The new maxon motor magazine is here.

Applications, interviews with experts, drives in depth. Interactive and exclusively for tablet computers.

As of October 25, 2012, there is a new publication from the drive specialist maxon motor. “driven – the maxon motor magazine” will be issued three times a year for iPads and Android tablet PCs. At the end of each year, the highlights from the three tablet issues will be compiled in a print edition.

“Experience drive technology on an interactive platform where you can discover exciting applications or interviews with experts and expand what you know about selecting drives. “driven – the maxon motor magazine” offers something for everyone and provides readers with an inside view of the fascinating world of microdrives,” says Eugen Elmiger, CEO of maxon motor. The publication will be launched in English and German, with three issues a year (April, July, October). Each issue of the magazine will have a special focus topic: In the first issue 1/2012, the focus will be on intelligent robots. At the end of the year, maxon motor will compile the most successful stories in a print edition. Via the Twitter channel @maxonmotor or the e-mail address [email protected], readers can give feedback on the magazine’s content and make suggestions for future topics and articles.

“driven – the maxon motor magazine” is available for free as a download from the Apple App Store and from Google Play. Complete information on the new magazine by maxon motor can be found at: magazine.maxonmotor.com

About maxon motor
maxon motor is the leading provider of high-precision drives and systems up to 500 W. These include brushless and brushed DC motors, gearheads, sensors, and intelligent control electronics. The company is specialized in customized drive solutions. Markets supplied by maxon motor include medical technology, industrial automation, the automotive industry, measuring and testing technology, and the aerospace industry.

DC motor motion stability and dynamics – and this all on a servo driven ball?

Motor control experts have impressively brought to reality what sounds, at first, kind of crazy and appears to contradict most basic laws of physics. Their Ballbot1 “Rezero” accomplishes not only a balancing act on the ball, but equally impresses by its convincing technical servo solutions, unprecedented control agility and appealing design.
As a focus project of the Federal Institute of Technology, students of the Autonomous System Lab along with their fellow colleagues at the University of Applied Sciences and the University of the Arts have formed a cooperation of a special kind. The result of this collaboration is named Rezero, being the first motor driven Ballbot that not only perfectly masters balancing on a ball via motion control. It also exploits its movement potential and shows that a robot can look appealing without bystanders needing to overcome their inhibition threshold. As motorised tour guide, servant, assistant or as toy, Rezero feels comfortable when space is limited or in crowded places. It is a most-talented artiste and entertainer, it impresses, unfolds emotions and interacts with persons standing nearby in a very impressive way.

The Ballbot Principle
One obvious attribute of a Ballbot is the „ball“ on which it stands. Its contact area to level ground is actually a single point, making the robot generally instable by design and highly at risk to keel over. On the other hand, this fact enables free movement in any direction as well as the rotation around its own axis.
Another aspect: Rolling in a particular direction produces counter torque – the tilt of the robot in opposition to the direction of motion – in turn, would actually make it tumble. But, a Ballbot makes use of this fact as it slightly leans in the opposite direction to, quasi, chase behind its center of gravity. To further accelerate, the Ballbot lets itself fall even further in direction of travel. For deceleration however, additional motor acceleration is required to first “out-compete” its center of gravity before coming to a synchronized standstill in the fully upright position. Yet; total “standstill is the Ballbot’s death“. Even when appearing standing erect, it equilibrates by continuously slightly revolving the ball underneath its center of gravity.
An obstacle to be overcome is the actuation of the ball itself: A „normal“ motor driven wheel rotates radially around its own axis, either forward or backward. Yet, a movement in the wheel’s axial direction can only be achieved by overcoming the friction.

Applied to the drive of a ball it means that, when moving in one direction, at least one of the drive wheels will radially jam. This fact requires the employment of a multi-directional motor drive system. Thereby, so called omniwheels2 take care of load transmission in one direction, while simultaneously providing free-wheeling in the other direction.
2 Multi-directional wheels that work like “normal” wheels, being capable to transmit force in radial direction. In axial direction, they feature self-rotating elements capable to freely turn under axial load.

“Ball”
The ball is a project-own design that distinctly differentiates from other approaches. Its structure and the consequently required manufacturing process have been made-up in collaboration with an industrial partner.
It is based on a geometrically highly accurate aluminum hollow sphere covered by a 4 mm thick rubberized, low-wear surface providing a very high coefficient of static friction. Both factors, precise spherical shape and high friction result in supremely quite running, extreme dynamic acceleration capability, and high velocity of up to 3.5 m/s (almost 13 km/h, that is close to 8 mph!).Most other known Ballbots travel somewhat “out of the true” and seem to stand out rather by their sluggishness and slowness.

