Isela Bonilla

A Dynamic-compensation Approach to Impedance Control of Robot Manipulators

This paper presents an impedance–control strategy with dynamic compensation for interaction control of robot manipulators. The proposed impedance controller has been developed considering that the equilibrium point of the closed-loop system, composed by the combination of the controller and the full nonlinear robot dynamics is, locally, asymptotically stable in agreement with Lyapunov’s direct method. The performance of the proposed controller is verified through simulation and experimental results obtained from the implementation of an interaction task involving a two degree-of-freedom, direct-drive robot.

Path-Tracking Maneuvers With Industrial Robot Manipulators Using Uncalibrated Vision and Impedance Control

This paper presents an interaction control strategy for industrial robot manipulators which consists of the combination of a calibration-free, vision-based control method with an impedance-control approach. The vision-based, robot control method known as camera-space manipulation is used to generate a given, previously defined trajectory over an arbitrary surface. Then, a kinematic impedance controller is implemented in order to regulate the interaction forces generated by the contact between the robot end-effector and the work surface where the trajectory is traced. The paper presents experimental evidence on how the vision-force sensory fusion is applied to a path-tracking task, using a Fanuc M16-iB industrial robot equipped with a force/torque sensor at the wrist. In this task, several levels of interaction force between the robot end-effector and the surface were defined. As discussed in the paper, such a synergy between the control schemes is seen as a viable alternative for performing industrial maneuvers that require force modulation between the tool held by the robot and the working surface.

A vision-based, impedance control strategy for industrial robot manipulators

This paper presents a control strategy for industrial robot manipulators which consists of the combination of a calibration-free, vision-based control method with an impedance control approach. The vision-based, robot control method known as camera-space manipulation is used to generate a given trajectory over an arbitrary surface. Then, a kinematic posture-based impedance controller is implemented in order to regulate the interaction forces generated by the contact between the robot end-effector and the work surface where the trajectory is traced. The paper presents experimental evidence on how the vision-force sensory fusion improves the precision of a robot-interaction task, by using a Fanuc M16-iB industrial robot equipped with a wrist force/torque sensor. As discussed in the paper, such a synergy between the control schemes is seen as a viable alternative for performing industrial maneuvers that require force modulation between the tool held by the robot and the working surface.

Analysis of distributed power control under constant and time-varying delays

This work studies the distributed power control algorithm proposed in 1993 by Foschini-Miljanic, standardised for universal mobile telecommunication systems. Continuous and discrete time versions of this algorithm are analysed. First, the stability of the distributed power allocation schemes was studied, where sufficient conditions to guarantee stability and convergence to a desired quality of service were provided. In this study, the channel gains are assumed to be slowly time-varying or piece-wise constant. For closed-loop control, a proportional controller is then employed under integral action in order to achieve good tracking despite time-varying and unknown channel gains. Next, the effects of constant and time-varying time delays in the closed-loop structure are studied. Explicit stability regions for the control gains in the Foschini-Miljanic scheme are derived for both the continuous and discrete-time versions of the algorithm, under constant and time-varying delays. For time-varying scenario, the resulting stability regions do not impose limitations on the rate change of the time-varying profiles. A comprehensive evaluation using simulations is performed to validate the analytical derivations described in the paper.

Precise industrial robot positioning and path-tracking over large surfaces using non-calibrated vision

This paper presents a methodology for precise robot positioning and path tracking, performed by industrial robots over large surfaces of arbitrary size, shape and orientation. The methodology is based on a vision-based, calibration-free robot control method known as camera-space manipulation. The path, defined and stored in a CAD file, is later adapted to the curved, work-surface by using a mapping procedure. When applied to large surfaces, the precision of the positioning and path-tracking maneuvers depends on several factors like the resolution of the cameras per unit physical space and the mapping procedure, which may introduce distortion specially in the case of non-developable surfaces. In order to reduce the influence of camera-resolution, this paper presents two alternatives: the use of multiple cameras and the application of cameras mounted over non-expensive, sensorless pan/tilt units. In the case of the distortion produced by the mapping procedure, the paper discusses several options like a modified geodesic mapping and virtual projection. The proposed techniques were tested multiple times over flat and deformed surfaces, by using a large work-envelope, industrial robot.

