GB2165182A - Light reflector apparatus and method of making same - Google Patents

Abstract

A light reflector apparatus for use in an electronic flash unit, automobile headlamps, searchlight or the like is formed by an injection moulding operation. A light-reflecting flexible sheet 72 is placed in a mould so that its light-reflecting surface 73 is positioned adjacent a male mould forming surface. The forming surface is larger than the sheet. Liquid plastics material is injected into the mould under pressure against the opposite surface of the sheet 72, thus pressing the light-reflecting surface into intimate contact with the forming surface. Because the sheet is smaller, the border 86 of the forming surface is not covered by the sheet Plastics material flows beyond the outer edges of the sheet against the uncovered border of the forming surface. The plastics material solidifies to form a housing having a supporting body overlying the sheet and a shoulder, integral with the supporting body and contiguous with and surrounding the outer edges of the sheet. The shoulder traps the sheet against the underlying supporting body for maintaining the contour of the sheet caused by the monitoring surface. <IMAGE>

Description

SPECIFICATION Light reflector apparatus and method of making same The invention relates to an improved method of making light reflector apparatus usable, for example, in a photographic electronic flash unit or the like, and to improved light reflector apparatus.

Photographic flash apparatus includes a reflector, a source of light, such as a flash bulb or flash tube, and a housing for mounting the light source and the reflector relative to each other.

The flash apparatus produces a beam of illumination which includes direct illumination from the light source, as well as source illumination reflected from the reflector. In photographic flash apparatus it is commonly intended that the projected light should, as well as possible, be uniformly distributed within an imaginary plane located a particular distance from the flash apparatus. However, in some photographic flash apparatus, non-uniform light patterns may be desirable, as disclosed in U.S. Patent No.

4,304,479. Regardless of the desired light distribution, it is important that the reflector conform accurately to a predetermined shape to provide the desired light distribution, and that both the reflector and the light source are accurately mounted within the flash housing and thus with respect to each other, to prevent skewing of the projected light beam.

It is known in the photographic flash reflector art to make flash reflector apparatus by vacuum depositing aluminium, which serves as the reflector, directly onto a plastics material, which forms at least a portion of the flash housing assembly. In order to have a high reflectivity surface, the aluminium coating is made very thin about .05 to .075 millimeter. However, with an electronic flash unit is has been found that when the flash tube is located close to the reflector andlor a high-energy flash tube is employed, heat from the tube can burn such a thin reflector. Also, because there is intimate contact between the reflector and the plastics material, the latter is also heated and may separate from the reflector.This can both change the shape of the reflector, and/or shift the position of the reflector relative to the flash tube, thus creating errors in both light distribution and direction of the projected light beam.

Heating of the reflector and the plastics material is not as severe if the aluminium is made thicker.

However, it is not practical in a flash reflector to vacuum deposit a thicker coating of aluminium because the reflectivity of vacuum-deposited aluminium decreases in proportion to its thickness. Furthermore, a thicker coating increases manufacturing time.

An alternative solution has been adhesively to attach an aluminium coated sticker directly onto a plastics material housing. Two advantages achieved with this operation are (1) the sticker and aluminium coating form a thicker reflector, which is, thus, better able to resist burning and thermally to shield the plastics material, and (2) the adhesive for securing the sticker serves as a thermal insulator, which further shields the plastics material. However, this solution adds to reflector manufacturing costs, and further complicates the manufacturing process, in part because precise sticker alignment tolerances must be met.

It is also known in the photographic flash reflector art to pre-shape a highly polished aluminium sheet into a reflector. The pre-shaped reflector is then attached to a moulded plastics material housing. The sheet, in this case, can be made thicker than the aluminized coating described above, without a reduction in reflectivity, and thus is less susceptible to burning and is more suited to thermally shielding its housing. However, because the reflector and its housing no longerform a unitary structure, the thickness of the aluminium sheet must be controlled precisely, and the housing must include reference mounting surfaces, retaining ribs, fingers and the like, for accurately and securely mounting the reflector. U.S.Patent No. 4,317,625 discloses some assembly requirements which should be met when a pre-shaped reflector is mechanically attached to a housing.

