A variable-fractional order admittance controller for pHRI

In today’s automation driven manufacturing environments, emerging technologies like cobots (collaborative robots) and augmented reality interfaces can help integrating humans into the production workflow to benefit from their adaptability and cognitive skills. In such settings, humans are expected to work with robots side by side and physically interact with them. However, the trade-off between stability and transparency is a core challenge in the presence of physical human robot interaction (pHRI). While stability is of utmost importance for safety, transparency is required for fully exploiting the precision and ability of robots in handling labor intensive tasks. In this work, we propose a new variable admittance controller based on fractional order control to handle this trade-off more effectively. We compared the performance of fractional order variable admittance controller with a classical admittance controller with fixed parameters as a baseline and an integer order variable admittance controller during a realistic drilling task. Our comparisons indicate that the proposed controller led to a more transparent interaction compared to the other controllers without sacrificing the stability. We also demonstrate a use case for an augmented reality (AR) headset which can augment human sensory capabilities for reaching a certain drilling depth otherwise not possible without changing the role of the robot as the decision maker

Розробка методу визначення динамічних параметрів оператора мобільної пожежної установки на базі сігвею

A method for determining the dynamic parameters of the operator of a mobile fire engine based on a segway, which fully characterize its dynamic properties – delay time and inertia was developed. The development of the method includes four stages. At the first stage, the problem of obtaining analytical relationships for determining the dynamic parameters of the operator is solved. These relationships include the frequency characteristics of the operator at a fixed frequency and its static parameter. At the second stage, the choice of a fixed frequency is substantiated using a criterion that minimizes errors in determining the dynamic parameters. It is shown that the fixed frequency for the characteristic parameters of the operator does not exceed 0.5 Hz. The third stage includes substantiation of the procedure for determining the frequency characteristics of the operator and its static parameter. The frequency characteristics of the operator at a fixed frequency and its static parameter are determined numerically. This procedure is based on using the data obtained by measuring the values of the operator’s transfer function at fixed time intervals. To obtain data, an interactive analog engine is used, which can also perform the functions of a simulator. The time intervals are chosen according to the Kotelnikov-Nyquist-Shannon theorem. At the last stage, the procedure for determining the dynamic parameters of the operator of a segway-based mobile fire engine is described. It is shown that the error in determining the dynamic parameters of the operator of a mobile fire engine does not exceed 9.0 %, if the error in determining its frequency characteristics at a frequency of 2.5 s–1 does not exceed 2.0 %Применительно к оператору мобильной пожарной установки на базе cигвея разработан метод определения его динамических параметров, которые полностью характеризуют его динамические свойства – время запаздывания и инерционность. Разработка метода включает четыре этапа. На первом этапе решается задача по получению аналитических зависимостей для определения динамических параметров оператора. Эти зависимости включают значение частотных характеристик оператора на фиксированной частоте и его статический параметр. На втором этапе обосновывается выбор фиксированной частоты, осуществляемый с использованием критерия, который минимизирует величины погрешностей определения динамических параметров. Показано, что величина фиксированной частоты для характерных параметров оператора не превышает 0,5 Гц. Третий этап включает обоснование процедуры получения значений частотных характеристик оператора и его статического параметра. Частотные характеристики оператора на фиксированной частоте и величина его статического параметра получены численным путем. Эта процедура основана на использовании массива данных, который получен путем измерения значений переходной функции оператора через фиксированные интервалы времени. Для получения массива данных используется интерактивная установка-аналог, которая может выполнять и функции тренажера. Интервалы времени выбираются согласно теореме Котельникова - Найквиста - Шеннона. На последнем этапе дается описание процедуры определения динамических параметров оператора мобильной пожарной установки на базе сигвея. Показано, что погрешность определения динамических параметров оператора мобильной пожарной установки не превышает 9,0 %, если погрешность определения его частотных характеристик на частоте 2,5 с-1 не превышает 2,0 %Стосовно до оператора мобільної пожежної установки на базі сігвею розроблено метод визначення його динамічних параметрів, які повністю характеризують його динамічні властивості – час запізнення та інерційність. Розробка методу включає чотири етапи. На першому етапі вирішується задача по одержанню аналітичних залежностей для визначення динамічних параметрів оператора. Ці залежності включають значення частотних характеристик оператора на фіксованій частоті та його статичний параметр. На другому етапі обґрунтовується вибір фіксованої частоти, що здійснюється із використанням критерію, який мінімізує величини похибок визначення динамічних параметрів. Показано, що величина фіксованої частоти для характерних параметрів оператора не перевищує 0,5 Гц. Третій етап включає обґрунтування процедури одержання значень частотних характеристик оператора та його статичного параметра. Частотні характеристики оператора на фіксованій частоті та величина його статичного параметра одержані чисельним шляхом. Ця процедура основана на використання масиву даних, який одержаний шляхом вимірювань значень перехідної функції оператора через фіксовані інтервали часу. Для одержання масиву даних використовується інтерактивна установка-аналог, яка може виконувати функції тренажера. Інтервали часу обираються згідно до теореми Котельнікова – Найквіста – Шеннона. На останньому етапі надається опис процедури визначення динамічних параметрів оператора мобільної пожежної установки на базі сігвею. Показано, що похибка визначення динамічних параметрів оператора мобільної пожежної установки не перевищує 9,0 %, якщо похибка визначення його частотних характеристик на частоті 2,5 с-1 не перевищує 2,0 

