Design of a Haptic Arm Exoskeleton for Training and Rehabilitation

A high-quality haptic interface is typically characterized by low apparent inertia and damping, high structural stiffness, minimal backlash and absence of mechanical singularities in the workspace. In addition to these specifications, exoskeleton haptic interface design involves consideration of additional parameters and constraints including space and weight limitations, workspace requirements and the kinematic constraints placed on the device by the human arm. In this context, we present the design of a five degree-of-freedom haptic arm exoskeleton for training and rehabilitation in virtual environments. The design of the device, including actuator and sensor selection, is discussed. Limitations of the device that result from the above selections are also presented. The device is capable of providing kinesthetic feedback to the joints of the lower arm and wrist of the operator, and will be used in future work for robot-assisted rehabilitation and training.

High Speed Ring-Based Distributed Networked Control System for Real-Time Multivariable Applications

A networked control system (NCS) is a control architecture where sensors, actuators and controllers are distributed and interconnected. It is advantageous in terms of interoperability, expandability, installation, volume of wiring, maintenance, and cost-effectiveness. Many distributed network systems of various topologies and network type have been developed, but NCS systems tend to suffer from such issues as nondeterminism, long network delays, large overheads and unfairness. This paper presents the ring-based protocol, called the ExoNet, and its network architecture which are built to achieve better performance as a distributed networked system. A Cypress transceiver CY7C924ADX is applied to the network as a communication unit. The protocol is based on the transceiver and developed to achieve fast communication and allowable latency for controls with high control loop frequency. Compared with other standard network types such as Ethernet, ControlNet or DeviceNet, the network is characterized by its ring-based architecture, simple message and packet formats, one-shot distribution of control data and collection of sensor data, multi-node transmission, echo of a message, and other features. The network also guarantees determinism, collision-free transmission, relatively small overhead, fairness between nodes and flexibility in configuration. Its analysis and comparison with these network types are also provided and its application on the Berkeley Lower-Extremity Exoskeleton (BLEEX) is described.

Nonlinear Positioning Compensation of Thin-Disc Ultrasonic Motor Using Fuzzy Sliding-Mode Control

The study intends to focus on the design of a thin-disc piezoceramic-driving ultrasonic actuator dedicated to discrete stepping motors. By the improved design and construction, the innovative ultrasonic actuator was developed and used as a stator. The electromechanical coupling characteristics based on the composite structure would produce the flexural wave on the stator, which consisted of a piezoceramic membrane bonded on a metal sheet. Due to the converse piezoelectric effect, the driving ability of the actuator came from the vibration of extension-shrinkage of a metal sheet corresponding to the frequency of a single-phase AC power. Under constraints at the specific geometry positions on the metal sheet, the varying behaviors of flexural waves were formed. The simple structure of an actuator demonstrated that the mechanical design of the actuator and the rotor could be separated, depending on what we need in pragmatic applications. And, its positioning accuracy could be reached through a closed loop servo control, i.e. Fuzzy Sliding Mode Control (FSMC). FSMC was used to automatically compensate nonlinearly mechanical behaviors such as dead-zone and hysteresis phenomena. Furthermore, FSMC scheme has successfully overcome the high frequency chattering phenomena with lower control effort while the motor is applied to position tracking, and also has been proven in the excellent robust ability for noise rejection.

A Multi-Cylinder HCCI Engine Model for Control

Homogeneous charge compression ignition (HCCI) engines are a promising engine technology due to their low emissions and high efficiencies. Controlling the combustion timing is one of the significant challenges to practical HCCI engine implementations. In a spark-ignited engine, the combustion timing is controlled by the spark timing. In a Diesel engine, the timing of the direct fuel injection controls the combustion timing. HCCI engines lack such direct in-cylinder mechanisms. Many actuation methods for affecting the combustion timing have been proposed. These include intake air heating, variable valve timing, variable compression ratios, and exhaust throttling. On a multi-cylinder engine, the combustion timing may have to be adjusted on each cylinder independently. However, the cylinders are coupled through the intake and exhaust manifolds. For some of the proposed actuation methods, affecting the combustion timing on one cylinder influences the combustion timing of the other cylinders. In order to implement one of these actuation methods on a multi-cylinder engine, the engine controller must account for the cylinder-to-cylinder coupling effects. A multi-cylinder HCCI engine model for use in the control design process is presented. The model is comprehensive enough to capture the cylinder-to-cylinder coupling effects, yet simple enough for the rapid simulations required by the control design process. Although the model could be used for controller synthesis, the model is most useful as a starting point for generating a reduced-order model, or as a plant model for evaluating potential controllers. Specifically, the model includes the dynamics for affecting the combustion timing through exhaust throttling. The model is readily applicable to many of the other actuation methods, such as variable valve timing. Experimental results validating the model are also presented.

