工业机器人-第八章-机器人机械设计

1、机器人系统的组成大体可分为以下几个部分： 1 本体 2 执行器 3 传感器 4 驱动器 5 控制器,1. 自由度的数目 机器人的自由度数目应该与所完成的任务相匹配，并不是在完成任何任务时，机器人都需要6个自由度. 1) 大多数情况下，末端执行器均具有 一个对称轴,2) 末端执行器具有对称轴，可以减少自由度 3) 在一些任务中，当由主动定位装置来放置零件时则可以使用少于6个自由度的机器人,4) 很多任务都可以在少于6个自由度的情况下完成 Placement of components on circuit bourds provides a common example of this. Circuit boards generally are planar and contain parts of various heights. Positioning parts on a planar surface requires three degrees of freedom ( ); in order to lift and insert the parts, a fourth moti

2、on normal to the plane is added ( ).,2. 工作空间 工作任务的规模决定了需要的工作空间. 避免自身干涉. 避免执行器与周围发生碰撞.,3. 速度: 一个明显的目标是使操作臂具有越来越高的速度. 高速度提供了明显的竞争优势，比人工劳动具有经济竞争力. 速度大小由操作性质决定，而不是操作臂本身限制了速度，例如焊接机器人. 加速能力也非常重要.,4. 负载能力 负载能力与操作臂的结构尺寸、动力传递系统和驱动器有关. 5. 重复精度和定位精度 机器人的精度与其制造的具体过程有关，而不在于操作臂的设计。,一旦所需要的自由度确定之后，必须合理布置各个关节来实现这些自由度. 1、关节数目等于要求的自由度数目 2、大多数采用最后n-3个关节的腕部结构来确定姿态，而前三个关节来确定位置 3、也存在其他一些具有封闭运动学解的构形。 .,1. 笛卡尔操作臂 Joint 1 through 3 are prismatic, mutually orthogonal. -The inverse kinematic solution is trivial, and preven

3、ts kinematic singularities. -Produces robots with very stiff structures. Very large robots can be built, But retrofitting into existing workcells extremely difficult.,铰接型操作臂 关节1-关节3都是移动副，且互相垂直，自然解耦.,SCARA 操作臂 SCARA构形具有三个平行的旋转关节，第四个移动关节可以使得执行器垂直于该平面. 前三个关节不必支撑操作臂或负载的任何重量. 便于在连杆0中固定前两个关节的驱动器，从而使得机器人快速移动.,球面坐标操作臂 Has many similarities to the articulated manipulator, but with the elbow joint replaced by a prismatic joint. This design is better suited to some applications than is the elbow design. Th

4、e link that moves prismatically might telescopeor even “stick out the back” when retracted.,Unimate,圆柱面坐标型操作臂 一个使手臂竖直运动的移动关节和一个带有竖直轴的旋转关节组成，另一个移动关节与旋转关节的轴正交.,Verstran,仿生构形,仿生构形,腕关节 最常见的腕关节构形由两个或三个正交的旋转关节组成，第一个腕关节通常是操作臂的第四个关节.,实际中很难制作出这种三轴正交且不受关节角度限制的腕关节. 辛辛那提制造的许多机器人采用另一种方法，腕关节采用由三个相交但不垂直的轴构成.,有一些工业机器人的腕关节没有相交轴，如果将腕关节安装在铰接型操作臂上，那么它的第四个关节轴与第二个、三个关节轴平行，这时可以得到一个封闭形式的运动学解。,2. 工作空间属性的定量测量 操作臂设计者提出了几种有效的关于各种工作空间属性的定量测量方法. 按照生成工作空间设计的效果 制造笛卡尔操作臂比制作铰接型操作臂要消耗更多的材料. -定义操作臂的长度和: -定义结构长度指标,Hence, attempts t

5、o index the relative amount of structure (linkage length) required by different configurations to generate a given work volume. Good design: a manipulator with a small length sum nonetheless possessed a large workspace volume. Good design have a low . -Cartesian manipulator: the value of is minimized when all three joints have the same length of travel: . -Articulated manipulator: . In any real manipulator structure, the figure just given would be made somewhat larger by the effect of joint limi

6、ts in reducing the workspace volume.,设计良好条件的工作空间 在奇异点处，操作臂会失去一个或者多个自由度，所以在该位置某些任务将无法完成. 操作臂离奇异点越远，操作臂越能均匀地在各个方向上移动和施力。. 奇异位型由下式给出:,可操作度被定义为: 对于非冗余操作臂: . 的值越大，其灵巧工作空间越大，该操作臂的设计则越好。,把笛卡尔质量矩阵的特征根作为评判操作臂在各个笛卡尔方向的加速能力的方法： n维椭球方程：,冗余机构 更多的可控关节会带来一定好处. 微操作臂安装在传统操作臂末端，负责较小范围的精细与力的控制. 冗余机器人可以以无穷方式到达期望位姿，以免因障碍影响路径的选择.,闭链机构 很多操作臂具有闭链机构,1. 驱动器布局 直接驱动 减速系统.,2. 减速和传动系统 1) 齿轮: 平行轴、正交轴、倾斜轴 间隙、摩擦、传动比,2) 柔性带、钢缆、皮带:,3) 普通丝杠和滚珠丝杠,1) 并联和串联的柔性元件 并联: 串联: 2) 轴:,3) 齿轮: where is the face width of the gears, is the radius

7、 of the output gear, and for steel. Gearing also has the effect of changing the effective stiffness of the drive system by a factor of . Hence, a gear reduction has the effect of increasing the stiffness by the squre of the gear ratio.,4) 带: where is the cross-sectional area of the belt, is the modulus of elasticity of the belt, and is the length of the free belt between pulleys plus one-third of the length of the belt in contact with the pulleys. 5)连杆: we might model a single link as a cantilev

8、er beam and calculate the stiffness at the end point. For a round hollow beam, the stiffness is given by: where and are the inner and outer diameters of the tubular beam, is the length, and E is the modulus of elasticity( about for steel ).,For a square-cross-section hollow beam: where and are the outer and inner widths of the beam(i.e. the wall thickness is ).,Example: A square-cross-section link of dimensions 5*5*50 cm with a thickness of 1 cm is driven by a set of rigid gears with , and the i

9、nput of the gears is driven by a shaft having diameter 0.5 cm and length 30 cm. What deflection is caused by a force of 100 Nt at the end of the link?,The stiffness of the link: For a load of 100 Nt, the deflection in the link itself: Additionally, 100Nt at the end of a 50-cm link is placing a torque of 50 Nt-m on the output gear. The gear are rigid, but the flexibility of the input shaft is:,which, viewed from the output gear: Loading with 50 Nt-m causes an angular deflection of: so the total linear deflection at the tip of link is:,We have examined some simple formulas for estimating the stiffness. They are meant to give some guidance in sizing structural members and transmission elements. In practical applications, many sources of flecxibility are very difficult to model. Finite-element techniques can be used to predict the stiffness of more realistic structural element

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