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Precise cable drive is a flexible frictional transmission method that transmits power from drive capstans to driven pulleys by a properly preloaded transmission medium. Since most of precise cable drive mechanism with high pointing precision proposed in previous studies suffer from low transmission stiffness and small output torque, this paper presents a novel many-to-one configuration precise cable drive mechanism (MCCDM) with high precision and large torque. The design methods of many-to-one configuration are studied including the system optimal design and cable wrapping design. The transmission characteristics of the developed configuration are analyzed, considering transmission capacity, transmission backlash, and transmission stiffness. The corresponding parameter sensitivities are also investigated. Moreover, a prototype of the MCCDM has been built, with which a series of experiments are carried out. It is noted that the developed mechanism has a motion range of ±2 rad. The steady-state error to a step reference of 1 rad amplitude is only 1.39 µrad and the position resolution is better than 0.5 µrad. This mechanism could achieve maximum output torque of 35 Nċm with compact size and light weight. It has reached a considerable toque-to-weight ratio of 8.997 N·m/kg. The experimental results show that the self-excited oscillation and backlash are dominant nonlinear effects in the MCCDM system. It shows that the self-excited oscillation is a function of the rotational displacement in such a system, with the highest peak at 0.1669 cycle/mrad and the amplitude of 34.63 µrad. The backlash could be measured about 60 µrad under exciting of a small amplitude and low frequency sinusoidal signal. The proposed technologies could have strong technological implications in some special applications such as antenna servo system. [ABSTRACT FROM AUTHOR]

Since most of the XY positioning stages with large travel range proposed in previous studies suffer from low out-of-plane stiffness and loose structure, this paper presents a novel two degrees-of-freedom large travel linear compliant positioning stage with high out-of-plane stiffness and compact size. The linear guide compliant mechanism of the stage takes spatial leaf spring parallelograms as the basic units, which are serially connected to obtain large travel, high out-of-plane stiffness, and compact size simultaneously. The theoretical static stiffness and dynamic resonant frequency are obtained by matrix structural analysis. Finite element analysis is carried out to investigate the characteristics of the developed stage. The analytical model is confirmed by experiments. It is noted that the developed stage has a workspace of 4.4 × 7.0 mm2, and the area ratio of workspace to the outer dimension of the stage is 0.16%, which is greater than that of any existing stage reported in the literature. The results of out-of-plane payload tests indicate that the stage can sustain at least 20 kg out-of-plane payload without changing the travel range. And the positioning experiments show that the developed stage is capable of tracking a circle of radius 1.5 mm with 10 µm error and the resolution is less than 2 µm. [ABSTRACT FROM AUTHOR]

In the harmonic gear servo system, friction is associated with not only the velocity of the input shaft but also its angle position. Traditional friction compensation based on the velocity cannot guarantee the high motion accuracy. To address this problem, this article proposed a new friction model of harmonic gear servo system, which is related to both its velocity and position. The new model includes two parts: in the presliding region, the static friction is determined by the maximum elastic deformation recovery angle of the input shaft, and in the sliding region, the friction not only has Stribeck effect from velocity but also has harmonic series relative to the input shaft’s position. In this article, the parameters of friction model were obtained by preliminary experiments. A control diagram based on this model was established for friction compensation and the proposed control algorithm showed its superiority in the experiments. [ABSTRACT FROM AUTHOR]

In this article, an additional feedback control using the speed difference between the motor and load is proposed to suppress the mechanical resonance in the flexible framework of inertially stabilized platforms. The disadvantages of the classic control scheme of the stabilized loop about the disturbance and resonance suppression are analyzed. In order to damp the torsional vibration effectively, two kinds of additional feedbacks based on the inner motor speed loop are used. The control parameters are given by analytical equations; the disturbance and resonance suppression performance of the stabilized loop with additional feedbacks are comparatively analyzed. Finally, experimental verification is performed on the proposed control algorithms, and the additional feedback signal which is added on the feedback channel of the inner motor speed loop exhibits its superiority in the resonance and disturbance suppression. [ABSTRACT FROM AUTHOR]

A brief overview of previously built acquiring tracking and pointing devices reveals a trend toward smaller, more agile systems. A differential cable drive mechanism is developed to realize large look angle, high precise and compact structures. The mechanical design, including structure configuration, transmission system, and feathers, is introduced. The kinetic principle is studied and the differential relation between the motors orientations and gimbals pointing positions is investigated. Dynamics of the differential cable drive mechanism is studied based on the Lagrange equations, and the dynamics coupling and kinetic coupling is analyzed. The differential cable drive mechanism is machined and assembled. Experimental setup is built, and the frequency response in different operating conditions is investigated and the transmission performance is tested. Studies and analysis in this paper could provide a basis for further decoupled control of the differential cable drive mechanism. [ABSTRACT FROM AUTHOR]

In this article, a decoupling control method is proposed to solve the coupling problem of the differential cable drive inertially stabilized platform. First, the transmission chain and motion of the inertially stabilized platform are briefly illustrated, and the dynamics is analysed based on the Lagrange equation. According to the established dynamic equation, the coupling of inertia, torque and angular position between two motors are analysed. Then, the decoupling controller is used to address the coupling problems, and the numerical simulation is realized in the MATLAB/Simulink. The experimental results show that the dynamic equation can accurately describe the dynamic characteristic of the differential cable drive inertially stabilized platform, and the control performance is improved by suppressing the coupling factors. [ABSTRACT FROM AUTHOR]

Precise cable drive has been developed as an alternative transmission element to gears, belts and pulleys, chains and sprockets in electro-optical tracking system. The analytical method is developed to predict the transmission backlash of precise cable drive to enable designers to better assess the precision performance in the design study phase. Slip angle of precise cable drive is studied, and the effect of the rotational velocity and inertia of cable on the force equilibrium of contact region is considered. The deformation of cable in slip region and free region is calculated respectively and theoretical formulation of transmission backlash for precise cable drive system is carried out. Parametric sensitivity is investigated to evaluate the relationship between the transmission backlash and precise cable drive parameters including preload tension, load tension, friction coefficient, center distance and output drum radius. Experimental setup is built and the transmission backlash is tested. Effect of preload tension on the transmission backlash is tested. Results show that the experimental value and the theoretical curve of the transmission backlash fit well, which validates the theoretical method developed in this article. [ABSTRACT FROM PUBLISHER]

This article investigates modeling and calibration issues that are associated with inertially stabilized platforms to achieve accurate pointing. In modeling part, the Denavit–Hartenberg notation is used to perform an error analysis of the kinematics of inertially stabilized platforms. A physical model is then established to illustrate the effects of geometric errors that are caused by imprecision in the manufacturing and assembly processes on the pointing accuracy of inertially stabilized platforms. In the calibration part, an improved hybrid model denoted as the semi-parametric regression model is developed to compensate for remaining nonlinear errors. With applications to a two-degree-of-freedom miniature inertially stabilized platform, semi-parametric regression model is shown to outperform physical model substantially in all cases. The experimental results also indicate that the proposed semi-parametric regression model eliminates both the geometric and nonlinear errors, and that the pointing accuracy of miniature inertially stabilized platform significantly improves after compensation. [ABSTRACT FROM PUBLISHER]