William J. O'Connor

Wave-Based Analysis and Control of Lump-Modeled Flexible Robots

Flexible robots are frequently represented by lumped models. In the mechanics of lumped systems, wave concepts have been avoided, for good reasons, generally. In the control of lumped flexible systems, however, wave concepts prove very fruitful. This paper provides a foundation for the wave-based control application by exploring the validity and nature of wave concepts in lumped robotic systems. A new wave-based model of uniform mass-spring systems is proposed and verified. The model is exact but not unique. Useful simplifications and approximations are also presented. The model leads to control strategies for flexible robotic systems that are simple, powerful, robust, and generic. The wave approach also provides a new analysis tool and conceptual framework for lumped dynamic systems

Control of flexible mechanical systems: wave-based techniques

The dynamics of flexible systems can be complex, imperfectly modelled and variable, which severely limits the usefulness of standard control strategies. Wave-based control easily and robustly copes with these challenges, by properly understanding, measuring and controlling the two-way energy and momentum flow through the actuator-system interface. The actuator then controls the remote load, close to optimally. The tutorial will briefly review traditional and recent approaches to this problem. It will then develop the wave-based idea, and illustrate its application to a range of flexible systems, including gantry cranes, lumped mass-spring systems, robots and space structures.

Transmission line matrix acoustic modelling on a PC

Abstract The Transmission Line Matrix method is applied to the modelling of acoustic waves and is implemented on a 486 PC. The model is verified using analytically solvable cases. General implementation issues and the limitations of a PC based simulator are discussed. The TLM acoustic model is then applied to the design of an active noise control system for an engine exhaust duct. Auralization of outputs from the model is also considered.

The Effect of Stevia Rebaudiana on Serum Omentin and Visfatin Level in STZ-Induced Diabetic Rats

ABSTRACT Recently the role of adipocytokines in relationship to incidence of diabetes has been demonstrated. One of the medicinal plants that are used in the treatment of diabetes is stevia. This study investigates the effect of stevia on serum omentin and visfatin levels as novel adipocytokines in diabetic induced rats to find potential mechanisms for the anti hyperglycemic effect of stevia. Forty male wistar rats weighing 180–250 g were induced with diabetes by intraperitoneal injection of streptozotocin (STZ). The animals were divided into 5 groups of 8. Rats in group 1 (non-diabetic control) and group 2 (diabetic control) were treated with distilled water, and the rats in the treated groups, group 3 (T250), group 4 (T500), and group 5 (T750) were treated with stevia, gavaged every day at 9 a.m. in doses of 250, 500, and 750 mg/kg, respectively. At the end of the study significant reductions in fasting blood sugar (FBS), the homeostasis model assessment insulin resistance (HOMA-IR), triglyceride (TG), alkaline phosphatase (ALP), and Omentin level were found in groups 3 and 4 in comparison with group 2. Pancreatic histopathology slides demonstrated that stevia extract did not induce any increase in the number of β-cells. The conclusion is that prescription of stevia in the doses of 250 and 500 mg/kg/d decreases the omentin level indirectly via activating insulin sensitivity and lowering blood glucose in STZ-induced diabetic rats.

Wave-based control of under-actuated flexible structures with strong external disturbing forces

Wave-based control of under-actuated, flexible systems has many advantages over other methods. It considers actuator motion as launching a mechanical wave into the flexible system which it absorbs on its return to the actuator. The launching and absorbing proceed simultaneously. This simple, intuitive idea leads to robust, generic, highly efficient, precise, adaptable controllers, allowing rapid and almost vibrationless re-positioning of the system, using only sensors collocated at the actuator–system interface. It has been very successfully applied to simple systems such as mass–spring strings, systems of Euler–Bernoulli beams, planar mass–spring arrays, and flexible three-dimensional space structures undergoing slewing motion. In common with most other approaches, this work also assumed that, during a change of position, the forces from the environment were negligible in comparison with internal forces and torques. This assumption is not always valid. Strong external forces considerably complicate the flexible control problem, especially when unknown, unexpected or unmodelled. The current work extends the wave-based strategy to systems experiencing significant external disturbing forces, whether enduring or transient. The work also provides further robustness to sensor errors. The strategy has the controller learn about the disturbances and compensate for them, yet without needing new sensors, measurements or models beyond those of standard wave-based control.

