Input Link Research Articles

Social humanoid robot SARA: development of the wrist mechanism

This paper presents the development of a wrist mechanism for humanoid robots. The research was conducted within the project which develops social humanoid robot Sara – a mobile anthropomorphic platform for researching the social behaviour of robots. There are two basic ways for the realization of humanoid wrist. The first one is based on biologically inspired structures that have variable stiffness, and the second one on low backlash mechanisms that have high stiffness. Our solution is low backlash differential mechanism that requires small actuators. Based on the kinematic-dynamic requirements, a dynamic model of the robot wrist is formed. A dynamic simulation for several hand positions was performed and the driving torques of the wrist mechanism were determined. The realized wrist has 2 DOFs and enables movements in the direction of flexion/extension 115°, ulnar/radial deviation ±45° and the combination of these two movements. It consists of a differential mechanism with three spur bevel gears, two of which are driving and identical, while the last one is the driven gear to which the robot hand is attached. Power transmission and motion from the actuator to the input links of the differential mechanism is realized with two parallel placed identical gear mechanisms. The wrist mechanism has high carrying capacity and reliability, high efficiency, a compact design and low backlash that provides high positioning accuracy and repeatability of movements, which is essential for motion control.

Bioinspired sprawling robotic leg and a path-planning procedure

This article shows the characteristics of a sprawling robotic leg inspired by the limb postures of certain reptilian animals known as sprawling-legged creatures. The main part of the robotic limb is based on the eight-bar Peaucellier–Lipkin linkage, and its main attribute is the ability to trace a true straight line, due to the rotational motion of the input link. However, when the eight-bar linkage is modified, it is capable of tracing true circular concave or convex arcs, when two of its constitutive links have distinct and precise lengths. This gives rise to the concepts of concavity and convexity, related to a robotic leg based on the Peaucellier–Lipkin mechanism, such as the one described herein. Our bioinspired robotic leg can trace concave or convex curves, as well as straight lines, making it a reptile-like robotic limb that is very similar to the natural one. We also introduce the concept of rotation center tuning, which refers to the ability of the leg to adapt its posture to the center of rotation of the entire walking machine, resulting in an easy and suitable gait process. The theoretical information is illustrated through the simulation of an example that provides a path-planning procedure, focusing on the rotation center tuning process and a walking gait. The example also includes the design of an elliptical path projected onto the cylindrical workspace and followed by the reptilian foot.

The opercular mouth-opening mechanism of largemouth bass functions as a 3D four-bar linkage with three degrees of freedom.

The planar, one degree of freedom (1-DoF) four-bar linkage is an important model for understanding the function, performance and evolution of numerous biomechanical systems. One such system is the opercular mechanism in fishes, which is thought to function like a four-bar linkage to depress the lower jaw. While anatomical and behavioral observations suggest some form of mechanical coupling, previous attempts to model the opercular mechanism as a planar four-bar have consistently produced poor model fits relative to observed kinematics. Using newly developed, open source mechanism fitting software, we fitted multiple three-dimensional (3D) four-bar models with varying DoF to in vivo kinematics in largemouth bass to test whether the opercular mechanism functions instead as a 3D four-bar with one or more DoF. We examined link position error, link rotation error and the ratio of output to input link rotation to identify a best-fit model at two different levels of variation: for each feeding strike and across all strikes from the same individual. A 3D, 3-DoF four-bar linkage was the best-fit model for the opercular mechanism, achieving link rotational errors of less than 5%. We also found that the opercular mechanism moves with multiple degrees of freedom at the level of each strike and across multiple strikes. These results suggest that active motor control may be needed to direct the force input to the mechanism by the axial muscles and achieve a particular mouth-opening trajectory. Our results also expand the versatility of four-bar models in simulating biomechanical systems and extend their utility beyond planar or single-DoF systems.

