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Manufacturing Best Practices Include the Best Robotic Peripherals
by Bennett Brumson, Contributing Editor
Robotic Industries Association Posted 06/13/2002
When setting up a robotic workcell, there is a tendency for robot makers and end users to focus on the robot itself. This is understandable as the robot arm is at the heart of the system.
However, there are other ingredients-peripherals-that are vital to its effective and efficient function. These include shuttles, tool changers and gauging mechanisms to name a few.
'As robots get more and more flexible, tooling and other peripherals need to match that flexibility,' said Robert Little, a sales and product manager of ATI Industrial Automation. ATI, of Apex, NC, is a maker of crash protection devices, center compliance instruments, torque sensors and tool changers.
Robotic 'Space Shuttles'
Shuttles, a type of linear slide, operate on a shaft or bearing. Some shuttles can be positioned horizontally, vertically, or, on an X/Y orientation.
'Rixan's shuttle is integrated into the controller, and moves the robot, acting as its sixth or seventh axis,' said Kent Walker. Walker is director of engineering at Dayton, OH-based Rixan Associates, Inc. 'Shuttles are used in bioscience and machine loading applications. In the biosciences, the shuttle moves the robot, or samples it is working with, from one piece of test equipment to another. The working range can be up to five meters,' according to Walker.
The layout of a workcell is more challenging with the addition of a shuttle, said Walker This is partially addressed by having the shuttle mounted on a tabletop or inverted from the ceiling. The latter configuration, which keeps the robot work area open, saves on valuable floor space.
What do some robotic shuttle users like to see in these items?
'In the laboratory markets, they would like to see smaller, narrower, lighter shuttle devices that make the work envelope greater. This, while maintaining strength. They also want a good, clean software interface integrated in their applications within their master software,' Walker said.
Access is Everything
While robots are able to access most areas of parts being manipulated, there are peripheral components that make this easier. Robohand, Inc., of Monroe, CT, makes several of these modules, including rotary actuators, liner slides, and lift tables.
'Our rotary actuator is designed for redirecting the part, so that the robot can have access to the part's back or underneath,' said Robohand's Scott Ames. Ames is an application engineer at Robohand. 'This enables a robot that has only four axes to have greater access. Also, there can be multiple parts in a workcell. As one part is being worked on, another is ready to be loaded or unloaded.'
Other devices that facilitate access for robots include mounting modules. These are particularly useful in welding and extruding applications. Feed escapements for part control, clamps for temporarily holding end-of-arm tooling, and thrusters are also part of the robotic mix. Thrusters are mounted to the X-axis and are good for pick and place operations. Space savings and accessibility is also achieved through the use of lift tables that raise and lower parts for more precise positioning.
The speed and size of these components are potential hurdles in creating an efficacious and proficient robotic workcell.
'If the workcell is small, the difficulty is getting the robot, the end-of-arm tooling, the part and all the peripherals in,' Ames pointed out. 'There is a need to have a small but robust workcell'
Tool Changing Time
As robots become more versatile, there is a need for the more frequent tool changing, which is performed by tool changers.
'Robots can be programmed for different applications and the tooling has to be as flexible,' said Little. 'Take stamping for example. Robots are being used for press tending and stamping, but the same robot can be programmed to pick and place parts in and out of the press. In this case, there is a need to change tools repeatedly. Robots have to be able to change tools as often as applications change. Customers are using this feature more and more often.'
There are a myriad of industries that use robotic tool changers. The automotive industry is the major player in this area of robotics, but is by no means the only.
'About two years ago, ATI's tool changers made major leaps and bounds into industries such as semiconductors and telecommunications, asserted Little. 'During the recession, both semi-conductors and telecommunications virtually stopped automating. While the automotive sector never stopped automating, it did slow down. Things are picking up and semiconductors are starting to automate again.'
The telecommunications industry uses robots with a payload capacity of five kilograms or less. The requirement in this application is not high payload but high volume and high speed. These robots are used to assemble cell phones, computer equipment, electrical and mechanical components. Because of the small mass and relative fragility of electronics, the workcells they are in tend to have small tool changers.
Crash and Burn
Collision protection is a necessity to prevent damage to the robot, its tooling and the item being worked. Peter Tarbell, a sales manager at Robotic Accessories described the Tipp city, OH, firm's crash protection device as having a piston that compresses upon an undesired impact. Within the unit, a nondirectional mechanical switch is connected to a plunger. Impact separates two contacts, signaling the robot to halt.
