حفاری مقرون به صرفه با استفاده از روبات های صنعتی با بازخورد نیروی پهنای باند بالا

Here we present a method for high-precision drilling using an industrial robot with high-bandwidth force feedback, which is used for building up pressure to clamp-up an end-effector to the work-piece surface prior to drilling. The focus is to eliminate the sliding movement (skating) of the end-effector during the clamp-up of the end-effector to the work-piece surface, an undesired effect that is due to the comparatively low mechanical stiffness of typical serial industrial robots. This compliance also makes the robot deflect due to the cutting forces, resulting in poor hole position accuracy and to some extent in poor hole quality. Recently, functionality for high-bandwidth force control has found its way into industrial robot control systems. This could potentially open up the possibility for robotic drilling systems with improved performance, using only standard systems without excessive extra hardware and calibration techniques. Instead of automation with expensive fixtures and precise machinery, our approach was to make use of standard low-cost robot equipment in combination with sensor feedback. The resulting sliding suppression control results in greatly improved hole positioning and quality. The conceptual idea behind the force control is useful also in many other robotic applications requiring external sensor feedback control.

The traditional application areas for industrial robots involve highly repetitive operations such as spot welding. Hence, robotic development has been focused on high precision (repeatability) in repetitive operations. For example, a standard ABB IRB4400 robot for 60 kg payload has a repetitive accuracy of View the MathML source±0.05mm. If, however, the same robot is given a new coordinate that it has never visited before, the accuracy is in general around View the MathML source±3mm, which is 60 times the size of the repetitive accuracy. Today it is possible to buy the same robot with an option pack that includes calibration for high accuracy. This will improve accuracy to become within View the MathML source±0.5mm, which is still 10 times the repetitive accuracy. In addition, this accuracy is only guaranteed under the condition that no unmodeled external forces act on the robot, i.e., only during motion in free space. For contact tasks such as polishing, drilling, and riveting, the effects of the limited mechanical stiffness of the robot must be taken into account in order to maintain the positioning accuracy, which is not feasible unless a detailed model of the particular robot specimen is available.

The use of industrial robots in automatic drilling applications has been limited, mainly due to the presence of rapidly varying interaction forces in combination with compliance in gear boxes and links. Functionality for high-bandwidth force control in modern industrial robot control systems could potentially lead to robotic drilling systems with significantly improved performance, without the use of costly hardware modifications and calibration procedures. In this paper, we have presented methods and systems for force-controlled robot drilling. Using a 6-DOF force/torque sensor, an outer force control loop and a model-based inner-loop disturbance compensation scheme have been designed, and used to control the axial contact force and suppress the sliding of a tripod contact while the drilling is performed. The advantage of the proposed controller is demonstrated in reproducible drilling experiments using an industrial robot system. Moreover, the application potential for high-precision robotic drilling operations in airframe assembly has been demonstrated.