MATHEMATICAL SIMULATION OF TECHNOLOGICAL EQUIPMENT FOR PROCESSING OF OPTICAL PARTS

The paper describes a functional scheme of a machine-tool for simultaneous abrasive machining of lenses with shallow high-accuracy executive surface. The machine-tools permits flexibly and within long range to control shape-formation process through changing such adjustment parameters as tool and rough workpiece frequency rotation, amplitude value of tool oscillatory motion, their diameters and number of double strokes per minute. While using the given machine-tool for machining process an operating force is directed along normal to the working surface and due to this there is a possibility to accelerate a shape-formation process of optical parts that leads to reduction of local errors on their executive surfaces. The paper considers a structure of the executive machine-tool mechanism which transfers translational motion to the tools and consists of rotational and rectilinear kinematic pairs forming a four-bar linkage and its crank is a guide link. A turning angle of the link is selected as a generalized coordinate of the executive mechanism. A relationship between the generalized coordinates and link positions of the executive machine-tool mechanism has been established in the paper and it permits to obtain analytical dependence between motions of input and output mechanism links with due account of its kinematic transfer function which represents in itself a ratio of angular output link speed to an angular velocity of the input link. An analysis of geometric parameters for backward-rotational motion of the top link in the proposed machine-tool has made it possible to obtain an expression to calculate a rod length of the executive mechanism which ensures symmetrical center position of the above-mentioned link relative to a symmetry axis of the bottom link. As an amplitude value of oscillatory motion for an out-put link in the executive mechanism is regulated in the machine-tool for two-sided lens machining while changing length of its input link (crank) an analytical relationship has been established between these geometric parameters and the rela- tionship provides a possibility purposefully to change a machining intensity in the central or edge zone of a part according to technological blank heredity in the context of allowance which is to be removed and which is distributed along its surface.

CBM First-level Event Selector Input Interface Demonstrator

CBM is a heavy-ion experiment at the future FAIR facility in Darmstadt, Germany. Featuring self-triggered front-end electronics and free-streaming read-out, event selection will exclusively be done by the First Level Event Selector (FLES). Designed as an HPC cluster with several hundred nodes its task is an online analysis and selection of the physics data at a total input data rate exceeding 1 TByte/s. To allow efficient event selection, the FLES performs timeslice building, which combines the data from all given input links to self-contained, potentially overlapping processing intervals and distributes them to compute nodes. Partitioning the input data streams into specialized containers allows performing this task very efficiently.The FLES Input Interface defines the linkage between the FEE and the FLES data transport framework. A custom FPGA PCIe board, the FLES Interface Board (FLIB), is used to receive data via optical links and transfer them via DMA to the host’s memory. The current prototype of the FLIB features a Kintex-7 FPGA and provides up to eight 10 GBit/s optical links. A custom FPGA design has been developed for this board. DMA transfers and data structures are optimized for subsequent timeslice building. Index tables generated by the FPGA enable fast random access to the written data containers. In addition the DMA target buffers can directly serve as InfiniBand RDMA source buffers without copying the data. The usage of POSIX shared memory for these buffers allows data access from multiple processes. An accompanying HDL module has been developed to integrate the FLES link into the front-end FPGA designs. It implements the front-end logic interface as well as the link protocol.Prototypes of all Input Interface components have been implemented and integrated into the FLES test framework. This allows the implementation and evaluation of the foreseen CBM read-out chain.

Modeling and simulation of planar multibody systems considering multiple revolute clearance joints

This paper presents a general procedure for dynamic modeling and simulation of planar multibody systems considering multiple revolute clearance joints. The normal contact force is evaluated by a hybrid continuous contact force model, established on the base of the Lankarani–Nikravesh (L–N) model and the elastic foundation model. The LuGre friction law is employed to describe the tangential effect. The effectiveness of the presented methodology is demonstrated through the comparisons with the MSC ADAMS software simulation results of a slider–crank mechanism with clearance joints. Then, the system behavior affected by dynamic interaction of three revolute clearance joints is analyzed and some kinds of 27 combination modes are presented. Additionally, a comprehensive analysis of the system responses in a wide range of dynamic simulation parameters is conducted to find out some inner rules existed in the mechanical system with revolute clearance joints. Results show that there exists a strong dynamic interaction between different clearance joints, indicating that all joints should be modeled as imperfect to achieve a further understanding of multibody system behavior. Also, the clearance joint nearer to the input link is found to suffer more serious contact effects, require more input torque and cost longer computational time. Furthermore, the system dynamics relies on many factors, even a small change of which may lead to different system responses, changing from periodic to chaotic and the other way around. In addition, several characteristic values have been captured from the simulation results, which need to be paid more attention in use.

