Tripod Mechanism Research Articles

Tunable High-Static-Low-Dynamic Stiffness Isolator under Harmonic and Seismic Loads

High-Static-Low-Dynamic Stiffness (HSLDS) mechanisms exploit nonlinear kinematics to improve the effectiveness of isolators, preserving controlled static deflections while maintaining low natural frequencies. Although extensively studied under harmonic base excitation, there are still few applications considering real seismic signals and little experimental evidence of real-world performance. This study experimentally demonstrates the beneficial effects of HSLDS isolators over linear ones in reducing the vibrations transmitted to the suspended mass under near-fault earthquakes. A tripod mechanism isolator is presented, and a lumped parameter model is formulated considering a piecewise nonlinear–linear stiffness, with dissipation taken into account through viscous and dry friction forces. Experimental shake table tests are conducted considering harmonic base motion to evaluate the isolator transmissibility in the vertical direction. Excellent agreement is observed when comparing the model to the experimental measurements. Finally, the behavior of the isolator is investigated under earthquake inputs, and results are presented using vertical acceleration time histories and spectra, demonstrating the vibration reduction provided by the nonlinear isolator.

Design of a Tripod LARMbot Arm

A new design for humanoid arms is presented based on a tripod mechanism that is actuated by linear servomotors. A specific prototype is built and tested, with the results of performance characterization verifying a possible implementation on the LARMbot humanoid. The design solves the main requirements in terms of a high payload ratio with respect to arm weight by using a tripod architecture with parallel manipulator behavior. The built prototype is assembled with commercial components to match the expectations for low-cost user-oriented features. The test results show satisfactory operation characteristics both in motion and force performance, which will ensure a future successful implementation in the LARMbot humanoid structure.

Kinematic analysis of an augmented 3-RPSP tripod mechanism with six degrees of freedom for bone reduction surgery

Robotic-assisted bone reduction surgery consists in using robots to reconnect patients’ bone fragments prior to fracture healing. The goal of this study is to propose a novel augmented 3-RPSP tripod mechanism with six degree of freedom for longitudinal bone reduction surgery. Its inverse kinematic model is studied and its forward kinematic model is solved by establishing the constraint equations, applying Sylvester’s dialytic method and finding the solutions of the resulting polynomial equation. The velocity model is calculated and its Jacobian matrix is used to identify its singular configurations. In comparison to the Stewart–Gough platform that is a typical mechanism used in this application, the proposed mechanism offers larger reachable workspace which is an important aspect in the femoral shaft bone reduction. A Physiguide and Msc Adams software are used to carry out a simulation of a real femur fracture reduction using the proposed mechanism to validate its suitability. A robotic prototype has been designed and manufactured in order to test its capability of performing diaphyseal femur reduction surgery.

Kinematic Analysis and Design of a Six-Degrees of Freedom 3-RRPS Mechanism for Bone Reduction Surgery

Abstract Robot-assisted bone reduction surgery consists in using robots to reposition the bone fragments into their original place prior to fracture healing. This study presents the application of a 3-RRPS augmented tripod mechanism with six degrees-of-freedom for longitudinal bone reduction surgery. First, the inverse and forward kinematic models of the mechanism are investigated. Particularly, the forward kinematic is solved by applying Sylvester's dialytic method. Second, the velocity model is studied and its singular configurations are identified. The workspace of the 3-RRPS mechanism is then outlined and compared with the Stewart platform, which is a classical mechanism for the targeted application. The results show that this mechanism provides a larger workspace, especially its rotation angle about the vertical axis, which is an important aspect in the bone reduction. A series of simulations on the numerical and graphic software is performed to verify the entire analysis of the parallel mechanism. A physiguide and mscadams software are used to carry out a simulation of a real case of femur fracture reduction using the proposed mechanism to validate its suitability. Finally, a robotic prototype based on the mechanism is manufactured and experimented using an artificial bone model to evaluate the feasibility of the mechanism.

