Kinematic Issues Research Articles

Feedrate-preserved motion planning for five-axis directed energy deposition of freeform metal parts

Laser-powder DED (LP-DED) has been investigated extensively for the rapid prototype of complex and customized metallic parts and in-situ repairing tasks. However, unlike the material extrusion type which allows a relatively large overhang angle, the conventional 2.5-axis LP-DED faces a severe overhang issue that deteriorates the printing stability and quality. While five-axis LP-DED is able to effectively resolve the overhang problem, it however introduces new kinematic issues and limited nozzle orientation range due to physical restrictions of DED. The existing computer numerical control systems are mainly designed for machining, where the above issues can be mostly solved by feedrate scheduling, which, however, is not applicable for LP-DED processes, as the feedrate must be preserved as programmed lest deposition height would be altered since in most cases it is not practical to vary the powder flow rate in real-time. In this paper, a feedrate-preserved motion planning method is proposed to optimize the rotational angles of the machine tool in the machine coordinate system (MCS) under the constraints of MCS and workpiece coordinate system (WCS). Given a five-axis DED path as well as its accompanying initial nozzle orientation in WCS, we first map them via inverse kinematics to MCS, which is represented by a cylindrical coordinate system. Then, the motion path in the cylindrical coordinate system is optimized to avoid the singularity. Finally, the physical constraint of nozzle orientation in WCS is introduced into the time-weighted constrained Laplacian smoothing in MCS with the axial speed limits upheld. The experimental results confirm that the actual feedrate is successfully preserved as the theoretical one under the constraints of the axial kinematic limits, while the singularity is avoided.

Current deformation along the northern Caribbean plate boundary from GNSS measurements in Cuba

Global Navigation Satellite System (GNSS) measurements at episodic sites or continuously operating stations have been used in most actively deforming regions to determine strain rates, fault slip rates, and contribute to assessing regional seismic hazard. However, the central part of the northern Caribbean plate boundary in Cuba has so far been exempt from sufficient GNSS data to study these classic issues of plate boundary kinematics and the associated hazard. Here, we describe the first position-velocity GNSS solution for Cuba and its close surroundings, providing new information on the seismotectonics of the southern boundary of the North American plate. We find that (1) western and central Cuba are rigidly attached to the North American plate, with internal deformation – if any – that is <1 mm/yr, (2) eastern Cuba shows systematic east-trending residual velocities with respect to the North American plate at 2–4 mm/yr, (3) sites on the Cayman Ridge, although located <50 km from the Oriente fault, show negligible residual velocities with respect to the North American plate. A series of kinematic models shows that the data are best explained by a 10 mm/yr slip deficit between the Gonâve microplate and the North American plate accommodated on a vertical, left-lateral Oriente strike-slip fault with a 25 km locking depth along the eastern Cuban margin, and a much shallower locking depth further west along the Cayman Ridge segment of the Oriente fault, which is possibly creeping. The transition from deep to shallow locking coincides with a drastic change in seismicity distribution, possibly indicative of lateral variation in the stress state or fault rheology along the Oriente fault. Additional GNSS observations and longer time series will help consolidate these initial findings and determine whether and how other active faults may contribute to the seismotectonics of Cuba.

КОМПЛЕКСНИЙ СПОСІБ ФОРМУВАННЯ СПРЯЖЕНИХ КРИВОЛІНІЙНИХ ПОВЕРХОНЬ

This article discusses the development of a complex method for processing helical curved surfaces of the cutting tool of a worm cutter for processing the working bodies of hydraulic pumps. Helical curved surfaces with a large angle of elevation of the turns are considered and new methods of profiling are created. A complex geometric method for solving kinematic issues related to determining the characteristics of a curvilinear surface characteristic in conjugated screw elements of hydraulic pumps is presented. The complex solution of such problems is a certain scientific problem, the solution of which is undoubtedly of great importance for the development of a complex screw cutting tool. As a result of traditionally designed screw cutting tools, the effect of chance prevails, and in the process, as a rule, defects occur in the processing of the helical surface of the screws, which reduces their service life. The solution of this problem will reduce the design time for the mating curved surfaces of the propellers and provide the necessary computational and graphical accuracy. When studying a complex method for designing helical conjugated curved surfaces, it was found that the existing methods are not enough in practice in production and have limitations in terms of design requirements. Therefore, for the manufacture of a conjugated curved helical surface of the cutting tool with technological accuracy, parameters are set with given conditions for the manufacture of hydraulic pump screws. The proposed geometric complex method for determining the characteristics of the curved helical surface of the cutting tool, namely the worm cutter, will allow designing and manufacturing automatically with maximum accuracy the conjugated curved surfaces of hydraulic pumps. Keywords: complex method, curved surfaces, kinematic screw, mating surfaces, worm cutter, hydraulic pumps, screws, characteristics, cutting tool.

