Jouni Mattila

Energy-efficient motion control of a hydraulic manipulator

In this paper a novel hydraulic closed-loop motion control system has been proposed, designed and implemented on a heavy-duty 2-DOF hydraulic manipulator. A new unconventional hydraulic drive is introduced to remove the complex nonlinear interconnection between cylinder pressure levels, supply pressure and load force. The remaining nonlinear coupling of force and velocity is then removed by nonlinear controller design. New hardware combined with this proposed controller design is able to improve the controllability of the load with lower supply pressure values than conventional controllers. This leads to improved energy efficiency and is therefore of great practical and economic importance. This is a significant result since energy efficiency of closed-loop controlled hydraulics is generally known to be very low and improvements very difficult to obtain.

A novel time optimal path following controller with bounded velocities for mobile robots with independently steerable wheels

Mobile robots with independently steerable wheels possess many high maneuverability features of omnidirectional robots while benefiting from better performance and capability of moving on rough terrains. However, motion control of such robots is a challenging task due to presence of singular configurations and unboundedly large steering velocities in the neighborhood of those singularities. Many proposed approaches rely on numerical solutions that keep the robot out of bulky regions around the singular points and hence lose some of the robot maneuverability. Based on a class of traditional path followers we design a new globally stable path following controller that exploits the high maneuverability of the platform. This design allows us to derive a set of closed-form analytical functions that describe the robot base velocity as a function of the wheels driving and steering velocities while abide to the robot non-holonomic constraints. Those functions are then utilized to find the maximum instantaneous velocity of the body that keeps the wheels velocities under the pre-specified bounds no matter how much the robot gets close or far from its singular configurations. The control algorithms developed in this paper have been evaluated on iMoro, a four wheel independently steered mobile manipulator designed and developed at IHA/TUT. Experimental data is also shown that show efficacy of the method.

Geometry-aided angular acceleration sensing of rigid multi-body manipulator using MEMS rate gyros and linear accelerometers

We consider full motion state sensing of a rigid open-chain multi-body linkage assembly using rate gyros and linear accelerometers. The research is built upon micro-electromechanical systems (MEMS) components for low-cost “strap-down” implementation. Our emphasis is on direct lag-free joint angular acceleration sensing, for which a novel multi-MEMS configuration is motivated by motion control requirements. By using the multi-MEMS configuration, the bandwidth of the angular acceleration sensed is mostly proportional to the physical distances of linear accelerometers. The related joint position sensing, which is robust against linear and angular motion, is founded on the complementary and Kalman filtering principles for exclusive low delay. Experiments on a robotic vertically mounted three-link planar arm demonstrate the advantage of our key theoretical finding.

Bounded-velocity motion control of four wheel steered mobile robots

In this paper, we address the problem of motion control for a mobile robot with four independently steer and drive wheels. Our solution fully takes advantage of steerability of all wheels and provide capability of independent control of translation and rotation of the robot. Using non-linear control techniques, we provide a motion control law that makes the base follow a given desired smooth path and heading profile. Derivation of motion control is three folded. Assuming velocity vector orientation and angular velocity of the base as control signals, control laws are derived to solve the path and heading profile following problem. Then these control signals are mapped to eight actuator signals (driving and steering). In a later stage, robot base speed magnitude is controlled in such a way to keep the control signals under predefined limits. Simulations as well as experiment on a real robot show the efficacy of the proposed method.

Global path planning with obstacle avoidance for omnidirectional mobile robot using overhead camera

Path planning is one of the indispensable modules of autonomous mobile robots that delineates a collision-free path between two desired positions in an obstacle-cluttered workspace. In this paper, we propose a global path planning method in the image plane using a single overhead camera based on the principle of artificial potential fields. Our algorithm optimally fuses an image-based technique for obstacle avoidance with path planning in the image space and integrates the CAD-based recognition method. The proposed method is suitable for planning the desired path for the omnidirectional mobile robots, and it is used as an input to our previously developed path-following controller. Experiment results show the efficiency of the generated path using an overhead camera for the omnidirectional robot iMoro which is a four-wheeled, independently steered mobile robot.

