 4 cm wide.
100 lines, each extending in the direction of the length of the material, are eut aeross its width with a 400 micron spaeing between the lines.
The master is then photographed with a high degree of accuracy and reduced in size by a factor of 10, as indicated by block 82. The negative which is so produced is col~nonly referred to as a reticle plate.
'~e reticle plate is then placed, as indicated by block 83, in a known step and repeat camera, for example of the type described on pages 200 - 205 of the book by D.F. E[orne referred to ~bove, and photographically reduced in size by a further factor of 10 on to a part of a final master plate, which may be a photographic plate or a photo-resist coated chromium plate. The relative positions of the reticle plate and the final master plate in the s~ep and repeat camera are then changed so that an image of the reticle plate is obtained at a very accurate interval along the master plate from the first image and an im~ge of the reticle plate is again photographically produ~ed on an adjacent part of the final master plate reduced by a factor of 10. The process is repeated until a photographic image is produced on the final master plate of a grating of the required length. The image is then developed, as indicated by block 84, and the grating on the final master grating can then be used in the making of line and space gratings on glass blocks, as described with refer~n~e to Figs. 2A, 2B and 2C.
Although the invention has been described with reference to particular embodiments, it will be understood that variations and modifications can be made within the scope of the invention claimed.
For example the sliding spindle 1 could be caused to slide in the bearings 7 and 8 by the rotation of an a.ssociated knob or wheel, even though the spindle itself does not rotate.
,'' :
It will also be appreciated that other faces of the glass block 23, for example,the bevelled'surface, than those referred to can have a coating of lubricating material applied to it.
It will also be understocd that the spacer rails 44 and 45 on the surfaces 25 and 26 of the blocks 23 and 27 could be replaced by a continuous rail on one of the surfaces and a series of separate regions of lubricant material, for example dots, on the other surface. Further-more, the lubricant material on one of the surfaces need not be the same as the lubricant material with which it co-operates on the other surface.
In order to give good adhesion between the surfaces 25, 26 and the lubricant material, the lubricant material is applied in particulate form, for example by spraying or vacuum,deposition and not by causing a preformed body to ' adhere to either of the surfaces.
:
, 20 .
.
~ 30 , ':
: '
Claims (8)
1. A digital read-out measuring instrument including a first measuring member, a second measuring member, the first measuring member being slidable relative to the second measuring member to effect a measuring operation, a first measurement-providing member of an electromagnetic radiation-transmissive material having first and second surface portions at a given angle relative to one another, a first diffraction grating on the first of the surface portions, the first diffraction grating being coupled through said first measurement-providing member to and movable in accordance with movements of the first measuring member, a second measurement-providing member of an electromagnetic radiation-transmissive material having third and fourth surface portions at said given angle relative to one another, a second diffraction grating on the third of the surface portions, the second diffraction grating being fixed relative to the second measuring member and being so arranged in relation to the first diffraction grating that interference fringe patterns can be produced by electromagnetic radiations passed success-ively through the two gratings, a source of electro-magnetic radiations, means to detect radiations from the source, the source being so arranged that radiations emitted by the source are directed successively through the gratings and the detector means being arranged to detect the-interference fringe pattern resulting from the trans-mission of the radiations through the gratings and to provide a pulse output according to changes in the fringe pattern, a pulse counter connected to the output of the detector means, digital display means connected to the output of the counter, spacer means in the form of a non self-supporting coating on one of the first and third and one of the second and fourth surface portions to slidably space the first and third surface portions and the second and fourth surface portions apart respectively, and means for controlling the speed of movement of the first measuring member.
2. A measuring instrument, as claimed in claim 1, including resilient means exerting a substantially constant force on the first measuring member to urge the first measuring member towards the second measuring member.
3. A measuring instrument as claimed in claim 1 wherein the spacer means comprises solid lubricant material.
4. A measuring instrument as claimed in claim 1 wherein the spacer means comprises liquid lubricating material.
5. A measuring instrument as claimed in claim 1 including a universal joint coupline the first measuring member and the first grating.
