New System Simultaneously Corrects Tool Position for 5-axis Machine Tools

Traditional piecemeal compensation of one axis at a time does not consider axis kinematic relationships and their effect on volumetric accuracy, an ability needed to meet today’s higher cutting accuracy requirements. The multi-axis methodology of volumetric error compensation (VEC) originated in Boeing R&D, St. Louis MO, and uses laser technology from Automated Precision, Inc. (API), Rockville MD.

Executives at MAG recently announced what they claim to be the “industry’s fastest VEC system,” the MAG VEC, which analyzes and corrects positioning errors in all machine-tool axes simultaneously reducing the time needed to determine error compensations from days to hours, and integrating both linear and rotary axes into the tool point compensation process, noted Jim Dallam, MAG’s VEC product manager.

Developed and proven by a government/industrial consortium, multi-axis VEC was developed to improve machining accuracies on large machine tools used to produce today’s large, monolithic and complex-shaped parts. The MAG system received a Defense Manufacturing Excellence Award from the National Center for Advanced Technologies (NCAT) in December 2009. A Boeing official called it a “groundbreaking process” that will dramatically reduce assembly and fitting costs — $100 million a year on large programs like the F-18 or 700 aircraft series.

“It gives you a practical and affordable way to raise a machine’s process capability, typically in less than a day, to meet the tighter accuracies required on new parts and programs in the aerospace industry,” said Dallam. “It’s one thing to hold tight tolerances over short distances along a linear axis, but it’s far more difficult along all arbitrary contours and orientations within a volume encompassing several meters.”

Multi-axis VEC collectively treats all of a machine’s degrees of freedom that affect tool point positioning, unlike conventional calibration methods that sequentially examine machine motion one axis at time. Conventional approaches to volumetric compensation are generally limited to three linear axes and the associated total of 21 potential motion error sources. However, a typical five-axis machine with linear and rotary axes can have 43 potential error sources, not just 21. The multi-axis VEC system compensates for all these.

“Dallam said. “The MAG VEC considers the full interrelated effects from the kinematic stack-up of the machine tool axes. This holistic methodology enables volumetric error compensation for every point orientation and path combination inside the work volume.”

To operate, an NC program positions the Active Target to a cloud of some 200 points representing a series of statistically random multi-axis “poses” within the work envelope. The same NC program is run three times, first with the Active Target at a long tool length, then twice again at a short tool length. The 200 commanded and measured positions from the first two runs are mathematically combined to establish each tool axis vector orientation and the third run gives a measure for repeatability. Automated software processes all pose/point data as simultaneous polynomial equations to determine volumetric compensation based on the kinematic error model of the machine.

The compensation solution is then entered into the control, where “compile cycle” technology integrates the compensations into real-time CNC path control algorithms. The volumetric accuracy compensations work in conjunction with, and on top of, traditional, underlying single axis and cross-axis comps.

Measurements are automated within a single coordinate system using laser tracker technology, a simple metrology tool that does not require extensive training to use. Calibration is performed in just a few hours in a single setup, compared to conventional methods that require multiple setups and several days of time, yet fail to capture volumetric axis interactions.

Boeing, MAG, API and Siemens were members of the industry/government consortium that developed the VEC under the program for Volumetric Accuracy of Large Machine Tools (VALMT). Other participants were the National Center for Manufacturing Science, U.S. Air Force Logistics Center, Naval Foundry and Propeller Center, U.S. Navy Fleet Readiness Center, East, and U.S. Army Anniston Depot. The system was tested and proved out on three large machine tools offering different axis configurations.

MAG
www.mag-ias.com

More on Motor & Drive integration

The motor and drive combination is a basic building block of motion control.  Each component is useless without the other.  So it’s pretty important to come up with a good definition for what the “system” performance needs are to make sure that you end up where you need to be in your design.

Generally, we go to single source suppliers whose motors and controls are designed to operate together.  This approach guarantees minimum performance levels which the supplier can be held accountable for, and that’s a great thing.  But it usually comes with a huge list of features that will not be used in the application, but which you must pay for anyway.

In the industrial user community this is a great benefit because common environmental conditions such as dust, dirt, oil, or washdown conditions are more difficult to deal with and many products are built to these environmental standatds.  No special precautions are needed to make the equipment work.  And the suppliers warranty their equipment for continuous operation at stated speed, torque and environmental conditions.

