Bengt Oelmann

Joint-Angle Measurement Using Accelerometers and Gyroscopes—A Survey

This paper presents an analysis of rigid-body joint-angle measurement based on microelectromechanical-system (MEMS) biaxial accelerometers and uniaxial gyroscopes. In comparison to conventional magnetic and optical joint angular sensors, this new inertial sensing principle has the advantages of flexible installation and true contactless sensing. This paper focuses on the comparison of four different inertial-sensor combination methods that are reported in reference papers and utilizes the theory of rigid-body kinematics to explain and analyze their advantages and weaknesses. Experiments have also been conducted to further verify and strengthen the arguments put forward in the analysis. All experiments in this paper took place on a custom-built rigid-body robot arm model that can be manipulated by hand. Sensor calibration and accelerometer alignment issues are also described, and their details are discussed. The experiment results presented in this paper show significant differences with reference to the achieved angular accuracy for various situations when using the four different sensor combination methods. In some cases, the angular error based on one method is more than 0.04 rad, while that from another method is within ±0.005 rad. The noise levels of angular readings from different methods are also experimentally compared and analyzed. The conclusion drawn serves to guide readers toward a suitable method for their particular application.

Architecture Exploration for a High-Performance and Low-Power Wireless Vibration Analyzer

Vibration based condition monitoring is considered to be the most effective method for analyzing the performance of rotating machinery and for early fault detection. Traditional vibration analyzers used for this purpose provide wired interface(s) to connect sensors with the system that analyzes the vibration data. A wireless vibration analyzer can be useful to monitor and analyze the vibration of rotating as well as inaccessible parts of the machinery. However, for a wireless vibration analyzer, both the performance and power consumption are of major concern, especially for real-time tri-axes (horizontal, vertical, and axial) vibration data processing and analyses at a high sampling rate. To evaluate the performance of such an analyzer, we explore different architectures in order to realize a high-performance and low-power wireless vibration analyzer that can be used in addition to traditional analyzers. For this purpose, four different architectures have been implemented in order to evaluate them in terms of performance, power consumption, cost, and design complexity.

Printed touch sensor for interactive packaging and display

In this work we present a study on the performance of printed touch sensor fabricated using conductive ink on paper substrates. The sensor system is intended to add values in surveillance of packages or in interactive point-of-purchase displays. The printed sensor changes its capacitance when it is touched or manipulated. The capacitance variations are readout using either a wireless or wired communication link. The most advanced system will utilize RFID or ZigBee readout technology while the simplest systems utilize a simple analog wire solution. The sensor technology has been developed to be easily integrated into high quality prints targeting applications such as large area touch sensitive commercial stands, flat keyboards at point-of-purchase and touch and manipulation surveillance in logistic chains.

Enabling Battery-Less Wireless Sensor Operation Using Solar Energy Harvesting at Locations with Limited Solar Radiation

Environmental monitoring applications demand wireless sensor networks to operate over a long period of time. Although energy consumption of these systems has been tremendously reduced, lifetime of sensor nodes is still limited by the capacity and lifetime of batteries used as energy sources. Energy harvesting, and in outdoor deployments particular, solar energy harvesting becomes a suitable way of powering wireless sensor nodes as their power consumption decreases. In this paper we address the feasibility of battery-less operation of wireless sensor nodes using solar energy harvesting at locations where the amount of solar radiation is severely limited and seasonal variations are large. We present two circuit architectures optimized for low energy leakage and evaluate their performance based on data gathered in a deployment during winter in Sundsvall, Sweden. We show that both architectures allow operation of sensor nodes even in the darkest period of the year. Furthermore comparisons between the two architecture designs are provided.

