Multi-axis Motion Research Articles

Development of a slender continuum robotic system for on-wing inspection/repair of gas turbine engines

The maintenance works (e.g. inspection, repair) of aero-engines while still attached on the airframes requires a desirable approach since this can significantly shorten both the time and cost of such interventions as the aerospace industry commonly operates based on the generic concept power by the hour. However, navigating and performing a multi-axis movement of an end-effector in a very constrained environment such as gas turbine engines is a challenging task. This paper reports on the development of a highly flexible slender (i.e. low diameter-to-length ratios) continuum robot of 25 degrees of freedom capable to uncoil from a drum to provide the feeding motion needed to navigate into crammed environments and then perform, with its last 6 DoF, complex trajectories with a camera equipped machining end-effector for allowing in-situ interventions at a low-pressure compressor of a gas turbine engine. This continuum robot is a compact system and presents a set of innovative mechatronics solutions such as: (i) twin commanding cables to minimise the number of actuators; (ii) twin compliant joints to enable large bending angles (ź90°) arranged on a tapered structure (start from 40mm to 13mm at its end); (iii) feeding motion provided by a rotating drum for coiling/uncoiling the continuum robot; (iv) machining end-effector equipped with vision system. To be able to achieve the in-situ maintenance tasks, a set of innovative control algorithms to enable the navigation and end-effector path generation have been developed and implemented. Finally, the continuum robot has been tested both for navigation and movement of the end-effector against a specified target within a gas turbine engine mock-up proving that: (i) max. deviations in navigation from the desired path (1000mm length with bends between 45° and 90°) are ź10mm; (ii) max. errors in positioning the end-effector against a target situated at the end of navigation path is 1mm. Thus, this paper presents a compact continuum robot that could be considered as a step forward in providing aero-engine manufacturers with a solution to perform complex tasks in an invasive manner. A novel slender continuum robot is introduced for in-situ repair/inspection of jet engines.A new kinematic model is introduced for the new tapered design.Modes of control for the continuum robot were developed, including tip-following, feeding-in/out, Machining commands.Navigation and inspection/machining tests in engine model were introduced.

Prototype of 6-DOF Magnetically Levitated Stage Based on Single Axis Lorentz force Actuator

We present a prototype of 6-DOF magnetically levitated stage based on single axis Lorentz force actuator is capable of positioning down to micron in several millimeter travel range with a simple and compact structure. The implementation of the Lorentz force actuators, instrument modeling, and motion controller of the maglev system are described. With the force-gap relationship of the actuator solved by Gaussian quadrature, 2-demsional (2D) lookup table is employed to store the result for the designing of control system. Based on the force-gap relationship, we choose the suitable stroke of each actuator to develop the stability of the maglev stage. Complete decoupling matrix is analyzed here to establish a decoupled dynamics between resulting six axis motion and eight outputs to the actuators. The design travel volume of the stage is 2mm×2mm×2mm in translation and 80mrad×80mrad×40mrad in rotation. With a constant gain and critical damping PID controller, the resolution of the translation is 2.8um and 4um root mean square in horizontal and vertical direction respectively. Experimental results are presented to illustrate the positioning fluctuations, step responds and multi axis motion. Some comparative tests are taken to highlight the advantage resulted from the accurate force-gap relationship, suitable stroke, and complete decoupling matrix.

