Browsing by Author "Cheng, Kuei-Jen"

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Evaluation of the dynamic performance variation of a serial manipulator after eliminating the self-weight influence
(2011-09-01)
Cheng, Pi-Ying
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Cheng, Kuei-Jen
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機械工程學系
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Department of Mechanical Engineering
Manipulators used in the industrial field usually have a very stiff structure but without an equivalent payload on their end-effectors. This is because the stiff structure is used to prevent excessive deformation which will negatively impact the positioning accuracy of the manipulator, especially when the manipulator is fully extended. However, the stiff structure increases the weight of the manipulator and consumes much of the output of the constituent joint actuators in order to overcome the gravitational force resulting from the heavy structure. To cope with this problem, the concept of gravity balance was proposed decades ago, and there have been several approaches suggested to eliminate the influence of the self-weight of the structure. With the help of gravity balance, the output of the constituent joint actuators can fully be used to drive the manipulator and save considerable energy when the manipulator is in static or low-speed applications. For decades, many papers have discussed how to make a manipulator in gravity balance or how to design and apply a gravity balance mechanism to satisfy a certain application. However, none of them discuss what the influence on the dynamic performance of a manipulator is after it is equipped with a gravity balance mechanism or how to evaluate that influence. To rectify this insufficiency, this article utilizes acceleration radius to be the index of measuring the dynamic performance before and after a manipulator is equipped with a gravity balance mechanism and proposes a new index, the maneuverability ratio, to provide quantitative information to measure whether the dynamic performance of the manipulator increases or not after the gravity balance mechanism is applied. (C) 2011 Elsevier Ltd. All rights reserved.
INVESTIGATION ON VELOCITY PERFORMANCE DEVIATION OF SERIAL MANIPULATORS RESULTED FROM FABRICATION ERRORS
(2017-01-01)
Cheng, Kuei-Jen
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Cheng, Pi-Ying
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機械工程學系
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Department of Mechanical Engineering
Manipulators were adopted in industrial field decades ago, but uncertainty still exists in their performance because of errors produced during the fabrication processes. This uncertainty would deteriorate the performance of manipulators and causes these manipulators unable to meet what are required in their specifications. Although the performance of manipulators has been discussed in many researches, these studies all focused on the positioning accuracy or the kinematic performance over a specific trajectory with or without the influence of fabrication errors. However, manipulators always need to perform tasks with requirements on velocity over its workspace, and fabrication errors always have influence on it. It is not practical to define the performance of a manipulator only based on its positioning accuracy or kinematic performance over a specific trajectory with or without the influence of fabrication errors. To complement this insufficiency, this article utilizes the concept of force ellipsoid to conduct the maximum achievable and sustainable velocity of a non-redundant serial manipulator and evaluates the effect of fabrication errors on the velocity performance of the manipulator over its workspace.
The investigation of the maneuverability deterioration based on acceleration radius theory
(2009-12-01)
Cheng, Kuei-Jen
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Cheng, Pi-Ying
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機械工程學系
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Department of Mechanical Engineering
Maneuverability is the measure of the dynamic performance of a manipulator in a specific posture or configuration, and acceleration radius is one of the most utilized indices of it. Acceleration radius can be utilized as the reference to judge whether further dynamic analysis should be performed when evaluating the controllability and feasibility of the manipulator following the prescribed path with assigned kinematic and kinetic requirements in the planning phase. When utilizing acceleration radius as the dynamic reference in the planning phase, it can prevent wasting the calculation cost due to these non-necessary dynamic analyses, and it can also be utilized as the benchmark in the on-line control. However, the existence of the configuration errors is inevitable in reality, and it deteriorates the dynamic performance of a manipulator with the ideal configuration parameters and leads to the potential risk of failing to achieve an assigned dynamic task. To investigate the adverse behavior caused by the configuration errors and to provide some clues to avoid or reduce their influence, this article proposes a novel and systematic method which can be used to evaluate the maneuverability deterioration of a non-redunclant serial manipulator system due to the influence of configuration errors, and it also provides an index, deterioration rate, to quantitate this kind of deterioration. Deterioration rate can be utilized to quantitate the maneuverability deterioration due to the influence of configuration errors in a prescribed workspace or region and can also be treated as the safety or derating margin when proceeding with the control or path planning. (C) 2009 Elsevier Ltd. All rights reserved.