Closed-loop Mechanism Research Articles

Optimal active pointwise control of thin plates via state-control parametrization

A direct method to solve an optimal control problem by parametrizing both state and open-loop control variables is developed. This technique is designed to suppress the undesirable vibrations of a rectangular plate by open-closed loop control applied at discrete points in space. The closed-loop mechanism is assumed to be proportional to displacement. The measure of performance of the structure is taken as a combination of its total energy and the penalty terms describing the expenditure of the open-closed loop forces used in the control process. Using modal expansion and an appropriate transformation, the optimal control of a distributed parameter system is reduced to the optimal control of a linear time-varying lumped parameter system. Next, a computationally efficient formulation to evaluate the optimal control and trajectory of the structure, based on shifted Legendre polynomial approximations of the state variable and each open-loop control variable, is developed. This converts the linear quadratic problem into a mathematical programming problem, where a necessary condition for optimality is derived as a system of linear algebraic equations. A minimization algorithm is then used to determine numerically the feedback parameters of the closed-loop control. A numerical example involving a simply supported plate is provided to substantiate the theoretical results by demonstrating the effectiveness of the proposed method. The results of computer simulation studies compare favourably to optimal solutions obtained by the variational method (Blanton and Sadek 1992), indicating that the suggested approach provides better control of the vibrating plate

Analysis of Errors in Precision for Closed Loop Mechanisms

An algorithm to analyze the relations of error components for closed loop mechanisms is introduced. The error components considered are errors in link dimensions and error motions due to joint clearances. In order to completely characterize the physical shape of a link, first a revision of the Denavit-Hartenberg symbolic notation is introduced. Then, an error matrix is proposed to account for the effects of error motions due to joint clearances. Six independent equations are obtained. The major benefit from these equations is the capability of assessing the influence of each error component on a machine’s accuracy. This analysis is particularly useful to allocate a machine’s tolerances at its design stage and to characterize the performance of an existing machine.

Insect-model based microrobot with elastic hinges

This paper describes the new concept of making a microrobot based upon insects and its implementation using rigid plates and elastic hinges. One unique feature of an insect's structure is its deformable external skeleton, to which wings and legs are attached, forming a closed-loop mechanism. Frictionless deformation of elastic elements, instead of conventional rotational joints, allows for efficient actuation in the microscale. We propose three-dimensional micromechanisms based on an external skeleton and have fabricated several examples using polysilicon plates and polyimide hinges. By folding the polysilicon plates along the polyimide hinges just like paper, 3D structures can be constructed on silicon wafers. These structures can be easily actuated by electrostatic force. Closed-loop flapping mechanisms have been fabricated and electrostatically actuated to demonstrate the motion of the external skeleton system. Resonant vibration was observed in a frequency range of around 10 kHz. Actuation using electrostatic induction is also considered.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A simple method of accuracy enhancement for industrial manipulators

A robot calibration method which includes identification of kinematic parameters and error compensation is presented. The parameter identification process features an easy-to-perform measurement procedure using a low-cost, instrumented, articulated linkage, and with proper planning of the data collection process, the measurement of actual end effector positions can be performed automatically. The basis of the parameter identification approach is akin to that of closed-loop mechanism synthesis. For error compensation, a computation scheme based on the nominal model as opposed to the calibrated one is presented. The resulting algorithm, allowing the exploitation of the closed-form inverse kinematics solutions available for most industrial robots, is computationally efficient and therefore suited for on-line applications. Examples based on simulation studies, devised to include realistic operating conditions, are presented to demonstrate the feasibility of this method. The effects are also investigated of the number of measurements and of the sensor resolution on the overall quality of the identification.

Characteristic Evaluation and Comparisons of Robotic Mechanisms. 1st Report, Evaluation and Comparisons Based on Static Characteristics.

This paper compared and evaluated several kinds of representative robotic mechanisms based on static characteristics. In particular, open-loop mechanisms and two kinds of closed-loop mechanisms, that is, parallel crank mechanisms, were adopted as the representative robotic mechanisms. On the characteristic comparisons of the robotic mechanisms, former research had been carried out on the condition that the configurations of the mechanisms were limited to a certain form. However, static characteristics of the robots are greatly changed by the mechanism configurations. Therefore, this paper paid special attention to the changes of each mechanism characterized by those configurations. Geometrical characteristics, strength characteristics and characteristics based on input/output displacement of these robotic mechanisms were compared and evaluated. As a result, the superior and inferior characteristics of each robotic mechanism were revealed.

In-parallel actuated mechanisms as a new robotic mechanism

The concept of parallel connection or in-parallel actuation is described for the closed-loop mechanisms with multiple degrees of freedom which compose those manipulators or robots called parallel. The structural, kinematic, static and dynamic characteristics of the mechanisms are also explained. Then, possible applications of the mechanisms to robots as an alternative to conventional serial robots are introduced together with problems to be solved.

In-parallel actuated mechanisms as a new robotic mechanism

The concept of parallel connection or in-parallel actuation is described for the closed-loop mechanisms with multiple degrees of freedom which compose those manipulators or robots called parallel. ...

