Device for detecting movements of an object surface

The present invention relates to a device for the detection of displacements of a surface of an object, including a pointing device for computer, comprising a light source, guide means for directing the light from the source obliquely onto a field of said surface, a sensor optoelectronic provided with an array of photodetectors, and an optical system for forming an image of said field on the optoelectronic sensor.

In US Patent No. 6124587, there is described a ball pointing device in which the displacements of the surface of the ball by rotating thereof are detected by optical means, said surface being provided with a pattern formed of points regular or irregular. A small portion of the surface of the ball, forming a field defined by a fixed window and in which one wishes to detect the displacements of the surface of the ball is illuminated obliquely by means of two diodes emitting (LED) mounted in a support on either side of a lens. The light reflected by the illuminated field and is reflected by a mirror associated with the lens to an optoelectronic sensor comprising an array of photodetectors. The signals from this sensor are processed by electronic circuits mounted on a printed circuit board, to provide information relating to the movement field following two components in its plane.

The construction illustrated in particular in Figures 7 to 12 of patent above includes an optical housing into two parts used to mount LEDs, mirror, lens and optoelectronic sensor. The mirror consists of a reflective surface on a flat face of the lens. The housing is secured by latching the one hand to the housing of the ball guide and on the other hand to the card printed circuit boards. The sensor and LED have metal legs connection to their electrical connection to the printed circuit card.

In such an arrangement, it is necessary to use two light sources spaced from each other to obtain a sufficiently uniform illumination of observed field, so that the detection of its movements can take place in good conditions. The LED light is conducted to end this field by respective channels in the optical housing. As a result, this case is relatively complicated and that several connection leads groups are necessary for connecting the LED and the sensor to the printed circuit board.

Another disadvantage of this construction lies in the cost of the mirror, which the role is to get a bent path of light from the observed field sensor, to prevent the latter is exposed to stray light from elsewhere.

Other drawbacks are linked to the fact that the optic housing, ensuring a precise mutual positioning of all the components it supports, is a complicated piece that requires a costly mold to its mass production. If we must change any component or position, create a new mold, at significant cost. Furthermore, this construction requires a step of realization of numerous electrical connections with the printed circuit board after mounting the optical box on the map, complicating production.

US Patent No. 5686720 discloses a construction that avoids some of the drawbacks mentioned above. This is one said sensor navigation incorporated in a hand-held scanner is designed to measure the displacements of the scanner on a document. In the example illustrated by Figure 5 of that patent, a small field of the document is illuminated by a light source through a prism placed just above it. The prism deflects the light beam so that the light reaches the paper document at a small angle, typically less than 16 °. Light scattered by the paper passes back through the lens and is collimated to a photodetector array by means of a convex surface of the prism, forming a lens. This allows to mount the light source and the optoelectronic sensor photodetectors directly on the printed circuit board. Against by this arrangement does not effectively protect the sensor against light stray from the prism of the region.

The present invention relates to a device able to avoid at least some the aforementioned drawbacks of the prior art, while being able to ensure particularly effective detection of movement, secure positioning and accurate components and a moderate cost of manufacture.

To this end, the invention concerns a device of the kind indicated in the preamble above, characterized in that the guide means include a prism having a reflection face, on which the light from the source undergoes total reflection, said face having a non-uniformly planar arranged to focus the light towards the field to be observed on the surface of the object.

This provision has a double benefit. On the one hand the prism creates an elbow in the path of light from the source to the observed field, allowing placing the optical system and the optoelectronic sensor directly in front of this field, while the light source may be located next to the sensor and be fixed on the same printed circuit board. This results in a very compact construction Overall and simplified electrical connections. On the other hand, a proper configuration of the prism reflective face standardizes the distribution of light on the field to observe, without the addition of an element additional optics.

In a particularly simple and inexpensive embodiment, the face of the reflection prism includes two plane surfaces forming an angle therebetween. This allows to compensate for the divergence of the beam from the light source dividing the beam into two partial beams directed towards the field to observe, so as to obtain a correct distribution of the illumination thereon. At the same time, can be used a prism which all outer surfaces are planar, which simplifies its manufacture and positioning. However, in other modes of implementation, it is expected that the prism reflective face to be convex forming a concave reflector capable of ensuring the uniformity of the illumination. She could also comprise a series of planar facets.

Other characteristics and advantages of the present invention will in the following description of a preferred embodiment, given by way of non-limiting example with reference to the accompanying drawings, in which:<ul><li>Figure 1 is a schematic sectional view of a detection device movement according to the invention, to a pointing device for computer;</li><li>Figure 2 is an exploded perspective view of the main components of device of Figure 1;</li><li>3 shows the object of Figure 2 in the assembled state;</li><li>Figure 4 is a view similar to Figure 3, wherein a was removed optical element;</li><li>5 shows in perspective the bottom of the object of Figure 3;</li><li>Figure 6 is a side view of the prism shown in Figure 1;</li><li>FIG 7 is a view along arrow VII of Figure 6;</li><li>Figure 8 shows schematically the optical effect of the prism, and</li><li>Figure 9 is a diagram of the distribution of illuminance E along a longitudinal direction X of displacement sensing field.</li></ul>

In the drawings shown device is intended to be incorporated into a pointing apparatus rotating ball like "trackball" for example of the type described in US Patent No. 6124587 to which the reader is referred to regarding other structural and functional characteristics of such a device. We will note however, that the device according to the invention may also find application in Other devices, especially computer without ball mouse, where it detects relalits travel between the mouse and the flat surface of a table or a carpet mouse, or a hand scanner of the type described in US Patent No. 5,686,720.

