Study on cutting force of reaming porcine bone and substitute bone

Accurate mechanical feedback systems are critical to the successful implementation of virtual and robotic surgical assistant systems. Experimental measurements of reaming force could further our understanding of the cancellous bone reaming process during hip arthroplasty to help develop surgical simulators with realistic force effects and improve the protection mechanism of robot-assisted surgical systems. In this study, reaming experiments with natural bone (porcine femur) and a bone substitute (polyurethane blocks) were performed on a CNC lathe. This paper proposes using the maximum reaming force of the steady reaming stage to represent the force characteristic. The reaming force is biased to one side in the overlap direction and the maximum reaming force will vary when the reamer is not coincident with the long axis of the bone. The diameter of the reamer has the greatest influence on reaming force, which clearly increases with increasing reamer diameter. During operation, a medium rotation speed and high feed speed can reduce the reaming force. After cutting, the morphology of the cut surface is not flat, but arc-shaped, which will have a significant impact on implantation of the femoral prosthesis. In in vitro cutting experiments, polyurethane blocks can be used as a substitute for cancellous bone.

A Portable Intuitive Haptic Device on a Desk for User-Friendly Teleoperation of a Cable-Driven Parallel Robot

This paper presents a compact-sized haptic device based on a cable-driven parallel robot (CDPR) mechanism for teleoperation. CDPRs characteristically have large workspaces and lightweight actuators. An intuitive and user-friendly remote control has not yet been achieved, owing to the unfamiliar multiple-cable configuration of CDPRs. To address this, we constructed a portable compact-sized CDPR with the same configuration as that of a larger fully constrained slave CDPR. The haptic device is controlled by an admittance control for stiffness adjustment and implemented in an embedded microprocessor-based controller for easy installation on an operator’s desk. To validate the performance of the device, we constructed an experimental teleoperation setup by using the prototyped portable CDPR as a master and larger-size CDPR as a slave robot. Experimental results showed that a human operator can successfully control the master device from a remote site and synchronized motion between the master and slave device was performed. Moreover, the user-friendly teleoperation could intuitively address situations at a remote site and provide an operator with realistic force during the motion of the slave CDPR.

Probabilistic Multiple Pedestrian Walking Force Model including Pedestrian Inter- and Intrasubject Variabilities

A probabilistic walking load model that accounts for inter- and intrasubject variabilities has been developed to generate synthetic vertical load waveforms induced by pedestrians. The mathematical model is based on a comprehensive database of continuously recorded pedestrian walking forces on an instrumented treadmill, having a wide range of walking frequencies. The proposed model is able to replicate temporal and spectral features of real walking forces, which is a significant advantage over conventional Fourier series models. The load model results in more realistic force time histories than previous models, since it incorporates significant components of the spectra that are omitted in Fourier series approaches. The proposed mathematical model can be implemented in vibration serviceability assessment of civil engineering structures, such as building floors and footbridges, to estimate more realistically dynamic structural responses due to people walking.

P.118 Excalibur, a novel haptic hand-controller for robot-assisted microsurgery

Background: For robot-assisted telesurgery, the workstation, in particular the haptic handcontroller itself a robot, is paramount to the performance of surgery. Based on the requirements for microsurgery, a novel haptic handcontroller Excalibur has been developed. Methods: Thirty-two surgeons performed a peg-in-hole task (simulating micromanipulation) with Excalibur and two commercially available handcontrollers (Sigma 7 and PHANToM Premium 3.0). A modified Kuka endeffector with bipolar forceps, and Leica microscope completed the remote robotic site. Comparisons were made based on training time, task completion time and number of errors. All participants completed a questionnaire. Results: Repeated measures ANOVA demonstrated significance for task completion time (p=0.004), training time (p=0.021) and number of errors (p=0.004). Surgeons were faster with Excalibur (72s) than with Sigma (96s,p=0.005) and PHANToM (96s,p=0.036). Training time was shorter with Excalibur than with PHANToM (210s vs 310s,p=0.013), and users made fewer errors (0.7 vs 2.1,p=0.008). Training time required for Sigma (285s) and the number of errors (1.3) were not significant. The surgeons found Excalibur smoother, more comfortable, less tiring and easier to maneuver, with more realistic force feedback and superior movement fidelity. Conclusions: Surgical performance was superior with Excalibur compared to the other handcontrollers. This may reflect the microsurgical requirements and unique design architecture of Excalibur.

Comparison of lower limb segment forces during running on artificial turf and natural grass

Introduction: Artificial turf, soon after being introduced in the 1980s, became associated with an increased injury incidence in football players. While more recent generations of artificial turf have mitigated the problem, perception of the material is still widely negative. So, the decision to play the 2015 Fe'de'ration Internationale de Football Association Women s World Cup in Canada on artificial turf was met with vocal criticism by many players. One common approach is to assess injury incidence to quantify risk differences in playing surfaces. This, however, does not account for possible confounding variables or chronic injuries. Direct measurement of ground reaction forces is difficult because conventional multicamera-based motion capture and force plate equipment are limited in its use outside of dedicated laboratories. Methods: We describe a method of generating realistic force data by using miniature load cells that are installed directly into the weight-bearing structure of the body. Results: Pilot data show a significant (p<0.01) difference in peak forces on artificial turf (272% of body weight) and natural grass (229% of body weight). Discussion: Invasive surgical procedures were avoided by installing the load cell into the prosthesis of an athlete with lower limb loss. As modern prosthetic devices allow a close approximation of able-bodied kinematics and kinetics, such prosthesis-based data are transferable to a general population.