But as we migrate into other businesses, machinery builders and equipment manufacturers have to apply the same motors and controls in larger numbers, and the overhead costs of motors and controls designed for industrial use become very expensive and make the cost of machinery less competitive.

In the machinery world, much of the electrical components will be built into control cabinets.  So if the packaging is going to be provided, is an enclosed controller somewhat redundant? Or can the motor speed control be integrated into the motor physically to reduce cost?  This is especially attractive if the cost of cabling a single motor can run 10-20% of the total cost of the motor and control.

There are performance elements that need to be considered in the applications as well.  How should the motor behave at zero speed?  What kind of torque regulation is needed?  What is the exact duty cycle of the application (on time versus off time)?   In these areas of motor and control operation the relationship of the motor to the drive is critical.  The drive electronics must have the ability to regulate current going through the motor without casusing overheating.  Some type of sensor on the motor must provide information about the position of the rotor at fairly high resolution, certainly more than every 120 degrees of rotation as with the common Hall effect sensors.

So as much as we may look at the purchase of a motor and controller as a system, there are a lot of nuances involved in the search process for the right hardware for any given application.  And that is probably one of the more difficult parts of doing motion control applications.

Custom Transfer System Adds Value by the Millisecond

Services and products from hydraulics, pneumatics, electrics, and linear technology were linked by Rexroth engineers to produce a custom engineering concept for Swiss company Mikron Machining Technology. “The fact that Rexroth offers coordinated components from pneumatic, hydraulic and electric drive technology right through to high speed control enabled us to select the most suitable characteristics for specific functions,” said Rolf Held, design manager, Mikron. The result was a machine tool that makes real added value out of milliseconds.

In a production environment, fractions of a second count and can accumulate to the extent that they affect cycle times. Automated transfer systems play a key role in many industries, particularly when metal parts must be processed using a number of different machining sequences. Suppliers to the automotive industry, for example, machine a number of items considerably more economically using intelligent transfer units. The machines pick up workpieces in clamping devices and transfer them automatically to the individual machining stations where they are drilled, milled, turned, chamfered or de-burred. Threads are cut and knurled profiles applied. Even peripheral processes such as installation operations or checks can be integrated into these transfer operations. With the transfer concept, all parts can be machined simultaneously.

The Multistep™ XT-200 is setting new standards for transfer systems – especially for the control speeds and the drives used for the various functions. The system makes precision manufacturing possible in non-stop operation. At the same time, the individual stations work practically hand in hand.

Extremely short chip-to-chip times ensure nearly continuous machining, and the system can even be used for high speed cutting. A key advantage is that it combines the productivity of a linear transfer machine with the flexible re-tooling capability of a machining center.

The concept is based on individual interlinked dual spindle modules, which can be used on a stand alone basis, or spread over up to four modules. Five interpolating CNC axes and up to 144 tools machine complex small and medium series parts on five and a half sides without remounting. If the parts are automatically re-mounted in-process, it is possible to machine six sides. The Multistep™ can be adapted to the production volume at any time. In addition, a loading and unloading station can assume the component feed function.

Without a break
While the main advantage of this machine is precision manufacturing almost without a break, further advantages come from the short chip-to-chip time of less than a second and the unusual dynamics. Accelerating the Rexroth CKK linear systems up to 1.4 g to 52 m per minute and spindles with speeds up to 40,000 rpm make for short machining cycles. This is where drive technology from Rexroth comes in: rodless pneumatic cylinders from the BRP Rexmover Series with a diameter of 50 mm and a stroke of 400 mm, as well as a linear axis Type CKK20-145 for strokes of up to 1,100 mm. The maximum force on this axis is around 72 kN in the direction of movement.

“At the end of the day it’s the number of milliseconds that we gain from a number of different points that is the decisive factor,” said Held.

In the standard version, the Multistep™ is fitted with a high-speed CNC Rexroth IndraMotion MTX. Up to 64 axes can be operated in twelve CNC channels independently of one another. The maximum extended version features 54 axes that are required to work in parallel. “Using any other approach would mean that we would need at least two controls and we would have to combine these with each other,” said Held.

