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Pick and Place Evolves Beyond Traditional Roles
by Winn Hardin, Contributing Editor
Robotic Industries Association Posted 09/13/2002
Once the domain of pneumatics, pick and place robotic systems are finding themselves in a more favorable competitive light as production lines move to greater varieties of products moving at faster speeds. Today, low price points and greater education among manufacturers are prompting more customers to realize that the flexibility of robotics means more long term savings than pneumatic, vibratory or other dedicated systems.
AS PRODUCT LINES CHANGE, new technology is turning robotics into the plant manager's strong right hand as we strive to reduce the risk of new manufacturing lines and boost margins. What is enabling this shift to more flexible automation? Robots have especially seen improvements for sensors, vision capabilities and distributed control electronics.
Fast and Flexible
Known for its fast slides and SCARA robots, Bosch Rexroth Corp. focuses on the long-term bottom line concerns of manufacturers when it comes to choosing a pick and place mechanism. The emphasis is on flexibility for product changes.
'Right now the trend is go more numeric than pneumatic,' said Bosch Rexroth's manager of business development, George Martin. 'SCARA robots don't just offer you accuracy and speed. The thing that makes SCARA robots stand out over pneumatics is that sometimes you have to make changes to the production line halfway through a product's life cycle. We used to call it mission creep. Sometimes mission creep required hard tool changes, which take time and money. With robots you make programming changes. Also, you can't always reuse pneumatics when a production line changes; with robotics, you can.'
The flexibility of robotic pick and place systems over pneumatics also helps a factory justify the cost of a new production line.
'You might have to put a whole family of telephones together with one assembly line in order to have high enough volumes to justify that line. This typically requires multiple part pick-up or drop points, which means more axis control. Numeric (or robotic) controls offer that kind of flexibility,' Martin said.
Robotic Reach Exceeds Pneumatic Grasp
By adding vision to robotic pick and place systems, integrators are able to bring additional capabilities to a manufacturing line, capabilities that boost the bottom line.
'The biggest advantage to programmable slides and pick and place machines, whether they're Cartesian, SCARA or other, is you can integrate more vision with the pick and place machine. If you try to pick up a part and miss it a few times, you can go back, look at the part and do a quick inspection to make sure you're not adding value to a defective part. So much depends on part and pallet tracking. We use vision, RFID, bar and data matrix codes. You can do this with dedicated [systems] but you have to use a whole lot of gap stops and its very costly,' explained Earl Cooper, vice president of sales at Dane Systems (Stevensville, MI).
More than just seeing and inspecting the part, pick and place machines are getting better at acting on information.
'We're also getting more smart grippers that emulate the human hand,' said Dane's Chief Operating Office, Steven Harder. 'Today, gripper manufacturers have open/close sensors, but they're working hard to bring force/pressure sensors into the actuator. With force sensors, you can measure 30 pounds of insertion pressure with the pick and place machine, which is an inspection step right there. You just plug in a RS422 connection and you're ready to go.'
Distributed Network Delivers Reflexive Control
Putting 'feel' in pick and place actuators is in effect mimicking human reflexive responses for greater control of an assembly process. We don't think about the screwdriver in our hand, but if the tactile feeling were gone, we would notice the absence of the screwdriver.
This concept is not foreign to Adept Technology. Adept has a vision for pick and place robotics that moves control of each servo away from a central panel and out to the motor, servo or actuator. Putting this human nervous system analogy in Adept terms, the company is using 1394 (FireWire) as the nerve cells and storing mini-programs on power amplifiers with integrated digital signal processors (DSP).
'We're using 1394 as the basis for our control architecture,' explained Adept's vice president of marketing, Joe Campbell. 'This network is replacing what was traditionally a hard back plane in a controller chassis, plus most of the cabling in a work cell. The big benefits are reduced cost, simplified installation, quicker start up times, smaller form factors flexibility and salability. We also think this will make the machines more reliable because the cable and connectors are the service managers dirty little secret. They're a constant source of failure.'
IEEE's 1394 delivers asynchronous digital parallel control signals with plug-and-play networkability. Although the huge promise of 1394 failed to materialize in the consumer PC and digital device market, Campbell says that it is unique suited for controlling complex mechanisms.
'When you have a complex mechanism with sensors, like vision, FireWire is ideally suited because of bandwidth and multiple transfer modes. A primary transfer protocol makes sure that time sensitive commands reach the servo when you need them, while a secondary protocol gives greater bandwidth that is still reliable. When you do motion control, you have to be time critical.'
Table 1: Summary of Distributed Servo Network Benefits. Courtesy of Adept Technology
Reduced Installation Costs
Large multi conductor cables are difficult to install, often requiring a dedicated wireway or large diameter conduit. Distributed servo networks dramatically reduce the wiring requirements to a few twisted pairs.
Distributed control architectures such as Adept's SmartLink, eliminate the servo amp panel and the motion interface board and expansion slots in the primary controller, a 70% reduction in panel space.
Cables have historically been a reliability problem, as each wire crimp and contact connection point is a potential failure point. Distributed controls architectures replace hundreds of contact points with a simple, standard network connection.
Distributing servo processing to the individual intelligent amplifiers reduces the load on the main controller CPU, leaving more capacity for other functions such as machine vision or conveyor tracking.
Additional functionality is added via a simple network connection, rather than worrying about how many open slots and how much power is available in the main controller chassis.
Simplified Troubleshooting, Reduced MTTR
Network modules can easily be isolated for troubleshooting, and replacement is reduced to a few simple power and network connections.
Reduced Installation Costs
By pushing power amps out of the robot controller, nesting them with the servo, and marching the amps DSP capabilities with a pared down programming language called MicroV+, Adept has reduced the number of connectors on typical robot from 150 to a little more than a dozen. 'And we're routinely seeing that kind of reduction,' Campbell said.
Adept's distributed control system complete with drastically lower cable and connector costs, force feed-back actuators and integrated automated vision systems are all adding flexibility to part pick and place assembly lines - flexibility that PLCs simply do not have.
PLCs may be more familiar but that is changing too. ('Robot technology far outstrips their ability to use it,' according to Dane System's Steven Harder.) In today's fast paced manufacturing environment, flexibility means less risk, and 'system integration is all about risk management,' according to Bosch/Rexroth's Martin. 'With the downward pushing of prices for numeric axis control, greater flexibility for more profit is what is going to ultimately revolutionize the manufacturing industry.'