CROSS REFERENCE

This application is the U.S. National Phase under 35 US.C. § 371 of International Application No. PCT/JP2018/041491, filed on Nov. 8, 2018, which claims the benefit of Japanese Application No. 2018-018125, filed on Feb. 5, 2018, the entire contents of each are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to an image acquisition technique for obtaining an image of an object (hereinafter, referred to as a “workpiece”) for each light source in a state where the object is successively irradiated with light from N (N is a natural number equal to or greater than 2) light sources having mutually different irradiation directions and an inspection technique for inspecting a workpiece based on a plurality of images obtained by the image acquisition technique. Note that an “image of an object for each light source” means an image obtained by imaging the object in a state where the object is irradiated only with the light from each light source, and N object images are obtained in a device having N light sources.

The disclosure of Japanese Patent Application No. 2018-018125 filed on Feb. 5, 2018 including specification, drawings and claims is incorporated herein by reference in its entirety.

BACKGROUND ART

A device is known which inspects a workpiece based on a plurality of images obtained by imaging the three-dimensional workpiece such as a metal component, a resin component or a rubber component from various angles. For example, a plurality of light source units for respectively irradiating light to a workpiece held on a stage from a plurality of directions are provided in an inspection apparatus of patent literature 1. After the workpiece is positioned by rotating the stage by a predetermined angle, light is irradiated to illuminate the workpiece in a stationary state from the light source units and images of the workpiece are obtained by an imager. The workpiece is inspected based on a plurality of images obtained in this way.

CITATION LIST

Patent Literature

[Patent literature 1] JP 2016-57075A

SUMMARY OF INVENTION

Technical Problem

In the above conventional technique, each light source is switchingly turned on and off every time the workpiece is moved, illumination is changed by successively irradiating light to the workpiece in the stationary state from each of the plurality of light sources, and the image is obtained for each light source. By alternately performing a movement of the workpiece and an illumination change by switching the light sources in this way, images necessary for inspection are obtained. Thus, there is a limit to the shortening of a time required for image acquisition and the shortening of this time is desired. Further, such a request is not limited to workpiece inspection apparatus and a similar request is made, for example, for devices using a photometric stereo method. That is, in the photometric stereo method, an image of a workpiece is obtained for each light source in a state where light is successively irradiated to the workpiece from three or more light sources having mutually different irradiation directions and those captured images are combined. Thus, it is important in enhancing the operation efficiency of the device to obtain the image of the workpiece for each light source in a short time.

This invention was developed in view of the above problem and aims to shorten a time required to obtain an image of an object for each light source in a state where light is successively irradiated to the object from N (N is a natural number equal to or greater than 2) light sources having mutually different irradiation directions.

Solution to Problem

A first aspect of the invention is an image acquisition device that obtains images of an object for each light source in a state where the object is successively irradiated with light from N (N is an natural number equal to or greater than 2) light sources having mutually different irradiation directions. The device comprises: a mover that moves the object in a first direction; an imager having a strip-like imaging area extending in a second direction orthogonal to the first direction, the imager obtaining a partial image of the object by imaging a partial area of the object passing through the imaging area; a light source switch controller that successively switches the light to be irradiated to the object every time the object is moved in the first direction by a unit distance obtained by dividing a size of the imaging area in the first direction by the number N of the light sources; a storage that stories the partial images obtained by the imager every time the light is switched; and an object image acquisitor that obtains N images of the object by deleting a part of a composite image obtained by combining a plurality of the partial images stored in the storage for each light source according to a switching order of the light sources.

A second aspect of the invention is an image acquisition method that obtains images of an object for each light source in a state where the object is successively irradiated with light from N (N is an natural number equal to or greater than 2) light sources having mutually different irradiation directions while the object is moved in a first direction, the method comprises: preparing an imager having a strip-like imaging area extending in a second direction orthogonal to the first direction, the imager obtaining a partial image of the object by imaging a partial area of the object passing through the imaging area; successively switching the light to be irradiated to the object every time the object is moved in the first direction by a unit distance obtained by dividing a size of the imaging area in the first direction by the number N of the light sources and storing an image obtained by imaging the partial area by the imager as the partial image every time the light is switched; and forming a composite image by combining a plurality of the partial images stored in the storage for each light source and obtaining N images of the object by deleting parts of the composite images according to a switching order of the light sources.

A third aspect of the invention is an inspection apparatus that comprises: the image acquisition device; and an inspector for inspecting the object based on the N images of the object obtained by the image acquisition device.

In the invention thus configured, a movement of the object and the light source switch are performed in parallel and a plurality of partial images are obtained. An image of the object is obtained by deleting a part according to the switching order of the light sources from a composite image obtained by combining the plurality of partial images for each light source. As a result, as many images of the object illuminated only by one of the N light sources as the N light sources, i.e. N images of the object, are obtained. [Effect]

As described above, since the image of the object for each light source is obtained by performing the movement of the object and the light source switch in parallel, a time required for image acquisition for each light source can be shortened.

All of a plurality of constituent elements of each aspect of the invention described above are not essential and some of the plurality of constituent elements can be changed, deleted or replaced by new other constituent elements or limitation contents can be partially deleted as appropriate to solve some or all of the problems described above or achieve some or all of effects described in this specification. Further, some or all of technical features included in one aspect of the invention described above can be combined with some or all of technical features included in another aspect of the invention described above into one independent aspect of the invention to solve some or all of the problems described above or achieve some or all of effects described in this specification.