Design of Active Display Stand Combing the Pressure Sensor and Kinematics Algorithm

To solve the trouble of cervical vertebra disease caused by long working hours, this work is aimed at designing an active monitor stand to achieve the best dynamic trajectory planning. The stand operation system consists of image input, face positioning, and robotic arm. According to the user’s face positioning, the inverse kinematics method is used to calculate the steering angle in each direction, and the height and angle are adjusted to make the corresponding selection for the user’s display position on the screen. The C++ is used to program the algorithm, and its core is to control the rotation speed of the motor to ensure that the display screen will not cause any interference to the normal work of the user when the bracket moves. In the inverse operation, the Piper method is used to solve the inverse kinematics issues. After testing, the sliding wedge stroke of the developed active display stand is 0.6 mm, and the height position difference at the reference zero point after the display stand is measured with a digital altimeter is 7.12 mm, which indicates that the stand shows a large deformation after being mounted. This work is of important reference value for realizing the movement of active display stand.

A novel partially-decoupled translational parallel manipulator with symbolic kinematics, singularity identification and workspace determination

This paper presents a novel three-degree-of-freedom (3-DOF) translational parallel manipulator (TPM) by using a topological design method of parallel mechanism (PM) based on position and orientation characteristic (POC) equations. The proposed PM is only composed of lower-mobility joints and actuated prismatic joints, together with the investigations on three kinematic issues of importance. The first aspect pertains to geometric modeling of the TPM in connection with its topological characteristics, such as the POC, degree of freedom and coupling degree, from which its symbolic direct kinematic solutions are readily obtained. Moreover, the decoupled properties of input-output motions are directly evaluated without Jacobian analysis. Sequentially, based upon the inverse kinematics, the singular configurations of the TPM are identified, wherein the singular surfaces are visualized by means of a Gröbner based elimination operation. Finally, the workspace of the TPM is evaluated with a geometric approach. This 3-DOF TPM features less joints and links compared with the well-known Delta robot, which reduces the structural complexity. Its symbolic direct kinematics and partially-decoupled property will ease path planning and dynamic analysis. The TPM can be used for manufacturing large work pieces.

Analysis and design of fuzzy-based manoeuvring model for mid-vehicle collision avoidance system

This paper offers a fuzzy-based manoeuvring model labeled as Fuzzy-based Midvehicle Collision Avoidance System (FMCAS) resolving two road crash scenarios. The first scenario covers dual situations (a) Mid vehicle collision avoidance with the rear vehicle under no front vehicle condition and (b) Curvilinear path strategy based on real road conditions. While the suitable curvilinear motion to fit the constrained path for parallel parking is the other scenario. Curvilinear fitting strategy on the left and right sides is achieved by the mid (host) vehicle using fuzzy interpolation techniques modeled by FMCAS. Also, the offset-based curvilinear path determined by FMCAS automatically fits the constraint path to avoid vehicle crashes in highly occupied lanes. In this methodology, path constraint is applicable for both scenarios in forward and reverse directions. The appropriate constraint paths estimated using the developed fuzzy-based polynomial fitting addresses the diverse vehicle kinematic issues. Mean square error values of $$3.9443 \times {10}^{-28}$$ m and 0.0148–0.7210 m about the proposed fuzzy respect to crisp and FMCAS are also capable of delivering diverse consequents in highly intact road scenarios. The fuzzy rule base is motivated in this research article to obtain a collision-free environment addressing many collision conditions in the real-time scenario.