Drive System
Another in-house development are the three omniwheels which are arranged in 120° angles around the ball’s circumference. This in particular, since available standard solutions could not satisfy the requirement of an entirely encapsulated outer shape .Their complex geometry, low-loss design of the individual components and load transmission-optimized surface all contribute to the exceptionally high-grade construction design. The wheels are driven by a motor/gearhead combination made by maxon motor. They compose of a maxon EC-4pole brushless DC motor 303, a ceramic planetary gearhead GP 42 C4 and an angular encoder HEDL 55405. The drives’ suspension is designed that the ball remains ideally positioned underneath the three motorised omniwheels to provide continuous traction. The drives are regulated by maxon EPOS 70/10 positioning controllers 6 in
3 Compact, brushless, electronically commutated high performance motor delivering 200 W power output, Ø30 mm, efficiency above 85%, speed/torque gradient approximately 5 rpm/mNm
4 2-staged planetary gearhead with ceramics axes, Ø42 mm, gear reduction 26:1, torque (continuous/max) 7.5/11.3 Nm, efficiency 81%
5 3 channel encoder with Line Driver, 500 impulse
6 Positioning controller with 700 W power output, operating voltage 11…70 VDC, output current (continuous/max) 10/25 A, slave within CANopen network Stability and Dynamics – and this all on a Ball?
Current control mode, being addressed as slaves within the CAN network. The three drives are being coordinated by the real time low-level computer.
The drive system impresses by its remarkable maximum dynamics during acceleration and deceleration, high velocities and, at the same time, high-precision positioning and quite running.
Control, Position Monitoring and Sensor Technology
In control are two data processors; a real time low-level computer for fast, accurate equilibration and position monitoring, and a high-level processor in Linux running the Robot Operating System (ROS) which takes care of interaction with the surroundings. Rezero can be controlled by various input methods, such as joystick or trajectory planning via MATLAB. Additionally, Rezero features a “game mode” by which, within preset parameters (such as, for example, maximum speed, acceleration, range of movement), a group of people can take control by jostling and tapping it.
The Inertial Measurement Unit (IMU) represents one of the robot’s core components. The system measures translative and rotatory accelerations, as well as spatial tilt angles and features a compass. Data are being smoothened by an internal Kalman filter and transmitted to the low-level computer. The unit operates at a frequency of 160 Hz and represents the clocking link within the regulation chain.
To perceive its surrounding, Rezero is equipped with various laser and ultrasonic detectors. Their arrangement allows full 360° detection of objects within a range of approximately 6.5 m (21 feet). Depending on the selected mode, detected objects are assessed as obstacles, or they can be incorporated in the robot’s behavior. Thus, for example, allowing Rezero “to take chase”. The sensory capabilities are being enhanced by surround microphones, whereby their signals can also be integrated into the robot’s actions.
Casing

Kids (and not just small ones!) can hardly resist the temptation to touch the robot, to play with it or to bring it to heel. Not just due to its incredibly organic movements, but also because of its very friendly, inviting appearance. The kinetic behavior reflects also in its exterior packaging; curved, nicely shaped, of strong character, dynamic and elegant.

The result
Rezero it the first Ballbot that not only perfectly commands the act of balance, but also outbids the moving capabilities of a Ballbot in an incomparable manner. The project team’s well-elaborated concept impresses: The successful in-house development of the mechatronic elements, the high grade design and the interdisciplinary total package solution make Rezero an outstanding eye catcher.
Hence, it does not come as a surprise that Rezero has attracted the attention of renowned companies in the film and entertainment industry. In the near future, Rezero for sure can be admired by a large audience when performing at its best.

www.maxonmotor.com.au

The successful series of brushless EC 45 flat motors gets an addition to the family.

Two completely newly designed 70 Watt versions join the family, which pushes the power limits, once again.

The new EC 45 flat 70 W is available in two versions; one with socket connector and one with prefab cable. It displays a very flat speed/torque gradient and unifies novel features with proven characteristics: flange pattern, fixation and socket are identical to the existing EC 45 flat 50 W.

The new EC 45 flat 70 W is available with Hall sensors with four winding types (24, 30, 36, 48 V) and can be combined as follows:

• Gears: GP 42 C, GS 45 A

• Controllers: compatible with numerous types of servo controllers (DEC, DECS, DECV and DES) positioning controllers (EPOS2 and EPOS2 P)

The new EC 45 flat 70 W features extraordinary key data:

• Max. continuous torque of 130 mNm (about 38% more than EC 45 flat 50 W)

• Efficiency 83…85 %

The new EC 45 flat 70 W is perfectly made for pump drives and the use in industrial automation etc.

www.maxonmotor.com.au

maxon motor hits the right note

In the field of robotics, there are many interesting applications, from industrial robots and autonomous vehicles to humanoids. But have you ever heard of a complete robot orchestra? A project team from the Netherlands has been letting robots make music for several years now. Motors by maxon motor ensure that they hit the right note.

With a robot orchestra no drummers, guitarists or panpipe players are required any more – all these instruments are played completely by robots. All features needed for the orchestra, from the mechanical components, to the electronics and the software, were developed by TeamDARE from the Netherlands. This team consists of a group of enthusiastic engineers that share a hobby in their free time: building robots. The project originated from an internship at the Eindhoven University of Technology in 2001. Ever since, TeamDare has been participating in various competitions, such as the “Eurobot” international robotic contest and the “Artemis Orchestra Competition”.

