Kalervo Nevala

Shape Control of a FRP Airfoil Structure Using SMA-Actuators and Optical Fiber Sensors

The aim of this work was to design a control system for the shape memory alloy (SMA) actuator operated airfoil (a cross section of wind turbine blade). Design of SMA control is focused on the reliable operation of the SMA actuators. The actuator should follow the targeted shape accurately and without too much delay. Another objective is to avoid overheating which is the most critical damage to the structure. SMA actuator shape control is in principle possible to do with any position control method, but the specific properties of the SMA actuators, like the hysteresis, the first cycle effect and the long term changes, need to be taken into account. In this work, a wing profile prototype was measured using optical fiber sensors and traditional strain gauges. Also, external laser sensors were used to measure displacements of upper/lower surface and trailing edge. Shape change was obtained by embedding SMA wire actuators into fiber reinforced polymer (FRP) composite structure. SMA actuators were laminated in such way that bending of trailing edge is always downwards. Actuators are activated with Joule heating and the temperature is measured with integrated thermocouples and optical fiber temperature sensors. As a result, this work gave information about the usability of optical fibers sensors in active FRP composite structures. Measurements also give information about the efficiency of SMA actuators in shape control of relatively stiff FRP structures.

Comparison of position control algorithms of embedded shape memory alloy actuators

This paper presents a comparison of the algorithms for control of shape memory alloy (SMA) actuators. An adaptive airfoil is a case of smart composites which utilize embedded SMA actuators. The airfoil is deformed by the SMA actuators which are heated with electric current. The controller adjusts the electric current of the actuators to reach the desired shape of the airfoil.

Development of an accuracy assessment phantom for surgical navigators

The objective of this study was to design a calibration phantom for a surgical navigator used in a hospital environment. It addresses two major issues: the design of an accuracy phantom and the accuracy analysis of the surgical navigator in a hospital setting. The designed phantom was used to assess the accuracy of the optical tracking modality of the surgical navigator used at Oulu University Hospital, Oulu, Finland. The phantom functioned according to the design criteria, it was easy to use and it had enough calibration points that were localized by the navigator according to the accuracy assessment protocol to assess the accuracy error. The distances measured from a fixed origin with the surgical navigator were compared to the known phantom calibration point coordinates. The mean error was within the manufacturer specifications of 1.00 mm. The analysis done using the designed phantom and accuracy assessment protocol showed that the error increased with the distance from the center of the phantom. The accuracy assessment protocol using the present phantom proved to be a suitable method for accuracy analysis of a surgical navigator in a hospital setting.

Digital Product Process for Construction Product Industry

A large research program of digital product process has been active (2008-2012) in Finland. The goal of the program has been to increase customer orientation and productivity in company networks that design and deliver products, systems and services to global markets. For small and medium sized companies the developing of multitechnical products usually has to be done in a network of companies. This requires a lot of data transfer and integration between various computer systems. To improve these processes the research project “Developing the digital product process of multitechnical products to improve the designing and manufacturing of small series product” (Monidigi) has been started. The aim of the Monidigi research was to improve the design process by using solely digital product information that is handled by proper product lifecycle management systems. The product development is guided by the philosophy of the digital prototype that is tested in a virtual working environment. Products are modeled in 3D and developed by various simulations and analyses before real prototypes are made. This allows a flexible design process and coordinated change management. Digital product processes allow easy data transfer, collaborated engineering and modern manufacturing in a network of companies. Several examples and development possibilities and the state of the art in construction industry are introduced and evaluated.

Model-Based Control of SMA Actuators with a Recurrent Neural Network in the Shape Control of an Airfoil

This paper describes the development of a neural network control for shape memory alloy (SMA) actuators as well as the control tests. Precise control of SMA actuators that are integrated in the composite structure is difficult because of the hysteretic behaviour of SMA and time delays in the control system. The weakness of the static model of SMA is that it does not take into account the actuator dynamics. The NARMA-L2 neural network model enables us to solve the inverse dynamic model of the nonlinear discrete-time dynamical system. In this study the NARMA-L2 model of the airfoil (a cross section of wind turbine blade) was created using Matlab Simulink software and neural networks. Data for network training was measured from the specimen. The performance of the constituted NARMA-L2 controller was tested in control tests. According to the control tests the NARMA-L2 controller is well suited for controlling embedded SMA actuators. The constituted controller enabled fast and stable actuation in step responses and it was also able to compensate for changes in cooling conditions.

Enhancing the Accuracy of MRI-Compatible Robots with an Optical Tracking System

Magnetic resonance imaging (MRI) is currently a widely used technology for obtaining a three-dimensional image of a patient’s internal structures. This study examines the measurement properties of an optical tracking system utilised in the MRI room. The results were used to assess the suitability of the device to be used as a part of the control system of a surgical robot. The position and orientation of the instrument, MRI scanner and the patient are measured using an optical tracking system in the MRI room. The measurement data can be used to display the instrument used as a part of the image of the patient. The optical tracking system used in the MRI room can also be considered as a part of the control system of a robot located in the room. When considering such use, the operations of the measuring device in different measurement conditions must be known. In terms of robot control, it is important to know the deviation attributed to measurement when defining the translation vector and orientation between two trackers. Five measurement series were carried out using the measurement device to examine the deviation in the translation vector and orientation data between two trackers. The distance and position between the trackers were changed between the measurement series. During the measurement series, the measurement device was moved to different distances from the trackers and the translation vector and orientation between the trackers were defined on the basis of the measurement results obtained. The measurements showed that the deviation of the translation vector did not significantly change as the measurement distance increased, but the deviation of orientation data between different trackers increased significantly. Deviation in the translation vector increased as the distance between trackers increased, but deviation in orientation did not change significantly.

Automation of an Excavator Based on a 3D CAD Model and GPS Measurement

This study examines the possibilities of controlling a six degrees of freedom excavator with the final objective of controlling the movements of the excavator by using a CAD model of the road surface. Compared to the traditional excavator with 4 DOF, the excavator was provided with two additional degrees of freedom by applying the 2 DOF Rototilt, an accessory commonly in use. The advantages of automation are faster process of working and less demands on the operator. To study this problem, an Msc.Adams with Matlab/Simulink simulation environment was used.