Robotic Machining Cuts Part Lead-Time From Months To Days
August 19, 2010 by admin
Filed under Automation, Design, Industry, Manufacturing Trends, Robotics, Technology
Subtractive processes, often referred to as CNC machining, have not stood still in the rapid prototyping arena. Faster tool path generation is just one of the newer developments enabling machining to play a strong role in the rapid prototyping and direct digital manufacturing arena. Now, robotic machining has the potential to significantly affect the rapid casting arena, especially in the area of large castings. Tooling costs as well as lead times increase dramatically as parts get larger. The equipment needed to deal with the size and weight of extremely large parts becomes more rare and thus, more expensive. The larger the equipment used for these large parts, the slower it will operate due to its heavy physical characteristics. The most significant advantage that robotic machining seems to have is the fact that the robot moves independently of the work piece giving it the ability to feed as quickly on a large part as it does on a smaller, lighter part.
The US Department of Defense (DoD) has been seeking a way to reduce the cost of producing cast spare parts. The Advanced Technology Institute (ATI) currently leads several national collaborations that are developing advanced robotics capabilities and implementing both new and existing robotics technologies in response to the DoD’s need.
One collaboration is with the American Metalcasting Consortium (AMC). The ATI-managed AMC partner companies, like Clinkenbeard, are using robotics technologies to support legacy weapon systems; which could help meet the Defense Logistic Agency’s goal of dramatically shorter lead times for the production of legacy weapon systems parts. The patented Clinkenbeard® Toolingless Process proved that it could reduce lead times for military cast spare parts from six to twelve months to six to twelve days.
The results, according to ATI, also demonstrated that the Toolingless Process can reduce capital investment by as much as 35%, reduce individual parts cost by up to 20%, and improve cycle time by 25%.
Lead times often exceed a year because technical data may require reworking, including the development of a solid model of the part. But, even when a solid model is generated first, the Clinkenbeard process can supply a cast part in less than a month. The secret is computer-generated molds with no tooling.
The Toolingless Process consists of machining sand cores and molds, and is accurate. According to the company, this process can reduce the lead-time to obtain development castings by up to 90%. With this process, you can:
• eliminate the need for prototype tooling, depending on project requirements.
• make and test multiple design iterations during product development, from the simple to complex parts.
• reduce the cost of production tooling for one-of and small quantities.
• obtain accurate, prototype parts while large quantity tooling is made.
• eliminate tooling inventory.
• match exact production core materials and chemical levels so that prototype castings emulate production.
• incorporate engineering changes into high-volume production sand cores.
Clinkenbeard developed the sand machining process using CNC machining centers. By using robots with sand machining, company technicians can use the process on much larger molds and cores. Robotic technology will reduce the cost dramatically compared to the same expenditure for CNC machining centers.
Clinkenbeard
www.clinkenbeard.com
American Metal Consortium
http://amc.aticorp.org/
Defense Logistic Agency
www.dla.mil
Advanced Technology Institute (ATI)
www.aticorp.org
Robots and the Future
August 15, 2010 by Steve Meyer
Filed under Automation, Commentary, Design, Industry, Mechanical, Motion Control, Robotics, Technology
In the field of Robotics, where is the line between between remote control, software control and autonomous control? (No, I’m not going after the consciousness thing, it’s way too complicated)
Part of the problem may have to do with our use of the word “intelligence”. We talk about the increasing “intelligence” of processors and particularly about the cost of “intelligent” control dropping to the point where it is suddenly economical to put a microcontroller together with a motor in order to achieve new levels of performance in either energy management or some other critical parameter. Which opens new performance capability in robot design.
Increasingly, industrial robotics involve the use of vision systems to acquire information about the location and orientation of parts so that the robot system can interface smoothly to the “real world”. If any of you have been to an industrial trade show and witnessed the Delta Robots making cookies, it is a very impressive sight to behold. Incredible throughput and accuracy. And that’s what it’s all about in industry. Higher productivity, improved product quality.
But where is the line between remote control and automatic control? A remote manipulator for working in the nuclear industry, which was the big application that drove early robots, is a remote servo loop operating a series of servo motors and controls and powering mechanical systems, in order to do work that is dangerous to humans from a safe distance. The DaVinci medical robot is a phenomenally improved version of the same thing. A remote controlled robot, guided by direct haptic inputs from a surgeon, and with very sophistical tactile feedbacks, whose end effectors operate a variety of surgical instruments and actually increase the precision and speed with which doctors may perform certain procedures.
Is this a robot? Sure!
