The Research on a 3D Dual-Arm Flexible Manipulator

English/Japanese

The research on flexible manipulators extends to various fields like modeling, vibration suppression control, inverse dynamics and force control etc. If the tasks of a flexible manipulator are thought as a space robot, there exist many tasks like inserting connectors, opening and closing the panels etc., demanding force control. Moreover, in case of rigid manipulators, the end-effector position errors give rise to excessive forces between the environment and manipulator, while in the case of flexible manipulators, due to elasticity of the links, the forces get absorbed and it is not possible to generate excessive forces.

Besides this, the practical manipulators of these days are almost all single-armed. However in the transportation of heavy and big objects, or in the assembly of components, the task execution efficiency can be improved by using two arms.

We developed the Aerospace Dual-Arm Manipulator (ADAM), that has 2 flexible links and 7 joints in each arm [1], and conducted research on the force control of a flexible manipulator and the cooperative control of two arms. In the whole world, there is no other example of such a 3-dimensional, multiple degree of freedom dual flexible arms manipulator. The overview of the experimental setup ADAM is shown in Fig. 1.

Fig. 1 Overview of ADAM.

To realize complicated and advanced tasks with a manipulator, not only the end-effector position but also the force being exerted on the object need to be controlled. Therefore, we proposed the model of a 3D flexible manipulator constrained by the environment using the lumped mass and spring modeling method. Moreover, based on this model, we constructed a hybrid law to control for the position and force of the flexible manipulator [2],[3].

Besides this, as an attempt to utilize the mechanical compliance of the elastic arm, a control was realized without force/torque sensor [4], the analysis and control of this mechanical compliance were also performed.

Fig. 2 gives a look of a hard planar surface tracking task with ADAM.

Fig. 2 Hard planar surface tracking task.

Uchiyama et al. analyzed the static relation between two robots holding an object, introducing the concept of a virtual stick, and defined a generalized force vector including external and internal forces and moments. Then, using the principle of virtual work, they derived a generalized velocity vector including the absolute velocity of the object and the relative velocity between the tips of the virtual sticks [5]-[9]. The concept of the virtual stick is described in Fig. 3.

Fig. 3 Object handling with dual arms.


Fig. 4 Dual-arm cooperative control scheme.


We applied this concept of the virtual stick to the experimental setup ADAM and built a dual-arm cooperative control scheme shown in Fig. 4. With this control scheme, we have been able to realize the object transportation task while suppressing the vibrations of the flexible arms [10],[11],[14]. Reference and current values of the absolute positions/orientations and the internal forces/moments are shown in Fig. 5 and Fig. 6. Desired internal forces are [0 N   30 N   0 N   0 Nm   0 Nm   -0.7 Nm].


Fig. 5 Absolute positions/orientations.


Fig. 6 Internal forces/moments.


The experimental setup ADAM has two arms. For an object manipulation by two arms, twelve DOFs are sufficient to control the absolute object position/orientation and for the development of the internal forces/moments. ADAM does have a redundancy. Two different approaches were introduced to solve the kinematics of a two-arm flexible manipulator with redundancy. The first approach was a gradient-projection method that utilizes a Moore-Penrose inverse of the manipulator Jacobian matrix. The second approach was the popular elbow control of the anthropomorphic arms. These approaches were originally proposed for a single-arm redundant manipulators, and were straightforwardly extended for a two-arm flexible redundant manipulator system. In the experiments, the resulting mechanical compliance at the end-effector of each arm was applied as the performance criterion, and was minimized to accomplish a robust handling [13]. Fig. 7 shows the movie of an object transportation using redundancy of the experimental setup ADAM.


Fig. 7 Redundancy resolution of a two-arm flexible manipulator.

Movie [mpg] (6.3 MB)


Moreover, we also executed an object capture task to simulate the capture of a satellite in space. In the case of capturing a spinning object, two end-effectors synchronized with the object around the rotational axis, and came in contact with the object at the same time. Therefore, the spinning object was braked surely [12]. For a case of retrieving a free floating object, the visual servoing was applied for the relative positioning between the end-effector and the surface of the object. Furthermore, the object capture task was executed in the optimal configuration, in which the resulting compliance of each arm was minimized, and the quick convergence to the reference internal forces was then accomplished [15]. Fig. 8 and Fig. 9 give movies of an object capturing task with the experimental setup ADAM.


Fig. 8 Experiment of capturing a spinning object.

Movie [mpg] (4.5 MB)



Fig. 9 Experiment of capturing a free floating object.

