GB1565838A

GB1565838A - Portable axis definition apparatus

Info

Publication number: GB1565838A
Application number: GB4621276A
Authority: GB
Original assignee: UK Secretary of State for Industry
Current assignee: UK Secretary of State for Industry
Priority date: 1977-09-13
Filing date: 1977-09-13
Publication date: 1980-04-23

Description

(54) IMPROVEMENTS IN OR RELATING TO PORTABLE AXIS DEFINITION APPARATUS (71) I, THE SECRETARY OF STATE FOR INDUSTRY, LONDON, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which is it to performed, to be particularly described in any by the following statement: This invention relates to axis definition apparatus, and more particularly to portable optical means for performing the function of a plumb line.

Attention is particularly directed to applicant's British Patent Specification No. 1501637 which describes and claims the use of freely suspended optical systems in combination with laser light sources for the provision of accurate vertical light beams. The production of light beams having accurately known inclinations to the vertical is also described in this specification.

The object of the present invention is to provide axis definition apparatus in conveniently portable form.

According to the present invention, portable axis definition apparatus includes a laser retained by a support member, a gimbal mounted for rotation about the defining axis having a first member and a second member pivotally connected thereto, the laser support member being attached at one end thereof to the second member for free suspension of the laser, laser positioning means for aligning the axis of the laser output beam to pass vertically through the pivotal centre and along the rotational axis of the gimbal, and an optical image forming device positioned in the path of the laser output beam when aligned with the said pivotal centre.

Preferably the optical image forming device includes a diverging lens to expand the laser output beam and a converging lens having a combination of focal length and separation from the diverging lens appropriate to focus the expanded laser beam at infinity.

The laser is necessarily supplied by high-voltage electrical power from a power pack. The power pack is conveniently attached directly or indirectly to the laser support member and located adjacent to the laser. Low voltage power to the power-pack may conveniently be fed through leads located within the first and second members of the gimbal.

The laser positioning means preferably includes adjustment screws to locate the laser relative to the laser support member and the optical image forming device. The laser positioning means may conveniently additionally include one or more balance weights attached to the laser support member and adjustable in position relative thereto.

The laser support member is preferably a tube surround the laser. One end of the tube remote from the gimbal is conveniently attached to a base plate, the base plate being arranged to support a high voltage laser power pack.

Damper means are preferably employed to damp the motion of the laser when freely suspended from the gimbal. The damper means conveniently comprises an oil bath and a projecting arm attached to the laser support member positioned such that the projecting arm engages the oil in the oil-bath.

The laser and the support member are advantageously arranged within a housing, the first member of the gimbal being mounted rotatably on the upper surface of the housing.

The laser and the optical image forming device may be arranged to produce either upwardly or downwardly directed beams.

The apparatus, and in particular the housing, is preferably provided with clamps operable to restrict or arrest any movement of the laser and support member when the apparatus is not in use. The clamps are preferably operable to engage against a resilient member, such as for example an O-ring, attached to the laser support member.

In order that the invention may be more fully understood, and further features appreciated, one embodiment thereof will now be described with reference to the drawings accompanying the provisional specification in which: Figure 1 shows a sectional view of an axis definition apparatus in accordance with the invention, the apparatus producing an upwardly directed light beam, Figure 2 shows a gimballed mounting as employed in the apparatus of Figure 1, and Figure 3 shows a schematic drawing of an apparatus of the invention adapted to produce a downwardly directed light beam.

With reference to Figure 1, a Helium-Neon laser 1 is retained within a support member in the form of a support tube 2. The laser 1 is retained within the support tube 2 by positioning means comprising upper adjustment screws 3 and lower adjustment screws 4. A diverging lens 5 is located close to the output window 6 of the laser, the lens 5 being coaxial with the axis 7 of the output beam of the laser 1.

The support tube 2 is attached to a hollow generally cylindrical assembly 8 itself attached to the second member 9 of a gimbal mounting 10 having a pivotal centre 11. A converging lens 12 is mounted in the hollow assembly 8 remotely from and coaxially with, the diverging lens 5, the converging lens being located close to the pivotal centre 11. The gimbal mounting 10 also includes a first member 13 retained in bearings 14. The bearings 14 are attached to the closure plate 15 of a housing lid 16 forming the upper surface of a housing 17. The closure plate 15 is fitted with a window 18 through which laser light may emerge.

