Limited Workspace Research Articles

Design of exoskeleton-type wrist human–machine interface based on over-actuated coaxial spherical parallel mechanism

In this study, a wrist human–machine interface with a single internal rotation center, which is efficient in terms of performance, size, and avoidance of kinematic interference, is proposed to realize the 3-degree-of-freedom rotational motion of the human wrist. For this purpose, an over-actuated coaxial spherical parallel mechanism is applied. The over-actuated mechanism is specially considered to improve the force feedback performance and to overcome the workspace limitations caused by the singularity. From a mechanical perspective, two links are coaxially connected to the base, and this rotation axis is designed to coincide with the wrist pronation–supination, which has the largest operating range in wrist motion. A prototype was fabricated and evaluated to validate the proposed mechanism. In addition, a usable design index was proposed for the design that prevents interference with the user in the workspace while minimizing the link inertia to optimize the device. This index is optimized with the general performance indices, that is, condition index and stiffness index. It was verified through simulation that the optimized wrist human–machine interface exhibited higher performance than other similar devices. In addition, range of motion is at least 104.3% than a daily living range of motion of the human wrist, guaranteeing all ranges of motion.

Development master arm of 2-DOF planar parallel manipulator for In-Vitro Fertilization

Micromanipulator is a mechanical device used for manipulating miniature objects in the order of micron. It is widely used in In-Vitro Fertilization (IVF) in which sperms will be held in a micro-needle and penetrate to an oocyte for fertilization. IVF needs to be performed by high skill embryologists to control the movement of the needle accurately due to the lack of tactile perception of the user. Haptic device is a device that can transmit and simulate position, velocity and force in order to enhance interaction between the user and system. However, commercially available haptic devices have unnecessary degrees of freedom and limited workspace which are inappropriate for IVF process. This paper focuses on development of a haptic device for using in IVF process. It will be used as a master arm for the master-slave system for IVF process in order to enhance the ability of users to control the micromanipulator. As a result, the embryologist is able to carry out the IVF process more effectively with having tactile perception.

Parasitic Inclinations in Cable-Driven Parallel Robots using Cable Loops

Cable-Driven Parallel Robots (CDPRs) also noted as wire-driven robots are parallel manipulators with flexible cables instead of rigid links. A CDPR consists in a base frame, a Moving-Platform (MP) and a set of cables connecting in parallel the MP to the base frame. CDPRs are well-known for their advantages over the classical parallel robots in terms of large workspace, reconfigurability, large payload capacity and high dynamic performance. In spite of all the mentioned advantages, one of the main shortcomings of the CDPRs is their limited orientation workspace. The latter drawback is mainly due to cable interferences and collisions between cables and surrounding environment. Hence, a planar four-Degree-of-Freedom (DoF) under-constrained CDPR with an articulated MP is introduced and studied in this paper. The end-effector is articulated through a cable loop, which enables the robot to obtain a modular pose determination, namely orientation and positioning. As a result, the mechanism under study has an unlimited and singularity-free orientation workspace in addition to a large translational workspace. It should be noted that some unwanted rotational motions of the moving platform, namely, parasitic inclinations, arise due to the cable loop. Finally, those parasitic inclinations are modeled and assessed for the mechanism at hand.

Learning CP-Nets Structure From Preference Data Streams

With the sharp increase of digital data emerging at present, the data in new applications are generated fast. Continuous cumulative data have gradually become massive and difficult to be handled due to limited workspace and limited amount of time. The conventional learning conditional preference networks’ algorithm cannot successfully process the data streams. In this paper, we introduce the model of learning CP-nets from preference data streams and formalize the question. Then, an incremental approach is presented through which we can learn the CP-nets with gradually increasing data streams. The proposed method is verified on simulated data and real data, and it is also compared with other works.

