Robert H. Sturges

Framework for the control of automated material-handling systems using the holonic manufacturing approach

In todays global economy, manufacturing companies must be able to change both the product variety and production quantity without incurring major disturbances in the production process. A manufacturing system capable of performing these changes efficiently needs a control system flexible enough to go from one state to another without significant delays in production. To compensate for the deficiencies of both hierarchical and heterarchical control systems, a control architecture based on the holonic concept is proposed. After presenting the general holonic control architecture, the paper focuses on the integration of the holonic-based control concept in the design of an automated material-handling control system. When performing transport activities in a manufacturing system, due to its architecture, the holonic system can operate both as a hierarchical system, following a predefined schedule during normal operation conditions, and as a heterarchical system in the presence of disturbances.

Jamming conditions for multiple peg-in-hole assemblies

Reliable flexible assembly workstations depend ultimately on the physics of assembly tasks performed. Multiple-peg insertions, as a practical assembly class, is complicated by the large number and kind of interaction between mating parts.In this article, geometric and quasi-static analyses of multiple-peg insertions are presented. First, a possible contact-state enumeration, geometric conditions for each contact-state, and the force-moment equations for static-equilibrium states of two dimensional dual-peg insertions are derived. The jamming diagrams and the taxonomy of dual-peg insertions are obtained. Then, an experiment to verify the analysis is presented.

Design of a sensor for on-line measurement of loaded bend angle for pressbrake control

Abstract Controlling springback in small radius pressbrake bending operations is motivated by the need to produce small lot parts of high quality. A new technique for springback control has been developed based on a simplified analytic model of material and tooling geometry variables. This technique requires the on-line measurement of loaded angle with a robust, high resolution optical sensor which is insensitive to material surface finish. The design of the sensor minimizes systematic error due to placement on the press bed. Loaded angle measurement accuracy of less than one arc minute is achieved. In combination with a press ram position control scheme, this sensor provides a more accurate bending process necessary for the further development of precision, small-lot sheet metal assembly manufacture.

Agile Inspection Planning Based on CAD-Data

Variations in components are inevitable and have to be dealt with efficiently. One way to reduce variation is by implementing efficient inspection plans that can minimize the total cost of the product. Manufacturers deal with this problem with many different strategies when minimal information is known about the product (newly launched products). In this paper, we develop a methodology for inspection planning for a new product based on CAD data and simulation. Decision variables in this formulation includes: how often to inspect a quality characteristic in a subassembly (probability of inspection), and the corrective action if the inspected quality characteristic is found to be out-of-tolerance. Inspection frequency as a decision variable was not proposed in this context before. Additionally, the proposed action plan is more realistic here than what has been proposed in the literature. Illustrative examples are presented and solved for demonstrative purposes and validation of our findings.

A control design strategy of a reconfigurable manufacturing system

A Reconfigurable Manufacturing System (RMS) is defined as one that can provide adaptability to quickly adjust the production capacity and functionality in response to fluctuations in customer demand. An advanced analytical modelling approach and control design strategy is introduced to improve the system responsiveness of multistage feedback control RMS. A System Dynamics (SD)-based multistage RMS model is mathematically translated into block diagram representations and transfer functions. A control design technique called Root-Locus is presented to propose a new operation management policy to better predict and control the dynamic responses of a RMS in reduction of inventory and Lead-Time (LT). By applying this graphic view approach, one can improve the RMS responsiveness and also determine its relative system stability without iterative trial-and-error simulation replications as found in discrete event simulation and SD approach.

Non-iterative control of small-radius bend angle

Abstract Controlling first-part quality in small-radius press brake bending operations is motivated by the need to produce small-lot parts of high quality. A new technique for angle control has been developed based on an experimentally measured model of material properties, tooling geometry variables, and on-line measurements of part deformation. This technique requires the off-line measurement of part thickness and hardness, plus the on-line measurement of loaded angle and press ram position. Linear regression and neural network techniques are compared to develop a robust model of springback. A control scheme is introduced that provides accurate first-part bend angles for small-lot sheet metal manufacture.

Complex plane design strategy for a responsive lean manufacturing system

The future success of manufacturing-based businesses depend on continuous exploration of technologies and innovative ways of thinking. Today, enterprises need to respond quickly with frequent change of product design, without carrying excess inventory and long production delays. In this paper, we introduce the Root-Locus method to study the sensitivity of the closed-loop poles location of a multistage feedback-control manufacturing system on a complex s-plane. This complex plane analysis offers a new control design strategy for production management to better predict and improve the dynamic response of particular manufacturing systems in terms of inventory build-up (leanness) and lead-time.

Design and Simulation of a Smart Endoscope: Part II

In this research, we are developing a noninvasive and safe endoscope for human colonoscopy. To minimize the invasiveness and discomfort, a smart endoscope is composed of a sheath with controllable stiffness that has an exoskeleton structure. A smart endoscope is comprised of an endoscope and a sheath. The stem has more flexibility than a conventional endoscope and the sheath portion maintains controllable flexibility. In principle, this approach could be used for other procedures. The stem of a conventional protoscope has stiffness and it can scratch the inside surface when it pushes into a human colon. It may also deform the colon’s shape. Important parameters used in designing a smart endoscope include the radius of curvature of a sigmoid colon, an appropriate unit diameter for the sheath part, and an ability to lock the units together. An analysis of the cable tensions and external forces is completed for a given configuration based on selected geometric parameters. By applying external forces to the stem of the endoscope, we can solve for the maximum external resisting forces. These are required to maintain the locking ability of the endoscope and the corresponding cable forces.Copyright

Analysis and Design for Two-Handed Heavy Part Assembly Methods

In spite of advances in industrial automation, manual assembly tasks continue to be an important feature of many industrial operations. In heavy part assembly, some pieces of raw material or equipment are too heavy to be safely handled by just one operator. Material handling devices such as Jib cranes or overhead cranes are employed to help operators work safer and, in some cases, faster. However, during full-load productions, access to these devices could become limited due to insufficient resources and hence, delay or extend the cycle times. The authors studied how people perform the assembly and subsequently applied Fitts’ Index of Difficulty to develop a model which indicates factors that increase the task difficulty. This model can also be used as an assembly time predictor. Since improving the efficiency of an overhead crane could significantly reduce the total cycle times and production costs, the authors modified the crane by adding a spring between the hook and the gripper to help support the weight. Two sets of experiments were conducted. The first set was to investigate the effect of spring stiffness on assembly time. The result indicated that using a spring that was too soft could create a parasitic oscillation, which increases the assembly time. The objective of the second set was to compare the assembly time of using the regular crane to that of the modified crane in situations where the part weights and the task difficulty vary. As a result of the modifications, assembly performance tended to increase by approximately 250% from using the modified crane.Copyright