外部環境に対するマニピュレータの最適接近速度

In teleoperation tasks, communication delays between master and slave sides negatively affect the stability and transparency of closed loop system, and make it difficult to maintain a desired contact force. In order to improve the performance of contact force control in teleoperation under large time delays, a shared compliant control method is proposed in this paper. On the master side, the operator issues a desired contact force command according to the feedback of the contact stiffness identified on line besides motion commands. And on the slave side, a local contact force controller is designed using an adaptive Smith predictor, so as to shares control load with the operator. Experimental results show that this method can improve the force control performance, lower the difficulty of operation, and help the operator complete contact tasks with proper forces.In teleoperation tasks, communication delays between master and slave sides negatively affect the stability and transparency of closed loop system, and make it difficult to maintain a desired contact force. In order to improve the performance of contact force control in teleoperation under large time delays, a shared compliant control method is proposed in this paper. On the master side, the operator issues a desired contact force command according to the feedback of the contact stiffness identified on line besides motion commands. And on the slave side, a local contact force controller is designed using an adaptive Smith predictor, so as to shares control load with the operator. Experimental results show that this method can improve the force control performance, lower the difficulty of operation, and help the operator complete contact tasks with proper forces.

SUMMARYThis paper addresses the problem of contact force control for multiple contacts distributed over multiple links in a robot. This is of importance when performing complex tasks in unstructured environment, particularly in humanoid robot applications. The proposed multicontact control framework provides a new way of defining the operational space coordinates, which facilitates the specification of multiple contact control. The contact force space on multiple links is constructed as an operational space for the highest priority task. Motion control, given lower priority, can be executed using the rest of degree of freedom within the null-space of the force control. The dynamic control structure, then, provides a means to control each contact force and motion independently. This dynamic decoupling enables each contact force controller to utilize linear control theories. In particular, the contact force controllers adopt full state feedback control and estimation methods to produce robust performance with respect to modeling and parameter uncertainties. The effectiveness of the multiple contact control framework was demonstrated using a PUMA560 manipulator, with multiple contacts on the end-effector and third link. The demonstrated tasks involved controlling each of the contact forces with null-space motion.

The quadruped robot can achieve stable locomotion with contact force control. The crucial technique of it is to convert the control of the center of mass (COM) to the control of supporting legs. In this paper, we propose a force distribution and control strategy based on model decomposition and optimal contact constrains for the quadruped robot with trotting gait. The quadruped robot can be modeled as a virtual planar seven-link and a virtual planar three-link under the supposition that the control of the COM is decoupled. Meanwhile, an optimal contact constraint will be proposed and the desired contact force can be found. The simulation and experiment results show that the robot can track the desired trajectories exactly and steadily.

In this study, the stable detection principle of a MEMS hardness sensor with “reference plane” structure is theoretically analyzed and demonstrated with experimental results. Hardness measurement independent of contact force instability is realized by the optimum design of the reference plane. The fabricated devices were evaluated, and a “shore A” hardness scale (JIS K 6301 A) was obtained as the reference in the range from A1 to A54 under a stable contact force. The contact force dependence on hardness sensor signals was effectively reduced by 96.6% using our reference plane design. Below 5 N contact force, the maximal signal error of hardness is suppressed to A8. This result corresponds to the detection capability for fat hardness, even when the contact force is unstable. Through experiments, stable detection of human body hardness has been demonstrated without any control of contact force.

This paper investigates the role of precise estimation of contact points in force control. This analysis is motivated by scenarios in which robots make contacts, either voluntarily or accidentally, with different parts of their body. Control paradigms that are usually implemented in robots with no tactile system, make the hypothesis that contacts occur at the end-effectors only. In this paper we try to investigate what happens when this assumption is not verified. First we consider a simple feedforward force control law, and then we extend it by introducing a proportional feedback term. For both controllers we find the error in the resulting contact force, that is induced by a hypothetic error in the estimation of the contact point. We show that, depending on the geometry of the contact, incorrect estimation of contact points can induce undesired joint accelerations. We validate the presented analysis with tests on a simulated robot arm. Moreover we consider a complex real world scenario, where most of the assumptions that we make in our analytical derivation do not hold. Through tests on the iCub humanoid robot we see how errors in contact localization affect the performance of a parallel force/position controller. In order to estimate contact points and contact forces on the forearm of the iCub we do not use any model of the environment, but we exploit its 6-axis force/torque sensor and its sensorized skin.

