Motion Control Tutorial – Slotted vs. Slotless Motor Technology

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When first introduced, brushless DC motors, despite their many advantages, were cast as a costly alternative to brush-commutated motors and were typically only specified for low-power applications where long life was the primary desired requirement. Without the mechanical brush-commutator mechanism that would wear and eventually result in motor failure, brushless motors could be relied upon to deliver performance over time. As for other advantages, conventional wisdom held that brushless motors provide high speed and fast acceleration, generate less audible noise and electromagnetic interference, and require low maintenance. Brush-commutated motors, on the other hand, would afford smooth operation and greater economy. In the past decade, though, brushless motors have gained broader appeal and greater acceptance in industry for a wider range of applications previously dominated by brush-commutated products, due in part to dramatic reductions in the cost and size of electronic components and advances in motor design and manufacturing.

At the same time, manufacturers have further sought to challenge conventional wisdom by improving brushless motor design in an effort to combine the traditional advantages of brush-commutated and brushless types. A noteworthy example of how far these innovations have progressed involves the slotless (instead of slotted) construction of the brushless motor’s stationary member, or stator.

The slotless stator design originated with the goal to deliver smooth running performance and eliminate cogging, which is an unwanted characteristic especially in slower-running applications (less than 500 rpm). The absence of cogging is, in fact, the most-often cited reason for selecting a slotless brushless motor.

Slotted Motor Construction

Most brushless motors (slotted or slotless) use electronic commutation, usually Hall-effect sensors and magnets, in place of brushes. The motor’s rotor consists of a steel shaft with permanent magnets or a magnetic ring fixed around the circumference of the shaft. The magnets are responsible for producing torque. As the flux density of the magnet material increases, the amount of torque available from the rotor assembly increases.

In traditional slotted brushless motors, the stator features a group of slotted steel laminations (0.004 in. to 0.025 in. thick), which are fused to form a solid uniform stack and create a series of teeth. Wound copper coils, which produce electromagnetic fields, are then inserted into each of the slots. Together, the laminated stack and wound copper coil form the stator assembly. The return path completing the magnetic circuit consists of the laminated material outboard of the copper windings in the stator and the motor housing.

These brushless slotted motors are especially powerful, because the teeth around which the copper wire is wound place the iron closer to the magnets, so the magnetic circuit is completed more efficiently. As the air gap between iron and magnets is reduced, the torque available for the motor is increased.

However, slotted stators are known to cause cogging, which is attributed to the teeth in their construction. Cogging occurs when the permanent magnets on the rotor seek a preferred alignment with the slots of the stator. Winding copper wires through the slots tends to increase this effect. As magnets pass by the teeth, they have a greater attraction to the iron at the ends of the teeth than to the air gaps between them. This uneven magnetic pull causes the cogging, which ultimately contributes to torque ripple, efficiency loss, motor vibration, and noise, as well as preventing smooth motor operation at slow speeds. A slotless stator offered a solution to the problems experienced with cogging in slotted brushless DC motors.

Advantage of the BLDC Slotted Motor Technology

The main advantages of the slotted technology are:

  • ease of winding customization
  • increased heat dissipation
  • ability to withstand high peak torque
  • high power density

Slotted Motor Applications

The Slotted Motor is ideal for applications such as:

  • Medical Hand Tools
  • Hand held shaver system for arthroscopic surgeries
  • High speed surgical drills for ENT surgeries

Slotless Motor Construction

Instead of winding copper wires through slots in a laminated steel stack as in conventional slotted brushless motors, slotless motor wires are wound into a cylindrical shape and are encapsulated in a hightemperature epoxy resin to maintain their orientation with respect to the stator laminations and housing assembly. This configuration, which replaces the stator teeth, eliminates cogging altogether and results in desired quiet operation and smooth performance.

The slotless design also reduces damping losses related to eddy currents. These currents are weaker in a slotless motor, because the distance between the laminated iron and magnets is greater than in a slotted motor.

Slotless motors are typically designed with sinusoidal torque output that produces negligible distortion, rather then a trapezoidal voltage output. The sinusoidal output reduces torque ripple, especially when used with a sinusoidal driver. Because the slotless design has no stator teeth to interact with the permanent magnets, the motor does not generate detent torque. In addition, low magnetic saturation allows the motor to operate at several times its rated power for short intervals without perceptible torque roll-off at higher power levels.

