【導讀】并以此作為本次無級變速器設計的理論基礎。本設計采用的是以鋼球作為中間傳動元件，通過改變。鋼球主動側和從動側的工作半徑來實現(xiàn)輸出軸轉速連續(xù)變化的鋼球錐輪式無級變速器。動錐輪、從動錐輪和內(nèi)環(huán)所組成。動力由輸入軸輸入，帶動主動錐輪同速轉動，經(jīng)鋼球利用摩擦力。的傾斜角β就可達到變速的目的。本設計為恒功率輸出特性，輸出轉速恒低于輸入轉速，運用于低。本文分析了在傳動過程中主、從動輪，鋼球和外環(huán)的工作原理和受力關系；通過。并對調速結構進行合理設計。

　　

【正文】 roup In order to generate spatial translation with parallel mechanisms, we are led to look for displacements subgroups the intersection of which is the spatial translation subgroup {T}.We will consider only the cases for which the intersection subgroup is strictly included in the two “parallel” subgroups. The most important case of this sort is the parallel association of two {X (w)} subgroups with two distinct vector directions w and w’. It is easy to prove: {X(w)}? {X(w’)}={T},w≠ w’ The subgroup {X (w)} plays a prominent role in mechanism design. This subgroup bines spatial translation with rotation about a movable axis which remains parallel to given direction w , well defined by the unit vector w. Physical implementations of {X(w)} mechanical liaisons can be obtained by ordering in series kinematics pairs represented by subgroups of {X(w)}. Practically only prismatic pair and a revolute pair P, R, H are use to 22 build robots (the cylindric pair C bines in a pact way a prismatic pair and a revolute pair). A plete list of all possible binations of these kinematics pairs generating the {X (w)} subgroup is given in [6]. Two geometrical conditions have to be satisfied in the series: the rotation axes and the screw axes are parallel to the given vector w。 there is no passive mobility. The displacement operator for the {X {w}} subgroup, acting on point M is: M → N + ａ u + bv + cw +exp(hw^) N M ^ is the symbol of the vector product. Point N and the vectors u, v, w make up an orthogonal frame of reference in the space and a, b, c, h are the four parameters of the subgroup which has the dimension 4. Parallel robots for spatial translation To produce spatial translation it is sufficient to place two mechanical generators of the subgroups {X(w)} and {X(w’)},w≠ w’, in parallel, between a mobile platform and a fixed motors then three generators of the three subgroups {X(w)},{X(w’)},{X(w’’)},w≠ w’, is needed. Any series of P, R or H pairs which constitute a mechanical generator of the {X (w)} subgroup can be implemented. Morever, these three mechanical generators may be different or the same depending on the desired kinematics results. This wide range of binations gives rise to an entire family of robots capable of spatial translation. Simulation of the most interesting architectures can easily be achieved and the choice of the robot to be constructed can therefore meet the needs of the missioner. Clavel’s Delta robot belongs to this family as it is based on the same kinematics principles [7]. The parallel manipulator YSTAR STAR [16] is made up by three cooperating arms which generate the subgroups {X (u)}, {X (u’)}, {X(u’’)}, (fig 1). The three arms are identical and each one generates a subgroup {X(u)} by the series RHPaR where Pa represents the circular translation liaison determined by the two opposite bars of a planar hinged parallelogram. The axes of the two revolute pairs and of the screw pair must be parallel in order to generate a {X (u)}, subgroup. For each arm, the first two pairs, . the coaxial revolute pair and the screw pair, constitute the fixed part of the robot and form at the same time the mechanical structure of an axes lie on the same plane and divide it into three identical parts thus forming a Y shape. Hence the angle between any two axes is always 2? /3. The mobile part of the robot is made up by three PaR series that all converge to a mon point below which the mobile platform is located. The platform stays parallel to the reference plane and cannot rotate about the axis perpendicular to this plane. Any kind of appropriate end effectors can be placed on this mobile platform. The derivation of the {T} subgroup, which proves the mobile platform can only translate in the space, is given in [8]. 23 The H – Robot For a great majority of parallel robots including the Delta Robot and the Y Star, the working volume of the end effectors is small relative to the bulkiness of the whole device. It is the essential drawback of such a kind of manipulator. In order to avoid this native narrowness of the working volume, it can be imagine to implement three input electric jacks with three parallel axes instead of converging axes. Three arms similar to those of the Y Star cannot be employed: the intersection set of three equal set {X (v)} will be equal to {X (v)} instead of {T}. Hence, designing the new HRobot [16], we have chosen two arms of the Y Star type and a third pattern which may be pared with the Delta arms. This third mechanism begins from the fixed frame with a motorized prismatic pair parallel to the first two electric jacks. It is followed by a hinged planar parallelogram which is free to rotate around an axis perpendicular to the P pair thanks to a bar of the parallelogram. The opposite bar is connected to the mobile platform via a revolute pair R of parallel axis. This property is maintained when the parallelogram changes of shape (with one degree of freedom). In a first prototype built at “IUT de Ville D’Avray ”(France) by a team a students directed by the professor Pastor233。, a HRobot implements 3 systems screws (1) / nut (2) with a large pitch , which allow rapid movements. It is hold by bearings (6) and animated by the actuators M. Three planar hinged parallelograms, on both sides (4) and at the center (5) make the connection from the nuts to the horizontal platform (3). The stand (7) supports the whole structure (fig 2). The side screws permit rotation and translation along their axes. The central nut does not allow the rotation of the parallelogram plane about the screw axis. The mobile platform can only translate with 3 degrees of freedom inside the working space which may be assimilated to a halfcylinder. The main advantage of this device is that the working volume is directly