Lighting unit

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to lighting units for use in inspecting products for their outward appearances, flaws or finished conditions, or in position detection or like applications.

[0003] 2. Description of the Related Art

[0004] Hitherto, halogen lamps are known as representatives of light sources for use in lighting units of this type. Since such a halogen lamp has limited freedom in selection of a suitable place to which the halogen lamp is to be installed due to its bulkiness and since it is difficult to condense light from the halogen lamp, it has been a conventional practice to illuminate a work not directly from a halogen lamp but indirectly by guiding light from the halogen lamp through an optical fiber to a head attached to the front end of the optical fiber, as described in Japanese Patent Laid-Open Gazette No. HEI 5-248820. Such an optical fiber is used because it has flexibility and can be cut to a desired length and hence allows the halogen lamp to be freely located at an easy-to-install place even if the place is, for example, remote from the lighting site.

[0005] A lighting unit for illuminating works that are constantly at non-fixed positions such as those inaccurately positioned on and fed one after another by a conveyor unit, needs to have a function allowing the head having an illuminating aperture to move frequently in accordance with the position of each work.

[0006] Of course, the optical fiber used in such a lighting unit moves with frequent movements of the illuminating aperture. Since such an optical fiber has flexibility, it has heretofore been considered that such a lighting unit can accommodate well to applications where the head needs to move as described above.

[0007] Actually, however, particularly where a relatively long (for example 2 or 3 meters or longer) optical fiber is used, it is likely that an up-sized driving mechanism is needed for moving the head while causing the associated optical fiber to accompany the head or that movement of or position control over the head becomes difficult, because generally an optical fiber is relatively bulky and heavy as compared to electric wires or the like.

[0008] Further, since optical fibers are less flexible than electric wires, they are likely to be damaged in a relatively short time by frequent bending and moving, which may result in problems in respect of the reliability, lifetime and the like of the lighting unit.

[0009] It is possible to use an LED, which recently has been attracting attention as a substitute for a halogen lamp, as a light source. However, where a multiplicity of LEDs are directly fitted to a head without using an optical fiber, a problems arises that downsizing of the head and light condensing are difficult. For example, when a very small object, such as a component mounted on a printed circuit board, is to be illuminated, such a head fitted directly with LEDs has a relatively large minimum focal diameter and hence illuminates the object as well as unwanted portions, which results in inefficient lighting.

[0010] The present invention, which is not made until the conventional concept of moving the head by utilizing the flexibility and the length adjustability of an optical fiber has been abandoned completely, intends to solve the foregoing problems at a time by taking advantages of the lightness, compactness and the like of an LED light source device as well as the advantage of an optical fiber head in its possibility to reduce the size thereof.

SUMMARY OF THE INVENTION

[0011] According to one aspect of the present invention, there is provided a lighting unit comprising: a head defining an illuminating aperture for directing light to an object to be illuminated, the head being supported by a movable support member; an LED light source device mounted at the movable support member for emitting light when electric power is supplied thereto from an electric power source disposed separately from the movable support member through an electric cable; and at least one flexible optical fiber for guiding light from the LED light source device to the illuminating aperture of the head.

[0012] With the lighting unit of the construction described above, the weight and size of the LED light source device can be reduced easily and, therefore, the LED light source device thus reduced in weight and size, though mounted at the movable support member, can hardly exert influence on the driving of the movable support member, hence, of the head.

[0013] If the head is fixedly supported by the movable support to maintain the relative positional relation between the LED light source device and the head, it is possible to reduce the burden to be imposed on the optical fiber, thereby to eliminate the influence of such a burden on the reliability, lifetime and the like of the optical fiber. Of course, the head may be mounted at the movable support member so as to be slightly movable or slowly movable relative to the movable support member unless such movement affects the reliability, lifetime and the like of the optical fiber.

[0014] Since the head is connected to the optical fiber and is separate from the LED light source device, it is possible to make the size of the head very small as well as to condense light onto a small area. Further, since the light source can be spaced apart to a certain extent from the object to be illuminated or from an image pick-up device for imaging the object, it is also possible to prevent the object or the image pick-up device from being affected by heat generated from the light source.

[0015] The LED light source device may be supplied with electric power either from a battery provided in or incident to the lighting unit or from an electric power source disposed separately from the movable support member through an electric cable. With the former arrangement, the lighting unit can be rendered cableless. Alternatively, though the latter arrangement requires an electric cable, the electric cable is far superior to an optical fiber in flexibility, durability, price and the like. Therefore, the latter arrangement is capable of highly reliably driving the movable support member and the head with a very light burden on the electric cable as compared to the burden that has been conventionally imposed on an optical fiber when the optical fiber is moved with the movement of the head. An arrangement for supplying electric power from an image pick-up device may also be conceived.

