Zero Moment Control for Lead-Through Teach Programming and Process Monitoring of a Collaborative Welding Robot

2021 ◽  
pp. 1-12
Author(s):  
Stephen L. Canfield ◽  
Joseph S. Owens ◽  
Stephen G. Zuccaro
Keyword(s):  
Direct Interaction ◽  
Viscous Friction ◽  
Friction Model ◽  
Task Instruction ◽  
Sigmoid Function ◽  
Robotic Welding ◽  
Estimation Model ◽  
Automotive Manufacturing ◽  
Time Required ◽  
Torque Observer

Abstract Robots are commonly used for automated welding in many industries such as automotive manufacturing. The complexity and time required for programming presents an obstacle in using robotic automation in welding or other tasks for small to medium enterprises that lack resources for training or expertise in traditional robot programming strategies. It also dictates a high level of repeated parts to offset the cost of weld programming. Collaborative Robots or Cobots are robots designed for more collaborative operations with humans. Cobots permit new methods of task instruction (programming) through direct interaction between the operator and robot. This paper presents a model and model calibration strategy for a collaborative robot methods to aid teaching for and monitoring of welding tasks. The method makes use of a torque estimation model based on robot momentum to create an observer to evaluate external forces. The torque observer is used to characterize the friction that exists within the robot joints. This data is used to define the parameters of a friction model that combines static, Coulomb and viscous friction properties with a sigmoid function to represent transition between motion states. With an updated friction model, the torque observer is then used for collaborative robotic welding, first to provide a mode in which the robot can be taught weld paths through physical lead through, and second a mode to monitor the weld process from expected motion/force characteristics. The method is demonstrated on a commercial robot.

Zero Moment Control for Lead-Through Teach Programming on a Collaborative Robot

2020 ◽  
Author(s):  
Stephen L. Canfield ◽  
Joseph S. Owens ◽  
Stephen G. Zuccaro
Keyword(s):  
Direct Interaction ◽  
Viscous Friction ◽  
Friction Model ◽  
Task Instruction ◽  
Sigmoid Function ◽  
Estimation Model ◽  
Automotive Manufacturing ◽  
External Forces ◽  
High Level ◽  
Collaborative Robot

Abstract Robots are commonly used for automated welding in many industries such as automotive manufacturing. The complexity and time of programming presents an obstacle in using robotic automation in welding or other tasks for small to medium enterprises that lack resources for training or expertise in traditional robot programming strategies. It also dictates a high level of repeated parts to offset the cost of weld programming. Collaborative Robots or Cobots are robots designed for more collaborative operations with humans. Cobots permit new methods of task instruction (programming) through direct interaction between the operator and robot. This paper presents a model and calibration strategy for a collaborative robot to aid intuitive teaching methods for tasks such as welding. The method makes use of a torque estimation model based on robot momentum to create an observer to evaluate external forces. The torque observer is first used to characterize the friction that exists within the robot joints. This data is used to define the parameters of a friction model that combines static, Coulomb and viscous friction properties with a sigmoid function to represent transition between motion states and a second level Fourier series to represent position dependency of the Coulomb friction terms. The friction model is then integrated into the robot control and used to provide a mode in which the robot can be easily dragged around the workspace to provide weld path training.

Developing a Kinematic Estimation Model for a Climbing Mobile Robotic Welding System

2010 ◽  
Author(s):  
Aaron T. O’Toole ◽  
Stephen L. Canfield
Keyword(s):  
Kinematic Model ◽  
Robotic Welding ◽  
Estimation Model ◽  
Mobile Platforms ◽  
Low Profile ◽  
Turning Radius ◽  
Equivalence Model ◽  
Kinematic Equivalence ◽  
Welding System ◽  
Robot Platform

Skid steer tracked-based robots are popular due to their mechanical simplicity, zero-turning radius and greater traction. This architecture also has several advantages when employed by mobile platforms designed to climb and navigate ferrous surfaces, such as increased magnet density and low profile (center of gravity). However, creating a kinematic model for localization and motion control of this architecture is complicated due to the fact that tracks necessarily slip and do not roll. Such a model could be based on a heuristic representation, an experimentally-based characterization or a probabilistic form. This paper will extend an experimentally-based kinematic equivalence model to a climbing, track-based robot platform. The model will be adapted to account for the unique mobility characteristics associated with climbing. The accuracy of the model will be evaluated in several representative tasks. Application of this model to a climbing mobile robotic welding system (MRWS) is presented.

scholarly journals Study on Friction in Automotive Shock Absorbers Part 1: Friction Simulation Using a Dynamic Friction Model in the Contact Zone of an FEM Model

Vehicles ◽  
2021 ◽  
Vol 3 (2) ◽  
pp. 212-232
Author(s):  
Ludwig Herzog ◽  
Klaus Augsburg
Keyword(s):  
Ride Comfort ◽  
Viscous Friction ◽  
Simulation Method ◽  
Friction Model ◽  
Model Parameters ◽  
Dynamic Friction ◽  
Friction Modeling ◽  
Shock Absorbers ◽  
Operation Conditions ◽  
Wide Range