Reconsideration of terminal constraint/mobility and kinematics of 5-DOF hybrid manipulators formed by one 2R1T PM and one RR SM

Hybrid manipulators formed by one 2R1T parallel manipulator (PM) and one RR serial manipulator (SM) have been widely studied. However, the previous researches only focused on the PM part. The basic terminal constraint/mobility and kinematics issues of the integrated hybrid manipulators have been ignored and thus should be reconsidered. The paper studies the basic motion and constraint issues of the integrated hybrid manipulators by using the Exechon hybrid manipulator as a case. First, using Grassmann–Cayley algebra(GCA), a method for deriving the terminal constraint of the 5-DOF hybrid manipulator is proposed and the terminal DOF property is solved. Second, the terminal position and orientation coupling relation in the hybrid manipulator is revealed based on the elimination method and the inverse displacement is solved. Third, the 6 × 6 form full Jacobian containing all actuation and constraint information of the manipulator is derived. The established models in this paper are applicable for the 5-DOF hybrid manipulators.

Bilateral telemanipulation of unknown objects using remote dexterous in-hand manipulation strategies

Abstract This paper presents an approach to perform bilateral in-hand (dexterous) telemanipulation of unknown objects. The proposed approach addresses three of the main problems in telemanipulation: kinematic issues due to the physical differences between the robotic and the human hands; obtaining coherent haptic feedback to provide information about the manipulation at any time; and time-delays that can affect the stability of the overall closed-loop system. The novelty of the approach lays on the shared control scheme, where the robotic hand uses the tactile and the kinematic information to manipulate an unknown object while the operator commands a desired orientation of the object without caring about the relation between her/his commands and the actual hand movements. The viability of the proposed approach has been tested through transatlantic telemanipulation experiments between Mexico and Spain.

Computer Simulation of Kinetics of Parallel Mechanisms

The paper considers the issues of kinematics and dynamics of a parallel mechanism and computer simulation of its movement. To solve the problems of dynamics of parallel mechanisms, the method of Lagrange equations of the second kind was used. In computer modeling, the Matlab and Simulink application were used.

Kinematic issues of a spatial disorientation simulator

Spatial disorientation (SD) is one of the major threats to aircraft pilots, therefore a ground-based SD training is an important factor in reducing the SD‐related accidents. This paper examines some of the kinematic issues relating to the motion control of the SD simulator. The problem of kinematics concerns the evaluation of the impact of the pilots’ head position on their own perceived motion cues. It was interesting whether the simulator was able to replicate the leans illusion with the same quality when the translational position of the head has been changed. This problem was solved by numerical calculations, in which the pilot's head kinematics were used. The SD simulator was modeled as a three-joint revolute robotic manipulator, where the head is the end effector. We found that the simulator was able to replicate the leans illusion with the same quality when the head position was changed. Obtained results can help to choose the kinematic characteristics of an actual SD simulator, and could be useful in developing an illusion at novel flight profile.

Kinematic analysis of the X4 translational–rotational parallel robot

High-speed pick-and-place parallel manipulators have attracted considerable academic and industrial attention because of their numerous commercial applications. The X4 parallel robot was recently presented at Tsinghua University. This robot is a four-degree-of-freedom spatial parallel manipulator that consists of high-speed closed kinematic chains. Each of its limbs comprises an active pendulum and a passive parallelogram, which are connected to the end effector with other revolute joints. Kinematic issues of the X4 parallel robot, such as degree of freedom analysis, inverse kinematics, and singularity locus, are investigated in this study. Recursive matrix relations of kinematics are established, and expressions that determine the position, velocity, and acceleration of each robot element are developed. Finally, kinematic simulations of actuators and passive joints are conducted. The analysis and modeling methods illustrated in this study can be further applied to the kinematics research of other parallel mechanisms.

Simulation of fire resistance behaviour of pultruded GFRP beams – Part II: Stress analysis and failure criteria

This two-part paper presents a numerical study on the fire resistance behaviour of pultruded GFRP profiles with square tubular cross-section simultaneously subjected to four-point bending and the standard fire of ISO 834. The first part [1] presented the numerical models and results focused on the most relevant kinematic issues (deflections and strains), while this second part (present paper) reports numerical results associated to the static issues, particularly the evolution of stress distributions and failure initiation with fire exposure time. The paper first presents and discusses the evolution of stress distributions in both longitudinal and transversal directions of an unprotected GFRP beam under one-side fire exposure (reference beam). Next, the influence of using a fire protection system and exposing the beams to fire in three sides is assessed by comparison with the case of reference beam. Additionally, the Tsai-Hill failure (initiation) criterion was used to identify the zones (sections and points) of GFRP beams that are most sensitive to failure due to high temperatures. The numerical results obtained show that (i) longitudinal stresses across the section become highly nonlinear as a result of temperature increase; (ii) shear stress diagram is severely affected by fire exposure in three sides; (iii) transversal stresses are negligible compared to the longitudinal and shear ones; and (iv) the collapse of beams (considering Tsai-Hill failure analysis) occurs due to top flange and web (top part) failure, which generally agrees with experimental observations.