The automation of multi degree of freedom hydraulic crane by using Virtual Decomposition Control

In this paper heavy-duty hydraulic crane automation is addressed by applying the Virtual Decomposition Control (VDC) approach. The VDC approach allows the control problem of the entire system to be converted into the control problem of individual components, i.e. subsystems while rigorously guaranteeing the stability of the entire system without jeopardizing the control performance. The experimental results demonstrate that the VDC approach is applicable to robust and high performance control of low-cost hydraulic multi Degree of Freedom (DOF) applications, in which the controller is challenged by a significant number of different nonlinearities and parameter uncertainties. When a VDC controller was compared with a conventional PID controller, approximately 7 times lower piston position maximum error was achieved. Moreover, a VDC controller was given roughly the same control accuracy with low, medium and high velocity trajectory references without any additional tuning, whereas the performance of the PID controller significantly changed between different velocity trajectories. The achieved results with the VDC controller are comparable with the reported state-of-the-art studies on nonlinear model-based control of hydraulic multi DOF applications.

MEMS-based state feedback control of multi-body hydraulic manipulator

This paper presents closed-loop state feedback motion control of a heavy-duty hydraulic manipulator using solely micro-electro-mechanical systems (MEMS) rate gyroscopes and linear accelerometers for joint angular position, velocity and acceleration feedback. For benchmarking, incremental encoders with 2 million counts per revolution are also used to supply the joint motion state feedback. The two motion state estimation methods are compared using Cartesian path trajectory closed-loop control experiments with both position feedback-based proportional control and motion state-based feedback control. The experiments show that the proposed MEMS-based state feedback control yields comparable tracking results compared with the high accuracy encoder. Furthermore, the MEMS-based angular acceleration estimation in particular is free from typical differentiation induced noise amplification and post-filtering phase-lag.

Unified framework for rapid prototyping of Linux based real-time controllers with Matlab and Simulink

We propose a systematic solution for real-time software development for safety critical mechatronic systems. The solution is based on Matlab/Simulink toolboxes and off-the-shelf drivers provided by hardware manufacturers, to address software development challenges in the area of PC based automation. In many cases, developers especially control systems designers found themselves immersed in technical difficulties of real-time programming and hardware interfacing. The remote development environment described here is used to develop real-time software based on Linux operating systems. Unlike other solutions that supports only limited interfaces, it demonstrates systematic methodology to develop reusable Simulink blocks for communicating with wide variety of device drivers and services. Some examples are given based on Xenomai realtime Linux. As a case study, the software development for a mobile robot based on this methodology is presented. The models and blocks developed for this study are available to interested developers for download and test.

Geometry-aided MEMS motion state estimation for multi-body manipulators

We consider full motion state sensing of a rigid multi-body linkage assembly using rate gyros and linear accelerometers. The research is built upon micro-electromechanical systems (MEMS) components for low-cost “strap-down” implementation. An open-chain geometrical assembly motion model is proposed and validated experimentally using a minimum MEMS-configuration per link. The related inclination sensing, which is robust against linear and angular motion effects, proceeds in a novel cascaded manner and is founded on the complementary and Kalman filtering principles for exclusive low delay. This is demonstrated by a suite of experiments on a robotic vertically mounted three-link planar arm rig.

A New Hybrid Approach for Augmented Reality Maintenance in Scientific Facilities

Maintenance in scientific facilities is a difficult issue, especially in large and hazardous facilities, due to the complexity of tasks and equipment. Augmented reality is a technology that has already shown great promise in the maintenance field. With the help of augmented reality applications, maintenance tasks can be carried out faster and more safely. The problem with current applications is that they are small-scale prototypes that do not easily scale to large facility maintenance applications. This paper presents a new hybrid approach that enables the creation of augmented reality maintenance applications for large and hazardous scientific facilities. In this paper, a new augmented reality marker and the algorithm for its recognition is proposed. The performance of the algorithm is verified in three test cases, showing promising results in two of them. Improvements in robustness in the third test case in which the camera is moving quickly or when light conditions are extreme are subject to further studies. The proposed new approach will be integrated into an existing augmented reality maintenance system.