Ming-June Tsai

Geometric optimization of serial chain manipulator structures for working volume

Broadly speaking, the regional structure of a manipulator, which consists of the three inboard joints and their associated members, determines the workspace shape and volume. The orientation structure, which for a six-degrees-of-free dom manipulator consists of the three outboardjoints and members, determines the geometric dexterity or orientation potential of the manipulator. It is possible to determine the optimal dimensions of the regional structure for a given total length, using straightforward geometric arguments. By the use of the spherical counterpart of Grashofs theorem formu lated by Freudenstein (1964-65), it is also possible to show that there is an optimum geometry of the orientation structure. Two methods of characterizing geometric dexterity are utilized in this paper. The first is the concept of a dexterous workspace, which is a portion of the workspace within which the hand may assume any orientation. Although the dex terous workspace is a very useful concept for theoretical purposes, it is of limited practical utility because mechanical joint motion limits usually preclude its existence in real industrial robot structures. The second method of character izing geometric dexterity is to trace the portion of the work space within which the hand can assume a specified orienta tion. In this paper, the geometric conditions for the existence of a dexterous workspace are formulated for geometrically optimum, six-revolute manipulator structures. The optimiza tion criteria used include,freedom from geometric singular ities. We show that for an optimal geometry, singular posi tions can be completely excluded with small reductions of the joint motion ranges. These reductions have a negligible effect on the geometric performance of the system.

Automatic body feature extraction from a marker-less scanned human body

In this paper, we propose a novel method of body feature extraction from a marker-less scanned body. The descriptions of human body features mostly defined in ASTM (1999) and ISO (1989) are interpreted into logical mathematical definitions. Using these significant definitions, we employ image processing and computational geometry techniques to identify, automatically, body features from the torso cloud points. We have currently extracted 21 feature points and 35 feature lines on the human torso; this number may be extended if necessary. Moreover, less than 2 min processing time is taken for body feature extraction starting from the raw point cloud. This algorithm is successfully tested on several Asian female adults who are aged from 18 to 60.

Generalized evaluation for the transmission performance of mechanisms

Abstract In this paper the concept of generalized transmission wrench screw (GTWS) that characterizes the transmission properties of mechanisms is introduced. Based on this concept, measurements of the transmissivity and the manipulability are defined. Both of them have the expressions similar to the manipulability index, which is a quantitative measure of the closeness of a robot configuration to singularity. The variable lead screw transmission mechanism provides an example for illustrating evaluation of transmission performance.

Geometric optimization of manipulator structures for working volume and dexterity

Broadly speaking, the regional structure of a manipulator, which consists of the inboard three joints and the members associated with them, determines the workspace shape and volume. The orientation structure, which, for a six degree of freedom manipulator, consists of the three furthest outboard joints and members, determines the geometric dexterity or orientation potential of the manipulator. It is possible, using straightforward geometric arguments, to determine the optimal dimensions of the regional structure for a given total length. By the use of the spherical counterpart of Grashofs theorem formulated by Freudenstein, it is possible also to show that there is an optimum geometry of the orientation structure.

Two-phase optimized inverse kinematics for motion replication of real human models

This paper proposes a novel two-phase optimization method to solve the joint variables of a real human model using captured motion data. A dual-mode 3D vision system was used to generate a body geometric model. Twenty-three link segments were separated from the body model. Markers were then affixed on each link for motion capturing by the same vision system. A body kinematic model was then constructed from the geometric model by assigning joint constraints between every two adjacent links. The model contains five kinematic chains with 48 joint freedoms. Joint variables were solved by the first-phase optimization to obtain an appropriate initial posture between two adjacent links. For each kinematic chain, redundant joint variables were solved using the second-phase optimization. By setting proper weightings, the resulting postures of the kinematic model closely match up with those of the motion captured data, while the endpoints can trace the original trajectories as well. Furthermore, the kinematic model offers more reasonable motions than the geometric model that replicates the raw motion data since some excessive movements are corrected by the joint constraints.

Development of a high-precision surface metrology system and its uncertainty analysis

In this paper, we present a high-precision surface metrology system based on structured light projection. Gray code patterns are projected onto the object surface by a DMD projection device and a CCD camera captures the distorted pattern images. For the purpose of precision measurement, a 3D mathematical model is proposed for the system and a calibration process is developed to obtain system parameters. The surface profile can be computed based on the calibrated model. In order to acquire higher measurement resolution, we propose a correspondence matching method which combines Gray codes encoding and sub-pixel edge detection. With a line-shifting procedure, the measurement resolution is elevated four times higher. Furthermore, an uncertainty analysis is performed to evaluate the performance of the developed system. Experiment results demonstrate the system has measurement area of 12 times 9 mm2 with lateral resolution about 10mum and vertical resolution about 3mum.

CUSTOM-MADE BRACKETS FABRICATION BY AN ADDITIVE MANUFACTURING PROCESS FOR ORTHODONTIC TREATMENT

Brackets are basic elements of orthodontic systems. Traditionally, they are produced by a powder-injection mass production process, by which it is difficult to develop individualized products. This study applies computer-aided engineering techniques, including digitizing, virtual model design, and additive manufacturing (AM) to orthodontics for the production of customized brackets. First, a digital model of the teeth was obtained via a 3D scanning process, in which an individual teeth plaster mold was digitized; customized brackets were then designed based on the model, and physical brackets were rapidly fabricated by AM processing. Finally, key dimensional measurements of the brackets were taken to confirm whether the brackets fulfilled the functional requirements for clinical usage. By this process, brackets designed for different teeth pads were obtained by digital planning, CAD design and rapid manufacturing. The custom-made brackets include complete dental profile information, and increase the efficiency of treatment, save clinical setup time, and reduce the treatment duration and cost for the patient. The direct manufacture of metal brackets by an AM process is a modern method with great potential to be used in the generation of customized brackets for orthodontic treatment.

Using haptic manipulator in a virtual design studio

In this research, we designed and constructed a 5-axis motion with 3-axis force feedback manipulator as an open loop I/O device to use in three-dimensional virtual environments. The manipulator features five encoders to obtain the stylus position and orientation. In order to augment the visual output, the manipulator is equipped with three motors to provide a corresponded reaction force at the moment of colliding with virtual objects in the virtual environment. The research is carried out by four phases: design and construction of the haptic manipulator, virtual design studio creation, collision detection algorithms, and contact force model generation.

New design curves for fillet welded t‐joint

Abstract The stress distribution in fillet welded T‐joints was investigated with computer modeling. The finite element method was used for the analysis of T‐joints in the plane stress condition, under static load. Photoelastic stress measurement was employed to check the validity of the computer calculations. Following the American Welding Society (AWS) welding design procedure, the AWS permissible design loads were used as a reference for the stress analysis. The ultimate strength of the welded T‐joints was determined when the plastic hinge first occurred in the joints during the loading. A set of newly designed curves for fillet welded T‐joints with various degrees of flange flexibility were obtained. The curves were compared with the AWS Code and the American Institute of Steel Construction (AISC) Specifications. As a result, a revision in the application of these two design concepts was conceived. The full strength weld size was also evaluated with different web lengths and flange flexibilities accord...