The important change in the transition from partial to high automation is that a vehicle can drive autonomously, without active human involvement. This fact increases the current requirements regarding ride comfort and dictates new challenges for automotive shock absorbers. There exist two common types of automotive shock absorber with two friction types: The intended viscous friction dissipates the chassis vibrations, while the unwanted solid body friction is generated by the rubbing of the damper’s seals and guides during actuation. The latter so-called static friction impairs ride comfort and demands appropriate friction modeling for the control of adaptive or active suspension systems. In this article, a simulation approach is introduced to model damper friction based on the most friction-relevant parameters. Since damper friction is highly dependent on geometry, which can vary widely, three-dimensional (3D) structural FEM is used to determine the deformations of the damper parts resulting from mounting and varying operation conditions. In the respective contact zones, a dynamic friction model is applied and parameterized based on the single friction point measurements. Subsequent to the parameterization of the overall friction model with geometry data, operation conditions, material properties and friction model parameters, single friction point simulations are performed, analyzed and validated against single friction point measurements. It is shown that this simulation method allows for friction prediction with high accuracy. Consequently, its application enables a wide range of parameters relevant to damper friction to be investigated with significantly increased development efficiency.

Viscous Friction Effect During the Process of Tightening and Loosening of Bolted Joints

2021 ◽  
Author(s):  
Qingyuan Lin ◽  
Yong Zhao ◽  
Qingchao Sun ◽  
Kunyong Chen
Keyword(s):  
Friction Coefficient ◽  
Viscous Friction ◽  
Normal Pressure ◽  
Friction Model ◽  
Bolted Joints ◽  
Critical Parameters ◽  
Bolted Joint ◽  
Sliding Velocity ◽  
Friction Effect ◽  
Bearing Friction

Abstract Bolted connection is one of the most widely used mechanical connections because of its easiness of installation and disassembly. Research of bolted joints mainly focuses on two aspects: high precision tightening and improvement of anti-loosening performance. The under-head bearing friction coefficient and the thread friction coefficient are the two most important parameters that affect the tightening result of the bolted joint. They are also the most critical parameters that affect the anti-loosening performance of the bolted joint. Coulomb friction model is a commonly used model to describe under-head bearing friction and thread friction, which considers the friction coefficient as a constant independent of normal pressure and relative sliding velocity. In this paper, the viscous effect of the under-head bearing friction and thread friction is observed by measuring the friction coefficient of bolted joints. The value of the friction coefficient increases with the increase of the relative sliding velocity and the decrease of the normal pressure. It is found that the Coulomb viscous friction model can better describe the friction coefficient of bolted joints. Taking into account the dense friction effect, the loosening prediction model of bolted joints is modified. The experimental results show that the Coulomb viscous friction model can better describe the under-head bearing friction coefficient and thread friction coefficient. The model considering the dense effect can more accurately predict the loosening characteristics of bolted joints.

Comparison of Four Friction Models: Feature Prediction

2015 ◽  
Vol 11 (3) ◽  
Author(s):  
Yun-Hsiang Sun ◽  
Tao Chen ◽  
Christine Qiong Wu ◽  
Cyrus Shafai
Keyword(s):  
Numerical Model ◽  
Viscous Friction ◽  
Friction Model ◽  
Dynamic Features ◽  
Numerical Predictions ◽  
Wide Range ◽  
Model Predictions ◽  
Friction Models ◽  
Parameter Identifications ◽  
Model Structures

In this paper, we provide not only key knowledge for friction model selection among candidate models but also experimental friction features compared with numerical predictions reproduced by the candidate models. A motor-driven one-dimensional sliding block has been designed and fabricated in our lab to carry out a wide range of control tasks for the friction feature demonstrations and the parameter identifications of the candidate models. Besides the well-known static features such as break-away force and viscous friction, our setup experimentally demonstrates subtle dynamic features that characterize the physical behavior. The candidate models coupled with correct parameters experimentally obtained from our setup are taken to simulate the features of interest. The first part of this work briefly introduces the candidate friction models, the friction features of interest, and our experimental approach. The second part of this work is dedicated to the comparisons between the experimental features and the numerical model predictions. The discrepancies between the experimental features and the numerical model predictions help researchers to judge the accuracy of the models. The relation between the candidate model structures and their numerical friction feature predictions is investigated and discussed. A table that summarizes how to select the most optimal friction model among a variety of engineering applications is presented at the end of this paper. Such comprehensive comparisons have not been reported in previous literature.

scholarly journals Time Delay and Feedback Control of an Inverted Pendulum With Stick Slip Friction

2007 ◽  
Author(s):  
Sue Ann Campbell ◽  
Stephanie Crawford ◽  
Kirsten Morris
Keyword(s):  
Time Delay ◽  
Basin Of Attraction ◽  
Critical Time ◽  
Viscous Friction ◽  
Experimental System ◽  
Friction Model ◽  
Stable Equilibrium Point ◽  
Feedback Controllers ◽  
Stick Slip ◽  
The Basin Of Attraction