When we watch welding and painting robots making cars, we are watching decades of technology development in action. There has been significant effort to improve the actuator hardware, and probably many man-years of software development to improve our description of the task and its safety and performance constraints in order to create not only reliable, but increasingly efficient machines to do the tasks that humans cannot compete with for productivity. These are very sophisticated automatic applications, but certainly not autonomous. The boundaries of the application and the programming for it are very finite. Again, its about repetition, speed and accuracy.
And, yes, we call these robots, too.
But increasingly, there is discussion about the next frontier of robotics. Where are the next big apps coming from? Most of the big robotic companies in Japan and Europe are talking about personal service robots. You can let your imagination run wild here. Anything is possible. Certainly the service robot for NASA is interesting because it, again, follows the concept of doing tasks where it is difficult for humans to operate.
Is a Jeep that can be programmed to find a path and drive from one place to another autonomously a robot? Yes, but we may be pushing the boundaries here just a bit. These applications fall into the realm of Artificial Intelligence. The programming and software languages for which were just being described for the first time about 30 years ago. And at this point we are forced into the debate about what is intelligence. In addition, are these systems which are capable of “learning” and what is learning exactly? And more importantly, as all good science fiction movie watchers will ask, can a machine exceed it’s programming? (See? I didn’t even start on consciousness yet)
These are all serious considerations for the Future of Robotics which I will pick up further next week.
Universal Robotics Lauches 3D Software Compatible With Webcams
August 12, 2010 by admin
Filed under Design, Industry, Manufacturing Trends
Universal Robotics, Inc., a software engineering company, announced the launch of two simple-to-use 3D vision software products: Spatial Vision and Spatial Vision Robotics. The products can turn any pair of webcams into a highly accurate, cost-efficient 3D vision system that can be employed in virtually any setting without expensive equipment.
With Spatial Vision and Spatial Vision Robotics, a user can plug in the cameras, calibrate their space and receive highly accurate measurements in under 30 minutes. These products will expand the use of 3D vision to markets where it hasn’t been feasible before.
3D vision systems offer many benefits over their 2D counterparts, including better accuracy and object identification and tracking, which are essential features in security, engineering and robotics applications from biometrics to real-time control of machines. Despite their benefits, broad adoption of 3D vision systems has been limited in many markets because the systems can be costly to implement and maintain.
Universal’s Spatial Vision products eliminate the need for the precision mounting, specialized cameras, and time-consuming set up that is required for many 3D vision systems. Using two webcams that can be set up and calibrated within a matter of minutes, Spatial Vision and Spatial Vision Robotics can determine the 3D position of any point relative to the cameras with millimeter accuracy.
The Spatial Vision product can be easily deployed in any setting in which cameras can be installed, including laboratories, office buildings, department stores and warehouses, and is an affordable solution for anyone looking for an accurate way to observe and measure an environment. It can be employed in security applications, measuring in-store foot traffic patterns, and more scientific applications requiring object tracking and visual analytics without a wand or sensing device. Spatial Vision offers 30 percent improved accuracy over 2D systems used in object identification and tracking applications, such as facial recognition and other biometrics. It is optimized for use with popular Logitech 9000 webcams, but can be customized to work with any USB 2.0 camera.
Spatial Vision Robotics has been specially designed to be used in concert with automated machines. By adding LEDs to points of interest on moving machinery, Spatial Vision Robotics provides 3D position on the machine and its surroundings in robot coordinates as seen from the camera. The program enables 3D calibration between the extrinsic object of interest, the robot and the cameras, as well as intrinsic calibration with the cameras. It can work with any robot and is currently optimized for Yaskawa America (Motoman) SDA-series robots. Spatial Vision Robotics can be integrated with path planning and high-speed inverse kinematics to enable real-time control of robots.
Spatial Vision and Spatial Vision Robotics were created as part of the development of Universal’s signature technology, Neocortex™, a sensory-motor based form of artificial intelligence that enables moving machines to learn from their experiences and perform tasks that are unsafe or difficult for humans. Neocortex was developed over seven years with NASA and Vanderbilt University, and was funded by U.S. Department of Defense.
Top 5 Electrical Considerations for Mechanical Engineers
August 10, 2010 by admin
Filed under Commentary, Design, Featured Mechatronic Articles
Previously, we covered mechanical considerations for electrical engineers. Now, we give the other side a chance to speak. Here are five targeted pieces of advice for mechanical engineers responsible for electromechanical systems, from the perspective of an electrical engineer.
Mechatronics systems intelligently integrate mechanical and electrical elements to perform increasingly complex and demanding functions. When designing electromechanical systems, mechanical engineers and electrical engineers may tend to emphasize the technologies, components, and design principles from their single area of expertise—which can lead to systems with higher operating costs, increased maintenance demands, and less than optimal performance. As an electrical engineer involved in helping OEMs and manufacturers design and build mechatronic systems, I’ve seen how inefficiencies and unnecessary complexity can be unintentionally designed into machines.
