Marco Mendoza

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.

A generalised PID-type control scheme with simple tuning for the global regulation of robot manipulators with constrained inputs

In this paper, a globally stabilising PID-type control scheme with a generalised saturating structure for robot manipulators under input constraints is proposed. It gives rise to various families of bounded PID-type controllers whose implementation is released from the exact knowledge of the system parameters and model structure. Compared to previous approaches of the kind, the proposed scheme is not only characterised by its generalised structure but also by its very simple tuning criterion, the simplest hitherto obtained in the considered analytical framework. Experimental results on a 3-degree-of-freedom direct-drive manipulator corroborate the efficiency of the proposed approach.

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.

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.

Output-feedback proportional-integral-derivative-type control with multiple saturating structure for the global stabilization of robot manipulators with bounded inputs

An output-feedback proportional integral derivative-type control scheme for the global regulation of robot manipulators with constrained inputs is proposed. It guarantees the global stabilization objective—avoiding input saturation—releasing the feedback not only from the exact knowledge of the system structure and parameter values but also from velocity measurements. With respect to previous approaches of the kind, the proposed controller is expressed in a generalized form whence multiple saturating structures may be adopted, thus enlarging the degree of design flexibility. Furthermore, experimental tests on a two-degree-of-freedom direct-drive manipulator corroborate the efficiency of the proposed scheme.