Force Feedback Control Research Articles

Multi-dimensional dynamic measurement uncertainty analysis for the six-axis force sensor used in docking system

The tough space environment has a great influence on the reliability of the measurement results owing to the rapidly aging sensor. Also, the measurement uncertainty caused by the random factors seriously affects the accuracy of the sensor. Aiming at the multidimensional dynamic uncertainty problem of the six-axis force measurement, a six-axis force sensor for docking system is presented based on the piezoelectric force sensing element. The decoupling algorithm of the six-axis force sensor is proposed. Grey prediction model is employed to establish the dynamic uncertainty model in single channel. Residual test, correlation test and posterior error test are conducted to verify the reliability of the prediction model. The multidimensional dynamic uncertainty model of the six-axis force sensor is derived by combination of the decoupling algorithm and the dynamic uncertainty in single channel. The multidimensional dynamic uncertainty model of the six-axis force sensor can avoid the error signals for the force feedback control in the space environment, and the model can also be employed for the measurement of six-axis force in any other harsh conditions.

Instrumented Compliant Wrist with Proximity and Contact Sensing for Close Robot Interaction Control.

Compliance has been exploited in various forms in robotic systems to allow rigid mechanisms to come into contact with fragile objects, or with complex shapes that cannot be accurately modeled. Force feedback control has been the classical approach for providing compliance in robotic systems. However, by integrating other forms of instrumentation with compliance into a single device, it is possible to extend close monitoring of nearby objects before and after contact occurs. As a result, safer and smoother robot control can be achieved both while approaching and while touching surfaces. This paper presents the design and extensive experimental evaluation of a versatile, lightweight, and low-cost instrumented compliant wrist mechanism which can be mounted on any rigid robotic manipulator in order to introduce a layer of compliance while providing the controller with extra sensing signals during close interaction with an object’s surface. Arrays of embedded range sensors provide real-time measurements on the position and orientation of surfaces, either located in proximity or in contact with the robot’s end-effector, which permits close guidance of its operation. Calibration procedures are formulated to overcome inter-sensor variability and achieve the highest available resolution. A versatile solution is created by embedding all signal processing, while wireless transmission connects the device to any industrial robot’s controller to support path control. Experimental work demonstrates the device’s physical compliance as well as the stability and accuracy of the device outputs. Primary applications of the proposed instrumented compliant wrist include smooth surface following in manufacturing, inspection, and safe human-robot interaction.

Force Feedback Control Assisted Tympanostomy Tube Insertion

Otitis media with effusion (OME) is a common ear disease affecting children and adults all over the world. After medication as the first treatment fails, the tympanostomy tube insertion is the frequently performed otologic surgical procedure to treat OME. During the surgery, an incision is made on the tympanic membrane first and followed by the tube insertion through the incision on the eardrum. To overcome the disadvantages of the current surgical treatment for OME, an office-based surgical device suitable for patients with OME is developed and introduced in this paper. Since the tube insertion is the key to success in this surgery, it is necessary to ensure that the procedure is carried out in a quick and safe manner with a high success rate via the proposed surgical device. Moreover, the insertion time should be as short as possible so that the discomfort on the patient can be minimized. To this end, a control scheme with a new insertion method using force feedback is proposed, implemented, and tested in a mock-up system. The experimental results show that the proposed insertion method can achieve better performance on tube insertion than a pure motion controller or a pure force feedback controller. The success rate of the proposed insertion method is close to 100% and the insertion time is less than 0.19 s while it is carried out on a stable setup.