A decoupled flexure-based rotary micropositioning stage with compact size

This paper presents the design and analysis of a novel compact flexure-based rotary micropositioning stage driven by piezoelectric actuator. The developed stage possesses a double four-bar rotary mechanism with rotational symmetric configuration and totally kinematic decoupling, which can convert the linear motion of the piezoelectric actuator into the pure rotational motion, significantly minimizing the parasitic error at the rotation center. Based on the configuration, a single piezoelectric actuator is employed to drive the stage, avoiding actuator redundancy and large configuration size. Meanwhile, we introduce a compliant rotational guiding mechanism to enhance the rotational stiffness and dynamics of the stage. Analytical modeling and finite element analysis are adopted to facilitate the design of dimension. Finally, a prototype of the stage is manufactured and tested, which is capable of a rotational angle of [Formula: see text] with the first natural frequency of 430 Hz, whilst the well-constrained maximum center shift along the X- and Y-axis are 0.29 µm and 0.12 µm, respectively, indicating good decoupling capability. Furthermore, the compact size of [Formula: see text] is beneficial for limited working space.

Task planning for mobile painting manipulators based on manipulating space

PurposeTo paint large workpieces automatically, painting manipulators with hollow wrists must be transported by mobile platforms to different positions because of their limited workspaces. This paper aims to provide a visualization method for finding appropriate base positions (BPs) and maximum painting areas for manipulators.Design/methodology/approachThis paper begins by analyzing the motion characteristics of manipulators possessing a spherical wrist and summarizing them into three constraints – positioning, orientation and singularity avoidance. The hollow wrist is simplified and considered as spherical by introducing the concepts of an inner wrist center and an outer wrist center. Taking the three constraints into consideration, the boundaries of the manipulating space are formulated analytically. Finally, to verify the method, the space obtained is applied to determine the maximum painting areas for flat, cylindrical and conical surfaces. Experiments of robotic painting were used to confirm the results.FindingsCompared with previous studies, the maximum areas obtained using the proposed method increased by 17-131 per cent with an algorithm of lower complexity, and the process remained visually intuitive, thereby demonstrating that the method of manipulating space is more effective.Originality/valueSuch a method allows individuals to visualize the entire painting area at the current BP, thereby maximizing painting areas or optimizing BPs. It opens a black box that is the relationship between BPs and blocks. The method can also be used to choose the best configuration for painting manipulators, select the end-effector structure parameters, split surfaces into blocks, etc.

Changes in motor performance and mental workload duringpractice of reaching movements: a team dynamics perspective.

Few investigations have examined mental workload during motor practice or learning in a context of team dynamics. This study examines the underlying cognitive-motor processes of motor practice by assessing the changes in motor performance and mental workload during practice of reaching movements. Individuals moved a robotic arm to reach targets as fast and as straight as possible while satisfying the task requirement of avoiding a collision between the end-effector and the workspace limits. Individuals practiced the task either alone (HA group) or with a synthetic teammate (HRT group), which regulated the effector velocity to help satisfy the task requirements. The findings revealed that the performance of both groups improved similarly throughout practice. However, when compared to the individuals of the HA group, those in the HRT group (1) had a lower risk of collisions, (2) exhibited higher performance consistency, and (3) revealed a higher level of mental workload while generally perceiving the robotic teammate as interfering with their performance. As the synthetic teammate changed the effector velocity in specific regions near the workspace boundaries, individuals may have been constrained to learn a piecewise visuomotor map. This piecewise map made the task more challenging, which increased mental workload and perception of the synthetic teammate as a burden. The examination of both motor performance and mental workload revealed a combination of both adaptive and maladaptive team dynamics. This work is a first step to examine the human cognitive-motor processes underlying motor practice in a context of team dynamics and contributes to inform human-robot applications.

Magnetic Levitation Haptic Augmentation for Virtual Tissue Stiffness Perception.

