Multi-axis Motion Research Articles

Adaptive probe position correction for automated complex weld inspection based on structural signal monitoring

ABSTRACT To ensure comprehensive coverage of welds, multi-axis motions are necessary for the probe during the automatic detection of complex welds. Guaranteeing the effectiveness of ultrasonic data during this process is crucial for ensuring detection accuracy and reliability. Taking tubular Y-joints as an example, this paper presents an adaptive probe posture correction method based on structural signal monitoring: (1) The structural and acoustic model of tubular Y-joints is established to select and predict the target structural signal. (2) Feature extraction and signal tracking algorithms are developed to achieve real-time monitoring of signals. (3) A posture correction method is proposed based on signal characteristics: time-domain characteristics correspond to position adjustments, while amplitudes correspond to orientation corrections. Building upon this, a feedback mechanism for probe posture is established. The effectiveness of the developed method is verified through underwater automatic detection experiments of tubular Y-joints. Results demonstrate that, with the assistance of the probe posture correction method, the coverage of the effective area increases to more than 95%, and embedded defects are fully detected through a single scan. In conclusion, the adaptive probe posture correction method based on structural signal monitoring presents a promising approach for the automatic ultrasonic examination of complex welds.

3D Printing-Induced Hierarchically Aligned Nanocomposites With Exceptional Multidirectional Strain Sensing Performance.

High-performance sensors capable of detecting multidirectional strains are indispensable to understand the complex motions involved in flexible electronics. Conventional isotropic strain sensors can only measure uniaxial deformations or single stimuli, hindering their practical application fields. The answer to such challenge resides in the construction of engineered anisotropic sensing structures. Herein, a hierarchically aligned carbon nanofiber (CNF)/polydimethylsiloxane nanocomposite strain sensor is developed by one-step 3D printing. The precisely controlled printing path and shear flow bring about highly aligned nanocomposite filaments at macroscale and orientated CNF network within each filament at microscale. The periodically orientated nanocomposite filaments along with the inner aligned CNF network successfully control the strain distribution and the appearance of microcracks, giving rise to anisotropic structural response to external deformations. The synergetic effect of the multiscale structural design leads to distinguishable gauge factors of 164 and 0.5 for applied loadings along and transverse to the alignment direction, leading to an exceptional selectivity of 3.77. The real-world applications of the hierarchically aligned sensors in multiaxial movement detector and posture-correction device are further demonstrated. The above findings propose new ideas for manufacturing nanocomposites with engineered anisotropic structure and properties, verifying promising applications in emerging wearable electronics and soft robotics.

The Design and Real-Time Optimization of an EtherCAT Master for Multi-Axis Motion Control

To address the issues of low bandwidth, weak real-time performance, and poor synchronization in traditional fieldbuses for multi-axis motion control, a solution for the implementation of an EtherCAT master based on the IgH EtherCAT Master open-source software framework and an embedded hardware platform is proposed. On a hardware platform centered around the AM64x Sitara processor, a Linux real-time operating system based on the Xenomai real-time kernel is constructed, and the IgH master framework is ported to realize a high-performance EtherCAT master. The configuration process of the EtherCAT bus is detailed, a master application program is developed, and methods for the real-time performance optimization of the master—such as exclusive CPU usage by the master process and the optimization of the network card driver—are proposed. Finally, experiments are conducted on a six-axis servo control platform, with the packet analysis of the periodic EtherCAT data frames sent by the master. The experimental results show that the optimized master, under a high-speed communication cycle of 500 microseconds, maintains maximum jitter within 20 microseconds and average jitter within 1 microsecond, meeting the requirements for high-precision multi-axis motion control.

Trajectory optimization of B-splines interpolation based on dynamic error adjustment

In this paper, we propose a motion planning algorithm based on the five-fold B-spline curve for multi-axis motion control systems with non-smooth trajectories, acceleration, plus acceleration over the limit, etc. We construct a smooth transition model for the micro-line segment G3 of the continuous five-fold B-spline curve. A derivation of the corresponding theoretical equation is given. Using the transition model, we propose an optimization method for dynamic adjustment of motion trajectory errors based on the velocity forward planning constraints by smoothing the transition after the trajectory of the micro-line segment for the forward planning velocity. Finally, the design flow for the forward planning of the velocity is given. Finally, the above algorithm is used to perform simulation experiments for the optimization algorithm. Experimental results show that the proposed optimization improves the accuracy of fitting motion trajectories under the constraints of acceleration and deceleration addition, which validates the proposed algorithm.