Auto-tracking single point diamond cutting on non-planar brittle material substrates by a high-rigidity force controlled fast tool servo

This paper presents auto-tracking single point diamond cutting, which can conduct precision cutting on non-planar brittle material substrates without prior knowledge of their surface forms, by utilizing a force controlled fast tool servo (FTS). Differing from traditional force feedback control machining based on a cantilever mechanism such as an atomic force microscope (AFM) that suffers from low-rigidity and limited machining area, the force controlled FTS utilizes a highly-rigid piezoelectric-type force sensor integrated with a tool holder of the FTS system to provide sufficient stiffness and robustness for force-controlled cutting of brittle materials. It is also possible for the system to be integrated with machine tools to deal with the difficulties in the cutting of large area non-planar brittle materials, which requires not only high machining efficiency but also a high stiffness. Experimental setup is developed by integrating the force controlled FTS to a four-axis ultra-precision diamond turning machine. For the verification of the feasibility and effectiveness of the proposed cutting strategy and system, auto-tracking diamond cutting of micro-grooves is conducted on an inclined silicon substrate and a convex BK7 glass lens, while realizing constant depths of cuts under controlled thrust forces.

Stabilization system on an office-based ear surgical device by force and vision feedback

An “office-based surgical device” is a kind of device which aims to shift the conventional surgical procedures from the operating room to the confines of the doctor’s/surgeon’s office as well as to assist the surgeons to carry out the surgeries on the patients automatically or semi-automatically. In this paper, an office-based surgical device suitable for patients with Otitis Media with Effusion (OME) is introduced. Due to the office-based design, it is not possible to subject the patient to general anesthesia, i.e., the patient is awake during the surgical treatment with the device. To ensure a high success rate and safety, it is very important that the relative motion and the contact force between the tool set of the device and the tympanic membrane (TM) can be stabilized. To this end, a control scheme using force and vision feedback is proposed. The force feedback controller is a PID-based (proportional-integral-derivative) controller, which is designed for force tracking. The vision feedback controller is a vision-based motion compensator, which is designed to measure and compensate the head motion since it is equivalent to TM motion. Furthermore, the control scheme is implemented and tested in a mock-up system. The experimental results show that the proposed composite controller can achieve much better performance in force tracking than a pure force feedback controller. The performance can at least improve by 20% after augmenting the motion compensator, which helps the system to stabilize the relative motion indirectly and maintain the contact force precisely.

Force Feedback Control Method of Active Tuned Mass Damper

Active tuned mass dampers as vibration-control devices are widely used in many fields for their good stability and effectiveness. To improve the performance of such dampers, a control method based on force feedback is proposed. The method offers several advantages such as high-precision control and low-performance requirements for the actuator, as well as not needing additional compensators. The force feedback control strategy was designed based on direct-velocity feedback. The effectiveness of the method was verified in a single-degree-of-freedom system, and factors such as damping effect, required active force, actuator stroke, and power consumption of the damper were analyzed. Finally, a simulation study was performed by configuring a main complex elastic-vibration-damping system. The results show that the method provides effective control over modal resonances of multiple orders of the system and improves its dynamics performance.

A Low Cost Linear Force Feedback Control System for a Two-fingered Parallel Configuration Gripper

This paper presents a simple linear control based force feedback for the gripper of a SCORBOT ER-4u robotic arm. The SCORBOT ER-4u is a 5 degree of freedom (DOF) dexterous robotic arm with a rigid 2-fingered parallel configuration gripper. A Flexi-Force Force Sensitive Resistor (FSR) is attached to one of the claws of the gripper and interfaced to a notebook computer using Arduino Uno microcontroller. The force sensor aids the robotic arm in three different ways: one, senses if an object has been successfully grasped, second determine the coefficient of friction of the object, and third prevent damage when the object will be grasped. The gripper along with the force sensor is calibrated prior to grasping objects. During calibration, samples of the object to be manipulated are used to establish the extents of the gripper on the basis of its grasping force. By following calibration pattern, the gripper is able to grasp objects with approximately the same coefficient of friction. Most importantly, it ensures that the object to be grasped is not damaged by applying sufficient amount of force based on the object's weight. The experimental analyses of the proposed work have shown interesting results to control both the SCORBOT ER-4u robotic arm and the force sensor for grasping masses, strictly conforming to the safety margin of the object.

