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 firstname.lastname@example.org, 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 specialised in customised drive solutions. Markets supplied by maxon motor include medical technology, industrial automation, the automotive industry, measuring and testing technology, and the aerospace industry.
maxon drives help “Roboy” stand on its own legs.
A project team with experts from science and industry, including the drive specialist maxon motor, is developing a new humanoid robot: “Roboy”. On March 9, 2013, “Roboy” will be presented to the public at the “Robots on Tour” international robotics fair that will take place in Zurich as part of the 25th anniversary of the Artificial Intelligence Laboratory (AI Lab) of the University of Zurich. This development can now be followed and supported.
Since June 2012, the project team has been busy implementing the latest knowledge in the field of robotics to create a new humanoid robot. “Roboy” will be 1.30 m big, with an anatomy and motion characteristics that mimic that of humans. With “Roboy”, the project team wants to show what topics are being researched in the field of robotics and which technologies are ready for series production. “Roboy” is a further development of the technology used in the famous “ECCE Robot”. Both robots, “ECCE Robot” and “Roboy”, are equipped with tendon-controlled drive technology, which gives the robots the ability to perform humanoid movements and to react to their environment. “Because robots physically move within their environment, completely new types of interaction between humans and machines result, far beyond what is possible with customary information technology such as laptops or smartphones,” says Prof. Rolf Pfeifer, initiator of the ambitious project. “The development of “Roboy” can be shaped and supported by everybody,” he adds. To make “Roboy” a reality by March 2013, the researchers need the support of partners and robotics fans. At http://www.roboy.org, everybody can take part.
Swiss robotics and drive expertise
In addition to the scientists of the AI Lab, international research groups from Germany and Japan are participating in the project. Furthermore it has the support of partner companies that are providing cutting-edge Swiss high-tech expertise. As main project partner, maxon motor is supplying numerous DC and EC motors, as well as sensors that enable “Roboy” to make high-precision movements. The drive specialist from Sachseln has many years of experience in robotics, e.g. for medical technology, industrial automation or the astronautics industry. Currently maxon products are in use in the two Mars rovers “Curiosity” and “Opportunity”. “High-precision electric motors are the artificial muscles of a robot. Our drives are small, dynamic and efficient – just what robotics need,” says Eugen Elmiger, CEO of maxon motor. Drive systems from Obwalden already powered the movements of the “ECCE Robot”. “For us, creative and ambitious projects such as “Roboy” are always an incentive to challenge ourselves and to try new things,” elaborates Eugen Elmiger.
The know-how generated as part of the “Roboy” project is freely available to researchers, robotics fans and people who are interested in technology. “With “Roboy”, we are defining a new development platform for humanoid robots that can and should be used and further developed by everybody!” explains Rolf Pfeifer.
Factory automation and robotic application engineers are often faced with the challenge of requiring fast, accurate and powerful linear actuation within a small allocated volume. The two most commonly available technologies are rotary DC motor driven actuators and linear DC motor actuators. There are of course advantages and disadvantages with all technologies and they are sometimes easily overlooked. This short summary contains some common considerations.
An easy way to think of a linear DC motor is to take a standard DC motor and lay it out flat. For example: A line of motor stator coils over or along which is passed the permanent magnet sliding actuator. They can also be manufactured as a rail of magnets with a moving coil. These can be flat or circular shapes.
- The main advantage of a DC linear motor is speed. Smaller and high quality units can achieve outstanding acceleration rates.
- The other advantage is operational life. Because there is no gearing and the only friction points are the required linear guides, the lifespan is therefore relatively long.
- Linear DC motors have a very low force or in particular a very low speed force gradient compared with DC linear Actuators. Of particular importance is the need to compare the same figure. Manufacturers from different parts of the globe often use a completely different standpoint from which to select catalogue ratings related to force. Peak force, stall force, rated force, holding force, back driving force to name a few. The most comprehensive test is to use a force gradient. This can be calculated or informative companies will supply you with the figure representing metres per second per Newton (m/s/N). The gradient of this speed force line represents how much the unit slows down for every Newton of load that is applied and this is a true test of its strength.