6. A measuring instrument as claimed in claim 2 wherein the first and second gratings are planar.
7. A measuring instrument as claimed in claim 2 including a piston and cylinder arrangement, the said piston and cylinder arrangement being coupled to the first measuring member for controlling the speed of movement of the first measuring member.
8. A measuring instrument as claimed in claim 1 when made by a method which includes the steps of exposing a photo-resist material to an image of a master grating, developing the exposed material to expose a part of a metal layer and etching the exposed part of the metal layer away.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB14846/75 | 1975-04-10 | ||
GB14846/75A GB1550185A (en) | 1975-04-10 | 1975-04-10 | Distance measuring gauge |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1087389A true CA1087389A (en) | 1980-10-14 |
Family
ID=10048521
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA249,931A Expired CA1087389A (en) | 1975-04-10 | 1976-04-09 | Distance measuring gauge using relative movement between diffraction gratings |
Country Status (13)
Country | Link |
---|---|
JP (1) | JPS51123657A (en) |
AU (1) | AU500342B2 (en) |
BR (1) | BR7602203A (en) |
CA (1) | CA1087389A (en) |
DE (1) | DE2615676A1 (en) |
ES (1) | ES447179A1 (en) |
FR (1) | FR2312758A1 (en) |
GB (1) | GB1550185A (en) |
HK (1) | HK19480A (en) |
IT (1) | IT1059741B (en) |
NL (1) | NL7603700A (en) |
SE (1) | SE413941B (en) |
ZA (1) | ZA762090B (en) |
Families Citing this family (14)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE2727769C2 (en) * | 1977-06-21 | 1979-01-25 | Dr. Johannes Heidenhain Gmbh, 8225 Traunreut | Encapsulated length measuring device for long measuring lengths |
JPS54145562A (en) * | 1978-05-04 | 1979-11-13 | Mitsutoyo Seisakusho | Slide calipers with digital display |
US4403860A (en) * | 1980-03-27 | 1983-09-13 | Diffracto Ltd. | Apparatus for determining dimensions |
DE3125184A1 (en) * | 1981-06-26 | 1983-01-13 | Adolf 7118 Ingelfingen Mütsch | Electrooptical measuring device |
ATA395181A (en) * | 1981-09-14 | 1986-12-15 | Rieder Heinz | HAND MEASURING DEVICE |
US4554742A (en) * | 1983-09-16 | 1985-11-26 | Ford Motor Company | Dimensional checking tool |
GB2223845B (en) * | 1988-10-14 | 1992-10-28 | Brian Arthur Evans | Digital tyre pressure gauge |
US5239307A (en) * | 1989-10-10 | 1993-08-24 | Micro Encoder Inc. | Method and apparatus for sensing of position |
JPH087054B2 (en) * | 1990-10-22 | 1996-01-29 | 株式会社ミツトヨ | Displacement detector |
US5125165A (en) * | 1990-11-28 | 1992-06-30 | Mitutoyo Corporation | Precision linear measuring device having an improved spindle mounting device |
US5172485A (en) * | 1991-10-17 | 1992-12-22 | Mitutoyo Corporation | Precision linear measuring suspension system having sliding contact between the scale and the pick-off |
DE29916394U1 (en) * | 1999-09-17 | 2001-02-15 | Heidenhain Gmbh Dr Johannes | Optical position measuring device |
DE10356328A1 (en) * | 2003-10-27 | 2005-06-16 | Sick Stegmann Gmbh | Optical path length or rotation angle sensor |
EP1528369B1 (en) | 2003-10-27 | 2014-03-12 | SICK STEGMANN GmbH | Optical rotation angle sensor |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB760321A (en) * | 1953-03-14 | 1956-10-31 | Ferranti Ltd | Improvements relating to measuring apparatus |
US2996806A (en) * | 1959-08-17 | 1961-08-22 | Zeiss Carl | Vertical length measuring device |