Design and test of an efficient seedling pick-up device with a combination of air jet ejection and mechanical action

Low degree of transplanting automation will affect production efficiency and planting quality in vegetable cultivation. A new seedling pick-up device was designed and constructed to reduce direct grasping damages to seedlings and improve transplanting efficiency. The pick-up device consists of an air jet loosening device, a flexible pick-up manipulator, a parallel feeding device, and a multi-axis motion control system. Its working principle is to use air jet ejection to assist in loosening of seedling roots from the tray cells, grasp their stems for extracting with the pick-up manipulator, and finally transfer them to the delivery device for feeding into the planting device as needed. The mechanical structure and working parameters of each component were designed, and the control system was constructed according to the working requirements of ejecting, extracting, transferring, and discharging operations. A prototype of the new pick-up device was constructed, and its performance evaluation was conducted using an orthogonal experimental design using cucumber, pepper and caluiflower as test objects. The results showed that the test object, the root lump's moisture content and the loosening way (either as a whole or individual loosening of seedlings) had significant effects on the success ratio in picking up seedlings. Overall, the success in picking up seedlings from the cell was found to be influenced by horticultural and mechanical factors. Under the optimal level group, the maximum success ratio for automatic picking up seedlings was up to 94.49% for pepper while that of cucumber and cauliflower recorded 90.75% and 92.62%, respectively. The seedling pick-up performance was satisfactory for efficient transplanting requirements.

Multi-Layer Polyurethane-Fiber-Prepared Entangled Strain Sensor with Tunable Sensitivity and Working Range for Human Motion Detection.

The entanglement of fibers can form physical and topological structures, with the resulting bending and stretching strains causing localized changes in pressure. In this study, a multi-layer polyurethane-fiber-prepared (MPF) sensor was developed by coating the CNT/PU sensing layer on the outside of an elastic electrode through a wet-film method. The entangled topology of two MPFs was utilized to convert the stretching strain into localized pressure at the contact area, enabling the perception of stretching strain. The influence of coating mechanical properties and surface structure on strain sensing performance was investigated. A force regulator was introduced to regulate the mechanical properties of the entangled topology of MPF. By modifying the thickness and length proportion of the force regulator, the sensitivity factor and sensitivity range of the sensor could be controlled, achieving a high sensitivity factor of up to 127.74 and a sensitivity range of up to 58%. Eight sensors were integrated into a sensor array and integrated into a dance costume, successfully monitoring the multi-axis motion of the dancer's lumbar spine. This provides a new approach for wearable biomechanical sensors.

Time-optimal and Smooth Trajectory Planning for Multi-axis Motion Systems Based on ISC Similarity

Time-optimal and Smooth Trajectory Planning for Multi-axis Motion Systems Based on ISC Similarity

A three-degree-of-freedom piezoelectric actuator with sandwich structure: Design, modeling, and experiment

With the increased motion requirements of precision drive devices, multi-degree-of-freedom piezoelectric actuators have become key technologies for realizing multi-axis motion control. To expand upon the three-degree-of-freedom piezoelectric stick-slip driving method, a sandwich-type three-degree-of-freedom rotating inertial stick-slip piezoelectric actuator is proposed in this paper. Firstly, the structure and control strategy of the actuator were introduced. Statics analysis of the core component of the piezoelectric vibrator was carried out, and the relationship between the structural parameters and the deformation of the driving foot was obtained. Then the free and forced vibrations of the piezoelectric vibrator are analyzed to determine the dynamic response of the driving foot in the time domain. Finally, a prototype was fabricated and an experimental system was built to test its output characteristics. The test results show that when the driving voltage was 150 V and the frequency was 320 Hz, the proposed actuator achieves maximum speeds and load torques around the x-axis and y-axis of 306 mrad/s and 2 mN m, respectively. When the driving voltage was 150 V and the frequency was 450 Hz, the proposed actuator achieves a maximum speed and load torque around the z-axis of 140 mrad/s and 1.55 mN m, respectively.