Influence of friction wedge characteristics on lateral response and hunting of freight wagons with three-piece bogies

In this study, the nonlinear damping characteristics of friction wedges in the secondary suspension of a freight wagon are investigated considering nonsmooth unilateral contact, multiaxis motions, slip–stick conditions, and geometry of the wedges. The parameters of the contact pairs within the suspension were identified to achieve smooth and efficient numerical solutions, while ensuring adequate accuracy. A simulation model of the friction wedge was formulated and analyzed, which revealed highly nonlinear dependence on vertical, roll, and lateral motions between the bolster and the side frames. The friction wedge model was integrated into the multibody dynamic model of a three-piece bogie to study the effects of wedge properties on hunting characteristics. The resulting 114-degrees-of-freedom wagon model incorporated constraints due to side bearings, axle boxes, and the center plates, while the wheel–rail contact forces were obtained using the FASTSIM algorithm. The simulation results were obtained to study hunting properties of the wagon in terms of critical speed and the predominant oscillation frequency, and the effects of wedge friction and geometry on stability characteristics of the freight car. The results showed subcritical Hopf bifurcation of dynamic responses of the wagon. Moreover, an increase in the wedge angle, friction coefficient, and springs free length resulted in a higher critical speed.

Improving Contouring Accuracy by Using Gain Matching Method

Motion axes should coordinate exactly in order to get high contouring accuracy. Gain matching is one of the coordinating problems. In this paper, gain matching effects on contouring accuracy are analyzed for both full-closed and half-closed control loop structures. A simple gain matching model is proposed in order to reduce the contouring error caused by unmatched gains of a multi-axis motion control system. According to this model, the contouring error can be reduced by tuning the proportional gain in the position loop of each axis. Finally, experiments are made to verify the proposed model, and the results show that the gain matching model can effectively reduce the contouring error of both linear and circular trajectory of motion control systems.

Contouring Control of Multi-Axis Motion Systems for NURBS Paths

A contouring control method that integrates the equivalent errors and non-uniform rational B-spline (NURBS) interpolator is proposed in this study. The method of equivalent errors has been shown to possess many advantages for the contouring control of multi-axis motion systems. A key requirement of the method is that the desired path should be represented by algebraic path equations in generalized coordinates. On the other hand, complicated curves are usually described by NURBS, which is in a parametric form. To be integrated with the method of equivalent errors, the parametric NURBS curve is transformed into a set of algebraic path equations by the Sylvester’s implicitization method. As a result, the proposed method is useful for the contouring control of multi-axis motion systems following free form complicated paths. The effectiveness of the proposed method is verified experimentally through the application to a biaxial system following a star-like NURBS curve of degree 5.

Deformation characteristic of thread and spline synchronous rolling process

In the thread and spline synchronous rolling (TSSR) process, the thread rolling deformation couples with the spline rolling deformation. The deformation behavior in the synchronous rolling process is very complex due to multi-die constraint, multi-axes motion, and multi-parameter association. Exploring the deformation characteristics in the TSSR process is important for parameter optimization and process control of the TSSR process. In this paper, the finite element method (FEM) was adopted to investigate the deformation in the TSSR process. The data were extracted from FE code DEFORM and were processed in code MATLAB. The deformation characteristics in the TSSR process were studied by mean of analyzing displacement, strain, and invariants of deviatoric stress tensor. The results in the present study indicated that: direction of rotation of workpiece has an influence on the direction of axial displacement in cores of threaded section and splined section; the influence of tooth profiles (such as threaded profile, splined profile) on the TSSR process only presents in the superficial zone; the deformation-affected region along radial direction in the threaded section is larger than that in the splined section; the deformation in the threaded section and splined section has little influence on axial regions.

Notochord Cells in Intervertebral Disc Development and Degeneration.

The intervertebral disc is a complex structure responsible for flexibility, multi-axial motion, and load transmission throughout the spine. Importantly, degeneration of the intervertebral disc is thought to be an initiating factor for back pain. Due to a lack of understanding of the pathways that govern disc degeneration, there are currently no disease-modifying treatments to delay or prevent degenerative disc disease. This review presents an overview of our current understanding of the developmental processes that regulate intervertebral disc formation, with particular emphasis on the role of the notochord and notochord-derived cells in disc homeostasis and how their loss can result in degeneration. We then describe the role of small animal models in understanding the development of the disc and their use to interrogate disc degeneration and associated pathologies. Finally, we highlight essential development pathways that are associated with disc degeneration and/or implicated in the reparative response of the tissue that might serve as targets for future therapeutic approaches.

