Virtual Axis Research Articles

Automated fabrication of hybrid printed electronic circuits

Printed electronics offer great potential for new applications such as Internet of Things devices and wearables. However, to date, only a limited number of electronic functions and integration densities can be realised by printing processes. Hence, hybrid printed electronic circuits are actually created by mounting silicon electronic components. Since both printed materials and processes are continuously evolving, an accompanying structured development methodology is required. This paper highlights a digital workflow from design to automated fabrication using the example of a demonstrator circuit. A multi-layer vector ink-jet printing process to print electronic devices onto foil substrates with three functional inks is presented. This printing process is improved using a newly set-up printing system: Integrating a piezo print head into the path planning of the printing system and its control as a virtual stepper axis enable highly precise vector printing. This leads to printed resistors with low tolerances. Adaptations of surface mount technology for assembling silicon electronic components onto printed foil substrates are discussed. Finally, image processing methods to cope with deformations of the flexible foil substrates in the fabrication process are introduced.

A Tunable Variable-Torque Compliant Hinge Using Open-Section Shells

Abstract This paper is concerned with a compliant-hinge mechanism that can provide a wide range of torque-angle profiles. The mechanism consists of thin-walled open-section shells that are subjected to combined twisting and bending. A pair of open-section shells is so arranged as to get a large rotation about a virtual axis with high stiffness along other axes. A replaceable cam-like guideway regulates the bending of the open-section shells as they twist, thereby generating the desired torque profile. An energy-based, graphical, and computational design method is formulated to obtain the guideway profile for a specified torque profile. A physical prototype is constructed for an assistive chair for the elderly to demonstrate the variable-torque output and the efficacy of the hinge.

Reinforcement learning-based collision-free path planner for redundant robot in narrow duct

Compared with obstacle avoidance in open environment, collision-free path planning for duct-enter task is often challenged by narrow and complex space inside ducts. For obstacle avoidance, redundant robot is usually applied for this task. The motion of redundant robot can be decoupled to end-effector motion and self-motion. Current methods for duct-enter task are not robust due to the difficulty to properly define the self-motion. This difficulty mainly comes from two aspects: the definition of distances from robot to obstacles and the fusion of multiple data. In this work, we adapt the ideas underlying the success of human to handling this kind tasks, variable optimization strategies and learning, for one robust path planner. Proposed planner applies reinforcement learning skills to learn proper self-motion and achieves robust planning. For achieving robust behavior, state-action planner is creatively designed with three especially designed strategies. Firstly, optimization function, the kernel part of self-motion, is considered as part of action. Instead of taking every joint motion, this strategy embeds reinforcement learning skills on self-motion, reducing the search domain to null space of redundant robot. Secondly, robot end orientation is taken into action. For duct-enter task, robot end link is the motion starter for exploring movement just like the snake head. The orientation of robot end link when passing through some position can be referred by following links. Hence the second strategy can accelerate exploring by reduce the null space to possible redundant robot manifold. Thirdly, path guide point is also added into action part. This strategy can divide one long distance task into several short distance tasks, reducing the task difficulty. After these creative designs, the planner has been trained with reinforcement learning skills. With the feedback of robot and environment state, proposed planner can choose proper optimization strategies, just like the human brain, for avoiding collision between robot body and target duct. Compared with two general methods, Virtual Axis method with orientation Guidance and Virtual Axis, experiment results show that the success rate is separately improved by 5.9% and 49.7%. And two different situation experiments are carried out on proposed planner. Proposed planner achieves 100% success rate in the situation with constant start point and achieves 98.7% success rate in the situation with random start point meaning that the proposed planner can handle the perturbation of start point and goal point. The experiments proves the robustness of proposed planner.

Three-Dimensional (3D) Model-Based Lower Limb Stump Automatic Orientation

Modern prosthetics largely relies upon visual data processing and implementation technologies such as 3D scanning, mathematical modeling, computer-aided design (CAD) tools, and 3D-printing during all stages from design to fabrication. Despite the intensive advancement of these technologies, once the prosthetic socket model is obtained by 3D scanning, its appropriate orientation and positioning remain largely the responsibility of an expert requiring substantial manual effort. In this paper, an automated orientation algorithm based on the adjustment of the 3D-model virtual anatomical axis of the tibia along with the vertical axis of the rectangular coordinates in three-dimensional space is proposed. The suggested algorithm is implemented, tested for performance and experimentally validated by explicit comparisons against an expert assessment.

