Oliver Schwaneberg

Design of an LED-based sensor system to distinguish human skin from workpieces in safety applications

Commercial light curtains use a technique known as muting to differentiate between work pieces and other objects (e.g., human limbs) based on precise model knowledge of the process. At manually fed machinery (e.g., bench saws), such precise models cannot be derived due to the way the machinery is used. This paper presents a multispectral scanning sensor to classify an objects surface material as a new approach for the problem. The system is meant to detect the presence of limbs and therefore optimized for human skin detection. Evaluation on a test set of skin and (wet) wood samples showed a sufficiently high reliability with respect to safety standards.

A Near-Infrared LED-based Material Classification Sensor System

In safety applications it is often desired that certain materials do not enter a dangerous area. This paper presents a near-infrared LED-based sensor system for robust material classification and ranging up to a distance of 1,000mm.

The top down design flow of a-Si:H photodiodes with multivariate methods of analysis

A fast and reliable detection of potentially dangerous substances has become very important in ensuring civilian security. Currently, modern security systems have proven to be more effective on the basis that objects should be properly characterized and identified. For instance, chemical tests are used to identify samples of whitish powder that is suspected to be dangerous or illegal. Although these chemical tests are conducted very quickly, they are relatively expensive. However, well established methods of optical characterization offer a suitable alternative. The demand for low-cost and disposable devices have escalated the development of intelligent photodiodes, especially of tunable a-Si:H multispectral photodiodes1. Our aim of reengineering is to develop the best match for the spectral response adjustment. Unfortunately, it is not sufficient to optimize the spectral response only. The top down design flow begins with the calculation of the photocurrent for different combinations of light sources, spectral responses and whitish powder samples to build up a multivariate data set. The optimum combination is found at the point of intersection in the factor values in a 2-D scattergram. It is therefore, required that the use optimized photodiodes would simplify and accelerate the identification of potentially dangerous substances.

Material classification through distance aware multispectral data fusion

Safety applications require fast, precise and highly reliable sensors at low costs. This paper presents signal processing methods for an active multispectral optical point sensor instrumentation for which a first technical implementation exists. Due to the very demanding requirements for safeguarding equipment, these processing methods are targeted to run on a small embedded system with a guaranteed reaction time T < 2 ms and a sufficiently low failure rate according to applicable safety standards, e.g., ISO-13849. The proposed data processing concept includes a novel technique for distance-aided fusion of multispectral data in order to compensate for displacement-related alteration of the measured signal. The distance measuring is based on triangulation with precise results even for low-resolution detectors, thus strengthening the practical applicability. Furthermore, standard components, such as support vector machines (SVMs), are used for reliable material classification. All methods have been evaluated for variants of the underlying sensor principle. Therefore, the results of the evaluation are independent of any specific hardware.

Hand and Finger Protection for Circular Saws

In the presented project, a new approach for the prevention of hand movements leading to hazards and for non-contact detection of fingers is intended to permit comprehensive and economical protection on circular saws. The basic principles may also be applied to other machines with manual loading and / or unloading. With an automatic blade guard an improved integration of the protection system can be achieved. In addition a new detection principle is explained. The distinction between skin and wood or other material is achieved by a dedicated spectral analysis in the near infrared region. Using LED and photodiodes it is possible to detect fingers and hands reliably. With a kind of light curtain the intrusion of hands or fingers into the dangerous zone near the blade guard can be prevented.

Application specific band selection with multivariate methods of analysis for a-Si:H multispectral photodiodes

In the recent past the generation and processing of multispectral data have had an immense impact on optical characterization systems. A virtual test environment is used to examine which bands provide a high information density. The photocurrent j = ∫ E(λ)*Sabs(λ)*r(λ) dλ was calculated for different light sources E, spectral response curves Sabs (bands), and the reflectance r of whitish powder samples that were suspected to be dangerous or illegal. The multivariate dataset will have to be determined whether we can gain any knowledge from this. The employed factor analysis is a common method of the group of structure-discovering methods and provides good results in the discovery of connections between parameters. It is particularly used if a variety of parameters must be reduced for some reason. For the verification, a dimension of the external separation is defined. To carry out this an n-dimensional vector P must be assigned to each measurement that is registered in the matrix M to determine the volume V of this dot cloud. The dimension normalized volume is defined as ΔCL, where n is the quantity of employed bands. The reliability of the complete measurement system is made by a membership function μ(P) comparable to the definitions from the area of the fuzzy sets. The parameter μ indicates with which reliability a measured pattern P could be assigned to a sample S from a dataset. The use of such optimized multispectral photodiodes would simplify and accelerate the identification of potentially dangerous substances.