scholarly journals Development of a Virtual Force Sensor for a Low-Cost Collaborative Robot and Applications to Safety Control

Sensors ◽  
2019 ◽  
Vol 19 (11) ◽  
pp. 2603 ◽  
Author(s):  
Shih-Hsiang Yen ◽  
Pei-Chong Tang ◽  
Yuan-Chiu Lin ◽  
Chyi-Yeu Lin
Keyword(s):  
Contact Force ◽  
External Force ◽  
Force Control ◽  
Low Cost ◽  
Force Sensor ◽  
Production Costs ◽  
Robot Arm ◽  
Robot Arms ◽  
Virtual Force ◽  
Collaborative Robot

To protect operators and conform to safety standards for human–machine interactions, the design of collaborative robot arms often incorporates flexible mechanisms and force sensors to detect and absorb external impact forces. However, this approach increases production costs, making the introduction of such robot arms into low-cost service applications difficult. This study proposes a low-cost, sensorless rigid robot arm design that employs a virtual force sensor and stiffness control to enable the safety collision detection and low-precision force control of robot arms. In this design, when a robot arm is subjected to an external force while in motion, the contact force observer estimates the external torques on each joint according to the motor electric current and calculation errors of the system model, which are then used to estimate the external contact force exerted on the robot arm’s end-effector. Additionally, a torque saturation limiter is added to the servo drive for each axis to enable the real-time adjustment of joint torque output according to the estimated external force, regulation of system stiffness, and achievement of impedance control that can be applied in safety measures and force control. The design this study developed is a departure from the conventional multisensor flexible mechanism approach. Moreover, it is a low-cost and sensorless design that relies on model-based control for stiffness regulation, thereby improving the safety and force control in robot arm applications.

Utilizing the Nonlinearity of Tendon Elasticity for Compensation of Unknown Gravity of Payload

2018 ◽  
Vol 30 (6) ◽  
pp. 873-879
Author(s):  
Chao Shao ◽  
Junki Togashi ◽  
Kazuhisa Mitobe ◽  
Genci Capi ◽  
◽  
...  
Keyword(s):  
Low Cost ◽  
Cost Effective ◽  
Force Sensor ◽  
Error Reduction ◽  
Position Error ◽  
Gravity Compensation ◽  
Robot Arm ◽  
Positioning Control ◽  
State Position ◽  
Significant Cost Reduction

This paper discusses the positioning control of an elastic tendon-driven robot arm under gravity. The robot is driven by rubber string tendons and winding drums attached on the outside frames. Low-cost rubber strings that are available commercially are used as tendons. The goal is to utilize the nonlinear nature of the rubber materials to control a low-cost and soft robot arm. Theoretically, a mathematical model with accurate parameters and accurate measurement of the payload weight is necessary for rigorous gravity compensation. However, the necessity for the information of the robot parameters is hindering easy adaptability, versatility, and cost-efficiency. This paper presents an iterative estimation and compensation method for unknown payloads based on the steady-state position error and the nominal stiffness coefficient. Owing to the nonlinearity of the actual rubber strings, the position error remains after a single operation of the gravity compensation. However, experiments indicate that the error reduces by a simple iteration of the same compensation operation. Considering the nonlinearity in rubber strings, the mechanism of the error reduction is analyzed theoretically. Although the iterative process is time consuming, the method requires less prior information. In addition, it is cost effective because a sophisticated force sensor is not required. As the mechanism of error reduction applies to typical rubber string materials, it is useful for significant cost-reduction and reconfigurable robotics.

Identification of Dominant Error Force Component in Hydraulic Pressure Reading for External Force Detection in Construction Manipulator

2012 ◽  
Vol 24 (1) ◽  
pp. 95-104 ◽  
Author(s):  
Mitsuhiro Kamezaki ◽  
◽  
Hiroyasu Iwata ◽  
Shigeki Sugano ◽  
◽  
...  
Keyword(s):  
External Force ◽  
Low Cost ◽  
Force Sensor ◽  
Detection Algorithm ◽  
Waveform Analysis ◽  
Hydraulic Pressure ◽  
Control Input ◽  
Force Detection ◽  
Force Components ◽  
External Force Detection

The purpose of this paper is to develop a fundamental external-force-detection framework for construction manipulators. Such an industrial application demands the practicality that satisfies detection requirements such as the accuracy and robustness while ensuring (i) a low cost, (ii) wide applicability, and (iii) a simple detection algorithm. For satisfying (i) and (ii), our framework first adopts a hydraulic sensor as a force sensor. However, hydraulic-pressure readings essentially include error force components. These components depend strongly on the joint kinetic state and differ in the identification difficulty owing to a nonlinear and uncertain hydromechanical system. For satisfying (ii) and (iii), our framework thus focuses on the dominant error-force components classified by the control input states, such as self-weight, cylinder driving, and oscillating forces, and identifies and removes them by using a theoreticalmodel, an experimental estimation, and a waveform analysis without complex modeling, respectively. Experiments were conducted using an instrumented hydraulic arm system. The results of a no-load task indicate that our framework greatly lowers the threshold to determine the on-off state of external force application, independent of the joint kinetic states. The results of an on-load task confirm that our framework robustly identifies the off states in which an external force is not applied to the hydraulic cylinder.

