| In the manufacture of consumer products, quality | | | | These latter quality problems are often not easy to |
| control is of utmost importance. In most instances | | | | detect in the processing of plastics. In this paper, the |
| where manual processes are involved, the individual | | | | application of a smart vision system in the automatic |
| who operates the machinery also performs this task. In | | | | detection of poor or improperly oriented print templates |
| injection molding, for instance, this means ensuring the | | | | is presented. The method used to detect improper |
| correct orientation and quality of print on the | | | | orientation is based on edge detection and feature |
| manufactured parts and components. In manually | | | | identification. More advanced algorithms like |
| operated equipment, this inspection process presents a | | | | segmentation, template matching, and character |
| challenging task because often, after prolonged hours | | | | recognition are utilized for ensuring proper print quality. |
| of work, fatigued operators will insert labels inside the | | | | To achieve machine vision successfully, and implement |
| molding dies in improper orientation, resulting in rejected | | | | the use of computer software, the viewing area must |
| parts. In other cases, because of the heat in the | | | | be represented in digital form.The purpose of image |
| molding process, if there is excess ink on the labeling | | | | acquisition therefore is to capture the optical data and |
| equipment, the prints may be smeared or distorted. | | | | change it to a form that will facilitate convenient and |
| Machine operators occasionally miss or overlook | | | | efficient processing using a computer. An image is |
| quality issues. To alleviate this inspection and operation | | | | typically embedded within a viewing area covered by |
| problem, it is now possible to incorporate vision | | | | the video capturing mechanism or sensor. The most |
| systems which will ease the inspection task for the | | | | common type of capturing mechanism is the charged |
| operators, allowing them to concentrate more on the | | | | coupled device (CCD). When a light source hits an |
| manufacturing process. Vision systems provide means | | | | object, it is reflected to the sensor through appropriate |
| by which continuous and autonomous inspection can | | | | lenses. The photons cause electrical charges to be |
| be achieved during production. | | | | created in the CCl), thus generating analog signals on a |
| Computer vision techniques are increasingly being used | | | | 2-D array. The intensity of the charge at each discrete |
| as alternative methods to conventional inspection and | | | | point in the 2-D array is proportional to the photon |
| monitoring applications, due to their simplicity and ease | | | | energy impinging on that point, determining the |
| of set-up, relative insensitivity to ambient noise, | | | | brightness or intensity of the light. Therefore a typical |
| noninvasive means of gathering information on objects | | | | optical image system is a continuous 2-D function, |
| without contact, marking or specimen preparations, and | | | | h(x,y) whose value at any pair of spatial coordinates |
| the potential for online applicability.1"3 Machine vision | | | | represented by the Cartesian coordinate system (x,y) |
| has continued to play a major role in the integration of | | | | is the intensity of light at that point. The continuous |
| automated manufacturing, both from a quality and | | | | function h(x,y) must be quantized (or digitized) so that it |
| inspection perspective to more advanced applications | | | | can be easily processed by computer. |
| such as motion control and robot guidance. For | | | | The most common method of digitization is a |
| example casting mould,mold making,plastic injection | | | | combination of spatial and amplitude quantization in |
| mold etc.The role of machine vision in providing | | | | which the viewing area is divided into a matrix of m by |
| solutions to manufacturing automation has been | | | | n cells or pixels: m and ç are integers. The image is |
| recognized by both researchers and engineers in | | | | sampled at these discrete points in the viewing area. |
| industry. | | | | Each pixel is then assigned a numerical value that is a |
| In the plastics manufacturing industry, vision applications | | | | digital representation of the initial analog value. h(x,y). |
| have been used mainly to inspect the quality of | | | | through the analog-to-digital (A/D) conversion |
| molded parts, especially for missing features or badly | | | | system.The numerical value will depend on the bit |
| formed sections. Although fairly automated, the plastics | | | | resolution of the A/D converter which in turn |
| molding industry still has a large component of its | | | | determines the number of gray-scale levels in which |
| operations carried out manually, especially for medium- | | | | the image can be represented. Therefore the new |
| and low-volume rates of production. For instance, the | | | | image data, I(m.n). will have values between O (dark or |
| placement of print template or metallic parts to be | | | | lowest intensity) and 2^sup r^-l. where r is the bit |
| included in the finished product is still done manually. | | | | resolution of the A/D converter.The acquired image |
| Under such circumstances, it is possible to have a | | | | must then be filtered to remove any noise, and |
| wrongly inserted print template which would result in | | | | enhanced for analysis.This stage is known as |
| the rejection of the part. | | | | processing. There are five common types of |
| In some cases, due to process variations, a particular | | | | operational approaches for primary processing of |
| plastic part may posses a smudged or faint print. | | | | pixels. |