The housing 17 has a tubular body portion 19 and a base plate 20.

The closure plate 15 is formed with a bearing surface 21 to engage a corresponding bearing surface 22 formed on the housing lid 16. The surfaces 21 and 22 constitute a vertical bearing allowing the gimbal member 13, and the laser 1 depending therefrom, to be rotated about a vertical axis. A clamp 23 is screwed to the lid 15 and engages the closure plate 15 to provide clamping when the apparatus is not in use.

A disc-shaped end-plate 24 is attached to one end of the support tube 2 remotely from the gimbal mounting 10. The end plate 24 has a circumferential groove 25 in which is located an O-ring 26. A clamping device 27 rotatable about a horizontal axis protrudes through the housing body portion 19 and is fitted with a projecting arm 28. The arm 28 when rotated into the "up" position as shown can engage the 0being 26 when the end-plate 24 is disturbed from the symmetry position shown. A second clamping device 29 (not shown in detail) is mounted diametrically opposite the device 28 with respect to the tubular body portion 19.

The end-plate 24 supports a power-pack casing 30 within which is located the high voltage power-pack 31 for the laser 1. Balance weights 32 are attached to the casing 30.

Low-voltage power is fed to the power-pack 31 via line and earth leads 33 and 33A respectively. The leads 33 and 33A each connect with a respective stud contact (not shown).

Each stud engages through the bearings 14 a respective carbon brush contact (not shown, see Figure 2) inserted into the first gimbal member 13. Each carbon brush is connected to a respective second carbon brush (not shown) within the first gimbal member 13 located so as to contact through the bearings between the first and second gimbal members 13 and 9 a respective second stud (not shown) to which the power-pack 31 is connected.

A projecting rod 34 protrudes from a support assembly 35 attached to the underside 36 of the end-plate 24. The rod 34 engages the liquid surface 37 in a bath 38 ofhigh-viscosity sillicone oil 39. The bath 38 or dash-pot has an inwardly turned lip portion 40 adapted to minimise possible spillage in a manner well-known for other non-spill liquid containers.

Figure 2 is a sectional view of the gimbal mounting 10 shown in Figure 1. The first cruciform gimbal member 13 is mounted in bearings 14 and the second gimbal member 9 is mounted thereon in bearings 14a arranged to permit rotation of the second gimbal member 9 and the laser 1 attached thereto about two orthogonal axes 45 and 46 in the plane of Figure 2 corresponding to the horizontal plane in Figure 1. Each arm 41 of the cruciform first member 13 includes an electrically conducting insert consisting of a spring-loaded carbon brush 42. One pair of adjacent carbon brushes 42 is electrically insulated from the first member 13 by means of insulating sleeving 43, the other pair being non-insulated. The adjacent insulated brushes 42 are connected together by an insulated lead (not shown). The line voltage and earth leads 33 and 33A are respectively connected through bearings 14 to an input insulating and an input conducting brush 42. The input insulated and non-insulated brushes 42 are connected to respective insulated and non-insulated brushes 42 which connect through bearings 14a with flexible wires which are connected to the laser power pack 31.

The adjustment and operation of the apparatus of Figures 1 and 2 will now be described.

The upper adjustment screws 3 are employed to position the laser 1 such that the laser beam passes centrally through the diverging lens 5. The diverging lens 5 and the converging lens 12 are designed to be coaxial with their common axis passing through the pivotal centre 10.

After ajustment of the screws 3, the adjustment screws 4 are employed to ensure that the laser beam is symmetrically disposed about the common axis of the lenses 5 and 12.

The focal lengths and positions of these lenses are selected such that the laser beam is expanded by the diverging lens 5 to fill the converging lens 12, and the converging lens 12 is separated by its focal length from the virtual point from which the laser beam appears to diverge. This arrangement produces images at infinity, ie a nominally parallel beam of light extends upwards from the apparatus, and the beam is symmetrical about an axis through the pivotal centre 10.

