Quick completion guide for manipulator (III): mechanical structure of manipulator

Directory ：

Quick completion guide of mechanical arm （ zero ）： Main contents and analysis methods of the guide

Quick completion guide of mechanical arm （ One ）： The development of manipulator

Quick completion guide of mechanical arm （ Two ）： Application of mechanical arm

         Matter is the basis , therefore , To figure out how the manipulator controls , You first need to know what's on the robot arm , What is the relationship between them , That is, the mechanical arm Mechanical structure and Core components .

        This chapter mainly introduces the mechanical structure of the manipulator .

One 、 summary

         The mechanical mechanism of the manipulator consists of a series of rigid members （ connecting rod ） Through the link （ The joints ） Connect , The manipulator is characterized in that it has the function of ensuring mobility arm （ arm ), Providing flexibility Wrist （ wrist ） And execute what the robot needs to accomplish
Mission End actuators （ end - effector ).
        The manipulator is divided into series manipulator and parallel manipulator . In the guide , Our main research is Serial manipulator .

Serial manipulator	Parallel manipulator

         The movement ability of the manipulator is guaranteed by the joints . Two adjacent links can be connected by moving the joint （ prismatic joint） Or rotate the joint （ revolute joint） Realization . In an open kinematic chain , Each moving or rotating joint provides a degree of freedom for the mechanical structure （ degrees of freedom , DOF ). Moving the joint can realize the relative translation between the two connecting rods , The rotary joint can realize the relative rotation between the two connecting rods （ Rotating joints are simpler and more reliable than moving joints ）. And in a closed kinematic chain , Constraints due to closed loop , The degree of freedom should be less than the number of joints .
         The degree of freedom must be reasonably arranged along the mechanical structure on the manipulator , To ensure that the system can have enough freedom to complete the specified task . Usually in a task of arbitrary positioning and orientation in three-dimensional space 6 A degree of freedom , among 3 Degrees of freedom are used to locate the target point , in addition 3 Degrees of freedom are used to orient the target point in the reference coordinate system . If the available degrees of freedom of the system exceed the number of variables in the task , From a kinematic point of view , The manipulator is redundant （ redundant ） Of .

Two 、 Serial manipulator

         In the mechanical hand , The task of the arm is to meet the positioning requirements of the wrist , Then the wrist can meet the orientation requirements of the end effector . Start at the base joint , It can be done according to the type and order of the arms , Divide the manipulator into Cartesian type （ Cartesian )、 Cylindrical （ cylindrical )、
Ball shape （ spherical ), SCARA Type and anthropomorphic （ anthropomorphic ） etc. .

Schematic diagram of structure and working space of different types of manipulator

a  Cartesian manipulator	b  Cylindrical manipulator
c  Spherical manipulator	d  SCARA Type a mechanical arm

1. Cartesian manipulator

         The geometric configuration of Cartesian manipulator is realized by three moving joints , Its characteristic is that its three axes are perpendicular to each other （ chart 1.2). From a geometric point of view , Each degree of freedom corresponds to a Cartesian space variable , Therefore, it is natural to complete linear motion in space . Cartesian structure can provide good mechanical rigidity . The positioning accuracy of the wrist in the workspace is constant everywhere . This is the workspace composed of cuboids , As shown in the figure above a Shown . Because all joints are moving joints , Therefore, the structure has high accuracy , But less flexible . To manipulate the target , Need to approach the target from the side . On the other hand , If you want to get close to the target from the top , Descartes manipulator can pass through gantry （ gantry ） Structure implementation , As shown in the figure below .

This structure can bring a large volume to the operation space , And it can operate the target with large volume and weight .
Cartesian manipulator is often used for grasping and assembling materials .

2. Cylindrical manipulator

         The difference between cylindrical manipulator and Cartesian manipulator lies in that the first moving joint is replaced by rotating joint . Cylindrical structure provides good mechanical stiffness , The positioning accuracy of the wrist is reduced , The horizontal movement ability is improved .

         The working space of cylindrical manipulator is a part of hollow cylinder . Because the cylindrical manipulator has a horizontal moving joint , The wrist of the cylindrical manipulator is suitable for operating the workpiece in the horizontal direction .

         meanwhile , Cylindrical manipulator is mainly used to transport large workpieces smoothly , In this case, it is more appropriate to use hydraulic drive than motor drive .

3. Spherical manipulator

        The difference between the spherical manipulator and the cylindrical manipulator is that the second moving joint is replaced by the rotating joint . The mechanical strength of spherical manipulator is lower than that of Cartesian manipulator and cylindrical manipulator , The mechanical structure is more complicated .

        The radial operation ability of the spherical manipulator is strong , Its workspace is part of a hollow sphere .

        The joints of spherical manipulators are usually driven by electric motors .

4.SCARE Mechanical arm

        World's first SCARE The manipulator is Yamanashi University, Japan （University of Yamanashi） Makino ocean （Hiroshi Makino） On 1978 From R & D in ,SCARA It is a compliant assembly robot arm （Selective Compliance Assembly Robot Arm） English abbreviations .

        SCARE The special mechanical structure of the manipulator makes all the moving axes parallel , This makes it highly stable for vertical operation and superior flexibility for horizontal loading .

        SCARE The manipulator is suitable for manipulating small targets , The joints are driven by electric motors .

5. Anthropomorphic manipulator

         The geometric configuration of humanoid manipulator is realized by three rotating joints . The rotation axis of the first joint is perpendicular to the rotation axis of the other two joints , The rotation axes of the other two joints are parallel , As shown in the figure below . Because its structure and function are similar to the human arm , Correspondingly, the second joint is called the shoulder joint , The third joint connects the arm and forearm , So it is called elbow joint . The structure of humanoid manipulator is the most flexible one , Because all its joints are rotational . On the other hand , There is no correspondence between the degrees of freedom of the humanoid manipulator and the Cartesian space variables , Therefore, the positioning accuracy of the wrist varies in the workspace . The workspace of the humanoid manipulator is similar to a part of the spherical space , Compared with its burden , The volume of the workspace is large . Its joints are usually driven by electric motors . Humanoid manipulator has a wide range of industrial applications .

  3、 ... and 、 Parallel manipulator