On‐off iterative adaptive controller for low‐power micro‐robotic step regulation

A novel model‐free iterative adaptive controller is presented for low‐power control of piezoelectric actuators. The controller uses simple adaptation rules based on known general behavior of piezoelectric actuators to adjust on‐off switching times to drive piezoelectric actuators through a desired transient step motion. Adaptation rules are based on small numbers of measurements taken during each iteration of the actuator movement. Combined with the use of only on‐off control inputs, controller implementation can be possible at much lower overall power levels than would be needed to implement a conventional control strategy such as through pulse‐width‐modulation (PWM) with real‐time feedback. Such power savings are particularly important for the intended controller application to piezoelectric microactuators driving autonomous terrestrial micro‐robots. A method for predicting convergence of systems with nominally linear dynamics and unknown, bounded nonlinearities is described, and applied to a sample target piezoelectric actuator. The controller is tested in simulation and experimentally on a piezoelectric cantilever actuator, and shows predicted convergence to the desired response. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Real‐time hybrid control of electrohydraulic active suspension

Electrohydraulic actuators are an attractive choice for active suspension, because these systems provide a high power‐to‐weight ratio. However, their dynamics are highly nonlinear. In addition, the use of one simple controller for both position and force is complicated, because there is a compromise between them in the case of active suspension. Most existing controllers do not efficiently fulfill the requirements, because only one state variable is considered. In this paper, we address these problems by developing a new hybrid controller for both position and force and implementing it in a real‐time test bench. Our goal is to control the vertical position of the passenger seat while tracking the force transmitted to passengers and keeping it within tolerable and comfortable limits. Therefore, the proposed controller is a combination of two controllers. Its flexible structure redirects the control signal to control the proper controlled state variable. The real‐time results of the newly designed hybrid controller are compared with those obtained using a classical proportional integral derivative controller, because this is the most widely used controller in the industry. As expected, the proposed controller demonstrates better performance in real‐time operation. Copyright © 2017 John Wiley & Sons, Ltd.     

(31)P-MR Spectroscopy for the evaluation of energy metabolism in intact residual myocardium after acute myocardial infarction in humans

Objective experimental studies have demonstrated that acute myocardial infarction (MI) alters energy metabolism even in non-infarcted adjacent tissue. In patients with subacute MI, the influence of the regional ischemie insult on energy metabolism of intact septal myocardium was analyzed using³¹P-Magnetic resonance spectroscopy (MRS). Patients and Methods in eight patients with wall motion abnormalities in the anterior wall³¹P-spectra were obtained from non-infarcted adjacent scptal myocardium, as well as infarcted anterior myocardium (voxel size 25 ccm each) 29 ±8 days after MI using a 3D-CSI technique. Additionally, cardiac function was analyzed using breath-hold cine MRI. MR1 was repeated 6 months after revascularization to assess viability of infarcted segments. Eight age-matched healthy volunteers served as control group. Results according to follow-up MRI 4/8 patients showed regional wall motion recovery. Here, PCr/ATP-ratios were not significantly reduced in intact septal myocardium as well as infarcted anterior myocardium compared to healthy volunteers (1.28 ±0.10 and 1.14 ±0.09 vs. 1.45 ±0.29). No recovery of regional function was detected in 4/8 patients with —therefore—non-viable anterior myocardium. PCr/ATP-ratios were significantly reduced in intact and infarcted myocardium compared with healthy volunteers as well as to patients with wall motion recovery (0.77 ±0.17 and 0.49 ±0.23;P < 0.05). Discussion these preliminary results indicate that energy metabolism is reduced in patients with persisting wall motion abnormalities after myocardial infarction and revascularization in ischemically injured as well as in adjacent non-injured myocardium.     

Production control of hybrid manufacturing–remanufacturing systems under demand and return variations

Hybrid manufacturing systems that use both raw materials and returned products as a supply for their production process are considered. Specifically, the system under study contains two machines: one uses raw materials for manufacturing, while another utilises end-of-life products returned from the market for remanufacturing. Machines are failure-prone, demand and return rates fluctuate in time reflecting market behaviour due to economical, seasonal and environmental changes. The system performance is characterised by a long-term discounted cost that integrates several partial costs (those of manufacturing, remanufacturing, disposal, holding costs in serviceable and return inventories). Optimisation of the hybrid system behaviour requires to determine the combined manufacturing, remanufactruring and disposal policy, withstanding machine failures under dynamic market conditions. Optimality conditions in the form of Hamilton–Jacoby–Bellman equations are obtained and a novel numerical approach, based on the estimation of value function timederivative, is proposed in order to deal with demand and return variations. Extensive simulations are performed to address the numerous scenarios corresponding to evolving relationship between manufacturing capacities and varying demand and return levels. Simulation results show that the optimal policies have an important property of anticipating the future changes in the demand and return, and making the timely decisions relevant to these changes.     

