Akihiko Kumagai

Control of Shape Memory Alloy Actuators with a Neuro-fuzzy Feedforward Model Element

This paper describes development of a motion controller for Shape Memory Alloy (SMA) actuators using a dynamic model generated by a neuro-fuzzy inference system. Using SMA actuators, it would be possible to design miniature mechanisms for a variety of applications including miniature robots for micro manufacturing. Today SMA is used for valves, latches, and locks, which are automatically activated by heat. However it has not been used as a motion control device due to difficulty in the treatment of its highly nonlinear strain-stress hysteresis characteristic. In this paper, a dynamic model of a SMA actuator is developed using ANFIS, a neuro-fuzzy inference system provided in MATLAB environment. Using neuro-fuzzy logic, the system identification of the dynamic system is performed by observing the change of state variables (displacement and velocity) responding to a known input (input voltage to the current amplifier for the SMA actuator). Then, using the dynamic model, the estimated input voltage required to follow a desired trajectory is calculated in an open-loop manner. The actual input voltage supplied to the current amplifier is the sum of this open-loop input voltage and an input voltage calculated from an ordinary PD control scheme. This neuro-fuzzy logic-based control scheme is a very generalized scheme that can be used for a variety of SMA actuators. Experimental results are provided to demonstrate the potential for this type of controller to control the motion of the SMA actuator.

Near-minimum time feedback controller for manipulators using on-line time scaling of trajectories

A near-minimum time feedback controller for robotic manipulators with bounded input torques is developed. Since the bang-bang input torque obtained from the time-optimal control theory leaves little or no room for the extra torque of the feedback control action, it is difficult to combine a minimum time open-loop controller with an additional feedback controller. A simple solution to this problem has been to solve the minimum time problem using arbitrarily reduced torque bounds so that a torque head room is created for the feedback control action. Such a scheme, however, wastes considerable input torque potential and gives significantly larger execution time of the trajectory than the theoretical minimum time calculated from the time-optimal control theory. A stable feedback controller is developed in this paper which applies a time scaling method to move a manipulator in near-minimum time using the allowable input torques efficiently. This new feedback controller algorithm adapts to an uncertain environment and automatically adjusts the desired speed along a specified path to be as fast as possible while avoiding the velocity saturation condition. Numerical examples of the near-minimum time feedback controller are provided using a two-link SCARA manipulator.

Intelligent Detection of Boring Tool Conditions

Adaptive neuro-fuzzy inference systems (ANFIS) were used for on-line classification and measurement of tool wear for the boring of titanium parts. The input vectors consist of extracted features from cutting force data. A total of fourteen features were extracted by processing cutting force signals using virtual instrumentation. Feature selection was carried out using a Sequential Forward Search (SFS) algorithm to select the best combination of features. For the on-line classification, the outputs are boring tool conditions, which are either usable or worn out. For the on-line measurement, the outputs are estimated values of the tool wear. Using ANFIS, three features were selected for the on-line classification of boring tools. They are the average longitudinal force, average of the ratio between the tangential and radial forces, and kurtosis of the longitudinal force. Only one feature, kurtosis of the longitudinal force, was needed for the on-line measurement of tool wear using ANFIS. A 3×5 ANFIS can achieve a 100% success rate for the on-line classification of boring tool conditions. Using a 1×5 ANFIS, the average flank wear estimation error is below 5% for on-line measurement of tool wear.Copyright

Vibration Suppression Drafting Arm for Tremor Patients

Essential Tremor (ET) is a progressive neurological condition that affects over 10 million Americans. It causes a rhythmic trembling of the body that is most pronounced in the hands. Many ET patients lose the ability to perform simple yet vital tasks, such as writing. Current writing assisting devices are not able to efficiently cancel or restrict the trembling experienced by these patients when they write. We have developed a drafting arm that diminishes the arm and hand vibrations of ET patients by dampening the motion of the pen. Our design incorporates a two-segment arm with variable dampers at its joints. One end of the arm attaches to any table while the other holds a writing device. The two dampers resist the rotation at each joint. ET patients using this tool have shown significant improvement in their writing ability in comparison to using other consumer devices available today. As the final development stage, considerable effort is being put into engineering the device to be of practical use and to function well in the everyday lives of people.Copyright

Manufacturing Methods for Producing Water Pasteurization Indicators (WAPI)

Securing safe drinking water in developing countries is a significantly important problem for engineers to be aware of. Out of 6.5 billion people in the world, 1.1 billion people still do not have access to safe drinking water in their daily lives. A team lead by the Department of Biological Science at our institution developed a prototype device called Water Pasteurization Indicator (WAPI). This device is used to check if water temperature heated by a solar ray reflector panel reached above the pasteurization temperature. The WAPI consists of Carnauba wax in a polycarbonate tube with both ends sealed, a washer for adding weight and setting up the orientation of a WAPI when it is submerged in water, and a fishing string for pulling the WAPI out of water. This paper describes development of a mass-production method for WAPIs. It is essential to establish a mass production method for WAPIs so that it can be made available to people in developing countries in large quantities with an affordable price. The manufacturing method was developed considering appropriate technologies which can be adapted by people in developing countries. In addition, the manufacturing method should be simple, economical, productive, and consistent in quality of WAPIs produced. After the prototype WAPI processing device was developed, a full-factorial design of experiment (DOE) was conducted to optimize three critical process parameters for sealing both ends of a polycarbonate tube by a pair of heat-clamping plates. These parameters are claming temperature, claming time, and clamping gap. During the period of Summer 2004 through Spring 2005, approximately 2000 WAPIs were produced by the WAPI processing device and were sent to Kenya and Tanzania, and all were tested to work successfully.Copyright