A force rendering model for virtual assembly of mechanical parts with clearance fits

Purpose Realistic force sensation can help operators better feel and manipulate parts for virtual assembly (VA). Moreover, for VA of mechanical parts, it is necessary to consider their tolerance levels so as to apply proper assembly forces. Out of the three common assembly fit types, the type of clearance fit is the focus of virtual manual assembly, as parts with such fit type require precise force feedback to assist users’ assembly operations. Design/methodology/approach This study proposes a novel force rendering model for VA of mechanical parts with clearance fits. By decomposing an actual assembly operation into three consecutive states, the corresponding forces are formulated. Findings A prototype system is designed and developed to implement the model, and comparative case studies are conducted to investigate the users’ performance with the other three common approaches, namely, a typical WIMP (window-icon-menu-pointer) interface with CAD software, a physics simulation with collision detection and the approach that combines physics simulation and geometric constraints restriction. The results have shown that the proposed model is more realistic by providing continuous and realistic force feedback to the users. Originality/value The users’ feeling of immersion and their operational efficiency are greatly enhanced with the force sensation provided.

Theoretical simulation of the infrared signature of mechanically stressed polymer solids

Mechanical stress leads to deformation of strands in polymer solids, including elongation of covalent bonds and widening of bond angles, which changes the infrared spectrum. Here, the infrared spectrum of solid polymer samples exposed to mechanical stress is simulated by density functional theory calculations. Mechanical stress is described with the external force explicitly included (EFEI) method. The uneven distribution of the external stress on individual polymer strands is accounted for by a convolution of simulated spectra with a realistic force distribution. N-Propylpropanamide and propyl propanoate are chosen as model molecules for polyamide and polyester, respectively. The effect of a specific force on the polymer backbone is a redshift of vibrational modes involving the C–N and C–O bonds in the backbone, while the free C–O stretching mode perpendicular to the backbone is largely unaffected. The convolution with a realistic force distribution shows that the dominant effect on the strongest infrared bands is not a shift of the peak position, but rather peak broadening and a characteristic change in the relative intensities of the strongest bands, which may serve for the identification and quantification of mechanical stress in polymer solids.

Approaching a realistic force balance in geodynamo simulations

Earth sustains its magnetic field by a dynamo process driven by convection in the liquid outer core. Geodynamo simulations have been successful in reproducing many observed properties of the geomagnetic field. However, although theoretical considerations suggest that flow in the core is governed by a balance between Lorentz force, rotational force, and buoyancy (called MAC balance for Magnetic, Archimedean, Coriolis) with only minute roles for viscous and inertial forces, dynamo simulations must use viscosity values that are many orders of magnitude larger than in the core, due to computational constraints. In typical geodynamo models, viscous and inertial forces are not much smaller than the Coriolis force, and the Lorentz force plays a subdominant role; this has led to conclusions that these simulations are viscously controlled and do not represent the physics of the geodynamo. Here we show, by a direct analysis of the relevant forces, that a MAC balance can be achieved when the viscosity is reduced to values close to the current practical limit. Lorentz force, buoyancy, and the uncompensated (by pressure) part of the Coriolis force are of very similar strength, whereas viscous and inertial forces are smaller by a factor of at least 20 in the bulk of the fluid volume. Compared with nonmagnetic convection at otherwise identical parameters, the dynamo flow is of larger scale and is less invariant parallel to the rotation axis (less geostrophic), and convection transports twice as much heat, all of which is expected when the Lorentz force strongly influences the convection properties.

Design and Evaluation of a Haptic Keypad System for Realistic Touch Interaction

This paper presents design and testing of a haptic keypad system using an array of haptic actuators. The research goals are to construct a prototype haptic keypad system using haptic actuators and to evaluate the performance of the prototype keypad for haptic rendering. To this end, an MR haptic actuator was designed and fabricated such that it can convey realistic force feedback to users. To demonstrate haptic applications of the MR actuator, a haptic keypad system was constructed, which consists of following components: (1) 3 × 3 array of haptic actuators, (2) 3 × 3 array of force sensing resistors (FSR), (3) a controller including a micro-processor, a current amplifier and a wireless communication module, (4) a graphic display unit with PC. After constructing a prototype keypad system, a haptic rendering technology was employed to interface the hardware keypad system with test software (virtual environment). The prototype system enabled human operators to interact with the target contents in a virtual environment more intuitively. The evaluation results show a feasibility of applications of MR fluids-based haptic actuators in real-world mobile applications.

Electro-Mechanical Control Loading System for Rotary Wing Aircraft Simulators

The focus of this paper is on the development of a high-fidelity electro-mechanical Control Loading System (CLS) for a rotary wing aircraft simulator. CLS is one of the major components of a flight simulator. It is used for providing realistic force feedback to pilots. The pilot in a real aircraft feels the forces acting on control surfaces through cockpit controls. During simulation, these forces are produced by CLS actuators. For this reason, CLS must behave exactly like the aircraft control hardware, statically and dynamically. The fidelity of the force feel simulation is a key criterion for flight simulation certification. It is also important that a CLS design is reconfigurable and modular such that it conforms easily to different simulator models and simulations of different aircrafts. The work also includes system integration of a research simulator for testing purposes. Design and selection of hardware and software components of the CLS and the simulator are presented along with the overall system architecture.