This article presents a back-drivable spherical wrist with smart compliance for rendering human wrist-like capabilities in robotic applications. In order to synthetically impose both motion accuracy and active compliance for dedicated wrist manipulations, a robust hybrid control method is proposed that can switch between motion control (at free motion) and impedance control (at interactions with the environment). A sliding manifold is formulated so that when the control law drives the sliding manifold to zero, the motion/impedance errors will automatically converge to bounded regions despite system uncertainties/inaccuracies. Due to the direct-drive configuration of the proposed spherical wrist, the contact torque can be precisely estimated with an observer, providing an intuitive criterion of contact based on which the control modes can switch autonomously without external force/torque sensors and predefined geometric boundaries that are usually required in conventional hybrid force/position control. The concept is validated on a spherical wrist test-bed in the context of a throat swabbing process. The performance of the hybrid motion-impedance control evaluated against conventional impedance and admittance control methods demonstrate that the proposed spherical wrist enables a robotic system with both fine manipulations and smooth compliant interactions in wrist space.

This paper presents an active control method, consisting of an adaptive sliding-mode controller (ASMC) and a displacement field reconstruction (DFR) method, for chatter suppression in turning of thin-walled workpieces (such as compressor disks and casings in aircraft engines) where low workpiece stiffness renders machining with potential regenerative chatter. Due to the presence of multi-modal dynamics, variant modal parameters, and measurement difficulties, active chatter control of thin plate turning has been challenging. Unlike existing controls based on a lumped-parameter single degree-of-freedom cutting model, a distributed-parameter dynamic model of a rotating thin plate with multiple vibration modes is used to analyze the machining stability with the designed controller. Moreover, model parameters of the plate are not needed to construct the controller. The DFR is employed to capture the plate dynamic behavior for feedback to the ASMC during turning, overcoming the long existing difficulties to measure plate vibration at the cutting point. A fast tool servo is utilized in the control implementation. Theoretical analyses, numerical simulations, and experimental evaluation on a lathe demonstrate that chatter in thin plate turning can be effectively attenuated with the proposed active control method.

This paper presents a new method that combines a physics-based model and finite-element (FE) based digital image correlation (DIC) with an interfacial continuity condition for simultaneous deformation measurements of strain field and material mechanical properties. The dual-domain global DIC method incorporates a model-based kernel that offers useful physical insights into the complex deformation and constrains the solutions to the iterative minimization of the DIC criterion, which leads to a faster convergence. Unlike local subset-based and global FE-based methods where the DIC is formulated to solve for the nodal displacements, the model-based DIC that accounts for complex deformation in the specific region is formulated to identify system parameters. Both domains, along with their interface and the continuity condition enforced on the global displacement field, are discretized and solved simultaneously in a single calculation. The dual-domain global DIC method has been investigated by comparing reconstructed strain fields and estimated parameters against targets simulated using the commercial FEA software COMSOL and published experimental data. Unlike FE-DIC which is noise sensitive, the model-based DIC is robust against the Gaussian noise effects.

Smart sensing is a prerequisite to information sharing in intelligent manufacturing where online measurements of multiple parameters are essential to infer system properties for process analysis and product-quality control. This paper presents methods to develop a novel eddy-current (EC) sensor capable of simultaneously measuring multiple parameters of a nonferrous electrically conductive workpiece (WP). Unlike traditional EC-sensors that base principles on lumped-parameter impedance or voltage change, the proposed method (referred to here as a multiparameter EC-sensor) directly measures the EC-generated magnetic flux density (MFD) to determine the displacement, thickness, and electrical conductivity of the WP. Specifically, an analytical model that characterizes the impedance and MFD field generated by the induced EC is presented, from which the design criteria for developing a multiparameter EC-sensor are established. The proposed methods, along with a prototype MFD-based EC sensor, have been validated and evaluated experimentally for simultaneous distance and thickness measurements and conductivity estimation of a titanium thin-walled WP in a lathe-turning process.

This paper presents a new machine perception method based on eddy-current (EC) effects to reconstruct physical fields (EC field, electrical-conductivity field, and hidden geometrical features) of a nonferrous material commonly encountered in intelligent manufacturing using one-time finite magnetic flux density (MFD) measurements. An analytical model for EC testing system with conductor discretization is established and expressed in state-space representation. Two improvements (physical constraints and adaptive element refinement) are developed and integrated into the system model. The measurement models of physical fields using discrete MFD measurements are linearly established, reducing the physical field reconstruction to a linear inverse problem for solving using the Tikhonov regularization method. The EC-based machine perception is numerically illustrated by reconstructing the EC density field, conductivity field, and hidden geometrical features of aluminum plates. Additionally, the effects of element refinement, physical constraints, and sensor configurations on the reconstruction results are analyzed numerically. Using an experimental prototype consisting of an air-cored electromagnet and a two-dimensional (2-D) array of magnetic sensors with associated electronics, the effectiveness of the machine perception method and the accuracy of the reconstructed physical field are demonstrated experimentally.