Control of elevator muscle activity during simulated chewing with varying food resistance in humans.

1. During chewing, a small part of the observed muscle activity is needed for the basic open-close movements of the mandible, and much additional muscle activity (AMA) is needed to overcome the resistance of the food. In chewing cycles in which a counteracting force is expected, the AMA is mainly generated by peripheral induction with a latency of approximately 23 ms. It was investigated whether an open-loop or closed-loop mechanism is involved in the control of the AMA in these cycles. 2. Subjects made rhythmic open-close movements at their natural chewing frequency controlled by a metronome. Food resistance was simulated by an external force, acting on the jaw in a downward direction during part of the closing movement. Sequences of cycles with a force were unexpectedly alternated with sequences of cycles with a different force. The force changed from 19 to 0 N and vice versa, and from 25 to 6 N and vice versa. Jaw movement and surface electromyogram of the masseter, temporalis, and suprahyoid muscles on both sides were recorded during cycles before and after the transition from one force condition to another. 3. The movement trajectory and AMA of the second and following cycles with a new force appeared to be similar. Thus adaptation to the changed circumstances occurred within two open-close cycles. 4. In the first cycle with 0 or 6 N in the 19----0 N and 25----6 N experiments respectively, a large part of the AMA had disappeared. The AMA in this cycle started to differ from the AMA in the previous cycle approximately 23 ms after the moment the force in this cycle started to differ from the previous cycle. 5. In the first cycle with 19 or 25 N in the reverse experiments, the AMA increased 120-136 ms after the moment the force in this cycle started to differ from the previous cycle. 6. During the closing phase of each open-close cycle, no muscle activity of the suprahyoid muscles was observed; thus co-contraction with the elevator muscles did not occur. 7. It was concluded that the AMA is under control of a closed-loop mechanism with a latency of approximately 23 ms. However, the reflex output has a maximum, depending on information about the food resistance gained in previous cycles.(ABSTRACT TRUNCATED AT 400 WORDS)

Approximated Grashof-Type Movability Conditions for RSSR Mechanisms With Force Transmission Limitations

Closed-form Grashof-type movability conditions are derived for closed-loop RSSR mechanisms using a geometrical approximation technique. The conditions that ensure the presence of crank-rocker and drag-link type mechanisms are derived with and without force transmission limitations. The force transmission limitations may be specified as a function of the output link angle. The accuracy of the approximated conditions is analyzed. As an example, the conditions are used to synthesize a function generating mechanism with fully rotatable crank and with various force transmission requirements. The developed technique is general, and can be applied to other similar spatial mechanisms. The application of this approach to geometrical synthesis of open-loop chain manipulators is discussed.

Inference of link positions for planar closed-loop mechanisms

A system is presented for the automated assembly of planar closed-loop mechanisms. The system is a combination of an inference-of-position technique and a kinematic orientation analysis method. Given a set of mechanism components in unassembled position and orientation, the system automatically calculates the assembly transformation matrices for each component such that a feasible configuration of the mechanism is obtained. The system requires relatively simple input data: the position of the joint location and the mating relationships of associated geometric features. The system facilitates the design and analysis of mechanisms by relieving the user of the manual specification of the assembly configuration. Several examples are presented that demonstrate the capabilities of the automated assembly system.

Dynamic analysis of spatial flexible multibody systems using joint co‐ordinates

AbstractThis paper presents a systematic method for deriving the minimum number of equations of motion for spatial flexible multibody systems. Relative kinematics are developed using relative joint co‐ordinates and relative joint velocities to formulate a minimum number of equations of motion. The present method takes advantage of the simplicity of the absolute co‐ordinate formulation and computational efficiency of the relative joint co‐ordinate formulation. The system equations of motion are first formulated in terms of a coupled set of absolute reference co‐ordinates and elastic modal co‐ordinates. These equations are transformed to the joint co‐ordinate space by use of a velocity transformation matrix including the elastic modal velocities. A computer algorithm is proposed and extended to closed loop mechanisms. One example of a flexible vehicle is presented and the results are discussed to illustrate the computational efficiency of the method.

Analyse geometrique des mecanismes a l'aide d'angles d'euler duaux

The displacements of solid bodies are represented by six real numbers corresponding to a generalization of Euler's angles, with dual numbers and screw operators. The relations between these real numbers are derived from the combination of motion. This method allows us to develop a new and systematic approach to the determination of the inverse model of a robot and in the analysis of a closed loop mechanism. For a spatial triangular system the corresponding formulae are derived and special cases appear naturally. Three examples illustrate the method. The first one concerns a five-axis classical robot, the particularities (parallelism and intersected axes) are automatically and immediately taken into account, for the computation of the inverse geometrical model. The inverse model does not need the derivation of the direct model. In the example of the four-bar RCCC mechanism, the method allows us to obtain immediately the input-output relations in an explicit form.

