Impedance Control Scheme Research Articles

Robot-assisted Tactile Sensing for Minimally Invasive Tumor Localization

The 10 mm incisions used in minimally invasive cancer surgery prevent the direct palpation of internal organs, making intraoperative tumor localization difficult. A tactile sensing instrument (TSI), which uses a commercially available sensor to measure distributed pressure profiles along the contacting surface, has been developed to facilitate remote tissue palpation. The objective of this research is to assess the feasibility of using the TSI under robotic control to reliably locate underlying tumors while reducing collateral tissue trauma. The performance of humans and a robot using the TSI to locate tumor phantoms embedded into ex vivo bovine livers is compared. An augmented hybrid impedance control scheme has been implemented on a Mitsubishi PA10-7C to perform the force/position control used in the trials. The results show that using the TSI under robotic control realizes an average 35% decrease in the maximum forces applied and a 50% increase in tumor detection accuracy when compared to manual manipulation of the same instrument. This demonstrates that the detection of tumors using tactile sensing is highly dependent on how consistently the forces on the tactile sensing area are applied, and that robotic assistance can be of great benefit when trying to localize tumors in minimally invasive surgery.

Immersion and invariance‐based impedance control for electrohydraulic systems

AbstractThis work deals with the impedance control of electrohydraulic systems based on the concept of immersion and invariance. In the first step, the impedance control task for a basic electrohydraulic system comprising a hydraulic cylinder and a 4/3 proportional valve is analyzed. In order to mitigate the problem of energetic inefficiency and the high demands on the dynamics of the valve, an extended electrohdydraulic system is proposed. By means of a suitable choice of the parameters and an immersion and invariance‐based controller strategy, a significant reduction of both energy consumption and required dynamics of the valve can be obtained. The feasibility of the proposed impedance control strategies is demonstrated by extensive simulation studies. Copyright © 2009 John Wiley & Sons, Ltd.

Six-DOF Impedance Control of Dual-Arm Cooperative Manipulators

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, the problem of impedance control of dual-arm cooperative manipulators is studied. A general impedance control scheme is adopted, which encompasses a centralized impedance control strategy, aimed at conferring a compliant behavior at the object level, and a decentralized impedance control, enforced at the end-effector level, aimed at avoiding large internal loading of the object. Remarkably, the mechanical impedance behavior is defined in terms of geometrically consistent stiffness. The overall control scheme is based on a two-loop arrangement, where a simple proportional integral derivative inner motion loop is adopted for each manipulator, while an outer loop, using force and moment measurements at the robots wrists, is aimed at imposing the desired impedance behaviors. The developed control scheme is experimentally tested on a dual-arm setup composed of two 6-DOF industrial manipulators carrying a common object. The experimental investigation concerns the four different controller configurations that can be achieved by activating/deactivating the single impedance controllers. </para>

Self-calibrated robotic manipulator force observer

In the robotic manipulation context, end-effector contact forces may be difficult to measure mainly due to the tool dynamic interferences such as the inertial forces. In this paper, a whole methodology is proposed to estimate these forces. The new approach is based on a sensor fusion technique that integrates the information of a wrist force sensor, of a 3D accelerometer placed at the robot tool and the joint position sensors measurements. The proposed methodology not only offers a suitable estimator in terms of response and filtering, but also presents a self-calibrating feature that allows an easy integration into any industrial setup. To experimentally validate the performance of the proposed methodology, two different industrial manipulators were used: an ABB robot and a Stäubli robot, both with open control system architectures. An impedance control scheme was used as force/position control law to demonstrate the need and results of the proposed calibration result.

