- SPECIAL REPORTS
ASSEMBLY magazine recently asked a group of experts to share their thoughts on the subject. Participants included Claude Dinsmoor, general manager of controller product development at FANUC Robotics America Inc. (Rochester Hills, MI); Michael Gerstenberger, senior engineer at KUKA Robotics Corp. (Clinton Township, MI); and Jerry Hendrickson, engineering program manger at Adept Technology Inc. (Livermore, CA).
ASSEMBLY: What are the benefits of “safe motion” systems for assembly and material handling robots?
Dinsmoor: Safety-rated software is a significant breakthrough in robot system construction because it allows the safety design of the robot system to use the robot itself for some of the safety functions. Prior to the application of safety-rated robot software, all safeguarding of the robot needed to be external to the robot, either as a safety-rated limit switch or cam system, safety-rated area scanners, or other devices arrayed around the robot to provide the robot travel limiting or protections required for the robot cell. By moving some of the safety functions to within the robot, significant savings can be seen in floor space of the robot system, overall system cost (few discrete components), and overall reliability of the robot system during daily operation.
The most significant benefits are found in robot system applications where the travel of the robot needs to be restricted (due to floor space or process constraints) to much less than the full reach of the robot. Features that can restrict the robot motion in Cartesian space provide great flexibility in the layout of systems using the robot without using specialized limiting devices. Cartesian space zone restriction means the robot can be constrained to exactly the area in which it works; something that is not possible with the current systems that limit robot motion externally using joint-based limit switches.
With the correct robot product design, the safe zones can be enabled and disabled from an external source such as a safety PLC. Using multiple zones, it is possible to design a flexible robot system where the operator can enter and leave the space of the robot in a safe fashion. This can greatly simplify and streamline the design of robot cells where, for example, the load area of the robot can be protected from having the robot enter it when an operator needs to be in the same area. This sort of application can be done with today’s existing technology, but is typically difficult to setup, is expensive to implement, and requires more floor space than a system using safety-rated software features.
Gerstenberger: The features of safe motion systems can be used in any robot system to design the robot’s restricted space (where the robot and its tooling could possibly reach) to be very close to its operating space (where the robot is normally programmed to move). By doing this, the footprint of robotic cells can be reduced without reducing the clearance to dangerous pinch points, such as fences and building columns.
Another use of safe motion is to eliminate some of the fixturing in robot workcells. In this case, the workpiece is directly loaded onto the robot tooling. The safe operational stop is used to ensure that the robot does not move while the operator is in the collaborative workspace.
Hendrickson: Assembly and material handling are generally high-speed applications, requiring high throughput. Separation is in place to prevent people from entering the robot workspace. During programming, teaching, servicing and troubleshooting-when a technician may be within the work envelope-slow speed or slow power operation is sufficient.
Removal of separation in the factory could lower costs and create new opportunities. This would likely be offset by the cost of safe motion of the robot. Future applications could include automated stocking systems.