Optical head for reading an image of an object

An optical head that can be easily assembled is for reading an image of an object and includes a housing, a diffuser, a light source module and a light sensing module. The diffuser is connected to the housing. The light source module has a substrate and a first light source mounted on a front side of the substrate. The front side of the substrate is fixed to an external surface of the diffuser. The first light source provides an initial light ray incident to the diffuser. The diffuser processes the initial light ray into uniform light for output. The light sensing module fixed in the housing senses reflected light, which is generated from the uniform light reflected by the object.

This application claims priority of No. 097126009 filed in Taiwan R.O.C. on Jul. 10, 2008 under 35 USC 119, the entire content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to an optical head that can be easily assembled.

2. Related Art

FIG. 1is a schematic illustration showing application of a conventional optical head101. Referring toFIG. 1, the optical head101for reading an object102includes a hollow housing110, a light source module120and a light sensing module140. The light source module120is fixed in the hollow housing110and provides a light ray. The light ray is reflected in the hollow housing110and then illuminates the object102. The light sensing module140fixed in the hollow housing110senses the light ray reflected by the object102.

The light ray reflection may include specular reflection, spread reflection and diffuse reflection. The specular reflection represents that the incident angle of the light ray is the same as the angle of reflection of the light ray. The spread reflection occurs on an uneven surface. When the number of angles of reflected light rays exceeds the value, the angles of reflection of some reflected light rays are the same as the incident angle. The diffuse reflection occurs on a rough or uneven surface, and the reflected light rays have different angles.

Because the inner wall surface of the hollow housing110does not pertain to a specular surface, stray light L10may enter the light sensing module140. The currently used light sensing module140includes a CMOS (Complementary Metal Oxide Semiconductor) sensor having the resolution of about 100*100 DPI. The field of view (FOV) of the lens in the CMOS sensor of the light sensing module140is about ArcTan(pattern diagonal/2/EFL)*2, wherein EFL is an equivalent focal length of the lens. The light source module120is usually a light-emitting diode (LED) for emitting infrared light with the wavelength of about 800 to 950 nm. A lens fixing structure of the light sensing module140may adjust the image acquiring distance from the lens to the object102. The illumination effect of the optical head101on the object102is controlled by adjusting the lens fixing structure of the light sensing module140, designing the reflection property of the inner wall surface of the hollow housing110and adjusting the position of the light source module120.

For example, the resolution of the lens is about 50 to 80 lp/mm, wherein RI>80%, and the f-number (F/N) cannot be too high to increase the illumination loading. The allowable tilt angle of the optical head for reading the object has to reach 30 to 40 degrees, and the depth of field of the lens is greater than ±0.7 mm. The object102may be an E-book on which two-dimensional bar code patterns are printed. Because the surface material of the sheet of the e-book can easily reflect light and the tilt angle A between the optical head and the surface of the sheet may reach 0 to 30 degrees or even 0 to 40 degrees when the user holds the optical head to read the e-book. Thus, it is necessary to prevent the strong light reflected by the surface of the sheet from entering the light sensing module140so that the object cannot be recognized.

InFIG. 1, the light ray outputted from the light source module120of the LED, for example, impinges on the inner wall surface of the hollow housing110of the conical pen head to increase the intensity of the incident light. However, there is the reflected light that still can enter the light sensing module140when the incident angle is equal to 24 degrees. In addition, the inner wall surface (typically referred to as a reflective shell) having the reflecting effect also makes the stray light travel back to the light sensing module140so that the contrast is further decreased.

FIG. 2is a schematic illustration showing application of another conventional optical head. As shown inFIG. 2, the optical head is similar to that ofFIG. 1except that the light ray of a LED120directly illuminates the object102. Such a condition tends to make the reflected light enter the light sensing module140so that the contrast is further decreased.

Consequently, the drawback of the conventional optical head is that the dead spots of recognition caused by the reflected strong light cannot be eliminated so that the illumination efficiency cannot be effectively increased, the usage and power consumption of the LED cannot be decreased, and the allowable range of the tilt angle cannot be effectively broadened. In addition, the fabrication of the conventional optical head is also very complicated.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an optical head that can be easily assembled, can eliminate the dead spot of recognition caused by the strong reflected light, can enhance the illumination efficiency to reduce the number and the power consumption of light sources, and can enhance the illumination uniformity to enhance the allowable range of a tilt angle.

To achieve the above-identified object, the invention provides an optical head, which can be easily assembled and is for reading an image of an object. The optical head includes a housing, a diffuser, a light source module and a light sensing module. The diffuser is connected to the housing. The light source module has a substrate and a first light source mounted on a front side of the substrate. The front side of the substrate is fixed to an external surface of the diffuser. The first light source provides an initial light ray incident to the diffuser, and the diffuser processes the initial light ray into uniform light for output. The light sensing module fixed in the housing is for sensing reflected light generated from the uniform light reflected by the object.

Thus, the size of the optical head can be significantly reduced so that the user can carry the optical head conveniently. In addition, the light source may be disposed at a location very close to the to-be-measured object, and most light rays outputted from the light source may be incident to the diffuser substantially vertically, so the illumination efficiency and the recognition ability can be effectively enhanced. Furthermore, the LED may be directly bonded to the flexible circuit board so that the so-called surface mount LED is obtained and the light source module may be mounted more simply because the flexible circuit board only needs to surround the diffuser over 360 degrees. Thus, the optical head can be easily assembled.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3is a schematic illustration showing application of an optical head1according to a first embodiment of the invention. Referring toFIG. 3, the optical head1of this embodiment is for reading an image of an object2. The object2may be, for example, an e-book, on which patterns of two-dimensional bar codes are printed. The optical head1includes a housing10, a diffuser20, a light source module30and a light sensing module40.