'A collision sensor has moment resistance built in, with a preset limit, said Tarbell. When the robot hits something that it shouldn't have, the sensor overrides that resistance. The E-stop signals the robot to shut down, while providing compliance much like a shock absorber. The workcell shuts down within microseconds.'
Other types of crash protection peripherals utilize pneumatic pressure switches. Once the pressure is overridden, the switch releases the pressurized air. Other systems work off of a proximity sensor, while some use a contact sensor.
Gauging applications are an important element in robotic production. Manufacturers need to have a fast, easy and accurate means to determine if the products they are fabricating are built to specification and are of sufficient quality.
Prior to using robotic measuring in automobile body production, one of every 50th car had to be removed from the production line and brought into a controlled metrology room to size it up for quality. This process was slow and expensive.
'There are several advantages to robotic gauging systems,' said Gerald Vogt, director of strategic marketing for Staubli Unimation, Inc.'s French division. Staubli is headquartered in Duncan, SC. 'First, the gauging system can be used in the production line, just after the welding phase. Another advantage is that each part can be controlled, because the robot is fast. Each of up to four robots measures 20 to 40 points. Instead of moving the part, the system moves a camera that does point to point gauging. The third advantage is that the system is less expensive and less inconvenient than a coordinate measuring machine.'
Staubli's package, the Flexible Robotic Absolute Measuring System (F.R.A.M.S.) consists of a robot from their RX series, a CS7B controller, a three dimensional sensor device, and software that compensates for temperature. This temperature compensation feature is important due to the fact that structures vary with ambient warmth of the manufacturing zone.
The F.R.A.M.S system is used by several automakers in Europe and North America. A B.M.W. plant in South Carolina uses four RX130L robots to measure 137 points on car bodies. This is executed in just over 90 seconds, with the robots operating at 80 percent speed. Up to 300 car bodies are measured per day using this system.
Determining a valid reference point is one challenge of successfully implementing a robotic gauging system for automobile body.
'If you want to measure in body coordinates, first you need to find the zero coordinate and use an external measuring device,' explained Vogt. 'Often, this is a laser tracker that correlates the robot world into the real world.'
Stay in Control
There is a necessity with all of these robotic accessories for them to be controlled so that they perform their jobs properly and precisely.
'Epson's RC+ controller can control digital I/O components, and solid state devices like solenoids, relays, and valves,' said Philip Baratti, an applications engineering manager in the robotics division of Epson America, Inc. Epson, a maker of robots and controllers, is based in Carson, CA. 'The controller communicates to peripheral devices via Ethernet. Our software package allows the controller to manage things like escapements, light towers, grippers, cylinders, and machine relays. There can be up to 6,400 points of digital I/O.'
According to Baratti, one of the difficulties of harmonizing controllers with robotic peripherals is the type of software architecture used to link the two.
'If you want to control peripheral devices such as servo amplifiers, you have to have an open architecture controller, or make custom drivers for it,' said Baratti. 'Closed architecture may not coexist with third party peripherals.'
What features in controllers do customers ask for when it comes to peripherals? Again, Phil Baratti:
'Epson's customers are asking for custom drivers to communicate with PLC's, which typically have their own communications methods. Some customers want our programming environment to directly link to other PLC environments. That is the biggest request I have. Most of the other things like peripheral axes control can be done with our Active X controls.'
What is successful in the tough robotic market? The trend is toward more customization of peripherals.
'There is a requirement for more customization in our peripherals and end effecters,' said Little. 'We can make a square peg for a square hole. Sometimes this customization is major, sometimes minor. To be successful in the market, the end effecter has to evolve, by getting more powerful, to have more flexibility. They have to be able to withstand the rigors of production.'
Whether it is the demanding conditions of today's budgets or the pressure to produce more with less, robotics automation brings success with the right mix of innovative and proven peripherals. Bringing it all together in one convenient forum is the Robotic Industries Association (RIA), where users connect with leading suppliers of robotics and peripherals to capitalize on best practices for manufacturing success.
'RIA is the industry's advocate for education, information, networking and reference material like case studies and Buyers Guides,' said Brian Huse, Director, Marketing & Public Relations. 'And RIA is part of a unique partnership of Associations, including the Automated Imaging Association and Metrology Automation Association, that allows the user and supplier communities to connect on applications and solutions that improve production strategies in all manner of industries.'