When a UK-based electricity producer was experiencing frequent breakdowns due to bearing failures in two industrial fan units, the plant requested the services of NSK to propose and implement a suitable solution. After performing an application review as part of NSK´s AIP (Added Value Programme), a change of bearing and fixing arrangement led to significant cost savings. An NSK application review attributed the root cause of industrial fan unit failure to incorrect bearing arrangement
The two direct-drive overhung fans, which are supported by spherical roller bearings in plummer blocks, operate 24/7. As primary total air fans, their role is to feed air to the boiler at a rate of 8 m3/second with an output pressure of 13 kPa. However, the bearings in each unit were failing every three months on average, a situation that would take three engineers 10 hours to remedy each time, incurring high costs per breakdown. The long time and high cost of replacement was largely due to the size of the task. Each fan is around 3.5 m in diameter and attached to the end of a 2 m long, 135 mm diameter shaft. Shaft rotation is 1487 rpm, powered by a directly coupled 350 kW electric motor. ”Condition monitoring was being performed by the plant on both bearing units for each fan,” explains NSK Sales Engineer Dennis Briggs-Price. “Temperature would be monitored continuously by a magnetic probe, with weekly vibration checks performed on each bearing, measuring velocity in a radial position [vertical]. Normal condition readings would be around 70°C, with a velocity of 5 mm/s. Every time these values were significantly exceeded, the bearings would be replaced by the plant as a precautionary measure as imminent failure was perceived. Typical values achieved before replacement would be 90-100°C and 20-33 mm/s velocity. Indeed, a recent bearing failure on one unit broke the steel frame/mounting brackets, with excessive temperatures and vibration figures recorded. In the past, the plant had even tried balancing the fans using a third-party resource, but the bearing failures continued.” NSK´s comprehensive application review included a failed bearing examination from the drive and non-drive end bearings. A number of issues, including fretting corrosion, were noted to the external diameter of the outer ring. It was also clear that both bearings exhibited a raceway which had supported an axial load; evident from a wider and more pronounced running band. This is unusual as the fan configuration had a fixed and free-end arrangement – to allow for shaft expansion from operating temperatures – thus the free end should only support a radial load. As the free end bearing at the energy plant exhibited axial loading, NSK was able to attribute the root cause of the ongoing failures to incorrect bearing arrangement. High-capacity Spherical Roller Bearings within SNN Plummer Blocks were therefore recommended, along with correcting the fixing arrangement. NSK´s Spherical Roller Bearings use state-of-the-art materials that make them suitable for high speeds and loads. Offering special ring tolerances to withstand vibration, shock loads and misalignment, the bearings are heat stabilised up to 200°C. Furthermore, high-capacity Spherical Roller Bearings were the preferred choice as the internal design is more reliable for direct-coupled overhung industrial fan units, thanks largely to inner ring ribs that provide better roller guidance. ”A trial was conducted with our engineering team overseeing the installation and implementation of our recommendations,” explains Mr Briggs-Price. “The result was zero bearing failures over a 12-month period. Furthermore, our solution offered increased productivity with reduced maintenance and downtime costs, with four times greater bearing lifetime.” As can be seen in this example, using the wrong bearings or fitting them incorrectly can reduce the output of machines or industrial units, and even cause a whole plant to grind to a halt. NSK´s AIP is designed to make operations and maintenance processes more efficient and more profitable by saving money at each value-added step. Experienced NSK specialists use a tried and tested method to develop the ideal solution for each specific application, working with the customer and taking every requirement detail into account. At the UK energy plant, the AIP process encompassed services from initial survey and product selection, through to customer training and final inspection. The results speak for themselves. Due to the new solution, savings of €134,040 are being achieved annually based on reductions in bearing costs, fitting costs and downtime costs.
Spherical Roller Bearings from NSK – which were chosen as the internal design is more reliable for direct coupled overhung industrial fan units – use state-of-the-art material technology that makes them suitable for high speeds and loads.