- The second disadvantage is current draw. Because linear motors are a direct drive solution and there is a higher level of current rise with the required feed force, a geared solution will be proportionally lower.
In this comparison we are looking at DC motor driven linear actuators only. These are supplied in many forms from inline OEM style units to off the shelf self-contained units. In the interest of fairness we should also do a quick comparison within this sub category.
These are units that are designed specifically for integration into a product being developed from the ground up, where the actuator section of the unit becomes part of the product itself. This is done in the interest of keeping the overall size and weight to a minimum. This could be a system as simple as a DC motor driving a threaded section using an actuation nut or a more robust design of an integrated ball screw, thrust block, DC motor, gearhead and encoder assembly.
These are commonly available linear actuators that typically have a DC motor mounted beside the threaded section that is driven by a belt and pulley. The threaded or spindle section is contained in a tube. A fixed nut is connected to an overtube that pushes an actuation rod in and out. These are bolt on units typically used on hospital beds and low duty cycle applications that seem at first glance to be a good solution, however they are bulky and inefficient compared to an OEM style spindle drive. The low cost DC motors commonly used in this style of actuator can have quite high radial load applied from the belt and pulley mechanism. This can result in premature failure of the motor bearings.
Because this application note is written for automation and robotic design engineers we can assume the OEM style will be far more applicable in terms of space, power, efficiency and reliability so we will make a comparison of advantages and disadvantages between the OEM style actuators and linear motors.
- DC motor driven actuators can produce much higher forces per volume than linear motors.
- The nature of the thread or spindle section gives both self-locking and free running options.
- High efficiency is possible. Particularly with the recent advances in ceramic and other high grade running materials.
- Controllability is very easy with the simple mounting of standard encoders on the rear of the motor. Combined with the gearing ratio and the thread pitch this gives a very high positioning resolution from standard motor position controllers.
- Cost: One must compare the additional system components required for the same overall result. Linear encoders, linear guide rail, limit switches etc. are typically required with linear motors. Much of this additional cost can be avoided with integrated OEM style units that do not require all of these add-ons’.
- The main disadvantage of a DC linear actuator over a linear motor is speed. Top speeds of around 180 to 200mm/s are typical.
- The second main disadvantage is integration. In order to reduce the overall machine size and by design, the fixation of the spindle nut is part of the application load itself and as such a certain level of system design and integration is required from the customer.
This short document touches only on some of the issues considered in complex design projects and the detail needs to be thoroughly investigated before the purchase of a product. This highlights the importance of dealing with a supplier with worldwide representation, data sheets that you can trust and a willingness to customise the product for the application requirements. www.maxonmotor.com.au
The Project: A multi-leaf collimator device needed to offer greater levels of accuracy than any similar product on the market.
The Solution: Multiple devices were incorporated, including 180 motors, to shape gamma ray radiation therapy beams, controlled by one interlinked motion control system.
When it came to designing a multi-leaf collimator (MLC) device, ViewRay took on the challenge to produce an end product that would be more accurate than others on the market. ViewRay collaborated with Maxon Precision Motors for critical components, including a custom motherboard, motors, encoders, gearheads, and individual motor control modules, according to an engineering team member.
ViewRay Incorporated is a privately held medical device company developing advanced radiation therapy technology for the treatment of cancer. The ViewRay system provides continuous soft-tissue imaging during treatment, using MRI-guided radiotherapy, so that clinicians are able to see where the actual radiation dose is being delivered and adapt to changes in the patient’s anatomy.
Overall, the ViewRay system includes five sub-systems, which are seamlessly integrated to provide optimal patient care. The major subsystems are: real time MR imaging, treatment planning, dose prediction and optimisation, real time soft-tissue targeting, and remote review and approval. The treatment delivery is performed in a split-magnet MRI system with rotating gantry assembly to position three shielded Cobalt-60 sources with the three multileaf collimator’s.