Compared with slotted motors, slotless construction also can significantly reduce inductance to improve current bandwidth. The teeth in a slotted motor naturally cause more inductance: the coils of copper wire around the teeth interact with the iron in a slotted motor, and this interaction tends to send the current back on itself, resulting in more damping (or dragging) and impacting negatively on slotted motor response and acceleration.

In terms of delivering power, conventional slotted motors used to enjoy the advantage over slotless types, due (as noted) to the proximity of iron and magnets and the reduced air gap.

However, this advantage has virtually evaporated, in large part due to the utilization of high-energy, rare-earch magnets (such as samarium cobalt and neodymium iron boron). By incorporating these magnets, manufacturers of slotless brushless motors have been able to routinely compensate for the greater air-gap distance. These more powerful magnets effectively enable the same (or better) torque performance for slotless products compared with slotted. Eliminating the teeth and using stronger magnets both serve to maximize the strength of the electromagnetic field for optimum power output. Rare-earth magnets, along with the fact that fewer coils, or “turns,” of the wire are required in slotless motors, also help contribute to low electrical resistance, low winding inductance, low static friction, and high thermal efficiency in slotless motor types.

One more important difference between slotless and slotted designs is the rotor diameter. Slotless motors have a larger rotor diameter than slotted construction for the same outside motor diameter and will generate a higher inertia, as well as accommodating more magnet material for greater torque. For applications with high-inertia loads, the slotless product is more likely to be specified.

Slotless Motor Applications

In general, brushless motors are usually selected over brushcommutated motors for their extended motor life. (While motor life is application-specific, 10,000 hours are usually specified.) Other reasons for specifying brushless motors include a wide speed range, higher continuous torque capability, faster acceleration, and low maintenance.

In particular, slotless versions of brushless DC motors will suit those applications that require precise positioning and smooth operation. Typical niches for these motors include computer peripherals, mass storage systems, test and measurement equipment, and medical and clean-room equipment.

As examples, designers of medical equipment can utilize slotless motors for precise control in machines that meter and pump fluids into delicate areas, such as eyes. In medical imaging equipment, slotless brushless DC motors decrease banding by providing the smoother operation at low speeds. Airplane controls supply smoother feedback to pilots. And, by eliminating cogging and resulting vibration, these motors can reduce ergonomic problems associated with hand-held production tools. Other appropriate applications include scanners, robots for library data storage, laser beam reflector rotation and radar antenna rotation equipment, among many others./span)

Customization Options

Slotless brushless DC motors, as with most motors today, feature a modular design so they can be customized to meet specific performance requirements. As examples, planetary or spur gearheads can be integrated on motors for an application’s specific torque and cost requirements. Planetary gearheads offer a higher-torque alternative. Slotless motors can further be customized with optical encoders, which provide accurate position, velocity, and direction feedback that greatly enhances motor control and allows the motors to be utilized in a wider range of applications. As a low-cost alternative to optical encoders, rotor position indicators (ie. Hall Sensors) can be specified.

When using optical encoders, differential line drivers can be utilized to eliminate the effects of electrically noisy environments. Differential line drivers are designed to ensure uncorrupted position feedback from the encoder to the control circuit.

Motor Selection Guided by Application

Despite the overall design and performance comparisons reviewed here for slotless and slotted brushless DC motor types, one should remain cautious in drawing any conclusion that one type is the ultimate choice over the other. There are simply too many variables that must be evaluated, ranging from rotor size and windings to housing and special components. A given application and its requirements should (and will) be the guiding factors in selecting a particular motor type and the customized components to be incorporated.

Some encouraging news in those applications that would clearly benefit from a slotless brushless motor is that costs are coming down to be more in line with those for slotted motors. This is because of new streamlined manufacturing techniques and an increasingly available supply of powerful magnets, which are both beginning to have a positive impact on end-product costs.

Regardless of any cost differential, however, for many applications, slotless brushless DC motors will be the preferred choice to resolve specific requirement issues. While advances in electronics are beginning to be applied that promise to reduce normal cogging in slotted products as a step toward making these motors more smooth running and quiet, the industry is not there yet: slotless motors remain the best alternative where cogging and life are defining performance issues

This Tutorial and other Motion Control Tutorials are available through www.Servo2Go.com

For further information on this new product or others in our extensive product portfolio, call 1- 877-378-0240 or e-mail Warren Osak at warren@servo2go.comor visit Servo2Go.com at: www.Servo2Go.com

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Motion Control – Custom Linear Mechanisms

Custom Linear Mechanisms from Steinmeyer …

Welcome to Where Precision Is.  You Can Turn to Steinmeyer for Design and Assembly of Custom Linear Mechanisms for your Precision Positioning Systems
Modern mechatronic systems consist of numerous precision components that must be assembled in complex configurations. Here, every detail counts.Steinmeyer Mechatronik, a division of August Steinmeyer GmbH, offers design and assembly services for a variety of demanding applications.We have deep experience in medical devices, laboratory instrumentation, optical inspection & semiconductor positioning. Our engineers can implement your finished design or optimize your concept.