The next revolution in motor control
The continued focus on improving energy efficiency and sustainability remains a major driving force for innovation in mechanical and electrical engineering arenas. Improved speed control using variable speed drives (VSDs) has produced significant energy savings, but the next step needs to be much bolder – the implementation of a direct current (DC) grid within industrial premises has the potential to reduce operating costs and take advantage of renewable energy sources.
The German Electrical and Electronic Manufacturer’s Association [Zentralverband Elektrotechnik und Electronikindustie (ZVEI)] initiated the DC-INDUSTRIE research project along with 21 industrial companies and four research institutes. Together they are jointly working on the project to implement the energy transition in industrial production and, therefore, bring more energy efficiency and energy flexibility into industrial production.
Among those involved is Bauer Gear Motor, which is part of the Altra Industrial Motion Corporation, and Karl-Peter Simon, Bauer’s Managing Director, who is taking a leading role in the research.
Karl-Peter Simon: “This research project has the potential to benefit a large number of manufacturing industries, with one large automotive company already planning to implement some of the recommendations in a new test facility. Bauer is keen to use its expertise to help deliver this innovative vision and make a significant contribution to improving energy efficiency.”
In the industrial sector, electric motors account for about 70% of electricity consumption and are thus the most significant load of electrical energy. Reducing the energy requirements of these drive systems by increasing their efficiency contributes to an equivalent reduction in CO2 emissions.
Since January 1, 2017, all new 3-phase motors sold in Europe with rated power from 0.75 to 375 kW must conform to energy efficiency class IE3, or alternatively, IE2 for use in frequency inverter operation. These efficiency classes are specified for three-phase asynchronous motors operating at nominal speed and nominal torque. However, experience has shown that an energy efficiency regulation of a component can only sustainably reduce energy in certain operating modes.
With this in mind, the DC-INDUSTRIE project, by means of direct current networks, aims to support both the energy transition and energy efficiency, as well as Industry 4.0. The project is sponsored by the Federal Ministry for Economic Affairs and Energy [Bundesministerium für Wirtschaft und Energie (BMWi)] and has a term of three years.
Inefficiencies in speed control
The advantage of using a frequency inverter is the continuous adaptation of the motor speed to the actual need, which can very often also lead to energy savings. A frequency inverter is supplied with the alternating current, which is first converted into direct current using a rectifier. The direct current is then converted into alternating current with variable frequency and voltage through a voltage feed inverter in order to electronically change the speed of a three-phase motor.
However, if the three-phase motor is operating in the braking mode, e.g. in a crane that is in lowering mode, the energy flow changes. But, this energy cannot be fed back into the grid by the frequency inverter because the input rectifier only allows the energy to flow in one direction. Therefore, the energy that is fed back must be dissipated via the direct current voltage circuit of the frequency inverter.
For this purpose, a brake chopper is connected to the intermediate circuit. This monitors the intermediate circuit voltage with regard to the voltage level. If the intermediate circuit voltage exceeds a set threshold value, the brake chopper switches the braking resistor between the positive and the negative pole of the intermediate circuit. This is usually an additional external braking resistor that converts the braking energy into heat energy.
Reducing harmonics issues
The increasing use of frequency inverters to control motor speeds has led to problems with mains effects, causing harmonics and distorting the voltage. There is no standard solution for harmonics, since each grid and its electrical load are very different. Ultimately, the operator is responsible for the voltage quality of its own production facilities. If frequency inverters or other devices with power electronics are increasingly installed, grid effects will increase.
The challenges presented show that a further increase in the use of inverters for the flexible control of electric motors is desirable and very often even necessary. This is the only way to improve both production processes and energy efficiency. However, line perturbation due to harmonics and equipment costs limit the increase.
In order to achieve significant progress in energy efficiency and system cost optimization, new approaches are needed. To enable energy efficiency, energy transition and Industry 4.0, new grid structures are required.
