Light irradiation device and light irradiation method

Abstract

The present invention comprises a plurality of light source bodies (2) that are aligned in a prescribed direction and a lens (3) that has no curvature in the prescribed direction, has curvature in a plane that is orthogonal to the prescribed direction, and focuses light of components that are emitted from the light source bodies (2) and advance along the orthogonal plane. An optical constant of the lens (3) as seen from the prescribed direction is defined such that the area of an aberration curve is greater on the positive side than on the negative side on a longitudinal aberration diagram for which the origin is the intersection of the optical axis (C) of the lens (3) and the surface of a workpiece, the horizontal axis is the optical axis (C), the direction in which light advances being the positive side, and the vertical axis is a normalized pupil coordinate.

Description

Light irradiation device and light irradiation method

[0001] The present invention relates to a light emitting device used in a surface inspection device, an exposure device, etc., and more particularly to a light emitting device that irradiates a workpiece with linear or band-like light, also known as line light.

[0002] As an example of this type of light irradiation device, as shown in Patent Document 1, a so-called line light irradiation type is known, in which light is emitted from multiple LEDs arranged in series through a rod lens and a line or band of light is irradiated onto the workpiece.

[0003] Conventionally, when using such a light irradiation device, it is recommended that the workpiece be placed in a position where the light emitted from the LED is most concentrated when viewed from the serial direction of the LED (hereinafter also referred to as the Z direction).

[0004] Conversely, if the separation distance between the light irradiation device and the workpiece, i.e., the recommended installation distance, is determined in advance, the optical constants (curvature, etc.) of the lens are determined so that the LED light is most concentrated at the position at that distance.

[0005] Therefore, if the workpiece is placed at this recommended installation distance, the irradiance on the workpiece will be at its highest, so in the field of surface inspection, for example, it will be possible to increase the camera shutter speed when photographing the workpiece, or to increase the speed at which the workpiece is being transported without stopping, thereby shortening the inspection lead time.

[0006] However, after extensive research, the inventor discovered for the first time that the irradiance of a line light irradiation device is highest not at the recommended installation distance as previously thought, and thus completed the present invention.

[0007] Japanese Patent Application Laid-Open No. 2017-150875

[0008] The present invention has been made by overturning the conventional common technical knowledge in the field of line light irradiation type light irradiation devices, and is intended to fully utilize the performance of the light irradiation device.

[0009] That is, the light irradiation device according to the present invention is as follows.

[0010] [1] A light irradiation device that irradiates a workpiece with linear or band-like light extending along a predetermined direction, comprising: a plurality of light source bodies lined up along the predetermined direction; and a lens that has no curvature in the predetermined direction but has curvature in a plane perpendicular to the predetermined direction, and that collects light components emitted from the light source bodies and traveling along the perpendicular plane; wherein, when viewed from the predetermined direction, a longitudinal aberration diagram, in which the origin is the intersection of the optical axis of the lens and the surface of the workpiece, the horizontal axis is the optical axis with the direction in which light travels on the positive side, and the vertical axis is normalized pupil coordinates, has a first requirement that the area on the positive side of the aberration curve represented by the longitudinal aberration diagram is larger than the area on the negative side, and the optical constants of the lens are determined so that this first requirement is satisfied.

[0011] Such a lens can maximize the irradiance on the workpiece surface. Furthermore, since it is possible to eliminate any deviations from the first requirement, optical design becomes easier. The optical constants of the lens include at least one of the lens curvature, refractive index, thickness, number of lenses, installation position, front and rear surfaces, aspherical coefficient, and conic constant.

[0012] [2] The light irradiation device according to [1], wherein the second requirement is that the sum of the slopes at points spaced apart by a small distance in the aberration curve is positive, and the optical constants of the lens are determined so that this second requirement is further satisfied.

[0013] With this configuration, the distance at which the irradiance is at its maximum, i.e., the degree of decrease in irradiance before and after the recommended installation distance, can be set to be approximately symmetrical. Therefore, even if the separation distance between the workpiece and the light irradiation device shifts either before or after the recommended installation distance due to placement errors, etc., a sudden decrease in irradiance can be prevented.

[0014] [3] The light irradiation device according to either [1] or [2], characterized in that the optical constants of the lens are set so that the focusing position of the light from the LED changes continuously or stepwise along the optical axis of the lens as it moves from the center of the lens toward the outer edge.