Movie [mpg] (9.2 MB)




References

  1. M. Uchiyama, A. Konno, T. Uchiyama, and S. Kanda: Development of a flexible dual-arm manipulator tested for space robotics, Proceedings of IEEE International Workshop on Intelligent Robots and System, (1990), 375-381.
  2. Jin-Soo Kim, Kuniaki Suzuki, Atsushi Konno and Masaru Uchiyama: Force Control of Constrained Flexible Manipulators, Proceedings of the 1996 IEEE International Conference on Robotics and Automation, Minneapolis, Minnesota, USA, (1996/4), 635-640.
  3. Jin-Soo Kim, Kuniaki Suzuki, Mitsuhiro Yamano and Masaru Uchiyama: Vibration Suppression Control of Constrained Spatial Flexible Manipulators, Proceedings of the 1997 IEEE International Conference on Robotics and Automation, Albuquerque, New Mexico, USA, (1997/4), 2831-2837.
  4. Jin-Soo Kim, Kuniaki Suzuki and Masaru Uchiyama: Force Control of a Flexible Manipulator Based on the Measurement of Link Deflections, Proceedings of the 1996 IEEE/RSJ International Conference on Intelligent Robots and Systems, Osaka, Japan, (1996/11), 238-245.
  5. Masaru Uchiyama and Pierre Dauchez: Statics, Kinematics, and Hybrid Control Scheme for a Two Arm Robot, Proceedings of the IASTED International Symposium Robotics and Automation, Santa Barbara, (1987-5), 28-32.
  6. Pierre Dauchez and Masaru Uchiyama: Kinematic Formulation for Two Force-Controlled Cooperating Robots, Proceedings of the 3rd International Conference on Advanced Robotics, Versailles, (1987-10), 457-467.
  7. Masaru Uchiyama and Pierre Dauchez: A Symmetric Hybrid Position/Force Control Scheme for the Coordination of Two Robots, Proceedings of the 1988 IEEE International Conference on Robotics and Automation, Philadelphia, (1988-4), 350-356.
  8. Masaru Uchiyama: A Unified Approach to Load Sharing, Motion Decomposing, and Force Sensing of Dual Arm Robots, Robotics Research: The Fifth International Symposium, Edited by Hirofumi Miura and Suguru Arimoto, The MIT Press, (1990), 225-232.
  9. MASARU UCHIYAMA and PIERRE DAUCHEZ: Symmetric kinematic formulation and non-master/slave coordinated control of two-arm robots, ADVANCED ROBOTICS: The International Journal of the Robotics Society of Japan, 7-4 (1993), 361-383.
  10. Mitsuhiro Yamano, Jin-Soo Kim and Masaru Uchiyama: Hybrid Position/Force Control of Two Cooperative Flexible Manipulators Working in 3D Space, Proceedings of the 1998 IEEE International Conference on Robotics and Automation, Leuven, Belgium, (1998/5/16-20), 1110-1115.
  11. Mitsuhiro Yamano, Atsushi Konno and Masaru Uchiyama: Vibration Suppression Control of Two Cooperative Flexible Manipulators Working in 3D Space, Proceedings of the Ninth International Conference on Advanced Robotics ('99 ICAR), Tokyo, Japan, (1999/10/25-27), 385-390.
  12. Mitsuhiro Yamano, Atsushi Konno, Masaru Uchiyama and Tomohiro Miyabe: Capturing a Spinning Object by Two Flexible Manipulators, Proceedings of the 2000 IEEE/RSJ International Conference on Intelligent Robots and Systems, Takamatsu, Japan, (2000/10/31-11/5), 2036-2041.
  13. Tomohiro Miyabe, Atsushi Konno and Masaru Uchiyama: Cooperative Control of a Two-Arm Flexible Manipulator with Redundancy, Proceedings of the 2002 IEEE/RSJ International Conference on Intelligent Robots and Systems, Lausanne, Switzerland, (2002/9/30-10/4), 2708-2713.
  14. MITSUHIRO YAMANO, JIN-SOO KIM, ATSUSHI KONNO and MASARU UCHIYAMA: Cooperative Control of a 3D Dual-Flexible-Arm Robot, Journal of Intelligent and Robotic Systems, 39-1 (2004/1), 1-15.
  15. Tomohiro Miyabe, Atsushi Konno, Masaru Uchiyama and Mitsuhiro Yamano: An Approach Toward an Automated Object Retrieval Operation with a Two-Arm Flexible Manipulator, The International Journal of Robotics Research, 23-3, (2004/3), 275-291.


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