The PLC can process 1,000 instructions in 60 ms. At the same time the CNC offers, when controlling eight axes, an interpolation cycle time of 1 ms maximum. The Rexroth IndraDrive servo drives have integrated safety functions for secure hold and safe movement. “Also of interest is the so-called feedback capability, with which the generator capacity of the motors is fed back into the network during the braking operation,” noted Held. Mikron uses the force of hydraulic components for clamping the direct drive B/C axes. The tool clamping mechanisms in the motor spindles that close by means of spring assemblies are opened hydraulically. Here the valve blocks are the same for all spindle variations.

When it comes to workpiece handling in the loading and unloading station as well as workpiece transfer, it is pneumatics that takes care of speed and safety. With the HF03-LG “light generation,” Mikron uses a light and compact variant of the HF valve series. It has a narrow valve width, yet can flow up to 700 standard liters. By using plastic plates, the weight can be reduced even further. The pneumatic and electric controls are located towards the front and arranged in one direction, thus offering increased installation potential, compactness and the possibility of adapting to the space available. By way of an alternative to the traditional multi-pole connection, a field bus connection is used.

From a single source
When it comes to compressed air treatment, Series AS2 maintenance units feature a modular structure. The individual air treatment processes are brought together in maintenance units made from high quality plastic. Filtering, closed-loop control, lubricating and draining – the configuration is geared to user requirements. With the patented oil-fill system, the oil is directly extracted from the storage tank by suction using a hose. This means that the maintenance unit is protected against fouling by oil.

The maintenance units for the pneumatics are located, like the hydraulic power unit and the master control, in a separate control cabinet. The cabinet also houses the central lubrication, power connection and the fire extinguishing system. This arrangement corresponds to the modular structure of the Multistep™ and, by ensuring simple and rapid access to central components, guarantees that the unit is maintenance friendly.

Bosch Rexroth Group
www.boschrexroth-us.com

Motor and Drive Combinations

There is a subtle premise that often escapes us as we talk about motors and the controls that run them.  It is that the motor and controller operate as a package.  In most situations, a customer specification is for input voltage and output torque and speed.  That’s all that is important.  How you get there doesn’t matter a great deal.

But ironically, most motor manufacturers are predominately mechanical engineering centered.  And most drive electronics companies are electronics centered.  And they have very little in common with each other.  Except that their products must work together.  And oftentimes, that’s where the trouble starts.

The drive manufacturer warrants that his drive will produce current and voltage.  But the the motor can have very complex constraints to deal with in response to the excitation of the electronics.  How accurately a 6 step approximation of the sine wave performs, for example, can result in overheating in the motor depending on the loading of the system.  And as the motor winding heats up, the resistance in the motor can change dramatically, especially in the low inductance windings that are common in many specialty motors available today.

Then there are the cabling issues for connecting the motor and drive electronics.  The ac drive industry found out quickly that long wire runs can result in stored energy in the wires themselves.  Standing wave phenomena could cause higher voltages than expected and blow holes in the winding insulation in the motor.

Power semiconductor prices have fallen considerably in the last few years creating situations where it is sometimes cheaper and more reliable to put in parallel devices than to attached single power devices to large heat sinks.  This leads to some serious new options for packaging the electronics.  How about drive circuits in the end bell or junction box attached to the motor?  Actually, some models of the GE ECM motor (now owned by Beloit) are ac fan motors with variable frequency drives and intelligent controls built directly into the motor end bell.  You may have one in your main air handler in the air conditioning system of your home.  I was surprised to find out that I did.

I used to think that thermodynamics of these systems would be impossible to manage.  But the fact is that the drive efficiencies are getting really good.  One team I worked with was producing a 500 Watt brush drive that only shed about 20 Watts of loss at full load.  That’s some incredible efficiency.  So the notion of integrating motors and drive electronics is much more reasonable than it used to be.  And there are stepping motor packages that have been doing it for years.

So where is this all heading?

The fact is that the motor and drive electronics must work together as a package.  There is an increasing need, and an opportunity to create further performance enhancements, by the two technologies working more closely together.  More innovation will lead to better energy efficiency and new design opportunities and a chance to recharge (pun intended) an industry that has been losing share to offshore competition in the last few years.

