Today, anyone who switches on a kitchen oven benefits from the modern components made of technical ceramics. The material withstands extreme temperature fluctuations, exhibits high strength and is resistant to wear. However, hair cracks, contamination and air entrapment repeatedly occur during production, considerably depreciating quality. Automated optical quality inspection is therefore essential.

When, in the 19th century, the large-scale construction of electricity supply grids began, the engineers discovered the positive characteristics of porcelain as a corrosion-proof insulator. Technical ceramics were born. Strength, resistance to temperature fluctuations, surface quality and differing electrical properties make ceramics versatile in application. The production process makes this material something special. In contrast to metals, for example, the material characteristics are not predetermined from the outset, but originate exclusively through the method of production. The achievement of the manufacturer lies in the ability to control this process, so that the respective desired material characteristics are generated. Just as the shape and characteristics of a porcelain plate are virtually unchangeable following the firing pro-cess, the same also applies to technical ceramic components.

100% Reliability at 900 Parts per Hour
Ceramic components can be shaped by means of pressing or by injection molding. Axially symmetrical components such as axles or tubes can also be produced by extrusion, similar in principle to the potter‘s wheel. However, quality inspection is required at the end of the process. The surface quality of the work pieces must be inspected in accordance with the subsequent loading. For example, a component intended for use as the combustion chamber in an engine must be scanned for fine hair cracks. Contamination or the entrapment of minute quantities of air in the material can also significantly impair the quality. Therefore, automated inspection processes based on image processing are required. In this, the engineering firm ICW Christian Wölz in Augsburg, Germany, is specialized. The company works as system integrator for Omron and has recently constructed a complete inspection system for a customer from the ceramics sector which, even at the high throughput capacities of up to 900 components per hour, guarantees 100% reliability in the detection of defects.
The heart of the inspection system is the Xpectia machine vision system from Omron. At present, it can process the signals from up to four five-megapixel cameras and is suitable for both two- as well as three-dimensional inspection of components. Like the human eye, this system can detect all types of objects, of any size and color combination (16 million colors), from any distance. The camera images can be evaluated in real time, according to the specified parameters. These parameters are freely configurable on an IPC platform. In this way, individual inspection sequences and decision-tree structures can be defined, which ultimately result in each work piece receiving an overall assessment as good or defective, in accordance with these quality characteristics. ICW not only took charge of the system adaptation on the information-technology level, but has also designed the mechanics of the entire inspection system, so that quality inspection is integrated directly into the ceramic production process.

Quality Inspection in Multiple Stages
Firstly, the machine for ceramic production is configured in accordance with the formula, in which the characteristics of the relevant material type are precisely described. Thus, any number of work pieces from a particular batch can be inspected. The automatic process then begins. The system is loaded by means of a changeable magazine. The work pieces may be of differing diameter and material thickness. There are three different magazine sizes for diameters of 18 mm, 32 mm and 38 mm. Material thickness can vary from 0.1 mm to 6.35 mm. The mechanics of the device are infinitely adjustable and can therefore be ideally configured for a wide range of ceramic thicknesses.

Inspection Point by Point
The inspection system consists of three camera fields of view. The first camera serves the position determination. With this camera, the system detects the geometry of the work piece, i.e. the product-dependent surface characteristics such as holes, grooves and recesses. In this way, the optimal rotational position for the actual quality inspection is determined, which is sequentially performed by the other two cameras. This first step is decisive, as it is essential that all inspected pieces are assessed in the same initial position. The machine vision system determines the alignment with absolute accuracy. The further transport of the work piece is by means of ceramic-covered rotational suction devices in order to prevent possible contamination through the system itself.
The quality inspection then takes place with the second camera - firstly on the front side. For this purpose, the camera scans the material structure as finely as possible. This produces four high-resolution images which, together, depict the entire front surface of the ceramic component. The freely rotating suction elements move the work piece to any desired position. Precise regulation of the vacuum ensures that the components are not damaged.
The inspection itself is on the basis of homogeneity, as the system does not work using a model, but examines the surface structure of each individual work piece. The surface is compared point for point with reference to itself and is examined for defects. The image processing system is so accurate that it can detect defects down to a value of 10 µm, or even smaller tolerances. In accordance with the specified parameters, the Omron vision system identifies all irregularities in the surface, including for example pores, hair cracks, contamination, discoloration and bumps.
The work piece is reliably transported to the third camera, where the same procedure is performed once again, this time for the back of the component. After completion of the entire procedure, the inspected components are deposited in magazines sorted into "good" and "defective" products. Laser distance sensors continuously monitor the levels in the magazines. The entire system is of a flexible design and can, within a few minutes, be converted for quality inspection of ceramic components with a completely different shape.

Core Components from One Source
The system designed by ICW is a sophisticated complete solution, consisting of 70% Omron components, thus uniting all customer-relevant quality assurance characteristics in one machine. In addition to machine vision technology, Omron also developed the control and parts of the drive system. Both were selected according to the criteria reliability, speed and precision. The high proportion of technology from one source is thus also the main advantage of the inspection system.
The system is particularly economical for all inspections which require not only random samples but large numbers of work pieces and a quality level at 100%. The advantages of an automated solution lie in the clear definition of good products as opposed to rejects. In this way, the same high quality standard is achieved for all inspected parts, which would not be possible by manual inspection.