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Posted by Electromechanical Team on 5 Oct 2017
The basic theory of operation for brushless servo motors revolves around the principles of magnetism where like poles repel and opposite poles attract. There are two magnetic sources found within a servo motor: Permanent magnets that are typically located on the rotor of the motor, and the stationary electromagnet that surrounds the rotor. The electromagnet is called either the stator or motor winding and is made up of steel plates called laminations, that are bonded together. The steel plates typically have “teeth” that allow copper wire to be wound around them.
Going back to the principles of magnetism, when a conductor like copper wire is formed into a coil, and the conductor is energized so that current flows through it, a magnetic field is created.
This magnetic field created by current passing through the conductor will have a north pole and a south pole. With magnetic poles located on the stator (when energized) and on the permanent magnets of the rotor, how do you create a state of opposite poles attracting and like poles repelling?
The key is to reverse the current going through the electromagnet. When current flows through a conducting coil in one direction, north and south poles are created.
When the direction of the current is changed. the poles are flipped so what was a north pole is now a south pole and vice versa. Figure 1 provides a basic illustration of how this works. In figure 2, the image on the left shows a condition where the poles of the rotor magnets are being attracted to the opposite poles of the stator. The rotor poles, which are attached to the motor shaft, will rotate until they are aligned with the opposite poles of the stator. If all stayed the same the rotor would then remain stationary.
The image on the right in figure 2 shows how the stator poles have flipped. This would happen every time the rotor pole caught up with the opposite stator pole by reversing the current flow through that particular stator location. The continual flipping of stator poles creates a condition where the permanent magnet poles of the rotor are always “chasing” their stator opposites which results in the continuous rotation of the rotor/motor shaft.
The flipping of the stator poles is known as commutation. The formal definition of commutation is “The action of steering currents to the proper motor phases so as to produce optimum motor torque and motor shaft rotation”. How are the currents steered at the correct time to maintain shaft rotation?
The steering is done by the inverter or drive that is powering the motor. When a drive is being used with a particular motor an offset angle is identified in the drive software along with other things like motor inductance, resistance, and other parameters. The feedback device that is used on the motor (encoder, resolver, etc..) provides the position of the rotor shaft/magnetic pole to the drive.
When the magnetic pole position of the rotor matches the offset angle, the drive will reverse the current going through the stator coil thereby changing the stator pole from north to south and from south to north as shown in Figure 2. From this you can see that letting the poles align will stop the motor shaft rotation, or changing the sequence will get the shaft spinning in one direction vs. the other, and changing them quickly allows for high speed rotation, or just the opposite for slow shaft rotation. Learn more about servo motors here.
Article contributed by Jeff Nazzaro, gearhead and motor product manager, Electromechanical & Drives Division, Parker Hannifin Corporation.
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The automotive vehicle industry has experienced introductions of several new technologies and upgrades. One significant example is the rising amount of electrical content per vehicle. Testing for vehicle and engine performance is essential in the wake of additions and conversions from each of the new technologies.
Concurrently, OEM manufacturers are facing a number of cost pressures that are fueling the dynamometer market, from both regulatory and the consumer base, leading to higher investments in R&D and testing.
The major drivers for dynamometers use for in-plant automotive facilities are test stands with enhanced accuracy, increasing demand for vehicle quality standards and increasing awareness toward quality in new markets. The challenge faced is how to get the price down on vehicles when all other costs are increasing.
Increasing electric and hybrid vehicle production will require more specialized testing stands:
Automotive plants are looking at purchasing new test stands to support the production of electric and hybrid vehicles.
Drive/control equipment on existing test stands may go obsolete, so parts and service will be hard to come by.
Production costs will rise with energy prices if existing equipment is not replaced with a more energy efficient solution.
Automotive or truck manufacturers or makers of components or sub-systems that go into a new vehicle already have test stands and dynamometer equipment that may be outdated and in need of drive/control retrofit. These customers who already have older test stands suffer from down time, trouble obtaining parts and excessive energy consumption.
OEMs looking to purchase test stands may want specialized features in the drive/control system and not every supplier can offer that. Or, they may be looking to purchase a new test stand or dynamometer and may want to specify certain equipment in addition. Our engineers will work with the test stand manufacturer on a special design as needed.