Control of Low-Cost Customizable Robot Arm Actuated by Elastic Tendons

2016 ◽  
Vol 28 (4) ◽  
pp. 509-522 ◽  
Author(s):  
Junki Togashi ◽  
◽  
Kazuhisa Mitobe ◽  
Genci Capi ◽  
Keyword(s):  
Force Control ◽  
Control Method ◽  
Low Cost ◽  
String Tension ◽  
Machining Accuracy ◽  
Robot Arm ◽  
Compliant Joints ◽  
Low Stiffness ◽  
Static Conditions ◽  
The Cost

[abstFig src='/00280004/09.jpg' width='300' text='Elastic tendon driven robot arm' ] This paper presents a low-cost, lightweight robot arm with very low stiffness actuated by elastic tendons. To simplify the string tension control, a new winding device was developed. Small pulleys were incorporated into the winding drum to reduce friction between the tendon and the drum. A marionette-style two-link robot arm with compliant joints was prototyped. Because the arm and winding devices were separate from each other, the cost and weight of the robot were reduced. The links are made with lightweight wood connected by simple shaft joints. The robot design can be easily modified by the user because the mechanical parts do not require high machining accuracy. This robot is intended for implementation in tasks that do not require high positioning accuracy using a simple force control under environmental constraints. Because of its low stiffness, simple and sensor-less force control can be easily implemented based on the relationship between forces under static conditions. The proposed simple control method was evaluated experimentally by conducting position, static force, and hybrid position/force control tasks and was shown to perform well. The results also demonstrate that employing additional sensors, such as a camera, improves the accuracy of the controller.

Educational Force Control Using a Modular 2-DOF Serial Robot Manipulator and Low-Cost 2-DOF Force Sensor

2019 ◽  
Author(s):  
Stephen Mascaro
Keyword(s):  
Force Control ◽  
Degrees Of Freedom ◽  
Hybrid Control ◽  
Robot Manipulator ◽  
Impedance Control ◽  
Low Cost ◽  
Force Sensor ◽  
Physical Contact ◽  
Dynamic Force ◽  
Control Techniques

Abstract This paper describes a modular 2-DOF serial robotic system and accompanying experiments that have been developed to instruct robotics students in the fundamentals of dynamic force control. In prior work, we used this same robot to showcase and compare the performance of a variety of textbook techniques for dynamic motion control (i.e. fast/accurate trajectory tracking using dynamic model-based and robust control techniques). In this paper we now add a low-cost 3D-printed 2-DOF force sensor to this modular robot and demonstrate a variety of force control techniques for use when the robot is in physical contact with the environment. These include stiffness control, impedance control, admittance control, and hybrid position/force control. Each of these various force control schemes can be first simulated and then experimentally implemented using a MATLAB/Simulink real-time interface. The two-degrees of freedom are just enough to demonstrate how the manipulator Jacobian can be used to implement directional impedances in operational space, and to demonstrate how hybrid control can implement position and force control in different axes. This paper will describe the 2-DOF robot system including the custom force sensor, illustrate the various force control methods that can be implemented, and demonstrate sample results from these experiments.

An Approach to Motion and Force Control of Coordinated Robot Arms in the Presence of Joint Flexibility

1994 ◽  
Vol 116 (3) ◽  
pp. 326-335 ◽  
Author(s):  
Yan-Ru Hu ◽  
Andrew A. Goldenberg
Keyword(s):  
Contact Force ◽  
Force Control ◽  
Lyapunov Stability Theory ◽  
Internal Force ◽  
System Stability ◽  
Motion Controller ◽  
Flexible Joint ◽  
Robot Arms ◽  
Simulation Results ◽  
And Control

A system consisting of several flexible joint robot arms is studied in this paper. The paper addresses the motion and force control problem of such systems. A coordinating controller, consisting of a motion controller, contact force controller, and internal force controller, is designed to distribute the load between the coordinated flexible joint robot arms, and control the motion of the object, the internal force and contact force between the object and the environment, as well generate the desired joint elastic force. The system stability is analyzed based on Lyapunov stability theory. It is shown that with the proposed controller the motion and force control variables can be regulated to track asymptotically their desired trajectories. Simulation results are given to illustrate the performance of the proposed controller.