The objective of TeamDARE is to show, in a playful way, what is currently possible with robotics. With the music robots, the team proves that, to a certain extent, it is already possible to replace musicians with technology. The strength of the team lies in the balance and synergy between the different subject fields, from mechanical engineering and electronics to computer science. Thus a multi-disciplinary team has formed that closely cooperates to develop more music robots. The shared passion for technology is the largest motivation for the eight team members.

maxon motors for the right sound

Simplicity, robustness and the reliability of the individual components are important prerequisites for the implementation of the respective robot projects. However, the robots also frequently have to be transported to other locations for presentations. This demands great care, because any repairs that become necessary cost time that could otherwise be used for new projects. “Therefore we have been counting on motors by maxon for many years,” says Bart Janssen, the team leader.

The heart of the orchestra are the 17 maxon motors built into the three music robots. For example, the panpipe robot is equipped with three RE 25 maxon DC motors, with GP 32C planetary gearheads for driving the instrument. A total of eight motors are behind the beat of the complex drummer kit. This includes three maxon RE35 DC motors. The centerpiece of the DC motors is the worldwide patented ironless rotor.

“Using maxon’s motors gives us great creative freedom. Especially as the large variety offered by maxon includes the right solution for every function,” explains Janssen. In June 2010, the engineers completed the development of the panpipe robot. After a short break, the team is already hard at work on the next instrument. At the moment, TeamDARE will only reveal that the new music robot will not simply supplement the current “band members”—instead, it will surpass all the other instruments built until now in both scope and complexity. The suspense continues… Which musical robot will soon jam with the rest of the orchestra?

www.maxonmotor.com.au

DC motors in Intensity-Modulated Radiosurgery System

Intensity-Multi Axis Modulated Radiosurgery System
Driven by more than 100 maxon DC motors, the shape-shifting multileaf collimator motors focus radiation on tumors while protecting surrounding healthy tissue in sensitive areas of the body.
The problem can be a matter of life and death to the patient. Until a few years ago, head and neck tumors could not be safely bombarded with radiation without the possibility of damaging organs like the spinal cord or salivary glands. Doctors were forced to keep radiation doses low – too low to be completely effective in eradicating tumors – in order to avoid paralyzing or even killing their patients. Many spinal column tumor treatments ran the same risks. The situation presented doctors with a Hobson’s choice. A tu-moricidal radiation dose might cure the cancer but seriously harm the patient. On the other hand, lower radiation doses could fail to stop the cancer.
Hospitals needed a machine that combined superior technology with an efficient, reliable process for targeting tumors while sparing normal healthy tissues. The components had to deliver radiation in different modes, including segmental, dynamic, combinations of the two, and ‘conformal arc’ radiation treatment, all on one treatment machine. A computer system had to be able to translate multiple views of a single tumor into three-dimensional anatomical images. Using this image data, a complex radiation therapy treatment plan would be created. From the treatment plan, the computer would create the instructions needed to operate the motion system used to provide treatment.
The Healing Capabilities
Cancer treatment technology from Varian Medical Systems is aimed at being able to ‘paint’ or conform a radiation dose very tightly to a small or irregularly shaped target. These systems have the ability to minimize hot spots, improve target dose homogeneity, and sculpt dose delivery around critical structures more effectively.
These systems are used accurately and repeatedly to treat tumors very close to sensitive structures like optic nerves, spinal columns, and other glands and organs. Despite their complexity, the high-resolution treatments are delivered quickly, fitting into the conventional 10- to 15-minute time slots generally reserved for such treatments. The process is further streamlined through DC motor automation and the ability to customize a process, save it, and repeat it. Varian also provides software that incorporates data analysis and reporting tools.
The Technology
Varian has received FDA 510(k) clearance for its latest high-definition multileaf collimator (MLC), an ultra-fine beam shaping device for radiosurgery. The “HD120 MLC” consists of a computer-controlled array of up to 120 parallel, individually adjustable tungsten slats or leaves that can block the path of an X-ray beam. The MLC is attached to the head of the medical linear accelerator, which generates the beam. The leaves of the MLC situated in two parallel rows, and can be moved in and out to create an adjustable aperture through which radiation beams are directed at a patient’s tumor. The shape of the aperture is dynamically changed as treatment progresses, to match the shape of the tumor as seen from each of the angles from which the beam is being delivered. By using the MLC to precisely shape the beams from multiple angles, it is possible to deliver a radiation dose that closely matches the three-dimensional volume of the tumor.
The MLC also facilitates intensity-modulated radiation therapy (IMRT). Using the adjustable motor driven leaves of an MLC to shape the beam and by controlling exposure times, clinicians can deliver a different dose to different segments of the tumor, modulating the dose intensity across the entire treatment field. Consequently, the dose can be higher in the most aggressive areas of the tumor and lower in areas where the beam is near or passing through sensitive healthy tissues.
Prior to the new HD120 MLC multileaf collimator, Varian’s finest MLC had a central group of beam-shaping leaves that were each 5 mm wide. The HD120 has reduced the width of the central leaves to just 2.5 mm, increasing the beam-shaping precision by 100 percent. Each side of the Varian collimator is configured with 60 leaves distributed in an 8 cm wide central region with 32×2.5 mm leaves, flanked by two 7 cm wide outer regions with 14×5.0 mm leaves, for a total width of 22 cm. The HD120 MLC was also designed for durability, so that it could be relied upon during continual use in a busy clinic.
The Motor Drives
If the leaves are designed too tightly together, they jam. If the leaves are designed too loosely, radiation leakage occurs. Consequently, careful engineering that optimized how the leaves were packaged into the system was critical. The leaves move in and out through the use of 120 tightly packaged DC motors by maxon.
maxon DC motors are known for their long life due to their unique construction, and the fact that they are manufactured on specialized machines. Yet, above and beyond their longevity, the motors offered Varian engineers excellent packaging options. Packing 120 DC motors into a 40cm by 40cm space meant that motor size was almost as critical as motor specifications. Through the use of maxon’s Rare Earth 8mm, Rare Earth 10mm and Rare Earth 13mm motors, Varian was able to package 120 tungsten leaves into the limited space available. While the minimotors are indeed small, the truly impressive miniaturization occurred with the required encoder feedback. Each motor has an encoder to close the servo loop that must deliver suitably high resolution while remaining as small as possible in order to meet the packing requirement. Further, these encoders must be modified to be radiation resistant as the high field dose would destroy conventional encoder technology.
Varian’s radiation system was designed to deliver distinct radiation doses to thousands of different segments per tumor – almost like a free-flowing radiation gun. To do this, the multileaf collimator reshapes the opening for radiation quickly and automatically according to preprogrammed data. Consequently, each motor must handle high torque and high speed to create the programmed shape changes as quickly and accurately as possible. Motor torque needed to be at a level where the plates could operate in a tightly synched formation, even against the high friction that could occur. Maxon are able to supply the smallest, highest power DC motor gearhead and encoder packages.