A surface-to-surface contact search method enhanced by deep learning

This paper describes a new surface-to-surface contact search method for contact problems between curved surfaces defined by the non-uniform rational B-spline basis functions. The method consists of a global search method based on the hierarchical virtual axis aligned bounding boxes and a local contact search method enhanced by the deep learning. The artificial neural network is employed to simulate the mapping from the parameters of contacting surface to the contact state: whether contact occurs or not, where the contact occurs and how far the slave surface penetrates to the master surface. With the proposed method, the time-consuming local contact search is successfully performed independently from the dynamic contact analysis part, where its computational efficiency is quantitatively discussed through some numerical examples.

View-Independent Gait Recognition Using Joint Replacement Coordinates (JRCs) and Convolutional Neural Network

Gait recognition has received increasing attention for security and authentication since it can be done unintrusively from afar and without a subject’s awareness. In this work, we propose a new model-based gait recognition technique called JRC-CNN gait recognition. We introduce three new concepts. (1) We create a new way to preprocess skeleton data by rotating skeleton data using two virtual axes. This process reduces the fluctuation in movements and resolves the multi-viewpoint issue. All postures in a walk are observed from the same angle. (2) We introduce new Joint Replacement Coordinates (JRCs), which represent the movements of the left and right joints in a group of three connected joints. These JRC gait features are designed to put more emphasis on local movements than the movements of non-connected joints. (3) We construct a new Convolution Neural Network (CNN) for the classification process, which consists of a convolutional layer on each JRC and two fully-connected layers. A convolutional layer is designed to discover relations within a group of three connected joints. Fully-connected layers also find the relations of all groups of three connected joints throughout an entire body (in a posture). Our JRC-CNN technique achieves above 98.4% accuracy and significantly outperforms other existing techniques for all free-direction walk datasets. It also performs well under the gallery-size test and the CMC curve test. This means that our proposed JRC-CNN gait recognition technique can be used in a real-world situation. Experimental results also suggest that a person can be identified by a unique posture (an entire body is observed as a whole) with the focus on the movements of connected joints.

Interpretation of Gyro Stability and Precession Mechanism by Law of Rotational Inertia

The precession mechanism and stability of gyroscope is an outstanding problem. It has been widely believed for a long time that the precession of gyroscope is the result of the action of heavy moment. But this is not completely consistent with the experimental facts. This paper introduces the experimental phenomena of gyroscopic precession on the horizontal plane, presents the laws of rotational inertia and micro deformation action, gives the empirical expression of micro deformation action. The experimental phenomena of gyro precession are analyzed based on the principle of virtual fixed axis rotation balance and the law of conservation of momentum moment. The condition of whether the gyro can recover stable rotation state in certain condition is given, the determinants of precession angular velocity and rotation angular velocity of gyroscope and their relations are also given. The stability and precession mechanism of the gyroscope on the horizontal plane are explained comprehensively.

A Coordinated Droop Control Method Using a Virtual Voltage Axis for Power Management and Voltage Restoration of DC Microgrids

In this paper, a coordinated droop control method through virtual voltage axis is proposed for voltage restoration and energy management of dc microgrids (MGs). Droop control is a control method that operates a dc MG using only local information. However, there are several drawbacks in that output voltage deviations occur, and the utilization priorities of various sources are not considered. To solve these problems, the voltage compensation term is defined as the virtual axis voltage value. It can minimize the voltage deviation of the dc MG and enable energy management by determining the operation band. However, the value of the virtual voltage axis is affected by communication delays. Therefore, its influence on the values of the virtual voltage axis was analyzed. The reference voltage and the droop gain of the droop control were designed, and the validity of the proposed method was verified using a lab-scale dc MG.