Mixed synchronous/asynchronous state memory for low power FSM design

Finite state machine (FSM) partitioning proves effective for power optimization. In this paper we propose a design model based on mixed synchronous/asynchronous state memory that results in implementations with low power dissipation and low area overhead for partitioned FSMs. The state memory here is composed of the synchronous local state memory and asynchronous global state memory, where the former is used to distinguish the states inside a sub-FSM, and the latter is responsible for controlling sub-FSM communication. The input and output behaviour of the decomposed FSM is cycle by cycle equivalent to the undecomposed synchronous FSM. Together with clock gating technique, substantial power reduction can be demonstrated.

Asynchronous control of low-power gated-clock finite-state-machines

An efficient approach to reduce power consumption in a synchronous Finite-State Machine (FSM) is to de-compose it, according to a partitioning algorithm, to a number of sub-FSMs that interact through some communication signals. Only one sub-FSM is clocked at a time and low power operation is obtained by only clocking the active sub-FSM. In this paper we introduce a new asynchronous communication control for the interacting sub-FSMs, which reduces the total capacitance switched by the system clock. Experimental results show that this leads to significant power savings when the FSM is partitioned into many sub-FSMs.

Design and Implementation of a Stator-Free RPM Sensor Prototype Based on MEMS Accelerometers

This paper presents the design and implementation of a prototype of a stator-free revolutions-per-minute (RPM) sensor based on two microelectromechanical-system uniaxial accelerometers. This paper first introduces the operating principle of the stator-free RPM sensor. It then discusses the associated architecture and design issues of this new sensing method. It then describes the detail of the prototype sensor hardware and software design of the common-mode rejection method and its signal processing. Experiments using the prototype sensor have been also conducted to further verify and strengthen the arguments put forward in the previous discussion. All experiments in this paper took place on a lathe machine in a laboratory. Sensor calibration under a MATLAB environment is also described. Experimental results confirm the interesting property of this sensor, namely, that it provides higher precision at higher RPM. The conclusion summarizes the design considerations, the experimental results, and the motivation in relation to future works for this stator-free RPM sensing method.

Real-Time Reconfigurable Subthreshold CMOS Perceptron

In this paper, a new, real-time reconfigurable perceptron circuit element is presented. A six-transistor version used as a threshold gate, having a fan-in of three, producing adequate outputs for threshold of T = 1,2 and 3 is demonstrated by chip measurements. Subthreshold operation for supply voltages in the range of 100-350 mV is shown. The circuit performs competitively with a standard static complimentary metal-oxide-semiconductor (CMOS) implementation when maximum speed and energy delay product are taken into account, when used in a ring oscillator. Functionality per transistor is, to our knowledge, the highest reported for a variety of comparable circuits not based on floating gate techniques. Statistical simulations predict probabilities for making working circuits under mismatch and process variations. The simulations, in 120-nm CMOS, also support discussions regarding lower limits to supply voltage and redundancy. A brief discussion on how the circuit may be exploited as a basic building block for future defect tolerant mixed signal circuits, as well as neural networks, exploiting redundancy, is included.

Analysis of the IEEE 802.15.4 Standard for a Wireless Closed Loop Control System for Heavy Duty Cranes

In this paper the use of the IEEE 802.15.4 standard in a wireless control system is analyzed and discussed. The standard is described and applied on a heavy duty crane application and the discussion focuses on the possibilities and limitations of the standard in the application. A formula is presented which can be used to calculate maximum sample rate according to the number of sensor nodes and the payload the nodes may carry. The discussion reveals that the standard may be utilized in the crane application but that it is not a good solution. Several limitations within the standard, such as network size and system sample rate, will put a stop to future extensions of the wireless control system. As a result, the 802.15.4 standard protocol shall not be employed in the heavy duty crane application.

Multifunction subthreshold gate used for a low power full adder

This paper presents a full-adder based on realtime reconfigurable CMOS perceptron circuits operating in subthreshold. The Perceptron is based on three output wired inverters that is configured through well biasing. The full-adder is demonstrated by simulations for a 0.12 um CMOS process. Functionality is proven for 200-400 mV power supply voltages. Minimum power consumption is 7.4 nW and power-delay-product 7.8 fJ, for a Vdd of 200 mV, according to simulations.