Figure 1 & 3Figure 1 & 3.  Figure 2 Figure 2.   Figure 4 Figure 4. Figure 5 Figure 5.  Figure 6 Figure 6.  Figure 7 Figure 7.  Figure 8 Figure 8.

www.maxonmotor.com.au

Let’s Talk Accuracy

Gurley Encoders explain motor encoder accuracy. In the world of motion control encoders, the terms resolution, accuracy and repeatability are often confused. Definitions: This document refers to rotary encoders because they are more common than linear encoders, however information can be extend to linear encoders also.
The resolution is a measure of how many counts per unit distance the encoder generates, or, the size of the measuring step. With rotary encoders, resolution is expressed in either units of angle (degrees-minutes-seconds, decimal degrees, grads, or radians) or in number of measuring steps per revolution (e.g., 10,000 counts/rev). [PPR, or pulses per rev, is quite common, but we avoid this term on purpose. Often, when a binary number of measuring steps per revolution is required, the term “bit” is used to indicate the resolution’s highest power of 2; for example, a 16-bit encoder generates 216 = 65,536 counts/rev. Resolution is a basic encoder parameter.

Accuracy is a measure of where the encoder says it is as apposed to where it actually is. They are expressed as units of an angle, although sometimes also expressed as electrical degrees. Accuracy and error are expressions of the difference between actual and reported position, However with a slightly different meaning. The accuracy is the difference between the indicated reading and the true position. Error is how far the indicated position is off true.The higher the accuracy is better.
The resolution of an encoder is fixed on the electronics or the optic wheel when the encoder is made however, encoder errors can crop up later with influences from temperature, shaft loading, service life and dust. The number of counts per revolution does not change unless in the case of severe damage. Accuracy effects all encoders but not all manufacturers specify it. The reported position over time is expressed as repeatability.

Instrument Error + Quadrature Error + Interpolation Error + Quantisation Error = Total Optical Encoder Error.
Phasing and duty-cycle tolerances is Quadrature Error It is usually expressed as electrical degrees or an angular measure.
Interpolation Error is the error in an electronically increased value.
Quantisation Error = the characteristic of a digital instrument. To measure encoder accuracy it is possible rotate the encoder at a controlled speed and measure the time interval between transitions of the output.

The classic way to measure position errors is with an autocollimator a multi-faceted mirror that attached to the encoder shaft.

www.maxonmotor.com.au

Crawling Search and Rescue Robot

As part of their Bachelor studies, students at the Swiss Federal Institute of Technology Zurich (ETHZ) have gathered in a focus project to develop a multiparite articulated crawling robot. It’s name is the agenda; because Traloc is acronym for “track” and “localisation”. Hence, it is already said how the robot moves – just as in a tractor crawler’s track – and the purpose it is being used for – localisation and detection of buried or trapped persons.

What if the search for survivors could be performed by a robot that would be remotely controlled through the scene of devastaion from a safe distance? How can the risks for on-site rescue teams be minimalised? How can the critical, truly limited timeframe following a quake be used most efficiently? How can trapped persons be pinpointed with high accuracy and how can communication with survivors be established? These and similar questions were the team member’s particular focus.

And their answer is not bad at all: Trapped victims can be buried under metres of debris. Localisation and rescue can be a high risk and time critical endeavor, thus demanding the utmost from victims and rescue workers. In this exceptional situation, vibration-free but at the same time rapid and precise localisation of a victim is crucial for an effective rescue. because the probability of survival decreases very rapidly over time.