[0016] In the present invention, the light source device may be disposed adjacent the illuminating aperture to shorten the optical fiber (to 1 m or less for example), thereby reducing the weight of the optical fiber. With this feature, the head can be driven smoothly even if it is movably mounted at the movable support member. In this case, it is preferred that the head be mounted at the movable support member so as to be slightly movable or slowly movable relative to the movable support member unless such movement affects the reliability, lifetime and the like of the optical fiber.

[0017] For obtaining an improved light-condensing characteristic, the optical fiber is preferably fitted with a lens at a front end thereof on a head side.

[0018] One desirable form of the electric cable is a robot cable.

[0019] According to another aspect of the present invention, there is provided a lighting unit for use in line inspection, which is developed from the technical concept described above.

[0020] The lighting unit for use in line inspection comprises: a fiber cable in which a multiplicity of optical fibers extending from light-receiving ends thereof facing a light-emitting surface of an LED light source into a head unit body are bundled and accommodated; an optical fiber aligning and holding member holding light-emitting ends of the respective optical fibers as aligned in a horizontal row by releasing the bundled state of front end portions of the multiplicity of optical fibers introduced into the head unit body from a rear end thereof within the head unit body and sequentially juxtaposing the front end portions with each other in a same plane; and a pair of lenses fitted at a front end portion of the head unit body, the pair of lenses consisting of a first lens for turning a band of light emitted from the horizontal row of the light-emitting ends of the optical fibers into substantially parallel rays of light and a second lens for causing light outgoing from the first lens to converge into line light consisting of an elongated band of light.

[0021] In the above-described construction, the optical fiber aligning and holding member may be mounted at the head unit body so as to be position-adjustable in fore-and-aft directions, thereby adjusting the focusing position of line light. Thus, the lighting unit is capable of lighting in accordance with objects to be illuminated.

[0022] The lighting unit of the above-described construction may further comprises an optical member for providing a uniform luminance distribution in a direction in which the line light extends, the optical member being disposed at the front end portion of the head unit body so as to be associated with the pair of lenses.

[0023] In the above-described construction, the head unit body has opposite inner wall surfaces formed with respective plane mirrors extending to cover from opposite ends of the horizontal row of the light-emitting ends of the multiplicity of optical fiber and to opposite extremities of the pair of lenses. This feature allows the opposite inner surfaces to reflect light deviated in opposite directions in a same plane outwardly of the opposite ends of the row of the light-emitting ends, thereby compensating for a loss in light quantity at opposite ends of the line light.

[0024] There is also provided a light unit comprising a plurality of lighting units as recited above with respective head units arranged in a row for forming a continuous line light illumination pattern having a length corresponding to a total width of the head units.

[0025] According to yet another aspect of the present invention, there is provided a lighting unit for use in line inspection, comprising: a fiber cable in which a multiplicity of optical fibers extending from light-receiving ends thereof facing a light-emitting surface of an LED light source into a head unit body are bundled and accommodated; an optical fiber aligning and holding member holding light-emitting ends of the respective optical fibers as aligned in a horizontal row by releasing the bundled state of front end portions of the multiplicity of optical fibers introduced into the head unit body from a rear end thereof within the head unit body and sequentially juxtaposing the front end portions with each other in a same plane, the optical fiber aligning and holding member being position-adjustable in fore-and-aft directions within the head unit body; converging and illuminating means provided at a front end portion of the head unit body for causing a band of light emitted from the horizontal row of the light-emitting ends of the optical fibers to converge into a thinner band of light at a position forward of the head unit body; a lenticular screen for providing a uniform luminance distribution in a direction in which line light extends, the lenticular screen being disposed at the front end portion of the head unit body so as to be associated with the converging and illuminating means; and a pair of plane mirrors formed on opposite inner wall surfaces of the head unit body so as to extend to cover from opposite ends of the horizontal row of the light-emitting ends of the multiplicity of optical fibers to opposite extremities of the converging and illuminating means.

[0026] The foregoing and other objects, features and attendant advantages of the present invention will become apparent from the reading of the following detailed description in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is an overall perspective view of a lighting unit according to one embodiment of the present invention;

[0028] FIGS. <b>2</b>(A) and <b>2</b>(B) are a vertical sectional view and a rear view, respectively, of a first LED light source device in the same embodiment;

[0029]FIG. 3 is a partially cutaway front elevational view of a second LED light source device in the same embodiment;

[0030]FIG. 4 is a partially cutaway side elevational view of the second LED light source device in the same embodiment;

[0031]FIG. 5 is an overall view of a first head device in the same embodiment;

[0032]FIG. 6 is a vertical sectional view of a second head device in the same embodiment;

[0033]FIG. 7 is a bottom view of the second head device in the same embodiment;

[0034]FIG. 8 is a fragmentary sectional view of the second head device in the same embodiment;

[0035]FIG. 9 is an end view illustrating a tightly bundled state of optical fibers in the same embodiment;