In the example described here, the object whose movement is detected is a 1 ball surface bearing a known manner a formed pattern of lines or points. The ball 1 is rotatable in a housing represented only 2 schematically in Figure 1 and comprising a transparent window behind 3 which appears an object field 4 of the surface of the ball 1. The field 4 being small, with a diameter of about 2.8 mm, it may be regarded as approximately plan. The detection device shown schematically in Figure 1 is mounted within the housing 2. It includes a printed circuit board 6 which is fixed in the housing 2 and supports all of the device described here, including a light emitting diode (LED) 7 forming the only source of light device, an 8 placed prism to direct light from the LED 7 to the subject field 4, an optical system 9 formed by a lens 10 and a diaphragm 11, a support 12 of the optical system and an optoelectronic sensor 13 constituted as known by an integrated circuit provided with a photosensor array on its surface higher. The optical system 9 is arranged to form an image of the field 4 on this network. This system disposed in front of the window 3 and has an optical axis straight 14 perpendicular to the field 4. There is thus obtained for the sensor 13 a good image quality of the field 4 with simple means. A plate transparent protection 15 can be placed in front of the window 3.

The circuit board 6 is a single-sided board, that is to say that all printed circuits are on its upper surface 16, which reduces the cost of manufacture of the card and mounting of components thereon. The sensor 13 is mounted directly on the face 16 of the card by the method of "chip-on-board" (COB), providing direct electrical connections. LED 7 is inserted from below in a hole 17 of the card 6, which firmly maintains in a position precise. His two legs of electrical connection 18 are bent upwards to engage in two holes in the board and can be connected to printed circuits by soldering onto the upper face 16 of the card. a capacitor 19 fixed to the underside of the board 6 is electrically connected to the same way.

The other electrical components such as 20, 21 of the device are mounted on the upper face 16 of the card. The printed circuit card 6 are connected to other circuits of the device by means of a flat cable 24.

The support 12 of the optical system is constituted by a plastic part which is molded snap-fitted on the map 6, with two lugs hook elastic 22 engaging in holes 23 of the card. This ensures precise positioning of the support 12, which covers and protects the sensor further 13. Above the diaphragm 11, the support 12 comprises two side walls 25 and 26 curved shielding around the lens 10 to prevent it receives of stray light. In general, the support 12 forms a housing preventing the sensor 13 receive light from other than the field to observe.

The prism 8 and the lens 10 are advantageously made in the form of a same molded part 27 of a transparent synthetic material, for example in polycarbonate or PMMA, this piece includes two side arms 28 connecting rigidly the prism lens. This part 27 is mounted on the snap upper surface 29 of support 12, which is provided with two resilient hooks 30 clinging to the arm 28 to secure the workpiece 27 by snapping. This method of fixing and the bent shape right angle arm 28 engaging between the two walls 25 and 26 of the support provides precise positioning of the two optical elements 8 and 10 with respect to the other components of the device. In addition, the manufacturing cost of the molded part 27 is low and installation is extremely simple.

We will now describe the preferred form and function of the prism 8 Referring to Figures 6 to 9. In Figure 6, the position of the prism is represented by relative to a reference plane 32 which is parallel to the printed circuit board 6 and the plane of the object field 4. All exterior surfaces of the lens are flat. The Input face 33 of the prism is inclined about 3.47 ° relative to the plane 32. The front Release 34 is tilted about 86.7 degrees to this plane. The third face 35 is a reflection face comprising two planar surfaces 36 and 37 which adjoin the along an edge 38 forming between them a relatively small angle, in namely about 6.5 °. In the example shown, the inclination of the surface 36 by relative to the plane 32 is about 57.26 ° and that of the surface 37 is about 50.71 °. The side faces 39 of the prism are parallel in this case, but they could also be slightly converging upward to direct light undergoing total reflections on these faces.

As schematically shown in Figure 8, a light beam 40 from the LED 7 enters the prism by the underside 33 thereof and is totally reflected on the reflection face 35 of the prism. Both surfaces planar 36 and 37 of this face, having different inclinations, divide the beam 40 into two partial beams 41 and 42 one of which is drawn in broken lines and one continuous line. After refraction on the exit face 34 of the prism 8, the two beams go on the object field 4 to shine.

The diagram of Figure 9 represents the distribution of the illuminance E and obtained on the object field 4, in function of the abscissa in the longitudinal direction X field 4. Curve 43 represents the illumination produced by the beam 41, and curve 44 that produced by the beam 42. The curve 45, representing the illumination total produced by the two beams, shows excellent uniformity of illuminance on the field length 4. This ensures a very good network response photodetectors of the sensor 13 and allows easy processing of the output signals photodetectors.

It should be noted that a good uniformity of illumination of the field 4 could also be obtained with a domed or faceted of the reflection face 35 of the prism 8.

The foregoing description shows that the present invention allows a simple and robust sensing device, which can be mass produced for a low cost while offering good performance. In addition, if one of the components the device must be changed in mass production, it can be done without difficulty or significant cost, since the necessary changes can be simply made on the printed circuit board or, where appropriate, on the support 12 or the optical component 27 without changing the other elements of the device.