That’s where Traloc comes in. It is designed to explore hard to reach, unstable terrain, to detect signs of life and to perform precise detection and localisation tasks.

From Vision to reality

The project focuses on theoretical feasibility and possible implementation of a rescue system capable to support and supplement known, well established rescue methods.

Traloc is a modular system, which currently comprises five autonomously propelled, self contained base elements. Each of them features a central drive system that propels tracks on all four long sides to guarantee forward motion regardless of the spatial orientation. Two base elements are thereby interconnected by concept comprises a microcontroller for each base element. It manages propulsion and deflection of the corresponding base element, as well as communication with the other microcontrollers in the system. To provide even higher capabilities, the modular design allows the Traloc’s extension with additional base elements.

Base Element

Foundation stone of the Traloc is a set of self-supporting, cuboidal light-weight structures of about 200 mm side length, each. They are constructed as self-contained modules and provide space for the drives for the tracks and the joint, associated electronics, sensors, and interfaces. The elements are equipped with a pair of tracks on each side which are simultaneously driven by the central drive system. At their front faces, they feature a freely movable, motorised gimbal joint.

Main Drive

The track pairs along the sides of each base element are made of double toothed belts. They are simultaneously driven by a single motor via a central worm reduction gear with four output shafts – another development of the Traloc team. This drive principle has the advantage of being capable to dependably move the Traloc, regardless of its actual contact faces. Sensor-based monitoring was deliberately not used. maxon motor’s EC 32 flat IE, brushless flat motors with integrated 1-Q speed controller serve as main drives.

Intermediate Joint

One of the mechanical core components is an innovative , self-designed joint. The idea is based on an actively powered gimbal joint permitting a deflection angle of more than 45° in both planes. The two degrees of freedom are mechanically decoupled, making it easy to control and very robust against external impacts. Each degree of freedom is actuated by an electric motor via a two stage chain reduction drive. In addition, a contactless rotary angle sensor is used to accurately position the joint. Each axis is driven by a brushless DC motor EC-max 22 with a downstream planetary gearhead with ceramic components GP 32C and a 1-Q-EC servo controller DEC Module 50/5.

Control

The modular setup of the system bears great potential for the implementation of sophisticated algorithms for specific control of the individual base elements. In order not to stress the project’s very restricted timeframe too much, complex motion control has not been implemented with the present prototype. Nevertheless, alternative options could be demonstrated in detail.

Traloc features an interface, by which rotating angles of the individual intermediate joints and driving speed are transmitted. For the drive control, a number of methods, such as trajectory planning via MATLAB, a graphical control console or the pioneering self-designed “snake controller” are available.

With the latter, the operator holds a miniturised model of the Traloc in their hands. The desired changes in the shape can be determined by adjusting or moulding the individual limbs of the “snake controller” against each other. The driving speed is preset with a slider control. The Miniature Traloc’s deviations are then flatened and sent as parameters to the corresponding controllers of the base elements, thus recreating the form and position of the “snake controller”.

The control parameters are transmitted via trailing cable which also hosts lines for energy supply and for data transmission of the robot’s onboard environment sensing instrumentation.

Sensors

The camera mounted up-front on the first base element can move in all axes. Besides horizontal and vertical pans it can also look backward, over the Traloc opposite to the direction of travel.

An inertial measuring system is located in the middle base element. It monitors the Traloc’s spatial orientation and transmits the data on location, position, and geographic orientation to an extrenal CPU. The data is then used to determine the position of pinpointed victims as well as for calculation of the Traloc’s safe returning path. Originally, provision of all the base elements with individual inertial measuring systems was planned, but could not be implemented due to lack of time.

True Fact and Fictional Future

The Traloc team deserves extra compliments for its “robot of another kind” and the associated methods of resolution. Within the scope of the focus project, the principle objectives have all been fulfilled. Obviously, the project has not conclusively answered all aspects in respect to an in-practice application in a real disaster situation. Yet, the basic design structure has been successfully completed and has proven practical. Further investigation analyses are under way. With the participation of the Military Disaster Relief (search and rescue operations, part of the disaster relief framework of the Swiss Armed Forces and Civil Affairs Support), of RUAG Defence and various disaster relief organisations, the potential for further development and future utilisation of Traloc are being evaluated.

www.maxonmotor.com.au

Case Study – Gearmotor driven Hull Cleaning Robot for Large Ships

New design Servo gearmotors have enabled a Florida company to design a robotic crawler that can navigate around the underwater portion of a ship and remove accumulated biofilm layers. As DC motor and battery operated, autonomous vehicle, component selection made up a highly critical part of the design and manufacturing process.

Toxic paint is used on the bottom of large ships to prevent biofilm growth, a form of fouling that increases the ship’s drag and decreases efficiency. Although it is quite effective, the downside is that the toxic paint continually leeches copper and other heavy metals into the underwater environment and damages the organisms that live there. To make the matter more complex, the paint must be blasted off and replaced every 5 to 10 years, at which time tons of toxic waste is produced and must be properly disposed.

