LIGHT PROJECTION APPARATUS

Abstract: A light projection apparatus (10) for projecting an illuminated line onto a surface which comprises a light source (11) for emitting a light beam and a light beam deflection lens (13) which is adapted to receive the emitted light beam and project a work light beam which will be visible as a straight line on the surface, the light deflection lens (13) is configured so that the visible line on the surface is of generally equal illumination along its entire length. The light beam deflection lens preferably comprises an optical lens which is adapted to refract and reflect the emitted light beam.

Description: LI GHT PROJECTI ON APPARATUS BACKGROUND OF THE INVENTION THIS invention relates to a light projection apparatus, in particular for projecting an illuminated line onto a workpiece. In a number of industries, for example, timber sawmills, stone masonry, the textile industry, etc., frequently a requirement is to saw, grind or cut the products concerned along straight lines which may be of considerable lengths, sometimes up to 12 metres or more. The conventional methods of guiding the cutting machinery involved include the use of chalk lines, strips, straight edge rules and so forth. These methods are clumsy, difficult to apply and are easily displaced by die operations in progress. More recently, the use of lasers projecting a long, thin line of light on the workpiece have come into use. This system represents a major improvement over the older conventional methods. However, a disadvantage of existing laser systems, particularly where very long lines are required, is that the intensity of the light becomes greatly reduced towards the far end of the projected line, and this, combined with the unavoidable small angle of incidence of the beam on to the workpiece at the far area, makes it difficult to distinguish the line clearly. The known art utilizes a lens system comprising a solid cylindrical glass rod to fan out the rays of a laser beam to produce a line of laser light on the surface of the object when the beam is projected on to such object. Figure 1 shows the comparative intensities of the light produced by this system at different angles emanating from the light source. As can be seen, the intensity is greatest over the centre portion of the beam (at x), gradually reducing to zero towards the outer ends of the beam. Figure 2 shows a typical layout of an arrangement for projecting a line of light AB, from laser 1, on to a workpiece. Curve C shows the comparative brightness resulting at various points along this line. As can be seen, bright illumination is provided on die portion of the line nearest to the light source, while on the portion further from the source the level of illumination is substantially lower. This is accounted for by a combination of factors, each of which materially contributes to this unsatisfactory situation. These factors are: 1) The greater distance from the light source. 2) The comparatively lower intensity of light emanating from the lens in the outer portion of the beam. 3) The very oblique angle at which the light strikes the surface of the work piece at this end of the line, resulting in an already reduced relative light intensity being spread over a long length of the line. Curve D, shown in Figure 2, depicts the comparative brightness with a prior art device which the beam from the light source is offset from the axis of the lens used to deflect that beam onto the work surface. The result will be a bright line at a point remote from the light source but that line fades rapidly nearer to the light source. A device sometimes employed to improve this result is to offset the solid cylindrical lens from the centre line of the laser beam. This results in a higher proportion of light being projected from the lens to one side of the beam as compared with the other side, and this effect is utilised to increase to some extent the proportion of light transmitted to the more distant portion of the line. However, even with this modification, the variation in illumination of die line from one end to the other is considerable. OBJECT OF THE INVENTION It is an object of the invention to provide a system in which a line of laser light may be projected on to a surface situated obliquely relative to d e light source, such a line of light being substantially evenly illuminated drroughout its leng , and thus more easily visible at all points along its length. SUMMARY OF THE INVENTION According to the present invention there is provided a light projection apparatus for projecting an illuminated line onto a surface, the apparatus comprising: a light source for emitting a light beam; and a light beam deflection means adapted to receive the emitted light beam and project a work light beam having a fanned, planar configuration which will be visible as a straight line on the surface, the light deflection means being configured so that the visible line on the surface is of generally equal illumination along its entire length. The light beam deflection means is preferably configured so as to produce a work light beam which increases in intensity in a direction away from the light beam deflection means. The light beam deflection means preferably comprises a lens, in particular a lens of generally cylindrical configuration having concentric concave and convex surfaces, the lens being adapted to reflect and refract d e emitted beam to produce die fanned work light beam. The lens is typically of a hollow generally circular cylindrical