Lasky, T.A., Hsia, T.C., Tummala, R L, Odrey, N.G. Robotics The Electrical Engineering Handbook Ed. Richard C. Dorf Boca raton crc Press llc. 2000
Lasky, T.A., Hsia, T.C., Tummala, R.L., Odrey, N.G. “Robotics” The Electrical Engineering Handbook Ed. Richard C. Dorf Boca Raton: CRC Press LLC, 2000
10l Robotics Cartesian Configuration . C Ty A. Lasky Configuration. Articulated Configurati Configuration. Gantry Configuratio 101.2 Dynamics and Control Independent Joint Control of the Robot. Dynamic Models iversity of California, Dav omputed Torque Methods. Adaptive Control. Resolved R Lal tummala Motion Control. Compliant Motion. Flexible Manipulators Justification. Implementation Strategies. Applications in Nicholas G. Drey Manufacturing. Emerging Iss 101.1 Robot Configuration Ty A. Lasky and Tien C. hsia Configuration is a fundamental classification for industrial robots. Configuration refers to the geometry of the robot manipulator, i.e., the manner in which the links of the manipulator are connected at each joint. The Robotic Industries Association(RIA) defines a robot as a manipulator designed to move material, parts, tools, or specialized devices, through variable programmed motions for the perfo rmance or a riety of tasks. With this finition, attention here is focused on industrial manipulator arms, typically mounted on a fixed pedestal base. Mobile robots and hard automation [ e.g., Computer Numerical Control( CNC)machines] are excluded The emphasis here is on serial-chain manipulator arms, which consist of a serial chain of linkages, where each link is connected to exactly two other links, with the exception of the first and last, which are connected to only one other link. Additionally, the first three links, called the major linkages, are focused on, with only a brief mention of the last three links, or wrist joints, also called the minor linkages Robot configuration is an important consideration in the selection of a manipulator. Configuration refers to the way the manipulator links are connected at each joint. Each link will be connected to the subsequent link by either a linear(sliding or prismatic) joint, which can be abbreviated with a P, or a revolute (or rotary) int,abbreviated with an R. Using this notation, a robot with three revolute joints would be abbreviated as RRR, while one with a rotary joint followed by two linear (prismatic) joints would be denoted RPP. Each configuration type is well suited to certain types of tasks and ill suited to others. Some configurations are more versatile than others. In addition to the geometrical considerations, robot configuration affects the structural stiffness of the robot, which may be an important consideration. Also, configuration impacts the complexity the forward and inverse kinematics, which are the mappings between the robot actuator (joint)space, and the Cartesian position and orientation of the robot end-effector, or tool. There are six major robot configurations commonly used in industry. Details for each configuration are presented in subsequent subsections. The simplest configuration is the Cartesian robot, which consists of three rthogonal, linear joints(PPP), so that the robot moves in the x, y and z directions in the joint space. The c 2000 by CRC Press LLC
© 2000 by CRC Press LLC 101 Robotics 101.1 Robot Configuration Cartesian Configuration • Cylindrical Configuration • Spherical Configuration • Articulated Configuration • SCARA Configuration • Gantry Configuration • Additional Information 101.2 Dynamics and Control Independent Joint Control of the Robot • Dynamic Models • Computed Torque Methods • Adaptive Control • Resolved Motion Control • Compliant Motion • Flexible Manipulators 101.3 Applications Justification • Implementation Strategies • Applications in Manufacturing • Emerging Issues 101.1 Robot Configuration Ty A. Lasky and Tien C. Hsia Configuration is a fundamental classification for industrial robots. Configuration refers to the geometry of the robot manipulator, i.e., the manner in which the links of the manipulator are connected at each joint. The Robotic Industries Association (RIA) defines a robot as a manipulator designed to move material, parts, tools, or specialized devices, through variable programmed motions for the performance of a variety of tasks. With this definition, attention here is focused on industrial manipulator arms, typically mounted on a fixed pedestal base. Mobile robots and hard automation [e.g., Computer Numerical Control (CNC) machines] are excluded. The emphasis here is on serial-chain manipulator arms, which consist of a serial chain of linkages, where each link is connected to exactly two other links, with the exception of the first and last, which are connected to only one other link. Additionally, the first three links, called the major linkages, are focused on, with only a brief mention of the last three links, or wrist joints, also called the minor linkages. Robot configuration is an important consideration in the selection of a manipulator. Configuration refers to the way the manipulator links are connected at each joint. Each link will be connected to the subsequent link by either a