In summary, prior art light reflector apparatus and manufacturing methods therefor, are relatively complex and/or expensive or the apparatus is deficient in use. The present invention seeks to overcome the disadvantages of the prior art.

According to the present invention there is provided a method of making light reflector apparatus said method comprising: (a) placing a flexible material having a lightreflecting surface adjacent a forming surface having contours arranged to form the light-reflecting surface of the flexible material into a shape for reflecting light into a beam; b) enclosing the material in a moulding chamber a portion of which is defined by the forming surface; c) injecting liquid plastics material under pressure into the chamber against a rear surface of the flexible material so as to press the light-reflecting surface into intimate contact with the forming surface to shape the material to the contours of the forming surface; and d) solidifying the plastics material to form a solid housing against the rear surface of the flexible material to maintain the shape.

Preferably, discrete zones of the flexible material are clamped against the forming surface. With this step, the flexible material is retained in a shape generally according to that of the forming surface prior to the injection of the liquid plastics material.

Advantageously, the forming surface is larger than the flexible material and the flexible material is located on the forming surface suring placement.

Intimate contact created between the light-reflecting surface and the forming surface serves to prevent leakage of the liquid plastics material onto the light-reflecting surface. A shoulder is created at edges of the flexible material which serves to retain the flexible material in its formed shape.

The present invention also resides in light reflecting apparatus for reflecting light from a source into a beam and manufactured by a method as recited in any of the preceding three paragraphs. Such apparatus includes flexible material having a reflective surface and formed into the desired shape, and a plastics material housing in intimate contact with the other surface of the flexible material.

The housing may have shoulders engaging edges of the flexible material for retaining the flexible material in its formed shape.

Advantageously, the housing includes two aper turestogether bounding a bridge portion of the housing. The bridge portion is resiliently flexible and integral with the remainder of the housing at its ends. The bridge portion serves to retain a light source which extends through one of said apertures, in contact with the reflective surface of the flexible material.

In a detailed description of preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which: Figure 1 is a schematic view of an injection moulding machine for use in manufacturing light reflector apparatus according to the invention; Figure 2 is an exploded, perspective view of moulding sections of the injection moulding machine of Figure 1; Figure 3 illustrates a light-reflecting flexible sheet which is to be shaped into a reflector for light reflector apparatus according to the invention; Figures 4 to 7 are cross-sectional views of the sheet of Figure 3, and the upper and lower moulding sections of Figure 2, during various stages of an injection moulding operation; Figure 8A is a perspective view, a portion of which is cut away, of trough-shaped light reflector apparatus manufactured in accordance with the invention.

Figure 8B is an enlarged perspective view of the lower left-hand corner of the light reflector apparatus shown in Figure 8A; and Figure 9 is an end view of a second preferred embodiment of light reflector apparatus, manufactured in accordance with the invention, for an electronic flash unit.

The ensuing description is directed to a particular type of light reflector apparatus, namely light reflector apparatus for a photographic flash device, and a method of its manufacture, in accordance with the present invention. However, it is to be understood that the invention is applicable to other light reflector apparatus, for example, as used in automobile headlights, flashlights, searchlights, and photographic chemical flash apparatus.

Figure 1 schematically shows an injection moulding machine 10, which is to be used in the manufacture of light reflector apparatus, according to the invention. Generally, the equipment 10 includes an injection unit 12 and a clamping unit 14.

The injection unit 12 includes a hopper 22 in which pelletized plastics material is loaded. The hopper 22 funnels the pelletized plastics material into a heated extruder 24 wherein the plastics material is converted to a liquid state. The extruder 24feeds liquid plastics material through a check valve 26 into a shooting pot 28, which contains an injection piston 30. The piston 30, under control of motorized drive means 32, forces the liquid plastics material through a shut-off nozzle 34 into the clamping unit 14.

