Human experience and expertise have also been involved in the plan- ning process. For example, real-time strategies based on impedance and force control for the interactions between robot and the cutting of ma- terial, which accommodate uncertainties and critical contact effects in hard-metal machining, and various force/impedance machining-control algorithms contribute to confirm high quality and precision in grinding and polishing operations and considerably extend the accuracy  limits of the robot. Subsequent re-planning and re-programming also enhance the iterative-machining process through existing sensor technology.

Through this paradigm, Hephestos has combined robotic advantages with the flexibility of human-like strategies of dextrous artisans and workmen to develop a plug-and-play flexible robotic-machining system. In addition, Hephestos has demonstrated benefits of utilisation of flexi- ble and truly open robot control and planning  platforms.

The aim of Hephestos is not to compete with or replace general CNC technologies by robots, rather its goal is to identify and demon- strate the position, performance and benefits (Fig. 1) of robot-hard- material machining in the boundary processes shared by manual-work and CNC technology. The focus is on releasing the human-hard work in small-batch machining activities by partial automations using industrial robots, especially by sharing models based on human-robot collabora- tion and cooperation.

The key innovations of Hephestos, presented in Section 3, improve industrial-robots technology in hard-material machining and establish cost-efficient robotic applications in industry that are of considerable commercial benefits for the European-machining sectors; in addition, they are pertinent and affordable to both small-and-medium enterprises and large-scale producers.

2. State of the art

During the last years, a significant effort has been addressed to solve the mentioned difficulties to apply robots for hard materials machining. Both, the robotic industry and the academic research, have recently pro- posed different approaches.

To cope with the stiffness and precision barriers for the hard ma- terials robotic machining, the robotic industry has recently adopted several strategies to improve robot structural performance. The paral- lel link robots (e.g. Fanuc F-200iB) provide substantially more rigid- ity, however, at considerably smaller work envelopes. Applying closed kinematic chains along serial robotic structures represents a  further step to stiffer robot mechanical structures. Almost each robot producer offers recently special robot for pre-machining (e.g. ABB-IRB 6660, KUKA KR-500MT, etc.). Stäubli offers high speed machining robots (HSM) with a Fisher-Precise high speed spindle integrated directly into forearm.

Refining the robot accuracy represents another robot builders ap- proach towards high precision robots. The adopted strategies include calibration, position mastering, and even the usage of new encoder tech- nology in each joint at output shafts to compensate for inaccuracies in the transmission chain. Achievable accuracy is sufficient for some high- precision operations (e.g. drilling and routering in the aerospace indus- try), but still insufficient for the precision machining. Moreover, all spe- cific robotic systems are considerably more expensive in comparison to standard industrial robots.

To manage the lack of standardized robot programming, in a way that is comparable with the standardization in the CNC  world, the robot producers offer recently a wide range of software solutions (e.g. KUKA CAMRob, Motoman standard CNC G-Code Converter, FANUC- Roboguide, etc.) to transfer CAD/CAM generated CNC codes in pro- prietary robot programs. By this means users can greatly reduce pro- gramming time and costs required for programming complex objects shapes. Several SW companies offer specific robot programming add-ons to CAD/CAM tools, such as Robotmaster (Jabez Technologies), Power- Mill (Dellcam), IRBCAM, etc.