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 impedancecontrol 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.

The stiffness controller proposed by Salisbury is an interaction control strategy designed to achieve a desired form of static behavior as regards the interaction of a robot manipulator with the environment. The main idea behind this approach is the simulation of a multidimensional linear spring -or linear elastic material -using the difference between the actual position of the end-effector and a constant position (relaxed point), multiplied by a constant stiffness matrix. In this paper, this idea is generalized with the objective of proposing a controller structure that includes a family of stiffness models based on the idea of linear elastic materials. The new controller structure also includes a damping term in order to have control over energy dissipation, as well as a term added for the purpose of compensating the gravity forces of the links. The stability analysis of the proposed controller was performed in the Lyapunov sense. The new stiffness controller is presented as a case study and compared to other cases, such as the Salisbury controller (Cartesian PD) and the tanh-tanh controller. Experimental results using a three degrees-offreedom direct-drive robot for the evaluation of controllers in a constrained motion task are presented.

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.

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.

The inertial and friction parameters of a robot are used in the development and evaluation of modelbased control schemes and their accuracy is related directly to the performance. These parameters can also be used for a realistic simulation, which may be useful before implementation of new control schemes. In principle, the numerical value of the parameters could be obtained via CAD analysis, but inevitably assembly and manufacturing errors exist. Direct measurement is not a realistic option because the complex nature of the system involves intense, time-consuming effort. Alternatively, we can deduce the values of the parameters by observing the natural response of the system under appropriate experimental conditions, i.e., by using identification schemes, which is an efficient way. This paper presents the experimental evaluation of five identification schemes used to obtain the inertial and friction parameters of a three-degrees-of-freedom direct-drive robot. We assume that the inertial and friction parameters are totally unknown but, by design, the dynamic model is fully known, as in many practical cases. We consider the schemes based on the dynamic regression model, the filtered-dynamic regression model, the supplied-energy regression model, the power regression model and the filtered-power regression model. This paper presents a comparison between experimental and simulated robot response, which enables us to verify the accuracy of each regression model.

The dynamic and friction parameters of a robot are used in advanced control schemes, and their accuracy significantly affects their performance. These parameters can also be used for a realistic simulation. In principle, the numerical value of the parameters could be obtained via computer-aided design analysis but inevitable assembly and manufacturing errors exist. Direct measurement is not a realistic option because the complex nature of the system would involve an intense time-consuming effort. Alternatively, we can deduce the values of the parameters by observing the natural response of the system under appropriate experimental conditions, that is, by using identification schemes. This article presents the experimental evaluation of five identification schemes used to obtain the dynamic and friction parameters of a two-degree-of-freedom, direct-drive robot. We assume that the dynamic and friction parameters are totally unknown but, by design, the dynamic model is fully known. We consider the schemes based on the dynamic regression model, filtered-dynamic regression model, supplied-energy regression model, power regression model, and filtered-power regression model. The article presents a comparison between experimental and simulated robot responses, which enable us to verify the accuracy of each regression model.

Original scientific paperThis paper presents a new interaction control structure that generates a family of explicit force regulators for robot manipulators. The proposed structure includes a term of a class of proportional-type functions in terms of force error; the force error is defined as the difference between a desired force and the actual force measured with a force sensor located at the end-effector. Also, the structure includes a generalized active velocity damping term in order to have a control of the energy dissipation, and a term used to compensate the gravity forces of the links. The stability analysis is performed in Lyapunov sense. An experimental comparison of two new explicit force regulators and the linear proportional structure, on a three degree-of-freedom, direct-drive robot, is presented. Also, proofs of the most important properties of the Cartesian dynamic model, are presented.Key words: Interaction control, Explicit force control, Direct-drive robot, Lyapunov stability, Cartesian robot control Eksplicitna regulacija sile robotskog manipulatora aktivnim prigušenjem brzine. Ovaj rad predstavlja novu interakcijsku kontrolnu strukturu koja predstavlja skupinu exsplicitnih regulatora sile za robotske manipulatore. Predložena struktura uključuječlan klase funkcija proporcionalnog tipa u smilsu pogreške sile; pogreška sile se definira kao razlika izmeu željene sile i stvarne sile koju mjere senzori postavljeni na kraju manipulatora. Takoer, struktura uključuječlan za generalizirano aktvino prigušenje brzine kako bi se omogućila kontrola disipacije energije ičlan kojim se kompenzira utjecaj sile gravitacije načlanke manipulatora. Analiza stabilnosti je napravljena u smislu Lyapunova. Prikazana je eksperimentalna usporedba dva nova eksplicitna regulatora sile i linearno-proporcionalne strukture na robotu s direktnim pogonom i tri stupnja slobode. Takoer su prikazani dokazi najvažnijih svojstava kartezijskog dinamičnog modela.

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