[0036]FIG. 10 is a vertical sectional view of a head device in another embodiment of the present invention;

[0037]FIG. 11 is a bottom view of the head device in the same embodiment;

[0038]FIG. 12 is a vertical sectional view of a head device in yet another embodiment of the present invention;

[0039]FIG. 13 is a vertical sectional view of a head device for line inspection in still another embodiment of the present invention;

[0040]FIG. 14 is a cross sectional view of the head device in the same embodiment;

[0041]FIG. 15 is a bottom view of the head device in the same embodiment;

[0042]FIG. 16(A) is a partially sectional perspective view of a specific form of the head device for line inspection shown in FIGS. <b>13</b> to <b>15</b> and FIG. 16(<i>b</i>) is a perspective inverted view of a portion of interest of the head device;

[0043] FIGS. <b>17</b>(A) to <b>17</b>(D) show the structure of the head device for line inspection in more detail; specifically, FIGS. <b>17</b>(A), <b>17</b>(B) and <b>17</b>(C) are a plan view, a side view in section and a front end view, respectively, of a portion of interest of the head device and FIG. 17(D) is a schematic view illustrating an out-of-focus state assumed when a cylindrical lens is used; and

[0044]FIG. 18 is a vertical sectional view of a head device in still another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] The present invention will now be described in detail with reference to the accompanying drawings wherein like reference characters designate like or corresponding parts throughout several views.

[0046] Referring to FIG. 1, there is shown a lighting unit according to one embodiment of the present invention, which utilizes an XY stage <b>1</b> as a movable support member that is biaxially movable in a horizontal plane, i.e., horizontally movable along X-axis and Y-axis. The lighting unit includes a unit body <b>2</b> supported by the XY stage <b>1</b>, an electric power source <b>3</b> installed separately from the XY stage <b>1</b>, LED light source devices <b>5</b>A and <b>5</b>B to be supplied with electric power from the electric power source <b>3</b> through a robot cable <b>4</b>, heads <b>6</b>A and <b>6</b>B mounted on the unit body <b>2</b> and defining illuminating apertures <b>6</b>Aa and <b>6</b>Ba, respectively, for directing light to a work W as an object to be illuminated, optical fiber bundles <b>7</b>A and <b>7</b>B as light guides for guiding light from the LED light source devices <b>5</b>A and <b>5</b>B to the heads <b>6</b>A and <b>6</b>B, and an image pick-up device <b>8</b> for imaging the work W. The lighting unit is adapted to apply light outgoing from the illuminating apertures <b>6</b>Aa and <b>6</b>Ba onto the work W as an object to be inspected that has been conveyed to a predetermined position by a conveyor unit and inspect the outward appearance of the work W by means of the image pick-up device <b>8</b>.

[0047] Description will be made of each part of the lighting unit.

[0048] The XY stage <b>1</b> comprises, for example, an X stage <b>11</b> supported for horizontal sliding along the X-axis by a stationary member K placed on the conveyor unit or the floor for example, and a Y stage <b>12</b> supported by the X stage <b>11</b> for horizontal sliding along the Y-axis. Thus, the Y stage <b>12</b> can be freely positioned in a horizontal plane by moving biaxially in the horizontal plane. Each of the stages <b>11</b> and <b>12</b> is driven to position either under remote control or automatically with use of a non-illustrated driving mechanism such as a stepping motor for example.

[0049] The unit body <b>2</b> is fixed to the XY stage <b>1</b>, specifically to the Y stage <b>12</b> via a bracket B, and includes a cylindrical light path tube <b>21</b> standing vertically and accommodating therein non-illustrated optical components such as a half mirror and a lens. By driving the XY stage <b>1</b>, the unit body <b>2</b> can be moved so that the light path tube <b>21</b> becomes positioned just above the work W.

[0050] The image pick-up device <b>8</b> is, for example, a CCD camera and is fixed to an upper end portion of the light path tube <b>21</b> so that its image pick-up side is oriented downward.

[0051] The electric power source <b>3</b> is a DC power source for supplying power to the LED light source devices <b>5</b>A and <b>5</b>B and is disposed at a predetermined location remote from the XY stage <b>1</b>. The robot cable <b>4</b> extending from the electric power source <b>3</b> passes through a cable bearer <b>41</b> of a bellows configuration and reaches the LED light source devices <b>5</b>A and <b>5</b>B. In FIG. 1, the cable bearer <b>41</b> has one end attached to the X stage <b>11</b> and the other end attached to the Y stage <b>12</b> and functions to prevent the cable <b>4</b> from being twisted or entangled due to movement of the Y stage <b>12</b> relative to the X stage <b>11</b>. It is, of course, possible to provide another cable bearer between the stationary member K and the X stage <b>11</b>.