Maxon Announces Strategic Collaboration with National Instruments

Maxon Precision Motors is pleased to announce a strategic collaboration with National Instruments (Austin, TX). The initiative will look to highlight mutual areas of interest in the field of robotics. An informal relationship between the two companies was initiated as early as 2006, with the inclusion of NI LabVIEW VIs in Maxon’s EPOS family of digital position and speed controllers. Most recently the two companies collaborated on the design and development of ViNI , an all inclusive robotics platform created by engineers at National Instruments. ViNI is driven exclusively by Maxon motors, gearheads and encoders and NI CompactRIO embedded controls.

“NI and Maxon have worked together to integrate the high productivity of NI LabVIEW graphical software and the high-precision drive systems of Maxon Motors so roboticists don’t have to assume the integration workload,” said Shelley Gretlein, Senior Group Manager of LabVIEW Real-Time & Embedded at National Instruments. “Also, with the release of LabVIEW Robotics software, design engineers now can access native Maxon Motor interfaces ready-to-run on their next autonomous system.”

Other notable robotic applications driven by Maxon motion control products include the Mars “Rover” by Jet Propulsion Laboratory, “Da Vinci” surgical robot by Intuitive Surgical and “DARwin” the humanoid robot developed at RoMeLa, the Robotics & Mechanisms Laboratory at Virginia Tech University.

Both Maxon and National Instruments recognize that advancements in each respective area of expertise are complementary and look to provide designers with state-of-the-art hardware and software solutions for developing new robotic products and applications. Several joint marketing efforts are slated for 2010. Maxon will continue to focus its R&D efforts on electric motors, sensors and motion controllers while National Instruments will leverage its LabVIEW platform, NI LabVIEW NI SoftMotion Module, and CompactRIO.

“It is an exciting time to be involved in the robotics industry. Over the years Maxon has directed a significant portion of our engineering efforts toward the development of specialized products for robotic applications, and we are just beginning to realize the benefits of our investment. We are pleased to be working with NI and their talented group of engineers”, states Kirk Barker, Electronics Product Manager.

CompactRIO, LabVIEW, National Instruments, NI, ni.com and SoftMotion are trademarks of National Instruments. Other product and company names are trademarks or trade names of their respective companies.

National Instruments
www.ni.com

maxon motor
www.maxonmotorusa.com

Wind Energy Equipment Testing

Some friends were discussing the recent visit of Department of Energy Secretary Steven Chiu to Clemson University to deliver a check for $45 million to start a test facility for horizontal wind turbine gearboxes.  It seems that there have been a number of gearbox failures in recent years that suggest a wider problem that will need to be solved in order for wind energy to become as reliable and cost effective as promised.  Gear boxes are failing in the range of 10 years of operation, and occasionally, sooner than that.

This is not difficult to understand.  The forces acting on the gearbox are huge.  On the input side you have 3 blade propeller with blades that are now approaching 200 feet in length.  I don’t care how light weight they are, carbon fiber epoxy or Kevlar or whatever, the forces are tremendous.  In addition the blades have to rotate to take them out of the wind when the wind is too fast for the system to operate.  So there are actuators at the base of the blades adding to the weight and mechanical complexity.

Then there is the intermittency of the wind itself.  This can manifest itself as bursts of wind or winds of different speeds hitting the same rotor.  Which can lead to all kinds of impulse loads on the gearbox.  Gear teeth becoming momentarily unloaded and loaded in response to the wind.  This is actually one of my favorite “Stump the Band” questions for mechanical engineers; what is the formula for the shock load of gear tooth reversal?  It’s big, whatever it is.  And the shock load of the propellers is driving the gearbox against a high inertia load, the generator.  So there is a lot of resistance to overcome.

But the really scary part is that the gear systems are often in the range of 30,000 pounds in weight.  And they are mounted on metal masts at heights of 1.5 times the blade length.  So that would be 300 feet up in the air in the case of a system with a 200 foot blade.  Making the replacement of a failed gearbox a bit more complex than dropping the transmission out of a car, for example.  Especially since most wind farms are in very remote locations where the land is cheap and the wind blows some of the time.