Haptic-based tissue stiffness perception is essential for palpation training system, which can provide the surgeon haptic cues for improving the diagnostic abilities. However, current haptic devices, such as Geomagic Touch, fail to provide immersive and natural haptic interaction in virtual surgery due to the inherent mechanical friction, inertia, limited workspace and flawed haptic feedback. To tackle this issue, we design a novel magnetic levitation haptic device based on electromagnetic principles to augment the tissue stiffness perception in virtual environment. Users can naturally interact with the virtual tissue by tracking the motion of magnetic stylus using stereoscopic vision so that they can accurately sense the stiffness by the magnetic stylus, which moves in the magnetic field generated by our device. We propose the idea that the effective magnetic field (EMF) is closely related to the coil attitude for the first time. To fully harness the magnetic field and flexibly generate the specific magnetic field for obtaining required haptic perception, we adopt probability clouds to describe the requirement of interactive applications and put forward an algorithm to calculate the best coil attitude. Moreover, we design a control interface circuit and present a self-adaptive fuzzy proportion integration differentiation (PID) algorithm to precisely control the coil current. We evaluate our haptic device via a series of quantitative experiments which show the high consistency of the experimental and simulated magnetic flux density, the high accuracy (0.28 mm) of real-time 3D positioning and tracking of the magnetic stylus, the low power consumption of the adjustable coil configuration, and the tissue stiffness perception accuracy improvement by 2.38 percent with the self-adaptive fuzzy PID algorithm. We conduct a user study with 22 participants, and the results suggest most of the users can clearly and immersively perceive different tissue stiffness and easily detect the tissue abnormality. Experimental results demonstrate that our magnetic levitation haptic device can provide accurate tissue stiffness perception augmentation with natural and immersive haptic interaction.

Social network analysis for construction crews

ABSTRACTConstruction crews usually have to share the limited working space with each other during construction to perform their tasks, which increases the chance of interference/conflict and productivity lost. Social network analysis (SNA) has been known as a methodology to determine the conditions of social structures by investigating the interdependencies among a set of actors. The impact of jobsite social network on the performance of the crews has not been well documented in previous research. This research proposes an analytical approach by combining SNA and work plan variation analysis to (1) quantify the influence construction crews receive from jobsite social network, and (2) explore the impact of jobsite social network on the crews’ performance particularly on their work plan variation through a case study. The results indicated that there is a positive monotonic association between each of the centrality indices (representing network influence on each crew) and each of the work plan variability indices (representing crew's performance). The more influences a crew receives form the network, the more work plan variation it will have. A better understanding of the existing jobsite interdependencies will help project managers to control it through better planning and leadership, consequently increasing jobsite productivity.

Inverse kinematics for a novel hybrid parallel–serial five-axis machine tool

A unique successful postprocessor for a hybrid parallel-serial machine tool is developed.Smart machining must be accomplished without forcing the tool to make sharp turns when HSM controls detect a turn approaching.NC codes are recalculated to form a new path for the pivot that can avoid the discretization near the singularity points in this study.The novelty of the paper is successfully to propose a new hybrid parallel-serial five-axis machining model.The manufacturers that are interested in integrating the inverse kinematics into the design process of their hybrid product. Instead of obsessively emphasizing to interpolate more points from the linearization algorithm, the NC codes are recalculated to form a new path for the pivot that can avoid the discretization near the singularity points in this study. In previous studies, orientable-spindle machines were directly used to generate smooth tool paths traversing singular positions through inverse kinematics. In many characteristics and practices, PKMs (parallel kinematic machines) and serial machines are the opposites of each other. Fully PKMs have relatively very limited working-space, especially in terms of orientation characteristics. Fully serial machines have a problem of error accumulation. This paper presents a modular method to construct a postprocessor system for a novel hybrid parallel-serial five-axis machine tool. A hybrid parallel-serial mathematical model is introduced to analyze a structural configuration. The configuration decomposition of machine tools is used to create the kernel of the postprocessor. The proposed modified DenavitHartenberg notation is used in the coordinate conversion procedure, and then an algorithm is used for developing the inverse kinematics of five-axis machines. The feasibility of solutions depends on the surface normal along the tool path satisfying certain orientation constraints. The proposed algorithm can be easily adapted to convert between cutter contact path and cutter location code and implemented on computer-aided design and computer-aided manufacturing systems. Examples with end-milling and side-milling tools are demonstrated and real cutting parts are implemented for verifying the algorithm.