A clean design balances mass and motion: sturdy, durable framing withstands years of vibration and shock, combined with lighter-weight components helps to reduce mass and enable the use of smaller motor/drive components.
Better mechatronic systems can be created when mechanical engineers consider five crucial concepts while designing manufacturing systems, to derive the greatest value and efficiency electronics systems can offer to the manufacturing process.
1: Create a clean design
Good mechatronics design starts with good mechanical design – the best electronics and electrical systems cannot compensate for poor mechanical design. The most successful designs are “clean.” They feature a strong, rigid frame, using materials and structural principles to ensure that, whatever motion the machine undergoes, its long-term stability is “engineered” in.
Make sure that rigid bearings and support are used where motors are mounted on machines; this helps prevent shafts from being sheared off due to microfractures that occur because the motor shaft is mounted out of alignment with a pillow block bearing or gearbox input planetary gear. Place motors on the machine in the best location so that operators aren’t accidentally stepping on cables and connectors and causing damage; and design machine guarding with easy access points to get to motors mounted under the wing base of the machine while still protecting them against harsh environments.
Most importantly, a clean design balances mass and motion: sturdy, durable framing that withstands years of vibration and shock, combined with lighter-weight components for the moving parts of the machine. This combination helps reduce mass, delivers more energy-efficient motion, and makes it easier to size-up smaller motor/drive components for the machine. We’ve seen a lot of very innovative mechanical machine designs over the years, and a clean design makes the largest contribution to a machine’s longevity, robustness, and lowest overall cost of ownership.
2: Directly couple the motor to the load
Effective mechatronics starts with a “clean slate” design. In the past, machines were often built around a single ac motor powering a machine line shaft, to which were attached gearboxes, pulleys, sprockets, chain drives and other mechanical devices for moving individual areas of the machine in synchronization – an approach to powering manufacturing that literally can be traced back to the dawn of the Industrial Revolution.
A clean design makes the largest contribution to a machine’s longevity, robustness and lowest overall cost of ownership.
Consider replacing this architecture with individual servomotors coupled directly to the load you are moving. There are multiple design, machine cost, and operational advantages to this idea (which a surprising number of machine designs do not use). First, consider cost: every time you add a gearbox, you add multiple costs: it’s an additional point of failure, it has to be lubricated, and it needs spare parts. Plus, you add mechanical backlash that must be compensated for during machine commissioning every time you have a product changeover – motion and axes synchronization complexity that today’s intelligent drives and servomotors eliminate.
When you strategically locate servomotors as close as possible to the area of motion they are serving, the incremental cost of electric drive components is almost completely offset by eliminating the cost of mechanical components and labor that must be purchased, machined, assembled and configured. In particular, not having to stock multiple sets of sprockets, gears and cams, as well as the time involved in changeovers with mechanical drives, can really drive down the total cost of ownership for the machine.
Ultimately, this design approach greatly reduces windup and backlash, as well as improves machine commissioning time; and current state-of-the-art direct drives, direct motors, and linear motors let you run higher gains and improve the machine’s performance.
Consideration #3: Use electronic gearing and camming
Today’s electronic drives and motion control platforms give mechanical engineers, a powerful, flexible tool to improve the accuracy and performance of the machines you design. This technology lets you create a virtual “electronic line shaft” that can electronically synchronize all the drives and motors on the machine, eliminating the mechanical line shaft. In the process, you can dramatically improve axes synchronization and accuracy – from 1/16th or 1/32nd of an inch typical with mechanical line shafts, down to motion precision closer to hundredths or even thousandths of an inch with electronic line shafting.
And this synchronization can be accomplished with zero mechanical backlash – and fewer product jams. It also eliminates a host of mechanical adjustments to bring the machine online, as well as the operator adjustments each time the machine is stopped and restarted.
Electronic gearing and camming makes machine changeover completely programmable: For example, the use of FlexProfile technology lets operators load machine recipes with the touch of a button on the HMI screen, and the changes are made in the control and servo system to run the next product.
The FlexProfile camming technology makes it possible to build multisegmented cam profiles based on position, velocity, or time-based motion profiles. When you change a section of the electronic cam with a recipe change through the HMI, the control platform will automatically optimize the rest of the cam profile across all of the machine’s motion elements. This enables the machine to run a shorter cycle time, or provide smoother dynamics for the machine, even though a change has occurred such as a different bag seal time or flap tucking cam position on a cartoning machine.