[0052] Two types of LED light source devices <b>5</b>A and <b>5</b>B, for example, are used in this embodiment. The LED light source device <b>5</b>A comprises a single power LED <b>52</b> accommodated in an enclosure <b>53</b>, while the LED light source device <b>5</b>B comprises a plurality of power LEDs <b>52</b>A for emitting light of different colors (three colors R, G and B) accommodated in an enclosure <b>53</b>A.

[0053] As shown in FIG. 2, one LED light source device <b>5</b>A includes the LED <b>52</b> mounted on a substrate <b>51</b>, a lens mechanism <b>54</b> for condensing light emitted from the LED <b>52</b>, and an optical output connector <b>55</b> for guiding light outgoing from a light-condensing portion <b>54</b><i>a </i>of the lens mechanism <b>54</b> to the optical fiber bundle <b>7</b>A. The LED <b>52</b> is a bare chip of a surface emitting type, and the substrate <b>51</b> supporting the LED <b>52</b> is connected to the electric cable <b>4</b> which extends from a side of the enclosure <b>53</b>. The lens mechanism <b>54</b> comprises a pair of first and second lenses arranged serially and intervenes between the LED <b>52</b> and the optical output connector <b>55</b>. The first lens positioned on the LED <b>52</b> side turns light emitted from the LED <b>52</b> into parallel rays of light and then the second lens condenses the parallel rays of light. In the subject embodiment, a conical lens <b>541</b> and a convex condenser lens <b>542</b> are arranged to face each other. The light-emitting surface of the LED <b>52</b> is embedded in a base end portion of the first lens <b>541</b>. A base end portion of the second lens <b>542</b> serves as the light-condensing portion <b>54</b><i>a </i>for causing light emitted from the LED <b>52</b> to converge.

[0054] As shown in FIGS. 3 and 4, the other LED light source device <b>5</b>B comprises three LEDs <b>52</b>A arranged in a row. Accordingly, the LED light source device <b>5</b>B includes three substrates <b>51</b> and three lens mechanisms <b>54</b> for respective LEDs <b>52</b>A. The LED light source device <b>5</b>B uses only a single optical output connector <b>55</b> having a shape identical with that used in the LED light source device <b>5</b>A. One end portion of an internal optical fiber bundle <b>56</b> in which end portions of respective optical fibers are tightly bundled is attached to the light-condensing portion <b>54</b><i>a </i>of each lens mechanism <b>54</b>. The other end portion of the internal optical fiber bundle <b>56</b> in which end portions of respective optical fibers are unitarily, randomly and tightly bundled is connected to the optical output connector <b>55</b>.

[0055] The optical fiber bundles <b>7</b>A and <b>7</b>B as flexible light guides sheathed with respective outer tubes extend from the LED light source devices <b>5</b>A and <b>5</b>B, respectively, and are exposed to the outside before connecting to respective heads <b>6</b>A and <b>6</b>B mounted on the unit body <b>2</b>. The optical fiber bundles <b>7</b>A and <b>7</b>B, which are each as very short as about <b>30</b> to about <b>40</b> cm, have respective rear ends each attached to an optical input connector <b>71</b> fitted in the optical output connector <b>71</b> and respective front ends attached to respective heads <b>6</b>A and <b>6</b>B. The optical input connector <b>71</b>, optical fiber bundle <b>7</b>A (<b>7</b>B) and head <b>6</b>A (<b>6</b>B) are combined to form a head device HA (HB) as shown in FIGS. 5 and 6. It is to be noted that FIG. 9 illustrates examples of the optical fiber bundle <b>7</b>A (<b>7</b>B) comprising tightly bundled optical fibers. In this figure, optical fibers forming bundle (a) are each smaller in diameter than those forming bundle (b).

[0056] The two heads <b>6</b>A and <b>6</b>B, which are mounted on the unit body <b>2</b> corresponding to the two LED light source devices <b>5</b>A and <b>5</b>B, are each very small in size, having an outer diameter of about 10 to about 30 mm.