This paper presents a control scheme to maintain consistent contact force using a handheld robot during soft tissue interaction with imaging instruments such as probe-based confocal laser endomicroscopy (pCLE). The handheld robot incorporates a 6-DOF miniature micromanipulator and a force sensor for the control. Given force set for clearly visualizing tissue on contact, the handheld robot can maintain such a tiny force by actively controlling its tool tip using the micromanipulator. It allows keeping locating the tool tip within the depth-of-focus region of the imaging instrument regardless of actual force on the soft tissue engaged by hand motion delivered to the handpiece of the robot. The contact force is regulated primarily by controlling the depth of the tool tip from the tissue surface. This procedure is accomplished by controlling the position of the tool tip via closed-loop force control. To validate the control scheme, we evaluated force tracking performance at the tool tip given a sinusoidal force input with an amplitude of 0.1 N for various frequencies, while firmly fixing the robot. As a result, the handheld robot could maintain the target force with an RMS error of less than 7.8 mN. The handheld task holding the robot on top of a single contact point was also evaluated, which yields an RMS error of 22.6 mN along the Z-axis of the sensor. Finally, the robot-aided scanning over the surface of the soft tissue was performed using the handheld robot, and the error was significantly reduced by 31.6% on average compared to unaided operation.

As the application range of present day industrial robots is expanded beyond pick‐and‐place operations, spray painting and spot welding, there is an increasing need for the control of contact forces between the manipulator end point and environment. One important force control task is robotic drilling in hazardous environments. This paper addresses the analysis and characterisation of forcecontrolled robotic drilling, generation of a control strategy in the light of specifications obtained from the characterisation of this task, and the completion of a drilling operation with robot manipulator under contact force control. The experimental results demonstrate that a robot manipulator can perform drilling if enough contact thrust‐force is provided between a workpiece and drill, and is controlled properly. It follows that the analysis and characterisation of a task, especially investigation of the dynamic interactions between the tool carried by a manipulator and a workpiece, strategy generation, and controller design proceed simultaneously in order to develop a force control system for a specific task.

Robust hybrid position/force control of redundant robots

Moving a robot arm quickly in cluttered and unmodeled workspaces can be difficult because of the inherent risk of high impact forces. Additionally, compliance by itself is not enough to limit contact forces due to multi-contact phenomena (jamming, etc.). The work in this paper extends our previous research on manipulation in cluttered environments by explicitly modeling robot arm dynamics and using model predictive control (MPC) with whole-arm tactile sensing to improve the speed and force control. We first derive discrete-time dynamic equations of motion that we use for MPC. Then we formulate a multi-time step model predictive controller that uses this dynamic model. These changes allow us to control contact forces while increasing overall end effector speed. We also describe a constraint that regulates joint velocities in order to mitigate unexpected impact forces while reaching to a goal. We present results using tests from a simulated three link planar arm that is representative of the kinematics and mass of an average male's torso, shoulder and elbow joints reaching in high and low clutter scenarios. These results show that our controller allows the arm to reach a goal up to twice as fast as our previous work, while still controlling the contact forces to be near a user-defined threshold.

An exact dynamic model of a constrained two-link manipulator with a flexible forearm moving in a horizontal plane is derived using Hamilton's principle. A new variable is introduced before the procedure of modal expansion in order to convert the non-homogeneous boundary condition into a homogeneous one in the model formulation. The static tip deflection of the flexible link is allowed in order to maintain the contact force between the end-effector and the constrained surface and this tip deflection is considered in both the inverse kinematics and the order reduction procedures. The state vector of the reduced model for controller design consists of joint angle of the rigid link, its derivative and integral, the first deflection mode and its derivative, and the integral of contact force. A multivariable controller is proposed for a simultaneous control of end point position and contact force of the manipulator. The controller consists of a feedforward term which contributes the torque for the expected joint angles and the contact force, and a feedback term with the time varying optimal gains obtained from the matrix Riccati equation. Computer simulation results show that this proposed controller is capable of performing the straight line tracking task satisfactorily under three different conditions.

In this paper, a new continuum-based pantograph/catenary model based on the absolute nodal coordinate formulation (ANCF) is proposed and used to develop an effective method to control the contact force which arises from the pantograph/catenary interaction. In the proposed new model, only one ANCF gradient vector is used in the formulation of the pantograph/catenary contact conditions, thereby allowing for using the proposed approach for both fully parameterized and gradient deficient ANCF finite elements. A three-dimensional multibody system (MBS) model of a pantograph mounted on a train is developed using a nonlinear augmented MBS formulation. In order to take into account the catenary large deformation, ANCF finite elements are used. The contact between the pantograph and the catenary system is ensured using a sliding joint constraint whereas the contact between the rail vehicle wheels and the train track is modelled using an elastic contact formulation. In addition to the use of the new MBS approach to model the pantograph/catenary interaction, the contact force between the pantograph and the catenary is computed using a simpler lumped parameter model which describes the pan-head and the plunger subsystem dynamics. In order to reduce the standard deviation of the contact force without affecting its mean value, a control actuator is used between the pan-head and the plunger. To this end, three types of control laws for the control action are designed to improve the contact quality both in the transient phase and in the steady state phase of the pantograph/catenary interaction. The first control law proposed features a feedback structure whereas the second and the third control strategies employ a feedback plus feed-forward architecture. In order to demonstrate the effectiveness of the proposed method, the results of a set of numerical simulations with and without the controllers are presented.