A dynamometer is a necessity in automotive vehicle testing equipment used by OEMs, component suppliers and automotive testing service providers for recording several parameters such as force, torque, power and speed of the vehicle.
The use of this testing equipment is essential throughout the production cycle of an automobile, making it a necessary component of all vehicle assembly lines. This testing equipment is also used in vehicle engine manufacturing factories and dynamometer laboratories or the automotive testing service facilities to evaluate vehicle and engine performance.
Test stands and dynamometers cover a wide range of applications, but are most commonly used to test manufactured items for adherence to specification while simulating real-world operating conditions. While “test stand” is a more general term defining a machine that could test nearly any item including pumps, automotive components or electrical components, a “dynamometer” is used to measure torque or power and is more closely associated with motor or motor vehicle testing.
A drive system is used in these applications to either provide motive force or absorb it, depending upon the type of test stand:
A pump test stand requiring a motor to spin the pump and a drive/control system to regulate the speed and torque delivered to said pump.
A dynamometer used to test an electric motor would require a second motor that would effectively act as a braking device to load the motor under test.The drive and control system would be required to absorb this energy while regulating the speed and torque during the test.
A third example would be a test stand designed to test rechargeable batteries. Here, no motive force is involved, but the test gear would charge and discharge the batteries in a controlled manner, allowing the batteries’ functionality to be evaluated.
Many test cell designs are energy wasters. Older technologies like water brakes, fan brakes or eddy current devices, for example, convert kinetic energy from the testing process to heat. Replacing these methods with a regenerative drive system can allow this wasted energy to be recaptured and returned to the power grid. In addition to reducing your carbon footprint, a solid-state drive system will quickly pay for itself in power bill savings. Energy saving features exist even within the drive system, like smart ventilation in the AC890PX series that senses internal temperature and adjusts fan speed to save energy when the unit is lightly loaded, or in cooler ambient temperatures.
Parker regenerative drives can harvest energy from the testing process and return it to the power grid, providing a substantial net reduction in a plant’s electric use. Older dynamometers that are widely in use simply burn off the excess power and dissipate it as heat, which is wasteful of resources. In the grand scheme of things, our engineering expertise in special equipment for electric and hybrid vehicle manufacturers contributes to these vehicles being efficiently manufactured and sold, resulting in less polluting gas and diesel-powered vehicles on the road.
Parker can provide a drive/control retrofit that will allow you to keep your existing mechanical equipment and enjoy more efficient operation. And, in many cases, better performance, and have the knowledge that the drive/control system is up to date and serviceable.
For example, if you have an existing test cell using DC motors as prime movers or absorbers, and do not wish to upgrade to AC technology, the DC590+ digital DC series is a flexible and economical solution for test rigs through 2000 HP. Replace your obsolete SCR units with the latest in digital DC to eliminate costly repairs and downtime, with the added benefit of IoT capabilities.
For OEMs of vehicle test stands who are looking to expand into new markets of electric and hybrid vehicle manufacturing, Parker can provide custom or specialized drive and control systems that meet the unique testing needs of these vehicles. For those competing in the more traditional markets, Parker draws from over 30 years of experience in drives and controls to provide systems that are compact, easy to maintain, and energy efficient.
Have a dynamometer application or just want to learn more? Download our Test Stands and Dynamometers Solutions brochure.
Article provided by Lou Lambruschi, marketing services manager for Parker's Electromechanical and Drives Division.
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When it comes to linear actuators, selecting the right drive technology can be a precise balancing act as there is no ‘one size fits all’ solution.
Due to the breadth of applications – from automated packaging lines and pick-and-place operations to complex machines such as 3D printers – making the correct choice is less about concentrating on a single aspect than finding the optimum balance of performance from a variety of different factors.
Most electromechanical linear actuators rely on one of five common drive train types: ball screws, lead screws, timing belts, rack and pinion tracks and linear motors.
Ball screws are ideal for high duty cycle applications and where high force density, precision and repeatability are required. The rolling ball bearings reduce friction and deliver high mechanical efficiency, even in continuous use. Ball screws can achieve moderate speed.