The next stage is to adjust the balance weights 32 until the axis 7 of the laser beam is vertical. To identify the point at which the axis 7 is vertical, the clamp 23 is released and the closure plate 15 is rotated horizontally on the vertical bearing formed by the contiguous surfaces 21 and 22. The laser 1, freely suspended from the closure plate 15, revolves with it, and the axis 7 of the laser beam sweeps out the surface of a cone when non-vertical. The semi-angle of the cone goes to zero as the axis 7 approaches the vertical.

The position of the laser beam is detected on a screen (not shown) placed above the apparatus, and the laser spot produced on the screen by the beam is monitored as the closure plate 15 is rotated. The balance weights 32 are adjusted until the position of the spot on the screen is independent of rotation of the closure plate. When this is achieved, the laser beam is accurately vertical.

Table 1 lists possible combinations of converging (positive) and diverging (negative) lenses suitable for use in the apparatus of Figure 1. The focal lengths in Table 1, the distance between the two lenses and the output beam diameter are given in millimetres, and the useful range is given in metres, assuming a laser beam of 0.5mm diameter.

TABLE 1 Possible Lens Combinations Neg Pos Mag Output Length Range lens lens x dia L in m f in mm f in mm in mm in mm + 140 28 14 135 245 + 120 24 12 115 180 -5 + 100 20 10 95 125 + 80 16 8 75 80 + 140 17l/2 9 132 100 + 120 15 7.5 112 70 -8 + 100 12l/2 6.5 92 50 + 80 10 5 72 30 The apparatus illustrated in Figures 1 and 2 possesses the important advantage that is does not require a complex levelling procedure before use. The foregoing alignment operation need only be carried out once for a particular instrument, with periodic checks (rotation of closure plate) to ensure that settings have not drifted.It is merely necessary to level the instrument by eye only, say within + 5 . Provided that the laser is suspended freely without contacting either the housing 19 or the clamps 27 and 29, the laser beam is a true vertical reference. The apparatus is therefore self-adjusting, and accordingly is ideally suited to applications in the field remote from laboratories or workshops. In field applications, lengthy adjustment procedures are normally extremely inconvenient. In such situations the accuracy of the vertical reference may also easily be checked by rotating the closure plate 15.

A typical specification for the apparatus is as follows. A 1-2 milliwatt Helium-Neon laser is suitable with a power-pack adapted for a 12v dc input. Conveniently, a 20X beam expander is employed, the lenses being chosen from Table 1. The beam expander improves working range and also reduces errors due to laser misalignment. As has been said, the apparatus is self-adjusting within a + 5 excursion either side of the symmetry position, and this excursion can be increased at the expense of a bulkier instrument.

The overall working range would be about 125 metres using a simple grid screen as a detector to receive the laser beam spot. The accuracy of the vertical reference axis generated would depend on the care taken in the setting-up procedure, but an accuracy to better than + 10 seconds of arc is easily realisable. The silicon oil preferably used in the non-spill oil bath 38 or dashpot incorported in the apparatus to damp pendular oscillations is highly viscous and therefore flows extremely slowly. Together with the non-spill lip 40, this means that the possibility of oil spillage from the bath 38 is very small indeed. Other oils may of course be employed.

Referring to Figure 1 once more, the leads 33 and 33A interfere with rotation of the gimballed mounting 10; to deal with this, it is necessary to restrict rotation of the mounting 10 to within say i1800, and to use coiled leads. Alternatively, the leads 33 and 33A may be connected to slip rings remote from the mounting 10 to permit l3600 rotation.

