Degrees Of Freedom Force Research Articles

Enhanced Modeling and Control for Multilinked Aerial Robot With Two DoF Force Vectoring Apparatus

The multilinked or modular structure is one of the state-of-the-art topics in aerial robot field. One type of the multilinked aerial robot called DRAGON containing a two degree-of-freedom (DoF) force vectoring apparatus in each link has been developed in our previous work to augment both maneuvering and manipulation ability. However, several types of invalid robot poses, which are due to the mechanical structure, the previous control method and the interrotor aerodynamic interference, significantly reduce the region of deformation. Thus, enhanced modeling and control methods are necessary to overcome these problems. In this letter, we first develop an integrated thrust and vectoring control method with a rigorous allocation to solve the control singularity. Second, we present a vectoring configuration planning method, which solves the mechanical singularity by locking one of the axes in the two DoF vectoring apparatus. Finally, we propose an estimation method and an active compensation control regarding the aerodynamic interference to improve the flight stability. In the end, simulation studies and experiments involving the hovering and deformation along a vertical plane are performed to evaluate the whole modeling and control framework.

Spatial force measurement using a rigid hexapod-based end-effector with structure-integrated force sensors in a hexapod machine tool

In machine tools, in-process force measurement is required by many manufacturing applications, where a particular demand for spatial measurements in up to 6 degrees of freedom (DoF) is growing. Beside expensive commercial 6 DoF force/torque sensors or vague drive current evaluation, sensor integration as part of machine components or joints has been discussed for a long time. The approach presented here, integrates 6 cost-efficient commercial 1 DoF force sensors in hexapod structures and kinematics, that are particularly suitable for sensor integration due to the absence of friction, the presence of mainly longitudinal forces and the availability of 6 DoF. These sensors can be placed at different positions, whereby this article focuses on a rigid hexapod-based end-effector. As the end-effector is not an independent measuring system, but part of a machine, that moves dynamically through the workspace and carries workpieces or tools, a suitable measurement model is necessary that addresses all those influences. After a brief literature overview and introduction to the approach, this work presents the dynamic measurement model including sensor and quasi-static error parameters, aspects about optimal framework design and several steps of validation and evaluation of the new measuring system. These include application of static loads, workspace analysis, dynamic transfer behaviour, rigid body dynamics compensation and, finally, process force measurement during a milling process.

A semi-empirical multi-degree of freedom body force propeller model

Efficient and accurate modelling of a self-propelled vessel in a large amplitude seaway with CFD-based numerical methods is a challenging task and is prohibitively expensive for most designers and engineers. Viscous CFD methods can accurately model viscous effects, but the small numerical time step required to analyze the rotating propeller leads to a large computational cost. A method for efficiently and accurately modelling the six degree of freedom force on the propeller is required to feasibly model a self propelled vessel maneuvering in a high amplitude seaway. This paper outlines the framework for developing an unsteady body force propeller model for unsteady conditions. The purpose of this study is to train a semi-empirical algorithm to accurately prescribe the unsteady body force to model the propeller. The MOERI Container ship propeller is analyzed with RANS CFD. Open water data is compared to the RANS CFD results of a steady Moving Reference Frame approach. Unsteady surge and propeller revolution rate are applied to a transient rotating mesh model in open water and behind condition. The predictions of the algorithm match well with the CFD results.

Robotic grinding of a blisk with two degrees of freedom contact force control

This paper presents a novel two degrees of freedom (DOFs) contact force control method for robotic blisk grinding. The grinding tool is controlled to automatically adapt to the curvity change of the blisk blade and maintain a constant contact force as expected. A smart end effector is used as the actuating device for contact force control. The proposed force controller includes a gravity compensation module, a force prediction module, and a force-position controller. The direction and amplitude of the contact force are predicted with the force prediction module and are controlled with the force-position controller. The tool path of the robotic blisk grinding process is generated and optimized so that the contact points between the tool tip and the workpiece are evenly distributed along the grinding path. Both simulations and experiments are carried out to validate the effectiveness of the proposed method. The results show that the proposed method provides a good contact force control performance, with less than 1 N force fluctuation. The surface finish and roughness are significantly improved compared to the case without force control. The grinding efficiency is raised by about sixfold compared to the case with one DOF force control.