Numerical Method for Determining the Operating Area of a Robot with Relative Manipulation Mechanisms

In this paper, we consider the application of optimization algorithms to solve the problem of determining the operating area of a robot with mechanisms of relative manipulation based on a plane 3-RPR mechanism and a tripod mechanism. A method for approximating the set of solutions to a system of nonlinear inequalities describing constraints on the geometric parameters of the robot is considered. Algorithms for constructing the operating areas of individual mechanisms were synthesized. The orientation effect of the output link on the size and shape of the operating area of each mechanism is analyzed. The operating area of the robot is obtained taking into account the constraints on the geometric parameters of the workpiece being in a moving coordinate system located in the center of the flat 3-RPR mechanism, as well as taking into account design constraints, intersections of links, and special positions.

Kinematic design of a hybrid planar-tripod mechanism for bone reduction surgery

In the most severe cases of longitudinal bone fractures such as femur, tibias, humerus etc., the bone can be completely separated into two fragments. In order to guarantee the re-ossification of the bone, it is required to reposition the bone fragments together. This process requires a delicate surgery called “bone reduction surgery”. The most advanced technique relies on the use of a robotic manipulator to reposition the bone fragments with higher precision and stability than manual surgeries. The present work introduces the kinematic design of a new hybrid mechanical architecture to perform this task. It is composed of a 3-PRP planar mechanism attached with a 3-RPS tripod mechanism. The kinematic analysis of this mechanism is provided while taking account the tripod parasitic motion. Kinematic simulations using Matlab and Adams are performed to validate the kinematic and velocity models and the parasitic motion compensation provided by the planar mechanism. The workspace of this hybrid mechanism is then compared to the standard hexapod mechanism that is widely used in bone reduction surgery. It reveals that the proposed mechanism can generate a larger workspace with the same linkage dimensions.

Kinematic analysis and evaluation of a hybrid mechanism for computer assisted bone reduction surgery

Abstract. In severe fracture cases, a bone can be separated into two fragments and it is mandatory to reposition the bone fragments together. This type of surgery is called “bone reduction surgery”. Originally, the operation consisted in manipulating the bones fragments by hand in open surgery. The most advanced technique relies on robotic manipulators providing higher precision and stability. A new mechanical architecture is proposed based on a 3-RPS tripod parallel mechanism combined with a Double Triangular Planar parallel mechanism. Its kinematic and velocity models are calculated and the parasitic motion generated by the tripod mechanism is considered in the final result. The workspace it can generate is compared to the Stewart manipulator, which is a classical mechanism for the targeted application. The use of a robotic manipulator is due to be part of an entire surgical procedure involving a pre-operative simulation software dedicated to pre-planning reduction surgery, namely PhysiGuide. It is used to measure the kinematic associated with bone fragments manipulation and transfer it to the robot during the intra-operative phase. Simulations are then performed based on a real patient's fracture images showing the suitability of the present mechanism with bone reduction surgery.

Approximation of the parallel robot working area using the method of nonuniform covering

The article describes the application of optimization algorithms for solving the problem of determining the working area of a parallel 6-DOF relative mechanism device, which includes a flat 3-RRR mechanism and a tripod mechanism. The method for approximation of the set of nonlinear inequalities system solutions describing constraints on the geometric parameters of the robot, based on the concept of nonuniform coverings, is considered. Based on the method, external and internal approximations are obtained, given as a set of parallelepipeds. The working area of the relative mechanism device has been obtained, taking into account the restrictions on the geometric parameters of the workpiece located in a moving coordinate system located in the center of a flat 3-RRR mechanism. The moving coordinate system is located in the center of the planar mechanism.

Research on Low Cost Automatic Polishing Machine for Die/Mold Manufacturing

In order to improve die/mold polishing worker’s environment and polishing automation level, we introduce a kind of low cost automatic polishing machine (LCAPM) with compliant actuator. The actuator is composed of a Tripod mechanism driven by pneumatic cylinders. Proportional valve is used to guarantee precision of cylinder’s position, and a 3D force sensor is used to adjust polishing contact force between grind stone tool and workpiece. Structure of LCAPM is described in detail; pneumatic control circuit and cylinder’s position are modeled in succession. Finally, a computing case of cylinder’s position for given workpiece is shown.