It is frequently desirable to generate a downwardly directed reference axis. Figure 3 schematically illustrates a modified version of the embodiment shown in Figure 1, the apparatus of Figure 3 being adapted to generate a downwardly directed light beam. A laser 51 beam-expanding (diverging) lens 52 and image forming (converging) lens 53 together form an optical reference beam generating system. This system is inverted with respect to a support tube 54 are compared to the arrangement of Figure 1. The reference beam emerges through a window 55 in the base 56 of the apparatus housing 57. The apparatus is provided with a gimbal mounting 58 and a vertical bearing 59. The laser power-pack 60 is supported on an end-plate 61 bearing projections 62 engaging oil 63 in an annular oil-bath 64. The apparatus is equipped with balance weights 65 and adjustment screws 66.Electrical connections (not shown) to the laser power-pack 60 are similar to those described for Figure 1. The setting up procedure is as described for the upwardly-directed light beam, except that the laser beam spot is detected below the apparatus, rather than above it as in the earlier case. The only major design changes as compared to Figure 1 consist of inverting the optical system and employing an annular oil bath. The oil bath design is changed to clear the downwardly emerging light path while retaining the ability to rotate the laser.

Both the embodiments hereinbefore described generate a vertical reference beam. As is well-known to those skilled in the art of optics, a number of reflective devices exist for deflecting a light beam through a known angle. In particular, a pentagonal prism gives a 90" deviation, and can be used to produce an accurately horizontal beam from the vertical reference generated as illustrated in either of Figures 1 and 2. Rotation of the pentagonal prism about the axis of the vertical reference beam then sweeps out a horizontal plane accurate to a few seconds of arc. Clearly, many such variations on and additions to the apparatus hereinbefore described can be envisaged, and accordingly it is to be understood that the scope of the invention is in no way restricted by the disclosure of the foregoing embodiments.

WHAT WE CLAIM IS: 1. A portable axis definition apparatus comprising a laser retained by a support member, a gimbal mounted for rotation about the defining axis having a first member and a second member pivotally connected thereto, the laser support member being attached at one end thereof to the second member for free suspension of the laser, laser positioning means for aligning the axis of the laser output beam to pass vertically through the pivotal centre and along the rotational axis of the gimbal, and an optical image forming device positioned in the path of the laser output beam when aligned with the said pivotal centre.

2. A portable axis definition apparatus according to claim 1 wherein the optical image forming device comprises a diverging lens located in the path of the output beam from the laser to expand the laser output beam and a converging lens having a combination of focal length and separation from the diverging lens appropriate to focus the expanded laser beam at infinity.

3. A portable axis definition apparatus according to claim 1 or 2 wherein the laser and the support member are arranged within a housing, the first gimbal member being rotatably mounted on the upper surface of the housing.

4. A portable axis definition apparatus according to any one of claims 1 to 3 wherein the positioning means includes adjustment screws to locate the laser relative to the laser support member and the optical image forming device.

5. A portable axis definition apparatus according to claim 4 wherein the positioning means additionally includes one or more balance weights attached to the laser support member and adjustable in position relative thereto.

6. A portable axis definition apparatus according to any one of claims 1 to 5 wherein the laser support member is a tube surrounding the laser.

7. A portable axis definition apparatus according to any one of claims 1 to 6 wherein the laser support member has attached at one end remote from the gimbal a base plate arranged to support a high voltage power pack for the laser.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

The overall working range would be about 125 metres using a simple grid screen as a detector to receive the laser beam spot. The accuracy of the vertical reference axis generated would depend on the care taken in the setting-up procedure, but an accuracy to better than + 10 seconds of arc is easily realisable. The silicon oil preferably used in the non-spill oil bath 38 or dashpot incorported in the apparatus to damp pendular oscillations is highly viscous and therefore flows extremely slowly. Together with the non-spill lip 40, this means that the possibility of oil spillage from the bath 38 is very small indeed. Other oils may of course be employed.

Referring to Figure 1 once more, the leads 33 and 33A interfere with rotation of the gimballed mounting 10; to deal with this, it is necessary to restrict rotation of the mounting 10 to within say i1800, and to use coiled leads. Alternatively, the leads 33 and 33A may be connected to slip rings remote from the mounting 10 to permit l3600 rotation.

