Category Archives: White Papers

Motion Control -What To Consider When Specifying A Linear Slide

Motion Control – Tutorial

Considerations when specifying a linear slide for a new or existing application.

By Mike Quinn • LM76

When a design engineer has fully defined a linear-motion application’s requirements regarding travel length, speed, force, and accuracy as well as repeatability, the next question to answer is this:

Does an off-the-shelf linear slide (or a stock linear slide from a catalog) fully satisfy the application?

motion control - lm76

Off-the-shelf linear slides are advantageous for their quick delivery and lower cost than that of custom components. No wonder most linear-motion designs do in fact employ off-the-shelf linear slides from various component and system suppliers.

motion control - linear stage

Motion Control Tutorial – Slotted vs. Slotless Motor Technology

motion control - tutorial

 

Motion Control – Tutorial Motor Technology

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 White Paper – Unlocking the Linear Motion Specification Query

Motion Control White Paper

Understanding the specifications needed to properly size my motion control application –  

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Santa Clarita, CA —– Motion Control Tutorial – Every motion control problem begins with a need to move a certain payload over a certain distance. However, there are many types of moves possible, and determining the right motion control solution may require some calculations to match the specifications found on a given motors data sheet. Most sales engineers will ask you for three basic questions when directing you to the proper motor or motion control solution. What is the stroke or displacement required What is the force or thrust required? At what duty cycle do you plan on operating the motor? Travel Distance The travel distance is the first piece of information needed to unlock any specification, because a solution to move a few microns would utilize different motion technology from an application requiring several meters of travel. In addition to understanding the total travel required, it would be necessary to determine whether the travel is oscillatory, constant velocity, or the motion profile is defined by a pick-and-place application. Oscillatory systems typically will move back and forth at a specific frequency or range of frequencies. While constant velocity systems either need to operate for a known distance or time at a constant velocity, or they need to get a payload up to a velocity, in these cases the distance and time to accelerate up to the velocity needs to be understood and accounted for in the overall displacement. With this information you can determine the acceleration necessary to make the move. To learn more about calculating acceleration you can read our white paper about calculating acceleration for linear motion. Force

The next step is determining the amount of thrust or force required. Force is simply the amount of acceleration multiplied by the mass of the moving object. If the motion is horizontal, this equates to the mass of the payload added to the mass of the moving part of the linear motor or stage and multiplied by the amount of acceleration required by the motion. Vertical applications must add or subtract the acceleration due to gravity depending on the direction of motion.

motion control specification formula Duty Cycle

Finally, how long is power going to be applied to the motor? Many oscillatory systems will be operating continuously, and thus would have a duty cycle of 100%, while other applications will be short bursts of power, 1 second or less, while being off for several seconds, and will have a duty cycle of less than 10%. Duty cycle is defined as the time on divided by the total time per cycle (time on + time off). Depending on the linear motor selected, the amount of force available at a duty cycle of 10% can be as much as 3 times the continuous force rating. This last piece of the puzzle helps break down the necessary components required to properly size any motion control problem.

motion control specification formula - Duty Cycle

Once these three pieces are determined, any application can be sized and verified that it is sufficient based on the specifications found on any standard data sheet.   About H2W Technologies, Inc. H2W Technologies, Inc. is dedicated to the design and manufacture of linear and rotary motion products that are used in the motion control industry. The complete line of linear electric motors includes: Single and dual axis linear steppers, DC brush and brushless linear motors, voice coil actuators, and AC induction motors. Also offered is a complete line of ball screw, lead screw and belt driven positioning stages. Other motion control products include: Limited angle torque motors for compact, limited angular excursion rotary servo applications, 3 phase brushless rotary servo motors with matching digital servo amplifiers and permanent magnet linear brakes for fail-safe, zero power braking for baggage handling and people moving applications as well as amusement park rides. With over 75 years combined experience in the linear and rotary motion field, the H2W Technologies team of engineers offers the optimal solution to the most demanding motion control, requirements. For other Motion Control Components, Applications, and Technology from H2W Technologies visit: http://MotionShop.com For additional information contact Mark Wilson at H2W Technologies, 26380 Ferry Ct, Santa Clarita, CA 91350; Tel: 888-702-0540, Fax: 661-251-2067, E-Mail: info@h2wtech.com or visit the website at http://www.h2wtech.com  

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Linear Bearing Engineers Design Camera Sliders for the Pro and Beginner!