For Example …


Motion Control Linear Stage

Demanding series production for a medical instrument

The task was to develop a motion unit for a computer tomography scanner which moves tungsten collimators during X-ray source rotation so that the X-ray beam can be adjusted to the minimum radiation dose required. The assembly itself is continuously moved in a circular path around the patient during use. A special challenge was the high acceleration caused by the rotation on a large diameter transverse to the direction of movement. This additional load requires a particularly stable construction with minimal potential for error.

Highest stability and reliability

Since this is used in a durable medical device, the requirements for functional safety and reliability are very high. The positioning system has been tested for three million application cycles and has proven this claim with statistical certainty in an endurance test.

CLICK HERE to see this solution and others from Steinmeyer Mechatronik

Steinmeyer has decades of experience in precision assembly. All of our systems, whether single or multi-axis, are manufactured carefully. Our high standards, monitored continuously through vigorous quality systems, are evident in every assembly we produce. We pay attention to every detail.


Trust Steinmeyer With Linear Mechanism Solutions:

    • We can assemble custom linear mechanisms of all sizes – from miniature actuators using 3 mm linear rails, to 3 m long lifting mechanisms.
    • As an added value, our engineers will offer innovative ideas for optimizing your design.
    • We can quote a completely assembled module, including sourcing of key components!
    • We offer our customers the advantage of a close working relationship, enabling us to provide you with the best possible solution to meet your needs.

Contact Person for Custom Linear Modules

Bruce Gretz

Phone: 781-273-6220

Bruce Gretz   bruce.gretz@steinmeyer.com

About Steinmeyer

In the realm of linear motion control, Steinmeyer is synonymous with precision, innovation, and exacting standards of quality. We are the world’s longest continuously-operating manufacturer of commercial ball screws, our main product line. As an added value, we offer customized linear modules from our highly innovative and experienced Mechatronik division. Designed and manufactured in Germany, our products are used globally in precision positioning for medical devices, lab instruments, and other mechatronic applications. Steinmeyer engineers will work closely with you to customize our offering to deliver a solution that meets your technical requirements and budget.

For further information on Steinmeyer our extensive product portfolio, call 1-781-273-6220 or e-mail Rosemary Belt at rosemary.belt@steinmeyer.com or visit the Steinmeyer FMD group at: www.steinmeyer.com

 

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Motion Control – A Powerful and Cost-effective Drive from Maxon!

Motion Control Components – Maxon motors introduces the brushless EC-i 30 motor.

motion control Maxon ECi 30 Brushless DC motors

 

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Fall River, MA — Motion Control Components – Miniature Motors – Several different versions of the high-torque, brushless EC-i motors from maxon motor are now available in small diameters. They are perfect for hand-held devices and robotic applications.

With the EC-i 30, maxon motor is introducing a new brushless DC motor. It has a diameter of 30 millimeters and is smaller than the EC-i 40 currently available. This motor stands out for its high dynamics, low cogging torque, and high torque. It is available in two lengths, each in a Standard and a High Torque version, with a maximum nominal torque of up to 110 mNm at 75 W.

Many possible combinations

Despite their impressive performance, EC-i 30 DC motors are a cost-effective alternative to existing drives. The compact design is especially suitable for hand-held devices and for robotic applications

All versions of the new EC-i 30 motors may be combined with encoders, gearheads, and servo or positioning controllers from maxon motor – quickly and easily in the maxon online shop: shop.maxonmotorusa.com

Comprehensive documentation and software are included with every delivery, and are also available for you to download from our website at www.maxonmotor.com.

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Water Dog Sliders from LM76 are FDA/USDA/3-A Dairy Compliant!

The Engineering Edge - FDA/USDA/3-A Dairy Compliant Linear Slides
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About LM76 and “The Engineering Edge”

Founded in 1976, LM76 has been a leading designer/manufacturer of linear bearings, slides and linear motion systems. LM76 is renowned for its industry leading Minuteman PTFE Composite linear bearings. LM76 is a leading supplier of precision linear shafting: RC60, 300 Series Stainless Steel, and ceramic-coated aluminum shafting. LM76 also offers several FDA/USDA compliant linear bearings and slides for the food processing, pharmaceutical, medical, and packaging industries.

