Geo-Ry Tang

Component tolerance design for minimum quality loss and manufacturing cost

Optimal tolerance designs imply the tolerance assignments by which products are produced with a minimum total cost. In this paper, both the manufacturing cost and the quality loss of assemblies are considered as part of total cost in determining their component tolerances. A systematic design procedure is given for products with either symmetric or asymmetric loss function. Under the new arrangement, the problem of tolerance assignment can be solved by a single optimization process. The software necessary to complete the tolerance design can be installed on a standard personal computer.

Tolerance design for products with correlated characteristics

Abstract This paper presents a design method for controlling dimensional tolerances of components with multiple functional characteristics. The discussions focus on the characteristics derived from common geometric dimensions. In order to approach the robust design, the tolerance design is achieved by minimizing the total expense, which is the sum of the manufacture cost and the quality loss. Since a product may fail because of any imperfect characteristic, the total quality loss includes all the contributions from individual losses. It is recommended that the losses in correlated characteristics be calculated in separate groups. The computation of the total loss involves the evaluation of the variances–covariance matrix of the related characteristics.

Robot calibration using a single laser displacement meter

Abstract A high level of accuracy in industrial robots has been specified as an essential requirement in many advanced robot applications. Instead of hardware modifications, robot positioning capability may be improved by a successful calibration procedure. Since variations of robot geometry will result in serious robot positioning error, this paper presents an algorithm to accurately identify the robots geometric parameters through a new calibration procedure. The proposed calibration scheme utilizes a non-contact, automatic data acquisition system which includes a single laser displacement meter. Without the necessity of three-dimensional measurements around the workspace, the calibration process can be effectively implemented on commercial robots located in an industrial environment. A comparison of the robot static positioning performance, before and after the calibration, reveals the success of the proposed calibration procedure.

AUTOMATED OPTICAL INSPECTION SYSTEM FOR THE RUNOUT TOLERANCE OF CIRCULAR SAW BLADES

Circular saw blades are fundamental cutting tools applied to cut off materials. Inspection of finished products of circular saw blades is important in order to ensure their manufacturing quality and sawing performance. Traditionally, a contact inspection method is adopted to measure the runout amounts of circular saw blades. In order to improve the quality of the runout inspection, a non-contact inspection method based on machine vision is required. In this paper, an automated optical inspection (AOI) system was developed exclusively for inspecting the runout tolerance of circular saw blades. Based on the integration of motion control and image processing techniques, calibration and automated inspection processes for the developed AOI system were then established. Experiments to inspect circular saw blade samples were also conducted in order to test the feasibility and reliability of the developed AOI system. From the experimental results, the developed AOI system, in combination with the automated inspection process, could achieve sufficient repeatability and was verified to be able to inspect the runout tolerance of certain circular saw blades.

Plane-motion approach to manipulator calibration

It is well known that identification of geometric parameters can significantly enhance the accuracy of robot manipulators. A number of different approaches to manipulator calibration have been demonstrated in the recent literature. A part of the calibration process that is common to all of the proposed techniques is the collection of a dataset that relates the measured position and possibly the orientation of the end-effector to the joint displacements for a number of poses. This data-acquisition step is usually the most tedious part of the calibration process. Accurate location of points on the end-effector can be quite time consuming to accomplish manually and the equipment for automated data acquisition is expensive.The purpose of this work, therefore, is to demonstrate a simplified approach to acquiring the data necessary for manipulator calibration. In the proposed approach, the only equipment used for data measurements is a flat plate and a test block mounted on the end of the robot arm. To demonstrate the method, a model and an identification algorithm for a PUMA 560 manipulator are developed. The data-collection process is described and the procedure is validated through a computer simulation. Finally, an experiment is conducted whereby data is collected for a PUMA manipulator and used to identify the kinematic parameters. The resulting manipulator model leads to a significant improvement in accuracy.

A list approach to tolerance charting

Abstract Tolerance charts for mechanical components are essential to the planning of manufacturing processes as well as to the assurance of product quality. The design of such a chart, however, is not only a time-consuming job but also highly reliant upon engineers expertise. This paper presents a new approach which utilizes list representation to assist the analysis as well as the computation during the generation of tolerance charts. The method has been successfully implemented on a computer-aided design software based on a personal computer.

Optimal allocation of process tolerances and stock removals

Tolerance charts have been used as an effective tool to ensure that a specific processing sequence is appropriate for a product of the required dimensions. Different arrangements of manufacturing tolerances and amount of stocks to be removed at each machining operation result in different production costs. Instead of existing heuristic, experience-based methods, this paper presents a new approach by means of which process tolerances and stock removals are simultaneously allocated through an optimization program, In approaching the optimal design, a cost function, the value of which varies with design variables (process tolerance and stock removal at individual cuts), is chosen as the objective to be minimized. During the searching process, the variables are subject to the constraints derived from dimension chains associated with a tolerance chart.

A study of three robot calibration methods based on flat surfaces

Abstract Among the various calibration techniques proposed by researchers, three of them applied a similar algorithm of which the data collection was constrained on two-dimensional surfaces even though the kinematic calibration was designed for improving a robots position accuracy in a three-dimensional workspace. In addition to introducing the hardware and calibration algorithms applied, this paper also presents a comparison of the three methods. The calibration results are based on equal quantities of experimental data.

Microfabricated microfluidic platforms for creating microlens array

The paper presents a novel and economic manufacturing process for microlens arrays (MLAs). This process uses micromilling machining, PDMS casting, and hybrid bonding between a glass substrate and PDMS membrane to create a microfluidic chip which is used for manufacturing MLAs on a PDMS substrates. MLAs of various diameters were fabricated for experiments, including 1000 μm, 500 μm, and 200 μm. The sag height of the MLAs is easily adjusted by controlling the pressure inside the microchannel to deform the PDMS membrane. Multiple experiments were conducted to characterize the performance of MLAs, the results of which demonstrate: (1) this fabrication process is able to manufacture MLAs with various dimensions and the diameter of an MLAs is determined by the size of micromilling bit and cutting path; (2) the sag height and curvature of MLAs can be controlled by the PDMS membrane thickness and the hydraulic pressure inside the microchannel; (3) an optical system was built to investigate the uniformity of MLAs and the experiment results showed uniform focal length of MLAs; (4) the resulting MLAs magnify tiny objects and significantly enhance the fluorescence signal emitted from the microchannel.

Computer-aided design of instrument loop sketch diagrams

Abstract The schematic expressions of control loops are essential for process instrumentation. By means of loop sketch drawings, control strategies are specified and hardware configurations can be determined at the beginning of a design project for a new plant. With the assistance of computer graphic software, the quality of loop sketch drawings has been improved. The engineering man-hours required to generate these diagrams, however, has not decreased significantly. An integrated computer-aided design system has been proposed. This system employs the techniques of design optimization, database management and artificial intelligence in addition to the computer graphics. The system generates loop sketch drawings automatically, and then initiates an instrument connection database for the succeeding design items used for process instrumentation.