[0057] As shown in FIGS. <b>6</b> to <b>8</b>, one head <b>6</b>A separates front end portions of optical fibers <b>7</b><i>a </i>forming the front end portion of the optical fiber bundle <b>7</b>A extending from the associated LED light source device <b>5</b>A from each other therewithin and holds the separated front end portions as annularly arranged with spacing from each other. Specifically, the head <b>6</b>A includes an annular head body <b>6</b>A<b>1</b> having fiber holding holes F<b>1</b> equispaced and arranged annularly, the fiber holding holes F<b>1</b> receiving therein respective front end portions of the optical fibers <b>7</b><i>a </i>to hold them, an annular lens presser plate <b>6</b>A<b>2</b> having ball lens holding holes <b>9</b><i>a </i>arranged at portions superposed on the fiber holding holes Fl to hold ball lenses <b>9</b>, and a cylindrical fixture <b>6</b>A<b>3</b> for attaching the head <b>6</b>A to the light path tube <b>21</b>. The head <b>6</b>A is so configured that the ball lenses <b>9</b> are brought into contact with or positioned close to respective front ends of the optical fibers <b>7</b>A at a time by coaxially fixing the lens presser plate <b>6</b>A<b>2</b> to the head body <b>6</b>A<b>1</b> with a screw. As shown in FIG. 1, the head <b>6</b>A is vertically slidably fitted in a lower end portion of the light path tube <b>22</b> by means of the fixture <b>6</b>A<b>3</b>. Apertures defined under the respective ball holding holes <b>9</b><i>a </i>serve as illuminating apertures <b>6</b>Aa for illuminating the work W positioned under the head <b>6</b>A from above and around. The front end of each optical fiber <b>7</b><i>a </i>is attached slightly outwardly from the top of the associated ball lens <b>9</b> so that the ball lenses <b>9</b> refracts light from the optical fibers <b>7</b><i>a </i>to strengthen the directionality thereof while deviating light inwardly to concentrate on a portion of the work W to be illuminated.

[0058] As shown in FIG. 5, the other head <b>6</b>B is of an elongated tubular shape for tightly bundling and holding front end portions of optical fibers forming the optical fiber bundle <b>7</b>B extending from the associated LED light source device <b>5</b>B. Light is emitted from front end faces of the tightly bundled optical fibers through a circular illuminating aperture <b>6</b>Ba defined at the front end of the head <b>6</b>B. As shown in FIG. 1, the head <b>6</b>B is attached to an upper end portion of the light path tube <b>21</b> with its illuminating aperture <b>6</b>Ba oriented in a direction perpendicular to the axis of the light path tube <b>21</b> so that light outgoing from the illuminating aperture <b>6</b><i>a </i>is reflected or refracted through the optical components, such as a half mirror, disposed within the light path tube <b>21</b>, advances downwardly along the axis of the light path tube <b>21</b> and is emitted from a lower open end of the light path tube <b>21</b> to illuminate the work W.

[0059] The lighting unit thus constructed operates as follows.

[0060] First, when the work W such as a printed circuit board is conveyed to a predetermined position by the conveyor unit, the image pick-up device <b>8</b> reads, for example, an alignment mark of the work W, causes a non-illustrated image recognition section to recognize the mark and calculates the positional information about the mark. In turn, the XY stage <b>1</b> is automatically controlled based on the positional information so that the light path tube <b>21</b> is positioned just above a portion of the work W to be illuminated. As a result, the portion of interest is illuminated from just above and from around with light emitted from the heads <b>6</b>A and <b>6</b>B and the image pick-up device <b>8</b> obtains the image of the portion of interest.

[0061] In reverse, the positional information about the work W may be obtained by controlling the position of the XY stage <b>1</b> instead of reading such an alignment mark or the like. Since the positional information thus obtained can be utilized in the subsequent or later procedure, the lighting unit according to this embodiment can be utilized as a work position determining device. The lighting unit can also be utilized in reading bar codes or the like. Since such a lighting unit allows the weights and sizes of the LED light source devices <b>5</b>A and <b>5</b>B to be reduced easily, the LED light source devices <b>5</b>A and <b>5</b>B, though mounted at the XY stage <b>1</b>, can hardly exert influence on the driving of the XY stage <b>1</b>, hence, of the heads <b>6</b>A and <b>6</b>B.

[0062] Since the electric cable <b>4</b> is far superior to an optical fiber in flexibility, durability, price and the like, the lighting unit according to the subject embodiment is capable of driving the XY stage <b>1</b> and the heads <b>6</b>A and <b>6</b>B with a very low burden on the electric cable as compared to the burden which has been conventionally imposed on an optical fiber when the optical fiber is moved with movements of the XY stage <b>1</b> and the heads <b>6</b>A and <b>6</b>B. Thus, the lighting unit exhibits superior durability and reliability.

[0063] Further, since the heads <b>6</b>A and <b>6</b>B are positioned at the respective front ends of the optical fiber bundles <b>7</b>A and <b>7</b>B, it is possible to make the sizes of the heads <b>6</b>A and <b>6</b>B very small as well as to condense light onto a small area. Furthermore, since the heads <b>6</b>A and <b>6</b>B are fixedly supported by the XY stage <b>1</b> to maintain the relative positional relation between the LED light source devices <b>5</b>A and <b>5</b>B and the heads <b>6</b>A and <b>6</b>B generally, the optical fiber bundles <b>7</b>A and <b>7</b>B will not deform. For this reason, destruction due to movement of the optical fiber bundles <b>7</b>A and <b>7</b>B can be avoided, which can eliminate the deleterious influence on the reliability, lifetime and the like of the lighting unit.

[0064] Moreover, since the subject embodiment has the feature that each of the optical fibers is attached to one lens at its front end on the head side, condensing of light can be improved substantially.