Designed by Linear Bearing Engineers Camera Sliders for the Beginner and the PRO

PRODUCTS | CONTACT US | NEWS | VIDEOS | Designer Spotlight | Artist Spotlight | NEW SLIDER

The difference between rolling and sliding friction in camera sliders. Mike Quinn

Take a quarter and roll it on its edge across a table – goes forever and moves quickly. Now take that quarter and lay it on its side and push it…that’s the difference. Sleeve bushings inherently have much more surface area under load. Simply put, they have big feet. Conversely, a ball and roller have much smaller feet ensuring them a meaningfully lower co-efficient of friction. A ball offers point contact loading and loosely reside in 4 rows within a steel or plastic shell:

ball

These balls literally kick each other along as the balls roll down the shaft. Because they have so little contact area, the coefficient of friction is as low as .001 – they roll easily and smoothly. The drawbacks in a camera slider are readily recognizable:

1. Resonance – noise – ZING! ZING! ( Metal on metal contact and because they push each other from load to preloads, they create resonance, noise and vibration.
2. They are made from steel and can rust – they require lubrication.

Rollers have internal ball or needle bearings at their core, between the inner and outer race. They are separated in a retainer, unlike linear ball bushings which run loose in their track ways.

roller roller

These are sealed and lubricated for life. They have more contact area but the coefficient of friction remains low approximately .003 – not as low as the ball – but very close. These rollers come in dual angular contact ( gothic arch ) or V geometries. They are very smooth, take high loads/moment loads ( overhanging loads )and provide great stiffness. They are however steel and they run on steel shafting or V groove rails. They can produce noise and are vulnerable to the elements.

Plastic Sleeve Bearings are truly all weather and can run very smoothly and tolerate debris. However, the real world coefficient of friction is around .2 – factors higher than ball and rollers. They are also prone to a phenomena called edge loading. This effect can cause the carriage plate ( slider ) to ratchet or get sticky due the bearings digging into the shaft. This is particularly troublesome when you attempt to slide the carriage plate with top heavy rigs like a DSLR with a Red Rock system. You will need two hands.

There is an answer…Camera Motions new ” Silent Slider “

Why? Because we offer a solid, 1 piece precision machined aluminum carriage block that is black anodized. Not an extrusion that is cheap and has varying tolerances one lot to another. We have selected the best industry urethane cam followers with needle bearing rollers – tight and true. Moreover, the rollers damp any noise or vibration yet hold a 25 pound load. Smooth, quiet and solid. The Silent Slider is a product of linear motion engineering – pure and simple. It was was designed to run on a 16mm twin extruded rail which is ubiquitous in the the camera slider industry. Keep your rail and tripod shoe and move to the future – The” Silent Slider!”

Let engineering win – not salesmen. Only $ 230.00. Call Mike Quinn @ 1-800-698-5820.

Motion Control Technology – Have You Considered a “Torquer?”

Santa Clarita, CA – Motion Control Technology – The Limited Angle Torque Motors or “Torquers,” technology explained: A current carrying conductor placed in a magnetic field will have a force (or torque) exerted on it. This force is proportional to the direction and magnitude of the current and the flux density field. Since the permanent magnet flux density field is fixed, the direction of the rotation depends on the polarity of input current and the amount of torque that is produced is directly proportional to the magnitude of the input current.

A DC linear servo amplifier is required to provide power to the torquer.

The torquers are typically supplied unhoused without bearings or a shaft, but can be supplied housed if required.

Coupling the torquer to your bearing system and a rotary encoder or other feedback device yields a system that is capable of intricate angular position, velocity, and acceleration control.

Low moving inertia of the rotor assembly allows for high angular acceleration of the payload.

The small length to diameter ratio allows the torquers to fit in spaces where conventional rotary brush and brushless DC motors will not.

It should be noted that, angular excursions of greater than 180º (up to 360º) can be achieved by modifying the winding of the stator assembly. In this case the coil assembly will have 4 leads and it will have to be commutated.

