Tripod Dynamics and Its Inertia Effect

2005 ◽  
Vol 127 (1) ◽  
pp. 144-149 ◽  
Author(s):  
Fengfeng Xi ◽  
Ottavio Angelico and ◽  
Rosario Sinatra
Keyword(s):  
Dynamic Equations ◽  
Inertia Effect ◽  
Quantitative Studies ◽  
Parallel Structures ◽  
Parallel Kinematic ◽  
Hybrid Machine ◽  
Moving Platform ◽  
Total Leg ◽  
Two Parameters ◽  
And Control

In this paper the tripod dynamics and its inertia effect is studied. The tripod design is becoming popular for the development of parallel kinematic machines (PKMs). The combination of a tripod with a gantry system forms a hybrid machine that offers the advantages from both serial and parallel structures. The tripod dynamics under study includes the mass of the moving platform as well as those of the legs. The natural orthogonal complement method is applied to derive the dynamic equations. The inertia effect of the moving platform and the legs is investigated in terms of two parameters, namely, the ratio of the total leg mass to the mass of the moving platform, and the velocity of the moving platform. The dynamic equations are separated by three terms, inertia, coupling, and gravity. Quantitative studies are carried out by simulation to examine how the two parameters affect the three respective terms. Based on the simulation results, the dynamic equations can be simplified by retaining the dominant terms while neglecting less significant ones. The simplified dynamic equations provide an efficient model for design and control of tripods.

Effect of Leg Inertia on Dynamics of Sliding-Leg Hexapods

2001 ◽  
Vol 123 (2) ◽  
pp. 265-271 ◽  
Author(s):  
Fengfeng Xi ◽  
Rosario Sinatra ◽  
Wanzhi Han
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
High Speeds ◽  
Numerical Studies ◽  
New Type ◽  
Moving Platform ◽  
Low Speeds ◽  
Total Leg ◽  
Two Parameters

In this paper the effect of leg inertia on hexapod dynamics is investigated. Hexapods under investigation are a new type that is made of sliding legs with constant lengths. A complete dynamic model of sliding-leg hexapods is developed including leg inertia. Based on this dynamic model, the effect of leg inertia on hexapod dynamics is investigated in terms of two parameters. The first parameter is the ratio of the total leg mass to the mass of the moving platform, and the second parameter is the acceleration of the moving platform. Numerical studies reveal that the effect of leg inertia may be negligible at low speeds, but becomes significant at high speeds. Hence, leg inertia must be included for modeling hexapod dynamics for high-speed applications.

Residual Gas Reaction in the Electron Microscope: II The Design of a Gas-Control Chamber for Quantitative Observations

1969 ◽  
Vol 27 ◽  
pp. 82-83
Author(s):  
Chester J. Calbick ◽  
Richard E. Hartman
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Local Environment ◽  
Chamber Pressure ◽  
Objective Lens ◽  
Ion Pump ◽  
Quantitative Studies ◽  
Precise Knowledge ◽  
Differential Pumping ◽  
And Control

Quantitative studies of the phenomenon associated with reactions induced by the electron beam between specimens and gases present in the electron microscope require precise knowledge and control of the local environment experienced by the portion of the specimen in the electron beam. Because of outgassing phenomena, the environment at the irradiated portion of the specimen is very different from that in any place where gas pressures and compositions can be measured. We have found that differential pumping of the specimen chamber by a 4" Orb-Ion pump, following roughing by a zeolite sorption pump, can produce a specimen-chamber pressure 100- to 1000-fold less than that in the region below the objective lens.

Texture Analysis and Genetic Algorithms for Osteoporosis Diagnosis

2019 ◽  
Vol 34 (05) ◽  
pp. 2057002
Author(s):  
Laatra Yousfi ◽  
Lotfi Houam ◽  
Abdelhani Boukrouche ◽  
Eric Lespessailles ◽  
Frédéric Ros ◽  
...  
Keyword(s):  
Genetic Algorithms ◽  
Texture Analysis ◽  
Image Features ◽  
Diagnosis Of Osteoporosis ◽  
Occurrence Matrix ◽  
Two Parameters ◽  
And Control ◽  
Parameter Dependent ◽  
Two Populations ◽  
Distance Parameter

Early diagnosis of osteoporosis can efficiently predict fracture risk. There is a great demand to prevent this disease. The goal of this study was to distinguish osteoporotic cases from healthy controls on 2D bone radiograph images, using texture analysis and genetic algorithms (GAs). Gray Level Co-occurrence Matrix (GLCM), Run length Matrix (RLM) and Binarized Statistical Image Features (BSIF) were used for texture analysis. Features are numerous and parameter-dependent. The related experts can pick out the useful input features for the classifier. It however remains a difficult task and may be inefficient or even harmful as the data pattern is not clear. In this paper, GAs were used to optimize the two parameters of the co-occurrence matrix (distance parameter or pixel separation, orientation or direction) and the number of gray levels used in the preprocessing quantification step. GAs were also used to select the best combination of features extracted from GLCM and RLM matrices. Experiments were conducted on two populations composed of Osteoporotic Patients and Control Subjects. Results show that GAs combined with GLCM and BSIF features can improve the classification rates (ACC = 87.50%) obtained using GLCM (ACC = 77.8%) alone.