Neural Control of Motion-to-Force Transitions with the Fingertip

The neural control of tasks such as rapid acquisition of precision pinch remains unknown. Therefore, we investigated the neural control of finger musculature when the index fingertip abruptly transitions from motion to static force production. Nine subjects produced a downward tapping motion followed by vertical fingertip force against a rigid surface. We simultaneously recorded three-dimensional fingertip force, plus the complete muscle coordination pattern using intramuscular electromyograms from all seven index finger muscles. We found that the muscle coordination pattern clearly switched from that for motion to that for isometric force approximately 65 ms before contact (p = 0.0004). Mathematical modeling and analysis revealed that the underlying neural control also switched between mutually incompatible strategies in a time-critical manner. Importantly, this abrupt switch in underlying neural control polluted fingertip force vector direction beyond what is explained by muscle activation-contraction dynamics and neuromuscular noise (p < or = 0.003). We further ruled out an impedance control strategy in a separate test showing no systematic change in initial force magnitude for catch trials where the tapping surface was surreptitiously lowered and raised (p = 0.93). We conclude that the nervous system predictively switches between mutually incompatible neural control strategies to bridge the abrupt transition in mechanical constraints between motion and static force. Moreover because the nervous system cannot switch between control strategies instantaneously or exactly, there arise physical limits to the accuracy of force production on contact. The need for such a neurally demanding and time-critical strategy for routine motion-to-force transitions with the fingertip may explain the existence of specialized neural circuits for the human hand.

Force Tracking Impedance Control with Variable Target Stiffness

In this paper, a novel force tracking impedance control strategy is presented in which target stiffness is varied on-line to regulate the desired contact force without any knowledge of the environment. Humans can control contact force by adjusting their arm stiffness. The contact force can be either increased by making one's arm stiffer or decreased by reducing the arm stiffness. Furthermore, humans can keep the force tracking error within a certain range without any knowledge of environmental parameters as long as how much force they exert on the object is known to them. Analogously, the proposed control scheme achieves a contact force regulation control by adjusting the target stiffness of the impedance control. The new force tracking impedance control scheme does not require estimating environment stiffness or locations since the controller is adapted only based on the previous force tracking error between the desired and real contact force. Stability of the proposed scheme is discussed with a quadratic Lyapunov function. Extensive simulation studies with a 7 degree of freedom (DoF) robot manipulator using full arm dynamics are conducted to demonstrate the validity of the proposed scheme.

An Experimental Study on Cartesian Impedance Control for a Joint Torque-Based Manipulator

The purpose of this paper is to present our results on experimental investigations on Cartesian impedance control and nonlinearity compensation for our harmonic drive robot based on joint torque sensors. The imperfection of the cubic model for harmonic drive friction is detected according to friction identification experiments. In addition, five different Cartesian impedance control schemes are considered and four of them are tested by corresponding experiments with/without friction compensation. Experimental results tell us that the force-based impedance control strategy is more suitable than the position-based strategy for the harmonic drive robot based on joint torque feedback.

Sliding Mode Control

Sliding Mode Control

Interaction control of robotic manipulators via second‐order sliding modes

AbstractThis paper deals with the interaction control of robot manipulators. The ideal goal is to control the manipulator so that its end‐effector reaches a desired position in the operative space. The attainment of this goal can be prevented by the fact that during its motion the end‐effector can interact with the environment. So, a realistic goal is regarded as control objective in the paper, that of asymptotically reaching an equilibrium position jointly determined by the choice of the ideal desired position, and by the presence of the environment. The model of the manipulator is supposed to be affected by uncertainties, so that a classical impedance control scheme cannot be adopted. The approach proposed in this paper relies on the theory of sliding mode control. In general, this methodology is deemed nonappropriate to control mechanical systems like robot manipulators, since it introduces the so‐called chattering phenomenon, which produces undesired wear and vibrations. Yet, the final control solution proposed in this paper is based on the generation of sliding modes of the second order, which practically reduces the degradation of performances, and the mechanical stress due to the chattering effect. Indeed, the proposed second‐order sliding mode control scheme relies on the use of a continuous control law, in contrast to conventional sliding mode control schemes. Copyright © 2007 John Wiley &amp; Sons, Ltd.

2A1-B06 外力に感応するアドミッタンス制御の特性と構造(安全・安心なロボットを目指して)

Mechanical impedance control schemes are classified into torque-control-based and position-control-based. The former is used for a direct-drive manipulator. The latter is also called Admittance Control and often used for a geared manipulator, which control the position determined from a force sensor. Since the admittance control uses the high-gain position controller, the manipulator hardly move against the force without involving the force sensor. In this paper, we show the characteristics and structure of admittance control responsive to unmeasurable external force.