[0065] It is to be noted that the present invention is not limited to the embodiment described above and may be subject to various changes and modifications.

[0066]FIGS. 10 and 11 illustrate a head device H having a head <b>6</b> defining illuminating apertures <b>6</b><i>a </i>on a concave spherical surface. The illuminating apertures <b>6</b><i>a </i>are densely arranged on the concave spherical surface and each face a front end of each optical fiber <b>7</b><i>a </i>via a ball lens <b>9</b>. The head device H has plural (three) optical input connectors <b>71</b> and plural (three) optical fiber bundles <b>7</b> corresponding thereto. Unlike the former embodiment, optical fibers <b>7</b><i>a </i>forming respective optical fiber bundles <b>7</b> are connected correspondingly to lower, middle and upper sections, whereby the lighting unit can be used for color highlight illumination. As in the former embodiment, the head device H defines a through-hole vertically extending through a central portion thereof for inspecting a work W therethrough. The optical fiber bundles <b>7</b> may be gathered randomly in the head <b>6</b>.

[0067]FIG. 12 illustrates a head device H having plural heads <b>6</b> which are each capable of varying the spacing between a ball lens <b>9</b> and the front end of each optical fiber bundle <b>7</b> at which front ends of optical fibers are tightly bundled. These heads are each capable of varying the focal length and hence are suitable for spot lighting. Specifically, each head <b>6</b> is of a structure comprising two head elements <b>6</b><i>c </i>and <b>6</b><i>d </i>fitted with each other for making variable the spacing between the ball lens <b>9</b> and the front end of the corresponding optical fiber bundle <b>7</b> by varying the depth of the fitting between the head elements <b>6</b><i>c </i>and <b>6</b><i>d</i>. Unlike the former embodiment wherein the optical fibers are provided with the ball lenses in a one-to-one relationship, only the single ball lens is provided for each head <b>6</b>.

[0068] FIGS. <b>13</b> to <b>15</b> illustrate a head device H for use in line inspection wherein optical fibers are held with their respective front ends arranged in a single line or plural lines by a head <b>6</b>. While a lens array <b>9</b> comprising linear Fresnel lenses on two stages is used for condensing light in these drawings, a cylindrical lens may be used instead of the linear Fresnel lenses.

[0069]FIGS. 16 and 17 illustrate a specific form of the above-described head device H for use in line inspection. FIG. 16(A) is a perspective view of the head device H including plural (two in this embodiment) head units <b>60</b> juxtaposed on a substrate <b>100</b>, with the proximal head unit <b>60</b> in this view being drawn as cut vertically in half to show the internal structure thereof. FIG. 16(B) is an inverted perspective view showing a portion of interest of an optical fiber aligning and holding member. In these views, a fiber cable <b>7</b> in which a multiplicity of optical fibers <b>7</b><i>a </i>are bundled and accommodated extends from an optical input connector <b>71</b> serving as a light-receiving end disposed to face an light-emitting surface of a light output connector serving as an LED light source to a rear end of each head unit <b>60</b>. The front end portions of the multiplicity of optical fibers <b>7</b><i>a </i>are released from the bundled state within the body of the head unit <b>60</b> and are aligned and held so as to be sequentially juxtaposed with each other in a same plane by upper and lower pinch plates <b>80</b><i>a </i>and <b>80</b><i>b </i>of optical fiber aligning and holding member <b>80</b>.

[0070] The front end portions of the multiplicity of optical fibers <b>7</b><i>a </i>are in an irregularly projecting state at the time when they are held as juxtaposed with each other between the upper and lower pinch plates <b>80</b><i>a </i>and <b>80</b><i>b</i>. Then, the front end portions of the optical fibers <b>7</b><i>a </i>are made flush with the front end surfaces of the pinch plates <b>80</b><i>a </i>and <b>80</b><i>b</i>. Specifically, the front end portions of the optical fibers <b>7</b><i>a </i>irregularly projecting from the front end surfaces of the pinch plates <b>80</b><i>a </i>and <b>80</b><i>b </i>are first cut so as to be coplanar with the front end surfaces by a hot cutter or the like, and then the cut surfaces of the optical fibers <b>7</b><i>a </i>are smoothed and extended by grinding or by a heat treatment using a hot plate. Thus, adjacent cut surfaces of the optical fibers <b>7</b><i>a </i>become substantially completely in contact and continuous with each other at the front edge (see FIG. 16B) of a fiber holding slit <b>80</b><i>c </i>defined by the upper and lower pinch plates <b>80</b><i>a </i>and <b>80</b><i>b</i>, thereby forming a very thin unitary light-emitting surface.

