We show that the genetic algorithm that Leu described to plan component placement sequences and feeder assignments for pick-and-place printed circuit board assembly tasks is a special case of a more general model that supports multiple placement-nozzles and independent feeder and board link (chromosome) evaluation methods. We also show that independent link evaluation can be used to offset a reduction in the parent link sample space and that these results are better than what can be achieved through link-pair evaluation. These generalizations extend the capabilities of the genetic algorithm to a broader range of manufacturing scenarios.

We previously proposed a general algorithm for coordinating the motions among multiple machines in a shared assembly environment based on a constant-speed motion model. In this paper, we extend this work to a minimum-jerk polynomial motion model and describe a new speed-planning algorithm to plan automated assembly machines' motions. Machines are planned sequentially, based on their priorities, by mapping the motions of higher-priority machines into forbidden regions in two-dimensional space-time graphs. Collision-free minimum-jerk motions are then planned between the forbidden regions in the graphs. The new speed-planning algorithm is evaluated on a dual-robot surface-mount technology assembly machine in which both robots share a common workspace. Note to Practitioners-Automated assembly processes, especially surface-mount technology manufacturing, require a high degree of precision when placing certain components. This motivated us to find a way of maintaining good positional accuracy by planning smooth motions for the machines that perform these tasks. Since many of these machines have two or more robots, their motions must also be coordinated. We developed an algorithm that combines coordinated motion concepts with a minimum-jerk motion model that can solve these problems. The algorithm plans segmented paths for the robots and then sequentially plans their speeds to prevent collisions between them. The planned speeds ensure position, velocity, and acceleration continuity between path segments. The smooth motions resulting from this method enable high-accuracy component placement. The tradeoff for this improvement is increased cycle time compared to other speed-planning methods

Virtual design and manufacturing has become a key technology in reducing both design errors and manufacturing cost. In order to have a realistic evaluation, the cost of assembling, disassembling, and manufacturing a product has to be realized. A product's design and its manufacturability will give an overall manufacturing efficiency and production cost. To eliminate future production failure and control the cost, management has to be able to foresee and evaluate the whole process from design to production, easily and wisely. In recognizing the importance of this capability, a CAE/CAD/CAM Product (C3P) management tool based on a structured product coding system (SPCS) is developed for the process of virtual design and manufacturing.

A general, hierarchical model for describing automated assembly systems is developed. This hierarchical model allows any complex assembly system to be decomposed into simpler sub-systems. This decomposition can be applied recursively to generate a multi-level system structure. Planning and control can be performed on each part of this structure and, if necessary, between parts. The model was applied to a simulated dual-robot, surface-mount assembly system to simplify the problem of planning coordinated motions between the robots. For the purpose of illustration, both linear and polynomial motion-planning models were analyzed. Part pick-up and placement delays were also introduced. Furthermore, system performance as a function of the number of placement-nozzles was also quantified. By weighing the benefits of additional placement-nozzles against their costs, the ideal number of placement-nozzles may be determined.

An automatic method for generating assembly instructions using CAD files is presented. Algorithms for extracting geometrical information of objects stored in a non-proprietary format, ISO-10303, STEP-CAD data file are explained. The developed algorithms form an important link between design and manufacturing. In our previous work, (Mok et al., 2000, 1999, Wu and Kim, 1994, and Kim and Wu, 1990) we designed a hierarchical assembly model that allows designers to evaluate products for manufacturing cost using a structured assembly coding system (SACS). Each SACS code represents a sequence of assembling/disassembling operations for mating two parts. The developed algorithms in this paper generate the required SACS codes based on the geometrical and topological information extracted from the STEP files of a product in a CAD environment. Based on the generated SACS codes, the proper assembly operations can then be derived for assembling the designed product. An example of assembly with simple parts is presented to verify the method.

A system for evaluating products in their design phase has been developed for virtual manufacturing. It is integrated into a CAD/CAM environment to calculate the cost for assembling and disassembling parts. In our earlier work, a generic assembly and disassembly model was developed to represent operations required for product manufacturing and de-manufacturing. To be useful, the model requires a method for translating high-level instructions from product designers into low-level assembly and disassembly instructions. This paper presents a set of rules for accomplishing this task. The developed rules are used for manipulating strings representing parts and handlers in binary assembly and disassembly operations. A telephone assembly and disassembly simulation is used to illustrate the developed system.

