Nenad Kircanski

Real-time dynamics of manipulation robots

1 Survey of computer-aided robot modelling methods.- 1.1. Introduction.- 1.2. Methods based on Lagranges equation.- 1.2.1. Uicker-Kahns method v.- 1.2.2. Algorithms by Mahil, Megahed and Renaud.- 1.2.3. Algorithms by Waters and Hollerbach.- 1.2.4. Vukobratovi?-Potkonjaks recursive method.- 1.3. Methods based on Newton-Eulers equations.- 1.3.1. Vukobratovi?-Stepanenkos method.- 1.3.2. Huston-Kanes method.- 1.3.3. A new recursive method.- 1.4. Methods based on Appels equations.- 1.5. Symbolic methods.- 1.6. Numeric-symbolic method.- 2 Computer-aided method for closed-form dynamic robot model construction.- 2.1. Introduction.- 2.2. Model based on Newton-Eulers equations.- 2.3. Closed-form dynamic model.- 2.4. Properties of dynamic model matrices: symmetry, positive definiteness and antisymmetry.- 2.5. Closed-form linearized model.- 2.6. Closed-form sensitivity model.- Appendix 2.1.- Appendix 2.2.- 3 Computer-aided generation of numeric-symbolic robot model.- 3.1. Introduction.- 3.2. Numeric-symbolic representation of variables.- 3.3. Algebra of polynomial matrices.- 3.4. Optimization of polynomial matrices.- 3.5. Nonlinear model.- 3.6. Linearized and sensitivity model.- 3.7. Approximate models.- Appendix 3.1.- 4 Model optimization and real-time program-code generation.- 4.1. Introduction.- 4.2. Optimal computation of polynomial matrices.- 4.3. Real-time program-code generation.- Appendix 4.1.- 5 Examples.- 5.1. Introduction.- 5.2. A cylindrical robot.- 5.3. An arthropoid robot.- 5.4. An anthropomorphic robot.- 5.5. Microcomputer implementation of analytical robot models - - time-memory requirements.- Appendix 5.1.- References.

Design of the IRIS facility-a modular, reconfigurable and expandable robot test bed

The integrated raster imaging system (IRIS) facility is a robot system to be used for experiments in grasping, manipulation and force control. The facility has two manipulators with four rotary joints each. Each manipulator can assume a multitude of configurations. Each joint is driven by DC brushless motors coupled with harmonic cup drives, and instrumented with position and torque sensors. A six-degrees-of-freedom (DOF) force/torque sensor is mounted at the tip link. The real-time controller of the IRIS facility is based on a nodal architecture. Each node is capable of controlling 8 joints at 1 kHz while executing over 1000-FP (floating point) operations per joint in each sampling method. The design of the IRIS facility and its functional capabilities are described. In addition, the rationale behind the major design decisions is given.<<ETX>>

Articulated robotic scanner for mine detection: a novel approach to vehicle-mounted systems

Conventional vehicle-mounted mine detector system employ an array of sensor elements to achieve a detection swath. Some systems employ more than one type of sensor technology. These systems, while being very useful, are often expensive, complex and inflexible. A human operator, on the other hand, sweeps a mine detector from side to side while moving forward to cover ground. The operator can follow the ground profile with the detector head close to the ground without hitting the ground or any objects on it. She can also vary the width of sweep to suit a particular situation, and is usually not limited by terrain. In this paper we present the concept and early prototype of a system that incorporates the advantages of the two methods described above while minimizing the disadvantages of both. For example, it will have the flexibility of a manual system with the rapid and safer mechanized scanning of the vehicle-mounted system but at a reduced cost, size and overall system complexity, when compared to existing approaches. Our approach uses an articulated robotic device capable of automatically moving mine detection sensor over natural ground surfaces including roads and tracks in a manner similar to a human operator. The system can also easily be used to place a confirmatory point sensor at a specific location if needed. The early prototype, which incorporates only a metal detector for a mine sensor, implements ground following by using a laser range finder and four ultrasonic sensors.