linear (sliding or prismatic) joint, which can be abbreviated with a P, or a revolute (or rotary) joint, abbreviated with an R. Using this notation, a robot with three revolute joints would be abbreviated as RRR, while one with a rotary joint followed by two linear (prismatic) joints would be denoted RPP. Each configuration type is well suited to certain types of tasks and ill suited to others. Some configurations are more versatile than others. In addition to the geometrical considerations, robot configuration affects the structural stiffness of the robot, which may be an important consideration. Also, configuration impacts the complexity of the forward and inverse kinematics, which are the mappings between the robot actuator (joint) space, and the Cartesian position and orientation of the robot end-effector, or tool. There are six major robot configurations commonly used in industry. Details for each configuration are presented in subsequent subsections. The simplest configuration is the Cartesian robot, which consists of three orthogonal, linear joints (PPP), so that the robot moves in the x, y, and z directions in the joint space. The Ty A. Lasky University of California, Davis Tien C. Hsia University of California, Davis R. Lal Tummala Michigan State University Nicholas G. Odrey Lehigh University
cylindrical configuration consists of one revolute and two linear TABLE 101.1 Robot Arm Geometry Usage coordinate system. The spherical configuration consists of two rev Percent of Use olute joints and one linear joint(RRP), so that the robot moves in Cartesian a spherical, or polar, coordinate system. The articulated(arm-and elbow) configuration consists of three revolute joints(RRR), giving Articulated 85025 the robot a somewhat human-like range of motion. The SCARA SCARA (Selectively Compliant Assembly Robot Arm) configuration con- sists of two revolute joints and one linear joint(RRP), arranged in York: Elsevier, 1988. With permission. different fashion than the spherical configuration. It may also be equipped with a revolute joint on the final sliding link. The gantry configuration is essentially a Cartesian configuration, with the robot mounted on an overhead track system. One can also mount other robot config urations on an overhead gantry system to give the robot an extended workspace, as well as free up valuable factory floor space. The percentage usage of the first five configuration types is listed in Table 101.1. This table does not include gantry robots, which are assumed to be included in the Cartesian category. Additionally, this information is from 1988, and does not accurately represent current usage In general, robots with a rotary base have a speed advantage. However, they have more variation in resolution and dynamics compared to Cartesian robots. This can lead to inferior performance if a fixed controller is used over the robot's entire workspace. Cartesian Configuration The Cartesian configuration consists of three orthogonal, axes, abbreviated as PPP, as shown in Fig. 101.1. Thus, the space of the robot corresponds directly with the standard right handed Cartesian xyz-coordinate system, yielding the simplest possible kinematic equations. The work envelope of the Carte sian robot is shown in Fig. 101.2. The work envelope encloses all the points that can be reached by the robot arm or the mounting point for the end-effector or tool. The area reachable by an end effector or tool is not considered part of the work envelope interaction with other machines, parts, or processes must take of a robot is assumed to be equivalent to the work envelope. There are several advantages to this configuration. As noted above, the robot is kinematically simple, since motion on each Cartesian axis corresponds to motion of a single actuator. This eases the programming of linear motions. In particular, it is easy to do a straight vertical motion, the most common motion in assembly tasks. The Cartesian geometry also yields a constant FIGURE 101.1 The Cartesian configuration arm resolution throughout the workspace; i.e., for any config ( Source: T. Owen, Assembly with Robots, Engle ration, the resolution for each axis corresponds directly to the wood Cliffs, N. Prentice-Hall, 1985. with per- resolution for that joint. The simple geometry of the Cartesian robot leads to correspondingly simple manipulator dynamics. The disadvantages of this configuration include inability to reach objects on the floor or points invisible from the base of the robot, and slow speed of operation in the horizontal plane compared to robots with a rotary base. Additionally, the Cartesian configuration requires a large operating volume for a relatively small workspace. Cartesian robots are used for several applications. As noted above, they are well suited for assembly opera- tions, as they easily perform vertical straight-line insertions. Because of the ease of straight-line motions, they are also well suited to machine loading and unloading. They are also used in clean room tasks c 2000 by CRC Press LLC
