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This paper examines the problem of link position tracking control of robot manipulators with bounded torque inputs. An adaptive, full-state feedback controller and
an exact model knowledge, output feedback controller are designed to produce semi-global asymptotic link position tracking errors. Simulation results are provided to validate the theoretical concepts, and a comparative analysis demonstrates the benefits of the proposed controllers.
This paper suggests an efficient approach to collision avoidance of a practical
two-robot system. The approach is based on the C-space of one robot, and we consider only two and three dimensional C-space in which nearly all industrial manipulators can be reasonably represented for collision avoidance problems. The C-space of one robot
is discretized with the concentric circles or spheres centered at the goal configuration. We then introduce the concept of free arc which is a set of the candidate configuration points on the concentric circle or sphere at each sampling time to avoid collisions. It is represented simply with respect to the coordinate frame attached to the goal configuration. The free arc is used as a tool for collision avoidance of a two-robot system and sub-optimality can be considered in determining a collision-free path. The main contribution of this paper is that it provides a method to construct C-obstacles in a time-varying environment more efficiently than the existing methods (e.g. slice projection method1) by restricting the search space at the expense of sacrificing completeness. Thus, it enables us to implement a practical collision avoidance algorithm for a two-robot system with decreased computational cost. Simulation results for two 2-d.o.f. manipulators and two PUMA robots are presented to show the efficacy of the proposed method.
Robotic manipulators mounted on spacecraft experience a number of kinematic, dynamic, and control problems because the motion of the spacecraft is affected by the robot motion. In this paper, the general three dimensional equations of motion are derived for an n link manipulator mounted on a non-fixed base object. Instead of performing a single inverse kinematic calculation at the beginning of a movement to determine the required joint setpoints, multiple inverse kinematic updates are done throughout a movement. The updating sequence is determined by an optimal inverse kinematic
updating algorithm. This motion control algorithm is based on experimental simulation results performed in Matlab and a set of performance indices that are used as guidelines. Simple PD joint controllers and a special joint trajectory generator are used for servoing
the manipulator joints for a planar robot application. The derived motion control techniques incorporate the base motion without base motion control.
The force distribution problem in multilegged vehicle is a constrained, optimization problem. The solution to the problem is the setpoints of the leg contact forces for a particular system task. In this paper, the efficient Compact QP method which takes into account both the linear and quadratic objective functions is adopted to resolve this constrained, optimization problem. Various objective functions such as minimum force, load balance, safety margin on friction constraints can be considered by the Compact QP method. This method can also be applied to smooth discontinuities in commanded forces by
manipulating the homogeneous solution and including smoothing periods when the leg phase alternates between support and transfer. This smoothing scheme does not require force sensors. Multiple goals which consider several alternative objective functions can also be achieved by the Compact QP method.
The paper deals with the kinematic redundancy control of a 3DOF linear hydraulic manipulator moving in the vertical plane. The analysis is carried out in actuator
coordinates so as to make the results usable in control schemes with actuator position feedback. The idea is to use the initial manipulator configuration as an optimization parameter in order to: (I) further minimize the actuator velocities obtained by a
pseudoinverse solution, (II) simultaneously avoid actuator limits without recourse to
a gradient projection approach. An improved pseudoinverse redundancy solution is thus obtained and implemented in a simple, non-iterative algorithm suitable for real-time applications. Simulations of a typical task with the proposed method show that minimizing the actuator velocity norm yields better results than minimizing the manipulator kinetic energy.
A small-scale flexure-based gripper was designed for manipulation tasks requiring precision position and force control. The gripper is actuated by a piezoelectric ceramic stack actuator and utilizes strain gages to measure both the gripping force and displacement. The position and force bandwidths were designed for ten Hertz and one hundred Hertz, respectively, in order to afford human-based teleoperative transparency. The gripper serves effectively as a one degree-of-freedom investigation of compliant mechanism design for position and force controlled micromanipulation. Data is presented that characterizes the microgripper performance under both pure position and pure force control, followed by a discussion of the attributes and limitations of flexure-based design.
Given the high occurence rate in assembly industry, mating a peg into a hole can be considered as one of the most classic problem in robotics. Such a task has been extensively examined by many researchers who have repeatedly attempted to find out a general solution for it. Peg in hole, which is, needlessly to mention, extremely trivial for any human operator, is surprisingly difficult to have it carried out by a robot manipulator. The reason is partly due to a physical limitation of the mechanical compliance of the robot wrist and arm and partly to a lack of a mating strategy allowing the successful execution of the task whatever the initial position of peg and hole axes is. The work presented in this paper tackles a particular class of peg-in-hole (tandem peg-in-hole) and proposes within the behaviour-based paradigm a solution to its two main components (hole search and peg insertion) loosely modeled on the equivalent strategies performed by a blind human being in possess solely of the same sensing
capability (i.e. a simple differential touch sensor).
This paper introduces the notion of kinematic redundancy in nonholonomic mechanical systems, identifies some of the interesting properties which result because of the presence of the redundancy, and initiates a study of the control and application of these systems. It is shown that kinematic redundancy in nonholonomic system can be exploited both to simplify the problem of controlling these systems and to enhance their performance capabilities. Moreover, it is demonstrated that these results can be obtained even in the presence of considerable uncertainty regarding the system model. The proposed ideas are illustrated through the study of three example systems: a space robot, a mobile manipulator, and a
tractor-trailer system with two steering inputs (fire truck).
Image compression is essential for applications such as transmission of databases, etc. In this paper, we propose a new scheme for image compression combining recursive wavelet transforms with vector quantization. This method is based on the Kohonen Self-Organizing Maps (SOM) which take into account features of a visual system in both space and frequency domains.