Kalman Babković

Passive Wireless Sensor for Force Measurements

The goal of this paper is to investigate fabrication and design of a wireless passive sensor, and its application for measuring normal forces. The proposed force sensor consists of a single coil as an essential part, realized in printed circuit board technology, commercially available elastomer, and ferrite core. Measurements are done wirelessly for variable values of applied force by phase-dip technique, using an external coil antenna. By applying force to the sensor, the elastomer deforms and ferrite approaches to the coil, causing changes to the inductance of the coil. As a result, the resonant frequency of the antenna-sensor system shifts toward lower frequencies. The experimental setup is conducted to test and characterize the developed force sensor. A high sensitivity of 311 kHz/N is achieved in the measured force range from 0 to 75 N. The measurement results proved the theoretical and analytical calculations, as well as the electrical simulations.

BLDC motor driver — Development of control and power electronics

This paper presents the development of control and power electronics parts for a BLDC motor drive. The signals from the most commonly used sensors for this application are used. The first one is the incremental encoder for speed and relative position detection, the other one is the three-signal Hall sensor which provides information about the absolute rotor position needed for electronic commutation. The contemporary three phase bridge driver integrated circuit used in this application provides good protection functionality to protect the bridge and the motor from excessive currents and short-circuit conditions. Hardware instead of software implementation of electronic commutation is implemented to provide more reliability. Both unipolar and bipolar PWM schemes are implemented. Besides the driver explanation, experimental results concerning speed and position control are presented.

Inverted Pendulum with a Sensored Foot

A two degrees of freedom inverted pendulum, standing on its flat foot is considered in this paper. The foot is equipped with force sensors in order to measure the vertical component of the ground reaction. The complete dynamics of the system is simulated. The usage possibility of such future measurements were further analyzed through simulation, using different motion patterns and pendulum parametrers.

Walk-Startup of a Two-Legged Walking Mechanism

There is a growing interest towards humanoid robots. One of their most important characteristic is the two-legged motion – walk. Starting and stopping of humanoid robots introduce substantial delays. In this paper, the goal is to explore the possibility of using a short unbalanced state of the biped robot to quickly gain speed and achieve the steady state velocity during a period shorter than half of the single support phase. The proposed method is verified by simulation. Maintainig a steady state, balanced gait is not considered in this paper.

Experiment platform for development of humanoid robot foot control

There is a growing interest towards humanoid robots. Our intention is to build and explore as much as possible, relatively simple elements of humanoid robots in order to gain a better understanding of their characteristics and possibilities of control. In this paper, an experiment platform of a sensored robot foot is presented. Our goal is to explore the control possibilities of this system, especially in compensating for sudden ground reaction force changes, ex. small obstacles in the ground plane or jump. In this paper, the results obtained by simulation are presented.

Inductive Displacement Sensor of Novel Design Printed on Polyimide Foil

Displacement sensors play a key role in many applications. In this paper, an inductive structure is presented which changes its inductance with deformation, which serves as a measure of displacement. The structure itself is produced by ink-jet printing on a flexible polyimide foil, using a conductive silver-based nanoparticle ink. The foil is subsequently cut in such a way to allow for extending in a direction perpendicular to the foil plane. The resulting dependence of the inductance on the amount of extension is analyzed both in calculation and experimental measurement. Calculation is done using a variation of the Neumann formula adjusted to calculating self-inductance. A simple mathematical model of the structure deformation is introduced which proved to give results very close to the results obtained by measurement. The displacement range of the experimentally verified structure is up to 25 mm; however, the structure is expected to be scalable and therefore it should be possible to adapt it to various measurement ranges.

DC Motor Drive for Small Autonomous Robots with Educational and Research Purpose

Many student robot competitions have been established during the last decade. One of them, and the most popular in Europe, is the European competition EUROBOT. The basic aim of this competition is to promote the robotics among young people, mostly students and high school pupils. The additional outcome of the competition is the development of faculty curriculums that are based on this competition. Such curriculum has been developed at the Faculty of Technical Science in Novi Sad. The curriculum duration is two semesters. During the first semester the theoretical basis is presented to the students. During the second semester the students, divided into teams of three to five students, develop the robots which will take part in the incoming EUROBOT competition. Since the time for the robot development is short, the basic electronic kit is provided for the students. The basic parts of the kit are two DC motor drives dedicated to the robot locomotion. The drives will also be used in the research concerning the multi segment robot foot. This paper presents the DC motor drive and its features. The experimental results concerning speed and position regulations and also the current limiting is presented too.

Force-dependent contact area excitation of FSR force sensor utilizing dome-shaped rubber element

This paper further investigates the novel way of exciting FSR sensors. The method introduces a force-dependent contact area excitation in which the engaged sensor area depends on the applied force. The deformation of the dome-shaped rubber element is used to introduce force-dependent contact area excitation. The assumption that the pressure distribution underneath the pressed dome-shaped rubber element is uniform is verified by the experiments.

Detection of Seat Occupancy Using a Wireless Inductive Sensor

The objective of this paper is to present an improved design of a wireless inductive sensor with novel compressive parts and its integration with a suitable mechanical device. The proposed system can be used as a seat occupancy detector with adjustable weight threshold. It consists of a sensor (inductor, steel springs, and ferrite plate), an antenna, and a mechanical device for transferring the scaled weight to the sensor. The sensor is designed in such a way that the weight applied to its surface causes the built-in springs to compression, and as a result, the reduction of the distance between the inductor and the ferrite plate, which in turn changes in the sensor’s inductance, and consequently the antenna-sensor resonant frequency, which is used as the electric output. The mechanical device, which serves as a weight converter, has also been developed. The prototype of the system is fabricated and experimentally tested in order to confirm its functionality and performance. A three-segment linear characteristic is obtained with the following sensitivities: 0.9 MHz/kg for the weights of 0–20 kg, 1.86 MHz/kg for the weights of 20–40 kg, and 0.19 MHz/kg for the weights of 40–50 kg. These results show that the developed system can detect the presence of weight and, therefore, can be used for seat occupancy detection in a vehicle safety restraint and airbag systems. It can also be used as the indicator in the airbag safety restraint systems when the occupant’s weight exceeds the defined weight threshold for the airbag activation.

Inductive tangential displacement sensor

The objective of this paper is to investigate a new design of an inductive sensor, and its application for measuring tangential displacement. The sensor consists of one stationary inductor and a movable ferrite plate relative to the inductor. Tangential displacement can be measured as a change in the overlapping area between the inductor and the ferrite plate, while their normal distance is constant. The inductance of the inductor changes, so does the resonant frequency of the antenna-sensor system when the ferrite plate moves in one - x axis direction with respect to the stationary inductor. The operating principle of the sensor is tested using the fabricated prototype. The resonant frequency of the system is wirelessly measured. The obtained sensitivity of the planar tangential inductive displacement sensor is 2.44 MHz/mm.