A ship that operates with a clean underwater surface free from fouling—even thin biofilm layers—will operate so much more efficiently that potential savings can easily reach over 5% in fuel costs alone. Without the concern for fouling, a ship’s underwater coating can be engineered for corrosion protection and longevity rather than its need to eliminate the potential for biofouling. If biofilm fouling was eliminated on all the ships operating in the world today, the energy savings would greatly reduce the presence of greenhouse gases.

To eliminate the requirement for toxic paint and its cleaning waste, there needed to be a method to “groom” the biofilm from the underwater portion of a ship. The idea was to create important changes for the ships being built as well as for the environment. That is where the HullBUG (Hull Bioinspired Underwater Grooming) concept originated.

Successful promotion of the HullBUG servo concept by SeaRobotics, Palm Beach Gardens, Fla., attracted the attention of the U.S. Navy and specifically The Office of Naval Research (ONR). A successful proposal was submitted to the ONR for funding and a project team was established. The team currently uses SeaRobotics as a system designer and integrator and the Naval Surface Warfare Center Carderock Division (NSWCCD) as the team manager. The Florida Institute of Technology is also employed to provide it’s strong system knowledge and research base for understanding how the biofilms affect ship efficiencies and what is necessary to combat them.

“The most important feature of the HullBUG is its small size,” says SeaRobotics’ Research Engineer, Dr. Kenneth Holappa. “It is only about half a meter in length.” This was a necessary design feature to allow the vehicle to maneuver over the curved surface of the hull while continually maintaining close contact with the surface. An additional benefit of the small system size was that it allowed a single operator to deploy the vehicle without the use of additional equipment such as a crane. Because of the hazards associated with operating such a device underwater and in a harbor environment, occasionally a HullBUG might be lost or destroyed during operation. Keeping the size and cost of the system low definitely helped to eliminate damage as a major obstacle to implementation. So, from the very beginning of the project, small size and low cost have been identified as being critical to the satisfactory implementation of the HullBUG project. As can be expected, this need to maintain a particular size and weight filtered into the selection of every component of the servo system design.

Motion Control Components
The selection of the DC gear motors to drive the HullBUG involved a number of critical engineering constraints and compromises. SeaRobotics decided to make two basic models, one with wheels and one with tracks, and offer several options for monitoring the system’s progress.

Motor sizing, for example, required a calculated estimate of the power, speed, and torque characteristics of the manufactured devices. Determining factors included the resistance caused from pushing the grooming tool across the surface of the ship, the hydrodynamic resistance of the vehicle itself as it moved through the water, friction losses in the shaft seals that were used to protect the motors from the saltwater, and track or wheel friction dependent on which version of the unit was used.

“After extensive component research, we chose to use Maxon DC motors and gearheads,” says Holappa. “Their motors not only provided a very cost effective solution, but they were highly efficient and extremely simple to implement.” The company used EC flat motors with planetary gearheads. Two brushless DC motors were used on the tracked version of the HullBUG (one for each track); while four brushless flat motors were needed for the wheeled version (one for each wheel). An additional EC flat motor was implemented in the grooming tool. That motor used a simple spur gear for speed reduction. In addition, a final motor, connected directly, was used for the negative pressure attachment device that held the HullBUG in place.

The EC45 4-pole flat DC motors selected for the HullBUG are very efficient and weigh only 0.997kg. Continuous output power is 200 W, while the maximum speed is 12,000 rpm (much faster than what was needed for this application). The important specification for this application was torque. Even under the potentially harsh environments in which the HullBUG would be engaged, the EC45 had a maximum continuous torque up to 37 oz-in. (265 mNm), depending on the winding chosen. The Maxon brushless motors are built to IP54 standards, which was critical to the application. Furthermore, the motors are also available in the system DC voltage that SeaRobotics requires for the HullBUG application. According to Holappa, the large load capacity of the shafts of the GP42 gearhead let the wheels mount directly to the gearhead shaft, which greatly reduced the complexity of the overall system design.

Because the HullBUG vehicle was to be completely autonomous, it had to be designed in such a way as to operate for many hours on batteries (cables would simply get in the way of the grooming operation). In order to maximize battery life, the biofilm grooming had to be done in the most efficient manner. Navigating in a random pattern may eventually get the job done, but not in a reasonable amount of time. In addition, a typical ship presents a very large underwater surface, often as much as 3000 m2. To keep this amount of area groomed, a user could employ multiple HullBUG vehicles to operate at the same time using sophisticated coordinated navigation.

Navigating the HullBUGA toolset of navigation modes has been created to let mul-tiple HullBUGs efficiently groom a ship by dividing the ship’s underwater surface into regions. Numerous algorithms have been incorporated to groom the ship accurately in steps down to the curve of the bilge. Additional algorithms and associated sensors are used to control efficient grooming on the flat bottom of the ship.

Miniature acoustic ranging sonar (MARS) is also an option for navigation control of the HullBUG. This is where a small, close-range pencil beam sonar was specifically developed to let the vehicle “see” an upcoming wall or cliff condition such as bilge keels and bow thrusters. Yet another mode of navigation uses a MEMS rate sensor for navigation information. Another feedback mode uses encoder-based odometry. Hall sensor feedback from the motor is used as an encoder signal to establish an accurate estimate of odometry. Hall sensors were used instead of optical encoders because of size and cost. The Hall sensors provide better than 1-mm accuracy in the measurement of odometry with the motor and gearhead combination chosen.