The study on rapid identification of the key error sources of multi axis motion system based on quasi-rigid body error model

In order to realise precision measurement of complex freeform surfaces, static and dynamic errors of the measurement instruments must be strictly controlled. During instrument assembly, it is very difficult to separate the main influence factors from the other various errors. This paper establishes a quasi-rigid body error model for a multi axis motion system composed of three linear axes and a rotating shaft, and presents a method of the reasonable simplification error model based on the measurement path to identify quickly the key error sources. Based on the example of standard gear measurement, the feasibility of this method is validated.

An FPGA-Based Multiple-Axis Velocity Controller and Stepping Motors Drives Design

A Field Programmable Gate Array based system is a great hardware platform to support the implementation of hardware controllers such as PID controller and fuzzy controller. It is also programmed as hardware accelerator to speed up the mathematic calculation and greatly enhance the performance as applied to motor drive and motion control. Furthermore, the open structure of FPGA-based system is suitable for those designs with the ability of parallel processing or soft code processor embedded. In this paper, we apply the FPGA to a multi-axis velocity controller design. The developed system integrated three functions inside the FPGA chip, which are respectively the stepping motor drive, the multi-axis motion controller and the motion planning. Furthermore, an embedded controller with a soft code processor compatible to 8051 micro-control unit (MCU) is built to handle the data transfer between the FPGA board and host PC. The MCU is also used to initialize the motion control and run the interpolator. The designed system is practically applied to a XYZ motion platform which is driven by stepping motors to verify its performance.

Vision and Force Feedback Control for Microassembly Process

Microassembly process is one of the difficulties in the field of manufacturing. According to the structural characteristics and assembly process difficultly of 3D meso-scale micro-devices and the requirement of multi-axis control in coaxial alignment assembly, this paper developed a vision and force feedback control method oriented to Microassembly System with Coaxial Alignment. This system combines multi-axis motion control with machine vision and force sensors, which can complete nondestructive assembly of parts and increase the precision of microassembly process into micron level.

Study on 4-axial precision milling of spatial freeform surface for individualized hip prosthesis stem

The fabrication of individualized hip prosthesis stem requires high machining freedom to dovetail precisely with the bond cavity of the patient. Hence, a 3-axial linkage motion is proposed in 4-axial milling along with a 1-axial differential drive and a cutter offset angle. Its advantage is to prevent from the accumulated errors of multi-axial motions. First, the centerline of spatial stem with the length of 200 mm was installed to a rotating axis; then, the transfer model of non-closed polar coordinate points was constructed to design 2D closed tool paths for the control of 3D cutting contact points; finally, the form error and the surface roughness of milled stem surface were investigated in connection with cutter posture angle. Theoretical analysis shows that the cutter offset angle contributes to an increase in cutter posture angle for high cutting velocity and the predication of the interference between cutter bar and workpiece. Experimental results show that the milled surface roughness and the milled form error are decreased by about 50 % and reach 0.26 and 126 μm when the cutter posture angle decreases to 20–40 °, respectively. It is confirmed that the 3-axial linkage milling along with 1-axial differential drive is likely to realize the precision machining of spatial hip prosthesis stem by controlling the cutter offset angle.

Precision control and compensation of helical gear hobbing via electronic gearbox Cross-Coupling controller

The gear generation process is strongly dependent on the accuracy of the multi-axis relative motion, which is controlled by the electronic gearbox (EGB). This research mainly focuses on helical gear hobbing and on EGB control error analysis, estimation and compensation in the generation process of a gear hobbing machine. First, a simple approach for estimation of the helical gear pitch error and the spiral line contour error is proposed. Then, in conjunction with this estimation method, an EGB cross-coupling controller (ECCC) architecture, which is connected by the EGB and the cross-coupling controller, is presented. Simulation results show that the proposed ECCC has higher control accuracy than an uncoupled controller, and its control accuracy can be further improved using friction compensation. Finally, experiments are conducted on an YS3118 six-axis hobbing machine. The helical gears machined using this machine have high precision. In addition, the proposed ECCC architecture can be implemented easily on most motion systems that are in current use.

