Arto Visala

Current state of digital signal processing in myoelectric interfaces and related applications

Abstract This review discusses the critical issues and recommended practices from the perspective of myoelectric interfaces. The major benefits and challenges of myoelectric interfaces are evaluated. The article aims to fill gaps left by previous reviews and identify avenues for future research. Recommendations are given, for example, for electrode placement, sampling rate, segmentation, and classifiers. Four groups of applications where myoelectric interfaces have been adopted are identified: assistive technology, rehabilitation technology, input devices, and silent speech interfaces. The state-of-the-art applications in each of these groups are presented.

Simultaneous Localization and Mapping for Forest Harvesters

A real-time SLAM (simultaneous localization and mapping) approach to harvester localization and tree map generation in forest environments is presented in this paper. The method combines 2D laser localization and mapping with GPS information to form global tree maps. Building an incremental map while also using it for localization is the only way a mobile robot can navigate in large outdoor environments. Until recently SLAM has only been confined to small-scale, mostly indoor, environments. We try to addresses the issues of scale for practical implementations of SLAM in extensive outdoor environments. Presented algorithms are tested in real outdoor environments using an all-terrain vehicle equipped with the navigation sensors and a DGPS receiver.

Tree Measurement in Forest by 2D Laser Scanning

Measurement of tree parameters, particularly tree diameter and location, in connection to forest harvesters, is discussed. Diameters are determined from laser scanner measurements using a simple method based on edge points of a feature, in addition to the point with the shortest range to the scanner. The measurement height is equal to 1.3 m from the ground. The data for this research have been collected in a pine forest using a 2D laser scanner mounted on a mobile ATV platform. The error of the tree diameter calculations is 4% in average. The evaluation of the tree localization is based on manually measured reference data of the forest.

Functional state modelling approach for bioprocesses: local models for aerobic yeast growth processes

Abstract The functional state of a process is a novel concept which helps in monitoring and control of complex processes such as bioprocesses. The concept was introduced originally by Halme. The main idea is to use a two-level hierarchy where on the top level the process is divided into macrostates, called functional states, according to behavioural equivalence. In a functional state, the process is described by a conventional type of model which is valid in this functional state — called the local model. To illustrate further the concept of functional state in fermentation processes, experimental data and simulations of an aerobic fed-batch bakers yeast fermentation are presented. It is shown how this process can be divided into functional states by considering the cell metabolism in more detail, how the local models can be obtained, and how the functional states of a fed-batch bakers yeast fermentation and recognized on-line. By simulation and comparing the results to experimental data, it is further shown how the concept works in practice. The results are also used to demonstrate an optimal substrate feed control policy.

Tree Measurement and Simultaneous Localization and Mapping System for Forest Harvesters

For the last decades, measurement and automation systems in Nordic cut-to-length forestry machines have evolved gradually. These heavy duty machines are lighter, faster and more accurate than ever before but the basic technologies and operation have remained the same. In many respects, their current automation systems have reached their limits. The Forestrix project studies how advances in mobile robotics could be applied in the field of forestry machine automation. Machine vision systems and scanning laser range finders have established themselves as standard equipment in mobile robotics. With the new sensor and computing technologies it is possible to get information about the surrounding forest, such as tree diameters, positions and stand density. This information can be used on-line in operator’s decision support system, or off-line in a forest asset management system. This paper describes the prototype measurement platform and the software algorithms developed in the Forestrix project. Results from tests with an all terrain vehicle are also presented.

Functional state modeling and fuzzy control of fed-batch aerobic baker's yeast process

Abstract A novel concept of functional state in combination of local modeling is presented as an aid in monitoring and control of complex bioprocesses. On the basis of this approach a fuzzy substrate feed rate control scheme for fed batch aerobic bakers yeast process is proposed. The control algorithm was modified to advantage by including a fuzzy term. The controlled variables were either respiratory quotient or specific growth rate estimated on-line. Effective and precise operation of the system was demonstrated by computer simulation.

OPEN CONFIGURABLE CONTROL SYSTEM FOR PRECISION FARMING

The goal of Agrix project is to develop a prototype of an open, generic and configurable automation platform for agricultural machinery. A typical configuration consists of a tractor and one or several implements. The main purpose of realizing the fast-prototype of the control system in 2003 was to get acquainted with the problems occurring in working with agricultural machines. Experiences from the fast-prototype are reported in this paper. The agricultural implement selected for the fast-prototype was a combined seed and fertilizer drill. The original hydraulic system was replaced with a new electro-hydraulic valve block. The tractor was equipped with ISOBUS (ISO 11783) compatible electronic control unit. A commercial CAN-controller with a high-power digital and analog I/O interface was used as the implement electronic control unit. The architecture of Agrix fast-prototype was designed according to ISOBUS standard. In industrial automation, standard inexpensive PCs are used as Human Machine Interface (HMI). Accordingly, it was tested if a standard PDA or handheld could be used as HMI or user terminal for the implement. The Agrix fast-prototype was finally tested in real drilling of wheat. The ISOBUS standard is very important as an open communication standard for agricultural machines. However, it does not have any features to support configurability. The biggest problems occurred with the PDA. Its display is quite small to be used as HMI in a moving vehicle. The inexpensive external keyboard was a bit too vague for its purpose. The processing power of the PDA was quite limited for this kind of use and real-time problems emerged in some situations.

Low-cost positioning system for agricultural vehicles

Accurate positioning is needed for agricultural vehicles now and in the future. Position is currently needed for mapping, precision farming, auto-steering vehicles and light-bar navigation and in the future for agrorobotic solutions. Although the accuracy of GPS based positioning can be improved using differential or RTK-solutions, such application may be too highly-priced. In this paper tractor positioning with a cheap GPS-receiver is improved by using inertial navigation and odometry. Kalman filtering is used for sensor fusion. In compensation of the bias type slow error in GPS measurements the low cost additional measurements are not sufficient. However, positioning in blind areas of GPS can be done with them.

New Measurement Concept for Forest Harvester Head

A new measurement concept for cut-to-length forest harvesters is presented in this paper. The cut-to-length method means that the trees are felled, delimbed and cut-to-length by the single-grip harvester before logs are transported to the roadside. The concept includes measurements done to standing trees before felling to calculate optimal length of logs. The modern forest harvesters use mechanical measurements for diameter and length.

Nonlinear Model Predictive Trajectory Control in Tractor-Trailer System for Parallel Guidance in Agricultural Field Operations

So called automatic guidance systems are becoming more common in agricultural tractors, so that a driver does not need to steer the vehicle. The systems are mostly relying on GPS with correction. However, these systems usually steer only the tractor itself, despite the fact that the implement is the one that has to be run side by side with the previous swath. With towed implements, or trailers, it is not easy to keep the position of implement on track if the angle of the steering wheels of a tractor is the only resource under control. In this paper, a system with a standard tractor with front steering wheels and an active joint in the drawbar of the trailer are both controlled by the automatic guidance system. Besides, the positioning is not only based on GPS, but also with a local sensor that detects an edge of the previous swath; and this sensor is installed on the trailer. To control this system with two inputs and two outputs with nonlinear kinematics, a multivariable controller is needed for trajectory control. In the paper, an approach to the trajectory control in case of the tractor-trailer system with nonlinear model predictive control (NMPC) is studied. The test results show that the performance is better than with linear model predictive control that was tested in earlier study. Tests were done in driving speeds 8, 10 and 12 km/h. In a curved path, the tractor following error was typically less than 12 cm and in the implement less than 8 cm. The constant control cycle is achieved by alternating the prediction horizon length. By that way, the best possible solution is always gained at the limits of computation time.