Kalevi Huhtala

Autonomous Motion Control of a Wheel Loader

This paper addresses the problem of autonomous control of a hydraulically actuated articulated-frame-steering (AFS) mobile machine— a wheel loader. Our autonomous motion control system includes a mission planning graphical user interface, an improved odometry algorithm and a GPS device for navigation purposes, together with a model based path-following control strategy, and speed control. The test platform is a small prototype wheel loader based on Avant-635 whose hydraulic components are substituted by electrically controlled equivalents. System development and preliminary calibrations are done using GIMsim— an elaborated semi-empirical hardware-in-the-loop simulator. Some field experiments are presented that demonstrate satisfactory performance of the system at this stage. Further tunings are required to reach a desired performance.Copyright

Position-based visual servoing for pallet picking by an articulated-frame-steering hydraulic mobile machine

This paper addresses a visual servoing problem for a mobile manipulator. Specifically, it investigates pallet picking by using visual feedback using afork lift truck. A manipulator with limited degrees of freedom and differential constraint mobility together with large dimensions of the machine require reliable visual feedback (pallet pose) from relatively large distances. To address this challenge, we propose a control architecture composed of three main sub-systems: (1) pose estimation: body and fork pose estimation in the pallet frame; (2) path planning: from the current pose to the origin (pallet frame); and (3) feedback motion control. In this architecture, the pallet becomes the local earth fixed frame in which poses are resolved and plans are formulated. Choosing the pallet as the origin provides a natural framework for fusing the wheel odometry/inertial sensor data with vision, and planning is required only once the pallet is detected for the first time (because the target is always the origin). Visual pallet detection is non-real-time and unreliable, especially owing to large distances, unfavorable vibrations, and fast steering. To address these issues, we introduce a simple and efficient method that integrates the vision output with odometry and realizes smooth and non-stop transition from global navigation to visual servoing. Real-world implementation on a small-sized forklift truck demonstrates the efficacy of the proposed visual servoing architecture.

The Electro-Hydraulic Valve Actuation (EHVA) for Medium Speed Diesel Engines - Development Steps with Simulations and Measurements

Electro-Hydraulic Valve Actuation (EHVA) is one of the most promising ways to improve the performance and reduce the emissions of the diesel engines. The EHVA gives fully variable lift and event duration of the gas exchange valves and thus the combustion process can be better controlled in different operation points such as idle and partial load situation. Also totally new kind of gas exchange processes are possible to achieve. This paper consists of alternative solutions of EHVA systems, the comparison of them by means of simulation and measurements, the empirical tests of EHVA system in a laboratory and finally conclusion and future research activities. The developed EHVA system fulfills the requirements very well. The lift of the gas exchange valve is fast enough, and the seating velocity is under control. The system is able to run with open and closed loop control.

A Survey of Analysis, Modeling, and Diagnostics of Diesel Fuel Injection Systems

Diesel engines are widely used due to their high reliability, high thermal efficiency, fuel availability, and low consumption. They are used to generate power, e.g., in passenger cars, ships, power plants, marine offshore platforms, and mining and construction machines. The engine is at heart of these applications, so keeping it in good working condition is vital. Recent technical and computational advances and environmental legislation have stimulated the development of more efficient and robust techniques for the diagnostics of diesel engines. The emphasis is on the diagnostics of faults under development and the causes of engine failure or reduced efficiency. Diesel engine fuel injection plays an important role in the development of the combustion in the engine cylinder. Arguably, the most influential component of the diesel engine is the fuel injection equipment; even minor faults can cause a major loss of efficiency of the combustion and an increase in engine emissions and noise. With increased sophistication (e.g., higher injection pressures) being required to meet continuously improving noise, exhaust smoke, and gaseous emission regulations, fuel injection equipment is becoming even more susceptible to failure. The injection systems have been shown to be the largest contributing factor in diesel engine failures. Extracting the health information of components in the fuel injection system is a very demanding task. Besides the very time-consuming nature of experimental investigations, direct measurements are also limited to selected observation points. Diesel engine faults normally do not occur in a short timeframe. The modeling of typical engine faults, particularly combustion related faults, in a controlled manner is thus vital for the development of diesel engine diagnostics and fault detection. Simulation models based on physical grounds can enlarge the number of studied variables and also obtain a better understanding of localized phenomena that affect the overall behavior of the system. This paper presents a survey of the analysis, modeling, and diagnostics of diesel fuel injection systems. Typical diesel fuel injection systems and their common faults are presented. The most relevant state of the art research articles on analysis and modeling of fluid injection systems as well as diagnostics techniques and measured signals describing the behavior of the system are reviewed and the results and findings are discussed. The increasing demand and effect of legislation related to diagnostics, especially on-board diagnostics (OBD), are discussed with reference to the future progress of this field.