This paper presents an efficient method, which reconstructs the temperature field around the tool/chip interface from infrared (IR) thermal images, for online monitoring the internal peak temperature of the cutting tool. The tool temperature field is divided into two regions; namely, a far field for solving the heat-transfer coefficient between the tool and ambient temperature, and a near field where an artificial neural network (ANN) is trained to account for the unknown heat variations at the frictional contact interface. Methods to extract physics-based feature points from the IR image as ANN inputs are discussed. The effects of image resolution, feature selection, chip occlusion, contact heat variation, and measurement noises on the estimated contact temperature are analyzed numerically and experimentally. The proposed method has been verified by comparing the ANN-estimated surface temperatures against “true values” experimentally obtained using a high-resolution IR imager on a custom-designed testbed as well as numerically simulated using finite-element analysis. The concept feasibility of the temperature monitoring method is demonstrated on an industrial lathe-turning center with a commercial tool insert.

This paper presents the design and analysis of a passive body weight (BW)-support lower extremity exoskeleton (LEE) with compliant joints to relieve compressive load in the knee. The biojoint-like mechanical knee decouples human gait into two phases, stance and swing, by a dual snap fit. The knee joint transfers the BW to the ground in the stance phases and is compliant to free the leg in the swing phases. Along with a leg dynamic model and a knee biomechanical model, the unmeasurable knee internal forces are simulated. The concept feasibility and dynamic models of the passive LEE design have been experimentally validated with measured plantar forces. The reduced knee forces confirm the effectiveness of the LEE in supporting human BW during walking and also provide a basis for computing the internal knee forces as a percentage of BW. Energy harvested from the hip spring reveals that the LEE can save human walking energy.

This paper presents the design concept of a weight-support lower-extremity-exoskeleton (LEE) with a compliant joint to relieve compressive load in the knee. Along with a leg dynamic model and a knee bio-joint model, a compliant exoskeleton knee-joint has been designed using topology optimization and experimentally evaluated. Results suggest that the gait-based design of a LEE can be divided into two parts in terms of knee angles; compliant coupling and body-weight support. The concept feasibility and dynamic models of the passive LEE design have been experimentally validated with measured plantar forces. Both simulation and experimental results agree with data in-vivo confirming the effectiveness of the LEE in supporting human body-weight during walking, and also provide a basis for computing the internal knee forces as a percentage of bodyweight.

Motivated by the needs to develop dexterous flexonic mobile node (FMN) for structural health monitoring where obstacle avoidance is among the most challenging tasks, this paper presents a novel FMN design for navigating on iron-based structures. Unlike most existing magnetic wheel designs, the FMN uses fixed-magnet configuration contributing to smooth motion, self-maintained orientation and automatic negotiation of concave corners. Taking into account of several stringent considerations (including tight dimension, efficient attachment and manipulation flexibility) to facilitate avoidance of structural obstacles in tight space, a prototype FMN incorporating a compliant beam (that results in more DOFs than designs with multiple links and pin/ball joints), along with a 3-step strategy for negotiating a convex corner, has been developed. Although controlling a continuous deforming beam is challenging given limited number of actuators, both simulation and experimental results confirm a simple input/output relation between the rear axle displacement and front axle rotation, which is anticipated to facilitate control implementation of FMN for obstacle avoidance.

This paper presents an alternative control strategy for permanent magnet (PM) based spherical actuators capable of multi-DOF precision manipulation. Unlike existing control methods which rely on separate sensing systems, this direct approach utilizes magnetic field measurements for feedback and eliminates the complicated multi-DOF orientation detection in closed-loop control which may cause time-delay and affect system sampling rate. By capitalizing on the rotor magnetic field implicit dependence on orientation, the control law derivation and torque coefficient estimation can be obtained simultaneously and directly from field measurements without explicit determination of the rotor orientation, thereby improving computational efficiency and eliminating error accumulation. The control method is simulated in 2-DOF motion with a CAD model of a spherical actuator.

This paper presents a dynamic model of a knee joint interacting with a two-link exoskeleton for investigating the effects of different exoskeleton designs on internal joint forces. The closed kinematic chain of the leg and exoskeleton has a significant effect on the joint forces in the knee. A bio-joint model is used to capture this effect by relaxing a commonly made assumption that approximates a knee joint as a perfect engineering pin-joint in exoskeleton design. Based on the knowledge of a knee-joint kinematics, an adaptive knee-joint exoskeleton has been designed by incorporating different kinematic components (such as a pin, slider and cam profile). This design potentially eliminates the negative effects associated with the closed leg/exoskeleton kinematic chain on a human knee. An investigation in the flexion motion of an artificial human knee joint is presented to compare performances of five exoskeleton designs against the case with no exoskeletons. Analytical results that estimate internal forces using the dynamic model (based on the properties of a knee joint) agree well with the experiments. These studies lead to an adaptive mechanism with a slider/cam as an alternative to pin joints for the exoskeleton, and illustrate the application of the model for designing an adaptive mechanism that minimizes internal joint forces due to a human-exoskeleton interaction.