When others think catalog …   … LM76 thinks solution!

For additional information contact Mike Quinn at: LM76, 140 Industrial Dr., E. Longmeadow, MA 01028; Telephone: 413-525-4166, Fax: 413-525-3735 or E-Mail: mquinn@lm76.com or visit the website at http://www.lm76.com

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Motion Control – 35mm diameter CBL35C Programmable Electric Moving Coil Servo Actuator Available from Electromate!

 

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With outer diameters of only 43mm to 90 mm, these frameless brushless servo motors are extremely compact. 

 

Vaughan, Ontario, Canada — Motion Control Components — Introducing the 35mm diameter CBL35C electric cylinder with built-in controller from SMAC Corporation. With its built-in controller, the CBL35C controls force, position and velocity and features simple installation.

Ideal for applications with limited space but requiring accurate control, the CBL35C provides significantly longer life, programmability, high speed, accuracy, and energy efficiency while remaining price-competitive.

The new CBL35C series also enables the direct replacement of existing pneumatic cylinders and retrofits without any machine modifications required.

It‘s Graphical User Interface allows for easy straightforward setup of parameters and permits the user to change product profiles on the fly thereby improving factory uptime.

Features:

  • Built-in controller
  • Programmable position, velocity and force
  • Long life expectancy over 100 million cycles
  • Airless and quiet operation
  • Graphical User Interface is available for simple set-up
  • Space saving

Specifications:

  • Dimensions [mm]: Ø35 x 135 – 217(depending on stroke)
  • Stroke [mm]: 10, 25 (+1/-0)
  • Acceleration[G]: up to 50 (zero payload)
  • Peak Force [N]: up to 61
  • Encoder Resolution [µm]: 5 (standard) 1 & 0.1 (Options)
  • SMAC’s Patented: ‘Soft-Land’ Technology

CLICK HERE Additional information on SMAC’s CBL35C Programmable Electric Moving Coil Servo Actuator

About Electromate:

Electromate’s Core Purpose is to help Manufacturers build better machines using differentiated automation technology. They specialize in Robotic and Mechatronic Solutions for the Industrial Automation marketplace. Respected by customers as a premiere source for High Performance Automation and Motion Control Components & Systems, Electromate® specializes in AC & DC Servo and Stepper Motors & Drives, Motion & Automation Controllers, Positioning Systems & Actuators, Feedback Devices, Gearing Products and HMI’s & Operator Displays, all supported via extensive product selection, just-in-timedelivery, dedicated customer service and technical engineering support.

More on Electromate can be found at

Website: http://www.electromate.com

LinkedIn: https://www.linkedin.com/company-beta/209277/

Twitter: https://twitter.com/Electromate

Facebook: https://www.facebook.com/electromateindustrial/

Google+: https://plus.google.com/104057418684128701566

Blog: https://electromate.wordpress.com/

To view Electromate’s new corporate video CLICK HERE

For further information on this new product or others in our extensive product portfolio, call 1-877-SERVO99 (737-8699) or e-mail Warren Osak at sales@electromate.com or visit Electromate at: www.electromate.com

 

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Motion Control – Custom Linear Mechanisms

Custom Linear Mechanisms from Steinmeyer …

Welcome to Where Precision Is.  You Can Turn to Steinmeyer for Design and Assembly of Custom Linear Mechanisms for your Precision Positioning Systems
Modern mechatronic systems consist of numerous precision components that must be assembled in complex configurations. Here, every detail counts.Steinmeyer Mechatronik, a division of August Steinmeyer GmbH, offers design and assembly services for a variety of demanding applications.We have deep experience in medical devices, laboratory instrumentation, optical inspection & semiconductor positioning. Our engineers can implement your finished design or optimize your concept.

For Example …

Zoom Unit

Sliding axes for the adjustment of two optics

Two lenses must be positioned relative to each other and also positioned together. Since the unit is exposed to stray radiation from the exposure process, lubrication must withstand these conditions in the long term. The basic solution consists of two sliding axes on a common guide system. Two moving sliding carriages have three carriages each, which allows them to move partially within each other in order to bring the lenses together as closely as possible. The drives consist of smoothened ball screw drives driven by a direct current motor with a rotary encoder. The motor encoder assembly is designed to be interchangeable for easy maintenance.