A system for evaluating products in their design phase has been developed. It is integrated into a CAD/CAM environment to calculate cost for assembling and disassembling parts. In previous work, a generic assembly and disassembly model was developed to represent operations required for product manufacturing and demanufacturing. To be useful, the model requires a method for translating high-level instructions from product designers into low-level assembly and disassembly instructions. This paper presents a set of rules for accomplishing this task. The developed rules are used for manipulating strings representing parts and handlers in binary assembly and disassembly operations. A telephone assembly and disassembly simulation is used to illustrate the developed system.

A general, hierarchical method of planning coordinated motions among multiple objects in a dynamic environment is developed. This model consists of a two-phase approach: planning a global path for each object and then locally optimizing along that global path. The applicability of this model to surface-mount manufacturing systems is studied in different scenarios. By changing the priorities of the machines, different results may be obtained. By comparing these results, the best one may then be determined. Simulation results using the two-phase algorithm show an improvement over other planning and control methods.

Inspired by the natural suspension capabilities in the biological limb system, a design of an active suspension system is developed for damping the undesired forces and displacements caused to vehicles by the irregularity on the road surface. The proposed controller for suspension is based on a muscular-like model fitted from the responses of different voluntary and involuntary limb movements. Because the muscular-like model emulates the property of biological damping behavior, the proposed active suspension controller has a very unique feature that will enable the controlled vehicle to adapt to varying loads and sudden impacting forces. This is in contrast to the conventional linear controller that has sensitivity and stability problems when the dynamic system is subjected to varying loads. To realize our controller, a small-scale, quarter-car model was built for our experiments on active suspension.

By modeling the nonlinear damping property of the biological muscle-reflex system, a neuromuscular-like controller has been proved to be capable of reflexing to any changing displacement and enhancing the compliant forces for the changing motion. The unique capability possessed by this controller presents a prominent application for designing a mechanical orthosis in aiding the limb motion of disabled people who have minimal or no voluntary control of limb muscle. To demonstrate the feasibility and effectiveness of the concept, the elbow and shoulder joints of a PUMA 560 robot were implemented with the neuromuscular-like control to emulate the limb motion.

From the concept of designing for automation, a system modeled from simple part-mating is proposed for helping automate the fine motion control phase of assembly operations. The proposed system consists of three subsystems. The first subsystem is a part-mating model categorized from different mating geometric constraints of simple parts. The second subsystem is a coding system, named structured assembly coding system (SACS), that codes different part-mating tasks with different levels of geometrical constraints. From this coding system, specific part-mating types can be identified for different tasks of assembly operations. Conversely, constraint configuration for each part-mating task can also be generated from the proposed part-mating model. After constraint configurations are identified for an assembly operation, the third subsystem is to automate an assembly operation by deducing the compliance control strategies. The proposed system is demonstrated through a case study of pump assembly.>

This study focuses on the characterization and control of voluntary movements by analyzing motor command patterns, ensuing analysis from involuntary limb movements. As a result, a neuromuscular-like model with two muscle-reflex models is proposed, and motor command patterns are approximated identified from the experimental data. Based on the identified motor command patterns, a control strategy, muscle modulation control, is proposed for possible applications in robotic control using neuromuscular-like models.>

The muscle-reflex mechanisms of private limbs are studied and modeled so that robotic controls may benefit from the findings. An extensive body of experimental evidence indictates that velocity-dependent force responses of the neuromuscular system have a nonlinear damping effect proportional to a fractional power of velocity. This highly nonlinear viscosity may help limbs adapt to different loads and bring movements to graceful terminations. To explore the characteristics of this nonlinear damping property, a theoretical study using the phase-plane approach is presented. The effects of different loads, damping constants, and stiffnesses are analyzed and simulated. From the results of this phase-plane analysis, a muscle-reflex model is developed and proposed for robotic compliance control.>