This paper presents an efficient method to adaptively determine the locations for taking measurements for automated calibration of electromagnetic systems using reconstructed magnetic fields. This coupled measurement- computation method solves the Laplace's equation with measured boundary conditions. Along with the formulation of two selection criteria (chord-height and data-spacing), an adaptive scanning algorithm has been developed, which bases four local measurements to determine the next measurement point. This adaptive method, which relaxes the assumption of approximately known structure, has been illustrated (with experimental verification) with three practical applications; electromagnetic velocity probe, electromagnetic flow-meter (EMF) and spherical motor. Comparisons against published data demonstrate that the adaptive measurement algorithm greatly reduces the number of measurements and shortens the scanning route length of all three applications without sacrificing the accuracy of the computed results. Dry calibration results of an EMF were also experimentally verified against test data obtained from a standard flow-rig confirming that a relative error of 0.2% can be achieved. This finding makes the cost-effective dry calibration a practical alternative to the conventional flow rig calibration. As demonstrated on a spherical motor, the flexibility to include a least-square curve fit offers a practical means to filter measurement noise.

This paper presents a sensing method that harnesses the capacity of modern sensors to measure vector fields. This approach directly maps distributed independent field measurements to the instantaneous orientation of a spherical joint embedded with low-cost permanent magnets. Unlike existing methods which require a priori and precise field models, this direct method engages an artificial neural network to associate a collection of measurements to joint orientation. The operation of both bipolar and unipolar single and multi-axis sensors were considered and evaluated experimentally.

This paper presents a method to determine the 2-D profile and motion of a live product (such as chicken for poultry meat processing) on a moving conveyor from a lateral optical sensor that consists of an orthogonal pair of line array (LA) scanners. Unlike most line array (LA) scanners designed to provide a 2-D image of a static object, the lateral optical sensor presented here offers a practical means to detect object slippage on the conveyor in real time. Three examples are given to illustrate the effectiveness of this sensing method. The first simulates the 2-D boundary of a geometrically well-defined object on an accelerating conveyor, which offers intuitive insights on the effects of conveyor dynamics and object slippage on the accuracy of the 2-D boundary measurement. The second experimentally demonstrates the extendibility of LA sensors to detect both engineering and natural objects. The final example illustrates the application of the lateral optical sensor as a real time feedback sensor for active singulation of natural objects.

This paper presents a new method for solving the magnetic forces/torques of a multi-DOF spherical actuator that has more controlling inputs than its mechanical DOF. Unlike methods that based on the Lorentz force equation or the Maxwell stress tensor, which require computing the volume or surface integrals to derive the forces, the dipole force method presented here offers the magnetic force solution in closed form. We validate the dipole force model against published experimental data, and demonstrate its application in solving the inverse torque model of a multi-DOF spherical motor, which computes the required set of maximum current inputs for a given design specifications.

This paper presents a ball-joint-like three-degree-of-freedom (3-DOF) permanent magnet (PM) spherical actuator which features a ball-shaped rotor with multiple PM poles and a spherical iron stator with air-core coils. Torque output of this PM spherical actuator is formulated analytically. Based on the torque model, simulation result of the actuator torque variation is presented. In addition, the effect of the stator iron on the torque output is evaluated.

This paper presents a method to determine the 2D profile and velocity of an object on a moving conveyor from a lateral optical sensor that consists of an orthogonal pair of line array (LA) scanners. Unlike most LA scanners which are designed to provide a 2D image of a static object, the lateral optical sensor presented here offers an additional and practical means to detect object slippage on the conveyor in real time. We illustrate numerically the effectiveness of this sensing method with two illustrative examples. The first simulates the 2D boundary of a geometrically well-defined object on an accelerating conveyor, which offers intuitive insights on the effects of conveyor dynamics and object slippage on the accuracy of the 2D boundary measurement. The second demonstrates the application of the lateral optical sensor as a real time feedback sensor for active singulation of natural objects.

Growing new robotic applications in agriculture, food-processing, assisted surgery and haptics, which requires handling of highly deformable objects, present a number of design challenges; among these are methods to analyze deformable contacts. Recently, meshless methods (MLM), which inherit many advantages of finite element method (FEM) and yet need no explicit mesh structure to discretize geometry, have been proposed as an attractive alternative to FEM for solving engineering problems where automatic re-meshing is needed. This paper offers an adaptive MLM (automatically inserting nodes into large error regions) for solving contact problems. We employ the sliding line algorithm with the penalty method to handle contact constraints; it does not rely on small displacement assumptions and thus, it can solve non-linear contact problems with large deformation. Along with three practical applications, we validate the method against results computed using commercial FEM software and analytical solutions.

Color information is useful in vision-based feature detection, particularly for food processing applications where color variability often renders grayscale-based machine-vision algorithms that are difficult or impossible to work with. This paper presents a color machine vision algorithm that consists of two components. The first creates an artificial color contrast as a prefilter that aims at highlighting the target while suppressing its surroundings. The second, referred to here as the statistically based fast bounded box (SFBB), utilizes the principal component analysis technique to characterize target features in color space from a set of training data so that the color classification can be performed accurately and efficiently. We evaluate the algorithm in the context of food processing applications and examine the effects of the color characterization on computational efficiency by comparing the proposed solution against two commonly used color classification algorithms; a neural-network classifier and the support vector machine. Comparison among the three methods demonstrates that statistically based fast bounded box is relatively easy to train, efficient, and effective since with sufficient training data, it does not require any additional optimization steps; these advantages make SFBB an ideal candidate for high-speed automation involving live and/or natural objects. Note to Practitioners-Variability in natural objects is usually several orders of magnitude higher than that for manufactured goods and has remained a challenge. As a result, most solutions to inspection problems of natural products today still have humans in the loop. One of the factors influencing the success rate of color machine vision in detecting a target is its ability to characterize colors. When unrelated features are very close to the target in the color space, which may not pose a significant problem to an experienced operator, they appear as noise and often result in false detection. This paper illustrates the applicability of the algorithm with a number of representative automation problems in the context of food processing applications. As demonstrated experimentally, the artificial color contrast and statistically based fast bounded box methods can significantly improve the success rate of the detection by reducing the standard deviation of both the target and noise pixels, enlarging the separation between feature clusters in color space, and more tightly characterize the feature color from its background. The algorithm presented here has several advantages, including simplicity in training and fast classification, since only three simple checks of rectangular bounds are performed