EARLY EXPERIENCE WITH DEL NIDO CARDIOPLEGIA IN MINIMALLY INVASIVE CARDIAC SURGERY

Del Nido cardioplegia (DNC) has been used in the paediatric population since the early 1990s, achieving adequate myocardial protection. In addition, initial investigations in adults have demonstrated reduced myocardial damage and improved functional recovery post-operatively. As the utiilization of minimally invasive cardiac surgery is increasing as an alternative to traditional sternotomy, application of a cardioplegia solution that could provide myocardial protection for a long period of time would be ideal given the limited working space available and longer cross-clamp time during minimally invasive procedures. Our objective was to describe our experience with DNC as a primary myocardial protection strategy in adult cardiac patients undergoing minimally invasive surgery. We performed a restrospective review of all patients from September 2016 to April 2017 that underwent minimally invasive aortic or mitral valve surgery utilizing DNC as myocardial protection strategy delivered using the microplegia system (Quest medical, Dallas, Tx ). During the study period, 10 patients underwent elective cardiac surgery with DNC. Mean [SD] age was 59.8 [11.5] years, and 4 (40%) patients were female. Isolated aortic valve replacement (AVR) was performed in 2 patients (20%), and mitral valve repair (MVR) in 8 patients (80%, 1 using robot assistance. Mean [SD] crossclamp time and bypass times were 127 [23.4] and 217 [38.4] minutes, respectively (Table 1). Seven patients only required single dose of cardioplegia, while 3 required the dose to be repeated once. Four (40%) patients required to be on inotropic support postoperatively. There was no post-operative mortality, myocardial infarction, reintervention, reoperation for bleeding or renal failure requiring dialysis. Median [IQR] intensive care and hospital lengths of stay were 2 [1,3] days and 7 [6,8] days, respectively (Table 1). DNC is becoming increasingly utilized in the adult cardiac surgical population given its efficacy and cost-effectiveness in the paediatric population. Our experience suggests DNC is safe in minimally invasive cardiac surgery. It facilitates the conduct of minimally invasive cardiac surgery by reducing the number of applications of cardioplegia. This will facilitate the conduct of minimally invasive cardiac surgery and possibly benefit high risk patients by providing excellent myocardial protection. Randomized studies are needed to further evaluate its efficacy in adult cardiac surgery undergoing minimally invasive surgery.

Optimizing Model Predictive Control horizons using Genetic Algorithm for Motion Cueing Algorithm

Driving simulators are effective tools for producing the feeling of driving a real car through generation of a similar environment and motion cues. The main problem of motion simulators is their limited workspace which does not allow them to produce the exact motions of a real vehicle, hence they need a Motion Cueing Algorithm (MCA). A high-fidelity motion simulator can be used for vehicle prototyping and testing as well as driver/pilot training to enhance transportation safety. Using motion simulators with the capability of replacing realistic motions for these purposes is less risky for drivers and more time and cost-effective. Due to workspace limitations, washout filters have been designed to bring motion simulators back to a neutral position; however, the problem of violation of platform constraints is still an issue. Recently Model Predictive Control (MPC) has become popular in driving simulators. The primary advantage of this control method is respecting constraints and consideration of future dynamics. The horizon windows of future control and prediction affect the computational burden and the output performance. As these horizons are chosen manually by the designer, they are sub-optimal and in some cases too wide or narrow. In this paper, a novel method based on Genetic Algorithm (GA) is employed to achieve the best control and prediction horizons considering minimization of several terms such as sensation error, displacement and the computational burden. This new method is proposed to eliminate the MPC-MCA drawbacks such as time-consuming empirical guessing by iterative trial-and-error for the initial control and prediction horizons as selecting the initial control and prediction horizons based on trial-and-error can lead to large sensation error, low motion fidelity, inefficient platform usage as well as the computational burden. Therefore, this method provides a new framework for tuning not only the MPC-MCA optimally but also all the MPC-based applications while minimizing the desired cost function and computational load. The simulation results show the effectiveness of the proposed method in terms of output performance improvement and the computational burden.