Self-Excited Oscillation of Transonic Flow Around an Airfoil in Two-Dimensional Channels

A self-excited oscillation of transonic flow in a simplified cascade model was investigated experimentally, theoretically and numerically. The measurements of the shock wave and wake motions, and the unsteady static pressure field predict a closed-loop mechanism, in which the pressure disturbance that is generated by the oscillation of boundary layer separation propagates upstream in the main flow and forces the shock wave to oscillate, and then the shock oscillation disturbs the boundary layer separation again. A one-dimensional analysis confirms that the self-excited oscillation occurs in the proposed mechanism. Finally, a numerical simulation of the Navier–Stokes equations reveals the unsteady flow structure of the reversed flow region around the trailing edge, which induces the large flow separation to bring about the antiphase oscillation.

Forward Calibration of Closed-Loop Jointed Manipulators

A method for performing forward kinematic calibration of manipulators with one or more closed-loop actuated joints is presented. The technique is an extension of algorithms de signed for open-loop jointed manipulators and is equivalent to minimizing a constrained objective function. The con straints arise from the closed-loop mechanisms in the manip ulator. The objective function is taken as the integral of end effector position and orientation error and is optimized using the method of Lagrange multipliers.

統一的機構動特性解析とロボットシミュレータへの適用

A unified method of the dynamic analysis for general spatial mechanisms and over-constrained mechanisms has been developed. When a screw space representing motion of a mechanism is a mobile space, the velocity and the acceleration motors of the mechanism belong to the mobile space which is invariant with the motion of the mechanism. All the motors in the equations of motion of the mechanism can be expressed by the elements in accord with the basis of the screw space and this make it possible to derive equations which can be applied to mechanisms with several constraint conditions. These equations can be utilized in the unified computer program for the dynamic analysis of serial mechanisms and closed loop mechanisms having arbitrary mobile screw space. They can also be applied to the robot simulator by combining them with the dynamics of servo-mechanisms of actuators.

On the elimination of branching in the synthesis of spatial single-loop mechanisms with lower pairs

SUMMARYA single-loop spatial mechanism kinematically becomes an open robot, if we separate the grounded joint of the input link which may then be considered as the end effector of the robot. Any position of the end-effector within the workspace of such an open robot can be reached via a number of different configurations of the links. These configurations are called “branches” of the open robot for that particular position of the end effector.If the open robot is now stretched to a limiting position by a force exerted on the end effector, all the possible branches of the mechanism approach each other. When they become coincident, they form the “limiting configuration”. Any two related branches are at opposite sides of the limiting configuration. From the relationship between the links in th elimiting configuration and in related branches, conditions for aviodance of branching of the original closed-loop mechanism can be obtained. This is necessary in order to assure that a set of consistent relative displacements are specified for the open robot to move displacements are specified for the open robot to move toward the desired end-effector position without jumping from one branch to another. As for the closed-loop mechanism, open robot branching aviodance ensures that a desired sequence of positions of a particular floating link in the loop will be generated without changing the branch of the link configuration.In this paper, the above approach is applied to RSSR, RRSC, RRSRR, RRRRRRR and RPCRRR spatial closed-loop motion-generator mechanisms and the corresponding conditions for aviodance of branching in the synthesis of the mechanisms are derived.

Modelling robot elastic links

Robot elastic links are modelled as superelements. This modelling is adapted to the measuring of robot elastic features in situ. Open- and closed-loop linkages are examined. In closed-loop mechanisms, the beam-links and the rod-links are defined; the superelements modelling beam-link has three nodal points and eleven nodal values. In open-loop linkages, all the links are beam-links and are modelled as superelements with two nodal points and twelve nodal values. The rigid-body degrees of freedom are separated and the rigid-body transfer matrix is calculated. This separation leads to the displacements which represent the elastic deformation of the link, and makes it possible to calculate its flexibility matrix from the displacements measured at the nodal points.

A transient thermal failure mode in metal film resistors

A failure mode has been observed in metal film resistors when they are subjected to single shot high voltage pulses. The conductor fails at a high field point which may be inherent in the design or may be due to manufacturing defects. The localised nature of the failure leads to the conclusion that there is a closed loop mechanism: the decrease in thermal diffusivity of the structure with rising temperature leads to an increase in the rate of temperature rise.

4556835 Operating mechanism for movable parts, especially for sliding roofs and sliding/lifting roofs: Wolfgang Vogel, Albert Zintler, Gauting, Federal Republic Of Germany assigned to Webasto-Werk W Baier GmbH & Co

In this paper, we propose a multi-fingered gripper, which is able to achieve manipulation of objects with six degrees of freedom by actuating exactly six joints. After grasping, adhesion forces, provided, e.g. by an electromagnet or a vacuum cup, ensure that the fingertips remain connected to the object to be manipulated. The resulting closed-loop mechanism, formed by the gripper and the object features a kinematic structure similar to that of parallel manipulators. Such a gripper has many advantages over existing industrial grippers, often used for simple gripping tasks, and existing mechanical hands with a complex and costly control architecture.

Application of linear algebra to screw systems

The elements of linear algebra are applied to screw systems. The theory developed in this paper provides a general method for determining the system of instantaneous screws of any link in a closed-loop mechanism. Further, a novel, simple expression is derived for determining the velocity ratio of any pair of screws which represent a pair of joint motions within a closed-loop spatial mechanism.