Simulation of fire resistance behaviour of pultruded GFRP beams – Part I: Models description and kinematic issues

This two-part paper presents a numerical study about the fire resistance behaviour of pultruded GFRP profiles with square tubular cross-section subjected to bending and the ISO 834 time-temperature curve. The first paper deals with the development of numerical and analytical models and the discussion of relevant kinematic issues, including the evolution of beam deflection and position of neutral axis with the fire exposure time. The second part [1] reports an in-depth investigation on the side of static issues, which include the evolution of stress distributions and failure initiation with the fire exposure time. In the present paper, three–dimensional finite element models were developed to simulate fire resistance tests previously conducted by the authors on GFRP beams, in which different degradation curves were considered for compressive, tensile and shear moduli, based on experimental data. In these numerical simulations, both effects of varying the assignment of material properties (depending on the position of neutral axis) and of considering different thermal expansion coefficients were taken into account, and some conclusions were drawn on their influence on mid-span deflection evolutions. Since no failure criterion was implemented, both models were not able to reproduce the failure of the beams, but the overall tendency of the numerical results was consistent with the experimental data. Alongside the numerical study, analytical models based on Timoshenko beam theory were also developed and allowed obtaining accurate predictions of the mid-span deflection evolution of the GFRP beams; the analytical results were in close agreement with the numerical ones and also with the experimental data.

Modeling and PDC fuzzy control of planar parallel robot

Many works in the literature have studied the kinematical and dynamical issues of parallel robots. But it is still difficult to extend the vast control strategies to parallel mechanisms due to the complexity of the model-based control. This complexity is mainly caused by the presence of multiple closed kinematic chains, making the system naturally described by a set of differential–algebraic equations. The aim of this work is to control a two-degree-of-freedom parallel manipulator. A mechanical model based on differential–algebraic equations is given. The goal is to use the structural characteristics of the mechanical system to reduce the complexity of the nonlinear model. Therefore, a trajectory tracking control is achieved using the Takagi-Sugeno fuzzy model derived from the differential–algebraic equation forms and its linear matrix inequality constraints formulation. Simulation results show that the proposed approach based on differential–algebraic equations and Takagi-Sugeno fuzzy modeling leads to a better robustness against the structural uncertainties.

A novel 3-PUU parallel mechanism and its kinematic issues

The modules of parallel tool heads with 2R1T degrees of freedom (DOFs), i.e., two rotational DOFs and one translational DOF, have become so important in the field of machine tools that corresponding research has attracted extensive attention from both academia and industry. A 3-PUU parallel mechanism with 2R1T DOFs is first proposed in this paper, and a detailed discussion about its architecture and geometry constraints are presented. Furthermore, the mobility analysis of the proposed 3-PUU mechanism is carried out by resorting to the reciprocal screw theory. In addition, on the basis of its special geometry constraint conditions, the parasitic motion of 3-PUU mechanism is derived and explicitly expressed. Then the inverse kinematics problem (IKP), the Jacobian matrix calculation, and the forward kinematics problem (FKP) are investigated. At last, the motion/force transmissibility characteristics, the singularity properties, and the reachable workspace are discussed, respectively. The above analyses illustrate that the 3-PUU parallel mechanism owns good motion/force transmissibility and orientation capability, which validate the feasibility of applying this mechanism as a tool head module.

A hybrid press system: Motion design and inverse kinematics issues

A hybrid machine (HM) is a system integrating two types of motor; servo and constant velocity with a mechanism. The purpose is to make use of the energy in the system efficiently with a flexible system having more than one degree of freedom (DOF). A review is included on hybrid press systems. This study is included as a part of an industrial project used for metal forming. The system given here includes a 7 link mechanism, one of link is driven by a constant velocity motor (CV) and the other is driven by a servo motor (SM). Kinematics analysis of the hybrid driven mechanism is presented here as inverse kinematics analysis. Motion design is very crucial step when using a hybrid machine. So motion design procedure is given with motion curve examples needed. Curve Fitting Toolbox (CFT) in Matlab® is offered as an auxiliary method which can be successfully applied. Motion characteristics are chosen by looking at requirements taken from metal forming industry. Results are then presented herein.