Measurement system based on virtual reference axis for evaluation form and location of surfaces and axes of rotary details

The system for measurement and control of the form and location of the surfaces and axes of large scaled rotational parts by means of a virtual reference base is used, by using a self-orientation multistage gauge allowing exclusion of the radial run-out of axis of rotation when access to the face surfaces of the workpiece is difficult or impossible.

Series Elastic Behavior of Biarticular Muscle-Tendon Structure in a Robotic Leg.

We investigate the role of lower leg muscle-tendon structures in providing serial elastic behavior to the hip actuator. We present a leg design with physical elastic elements in leg angle and virtual leg axis direction, and its impact onto energy efficient legged locomotion. By testing and comparing two robotic lower leg spring configurations, we can provide potential explanations of the functionality of similar animal leg morphologies with lower leg muscle-tendon network structures. We investigate the effects of leg angle compliance during locomotion. In a proof of concept, we show that a leg with a gastrocnemius inspired elasticity possesses elastic components that deflect in leg angle directions. The leg design with elastic elements in leg angle direction can store hip actuator energy in the series elastic element. We then show the leg's advantages in mechanical design in a vertical drop experiment. In the drop experiments the biarticular leg requires 46% less power. During drop loading, the leg adapts its posture and stores the energy in its springs. The increased energy storing capacity in leg angle direction reduces energy requirements and cost of transport by 31% during dynamic hopping to a cost of transport of 1.2 at 0.9 kg body weight. The biarticular robot leg design has major advantages, especially compared to more traditional robot designs. Despite its high degree of under-actuation, it is easy to converge into and maintain dynamic hopping locomotion. The presented control is based on a simple-to-implement, feed-forward pattern generator. The biarticular legs lightweight design can be rapidly assembled and is largely made from elements created by rapid prototyping. At the same time it is robust, and passively withstands drops from 200% body height. The biarticular leg shows, to the best of the authors' knowledge, the lowest achieved relative cost of transport documented for all dynamically hopping and running robots of 64% of a comparable natural runner's COT.

Automated fabrication of multi-layer printed electronic circuits using a novel vector ink-jet printing process control and surface mounting of discrete components

Printed electronics offer great potential for new applications such as Internet of Things devices and wearables. A methodology for integration of design and process assessment based on a stepwise transfer of the circuit to be printed from printed circuit board test vehicles to the final printed substrate is introduced. A multi-layer vector ink-jet printing process with three functional inks is presented using the example of the fabrication of a demonstrator circuit. This fabrication is realized using a newly set up printing system as enabling technology: Integration of a piezo print head into the path planning of the printing system and its control as virtual stepper axis enable highly precise vector printing yielding printed functional elements with low tolerances. Finally, process improvements for assembly of surface mounted devices on printed foil substrates are outlined.

New motion control machine elements representation for mechatronic education

The paper presents a new proposal for representing machine designs involving motion control. The new mechatronic approach for machine design is moving from a mechanic concept where mechanical transmissions, mechanical gears and coupling etc. are being implemented by electronic coupling, gears, etc. New concepts such as electronic virtual axis are also being employed very often. This brings that, in regards with machine design communication, mechanic elements represented in the past by mechanical drawings are being replaced by new electronic concepts. However, these new electronic motion control concepts should be also represented for a full understanding of the machine behaviors. Drawings are a fundamental tool to communicate preliminary designs, both in an academic and education environments as in professional ones. The new mechatronic elements graphical representation presented in the paper has the objective of bringing the gap between a pure mechanical machine design view and an automated one, including new electronic motion control concepts, and remarking the relevant “mechanic” information from the electronic motion control point of view. All this should facilitate the presentation and explanation of system-based mechatronic designs both in the classroom and at the professional level.

On-Line Inter-Turn Short-Circuit Fault Diagnosis and Torque Ripple Minimization Control Strategy Based on OW Five-Phase BFTHE-IPM

This paper proposed an on-line inter-turn short-circuit (ITSC) fault diagnosis approach by observing the dc component in the torque deviation for the open-end winding (OW) five-phase brushless fault-tolerant hybrid-excitation interior permanent magnet motor (BFTHE-IPM). To eliminate the impact of ITSC fault on torque and guarantee a disturbance-free operation, the strategy of torque ripple minimization is proposed, in which the virtual direct-quadrature axis current feedforward compensator is adopted. Moreover, the compensation is obtained by measuring the zero-sequence current without calculating short-circuit turns ratio and short-circuit current. Therefore, computational quantity and complexity of the algorithm are greatly reduced. Simulation and experimental results verify the effectiveness of the proposed method.