Alignment metrology for the Antarctica Kunlun Dark Universe Survey Telescope

Dome A is the highest point on the Antarctic Plateau, and the Chinese expedition team was the first to arrive there in 2005 January. It is an excellent site for astronomical observations. The Kunlun Dark Universe Survey Telescope (KDUST), a proposed next-generation Chinese Antarctic optical telescope, is currently being planned. KDUST is a coaxial three-mirror anastigmatic telescope with an entrance pupil diameter of 2.5 m and a field of view of 1|${^{\circ}_{.}}$|5. The telescope should be fully aligned in order to achieve diffraction-limited image quality. Based on the current optical model for KDUST, in this study we describe a modified alignment metrology and give the preliminary results of numerical simulations. Using the acquisition of field-dependent aberrations, the algorithm, which is based on double Zernike polynomial decomposition and the least-squares fitting method, delivers a suitable set of corrections for resolving misalignments including the multi-axis motion of the secondary and tertiary mirrors. Moreover, the algorithm can also be used to calculate the primary mirror's low-order figure errors mixing with the misalignments of the secondary mirror.

The Research of Multi-Axis Motor Control System Based on the Communication Technology of FP-X PLC and Inverters

We present a multi-axis motor speed control system based on the communication technology of FP-X PLC and VF0C inverter. The method is that change the three-phase input frequency of the motor to control the motor via the inverters. This paper presents PLC and inverters communication technology are used in electric drive systems, and explores PLC sent the commands to the inverters via the touchscreen and the RS485 port and write data to the drive to change its system parameters and output frequency to control the speed and state of the motor.

Contouring error modeling and simulation of a four-axis motion control system

A layered modeling method is proposed to resolve the problems resulting from the complexity of the error model of a multi-axis motion control system. In this model, a low level layer can be used as a virtual axis by the high level layer. The first advantage of this model is that the complex error model of a four-axis motion control system can be divided into several simple layers and each layer has different coupling strength to match the real control system. The second advantage lies in the fact that the controller in each layer can be designed specifically for a certain purpose. In this research, a three-layered cross coupling scheme in a four-axis motion control system is proposed to compensate the contouring error of the motion control system. Simulation results show that the maximum contouring error is reduced from 0.208 mm to 0.022 mm and the integration of absolute error is reduced from 0.108 mm to 0.015 mm, which are respectively better than 0.027 mm and 0.037 mm by the traditional method. And in the bottom layer the proposed method also has remarkable ability to achieve high contouring accuracy.

Design and Research of Multiple Fiber Tows Placement Control System

In view that present traditional composites forming technologies are difficult to guarantee the processing quality of complex components such as components with small curvature radius or with concave-convex surface. this paper used the fiber placement technology, and in order to achieve the single independent and overall joint movement control of each fiber tows ,it adopted the mainstream open control mode of a PC machine combined with a programmable multi-axis motion controller . At the same time, it introduced a feedback system to realize the accurate pressure control of multiple fiber tows, so as to ensure the quality of fiber placement.

