摘要
鉴于线矢力与机构的承载能力密切相关,对线矢力的各向同性条件进行了研究,得到了线矢力满足各向同性的一般条件,提出了一种事先考虑驱动副布置的冗余驱动移动三自由度并联机构构型综合方法。该方法首先综合与支链约束力螺旋和驱动力螺旋均互易的运动链;然后再构造与支链约束力螺旋互易而与驱动力螺旋不互易的驱动副,从而得到了数种典型的满足驱动线矢力各向同性的冗余驱动三自由度移动并联机构构型;最后,对其中的一种典型机构4-PRRR进行了分析,结果表明,该机构在运动过程中始终满足承载能力各向同性,验证了前述线矢力各向同性分析与构型综合理论的正确性。
The carrying capacity of a mechanism is closely related to its line vector force. A thorough isotropic analysis of line vector forces was presented. The results showed that the isotropic condition can be satisfied when the line vector forces were evenly distributed on a conical surface with a cone-top angle of 109. 472°. In addition,since few three degrees-of-freedom( DOFs) translational redundantly actuated parallel manipulators were reported,by combining the isotropic line vector forces,a method for the type synthesis of 3-DOF,redundantly actuated translational parallel mechanisms( PMs) was proposed,in which the arrangement of the active joints was taken into account in advance. Using this method,firstly a kinematic chain with a twist system reciprocal to both the constraint and actuation wrenches was constructed,and then the active joint reciprocal to the constraint wrenches but not to the actuation wrench was constructed. Thus,a series of typical redundantly actuated PMs with isotropic actuation forces were obtained. Finally,the 4-PRRR PM was analyzed as an example,and the results showed that the isotropy of the load-carrying capacity can always be satisfied during its movement,because the condition of force Jacobian matrix was always equal to one,which to some extent verified the correctness of the isotropic analysis and the synthesis method proposed in this research. For this method,it not only satisfied the expected requirements,but also meant that the active joints no longer needed to be selected,and the rationality of the selection did not need to be considered,which provided a new method for the type synthesis of parallel manipulators.
引文
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