Consideration #4: Incorporate energy-efficient technology
One of the fastest growing costs for any manufacturing operation is energy – and good mechatronic design can help control these costs through the application of electric drive and motor systems designed to save energy.
In machines that use servomotors directly coupled to critical axes of motion, and that also use electronic synchronization and camming, the proper sizing of the servo system can create a highly energy efficient machine.
Proper sizing requires an accurate assessment of several motion factors (motor by motor): How fast the axis needs to accelerate, the size of the mass you’re trying to move, and how precise the acceleration and deceleration needs to be. Undersizing will lead to strains on the drives and motors; oversizing will draw too much power to do too little work.
Some of today’s most cutting edge systems, such as the Rexroth IndraDrive Mi integrated drive/motor systems, include a highly energy efficient feature: bus sharing. Multiple drives are daisy-chained together and share power from the same bus; in many multi-axis machines, as some motors are accelerating up to speed (drawing power), others are decelerating (regeneration power). With bus sharing, rather than having to deliver maximum power to the accelerating motors and bleed off the decelerating motors into heat across a bleeder resister, power is shared, so the machine’s power consumption is significantly reduced.
A further energy-efficient technology is called regenerative power supplies. In many machines, multiple servomotors will decelerate at the same time, boosting the voltage to excess levels on the power bus. Older generation electrical drives would bleed that excess electrical energy as heat – wasting the power, and adding to the factory floor’s heat production, requiring additional cabinet cooling. With regenerative power supplies coupled to a shared bus system, what was once wasted power can now be fed back through the shared bus and sold back to the electric company.
The use of direct drive, direct motors and linear motors versus mechanical couplings lets you design a system to run higher gains.
Consideration #5: Use HMI’s for better troubleshooting
User-friendly intelligence is now available through today’s touchscreen HMIs. Machine layout drawings and schematics can be incorporated into control menus and diagnostic tools, to better manage the machine’s day-to-day operation and troubleshooting. Drawings and interactive instructional tools can not only show the precise point where a problem is – they can also step the operator through the tasks to restart production.
Advanced graphics like this can be combined with the distributed intelligence inherent in servomotor-driven machines, to prevent machine failures or faults before they happen. With such predictive maintenance, this capability lets you or machine designers set fault tolerance bands in drives and then monitor drive performance. Electric drives and motors allow a broad range of conditions to be monitored – conditions that are directly associated with mechanical performance; variations in load, temperature, vibration, torque, belt tightness, gear meshing are all mechanical events that generate changes in the torque profile of an electric drive and motor moving those machine elements. Mechanical engineers can set tolerance bands for these components, and if they exceed them, then predictive maintenance alerts can be clearly and intelligently displayed through the HMI to operators, along with specific advice about next steps to take to correct the issue before it becomes a serious production problem or something that can damage the machine.
With Rexroth’s IndraDrive Mi integrated motor/drive system, multiple drives are daisy-chained together and share power from the same bus, significantly reducing energy consumption.
Blending technologies for optimal value
Every electromechanical system should perform its designed function with the minimal use of energy, motion and components required to get the job done – that’s the fundamental goal of any engineer. Electrical drive and servomotor systems now offer a wealth of reliable, energy-efficient, digitally intelligent platforms to power the integrated vision of mechatronics to greater value and more innovative manufacturing and automation solutions.
Hopefully, the five considerations described here demonstrate the advantages that today’s electric drives and controls offer, helping you simplify certain mechanical design and engineering challenges and provide new resources for driving innovation and creativity in machine design.
Caterpillar’s Crawl May Hold Clues To Future Robotics
July 26, 2010 by admin
Filed under Design, Featured Mechatronic Articles, Robotics, Technology
Caterpillars have a unique “two-body” system of movement that may have implications for robotics and human biomechanics, U.S. researchers say.
The scientists found that the gut of the crawling hawkmoth caterpillar moves forward independently of and in advance of the surrounding body wall and legs, instead of moving with them. This is the first time this type of movement has been reported in an animal, the study authors noted.
“Understanding this novel motion system may help efforts to design soft-bodied robots. It may also prompt re-examination of the potential role soft tissues play in biomechanical performance of humans and other animals,” study senior author Barry Trimmer, a professor of biology and of natural sciences at Tufts University, said in a university news release.
The findings are published online July 22 in the journal Current Biology.
Hawkmoth Caterpillar That may look like a snake, but it’s actually a hawkmoth caterpillar
“Although internal tissue movement caused by locomotion has been identified in many organisms, the caterpillars seemed to be propelling themselves by means of a two-body system — the body wall container and the gut it contained. This may contribute to the extraordinary freedom of movement seen in these soft-bodied crawlers,” first author Michael Simon said in the news release.
