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This paper presents an impedance controller for five-finger dexterous robot hand DLR-HIT II, which is derived in Cartesian
space. By considering flexibility in finger joints and strong mechanical couplings in differential gear-box, modeling and
control of the robot hand are described in this paper. The model-based friction estimation and velocity o...
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... Cartesian impedance control experiment is carried out in the five-finger dexterous robot hand DLR-HIT II with a hard real time control cycle 200 μs . Multi-point LVDS serial communication system and QNX real time OS are uti- lized to fulfill the requirements of the proposed controller. D x and K k are designed by the double-diagonalization approach with the robot inertia matrix and the desired damping ratio, as presented in [23]. Other parameters needed for im- plementing the impedance controller (23) can be generated by directly using Pro/E model of the dexterous hand. In the following two experiments, the former one is conducted to test the performance of the controller, whereas the latter one is carried out to show the compliant behavior of the robot hand. The designed Cartesian impedance controller is implemented in a single finger of the robot hand. The finger tracks the desired position trajectory(red line) and makes contact with a rigid external object at the position offset Δx = 0 . 011 m in the x direction, as shown in Fig. 3. Together with Cartesian force response in Fig. 3, the experimental results show that the proposed impedance controller is effective in position tracking. As shown in Fig. 4, The robot overcomes the gravity and friction, returning to the equilibrium Cartesian position x d as soon as the external force is released. With the friction and gravity compensation proposed in this paper, the static error in the x axis is less than 0.2 mm, as well as y and z direction. It can therefore be concluded that the Cartesian impedance controller is successfully realized. In this paper, a Cartesian impedance controller with friction compensation is derived for the dexterous robot hand DLR-HIT II hand with flexible joints. Global asymptotic stability is guaranteed by LaSalle Principle analysis. To improve the performance of the proposed controller, model based friction compensation is adopted in this paper, in which friction parameters are estimated with the Least Squares Method. Together with joint velocity observed by extended Kalman filter, non-linear friction compensation can be derived. Two experiments are carried out on the DLR-HIT hand to show the effectiveness of designed impedance controller with friction compensation and its compliant behavior with the robot hand. For the harmonic drive robot hand with joint torque feedback, accurate position tracking and stable torque/force response can be achieved with the proposed Cartesian impedance ...
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This paper presents impedance controllers with adaptive friction compensation for the five-finger dexterous robot hand DLR-HIT II in both joint and Cartesian space. A FPGAbased
control hardware and software architecture with real-time communication is designed to fulfill the requirements of the impedance controller. Modeling of the robot finger wit...
Citations
... The robot grippers evolved from a gripper with a simple mechanism to a robotic hand with complex control laws and grasp methods. Among a large number of research works, notable ones can be listed as follows: Okada hand [7], Utah/MIT hand [8], shadow hand [9], stanford/jpl [10], DLR Hand [11], LMS hand [12], and NASA robonaut hand [13], etc. Since the robot hand is composed of a complex mechanical structure and many sensors, it can perform more delicate tasks with various postures and control laws. ...
In this paper, a two-way self-adaptive gripper that has adaptability to external disturbance loads during linear opening/closing pinch actions and adaptability to encompass a variety of shapes during grasping using a single actuator is proposed, unlike the previous self-adaptive robotic grippers capable of only shape adaptation. Therefore, both linear motion adaptability and shape adaptability during parallel grasping situations are enabled by the proposed design of the gripper. Adaptation to the linear pinch motion is provided through the use of a differential gear, the two outputs of which drive the two tips of the gripper. If facing uneven external loads, the differential gear adaptively alters the speeds of the two outputs, resulting in different closing speeds of the two gripper tips. Despite asymmetric closing, very stable grasping can be guaranteed for such a situation. The differential gear can even complete the grasping by intentionally or unintentionally fixing one of the gripper tips. The proposed design is also capable of shape adaptation in the encompassing grasping mode by adopting a parallel-linkage gripper mechanism, consisting of an exoskeleton and 6 internal joints with a spring element. The finger exoskeleton facilitates pinch and spread actions, while the encompassing action is carried out by adjusting the internal linkage. Based on the kinematic analysis and modeling of the proposed gripper, a prototype of the two-way adaptive gripper hardware was developed. Several experiments were performed to verify the feasibility and validity of the proposed gripper system. The actuator using the proposed differential gear was shown to be able to grasp objects in jammed conditions. In addition, the gripper was able to perform grasping actions, such as pinch, spread, and encompassing grasp.