[0015] This configuration reduces the degree of change in irradiance due to changes in the separation distance between the workpiece and the light irradiation device, ensuring a range of usable separation distances while maintaining a constant irradiance around the recommended separation distance. Furthermore, when the recommended separation distance is configured to be switchable while maintaining a constant irradiance, it becomes possible to reduce the number of switching steps.

[0016] In other words, the required irradiance on the workpiece can be secured while simplifying the configuration. The condensing position is the position where the beam diameter is smallest, and the beam diameter is a certain ratio (for example, 1 / e) of the maximum irradiance in a cross section perpendicular to the optical axis. ２ ) or more.

[0017] [4] The light irradiation device according to [3], further comprising a distance variable structure that enables the distance between the lens and the LED to be changed in stages.

[0018] With this arrangement, the recommended separation distance can be switched with a simple structure.

[0019] [5] The light irradiation device according to [3] or [4], characterized in that the optical constants of the lens are set so that the more light passes through the center of the lens, the closer its focusing position is to the lens.

[0020] This type of configuration can be achieved, for example, by setting the curvature of the center of the lens to be greater than that of the outer regions. As a result, the edge thickness can be set thicker and the center thickness thinner, making the lens easier to manufacture. Specifically, the thickness deviation ratio (center thickness / edge thickness) is reduced, improving injection moldability and enabling a smaller volume, thereby reducing manufacturing costs.

[0021] [6] The light irradiation device according to any one of [3] to [5], wherein the lens is divided into a plurality of zones between the center and the outer edge, and the curvature of each zone is made different.

[0022] Such a lens can realize performance and size that cannot be achieved with a continuously smooth lens surface, thereby increasing the degree of freedom in design. Here, the curvature in each zone refers to, for example, the curvature at the center of each zone.

[0023] [7] The light irradiation device according to [6], wherein the curvature of the lens surface onto which the light beam most nearly parallel to the optical axis of the lens is incident is made different for each of the zones.

[0024] With this configuration, even if a step occurs at the boundary between adjacent zones, it is possible to minimize the loss of light intensity and the generation of stray light due to the step. Also, the visual angle (collimation half angle) of the light source as seen from a point on the lens surface defining each zone can be set as small as possible, which eliminates the need to take care of obliquely incident light, makes it less susceptible to manufacturing variations, and allows multiple focusing positions to be set more accurately in the lens optical axis direction.

[0025] The present invention may also be a light irradiation method using a light irradiation device that includes a plurality of light source bodies lined up along a predetermined direction, and a lens that has no curvature in the predetermined direction but has curvature in a plane perpendicular to the predetermined direction, and that condenses light components emitted from the light source bodies and traveling along the perpendicular plane, and that irradiates a workpiece with linear or band-like light extending along the predetermined direction, wherein the recommended installation distance of the workpiece is determined so that, when viewed from the predetermined direction, the area on the positive side of an aberration curve shown in a longitudinal aberration diagram is larger than the area on the negative side, the origin of which is the intersection of the optical axis of the lens and the surface of the workpiece, the horizontal axis is the optical axis with the direction in which light travels being the positive side, and the vertical axis is normalized pupil coordinates.

[0026] According to the present invention configured in this way, the irradiance can be set to be the highest on the work surface.

[0027] FIG. 1 is a perspective view showing an entire light irradiation device according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing light traveling in a first XY plane including one LED in the embodiment. FIG. 3 is a schematic diagram showing a conventional recommended installation distance. FIG. 4 is a view from the Y direction for qualitatively explaining the focusing position of each LED in the first XY plane. FIG. 5 is a graph showing the irradiance by one LED, the irradiance by other LEDs, and their combined irradiance at each separation distance, as well as qualitatively showing the conventional recommended installation distance. FIG. 6 is a longitudinal aberration diagram showing an aberration curve in the embodiment. FIG. 7 is a qualitative graph showing the irradiance by one LED, the irradiance by other LEDs, and their combined irradiance at each separation distance, as well as showing the recommended installation distance in the embodiment. FIG. 8 is a schematic diagram showing the curvature of a lens in the embodiment. FIG. 9 is a schematic diagram showing the focusing position of light that has passed through each zone of the lens in the embodiment. FIG. 10 is a graph showing a plurality of switchable recommended installation distances, as well as qualitatively showing the change in irradiance depending on the installation distance of the workpiece, the maximum irradiance curve, and the minimum guaranteed irradiance curve in the embodiment. FIG. 11 is a schematic diagram showing the configuration of a lens in another embodiment of the present invention. 10 is a graph showing multiple switchable recommended installation distances when a lens with no zone division and small aberrations is used, and also qualitatively showing the change in irradiance with the installation distance of the workpiece, the maximum irradiance curve, and the minimum guaranteed irradiance curve.