This lead the Department of Energy to put out requests for proposals to address the technical question of providing the industry with a resource to help in the design of gearbox systems with much higher reliability than the current designs.  Total cost of this effort, approximately $100 million dollars.  The proposed test facility is targeting 20 megawatt power handling capability, or approximatley 27,000 horsepower depending on the exact rpm of the system.  This is an incredibly big piece of machinery.

Clearly, gearbox technology has to get better for the wind industry to continue to prosper.   I wonder if we are putting a band aid on a technology that is fundamentally flawed.  Maybe we need to be concentrating on the next generation of the technology and improving the cost performance by an order of magnitude.  Surely we can do better.

Innovation and Growth in Robotics

The robot industry has gone through some interesting changes over the years.  Most of the companies that were involved in the start of the real robot revolution are gone, unable to meet the extraordinary cost reductions that were sure tocome in order to make robots cost effective in most industries.  The biggest lesson, in my opinion, was the idea that robots had to be narrowly defined in terms of their application.   There was a time where there were only a few companies with the control technology to be able to make the multi-axis coordination work correctly.  So every application had to be programmed from scratch and the learning curve was huge.

The fact is that a welding robot is nothing like a Cartesian robot for electronic assembly.  And part of the learning curve of the industry was understanding what applications to focus on.  This first big reality set in when many companies began to compete for welding applications because the automotive market  opportunity was huge.  And just figuring out one application was a big enough task that it consumed most of the development resources available in  companies like GE and ABB robotics.

Consider the huge learning curve that has taken place in 35 years.  Medical robots have matured to the point where orthopedic surgery by a robot is faster and more precise than the best surgeons.  Researching the human genome would have been impossible without the high speed sample management systems of bio-assay robots.  And autonomous robots have searched the inside of volcanoes, taken samples on the moon and roamed and photographed Mars.  Pretty impressive.

Consider the forecast for the future of robotics. Motors and controls have become incredibly sophisticated and costs have dropped dramatically.   Computing power has increased to the point where memory and processing costs are almost trivial.  The First Robotics Competition is bringing 150,000 school children into the field of robotics through its programs with schools all over the US.  And the knowledge base and experience is so pervasive that we have Lego making teaching systems for grade school children to begin to get exposure to robotics.

Among the amazing developments, Barrett Technology has an anthropomorphic arm and “hand” gripper that is designed to low force, low power consumption and safe enough to be in proximity to humans.  The Robots and Mechanisms Lab at Virginia Polytechnic has demonstrated many new solutions to common problems of robot locomotion culminating in the Darwin soccer playing robot that operates autonomously.  Their goal?  Team Darwin wants to be able to compete with human soccer players by the year 2050.

With this kind of innovation, the future of robotics is going to be great.

Inventing Industry in the (near) Future

The future of the US economy, and our future as an industrial power will be the result of our cumulative creativity.  New industries will be the result of new ideas, new technologies, new thinking.  It’s gratifying to see programs like the First Robotic Competition getting 215,000 junior high school and high school students exposed to and involved in robotics.  Problem solving, finding solutions, getting their creativity flowing to make a box of parts into a working machine with real world performance.  It will be even more interesting to see what those same kids will be into 5 to 10 years from now as they begin their careers in the many technology pursuits they are likely to follow.

Technology is a major driving force in the economy.  The ability to create whole new industries that have never existed before.

And there is a second driving force, sometimes made less obvious by the flash of the latest technical breakthrough.  Cost.  What is the relationship of cost to the development of industry?  As costs decline volume goes up.  Steel manufacturing per man year of labor increased 500% during a period of intense competition between the US and Japan.  And interestingly, one of the breakthroughs was the creation of the “mini-mill” which could produce specialty steels more cost effectively by making them in smaller batches.  Sometimes the solution is counter intuitive.  The steel industry was all about increasing batch size.  But serving the market with more complex products turned out to be easier with smaller batches, ultimately increasing overall sales and defending the US market to some extent from foreign competition.

Are there other cases where innovation was economically driven?  In the machine tool world the majority of manufacturers develop bigger and more complex machines so that a single machine can handle any operation.  This complexity tends to drive costs up quickly.  So the tendency is to find high performance machine tools costing hundreds of thousands of dollars.  In contrast, the HAAS company re-invented the machine tool business by focusing on making a low cost, high quality machine tool that many shops could afford to buy.  They were one of the first companies to have several models of machine tool in the $50K range.

