一类具有弧形移动副的3-RPS并联机构研究

Research on a class of 3-RPS parallel mechanism with arc prismatic pairs

现有3-RPS并联机构运动支链中部的消极驱动副都采用直线移动副,导致机构的灵活度、承载能力均不高。基于TRIZ曲面化(Spheroidality)原理,通过改变运动副的形状以及增加运动副之间的接触面积,来提高机构的灵活度以及承载能力。提出了3种具有弧形移动副的3-RPS并联机构,其运动支链均由1个转动副R、1个弧形移动副P和1个球铰S构成。其中第1种并联机构的驱动副轴线共线,第2种的驱动副轴线相互平行,第3种的驱动副轴线共面并彼此相交。采用螺旋理论,建立运动支链中运动副在一般位形下的运动螺旋形式,并分析动平台所受的约束力,实现对这些机构自由度、运动特性和灵巧度的求解。结果表明:第1种机构的动平台转动中心为弧形连杆的中心,动平台绕Z轴的旋转相对其他2个方向的旋转具有解耦性,第2、第3种机构的动平台转动中心是各支链球铰中心与弧形连杆中心连线的交点,此交点随动平台位姿的变化而变化;此外,这3种机构的灵巧度较高,而第1种机构的灵巧度高于后2种机构,第2、第3种机构的灵巧度相同。这3种机构具有结构对称、机构简单、刚度高、承载能力大等特性,可应用于虚轴机床、航空模拟设备、医疗设备等领域。

The middle of kinematic chain in existing 3-RPS parallel mechanisms possess a passive straight prismatic pair,lead to lower dexterity and load capacity of mechanisms.Based on the theory of Spheroidality of TRIZ,the dexterity and load capacity of mechanisms can be improved by changing shape and increasing the contact area of the pairs.Three types of 3-RPS parallel mechanisms with arc prismatic pairs were proposed,for the limb kinematic chain consisted of a revolute pair R,aprismatic pair P and a spherical joint S.The axes of drive pairs in those three types of mechanisms were collinear,parallel,intersect each other and coplanar,respectively.The screw formulations of kinematic joints under ordinary configuration were establishedby using the screw theory and the constraint force screws of moving platform were analyzed,which were employed to solve the degree of freedom,motion characteristics and dexterity of those parallel mechanisms.Results demonstrated the rotational center of moving platform was the center of arc of arc rods in the first type of mechanism,and moving platform rotating around the Z-axis with respect to the other two directions was decoupled.For the second and third type of mechanism,the rotational center was an intersection point of three straight lines,which was passed through each center of arc rod and the center of spherical joint,and this intersection point was changed with the posture of the moving platform.In addition,these mechanisms had high dexterity,and the dexterity of the first type of mechanism was higher than other two mechanisms,the dexterity of last two mechanisms were the same essentially.These mechanisms have some characteristics like symmetric and simple structure,high rigidity and large load capacity.Therefore,it can be widely used in virtual axle machine tool,flight simulator and medical equipment fields.