Hardware implementation of dynamic fuzzy logic based routing in Network-on-Chip

This paper presents the hardware implementation of a generic fuzzy logic-based adaptive routing scheme for both buffered and bufferless Networks-on-Chip (NoC). The routing scheme considers the dynamic traffic load and power consumption on neighboring router links to select the output port of an incoming flit. Specifically, fuzzy logic control is used to build a simple, generic, and efficient nonlinear control law that dynamically calculates the input link cost. Basing the link cost on traffic load and power consumption and not on empty buffer slots, makes the proposed algorithm applicable to both buffered and bufferless NoCs. Hardware implementation in ASIC and FPGA technologies demonstrate that the hardware area overhead imposed by the fuzzy control logic is from minimal to negligible for practical flit sizes and scales excellently with network size. Furthermore, since the fuzzy control logic is not in the router critical path, it imposes no additional latency. Finally, we demonstrate the efficiency of the proposed routing scheme through simulative evaluation against representative conventional counterparts.

A Compliant Four-bar Linkage Mechanism that Makes the Fingers of a Prosthetic Hand More Impact Resistant.

Repeated mechanical failure due to accidental impact is one of the main reasons why people with upper-limb amputations abandon commercially-available prosthetic hands. To address this problem, we present the design and evaluation of a compliant four-bar linkage mechanism that makes the fingers of a prosthetic hand more impact resistant. Our design replaces both the rigid input and coupler links with a monolithic compliant bone, and replaces the follower link with three layers of pre-stressed spring steel. This design behaves like a conventional four-bar linkage but adds lateral compliance and eliminates a pin joint, which is a main site of failure on impact. Results from free-end and fixed-end impact tests show that, compared to those made with a conventional four-bar linkage, fingers made with our design absorb up to 11% more energy on impact with no mechanical failure. We also show the integration of these fingers in a prosthetic hand that is low-cost, light-weight, and easy to assemble, and that has grasping performance comparable to commercially-available hands.

Four-bar linkage-based automatic tool changer: Dynamic modeling and torque optimization

An Automatic tool changer (ATC) is a device used in a tapping machine to reduce process time. This paper presents the optimization of a Peak torque reduction mechanism (PTRM) for an ATC. It is necessary to reduce the fatigue load and energy consumed, which is related to the peak torque. The PTRM uses a torsion spring to reduce the peak torque and was applied to a novel ATC mechanism, which was modeled using inverse dynamics. Optimization of the PTRM is required to minimize the peak torque. The design parameters are the initial angle and stiffness of the torsion spring, and the objective function is the peak torque of the input link. The torque was simulated, and the peak torque was decreased by 10 %. The energy consumed was reduced by the optimization.

Phase 1 upgrade of the CMS drift tubes read-out system

In order to cope with up to two times the nominal LHC luminosity, the second level of the readout system of the CMS Drift Tubes (DT) electronics needs to be redesigned to minimize event processing time and remove present bottlenecks. The μ ROS boards are μ TCA modules, which include a Xilinx Virtex-7 FPGA and are equipped with up to 6 12-channel optical receivers of the 240 Mbps input links. Each board collects the information from up to 72 input links (3 DT sectors), requiring a total of 25 boards. The design of the system and the first validation tests will be described.

Mechanical sensitivity and the dynamics of evolutionary rate shifts in biomechanical systems.

The influence of biophysical relationships on rates of morphological evolution is a cornerstone of evolutionary theory. Mechanical sensitivity-the correlation strength between mechanical output and the system's underlying morphological components-is thought to impact the evolutionary dynamics of form-function relationships, yet has rarely been examined. Here, we compare the evolutionary rates of the mechanical components of the four-bar linkage system in the raptorial appendage of mantis shrimp (Order Stomatopoda). This system's mechanical output (kinematic transmission (KT)) is highly sensitive to variation in its output link, and less sensitive to its input and coupler links. We found that differential mechanical sensitivity is associated with variation in evolutionary rate: KT and the output link exhibit faster rates of evolution than the input and coupler links to which KT is less sensitive. Furthermore, for KT and, to a lesser extent, the output link, rates of evolution were faster in 'spearing' stomatopods than 'smashers', indicating that mechanical sensitivity may influence trait-dependent diversification. Our results suggest that mechanical sensitivity can impact morphological evolution and guide the process of phenotypic diversification. The connection between mechanical sensitivity and evolutionary rates provides a window into the interaction between physical rules and the evolutionary dynamics of morphological diversification.

