Helping Designers Make the Right Choices for Automation
by David Mollert
, Mechanical Engineer
FANUC America Corporation Posted 06/15/2006
I recently listened to a talk radio program about manufacturing. As the conversation went on, one caller’s statement stuck in my mind: ‘‘While automation has played a large part in increasing productivity, we have not gotten the help from robotics that we had hoped for.’‘ That took me by surprise, since I’ve worked as a designer of all-electric, articulated robot systems for over ten years, and know that robots have played a major role in improving manufacturing efficiency. I just assumed they were talking about some other type of hard automation besides robots. Then I got to thinking that there are still designers so comfortable with hard automation that they have not yet considered articulated robots.
Robots have matured from their birth in specific industries with specific tasks to becoming versatile mechanisms that are ideal for straightforward pick-and-place applications, as well as challenging applications that can utilize the unique capabilities inherently built into robotics. After working with automation equipment for 20 years, I feel it’s important to provide insights into my transition from hard tooling to robotics so that others can understand the significant differences between the two. The purpose of this article is to touch on several features that have made today’s robot a vital tool for any application.
The term flexibility means a variety of things when discussing robots. Let me first discuss flexibility in movement. With six-axis robots available, movement is virtually unrestricted. The designer spends less time on how the parts are moved and more time on the tooling at the end of the robot that picks the parts. This flexibility allows the tooling to be designed with an eye toward multiple tasks. For example, picking boxes and pallets or assembling two different parts and then setting them on an exit conveyor. The idea is having the robot do most of the work. In situations when the end-of-arm-tool cannot accommodate all of the different shapes or sizes of the parts, tool changers are added to allow the robot to pneumatically change end-of-arm tools. This type of flexibility in movement is very useful during the building of a robotic cell. Hard tooling does not lend itself to minor positional changes as well as robots do. These changes made ‘‘on the floor’‘ often help with the overall productivity of the cell.
Flexibility in mounting. Floor, ceiling or rail-mount robots offer the designer an option with most applications that does not require additional mounting structures. This speeds up the engineering needed to develop mounts, as well as the outside fabrication requirements.
Flexibility in your long-term investment. Traditionally, the thought of reusing hard tooling would be unheard of, but robots can be re-deployed to accommodate changes in products or procedures. When reusing robots, only the tooling and programming need modifications. They eliminate the question of compatibility when attempting to blend a variety of hard tooling products from different component manufactures together in one assembly. Because robots offer multiple axes and are self-contained, there is no need for a structural framework to mount the various components of hard tooling. They also greatly reduce the time needed for hard wiring of the system. For most applications, power is only required for the robot and air if needed for the end-of-arm-tool. Another advantage of re-deploying robots to new applications is that it breeds continuity throughout the plant. When reusing robots there is no learning curve or additional spare part requirements, and only one point of contact for its electrical and mechanical components.
When I first started designing with robots, I had a tendency to limit their flexibility by thinking of only a single task, similar to hard tooling. I now look at the overall system and incorporate the robot to do as many tasks as possible. The key point is that robot flexibility allows the designer more options without having to deal with the compromises of hard tooling.
Along with advances in the drives and the mechanical unit, a robot’s programming language is straightforward if you are accustomed to reading ladder logic. Each line represents a separate robot command. The command lines that move the robot have four components. These components tell the robot were to go, how fast, how to get there, and whether to use all of the axes in unison or individually. The development of these programs start with the hand held ‘‘teach pendant’‘ which is used to physically drive the robot to a desired point where the four variables can be selected and the point recorded. It is a point-by-point process after that. These programs can become as complicated as the process demands, but even then the basic structure of the language stays the same. This type of straightforward programming goes a long way in removing the stigma of complicated controls and allows for a short learning curve for any individual.
In addition, FANUC Robotics offers a simulation program to set up a virtual cell on a computer. Once the robot, tooling and other peripheral equipment are selected, the user can construct the program off-line. The software provides the ability to create and watch the process and adjust locations and speeds in order to refine the system’s cycle time. This program can then be loaded into a robot on the floor, and after verifying the positional points, it’s ready to run.
Robots have definitely made a positive impact on manufacturing, but there are a few key points to remember when designing with robots. The first point is the size of the control cabinet. With a footprint of 24 by 30 inches, it consumes more floor space than many smaller robots. Because of its size, designers must consider the controller during initial discussions of the system or cell space requirements.
The second point has to do with safety considerations. Because the available travel of a six-axis robot resembles a sphere, when working with a specific application it is advisable to limit the travel to only where the robot needs to go. These limits must be accomplished with physical stops in order to adhere to the Robotic Industries Association’s safety requirements. Software limits cannot replace the physical stops. Once the maximum travel has been established, guarding needs to be erected to prevent access by personnel. Including physical stops in the design helps to minimize the amount of floor space the robotic system consumes.
The last item is more of a caution when designing robot-mounting bases. With the high speeds of each axis, it is easy to underestimate the rigidity required of the base, even with smaller robots. An adequately sized base insures that the robot will be on solid ground and not quiver when stopping, and can help with the accuracy of the process.
FANUC Robotics is very supportive of its customers who are receiving their first robot system in order to help them overcome the mystique of robots. Many times during the installation of a system in their facility, employees seem to keep their distance, but after they see it running in production the question becomes ‘‘is that all it can do?’‘ My answer is…no, that’s not all.