The imaging in other radiotherapy technologies took place before or after treatment, not while the beam was on. This was a limitation in providing therapy because targeting could not be adjusted dynamically. Soft-tissue motion often allowed a tumours position to shift during treatment, causing soft tissue damage.
The ViewRay system solved this problem by using a combination of MR imaging and radiation therapy delivery technologies. With continuous soft-tissue imaging, during treatment and with the beam on, ViewRay tools can refine the target and re-optimise the dose while the patient is on the treatment table. This was the first MRI-guided Radiotherapy System produced.
According to the engineering team, “The MLC motor control system is a critical portion of the system. We knew it would also be one of the more challenging to design because of proximity to the MRI magnet, and volume constraints due to the gantry configuration.” The system uses three gamma ray sources, mounted in separate shielded heads. For ViewRay, the double-focused MLC is designed to sharpen field edges to produce penumbra comparable to conventional accelerators, so that clinicians can treat patients with greater confidence.
The team chose Maxon’s EPOS2 Module 36/2 compact digital positioning controllers for their small form factor, which allowed them to package 60 channels of motion control for each collimator. Thirty modules can fit on a single custom motherboard, and there are two motherboards per collimator. Each ViewRay system required three of these collimator’s, one for each of the three heads used in the system.
EPOS controllers are compact, fully digital, smart motion controllers designed for use as plug-in modules in customer-specific motherboards, and can be used for single-axis or multi-axis motion control systems. Each EPOS module implements a flexible and highly efficient power stage, and drives a brushed DC motor with digital encoder. They are especially designed to operate as a slave node in a CANopen network. They have a maximum current output capability of two amps, running from an eleven to thirty-six volt DC power supply.
In order to interface with the controllers, the ViewRay team used the resident EPOS2 firmware, which provided simple to implement operating modes and monitoring functions required by the control system. What made things easier was that the controllers are CANopen compatible, which allowed the design team to define up to 127 device addresses on a single bus segment.
Each of the collimator’s contains sixty leaves that are arranged in two opposing banks of thirty. Since there are three collimator’s, the device uses 180 EPOS controllers as well as 180 motor/encoder/gearhead assemblies. The MLCs are mounted on the gantry system to provide collimation of the three gamma radiation sources with respect to the target. While the gantry is moving into position, each collimator leaf is positioned according to the treatment plan. To position each leaf, CANopen bus commands are directed to the associated node consisting of a motor, encoder, gearhead, and controller. The result is a precisely collimated shape that matches the treatment plan.
The 180 motors used in the system are RE16 brushed DC, 4.5 Watt motors. Each motor operates at speeds up to 11,000 rpm. Along with the motors are MEnc13 Hall-effect encoders for precise motor control and GP16A gearheads with 19:1 reduction, providing adequate torque for positioning speeds of 1.0 cm per second.
The EPOS Studio software package provided an easy-to-learn, easy-to-use development environment for proof of concept and end-product development activities, according to engineering. Due to MRI magnetic field effects, the MLC controllers had to be remote from the motors, and housed in a convection-cooled chassis.
maxon motor launches a completely new product program.
maxon motor, leading provider of high-precision drives up to 500 W, is launching a new range of DC drives on November 13, 2012. These are characterised by innovative and powerful DC motors with ironless rotors. Matching gearheads and sensors will be available from the same date. “New magnets, new design, new processes. Our best brushed drives have been given a complete technical revision,” says Eugen Elmiger, CEO of maxon motor. “Furthermore our customers can in future fine-tune their drives to their specific needs in even more detail. With just a few clicks on our website,” explains the head of maxon.
Interested persons can already get a first impression of the new product program of maxon motor at dcx.maxonmotor.com. However, the technical data is not being revealed yet. Markus Schwab, the responsible product manager for the new maxon DCX program, is already very excited and says: “These are going to be the most powerful DC motors on the market. In comparison to our direct competitors, our new products provide 20% more power in the same size class.” This is a new milestone, as the product manager of maxon motor confirms.