Production Aspects Affecting the Final Precision Machining of Advanced Materials

When creating products of modern construction materials has a great influence on their endpoints right way and the quality of working on machine tools. The article deals with positioning accuracy of machine tools which is carried out in an unloaded condition, according to international standard ISO 230-2. Overall accuracy of working machining is determined mainly static rigidity, geometrical accuracy of mechanical components, positioning accuracy and dynamic stiffness. Static stiffness is defined in new machine tools in a limited workspace. Therefore, the article deals with the definition of static stiffness in the expanded work area and also defines its impact on the positioning accuracy at individual points in workspace of the machine tool.

Implementing pseudo haptic feedback in a semi-isometric master interface for robotic surgery

We have developed a master interface that uses an isometric velocity control technique for translation and an anisometric position control technique for rotation. Using the developed interface, the operator can concentrate on the slave side and control the robot without repositioning required in conventional master arm due to the workspace limitation. However, it cannot display haptic to the operator for the translation directions with the manipulator. In this article, we propose a method to feedback the external force on the slave side to the master manipulator without using actuators or link mechanism but using a pseudo haptic effect. A flexible wrist joint with a spring is used at the tip of the slave forceps to enhance visual effect. The spring stiffness is pneumatically controlled. At the same time, we change the reference velocity of the slave according to the external force applied to the slave manipulator. The changed velocity caused by the external force restrains the slave motion. Using both the visual feedback and the motion restrain, the master–slave system is able to display force to the operator as pseudo haptic feedback without actuators. Experiments of pulling suture threads are executed using the developed master–slave surgical robot. It is confirmed that the master–slave system with pseudo haptic feedback can decrease the variance of force.

Propagation characteristics of pulverized coal and gas two-phase flow during an outburst.

Coal and gas outbursts are dynamic failures that can involve the ejection of thousands tons of pulverized coal, as well as considerable volumes of gas, into a limited working space within a short period. The two-phase flow of gas and pulverized coal that occurs during an outburst can lead to fatalities and destroy underground equipment. This article examines the interaction mechanism between pulverized coal and gas flow. Based on the role of gas expansion energy in the development stage of outbursts, a numerical simulation method is proposed for investigating the propagation characteristics of the two-phase flow. This simulation method was verified by a shock tube experiment involving pulverized coal and gas flow. The experimental and simulated results both demonstrate that the instantaneous ejection of pulverized coal and gas flow can form outburst shock waves. These are attenuated along the propagation direction, and the volume fraction of pulverized coal in the two-phase flow has significant influence on attenuation of the outburst shock wave. As a whole, pulverized coal flow has a negative impact on gas flow, which makes a great loss of large amounts of initial energy, blocking the propagation of gas flow. According to comparison of numerical results for different roadway types, the attenuation effect of T-type roadways is best. In the propagation of shock wave, reflection and diffraction of shock wave interact through the complex roadway types.

Control of twisting manipulation using a multi-fingered robotic hand with a common rotational axis

The main purpose of the present study is to prove the usability of a mechanism with a common rotational axis during twisting manipulation using a multi-fingered robotic hand where two fingers and two other fingers can independently rotate in inner and outer circles with a dual turning mechanism. Although various types of conventional multi-fingered hands have potential capability to achieve twisting manipulations such as opening a bottle cap from within a hand, it is well-known that such tasks are difficult to execute quickly due to limited working space of the fingers and complexity of control. The proposed hand with a common rotational axis is effective in rotational manipulation around a particular axis, where each joint role assignment is completely decoupled into internal force control for grasping an object and velocity control around the axis for rotating the object. We prove the usability of this mechanism with a common rotational axis through the use of a control scheme, and show experimental results involving manipulation tasks where twisting manipulation is dominant.