The clamping unit 14 contains a mould 36 into which the liquid plastics material is injected. The mould 36 comprises female and male moulding sections 38 and 40, respectively. The section 38, which is mounted on a stationary platen 42, is connected to the shut-off nozzle 34 for receiving liquid plastics material from the injection unit 12.

The section 40 is mounted on a movable platen 44, which is driven by a ram 46 into a moulding position.

Rails 48 support the platen 44 and align the platens 42 and 44, to provide accurate mould alignment. The clamping unit 14 may also include an ejector (not shown) for removing the moulded part from the mould 36 after the liquid plastics material cools.

The injection moulding machine 10 described above is conventional and is available from a variety of sources, one of which is Huskey Injection Molding Systems Ltd, Bolton, Ontario, Canada.

A light reflector apparatus in accordance with the present invention and for use in electronic flash unit will now be described. The reflector apparatus includes a metallic reflector and a plastics material housing supporting the reflector. The reflector apparatus is shaped like a trough for reflecting light impinging on the reflector outthrough the mouth of the trough. Preferably, the reflector is shaped so that, with the light source in predetermined position, the reflected light is concentrated into a beam. An elongate flash tube is disposed in the base of the trough and the ends of the trough have openings through which respective ends of the flash tube protrude.

The plastics material housing is formed and unified with the reflector by an injection moulding operation. The reflector is shaped into its trough-like configuration in response to the injecting of liquid plastics material into a mould. The plastics material is allowed to solidify to form the housing, which maintains the contour of the reflector formed during the moulding operation.

It will be obvious to those having skill in the art and from the disclosure that follows that any of a variety of shapes for light reflector apparatus can be formed using the teachings of the invention.

Referring now to Figure 2, the female and male moulding sections, 38 and 40, form respectively the rear and front surfaces of the light reflector apparatus.

The male moulding section 40, which servesto form a forwardly facing surface of the light reflector apparatus, includes a projecting mandrel 56 having a generally elliptically curved, centrally located frontforming surface 57, which forms the trough shape of the reflector apparatus, and a pair of opposed end-forming surfaces 58 and 59, which form end walls at corresponding ends of the trough shape.

Each end-forming surface is comprised of two corresponding planar sections 58a, 58b and 59a, 59b, respectively. The sections 58a, 58b and 59a, 59b serve to orient corresponding side walls of the reflector apparatus at an angle for reflecting light.

For this purpose, the sections 58a and 59a are obtuse, and the sections 58b and 59b are approximately perpendicular to the longitudinal axis of the trough.

The female moulding section 38, which forms a rearwardly facing housing surface of the light reflector apparatus, includes a fixed, centrally located portion 65, and a pair of opposed side draws 67 and 69, which are mounted to respective ends of the central portion 65, for relative movement in the direction of the arrows A, to close and open the female portion of the mould 36. The centrally located portion 65 of the female moulding section 38 corresponds to the front-forming surface 57 of the male section 40. Likewise, the side draws 67 and 69 of the female section 38 correspond respectively to the end-forming surfaces 59 and 58 of the male moulding section 40.

The centrally located portion 65, and the side draws 67 and 69 include a plurality of depending inwardly facing shutoffs and holddown pads 70. The pads 70 have clamping surfaces 70a, the contours of which are chosen to provide clamping of a lightreflecting flexible sheet (Figure 3) about the mandrel 56 in discrete predetermined zones when the mould 36 is closed.

Referring now to Figure 3, there is shown a light-reflecting flexible sheet 72 which is to be shaped by the mandrel 56 into a reflector during an injection moulding operation. Preferably, the sheet 72 is aluminium. In a photographic flash application, its front surface, denoted 73, is highly polished to a mirror-like finish for reflecting light. Its back surface, denoted 75, need not be specially treated. In the illustrative embodiment, the sheet 72 may have a thickness of about .33 millimeter.

