The design and control of an actively restrained passive mechatronic system for safety-critical applications

Development of manipulators that interact closely with humans has been a focus of research in fields such as robot-assisted surgery and haptic interfaces for many years. Recent introduction of powered surgical-assistant devices into the operating theatre has meant that robot manipulators have been required to interact with both patients and surgeons. Most of these manipulators are modified industrial robots. However, the use of high-powered mechanisms in the operating theatre could compromise safety of the patient, surgeon, and operating room staff. As a solution to the safety problem, the use of actively restrained passive arms has been proposed. Clutches or brakes at each joint are used to restrict the motion of the end-effector to restrain it to a pre-defined region or path. However, these devices have only had limited success in following pre-defined paths under human guidance. In this research, three major limitations of existing passive devices actively restrained are addressed. [Continues.

Motion stabilization in the presence of friction and backlash: a hybrid system approach

In this paper a hybrid system approach is considered to deal with backlash and friction induced nonlinearities in mechanical control systems. To describe the low velocity frictional behaviour a linearized friction model is proposed. The novelty of this study is that based on the introduced friction model, the stability theorems developed for hybrid systems can directly be applied for controller design of mechanical systems in the presence of Stribeck friction and backlash. During the controller design it is assumed that the size of the backlash gap is unknown and the load side position and velocity cannot be measured. For motion control an LQ controller is applied. A condition is formulated for the control law parameters to guarantee the asymptotic stability of the control system. Simulation measurements were performed to confirm the theoretical results

Design and application of electromechanical actuators for deep space missions

During the period 8/16/92 through 2/15/93, work has been focused on three major topics: (1) screw modeling and testing; (2) motor selection; and (3) health monitoring and fault diagnosis. Detailed theoretical analysis has been performed to specify a full dynamic model for the roller screw. A test stand has been designed for model parameter estimation and screw testing. In addition, the test stand is expected to be used to perform a study on transverse screw loading

Continuous time controller based on SMC and disturbance observer for piezoelectric actuators

Abstract – In this work, analog application for the Sliding Mode Control (SMC) to piezoelectric actuators (PEA) is presented. DSP application of the algorithm suffers from ADC and DAC conversions and mainly faces limitations in sampling time interval. Moreover piezoelectric actuators are known to have very large bandwidth close to the DSP operation frequency. Therefore, with the direct analog application, improvement of the performance and high frequency operation are expected. Design of an appropriate SMC together with a disturbance observer is suggested to have continuous control output and related experimental results for position tracking are presented with comparison of DSP and analog control application

Development and characterization of a novel piezoelectric-driven stick-slip actuator with anisotropic-friction surfaces

Piezoelectric actuators (PEA) hold the most promise for precision positioning applications due to their capability of producing extremely small displacements down to 10 pm (1 pm = 10-12 m) as well as their high stiffness and force output. The piezoelectric-driven stick-slip (PDSS) actuator, working on the friction-inertia concept, has the capacity of accomplishing an unlimited range of motion. It also holds the promises of simple configuration and low cost. On the other hand, the PDSS actuator has a relatively low efficiency and low loading capability, which greatly limits its applications. The purpose of this research is to improve the performance of the PDSS actuators by employing specially-designed working surfaces. The working surfaces, referred as anisotropic friction (AF) surfaces in this study, can provide different friction forces depending on the direction of relative motion of the two surfaces, and are used in this research to accomplish the aforementioned purpose. To fabricate such surfaces, two nanostructure technologies are employed: hot filament chemical vapour deposition (HFCVD) and ion beam etching (IBE). The HFCVD is used to deposit diamond on silicon substrates; and the IBE is used to etch the diamond crystalloid with a certain angle with respect to the coating surface to obtain an unsymmetrical-triangle microstructure. A PDSS actuator prototype containing the AF surfaces was developed in this study to verify the function of the AF surfaces and characterize the performance of PDSS actuators. The designed surfaces were mounted on the prototype; and the improvement in performance was characterized by conducting a set of experiments with both the normal isotropic friction (IF) surfaces and the AF surfaces, respectively. The results illustrate that the PDSS actuator with the AF surface has a higher efficiency and improved loading capability compared to the one with the IF surfaces. A model was also developed to represent the displacement of the novel PDSS actuator. The dynamics of the PEA and the platform were approximated by using a second order dynamic system. The pre-sliding friction behaviour involved was investigated by modifying the LuGre friction model, in which six parameters (Note that three parameters are used in the LuGre model) were employed to represent the anisotropic friction. By combining the PEA mechanism model, the modified friction model, and the dynamics of end-effector, a model for the PDSS actuator with the AF surface was developed. The model with the identified parameters was simulated in MATLAB Simulink and the simulation results obtained were compared to the experimental results to verify the model. The comparison suggests that the model developed in this study is promising to represent the displacement of the novel PDSS actuators with AF surfaces