Stabilizing Series-Elastic Point-Foot Bipeds Using Whole-Body Operational Space Control

Whole-body operational space controllers (WBOSCs) are versatile and well suited for simultaneously controlling motion and force behaviors, which can enable sophisticated modes of locomotion and balance. In this paper, we formulate a WBOSC for point-foot bipeds with series-elastic actuators (SEA) and experiment with it using a teen-size SEA biped robot. Our main contributions are on devising a WBOSC strategy for point-foot bipedal robots, 2) formulating planning algorithms for achieving unsupported dynamic balancing on our point-foot biped robot and testing them using a WBOSC, and 3) formulating force feedback control of the internal forces—corresponding to the subset of contact forces that do not generate robot motions—to regulate contact interactions with the complex environment. We experimentally validate the efficacy of our new whole-body control and planning strategies via balancing over a disjointed terrain and attaining dynamic balance through continuous stepping without a mechanical support.

Position and force tracking in nonlinear teleoperation systems with sandwich linearity in actuators and time-varying delay

In this paper, a new bounded force feedback control law is proposed to guarantee position and force tracking in nonlinear teleoperation systems in the presence of passive and nonpassive input interaction forces, time varying delay in their communication channels and sandwich linearity in their actuators. The proposed control is a nonlinear-proportional plus nonlinear damping (nP+nD) controller with the addition of a nonlinear function of the environment force on the slave side and nonlinear function of the human force and force error on the master side, the transparency of the proposed scheme will be improved. The controller prevents the inputs from reaching their usual actuator bounds. Using a novel Lyapunov–Krasovskii functional, the asymptotic stability and tracking performance of the teleoperation system are established under some conditions on the controller parameters, actuator saturation characteristics and maximum allowable time delays.

Theoretical Analysis of the Force and Position Synergies in Two-Joint Movements

A theoretical approach is proposed to define the force and position singular points (FSPs and PSPs) in the circular, ellipsoidal, and linear planar two-joint movements produced under steady loadings directed along the movement traces. The FSPs coincide with changes in the direction of the force moments acting around the joints; the PSPs show the locations of the extrema at the joint angle trajectories. The force synergy (defined by the location of FSPs) provides a strong influence on the activation synergy; the latter is largely described by correlations between the activities recorded from the muscles participating in the movement. The position synergy (defined by the location of PSPs) is responsible for a hysteresis-related modulation of the activation synergy. Geometrical procedures are proposed to define positions of the FSPs and PSPs along various movement traces; this can provide a general description of the force and position synergies for the movements. The force synergies in the circular movements cover four sectors with diverse loading combinations of the flexor and extensor muscles belonging to different joints. The variability of the synergy effects for changes in the size and position of the circular trajectories is analyzed; the synergy patterns are also considered for ellipsoidal and linear movement traces. A Force Feedback Control Hypothesis is proposed; it allows one to explain the decrease in the number of controlled variables during real multi-joint movements.

Model Predictive Controller for a Micro-PMSM-Based Five-Finger Control System

This paper proposes the design and implementation of a model predictive control (MPC) algorithm for a micro-permanent-magnet synchronous motor (micro-PMSM)-based five-finger control system. First, the kinematic analysis and inverse kinematics of the micro-finger system are developed. The relationship between the rotor position of micro-PMSM and the position of the micro-fingertip is determined. Then, an MPC algorithm is designed to improve the performance of the micro-PMSM control system. An embedded system, cRIO-9024/9112, is used as a control center to execute the position control algorithm and force control algorithm. Experimental results show that the proposed system provides satisfactory transient responses, load disturbance responses, and tracking responses. In addition, the proposed five-finger system can grasp some objects by using the proposed force feedback control and a trajectory planning algorithm.

Tank testing of an inherently phase-controlled wave energy converter

Results from laboratory experiments on a pre-tensioned heaving buoy of 8.4m diameter, tested at scale 1:16 is presented. The wave energy converter, which is under development by the Swedish company CorPower Ocean, is designed with a passive pneumatic machinery component referred to as WaveSpring, invented at NTNU. The negative spring arrangement inherently provides phase control. The power take off system and the effect of the phase-enhancement component was represented by a motor rig run with a force-feedback controller. Responses with and without the WaveSpring unit were measured in order to compare performance in terms of motions, loads and power absorption.The experiments included decay tests, radiation tests, irregular wave tests with the system in normal operation, as well as extreme wave tests with the system in survival mode. The power was extracted through a linear damping force, where the damping coefficients were set close to their theoretical optimum for the heave mode.The results show that with the WaveSpring component, the system is able to absorb three times more power in realistic sea conditions than without it. This is achieved without increasing the damping force, thus giving a three times higher ratio of absorbed energy to PTO force. The maximum mooring line tension in storm conditions is found to be less than 2.5 times the pretension force.

