ACCURATE REPRODUCTION OF LARGE AND SMALL COMPONENTS

Abstract: When mounting electronic components (3, 3') by means of automatic machines, an accurate measurement of the components for positioning thereof on printed circuit boards is required. In such a measurement, an image of a surface of the components, on or at which there are electronic connection terminals, can be captured when the components are in a predetermined position. In order to make it possible to reproduce components having different sizes an image capture device of type colour video camera having a lens system (5) is used. Light rays from the surface of the component are led to the light sensitive surfaces (9, 9', 9") of the video camera through the single lens system (5) and a fixedly arranged beam splitter (11) of prism type dividing the light in three partial light beams. The video camera is modified by replacing the light sensitive elements with such having different pixel densities and removal of colour filters.

Description: ACCURATE REPRODUCTION OF LARGE AND SMALL COMPONENTS TECHNICAL FIELD The present invention relates to devices for reproducing accurately surfaces of electronic components, which can have different sizes. BACKGROUND AND STATE OF THE ART In machines for automatic mounting of electronic components on printed circuit boards, a very high accuracy is required for the positioning of a component, see e.g. the general discussion in U.S. patent US-A 5,251,266. The accuracy can be achieved by retaining and positioning the component in a predetermined manner or in a predetermined position on a pickup head and by capturing, after that, an image of its attachment surface, here termed its bottom surface, and by analysing the captured image automatically. In the case contemplated herein, the picking head is hence in a predetermined position and an image is captured of the component. However, the electronic components exist in very varying sizes, from a outer dimensions of below 1 mm to components having outer dimensions of 40 - 50 mm. If a reproduction system is fixedly and permanently adjusted for large components, so that a video camera over its projection area captures the whole image of large components, the same adjustment for a smaller component will result in an image, which can be poorly used for a position determination, since the image of the actual component will then cover comparatively few pixels of the photo sensitive surface of the video camera. To achieve reproductions of varying magnifications, it would be possible to employ a suitable, zoom type system of lenses, but it turns out that these not are sufficiently stable at different settings and that they, in particular, are not repeatable for changes of the lens system for different magnifications. Hence, at different settings of the degree of magnification, the image will, for instance, in a non-controllable or non-repeatable manner be displaced in different, lateral, directions. However, a repeatable, stable reproduction of a side of component can be achieved by arranging a beam-splitter and two video cameras having different magnifications, as is disclosed in the published European patent application EP-A1 0 449 481, the U.S. patents US-A 5,172,468 and US-A 4,951 ,383 and the Japanese patent applications JP-A 6-112 690 and JP-A 6-125 195. SUMMARY It is an object of the invention to provide a device, by means of which accurate reproductions of electronic components of varying sizes, for an accurate mounting thereof on a printed circuit board, can be achieved. In mounting electronic components of different sizes, two image capture devices having light or photo sensitive means, such as video cameras and lens systems, are used. Light rays from the surface of the component are directed to the light sensitive surfaces of video cameras through lens system and a fixedly arranged beam splitter. Commercially available colour video cameras comprise a suitable beam splitter and the basic configuration thereof is used, by modifying the light sensitive elements to such having different sizes but the same internal resolutions and by removing the colour filters. Thus, generally a device for accurately capturing images from a surface of a component has at least two image capture devices which each one has a light sensitive surface. An optical system such as a beam splitter is placed and arranged so that light rays emitted from the surface of the component reach the light sensitive surfaces. The light sensitive surfaces have different dimensions, one being substantially smaller than another one, for instance one having half the linear dimensions of another one and the same own resolution, that is the same number of scanning lines, picture elements, etc.. Then the image capture device associated with each light sensitive surface will produce pictures with fields of view having different sizes but with the same inherent resolution. A large component surface can be captured by a large light sensitive surface and a small component surface can be captured by a small light sensitive surface so that images of the component surfaces will each one cover a substantial or major portion of the generated, complete respective picture. The light sensitive surfaces can thus comprise different numbers of individual picture receiving elements per area unit to provide digitalized pictures with a lower effective resolution for large components and a higher effective resolution for small components. A single focusing means such as a lens system can be arranged between the location of the surface of a component and the beam splitter. The beam splitter means can comprise a composite prism for dividing the incoming light in light beams directed to the respective light sensitive surfaces. The imaging system can be used in a component mounting machine comprising a picking head for gripping, holding, transporting and accurate positioning of electronic component and suitable driver means for bringing the picking head to a predetermined positions. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to the accompanying drawings, in which Fig. 1 is a schematic view from the side of a device for an accurate reproduction of the bottom surface of electronic components of different sizes implemented by modifying a colour video camera, Fig. 2 is a perspective view of a component assembly device. DETAILED DESCRIPTION In Fig. 1 a portion of a picking head or component holding head 1 is shown of an automatic mount machine for electronic components, see Fig. 2. The pickup head 1 holds an electronic component 3 and the bottom of the electronic component is reproduced by means of a fixedly adjusted lens system 5 on the active, light detecting surfaces 9, 9\ 9" of a modified video camera. The component head 1 can be adjusted to be located in very accurately determined positions both laterally, in one coordinate direction in the preferred embodiment of a mounting machine, and in an elevation direction. A prism system 11 ' divides a primary light beam incident to the lens system 5 into three, secondary light beams, having different directions, one secondary light beam going straight through the prism, a second light beam being effectively deflected 90° and a third light beam being deflected about 60° to the side opposite to that of the second secondary light beam. These secondary light beams reach the light sensitive elements 9, 9' and 9" of CCD type, connected to three separate amplifier units 7, 7' and 7" respectively. In a colour video camera, all the CCD elements are the same type and are equipped with a suitable colour filter for typically red, yellow and blue light (RYB) and the video camera outputs a composite video signal, which represents the measured signal value of each point for every such colour. If the CCD elements are instead of different types, for instance having the same total number of pixel points and having different numbers of pixel points per unit area, i.e. that the CCD elements 9, 9\ 9" all have the same number of total pixel points but have differently sized active surfaces, different degrees of magnification and different fields of view are achieved for the different images. The device illustrated in Fig. 1 has only one lens system and has commercially available main parts, and it can thus be manufactured at a low cost. In Fig. 2 a component assembly or pick-and-place machine is illustrated in a perspective view showing the general configuration of such a machine. A wagon 201 is movable along a horizontal bar 203 to different locations, such as above magazine sites 205 intended to hold component feeders, which are movable in a horizontal direction perpendicular to the guide bar 203 and above a printed circuit board 207 retained on a slide, also movable in the same direction as the magazine sites 205. The wagon 201 carries a pickup unit 209, at the lower side of which a vacuum nozzle 1 is located which can be moved vertically and rotated about a vertical axis. The nozzle can pass through a frame 211 carrying suitable optical devices for directing light from a component to a modified video camera 213.