configuration which is orientated such d at its longitudinal axis is substantially perpendicular to die axis of the emitted light beam. In a preferred embodiment of d e invention, the emitted beam has a diameter which is less man half the diameter of d e lens, the emitted beam impinging on the lens to one side of die longitudinal axis of die lens. The apparatus is typically mounted to a support rail. The apparatus is preferably able to move along the support rail and tilt relative to the support rail in order to position die work line in a desired position and wid a desired angle of incidence relative to the surface. The light source for emitting a light beam is usually a laser diode, although a Helium-Neon plasma tube may also be used. When a Helium-Neon plasma tube is used, an anamorphic lens is preferably positioned between the plasma tube and the light beam deflection means in order to produce an elliptical shaped work beam. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the pattern of light distribution of light produced by a prior art light projection apparatus; Figure 2 shows the typical layout of a prior art arrangement for producing a line on a workpiece; Figure 3 shows the pattern of light distribution emerging from an embodiment of me light projection apparatus of the invention; Figure 4 shows the arrangement of the light projection apparatus of the invention for producing d e pattern of light of Figure 3; Figure 5 is a cross-section view of a preferred embodiment of the invention; and Figure 6 shows a perspective view of an apparatus according to the invention. DESCRIPTION OF AN EMBODIMENT A means whereby the pattern of light distribution emerging from the optical system may be changed from the symmetrical pattern of a conventional system to a pattern of the type described above is described below. Figure 3 shows diagrammatical ly the pattern of light distribution emerging from a light projection apparatus of the invention. As can be seen, die intensity of the light is greatest near an edge of the beam at a fairly large distance from the centre of the beam (at y). Referring to Figure 4, the intensity of light emerging from the optical system of the invention is highly concentrated in the upper portion of die beam (at E), trailing off more or less exponentially to die much lower intensity in the lower portion of die beam (at F). The result is that a substantial amount of light is projected on to die far portion of d e line towards die end B. The combination of ti ese factors results in the line of light AB being more or less evenly ittuminated along its full length, as illustrated in curve G. Referring to Figure 5, a light projection apparatus 10 comprises a laser diode module 11 which shines a beam of laser light 12 on to a hollow cylindrical lens 13. The centre line 14 of the laser beam 12 is spaced from the centre line 15 of the lens 13 by an off-set distance 16. The beam 12 is refracted and reflected into a fanned configuration. The refracted rays are produced nearer the centre line 15 of the lens between the illustrative rays 18 and 19, whilst die reflected rays are produced further away from die centre line 15 between illustrative rays 20 and 21. One point of interest in die curve shown in Figure 3 is the point H which depicts increased intensity in the region where reflected and refracted light emitting from the light protection apparatus overlap. The diode module 11 should be orientated so that the major axis of beam 12 is at right angles to the axis of lens 13, and d e offset distance 16 may preferably be such mat die lower limit of beam 12 does not pass the lower surface of lens 13. The effect of using a hollow cylindrical lens 13 off-set from the laser beam 12 is that the refracted rays emerging from nearer die centre line of the lens are closely spaced radially, while those emerging further away are more widely spaced radially. In the case of the reflected rays, tiiose nearer to the outer surface of lens 13 are reflected less ti an those closer to die centre line of die lens. Reflection occurs from both the external and internal surfaces of the lens. For this reason it is preferable to use a lens without an anti-reflection coating The proportion of light reflected is considerably less tiian the proportion refracted, but witii suitable adjustment of e amount of offset of the lens, the intenser portion of the reflected rays overlap part of die less intense portion of die refracted rays, resulting in a homogenous line of light on the workpiece, and providing a wider usable angular spread of die beam. This overlapping reflected portion causes a slight increase in light intensity over a small part of the intensity curve, as indicated by d e slight "hump" H in die curve, the effect of which is not significant, (refer to Figure 3). However, what is of considerable importance is the extension of the curve, which results in significant modification of the light distribution pattern on the workpiece. The pattern of light distribution thus obtained provides a near-ideal distribution of light along the full length of the line, even where an extremely long line relative to the height of the light source is required. The preferred embodiment described above employs a laser diode as die light source. It is also possible to employ a Helium-Neon plasma tube as the light source, preferably in conjunction with an anamorphic lens positioned between the laser and d e hollow cylindrical lens to produce an elliptical shaped beam. A wide range of sizes of hollow cylindrical