6-DOF force feedback control of robot-assisted bone fracture reduction system using double F/T sensors and adjustable admittances to protect bones against damage

During a long bone fracture reduction surgery, assistant surgeons suffer from physical fatigue due to tension in the surrounding muscles of the patient's broken bones. To mitigate this physical workload, a positioning robot can be utilized by attracting and aligning a broken femur following a surgeon's command. However, the excessive force that the positioning robot exerts can cause damage to bone tissue or muscles of the patient.In this work, a force feedback scheme using double force-torque sensors and adjustable admittances is proposed to reduce the excessive forces exerted on broken bones by the positioning robot, as well as providing force feedback to the surgeon to feel the contact force between the bones. For this purpose, first a force feedback scheme is implemented to reduce the excessive force exerted on bone by moving the positioning robot toward the direction of larger force between the operational force and the scaled value of contact force. Second, it is shown that the proposed 1-DOF and 6-DOF force feedback are feasible by verifying that the operational force/torque command input and the environment contact forces are almost identical. Third, the force feedback scheme is shown to be capable of adjusting a force-scaling by adjusting a ratio of admittances of the operational force/torque command input to that of the environment contact force. At last, we also show that the performance of the force feedback is affected by the stiffness of the environment that includes medical bone fixture.As above, it is expected that the reliability and ease of bone fracture reduction robotic surgery will become possible by applying the force feedback scheme; it is also expected that secondary damage to bone tissue can be prevented by limiting the force of the positioning robot.

Resonant passive–active vibration absorber with integrated force feedback control

A general format of a two-terminal vibration absorber is constructed by placing a passive unit in series with a hybrid unit, composed of an active actuator in parallel with a second passive element. The displacement of the active actuator is controlled by an integrated feedback control with the difference in force between the two passive elements as input. This format allows passive and active contributions to be combined arbitrarily within the hybrid unit, which results in a versatile absorber format with guaranteed closed-loop stability. This is demonstrated for resonant absorbers with inertia realized passively by a mechanical inerter or actively by the integrated force feedback. Accurate calibration formulae are presented for two particular absorber configurations and the performance is subsequently demonstrated with respect to both equal modal damping and effective response reduction.

Prototyping Force-Controlled 3-DOF Hydraulic Arms for Humanoid Robots

[abstFig src='/00280001/11.jpg' width=""230"" text='Hydraulic dual arm robot prototype' ]This paper reports on a hydraulic dual arm robot developed as a rapid prototype for our hydraulic humanoid robot. The lightweight arms (4 kg each) have three joints driven by hydraulic linear servo actuators that can achieve higher torque and speed than human arms. A double four-bar linkage provides a wide range of motion (210°) to the shoulder joint. Each joint has torque controllability that is fully utilized for compliant whole-body motion control tasks. Based on singular perturbation analysis, we discuss how damping on the joints is actively modulated by hydraulic force feedback control, which is then utilized in our passivity-based task-space force control scheme. The effectiveness of the proposed system is experimentally evaluated through zero-force tracking gravity compensation with a 10 kg payload and object manipulation tasks.

Classical Tuning of Force Feedback Control for Nanopositioning Systems with Load Variations

Abstract: In nanopositioning systems, force feedback control has been proposed as an advanced control technique to enhance the bandwidth of the system and improve the tracking performance. In direct tracking with force feedback control, the architecture employs an inner force feedback loop to damp the first resonance peak and enhance the bandwidth. The position feedback loop is then used to enhance the tracking performance of the overall system. This paper discusses the practical issues associated with the control design of force feedback. The paper presents hardware results to support the analysis and proposes a systematic tuning method to retain the advantages of the force feedback control in the face of load variations.