Resolved-rate and resolved-acceleration-based robot control in the presence of actuators' constraints

Experimental evaluation of various task-space control algorithms shows that significant deviations from desired trajectories may occur, especially at higher speeds, or in the vicinity of singularities. The experiments on a modular reconfigurable robotic setup confirmed this conclusion: the lateral deviations may range up to several centimeters from the closest point on the desired trajectory. The main reason is that the control output often reaches the saturation value of an actuator. The lateral error is also found very dangerous in obstacle cluttered environments due to possible damage of the manipulator arm while hitting an obstacle at high speed. This paper is devoted to solve this problem. Widely used task space control algorithms such as the resolved-rate and the resolved-acceleration algorithms are modified by introducing monitoring on the control output, and, accordingly, modifying the commanded control signal so that the end-effector is prevented from leaving the programmed path. As a consequence, the manipulator tip may slowdown along the path due to limited actuator power, but it will be accelerated after that to reach the desired position as soon as possible. The algorithms also take into account the presence of singularities to avoid uncontrollable excursions of the manipulator tip. Hundreds of experiments have been carried out to confirm the concept. Some of those with a desired trajectory reaching both the regular and the singular region of the workspace are provided to illustrate the method.

Control of robots with elastic joints: deterministic observer and Kalman filter approach

The authors extend the idea of a fourth-order model of an elastic link and introduce two complementary ways of controlling such systems. In the case of measurable joint forces/torques, they propose a control law based on a deterministic observer whose job is to recover immeasurable components of the state vector. If the forces/torques are not measurable, they propose a Kalman filter technique which uses the manipulators model to recover the unknown states of the system. Simulation results are presented. The example used is a 6-link manipulator, UMS-2. The results encourage implementation of these control structures on a real system.<<ETX>>

An efficient procedure for generating dynamic manipulator models

Robotica / Volume 3 / Issue 03 / September 1985, pp 147 152 DOI: 10.1017/S0263574700009061, Published online: 09 March 2009 Link to this article: http://journals.cambridge.org/abstract_S0263574700009061 How to cite this article: M. Vukobratović, Shi-Gang Li and N. Kirćanski (1985). An efcient procedure for generating dynamic manipulator models. Robotica, 3, pp 147-152 doi:10.1017/S0263574700009061 Request Permissions : Click here

Position control of robot manipulators with elastic joints using force feedback

Transmission flexibility, as a predominant source of mechanical resonance, often results in inaccurate tracking of prescribed robot trajectories. Thus, the control algorithm must compensate not only for nonlinear dynamics of the arm and payload variations, but also for resonant effects in joints. The compensation for all of these effects results in a very complicated control algorithms which are difficult to apply in practice. In this article we suggest the measurement of torque/force on the output shaft of elastic reducer in order to compensate for elastic effects. The torque measurement can be replaced by the simultaneous measurement of the joint and the motor-shaft angle. Then, we introduce a dynamic compensator with two zeros and two poles to filtrate the torque signal. It appears that the obtained control law is very simple and compensates for nonlinear system dynamics, variable payload parameters and resonant effects in joints. The proposed control scheme is illustrated by computer simulation of a six-degree-of-freedom robot.

An experimental study of resolved acceleration control in singularities: damped least-squares approach

In this paper the application of the damped least-squares method to the resolved-acceleration control is experimentally examined on a 2-DOF planar manipulator In order to decrease the position error introduced by the damping, only small singular values are damped. The symbolical expressions of the singular value decomposition of the Jacobian matrix were utilized in order to decrease the computational burden. Position error along the work-space boundary was only 15% greater than along the trajectories inside the reachable workspace.<<ETX>>

SYM-program environment for manipulator modeling, control and simulation

The structure of SYM, a program package for manipulator modeling, control law synthesis, and simulation, is described. SYMs research and educational aims are emphasized. The control law synthesis in symbolic form and the system simulation are discussed in detail. Several examples of SYM outputs which depict the main steps in the manipulator control system creation process, namely, manipulator structure as a 3-D scheme, control law definition form, and system simulation results as 2-D plots are presented.<<ETX>>

A method for computer-aided construction of analytical models of robotic manipulators

An algorithm for constructing dynamic models of single-arm robots is presented in this paper. Motion equations of robots in analytical form are derived applying a fully automated procedure. It is shown that the solution of direct and/or inverse problem based on the analytical model requires considerably fewer floating- -point multiplications/additions that is the case with previously developed numerical methods. The developed method is therefore very suitable for real-time application of the dynamic models of robots. The developed program package is illustrated using the example of Stanford manipulator.