... In the past few decades, many multi-finger dexterous hands have been designed, such as Utah/MIT hand [4], Shadow hand [5,6], Robonaut 2 hand [7,8], DLR-HIT hand [9,10] and Gifu hand [11]. These multi-finger dexterous hands imitate the shape of the human hand, and each degree of freedom is equipped with a driver. ...
... Kinematic model of the self-adaptive grasping mode.According to Euler's equation, l 2 cos θ 2 + l 3 cos θ 3 = −l 1 + l 5 cos θ 5 + l 4 cos θ 4 l 2 sin θ 2 + l 3 sin θ 3 = l 5 sin θ 5 + l 4 sin θ 4(8)From Eq. (8), the relationship between the angle of the third link θ 3 and the angle of the distal phalanx θ 4 is derived.Calculating the derivative of Eq. (8) with respect to time t, the angular velocity relationship is obtained as −l 2 sin θ 2 ω 2 − l 3 sin θ 3 ω 3 = −l 4 sin θ 4 ω 4 l 2 cos θ 2 ω 2 + l 3 cos θ 3 ω 3 = l 4 cos θ 4 ω 4(9) ...
When the under-actuated hand pinches the object on the worktable, the trajectory of the end of the finger is not a straight line, which makes it difficult for the hand to grasp the object from its both sides. In order to overcome this shortcoming, this paper proposes a new configuration of the linear-parallel and self-adaptive under-actuated hand which uses the four-link and sliding base mechanism to compensate for the vertical displacement of the end of the finger. Based on this new configuration, the mechanical structure of the under-actuated hand is designed, which has five degrees of freedom (DOFs), and is mainly composed of two fingers, a sliding base, four link compensation mechanisms and an outer base. These two fingers have exactly the same structure and size, where each finger uses only one motor to control two joints of the finger which realizes the under-actuated function. Through the cooperation of the four-link and sliding base mechanism, the under-actuated hand can realize the linear-parallel and self-adaptive hybrid grasping mode. Kinematics analysis and contact force analysis of the under-actuated hand are discussed, and the prototype of the under-actuated hand is developed to carry out the grasping experiments. The results of the simulation and experiment all show that the under-actuated hand has good motion performance and grasping stability and can be used as an end effector for intelligent robots.
... The impedance control technique proposed by Hogan [7] is one of the fundamental approaches for force tracking control of robot manipulators with constrained motion. Then, the performance of impedance control was improved and the application was expanded to other fields by many researchers8910. Differing from the hybrid position and force control approach [11], impedance control regulates the force between a manipulator and the environment by defining the target impedance between position and contact force. ...
In this paper, an impedance control algorithm based on velocity for capturing two low impact docking mechanisms (LIDMs) is presented. The main idea of this algorithm is to track desired forces when the position errors of two LIDMs are random by designing the relationship between the velocity and contact forces measured by a load sensing ring to achieve low impact docking. In this paper, the governing equation of an impedance controller between the deviation of forces and velocity is derived, and simulations are designed to verify how impedance parameters affect the control characteristics. The performance of the presented control algorithm is validated by using the MATLAB and ADAMS software for capturing simulations. The results of capturing simulations demonstrate that the impedance control algorithm can respond fast and has excellent robustness when the environmental errors are random, and the contact forces and torques satisfy the low impact requirements.
... The controller resembles a conventional PD controller and introduced a desirable compliance to the system. A number of impedance controller designs have addressed issues such as robustness [30,62], adding adaptive control techniques [100,124], extension with learning approach [24], dynamics of flexible robot [4,94], dexterous manipulation [14,3,32]. ...
... The controller resembles a conventional proportionalderivative controller and introduces a desirable compliance to the system. A number of impedance controller designs have addressed issues such as robustness [92], [93], adding adaptive control techniques [94], [95], extension with a learning approach [96], dynamics of a flexible robot [78], [97], and dexterous manipulation [77], [98], [99]. ...
Different branches of technology are striving to come up with new advancements that will enhance civilization and ultimately improve the quality of life. In the robotics community, strides have been made to bring the use of personal robots in office and home environments on the horizon. Safety is one of the critical issues that must be guaranteed for the successful acceptance, deployment, and utilization of domestic robots. Unlike the barrier-based operational safety guarantee that is widely used in industrial robotics, safety in domestic robotics deals with a number of issues, such as intrinsic safety, collision avoidance, human detection, and advanced control techniques. In the last decade, a number of researchers have presented their works that highlighted the issue of safety in a specific part of the complete domestic robotics system. This article presents a general survey of various safety-related publications that focus on safety criteria and metrics, mechanical design and actuation, and controller design.