Saturating stiffness control of robot manipulators with bounded inputs

Abstract A saturating stiffness control scheme for robot manipulators with bounded torque inputs is proposed. The control law is assumed to be a PD-type controller, and the corresponding Lyapunov stability analysis of the closed-loop equilibrium point is presented. The interaction between the robot manipulator and the environment is modeled as spring-like contact forces. The proper behavior of the closed-loop system is validated using a three degree-of-freedom robotic arm.

Impedance control in a wave-based teleoperator for rehabilitation motor therapies assisted by robots

This paper presents an improved wave-based bilateral teleoperation scheme for rehabilitation therapies assisted by robot manipulators. The main feature of this bilateral teleoperator is that both robot manipulators, master and slave, are controlled by impedance. Thus, a pair of motion-based adaptive impedance controllers are integrated into a wave-based configuration, in order to guarantee a stable human-robot interaction and to compensate the position drift, characteristic of the available schemes of bilateral teleoperation. Moreover, the teleoperator stability, in the presence of time delays in the communication channel, is guaranteed because the wave-variable approach is included to encode the force and velocity signals. It should be noted that the proposed structure enables the implementation of several teleoperator schemes, from passive therapies, without the intervention of a human operator on the master side, to fully active therapies where both manipulators interact with humans in a stable manner. The suitable performance of the proposed teleoperator is verified through some results obtained from the simulation of the passive and active-constrained modes, by considering typical tasks in motor-therapy rehabilitation, where an improved behavior is observed when compared to implementations of the classical wave-based approach.

Development of a haptic interface for motor rehabilitation therapy using augmented reality.

In this paper, a robot-assisted therapy system is presented, mainly focused on the improvement of fine movements of patients with motor deficits of upper limbs. This system combines the use of a haptic device with an augmented reality environment, where a kind of occupational therapy exercises are implemented. The main goal of the system is to provide an extra motivation to patients, who are stimulated visually and tactilely into a scene that mixes elements of real and virtual worlds. Additionally, using the norm of tracking error, it is possible to quantitatively measure the performance of the patient during a therapy session, likewise, it is possible to obtain information such as runtime and the followed path.

Adaptive Impedance Control of Robot Manipulators with Parametric Uncertainty for Constrained Path–Tracking

Abstract The main impedance control schemes in the task space require accurate knowledge of the kinematics and dynamics of the robotic system to be controlled. In order to eliminate this dependence and preserve the structure of this kind of algorithms, this paper presents an adaptive impedance control approach to robot manipulators with kinematic and dynamic parametric uncertainty. The proposed scheme is an inverse dynamics control law that leads to the closed-loop system having a PD structure whose equilibrium point converges asymptotically to zero according to the formal stability analysis in the Lyapunov sense. In addition, the general structure of the scheme is composed of continuous functions and includes the modeling of most of the physical phenomena present in the dynamics of the robotic system. The main feature of this control scheme is that it allows precise path tracking in both free and constrained spaces (if the robot is in contact with the environment). The proper behavior of the closed-loop system is validated using a two degree-of-freedom robotic arm. For this benchmark good results were obtained and the control objective was achieved despite neglecting non modeled dynamics, such as viscous and Coulomb friction.

Stiffness-based tuning of an adaptive impedance controller for robot-assisted rehabilitation of upper limbs

In this paper, the tuning procedure of an adaptive impedance control approach, for upper limb rehabilitation therapies assisted by robots, is presented. The main feature of the proposed approach is a custom tuning of the impedance parameters for the controller, based on the stiffness estimation of users (patients), thus achieving a suitable robot-assisted rehabilitation system according with the different conditions of users mobility. A set of simulation results are presented, in order to verify the suitable performance of the proposed approach in human-robot interaction tasks.