Early studies on robot machining were reported in the 1990s. Even though there are continuous worldwide researches on robot machining ever since, the potential of robot applications in machining has yet to be realized. In this paper, the authors will first look into recent development of robot machining. Such development can be roughly categorized into researches on robot machining system development, robot machining path planning, vibration/chatter analysis including path tracking and compensation, dynamic, or stiffness modeling. These researches will obviously improve the accuracy and efficiency of robot machining and provide useful references for developing robot machining systems for tasks once thought to only be capable by CNC machines. In order to advance the technology of robot machining to the next level so that more practical and competitive systems could be developed, the authors suggest that future researches on robot machining should also focus on robot machining efficiency analysis, stiffness map-based path planning, robotic arm link optimization, planning, and scheduling for a line of machining robots.

https://link.springer.com/content/pdf/10.1007%2Fs00170-012-4433-4.pdf

Robot machining: recent development and future research issues

https://isiarticles.com/bundles/Article/pre/pdf/812.pdf

Organizational structures and the performance of supply chain management

Conventional material removal techniques, like CNC milling, have been proven to be able to tackle nearly any machining challenge. On the other hand, the major drawback of using conventional CNC machines is the restricted working area and their produced shape limitation limitations. From a conceptual point of view, industrial robot technology could provide an excellent base for machining being both flexible and cost efficient. However, industrial machining robots lack absolute positioning accuracy, are unable to reject/absorb disturbances in terms of process forces and lack reliable programming and simulation tools to ensure right first time machining, at production startups. This paper reviews the penetration of industrial robots in the challenging field of machining.

Machining with robots: a critical review

Impedance control is to provide stable tracking by regulating the impedance response of a robot. In this paper, an asymmetrical nonlinear impedance control (ANIC) is proposed for a dual robotic machining system. The symmetrical linear impedance control (SLIC) is also analyzed as a comparison study. We compared two controllers in terms of the stability and the sensitivity property of the grinding force, as well as the trajectory design. The main advantage of the ANIC is that the grinding force is robust to the environmental disturbances and the variation in thickness of workpieces. In contrast to the traditional control concept, which is devoted to compensate the nonlinear effect of the original system, our design philosophy is to increase the system robustness by introducing an artificial nonlinearity to the system. As a result, the dual robotic system acts as variable stiffness actors to adapt the variation in the thickness of workpieces. Grinding experiments are conducted in the dual robotic machining test rig for both workpieces with the uniform and varied thickness. The experimental results show that the dual robotic system with the ANIC can achieve better grinding quality.

Asymmetrical nonlinear impedance control for dual robotic machining of thin-walled workpieces

Recent research has considered robotic machining as an alternative to traditional CNC machining. However, one of the problems with serial link manipulators is that they have a low inherent stiffness due to the cantilever design of the links and low torsional stiffness of the actuators. This problem is addressed during the resolution of a Cartesian-space tool path, defined relative to the blank, into joint space using the pseudo-inverse method of redundancy resolution. The two-armed system is modeled as a single system using a relative Jacobian to relate the joint motions to the relative motion of the tool and blank. The null space of the relative Jacobian is used to optimize the joint trajectories by minimizing the system compliance factor. A min-max optimization and a null-space search are investigated in order to produce a global optimum. Simulation results show that stiff trajectories lower the level of torque consumption, which allows for an increase in productivity. The deflection of the tool relative to the blank is decreased as well.

A multi-arm robotic system for optimal sculpting

With the advancement of CAD/CAM and robot technologies, applying robots for rapid prototyping applications has become a growing trend. However, a single robot can only perform limited prototyping tasks. Compared to a single robot, a dual-robot workcell can have greater structure flexibility, production efficiency, and system reliability due to the inherent parallelism and duality of robots. This paper presents the development and implementation of a dual-robot workcell for prototyping of 3D models. First, kinematic models of both robots in the workcell are established. Then, the concepts of five-axis machining configurations, postprocessing, off-line robot path generation and the dual-robot control scheme are presented. Finally, details of cutting experiments are provided to demonstrate the effectiveness of the system. The results show that the proposed dual-robot workcell is flexible and efficient for prototyping complex components in the current industrial environment.

Rapid and flexible prototyping through a dual-robot workcell

A dual-robot machining system has been developed for manufacturing complex objects. The system consists of two six-axis industrial robots with flexible tool changers, a CAD/CAM package for geometric design and toolpath generation, a robot simulation package for collision avoidance, and a vision system for robot calibration. It offers the flexibility to reconfigure the robots of the system to accommodate workpieces of different shapes and sizes. A prototype of the system has been successfully developed and tested, and shows satisfactory performance in machining quality and control over the configurations of the robots. Examples are given of the application of the system to machining objects with spherical and sculptured surfaces. The system has been shown to be flexible, reconfigurable, automatic, and capable of manufacturing complex prototypes in the current industry environment.

Hsuan-kuan Huang

Papers

Rapid and flexible prototyping through a dual-robot workcell

Development of a dual-robot system for prototype production