Perpendicularity measurement of multi-axis motion platform based on laser interferometry

Perpendicularity measurement of multi-axis motion platform based on laser interferometry

High-precise Motion Control Hardware System and Key Timing Management Research

High-precise and multi-axes motion control system is required in the application of semiconductor equipment and high-performance industrial equipment. To achieve the tight performance requirements, this paper presents the control system architecture, communication, and timing management solution. We use multiple cores DSP and FPGA as the main control chips, use SRIO @5Gbps *4 as the DSP and FPGA communication protocol, and use Aurora 8B/10B @5Gpbs as the inter-board communication protocol. This architecture with its high sampling rate and low latency can improve the motion control performance and raise the system sampling bandwidth. Analysis and test results of system communication and timing management are included to demonstrate the efficacy of the proposed scheme.

Research on Multiple-Axis Contour Error Suppression Method Based on Composite Layered Control

With the widespread application of multi-axis machining in the industrial manufacturing, aerospace, and military equipment sectors, the demand for machining ultra-precision components has been steadily increasing. Contour errors directly impact the quality of machined parts. In conventional multi-axis motion control systems based on cross-coupling, it is conventionally assumed that all individual axes are of equal significance during machine processing. However, in practical machining scenarios, diverse machining trajectories and accuracy requirements give rise to distinct control necessities for each axis. This complication leads to challenges in ensuring a consistent single-plane contour, thereby constraining the elevation of the overall contour accuracy. To address this issue, this study proposes a multi-axis contour error suppression method based on composite hierarchical control. The approach advocated in this paper initially ensures the precision of single-axis position control through the development of an advanced S-shaped function-based sliding-mode disturbance observer. Building on this foundation, the three-dimensional spatial contour is segregated into upper and lower layers. Subsequently, dedicated fuzzy PID cross-coupling controllers are devised for each layer. The experimental outcomes substantiate that in comparison to conventional cross-coupling control methods, the method introduced in this study, rooted in composite hierarchical control, not only guarantees the accuracy of single-plane contours but also further enhances the overall contour precision.

Self-calibrated defocused speckle imaging for remote surface motion measurements

Defocused Speckle Imaging (DSI) is a non-contact optical method that can measure multiaxial object motions at microscopic sensitivity using a simple and mechanically robust optical setup. The object surface is illuminated by a laser beam, and the scattered interference speckle pattern is tracked with a defocused camera. DSI measurement sensitivity increases with distance, and the sensitivity can be tuned by simple camera defocus adjustment. These characteristics make DSI an attractive choice for tracking remote objects in field conditions. However, the use of DSI for practical measurements is limited because the speckle signals due to linear and rotational surface motions mix together, and because the instrument calibration requires accurate object range and surface orientation parameters.To address these issues, the work described here combines two recently presented concepts: 1) a defocused camera pair, and 2) a diffraction-based self-calibration principle. The proposed approach was demonstrated by a series of self-calibrated multiaxial motion measurements performed at an extended (30.7-m) distance. The studied motions included in-plane displacements and out-of-plane rotations (tilts), whereas out-of-plane displacements and in-plane rotations were excluded. The experiments showed DSI's capability for high tilt sensitivity down to 0.0006°, standalone remote angle measurements, and suitability for retroreflective surfaces. The diffraction-based self-calibration approach could monitor sampling distances at a 6.4 % accuracy and the relative surface angles of 2.5–7.4° at a 0.2° accuracy. The defocused camera pair tracked microscopic in-plane displacements (400 µm) and very fine out-of-plane tilts (0.003°) at a high accuracy, with a maximum uncertainty of 6.0 %.The proposed DSI approach is particularly suited for monitoring large objects and for operating in hazardous environments. The findings pave a way for interesting new applications, like high-range remote angle measurements, high-sensitivity straightness measurements, and 3D-positioning utilizing retroreflective markers that already exist in the built infrastructure.

The influence of cross shear and contact pressure on the wear of UHMWPE-on-PEEK-OPTIMA™ for use in total knee replacement

PEEK-OPTIMA™ polymer is being considered as an alternative material to cobalt chrome in the femoral component of total knee arthroplasty to give a metal-free knee replacement system. Simple geometry pin-on-plate wear simulation can be used to systematically investigate and understand the wear of materials under many different conditions. The aim of this study was to investigate the wear of UHMWPE-on-PEEK-OPTIMA™ under a range of contact pressure (2.1–80 MPa) and cross-shear ratio (0–0.18) conditions.With increasing contact pressure, there was a trend of decreasing UHMWPE wear factor with a significant difference (p<0.001) in the wear factor of UHMWPE under the different contact pressure conditions of interest. Under uniaxial motion (cross-shear ratio = 0), the wear of UHMWPE was low, introducing multi-axial motion increased the wear of the UHMWPE. There was a significant difference (p<0.01) in the wear factor at different cross-shear ratios however, post hoc analysis showed only the study carried out under unidirectional motion to be significantly different from the other conditions.With varying contact pressure and cross-shear ratio, the wear of UHMWPE against PEEK-OPTIMA™ polymer showed similar trends to previous studies of UHMWPE-on-cobalt chrome.