We consider an experimental system consisting of a pendulum, which is free to rotate 360 degrees, attached to a cart which can move in one dimension. There is stick slip friction between the cart and the track on which it moves. Using two different models for this friction we design feedback controllers to stabilize the pendulum in the upright position. We show that controllers based on either friction model give better performance than one based on a simple viscous friction model. We then study the effect of time delay in this controller, by calculating the critical time delay where the system loses stability and comparing the calculated value with experimental data. Both models lead to controllers with similar robustness with respect to delay. Using numerical simulations, we show that the effective critical time delay of the experiment is much less than the calculated theoretical value because the basin of attraction of the stable equilibrium point is very small.

Experimental Identification and Analysis of the Dynamics of a PHANToM Premium 1.5A Haptic Device

2008 ◽  
Vol 17 (4) ◽  
pp. 327-343 ◽  
Author(s):  
Babak Taati ◽  
Amir M. Tahmasebi ◽  
Keyvan Hashtrudi-Zaad
Keyword(s):  
Inverse Dynamics ◽  
Viscous Friction ◽  
Force Sensor ◽  
Friction Model ◽  
Haptic Device ◽  
Gravity Compensation ◽  
Force Estimation ◽  
Experimental Identification ◽  
Hand Force ◽  
Haptic Simulation

The dynamics of a PHANToM Premium 1.5A haptic device from SensAble Technologies, Inc. is experimentally identified and analyzed for different installations of the device and its accessories, such as the typical upright, upside down, with gimbal and counterbalance weight, and with force sensor.1 An earlier formulation of the robot dynamic model is augmented with a friction model, linearly parameterized, and experimentally identified using least squares. The identified dynamics are experimentally evaluated with an inverse dynamics controller and verified by comparing user hand force estimates with the measured values. The contribution of different dynamic terms such as inertial, Coriolis and centrifugal, gravitational, and Coulomb and viscous friction are demonstrated and discussed. The identified model can be used for a variety of haptic applications, such as hand force estimation, accurate active gravity compensation and counterbalance weight determination for various installation conditions, and model-based control for haptic simulation and teleoperation.

Ensemble Grey and Black-box Nonlinear System Identification of a Positioning System

2020 ◽  
Author(s):  
Walisson Chaves Ferreira Pinto ◽  
Helon Vicente Hultmann Ayala
Keyword(s):  
Nonlinear System ◽  
Nonlinear System Identification ◽  
Viscous Friction ◽  
Black Box ◽  
Friction Model ◽  
Model Construction ◽  
Ensemble Model ◽  
Positioning System ◽  
Friction Models ◽  
Coulomb Model

In this work, grey and black-box approaches are used in order to model a electromechanical positioning system (EMPS). An ensemble model is then constructed by combining these two approaches, by using the predictions of both models in order to generate an improved estimated output. Four friction models, in their symmetric and asymmetric versions,namely (i) Coulomb model with finite slope at zero velocity and viscous friction, (ii) Coulomb model with viscous friction, (iii) Tustin friction model, (iv) Coulomb model with viscous friction and Stribeck effect were used to describe the dynamic behavior of the EMPS. The results have shown that the combination of grey and black-box models was able to perform better than the grey-box model and that the proposed friction models are also able to improve the relativeerror. This encourages further research on the application of the concept of ensemble model construction from machine learning to the nonlinear system identication context towards more accurate model construction.

scholarly journals Estimating Friction Parameters in Reaction Wheels for Attitude Control

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Valdemir Carrara ◽  
Hélio Koiti Kuga
Keyword(s):  
Attitude Control ◽  
Deterministic Model ◽  
High Reliability ◽  
Viscous Friction ◽  
Static Friction ◽  
Friction Model ◽  
Artificial Satellites ◽  
Wide Range ◽  
The Stability ◽  
Friction Parameters

The ever-increasing use of artificial satellites in both the study of terrestrial and space phenomena demands a search for increasingly accurate and reliable pointing systems. It is common nowadays to employ reaction wheels for attitude control that provide wide range of torque magnitude, high reliability, and little power consumption. However, the bearing friction causes the response of wheel to be nonlinear, which may compromise the stability and precision of the control system as a whole. This work presents a characterization of a typical reaction wheel of 0.65 Nms maximum angular momentum storage, in order to estimate their friction parameters. It used a friction model that takes into account the Coulomb friction, viscous friction, and static friction, according to the Stribeck formulation. The parameters were estimated by means of a nonlinear batch least squares procedure, from data raised experimentally. The results have shown wide agreement with the experimental data and were also close to a deterministic model, previously obtained for this wheel. This model was then employed in a Dynamic Model Compensator (DMC) control, which successfully reduced the attitude steady state error of an instrumented one-axis air-bearing table.

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