Design of switched reluctance motor with four controllable radial force degrees of freedom for self-bearing application

Design of switched reluctance motor with four controllable radial force degrees of freedom for self-bearing application

Research on Spacecraft Dynamic Interface Force Identification Based on Strain Detection

The static/dynamic interface force between spacecraft and rocket is an important reference for spacecraft structure design. The most conventional dynamic force identification method is finite element simulation combined with the telemeter acceleration data, which restricts the spacecraft design level owing to the large error. A dynamic force identification method according to the detected strain field of attachment and its optimization plans are proposed. Three-way strain rosettes are mounted outside the docking ring densely. And the six Degree Of Freedom force can be derived by strain field. Considering the requests of engineering application, under the premise that detection result would meet the accuracy requirement, an optimization plan which reduce the detecting point is proposed. Results of dynamic simulation show that, only X direction bending moment identification error is 19.8%, and other loads identification error are below 10%. The test results show that both identification errors of static and dynamic load are below 20%, which can meet the engineering requirements.

Simulating Haptic Feedback of Abdomen Organs on Laparoscopic Surgery Tools

Minimally invasive surgeries (MIS) such as laparoscopic procedures are widely used for many types of abdomen surgeries because of its numerous advantages over open surgeries. They require very high levels of skills of surgeons acquired through experience. The best and the safest way of getting hands on experience is the computer simulation or virtual reality (VR). The VR surgical simulators have a great potential to revolutionize the training paradigm of surgical interns. The haptic feedback plays as equally as visual feedback to provide realistic environment to trainees. In this paper, we present a method incorporate hapitics on VR simulator. A software procedure is developed using the Libraries of Open Haptic Toolkit along with the Open GL graphic libraries to implement three basic haptic ranges: soft, mild(firm) and hard into organ models. The feedback of the expert surgeons in the field was obtained to model the organs rather than measuring mechanical properties of soft tissues due to practical limitations. A commercially available six Degrees of Freedom (DoF) position sensing and three DoF force feedback haptic device is used to implement the interface.

An Experimental Investigation into the Effect of Flap Angles for a Piezo-Driven Wing

This article presents a comparison of results from six degree of freedom force and moment measurements and Particle Image Velocimetry (PIV) data taken on the Air Force Institute of Technology's (AFIT) piezoelectrically actuated, biomimetically designed Hawkmoth, Manduca Sexta, class engineered wing, at varying amplitudes and flapping frequencies, for both trimmed and asymmetric flapping conditions to assess control moment changes. To preserve test specimen integrity, the wing was driven at a voltage amplitude 50% below the maximum necessary to achieve the maximal Hawkmoth total stroke angle. 86° and 65° stroke angles were achieved for the trimmed and asymmetric tests respectively. Flapping tests were performed at system structural resonance, and at ±10% off system resonance at a single amplitude, and PZT power consumption was calculated for each test condition. Two-dimensional PIV visualization measurements were taken transverse to the wing planform, recorded at the mid-span, for a single frequency and amplitude setting, for both trimmed and asymmetric flapping to correlate with the 6-DoF balance data. Linear velocity data was extracted from the 2-D PIV imagery at ± 1/2 and ±1 chord locations above and below the wing, and the mean velocities were calculated for four separate wing phases during the flap cycle. The mean forces developed during a flap cycle were approximated using a modification of the Rankine-Froude axial actuator disk model to calculate the transport of momentum flux as a measure of vertical thrust produced during a static hover flight condition. Values of vertical force calculated from the 2-D PIV measurements were within 20% of the 6-DOF force balance experiments. Power calculations confirmed flapping at system resonance required less power than at off resonance frequencies, which is a critical finding necessary for future vehicle design considerations.

6 DOF force and torque sensor for micro-manipulation applications

This paper presents the design, fabrication and characterization of a piezoresistive 6 degrees of freedom (DOF) force and torque sensor to be used in micro-manipulation. The device has been fabricated with an IC-compatible process and contains 24 piezoresistors as sensing elements. Its partly asymmetric mechanical structure consists of 7 suspended beams providing force sensing functionality on a probing area, which includes a calibration structure. Thanks to this asymmetrical structure, micro-manipulation tools such as micro-grippers or probes can be easily implemented in the same substrate as the sensor, replacing the probing area. The geometry of the beams and the location of the piezoresistors in the structure are designed using finite element modeling to provide independent force measurements (i.e. low crosstalk) and high sensitivity, with limited geometrical size. The mechanical structure is 3mm×1.5mm×0.03mm in size and its first resonance frequency is estimated to be 4500Hz, as computed with a dynamical analysis. A calibration of the device is experimentally performed, and a linear regression model is fitted to the calibration data to extract the forces and torques from the resistance variations detected in the piezoresistors. The data acquisition system is programmable, allowing for dynamic adjustments of the trade-offs between noise levels, uncertainty and bandwidth. Depending on the axis, the linear range of the sensor reaches 4–30mN in forces and 4–50μNm in torques. During on-line measurements, noise levels up to 13–27μN/Hz0.5 and 11–43nNm/Hz0.5 were observed respectively, for forces and torques.