Data Fusion for Displacement Estimation and Tracking of UAV Quadrotor in Dynamic Motion

The fusion of MIMU and GPS data is generally used to estimate the displacement and tracking of quadrotor UAVs. Meanwhile, displacement estimation inaccuracies during dynamic motion often occur. This error is caused by noise and limited sensor sampling rate especially occurs when the quadrotor changes its attitude rapidly to generate an instantaneous horizontal force. This paper proposes data fusion based on Kalman filter to estimate orientation and displacement. Experiments were also carried out to verify displacement accuracy, i.e. in single-axis and multi-axis sensor motions. The algorithm combines data from MIMU and GPS sensors so that acceleration data is filled in points where GPS data is not available. With this method, the predicted displacement from the MIMU sensor can be corrected every second with data from the GPS and produce accurate displacement and trajectory estimates.

The use of the Classic and Modified Transfer of the Lower Trapezius Muscle (Elhassan Transfer) as a Primary or Secondary Method for Surgical Reconstruction of the Abduction and External Rotation of the Shoulder in Brachial Plexus Injury

Background. Brachial plexus injury (BPI) leads to severe dysfunction of the upper extremity (UE). Elbow flexion and multiaxial movements in glenohumeral joint (MGHJ) are prioritized in reconstruction strategy. Time-dependent (&lt; 6 months) nerve transfers (NT) allow effective restoring of MGHJ. Late (&gt; 6 months) reconstruction of MGHJ remains completely dependent on transfers of the functional tendon-muscle complexes.&#x0D; Objective: to compare the outcomes of the classic Elhassan (c) and modified (m) transfer of the lower trapezius muscle (LTT) on recovery of monoaxial MGHJ.&#x0D; Materials and Methods. Patient (P.) #3 with M4+ recovery of the deltoid muscle (DM) after NT and P. #4 without spontaneous recovery (SR) of DM – forward flexion (FF) was 170° and 0°, respectively, received cLTT. Patient #1 with M4+ recovery of DM after NT and P. #2 with M4+ SR of DM (FF was 160° and 50°, respectively), received mLTT – distal fixation point has been changed from the tendon of the infraspinatus to the tendon of supraspinatus muscle.&#x0D; Results. Shoulder abduction (ABD) has been restored to 50° in P. #1 and P. #2, while the recovery of the external rotation (ER) has not been achieved – upper arm remained internally rotated (IR). ABD has been restored to 40° and 80° in P. #3 and P. #4; simultaneously +15° and +70° of ER has been restored.&#x0D; Conclusions. The use of mLTT leads to more effective recovery of monoaxial MGHJ – ABD – 50° vs. 40° after cLTT. The use of cLTT leads to more effective recovery of another monoaxial MGHJ – ER – +15° and +70° vs. IR after mLTT; LTT should only be considered as a complementary surgical procedure, which utilization should cohere with a patient’s requirements to the MGHJ.

Multi-axis Current Loop Control Based on FPGA

In this paper, according to the three-loop control structure, FPGA is used as the control chip of the current loop, and the parallel control of the multi-axis motor is realized by hardware nation. The current loop code is written in Verilog HDL language, and the simulation results of each control module are given by the SignalTap simulation tool. The main contents include a parallel sampling of the multichannel encoder, parallel sampling of multichannel current, vector coordinate transformation control (CLARK module, PARK module, IPARK module), PI controller module, etc. The results show that the rich logic resources and powerful parallel processing ability of FPGA enable a single FPGA to control multiple motors at the same time. Compared with the traditional serial execution of the program, this method greatly reduces the whole calculation time of the servo system.

