Robot manipulators have been widely used in industry to increase flexibility and productivity. Dynamics of a manipulator are described by a set of highly coupled nonlinear differential equations. The objective of this project is to develop high performance nonlinear control algorithms for the coordinated control of robot manipulators in various applications:
Tasks such as painting, welding and material handling, require the end-effector of a manipulator to move from one place to another in a free workspace. In order to meet increased productivity requirement as well as tight tolerance requirements, it is essential for the manipulator to follow a desired trajectory as closely as possible at fast speed. Two ARC algorithms are developed: adaptive sliding mode control (ASMC) is based on the sliding mode control (SMC) and the conventional adaptation law, in which the regressor uses actual state feedback; desired compensation ARC (DCARC) only uses the desired trajectory information in forming the regressor. In order to show the advantages and disadvantages of conceptually different adaptive and robust control algorithms, three different adaptive or robust control schemes are also derived for comparison: a simple nonlinear PID type robust control, a gain-based nonlinear PID type adaptive control, which requires no model information, and a combined parameter and gain-based adaptive robust control. All algorithms, as well as two benchmark adaptive schemes, are implemented and compared on a two-link direct drive robot. Real time control code is written in C language. Comparative experimental results show the importance of using both proper controller structure and parameter adaptation in designing high-performance controllers. It is observed that in these experiments the proposed DCARC achieves the best tracking performance without increasing the control bandwidth and the control effort.
Reference:
Bin Yao, M. Tomizuka, and J. Litherland, "Implementation issues and experimental studies of adaptive robust controllers for robot manipulators," Proc. of American Control Conference, pp2203-2205, 1998.
Bin Yao, "Adaptive robust control of robot manipulators: Theory and Comparative Experiments," The second CWC on ICIA, pp442-447, 1997.
Bin Yao and M. Tomizuka, "Smooth robust adaptive sliding mode control with guaranteed transient performance," Trans. of ASME, J. of Dynamic Systems, Measurement and Control, Vol.118, pp764-775, December issue, 1996.
Bin Yao and M. Tomizuka, "Comparative experiments of robust and adaptive control with new robust adaptive controllers for robot manipulators," Proc. of IEEE Conf. on Decision and Control, pp1290-1295, 1994.
Bin Yao and M. Tomizuka, "Smooth robust adaptive sliding mode control with guaranteed transient performance," Proc. of American Control Conference, pp1176-1180, 1994.
Bin Yao and M. Tomizuka, "Robust desired compensation adaptive control of robot manipulators with guaranteed transient performance," Proc. of IEEE Conf. on Robotics and Automation, pp1830- 1836, 1994.
Tasks such as contour following, grinding, deburring, require the end-effector of a manipulator to make contact with its environment. In these applications, it is essential to control both motion and contact force simultaneously. For a constrained robot manipulator, in which the end-effector is in contact with rigid surfaces, a new constrained dynamic model is obtained to account for the effect of contact surface friction. The design takes into account some important practical problems in designing force controllers, such as acausality problems. The resulting ARC scheme has the expected PI type force feedback control structure with a low proportional gain. Possible impact problems caused by losing contact is alleviated because of the guaranteed transient performance. An adaptation law driven by both motion and force tracking errors guarantees asymptotic motion and force tracking without any persistent excitation conditions. Simulation results verify the effectiveness of the method.
Reference:
Bin Yao and M. Tomizuka, "Adaptive control of robot manipulators in constrained motion -Controller Design," Trans. of ASME, J. of Dynamic Systems, Measurement and Control, Vol.117, pp320-328, 1995.
Bin Yao and M. Tomizuka, "Robust adaptive constrained motion and force control of manipulators with guaranteed transient performance," Proc. of IEEE Conf. on Robotics and Automation, pp893-898, 1995.
Bin Yao and M. Tomizuka, "Adaptive control of robot manipulators in constrained motion," Proc. of American Control Conference, pp1128-1132, 1993.
Bin Yao, S.P.Chan, and Danwei Wang, "VSC motion and force control of robot manipulators in the presence of environmental constraint uncertainties," Journal of Robotic Systems, Vol.11, No.6, pp503-515, 1994.
Bin Yao, S.P.Chan, and Danwei Wang, " A unified approach to variable structure control of robot manipulators," Proc. of 1992 American Control Conference, pp1282-1286, 1992.
Bin Yao, S.P.Chan, and Danwei Wang, " Robust motion and force control of robot manipulators in the presence of environmental constraint uncertainties," Proc. of IEEE Conf. on Decision and Control, 1992.
Bin Yao and K.M.Tsang, " Variable structure control of constrained robot manipulators," Proc. of Singapore Int. Conf. on Intelligent Control and Instrumentation, pp1029-1034, 1992.
For assembly-related tasks, such as heavy material handling, several manipulators are required and coordination among manipulators is essential to accomplish the job successfully. For the coordinated control of multiple robot manipulators handling a constrained object, a set of transformed dynamic equations are obtained in the joint space. In the transformed domain, internal force and external contact force have the same form and can be dealt with in the same way as in constrained motion. Similar ARC motion and force controller as in constrained motion control is developed to preserve those nice properties mentioned above
Reference
Bin Yao and M. Tomizuka, "Adaptive coordinated control of multiple manipulators handling a constrained object," Proc. of IEEE Conf. on Robotics and Automation, pp624-629, 1993.
Bin Yao, S.P.Chan, and Danwei Wang, "Unified formulation of variable structure control schemes for robot manipulators," IEEE Trans. on Automatic Control , Vol.39, No.2, pp371--376, 1994.
Bin Yao, W.B.Gao, S.P.Chan, and M.Cheng, "VSC coordinated control of two manipulator arms in the presence of environmental constraints," IEEE Transactions on Automatic Control, pp1806-1812, Vol.37, No.11, 1992.
Bin Yao, W.B.Gao, S.P.Chan, and M.Cheng, "Robust coordinated control of two manipulator arms in the presence of environmental constraints," Proc. of American Control Conference, pp3072-3073, 1991.
Motion and force tracking control of robot manipulators in contact with compliant surfaces with unknown stiffness and time-varying equilibrium position is formulated. An ARC motion and force controller is developed to deal with unknown robot parameters and surface parameters such as stiffness and friction coefficient, as well as uncertain nonlinearities because of modeling errors.
Reference:
Bin Yao and M. Tomizuka, "Adaptive robust motion and force tracking control of robot manipulators in contact with compliant surfaces with unknown stiffness," ASME J. of Dynamic System, Measurement and Control, Vol.120, No.2, pp232-240, 1998.
Bin Yao and M. Tomizuka, "Adaptive robust motion and force tracking control of robot manipulators in contact with stiff surfaces," ASME WAM, Nonlinear Dynamics and Controls, pp143-150, DE-Vol.91, 1996.
Bin Yao and M. Tomizuka, "Robust adaptive motion and force control of robot manipulators in unknown stiffness environments," Proc. of IEEE Conf. on Decision and Control, pp142-147, 1993.
Bin Yao, S.P.Chan, and Danwei Wang, "Variable structure adaptive motion and force control of robot manipulators," Automatica, Vol.30, No.9, pp1473-1477, 1994.
S.P.Chan, Bin Yao, W.B.Gao, and M.Cheng, "Robust impedance control of robot manipulators," International Journal of Robotics and Automation, pp220-227, Vol.6, No.4, 1991.