H. Van Brussel

Optimal robot excitation and identification

This paper discusses experimental robot identification based on a statistical framework. It presents a new approach toward the design of optimal robot excitation trajectories, and formulates the maximum-likelihood estimation of dynamic robot model parameters. The differences between the new design approach and the existing approaches lie in the parameterization of the excitation trajectory and in the optimization criterion. The excitation trajectory for each joint is a finite Fourier series. This approach guarantees periodic excitation which is advantageous because it allows: 1) time-domain data averaging; 2) estimation of the characteristics of the measurement noise, which is valuable in the case of maximum-likelihood parameter estimation. In addition, the use of finite Fourier series allows calculation of the joint velocities and acceleration in an analytic way from the measured position response, and allows specification of the bandwidth of the excitation trajectories. The optimization criterion is the uncertainty on the estimated parameters or a lower bound for it, instead of the often used condition of the parameter estimation problem. Simulations show that this criterion yields parameter estimates with smaller uncertainty bounds than trajectories optimized according to the classical criterion. Experiments on an industrial robot show that the presented trajectory design and maximum-likelihood parameter estimation approaches complement each other to make a practicable robot identification technique which yields accurate robot models.

Compliant robot motion II. A control approach based on external control loops

A control approach for the execution of robot tasks in contact with the environment is worked out. The input to the con troller consists of the task specification described in part I. The control approach is based on external force and tracking loops, which are closed around the robot positioning system. The position control loops tend to decouple and linearize the complex robot dynamics, and therefore they present to the external controllers a system which is easy to model and easy to control. Design and properties of external control loops are discussed in great detail. In particular, the role of a passive compliance with respect to task execution speed and distur bance rejection is analyzed both qualitatively and quantita tively. The resulting compliant motion controller has been tested experimentally, and proved to be very robust and to yield the theoretically expected performance.A control approach for the execution of robot tasks in contact with the environment is worked out. The input to the con troller consists of the task specification described in part I. The control approach is based on external force and tracking loops, which are closed around the robot positioning system. The position control loops tend to decouple and linearize the complex robot dynamics, and therefore they present to the external controllers a system which is easy to model and easy to control. Design and properties of external control loops are discussed in great detail. In particular, the role of a passive compliance with respect to task execution speed and distur bance rejection is analyzed both qualitatively and quantita tively. The resulting compliant motion controller has been tested experimentally, and proved to be very robust and to yield the theoretically expected performance.

Holonic manufacturing systems

This chapter presents the earlier results in our development of a holonic manufacturing systems framework, with a clear emphasis on manufacturing and logistics. The insights discussed in the previous chapters were used as precious guidelines and as a check for soundness when comparing options. In particular, design for the unexpected (low and late commitment) and maximizing the potential for achieving critical user mass were important factors influencing the choices made during the development activities.

Reconfigurable Manufacturing Systems

Manufacturing companies in the 21st Century will face unpredictable, high-frequency market changes driven by global competition. To stay competitive, these companies must possess new types of manufacturing systems that are cost-effective and very responsive to all these market changes. Reconfigurability, an engineering technology that deals with cost-effective, quick reaction to market changes, is needed. Reconfigurable manufacturing systems (RMS), whose components are reconfigurable machines and reconfigurable controllers, as well as methodologies for their systematic design and rapid ramp-up, are the cornerstones of this new manufacturing paradigm.

Compliant robot motion: I. A formalism for specifying compliant motion tasks

A formalism is developed for specifying compliant motion tasks. It is based on the hybrid control functional specification method described by Mason. However, some new concepts are introduced: tracking directions, end-effector and task- frame motion constraints, feedforward velocity data, and task termination conditions. This formalism synthesizes all the information required in order to allow a completely auto matic execution of the task. As a result, it achieves strict separation between programming and control, which is of primary importance for the integration of compliant motion into a robot programming language. Several examples show that the formalism applies to a broad class of compliant motion tasks. The newly defined tracking directions contrib ute to the autonomy of the robot control system in case only partial geometric information about the environment is avail able.A formalism is developed for specifying compliant motion tasks. It is based on the hybrid control functional specification method described by Mason. However, some new concepts are introduced: trac...