Developing a case for the implementation of a control augmentation system to improve flying qualities in the EA-6B aircraft

The EA-6B aircraft was designed and built in the late 1960s by the Grumman Aerospace Corporation for the United States Navy and Marine Corps to be used as a tactical electronic warfare (EW) platform. High losses of U.S. attack aircraft to surface-to- air missiles (SAMs) in Southeast Asia led to the requirement for a carrier-based tactical aircraft capable of providing EW support in the form of electronic jamming in support of strike aircraft. The EA-6B became the aircraft that fulfilled the EW requirement. Forty years have passed since the introduction of the EA-6B and the demand for the tactical EW capability continues to increase. Meeting these requirements has taken a toll oh the aircraft\u27s wing fatigue life, and has produced a shortage of the aircraft\u27s Automatic Flight Control System (AFCS) computer. The replacement computer contracted to correct the current problem of the aging analog AFCS computer is an up-to-date digital flight control computer (Model EA-6B Aircraft Program, 1995). The implementation of this computer will allow greater processing power and should be used to the full extent of its capability. An up-to-date flight control computer will cost less to repair, be readily replaceable, and will improve mission readiness and safety of flight. This thesis will build a case to use the additional processing power of the replacement digital flight control computer to improve flying qualities through a Control Augmentation System (CAS) that should have the effect in the following areas; 1. Limit accelerations during flight and thereby control the current problem of Fatigue Life Expenditure (FLE). 2. Improve flying qualities, specifically in the landing configuration with an emphasis to improve shipboard operations. With the current SAS the aircraft demonstrates less than satisfactory flying qualities in all axes (lateral, directional, and longitudinal) and configurations. 3. Limit Angle of Attack (AOA) in certain abnormal configurations, that are commonly encountered in the EA-6B, due to the aging airframe. The configuration that is particularly dangerous is the no slat-flaps down approach. This approach requires the pilot to maintain AGA precisely. The consequences of slowing one degree (equivalent to approximately 2 KIAS) below the recommended approach AGA will result in an uncontrollable pitch up (longitudinal instability) and subsequent departure from controlled flight (mandatory ejection criteria in this configuration) (EA-6B NATOPS Flight Manual, 1997). 4. Improve departure resistance by limiting angle of attack and controlling side-slip. Jamming pods are on all wing stations when the airplane is in the normal configuration. Departures that develop into spins frequently result in loss of the aircraft due to large inertia, forces, caused by the weight of the stores carried on the wings stations, which can not be overcome by the aerodynamic forces required for recovery

Implementation of a friction estimation and compensation technique

This thesis reports implementation of a friction estimation and compensation technique on a special laboratory apparatus. In this work, experimental results are reported for the Coulomb friction observer. The Coulomb friction observer estimates the total friction present in a system, assuming it to be a constant function of velocity. An extension of the observer, utilizing a coupled velocity observer, is used when velocity is not measurable. A modification to the velocity observer is also implemented. Experimental results show a remarkable improvement in the friction estimates which are also compared to the actual friction measurements. The estimates are qualitatively similar to the actual friction, demonstrating the ability of the modified design to track a non-constant friction. Finally, extremely low velocities are experimentally obtained by using the friction compensation technique mentioned above, further proving that accurate control at low velocities is possible by friction estimation and compensation