The sheet 72 of Figure 3 is cut from flat sheet stock into a blank suitable for shaping into the aforementioned trough-like configuration. Central portion 77 forms the trough of the reflector, and mating pairs of end flaps 79 and 80 form a reflector end wall, at each end of the trough. For a reason made apparent below, the sheet 72 is somewhat smaller than corresponding portions of the forming surfaces of the mandrel 56.

Reference is now made to Figures 4 to 7 which are cross-sectional views of the mould 36 at various stages of manufacture. In manufacturing the flash reflector apparatus, the central portion 77 of the sheet 72 is first located on the front-forming surface 57 of the mandrel 56. A pin 82 on the surface 57, and a receiving eccentric pinhole 84 in the sheet 72 can be used for locating the sheet 72 on the forming surface 57. The polished, light-relecting, front surface 73 faces the mandrel 56 as shown in Figure 4.

To assist in shaping the sheet 72 to the contour of the mandrel 56, it is beneficial to pre-bend and prefold the sheet 72 prior to positioning it on the mandrel 56. This may be done manually or by automatic equipment (not shown) along bend lines, shown by the dashed lines 72a of Figure 3. In the prebending of the sheet 72, it is preferred that its polished surface 73 is slightly open, that is, less concave, relative to the contour of the mandrel 56.

This prevents scuffing of the surface 73 as the sheet 72 is brought into intimate contact with the mandrel 56.

Next, as is shown in Figure 5, the male moulding section 40 is moved into its moulding position, under the influence of the ram 46 (Figure 1). When the mould 36 is closed, the holddown pads 70 engage the back surface 75 of the sheet 72 and clamp isolated small zones of its polished surface 73 to corresponding areas on the front-forming surface 57 and the end-forming surfaces 58 and 59 of the mandrel 56.

As is shown in Figure 5, the sheet 72 is now shaped according to the general contour of the mandrel 56. Non-clamped areas of the sheet 72 may not be in intimate contact with the forming surface 57. Figure 5 also illustrates that, because the sheet 72 is smaller than the mandrel 56, border, or peripheral, portions of the front-forming surface 57, and the planar sections 58b, 59b of the end-forming surfaces 58 and 59 of the mandrel 56, denoted 86, are not covered by the sheet 72.

After the mould 36 is closed, heated, liquid plastics material, denoted 88 (Figures 6 and 7), is injected under pressure through the nozzle 34 into the female moulding section 38 against the back surface 75 of the sheet 72. The plastics material 88 spreads across the back surface 75 and lips around outer edges, denoted 90, of the sheet 72 against the uncovered peripheral portions 86 of the mandrel 56. Pressure relief means (not shown) are provided for removal of air trapped in the mould 36.

As the mould 36 fills with plastics material 88, the sheet 72 is subjected to progressively increasing forces on its back surface 75. These forces press the light-reflecting surface 73 of the sheet 72 into intimate contact with the mandrel 56, as shown in Figures 6 and 7. The intimate contact between the sheet 72 and the mandrel 56 shapes the lightreflecting, front surface 73 precisely according to the contour of the mandrel 56. Such contact also seals the boundary between the edges 90 of the sheet 72 and the mandrel 56. Thus, plastics material 88 is prevented from leaking between the mandrel 56 and the sheet 72 onto the light-reflecting, front surface 73.By selectively clamping the sheet 72 to the mandrel 56 prior to injecting the plastics material 88 into the mould 36, flash reflector apparatus can be made having a wide variety of shapes with the light-reflecting surface 73 being free of plastics material. Figure 6 illustrates the mould 36 when it is partially filled with plastics material 88, and Figure 7 illustrates the mould 36 when it is completely filled with the plastics material.

Next, the plastics material 88 is caused to harden by cooling it. The plastics material 88 is cooled quickly by passing waterthrough the female moulding section 38 by means not shown.

To open the mould 36, the male moulding section 40 is withdrawn from the female section 38. The side draws 67 and 69 are then moved away from their respective ends of the central portion 65 to open the female portion of the mould 36.