[0028] An embodiment of the present invention will be described below with reference to the drawings.

[0029] The light irradiation device 100 according to this embodiment is a line light irradiation type that irradiates a workpiece with light in a straight line or a straight band (hereinafter also referred to as line light), and is also called a line lighting device or a bar lighting device.

[0030] As shown in Figures 1 and 2, this light irradiation device 100 comprises a substrate 1, an LED 2 serving as a light source, a lens 3, a distance-variable structure 5 that can change the distance between the lens 3 and the LED 2 in stages, and a housing 4 that houses these.

[0031] Each part will be explained.

[0032] The substrate 1 is in the form of a linear strip and is a wiring board made of metal or resin.

[0033] The LEDs 2 are, for example, surface-mounted LEDs, and a plurality of LEDs 2 are mounted so as to be aligned linearly at regular intervals along the longitudinal direction of the substrate 1. Although these LEDs 2 are aligned in a single row here, they may be aligned in multiple rows, or may be aligned at irregular intervals rather than at regular intervals.

[0034] As shown in Figures 1 and 2, the lens 3 is a cylindrical type that has no curvature in a cross section cut along its extension direction but has curvature in a cross section perpendicular to the extension direction, and is arranged on the LED mounting surface side of the substrate 1 so that its extension direction coincides with the longitudinal direction of the substrate 1 and the lens optical axis C passes through the LED 2 when viewed from the longitudinal direction.

[0035] Although a double lens is shown in the figure, it may be a single lens or a triple lens or more. It may also be a lens in which both surfaces in the perpendicular cross section have curvature. It may also be a spherical or aspherical lens.

[0036] In the following, for convenience of explanation, the longitudinal direction of the substrate 1 or the extension direction of the lens 3 that coincides with the longitudinal direction of the substrate 1 will be referred to as the Z direction, the direction of the optical axis of the lens when viewed from the Z direction will be referred to as the X direction, and the direction perpendicular to the X and Z directions will be referred to as the Y direction. Also, Fig. 2 shows light traveling on a plane that includes any one LED 2 and is perpendicular to the Z direction (hereinafter also referred to as the first XY plane).

[0037] As shown in Fig. 2, the variable distance structure 5 is composed of, for example, a plurality of grooves extending in the Z direction (longitudinal direction) provided on both side walls of the housing 5. By fitting the lens 3 into one of these grooves, the distance between the LED 2 and the lens 3 can be switched in a plurality of stages. Note that, in this example, the position of the first lens 31 in the X direction is configured to be variable, but the position of the second lens 32 may also be variable, or both positions may be variable. Furthermore, the position of the substrate 1 may also be variable.

[0038] The housing 4 has a rectangular prism or rectangular parallelepiped shape and holds the substrate 1 and the lens 3 in the above-mentioned relative positional relationship. An opening 41 is provided on the surface of the housing 4 facing the lens 3, and the line light is emitted from this opening 41.

[0039] In the light irradiation device 100 configured as described above, a recommended installation distance is determined, which indicates the position at which the workpiece should be placed relative to the light irradiation device 100 or the position at which the light irradiation device 100 should be placed relative to the workpiece.

[0040] First, the conventional recommended installation distance will be explained.

[0041] Conventionally, as shown in Figure 3, focusing on light traveling on the first XY plane, in other words, light emitted from one LED (here referred to as the first LED) that does not include a Z-direction component, the recommended installation distance is the distance to the focusing position, where the beam diameter of this light is smallest. The relative positional relationship between the workpiece and the light irradiation device is then set to achieve this recommended installation distance, or the optical constants of the lens are set so that the light is focused at a predetermined recommended installation distance. Note that, for ease of understanding, the figure shows light rays without aberration.