[0071] The lower pinch plate <b>80</b><i>b </i>is formed with an adhesive groove <b>81</b> which fixes the aligned front end portions of the multiplicity of optical fibers <b>7</b><i>a </i>while holding the light-emitting ends as aligned in a horizontal row in the same plane with the front end surfaces of the upper and lower pinch plates <b>80</b><i>a </i>and <b>80</b><i>b</i>. A guide portion <b>82</b> of the aligning and holding member <b>80</b> fixed on top of the upper pinch plate <b>80</b><i>a </i>and protruding rearward is also held in the same plane with the front end surfaces of the upper and lower pinch plates <b>80</b><i>a </i>and <b>80</b><i>b</i>. A top surface of the guide portion <b>82</b> is formed with a tapped hole which allows the fore-and-aft position of the aligning and holding member <b>80</b> to be adjusted within the range corresponding to a slot <b>61</b> defined in the head unit <b>60</b> and permits the aligning and holding member <b>80</b> to be fixed by fastening means such as a screw <b>83</b>.

[0072] In a front end portion of the head unit <b>60</b> located forwardly of the fiber aligning and holding member <b>80</b>, there are disposed a first lens <b>9</b><i>a</i>, which consists of a line Fresnel lens for example, for turning a band of light outgoing from the aligned light-emitting ends of the optical fibers <b>7</b><i>a </i>into parallel rays of light, and a second lens <b>9</b><i>b</i>, which also consists of a line Fresnel lens, for causing light outgoing from the first lens <b>9</b><i>a </i>to converge into a very thin line light <b>90</b>, the first and second lenses <b>9</b><i>a </i>and <b>9</b><i>b </i>being spaced a predetermined distance therebetween. The head unit <b>60</b>, bodily, is fixed to a base plate <b>100</b> by means of a key <b>62</b>.

[0073] FIGS. <b>17</b>(A) to <b>17</b>(D) trigonometrically show the head device for line inspection for illustrating the structure thereof in more detail. It should be noted that the head unit <b>60</b> is shown with its top plate <b>60</b><i>a </i>omitted in the plan view at FIG. 17(A) and that like reference characters designate like functional parts throughout FIGS. <b>1</b> to <b>17</b>. In the example shown in FIGS. <b>17</b>(A) to <b>17</b>(D), an optical member <b>63</b> such as a lenticular screen is provided at a front end surface of the head unit <b>60</b> for making the luminance distribution uniform in a direction in which line light extends. The optical member <b>63</b> may be positioned either between or adjacent the aforementioned pair of lenses <b>9</b><i>a </i>and <b>9</b><i>b</i>. A dent portion <b>63</b>′ between the lenses <b>9</b><i>a </i>and <b>9</b><i>b </i>in FIG. 17(B) is a recess for receiving the optical member <b>63</b>.

[0074] Referring particularly to FIGS. <b>17</b>(A) and <b>17</b>(C), the opposite inner wall surfaces of the head unit <b>60</b>, which extend to cover from the opposite ends of the horizontal row of light-emitting ends of optical fibers <b>7</b><i>a </i>to the opposite extremities of the pair of lenses <b>9</b><i>a </i>and <b>9</b><i>b </i>are each formed with a plane mirror <b>64</b> by chrome plating for example. With this feature, a loss in light quantity at the opposite ends of line light, which would otherwise result due to diffuse reflection of light diffused from the light-emitting ends of the optical fibers <b>7</b><i>a </i>and becoming incident on the opposite inner wall surfaces, can be compensated for by the plane mirrors <b>64</b> regularly reflecting light inwardly.

[0075] As described above, the lighting unit emitting uniform line light for line inspection shown specifically in FIGS. 16 and 17 employs the pair of lenses <b>9</b><i>a </i>and <b>9</b><i>b </i>each consisting of a line Fresnel lens or an optical component equivalent thereto. For this reason, the lighting unit is capable of providing a precise focal line forwardly of the lighting head <b>60</b> without producing an out-of-focus state essential to a cylindrical lens (cylindrical abberation similar to spherical abberation) shown as a very small range Ra in FIG. 17(D) for example. Accordingly, the lighting unit is capable of providing uniform line light having an appropriate width when an illuminated surface of an object of interest is positioned appropriately before or behind the focal line.

[0076] For example, when the light-emitting ends of the optical fibers <b>7</b><i>a </i>are positioned at point P<b>1</b> spaced apart from the pair of lenses <b>9</b><i>a </i>and <b>9</b><i>b </i>in FIG. 17(B), the resulting focal line is positioned at point F<b>1</b> relatively close to the front end of the lighting head <b>60</b>. In contrast, when the light-emitting ends of the optical fibers <b>7</b><i>a </i>are positioned at point P<b>2</b> closer to the pair of lenses <b>9</b><i>a </i>and <b>9</b><i>b </i>in FIG. 17(B), the resulting focal line is positioned at point F<b>2</b> relatively apart from the front end of the lighting head <b>60</b>, thereby providing thinner line light. In this way the focal length of the lighting unit can be adjusted as desired in inspection.