Designed for extremely dry environments

By choosing a PFPE-based lubricant and a special surface coating, the requirements for clean room compatibility and UV resistance were met. All accuracy-relevant parameters are verified by a measuring station after installation. This measuring station is located in the clean room and records accuracy, repeat accuracy, straightness, evenness and current consumption. Additional tests are performed to ensure minimum clearance in the bearing and smooth running of the drive system.

Steinmeyer has decades of experience in precision assembly. All of our systems, whether single or multi-axis, are manufactured carefully. Our high standards, monitored continuously through vigorous quality systems, are evident in every assembly we produce. We pay attention to every detail.


Trust Steinmeyer With Linear Mechanism Solutions:

    • We can assemble custom linear mechanisms of all sizes – from miniature actuators using 3 mm linear rails, to 3 m long lifting mechanisms.
    • As an added value, our engineers will offer innovative ideas for optimizing your design.
    • We can quote a completely assembled module, including sourcing of key components!
    • We offer our customers the advantage of a close working relationship, enabling us to provide you with the best possible solution to meet your needs.

Contact Person for Custom Linear Modules

Bruce Gretz

Phone: 781-273-6220

Bruce Gretz   bruce.gretz@steinmeyer.com

About Steinmeyer

In the realm of linear motion control, Steinmeyer is synonymous with precision, innovation, and exacting standards of quality. We are the world’s longest continuously-operating manufacturer of commercial ball screws, our main product line. As an added value, we offer customized linear modules from our highly innovative and experienced Mechatronik division. Designed and manufactured in Germany, our products are used globally in precision positioning for medical devices, lab instruments, and other mechatronic applications. Steinmeyer engineers will work closely with you to customize our offering to deliver a solution that meets your technical requirements and budget.

For further information on Steinmeyer our extensive product portfolio, call 1-781-273-6220 or visit the Steinmeyer FMD group at: www.steinmeyer.com

 

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Motion Control – Low Cost, Highly Reliable Solenoid Control Modules Available from OES!

motion control solenoid modules

 

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Van Nuys, CA – — Motion Control Components– – Optimal Engineering Systems, Inc. (OES) offers seven types of advance solenoid control modules including: Pick-and-Hold Driver, Proportional (PWM) Driver, Closed Loop Solenoid Process Control, Pick-and-Drop, Load On-Off Power Cycling, Dual Proportional Valve Controller, and Serially Controlled Solenoid Driver modules. Applications of these compact modules measuring just 3.000 in. x 3.000 in. include: Solenoids, valves, actuators (including Voice Coils), DC motors, electromagnets, hydraulics, LEDs, power amplifiers for electro-pneumatic proportional valves, and pressure and flow control valves.

To precisely fit an application there are multiple variations of each of the seven basic types of modules listed above to select from, for example: Single device – low side driver, two device – low side driver, single device – selectable low and high side driver, two device – selectable low and high side driver, +50 VDC or +80 VDC versions, currant versions, serially controlled, and Bi-directional load cycling versions to name just a few.

Stand features of these compact, low cost off-the shelf, modules are: High efficiency, microcomputer based, very high reliability, simple supply from +9 VDC to +50VDC, and High output current 15 Amps peak , 4 Amps RMS. The modules also incorporates a Flyback (Snubber, Freewheeling) Diode per Output device. For details on each type of module and all the variations available go to http://www.oesincorp.com/solenoidelectronics.htm.

Optional accessories are: Solenoid Commander card, Solenoid Control Module, DIN Rail Mounting Bracket, Track Ball and Joystick controllers, Solenoid Control System, and various solenoids. Additionally, all components can be order as a complete Plug-and-Play System.

About OES Optimal Engineering Systems, Inc. (OES) is a manufacturer of motion control products including: Stepper motor controllers and drivers, solenoid electronics, and positioning stages and slides. Applications include: Animation, automated assembly systems, automation, CNC machines, flight simulation, inspection systems, linear and rotary stages, machine tools, medical devices, motion control camera boom systems, optical comparators, CMMs, pan-tilt gimbals, PCB assembly & inspection, pick-and-place, positioning stages, robotics, scanners, security cameras, telescope drive mechanisms, time-lapse photography and winders

Some of the industries OES serves are: Aerospace, Astronomy, Chemical, Communications, Educational Institutes, University, Colleges, Government Agencies, National Labs, Manufacturing, Medical, Metrology, Military, Motion Control, Museum, News Agencies, Semiconductor and Test Equipment. Optimal Engineering Systems, Inc’s. competitive advantage is its state-of-the-art in-house manufacturing facility in North America enabling OES to supply clients with custom designed orders or high volume just-in-time deliveries globally.