Creating the solution
The new network structure is based on an alternating current supply, which provides the direct current power supply for production plants via a central rectifier. Active grid filters are integrated into the central rectifier to ensure the voltage quality harmonic requirements.
The direct supply of the frequency inverter with direct current means that all decentralized energy conversion is no longer needed. Since central energy conversion (from AC to DC) is significantly more efficient, conversion losses are significantly reduced.
Through the direct supply of all electric motors via a frequency inverter with direct current power supply, all installed motors are connected via a common direct current voltage grid. Furthermore, a direct current voltage network essentially only causes ohmic transmission losses. Compared to an alternating voltage network, the capacitive and inductive line losses are eliminated.
In addition, the central direct current voltage network offers the possibility of integrating photovoltaics directly at the direct current voltage level. In this case also, conversion from DC to AC is not required to be done by an inverter. This grid infrastructure offers the possibility of optimizing the purchase of energy and to stabilize the grid.
Through the elimination of the input rectifier and the grid filter with frequency inverters, these can be designed more cost-effectively and more compactly. This simplifies integration into the motor, which can significantly increase the degree of acceptance. Variable speed motors allow for a reduction in variants and energy savings. They provide status signals from all DC-fed drivers, which are of great importance for flexible and safe production control.
Grid management makes it possible to optimize operational management in terms of energy costs. The accessible information enables preventive production control measures to significantly increase the availability of production. This is a prerequisite for the successful implementation of Industry 4.0.
Where the robots come from?
Collaborative robots were a big feature of the Hannover Messe trade show again in 2018. Small, intelligent, sensitive, and self-learning: The ways in which robots can be used are increasing all the time. And the level of acceptance is also rising – not least thanks to attractive prices and short ROI times. Off-the-shelf handling solutions are in demand and Yuanda Robotics has a range of market-ready robot systems. For its drive technology, this young company from Hannover depends on the robotics expertise of KOLLMORGEN.
You know about our horses, now find out where the power comes from! With slogans like this, Lower Saxony is confidently advertising its own innovative strength – something which is most apparent in its robotics expertise. The region’s claims to market leadership were once again made clear at the Hannover Messe 2018 – not least in the shape of start-up company Yuanda Robotics. Founded just over one year ago, the company exhibited a number of robots for performing various load-carrying tasks. Inside, they are powered by specially customized servo motors from KOLLMORGEN’s KBM range. What is remarkable about these is that the powerful synchronous machines are frameless and can be embedded in the construction of the robot straight from the kit. The main advantages of this are that it saves space, and heat can be extracted far more efficiently.
Dr. Jens Kotlarski likes to lead his new robots by the hand. “In the same way as I would show things to my child, I show them to the machine,” says the managing director of Yuanda Robotics GmbH – a successful spin-off set up by three scientists from the Leibniz University in Hannover with funding from the Shenyang Yuanda Aluminium Industry Group in China. The company from Hannover is aiming to successfully bring different types, such as the L.3, M.3 and M.6 versions which, they exhibited, to market by the end of the year. The robots are designed to act as automated handling assistants for manual assembly lines in industry. “That’s why our robots have a similar reach to the human arm,” explains Kotlarski. “Humans are not really able to move loads of 5 kg or more ergonomically for long periods – especially if the parts also have to be lifted from low down to high up”.
For example, one specific area of use for the new robots from Hannover would be the loading of machines. Insert the component, press the button, wait, remove the component, and put it in a box – all day long. These are monotonous tasks that are avoidable. Kotlarski believes that people can be used far more cost-effectively in other ways. Before setting up Yuanda Robotics, he worked as a group leader at the Institute of Mechatronic Systems at Leibniz University in Hannover. The first “Made in Hannover” robots are principally designed to serve as production assistants for continuous operation. Among other things, using them in this way raises the question of how the heat from the drive technology can be most effectively dissipated.