Figures 8A and 8B illustrate the flash reflector apparatus after it is removed from the mould 36. The reflector apparatus is in the form of an open trough and comprises a reflector lining the inner face of the trough and a hardened plastics material housing 91 supporting the reflector. The reflector consists of the sheet 72, which is now shaped according to the contour of the mandrel 56. The housing 91 comprises a concave supporting body 92, overlying the back surface 75 of the sheet 72, and a lip 94, integral with the body 92, and contiguous with and surrounding the outer edges 90 of the sheet 72. The lip 94 traps the sheet 72 against the body 92, so that the sheet 72 is maintained in the shape caused by the contour of the mandrel 56 during the molding operation.The openings 96 in the supporting body 92 expose those areas of the back surface 75 of the sheet 72 which were clamped by the holddown pads 70 while the mould 36 was closed.

An electronic flash unit 100 having a light reflector apparatus 102, manufactured in accordance with the teachings of the invention, is shown in Figure 9.

Elements of light reflector apparatus 102 similarto elements of light reflector apparatus of Figure 8 are identified by like numerals. An opening 104 in the base of each flash end wall 105 adjacent the trough of the light reflector apparatus means to receive a flash tube 106.

The tube 106 is supported at each end by a resilient, plastics material bridge 108. As viewed from the end of the light reflector apparatus, each bridge 108 extends from one side of the reflector apparatus to the other side, and is integrally attached at each end to an end wall 105. The bridge 108, which includes a cradle-shaped central portion 109 for supporting the tube 106, resiliently biases the tube 106 against the light-reflecting surface 73 of the sheet 72. The bridge 108 can accommodate variations in tube diameter, and assures centring of the tube 106 in the base of the trough. Each opening 104 and bridge 108 is provided by appropriate formation of the mould 36. The bridge is bounded by two openings, one of which is the opening 104 and the other is an opening 104'.The openings 104,104' are formed by pads (not shown) on the side draws 67 and 69 which exclude liquid plastic during the moulding process.

The underlying supporting body 92 includes an aperture 110 located to expose the back surface 75 of a portion of the sheet 72 adjacent the tube 106. The aperture 110 can be formed by clamping this area of the surface 75 by a holddown pad (not shown) in the female moulding section 38. The aperture 110 provides an area for electrically connecting the trigger transformer (not shown) for applying a tube triggering voltage directly to the sheet 72. Thus, the sheet 72 serves both as a light reflector and as a tube trigger electrode, U.S. Patent No. 3,484,597 discloses a reflectorforan electronicflash unit that also serves as a tube trigger electrode.

Polycarbonate M39-6823, sold by the Mobay Chemical Company of Pittsburgh, Pennsylvania under the trademark Merlon, is a plastics material ideally suited to this manufacturing operation. This polycarbonate, heated to about 290 and pressurized at about 45 kilograms per square centimeter for the moulding operation, has a high viscosity and, thus, a low flow rate. This is advantageous as it serves to further to assure that the plastics material does not leak to between the polished surface 73 and the mandrel 56, as the plastics material is injected into the mould 36. It has been found that the location at which plastics material 88 is injected into the mould 36 against the surface 75 is not particularly critical.

By using a coolant, the plastics material is hardened sufficiently within less than 20 seconds to allow the mould 36 to be opened. Full curing of the plastics material probably occurs within about 24 hours. Upon hardening, this polycarbonate has a high creep resistance and thus maintains the reflector in its desired shape.

A further advantage of this polycarbonate is that it is relatively clear. Thus, it more readily dissipates heat produced resulting from a light flash.

A still further advantage offered by its clarity is that this polycarbonate can be used for making a flash covering window (not shown). The mould 36 can be configured for making the window integral with the housing 91. Conveniently, the window is connected to the housing 91 by plastics material hinges so as readily to be swung into a tubecovering position. A further feature is that flash diffusing means such as a fresnel lens or the like can be placed within the window-forming portion of such a mould so that the window can be moulded around or integrally with the lens.