Derotational Osteotomy of the Distal Femur for the Treatment of Patellofemoral Instability Simultaneously Leads to the Correction of Frontal Alignment: A Laboratory Cadaveric Study.

Background:Derotational osteotomy of the distal femur allows the anatomic treatment of patellofemoral maltracking due to increased femoral antetorsion. However, such rotational osteotomy procedures have a high potential of intended/unintended changes of frontal alignment.Purpose/Hypothesis:The purpose of this study was to perform derotational osteotomy of the distal femur and to demonstrate the utility of a novel trigonometric approach to address 3-dimensional (3D) changes on 2-dimensional imaging (axial computed tomography [CT] and frontal-plane radiography). The hypothesis was that 1-step single-cut osteotomy can simultaneously correct torsion and frontal alignment based on preoperatively calculated cutting angles.Study Design:Controlled laboratory study.Methods:Eight human cadaveric whole legs (4 lower limb torsos) underwent derotational osteotomy of the distal femur of 20°. A straight leg axis, determined as a mechanical femorotibial angle (mFTA) of 0°, was chosen as a goal for postoperative frontal alignment. The inclination of the cutting angle from the lateral view was calculated individually for each cadaveric leg and was represented by a simple 3D-printed cutting guide for surgery. Specimens underwent CT for the measurement of torsion, while the frontal leg axis was determined on an upright radiograph preoperatively and postoperatively. Preoperative and postoperative angles were compared with the mathematical prediction model.Results:The preoperative mFTA ranged from –3.9° (valgus) to +3.4° (varus) (mean, –0.2° ± 2.6°). A postoperative mean mFTA of 0.37° ± 0.69° (95% CI, –0.22° to 0.95°) was achieved (P = .01). Derotation showed a mean of 19.1° ± 2.1° (95% CI, 17.3°-20.8°). The oblique cutting plane for the correction of valgus legs showed a mean of 5.9° ± 6.8° and, for the correction of varus legs, a mean of –10.0° ± 4.5° projected on the perpendicular plane to the virtual anatomic shaft axis from the sagittal view.Conclusion:Single-cut distal femoral osteotomy can be performed to simultaneously address rotational as well as frontal alignment using a preoperatively defined oblique cut, as determined by the presented reproducible calculation model.Clinical Relevance:This study adds important knowledge to the technique of derotational osteotomy. This approach provides an individual, oblique single cut for the correction of torsion and frontal axis within a clinically insignificant margin. Simplified tables for calculation and a surgical reference make this model reproducible and safe.

Tile cut synchronization control and compensation design and implement for multi-wire saw

Based on the tension analysis of multi-wire saw synchronization control system, improve tension dancer design, wire passing design, and wire traverse design. To reduce the emergency shock, design a flexible traverse direction switch method. To realize multi-axis synchronization, virtual main axis is used based on analysis of axis coupling relation. To avoid the shake of two main rollers, a master slave control method is designed and the two motors can get accurate torque synchronization. Multi-wire saw is very few used for tile cut before, for processing resistance produces a big error between wire theory position and fact position, so the accuracy is very bad. An intelligent compensation method is designed to improve the tile cut error and correct the error by segment to improve production quality. Tile cut error mechanism is analyzed, tile detection standard is given, error compensation theory is put forward, a compensation table is designed, and compensation solution error is analyzed. At last, the hardware and software structure are explained, control strategy of multi-wire saw is introduced, and sample tile product is shown by DX2240R machine.

A new method for motion synchronization among multivendor’s programmable controllers

This paper is aimed at increasing the number of possible architectures of distributed control systems by investigating and developing novel methods for the synchronization of axes between PLCs and iPCs of different vendors. In order to find a global solution to this problem, particular attention has been focused on programmable controllers that can manage axes by means of point-by-point control or motion instructions.Two synchronization algorithms have been developed and validated for real and virtual axes; they differ in computational load so that they can be used with programmable controllers having high or low computational performances.

