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

Abstract

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.

Safety System for an Industrial Cooperating Robot Based on Depth Cameras

“…Przykładowo Fanuc ma w swojej ofercie serię robotów CR (ang. Cooperative Robots) wyposażonych domyślnie w system detekcji kolizji przy wykryciu siły rzędu 150 N (z możliwością przeprogramowania progu), oparty na sensorach momentu siły [12]. Umożliwia wyposażenie manipulatora w maty ochronne oraz system wodzenia manipulatorem.…”

“…Pozwala on na wyliczenie momentu obrotowego dla każdego silnika (w każdym stopniu swobody), co jest proporcjonalne do poboru prądu pomierzonego na silnikach. W przypadku kolizji różnica między wyznaczonym poborem prądu a pomierzonym jest znacząca, dzięki temu wirtualny czujnik może wykryć kolizję [12,14]. Sensor taki jest stosowany w cobotach Universal Robots.…”

The Advanced Control Approach based on SMC Design for the High-Fidelity Haptic Power Lever of a Small Hybrid Electric Aircraft

“…The impedance control approach [124][125][126] is employed when a mechatronic device is in contact with its environment or with a human. It is an important control concept in modern robotics that is demonstrated by numerous applications [127][128][129][130][131][132][133][134][135][136][137][138][139][140]. The mechanical impedance, which features a force response of a body or a system of bodies on imposed velocity or position, can be described as a force-velocity relationship or force-position relationship.…”

Recycling and Updating an Educational Robot Manipulator with Open-Hardware-Architecture

“…On the other hand, the robot in [4] is built with recycled LEGO pieces, and it is controlled with an Arduino Mega board, which is programmed using the Simulink Support Package for Arduino Hardware. Yen et al [5] developed a low-cost collaborative robot that employs a virtual force sensor and stiffness control to safety collision detection and low-precision force control. The authors of [6][7][8] presented educational robot manipulators, whose movements are carried out by means of radio control servomotors that have controllers that cannot be modified.…”