Claims: CLAIMS 1. A device for accurately capturing images from a surface of a component, comprising - at least two image capture devices having light sensitive surfaces and - a beam splitter means, placed and arranged so that light rays emitted from the surface of the component reach the light sensitive surface on each of the at least two image capture devices, characterized in that the light sensitive surfaces have different dimensions, one being substantially smaller than another one, the image capture device associated with each light sensitive surface thus producing pictures with fields of view having different sizes, whereby a large component surface can be captured by one light sensitive surface and a small component surface can be captured by another light sensitive surface to provide pictures of the component surfaces each one covering a substantial portion of the generated, complete respective picture. 2. A device according to claim 1, characterized in that the light sensitive surfaces all comprise the same number of individual picture receiving elements to provide digital pictures. 3. A device according to one of claims 1 - 2, characterized in that the light sensitive surfaces comprise different numbers of individual picture receiving elements per area to provide digitalized pictures. 4. A device according to one of claims 1 - 3, characterized by a focusing means arranged between the location of the surface of a component and the beam splitter means for focusing light rays from the surface to form an image thereof on each one of the light sensitive surfaces, in particular these images being substantially equal to each other. 5. A device according to one of claims 1 - 4, characterized in that the beam splitter means comprises a composite prism for dividing the incoming light in light beams directed to the respective light sensitive surfaces. 6. A component mounting machine comprising a pickup head for gripping, holding, transport and accurate positioning electronic components, comprising means for bringing the pickup head to predetermined positions, means for an accurate capturing of images of a surface of the component when the picking head is in one predetermined position, which means comprise at least two image capture devices and a beam splitter, characterized in that the beam splitter and the light sensitive surface are so arranged that essentially the same image of a component, in particular an image having the same size, is formed on each of the light sensitive surfaces, and that the light sensitive surfaces have different dimensions, one being substantially smaller than another one, the image capture device associated with each light sensitive surface thus producing pictures with fields of view having different sizes, whereby a large component surface can be captured by one light sensitive surface and a small component surface can be captured by another light sensitive surface to provide images of the component surfaces which images each one covers a substantial portion of the generated respective complete picture that is fully recorded by the light sensitive surfaces and their associated capture devices.

Inventors: JACOBSSON NILS, JACOBSSON, NILS
Applicants: JACOBSSON NILS, MYDATA AUTOMATION AB, JACOBSSON, NILS
Application year: 1995
Main classification: H05K13
IPC codes: H05K13