Further research is needed to determine if this type of movement offers caterpillars an evolutionary advantage, and how this finding may prove valuable in robotics, added Simon, who conducted the study as part of his doctoral research in Trimmer’s lab.
“The focus to date has been on robots’ external design, but we also have to look at how it’s most advantageous to arrange the inside of the robot and any payload. Would motion be enhanced, for example, by packing more mass toward the rear, as these caterpillars seem to do?”
A grant from the U.S. National Science Foundation funded the research.
Linear Actuators
July 18, 2010 by Steve Meyer
Filed under Automation, Design, Electronics, Industry, Manufacturing Trends, Mechanical, Motion Control, Semicon, Technology
Linear Actuators are a class of mechatronic systems with some unique design constraints. As a result there are dozens of approaches, dozens of vendors, the option of designing the actuator from scratch, and, frankly, a lot of confusion. The problem lies in the fact that the actuator as a subassembly is the combination of a number of separate technologies. This means there are a number of design tradeoffs incorporated into the resulting actuator that must be acceptable in order to use that actuator.
Categorizing linear actuators is not entirely straightforward because many categories overlap. The “motive power” category can be any type of power source, rotary motor or linear motor powered. Linear motor solutions are much more commonplace in linear actuators today due to declining costs for this technology choice. But in a linear motor based actuator, the linear motor is both the motive power and the mechanical transmission at the same time.
Categorizing linear actuators by their mechanical transmission style is another approach. The most common categories are screw type, belt and linear motor. But the motive power for a screw based actuator could be a stepping motor or a servo motor. The stepping motor is predominant because of it’s suitability for positioning, but it may be underpowered for some applications where a servo is needed. So the linear actuator transmission category can have overlaps because of the different motor types that are used in conjuncion with it.
Price seems to be one means of eliminating the ambiguity. Stepping motor and lead screw combinations are popular because they are economical and maintaining 0.001″ accuracy is very easy. Linear motor systems are capable of .5 micron accuracy with little or no friction, acceleration and speed that is incredible, but generally the higher performance comes at a higher price.
But in the end, the selection process is best guided by the criteria of the application. The list is, thankfully, short. Load weight or force that must be generated, speed, accuracy and life expectancy or number of cycles of operation. This last is probably the key determinant in system selection. Long life or high cycling goals lead to linear motors actuators with little or no friction. You have to familiarize yourself with the overall field because the tendency of confusing the technology and the application needs.
At the recent Semicon gathering of manufacturers involved in semiconductor manufacturing, a lot of attention is given to the mechatronic content of machinery. And as far as I have been able to determine from many different market research projects, semiconductor manufacturing is one of, if not, the largest market for mechatronics every. So it’s also not a surprise that a lot of vendors come to the Semicon show with their latest and greatest product offerings.
Among the most interesting, Nanomotion continues to extend the reach of piezoelectric linear motors, yet another technology choice within the linear actuator sphere. Piezo motors have only one moving part, and meet the high precision, high reliability criteria. With increasing usage, there has been decreasing cost for this unique solution, along with superior position feedback technology and excellent packaging for space constrained applications.
In addition, IKO has released a number of new linear actuator assemblies, both screw driven and linear motor driven. They are also showing a number of unique 2-axis configurations one of which is the thickness of a tape reel and is targeted to unloading parts for electronic pick and place machinery.
Brilliant examples of manufacturers continuing to integrate mechatronic technology to make it more convenient for the customer.
Electric Car Prequel
July 9, 2010 by Steve Meyer
Filed under Commentary, Design, Featured Mechatronic Articles, Green Energy, Green Engineering
The electric car, hybrid or plug in, continues to be an elusive goal.
One model sports optional 2 wheel or 4 wheel in-hub mounted drive motors. With a large battery pack and a curb weight of 3300 pounds, it’s a bit ponderous. But it has a 50 mile drive radius and rarely requires any maintenance. What year will this vehicle be ready? 1899. It’s the Lohner-Porsche.
Recognizing that the weight the battery pack was a major obstacle, Ferdinand Porsche, still working for the Lohner Coachworks, came up with a hybrid model. The vehicle used a small gasoline engine to power a generator and a single motor mounted on the rear axle of the vehicle. Porsche raced the car himself in the Semmerling competition near Vienna, and with top speeds of 75 miles per hour, won against a very competitive field which included Benz gasoline powered cars. The 75 mile per hour top speed was unprecedented, especially from an electric hybrid. The year? 1900!