Real-Time Finger Gaits Planning for Dexterous Manipulation

Dexterous manipulation has broad potential applications in assembly lines, warehouses and agriculture, and so on. To perform large-scale, complicated manipulation tasks, a multi-fingered robotic hand sometimes has to sequentially adjust its grasping status, i.e. the finger gaits, to deal with the workspace limits and object stability. However, realizing finger gaits planning in dexterous manipulation is challenging due to the involved hybrid dynamics, complicated grasp quality metrics, and uncertainties during the finger gaiting. In this paper, a dual-stage optimization based controller is proposed to handle these challenges. First, a velocity-level finger gaits planner is introduced by combining object grasp quality with hand kinematic limitations. The proposed finger gaits planner is computationally efficient and can be solved in real-time. Second, a manipulation controller using force optimization is presented. To deal with mass uncertainties and external disturbances, a modified impedance control is integrated into the manipulation controller. The dual-stage controller does not require the shape of the object, nor does it rely on expensive 3D/6D tactile sensors. Simulation results verify the efficacy of the proposed dual-stage controller.

A Geometry Deformation Model for Braided Continuum Manipulators

Continuum manipulators have gained significant attention in the robotic community due to their high dexterity, deformability and reachability. Modeling of such manipulators has been shown to be very complex and challenging. Despite many research attempts, a general and comprehensive modeling method is yet to be established. In this paper, for the first time, we introduce the bending effect in the model of a braided extensile pneumatic actuator with both stiff and bendable threads. Then, the effect of the manipulator cross section deformation on the constant curvature and variable curvature models is investigated using simple analytical results from a novel geometry deformation method and is compared to experimental results. We achieve 24% simulation accuracy using our constant curvature model for a braided continuum manipulator in presence of body load and 10% error using our variable curvature model in presence of extensive external loads. With proper model assumptions and taking to account the cross section deformation, an 8-20% increase in the simulation accuracy is achieved compared to a fixed cross section model. The presented models can be used for the exact modeling and design optimization of compound continuum manipulators by providing an analytical tool for the sensitivity analysis of the manipulator performance. Our main aim is the application in minimal invasive manipulation with limited workspaces and manipulators with regional tuneable stiffness in their cross section.

On a simplified nonlinear analytical model for the characterisation and design optimisation of a compliant XY micro-motion stage

Abstract Compliant micro-positioning stages offer low-cost high precision and repeatability but limited workspace and nonlinear behaviour. The conventional modelling techniques used to characterise micro-motion stages are often either complex or inaccurate for large displacements. New methods have recently been developed with satisfying results. However, the presented models often focus on one part of the stage characterisation. This paper presents an analytical model used to characterise a compliant XY micro-motion stage in terms of stiffness and working range, taking into account the stress and buckling limitations, motion loss and parasitic displacements. The presented model combines a 6-degree-of-freedom (DOF) linear model and a simplified 2-DOF nonlinear static model. As a case study, this model is used for the design of a micro-motion stage which is intended to be the fine positioning system for a hybrid miniaturised product assembly system. The results generated by the analytical model, the finite element analysis (FEA) and the experimental testing are all in agreement. The analytical model is therefore proven to be suitable for a full characterisation and design optimisation; reducing the computation time from a few hours to a few minutes when using MATLAB rather than FEA software. Its ability to predict the output displacement as a function of the input displacement with a maximum error of less than 2% also makes it suitable for open-loop control. The travel range of the fabricated stage is greater than ±2.3 mm 2 and the maximum cross-coupling error is less than 2.5%.

Single Portal Subscapular Repair by a Cross Shuttle Loop Technique

With the rise in subscapular tendon tears, most of them being partial that eventually end up in complete tears, we present our experience in the management of such tears using a cross shuttle loop technique. This technique incorporates the advantages of a single portal for anchor placement and repair, easy to use cross loops in limited working space, and familiar viewing.