ModelSim/Simulink Cosimulation and FPGA Realization of a Multiaxis Motion Controller

This paper is to implement a multiaxis servo controller and a motion trajectory planning within one chip. At first, SoPC (system on a programmable chip) technology which is composed of an Altera FPGA (field programmable gate arrays) chip and an embedded soft-core Nios II processor is taken as the development of a multiaxis motion control IC. The multiaxis motion control IC has two modules. The first module is Nios II processor which realizes the motion trajectory planning by software. It includes the step, circular, window, star, and helical motion trajectory. The second module presents a function of the multiaxis position/speed/current controller IP (intellectual property) by hardware. And VHDL (VHSIC Hardware Description Language) is applied to describe the multiaxis servo controller behavior. Before the FPGA realization, a cosimulation work by ModelSim/Simulink is applied to test the VHDL code. Then, this IP combined by Nios II processor will be downloaded to FPGA. Therefore, a fully digital multiaxis motion controller can be realized by a single FPGA chip. Finally, to verify the effectiveness and correctness of the proposed multiaxis motion control IP, a three-axis motion platform (XYZtable) is constructed and some experimental results are presented.

Cyanea capillata bell kinematics analysis through corrected in situ imaging and modeling using strategic discretization techniques.

Obtaining accurate kinematic data of animals is essential for many biological studies and bio-inspired engineering. Many animals, however, are either too large or too delicate to transport to controlled environments where accurate kinematic data can be easily obtained. Often, in situ recordings are the only means available but are often subject to multi-axis motion and relative magnification changes with time leading to large discrepancies in the animal kinematics. Techniques to compensate for these artifacts were applied to a large jellyfish, Cyanea capillata, freely swimming in ocean waters. The bell kinematics were captured by digitizing exumbrella profiles for two full swimming cycles. Magnification was accounted for by tracking a reference point on the ocean floor and by observing the C. capillata exumbrella arclength in order to have a constant scale through the swimming cycles. A linear fit of the top bell section was used to find the body angle with respect to the camera coordinate system. Bell margin trajectories over two swimming cycles confirmed the accuracy of the correction techniques. The corrected profiles were filtered and interpolated to provide a set of time-dependent points along the bell. Discrete models of the exumbrella were used to analyze the bell kinematics. Exumbrella discretization was conducted using three different methods. Fourier series were fitted to the discretized models and subsequently used to analyze the bell kinematics of the C. capillata. The analysis showed that the bell did not deform uniformly over time with different segments lagging behind each other. Looping of the bell trajectory between contraction and relaxation was also present through most of the exumbrella. The bell margin had the largest looping with an outer path during contraction and inner path during relaxation. The subumbrella volume was approximated based on the exumbrella kinematics and was found to increase during contraction.

Study of System Design Based on Three Machine Vision of Three Axis Dispensing

With the rapid development of computer technology and electronic technology, the future will be a large number of the use of automation equipment instead of manual operation, to meet the complex control, high precision, multi axis motion control card applied in NC system will become more and more widely. This paper studies three axis dispensing machine positioning control system based on machine vision, not only uses CCD camera to clear description sheet dispensing area real time scanning, using the smoothing operation and the value of the two methods for the acquisition of image preprocessing, and the use of image morphological operation extraction dispensing location coordinates, to solve the traditional dispensing mode of open loop low control accuracy, low efficiency and poor stability problem. Experimental results show that this system is tested and used are able to meet the requirements, in the long time repetition work greatly reduce the use of artificial also can greatly improve the production efficiency and product quality are improved.

Controller design based on viscoelasticity dynamics model and experiment for flexible drive unit

In order to ensure that the system has the advantage of light weight and vibration absorption, the steel rope is used as a flexible transmission part. A flexible drive unit (FDU) is developed, whose features are guided by steel rope, increasing force by the movable pulley group, modular, convenient and flexible. Dynamics model for controller is deduced based on the constitutive equation of viscoelasticity. Controller is designed for position control and is based on the viscoelasticity dynamics model compensation control strategy proposed. The control system is based on the TURBO PMAC multi-axis motion control card. Prototype loading experiments and velocity experiments results show that the FDU can reach 2 Hz with no load and the max speed of 30 (°)/s. The FDU has the capability of the load torque 11.2 N·m and the speed of 24 (°)/s simultaneously, and the frequency response is 1.3 Hz. The FDU can be used to be the pitch joint of hip for biped robot whose walking speed is 0.144 km/h theoretically.