So all things old are made new again. If the 2200 pound weight of the Lohner Porsche battery pack could be reduced by 4:1 by using Lithium batteries, then a curb weight around 1500 pounds should be feasible. The reduced weight of the vehicle leads to significantly greater driving range. The Smart Car electric model is expected to have a range of 120 miles per charge. Which, actually, is enough for a lot of vehicle applications.
In wheel drive motors are not my favorite solution, but if the weight can be reduced, then problems relating to suspension dynamics can be managed. And that’s exactly what the folks at Protean Electric are doing. They have produced a number of conversion vehicles as demonstrations of their electric motor technology. And if the motors perform as expected, they will carve out a niche in the plug-in and hybrid electric vehicle world.
There are a couple of important points that need to made here.
#1) based on the “Absolute Value of Technology”, the only thing that matters is the vehicle costs per transportation mile. That is made up to two components, the purchase price and the expected cost per mile driven. Admittedly, if you can run an electric vehicle at $.04/mile, it is cost effective to own, even if the car costs more up front, because over the life of the vehicle, the low operating cost will overtake the purchase price.
The IRS deduction for vehicle operation is $.50/mile. Electric hybrids and especially plug-in electrics are not expected to have any major maintenance costs. Even if you add insurance, the cost per operating mile will be significantly lower.
But the higher price of the vehicle will be an obstacle from a pure economics standpoint. For this reason, some manufacturers have considered the option of the local power utility company supplying the battery pack and maintaining it. Since this is the single largest expense, leasing it to the vehicle owner in the monthly power bill is a good deal.
The second major point to be considered is plug in electrics, even with limited drive range, are the biggest contributor to American energy independence. These vehicles will directly reduce oil imports every day they are operated. Because almost none of the electricity in the United States is generated using fuel. It’s either coal, natural gas or nuclear.
So if we really want to get after the issue of energy independence and stop funding governments that support terrorist activity, the electric car is the path forward. As are 40+ mpg gasoline cars, and drilling and refining of oil in the US.
Let’s get after it!
The Top 5 Mechanical Considerations For Electrical Engineers
June 24, 2010 by admin
Filed under Commentary, Design, Featured Mechatronic Articles
Problems can arise in a mechatronics project because mechanical and electrical engineers often do not have sufficient experience or understanding of their counterpart’s discipline. Here is one application engineer’s advice on how to avoid five of these common problems when specifying parts for an electromechanical system.
Getting the right motor is critical, which means matching it up to the overall system’s mechanical components. In other words, electrical system design can only occur once the mechanical design has been fine-tuned to match the performance specs of the application.
Mechatronic systems require a complex inter-play of electrical and mechanical systems to accomplish increasingly demanding tasks. But, because mechanical engineers and electrical engineers are often educated within their single area of expertise, oversights occur that can lead to higher costs and less reliable performance. As a mechanical engineer involved in the sizing, selection, and start-up of mechatronic systems, I’ve seen these problems both during the design phase and in the field. To help bridge the gap, I’d like to offer my electrical colleagues five important things to consider in the design of mechatronic systems.
Complex mechatronic systems require careful advance planning to ensure optimum performance and the best total cost of ownership.
Consideration #1: Total Cost of Ownership is everything
Of course mechatronic systems should be designed to achieve the best possible performance for the lowest cost over the long term. However, the need to document cost-savings on an annual basis (rather than over the lifetime of the system) can be a powerful motivation to look for less expensive components to keep the up-front cost of the mechatronic system low. Indeed, the choice of seemingly simple components can cause painful headaches later. For example, the use of less expensive bellows-type couplings between the motor or gearbox and the actuator input shaft are a perfectly appropriate choice in many stepmotor driven applications. In fact, a slightly spongier coupling can provide a certain amount of damping in pick-and-place applications moving heavier loads. The sacrifice, of course, is precision, and in many mechatronic systems, which are typically servomotor driven, it is best to use stiffer elastomer-type couplings. Using less expensive couplings may save money in the short term, but if the required stiffness is not achieved, redesigning and retrofitting the motor mounting system can easily cost three or more times the money you initially saved with the “economy” coupling. Plus, you’ll have the added cost of downtime and lost production, which is not a good trade-off. Total Cost of Ownership (TCO) is really the single most important consideration in any mechatronic system design, and the four remaining points will also contribute, ultimately, to lower TCO.
