Dynamic and Compliant Characteristics of a Cartesian-Guided Tripod Machine

2004 ◽  
Vol 128 (2) ◽  
pp. 494-502 ◽  
Author(s):  
Jeng-Shyong Chen ◽  
Wei-Yao Hsu
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Mechanical Vibration ◽  
Maximum Amplitude ◽  
High Gain ◽  
Velocity Change ◽  
Flexible Mode ◽  
Look Ahead ◽  
High Acceleration ◽  
Acceleration And Deceleration

This paper is focused on the dynamic and compliant characteristics of a three-axis parallel kinematic machine called a Cartesian-guided tripod (CGT), which has a passive leg locking the platform three rotational degrees of freedom. Because no constraint mechanism is perfect with infinite rigidity, a compliance model has been developed to determine the maximum amplitude of the passive-leg parasitic motions using given loads. System compliance, dynamic characteristics, vibration modes, and servo-contouring errors of the CGT driving system have also been evaluated under high-speed machining conditions. The nonlinear dynamic effects, such as inertia and gravity, can be controlled within acceptable accuracy using the high-gain servo-feedback control techniques. The CGT dominant flexible mode occurs on the horizontal platform-leg vibration. The platform-leg flexible mode can produce significant jerk-induced mechanical vibration on the platform when a sudden velocity change is commanded. Look-ahead Cartesian-based path acceleration and deceleration control was found to be an efficient tool to reduce the jerk-induced mechanical vibration, although the CGT was drive controlled at the joint level. It was found that at high acceleration application, such as high-speed mold and die machining, the elastic elongation of the driving leg caused by the high acceleration force became the dominant contouring error sources.

Stator Whirl With Rotors in Bearing Clearance

1967 ◽  
Vol 89 (3) ◽  
pp. 381-389 ◽  
Author(s):  
F. F. Ehrich ◽  
J. J. O’Connor
Keyword(s):  
Physical Model ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Contact Point ◽  
Analog Computer ◽  
Vibration Response ◽  
Stable Operation ◽  
Bearing Clearance ◽  
Bearing Contact ◽  
Acceleration And Deceleration

In order to identify and assess the effects of stator dynamics on vibration of high speed rotating machinery, a physical model with two degrees of freedom (one for the rotor and one for the stator) has been defined. Assuming that vibratory motion, as excited by rotor unbalance, is synchronous and axisymmetric, the analysis is linear and straightforward. The calculated vibration response reveals and quantifies some new and important phenomena which are a function of the level of bearing clearance (as related to unbalance level) and of the relative values of the rotor and stator natural frequencies. In particular, the following phenomena are noted: 1. As in simpler models, bearing clearance results in a reduction in system critical speed and can result in a “rightward leaning” critical peak causing hysteresis in response on acceleration and deceleration. 2. In certain ranges of parameters, two vibration modes are possible at high supercritical rotational speeds. One, termed stator whirl, results in stator amplitudes proportional to bearing clearance which are much larger than would be expected with very tight or very loose bearings. 3. Amplitude jump phenomena are very often experienced at a rotational speed equal to stator natural frequency. 4. Hysteresis phenomena, opposite in direction to that associated with a right-leaning critical peak, can be experienced on the subcritical side of the critical peak. 5. Disconnected from the main vibration response curve, branches of stable operation are evident and are hypothesized to be realizable if the system is subjected to momentary disturbances. The results have been verified by an analog computer simulation of the same system, and the effects of component damping and friction at the bearing contact point have been evaluated. Some regimes of asynchronous nonaxisymmetric motion in the analog computer model have been sensed, even though the physical model is axisymmetric.

scholarly journals Study of Driving Torque through Dynamic Analysis of Robot

2018 ◽  
Vol 7 (3.7) ◽  
pp. 125
Author(s):  
Yeon Taek OH ◽  
. .
Keyword(s):  
Dynamic Characteristics ◽  
High Speed ◽  
Low Cost ◽  
Unit Cost ◽  
High Acceleration ◽  
Characteristics Analysis ◽  
Acceleration And Deceleration ◽  
Articulated Robot ◽  
Driving Torque ◽  
Dynamic Characteristics Analysis

These days, the interests on the low-cost handling robots are increasing because it is important to get down the unit cost of production to get the price competitiveness. The robot joint with simple mechanism is more suitable to implement the low-cost robot system as well known. The moving parts of robot have to be designed for simple and robust. But the dynamic characteristics analysis is induced by the robot links because they drive in high acceleration and deceleration. In this reason, the dynamic characteristics analysis of the high-speed robot is very important in the design process. In this paper, the study on robot driving torque analysis of a articulated robot has been done and the research results will be introduced   

An Interpolation Algorithm Based on S-Curve Feedrate Profile and Look-Ahead Function

2013 ◽  
Vol 300-301 ◽  
pp. 1389-1396 ◽  
Author(s):  
Ke Zheng Sun ◽  
Xue Feng Zhou ◽  
Gong Zhang ◽  
Xian Shuai Chen
Keyword(s):  
Machine Tools ◽  
High Speed ◽  
High Speed Machining ◽  
Interpolation Algorithm ◽  
Processing Efficiency ◽  
Look Ahead ◽  
Interpolation Accuracy ◽  
Acceleration And Deceleration ◽  
S Curve ◽  
Time Division