lenses may be used. It is also possible to use otiier configurations of lenses and light reflection devices such as curved mirrors or the like. The use of hollow cylindrical lenses for the applications described above represent a simple means of achieving the required pattern of light distribution. It can be seen from Figure 5 that only a portion of die lens is utilised. Thus, if preferred, it is possible to incorporate just a segment of a hollow cylindrical lens into the device. Hollow cylindrical lenses are in effect convex-concave lenses of which the outer and inner radii have a common centre. It is also possible to use convex/concave lenses of which the radii have separate centres. The apparatus of the invention will preferably be mounted on a rail which is aligned perpendicular to die plane of the work light beam and die apparatus will be slidable along d e rail so that the position of die beam relative to a surface or workpiece can be varied. The rail is preferably circular in cross-section and the apparatus may be rotatable on the rail. The apparatus is also movable along the lengtii of the rail so that die illuminated line on the work surface can be positioned. In addition, fine angular adjustment of d e beam is possible. That is, it will be possible to adjust me angle of the beam relative to the axis of the rail by means of a fine adjustment of d e screw numbered 22 in the drawings. This will allow the surface line to coincide witii a required datum or otiier feature on the work piece. Figure 6 depicts a perspective view of die apparatus in operation. The apparatus includes a clamping screw 23 for clamping the apparatus to the rail 24. As previously mentioned, the apparatus is rotatable on the rail 24 and is also slidable lengthwise along the length of the rail. In addition, d e angle of the apparatus relative to die rail is adjustable by means of me screw 22 so that the beam 25 emitting from the apparatus can be angled relative to the longitudinal axis of die rail. It is envisaged that d e angle of adjustment of the beam will be between 10° and 15°. The apparatus of the invention is, on account of the configuration of d e lens, able to illuminate a line on a surface at a position far closer to the apparatus than has been possible witii prior art devices of tiiis type. Thus, it will be noted, tiiat d e distance indicated by the letters A'-O' in Figure 4 is less than the distance A-0 depicted in Figure 2. In practice it is found tiiat the distance A'-0' will be approximately 0.5m whereas the distance A-0 of me prior art arrangement is approximately 2m. This is considered to be particularly advantageous, particularly in applications where tiiere are space confinements.

Claims: CLAIMS 1. A light projection apparatus for projecting an illuminated line onto a surface, die apparatus comprising: a light source for emitting a light beam; and a light beam deflection means adapted to receive die emitted light beam and project a work light beam having a fanned, planar configuration which will be visible as a straight line on the surface, die light deflection means being configured so tiiat the visible line on the surface is of generally equal illumination along its entire lengtii. 2. Apparatus according to claim 1 wherein the light beam deflection means is configured so as to produce a work light beam which increases in intensity in a direction away from die light beam deflection apparatus. 3. Apparatus according to eiti er preceding claim wherein the light beam deflection means comprises an optical lens which is adapted to refract and reflect die emitted light beam. 4. Apparatus according to claim 3 wherein the lens is of generally cylindrical configuration having concentric concave and convex surfaces, the lens being adapted to reflect and refract the emitted beam to produce d e fanned linear work beam. 5. Apparatus according to claim 4 wherein die lens is of hollow generally circular cylindrical configuration which is orientated such tiiat its longitudinal axis is substantially perpendicular to the axis of the emitted light beam. 6. Apparatus according to claim 5 wherein the emitted beam has a diameter which is less than half the diameter of die lens, die emitted beam impinging on the lens to one side of die longitudinal axis of die lens. 7. Apparatus according to any preceding claim which is adapted to be mounted to a support rail which is perpendicular to die plane of die work beam, die apparatus being movable relative to and securable in selected positions along such a support rail. 8. Apparatus according to claim 7 which further includes a fine adjustment mechanism for fine adjustment of the angle of die apparatus relative to die rail. 9. Apparatus according to eitiier claim 7 or 8 wherein the apparatus is adapted to move relative to the support rail. 10. An apparatus according to any one of d e preceding claims wherein die light source is a laser diode. 11. An apparatus according to any one of claims 1 to 9, wherein die light source is a Helium-Neon plasma tube. 12. An apparatus according to claim 11, wherein an anamorphic lens is positioned between the plasma tube and the light beam deflection means to produce an elliptical-shaped work beam. 13. A light projection apparatus substantially as herein described witii reference to any one of Figures 3 to 5 of the accompanying drawings.

Inventors: ANDERSON NIGEL IIVARI, ANDERSON, NIGEL, IIVARI
Applicants: ANDERSON NIGEL IIVARI, ANDERSON, NIGEL, IIVARI
Application year: 1996
Main classification: B25H7
IPC codes: B25H7