The kinematic analyses of the 3-DOF parallel machine tools

A 3-degree-of-freedom (3-DOF) parallel machine tool based on a tripod mechanism is developed and studied. The kinematics analysis is performed, the workspace is derived, and an analysis on the number of conditions of the Jacobian matrix and manipulability is carried out. A method for error analysis and manipulability is introduced. Hence, the manipulability analysis of the parallel machine tool is accomplished.

Tracking Error Transform in Parallel Kinematic Machining

Parallel kinematic machine tools (PKM) are developed to increase dynamic parameters for high speed and high accuracy machining to gain short lead times and high productivity. One of the most important components of machine tools is the numerical controller (NC). Most NCs are organized in a cascaded structure, comprising the position, velocity and current loops. Commonly applied servo controllers generate tracking errors in each axis. These tracking errors are a significant factor that affects machining accuracy, beside geometric machine errors, vibrations, temperature changes and tool errors. In this paper the contour error originated from servo tracking controller in Cartesian kinematic machine tools (CKM) with perpendicular arranged machine axes and PKM is presented. The effects of the forward transformation of the tracking errors in PKM are addressed with experiment and simulation results. The servo tracking effect on trace accuracy is discussed by a tripod mechanism and radial deviations are measured with double ball bar method (DBB).

Manipulability Analyses of the 3-DOF Parallel Machine Tool

A 3-DOF in-parallel machine tools based on a tripod mechanism is developed and studied, the kinematic is analytically performed, the workspace is derived, Analysis of the a number of conditions of the Jacobian matrix and manipulability is carried, The manipulability analytical of the parallel machine tool is investigated

On a Rigid Body Subject to Point-Plane Constraints

This paper investigates the location of a rigid body such that N specified points of the body lie on N given planes in space. Variants of this problem arise in kinematics, metrology, and computer vision, including some, such as the motion of a spherical four-bar, that are not at first glance point-plane contact problems. The case N=6, the minimum number to fully constrain the body, is of special interest: We give an eigenvalue method for finding all solutions, which may number up to eight. For N⩾7 there are, in general, no solutions, but if the constraints are compatible and not degenerate, we show how to find the unique solution by a linear least-squares method. For N⩽5, the body is underconstrained, having in general 6−N degrees of freedom; we determine the degree of the general motion for each case. We also examine the workspace of a particular three-degree-of-freedom parallel-link tripod mechanism.

Design of a Robotic Gait Trainer using Spring Over Muscle Actuators for Ankle Stroke Rehabilitation

Repetitive task training is an effective form of rehabilitation for people suffering from debilitating injuries of stroke. We present the design and working concept of a robotic gait trainer (RGT), an ankle rehabilitation device for assisting stroke patients during gait. Structurally based on a tripod mechanism, the device is a parallel robot that incorporates two pneumatically powered, double-acting, compliant, spring over muscle actuators as actuation links which move the ankle in dorsiflex ion/plantarflexion and inversion/eversion. A unique feature in the tripod design is that the human anatomy is part of the robot, the first fixed link being the patient's leg. The kinematics and workspace of the tripod device have been analyzed determining its range of motion. Experimental gait data from an able-bodied person wearing the working RGT prototype are presented.