For additional information contact Customer Service at Optimal Engineering Systems, Inc. (OES) , 6901 Woodley Ave, Van Nuys, CA 91406; Tel: 888-7071-1826, +1 (818) 222-9200, E-Mail: sales@oesincorp.com or visit the website at http://www.oesincorp.com

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Motion Control – Voice Coil Motor Features Higher Continuous Force and More Than 3 Times the Peak Force!

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Van Nuys, CA – Motion Control Components – Moticont has added a new, higher continuous force, higher peak force linear voice coil motor to it’s series of 2.750 in. (69.9 mm) diameter x 3.50 in. (88.9 mm) long (housing) voice coil motors. The LVCM-070-089-03 linear voice coil motor features 40.86 lbs. (181.5 N) continuous force and 129.1 lbs. (573.4 N) peak force. This clean, quiet, efficient, low inertia, high acceleration, brushless high speed linear motor has zero cogging and features high accuracy, and a high repeatability to less than1 micron (0.00004 in.) when operated in a closed loop as a DC servo motor

This compact, more powerful motor is ideal for: work holding and clamping, antenna positioning, medical devices, assembly, testing, laser machining and drilling, wafer handling, optical focusing, dynamic vibration absorption, scanners and laser beam steering and filtering. The LVCM-070-089-03 linear voice coil motor linear motor has a stroke length of 1.00 in (25.4 mm). and is easily added to new or existing applications using 10-32 UNC-2B mounting holes on each end of the motor which can be order as a complete plug-and-play system including an encoder and controller.

Is there a need for a smaller or larger diameter motor, one with longer travel, or more force? There are 12 series of Moticont’s LVCM series motors based on diameter of the motor, and over 50 models based on length of stroke and/or force to select from. To find the right motor for you application go to http://moticont.com/voice-coil-motor.htm

About Moticont – Moticont is a manufacturer of motion control products. Their product line includes voice coil motors, three phase brushless motors and positioning stages and slides.

Moticont is committed to exceeding Our customers’ quality expectations and industry standards throughout the design, manufacturing, service and technical support phases. Our modern manufacturing facility, highly controlled processes, committed staff, and extensive testing complement our product design strengths. This enables us to supply our clients with specialized small orders to high volume just-in-time deliveries.

We offer an extensive line of standard products ready to be shipped immediately from stock, and when standard products are not quite right for an application, highly trained design engineers are always available to develop custom motion control products to fit the specific needs or our customers.

For additional information contact Sales Team at Moticont, 6901 Woodley Ave, Van Nuys, CA 91406; Toll Free: +1 (888) 785-1804, Tel: +1 (818) 785-1800, moticont@moticont.comor visit the website at http://www.moticont.com

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Motion Control Tutorial – Slotted vs. Slotless Motor Technology

Motion Control Tutorial – Slotted vs Slotless 

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Motion Control Tutorial – When first introduced, brushless DC motors, despite their many advantages, were cast as a costly alternative to brush-commutated motors and were typically only specified for low-power applications where long life was the primary desired requirement. Without the mechanical brush-commutator mechanism that would wear and eventually result in motor failure, brushless motors could be relied upon to deliver performance over time. As for other advantages, conventional wisdom held that brushless motors provide high speed and fast acceleration, generate less audible noise and electromagnetic interference, and require low maintenance. Brush-commutated motors, on the other hand, would afford smooth operation and greater economy. In the past decade, though, brushless motors have gained broader appeal and greater acceptance in industry for a wider range of applications previously dominated by brush-commutated products, due in part to dramatic reductions in the cost and size of electronic components and advances in motor design and manufacturing.

motion control tutorial

At the same time, manufacturers have further sought to challenge conventional wisdom by improving brushless motor design in an effort to combine the traditional advantages of brush-commutated and brushless types. A noteworthy example of how far these innovations have progressed involves the slotless (instead of slotted) construction of the brushless motor’s stationary member, or stator.

The slotless stator design originated with the goal to deliver smooth running performance and eliminate cogging, which is an unwanted characteristic especially in slower-running applications (less than 500 rpm). The absence of cogging is, in fact, the most-often cited reason for selecting a slotless brushless motor.

Slotted Motor Construction

Most brushless motors (slotted or slotless) use electronic commutation, usually Hall-effect sensors and magnets, in place of brushes. The motor’s rotor consists of a steel shaft with permanent magnets or a magnetic ring fixed around the circumference of the shaft. The magnets are responsible for producing torque. As the flux density of the magnet material increases, the amount of torque available from the rotor assembly increases.