The applications of robotics are becoming more and more common in non-traditional industries such as the medical industry including robotic surgery and sample microtoming as well as food industry that include the processing of meats, fruits and vegetables. In this paper, the influence of the blade edge-shape and its slicing angle on the cutting of biomaterials are formulated and discussed based on the stress analysis that has been presented in part I. Through modeling the cutting force, an optimal slicing angle can be formulated to maximize the feed rate while minimizing the cutting forces. Moreover, the method offers a means to predict cutting forces between the blade and the biomaterials, and a basis for design of robust force control algorithms for automating the cutting of biomaterials

Bio-material cutting, such as meat deboning, is one the most common operations in food processing. Automating this process using robotic devices with closed-loop force control has shown some promise. The control of the force trajectory directly relates to the internal stress in the material being cut, and must provide enough force to initiate the cut. The ability to model the stress distribution in the bio-materials being cut would provide a better understanding of the influencing factors and help predict the required cutting force for the design of the cutting mechanism and for automating the cutting operations. This research is presented in two parts: part I models the stress distribution when a blade acts on the bio-material and part II discusses the principles of biomaterial cutting. Starting with modeling a point force in the normal and tangential direction on the boundary of a semi-infinite body, an analytical expression for the stress tensor has been obtained and simulated using direct integral method. This paper provides the theoretical basis for explaining the cutting phenomena and predicting the cutting forces, a topic to be presented in part II

The analysis of compliant mechanisms has traditionally based on known initial shapes and external forces. For applications, it is often required to find an initial shape for the specified deformed shape of the mechanism. We present here the global coordinate model (GCM) with a numerical solver that is capable of forward and inverse analysis. The model uses the arc length as the independent variable so that the shape of straight and curved links can be easily expressed. The resulting governing equations are a generalization of Timoshenko's beam theory that accounts for the effects of bending and shear deformations on large-deflected links. The effect of shear deformation on link deflection will also be investigated. Systematic procedures are developed to analyze generic compliant mechanisms. Both forward and inverse illustrations are presented. Their applications for robotic handling of bio-material are also shown. It is expected that the proposed model can give more insight on the analysis and design of compliant mechanisms

The ever increasing cost of energy and advance in permanent magnet technology have the incentives to develop geometrically compact and energy-efficient electro-magnetic (EM) actuators for robotic and automation applications. Design automation of these actuators often involves solving a magnetic field problem. This paper presents an adaptive meshless method (MLM) that inherits many advantages of FEM but needs no explicit mesh structure for design of EM actuators. Specifically, this paper offers a technique to estimate the distribution of numerical errors and a scheme automatically inserts additional nodes to improve computational accuracy and efficiency. Five examples are given; the first three are numerical examples, where exact solutions are available, provide a means to validate the adaptive MLM and evaluate its effectiveness against MLM with uniform node distribution. The other examples, where the magnetic forces are computed from the Lorenz's law, illustrate the use of adaptive MLM for the pole design of a three-DOF EM actuator. We also verify the results by comparing the computed forces against published experimental results

This paper presents a design concept of spherical actuators including a ball-shaped rotor with two layers of permanent-magnet (PM) poles and a spherical-shell-like stator with two layers of circumferential air-core coils. Corresponding to the poles configuration, the torque model of the spherical actuator has been derived. The magnetic field as well as torque output have been compared with that of spherical actuator with single-layer PM-pole configuration. This generic torque modeling method can be extended for spherical actuators with multi-layer PM&coil poles which can achieve high motion resolution as well as large working range

Motivated by a need for a method to derive practical and physical-based dynamic models that capture the essential characteristics of an optical-fiber draw process for precision control of diameter uniformity, we extend the Karhunen-Loeve decomposition technique with a Galerkin procedure to derive a reduced-order model (ROM) for a multivariable distributed-parameter system. We validated the ROM derived from a high-fidelity physics-based model by simulating a modern optical-fiber draw process, the numerical solutions for which have been experimentally verified in our earlier studies. Perturbation studies demonstrated that the 24th-order ROM agrees remarkably well with the original nonlinear semi-two-dimensional and quasi-one-dimensional distributed models. We further examine the efficiency of the ROM in the context of a model-based H/sub /spl infin///LQG fiber drawing control system for the regulation of the fiber diameter and tension. The results show that variations in fiber diameter can be reduced significantly by appropriately distributing the number of retained eigenmodes among the physical state variables in the ROM. We also demonstrate that controlling the surrounding air temperature in addition to the draw speed is very effective in regulating both the fiber diameter and tension while simultaneously keeping the draw speed and temperature fluctuations to a minimum. Note to Practitioners-Because of the stringent production requirements (on draw speed, tension, and temperature), diameter uniformity is a challenging distributed control problem in modern fiber production where progressively larger diameter preforms are drawn at higher speeds. The reduced-order model offers an effective way to observe physical variables in a multivariable distributed-parameter system, which may not be physically measured. While developed in the context of fiber diameter control, the modeling techniques presented in this paper are applicable to other material processing systems, such as deposition thickness control in semiconductor wafer manufacturing.