The diffuser20is directly connected to the housing10and has a chamber26. InFIG. 3, the diffuser20may be a hollow body or a hollow tube and may serve as a light integrating sphere. However, the diffuser20may also be a solid body or a solid cylinder. The diffuser20may have a circular cross-sectional shape, a rectangular cross-sectional shape or other cross-sectional shapes. When the diffuser20has the circular cross-sectional area, a substrate31surrounds the diffuser20. However, the invention is not limited thereto. The substrate31may also surround the diffuser20by an angle smaller than 360 degrees. For example, the substrate31may surround the diffuser20by an angle smaller than 180 degrees or ranging between 180 and 360 degrees.

The light source module30has the substrate31and a first light source32mounted to a front side31A of the substrate31. The front side31A of the substrate31is fixed to an external surface21of the diffuser20, the first light source32provides an initial light ray L1incident to the diffuser20, and the diffuser20receives the initial light ray L1and processes the initial light ray L1into uniform light L2for output in an axial direction20A of the diffuser20, wherein the initial light ray L1is reflected many times in the diffuser20to form the uniform light L2. Alternatively, the initial light ray L1may also be reflected and refracted many times in the diffuser20to form the uniform light L2.

The light sensing module40fixed in the housing10senses reflected light L3, which is generated from the uniform light L2reflected by the object2disposed outside the diffuser20. The reflected light L3enters the chamber26of the diffuser20in a direction opposite the direction of the uniform light L2, and the light source module30is entirely disposed outside the chamber26so that the initial light ray L1is transmitted through the diffuser20and enters the chamber26. An optical axis40A of the light sensing module40is substantially parallel to the axial direction20A of the diffuser20.

The substrate31is a flexible circuit board, the first light source32is electrically connected to the flexible circuit board, and the flexible circuit board is electrically connected to a mainboard50of the optical head1via wires60. The first light source32may be a light-emitting diode (LED). The mainboard50is formed with a plurality of electrical elements, which constitutes a processing circuit. After the optical head1has read the pattern on the object2, the processing circuit on the mainboard50may directly recognize this pattern and output a signal corresponding to the pattern. For example, the sound or light ray may be outputted to interact with the user.

In order to provide the brighter uniform light, the light source module30may further have a second light source33, which is mounted on the substrate31and electrically connected to the substrate31. The second light source33may also be a LED. The LEDs32and33may be accommodated within grooves24and25of the diffuser20so that most light rays may be incident to the diffuser20vertically. In another example, the second light source33may be mounted on another substrate. Therefore, the light source module30includes, without limitation to, one LED or multiple LEDs. The LEDs may output the same light ray or different light rays.

The light sensing module40includes a lens41and an image sensor42. The lens41is fixed in the housing10. The image sensor42is fixed in the housing10through the mainboard50, and receives the reflected light L3through the lens41.

In order to filter out the infrared light outputted from the first light source and the second light source, the light sensing module40may further include an infrared filter43, fixed in the housing10, for filtering the infrared light of the reflected light L3.

In order to facilitate the adjustment of focusing, the diffuser20may be configured such that its inner wall23may slide or move relatively to an outer wall11of the housing10. Alternatively, the inner wall23and the outer wall11may be formed with corresponding threads to facilitate the adjustment.

In this embodiment, the front side31A of the substrate31is fixed to the external surface21of the diffuser20through an adhesive35. In addition, the front side31A of the substrate31reflects a secondary light ray L4, which is not directly incident to the diffuser20and is outputted from the first light source32, to the diffuser20.

FIG. 4is a schematic illustration showing application of an optical head according to a second embodiment of the invention. In order to facilitate the clear illustration, the substrate and the adhesive are not shown inFIG. 4. As shown inFIG. 4, this embodiment is similar to the first embodiment except that the diffuser20has a stray light eliminating sector22for preventing the stray light from entering the light sensing module40. The stray light eliminating sector22is usually configured to have a cone-like shape to prevent the stray light from entering the light sensing module40.

In addition, the light sensing module40of this embodiment includes a lens barrel44, a lens41and an image sensor42. Similarly, the light sensing module40may further include an infrared filter43. The lens barrel44is fixed in the housing10. The lens41is fixed in the lens barrel44. The image sensor42is fixed in the housing10and receives the reflected light L3through the lens41.

Consequently, it is obtained that the length of the optical head1of this embodiment may be effectively shortened. The equivalent focal length (EFL) of the lens in the conventional optical head is greater than or equal to 5 millimeters. However, the EFL of the lens41of the optical head of this invention can be smaller than or equal to 3 millimeters.

According to the embodiments of the invention, the size of the optical head can be significantly reduced so that the user can carry the optical head conveniently. In addition, the light source may be disposed at a location very close to the to-be-measured object, and most light rays outputted from the light source may be incident to the diffuser substantially vertically, so the illumination efficiency and the recognition ability can be effectively enhanced. Furthermore, the LED may be directly bonded to the flexible circuit board so that the so-called surface mount LED is obtained and the light source module may be mounted more simply because the flexible circuit board only needs to surround the diffuser over 360 degrees. Thus, the optical head can be easily assembled.