In traditional slotted brushless motors, the stator features a group of slotted steel laminations (0.004 in. to 0.025 in. thick), which are fused to form a solid uniform stack and create a series of teeth. Wound copper coils, which produce electromagnetic fields, are then inserted into each of the slots. Together, the laminated stack and wound copper coil form the stator assembly. The return path completing the magnetic circuit consists of the laminated material outboard of the copper windings in the stator and the motor housing.

These brushless slotted motors are especially powerful, because the teeth around which the copper wire is wound place the iron closer to the magnets, so the magnetic circuit is completed more efficiently. As the air gap between iron and magnets is reduced, the torque available for the motor is increased.

However, slotted stators are known to cause cogging, which is attributed to the teeth in their construction. Cogging occurs when the permanent magnets on the rotor seek a preferred alignment with the slots of the stator. Winding copper wires through the slots tends to increase this effect. As magnets pass by the teeth, they have a greater attraction to the iron at the ends of the teeth than to the air gaps between them. This uneven magnetic pull causes the cogging, which ultimately contributes to torque ripple, efficiency loss, motor vibration, and noise, as well as preventing smooth motor operation at slow speeds. A slotless stator offered a solution to the problems experienced with cogging in slotted brushless DC motors.

Advantage of the BLDC Slotted Motor Technology

The main advantages of the slotted technology are:

  • ease of winding customization
  • increased heat dissipation
  • ability to withstand high peak torque
  • high power density

Slotted Motor Applications

The Slotted Motor is ideal for applications such as:

  • Medical Hand Tools
  • Hand held shaver system for arthroscopic surgeries
  • High speed surgical drills for ENT surgeries

Slotless Motor Construction

Instead of winding copper wires through slots in a laminated steel stack as in conventional slotted brushless motors, slotless motor wires are wound into a cylindrical shape and are encapsulated in a hightemperature epoxy resin to maintain their orientation with respect to the stator laminations and housing assembly. This configuration, which replaces the stator teeth, eliminates cogging altogether and results in desired quiet operation and smooth performance.

The slotless design also reduces damping losses related to eddy currents. These currents are weaker in a slotless motor, because the distance between the laminated iron and magnets is greater than in a slotted motor.

Slotless motors are typically designed with sinusoidal torque output that produces negligible distortion, rather then a trapezoidal voltage output. The sinusoidal output reduces torque ripple, especially when used with a sinusoidal driver. Because the slotless design has no stator teeth to interact with the permanent magnets, the motor does not generate detent torque. In addition, low magnetic saturation allows the motor to operate at several times its rated power for short intervals without perceptible torque roll-off at higher power levels.

Compared with slotted motors, slotless construction also can significantly reduce inductance to improve current bandwidth. The teeth in a slotted motor naturally cause more inductance: the coils of copper wire around the teeth interact with the iron in a slotted motor, and this interaction tends to send the current back on itself, resulting in more damping (or dragging) and impacting negatively on slotted motor response and acceleration.

In terms of delivering power, conventional slotted motors used to enjoy the advantage over slotless types, due (as noted) to the proximity of iron and magnets and the reduced air gap.

However, this advantage has virtually evaporated, in large part due to the utilization of high-energy, rare-earch magnets (such as samarium cobalt and neodymium iron boron). By incorporating these magnets, manufacturers of slotless brushless motors have been able to routinely compensate for the greater air-gap distance. These more powerful magnets effectively enable the same (or better) torque performance for slotless products compared with slotted. Eliminating the teeth and using stronger magnets both serve to maximize the strength of the electromagnetic field for optimum power output. Rare-earth magnets, along with the fact that fewer coils, or “turns,” of the wire are required in slotless motors, also help contribute to low electrical resistance, low winding inductance, low static friction, and high thermal efficiency in slotless motor types.

One more important difference between slotless and slotted designs is the rotor diameter. Slotless motors have a larger rotor diameter than slotted construction for the same outside motor diameter and will generate a higher inertia, as well as accommodating more magnet material for greater torque. For applications with high-inertia loads, the slotless product is more likely to be specified.

Slotless Motor Applications

In general, brushless motors are usually selected over brushcommutated motors for their extended motor life. (While motor life is application-specific, 10,000 hours are usually specified.) Other reasons for specifying brushless motors include a wide speed range, higher continuous torque capability, faster acceleration, and low maintenance.

In particular, slotless versions of brushless DC motors will suit those applications that require precise positioning and smooth operation. Typical niches for these motors include computer peripherals, mass storage systems, test and measurement equipment, and medical and clean-room equipment.