Many manufacturing processes require time-consuming setups before automation can begin. This paper investigates the applications of distributed-parameter computational thermal-fluid models for automating the design of a continuous manufacturing system, which aims at reducing process setup time. A generic draw process is used as an example throughout this paper, which involves practically all modes of heat transfer. Two physically accurate distributed-parameter models (semi-two-dimensional (2-D) and quasi-one-dimensional (1-D) are derived and experimentally validated. In deriving these models, we relax a number of assumptions commonly made in modeling draw processes, and extend the models to allow for 2-D static/dynamic response predictions. The semi-2-D model provides a means to accurately predict the free surface geometry and the location at which the glass solidifies into a fiber, which also serves as a basis to derive the quasi-1-D model. The quasi-1-D model that explicitly solves for the controlled variables is attractive for control system design and implementation. These results are particularly important in the optical-fiber industry because the difficulties in making precise in situ measurements in the harsh environment of the draw process have posed a significant challenge in the control of fiber diameter uniformity. Additionally, these numerically computed and experimentally measured neck-down profiles obtained in an industry setting can be used as benchmark data for future comparisons. The modeling approaches presented here are applicable to a variety of thermal-fluid systems, such as thermal processing of semiconductor wafer and food. Despite the emphasis in this paper on the faster draw of large-diameter glass that is a participating media in radiation, the technique for predicting the 2-D temperature distribution and the streamlines describing the fluid flow is equally applicable to processes involving nonparticipating media, such as composite, polymer, or synthetic fibers. Note to Practitioners-This paper is motivated by a problem in the fiber draw industry because of the progressive difficultly in maintaining the diameter uniformity resulting from the ever-increasing preform (or glass rod) diameter and draw speed. The larger diameter a preform is, the longer the fiber can be drawn in the furnace from a single preform and in much less time by drawing at a higher speed. The number of setups to initiate the draw can thus be drastically lowered. The tradeoff, however, is that the glass takes a longer distance to cool into a fiber after leaving the furnace, for which an insulated post-chamber is added to gradually cool the fiber to solidification in order to reduce optical losses in the final product. Existing models assuming a Dirichlet boundary condition at the furnace exit are valid only for drawing a small-diameter preform as long as the fiber solidifies inside the furnace. As larger preforms are drawn at higher speeds, it is necessary to locate the solidification for optimizing the post-chamber design, and to develop high-fidelity models for controlling the diameter uniformity. This paper formulates a general 2-D thermal-fluid dynamic model (which does not rely on assumptions commonly made for small preforms) to characterize the free-surface flow of the glass in both the furnace and the post-chamber. We demonstrated how a detailed description of the free surface geometry, temperature fields, and streamlines can be accurately computed from the 2-D model for process design, which also provides a basis to derive a distributed quasi-1-D model explicitly solving for the essential process state variables. Both models have been experimentally validated (with a 9-cm-diameter glass preform) by comparing against the data obtained (at 25 m/s) in an industry setting. These models have been successfully applied to the design of commercial draw towers.

We consider here a class of compliant mechanisms that consist of one or more flexible beams, the manipulation of which relies on the deflection of the flexible beams. As compared with traditional rigid-body mechanisms, compliant mechanisms have the advantages of no relative moving parts and thus involve no wear, backlash, noises and lubrication. In this paper, we present a formulation based on shooting method (SM) along with two numerical solvers to facilitate the analysis and the design process of a compliant mechanism. Unlike finite difference method (FDM) or finite element method (FEM) that offers accurate solutions at discrete nodes, the computed solution of SM, which treats the boundary value problem (BVP) as an initial value problem, is continuous. Three example compliant mechanisms are formulated to illustrate the generalized shooting method and the computed results are validated by comparing those obtained using FEM.

Abstract: This paper presents the design concept, models, and open-loop control of a particular form of a variable-reluctance spherical motor (VRSM), referred here as a spherical wheel motor (SWM). Unlike existing spherical motors where design focuses have been on controlling the three degrees of freedom (DOF) angular displacements, the SWM offers a means to control the orientation of a continuously rotating shaft in an open-loop (OL) fashion. We provide a formula for deriving different switching sequences (full step and fractional step) for a specified current magnitude and pole configurations. The concept feasibility of an OL controlled SWM has been experimentally demonstrated on a prototype that has 8 rotor permanent-magnet (PM) pole-pairs and 10 stator electromagnet (EM) pole-pairs.