Development and Validation of Online Models With Parameter Estimation for a Building Zone With VAV System

The energy consumption by building heating, ventilating, and air conditioning (HVAC) systems has evoked more attention for energy efficient HVAC control and operation. Application of advanced control and operation strategies requires robust online system models. In this research, online models with parameter estimation for a building zone with variable air volume (VAV) system, which is one of the most common HVAC systems, are developed and validated using experimental data. Building zone temperature and VAV entering air flow are modeled based on physical rules and using only the measurements that are commonly available in a commercial building. Different series of validation tests were performed in a real-building test facility to examine the prediction accuracies for system outputs. Using the online system models with parameter estimation, the prediction errors for all the validation tests are less than 0.5°F for temperature outputs, and less than 50 ft3/min for air flow outputs. The online models can be further used for local and supervisory control, as well as fault detection applications.

Geometric Design of Symmetric 3-RRS Constrained Parallel Platforms

The paper presents the kinematic synthesis of a symmetric parallel platform supported by three RRS serial chains. The dimensional synthesis of this three degree-of-freedom system is obtained using design equations for each of three RRS chains obtained by requiring that they reach a specified set of task positions. The result is 10 polynomial equations in 10 unknowns, which is solved using polynomial homotopy continuation. An example is provided in which the direction of the first revolute joint (2 parameters) and the z component of the base and platform are specified as well as the two task positions. The system of polynomials has a total degree of 4096 which means that in theory it can have as many solutions. Our example has 70 real solutions that define 70 different symmetric platforms that can reach the specified positions.

Estimation of SI Engine Load Torque: Adaptive Kalman Filter vs. Luenberger Estimator

The SI engine load torque is key information for many engine and power train control systems. Since the torque is not measured in production vehicles, it needs to be estimated on-line. The paper presents design and analysis of second-order and third-order Luenberger load torque estimators. With the aim to reduce the estimator noise sensitivity without deteriorating its transient performance, an adaptive Kalman filter is proposed and compared with the Luenberger estimator. The adaptation mechanism is based on a load torque change detection algorithm. The estimators are examined by computer simulations and experiments.

Identifying the Shapes of Coupled Vibrations and Deriving Reduced Order Models for Nonlinear Shafts: A Finite Element-Proper Orthogonal Decomposition Approach

The spatial structure of the dynamics of a rotating nonlinear shaft is identified by processing its finite element dynamics by the method of Proper Orthogonal Decompositions. The Proper Orthogonal modes furnish characteristic signatures for the rigid body and the whirling modes of a motion. The pattern of energy distribution over the components of a mode reveals the strength of coupling between rigid body rotations and coupled vibrations. These modes are used to derive a two-degree-of freedom reduced model for the whirling motion of the rotating shaft.

Determination of Strength and Damping Characteristics of Carbon Nanotube-Epoxy Composites

In this paper, the strength and damping properties of carbon nanotube-epoxy composites are examined. Carbon nanotubes (Single-walled and Multi-walled) were grown on stainless steel substrates using thermal chemical vapor deposition process. The nanotube-epoxy composites were then prepared by applying a layer of epoxy on the grown nanotubes and a PZT actuator was attached on this layer. The composite beam consisting of steel, nanotube-epoxy layer and PZT actuator was used as a cantilever beam for vibration experiments in order to determine the enhancement in strength and damping properties of the nanotube-epoxy layer. Several different samples were prepared for this purpose. Impulse and frequency sweep tests were conducted on these beams to obtain the impulse response and frequency response functions. Fast Fourier Transform of the impulse response was used to find the natural frequency of the composite beam. It was observed that there was an increase in the stiffness by using multi-walled nanotubes in the epoxy, while the damping ratio increased by using single-walled nanotubes. The stick-slip mechanism is discussed in order to explain the results obtained.

A Comparative Study of Single Loop and Multiple Loop Design for Uncertain Single Input Single Output Systems

In this paper, studied are the actual advantages offered by SISO cascade loop structures. In Quantitative Feedback Theory it is emphasized that the use of cascaded loops is primarily for the reduction of bandwidth of the controllers. This in turn helps in considerable reduction of the adverse effects of high frequency noise. The question that arises then is whether or not there are any substantial benefits to be gained by cascade loop design in the low frequencies. This issue is the focus of this paper. It is shown using Quantitative Feedback Theory methodology that there aren’t any advantages gained in the low frequencies with the use of cascaded design for meeting performance specifications. In effect it is concluded that if the design is properly executed a single loop controller closed from the output to the input will be sufficient to meet the typical performance specifications. This is shown using an example where the mold level of a continuous casting process is to be controlled. The plant being used has considerable uncertainty so that features of robust control can be highlighted.