Soft robots are increasingly being explored and developed in various settings that demand safe and adaptable interactions between robots and their environments. In addition, soft robots exhibit passive compliant behavior and generate continuous deformations when engaging with the environment. This imposes challenges on achieving active, on-demand interaction force control, especially when feedback force-sensing devices are not available. Consequently, there is a need to explore new model-based force control paradigms for soft robots. In this article, we propose a (quasi-)static force control approach for soft robots based on compliance modeling, avoiding the necessity for feedback control loops or extensive training data collection. The proposed approach can deliver contact force control along three Cartesian axes when the robot is actuated into various configurations. The compliance matrix is derived from the robot configuration, which allows the calculation of desired deflection displacements needed to generate on-demand forces. The resulting force control is achieved by solving inverse kinematics problems based on these deflection displacements. The efficacy of our proposed controller is validated through experiments with both one- and two-segment pneumatic-driven soft continuum robots. The results demonstrate effective static force control performance, with mean control errors below 5% of the desired peak forces.

Continuum robots, owing to their inherent compliance, have become essential in endoscopic surgical procedures, such as mucosal ablation. However, the prevalent design of endoscopic manipulators, which typically features only a single active bending segment, often results in limited dexterity and accessibility. Additionally, the incorporation of variable stiffness in these robots has attracted significant interest, with the aim to improve manipulation capabilities in confined spaces. In the paper, we propose a novel variable-length continuum robot with variable stiffness for endoscopic surgery. The robot’s stiffness can be altered either by modifying the catheter’s length or solid-liquid transition of low-melting-point alloy (LMPA). The design and fabrication methods of the robot are meticulously detailed. Additionally, a quasi-static stiffness model along with a learning-based stiffness compensation approach for accurate stiffness estimation are proposed. Leveraging this model, a contact force controller is designed for ablation procedure. The experimental results show that our robot possesses good flexibility and accessibility, making it highly adept at manipulating in confined spaces. Its variable stiffness feature significantly enhances its ability to counteract external disturbance and prevent tip deformation (with a average position change of 1.1mm). Finally, through force control experiments and a surgical demonstration in a gastrointestinal model, we have further validated the robot’s applicability in surgical contexts. Note to Practitioners—This paper proposed a variable-length continuum robot with variable stiffness for endoscopic surgery. The robot can achieve axial elongation and omnidirectional bending motion, having better dexterity and accessibility than traditional medical continuum robots with one active bending segment. The robot’s stiffness can be adjusted by the length changes or solid-liquid transition of low-melting-point alloy (LMPA). Besides, an accurate stiffness model and a contact force controller are proposed for endoscopic ablation surgery. By experimental results, the robot shows high flexibility and accessibility, allowing access to confined spaces for manipulation, and good control accuracy and variable stiffness capability for endoscopic surgery.

Calligraphic writing presents many challenges for motor control, including: learning and recall of stroke sequences; critical timing of stroke onsets and durations; fine control of grip and contact forces; and letterform invariance under size scaling, which entails fine control of stroke directions and amplitudes during recruitment and derecruitment of musculoskeletal degrees of freedom. Experimental and computational studies in behavioral neuroscience have progressed toward explaining the learning, planning, and control exercised in tasks that share features with calligraphic writing and drawing. This article highlights component operations ranging from parallel sequence representations to fine force control. Treated in succession are: competitive queuing models of sequence representation, performance, learning, and recall; letter size scaling and motor equivalence; cursive handwriting models in which sensory-motor transformations are performed by circuits that learn inverse differential kinematic mappings; and fine-grained control of timing and transient forces by circuit models that learn to solve inverse dynamics problems.

An aerial manipulator system consisting of a quadrotor UAV and a one-DOF manipulator is introduced for contacting operations in the air. As the system is interacting with external environment to do some operations, there will exist contact force. According to the practical aerial contact manipulation features, it is known that an aerial manipulator usually performs operations as the UAV platform is in hover flight or nearby. To realize controlling the force, the hovering UAV acting as a spring-mass-damper system is firstly proved. Then, based on the derived model and the impedance control algorithm, a contact force control method is presented. That is, the position error is controlled in order to control the contact force ultimately. The actual flight experiments show that the developed system is enable to realize the contact force control without a force sensor.