An actuator with 3-DOF spherical motion is developed based on layered arrangement of stator coils and rotor poles. Due to the use of air-core coils and permanent magnet poles, the torque model of the actuator cannot be obtained by traditional coenergy approach. This paper describes a generic torque modeling method based on Lorentz force law. The closed-form solution of the torque model is derived from the scalar potentials of the magnetic field. Experimental study on the torque model is carried out. A comparison between the closed-form solution and the experimental result shows that the proposed torque model is valid and can be used for real-time control.

This paper has proposed a design concept of a spherical actuator including a ball-shaped rotor with a full circle of permanent-magnet (PM) poles and a spherical-shell like stator with two layers of circumferential air-core coils. One key feature of this design is parameterization of the PM pole, which benefits the design optimization of the spherical actuator greatly. According to the magnetic field model, the variation of flux density with respect to PM-pole parameters can be revealed. Therefore, these parameters can be appropriately chosen to achieve a high magnetic flux density. Another advantage of this design is the singularity-free, which is verified within the workspace with torque model and condition numbers.

Motivated by the applications of flexible fingers (capable of offering large deflections to accommodate object variations) in grasping, we present several computational models that characterize the large deflection of a flexible finger (beam). Specifically, we develop analytical methods for analyzing the design of cantilever-like fingers or elements of a machine that is designed primarily to support forces acting perpendicular to the axis of the member. Both uniform and non-uniform beams are considered. The methods were numerically validated by comparing the computed results against those obtained using the closed-form solutions, where exact solutions are available for fingers with a uniform cross-section. To extend the closed-form solution for predicting the shape of a non-uniform finger, we compute numerically an effective EI that approximates the non-uniform finger as a uniform finger at the point of contact. The approximate model has been examined experimentally. The results show excellent agreement. We expect that the methods presented here will have other engineering applications.

Body rotation under free fall along a desired trajectory can be found in many applications such as sports, entertainment, and manufacturing. An appropriately designed body path could lower the forces at the joints during inversion and thus minimizing potential injury. This paper presents a method of developing dynamic models that characterize the interaction between the body of a live object undergoing inversion and the mechanical system driving the rotation. The method offers an effective means to analyze the sensitivity of the design and operational parameters on the body rotation. The models have been validated experimentally. The simulated and experimental results offer significant insights to the joint forces and a means to improve the body dynamics. While the results have immediate application in inverting live birds for poultry meat processing, we expect the model will provide a basis for analyzing body rotational dynamics in other applications such as gymnastics and roller coasters.

The need for simultaneous measurement of more-than-one degrees-of-freedom (DOF) motions of an object can be found in numerous applications such as robotic assembly, precision machining, optical tracking, wrist actuators, and active joysticks. Conventional single-axis encoders, though capable of providing high-resolution linear or angular measurements, require additional mechanical linkages that often introduce frictions, backlashes, and singularities. In this paper, a non-contact optical sensor for three-DOF orientation measurement is present. Unlike other contemporary designs, which often require a specific pattern to be drawn on a surface, this optical sensor presented here relies only on microscope features on natural surfaces to detect incremental motions. Here we offer a detailed description of the design and the development of a dual-sensor system capable of measuring three-DOF motions in real time. The analysis that is essential for optimizing the sensor design has been validated experimentally.

This paper presents the effects of fixture dynamics on the control of a variable-reluctance spherical motor (VRSM). The cascaded VRSM dynamics has the appropriate structure for the so-called back-stepping controller, however, requires the computation of the exact motor dynamics at each sampling time. This computational burden has an effect on the performance of the control algorithm and imposes constraints on the hardware/ software architecture of the control system. By only computing the dominant parts of the motor dynamics, this computational burden can be reduced. We have developed a robust back-stepping controller to compensate for uncertainties account for imperfect modeling and intentional computational simplification. The performance of the robust back-stepping controller has been evaluated experimentally against a classical PD controller and a standard back-stepping controller, which serve as bases for comparison.

This paper presents the method of modeling the torque generated by a variable reluctance spherical motor (VRSM) that presents some attractive possibilities by combining pitch, roll, and yaw motion in a single joint. Unlike prior works on the torque formulation of a VRSM, which were based on a lumped-parameter approach using equivalent magnetic circuits (widely used in developing force/torque models for electromechanical devices), this paper presents a distributed-parameter approach to predict the motor's magnetic field distribution for formulating the torque of a VRSM. A detailed three-dimensional finite-element (FE) analysis has been performed on a VRSM configuration that consists of both permanent magnet (PM) poles and air-cored electromagnets. The model obtained using FE methods offers more insight and an accurate representation of torque generated by a spherical motor.

Models quasi-statically the force acting on an object by a rotating flexible finger. As compared to fingers with multiple active joints, flexible fingers have many potential advantages; specifically, they are lightweight and have no relative individual moving parts in each of the fingers. Their ability to accommodate a limited range of varying sizes, shapes, and the natural reactions of some objects (without the need of a feedback mechanism such as a visual servo) makes a system using flexible fingers an attractive candidate for use as a grasper in a high-speed production setting. The advantages of flexible fingers are seldom exploited for grasping, however, because of complicated analyses involved in their design. The paper offers two methods to determine contact points/forces. The first analytical model, based on the Frisch-Fay (1962) flexible bar theory, provides an approximate closed-form solution for determining the contact points and forces. The second method using FEM predicts the stress distribution around the contact area. Both methods of predicting the contact forces have been verified experimentally. The effects of parameter variations are presented. Our results demonstrate that the model could be used as a practical means to measure the contact force between the finger and the live object.