... For arm-hand systems impedance control approaches have been devised in[6],[7], where the virtual object concept is exploited to design an Intrinsically Passive Control (IPC) that can be used both for approaching the object and for grasping tasks. Others impedance control schemes for robotic hands have been proposed in[8], combined with an algorithm for grasp forces optimization, in[9], combined with an extended Kalman filter for friction estimation and in[10], where an impedance framework with multi-priority tasking is designed. † School of Engineering of the University of Basilicata, via dell'Ateneo Lucano 10, 85100, Potenza, Italy {giuseppe.muscio, ...
This paper presents a control framework for arm/hand systems aimed at controlling internal forces exchanged between the fingers and the grasped object, and enforcing a compliant behavior in presence of environmental interactions. A dynamic planner computes the motion references for the fingers by using the feedback of the contact forces, while an impedance control, in which dynamic effects exerted by the hand on the wrist are explicitly taken into account, is designed for the arm. The approach is experimentally validated on a 7-DOFs Barrett WAM with a Barrett Hand280.
... τ ext and τ f,m are external torque vector and friction torque vector in joint space, respectively. The generalized actuator torque vector, τ m , is considered as the control input [33], [34]. ...
This paper presents an experimental study on impedance control in both Cartesian and object level with adaptive friction compensation for dexterous robot hand based on joint torque feedback. To adaptively decrease the effects of high friction caused by complex transmission systems and joint coupling, a friction observer is proposed based on the extended Kalman filter (EKF) in this paper. A Cartesian impedance controller is implemented on a multi-fingered dexterous robot hand with identical fingers, based on the modelling of each modular finger. In addition, a flexible n-fingered object frame is proposed in this paper, applicable to any finger configuration with three or more fingers (n≥3). This enables the design of a 6-DoF spatial impedance controller. Stability of the closedloop system with friction observer is analysed. A position error of less than 0.16? is achieved using joint impedance control with adaptive friction compensation, which shows significant improvement in performance, as compared to 1.5° without compensation, and 0.5° with fixed-parameters friction compensation. Experimental results confirm the improvement in performance for the robot hand with Cartesian impedance control and adaptive joint friction compensation, demonstrating the effectiveness of spatial impedance controller with the proposed object frame and estimation strategy.
... In recent years, this control strategy has become one of the key technologies in modern robot control. Some examples of areas in robotics where impedance control is widely used today are dexterous manipulation [4, 5], flexible joint robots [6, 7], haptics [8, 9] and telerobotics [10, 11, 12, 13, 14, 15]. In parallel to these developments, recent trends in robotics increasingly rely on logically or spatially distributed, modular robot control systems (e.g., ROS [16], RT-Middleware [17], MRDS [18] ), where communication time delays are unavoidable and unfavourably influence control performance. ...
The improvement of direct human–robot physical interaction has recently become one of the strongest motivation factors in robotics research. Impedance/admittance control methods are key technologies in several directions of advanced robotics such as dexterous manipulation, haptics and telemanipulation. In this paper, we propose a control scheme and a design technique for stabilising shared impedance/admittance-based bilateral telemanipulation under varying time delay. The proposed scheme introduces delay-adaptive non-linear damping to stabilise the impedance model. A modified version of the tensor product model transformation is applied to determine the tensor product type polytopic linear parameter varying (LPV) representation of the impedance controlled interaction model, such that the value of the actual time delay becomes an external parameter rather than an inherent property of the system. The main benefit of the proposed approach is that the model form it produces is amenable to the immediate application of modern, linear matrix inequality (LMI)-based multi-objective synthesis methods. The viability of the proposed methodology is demonstrated through a single DoF force reflecting tele-grasping application. The results are also confirmed through laboratory experiments which help to further highlight the perspectives of this novel approach.
Joint torque sensing is an important technique for high-performance control of modern robotic systems, especially in an environment that requires man-machine collaboration. However, in many cases, traditional torque sensors are not suitable for robots because of the inevitable increase of joint flexibility and joint size. To address this problem, two novel methods are proposed to estimate torque of robotic joint with harmonic reducer via calibration of its existing flexibility without the need for any additional elastic elements. The first approach utilizes a new harmonic drive compliance model, which is more convenient for calibration and less dependent on the manufacturer’s parameters to estimate the output torque. The second method relies on a system based on a back-propagation (BP) neural network to fit the non-linear relationship among the output torque, motor current, and other information that can be obtained from double encoders mounted on motor-side and load-side. The two proposed methods were experimentally investigated and the results show that the estimated torque values were in good agreement with the measurements obtained using a commercial torque sensor. Finally, different suitable application scenarios are presented according to the specific performance of each technique.