A new robot skin for force and position detection

2014 ◽  
Vol 41 (6) ◽  
pp. 534-542 ◽  
Author(s):  
Haibin Wu ◽  
Yixian Su ◽  
Jinjin Shi ◽  
Jinwen Li ◽  
Jinhua Ye
Keyword(s):  
Contact Force ◽  
Low Cost ◽  
Force Sensor ◽  
Viscoelastic Layer ◽  
Position Sensor ◽  
Content Type ◽  
Position Detection ◽  
Sensor Module ◽  
Contact Position ◽  
Robot Skin

Purpose – The aim of the research is to achieve a robot skin which is easy to use, and can detect both position and force interacted between robot and environments. Design/methodology/approach – The new type of robot skin proposed in this paper includes two functional modules – contact position sensor and contact force sensor. The contact position sensor module is based on the resistor divider principle, which consists of two perpendicular conductive fiber layers and insulated dot spacer between them. The contact force sensor module is based on capacitance change theory, which consists of two soft conductive plates and a viscoelastic layer between them. By combining the two modules, the soft robot skin was designed. Findings – Simulation and experiment results demonstrate that the proposed robot skin design is feasible and effective enough to sense contact position and contact force simultaneously. Practical implications – This robot skin is low-cost and easy to make and use, which provides safety solutions for most of the robot. Originality/value – For the first time, an integrated robot skin which can get contact position and force information simultaneously is designed. Unlike general tactile sensor matrices, this robot skin has only six leads. Furthermore, the number of leads does not increase with the enlarging of sensor area. Soft and simple structure of the robot skin makes it possible to cover any region of the robot body.

scholarly journals A New Design of the Miniature Force Sensor Based on Strain Gages for Ablation Catheter

2017 ◽  
Author(s):  
Xiaochan Shi ◽  
Xuelian Gu ◽  
Jiahong Tan ◽  
Bo Liang
Keyword(s):  
Contact Force ◽  
Force Measurement ◽  
Low Cost ◽  
Femoral Vein ◽  
Force Sensor ◽  
Heart Cells ◽  
Strain Gages ◽  
Ablation Catheter ◽  
Radio Frequency Energy ◽  
Catheter Tip

Recently, the radiofrequency ablation catheter is widely used in the treatment of atrial fibrillation. Radiofrequency catheter tip is inserted through femoral vein puncture and pushed to the heart cavity. The radio frequency energy is applied to the ablation lesion on the inner wall of the heart, and then the heart cells die to achieve the aim of treatment[1]. During the treatment, however, the patients need repeated ablation because of the ineffective ablation, and the complications may occur. Continuous pulmonary vein lesion and isolation of wall is very important to increase the success of surgery [2]. Research [3] shows that the contact force between catheter tip and the tissue of inner heart is a key factor influencing the lesion size. In order to monitor the contact force, many force sensors have been studied. Fukuda [4] used semiconductor strain gage outside of the catheter to monitor the contact force. Peirs [5] monitored the contact force by optical technology. The disadvantages of the current sensors are using special expensive signal detecting and analyzing instrument, such as Endosense (SMART touch), which will increase the cost tremendously. For clinical application, it is necessary to develop a low cost sensor with enough accuracy which can also be used in the catheter for contact force measurement. This paper focuses on designing a novel force-voltage transferring sensor. The sensor consists of a Ni-Ti alloy tube and several strain gages. With the compact design of a spiral structure, it can reduce the overall cost while keeping a good performance at the same time. The price of SMART touch catheter is 4, 348 dollars. The proposed design will be as much as 20–30 percent below SMART’s price.

Adjusting the active joint stiffness of a collaborative robot arm for force control

2021 ◽  
Author(s):  
Rodrigo Perez-Ubeda ◽  
Ranko Zotovic-Stanisic ◽  
Santiago C. Gutierrez Rubert ◽  
Joaquin Lluch-Cerezo
Keyword(s):  
Force Control ◽  
Joint Stiffness ◽  
Robot Arm ◽  
Active Joint ◽  
Collaborative Robot

scholarly journals Behavioural Study of the Force Control Loop Used in a Collaborative Robot for Sanding Materials

Materials ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 67
Author(s):  
Rodrigo Pérez Ubeda ◽  
Santiago C. Gutiérrez Rubert ◽  
Ranko Zotovic Stanisic ◽  
Ángel Perles Ivars
Keyword(s):  
Force Control ◽  
Feed Rate ◽  
Significant Variation ◽  
Industrial Robots ◽  
Control Loop ◽  
Saturation State ◽  
Collaborative Robots ◽  
Increase Productivity ◽  
Different Characteristics ◽  
Collaborative Robot

The rise of collaborative robots urges the consideration of them for different industrial tasks such as sanding. In this context, the purpose of this article is to demonstrate the feasibility of using collaborative robots in processing operations, such as orbital sanding. For the demonstration, the tools and working conditions have been adjusted to the capacity of the robot. Materials with different characteristics have been selected, such as aluminium, steel, brass, wood, and plastic. An inner/outer control loop strategy has been used, complementing the robot’s motion control with an outer force control loop. After carrying out an explanatory design of experiments, it was observed that it is possible to perform the operation in all materials, without destabilising the control, with a mean force error of 0.32%. Compared with industrial robots, collaborative ones can perform the same sanding task with similar results. An important outcome is that unlike what might be thought, an increase in the applied force does not guarantee a better finish. In fact, an increase in the feed rate does not produce significant variation in the finish—less than 0.02 µm; therefore, the process is in a “saturation state” and it is possible to increase the feed rate to increase productivity.

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