Wen-Tung Chang

The force transmissivity index of planar linkage mechanisms

In this paper, a new force transmissivity index (FTI) of planar linkage mechanisms is proposed. The index is used to quantitatively measure the force transmission quality from the input link to an output link. Traditionally, the transmission angle is used to measure the ability to transmit motion for planar four-bar linkages. However, the transmission angle is usually limited to be used at four-bar linkages due to the structural simplicity. For complex multi-loop mechanisms, it is often difficult to define the force transmissivity. Here we have established a procedure of force transmissivity analysis for planar linkage mechanisms. The method is based on the static force analysis and the concept of power flow path. It is found that the force transmissivity of a mechanism depends not only on the configurations of the mechanism, but also on the selection of the output link and the forms of the loading. We have compared the results based on the FTI with the results from the Jacobian matrix method and the joint force index (JFI) method for four-bar mechanisms. It shows that the proposed FTI can describe the force transmission performance more accurately than other methods do. It is concluded that the index can be used as a better measure of force transmissivity analysis for planar linkage mechanisms.

Mechanical Error Analysis of Disk Cam Mechanisms with a Flat-Faced Follower

By employing the concept of equivalent linkage, this paper presents an analytical method for analyzing the mechanical errors of disk cam mechanisms with a flat-faced follower. The resulting error equations do not really involve the location of the curvature center of the cam profile, and locating the curvature center of the cam profile is not essential. The resulting errors are significantly affected by the pressure angle, and the smaller pressure angle will result in the smaller mechanical error. In the worst case, owing to the joined effects of various design parameters, the accuracy of the follower motion may degrade considerably. For the oscillating follower case, all acceleration error functions have a sudden change at every beginning and at every end of the motion even though the theoretical follower displacement is cycloidal motion.

Force Transmissibility Performance of Parallel Manipulators

In this paper, a new force transmission index called the mean force transmission index (MFTI) is proposed, and the force transmissibility analysis procedure is established for parallel manipulators. The MFTI is an extended definition of the force transmission index (FTI) introduced by the authors previously. It is shown that the FTI is a function of the input velocity ratio (IVR) for a multi-DOF mechanism of the same configuration. To represent the force transmissibility by a definite value, the MFTI is defined as the mean value of the normalized FTIs function over the whole range of the IVR. The force transmissibility analysis of two planar parallel manipulators is illustrated using the MFTI method. The result is compared with that of the Jacobian matrix method and the joint force index (JFI) method. It shows that, especially for symmetric parallel manipulators, an approximate inverse-proportionality relationship exists between the JFI and MFTI, and between the maximum input torque/force and MFTI. It is concluded that the MFTI can be used as a quantitative measure of the force transmissibility performance for parallel manipulators. In the end, a design optimization problem is studied by taking the

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.

Examining the profile accuracy of grinding wheels used for microdrill fluting by an image-based contour matching method

Abstract The helical flutes in drills are usually made by grinding cylindrical rods to form helically swept grooves. In order to maintain the quality of the fluting process for microdrills, grinding wheels must be trued and dressed regularly. It is therefore quite important to examine the profile accuracy of trued and dressed wheels. With the aid of machine vision, this paper presents an image-based method for examining the profile accuracy of grinding wheels used for microdrill fluting. Using thin plate specimens ground to yield two-dimensional contours for duplicating the topographical profiles of inspected grinding wheels, digital images of the ground contours can be captured in order to detect their coordinate data by edge detection. A contour matching method is then developed to calculate the relative deviations between the theoretical and detected inspected contours, and the profile accuracy of the inspected grinding wheel can thus be indirectly evaluated. To test the proposed method, a machine vision system was built, and experiments examining diamond grinding wheels used for machining helical flutes in microdrills were conducted. The results showed that the proposed contour matching method could achieve sufficient repeatability in the examination of wheel contours.

A Simplified Method for Examining Profile Deviations of Conjugate Disk Cams

The profile errors of conjugate disk cams can be indirectly examined by means of measuring the conjugate condition of the assembled conjugate cam mechanism. This paper demonstrates how to measure the conjugate condition of the assembled conjugate cam mechanism to reveal the cam profile errors and also develops an analytical approach for relating the variation of the conjugate condition with the cam profile errors. For the machined conjugate cams with profile errors, if the subtending angle of the oscillating follower arms is intentionally changed to be variable, the variation of the subtending angle of the follower arms may indicate the variation of profile errors when the cams rotate. According to the magnitude of the subtending angle variation, the profile deviations of conjugate disk cams can be analyzed analytically. The profile errors of a pair of conjugate cams can be evaluated by means of the corresponding motion variation of the indicator reading. For such an examining method, the only required measuring instrument is a dial indicator. A pair of conjugate cams were examined by the method and also measured using a coordinate measuring machine to test the accuracy and efficiency of the method.