Presents the design criteria for developing machines to automate the process of transferring single live birds from a moving conveyor onto a processing line without causing damage or stress. The process includes inserting both legs of the bird into a shackle, then flipping and hanging the bird for subsequent processing. Unlike the traditional articulated robotic arm where the actuations are applied directly through the joint angles, the legs of a live object can only be manipulated indirectly. In addition, natural objects are typically characterized by varying sizes and shapes in batch processing and their natural reflexes (or voluntary motion) contribute to the overall dynamics. Specifically, the paper illustrates the operating principles of the transfer system and describes the method for manipulating the leg kinematics for shackling. The design criteria have been verified experimentally with live broilers (meat chickens) in a realistic environment. It is expected that the analytical model presented will provide an essential basis for the design, analysis, and control of the transfer mechanism.

Presents the design criteria for developing machines to automate the process of transferring live birds from a moving conveyor onto a processing line without causing damage or stress. The process includes inserting both legs of the bird into a shackle, flipping and hanging it for subsequent processing. Specifically, the paper illustrates the operating principles of the transfer system and describes the method for manipulating the leg kinematics for shackling. Unlike the traditional articulated robotic arm where the actuations are applied directly through the joint angles, the legs of a live object can only be manipulated indirectly. In addition, natural objects are typically characterized bp varying sizes and shapes in batch processing and their natural reflexes (or voluntarily motion) contribute to the overall dynamics. The design criteria have been verified experimentally with live broilers (meat chickens) in a realistic environment. It is expected that the analytical model presented would provide an essential basis for the design, analysis and control of the transfer mechanism.

Recent developments in several other emerging fields enable us to think of the fields of prototype design, development and automation in new ways and to consider new applications. This paper presents trends of prototyping design and automation with an emphasis on the following two sub-topics: 1) a review on prototyping discrete event and hybrid systems; and 2) the trends on prototyping real-time machine vision system design.

This paper describes a model for automated disassembly that accounts for workcell interaction and used product constraints. The model provides an essential means to determine, in real-time, the next component for disassembly using the knowledge of the product design and sensor feedback minimizing the steps to remove goal components. Sets of components for removal were resolved by minimizing setup time for disassembling the component. Given the model, a controller for product disassembly is defined that can account for missing and known replacement components. The controller can recover from unknown replacement components and jammed components when alternate removal sequences exist to meet the cell goal. Two case study examples are presented and experimentally simulated. Simulation results based on real product, vision sensor measure, and process input are presented and discussed. It is expected that the concepts demonstrated through these case studies can provide useful insights into other mechanical assemblies.

This paper addresses the problems of automating the process of transferring live broilers (meat chickens) from a conveyor to a moving shackle line. Specifically, we focus on establishing the criteria for designing for an automated system for singulating and orienting the birds for subsequent transferring to a moving shackle line. Since both the mechanical forces and the bird's natural reflexes contribute to the overall dynamics as the bird passes through the singulator, an experimental prototype singulator has been developed to facilitate the study of bird's natural reflexes to mechanical singulation. The system has been experimentally demonstrated and evaluated with live birds at the Gold Kist research farm and at a poultry-processing plant in Georgia. It is expected that the results will provide significant insights to the design and control of future mechanical singulators.

An important aspect in recycling and reuse for environmentally conscious manufacturing is disassembly. Although disassembly systems contain the same basic elements as assembly system, the disassembly problem differs significantly from the assembly problem due to the fact that the incoming disassembly product is not controlled. In addition, complete dismantling of products is not necessarily required for disassembly whereas assembly builds a product completely. This paper describes a model for automated disassembly that accounts for work cell interaction and used product constraints. The model provides an essential means to determine, in real-time, the next component for disassembly using the knowledge of the product design and sensor feedback to minimize the steps to removing goal components. Sets of components for removal were resolved by minimizing set-up time for disassembling the component. Simulation results based on real product, vision sensor measure, and process input are presented and discussed. It is expected that the concepts demonstrated through this product can provide useful insights to other mechanical assembly.

Presents high-precision control strategies and bearing support mechanisms for real-time motion control of a multiple degree-of-freedom (DOF) variable-reluctance (VR) spherical motor. In particular, a resultant magnetic force model is derived which, along with the torque model, is used to develop a reaction-free control strategy to establish a non-contact support mechanism through magnetic levitation to achieve high performance motion. An equivalent angle-axis based control is also designed and implemented for real-time applications. The designed control strategy only requires limited knowledge of system dynamics, and therefore is robust and practical. A look-up table based on-line nonlinear optimization scheme is devised to facilitate the control strategy for a prototype VR spherical motor. Control experimental results verify the reaction-free control strategy and demonstrate the motion capability of the multi-DOF VR spherical motor. The concepts, methodologies, and experimental techniques developed in the paper establish an essential analytical and engineering basis for real-time motion control of VR spherical motors.