Lead screws are suitable for low duty cycle applications, or those requiring small adjustments. They typically only offer about half the efficiency of ball screws, so require twice the torque to achieve the same thrust output. However, lead screws provide cost-efficient and compact solutions for high-force applications.
Timing belts are simple, robust mechanisms for high-speed applications requiring long life and minimal maintenance, where precision greater than 100 microns is sufficient. They are efficient and easy to operate and can run at 100 percent duty cycle. Timing belts are available in longer lengths than screw drives.
Rack and pinion systems are useful for very long travels requiring high speed but are not known for their precision. They offer high force density but require regular system lubrication. In addition, removing system backlash from this type of drive train is not always possible, and they can be quite noisy in operation.
Linear motors offer high speed, acceleration and precision. Cost is the principal drawback, while force density is also less than other drive systems. The absence of a mechanical connection between the moving and static components of linear motors makes their use difficult in vertical applications.
The selection options for a linear drive can be grouped into the following categories: precision, expected life, throughput and special considerations (PETS).
For precision, always start with an understanding of needs relative to resolution. The other considerations are repeatability and velocity control. Linear motors and ball screws are typically best in terms of precision characteristics.
With lifespan, mechanical efficiency is the primary consideration, unless the requirement is for a dirty or harsh operating environment. High drive train efficiency is synonymous with long life and reduced energy consumption. Factors such as wear resistance, dirt resistance and maintenance requirements are also important. Due to their high efficiency and limited maintenance needs, timing belts are the go-to option in this category.
Throughput can be considered by first scrutinising the speed and acceleration or deceleration characteristics of each technology – depending on the length of linear travel required. If the need is for longer travel where more of the cycle time is spent at top velocity, speed is the most important. If shorter moves are required, acceleration and deceleration characteristics will take precedence. Linear motors are unparalleled when it comes to throughput.
Some other considerations to take into account when looking at each technology include material and implementation costs, while force density is a further increasingly important factor to bear in mind as machine designs continue to miniaturise, particularly when specifying end effectors or tooling mounted to an axis.
For more information about the four key performance characteristics to consider when choosing a linear drive train from our white paper click here to download.
Article contributed by Olaf Zeiss, product manager, Actuators Electromechanical & Drives Division Europe.
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Select the Right Drive Train Technology for 3D Printing Precision Linear Motion Systems
In a world of constant technological advances, the photonics industry is seeing rapid growth with no signs of a slow-down. Photonics is the branch of technology concerned with the properties and transmission of photons. Photons are applications involving a laser. Lasers often conjure up images of an evil scientist plotting to destroy an unsuspecting city with a “laser death ray.” To the contrary, laser applications are commonly used in many markets to improve the quality of life – think healthcare or autonomous cars.
Applications in the photonics industry usually require a precise motion control system to function properly. In addition to these sub-micron specifications, many applications require high speeds and long lengths of travel. To meet these requirements, a linear motor stage is usually the best option. Parker offers a range of linear motor stages to satisfy these application needs. From miniature linear stages such as the miniature square rail, mSR, to completely custom designs, we can provide the linear stage that provides speed and precision.
Parker’s product and expertise in this area were on display at SPIE/Photonics West Exhibition, the world’s largest photonics technologies event in January in San Francisco. Parker displayed XY custom systems made of linear motor stages to simulate performance in laser based applications including laser scribing/cutting and cellular scanning. Customer feedback reiterated the need and desire for these products out in the field. Products need to be fast and accurate while maintaining their Abbe errors (stiffness, smoothness and flatness). Parker has designed products specifically to provide Abbe specs above the industry standard along with the drives and controllers to complete the motion system, Learn more about Parker’s linear motor stages.
Other types of electromechanics also apply. Many applications still use a screw-driven stage on the Z-axis. Designers will choose this route since they usually do not require the precision or speed provided by a linear motor stage for this axis. The other advantage is that a magnetic counterbalance is not needed when the unit is not in use. Parker’s MX80S and MX45 series are ideal for these applications as they provide the needed precision at a reasonable price.