Constrained Global Path Optimization for Articulated Steering Vehicles

This paper proposes a new efficient path-planning algorithm for articulated steering vehicles operating in semi-structured environments, in which obstacles are detected online by the vehicles sensors. The first step of the algorithm is offline and computes a finite set of feasible motions that connect discrete robot states to construct a search space. The motion primitives are parameterized using Bézier curves and optimized as a nonlinear programming problem (NLP) equivalent to the constrained path planning problem. Applying the A* search algorithm to the search space produces the shortest paths as a sequence of these primitives. The sequence is drivable and suboptimal, but it can cause unnatural swerves. Therefore, online path smoothing, which uses a gradient-based method, is applied to solve another NLP. Numerical simulations demonstrate that performance of the proposed algorithm is significantly better than that of existing methods when determining constrained path optimization. Moreover, field experimental results demonstrate the successful generation of fast and safe trajectories for real-time autonomous driving.

Constrained path optimization with Bézier curve primitives

This article suggests a novel path planning algorithm for a non-holonomic wheeled vehicle operating in a semi-structured environment. The first step of the algorithm is to compute offline a finite set of feasible motions connecting discrete robot states to construct a search graph. The motion primitives based on Bézier curves are generated by solving the constrained optimization problem (COP). Applying A* on the search graph produces paths in the form of a sequence of the primitives. Although the sequence is drivable and suboptimal, we perform online path smoothing to remove the jerky or extraneous motions. The post-procedure is done by using a gradient based method to solve another COP. The numerical simulations show remarkable performance improvement in the constrained path optimization by applying our algorithm, compared to other existing works. Also, field experimental results demonstrate successful generation of fast and safe trajectories for real-time autonomous driving.

Fuel optimal controller for hydrostatic drives and real-world experiments on a wheel loader

Abstract In this study, we design a fuel optimal controller for hydrostatic drive transmissions (HSD) that significantly improves their fuel economy. Contrary to great proportion of the literature, efficacy of the controller is demonstrated by real machine implementation equipped with online fuel consumption measurement system. The main control objective of the devised controller is to minimise consumed fuel per travelled distance. Control commands are determined utilizing steady-state equations of the system, which facilitates real-time implementation. Dynamic situations are addressed with auxiliary functions running at higher frequency than the fuel economy part of the controller. The machine is a 5-ton wheel loader with pure HSD and no energy storage devices installed. In addition, all the components are commercially available. Thus, structure of the HSD and presented improvements in fuel economy are comparable to commercial machines and retrofitting existing drive-by-wire machinery with proposed controller will require little cost. The optimal controller is compared to a rule-based alternative that is based on a control method utilized in commercial wheel loaders. In autonomously driven drive cycles, measured total fuel consumption reduced up to 16.6% with the devised controller. In addition, the functionality of the controller is proven in extreme hill climbing tests.

A mapping method tolerant to calibration and localization errors based on tilting 2D laser scanner

Autonomous mobile machines use onboard sensors for navigation and obstacle avoidance. The accuracy of the sensor data in global frame is however dependent on the localization accuracy of the machine. Simultaneous localization and mapping algorithms (SLAM) are widely used with 3D laser scanners for mapping the world. They use scan matching algorithms to solve the accuracy problem by matching prior sensor data of the environment with the newly acquired data. However matching scans is not always possible. Insufficient amount of prior data or too few features in the scan can prevent the scan matching algorithm from finding a match. Thus it is important that also the mapping algorithm is tolerant to some degree of error in localization and calibration. We present a method for generating obstacle maps from smaller data segments at a time, thus making the mapping system more tolerant to navigation and calibration errors. The obstacle mapping method is tested with modified Avant multipurpose loader.

Fuel Optimal Controller for Hydrostatic Drives: A Simulation Study and Model Validation

This paper presents an optimal controller for fuel efficiency of a hydraulic mobile machine with hydrostatic drive (HSD). The solution is validated using a semi-empirical simulated research platform. The drive transmission of the machine includes one variable displacement hydraulic pump and four two-speed hub motors. There is no energy storage installed. Thus, the structure of the HSD and presented improvements in fuel economy are comparable to traditional machines.The optimal controller is compared to a baseline controller that intuitively keeps the components at their high efficiency regions. In simulated hill tests, fuel economy was improved by up to 25.9 % depending on the slope of the hill and velocity reference.Copyright

Synchronization and more intelligent control in teleoperation process on skid steered mobile machine

This paper is a step forward in my research work about creating more intelligence in wireless teleoperation on hydraulics mobile machines. This paper deals with the importance of synchronization in the data transference between different elements to provide a reliable connection during the teleoperation process. A new module (G.P.S. receiver) is installed into the system to provide information about location and heading of the hydraulic mobile machine. In the future this information will be used to enable more autonomous teleoperation.