Claims (5)

1. A method of making light reflector apparatus said method comprising: a) placing a flexible material having a lightreflecting surface adjacent a forming surface having contours arranged to form the light-reflecting surface of the flexible material into a shape for reflecting light into a beam; b) enclosing the material in a moulding chamber a portion of which is defined by the forming surface; c) injecting liquid plastics material under pressure into the chamber against a rear surface of the flexible material so asto press the light-reflecting surface into intimate contact with the forming surface to shape the material to the contours of the forming surface; and d) solidifying the plastics material to form a solid housing against the rear surface of the flexible material to maintain the shape.

2. A method as claimed in claim 1, including clamping discrete zones of the flexible material against the forming surface whereby the flexible material is retained in a shape generally according to that of the forming surface prior to the injection of the plastics material.

3. A method as claimed in claim 1 or 2, wherein the forming surface is of area larger than the area of the flexible material and the flexible material is located on the forming surface during placement, intimate contact created between the light-reflecting surface and the forming surface serving to prevent leakage of the plastics material onto the lightreflecting surface, whereby a shoulder is created at edges of the flexible material serving to retain the flexible material in its formed shape.

4. A method of manufacturing a light-reflecting apparatus substantially as hereinbefore described with reference to Figures 1 to 7 of the accompanying drawings.

5. Light reflector apparatus as claimed in claim 1 substantially as hereinbefore described with reference to, and as shown in Figures 8A and 8B of the accompanying drawings.

5. Light reflector apparatus for reflecting light from a source into a beam, manufactured by a method as claimed material having a reflective surface and formed into the desired shape, and a plastics material housing in intimate contact with the other surface of the flexible material.

6. Light reflector apparatus as claimed in claim 5, wherein the housing has shoulders engaging edges of the flexible material for retaining the flexible material in its formed shape.

7. Light reflector apparatus as claimed in claim 5 or 6, wherein the housing includes two apertures together bounding a bridge protion of the housing, the bridge portion being resiliently flexible and integral with the remainder of the housing at its ends, the bridge portion serving to retain a light source, which extends through one of said apertures, in contact with the reflective surface of the flexible material.

8. A light reflector apparatus substantially as hereinbefore described with reference to and as illustrated in Figure 8A and 8B of the accompanying drawings.

9. An electronic flash apparatus including a light reflector apparatus as claimed in any of claims 5 to 8 and substantially as hereinbefore described with reference to and as illustrated in Figures 8A and 8B as modified by Figure 9 of the accompanying drawings.

Amendments to the claims have been filed, and have the following effect: (a) Claims 1 to 9 above have been deleted.

(b) New or textually amended claims have been filed as follows:

1. Light reflector apparatus for reflecting light from a source into a beam, said apparatus comprising: (a) a metallic sheet having a light-reflective surface and defining an open-ended chamber shaped to reflect impinging light into a beam of illumination projected through the open end of said chamber; and b) a unitary plastic housing having (1) a supporting body including a receiving surface complementary with and underlying said sheet and (2) a shoulder integral with said supporting body and contiguous with outwardly extending edges of said sheet defining the open end of said chamber, to secure said sheet in intimate contact against said receiving surface of said supporting body.

2. Light reflector apparatus as claimed in claim 1 wherein said light-reflective surface is located on a forwardly facing surface of said sheet, and said shoulder secures a rearwardly facing surface of said sheet against said receiving surface of said supporting body, said receiving surface being complementary with respect to said rearwardly facing surface, thereby to retain the shape of said sheet.

3. Light reflector apparatus as claimed in claim 1 or 2 wherein said shoulder is both contiguous with and surrounds said outwardly extending edges of said sheet.

4. Light reflector apparatus as claimed in claim 1, 2 or 3 comprising elastic means integral with said supporting body for resiliently biasing an illumination source into engagement with said lightreflective surface of said sheet.