Ongoing Software Development
An autonomous vehicle is often software heavy in terms of engineering effort after having selected and implemented the proper motion-control system. Obtaining smooth, reliable navigation maneuvers that result in accurate positioning in a widely varying environment was one of the more difficult challenges for the design team. Multiple layers of software were necessary for handling the number and variety of possible events that can occur during grooming. Also, the proper organization of the control logic to allow extensibility of navigation behavior was the most difficult part of this complex system.

“Software development will continue to be an ongoing effort even after the years already put into it,” says Holappa. “Though the vehicle is completely operational, there remains a considerable amount of on-ship testing to be done.” As the project moves forward and into the field, there will no doubt be additional issues that will crop up and need to be addressed. Even now, the vehicle must be able to accomplish its task reliably in a hostile environment and in an unmapped terrain. Then it has to be able to return to the waterline of the ship for retrieval. This operation must be done repeatedly for days, months, and years, and with multiple systems in the water at the same time.

Although this sounds as though it is overly difficult, according to Holappa, a technician was recently trained to use the vehicle and was fully competent in a short time. The user interface was borrowed from the SeaRobotics’ Unmanned Surface Vehicle (USV) product line, an intuitive graphics-driven interface that has logged hundreds of hours of use by many different customers. The next primary focus will be structuring the interface to improve ease-of-use and let non-engineering personnel manage operations.

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Eight Years Opportunity: Mars Rover Finds Signs of Water

Built for eternity.

In the eighth year of its Mars expedition, the Mars rover Opportunity has found evidence that water once existed on Mars. According to briefings by NASA, in late 2011 the rover found a vein of a notably light colored mineral – apparently gypsum – deposited by flowing water.

For scientists, the gypsum deposits found by Opportunity on Mars are a sensation. They are convinced that the discovery proves that water once flowed at this site. On its way through the desolate Meridiani plane, the rover came across the light colored streaks in the ground by chance. An analysis of the minerals should help scientists better understand the geological history of Mars. Billions of years ago, the atmosphere on Mars was significantly denser; evidence indicates that there was once water in abundance on the surface of the planet. Today, the atmosphere is too thin to allow water to exist in liquid form.

The deposits formed at the same point on Mars where they are located today. At this very point, water escaped from cracks in the bedrock. Calcium that had dissolved from the volcanic rock was washed away. In the process, the calcium reacted with sulfur that had either leached from the rock or was introduced by volcanic gases. One of the analyzed gypsum deposits on the edge of Endeavour Crater is approximately 50 centimeters long and two centimeters wide. Prior to this discovery, Opportunity had not found anything similar to the gypsum deposit, which scientists refer to as the “Homestake.” According to Steve Squyres, principal investigator for Opportunity and professor at Cornell University in Ithaca, this mineral is common on Earth, but on Mars, this discovery is almost a miracle; the type of event that makes geologists jump out of their chairs. “This tells a slam-dunk story that water flowed through underground fractures in the rock,” says Squyres.

Eight years breaking new ground with maxon motors

In January 2012, Opportunity will celebrate its eighth birthday on the Red Planet. Originally, the mission was planned to last just 90 days. Since January 25, 2004, the rover has been exploring Mars on behalf of NASA. Opportunity has covered approximately 35 kilometers and, in the process, transmitted almost 162,400 images of the surface and the atmosphere of the Red Planet to the mission control center in Pasadena, California.

Motors manufactured by maxon motor ensure that the Mars rover is able to safely navigate the surface of Mars. A total of 39 DC motors by maxon motor are at work in Opportunity, and they continue to diligently carry out their tasks. The precision drives are used to drive the robotic arm, the Rock Abrasion Tool (RAT), the camera operation, and the control mechanism for the six wheels that propel the 180 kilogram vehicle, 1.6 meters long and 1.5 meters high, across the surface of Mars.

The motors are largely standard products with diameters of 20 to 25 millimeters and an efficiency of over 90 percent. Minor modifications were necessary to adapt the motors for the harsh environmental conditions: the temperature on Mars can fluctuate from approx. -120 degrees Celsius to 25 degrees Celsius. In addition, the motors had to withstand the special conditions during the voyage to Mars. And the atmosphere, which largely consists of carbon dioxide, is also a very special environment for the high-precision motors. Originally, two rovers were active on Mars; however, since March 2010, NASA has been out of contact with Opportunity’s twin, “Spirit.” A next-generation rover is already on the way to resume where Spirit left off: “Curiosity,” a space lab launched by NASA in November, is scheduled to land on Mars in August 2012.

www.maxonmotor.com.au

Black gold and extreme motors

Petroleum is the black gold of the earth – to get to this treasure, innovative and modern technology for recovery of petroleum and natural gas is required. The materials used in deep drilling are subjected to extreme conditions: Up to 200°C, vibrations and very high pressures. Motors by maxon motor are used for many tasks, such as operation of the valve controllers, as well as for triggering mechanisms and measuring devices.