[0077] As shown in FIG. 17, the opposite sidewalls of the head unit <b>60</b> are each very thin as compared with the width of the horizontal row of optical fibers <b>7</b><i>a </i>and, hence, the length of line light at a required illuminating position is equal to or slightly larger than the width of the head unit. By arranging a plurality of such head units in a row, it is possible to form a uniform line light illumination pattern having a length corresponding to the total width of these head units.

[0078] The uniform line light illumination thus realized is capable of showing a surface illuminated with continuous and elongated line light having a relatively high luminance. For this reason, even when very minute roughness exists in the illuminated surface, such roughness is shown as a variation in the reflection of illuminating light, thus making precise optical observation possible. Particularly, the drawback of the prior art that a variation in luminance occurs for each optical fiber to cause discontinuity of brightness to result can be overcome by making the luminance distribution uniform with use of the lenticular screen. The use of the line Fresnel lens for condensing light prevents light from diffusing unnecessarily for the line sensor and hence makes it possible to reduce the power consumption. For this reason, the line light-emitting lighting unit can be preferably used in lighting for inspection of printed circuit boards and pin grid arrays in particular.

[0079]FIG. 18 shows a head device H of a ring type similar to the foregoing embodiment. The head device H has a thin head <b>6</b> and hence is suitable for use in applications where the distance between a work W and the illuminating aperture <b>6</b><i>a </i>is short, such as a microscope.

[0080] Of course, variations of other components than the head are conceivable. Since the length and weight of the optical fibers can be reduced if the LED light source devices are disposed adjacent the respective illuminating apertures, the heads can be driven smoothly even when they are movably supported on the XY stage. In this case, it is preferred that the heads be made movable slightly or slowly relative to the XY stage unless a problem arises in relation to the reliability, lifetime and the like of the optical fibers.

[0081] The lighting unit of the present invention can be constructed using a single optical fiber instead of using an optical fiber bundle. It is also possible that a battery is incorporated in or incident to each LED light source device as an electric power source. By so doing, the lighting unit can be rendered cableless. Alternatively, such an arrangement is possible that the LED light source devices are supplied with electric power from any other mechanism forming part of the lighting unit of the present invention than the electric power source such as the image pick-up device or the driving mechanism associated with the XY stage.

[0082] The movable support member is not limited to the XY stage and may be any one of various movable support members including one capable of three-dimensional positioning.

[0083] If full-color lighting is performed using LEDs emitting light of plural colors (three colors), it is preferable that optical fibers for emitting lights of respective colors are arranged homogeneously on the head <b>6</b>A, <b>6</b>B side.

[0084] As has been described in detail, the present invention makes it possible to reduce the weight and size of the LED light source device easily and, therefore, the LED light source device thus reduced in weight and size, though mounted at the movable support member, can hardly exert influence on the driving of the movable support member, hence, of the head.

[0085] If the head is fixedly supported by the movable support to maintain the relative positional relation between the LED light source device and the head, it is possible to reduce the burden to be imposed on the optical fiber, thereby to eliminate the influence of such a burden on the reliability, lifetime and the like of the optical fiber. Of course, the head may be mounted at the movable support member so as to be slightly movable or slowly movable unless such movement affects the reliability, lifetime and the like of the optical fiber.

[0086] Since the head is connected to the optical fiber and is separate from the LED light source device, it is possible to make the size of the head very small as well as to condense light onto a small area. Further, since the light source can be spaced apart to a certain extent from the object to be illuminated or from the image pick-up device for imaging the object, it is also possible to prevent the object or the image pick-up device from being affected by heat generated from the light source.

[0087] The LED light source device may be supplied with electric power either from a battery provided in or incident to the lighting unit or from an electric power source disposed separately from the movable support member through an electric cable. With the former arrangement, the lighting unit can be rendered cableless. Alternatively, though the latter arrangement requires an electric cable, the electric cable is far superior to an optical fiber in flexibility, durability, price and the like. The latter arrangement is capable of highly reliably driving the movable support member and the head with a very light burden on the electric cable as compared to the burden that has been conventionally imposed on an optical fiber when the optical fiber is moved with the movement of the head. An arrangement for supplying electric power from the image pick-up device may also be conceived.

[0088] In the present invention, the light source device may be disposed adjacent the illuminating aperture to shorten the optical fiber (to 1 m or less for example), thereby reducing the weight of the optical fiber. With this feature, the head can be driven smoothly even if it is movably mounted at the movable support member. In this case, it is preferred that the head be mounted at the movable support member so as to be slightly movable or slowly movable relative to the movable support member unless such movement affects the reliability, lifetime and the like of the optical fiber.

[0089] While only certain presently preferred embodiments of the present invention have been described in detail, as will be apparent for those skilled in the art, certain changes and modifications may be made in embodiments without departing from the spirit and scope of the present invention as defined by the following claims.