See below for a typical Torque vs. Displacement curve for a 4 pole LAT:

Advantages:

 

  • No Torque Ripple
  • High Angular Acceleration
  • No Commutation
  • Brushless
  • Low Profile

 

Applications:

 

  • Aerospace
  • Semiconductor
  • Medical
  • Military<

 


H2W Technologies offers 2 distinct types of limited angle torque motors.

1. MR Series Limited Angle Torque Motor – is a toroidally wound iron core stator with a 2 ,4 or 6 pole permanent magnet rotor. This torque motor can provide angular excursions up to 180º. It is typically supplied without bearings, shaft or housing to allow for direct mounting to customer supplied bearing system.

Linear Motion Technology - Torque Motors or Torquers from H2W
The MR Series is comprised of a toroidally wound, stationary, coil assembly with a multi-pole permanent magnet rotor.

Rotor: The rare earth permanent magnet rotor always has an even number of poles, with any where from 2 to 6 poles. The maximum angular excursion with a 2-pole rotor is 180º, with a 4 pole rotor is 90º, and with a 6 pole rotor is 60º. The torque will drop off to zero at the extreme ends of the travel. For constant torque over the required rotation, the angular excursion will always be less than numbers mentioned above.

The rotor assembly is installed within the ID of the stator assembly. There is a magnetic attractive force between the stator and the rotor. When the stator is perfectly concentric within the rotor, the radial magnetic attractive forces are equal and opposite and they cancel each other out.

Stator: The stator is comprised of a “soft”magnetic steel toroid that is electrically insulated. Multiple sections of insulated copper magnet wire are toroidally wound on the stator toroid. Only 2 leads are brought out from the stator assembly.

The rotor assembly is installed within the ID of the stator assembly. There is a magnetic attractive force between the stator and the rotor. When the stator is perfectly concentric within the rotor, the radial magnetic attractive forces are equal and opposite and they cancel each other out.

2. WR Series Limited Angle Torque Motor – is an arc segmented multipole permanent magnet stator with a low inertia copper magnet wire rotor. Angular excursions are typically less than 90º. This torquer is supplied with out a shaft or bearing.

Linear Motion Technology - Torque Motors from H2W
The WR Series is comprised of a stationary, arc segmented, multipole permanent magnet stator assembly with a low inertia wound wire rotor.

Rotor: The rotor is made up of a single coil of bondable copper magnet wire. The coil is wound and preformed into the desired shape. It is held together with the bonding agents in the wire. It can be encapsulated with aluminum or plastic brackets in order to provide a means for mounting the rotor to the bearing system and payload. The maximum angular excursion is less than 90º.

Stator: The stationary stator assembly consists of multipole permanent magnets that are bonded to steel plates. The 2 opposing steel plates are spaced apart to provide a gap using end plates. The coil rotor assembly moves angularly within this gap. There is no magnetic attractive force between the stator and the rotor.

The WR Series Torquers are available in 2 configurations.

The low profile (Type L) configuration has a smaller overall height which allows it to fit in a more compact space, but has less angular rotation for a given stator arc segment.

The second configuration (Type S) has a larger overall height but has typically twice the angular rotation per given stator arc segment when compared to the Type L torquer.

    • No Torque Ripple
    • High Angular Acceleration
    • No Commutation
    • Brushless
    • Low Profile

 

About H2W

H2W designs and manufactures a wide range of linear motors, positioning stages, and fully integrated single and multi-axis positioning systems. We will be happy to assist you with a custom design if you do not find a standard product that meets your needs.

Our Products

Voice Coil Linear Actuators, Single Axis Linear Stepper Motors, Dual Axis Linear Stepper Motors, AC Linear Induction Motors, DC Linear Brushless Motors, DC Linear Brush Motors, Limited Angle Torque Motors, Permanent Magnet Brakes, Motion Control System Integration, Voice Coil Positioning Stages, Linear Stepper Stages, Single Rail Stages, Dual Rail Stages, Air Bearing Stages, Cross Roller Stages, Belt Stages, Lead Screw / Ball Screw Stages, Multi-Axis Gantry Stages

Industries Served

Semiconductor, Medical, Military, Aerospace, Material Handling, People Moving, Amusement Park Rides, Packaging, Automotive, and Clean Room.

 

26470 Ruther Ave #102 | Santa Clarita, CA 91350
661-251-2081 | 888-702-0540 Toll Free | info@h2wtech.com | www.h2wtech.com