© 2000 by CRC Press LLC cylindrical configuration consists of one revolute and two linear joints (RPP), so that the robot joints correspond to a cylindrical coordinate system. The spherical configuration consists of two revolute joints and one linear joint (RRP), so that the robot moves in a spherical, or polar, coordinate system. The articulated (arm-andelbow) configuration consists of three revolute joints (RRR), giving the robot a somewhat human-like range of motion. The SCARA (Selectively Compliant Assembly Robot Arm) configuration consists of two revolute joints and one linear joint (RRP), arranged in a different fashion than the spherical configuration. It may also be equipped with a revolute joint on the final sliding link. The gantry configuration is essentially a Cartesian configuration, with the robot mounted on an overhead track system. One can also mount other robot configurations on an overhead gantry system to give the robot an extended workspace, as well as free up valuable factory floor space. The percentage usage of the first five configuration types is listed in Table 101.1. This table does not include gantry robots, which are assumed to be included in the Cartesian category. Additionally, this information is from 1988, and does not accurately represent current usage. In general,robots with a rotary base have a speed advantage. However, they have more variation in resolution and dynamics compared to Cartesian robots. This can lead to inferior performance if a fixed controller is used over the robot’s entire workspace. Cartesian Configuration The Cartesian configuration consists of three orthogonal, linear axes, abbreviated as PPP, as shown in Fig. 101.1. Thus, the joint space of the robot corresponds directly with the standard righthanded Cartesian xyz-coordinate system, yielding the simplest possible kinematic equations. The work envelope of the Cartesian robot is shown in Fig. 101.2. The work envelope encloses all the points that can be reached by the robot arm or the mounting point for the end-effector or tool. The area reachable by an end effector or tool is not considered part of the work envelope. All interaction with other machines, parts, or processes must take place within this volume [Critchlow, 1985]. Here, the workspace of a robot is assumed to be equivalent to the work envelope. There are several advantages to this configuration. As noted above, the robot is kinematically simple, since motion on each Cartesian axis corresponds to motion of a single actuator. This eases the programming of linear motions. In particular, it is easy to do a straight vertical motion, the most common motion in assembly tasks. The Cartesian geometry also yields a constant arm resolution throughout the workspace; i.e., for any configuration, the resolution for each axis corresponds directly to the resolution for that joint. The simple geometry of the Cartesian robot leads to correspondingly simple manipulator dynamics. The disadvantages of this configuration include inability to reach objects on the floor or points invisible from the base of the robot, and slow speed of operation in the horizontal plane compared to robots with a rotary base.Additionally, the Cartesian configuration requires a large operating volume for a relatively small workspace. Cartesian robots are used for several applications. As noted above, they are well suited for assembly operations, as they easily perform vertical straight-line insertions. Because of the ease of straight-line motions, they are also well suited to machine loading and unloading. They are also used in clean room tasks. FIGURE 101.1 The Cartesian configuration. (Source: T. Owen, Assembly with Robots, Englewood Cliffs, N.J.: Prentice-Hall, 1985. With permission.) TABLE 101.1 Robot Arm Geometry Usage Arm Geometry Percent of Use Cartesian 18 Cylindrical 15 Spherical 10 Articulated 42 SCARA 15 Source: V. D. Hunt, Robotics Sourcebook, New York: Elsevier, 1988. With permission
FIGURE 101.2 Cartesian robot work envelope. Cylindrical Configuration The cylindrical configuration consists of one vertical revolute joint and two orthogonal linear joints(RPP), as shown in Fig. 101.3. The resulting work envelope of the robot is a cylindrical annulus, as shown in ation responds with the cylindrical coordi- nate system. As with the Cartesian robot, the cylindrical robot is well suited for traight-line vertical and horizontal motions, so it is useful for assembly and machine loading operations. It is capable of higher speeds in the horizontal plane due to the rotary base. However, general horizontal straight-line motion is more complex and correspondingly more diffi cult to coordinate. Additionally, the end-point resolution of the cylin- drical robot is not constant but depends on the extension of the horizontal linkage. A cylindrical robot cannot reach around obstacles Additionally, if a monomast construction is used on the horizontal linkage, then there can be clearance problems behind the robot. Spherical Configuration The spherical (or polar)configuration consists of two revolute joints FIGURE 101.3 The cylindrical cor and one linear joint(RRP), as shown in Fig. 101.5. This results in a set figuration.(Source: T Owen, Assembly of joint coordinates that matches with the spherical coordinate syster th Robots, Englewood Cliffs, N. A typical work envelope for a spherical robot is shown in Fig. 101.6. Prentice-Hall, 1985. With permission.) FIGURE 101.4 Cylindrical robot work envelo e 2000 by CRC Press LLC
