Study of Dominant Performance Characteristics in Robot Transmissions

1993 ◽  
Vol 115 (3) ◽  
pp. 472-482 ◽  
Author(s):  
H. Schempf ◽  
D. R. Yoerger
Keyword(s):  
Force Control ◽  
Closed Loop ◽  
Stability Margin ◽  
Viscous Friction ◽  
Open Loop ◽  
Phase Lag ◽  
Stability Margins ◽  
Loop Bandwidth ◽  
Hard Contact ◽  
Following Error

Six different transmission types suitable for robotic manipulators were compared in an experimental and theoretical study. Single-degree-of-freedom mechanisms based on the different transmissions were evaluated in terms of force control performance, achievable bandwidth, and stability properties in hard contact tasks. Transmission types considered were (1) cable reducer, (2) harmonic drive, (3) cycloidal disk reducer, (4) cycloidal cam reducer, (5) ball reducer, and (6) planetary/cycloidal gear head. Open loop torque following error, attenuation and phase lag, and closed loop bandwidth and stability margin were found to be severely dominated by levels of inertia, stiffness distribution and variability, stiction, coulomb and viscous friction, and ripple torque. These aspects were quantified and shown to vary widely among all transmissions tested. The degree of nonlinearity inherent in each transmission affected its open and closed loop behavior directly, and limited the effectiveness of controller compensation schemes. Simple transmission models based on carefully measured transmission characteristics are shown to predict stability margins and achievable force-control bandwidths in hard contact to within a 5 to 15 percent error margin.

Design of a High-Bandwidth XY Nanopositioning Stage for High-Throughput Micro/Nano Manufacturing

2010 ◽  
Author(s):  
Sebastian Polit ◽  
Jingyan Dong
Keyword(s):  
Mechanism Design ◽  
High Throughput ◽  
Closed Loop ◽  
Open Loop ◽  
Dynamic Responses ◽  
Element Analysis ◽  
Loop Bandwidth ◽  
Decoupled Motion ◽  
High Bandwidth ◽  
Critical Requirement

A high natural frequency (open-loop bandwidth) is a critical requirement for nanopositioners in high-throughput nanomanufacturing and nano-metrology applications. This paper presents the design and analysis of a high-bandwidth nanopositioning XY stage. The monolithic stage design has two axes and each axis is comprised of a doubly-clamped beam and a parallelogram hybrid flexure with complaint beams and circular flexure hinges. The doubly-clamped beam that is actuated by a piezoelectric actuator acts as a linear prismatic axis. The parallelogram hybrid flexures are used to decouple the actuation effect from the other axis. The mechanism design decouples the motion in the X and Y directions and restricts parasitic rotations in the XY plane while allowing for an increased bandwidth with linear kinematics in the operating region (or workspace). Kinematic and dynamic analysis shows that the mechanical structure of the stage has decoupled motion in XY direction, while achieving high bandwidth and good linearity. Finite element analysis is adapted to verify the dynamic responses from theoretical analysis. The stage is actuated by piezoelectric stack actuators, and two capacitive gauges were added to the system to build a closed-loop positioning system. The results from frequency test show that the resonation frequencies of the two vibrational modes are over 8K Hz. The stage is capable of about 15 microns of motion along each axis with a resolution of about 1 nanometer. Due to parallel kinematic mechanism design, a uniform performance is achieved across the workspace. A PI controller is implemented for the stage and a high closed-loop bandwidth is obtained.

scholarly journals Fundamental Limits in Combine Harvester Header Height Control

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Yangmin Xie ◽  
Andrew G. Alleyne ◽  
Ashley Greer ◽  
Dustin Deneault
Keyword(s):  
Closed Loop ◽  
Open Loop ◽  
The Other ◽  
Specific System ◽  
Fundamental Limits ◽  
Height Control ◽  
Sensor Actuator ◽  
Loop Transfer Function ◽  
Loop Bandwidth ◽  
Combine Harvester

This paper investigates fundamental performance limitations in the control of a combine harvester's header height control system. There are two primary subsystem characteristics that influence the achievable bandwidth by affecting the open loop transfer function. The first subsystem is the mechanical configuration of the combine and header while the second subsystem is the electrohydraulic actuation for the header. The mechanical combine + header subsystem results in an input–output representation that is underactuated and has a noncollocated sensor/actuator pair. The electrohydraulic subsystem introduces a significant time delay. In combination, they each reinforce the effect of the other thereby exacerbating the overall system limitation of the closed loop bandwidth. Experimental results are provided to validate the model and existence of the closed loop bandwidth limitations that stem from specific system design configurations.