Production control and combined discrete/continuous simulation modeling in failure-prone transfer lines

In this paper, we consider a production system consisting of multiple tandem machines subject to random failures. The objective of the study is to find the production rates of the machines in order to minimize the total inventory and backlog costs. By combining analytical formalism and simulation-based statistical tools such as design of experiments (DOE) and response surface methodology (RSM), an approximation of the optimal control policy is obtained. The combined discrete/continuous simulation modeling is used to obtain an estimate of the cost in a fraction of the time necessary for discrete event simulation by reducing the number of events related to parts production. This is achieved by replacing the discrete dynamics of part production by a set of differential equations that describe this process. This technique makes it possible to tackle optimization problems that would otherwise be too time consuming. We provide some numerical examples of optimization and compare computational times between discrete event and discrete/continuous simulation modeling. The proposed combination of DOE, RSM and combined discrete/continuous simulation modeling allows us to obtain the optimization results in a fairly short time period on widely available computer resources.     

Production and quality control policies for deteriorating manufacturing system

In this paper, a novel model for a deteriorating manufacturing system is analysed, considering repairs and overhauls of random durations. The machine manufactures one product and the model is further complicated because the quality of the parts’ produced deteriorates according to the wear of the machine and human interventions. When a breakdown occurs, either a repair or an overhaul is performed. The machine is restored to as-good-as-new conditions if the overhaul is selected, and conversely, its condition deteriorates following repairs. Multiple operational states are considered to define an ageing process. The decision variables of the model are the production rate and the repair/overhaul switching strategy. This paper provides new insights to this research area by considering the simultaneous production and repair/overhaul control policy under the effect of deteriorations. The optimal decision policy minimises the total incurred cost comprising the inventory, backlog, repair and overhaul costs over an infinite planning horizon. Our paper differs from other research projects in its consideration of the machine’s history, defined by the number of repairs and multiple operational states. A numerical example is given to illustrate the proposed approach and a sensitivity analysis has been conducted to confirm the structure of the obtained control policies.     

Joint control of production, overhaul, and preventive maintenance for a production system subject to quality and reliability deteriorations

This research investigates the case of an unreliable manufacturing system subject to quality and reliability deterioration. In particular, we conjecture that the deterioration of the system leads to a continuous increase in the intensity of failures and a decrease on the quality of the parts produced. As such, deterioration implies a twofold effect on the manufacturing system. When the machine fails, minimal repair is conducted, leaving the machine at the same level of deterioration before failure. Hence, the quality of the parts produced and the failure intensity remain unchanged with this repair. Meanwhile, an overhaul refers to a perfect repair that completely restores the quality of the parts and the failure intensity of the machine. This option completely counters all the effects of the deterioration. Preventive maintenance may also be conducted, but it reduces the level of deterioration only partially, improving the quality of the units produced and the failure intensity just in part. This set of characteristics yields to the formulation of a new control model that simultaneously determines the optimal production plan, the overhaul, and preventive maintenance strategies. Such a joint control policy minimizes the total cost including the inventory holding, backlog, overhaul, preventive maintenance, and defective costs over an infinite planning horizon. Since the dynamics of the system change as a function of the level of deterioration, it is necessary to use its history for a proper formulation; therefore, a semi-Markov decision process is used. Numerical methods are applied to determine the control policy, and numerical examples are conducted as illustrations. An extensive sensitivity analysis is presented in order to confirm the structure of the control policy obtained and examine the effect of several parameters.     

Architectural requirements for rapid development of agile manufacturing systems

As product life cycle becomes shortened, high product quality becomes necessary for survival, and continuous and unexpected change becomes key obstacles in success, the need for a method of rapidly and cost-effectively developing products, production facilities and supporting software including design, process planning, shop floor control systems becomes urgent. The essence of this concept of manufacturing would be characterized by adopting a new term “agility”. Agile manufacturing can be successfully accomplished using various well-defined system architecture. This paper provides a primary sketch of architectural requirements for rapid development of agile manufacturing systems.There are several aspects of system architecture : control, function, process, information, communication, distribution, development, and implementation.In the past, the confusion of those architectures prohibited the successful construction of the automated CIM systems.