Implementation of cross-scale plane micro-scratching process driven by hybrid piezoelectric actuation

The atomic force microscope tip-based mechanical machining technique has been used to fabricate complex micro-structures successfully. However, the machining scope and depth are limited, which holds back this technique severely. This work presents the design and evaluation of a piezoelectric manufacturing system (PMS) for implementation of cross-scale (large scale and high resolution) plane micro-scratching. The PMS has the two-dimensional (2D) micro-machining ability with depths up to 0.98 μm in the millimeter machining scope through the combination of a travel range XY positioning stage and a three-degree-of-freedom (3-DOF) sandwich piezoelectric manipulator. The tracing property of the PMS is feasible for large scale machining by controlling the multi-axis cooperative motion of the 2-DOF stage. The experiments show that the micro-triangles and micro-circles arrays with dimensions from 40 μm to 400 μm are machined successfully. The deviations of the position determination and machined depths for all the micro-structures are less than 5%. Further, it is verified that the manipulator has potential to be used in vibration-assisted cutting to improve machining quality. To sum up, the PMS shows great prospects in the applications of machining cross-scale and large depth planar micro-structures.

Off-Axis Loading Fixture for Spine Biomechanics: Combined Compression and Bending.

The spine is a multi-tissue musculoskeletal system that supports large multi-axial loads and motions during physiological activities. The healthy and pathological biomechanical function of the spine and its subtissues are generally studied using cadaveric specimens that often require multi-axis biomechanical test systems to mimic the complex loading environment of the spine. Unfortunately, an off-the-shelf device can easily exceed 200,000 USD, while a custom device requires extensive time and experience in mechatronics. Our goal was to develop a cost-appropriate compression and bending (flexion-extension and lateral bending) spine testing system that requires little time and minimal technical knowledge. Our solution was an off-axis loading fixture (OLaF) that mounts to an existing uni-axial test frame and requires no additional actuators. OLaF requires little machining, with most components purchased off-the-shelf, and costs less than 10,000 USD. The only external transducer required is a six-axis load cell. Furthermore, OLaF is controlled using the existing uni-axial test frame's software, while the load data is collected using the software included with the six-axis load cell. Here we provide the design rationale for how OLaF develops primary motions and loads and minimizes off-axis secondary constraints, verify the primary kinematics using motion capture, and demonstrate that the system is capable of applying physiologically relevant, noninjurious, axial compression and bending. While OLaF is limited to compression and bending studies it produces repeatable physiologically relevant biomechanics, with high quality data, and minimal startup costs.

Learning-Enabled Output-Feedback-MPC-Based Synchronization Tracking Control of Multiaxis Motion Systems

The unknown and time-varying model parameters and measurement noises impose great influence on the highprecision synchronization tracking control performance of multiaxis motion systems (MAMSs). To deal with the influence of the factors on the high-precision synchronization tracking control performance in MAMSs, a learning-enabled output feedback model predictive control (MPC) strategy for MAMSs is proposed. Firstly, an efficient learning mechanism is introduced to capture the unknown and slow time-varying behavior of the system parameters. Then, considering both the existence of the measurement noises and the unavailability of the velocity signals in system and synchronization coupling errors, the learning-enabled output feedback MPC based synchronization tracking controller is designed to achieve the high-precision synchronization tracking control of the MAMSs. The stability of overall synchronization tracking system with proposed learning procedure is analyzed. Finally, simulations and experiments are performed on fourmotor motion system to demonstrate the practicability and effectiveness of the proposed control strategy.

Contour error dynamic analysis and predictive control for multi-axis motion system

Contour tracking accuracy is the key performance index of a multi-axis motion control system. In the previous design of the contour error feedback controller, the independent design idea of the tracking controller and contour controller of each logic axis is often adopted, which is not easy to realize the optimal control of tracking accuracy and contour accuracy. The coupling increment of each controller is inevitable in motion control compensation, which impacts the control system’s stability. Here, we propose a predictive control method for contour error. At first, through the state space model of the feed system, the system dynamics are judged to predict the contour accuracy in the future finite time domain. Besides, the linear quadratic performance index function of contour error is established, and the performance of the control objective is continuously optimized during the limited time domain with the form of rolling optimization. A closed-loop solution is obtained, which is most suitable for the current motion situation and could add to the system to realize the optimal control considering the trajectory contour and the tracking stability of each servo axis in the subsequent few sampling cycles. Finally, utilizing comparative experiments on the three-axis motion control platform, it is verified that the proposed contour predictive control strategy not only effectively reduces the tracking error but also significantly improves the contour accuracy, which is suitable for application in a complex industrial environment.