It is frequently desirable to generate a downwardly directed reference axis. Figure 3 schematically illustrates a modified version of the embodiment shown in Figure 1, the apparatus of Figure 3 being adapted to generate a downwardly directed light beam. A laser 51 beam-expanding (diverging) lens 52 and image forming (converging) lens 53 together form an optical reference beam generating system. This system is inverted with respect to a support tube 54 are compared to the arrangement of Figure 1. The reference beam emerges through a window 55 in the base 56 of the apparatus housing 57. The apparatus is provided with a gimbal mounting 58 and a vertical bearing 59. The laser power-pack 60 is supported on an end-plate 61 bearing projections 62 engaging oil 63 in an annular oil-bath 64. The apparatus is equipped with balance weights 65 and adjustment screws 66.Electrical connections (not shown) to the laser power-pack 60 are similar to those described for Figure 1. The setting up procedure is as described for the upwardly-directed light beam, except that the laser beam spot is detected below the apparatus, rather than above it as in the earlier case. The only major design changes as compared to Figure 1 consist of inverting the optical system and employing an annular oil bath. The oil bath design is changed to clear the downwardly emerging light path while retaining the ability to rotate the laser.

Both the embodiments hereinbefore described generate a vertical reference beam. As is well-known to those skilled in the art of optics, a number of reflective devices exist for deflecting a light beam through a known angle. In particular, a pentagonal prism gives a 90" deviation, and can be used to produce an accurately horizontal beam from the vertical reference generated as illustrated in either of Figures 1 and 2. Rotation of the pentagonal prism about the axis of the vertical reference beam then sweeps out a horizontal plane accurate to a few seconds of arc. Clearly, many such variations on and additions to the apparatus hereinbefore described can be envisaged, and accordingly it is to be understood that the scope of the invention is in no way restricted by the disclosure of the foregoing embodiments.

WHAT WE CLAIM IS: 1. A portable axis definition apparatus comprising a laser retained by a support member, a gimbal mounted for rotation about the defining axis having a first member and a second member pivotally connected thereto, the laser support member being attached at one end thereof to the second member for free suspension of the laser, laser positioning means for aligning the axis of the laser output beam to pass vertically through the pivotal centre and along the rotational axis of the gimbal, and an optical image forming device positioned in the path of the laser output beam when aligned with the said pivotal centre.
2. A portable axis definition apparatus according to claim 1 wherein the optical image forming device comprises a diverging lens located in the path of the output beam from the laser to expand the laser output beam and a converging lens having a combination of focal length and separation from the diverging lens appropriate to focus the expanded laser beam at infinity.
3. A portable axis definition apparatus according to claim 1 or 2 wherein the laser and the support member are arranged within a housing, the first gimbal member being rotatably mounted on the upper surface of the housing.
4. A portable axis definition apparatus according to any one of claims 1 to 3 wherein the positioning means includes adjustment screws to locate the laser relative to the laser support member and the optical image forming device.
5. A portable axis definition apparatus according to claim 4 wherein the positioning means additionally includes one or more balance weights attached to the laser support member and adjustable in position relative thereto.
6. A portable axis definition apparatus according to any one of claims 1 to 5 wherein the laser support member is a tube surrounding the laser.
7. A portable axis definition apparatus according to any one of claims 1 to 6 wherein the laser support member has attached at one end remote from the gimbal a base plate arranged to support a high voltage power pack for the laser.
8. A portable axis definition apparatus according to claim 7 wherein the supply for the

laser power pack is fed through leads located within the first and second members of the gimbal.
9. A portable axis definition apparatus according to any one of the claims 1 to 8 wherein means are provided to damp the motion of the laser support member when freely suspended from the gimbal.
10. A portable axis definition apparatus according to claim 9 wherein the means to damp comprises at least one projecting arm attached to the laser support member and an oil bath arranged such that the projecting arm engages oil in the oil bath.
11. A portable axis definition apparatus according to claim 10 wherein the oil is silicone oil.
12. A portable axis definition apparatus according to any one of claims 1 to 11 including clamping means operable to arrest movement of the laser and support member when not in use.
13. A portable axis definition apparatus according to claim 12 wherein the laser support member has a resilient member attached such that the clamping means operates to engage the resilient member.
14. A portable axis definition apparatus substantially as herein described with reference to Figures 1 and 2 or Figures 2 and 3.