Impedance Control of CPM Device with Flex-/Extension and Pro-/Supination for Upper Limbs

Continuous Passive Motion (CPM) is a surgical treatment or physiotherapy after surgery or trauma. Most of the CPM devices used for treatment of the elbow joint have one degree of freedom in flex-/extension. For this reason, the patients are limited in pro-/supination of the forearm with flex-/extension of the elbow joint according to the arm movement of the CPM device. In this paper, a novel impedance control scheme of pro-/supination is proposed for CPM device with flex-/extension and pro-/supination. Impedance control is designed for the reference trajectory measured from a normal subject, and the parameters for impedance control are designed in order to suppress the excessive force at the limitation of range of motion. The effectiveness of the proposed scheme is evaluated by experiments.

Force Sensor-less Workspace Virtual Impedance Control Considering Resonant Vibration for Industrial Robot

The motion control paradigm provides sufficient performance in many elementary industrial tasks. However, only stiff motion the robot cannot accommodate the interaction force under constrained motion. In such situation, the robot is required to perform interaction behavior with the environment. The conventional impedance control schemes require force-sensing devices to feedback force signals to the controllers. The force-sensing device is therefore indispensable and the performance of the system also depends on the quality of this device. This paper proposes a novel strategy for force sensor-less impedance control using disturbance observer and dynamic model of the robot to estimate the external force. In motion task, the robust D-PD (derivative-PD) control is used with feedforward inverse-dynamic torque compensation to ensure robustness and high-speed response with flexible joint model. When robot is in contact with environment, the proposed force sensor-less scheme impedance control with inner-loop D-PD control is utilized. D-PD control uses both position and speed as the references to implement the damping and stiffness characteristic of the virtual impedance model. In addition, the gravity and friction force-feedback compensation is computed by the same dynamic model, which is used in external force estimation. The flexible-joint robot model is utilized in both disturbance observer and motion control design. The workspace impedance control for robot interaction with human operator is implemented on the experimental setup three-degree-of-freedom (3-DOF) robot manipulator to assure the ability and performance of the proposed force sensor-less scheme for flexible-joint industrial robot.

空気式パラレルマニピュレータを用いた手首部リハビリ支援装置の開発―多自由度リハビリ動作の実現―

In this study, we focused on a rehabilitation motion of human wrist joint and aim at developing a mechanical equipment to support these rehabilitation motion. A pneumatic parallel manipulator is introduced since it can drive multiple D.O.F. enough to correspond to a wrist motion and has inherent compliance characteristics resulted from air compressibility works as safety mechanism and minute force regulating function. An impedance control strategy is applied on the manipulator to implement rehabilitation motion by adjusting impedance parameters appropriately. The validities of the proposed multiple D.O.F. rehabilitation system for the several rehabilitation motion are confirmed through experiments.

Impedance Control of Flexible Robot Arms with Parametric Uncertainties

This paper presents an adaptive impedance control strategy for flexible manipulators by using an end-effector trajectory control approach. The impedance control objective is converted into tracking a trajectory generated by a designed ideal impedance model. A manifold is designed to prescribe desirable performance of the system. An adaptive control scheme is derived in such that the motion of the system will converge and remain to the ideal manifold for the case of parametric uncertainties. Stability of the control system is analyzed. Simulations are carried out to demonstrate the effectiveness of the proposed control method.

1P1-N-065 人間とロボットの協調作業系におけるインピーダンス制御法を用いたパワーアシストシステム(人間機械協調1,生活を支援するロボメカ技術のメガインテグレーション)

1P1-N-065 人間とロボットの協調作業系におけるインピーダンス制御法を用いたパワーアシストシステム(人間機械協調1,生活を支援するロボメカ技術のメガインテグレーション)

Robotics, motor learning, and neurologic recovery.