Design and Assessment of an Adaptive Intermittent Cervical Traction Modality With EMG Biofeedback

1996 ◽  
Vol 118 (4) ◽  
pp. 597-600 ◽  
Author(s):  
M. Y. Lee ◽  
M. K. Wong ◽  
F. T. Tang ◽  
W. H. Chang ◽  
W. K. Chiou
Keyword(s):  
Force Control ◽  
Closed Loop ◽  
Traction Force ◽  
Open Loop ◽  
Emg Biofeedback ◽  
Paraspinal Muscle ◽  
Myoelectric Activity ◽  
Emg Signal ◽  
Cervical Traction ◽  
And Control

An intermittent cervical traction modality with closed-loop traction force control based on EMG biofeedback was developed and used for clinical study. This system consists of a EMG scanner, on-line self-adjusted traction force controller, audio/video alarm system, real time therapeutic status display, computer interface hardware, and control software. Twenty-four subjects with diagnosed cervical radiculopathy and muscle spasm symptom who were randomly divided into two groups served as subjects in this study. The control and experimental groups were treated with conventional open loop and new EMG biofeedback closed loop traction control protocols respectively. The results of this study indicate that the average reductions in paraspinal EMG signal during traction after 7 weeks treatment for experimental and control groups were 71 and 50 percent, respectively (p < 0.001). These results not only support the clinical use of intermittent, sitting traction to produce cervical paraspinal muscle relaxation, but also revealed that the average myoelectric activity of cervical paraspinal muscle during traction was reduced as traction force increased over the 7-week duration of traction treatment. Through EMG biofeedback traction force control, muscle injury, neck soreness, or pain after traction may be avoided.

CPG-fuzzy-based control of a cownose-ray-like fish robot

2019 ◽  
Vol 46 (6) ◽  
pp. 779-791
Author(s):  
Yong Cao ◽  
Yang Lu ◽  
Yueri Cai ◽  
Shusheng Bi ◽  
Guang Pan
Keyword(s):  
Closed Loop ◽  
Central Pattern Generators ◽  
Water Quality Monitoring ◽  
Open Loop ◽  
Phase Lag ◽  
Fish Robot ◽  
Fuzzy Algorithm ◽  
Content Type ◽  
Cownose Ray ◽  
Fin Ray

Purpose This paper aims to imitate a cownose ray to develop a fish robot with paired flexible multi-fin-ray oscillating pectoral fins (OPFs) and control it to accomplish vivid stable 3-D motions using central pattern generators (CPGs) and fuzzy algorithm. Design/methodology/approach The cownose ray’s asymmetric sine-like oscillations were analyzed. Then a cownose-ray-like fish robot named Robo-ray was developed, which has paired flexible multi-fin-ray OPFs to actively control the fin shape and two tail fins to control the depth. To solve the problem of coordinated control for multi-degree-of-freedom Robo-ray, CPGs were adopted. An improved phase oscillator as a CPG unit with controlled amplitude, phase lag, smooth frequency transition and asymmetric oscillation characteristic was established. Furthermore, the CPG-fuzzy algorithm was developed for vivid stable 3-D motions. The open-loop speed control, the closed-loop control of depth and yaw were established. Findings The kinematic comparisons indicate that Robo-ray imitates the cownose ray realistically. The experimental results of closed-loop are obtained that the depth error of Robo-ray is less than ±100 mm and the course error is less than ±3°. Furthermore, the comprehensive experiments demonstrate that Robo-ray has high mobility, stability and robustness. Originality/value This research makes the fish robot with OPF propulsion closer to practical applications in complex underwater environment, for instance, ocean explorations, water quality monitoring and stealth military reconnaissance. In addition, Robo-ray can be taken as a scientific tool for better understanding of the hydrodynamics of OPF batoid.