As examples, designers of medical equipment can utilize slotless motors for precise control in machines that meter and pump fluids into delicate areas, such as eyes. In medical imaging equipment, slotless brushless DC motors decrease banding by providing the smoother operation at low speeds. Airplane controls supply smoother feedback to pilots. And, by eliminating cogging and resulting vibration, these motors can reduce ergonomic problems associated with hand-held production tools. Other appropriate applications include scanners, robots for library data storage, laser beam reflector rotation and radar antenna rotation equipment, among many others./span)

Customization Options

Slotless brushless DC motors, as with most motors today, feature a modular design so they can be customized to meet specific performance requirements. As examples, planetary or spur gearheads can be integrated on motors for an application’s specific torque and cost requirements. Planetary gearheads offer a higher-torque alternative. Slotless motors can further be customized with optical encoders, which provide accurate position, velocity, and direction feedback that greatly enhances motor control and allows the motors to be utilized in a wider range of applications. As a low-cost alternative to optical encoders, rotor position indicators (ie. Hall Sensors) can be specified.

When using optical encoders, differential line drivers can be utilized to eliminate the effects of electrically noisy environments. Differential line drivers are designed to ensure uncorrupted position feedback from the encoder to the control circuit.

Motor Selection Guided by Application

Despite the overall design and performance comparisons reviewed here for slotless and slotted brushless DC motor types, one should remain cautious in drawing any conclusion that one type is the ultimate choice over the other. There are simply too many variables that must be evaluated, ranging from rotor size and windings to housing and special components. A given application and its requirements should (and will) be the guiding factors in selecting a particular motor type and the customized components to be incorporated.

Some encouraging news in those applications that would clearly benefit from a slotless brushless motor is that costs are coming down to be more in line with those for slotted motors. This is because of new streamlined manufacturing techniques and an increasingly available supply of powerful magnets, which are both beginning to have a positive impact on end-product costs.

Regardless of any cost differential, however, for many applications, slotless brushless DC motors will be the preferred choice to resolve specific requirement issues. While advances in electronics are beginning to be applied that promise to reduce normal cogging in slotted products as a step toward making these motors more smooth running and quiet, the industry is not there yet: slotless motors remain the best alternative where cogging and life are defining performance issues

This Tutorial and other Motion Control Tutorials are available through www.Servo2Go.com

For further information on this new product or others in our extensive product portfolio, call 1- 877-378-0240 or e-mail Warren Osak at warren@servo2go.comor visit Servo2Go.com at: www.Servo2Go.com

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Motion Control – High Performance Servo Gearbox is ideal for Cyclic or Continuous High Speed Applications!

Motion Control - Electromate offers GAM's Planetary Gearbox

 

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Motion Control Components – The SPH inline planetary gearbox available from Electromate is GAM’s latest solution for today’s demanding motion control challenges! 

Vaughan, Ontario, Canada — Motion Control Components — It is available in six frame sizes with nominal torque ratings from 15 to up to 900Nm. The SPH features precision cut helical gears that are ground for smoothness, quiet operation, and high accuracies. The face width of the SPH gears are up to 70% longer than the gears in comparable gearboxes on the market, which means more tooth contact and greater overall torque density. To carry the higher torques, SPH gears are case hardened which imparts strength deeper into the gear compared to nitriding which hardens just the surface. With several output configurations available, machine integration is simplified.

Motion Control - Electromate offers GAM's Planetary Gearbox

SPH Series Benefits

  • Helical Gearing
  • Lower backlashes
  • Lower noise levels
  • Smoother torque transmission.

CLICK HERE for additional information on the GAM SPG Gearbox

About Electromate:

Electromate’s Core Purpose is to help Manufacturers build better machines using differentiated automation technology. They specialize in Robotic and Mechatronic Solutions for the Industrial Automation marketplace. Respected by customers as a premiere source for High Performance Automation and Motion Control Components & Systems, Electromate® specializes in AC & DC Servo and Stepper Motors & Drives, Motion & Automation Controllers, Positioning Systems & Actuators, Feedback Devices, Gearing Products and HMI’s & Operator Displays, all supported via extensive product selection, just-in-timedelivery, dedicated customer service and technical engineering support.

More on Electromate can be found at

Website: http://www.electromate.com

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For more information on the “Best Place to Work”CLICK HERE!

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For further information on this new product or others in our extensive product portfolio, call 1-877-SERVO99 (737-8699) or e-mail Warren Osak at sales@electromate.com or visit Electromate at: www.electromate.com

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