An efficient approach is presented for solving the inverse Jacobian problem for wrist-partitioned robots; specifically, the differential inverse kinematics problems. By selecting the wrist coordinate frame as the reference coordinate frame, a simplified Jacobian relation can be obtained for deriving a set of orthogonal bases for the screw system. From these orthogonal screws, the instantaneous Cartesian motion can be separated into translational and rotational parts for solving the differential joint variable rates. As a result, a set of concise, closed-form equations for solving the above inverse problem can be easily generated. For illustration, the PUMA 560 robot is selected as an example. On the basis of the simplified equations, the exact form of the inverse Jacobian matrix can also be obtained.>

A novel geometric method for the planning and controlling the orientation of a robot's end-effector as it moves along a prescribed translational path is presented. To eliminate the influence of geometric changes to the path and to be able to predict the orientation, the proposed method plans rotational paths with respect to a natural local coordinate frame formed by three unit vectors, namely, the tangent, normal, and binormal vectors, defined by the geometry of the path. A motion control strategy is developed to maintain the desired rotational speed or acceleration of the end effector. Examples are presented which show the practicality of the method.>

A design is presented of a robot accuracy compensator after calibration, which can efficiently calculate and compensate the calibrated kinematic errors for robot manipulators. This compensator consists of a direct robot accuracy calculator (DRAC) that efficiently calculates the accurate robot Cartesian positions using a recursive formulation of the T/sub /i matrix, and an inverse robot accuracy compensator (IRAC), that calculates the equivalent changes in robot joint positions caused by the Cartesian errors obtained from the DRAC. By subtracting these equivalent joint position changes to the current existing kinematic joint solutions, the robot accuracy caused by the kinematic errors can be compensated. As an example, an efficient accuracy compensator designed for PUMA 560 robots is given.>

A method is presented for calibrating and compensating for the kinematic errors in robot manipulators. A method of selecting a set of independent kinematic errors for modeling any geometric errors in a manipulator's structure is developed. A calibration algorithm is presented for finding the values of these kinematic errors by measuring the end-effector position. These kinematic errors are experimentally determined for a PUMA 560 six-joint manipulator. Two general-purpose compensation algorithms are developed and the improvement in the Cartesian position of the end-effector is experimentally measured and these results are presented. The results show that the positioning accuracy of a robot manipulator can be substantially improved using a relatively simple technique for measuring the Cartesian position of a tool attached to the end of the manipulator.>

This paper presents a method of calibrating and compensating for the kinematic errors in robot manipulators. A method of selecting a set of independent kinematic errors for modeling any geometric errors in a manipulator's structure is developed. A calibration algorithm is presented for finding the values of these kinematic errors by measuring the end-effector Cartesian position. These kinematic errors are experimentally determined for a PUMA 560 six joint manipulator. Two general purpose compensation algorithms are developed and the improvement in the Cartesian position of the end-effector is experimentally measured and these results are presented.

A feasible Cartesian trajectory of a robot manipulator means that every point along the planned trajectory is within the workspace of the robot. The decision of a feasible Cartesian trajectory given to a robot manipulator is an important element of an intelligent robot system. In this paper, a method based on the robot workspace geometry to decide the feasibility of a given trajectory is presented. The method treats the workspace of a robot manipulator as a geometrical object, then this geometrical workspace can be properly described and utilized to determine the feasibility of a Cartesian trajectory. Due to the complexity of the general case, a robot manipulator system with six revolute joints is selected as the case study.

The positioning accuracy problem of robot manipulators has long been one of the principal concerns of robot design and control. In a previous work, a linear model that described the robot positioning accuracy due to kinematic errors was developed. However, the previous work considered only the small errors by ignoring the higher order terms and did not address the special case of two consecutive parallel joints. In this work a more detailed model is given that applies to consecutive parallel joints and includes the second-order terms. By comparing the results of the linear model and the second-order model, the accuracy of the linear model can be evaluated for a given manipulator and range of input kinematic errors. The error envelopes obtained using the linear model and the developed second order model for the Puma 560 are plotted and compared for various sets of input kinematic errors. A comparison of the computation complexity for the two models is also given.

A new Cartesian position control called resolved motion force control (RMFC) has been developed for robot manipulator. It adapts force convergence concept to control the Cartesian force and position instead of classical joint control. In this way, the changing configurations, gravity loading, and internal friction of the manipulator can be automatically compensated. Also, the method only uses the Jacobian transpose matrix such that it is applicable to more than six degrees-of-freedom manipulator without increasing the computational burden.