Vision and Force Feedback Control for Microassembly Process

Microassembly process is one of the difficulties in the field of manufacturing. According to the structural characteristics and assembly process difficultly of 3D meso-scale micro-devices and the requirement of multi-axis control in coaxial alignment assembly, this paper developed a vision and force feedback control method oriented to Microassembly System with Coaxial Alignment. This system combines multi-axis motion control with machine vision and force sensors, which can complete nondestructive assembly of parts and increase the precision of microassembly process into micron level.

Force Feedback Control System Dedicated for Robin Heart Surgical Robot

3D contact force sensors were developed and integrated in a demonstration system for testing the feasibility of their application in minimal invasive surgery (MIS). Piezoresistive MEMS based vectorial force sensors were designed and fabricated by 3D silicon micromachining technology and packaged according to their proposed transducer and sensor applications. In this work we demonstrated the integrability and functional applicability of the 3D force sensors in MIS robotic systems to improve their flexibility and reliability by providing real-time force and tactile information during the operation.The final goal is to integrate the new subsystems in the Robin Heart surgery robot of FRK. [1] Three different functions are targeted: 1. Micro-joystick actuator to be integrated in the hilt of the laparoscope to easily control robotic movement during operation. 2. Force sensor inside the laparoscopic jaw to provide feedback to the surgeon by measuring the grasping strength and 3. 3D force/tactile sensor which facilitates palpation for tissue diagnostics during operation. In this paper we demonstrate a feasibility study regarding these proposed applications.

Interaction Control Capabilities of an MR-Compatible Compliant Actuator for Wrist Sensorimotor Protocols During fMRI

This paper describes the mechatronic design and characterization of a novel MR-compatible actuation system designed for a parallel force-feedback exoskeleton for measurement and/or assistance of wrist pointing movements during functional neuroimaging. The developed actuator is based on the interposition of custom compliant elements in series between a nonbackdrivable MR-compatible ultrasonic piezoelectric motor and the actuator output. The inclusion of physical compliance allows estimation of interaction force, enabling force-feedback control and stable rendering of a wide range of haptic environments during continuous scanning. Through accurate inner-loop velocity compensation and force-feedback control, the actuator is capable of displaying both a low-impedance subject-in-charge mode and a high stiffness mode. These modes enable the execution of shared haptic protocols during continuous functional magnetic resonance imaging. The detailed experimental characterization of the actuation system is presented, including a backdrivability analysis, demonstrating an achievable impedance range of 22 dB, within a bandwidth of 4 Hz (for low stiffness). The stiffness control bandwidth depends on the specific value of stiffness: a bandwidth of 4 Hz is achieved at low stiffness (10% of the physical springs stiffness), while 8 Hz is demonstrated at higher stiffness. Moreover, coupled stability is demonstrated also for stiffness values substantially (25%) higher than the physical stiffness of the spring. Finally, compatibility tests conducted in a 3T scanner are presented, validating the potential of inclusion of the actuator in an exoskeleton system for support of wrist movements during continuous MR scanning, without significant reduction in image quality.

Real-time hybrid testing with equivalent force control method incorporating Kalman filter

Summary The equivalent force control (EFC) method has been developed for real-time hybrid testing to replace the numerical iteration of implicit integration with a force-feedback control loop. With this control loop, the EFC method can also compensate for the time delay in real-time hybrid testing. However, the delay compensation effect of the EFC can be influenced by factors such as noises in the measured displacement. This paper discusses the influence of the measurement noises on real-time hybrid testing with the EFC. The Kalman filter is proposed to filter the noises in the measured actuator displacement for improved performance. A higher proportional gain in the PID controller, which improves the effect of time delay compensation of the EFC method, can be allowed without losing stability when incorporating the Kalman filter. A series of real-time hybrid tests were conducted, and the results validated that the EFC method with Kalman filter can effectively compensate for the time delay. Copyright © 2015 John Wiley & Sons, Ltd.