This application claims priority of European application EP99811164.5, filed Dec. 15, 1999, and whose contents are hereby incorporated by way of reference.
The present invention concerns an opto-electronic system for a dimension-measuring device, in particular an opto-electronic system for a portable device for measuring linear and/or angular displacement. The present invention concerns in particular an opto-electronic system for a displacement-measuring device of comparator type.
Optical systems for measuring dimensions and angles are described notably in DE19505176 (Baumer Electric AG). They comprise generally a light emitter emitting a light ray sent by means of appropriate optics in the direction of a photo-detector. A graduated rule or disc is placed in the optical path between the emitter and the photo-detector. The illumination of the sensor is interrupted when a graduation of the rule or of the disc is in the optical path. A counter counts the number of interruptions of the signal supplied by the sensor in order to deduce therefrom the displacement of the rule or of the disc and to display a representative value of this displacement. Such devices are used notably in apparatus for measuring and comparing dimensions of machine parts.
A device of this type is described in patent CH683798 (TESA SA), to which the reader can profitably refer. This document describes an opto-electronic system comprising several photo-emitters mounted on a printed circuit board on one side of a rule provided with a double graduated track and several photo-detectors mounted opposite on a second circuit on the other side of the rule.
This device has the inconvenience of necessitating two printed circuit boards, and thus of having relatively important space requirements, so that it is difficult to integrate it within a portable device. Furthermore, it is difficult to align accurately the optical components mounted on two different boards, notably when the two circuits are subjected to temperature variations and thus to dilatations that are different.
Patent application WO87/07944 (Renishaw) describes another electro-optical device for measuring dimensions, in which the light beam emitted by a photo-emitter is reflected in the direction of the photo-detector by reflecting surfaces on the rule. The described construction makes it possible to place the photo-emitter and the photo-detector on the same printed circuit board and to use a single lens. However, the portion of the beam that is reflected is weak, so that the contrast of the signal received on the photo-detector is weak. Furthermore, the manufacture and aligning of the single lens are subjected to rather strict constraints in order for the optical beam to be focused on the rule and reflected precisely in the direction of the photo-detector by means of a single lens.
The abstract of patent application JP-A-61-000712, published May 29, 1986, in volume 10, No 147 (P460) of  less than  less than Patent Abstracts of JAPAN  greater than  greater than , describes an optical reading device comprising a large number of individual optical elements that are difficult and costly to align correctly. Furthermore, it makes use of optical fibers between the photo-emitter and the printed circuit board that only increases the complexity, volume and cost of the device.
It is an aim of the present invention to propose an opto-electronic system for a dimension-measuring device that is improved over the prior art systems, notably a system that does not have the inconveniences mentioned.
Another aim of the present Invention is to propose an opto-electronic system for a dimension-measuring device of low cost, of high precision and having reduced space requirements, adapted for example to use in a comparator or in any other portable or small dimension-measuring device.
Another aim is to propose an opto-electronic system enabling to determine the position of a rule or of a disc read in transmission and comprising a succession of transparent and opaque zones.
According to the invention, these aims are achieved by means of an opto-electronic system having the characteristics of the independent claims, variants of preferred embodiments being moreover described in the dependent claims.
According to the invention, these aims are achieved notably by means of an opto-electronic system comprising a transparent rule with at least one portion provided with a succession of opaque graduations, at least one photo-emitter, at least one photo-detector, an optical system capable of concentrating the light beam or beams generated by said at least one photo-emitter on said at least one portion, and of concentrating the light beam or beams having crossed rule on said at least one photo-detector, said rule and said optical system being able to be moved in relation to one another, and in which said photo-emitter and said photo-detector are on the same side of said rule. In a preferred embodiment, said photo-emitter and said photo-detector are mounted in the same plane, for example on a same printed circuit board.
This characteristic makes it possible to use the advantageous properties of a rule read in transmission, enabling an improved contrast, in a system in which the emitting and the receiving of light are made in approximately the same direction but in opposite sense. The system thus permits a rule read in transmission to be used with a photo-emitter and a photo-detector mounted on a same printed circuit board. This characteristic thus makes it possible to avoid the problems of mutual alignment and of positioning of the photo-emitter and photo-receiver.
According to the invention, these aims are further achieved by means of an optoelectronic system comprising a transparent rule with at least one portion having a succession of opaque graduations, at least one photo-emitter, at least one photo-detector, an optical system capable of concentrating the light beam or beams generated by said at least one photo-emitter on said at least one portion, and of concentrating the light beam or beams having crossed said rule on said at least one photo-detector, in which said optical system is constituted of an integrated optical bloc.
These characteristics thus allow the position of a transparent rule comprising opaque graduations to be determined with great accuracy, since all the optical surfaces are made in a same optical bloc. This characteristic has the advantage of avoiding the problems of mutual alignment of the optical components during assembly and the inaccuracies due to the different dilatations of the optical components. Furthermore, use of an ordinary transparent rule and of a single optical element manufactured for example by injection of synthetic material in a mould makes it possible to reduce the manufacturing cost of the system and to obtain an excellent contrast of the signal received on the photo-detector.
According to a preferred embodiment of the invention, the optical bloc, the photo-emitter and the photo-detector are mounted on the same printed board circuit, the rule moving for example in a plane perpendicular to that board. This arrangement makes it possible to reduce the system""s space requirements and to move the printed board closer to the rule without increasing the size of the optical bloc.
According to a preferred embodiment of the invention, the optical bloc comprises a first optical surface for collecting the light beam emitted by said photo-emitter, a second optical surface for reflecting this light beam and concentrating it on said portion, a third optical surface for concentrating and reflecting the light beam having crossed said rule, and a fourth optical surface for concentrating said beam on said photo-detector. Thanks to this advantageous arrangement, each optical surface of the optical bloc effects only simple optical operations of reflecting and/or collimation, which makes it possible to use relatively simple optical surfaces, for example only spherical or possibly elliptical surfaces. In a preferred embodiment, all the optical surfaces are spherical or cylindrical.
In a preferred embodiment of the invention, an additional diversion is provided in the optical path between the photo-emitter and the photo-detector, allowing the optical path to be lengthened without increasing the optical bloc""s space requirements, or, inversely, allowing these space requirements to be reduced without shortening the optical path. It is thus possible to use optical surfaces that are extremely easy to manufacture, for example spherical or even plane surfaces, even with devices of small size in which the focal distances are necessarily reduced.