二自由度機器人的結構設計與仿真畢業論文-資料下載頁

　　

【正文】 consists of three revolute pairs and two prismatic joints, in which the prismatic joints are usually actuated. The output of the robot is the translational motion of a point on the endeffector. This means the orientation of the end effector is also changed at any moment. Accordingly, some versions of the 2DOF translational parallel robot (TPR) have been disclosed. One of them has been applied in precise pick amp。 place operations at high speed at SFB in German, In 2001, another 2DOF TPR has been proposed for the conceptual design of a 5axis machine tool, The structure, kinematics and dynamics of the TPR were discussed in de tail, Recently, a 2DOF TPR with revolute actuators was introduced^. The TPR presented in Ref. [4] has been used in the design of a planer machine tool with a gantry structure instead of a traditional one with serial chains to improve its stiffness and inertia characteristics. However* all of these TPRs consist of at least of one parallelogram, which increases the difficulty of manufacturing and affects the accuracy.This paper introduces a novel planar translational parallel robot with simple kinematic structure. The robot can position an objective with constant orientation. Some kinematic problems, such as inverse and forward kinematics, workspace and singularity are discussed.1 Description of the 2DOF TPR and its topological architectures Architecture descriptionThe novel 2DOF translational parallel robot and its schematic are shown in Fig. 1. The endeffector of the robot is connected to the base by two kinematic legs 1 and 2. Leg 1 consists of three revolute joints and leg 2 two revolute joints and one cylinder joint, or three re volute joints and one prismatic joint In each leg, the re volute joints are parallel to each other. The axes of the revolute joints in leg 1 are normal to those of the joints in leg 2. The two joints attached to the endeffector are put in the adjacent sides of a square. The kinematic chain of the robot is denoted as RRRRRC (Ccylinder joint) or RRRRRRP, One may see that, if the P joint is fixed, the robot is actually the famous Sarrus mechanism.As introduced previously，other TPRs have at least one parallelogram in their structures. The TPR proposed here has no parallelogram. This makes the manufacturing easier. However, pared with the TPRs presented in Refs. [9,10]，the TPR studied here has some disadvantages. For example, the performance of the new TPR is not symmetric in its workspace. Additionally, the new TPR is likely to need more occupying space.(a) the CAD model (b) the schematic The 2DOF translational parallel robot CapabilityHere, an expression like is used to describe the capability of an object j. In , and express the translation and rotation of the object, respectively. If an element in is equal to 0, there is no such a translation or rotation. If it is equal to 1, there is the capability. For example, means that the object has no translation along the xaxis。 indicates that the object can rotate about the yaxis.Observing only leg 1, the capability of the endeffector in the leg can be expressed as . Letting leg 1 alone, the capability of the endeffector with leg 2 can be written as Then, the intersection of and is ， i. e, (1)which describes the capability of the robot, ., the translations of the endeffector along the x and y axes. This means the endeffector has two purely translational degrees of freedom with respect to the base.It is noteworthy that the capability analysis method used above cannot be applied to all parallel robots.2 Kinematics analysis Inverse kinematicsAs illustrated in Fig. 1(b), a reference frame :Oxy is fixed to the base at the joint point and a moving reference frame ： is attached to the endeffector, where is the reference point on the endeffector. Vectors are defined as the position vectors of points in the frame ，and vectors as the position vectors of points in frame .The geometric parameters of the robot are ，，，and the distance from point to the guideway is ,where and and are dimensional parameters, and and nondimensional parameters. The position of point in the fixed frame is denoted as vector (2)The vectors of in the fixed frame can be written as (3)where is the actuated input for leg 1. Vector in the fixed frame can be written as (4)The inverse kinematics problem of leg 1 can be solved by writing the following constraint equation (5)that is (6)Then, there is (7)where (8)For leg 2，it is obvious thats = x (9)in which s is the input of leg 2. From Eqs. (8) and (9), we can see that there are two solutions for the inverse kinematics of the robot. Hence, for a given robot and for prescribed values of the position of the endeffector, the required actuated inputs can be directly puted from Eqs. (7) and (9). To obtain the configuration as shown in Fig. 1, parameter a in Eq. (8) should be 1. This configuration is called the “ + ” working mode. When , the corresponding configuration is referred to as the “一” working mode. Forward kinematicsThe forward kinematic problem is to obtain the output with respect to a set of given inputs. From Eqs. (6) and (9),one obtains (11)andx = s (12)where and . Therefore , there are also two forward kinematic solutions for the robot. The parameter corresponds to the configuration shown in Fig. 1, which is denoted as the downconfiguration. When the configuration is referred to as the upconfiguration. These two kinds of configurations correspond to two kinds of assembly modes of the robot.3 Singularity analysis4 Workspace analysis5 Conclusion and future workIn this paper , a novel 2DOF translational robot is proposed. One characteristic of the robot is that it can position a rigid body in a 2D plane while maintaining a constant orientation. The proposed robot has potential application in light in