On the passivity of interaction control with series elastic actuation

Regulating the mechanical interaction between robot and environment is a fundamentally important problem in robotics. Many applications such as manipulation and assembly tasks necessitate interaction control. Applications in which the robots are expected to collaborate and share the workspace with humans also require interaction control. Therefore, interaction controllers are quintessential to physical human-robot interaction (pHRI) applications. Passivity paradigm provides powerful design tools to ensure the safety of interaction. It relies on the idea that passive systems do not generate energy that can potentially destabilize the system. Thus, coupled stability is guaranteed if the controller and the environment are passive. Fortunately, passive environments constitute an extensive and useful set, including all combinations of linear or nonlinear masses, springs, and dampers. Moreover, a human operator may also be treated as a passive network element. Passivity paradigm is appealing for pHRI applications as it ensures stability robustness and provides ease-of-control design. However, passivity is a conservative framework which imposes stringent limits on control gains that deteriorate the performance. Therefore, it is of paramount importance to obtain the most relaxed passivity bounds for the control design problem. Series Elastic Actuation (SEA) has become prevalent in pHRI applications as it provides considerable advantages over traditional sti actuators in terms of stability robustness and delity of force control, thanks to deliberately introduced compliance between the actuator and the load. Several impedance control architectures have been proposed for SEA. Among the alternatives, the cascaded controller with an inner-most velocity loop, an intermediate torque loop and an outer-most impedance loop is particularly favoured for its simplicity, robustness, and performance. In this thesis, we derive the necessary and su cient conditions to ensure the passivity of the cascade-controller architecture for rendering two classical linear impedance models of null impedance and pure spring. Based on the newly established passivity conditions, we provide non-conservative design guidelines to haptically display free-space and virtual spring while ensuring coupled stability, thus the safety of interaction. We demonstrate the validity of these conditions through simulation studies as well as physical experiments. We demonstrate the importance of including physical damping in the actuator model during derivation of passivity conditions, when integral controllers are utilized. We note the unintuitive adversary e ect of actuator damping on system passivity. More precisely, we establish that the damping term imposes an extra bound on controller gains to preserve passivity. We further study an extension to the cascaded SEA control architecture and discover that series elastic damping actuation (SEDA) can passively render impedances that are out of the range of SEA. In particular, we demonstrate that SEDA can passively render Voigt model and impedances higher than the physical spring-damper pair in SEDA. The mathematical analyses of SEDA are veri ed through simulations

Stable physical human-robot interaction using fractional order admittance control

In the near future, humans and robots are expected to perform collaborative tasks involving physical interaction in various environments, such as homes, hospitals, and factories. Robots are good at precision, strength, and repetition, while humans are better at cognitive tasks. The concept, known as physical human-robot interaction (pHRI), takes advantage of these abilities and is highly beneficial by bringing speed, flexibility, and ergonomics to the execution of complex tasks. Current research in pHRI focuses on designing controllers and developing new methods which offer a better tradeoff between robust stability and high interaction performance. In this paper, we propose a new controller, fractional order admittance controller, for pHRI systems. The stability and transparency analyses of the new control system are performed computationally with human-in-the-loop. Impedance matching is proposed to map fractional order control parameters to integer order ones, and then the stability robustness of the system is studied analytically. Furthermore, the interaction performance is investigated experimentally through two human subject studies involving continuous contact with linear and nonlinear viscoelastic environments. The results indicate that the fractional order admittance controller can be made more robust and transparent than the integer order admittance controller and the use of fractional order term can reduce the human effort during tasks involving contact interactions with environment

Stable physical human-robot interaction using fractional order admittance control

In the near future, humans and robots are expected to perform collaborative tasks involving physical interaction in various environments, such as homes, hospitals, and factories. Robots are good at precision, strength, and repetition, while humans are better at cognitive tasks. The concept, known as physical human-robot interaction (pHRI), takes advantage of these abilities and is highly beneficial by bringing speed, flexibility, and ergonomics to the execution of complex tasks. Current research in pHRI focuses on designing controllers and developing new methods which offer a better tradeoff between robust stability and high interaction performance. In this paper, we propose a new controller, fractional order admittance controller, for pHRI systems. The stability and transparency analyses of the new control system are performed computationally with human-in-the-loop. Impedance matching is proposed to map fractional order control parameters to integer order ones, and then the stability robustness of the system is studied analytically. Furthermore, the interaction performance is investigated experimentally through two human subject studies involving continuous contact with linear and nonlinear viscoelastic environments. The results indicate that the fractional order admittance controller can be made more robust and transparent than the integer order admittance controller and the use of fractional order term can reduce the human effort during tasks involving contact interactions with environment