They did it by concentrating on the economics of a machine tool that was profitable in operation.  That means a machine with a low cost to purchase, low operating and maintenance costs, and sufficient precision to meet the requirements of most operations.   In order to reduce their machine cost they had to develop their own controls platform.  They restructured everything in the design and manufacture of the CNC system to meet the cost objective.

In act, they are so successful, that HAAS is the largest CNC company in the western world.

Many similar situations exist in other industries.  In small plastic parts manufacturing there are a number of breakthroughs that have created lower cost parts in smaller batches based on innovative new tooling systems.  In metal fabrication there are new process like thixotropic molding and metal injection molding that have been developed to lower the cost of metal goods by making parts at lower costs.  These solutions are focused on reducing costs and other barriers to the entre of new products like tooling costs and minimum batch sizes.  And they represent major new markets that were not possible in the past, because they are focused on the economics of the industry they serve.  Decreasing the cost of entry and the cost of part manufacturing opens up new markets

So inventing the future can be technology.  Or as it can be economics.   It’s all innovation.  And it’s all about delivering value.

Robot Lowers Costs for Packagers

“Packaging manufacturers are finding the global market place increasingly competitive, which has spawned a new metric adherence within production and packaging environments,” said John Dulchinos, president and CEO of Adept Technology, Inc. “Companies are now closely examining Total Cost of Ownership (TCO) and Cost-Per-Pick (CPP) when they invest in new lines and automation equipment.”

The Adept Quattro s650H offers a blend of high-speed production capability with the flexibility of robotic automation. The system simultaneously addresses both ends of the production continuum.

The parallel robot handles high-speed manufacturing, packaging, material handling, and assembly applications. It features a four-arm rotational platform, which delivers maximum speed and acceleration across the entire work envelope. Compact controls and embedded amplifiers ease installation and reduce workspace requirements.

The Adept ACE PackXpert™ software programs the robot to stack and sort product. Designed specifically for packaging applications, the all-in-one program is flexible, enabling manufacturers to respond quickly to part changes without lengthy reprogramming. An easy-to-use intuitive graphic interface and 3D workspace display the system operation including physical and conceptual objects.

Adept Technology, Inc.
www.adept.com

Motion and Software

Rockwell Automation recently had it’s Automation Fair during which a number of new product announcement were made.  The company has announced a collaboration with Dassault Software Systems to create a suite of tools that deal with various applications of industrial automation and manufacturing on the plant floor.  Of particular interest to the mechatronics world is coordination between Solidworks modeling software and Rockwell’s Motion Analyzer.  In addition, Rockwell has made an important ease-of-use connection between the Motion Analyzer which has traditionally been used for sizing motors, and the control system software.

As an experienced user of early version of the Motion Analyzer, I used the software as a tool to analyze tradeoffs between time, torque and inertia to optimize customer machinery and processes in motion control applications.  Good motion control starts with good mechanical design, and there are so many variables and tradeoffs, that it’s often difficult to navigate your way to the best solution.  A good motion analysis tool automates the process so that you can examine an axis requirement and explore several options for how the axis can be optimized.

The results of the Motion Analyzer can be directly integrated into the PLC editor RSLogix.  This is usually an area where there is a major duplication of effort, since everything that you have to program in the control system is data that you have worked with in the Motion Analyzer.  So kudos to the Rockwell team for getting this feature added to the RSLogix suite.

The Motion Analyzer uses information about the Rockwell Automation motors and amplifiers to match inertias to loads and duty cycle requirements to the thermal capability of the equipment.  This is an often overlooked subltety of the equipment, but at the end of the day, it’s all about the amount of heat you can get rid of.  And the duty cycle contains all the critical information about how much energy you need, when you need it, and how long you have to dissipate it.  In addition, I have found that everyone’s idea of thermal modeling is different.  So it pays to do the simulation work at the front end of the design.

But, we always used to joke that we were doing solid modeling anyway.  Everything was a cylindrical object of a certain diameter, length, material density, etc.  So it stands to reason that integration with a 3D modeling system would make sense.  After all, a little step up in capability could lead to a lot better design work from the start. And the ability to link mechanical design at the earliest part of the design cycle, directly to the output at the motor and control system, makes for better outcomes every time.

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