The research presented in this thesis is about coating thickness measurements using eddy currents, and a capacitive detector for detecting humans, for safety in industry.

A method for determination of coating thickness of a copper-plated steel wire by measurement of the internal wire impedance, when this is forced by a constant, sinusoidal current, is presented. An electromagnetic model describes how the internal impedance depends on the thickness of the coat, taking into account non-linear effects in the steel. Numerical calculations based on the model are compared with results from measurements.

Determination of coating thickness on plane samples using an elliptically shaped coil is the objective of two investigations. The first is about determination of thickness of silver coatings on a flat brass substrate by measuring the impedance of a thin elliptic test coil. An electromagnetic model based on a dyadic Green function formulation of the problem is described. A Green function expansion in elliptic vector wave functions is derived, from which the electric field and hence the impedance is evaluated by scattering superposition. The model uses an elliptical co-ordinate system and gives an expression of the coil impedance in closed form. Results from calculations using this model and experimental measurements are presented for different values of the eccentricity of the coil and the thickness of the coating for some chosen frequencies. The second investigation also deals with determination of coating thickness with a thin elliptic coil, but is applied for a flat steel substrate, where the coating was made of copper. Thedescribed model, which allows the sample also to be permeable, is in this case based on a second-order potential formulation from which the magnetic vector potential and hence the coil impedance is evaluated. The derivation utilizes a proper choice of transversal field, giving a scalar Helmholtz equation from which the solution to the boundary value problem is separated. The resulting integral equation is expressed in closed form. Performed calculations and experimentsshow how the model can be used to model a steel surface with a coating of copper to find the impedance as a function of the coating thickness and the eccentricity.

Finally capacitive detection of humans for safeguarding in industry has been studied. The work describes how the electric and magnetic fields change when a human body, approximated by a dielectric prolate spheroid, is placed in an originally uniform homogeneous electric field. The evaluation of the fields utilizes a potential solution, arising from the Laplace equation, giving the fields in terms of the Legendre polynomials, from which the reactive power impinging into the detector volume is calculated. Numerical calculations and experiments have beenperformed both in a full-scale prototype for detection of humans and in a small-scale model with paraffin and aluminium bodies.

The research of the measurement group at Linköping university has for some time been focused on the role of measurements in robotics. The main objective of the group's research work has been to provide the robot with sensor information in order to increase its autonomy.

In this work I have studied problematic aspects of robot use that are related to robot safety as seen from the measurement technology point of view. The work can be divided into three subparts:

• a sensor for person presence detection

• a tool for robot control with built in emergency stop

• object recognition, a requirement for increased autonomy that can decrease human presence close to the robot.

In robot safety the aim was to develop a man-detecting sensor that could be used for safety purposes. The efforts were concentrated upon a capacitive sensor for the following reasons:

• man's electrical characteristics differ strongly from those of the air forced out of its place by the human body

• man can not change its electrical characteristics.

Both model calculations and practical tests have been made. Persons are detected as intended.

Industrial robots are equipped with a teach pendant, a hand held control device. It is connected to the control system of the robot and is used for work in close interaction with the robot. Work close to the robot might for instance be necessary during program verification or adjustments. It is important for a person, physically close to the robot, to be able to change command or initiate an emergency stop rapidly and easily. To that aim a user-friendly control tool with a built-in emergency stop is proposed. The tool is based on a glove that measures the finger flexions. The finger flexions form patterns that correspond to different commands. The commands are recognised by methods based on fuzzy principles. The glove is tested on gestures inspired by the manual alphabet used by deaf people. All gestures/commands were correctly recognised.

In the sensor system used by the measurement group a 2-D vision system is used for the localisation and recognition of different work pieces. This system does not in all cases provide the 3-D information needed, e. g. whether an object is a cylinder or a cube. A two-camera system or special illumination techniques can provide the information. A very simple laser scanner provides however enough information for the detection, i. e. gives unique signatures for differently shaped objects. We have investigated this simple and relatively cheap solution. Fourier transformation is used to recognise the differences in the detected laser scanner signal. The result shows that it is possible to recognise objects by this method.