scholarly journals Electrotactile feedback improves performance and facilitates learning in the routine grasping task

2016 ◽  
Vol 26 (3) ◽  
Author(s):  
Milica Isaković ◽  
Minja Belić ◽  
Matija Štrbac ◽  
Igor Popović ◽  
Strahinja Došen ◽  
...  
Keyword(s):  
Force Control ◽  
Closed Loop ◽  
Feedforward Control ◽  
Open Loop ◽  
Spatial Coding ◽  
Accuracy And Precision ◽  
Array Electrode ◽  
Grasping Force ◽  
Four Levels ◽  
And Training

Aim of this study was to investigate the feasibility of electrotactile feedback in closed loop training of force control during the routine grasping task. The feedback was provided using an array electrode and a simple six-level spatial coding, and the experiment was conducted in three amputee subjects. The psychometric tests confirmed that the subjects could perceive and interpret the electrotactile feedback with a high success rate. The subjects performed the routine grasping task comprising 4 blocks of 60 grasping trials. In each trial, the subjects employed feedforward control to close the hand and produce the desired grasping force (four levels). First (baseline) and the last (validation) session were performed in open loop, while the second and the third session (training) included electrotactile feedback. The obtained results confirmed that using the feedback improved the accuracy and precision of the force control. In addition, the subjects performed significantly better in the validation vs. baseline session, therefore suggesting that electrotactile feedback can be used for learning and training of myoelectric control.

Disturbance Observer Based Closed Loop Force Control for Haptic Feedback

2007 ◽  
Author(s):  
Abhishek Gupta ◽  
Marcia K. O’Malley ◽  
Volkan Patoglu
Keyword(s):  
Force Control ◽  
Disturbance Observer ◽  
Closed Loop ◽  
Force Feedback ◽  
Haptic Feedback ◽  
Open Loop ◽  
Contact Forces ◽  
Force Sensing ◽  
Haptic Interfaces ◽  
Simulation Fidelity

Most commonly used impedance-type haptic interfaces employ open-loop force control under the assumption of pseudostatic interactions. Advanced force control in such interfaces can increase simulation fidelity through improvement of the transparency of the device, and can further improve robustness. However, closed loop force-feedback is limited both due to the bandwidth limitations of force sensing and the associated cost of force sensors required for its implementation. In this paper, we propose the use of a nonlinear disturbance observer for estimation of contact forces during haptic interactions. This approach circumvents the traditional drawbacks of force sensing while exhibiting the advantages of closed-loop force control in haptic devices. The feedback of contact force information further enables implementation of advanced robot force control techniques such as robust hybrid impedance and admittance control. Simulation and experimental results, utilizing a PHANToM Premium 1.0A haptic interface, are presented to demonstrate the efficacy of the proposed approach.

Improving Contouring Accuracy of NC/CNC Systems With Additional Velocity Feed Forward Loop

1986 ◽  
Vol 108 (3) ◽  
pp. 227-230 ◽  
Author(s):  
O. Masory
Keyword(s):  
Closed Loop ◽  
Open Loop ◽  
Loop Gain ◽  
Time Constants ◽  
Feed Forward ◽  
Feed Forward Loop ◽  
Contouring Error ◽  
Contouring Accuracy ◽  
Servo Drives ◽  
Following Error

One of the factors which affects the contouring accuracy of multi-axis NC/CNC contouring systems is axes mismatch which means that the time constants and the open-loop gains of the machine servo drives are not identical. In conventional NC/CNC system each axis is separately controlled by a closed-loop velocity controller. Therefore, a position-following error which is a function of the open-loop gain and the time constant, is generated. Since the values of these parameters are different for each axis, a contouring error is produced. By adding a velocity feed forward loop to this controller, the position-following error can be reduced, or even eliminated, and consequently the contouring error is reduced.