Consideration #2: Always look at the mechanics first
It’s very important for electrical engineers to get involved in, or at least understand, the mechanical design of a mechatronic system before forging ahead with the electrical design and controls. Trying to size and spec the electrical components before the mechanics are defined can lead to wasted time and rework, since parameters such as inertia and torque are heavily influenced by the choice of mechanical components. Bosch Rexroth engineers use a system called LOSTPED to help size and select the mechanical components that are best matched to the performance requirements of the application. LOSTPED is simply an acronym that stands for Load, Orientation, Speed, Travel, Precision, Environment and Duty Cycle. It is a systematic review of all the performance and design attributes that need to be considered, with the end goal being the optimum system design for each application. Not following this process can result in larger or more expensive mechanical systems than are needed. For example, if an OEM or end user forces the design to accommodate a specific motor without considering the LOSTPED criteria, larger mechanical components may be required to handle the motor torque or inertia than those actually needed for the application. The same goes for control systems. If a ball-screw-driven actuator can achieve 0.01 mm repeatability, you need to make sure that the encoder can meet or exceed this spec; otherwise you won’t be able to take advantage of the ball screw’s precision. It is human nature to want to use components that are in stock or that the user is familiar with, but each system deserves its own review to ensure that the components and the overall system are optimized for cost and performance. Otherwise, you may leave money on the table or fail to get the system performance you need.
Clean and careful cable management is often overlooked, but can help you make sure that even tight spaces don’t cause problems. Failure to consider cable management can result in shortened system life, physical incompatibility with the ultimate operating environment, or even fires.
Consideration #3: Don’t try to fit a square peg into a round hole
The last example is common enough that it’s worth emphasizing as an important consideration of its own: Don’t try to fit a square peg into a round hole. Many electrical engineers are familiar with particular motors and drives, or are pressured to save money by using components they already have. Using a motor that’s physically too large, however, can cause mounting issues. It could supply too much torque for the linear module to handle (causing mechanical failure or breakage); or it could cause inertia and settling issues. Unpredictable settling can be a particular problem in precision applications, such as dispensing, pin insertion, or precision assembly in semiconductor and medical applications. If the motor is oversized and has too much inertia, the actuator may have a difficult time achieving the desired position, resulting in longer overall cycle times than required. Particularly in precision applications, you should try to size the mechanical and electrical components to achieve as close to a 1-to-1 inertia match as possible. Keeping power consumption to the minimum required for the application is also important for customers who are looking to reduce their environmental impact and make their manufacturing operations more green.
Consideration #4: Remember “Jerk”
“Jerk” is the rate of change of acceleration, or the “build-up” of the acceleration of the axis. It is the limitation of the jerk parameter (how fast you’re accelerating) that lets you experience the acceleration of the roller coaster without developing whiplash. Acceleration is important in mechatronic applications to achieve the desired move in the required time, but if the acceleration speed is too high, vibrations could result and cause a loss of positioning or premature wear of components. On the other hand, if electrical system designers don’t consider the magnitude of jerk required, the motor may be undersized and the system won’t perform as required.
Always look at the mechanics first. The LOSTPED acronym can help you consider every possible detail needed for sizing and selection of electromechanical components: Load, Orientation, Speed, Travel, Precision, Environment, and Duty Cycle.
Consideration #5: Cables must be managed
Cable management is one of the most frequently overlooked attributes in mechatronic systems; and it can be costly. Cables and cable tracks require physical space, and fast, multi-axis motion often requires cables that can handle tight bends and high duty cycles. Particularly when designing the cable management system, theoretical operation and space requirements can be very different from that required in the real world. Once installed in the machine or factory, the system’s active environment may include adjacent machinery, factory walls, posts or beams, and other parts or tooling that cause interference with the cable management system. Proper strain relief for cables is also critical, because cables that are bent and twisted beyond their specifications pose a safety hazard in the form of fire or short-circuits.
It all adds up to TCO
The ultimate goal in the design of any electromechanical system should be to achieve the optimum performance, mechanically and electrically, to get the job done with the lowest total cost. In the real world, many such systems are designed by teams of engineers from both disciplines working in tandem. This is the ideal model, but with the discipline of mechatronics being relatively young, the problems I’ve described here happen often because of insufficient experience or understanding of their counterpart’s discipline. These five tips aim to help bridge this gap and prevent costly, unwelcome and time-consuming surprises.
Igus Develops A Simpler Robotic Bionic Joint
June 24, 2010 by llangnau
Filed under Automation, Design, Featured Mechatronic Articles, Mechanical, Medical, Robotics
When it comes to robotic joints, engineers have had to put together complex custom configurations out of multiple components, which involved considerable development time with the mechanisms. This time requirement often reduced the amount of time artificial-intelligence programmers had with the system. So, two goals of robotics developers were to enable the programmers to be involved with the process earlier and develop a straightforward modular system. The realization of these goals is closer, thanks to a recently introduced innovative robot joint module system from igus. The company is currently looking for beta testers for this new product.