High power density
This is where the frameless structure of the KOLLMORGEN KBM motors can improve heat extraction simply by convection across the robot’s joints. The effect of these excellent thermal properties is that the KBM motors can reach peak performance without derating. “The high power and performance density were important reasons why we used these motors,” explains co-founder Matthias Dagen. Small motors with a high output are essential if the arms and the joints are to be made as compact as possible. “The thinner and more lightweight the design, the heavier the loads that the robot will later be able to carry,” explains Dagen. Overall, it improves inertia behaviour and the ratio between the robot’s own weight and the weight it can carry.
Nevertheless, the requirement for lightweight construction has its limitations because a certain surface area and mass are needed in order to dissipate the heat effectively. But this is where the KBM motor assemblies from KOLLMORGEN prove to have particularly robust thermal properties. The stator winding has been defined by the specialists in servo drive technology and motion control as having continuous capability at an internal winding temperature of up to 155°C. Aspects such as this were crucial criteria when the motors from the KBM range were being designed and dimensioned. There was close cooperation on the engineering between Yuanda Robotics and KOLLMORGEN – mainly in the person of KOLLMORGEN project manager Markus Grohnert. “Having a personal contact was also important to us when we were choosing the most suitable drive manufacturer,” emphasizes Matthias Dagen. In addition to the strict performance criteria, delivery times for the components were another key factor for the young start-up company. “We need to be able to rely on short timeframes, if we are aiming to bring new products to market quickly,” says Dr. Jens Kotlarski.
Quick delivery for quick start-ups
The short delivery times for the frameless motors in the KBM series are mainly possible because each bespoke drive system is the result of a clever combination of standard components. Refinements can be made, for example, to the rotor hub dimensions, stack length, diameter, assembly jigs, windings, connection type, and much more. Part of the work of the engineering project at Yuanda Robotics consisted of Markus Grohnert making sure that the direct drive was perfectly matched to the intended robot gear system.
When it comes to control units, by the way, despite the ready availability of products that have been tried and tested in industry, Yuanda Robotics relies on in-house development. “We are aiming for a highly integrated solution that can’t be achieved with standard control units – in terms of function or price,” explains Matthias Dagen. The main reason for this is the special algorithms which are supplied to the control unit. Dr. Jens Kotlarski: “To do that, we have to go deep into the control technology and we want to eliminate all the superfluous functions that standard control units inevitably bring with them.” The two men are happy that they are able to bring to market a solution that has been deliberately reduced to the essentials. Both are in agreement: “KOLLMORGEN’s experience with frameless direct drive motors made them perfect partners for us in this kind of robotics work, including on the electromechanics.”
The bottom line
With their new series of robots, the company from Hannover is marketing a solution that provides everything that is needed to automate assembly and handling tasks quickly and reliably. The overall package is nicely rounded off by the integrated camera technology in the robot. This enables the robot to identify the products it needs to pick up by itself. For the visualization, the company has taken advantage of the potential of so-called augmented reality. This means that, when the parameters for new tasks are being set, the movements of the robot in the workspace can be exactly simulated – and then they can be sent out to start production. Helping people to understand these complex systems is one of the main objectives for Yuanda Robotics, in the hope of further increasing the acceptance of robots.
Direct drive absolute value unit
Machinery in a variety of industrial sectors has benefited from the properties, safety standards, compactness and precision of the positioning units driven by KOLLMORGEN linear motors.
Today, the well-known Mondial linear motor modules, long-established on the market, are more efficient and have higher quality standards, smaller dimensions, and an excellent price-quality ratio thanks to the compactness and safety of KOLLMORGEN products.
Mondial Spa is one of the foremost companies in the power transmission sector. For more than half a century, it has represented leading foreign companies, designing and producing a wide range of specialist products which can meet the most varied demands of many different industrial sectors. It is a parent company of the group of businesses specializing in the design and manufacture of specialist bearings for a number of different industrial applications. Boasting a design department, unusual feature for a distribution company, the Mondial Group works very closely with its clients to meet their needs, optimizing costs and benefits.