Today, almost all cars require fuel and many heaters would not work without oil. In short: More than 85 percent of the global energy consumption is based on fossil fuel sources, i.e. oil, gas and coal. But to get to these valuable resources of our planet, it is necessary to drill deeper and deeper – no easy enterprise. Deep drilling technology (called “downhole drilling” in the field of oil and gas exploration) makes it possible to recover oil and gas from depths of more than 2,500 m. By combining downhole drilling with directional drilling (dynamic position alignment of a deep drill), previously unreachable oil reserves can be opened up, with drilling depths of currently approx. 5,000 m and drill lengths of up to 11,000 m.

Oil is a limited resource, but is an integral part of our modern way of living. Therefore, in many regions of the world, the black gold is recovered from deep inside the earth. In the USA, Russia, England, China and the Middle East, many oil and gas recovery plants, both onshore and offshore, produce several thousand barrels of petroleum or natural gas every day. To date (February 2008), the longest drill hole for oil recovery is 11,680 m long (Source: Wikipedia). It was drilled in 2007 in the course of opening up the Chayvo oil field offshore from the north-eastern coast of Sakhalin (Russia). This oil field is approx. 2,500 m deep, but it is several kilometers from the coast. These oil reserves are opened up mainly by means of directional drilling from onshore.

Power from mud flow

All drilling operations have one thing in common: The requirements on the materials used are very high. The drill heads, in particular, have to withstand extreme conditions. The temperatures and pressures at these depths, combined with the strong vibrations that occur during the drilling procedure, present unique challenges to the use of electronic drives. The conditions several kilometers below the surface of the earth are everything but technology-friendly. Robust materials that remain 100 percent reliable even at high temperatures of up to 200°C are required.

maxon motor’s EC22 HD (Heavy Duty) motor fulfills all requirements for these extreme ambient conditions. The electronically commutated motor, which has been designed for the exceptionally high requirements in the field of deep drilling, can withstand harsh conditions in which “normal” motors would fail. The constant development of electronics and motors today makes it possible to better monitor and control many functions throughout the entire drilling procedure. For example, the turbine in the drilling tool is driven by mud flow. Through the use of a magnetic coupling, motors become generators and supply the electrical energy for various drive functions. Thanks to this self-contained system, no expensive, polluting lithium batteries are needed. With the aid of the EC22 HD, the position of the drill head can be measured and aligned dynamically during the drilling process (MWD = measurement while drilling). This measurement is performed by means of accelerometers, inclination sensors and other instruments that allow precise recording of the position of the drill head. But how do the measured values get to the surface? To this end, the MWD technology converts the data to pulses that are sent to the drill platform. This system is driven by electromagnets or HD motors. Diverse deep drilling tools also use hydraulic valves or flaps that are operated by electromechanical drives.

A matching gearhead for the EC 22 HD is also available: the GP 22 HD (figure 3). Many applications, especially in the field of deep drilling, require a robust gearhead that accurately fulfill the requirements. Most underground applications require very high torques, sometimes for only very short durations (valve control, moving flaps). A special property of the gearhead is the integrated drill holes that are necessary for an unhindered oil flow, because the gearhead, just like the motor, can be operated in oil. The different versions of the EC 22 are optimized either for operation in air or for operation in oil (flooded in hydraulic oil). The motors are constructed without adhesives and do not have a mechanical commutation system. This enables the motor to withstand extreme temperatures and also ensures constant performance under ultrahigh vacuum conditions. The power rating depends on the surrounding medium and amounts to 80 W in air and, due to the much larger heat dissipation, 240 W in oil. The motors have been designed for ambient temperatures of more than 200°C and atmospheric pressures of up to 1,700 bar. If the motors are cooled with oil, they can even withstand temperatures up to +240°C. Other requirements on the motors, which have a diameter of 22 millimeters, are resistance against vibrations of up to 25 Grms, as well as against impacts of up to 100 times the gravitational acceleration of the earth (100 G). In comparison, Formula 1 race cars reach 2 G and fighter jets up to 13 G. A human can withstand approx. 10 G, in other words ten times his body weight. However, these are peak values and only astronauts and pilots can cope with such high physical stress for a certain period.

High efficiency at great depths

In addition to its very high resistance to the extreme ambient conditions at great depths, the maxon HD motors also have a very high efficiency. An efficiency of up to 88 percent is reached in air and more than 70 percent in oil. With these properties, the EC22 can be of benefit in countless other areas of application – for example under the extreme conditions in outer space. With their detent-free running properties, the motors have excellent control characteristics and are therefore optimally suited for high-precision positioning tasks in outer space, even at low rotational speeds. In the future, the motors will also be used on Venus – NASA is planning a space flight with this destination. However, there the motor will have to withstand temperatures of up to 480°C. The further development of precision motors for extreme conditions will therefore continue.

A view of the inside of the EC22 HD motor with the special coil, System maxon
A view of the inside of the EC22 HD motor with the special coil, System maxon
maxon motor also offers a matching gearbox for the EC22 HD: the GP22 HD
maxon motor also offers a matching gearbox for the EC22 HD: the GP22 HD