Optimal synthesis of the worm-lever mechanism for humanoid robots shrug

Emotions represent a significant means of nonverbal communication and their expression represents an important aspect of social robots functionality. There are two basic ways of expressing emotions. The first one is based on facial expressions that can be realized by moving a particular part of face or by displaying a picture on the screen that represents a face with characteristic features such as eyebrows, eyes, nose and mouth. Combining them is also possible. The second way of nonverbal communication is based on gestures, especially using arms. This paper presents an optimal synthesis of shrug mechanism for humanoid robots. Based on the set requirements the worm-lever mechanism is proposed. It has 1 DOF and enables simultaneous shrug of both shoulders. It consists of a worm which is meshed with two worm gears having different directions of rotation and two four-bar lever mechanisms whose input links are rigidly connected to the worm gears. Based on the kinematic-dynamic analysis the dynamic model is formed, the objective function is defined, the constraints are prescribed and the optimal synthesis is performed. The maximum torque on the input link of the lever mechanism, the driving torque of the complete worm-lever mechanism, the range of transmission angle and the rotation range of the worm gears are determined. The lever mechanism has high efficiency in all positions because the transmission angle has a high value during the whole movement. The worm mechanism enables a significant reduction of driving torque and has acceptable efficiency. The rotation range of the worm gear is small ? the mechanism movement is very quick and therefore the shrug speed is large, which was the basic requirement for realization.

Assistive humanoid robot MARKO: development of the neck mechanism

The paper presents the development of neck mechanism for humanoid robots. The research was conducted within the project which is developing a humanoid robot Marko that represents assistive apparatus in the physical therapy for children with cerebral palsy.There are two basic ways for the neck realization of the robots. The first is based on low backlash mechanisms that have high stiffness and the second one based on the viscoelastic elements having variable flexibility. We suggest low backlash differential gear mechanism that requires small actuators. Based on the kinematic-dynamic requirements a dynamic model of the robots upper body is formed. Dynamic simulation for several positions of the robot was performed and the driving torques of neck mechanism are determined.Realized neck has 2 DOFs and enables movements in the direction of flexion-extension 100°, rotation ±90° and the combination of these two movements. It consists of a differential mechanism with three spiral bevel gears of which the two are driving and are identical, and the third one which is driven gear to which the robot head is attached. Power transmission and motion from the actuators to the input links of the differential mechanism is realized with two parallel placed gear mechanisms that are identical.Neck mechanism has high carrying capacity and reliability, high efficiency, low backlash that provide high positioning accuracy and repeatability of movements, compact design and small mass and dimensions.

Dynamics of Planar Five-Link Hinged RRRRT Type Mechanism with Two Degrees of Freedom

The paper dwells on dynamic study of a 2-DOF planar five-link mechanism of RRRRT type. There is described the kinematic analysis of the mechanisms, by means of the results of which the formulas of kinetic energy, the reduced moment and the reduced force have been derived, and the non-linear differential equations of motion of second kind determining the motions, velocities and accelerations of the input links of a mechanisms have been obtained. The paper describes the example of solving the dynamic problem. The results obtained for the ideal and real mechanisms are shown in graphs.

Determination of a fourth-class Assur group position diagram by means of the revision of the linkage condition of a closure link

This paper describes an alternative method for the position analysis of a fourth-class Assur group, obviating the need for solving the system of nonlinear equations obtained using the analytical method. The objective of this study is to develop a methodology to determine the positions of the links and kinematic pairs that form the group, based on the position of the pairs that connect the group to the base mechanism. The proposed method consists in the separation of one of the closure links and the obtaining of the position diagram of the resulting 1-DOF (one degree of freedom) mechanism, using the connecting pairs of the group as a fixed support and considering one of the drag links as a driving link. Different configurations of the mechanism are obtained for different values of the input link´s coordinate. The position diagram of the group is determined when the resulting 1-DOF mechanism satisfies the linkage condition imposed by the removed closure link. Four examples of fourth-class Assur groups are used to validate the proposed method, the feasibility of which is confirmed by the accuracy of the results obtained in the analyzed examples.

Kinematic synthesis of spatial linkages with spherical pairs

A solution to the problem of synthesizing an initial three-dimensional kinematic chain with spherical and rotary kinematic pairs is presented. It is shown that this chain can be used as a structural module for structural-kinematic synthesis of motion of a three-dimensional four-link generating lever mechanisms by preset positions of the input and output links.