A Kinematic Approach to Understanding Performance in Upper-Extremity Function during a Goal-Directed Man-Machine Interface Task in a Submariner Environment.

In December of 2014, the United States Congress funded a fundamental shift in the recruiting policy of the US Navy Submarine Force to include the integration of women. As a result, design modifications became necessary, especially those that facilitate integration without inflating costs. Current cost levels associated with new submarine design(s) are maintained through the use of legacy components and systems. Additionally, many of the systems aboard are computer controlled, necessitating man-machine interfaces. As common practice, military activities that involve man-machine interfaces have always focused on the dexterity of the hands, often neglecting the role of movement in the task; therefore, there is a need to understand upper-extremity kinematics issues associated with man-machine interfaces. Joint kinematics of the right upper extremity of 10 subjects was measured using an optoelectronic motion capture system. Center of gravity displacements were measured using a force plate during touchscreen movement tasks paced by six different movement frequencies from a metronome (0, 1.0, 1.3, 1.7, 2.0, and 2.7 Hz). Results showed no significant difference in touch accuracy, task completion time, shoulder and elbow angular displacements, and shoulder and elbow flexion/extension velocity; however, a significant difference (0.002; p ≤ 0.05) in shoulder adduction/abduction velocity was observed. In arranging systems and components in submarine and surface vessel environments, consideration in not only providing a means of adjustability (e.g., height, proximity, and orientation) but in the dimensions of the systems and components themselves must also be considered based on the required operation.

Design, motion planning and control of a reconfigurable hybrid structure

Compared to traditional fixed-shaped structures, reconfigurable structures may provide various advantages with regard to space utilization, building form optimization and energy efficiency. The purpose of this study is to present the development and kinematic behavior of a reconfigurable hybrid structure. Hinge-connected beam members, stabilized through a secondary system of struts and continuous diagonal cables compose planar n-bar mechanisms arranged in parallel to formulate the spatial reconfigurable structure. The transformability of the system is based on the application of the ‘effective 4-bar’ concept using a sequence of 1-DOF motion steps through selectively locking (n−4) joints of the primary members and modification of the cables’ length. Different intermediate configurations depend on the motion planning, in order to adjust the system’s joints to the desired values during the motion steps involved in the respective transformation sequence. The proposed control system includes position sensors installed on the individual joints to provide feedback information, two motion actuators located at the structural supports, as well as brakes installed on each individual joint. The control system manages the operation of the motion actuators and the brakes to realize the reconfiguration sequences through tensioning the cables. The paper reports the structure’s design concept, motion planning and control. The implementation of the structural reconfiguration approach and related kinematics issues are investigated through a simulation example.

Robust Design Optimization of a 4-UPS-S Parallel Manipulator for Orientation-Regulating Control System of Solar Gather Panels

This paper proposes a redundantly actuated parallel manipulator 4-UPS-S that is applicable for orientation adjustment in the gathering process of solar power. A thorough analysis involving the kinematic issues is performed. Inverse kinematic problems are solved in the close-loop. The Jacobian matrix and some performance indexes are analytically derived. The multiobjective optimization model is established, and the determinacy optimization is completed on the basis of previous research works. Six-Sigma robust analysis is performed on the basis of the determinacy optimal solution. Results show that 4-UPS-S does not satisfy the quality requirement. Therefore, it is necessary to implement Six-Sigma robust optimization, and select optimial solution of robustness to complete the nondeterminacy optimization. The research results show that the proposed methodology has a simple operation and high optimization efficiency. The methodology commodiously obtains robustness parallel manipulator that satisfies the quality requirement.

Kinematic Issues of GPDs in DVCS

Generalized Parton Distributions (GPDs) in Deeply Virtual Compton Scattering (DVCS) have been widely recognized and used as a useful tool to explore the quark and gluon structure of the target hadrons. However, we recently pointed out treacherous kinematic issues in analyzing DVCS in terms of GPDs. We present our key findings in the simplest possible level of complete amplitude including the lepton current. We also discuss an implication on theoretical frameworks to cover the kinematic region of DVCS experiment with the 12 GeV upgrade at Jefferson Lab.