The robot unit, known as Robolink, was primarily designed for robot developers and laboratories that work with humanoid systems, as well as with lightweight engineering systems for handling and automation. The design was inspired by Dr. Rudolf Bannasch, Managing Director at the Berlin-based company EvoLogics, a high-tech company working in the field of bionics and humanoid robots. He provided both the motivation and developmental support behind this Robolink component.
It consists of a drive-and-control unit, joints in different lengths, and arms in different sizes, including a duct for additional control cables. The jointed arms are made from carbon fiber reinforced plastic and other lightweight materials. At the end of the jointed system is the option to connect to different types of tools.
The drive-and-control unit was purposely designed as a black box. Robot developers have the option to work with pneumatics, electro technology, or hydraulics.
The bionic core of the robot’s skeletal parts is the injection-molded plastic joints. They are controlled through cable pulls that transfer tensile forces, similar to the way tendons function in humans. The cable sheath is held and the inner cable moved. This way, the gripper, shovel, hook—or whichever tool the developer chooses—is moved and operated.
All data cables are routed safely through the jointed arms. The cable pulls are routed through from one joint to the next—just as joints are connected in humans. Only four cables are required for each plastic joint to rotate and swivel freely. These cables convey images, acoustics and forces, which are the artificial senses of humanoid robots.
The cables themselves are made from technical synthetic fibers. The fibers are extremely strong, hardly stretch at all, are resistant to chemicals, and are lubrication-free and wear resistant. When compared to steel, their lighter weight also makes them much more energy efficient.
Since the system is modular, it can be constructed with all kinds of humanoid robot configurations. This ranges from jointed arms, moving ‘digger’ arms, through to four-legged ‘creatures.’ The joints can be easily combined as required.
igus’ development objective was to keep the moving mass as low as possible, so that the actuators can be separated from functioning tools, such as grippers, hands, suction cups, and so on. Particular attention was given to enable quick assembly, as well as the use of tribo-optimized plastics to reduce lubrication needs and weight.
igus
www.igus.com
Mechatronics as Process
June 20, 2010 by Steve Meyer
Filed under Automation, Commentary, Design, Industry, Manufacturing Trends, Motion Control, Semicon, Technology
There are three basic disciplines of control. Discrete control which generally relates to making a product or dealing with sequential and event driven logic, process control which deals with the conversion of raw materials into more complex bulk products, and real time control of things like electric motors. In general, discrete control is not really time based, although there are exceptions. Process control is based on longer time periods due to the nature of the large batches of material that are being processed and the associated thermodynamics. The hardest of all real time control in the case of electric motors which requires nanosecond capability from the embedded control system to achieve the performance needed by energy conserving systems. As a by product of the different time bases, each technology has grown into it’s own discipline and control philosophy.
Occasionally the line between mechatronics as the design of mechanisms in discrete manufacturing and applications that are more process oriented blur the neat categories of the major control disciplines. More and more control system requirements involve the blending of 2 or 3 different types of control into a single architecture. This creates subtle problems in order to properly architect the system so that the final effects are achieved.
Polishing and grinding, for example, appear to be positioning applications. A grinding wheel or buffing wheel must be brought into position to make contact with a workpiece. So the normal control system behaviors must be dealt with in order to achieve position. But positioning the tool is only the beginning of the process.
How do we measure the process of grinding or polishing?
And most importantly, how do we know when it is done?
The process of grinding or polishing is a matter of torque in the application of the working tool to the workpiece it is in contact with. Generally through an electric motor that is turning the tool. By measuring the torque, which is current in the motor, we can know that the actual process is being achieved. It may require empirical measurement to determine how much torque is required to achieve the proper surface finish, but there is a direct correlation. Too much current means the tool is buried in the part, too little current and there is no work being done.
But at this point, there is a process that can be controlled. If the proper torque level is applied through the motor the runs the tool, there is also a corresponding value as the contact is reduced that indicates the completion of the process.
This behavior is completely separate from the position of the tool. However, if there is reduced contact with the workpiece due to the tool wearing out, that is, the size of the tool has decreased slightly, then the positioning system has to be updated to compensate.
These are simple concepts, but they are often overlooked. Ironically, there are many applications that require close consideration of the mixed control methods. Chemical mechanical planarization of silicon wafers suffers from similar difficulties with the need for extraordinary precision in polishing the surface of the wafer. Do we really know when the process is done or do we just leave it running an extra 20 minutes just in case?
There’s always room for improvement. And some of the recent control system innovations are delivering significant performance that should be considered as we pursue new applications.
