Bum-Hee Lee

A dynamic programming approach to a reel assignment problem of a surface mounting machine in printed circuit board assembly

We consider the problem of assigning reels of components to slots on feeder racks of a surface mounting machine which is used to populate printed circuit boards with surface mount technology. This reel assignment problem (RAP) is one of a series of optimization problems that should be addressed to improve the production rate. We preprocess RAP to facilitate the application of dynamic programming and then formulate it as an integer programming problem. We solve the problem by using a heuristic algorithm based on dynamic programming. We implement the algorithm as a computer program and perform computer simulations. The simulation results are compared to those of the Effective Algorithm previously proposed.

An approach to robot motion analysis and planning for conveyor tracking

Robot motion is analyzed and planned for conveyor tracking considering the speed of the conveyor belt and the locations of the part and the robot. The joint torque limit, joint velocity, acceleration, and jerk limits of the robot are taken into account in the motion analysis and planning. To include the robot arm dynamics, the problem is formulated as second order state equations using a parametric function. The conveyor tracking problem is then converted to an optimal tracking problem. The solution that minimizes the specified performance index is obtained using the dynamic programming approach. Numerical examples are presented to demonstrate the significance of the proposed method for conveyor tracking of the robot in a workcell.<<ETX>>

Time-varying obstacle avoidance for robot manipulators: Approaches and difficulties

This paper addresses an overview of time-varying obstacle avoidance problems for robotic manipulators. We propose four different approaches to solving these problems. They are the Heuristic Off-line (HOF) approach, the Heuristic On-line (HON) approach, the Analytic Off-line (AOF) approach, and the Analytic On-line (AON) approach. The AOF approach is particularly pursued and derived in this paper. Some fundamental difficulties are then discussed in the AOF approach. It is shown that the analytic approach is not always successful in solving the time-varying obstacle avoidance problems.

A Hierarchical Method to Improve the Productivity of Multi–Head Surface Mounting Machines

Abstract This paper considers the problem of improving the productivity of multi-head surface mounting machines which are used to populate printed circuit boards with surface mount technology. The complexity of this problem is highly dependent on the specific number of heads which are used to pick and place components. This paper proposes a method for surface mounting machines with any number of heads. That is, our method can be applied regardless of the number of heads. The PCB assembly time depends on two decision variables: (1) assignment of reels to slots on feeder racks; and (2) sequencing of pick-an-place movements. These two problems are decomposed into a hierarchy of related subproblems. Since all subproblems in the hierarchy are known to be of a combinatorial nature and computationally intractable, we develop heuristics which are based on dynamic programming and the nearest neighbor traveling salesman problem technique. We implement the method as a computer program and perform computer simulation...

An algorithmic approach to the improvement of efficiency for surface mounting machines

With rapid development of the surface mounting technology (SMT), continual efforts have been made to make the surface mounting machines efficient as well as reliable. The authors propose an algorithmic approach to the improvement of efficiency for surface mounting machines. For minimizing the set-up time, a CAD data conversion algorithm, which makes the data for the pick-and-place sequences from the CADSTAR output files, is proposed. Also, for optimizing the feeder arrangement and the traveling path of heads in the surface mounting machine, SCM 130 model, effective feeder arrangement algorithms are proposed. To evaluate their performance, the proposed algorithms are tested on the assembly tasks of PCBs manufactured through simulations. As a result, it is shown that the proposed algorithm reduces the time required to perform the assembly sequences by maximum 9 percent when the task time is compared with the time required to perform the assembly sequences made by an expert.

Redundancy optimization for cooperating manipulators using quadratic inequality constraints

In redundancy optimization problems related to cooperating manipulators, constraints should be considered for physical limits of the manipulators. The constraints have been imposed mostly in the form of linear inequality constraints, which lead to polyhedric feasible regions. We propose quadratic inequality constraints (QICs) which lead to ellipsoidal feasible regions to solve the optimization problem faster and to directly handle constraints on quadratic quantities. We investigate the effect of the use of QICs from the points of view of problem size and change of the feasible region. In order to efficiently deal with QICs, we utilize the dual quadratically constrained quadratic programming (QCQP) method. The proposed scheme and another well-known quadratic programming method are applied to numerical examples and compared with each other. The results show that the use of QICs makes it possible to make trade-off between optimality and fast computation capability and implements faster computation than the existing method.

Two-stage control approach of a robot manipulator for conveyor tracking application

A robot control scheme for the specific application to conveyor tracking is newly proposed. To improve the performance of conveyor tracking, the robot arm dynamics is incorporated into the control scheme. The proposed scheme also takes the torque and smoothness constraints into account for optimal conveyor-tracking. Dividing the conveyor speed into the nominal term and the perturbed term, a two-stage control strategy is employed to cope with the nonlinearity and uncertainty of the robot-conveyor system.<<ETX>>

Elasticity modeling and estimation for haptic contact using a DD‐robot

Purpose – To propose a new haptic modeling and contact analysis algorithm (modified long element method (MLEM)) to efficiently model deformation, to estimate elasticity, and to provide the characterization of contact with deformable objects, which is important in teleoperation and haptic system.Design/methodology/approach – Widely used finite element method for haptic rendering and visualization of deformable objects has limitations in real‐time applications because of its massive calculations and the absence of physical modeling. Using long elements method (LEM), the authors propose the MLEM which is capable of real‐time deformation rendering and elasticity estimation with reliable physical modeling. The authors applied MLEM to a simple haptic system composed of the three‐link SNU DD‐robot and a force‐feedback joystick.Findings – An efficient, real‐time haptic modeling for deformable objects has been developed. MLEM provides physically accurate deformation modeling in real time, and estimates the elastic...

Path constrained time-optimal motion of multiple robots holding a common object

This paper deals with a systematic analysis of the time-optimal motion of a multiple robot system carrying an object along a prescribed path. In our approach, the time-optimal motion planning problem is formulated in a concise form by employing a parameter describing the movement along the path and a vector representing the internal force. Various constraints governing the motion yield the so-called admissible region in the phase plane of the parameter. The orthogonal projection technique and the theory of multiple objective optimization make it possible to construct the admissible region, while taking into account the load distribution problem that is coupled with the motion. Furthermore, our approach provides a way of detailed investigation for the admissible region that is not simply connected. The resulting velocity profile of the path parameter and the internal force at every instant determine the optimal actuator torques for each robot.