Wave Based Robust Control of a Crane System

In this paper we propose a robust control strategy for a gantry crane system with hoisting. The trolley moves horizontally to translate a load mass, hanging at the lower end of a cable, from rest to rest. Due to the flexibility of the cable, load swing easily arises, and should be controlled. To this end, the trolley motion and load hoisting are designed carefully. The desired trolley motion is decided in real time by a wave-based approach, which interprets the cable motion as two superposed traveling waves, to eliminate the load swing at the end of a manoeuvre. The load hoisting is chosen to reduce the load swing during the manoeuvre. A robust algorithm, based on a nonlinear model of the crane system, is proposed for the tracking control, allowing for system parameter variations and uncertainties. This control algorithm works very well and is stable and robust to large load variations. As demonstrated in the numerical simulations, it lands the load rapidly and exactly at target and stops it dead, with zero swing

Wave-based control of flexible mechanical systems

There are many contexts, from space structures to disk drive heads, from medical mechanisms to long-arm manipulators, from cranes to robots, in which it is desired to achieve rapid and accurate position control of a system end-point by an actuator working through a flexible system. The systems actuator must then attempt to reconcile two, potentially conflicting, demands: position control and active vibration damping. Somehow each must be achieved while respecting the others requirements. Wave-based control is a powerful, relatively new strategy that has many advantages over most existing techniques. The central idea is to consider the actuator motion as launching mechanical waves into the flexible system while simultaneously absorbing returning waves. This simple, intuitive idea leads to robust, generic, highly efficient, adaptable controllers, allowing rapid and almost vibrationless re-positioning of the remote load (tip mass). For the first time there is a generic, high-performance solution to this important problem that does not depend on an accurate system model. The lecture will investigate the mathematical foundation for a wave-based interpretation of flexible system dynamics, both lumped and continuous. It will then show how this view can be used to interpret the actuator-system interface as a two-way energy flow, leading to the design of controllers that give close-to-optimal performance by controlling this energy flow, in ways that are simple, robust, generic, and energy efficient.

Theory of Wave Analysis of Lumped Flexible Systems

Flexible systems such as robots and space structures are frequently represented by lumped models. In the mechanics of lumped systems, wave concepts have been avoided, generally for good reasons. In the control of lumped flexible systems however, wave concepts prove very fruitful. This tutorial paper provides a foundation for the wave-based control application by exploring the validity and nature of wave concepts in lumped systems. A new wave-based model of mass- spring systems is proposed and verified. The model is exact but not unique. Useful simplifications and approximations are also presented. As seen in a companion paper, the model leads to control strategies for flexible robotic systems that are simple, powerful, robust, and generic. The wave approach also provides a new analysis tool and conceptual framework for lumped dynamic systems.

The famous 'lost' energy when two capacitors are joined: a new law?

Reflections on the lost energy when two capacitors are connected, or two masses collide, or similar problems, suggests a new law of nature: that stored energy of one kind cannot be transferred without loss unless it undergoes a change in energy form in the transfer process.

Saturable overlapping rectangular poles: Towards a functional relationship between force, overlap distance, mmf and saturation polarization

The transverse force and flux distributions are examined for the important case of overlapping rectangular poles of saturable material. Results from measurements on physical devices and from numerical iterative solutions of the field equations are presented, with flux plots for varying pole positions. Accuracy, as determined from control cases and other means, is better than 1%. The transverse force is presented in a novel way as a unique function of the three variables, the mmf, the overlap distance, and the saturation polarization of the pole material. This shows that the force is remarkably independent of overlap, and for large overlap is double the force for the corresponding linear case and directly proportional to both the mmf and the saturation polarization.