© 2000 by CRC Press LLC Cylindrical Configuration The cylindrical configuration consists of one vertical revolute joint and two orthogonal linear joints (RPP), as shown in Fig. 101.3. The resulting work envelope of the robot is a cylindrical annulus, as shown in Fig. 101.4. This configuration corresponds with the cylindrical coordinate system. As with the Cartesian robot, the cylindrical robot is well suited for straight-line vertical and horizontal motions, so it is useful for assembly and machine loading operations. It is capable of higher speeds in the horizontal plane due to the rotary base. However, general horizontal straight-line motion is more complex and correspondingly more diffi- cult to coordinate. Additionally, the end-point resolution of the cylindrical robot is not constant but depends on the extension of the horizontal linkage. A cylindrical robot cannot reach around obstacles. Additionally, if a monomast construction is used on the horizontal linkage, then there can be clearance problems behind the robot. Spherical Configuration The spherical (or polar) configuration consists of two revolute joints and one linear joint (RRP), as shown in Fig. 101.5. This results in a set of joint coordinates that matches with the spherical coordinate system. A typical work envelope for a spherical robot is shown in Fig. 101.6. FIGURE 101.2 Cartesian robot work envelope. FIGURE 101.4 Cylindrical robot work envelope. Ymax Ymin Xmin Xmax Z max Z min FIGURE 101.3 The cylindrical con- figuration. (Source: T. Owen, Assembly with Robots, Englewood Cliffs, N.J.: Prentice-Hall, 1985. With permission.) Z max Ymax Ymin Z min Xmax Xmin 0˚
FIGURE 101.5 The spherical configuration. (Source: T. Owen, Assembly with Robots, Englewood Cliffs, N J. Prentice-Hall 1985. With permission. FIGURE 101.6 Spherical robot work envelope. Spherical robots are typically heavy-duty robots. They have the advan- tages of high speed due to the rotary base, and a large work volume, but are more kinematically complex than either Cartesian or cylindrical robots. Generally, they are used for heavy-duty tasks in, for example, automobile manufacturing. They do not have the dexterity to reach around obstacles in the workspace. Spherical robots also do not have fixed resolution throughout the workspace. Articulated Configuration The articulated (or anthropomorphic, jointed, arm-and-elbow)configu- ration consists of three revolute joints(RRR), as shown in Fig. 101.7. The FIGURE 101.7 The articulated system. a slice of a typical work envelope for an articulated robot is shown figuration. Source: T. Owen in Fig. 101.8. The articulated robot is currently the most commonly used in research. Cliffs, N.J.: Prentice-Hall, 1985.With It has several advantages over other configurations. It is closest to dupli- permission. ting the motions of a human assembler, so there should be less need to redesign an existing workstation to utilize an articulated robot. It has a very large, dexterous work envelope; i.e., it can reach most points in its work envelope from a variety of orientations. Thus, it can more easily reach around or over obstacles in the workspace or into parts or machines. Because all the joints are revolute, high c 2000 by CRC Press LLC
© 2000 by CRC Press LLC Spherical robots are typically heavy-duty robots. They have the advantages of high speed due to the rotary base, and a large work volume, but are more kinematically complex than either Cartesian or cylindrical robots. Generally, they are used for heavy-duty tasks in, for example, automobile manufacturing. They do not have the dexterity to reach around obstacles in the workspace. Spherical robots also do not have fixed resolution throughout the workspace. Articulated Configuration The articulated (or anthropomorphic, jointed, arm-and-elbow) configuration consists of three revolute joints (RRR), as shown in Fig. 101.7. The resulting joint coordinates do not directly match any standard coordinate system. A slice of a typical work envelope for an articulated robot is shown in Fig. 101.8. The articulated robot is currently the most commonly used in research. It has several advantages over other configurations. It is closest to duplicating the motions of a human assembler, so there should be less need to redesign an existing workstation to utilize an articulated robot. It has a very large, dexterous work envelope; i.e., it can reach most points in its work envelope from a variety of orientations. Thus, it can more easily reach around or over obstacles in the workspace or into parts or machines. Because all the joints are revolute, high FIGURE 101.5 The spherical configuration. (Source: T. Owen, Assembly with Robots, Englewood Cliffs, N.J.: Prentice-Hall, 1985. With permission.) FIGURE 101.6 Spherical robot work envelope. Z max Ymax Ymin Z min Xmax Xmin 0˚ FIGURE 101.7 The articulated configuration. (Source: T. Owen, Assembly with Robots, Englewood Cliffs, N.J.: Prentice-Hall, 1985. With permission.)