Feasibility of novel four degrees of freedom capacitive force sensor for skin interface force

BackgroundThe objective of our study was to develop a novel capacitive force sensor that enables simultaneous measurements of yaw torque around the pressure axis and normal force and shear forces at a single point for the purpose of elucidating pressure ulcer pathogenesis and establishing criteria for selection of cushions and mattresses.MethodsTwo newly developed sensors (approximately 10 mm×10 mm×5 mm (10) and 20 mm×20 mm×5 mm (20)) were constructed from silicone gel and four upper and lower electrodes. The upper and lower electrodes had sixteen combinations that had the function as capacitors of parallel plate type. The full scale (FS) ranges of force/torque were defined as 0–1.5 N, –0.5-0.5 N and −1.5-1.5 N mm (10) and 0–8.7 N, –2.9-2.9 N and −16.8-16.8 N mm (20) in normal force, shear forces and yaw torque, respectively. The capacitances of sixteen capacitors were measured by an LCR meter (AC1V, 100 kHz) when displacements corresponding to four degrees of freedom (DOF) forces within FS ranges were applied to the sensor. The measurement was repeated three times in each displacement condition (10 only). Force/torque were calculated by corrected capacitance and were evaluated by comparison to theoretical values and standard normal force measured by an universal tester.ResultsIn measurements of capacitance, the coefficient of variation was 3.23% (10). The Maximum FS errors of estimated force/torque were less than or equal to 10.1 (10) and 16.4% (20), respectively. The standard normal forces were approximately 1.5 (10) and 9.4 N (20) when pressure displacements were 3 (10) and 2 mm (20), respectively. The estimated normal forces were approximately 1.5 (10) and 8.6 N (10) in the same condition.ConclusionsIn this study, we developed a new four DOF force sensor for measurement of force/torque that occur between the skin and a mattress. In measurement of capacitance, the repeatability was good and it was confirmed that the sensor had characteristics that enabled the correction by linear approximation for adjustment of gain and offset. In estimation of forces/torque, we considered accuracy to be within an acceptable range.

The Dynamics Analysis of Full Mounted Converter Vessel Tilting Mechaism

In order to definite the dynamic properties of full mounted converter tilting mechaism and analysis the mechanical condition of the main transmission parts in the operation process, the dynamics behavior of the converter tilting mechaism was analysied. Vibration properties of the mechaism was analyzed by using mode shapes analysis method in no external force and an external force two circumstances, tilting mechanism can be constructed 11 degree of freedom force modal, and it can further simplify 3 degrees of freedom force modal. It can find resonant frequency of tilting mechaism through the analysis of the torsion vibration angular displacement and the torsion torque. It can provide scientific basis for equipment maintenance of technical personnels.

6 DOF Force and Torque Sensor for Micro-manipulation Applications

This paper presents the design, fabrication and characterization of a piezoresistive 6 Degrees of Freedom (DOF) force and torque sensor to be used in micro-manipulation. The mechanical structure of the device consists of 7 suspended beams and a calibration structure, which can be replaced by micro-manipulation tools such as micro-grippers or probes. The geometry of the beams and the location of the piezoresistors in the structure are optimized to reduce crosstalk and improve the sensitivity. A linear regression model is fitted to the calibration data to exxtract the forces and torques from the resistance variations detected in the piezoresistors. The device has been fabricated with an IC-compatible process and successfully characterized. The data acquisition system is programmable, allowing for dynamic adjustments of the trade-offs between noise levels, accuracy and bandwidth. Depending on the axis, the linear range of the sensor reaches 4 to 30mN in forces and 4 to 50 uNm in torques. During calibration, root mean square errors up to 17 to 45μN and 14 to 40 uNmm were observed in the measured data, respectively.

