Force Control

Johansson, Rolf; Nilsson, Klas; Robertsson, Anders

doi:10.1007/978-1-4471-4670-4_108

Cited by 4 publications

(2 citation statements)

References 52 publications

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“…In robotic FSW, force control and motion control commonly run in parallel. Such structures are known as hybrid force/motion control or hybrid force/position control (Craig, 1989; Johansson et al , 2014). The control is then decomposed, so that a subspace of the tool’s configuration space is force controlled, whereas the complementary space is position controlled.…”

Section: Introductionmentioning

confidence: 99%

Robotic friction stir welding – seam-tracking control, force control and process supervision

Karlsson

Carlson

Holmstrand

et al. 2023

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Purpose This study aims to enable robotic friction stir welding (FSW) in practice. The use of robots has hitherto been limited, because of the large contact forces necessary for FSW. These forces are detrimental for the position accuracy of the robot. In this context, it is not sufficient to rely on the robot’s internal sensors for positioning. This paper describes and evaluates a new method for overcoming this issue. Design/methodology/approach A closed-loop robot control system for seam-tracking control and force control, running and recording data in real-time operation, was developed. The complete system was experimentally verified. External position measurements were obtained from a laser seam tracker and deviations from the seam were compensated for, using feedback of the measurements to a position controller. Findings The proposed system was shown to be working well in overcoming position error. The system is flexible and reconfigurable for batch and short production runs. The welds were free of defects and had beneficial mechanical properties. Research limitations/implications In the experiments, the laser seam tracker was used both for control feedback and for performance evaluation. For evaluation, it would be better to use yet another external sensor for position measurements, providing ground truth. Practical implications These results imply that robotic FSW is practically realizable, with the accuracy requirements fulfilled. Originality/value The method proposed in this research yields very accurate seam tracking as compared to previous research. This accuracy, in turn, is crucial for the quality of the resulting material.

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Section: Introductionmentioning

confidence: 99%

Robotic friction stir welding – seam-tracking control, force control and process supervision

Karlsson

Carlson

Holmstrand

et al. 2023

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“…It is hardly possible to use pure position-controlled Delta robots in the abovementioned tasks because they cannot safely interact with the external environment. Contact force generated by uncertain position error may exceed the tolerance of the robot or workpiece and cause damage to the system (Rolf Johansson and Robertsson, 2014). Passive compliance and active compliance are two feasible solutions.…”

Section: Introductionmentioning

confidence: 99%

Sensorless force estimation and control of Delta robot with limited access interface

Cheng

Jiang

2018

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Purpose Delta robot is a parallel robot specifically designed for high-speed pick and place tasks. However, sometimes they are asked to perform additional assembling and squeezing actions, which is beyond the capability of position-controlled Delta robots. Force sensors may be expensive and add mass to the system. Therefore, the purpose of this paper is to study sensorless force control of Delta robots using limited access interface. Design/methodology/approach Static force analysis is performed to establish a relation between joint torques and external forces. The joint torques are observed from signals provided by motor drivers. A distributed mass model is proposed to compensate the gravity of upper arms and forearms. To minimize the effect of backlash and nonlinear frictions brought by gearboxes, model parameters are calibrated in two separated modes: “LIFTING” and “LOWERING”. Finally, a hybrid force estimation model is built to deal with both cases simultaneously. Surrogate model-based force control law is proposed to increase the force control loop rate and handle the force control problem for discrete position-controlled Delta robots. Findings The results show that the force estimation model is effective and mode separation can significantly improve the accuracy. The force control laws indeed stabilize the robot in desired states. Originality/value The proposed solution is based on position-controlled commercial Delta robot and requires no additional force sensor. It is able to extend Delta robots’ capability and meet requirements of emerging complex tasks.

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Eliminating the Inertial Forces Effects on the Measurement of Robot Interaction Force

Gierlak

Burghardt

Szybicki

et al. 2019

Lecture Notes in Electrical Engineering

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Force Control

Cited by 4 publications

References 52 publications

Robotic friction stir welding – seam-tracking control, force control and process supervision

Robotic friction stir welding – seam-tracking control, force control and process supervision

Sensorless force estimation and control of Delta robot with limited access interface

Eliminating the Inertial Forces Effects on the Measurement of Robot Interaction Force

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