Search results

To improve the trajectory tracking accuracy of 6R decoupled manipulator in singularity region, this paper aims to propose a singularity avoidance algorithm named “singularity separation plus improved Gaussian distribution damped reciprocal”.

The manipulator is divided into forearm and wrist, and the corresponding singularity factors are separated based on kinematics calculation. Singularity avoidance is achieved by replacing the common reciprocal with the improved Gaussian distribution damped reciprocal.

Compared with common damped reciprocal algorithm and classical Gaussian distribution algorithm, the continuity of the proposed algorithm is improved and the tracking error is minimized. The simulation and experiment results prove effectiveness and practicability of the proposed algorithm.

This study has an important significance to improve the efficiency and operation accuracy of 6R decoupled manipulator.

DURING a test flight on a prototype Javelin aircraft, a flutter incident occurred involving the loss of both elevators. The pilot was fortunately able to continue flying the aircraft using the tail trimming control and subsequently made a crash landing. At the time of the incident all the recording instruments were running. These included an automatic observer, a chart recorder of control circuit forces and a two‐axis vibrograph which was mounted at the top of the fin. A copy of part of the record from the latter instrument is shown in FIG. 1. The upper stepped line is the timing signal and the lower trace gives the lateral displacement at the top of the fin, the rather spasmodic oscillations corresponding to the fin bending frequency of 4·8 c.p.s. The diverging oscillation shown on the centre trace corresponds to the vertical displacement at the top of the fin. From this and a similar record obtained from the elevator circuit force recorder, it was concluded that the elevators fluttered symmetrically at a frequency between 21 and 22 c.p.s.

THE eleventh annual meeting of the Institute was for the first time held simultaneously in three centres—in New York City at Columbia University, in Detroit at Rackham Educational Memorial, and in Los Angeles at the University of Southern California—from January 25 to 29. The purpose of the three simultaneous meetings was to minimize travel by executives and engineers from important war jobs in the present emergency. The same programme was offered at all three centres, papers being sometimes presented by proxies—experts in the same field as far as possible. In spite of the fact that attendance was divided between three centres, there was splendid representation at each place and a wide range of subjects was covered in the many papers. Naturally these were restricted more to analysis, and technology and information as to the latest design or production features of current aircraft or engines was withheld. The same ban applied to striking developments in accessories, instruments and armaments. All papers had to be approved by the Army or Navy and to be read substantially as written. While off‐the‐record discussions were permitted, these discussions were not made public. In particular there was a ban on comparisons between foreign and American materials, equipment or methods. The formula for control of comparison performance stated that the manufacturer's smooth curve calibrations and performance figures might be quoted, but no Wright field performance figures or data could be revealed. In spite of such restrictions a tremendous amount of valuable technical information was presented to the assembled engineers.

Usual definitions of damping in oscillatory modes are reviewed, a new definition is proposed and it is suggested that the latter offers certain advantages to both the theoretical and the practical worker in this field. An Appendix contains response formulae for three fundamental types of disturbance. These can be used for the derivation of the various expressions characterizing dynamic properties of any mode that is equivalent to a damped system of one degree of freedom. A collection of formulae, numerical tables and graphs permit a quick comparison to be made between the different definitions of damping.

The theory is presented of the increase in damping that can be obtained when a damping compound is added to a simple structure vibrating in a bending mode. Consideration has been given to the use of ‘Aquaplas’ damping compound on a vibrating stringer‐skin combination, and it has been shown that the maximum damping ratio is obtained when the material is applied to the stringer flange over the centre 40 per cent of the pin‐ended length of the beam. A preliminary experimental investigation is described, in which damping measurements were made on a simple structural specimen treated with Aquaplas. A new method was used successfully to determine the damping ratio of a heavily damped system. The damping properties of Aquaplas were evaluated, and some of the theoretical conclusions were verified. Some of the results obtained indicate that a more accurate mathematical representation must be sought for the visco‐elastic behaviour of Aquaplas than is provided by the ‘complex stiffness’ method.

Primordial pattern is the name given by Grigg to the curve representing the response of many biologic systems to a single stimulus. This curve consists of a fast ascent and a lingering descent. The equation had been chosen empirically to describe the primordial pattern. This equation taken in isolation does not reveal its close interconnection with the physical world. In this paper it is seen as one of the solutions of a second‐order damped system representable by the differential equation with zero initial displacement but some initial velocity. Such a system involves contributing responses by components of threekinds: inertial, restoring and resistive. This observation should stimulate scientists to extract these different components from any biologic response. The resistive component is a term proportional to the first derivative of the response with respect to time. Evidence for the necessity of this frictional component to obtain a primordial pattern is presented. Such frictional component imparts to a process an irreversible character in agreement with Poincarés thermodynamic formulation and provides the physico‐mathematical substrata to the concept of biologic relativity, namely: as the primordial pattern runs its course, there occurs an incessant change, not only in the recorded response, but also in the respondent's reactivity. This paper offers a unifying view of biology and physics. It should be the task of biologists henceforth to try to find the pertinent analogies with inertial, restoring and resistive components of biologic entities and responses. As an example, consider the fact that the primordial pattern requires of necessity the existence of frictional elements within the system. It will be of great interest to look into these elements and try to identify them. Then, perhaps, they could be manipulated from outside the system to increase or diminish them for mankind's advantage.

Introduces the fourth and final chapter of the ISEF 1999 Proceedings by stating electric and magnetic fields are influenced, in a reciprocal way, by thermal and mechanical fields. Looks at the coupling of fields in a device or a system as a prescribed effect. Points out that there are 12 contributions included ‐ covering magnetic levitation or induction heating, superconducting devices and possible effects to the human body due to electric impressed fields.

IN Part I wc saw how structural flexibility could introduce aerodynamic forces which might eventually lead to instability, or to the complete nullification of a desired aerodynamic effect. The phenomenon of flutter presents another problem in stability, but in this case an oscillatory instability is threatened. It must be realized at the outset that flutter is no mere resonance phenomenon such as the bad vibrations a motor‐car may exhibit at a particular engine speed. Flutter is a vibration in which energy is extracted from the airstrcam to help build up the amplitude, and a catastrophic failure can easily occur within a second of the start of the flutter.

Describes the McKibben muscle and its major properties. Outlines the analogy between this artificial muscle and the skeletal muscle. Describes the actuator composed of two McKibben muscles set into antagonism based on the model of the biceps‐triceps system, and explains its natural compliance in analogy with our joint litheness. Reports some control experiments developed on a two d.o.f. robot actuated by McKibben muscles which emphasize the ability of these robot‐arms to move in contact with their environment as well as moving loads of high ratio to the robot’s own weight. Also outlines control difficulties and accuracy limitations and discusses applications.

The adoption of a model‐building approach to marketing is today inevitable, due to improvements in hardware and software and the increased professionalisation of marketing and its techniques. Aggregate response models are focused upon, particularly the issues of which responses are realistic and should be modelled, how the response can be expressed and how a choice can be made between options available. The traditional model‐building process is described, and the inclusion of correct variables found to be critical, the primary means of doing this being statistical analysis. Simple expressions perform as effectively as more complex ones, and should be used if able to give operationally meaningful results. Cross‐correlation analysis and biased estimation techniques provide good guides to usable variables and their effects.