KINEMATIC SYNTHESIS OF PLANAR ADJUSTABLE SIX BAR MECHANISM FOR SPECIFIED OUTPUT

A method for the synthesis of planar adjustable six bar mechanism with a slider output is presented. The multi-loop six bar linkage considered here is a series combination of two four link mechanisms with first phase having regular RRRR linkage. The second phase consists of a slider crank with the slider being the output member. An analytical method is presented for the kinematic synthesis of a planar four bar adjustable mechanisms using Chebychev’s accuracy points and Fruedenstein’s equations for three point function generation that satisfy a given input output relationship. The length of the coupler link is taken as the adjustable parameter. An analytical method of computing the value of this variable for a four bar crank rocker mechanism as well as a slider crank mechanism is presented. A numerical example explains the synthesis procedure developed in which a function to be generated is considered. The unknown link lengths of the mechanism are then found for given range of input and output link parameters and assumed link length. The value of the adjustable length of the coupler is then computed and the results are presented numerically as well as graphically. The method adopted is coded using MATLAB for quick computation and ease of use. The motion and the path generated by the designed mechanism is found for different values of the adjusted parameter.

Linkage mechanisms in the vertebrate skull: Structure and function of three-dimensional, parallel transmission systems.

Many musculoskeletal systems, including the skulls of birds, fishes, and some lizards consist of interconnected chains of mobile skeletal elements, analogous to linkage mechanisms used in engineering. Biomechanical studies have applied linkage models to a diversity of musculoskeletal systems, with previous applications primarily focusing on two-dimensional linkage geometries, bilaterally symmetrical pairs of planar linkages, or single four-bar linkages. Here, we present new, three-dimensional (3D), parallel linkage models of the skulls of birds and fishes and use these models (available as free kinematic simulation software), to investigate structure-function relationships in these systems. This new computational framework provides an accessible and integrated workflow for exploring the evolution of structure and function in complex musculoskeletal systems. Linkage simulations show that kinematic transmission, although a suitable functional metric for linkages with single rotating input and output links, can give misleading results when applied to linkages with substantial translational components or multiple output links. To take into account both linear and rotational displacement we define force mechanical advantage for a linkage (analogous to lever mechanical advantage) and apply this metric to measure transmission efficiency in the bird cranial mechanism. For linkages with multiple, expanding output points we propose a new functional metric, expansion advantage, to measure expansion amplification and apply this metric to the buccal expansion mechanism in fishes. Using the bird cranial linkage model, we quantify the inaccuracies that result from simplifying a 3D geometry into two dimensions. We also show that by combining single-chain linkages into parallel linkages, more links can be simulated while decreasing or maintaining the same number of input parameters. This generalized framework for linkage simulation and analysis can accommodate linkages of differing geometries and configurations, enabling novel interpretations of the mechanics of force transmission across a diversity of vertebrate feeding mechanisms and enhancing our understanding of musculoskeletal function and evolution. J. Morphol. 277:1570-1583, 2016. © 2016 Wiley Periodicals, Inc.

Multi-objective optimization of mechanism design using a bi-level game theoretic formulation

This article considers the design of a high-speed mechanism as a multi-objective optimization problem wherein the kinematic and dynamic criteria are optimized simultaneously. The kinematic criteria include minimization of the structural error and a minimization of deviation of the transmission angle from its ideal value. The dynamic criterion used is minimization of the peak torque required to drive the input link over a cycle. A Stackelberg (leader–follower) game theoretic approach is proposed to solve the multi-objective problem. Three variants, wherein both the kinematic and the dynamic criteria are treated as the leader, are considered. The design variables are the mechanism dimensions. A computational procedure using sensitivity information is proposed for approximating rational reaction sets needed for capturing exchange of information between the leader and the follower problems. A numerical example dealing with the design of a path generating four-bar mechanism is presented. It is shown that significant improvement in both kinematic and dynamic performance measures is simultaneously achieved using the proposed approach.

Linking theorems for tree transducers

Linear extended multi bottom-up tree transducers are presented in the framework of synchronous grammars, in which the input and the output tree develop in parallel by rewriting linked nonterminals (or states). These links are typically transient and disappear once the linked nonterminals are rewritten. They are promoted to primary objects here, preserved in the semantics, and carefully studied. It is demonstrated that the links computed during the derivation of an input and output tree pair are hierarchically organized and that the distance between (input and output) link targets is bounded. Based on these properties, two linking theorems are developed that postulate the existence of certain natural links in each derivation for a given input and output tree pair. These linking theorems allow easy, high-level proofs that certain tree translations cannot be implemented by (compositions of) linear extended multi bottom-up tree transducers.