Electromagnetic Coupling in a dc Motor and Tachometer Assembly

2004 ◽  
Vol 126 (3) ◽  
pp. 684-691 ◽  
Author(s):  
Shorya Awtar ◽  
Kevin C. Craig
Keyword(s):  
Disturbance Rejection ◽  
Closed Loop ◽  
Electromagnetic Coupling ◽  
Dc Motor ◽  
Open Loop ◽  
Conventional Model ◽  
Open Loop System ◽  
Nonminimum Phase ◽  
Motion System ◽  
Loop Bandwidth

This paper presents an enhanced tachometer model that takes into account the effect of electromagnetic coupling that can exist between the actuator and sensor in an integrated dc motor-tachometer assembly, where the conventional model is found to be inadequate. The tachometer dynamics identified in this paper is experimentally verified, and incorporated in the modeling and parameter identification of a motion system that has multiple flexible elements. It is shown that the tachometer dynamics contributes additional nonminimum phase zeros that degrade the servo system performance in terms of closed-loop bandwidth, disturbance rejection and sensitivity to modeling uncertainty. The zeros of the open loop system are found to vary with the geometric parameters of the motor-tachometer assembly. Based on the insight gained by modeling the electromagnetic coupling, methods for eliminating it and its resulting detrimental effects are also suggested.

Disturbance-Observer-Based Force Estimation for Haptic Feedback

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Abhishek Gupta ◽  
Marcia K. O’Malley
Keyword(s):  
Force Control ◽  
Disturbance Observer ◽  
Closed Loop ◽  
Haptic Feedback ◽  
Open Loop ◽  
Contact Forces ◽  
Haptic Interface ◽  
Force Sensing ◽  
Force Estimation ◽  
Control Approach

In this paper, we propose the use of a nonlinear disturbance-observer for estimation of contact forces during haptic interactions. Most commonly used impedance-type haptic interfaces employ open-loop force control under the assumption of pseudostatic interactions. Advanced force control in such interfaces can increase simulation fidelity through improvement of the transparency of the device. However, closed-loop force feedback is limited both due to the bandwidth limitations of force sensing and the associated cost of force sensors required for its implementation. Using a disturbance-observer, we estimate contact forces at the tool tip, then use these estimates for closed-loop control of the haptic interface. Simulation and experimental results, utilizing a custom single degree-of-freedom haptic interface, are presented to demonstrate the efficacy of the proposed disturbance-observer (DO)-based control approach. This approach circumvents the traditional drawbacks of force sensing while exhibiting the advantages of closed-loop force control in haptic devices. Results show that the proposed disturbance-observer can reliably estimate contact forces at the human-robot interface. The DO-based control approach is experimentally shown to improve haptic interface fidelity over a purely open-loop display while maintaining stable and vibration-free interactions between the human user and virtual environment.

On closed-loop equilibrium strategies for mean-field stochastic linear quadratic problems

2020 ◽  
Vol 26 ◽  
pp. 41
Author(s):  
Tianxiao Wang
Keyword(s):  
Optimal Control ◽  
Closed Loop ◽  
Optimal Control Problems ◽  
Mean Field ◽  
Open Loop ◽  
Time Inconsistency ◽  
Control Problems ◽  
Linear Quadratic ◽  
Linear Quadratic Optimal Control ◽  
Equilibrium Strategies

This article is concerned with linear quadratic optimal control problems of mean-field stochastic differential equations (MF-SDE) with deterministic coefficients. To treat the time inconsistency of the optimal control problems, linear closed-loop equilibrium strategies are introduced and characterized by variational approach. Our developed methodology drops the delicate convergence procedures in Yong [Trans. Amer. Math. Soc. 369 (2017) 5467–5523]. When the MF-SDE reduces to SDE, our Riccati system coincides with the analogue in Yong [Trans. Amer. Math. Soc. 369 (2017) 5467–5523]. However, these two systems are in general different from each other due to the conditional mean-field terms in the MF-SDE. Eventually, the comparisons with pre-committed optimal strategies, open-loop equilibrium strategies are given in details.

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