In this paper, a novel interpolation algorithm for high speed machining is presented, which integrates S-curve acceleration/deceleration method in look-ahead function. A time division based speed planning method is used to implement discrete S-curve acceleration/deceleration method. The implementation of the proposed algorithm is given out. The proposed algorithm improves the processing efficiency and avoids the shock of machine tools caused by frequent acceleration and deceleration. The experiment shows that the proposed algorithm satisfies the requirements of interpolation accuracy and machining efficiency in high speed machining.

scholarly journals Identifying and Characterizing Types of Balance Recovery Strategies Among Females and Males to Prevent Injuries in Free-Standing Public Transport Passengers

2021 ◽  
Vol 9 ◽  
Author(s):  
Jia-Cheng Xu ◽  
Ary P. Silvano ◽  
Arne Keller ◽  
Simon Krašna ◽  
Robert Thomson ◽  
...  
Keyword(s):  
Public Transport ◽  
Ordinal Data ◽  
High Speed ◽  
Recovery Strategy ◽  
Free Standing ◽  
Balance Recovery ◽  
High Acceleration ◽  
Initial Strategy ◽  
Recovery Strategies ◽  
Acceleration And Deceleration

Free-standing passengers on public transport are subjected to perturbations during non-collision incidents caused by driver maneuvers, increasing the risk of injury. In the literature, the step strategy is described as a recovery strategy during severe perturbations. However, stepping strategies increase body displacement, ultimately subjecting passengers to higher risk of impacts and falls on public transport. This study investigates the influence of different recovery strategies on the outcome of balance recovery of free-standing public transport passengers, challenged in postural balance by the non-uniform vehicle dynamics. From high-speed video recordings, a qualitative investigation of the balance responses of volunteer participants in a laboratory experiment was provided. On a linearly moving platform, 24 healthy volunteers (11 females and 13 males) were subjected to perturbation profiles of different magnitude, shape and direction, mimicking the typical acceleration and deceleration behavior of a bus. A methodology categorizing the balancing reaction to an initial strategy and a recovery strategy, was used to qualitatively identify, characterize and, evaluate the different balance strategies. The effectiveness of different strategies was assessed with a grading criterion. Statistical analysis based on these ordinal data was provided. The results show that the current definition in the literature of the step strategy is too primitive to describe the different identified recovery strategies. In the volunteers with the most successful balancing outcome, a particularly effective balance recovery strategy not yet described in the literature was identified, labeled the fighting stance. High jerk perturbations seemed to induce faster and more successful balance recovery, mainly for those adopting the fighting stance, compared to the high acceleration and braking perturbation profiles. Compared to the pure step strategy, the characteristics of the fighting stance seem to increase the ability to withstand higher perturbations by increasing postural stability to limit body displacement.

Research on Feedrate Planning Model for Continuous Small Lines Contour with Look-Ahead

2012 ◽  
Vol 591-593 ◽  
pp. 414-418
Author(s):  
Qing Song Jiao ◽  
Shi Yong Wang
Keyword(s):  
High Speed ◽  
Machining Efficiency ◽  
Planning Model ◽  
Interpolation Function ◽  
Line Segments ◽  
Feedrate Planning ◽  
Look Ahead ◽  
Acceleration And Deceleration ◽  
Adjacent Segments

The traditional line or arc interpolation function treats small line segments separately and conducts feedrate planning within each of them. The rather small lengths of the segments result in low machining efficiency, and the frequent acceleration and deceleration also reduce the lifetime of the motor. To solve these problems, a look-ahead feedrate planning model for the continuous small lines contour (CSLC) is proposed in this paper to implement the high speed interpolating. The feedrate planning is elaborated from the aspects of the curvature characteristic of the contour, the turning feedrate, and the federate optimization between the adjacent segments. Simulations show that the proposed algorithm can efficiently improve the machining efficiency.

scholarly journals Recent advances in nano-opto-electro-mechanical systems

Nanophotonics ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Nan Xu ◽  
Ze-Di Cheng ◽  
Jin-Dao Tang ◽  
Xiao-Min Lv ◽  
Tong Li ◽  
...  
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
High Efficiency ◽  
Quantum Information Processing ◽  
Mechanical Vibration ◽  
Mechanical Systems ◽  
Multiple Quantum ◽  
Vibration Modes ◽  
Recent Developments ◽  
On Chip

Abstract Nano-opto-electro-mechanical systems (NOEMS), considered as new platforms to study electronic and mechanical freedoms in the field of nanophotonics, have gained rapid progress in recent years. NOEMS offer exciting opportunities to manipulate information carriers using optical, electrical, and mechanical degrees of freedom, where the flow of light, dynamics of electrons, and mechanical vibration modes can be explored in both classical and quantum domains. By exploiting NOEMS concepts and technologies, high speed and low-power consumption switches, high-efficiency microwave-optical conversion devices, and multiple quantum information processing functions can be implemented through on-chip integration. This review will introduce the principles of NOEMS, summarize the recent developments, and important achievements, and give a prospect for the further applications and developments in this field.