Dynamic Workspace and Control of Planar Active Tensegrity-Like Structures

2008 ◽  
Author(s):  
Andrew P. Schmalz ◽  
Sunil K. Agrawal
Keyword(s):  
Computer Simulation ◽  
Feedback Linearization ◽  
Null Space ◽  
System Dynamic ◽  
Initial Configuration ◽  
Dynamic Equations ◽  
Entire System ◽  
Tensegrity Structures ◽  
And Control

This paper addresses the issues of control and workspace determination of planar active tensegrity or tensegrity-like structures. The motion of such structures is generally produced by actuated cables, which cannot tolerate compressive forces. Hence, a controller which not only satisfies the system dynamic equations, but also maintains positive tension in cables is necessary. A null-space controller based on feedback linearization theory is developed for this purpose. This controller utilizes redundant active cables to overactuate the system. The concept of a ‘dynamic workspace’ for these structures is then introduced. This workspace consists of all configurations that are achievable from a given initial configuration while maintaining positive tensions throughout the entire system motion and is a powerful tool in analyzing the performance of a variety of tensegrity structures. This idea extends the concept of the static workspace, which consists of statically maintainable configurations, by incorporating system motion and dynamics to guarantee positive tensions during transition between the states. A critical benefit of this procedure is that it may be used to find the dynamic workspace of a system regardless of whether actuator redundancy is utilized, and thus can be used to objectively illustrate the degree to which overactuation improves mobility of a tensegrity structure. The effectiveness of the developed concepts is demonstrated through computer simulation and actual physical experimentation.

Optimal trajectory planning and sliding mode control for robots using evolution strategy

Robotica ◽  
2000 ◽  
Vol 18 (4) ◽  
pp. 423-428 ◽  
Author(s):  
Young-Kiu Choi ◽  
Jin-Hyun Park ◽  
Hyun-Sik Kim ◽  
Jung Hwan Kim
Keyword(s):  
Trajectory Planning ◽  
Sliding Mode ◽  
Evolution Strategy ◽  
Minimum Time ◽  
Dynamic Equations ◽  
Dynamic Constraints ◽  
Planning And Control ◽  
Explicit Dynamic ◽  
And Control ◽  
Kinematic Approach

Although robots have some kinematic and dynamic constraints such as the limits of the position, velocity, acceleration, jerk, and torque, they should move as fast as possible to increase the productivity. Researches on the minimum-time trajectory planning and control based on the dynamic constraints assume the availability of full dynamics of robots. However, the dynamic equation of robot may not often be exactly known. In this case, the kinematic approach for the minimum-time trajectory planning is more meaningful. We also have to construct a controller to track precisely the minimum-time trajectory. But, finding a proper controller is also difficult if we do not know the explicit dynamic equations of a robot.This paper describes an optimization of trajectory planning based on a kinematic approach using the evolution strategy (ES), as well as an optimization of a sliding mode tracking controller using ES for a robot without dynamic equations.

Dynamic Analysis of a Biglide Parallel Grinder

2005 ◽  
Vol 291-292 ◽  
pp. 495-500
Author(s):  
Ping Zou
Keyword(s):  
Machine Tool ◽  
Dynamic Analysis ◽  
Degrees Of Freedom ◽  
Jacobian Matrix ◽  
Lagrangian Formulation ◽  
Dynamic Equations ◽  
Six Degrees Of Freedom ◽  
Moving Platform ◽  
Drill Point ◽  
Joint Velocity

In this paper, the moving platform of the biglide parallel grinder with six degrees of freedom will keep moving horizontally at any time using parallelograms. Besides grinding the helical drill point, this grinder also can work as drilling and welding machine tool as well as a CMM. The joint-velocity Jacobian matrix is calculated. Moreover, the dynamic equations are derived by applying the Lagrangian formulation.

scholarly journals A Preliminary Design of a Hybrid Machine for Additive and Subtractive Manufacturing

2020 ◽  
Vol 5 (1) ◽  
pp. 48
Author(s):  
Nanang Ali Sutisna
Keyword(s):  
Additive Manufacturing ◽  
Structural Design ◽  
Control Design ◽  
Preliminary Design ◽  
Forming Process ◽  
Initial Shape ◽  
Subtractive Manufacturing ◽  
Hybrid Machine ◽  
And Control ◽  
Subtractive Machining

<p>Additive manufacturing (AM) or commonly called 3D printing (3DP) and rapid prototyping (RP) is a  technique of blending materials by either fusion, binding, or solidifying materials. Despite many advantages of AM, there is a drawback  of AM such as the surface quality may not be as good as subtractive machining  (SM) process, therefore it will be better to have the initial shape forming process with AM and then finishing the required surface with SM process within a single setup. This paper presents the preliminary design of hybrid AM-SM machine to process a resin based material. The design includes structural design and control design of the machine using the material and firmware widely available in the market.</p><p align="center"><strong> </strong></p><strong>Keyword: </strong>Additive, Subtractive,  Manufacturing,  Hybrid  Machine

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