Optimal Path Planning for Robotic Insertion of Steerable Electrode Arrays in Cochlear Implant Surgery

This paper presents an optimal path planning method of steerable electrode arrays for robot-assisted cochlear implant surgery. In this paper, the authors present a novel design of steerable electrode arrays that can actively bend at the tip. An embedded strand in the electrode array provides an active steering degrees-of-freedom (DoF). This paper addresses the calibration of the steerable electrode array and the optimal path planning for inserting it into planar and three-dimensional scala tympani models. The goal of the path planning is to minimize the intracochlear forces that the electrode array applies on the walls of the scala tympani during insertion. This problem is solved by designing insertion path planning algorithms that provide best fit between the shape of the electrode array and the curved scala tympani during insertion. Optimality measures that account for shape discrepancies between the steerable electrode array and the scala tympani are used to solve for the optimal path planning of the robot. Different arrangements of DoF and insertion speed force feedback (ISFF) are simulated and experimentally validated in this paper. A quality of insertion metric describing the gap between the steerable electrode array and the scala tympani model is presented and its correspondence to the insertion force is shown. The results of using 1DoF, 2DoF, and 4DoF electrode array insertion setups are compared. The 1DoF insertion setup uses nonsteerable electrode arrays. The 2DoF insertion setup uses single axis insertion with steerable electrode arrays. The 4DoF insertion setup allows full control of the insertion depth and the approach angle of the electrode with respect to the cochlea while using steerable electrode arrays. It is shown that using steerable electrode arrays significantly reduces the maximal insertion force (59.6% or more) and effectively prevents buckling of the electrode array. The 4DoF insertion setup further reduces the maximal electrode insertion forces. The results of using ISFF for steerable electrodes show a slight decrease in the insertion forces in contrast to a slight increase for nonsteerable electrodes. These results show that further research is required in order to determine the optimal ISFF control law and its effectiveness in reducing electrode insertion forces.

Physical Interaction with a Virtual Knee Joint—The 9 DOF Haptic Display of the Munich Knee Joint Simulator

In specific fields, medical education at many universities is rather theoretical and the amount of practical training is limited. A significant improvement can be achieved using virtual reality training stations with lifelike visual, acoustic, tactile, and kinesthetic feedback. Particularly, when simulating procedures that require direct contact with the patient body, a realistic haptic simulation addressing tactile and kinesthetic senses can be essential for the acceptance of virtual simulation stations. A purely passive phantom may provide realistic haptic feedback, but its properties cannot be changed over time. This paper presents the haptic display of the Munich Knee Joint Simulator, which was developed to improve training and education of physical knee joint examinations. The haptic interface comprises a combination of passive phantom segments providing realistic tactile sensations, and strong actuators generating highly dynamic kinesthetic force feedback. A 3 degree of freedom (DOF) manipulator was developed in this study to drive the thigh prosthesis and one 6 DOF industrial robot was used to actuate the shank prosthesis. Both manipulators are driven by hybrid admittance-impedance controllers capable of simulating the complex dynamics of the thigh and the shank. Both actuators are equipped with a 6 DOF force torque sensor and they are virtually coupled by an analytical knee joint model. The proposed setup is capable of simulating a mechanical stiffness as high as 80 kN/m in the translatory DOF and simultaneously allows free motion in the rotatory DOF. Experimental tests of the simulator with orthopedic physicians proved the usability of the proposed concept.

Robust tracking control of rigid-link electrically-driven robots

A robust tracking controller for rigid-link electrically driven (RLED) robot manipulators operating in free-space or under motion constraints is introduced. Using models of the robot dynamics and environmental constraints, a dynamic model with decoupled position and force degrees of freedom is obtained for the mechanical subsystem with respect to a set of task-space coordinates. A robust tracking control is then formulated for the decoupled manipulator dynamics and the electrical actuator dynamics, which yields a global uniform ultimate bounded (GUUB) stability result for the position and velocity tracking error. The controller is robust with respect to parametric uncertainties and additive bounded disturbances in the RLED dynamic model. The controller requires measurement of the robot link positions, link velocities, and motor armature currents.

A field consistent higher-order curved beam element for static and dynamic analysis of stepped arches

A field consistent shear flexible (cubic in W, θ and U) beam element has been developed for the static and dynamic analyses of stepped circular arches. The element has been proved to be useful for deep arches and thin beams in the static case and for stepped arches in the dynamic case. The element uses displacement with force degrees of freedom at the nodes to cater for discontinuities.