[0042] However, in reality, since the LEDs also emit light containing a Z-direction component, light from other LEDs also enters this first XY plane. For example, as shown in Figure 4, the light collection positions in the first XY plane of the LEDs on both sides of the first LED (the second LED and the third LED) are closer to the light irradiation device than the recommended installation distance.

[0043] FIG. 5 is a graph showing the irradiance for each separation distance between the light irradiation device and the work surface in the first XY plane, taking into account other LEDs.

[0044] Conventionally, the recommended installation distance was determined by focusing only on the first LED and estimating its irradiance at its maximum. However, as can be seen from the figure, the distance at which the combined irradiance, including the light from the other LEDs, is maximum is shorter than the recommended installation distance and is closer to the light irradiation device.

[0045] In this way, the inventors of the present invention have found for the first time that in a line light irradiation type light irradiation device, the position at which the combined irradiance is maximized is closer to the light irradiation device than the conventional recommended installation distance. Based on this finding, and taking into consideration the fact that there is actually aberration as shown in FIG. 2, the light irradiation device 100 of this embodiment is configured.

[0046] Specifically, it is as follows:

[0047] 6, consider a longitudinal aberration diagram in which the origin is the intersection of the lens optical axis C and the workpiece surface on the first XY plane, the horizontal axis is the lens optical axis C (where the light travels in the positive direction), and the vertical axis is the normalized pupil coordinate on the first XY plane. In this longitudinal aberration diagram, the first requirement is that the area on the positive side of the aberration curve of light emitted from one LED 2 on the first XY plane be larger than the area on the negative side, and the optical constants of the lens 3 (here, at least the curvature is included, but the optical constants excluding the curvature may also be used) or the recommended installation distance are determined so as to satisfy this first requirement.

[0048] The "pupil" here refers to the image of the aperture (opening 41 in FIG. 2) that defines the diameter of the light emitted when viewed from the workpiece side.

[0049] The "area on the positive side" of the aberration curve here refers to the area of ​​the region surrounded by the vertical axis passing through the origin and the aberration curve on the positive side of this vertical axis in the longitudinal aberration diagram, which corresponds to the area of ​​"A+" in Fig. 6. The "area on the negative side" refers to the area of ​​the region surrounded by the vertical axis passing through the origin and the aberration curve on the negative side of this vertical axis, which corresponds to the area of ​​"A-" in the same figure.

[0050] In the case of (a) of the same figure, there is no aberration curve on the minus side, that is, there is no "A-" region, and its area is 0, so this first requirement is met. In the case of (b) of the same figure, the area of ​​"A+" is larger than that of "A-", so this first requirement is also met.

[0051] By determining the recommended installation distance so as to satisfy at least the first requirement, the composite irradiance on the work surface can be maximized.

[0052] On the other hand, as shown in Figure 5, the inventors have found for the first time that in the conventional configuration, the (composite) irradiance on the work surface drops sharply in the direction away from the light irradiation device, with the irradiance maximum distance as the center.

[0053] Therefore, in this embodiment, the second requirement is that the sum of the slope values ​​at each point spaced apart by an infinitesimal distance on the aberration curve be positive, and the optical constants of the lens (which here include at least the curvature, but may also be optical constants excluding the curvature) are determined so as to satisfy this second requirement.

[0054] For example, in Figure 6(a), the slope is positive throughout the entire aberration curve, so the second requirement is met. Also, in Figure 6(b), although some of the aberration curves have negative slopes, the slopes are positive at other points, and it is clear that the sum of these slopes is positive, so the second requirement is met.

[0055] 7, the degree of decrease in irradiance can be made almost symmetrical around the maximum irradiance distance, preventing a sudden decrease in irradiance either before or after the maximum irradiance distance. As a result, it is possible to prevent an unexpected decrease in irradiance due to, for example, a positioning error of the workpiece or the light irradiation device 100.

[0056] Furthermore, in this embodiment, as shown in FIG. 8, the lens 3 is divided into a plurality of zones Z1 to Z3 from the center to the outer edge, and the optical constants (here, curvatures) of the lens 3 are made different in each of the zones Z1 to Z3, and as shown in FIG. 9, the focusing positions F1 to F3 of the light that has passed through each of the zones Z1 to Z3 are configured to change in stages along the lens optical axis C.

[0057] Here, the zones closer to the center are set to have a larger curvature, and the light that passes through the zones closer to the center is focused closer to the lens 3. For ease of explanation, the diagram shows the lens 3 as a series of lenses.