Robotic devices are helping shed light on human motor control in health and injury. By using robots to apply novel force fields to the arm, investigators are gaining insight into how the nervous system models its external dynamic environment. The nervous system builds internal models gradually by experience and uses them in combination with impedance and feedback control strategies. Internal models are robust to environmental and neural noise, generalized across space, implemented in multiple brain regions, and developed in childhood. Robots are also being used to assist in repetitive movement practice following neurologic injury, providing insight into movement recovery. Robots can haptically assess sensorimotor performance, administer training, quantify amount of training, and improve motor recovery. In addition to providing insight into motor control, robotic paradigms may eventually enhance motor learning and rehabilitation beyond the levels possible with conventional training techniques.

Adaptive Impedance Control of Robot Manipulators based on Function Approximation Technique

This paper presents an adaptive impedance control scheme for an $n$-link constrained rigid robot manipulator without using the regressor. In addition, inversion of the estimated inertia matrix is also avoided and the new design is free from end-point acceleration measurements. The dynamics of the robot manipulator is assumed that all of the matrices in robot model are unavailable. Since these matrices are time-varying and their variation bounds are not given, traditional adaptive or robust designs do not apply. The function approximation technique is used here to represent uncertainties in some finite linear combinations of the orthogonal basis. The dynamics of the output tracking can thus be proved to be a stable first order filter driven by function approximation errors. Using the Lyapunov stability theory, a set of update laws is derived to give closed loop stability with proper tracking performance. A 2 DOF planar robot with environment constraint is used in the computer simulations to test the efficacy of the proposed scheme.

Force Tracking Impedance Control of Robot Manipulators Under Unknown Environment

In this paper, a new simple stable force tracking impedance control scheme that has the capability to track a specified desired force and to compensate for uncertainties in environment location and stiffness as well as in robot dynamic model is proposed. The uncertainties in robot dynamics are compensated by the robust position control algorithm. After contact, in force controllable direction the new impedance function is realized based on a desired force, environment stiffness and a position error. The new impedance function is simple and stable. The force error is minimized by using an adaptive technique. Stability and convergence of the adaptive technique are analyzed for a stable force tracking execution. Simulation studies with a three link rotary robot manipulator are shown to demonstrate the robustness of the proposed scheme under uncertainties in robot dynamics, and little knowledges of environment position and environment stiffness. Experimental results are carried out to confirm the proposed controller's performance.

Evolutionary‐based virtual training in extracting fuzzy knowledge for deburring tasks

In this research, the problems of how to teach a robot to execute skilled operations are studied. Human workers usually accumulate their experience after executing the same task repetitively. In the process of training, a worker needs to find ways of adjusting his/her execution. In our system, the parameters for an impedance control scheme are considered as the targets for adjustment in the training process. The way to make adjustments is represented as a set of fuzzy rules in our research. Furthermore, a training scheme, called the evolutionary‐based virtual training scheme, is proposed to extract knowledge (a set of fuzzy rules) for robotic deburring tasks. In this approach, an evolutionary algorithm is employed to find the best set of fuzzy rules and a simulation system is built to evaluate the execution performances of candidates. This learning scheme has been applied in finding a set of fuzzy rules that can adjust the parameters of impedance controllers required in deburring operations with satisfactory performance in deburring tasks.

Design and control of a three degree of freedom pneumatic physiotherapy robot

Stroke is a common condition resulting in 30,000 people per annum left with significant disability. In patients with severe arm paresis after stroke, functional recovery in the affected arm is poor. Inadequate intensity of treatment is cited as one factor accounting for the lack of arm recovery found in some studies. Given that physical therapy resource is limited, strategies to enhance the physiotherapists' efforts are needed. One approach is to use robotic techniques to augment movement therapy.A three degree-of-freedom pneumatic robot has been developed to apply physiotherapy to the upper limb. The robot has been designed with a workspace encompassing the reach-retrieve range of the average male. Control experiments have applied force and then position only controllers to the pneumatic robot. These controllers are combined to form a position-based impedance control strategy on all degrees of freedom of the robot. The impedance controller performance was found to be dependent upon the specified impedance parameters. Initial experiments attaching the device to human subjects have indicated great potential for the device.