Conceptual development of an enhanced tripod mechanism for machine tool

In this paper, a spatial three degrees of freedom parallel mechanism enhanced by a passive leg is proposed. The proposed parallel mechanism can be used in several applications, e.g. motion simulator, micromanipulator and machine tools. First, the geometric model of the three degrees of freedom parallel mechanism is addressed, in which a fourth kinematic link—a passive link connecting the base center to the platform center—is introduced. This last link is used to constrain the motion of the platform to only three degrees of freedom, i.e. the degree of freedom of the mechanism depends on the passive leg. The passive leg also enhances the global stiffness of the structure and distributes the torque from machining. Second, the kinematic analysis with the consideration of link flexibility is conducted. A kinetostatic model of the three degrees of freedom parallel mechanism with a passive link is then established and analyzed using lumped-parameter model. With the proposed method, a significant effect of the link flexibility on the mechanism's precision has been demonstrated. The influence of the change of structure parameters, including material properties, on the system behavior is discussed. Compliance mapping is also illustrated. The kinetostatic model proposed in the paper can be extended for optimal design and control of parallel kinematic machines. Finally, design optimization is conducted using genetic algorithms and some design guideline is given.

Equivalent Kinematic Chains of Three Degree-of-Freedom Tripod Mechanisms With Planar-Spherical Bonds

The paper aims to analyze the equivalent kinematic chains of a family of three-degree-of-freedom (3-DOF) tripod mechanisms with planar-spherical bonds in order to determine the platform motions generated by the mechanisms, and then to develop a prototype of a 3-DOF 3-RPS type parallel mechanism, which can be used as a wrist robotic device. After a short introduction to mechanical generators of Lie subgroups of displacement, the mobility formula of a general 3-DOF tripod mechanism based on the modified Gru¨ebler’s criterion is given. Using displacement group theory theorems, the analyzed closed-loop system becomes finally equivalent to three contacts between a rigid assembly of three moving spheres onto three fixed planes. As an application of the above method, a prototype mechanism is designed and fabricated based on the kinematics analysis, the force capability and the simplicity.

DEVELOPMENT OF A SINGLE-PIVOT, SEAL-LESS MAGNETICALLY DRIVEN CENTRIFUGAL BLOO PUMP

A single-pivot supported, compact, seal-less, magnetically drive centrifugal blood pump has been developed. The design concept wa based on a tri-pod supported centrifugal blood pump we previousl reported. The single-pivot concept was employed to reduce frictio force due to tri-pod mechanism. Additionally, single-pivot supporte system eliminated the upper bearing system, allowing incorporatio of the eccentric inlet port. In this study, we evaluated the performance of the prototype single-pivot centrifugal blood pum and impeller's stability. [Materials] Male pivot consisting of a ceramic ball (4mm was mounted on the bottom surface of the impeller, whil polyethylene groove female pivot was mounted on the bottom pum casing. The prototype pump had an impeller diameter of 50mm, priming volume of 25ml, and an outer diameter of 60mm. The pum driver used a specially designed brush-less DC motor. [Methods] Flow-Pressure characteristics and system efficiency were measured as the prototype pump performance in a moc circulatory loop. The impeller stability was evaluated by measuring the distance from impeller to the top housing using a Hall-effect sensor with a magnet incorporated inside the impeller. [Results] The pump performance of the prototype single-pivot pum was acceptable as a left-ventricular assist device. In order to obtain pum flow of 5L/min against the head pressure of 90–100mmHg, required pum speeds ranged from 1800 to 2000rpm. The maximum efficiency was 14 at 2200rpm. The Hall sensor signal level change became more stable with the increase in pump RPM. [Conclusion] This result indicates that the single-pivot supporte centrifugal pump can meet both flow and pressure requirements as a left ventricular assist device without requiring the upper bearing or magneti support system as incorporated in other existing systems.

Development and Study of a New Kind of 3-DOF Tripod

A novel 3-DOF parallel machine tool based on a tripod mechanism has been developed and studied. The main aspects of its structure, kinematics, workspace, parameter design, error analysis and force analysis are introduced. Through theoretical analyses and operation tests, it shows some distinctive advantages, such as high ratio of force-to-weight, simple structure and simple kinematic equations, large workspace with no kinematic coupling and no singularity configuration. The unique performance of the tripod machine tool provides a high potential and a very good prospect for its practical implementation in manufacturing industry.