Shifted axis angular positioning mechanisms – unconventional use of exact constraint design

Paper presents some remarks about designing angular positioners having significant angular displacement and shifted axis of rotation. Those driving mechanism are useful in specific applications where mechanism wraps around other object or there is a need of rotation around virtual axis. Examples of those applications like orthotic robots or gimbals for panoramic motions where developed at Faculty of Mechatronics WUT. Usage of exact constraint method was described including its influence to a kinematic structure of designed mechanism.

Development of A Novel Integrated Corner Module for Narrow Urban Vehicles

Most current urban vehicles are scaled-down versions of standard passenger cars. This imposes serious limitations on the safety, comfort, efficiency, dynamic performance and, hence, customer acceptance of the vehicle. This paper provides a unique design of an integrated corner module including an in-wheel suspension, an electrical in-wheel motor, a friction brake, a steering system, and a camber mechanism, which can be used in any urban vehicle design without modification. For the first time, a dual four-bar linkage mechanism has been designed to generate a virtual kingpin axis and provide an active camber. This approach results in a highly compact design for the corner module that can be integrated into narrow vehicles. A full-size prototype of the proposed integrated corner module has been fabricated and tested to validate the new steering mechanism and the integrated corner module characteristics.

How to avoid unintended valgus alignment in distal femoral derotational osteotomy for treatment of femoral torsional malalignment - a concept study

BackgroundDefining the optimal cutting plane for derotational osteotomy at the distal femur for correction of torsion in cases of patellofemoral instability is still challenging. This preliminary study investigates changes of frontal alignment by a simplified trigonometrical model and demonstrates a surgical guidance technique with the use of femur cadavers. The hypothesis was that regardless of midshaft bowing, a cutting plane perpendicular to the virtual anatomic shaft axis avoids unintended valgus malalignment due to derotation.MethodsA novel mathematical model, called the Pillar-Crane-Model, was developed to forecast changes on frontal alignment of the femur when a perpendicular cutting plane to the virtual anatomical shaft was chosen. As proof of concept, eight different torsion angles were assessed on two human cadaver femora (left and right). A single cut distal femoral osteotomy perpendicular to the virtual anatomical shaft was performed. Frontal plane alignment (mLDFA, aLDFA, AMA) was radiographically analyzed before and after rotation by 0°, 10°, 20°, and 30°. Measurements were compared to the model.ResultsThe trigonometrical equation from the Pillar-Crane-Model provides mathematical proof that slight changes into varus occur, seen by an increase in AMA and mLDFA, when the cutting plane is perpendicular to the virtual anatomical shaft axis. A table with standardized values is provided. Exemplarily, the specimens showed a mean increase of AMA from 4.8° to 6.3° and mLDFA from 85.2° to 86.7 after derotation by 30°. Throughout the derotation procedure, aLDFA remained at 80.4° ± 0.4°SD.ConclusionsWith the use of this model for surgical guidance and anatomic reference, unintended valgus changes on frontal malalignment can be avoided. When the cutting plane is considered to be perpendicular to the virtual anatomical shaft from a frontal and lateral view, a slight increase of mLDFA results when a derotational osteotomy of the distal femur is performed.

Modeling the convergence accommodation of stereo vision for binocular endoscopy.

The stereo laparoscope is an important tool for achieving depth perception in robot-assisted minimally invasive surgery (MIS). A dynamic convergence accommodation algorithm is proposed to improve the viewing experience and achieve accurate depth perception. Based on the principle of the human vision system, a positional kinematic model of the binocular view system is established. The imaging plane pair is rectified to ensure that the two rectified virtual optical axes intersect at the fixation target to provide immersive depth perception. Stereo disparity was simulated with the roll and pitch movements of the binocular system. The chessboard test and the endoscopic peg transfer task were performed, and the results demonstrated the improved disparity distribution and robustness of the proposed convergence accommodation method with respect to the position of the fixation target. This method offers a new solution for effective depth perception with the stereo laparoscopes used in robot-assisted MIS.