Mondial needed to update and expand its range of modules driven by linear motors and upgrade the product design and performance in order to be able to offer customers a new and improved range of components in line with trends in the market as well as its own quality standards. The improved performance of the product has to be allied with the affordability of the proposed solutions; this was to be the key to success.
The Milan-based company began their search for a well-known partner in the market with which to operate in partnership. A meeting with KOLLMORGEN confirmed their interest in collaborating with a leading company capable of producing complete solutions. The result was a winning combination: both players immediately saw opportunities to increase their presence and competitive strength in the Italian market where the first applications combining the Mondial linear units with KOLLMORGEN linear motors were introduced at the start of 2017.
“The start of this partnership has been very exciting for us” explained Angelo Trombetta, Direct Drives and Mechanical Transmission Manager for Kollmorgen Italia, who has been with the project from the outset. “We have worked well with the Mondial team, mutual sharing has been useful and rewarding for all: this project has been a start, we want to tackle new challenges, continuing to provide the added value which is our hallmark”.
Complete linear movements with a high level of performance
Mondial uses KOLLMORGEN motors is its linear movement systems, which make up one of the most extensive ranges of direct drive linear modules on the Italian market. The benefits of direct drives are clear: very high performance, OEE (overall equipment efficiency) performance, no deterioration in performance over time, providing a transmission with maximum efficiency. The direct drive of a linear motor under load also means that mechanical transmission components, recirculating ball screws, gears, belts, and other components can be done away with, eliminating mechanical play, increasing rigidity and therefore productivity.
The linear units produced can be used in a wide range of machinery in applications such as printing, packaging, presses, plastic deformation, machine tools, handling, laser cutting, measurement, inspection, milling, assembly, textiles, simulators, and many more.
Transport and positioning unit MLM7 N
High levels of dynamic performance, considerable load capacity, and precision are the distinguishing features of the new MLM7 N series from Mondial. It is a complete feed and positioning unit, vital for linear movement in precision applications. The base component is made from high-strength extruded aluminium, which can be used as a free-standing element, the profile of which has been designed to suit different types of linear motors. It also provides high translation forces, whilst always ensuring fluidity of movement. The delivery programme, updated by Mondial, is structured in order to satisfy any application requirements in terms of speed, precision of positioning, load capacity, etc.
With regard to protection systems, the basic version has been designed with uncovered guide rails and protected recirculating ball slides with standard friction seals. The version with a linear motor has a stainless-steel plate to cover the motor. If the application requires, the MLM7 module can also be fitted with a PVC protective bellows. On request, Mondial can design and produce special protection systems to suit specific safety requirements or working environments. Maintenance is reduced to a minimum with this new range: the different versions incorporate a grease distribution system for all the moving components; the version with a linear motor uses lubricators integrated into the recirculating ball slides. The Mondial linear motor systems can also be fitted with inductive, magnetic, and optic linear encoders.
A direct drive linear motor is, in fact, a rotary engine laid flat and driven directly under load.
With no mechanical transmission components, the design offers an exceptional level of performance, very high rigidity, dynamic speed, and acceleration, a high level of positioning precision, compact dimensions, low cogging, maintenance-free running, and quiet operation as well as a high degree of precision.
Advantages of the ICH linear motors
- Maintenance free, increased precision and bandwidth
- Uniform speed profile and reduced noise
- Transmission of forces without mechanical components such as couplings, toothed belts, etc.
- No gear reducers, screws, or lubrication
- Increased reliability of the application
- Vast selection of motor sizes with differing power ranges for universal use in all linear drives
- Increase in performance of the entire system
- Compact drive solution with reduced height
- Simple and more compact design of the machine
- Increased bandwidth and response speed compared with ball screw or gear-wheel drives.
- Reduced noise, fewer components and lower overall operating costs
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