Device for detecting movements of an object surface

Translation of description of equivalent WO 03003287 A1

D ISPOSITI F MOVEMENT FOR DETECTION OF A SURFACE OF AN OBJECT

The present invention relates to a device for detecting movements of a surface of an object, including a pointing device for a computer, comprising a light source, guide means for directing the light from the source obliquely onto a field of said surface, an optoelectronic sensor 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 wherein the movements of the surface of the ball by rotation thereof are detected by optical means, said surface being provided with a pattern formed of regular points 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 obliquely illuminated by two light emitting diodes (LED) mounted in a carrier either side of a lens. The light reflected by the illuminated field and is returned 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 of the field along two components in its plane.

Construction in particular illustrated by Figures 7 to 12 of the above patent includes an optical housing into two parts used to mount the LED, the mirror, the lens and the optoelectronic sensor. The mirror is constituted by a reflecting surface on a flat face of the lens. The housing is snap-fitted on the one hand to the guide of the ball housing and the other hand to the printed circuit board. The sensor and LED comprise connection metal tabs for their electrical connection to the printed circuit card.

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

Another disadvantage of this construction lies in the cost of the mirror, whose role is to obtain an angled path of light from the field observed sensor, to prevent the latter is exposed to stray light from other.

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 requiring costly mold for its mass production. Whether to change any component or position, create a new mold, at significant cost. Moreover, this construction requires a step of producing the numerous electrical connections with the printed circuit board after mounting the optical housing on this map, which complicates the production. US Patent No. 5686720 discloses a construction that avoids some of the disadvantages mentioned above. This is a said navigation sensor, incorporated in a hand-held scanner is designed to measure the movements of the scanner on a document. In the example shown in Figure 5 of this patent, a small field in 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 enters the paper document at a small angle, typically less than 16 °. The light scattered by the paper passes again through the prism 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. By cons, this arrangement does not effectively protect the sensor against stray light from the prism region.

The present invention relates to a device able to avoid at least some of the above disadvantages of the prior art, while being able to ensure such effective detection of movement, safe and precise positioning of components and moderate manufacturing cost.

To this end, the invention concerns a device of the kind indicated in the preamble above, characterized in that the guide means comprises a prism having a reflection face, on which the light from the source undergoes total reflection, said face having a non-uniformly plane shape arranged to concentrate 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 a bend in the path of light from the source to the observation field, which allows to place the optical system and the optoelectronic sensor directly in front of the field, while the light source may be find the sensor, and be fixed on the same printed circuit board. This results in a very compact construction of the assembly and simplify the electrical connections. On the other hand, a proper configuration of the prism reflection face provides uniform light distribution on the field to observe, without the addition of an additional optical element.

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

Other characteristics and advantages of the present invention appear from the following description of a preferred embodiment, given by way of nonlimiting example with reference to the accompanying drawings, in which:

- Figure 1 is a schematic sectional view of a displacement detecting device according to the invention, for a pointing device for computer;

- Figure 2 is an exploded perspective view of major components of the Figure 1 device;

- Figure 3 shows the object of Figure 2 in the assembled state;

- Figure 4 is a view similar to Figure 3, in which was removed an optical element;

- Figure 5 shows in perspective the bottom of the object of Figure 3; - Figure 6 is a side view of the prism shown in Figure 1;

- Figure 7 is a view along the arrow VII of Figure 6;

- Figure 8 shows schematically the optical effect of the prism, and

- Figure 9 is a diagram of the distribution of illuminance E along a longitudinal direction X of the displacement detection field. The device shown in the drawings is intended to be integrated with a pointing device 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 features and functional characteristics of such an apparatus. Note however that the device according to the invention can also find applications in other devices, especially computer mouse without ball, where it detects the relative displacement between the mouse and the flat surface of a table or a mouse pad, 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 ball surface bearing 1 in a known manner a formed pattern of lines or dots. The ball 1 is rotatable in a casing 2 shown only schematically in Figure 1 and having a transparent window 3, behind 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 plane. 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 the whole device described herein, in particular a light emitting diode ( LED) 7 forming the single light source device, an 8 arranged prism to direct light from the LED 7 to the object 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 consisting in known manner by an integrated circuit provided with a photosensor array on its upper surface. The optical system 9 is arranged to form an image of the field 4 on the network. This system disposed in front of the window 3 and has a straight optical axis 14 perpendicular to the field 4. This gives the sensor 13 for a good quality of the picture of field 4 with very simple means. A transparent protective plate 15 may be placed in front of the window 3. The printed circuit board 6 is a single-sided board, that is to say that all the ICs are located 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), making direct electrical connections. LED 7 is inserted par- below in a hole 17 of the card 6 which firmly maintained in an accurate position. Its two legs of electrical connectors 18 are bent upwardly to engage in two holes in the board and be connected to the printed circuit by soldering onto the upper face 16 of the card. A capacitor 19 mounted on the underside of the board 6 is electrically connected in 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 electrical circuits of the apparatus by means of a flat cable 24. The support 12 of the optical system is constituted by a molded plastic part which is fixed rigidly to the board 6, with two pins with elastic hooks 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 curved side walls 25 and 26 forming a screen around the lens 10 to prevent it receives from stray light. In general, the support 12 forms a housing that prevents the sensor 13 receive light from other than the field to be observed.

The prism 8 and the lens 10 are advantageously formed as a single molded part 27 in transparent plastic, for example polycarbonate or PMMA, this part comprising two lateral arms 28 rigidly connecting the lens to the lens. This part 27 is mounted by snap-fastening on the 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 snap-fastening. This method of attachment and the bent shape at right angles to arm 28 engaging between the two walls 25 and 26 of the support provides precise positioning of the two optical elements 8 and 10 relative to other components of the device. In addition, the manufacturing cost of the molded part 27 is low and installation is extremely simple.

We now describe the preferred form and function of the prism 8 with reference to Figures 6 to 9. In Figure 6, the position of the prism is shown 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 output face 34 is inclined at about 86.7 ° relative to this plane. The third face 35 is a reflection surface comprising two planar surfaces 36 and 37 which adjoin along an edge 38 forming between them a relatively small angle, in this case about 6.5 °. In the example shown, the inclination of the surface 36 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 upwardly to direct light which undergoes total reflections on these faces.

As schematically shown in Figure 8, a light beam 40 from LED 7 enters the prism by the underside 33 thereof and is totally reflected on the reflection face 35 of the prism. The two flat surfaces 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 dashed lines and one in solid line. After refraction on the exit face 34 of the prism 8, the two beams are on the field object 4 to illuminate.

The diagram of Figure 9 represents the distribution of the illuminance E thus 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 the curve 44 that produced by the beam 42. The curve 45, representing the total illumination produced by the two beams, shows excellent uniformity of illuminance on the field length 4. This provides a very good response from the photosensor array sensor 13 and allows easy processing of output signals of the photodetectors.

Note that a good uniformity of the illumination of the field 4 could also be obtained with a domed or faceted of the reflection face 35 of the prism 8. The above description shows that the present invention enables to provide a device simple and robust detection, which can be mass produced at low cost while offering good performance. In addition, if any of the device components must be changed in mass production, it can be done without difficulty or significant cost, since the necessary changes can be simply operated on the circuit board or, where appropriate on the carrier 12 or the optical component 27 without changing the other elements of the device.