The development of a three-degree-of-freedom (DOF) micromotion in-parallel actuated manipulator is discussed. The micromotion manipulator, which has one translation and two orientation freedoms, is actuated by piezoelectric effect. A closed-form solution and an experimental verification of the forward kinematics are presented. In addition, the dynamic model of the piezoelectric actuated link was determined experimentally, providing a rational basis for the design and prismatic joint force control of the high-speed micromotion manipulator. A special configuration that approaches an optimal design, in terms of working range, rigidity, and bandwidth, is highlighted.>

The design concept of a spherical stepper motor capable of three-degrees-of-freedom (DOF) motion in a single joint is presented. The ball-joint-like motor has no singularities except at the boundary of the workspace and can perform isotropic manipulation in all three directions. Due to its relatively simple ball-like structure, undesired cross-coupling and centrifugal components of wrist rotor dynamics can be effectively minimized or eliminated. The spherical stepper motor has potential in robotic applications as a three-DOF shoulder or an eyeball, as well as a wrist actuator. In particular, the systematic conceptualization of a spherical stepper is presented, and the feasibility of constructing the spherical stepper is examined. Along with the experimental data, an analytical approach based on the permeance formula was used to predict the driving forces generated by a neodymium-iron permanent magnet. The force-displacement curves provide useful information for rational spherical motor design and control.>

The development is described of a three-degree-of-freedom (DOF) micro-motion in-parallel actuated manipulator, which has one translation and two orientation degrees of freedom. The micro-motion manipulation is achieved by piezoelectric effects, due to their fast response and high resolution. In particular, a closed-form solution and an experimental verification of the forward kinematics are given. In addition, the dynamic model of the piezoelectrically-actuated link was determined experimentally, providing rational basis for the design and prismatic-joint force control of the high-speed micro-motion manipulator. A special configuration which approaches an optimal design in terms of working range, rigidity, and bandwidth is highlighted.>

The static characteristics of a three-degree-of-freedom in-parallel actuated manipulator are discussed, along with its desired static actuator characteristics for clamping and bracing applications, where the term 'bracing' refers to a strategy to rigidize the wrist for subsequent fine motion performed by the end-effector or a second manipulator. The short-arm manipulator is characterized by its rigidity, high force-to-weight ratio, and relatively simple inverse kinematics. Particular attention is given to the influences of the joint reactions on the manipulator performance and the appropriate control strategy for clamping and bracing. The static analysis, along with the static representation of velocity and force ellipsoids, establishes a rational basis for minimizing the bending moments which tend to cause an increase in nonlinear friction. Also, it predicts the reaction forces acting at the ball joint for a specified payload, which appear as time-varying external forces/moments on the link actuation.>

The design concept is presented of a novel spherical stepper robotic wrist motor capable of three-degree-of-freedom (DOF) motion in a single joint for applications where high-speed manipulation of end-effector orientation is required continuously in all directions. Typical applications are plasma and laser cutting and microassembly. The spherical motor is developed based on the principle of the variable-reluctance stepper motor. The differences between the operation principle of the three-DOF spherical motor and that of the conventional stepper motor are pointed out. The authors seek to establish a theoretical basis for design, prototype development, and performance prediction. An analysis of torque prediction is discussed, along with the presentation of kinematic and dynamic relationships. A laboratory prototype hybrid digital/analog control circuitry has been developed to demonstrate proof of concept feasibility and to assist in achieving an optimum design.>

The authors present experimental results of an investigation of a prototype tactile sensor design based on microbending losses in fiber optics. The parameters which determine the sensitivity of a fiber to bending losses were identified, experiments were performed on a multimode optical fiber, and a prototype tactile sensor was constructed and tested. Results indicated that the limiting factor of the performance of the tactile sensor was the viscoelastic behavior of the fiber's cladding.>

An alternative design of a three-degrees-of-freedom manipulator based on the concept of an in-parallel actuated mechanism is presented. The manipulator has two degrees of orientation freedom and one degree of translatory freedom. The basic kinematic equations for use of the manipulator are derived and the influences of the physical constraints on the range of motion in the practical design are discussed. Several possible applications which include the in-parallel mechanism as part of the manipulation system are suggested.>

The dynamic analysis of a three-degrees-of-freedom in-parallel actuated manipulator is presented. The equations of motion have been formulated in joint-space using the Lagrangian approach. The analysis provides the solution to predict the forces required to actuate the links so that the manipulator follows a predetermined trajectory. A dynamic simulation program illustrates the influence of the link dynamics on the actuating force required. An example of tracing a helical path is chosen to illustrate the dynamic simulation and to show that the Cartesian position of the moving platform may be controlled at a sacrifice of orientation freedoms. The dynamic analysis provides a basis for future theoretical research to develop the control scheme, for experimental research to estimate the inertia parameters, and for design optimization of the prototype manipulator.>

This paper presents an alternative design of a three degrees of freedom manipulator based on the concept of in-parallel actuated mechanism. The manipulator has two degrees of orientation freedom and one degree of translatory freedom. The basic kinematic equations for use of the manipulator are derived and the influences of the physical constraints on the range of motion in the practical design are discussed. Several possible applications which include the inparallel mechanism as part of the manipulation system are suggested.