Holonic manufacturing execution systems

Abstract This paper presents the design of a holonic manufacturing execution system. The design is an instantiation of the PROSA reference architecture [1] augmented with coordination and control mechanisms inspired by natural systems – i.e. food foraging behavior in ant colonies. Research prototypes are implemented as multi-agent systems. The main coordination and control mechanisms ensure that the process plans are properly executed and emergently forecast the workload of the manufacturing resources as well as well as lead times and routings of the products. The design empowers the product instances to drive their own production; the coordination is completely decentralized. In contrast to many decentralized designs, the manufacturing execution system predicts future behavior and proactively takes measures to prevent impending problems from happening. A social control mechanism ensures that product instances adhere sufficiently to their declared intentions, which is necessary to guarantee adequate forecast accuracy. The design has been applied to an industrial test case, and the paper discusses results of this case study.

Assembly of microsystems

In the microworld, as well as in the macroworld, assembly is a crucial operation in the genesis of a product. This keynote paper focusses on the assembly problems occurring in the manufacturing cycle of microsystems. Scaling effects make that the assembly problems are different in the microworld. The different assembly operations and techniques, like manipulation by physical contact, non-contact manipulation, smart assembly techniques, and joining methods are thoroughly discussed. Finally, some relevant examples of micro-assembly systems and of assembled microproducts are given.

Friction Compensation of an

Uncompensated friction forces compromise the positioning and tracking accuracy of motion systems. A unique tracking error known as quadrant glitch is the result of complex nonlinear friction behavior at motion reversal or near-zero velocity. Linear-feedback control strategies such as PID, cascade P/PI, or state-feedback control have to be extended with model- and nonmodel-based friction-compensation strategies to acquire sufficiently high path and tracking accuracy. This paper analyzes and validates experimentally three different friction-compensation strategies for a linear motor-based xy feed drive of a high-speed milling machine: (1) friction-model-based feedforward; (2) an inverse-model-based disturbance observer; and (3) the combination of both techniques. The friction models considered are as follows: a simple static-friction model and the recently developed generalized Maxwell-slip (GMS) model. GMS friction-model-based feedforward combined with disturbance observer almost completely eliminates the radial tracking error and quadrant glitches.

XY

In this paper a new mathematically exact algorithm is described for dynamic map building with geometrical primitives for a mobile robot. The dynamic map is built up using a 2D range finder mounted on the mobile robot LiAS which is navigating in the environment. The dynamic map can be used for either planning or localisation purposes. The map is composed of line segments and circles. The parameters describing the geometrical primitives are provided with uncertainties which are used in the matching phase and which are necessary if the map is used for localisation. This paper describes in detail how the uncertainty on the robot position and the uncertainty on a single range measurement leads to the uncertainty on the parameters of a geometrical primitive. Promising experimental results obtained by the algorithm in real unstructured environments are presented.

Feed Table Using Friction-Model-Based Feedforward and an Inverse-Model-Based Disturbance Observer

This paper presents the Smoothly Constrained Kalman Filter (SCKF) for nonlinear constraints. A constraint is any relation that exists between the state variables. Constraints can be treated as perfect observations. But, linearization errors can prevent the estimate from converging to the true value. Therefore, the SCKF iteratively applies nonlinear constraints as nearly perfect observations, or, equivalently, weakened constraints. Integration of new measurements is interlaced with these iterations, which reduces linearization errors and, hence, improves convergence compared to other iterative methods. The weakening is achieved by artificially increasing the variance of the nonlinear constraint. The paper explains how to choose the weakening values, and when to start and stop the iterative application of the constraint.