Marco A. Arteaga

Robot control without velocity measurements: new theory and experimental results

Most robust control schemes for rigid robots assume velocities measurements to be available. Although it is possible to measure velocities by using tachometers, this increases costs, and the signals delivered may be contaminated with noise. Since the use of encoders allows reading joint position pretty accurately, sometimes it is desirable to estimate joint velocities through an observer. This paper presents a robust control scheme designed in conjunction with a linear observer. Uniform ultimate boundedness for the tracking and observation errors are guaranteed. Experiments are included to support the theoretical results and to show that the performance of the new control-observer law is better, in comparison with well-known algorithms reported in the literature.

Observer-based sliding mode impedance control of bilateral teleoperation under constant unknown time delay

Sliding mode control has been used extensively in robotics to cope with parametric uncertainty and hard nonlinearities, in particular for time-delay teleoperators, which have gained gradual acceptance due to technological advancements. However, since the slave teleoperator is in contact with a rigid environment, the slave controller requires a free of chattering control strategy, thus making first order sliding mode teleoperation control unsuitable. As an alternative, chatter free, higher-order sliding mode teleoperator control is proposed in this paper to guarantee robust tracking under unknown constant time delay. Moreover, complete order observers are proposed to avoid measurement of velocity and acceleration, along with a formal closed-loop stability proof of the observer-based controller. Experimental results are presented and discussed, which reveals the effectiveness of the proposed teleoperation scheme.

On the control of cooperative robots without velocity measurements

One of the main practical problems on dexterous robots is the complexity of integrating a large amount of sensors within a small robot architecture. In this brief, the control of cooperative robots, without using velocity measurements, is considered. Our main purpose is to analyze the feasibility of avoiding velocity measurements to manipulate an object firmly. Experimental results are shown to support the developed theory.

Decentralized control of cooperative robots without velocity-force measurements

One of the main practical problems on cooperative robots is the complexity of integrating a large amount of expensive velocity-force sensors. In this paper, the control of cooperative robots using only joint measurements is considered to manipulate an object firmly. Experimental results are shown to support the developed theory.

Dynamic model and simulation of cooperative robots: a case study

Cooperative robots are usually required in flexible manufacturing systems or complex working environments. In particular, when an object under processing is too big or too heavy, a single robot may not be enough to handle it. Two or more manipulators are to be used in such a case. This paper presents the study of the dynamic equations for two industrial robots holding a rigid object. To this end, holonomic constraints are combined with the manipulators and object equations of motion to obtain the dynamic model of the whole system, which can be used for simulation purposes. Experimental results are presented to validate the theoretical results.

Brief Robot control and parameter estimation with only joint position measurements

Most adaptive control schemes for rigid robots assume velocities measurements to be available. Although it is possible to measure velocities by using tachometers, this increases costs and the signals delivered may be contaminated with noise. Since the use of encoders allows to read joint position pretty accurately, it is desirable to estimate joint velocities through an observer. This paper presents an adaptive scheme designed in conjunction with a linear observer. Boundedness of the estimated parameters and uniform ultimate boundedness for the tracking and observation errors are guaranteed. Experimental results are included to support the developed theory.

Cartesian control of robots without dynamic model and observer design

Most control algorithms for rigid robots are given in joint coordinates. However, since the task to be accomplished is expressed in Cartesian coordinates, inverse kinematics has to be computed in order to implement the control law. Alternatively, one can develop the necessary theory directly in workspace coordinates. This has the disadvantage of a more complex robot model. In this paper, a control-observer scheme is given to achieve exact Cartesian tracking without the knowledge of the manipulator dynamics nor computing inverse kinematics. Also, only joint measurements are used.

Remote Visual Servoing of a Robot Manipulator via Internet2

Visual servoing is a powerful approach to enlarge the applications of robotic systems by incorporating visual information into the control system. On the other hand, teleoperation – the use of machines in a remote way – is increasing the number of applications in many domains. This paper presents a remote visual servoing system using only partial camera calibration and exploiting the high bandwidth of Internet2 to stream video information. The underlying control scheme is based on the image-based philosophy for direct visual servoing – computing the applied torque inputs to the robot based in error signals defined in the image plane – and evoking a velocity field strategy for guidance. The novelty of this paper is a remote visual servoing with the following features: (1) full camera calibration is unnecessary, (2) direct visual servoing does not neglect the robot nonlinear dynamics, and (3) the novel velocity field control approach is utilized. Experiments carried out between two laboratories demonstrated the effectiveness of the application.

Brief Tracking control of flexible robot arms with a nonlinear observer

The interest in flexible robot arms has become greater in the latest years. This contribution presents a nonlinear control scheme for solving the tracking control problem of this kind of manipulators. Since typically link coordinate rates cannot be measured, a nonlinear observer is presented which provides estimates of both joint and link coordinate rates while keeping stability of the system.

On output regulation of direct visual servoing via velocity fields

The velocity field approach has become very important in the last few years in robot control, since it has many advantages. For instance, it allows to describe a control objective for robot manipulators without providing a function of time. Despite this, on the contrary to usual point-to-point regulation, this method delivers a good transient response. Furthermore, most control algorithms assume that velocity measurements are available for feedback. For this reason, in this article it is shown that a well-known observer for robot manipulators can be used together with a visual servoing approach based on velocity fields. It is assumed that the robot is planar and the camera is fixed, so that the image plane is parallel to the manipulator workspace. Experimental results show the good performance of the complete system.