Helping Designers Make the Right Choices for Automation
By: David Mollert
I recentlylistened to a talk radio program about manufacturing. As the conversationwent on, one caller’s statement stuck in my mind: ‘‘While automation has playeda large part in increasing productivity, we have not gotten the help fromrobotics that we had hoped for.’‘ That took me by surprise, since I’veworked as a designer of all-electric, articulated robot systems for over tenyears, and know that robots have played a major role in improving manufacturingefficiency. I just assumed they were talking about some other typeof hard automation besides robots. Then I got to thinking that there arestill designers so comfortable with hard automation that they have not yetconsidered articulated robots.
Robots havematured from their birth in specific industries with specific tasks to becomingversatile mechanisms that are ideal for straightforward pick-and-placeapplications, as well as challenging applications that can utilize the uniquecapabilities inherently built into robotics. After working with automationequipment for 20 years, I feel it’s important to provide insights into mytransition from hard tooling to robotics so that others can understand thesignificant differences between the two. The purpose of this article isto touch on several features that have made today’s robot a vital tool for anyapplication.
The termflexibility means a variety of things when discussing robots. Let mefirst discuss flexibility in movement. With six-axis robots available,movement is virtually unrestricted. The designer spends less time on howthe parts are moved and more time on the tooling at the end of the robot thatpicks the parts. This flexibility allows the tooling to be designed withan eye toward multiple tasks. For example, picking boxes and pallets or assemblingtwo different parts and then setting them on an exit conveyor. The ideais having the robot do most of the work. In situations when theend-of-arm-tool cannot accommodate all of the different shapes or sizes of theparts, tool changers are added to allow the robot to pneumatically changeend-of-arm tools. This type of flexibility in movement is very usefulduring the building of a robotic cell. Hard tooling does not lend itselfto minor positional changes as well as robots do. These changes made ‘‘onthe floor’‘ often help with the overall productivity of the cell.
Flexibility inmounting. Floor, ceiling or rail-mount robots offer the designer anoption with most applications that does not require additional mountingstructures. This speeds up the engineering needed to develop mounts, aswell as the outside fabrication requirements.
Flexibility inyour long-term investment. Traditionally, the thought of reusing hardtooling would be unheard of, but robots can be re-deployed to accommodatechanges in products or procedures. When reusing robots, only the toolingand programming need modifications. They eliminate the question ofcompatibility when attempting to blend a variety of hard tooling products fromdifferent component manufactures together in one assembly. Because robotsoffer multiple axes and are self-contained, there is no need for a structuralframework to mount the various components of hard tooling. They alsogreatly reduce the time needed for hard wiring of the system. For mostapplications, 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 breedscontinuity throughout the plant. When reusing robots there is no learningcurve or additional spare part requirements, and only one point of contact forits electrical and mechanical components.
When I firststarted designing with robots, I had a tendency to limit their flexibility bythinking of only a single task, similar to hard tooling. I now look atthe overall system and incorporate the robot to do as many tasks aspossible. The key point is that robot flexibility allows the designermore options without having to deal with the compromises of hard tooling.
Along withadvances in the drives and the mechanical unit, a robot’s programming languageis straightforward if you are accustomed to reading ladder logic. Eachline represents a separate robot command. The command lines that move therobot 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 orindividually. The development of these programs start with the hand held‘‘teach pendant’‘ which is used to physically drive the robot to a desiredpoint where the four variables can be selected and the point recorded. Itis a point-by-point process after that. These programs can become ascomplicated as the process demands, but even then the basic structure of thelanguage stays the same. This type of straightforward programming goes along way in removing the stigma of complicated controls and allows for a shortlearning curve for any individual.
In addition,FANUC Robotics offers a simulation program to set up a virtual cell on acomputer. Once the robot, tooling and other peripheral equipment areselected, the user can construct the program off-line. The softwareprovides the ability to create and watch the process and adjust locations andspeeds in order to refine the system’s cycle time. This program can thenbe loaded into a robot on the floor, and after verifying the positional points,it’s ready to run.
Robots havedefinitely made a positive impact on manufacturing, but there are a few keypoints to remember when designing with robots. The first point is thesize of the control cabinet. With a footprint of 24 by 30 inches, itconsumes more floor space than many smaller robots. Because of its size,designers must consider the controller during initial discussions of the systemor cell space requirements.
The second pointhas to do with safety considerations. Because the available travel of asix-axis robot resembles a sphere, when working with a specific application itis 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 theRobotic Industries Association’s safety requirements. Software limitscannot replace the physical stops. Once the maximum travel has beenestablished, guarding needs to be erected to prevent access by personnel. Includingphysical stops in the design helps to minimize the amount of floor space therobotic system consumes.
The last item ismore of a caution when designing robot-mounting bases. With the highspeeds of each axis, it is easy to underestimate the rigidity required of thebase, even with smaller robots. An adequately sized base insures that therobot will be on solid ground and not quiver when stopping, and can help withthe accuracy of the process.