Wind Tunnel Measurements of Flow-Induced Vibration of a NACA0015 Airfoil Model

2014 ◽  
Author(s):  
Petr Šidlof ◽  
Václav Vlček ◽  
Martin Štěpán ◽  
Jaromír Horáček ◽  
Martin Luxa ◽  
...  
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Aerodynamic Force ◽  
Dynamic Pressure ◽  
Mechanical Vibration ◽  
Vertical Position ◽  
High Speed Camera ◽  
Flow Induced Vibration ◽  
Aeroelastic System ◽  
Stiffness Matrices

The paper reports on interferometric measurements of flow over a NACA0015 airfoil model during flutter limit cycle oscillations. The airfoil model is fixed on an elastic support allowing motion with two degrees of freedom — pitch and plunge. The structural mass and stiffness matrices can be tuned to certain extent, so that the eigenfrequencies of the two modes approach as needed. The model is equipped with dynamic pressure probes and sensors measuring the airfoil vertical position. The flow field around the airfoil was measured by Mach-Zehnder interferometer and registered using a high-speed camera synchronously with the mechanical vibration and pressure measurements. The Mach number of the incident airflow was gradually increased and the response of the aeroelastic system to initial impulse measured, until the flutter instability onset occurred. Flutter boundaries were evaluated for various additional masses attached (i.e., for various plunging mode eigenfrequencies), and post-critical behavior of the system investigated. The interferograms recorded by the high-speed camera were postprocessed, yielding pressure distribution around the airfoil during its vibration and an estimate of the total aerodynamic force and energy transfer from the airflow to the structure.

scholarly journals Aerodynamics of inclined cylindrical bodies free-flying in a hypersonic flowfield

2021 ◽  
Vol 62 (9) ◽  
Author(s):  
Patrick M. Seltner ◽  
Sebastian Willems ◽  
Ali Gülhan ◽  
Eric C. Stern ◽  
Joseph M. Brock ◽  
...  
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Numerical Data ◽  
Static Stability ◽  
Free Flight ◽  
Aerodynamic Coefficients ◽  
Flow Topology ◽  
Motion Data ◽  
Continuous Rotation ◽  
German Aerospace

Abstract The influence of the flight attitude on aerodynamic coefficients and static stability of cylindrical bodies in hypersonic flows is of interest in understanding the re/entry of space debris, meteoroid fragments, launch-vehicle stages and other rotating objects. Experiments were therefore carried out in the hypersonic wind tunnel H2K at the German Aerospace Center (DLR) in Cologne. A free-flight technique was employed in H2K, which enables a continuous rotation of the cylinder without any sting interferences in a broad angular range from 0$$^{\circ }$$ ∘ to 90$$^{\circ }$$ ∘ . A high-speed stereo-tracking technique measured the model motion during free-flight and high-speed schlieren provided documentation of the flow topology. Aerodynamic coefficients were determined in careful post-processing, based on the measured 6-degrees-of-freedom (6DoF) motion data. Numerical simulations by NASA’s flow solvers Cart3D and US3D were performed for comparison purposes. As a result, the experimental and numerical data show a good agreement. The inclination of the cylinder strongly effects both the flowfield and aerodynamic loads. Experiments and simulations with concave cylinders showed marked difference in aerodynamic behavior due to the presence of a shock–shock interaction (SSI) near the middle of the model. Graphic abstract

The Use of Modan 3D in Experimental Modal Analysis

2013 ◽  
Vol 486 ◽  
pp. 36-41 ◽  
Author(s):  
Róbert Huňady ◽  
František Trebuňa ◽  
Martin Hagara ◽  
Martin Schrötter
Keyword(s):  
Modal Analysis ◽  
Vibration Analysis ◽  
High Speed ◽  
Mechanical Vibration ◽  
Steel Sample ◽  
Experimental Modal Analysis ◽  
Image Correlation ◽  
Optical Methods ◽  
Mode Shapes ◽  
Vibration Modes

Experimental modal analysis is a relatively young part of dynamics, which deals with the vibration modes identification of machines or their parts. Its development has started since the beginning of the eighties, when the computers hardware equipment has improved and the fast Fourier transform (FFT) could be used for the results determination. Nowadays it provides an uncountable set of vibration analysis possibilities starting with conventional contact transducers of acceleration and ending with modern noncontact optical methods. In this contribution we mention the use of high-speed digital image correlation by experimental determination of mode shapes and modal frequencies. The aim of our work is to create a program application called Modan 3D enabling the performing of experimental modal analysis and operational modal analysis. In this paper the experimental modal analysis of a thin steel sample performed with Q-450 Dantec Dynamics is described. In Modan 3D the experiment data were processed and the vibration modes were determined. The reached results were verified by PULSE modulus specialized for mechanical vibration analysis.

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