Method and apparatus for providing omnidirectional lighting in a scanning device

#This invention relates to illuminators and more particularly to illuminators for image acquisition devices and machine vision systems.

#Machine vision systems use image acquisition devices that include camera sensors to deliver information on a viewed subject. The system then interprets this information according to a variety of algorithms to perform a programmed decision-making and/or identification function. For an image to be most-effectively acquired by a sensor in the visible, and near-visible light range, the subject should be properly illuminated.

#In the example of barcode scanning using an image sensor, good lighting is highly desirable. Barcode scanning entails the aiming of an image acquisition sensor (CMOS camera, CCD, etc.) at a location on an object that contains a bar code, and retrieval of an image of that barcode. The bar code contains a set of predetermined patterns that represent an ordered group of characters or symbols from which an attached data processor (for example a microcomputer) can derive useful information about the object (e.g. its serial number, type, model, price, etc.). Barcodes are available in a variety of shapes and sizes. Two of the most commonly employed barcode types are the so-called one-dimensional barcode, consisting a line of vertical stripes of varying width and spacing, and the so-called two-dimensional barcode consisting of a two-dimensional array of dots or rectangles.

#The invention description below refers to the accompanying drawings, of which:

#FIG. 1 is a perspective view of a handheld scanning system and subject employing a passive light pipe illuminator according to an embodiment of this invention;

#FIG. 2 is a perspective view of a fixedly mounted scanning system and subject employing a passive light pipe illuminator according to an embodiment of this invention;

#FIG. 1 shows a scanning system 100 adapted for handheld operation. An exemplary handheld scanning appliance or handpiece 102 is provided. It includes a grip section 104 and a body section 106. The sensor and other functional components described herein can be controlled and can direct image data to an onboard embedded processor 109. This processor can include a scanning software application 113 by which lighting is controlled, images are acquired and image data is interpreted into usable information (for example, alphanumeric strings derived from the barcode images). The decoded information can be directed via a cable 110 to a PC or other data storage device 112 having (for example) a display 114, keyboard 116 and mouse 118, where it can be stored and further manipulated using an appropriate application 120. Alternatively, the cable 110 can be directly connected to an interface in the scanning appliance and an appropriate interface in the computer 112. In this case the computer-based application 120 performs various image interpretation and lighting control functions as needed. The precise arrangement of the handheld scanning appliance with respect to an embedded processor, computer or other processor is highly variable. For example, a wireless interconnect can be provided in which no cable 110 is present. Likewise, the depicted microcomputer can be substituted with another processing device, including an onboard processor or a miniaturized processing unit such as a personal digital assistant or other small-scale computing device.

#The scanning application 113 can be adapted to respond to inputs from the scanning appliance 102. For example, when the operator toggles a trigger 122 on the appliance 102, an internal camera image sensor (150, shown and described further below) acquires an image of a region of interest 130 on an item 132. The exemplary region of interest includes a two-dimensional bar code 134 that can be used to identify the part 132. Identification and other processing functions are carried out by the scanning application 113, based upon image data transmitted from the appliance 102 to the processor 109.

#Simultaneously with, or in advance of acquisition of the image, the area of interest 130 is illuminated. In one embodiment, a switch 140 on the appliance 102 can be used to operate the illuminator, which consists of a novel light pipe arrangement 142 in accordance with this invention. Alternatively, as will be described below, the operation of the illuminator can be operated and controlled remotely by the scanning software application 120. The passive light pipe 142 consists of an extended barrel of light transmissive material terminating (in this embodiment) in an angled tip 144. As described further below, this tip is designed to cause internal reflection that projects a low-angle dark field illumination in the area of interest 130. As noted above, such dark field illumination is typically provided at an angle of no more than approximately 45 degrees with respect to the surface or more than 45 degrees normal to the optical axis. Extending through the center of the light pipe, which comprises a hollow tube, is a camera sensor 150 (shown in phantom and associated optics). The focal point of the camera is selected so that it is able to focus on the desired area of interest, as its field of view, in close proximity to the tip 144. In this manner, the tip can be placed very close to, or in contact with the area of interest for accurate viewing. As noted above, the bar code 134 in this embodiment is one that is best viewed using a dark field illumination. However, as will be described further below, the light pipes described in accordance with this invention also has the ability to provide bright field illumination for bar codes that are better suited to direct, high-angle illumination (for example, those printed with high contrast ink on a relatively smooth, matte surface).