[0058] In addition, in this lens 3, the curvature is made different in each zone on the lens surface 3a (hereinafter, to distinguish it from other lens surfaces, it will also be referred to as the variable curvature lens surface 3a) on which the light beam that is most parallel to the lens optical axis C is incident. In Figures 2 and 9, the variable curvature lens surface 3a is the surface closest to the workpiece. Note that in a multi-lens system having, for example, a concave lens, the variable curvature lens surface is not necessarily the surface closest to the workpiece.

[0059] In this configuration, even if the separation distance between the workpiece and the light irradiation device 100 is arbitrarily changed, by setting one of several recommended separation distances, the minimum guaranteed irradiance at any separation distance can be ensured. As shown in FIG. 10, the degree of decrease in irradiance before and after the recommended installation distance is small, and the peak angle of irradiance shown by the solid line is larger than when a lens with no zone division and small aberrations is used, as shown in FIG. 12. Therefore, the number of recommended separation distance switching steps can be reduced. In FIG. 10, for example, the recommended separation distance can be reduced to three steps. Note that in the same figure, the minimum guaranteed irradiance is set to a certain percentage (e.g., 70%) of the maximum irradiance.

[0060] Therefore, the number of steps for switching the recommended separation distance can be reduced, simplifying the configuration, while ensuring the required irradiance on the workpiece over a wide range of distances from the light irradiation device.

[0061] The present invention is not limited to the above-described embodiment.

[0062] For example, either the first requirement or the second requirement may be satisfied.

[0063] In the above embodiment, the lens has multiple zones and the curvature of each zone is changed in stages, but other optical constants related to the lens, such as the refractive index of each zone, may be changed to make the focusing position different.

[0064] As shown in FIG. 11, the surface of the lens 3 in each of the zones Z1 to Z3 may be discontinuous like a Fresnel lens.

[0065] The curvature of the lens may be varied continuously.

[0066] In order to change the recommended separation distance in multiple stages, multiple lenses with different curvatures may be prepared and configured to be interchangeable.

[0067] The recommended separation distance may be configured to be continuously variable.

[0068] The light source is not limited to an LED, but may be another light source such as a semiconductor laser.

[0069] Furthermore, the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0070] According to the present invention, in a line light irradiation type light emitting device, it is possible to maximize the irradiance on the work surface.

[0071] 100: Light irradiation device 2: LED (light source body) 3: Lens A+: Area on the plus side A-: Area on the minus side

Claims

1. A light irradiation device which irradiates a workpiece with linear or band-like light extending along a predetermined direction, comprising: a plurality of light source bodies lined up along the predetermined direction; and a lens which has no curvature in the predetermined direction but has curvature in a plane perpendicular to the predetermined direction, and which focuses light components emitted from the light source bodies and traveling along the perpendicular plane, wherein the first requirement is that when viewed from the predetermined direction, the area on the positive side of an aberration curve represented in a longitudinal aberration diagram, with the origin at the intersection of the optical axis of the lens and the surface of the workpiece, the optical axis on the horizontal axis with the direction in which the light travels on the positive side, and the vertical axis on the normalized pupil coordinate, is larger than the area on the negative side, and the optical constants of the lens are determined so that this first requirement is satisfied.

2. A light irradiation device as described in claim 1, wherein the second requirement is that the sum of the slopes of the aberration curve at each point spaced apart by an infinitesimal distance is positive, and the optical constants of the lens are determined so that this second requirement is further satisfied.

3. A light irradiation method using a light irradiation device that includes a plurality of light source bodies aligned along a predetermined direction, and a lens that has no curvature in the predetermined direction but has curvature in a plane perpendicular to the predetermined direction, and that condenses light components emitted from the light source bodies and traveling along the perpendicular plane, and that irradiates a workpiece with linear or band-like light extending along the predetermined direction, wherein a first requirement is that, when viewed from the predetermined direction, the area on the positive side of an aberration curve represented in a longitudinal aberration diagram, in which the origin is the intersection of the optical axis of the lens and the surface of the workpiece, the horizontal axis is the optical axis with the direction in which the light travels on the positive side, and the vertical axis is normalized pupil coordinates, is larger than the area on the negative side, and a recommended installation distance from the workpiece is determined so that this first requirement is satisfied.

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