Creative mechanism design for a prosthetic hand.

Abstract In this paper, an auxiliary methodology called the creative mechanism design is introduced into the innovation of gripping devices for prosthetic hands. This methodology is a systematic approach based on modification of existing devices for the generation of all possible topological structures of mechanisms and mechanical devices. An existing gripping device (Teh Lin ATG-5F prosthetic hand) constructed by a planar six-bar linkage with one degree of freedom is dealt with by using this methodology. Through the processes of generalization, number synthesis, specialization and particularization for the existing design, five new mechanisms are created in this study to apply to anthropomorphic prosthetic hands. The results show that the methodology for creative mechanism design is a powerful tool for creating new categories of mechanisms to avoid existing designs that have patent protection and can help designers in the conceptual phase. Also, this methodology is validated as a useful way to improve prosthetic hands for amputees.

Inspecting Profile Errors of Conjugate Disk Cams With Coordinate Measurement

To inspect cam profile errors, a coordinate measuring machine (CMM) is frequently employed. The coordinate data of discrete points at the cam surface are measured by a CMM in order to further evaluate the actual cam profile with complicated interpolation algorithms, and then the cam contour approximated by these algorithms may be compared with the theoretical one. In this paper, a direct and simple analytical method, instead of a numerical interpolation algorithm, is proposed for inspecting the profile deviations of conjugate disk cams with coordinate measurement data. The method is based on the derived correlation between the radial-dimension errors and the normal-direction errors of conjugate cam profiles. To verify the proposed method, an experiment of inspecting a pair of conjugate disk cam profiles was conducted. The experimental results obtained from the proposed method were compared with those obtained by using the Hermite interpolation method. It shows that this method is accurate and more efficient for inspecting the profile errors of conjugate disk cams.

Computerized tolerance analysis of disk cam mechanisms with a roller follower

The tolerance analysis is one of the key elements of design and manufacturing of cam mechanisms. This paper presents a computerized method for analyzing the tolerances in disk cam mechanisms with a roller follower. By employing the concept of simulated higher-pair contact analysis, the kinematic deviation of the follower motion arising from the tolerance amount of each design parameter can be determined numerically. The offset translating roller follower and the oscillating roller follower cases are given to illustrate the proposed method. The tolerance analysis results show that, owing to the combined effects of various design parameters, the position accuracy of the follower motion may degrade considerably. But, the tolerance amounts of the design parameters may also have a compensating effect to enhance the relative accuracy of the follower motion between its high and low dwell positions. Hence, it is possible to find the optimal tolerance combination for balancing the kinematic accuracy and the tolerance amounts of disk cam mechanisms with a roller follower.

Tolerance analysis and synthesis of cam-modulated linkages

Abstract Cam-modulated linkages that can achieve superior kinematic performance as compared with pure linkages have been widely applied in a variety of automation machinery. The tolerance analysis and synthesis are thus quite essential in the design and manufacture of precision cam-modulated linkages. This paper presents comprehensive and systematic mathematical tools for dealing with the tolerance analysis and synthesis of cam-modulated linkages. Based on the concept of equivalent linkage and the derived correlation between the radial-dimension errors and the normal-direction errors of the cam profile, the sensitivity analysis method for equivalent linkages is introduced for analyzing the tolerances in cam-modulated linkages, whose output error equations can be derived through an analytical means. Then, by incorporating the sensitivity analysis method and the concept of design for manufacturing and assembly (DFMA), an optimization model for synthesizing the tolerances in cam-modulated linkages is developed. The objective of this optimization model is to maximize the manufacturability and assembility of a cam-modulated linkage while maintaining acceptable kinematic accuracy of its output motion. A practical case study of analyzing and synthesizing the tolerances in a cam-modulated linkage type pick-and-place device is then performed to illustrate the presented methods. It shows that the mathematical tools presented can be helpful to the design and manufacture of precision cam-modulated linkages.