Brecht Corteville

Human-inspired robot assistant for fast point-to-point movements

A first step towards truly versatile robot assistants consists of building up experience with simple tasks such as the cooperative manipulation of objects. This paper extends the state-of-the-art by developing an assistant which actively cooperates during the point-to-point transportation of an object. Besides using admittance control to react to interaction forces generated by its operator, the robot estimates the intended human motion and uses this identified motion to move along with the operator. The offered level of assistance can be scaled, which is vital to give the operator the opportunity to gradually learn how to interact with the system. Experiments revealed that, while the robot is programmed to adapt to the human motion, the operator also adapts to the offered assistance. When using the robot assistant the required forces to move the load are greatly reduced and the operators report that the assistance feels comfortable and natural.

A mechatronic analysis of the classical position-force controller based on bounded environment passivity

Bounded Environment Passivity, presented in this paper, allows one to design teleoperation systems that behave passively provided that the environment with which interaction takes place belongs to an a priori defined range of environments. The use of such a priori knowledge on the environment reduces conservativeness with respect to classical design approaches. An additional advantage lies in its capability to get a clearer insight on which type of environments are problematic for the specific controller under investigation. On the basis of a case study, i.e. the well-known Position-Force controller, this paper describes and compares different passivity-based methods. First, the traditional methods of two-port passivity and absolute stability are applied. The restrictions of these methods to come up with useful design rules are explicitly demonstrated. Second, the Bounded Environment Passivity conditions of the Position-Force controller are derived. These conditions describe the relation between the specific controller implementation, the teleoperator dynamics and the environment characteristics. In addition, the effects of structural resonance frequencies and low-pass filters, often present in realistic teleoperator setups, are described. This analysis reveals fundamental mechatronic rules of thumb for the design of a teleoperator system with a Position-Force control architecture. The theoretical results are verified experimentally on a one-degree-of-freedom teleoperation system.

Bounded environment passivity of the classical Position-Force teleoperation controller

This paper derives analytic guidelines to tune the popular Position-Force bilateral controller and improve its performance by incorporating available knowledge on the bounds of the environment impedance. The proposed guidelines can prove especially useful in the domain of telesurgery where a need exists for well-understood bilateral teleoperation controllers, that show good performance and where many tasks can be characterized by restricted and relatively easily definable impedance regions. This paper firstly analyses the two-port passivity and absolute stability properties of two alternatives of the Position-Force controller. The limitations on achievable performance when guaranteeing absolute stability with arbitrary environments are detailed. Next, a novel method, called Bounded Environment Passivity method is introduced. This method enables the design of teleoperation controllers that show passive behaviour for interactions with an environment that varies over a given range of impedances. A set of guidelines that allow a smarter trade-off between performance and stability follows. The theoretical results are verified experimentally on a 1-d.o.f. teleoperation setup.

Transparency Trade-Offs for a 3-Channel Controller Revealed by the Bounded Environment Passivity Method

In this paper, the Bounded Environment Passivitymethod [1] is applied to a 3-channel controller. This methodenables the design of teleoperation controllers that show passivebehaviour for interactions with a bounded range of environments.The resulting tuning guidelines, derived analytically,provide interesting tuning flexibility, which allows to focuson different aspects of transparency. As telesurgery is themotivation behind this work, the focus lies on correctly reflectingthe stiffness properties of the environment. A comparisonbetween the transparency and stability properties of this 3-channel controller and the same properties of the Position-Force controller demonstrates the interesting properties ofthe 3-channel controller. The theoretical results are verifiedexperimentally on a 1 d.o.f. master-slave setup.

The development of a frictionless pneumatic actuator: a mechatronic step towards safe human-robot interaction

In the quest for a robot arm, which is capable of mechanical interaction with humans, biology can be a good source of inspiration. After all, the human arm is the best example of such a manipulator. A comparison between the human movement apparatus and an industrial robot arm reveals the most important criteria: the actuators of a human-like robot arm should have high compliance, no dry friction and low weight. The proposed solution combines air bearing technology and pneumatics to obtain a compact system with high performance. A thorough identification of the plant enables the design of a specialized controller which compensates for the plant nonlinearities like the dead zone of the pneumatic proportional valves. The prototype of the force controlled, frictionless pneumatic actuator (FPA) has a bandwidth of about 50 Hz and, compared to traditional robot drives, an extremely high compliance (or low stiffness) even for disturbances above the controller bandwidth.

Mechatronic design optimization of a teleoperation system based on bounded environment passivity

This paper presents a mechatronic analysis of a teleoperation system that provides haptic feedback. The analysis, based on the Bounded Environment Passivity method, describes the combined effect of the teleoperation controller and the master and slave hardware, including the effect of structural flexibilities, which have often been neglected in the domain of teleoperation. This results in rules of thumb for the design of the hardware and the tuning of the controller. As two of these rules of thumb pose a trade-off in hardware design, an unprecedented conceptual design optimization is described in a second part of this paper. The objective is to demonstrate the need for a mechatronic approach to the design of teleoperation systems in order to obtain maximal system performance.