In this study, we address the case of a horizontal two-link robot with flexible timing belts and present a structural design guideline to reduce its undesirable vibration. First, an equation of motion was constructed using Lagrange's equation, and its validity was examined by comparing the experimental and simulation results using an index to estimate the undesirable vibration. As a result, it was determined that the mathematical model could be used as a simulation tool for design optimization. Then, by a simple structural modification, a design guideline was proposed to reduce the undesirable vibration in the extension motion: namely, a robot arm was designed such that the location of its center of gravity is near the rotation center and its moment of inertia is small. Other optimum structural design may be obtained for the other motion of robot. The points of this study are to propose the design method that includes the definition of objective function for the optimum design and to show a design guideline to reduce the undesirable vibration for a certain motion of robot.
This paper describes a measurement method of three-dimensional (3D) forearm movement during pitching motion using an elbow-mounted sensor (3D sensor). The 3D sensor comprises accelerometers of two kinds with dynamic range of 4 [G] and 100 [G], and two kinds of gyroscopes with dynamic range of 300 [deg/s] and 4000 [deg/s], respectively, because the sensors used in measurement of sports activities require a wide dynamic range. The 3D sensor, attached on the forearm, measures 3D acceleration and angular velocity. The 3D trajectory of the forearm is estimated through double integration of the measured acceleration, which is transformed from the acceleration based on the system of moving coordinate on the forearm to that on the fixed system of coordinates. Because the estimated trajectory of the forearm is affected by the numerical integration of the measured data including errors, the 3D trajectory error is reduced by determining the position and posture of the forearm at the end of the pitching motion. Results of the pitching experiment show that the 3D trajectory and angle of the forearm estimated by the 3D sensor agree with those measured from a video camera image with an error margin of around 10 %.
This paper proposes a design method to improve or obtain the desired output motion characteristics of single degree-of-freedom (DOF) Four-bar mechanisms by varying the speed trajectory and the length of the input link. This approach adds a ternary link to the original mechanism. The ternary link is adjacent to the input link, roller link, and connecting link, and makes use of a sliding pair, revolute pair, and revolute pair, respectively. The roller link, which is adjacent to the ternary link and fixed link by a revolute pair and a rolling pair, is guided by a designed slot embedded in the fixed link while the input link is driven by a servomotor with a specific speed trajectory. A Bezier curve is applied to determine the input speed trajectory and contour of the guiding slot. Examples are given to verify the feasibility and effectiveness of this work.
ISO 16047 was published in 2005, where test method and conditions to quantify the tightening characteristics for threaded fasteners are specified. However, there is no testing apparatus applicable to various types of threaded fasteners due to the constraint on the accuracy of ±2% of the values to be measured. The goal of this study is to develop a new tightening testing machine to be used for the torque/clamp force testing in accordance with ISO 16047. In this study, the load/torque cell system having new constructions with piezoelectric force sensors were developed and evaluated, which can be used to measure the clamp force and torques acting on bolt shank and on bearing surfaces, respectively. The piezoelectric sensor has the merits in terms of the resolution of the measurement and its high rigidity. However, experience shows that there are some disadvantages as well to be removed to achieve the measurement with sufficient accuracy. Experimental and analytical considerations have been performed to seek the root causes that may generate the measuring error. Consequently, the possibility to exclude such bad effects as the crosstalk and the drift of the sensitivity was confirmed, and the appropriate design concepts and parameters were proposed.
The relationship between acoustic emission (AE) signals and tribological phenomena in the elementary processes of friction and wear is examined. The elementary processes of friction and wear were observed by a frictional surface microscope, which installed a friction system into the view of an optical microscope. In this paper, the elementary processes are focused on the plastic deformation of the friction surface and the formation of wear particles between friction surfaces. In-situ experiments with the frictional surface microscope were performed by a pin-on-block type sliding test for iron and zinc. The friction surface and its side face were also observed by an atomic force microscope. The results show that two types of AE signals—a continuous AE signal of low amplitude and a burst-type AE signal of high amplitude—are detected in the elementary processes of friction and wear. The continuous AE signal of low amplitude is detected by the generation of slip lines and wear elements. The burst-type AE signal of high amplitude is detected by the formation of a transfer particle.
This paper presents a novel unipolar magnetic encoder and a new Vector control method of AC servo which can enable the feedback of the rotor position with high accuracy in high speed occasion. The signal generator of encoder consists of three pairs of semiconductor hall elements and a rotor of alnico magnet with one pair of poles. This encoder is featured with the operation module and the communication module to transmit an angular data in the form of asynchronous serial transfer protocol. Besides, a delay compensation algorithm is proposed to ensure the accurate estimation of instant angular position and the estimation error is also analyzed. At last, an experimental apparatus was built for a 600W, 4 pairs of pole, at rated speed 20,000min-1, permanent-magnet synchronous motor drive and the proposed vector control scheme has been implemented. The experiment results supported the validity of the proposed magnetic encoder and vector control method for high-speed AC servo control within 0.05 % error of revolving speed.
A roller chain is a typical machine element used in bicycles, motorcycles and many other devices for power transmission. The life of a roller chain is determined by elongation. As a rule of thumb, a chain begins to skip cogs on the sprocket wheel when the percentage of elongation reaches approximately 3%. Mechanical wear between pins and bushes causes elongation of the roller chain. However, research on the evaluation of wear of the roller chain is rare and the achievement is unstated. We describe the following initiatives in the study of wear between pins and bushes of a roller chain: (1) development of a wear tester using only two chain links, (2) establishment of a specific evaluation method using a roundness tester, and (3) causal explanation of non-uniform wear using the finite-element method (FEM). The experimental results show that pins and bushes are not in contact at the centerline, and that wear occurs exclusively at the tips of the pins owing to the bending deformation under the condition of tensile load.
In this paper, the characteristics of traction grease are evaluated. The difference in film formation ability between traction oil and traction grease is focused on, and the state of film formation and the traction coefficient of traction oil and two types of traction grease with different consistencies are measured simultaneously while varying temperature, Hertzian pressure and rolling speed. The traction coefficient of traction grease at a low temperature, a low pressure and a high peripheral speed shows a value larger than that of traction oil. The film thickness of traction grease is measured by the contact ratio method and decreases markedly at a low temperature and a high peripheral speed compared with that of traction oil. An estimation formula for traction grease considering film thickness is developed. These results lead to the conclusion that the property change between traction oil and traction grease is caused by the change of the film formation state.
This paper proposes a representation model of the quality state change in an assembly process that can be used in a computer-aided process design system. In order to formalize the state change of the manufacturing quality in the assembly process, the functions, operations, and quality changes in the assembly process are represented as a network model that can simulate discrete events. This paper also develops a design method for the assembly process. The design method calculates the space of quality state change and outputs a better assembly process (better operations and better sequences) that can be used to obtain the intended quality state of the final product. A computational redesigning algorithm of the assembly process that considers the manufacturing quality is developed. The proposed method can be used to design an improved manufacturing process by simulating the quality state change. A prototype system for planning an assembly process is implemented and applied to the design of an auto-breaker assembly process. The result of the design example indicates that the proposed assembly process planning method outputs a better manufacturing scenario based on the simulation of the quality state change.