FR1323304A (en) * | 1962-05-18 | 1963-04-05 | Wenczler & Heidenhain | Device for determining the relative position of two parts |
DE1548874A1 (en) * | 1966-12-10 | 1970-10-01 | Wenczler & Heidenhain | Photoelectric device for determining the position of an object |
US3867037A (en) * | 1973-08-29 | 1975-02-18 | Dynamics Res Corp | Linear motion encoder |
-
1975
- 1975-04-10 GB GB14846/75A patent/GB1550185A/en not_active Expired
-
1976
- 1976-04-05 FR FR7610371A patent/FR2312758A1/en active Granted
- 1976-04-07 ZA ZA762090A patent/ZA762090B/en unknown
- 1976-04-07 AU AU12772/76A patent/AU500342B2/en not_active Expired
- 1976-04-08 SE SE7604176A patent/SE413941B/en unknown
- 1976-04-08 NL NL7603700A patent/NL7603700A/en not_active Application Discontinuation
- 1976-04-09 IT IT22133/76A patent/IT1059741B/en active
- 1976-04-09 ES ES447179A patent/ES447179A1/en not_active Expired
- 1976-04-09 DE DE19762615676 patent/DE2615676A1/en not_active Withdrawn
- 1976-04-09 CA CA249,931A patent/CA1087389A/en not_active Expired
- 1976-04-09 BR BR7602203A patent/BR7602203A/en unknown
- 1976-04-10 JP JP51039837A patent/JPS51123657A/en active Pending
-
1980
- 1980-04-10 HK HK194/80A patent/HK19480A/en unknown
Also Published As
Publication number | Publication date |
---|---|
JPS51123657A (en) | 1976-10-28 |
IT1059741B (en) | 1982-06-21 |
HK19480A (en) | 1980-04-18 |
GB1550185A (en) | 1979-08-08 |
DE2615676A1 (en) | 1976-10-21 |
AU500342B2 (en) | 1979-05-17 |
BR7602203A (en) | 1976-10-05 |
FR2312758A1 (en) | 1976-12-24 |
FR2312758B1 (en) | 1982-07-16 |
ES447179A1 (en) | 1977-12-01 |
AU1277276A (en) | 1977-10-13 |
ZA762090B (en) | 1977-04-27 |
NL7603700A (en) | 1976-10-12 |
SE413941B (en) | 1980-06-30 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
CA1087389A (en) | Distance measuring gauge using relative movement between diffraction gratings | |
US4215480A (en) | Distance measuring gauge | |
US3989385A (en) | Part locating, mask alignment and mask alignment verification system | |
US4070116A (en) | Gap measuring device for defining the distance between two or more surfaces | |
EP0132978B1 (en) | Displacement measuring apparatus and method | |
US3833807A (en) | Digital length measuring means | |
US5229836A (en) | Position detecting apparatus for a moving body | |
JPS6127682B2 (en) | ||
JP2586121B2 (en) | Rotary encoder origin detection system | |
US2604528A (en) | Photoelectric measurement translating means | |
KR20020060525A (en) | High precision displacement gauge and variable displacement measuring method used a unit displacement using conforcal theory | |
US3502414A (en) | Optical electric system | |
US2580498A (en) | Electrooptical pulse generator | |
JPS63140989A (en) | Positioning device | |
CA1060054A (en) | Scale optical detector with spring constant variation compensator | |
US3629945A (en) | Optical gage | |
US3884581A (en) | Diffractographic and other sensors utilizing diffraction waves | |
US4339198A (en) | Geodetic instrument | |
US3984185A (en) | Process and apparatus for filter value and exposure time determination in photographic color printing and enlarging | |
US4044847A (en) | Weighing system with a moire optoelectronic transducer | |
GB2153995A (en) | Coordinate measuring instrument | |
JP3041017B2 (en) | Position detection device | |
US4592650A (en) | Apparatus for projecting a pattern on a semiconductor substrate | |
US4808807A (en) | Optical focus sensor system | |
SU515939A1 (en) | Digital theodolite |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
MKEX | Expiry |