Mechanical PT - Motion Control Tips

New high performance clutch brake for outdoor power equipment

March 8, 2019 By Miles Budimir Leave a Comment

Ogura has developed a new model, GT2.75, clutch brake for the outdoor power equipment market. This new clutch brake is patented both in and outside of the United States and offers engineers advantages in both design and cost over older designs currently on the market. The clutch incorporates a six hard rivet design in the backing plated field shell that resists separation due to vibration from gas and diesel engines. The new design also has a built-in connector for easy wire attachment. A simple mounting slot on both sides of the clutch makes for easy assembly.

The big advantage for the end user is when the brake plate wears, the plate can be flipped and the end user can gain additional wear cycles without having to replace the clutch. All units come with an integral key and high strength roll formed low inertia pulleys. To handle high inertia loads, a six-spring, 12-rivet design was used between the pulley and armature.

Ogura can build custom products as well modify existing standard models to fit specific application needs.

For more information, visit www.ogura-clutch.com.

High-torque synchronous belt for industrial applications

February 20, 2019 By Paul Heney Leave a Comment

Gates has introduced the PowerGrip GT4 belt, a newly designed ethylene elastomer (EE) high-torque synchronous belt for industrial markets.

The PowerGrip GT4 reflects Gates’ dedication to innovation in materials science and process engineering.Many of the elastomer synchronous belts in the market today are made using chloroprene, a material that has performance limitations. The new Gates PowerGrip GT4 belt construction replaces chloroprene with a special EE formulation that delivers much higher performance. The company pioneered ethylene elastomer technology with its line of Micro-V belts in automotive markets and applied that materials science technology to PowerGrip GT4 for industrial markets.

PowerGrip GT4 has the highest power-carrying capacity in the segment, a larger temperature range and improved chemical resistance. This allows for narrower drives and a broader range of applications to be served. For machine builders, this creates design flexibility and improves the ability to fit a belt drive into smaller spaces or to utilize more torque. Distributors can differentiate with a higher-performance offering and end-users running industrial drives as part of their operations experience a lower total cost of ownership. The improved performance characteristics also support additional market opportunities with the conversion of roller chain to belt drive solutions, enabling a transformation from a high-maintenance chain to a high-performance belt.

“PowerGrip GT4 extends the success we’ve had with the PowerGrip family of industrial belts over many years by upping the performance bar,” said Tom Pitstick, CMO and SVP of Product Line Management for Gates. “It’s right at home in heavy-duty industrial environments driving pumps, conveyor systems and other machinery where efficiency, reliability and high quality are required. PowerGrip GT4 belts eliminate the need for lubrication and maintenance, run quietly and reduce contamination risks, further extending our ability to replace traditional chain drives in key end markets.”

Gates will offer a full portfolio of PowerGrip GT4 belts in 8mm and 14mm tooth pitches, and lengths exceeding 6.5 meters. Samples are available now with full-scale production beginning in North America and Europe in Q2 2019, with Asia to follow later in the year.

Gates
www.gates.com

New flexible coupling from SDP/SI features vibration damping technology

February 7, 2019 By Miles Budimir Leave a Comment

Stock Drive Products/Sterling Instrument (SDP/SI) has debuted several new series of high-gain couplings. These Antivibration Flexible Couplings are designed for use with high gain servomotors. When a servomotor drives a mechanism, as in applications such as semiconductor manufacturing equipment, blood analyzers or high-speed printers, a change in direction causes a phenomenon called hunting. Hunting is vibration in the system that reduces transit time, making the equipment less efficient.

The Antivibration Flexible Coupling features a unique construction of vibration reducing rubber (FKM) molded with aluminum hubs. The resulting rubber lined finger-like structure allows for optimal torsional rigidity and damping. Three types are available in bore sizes 3 mm thru 16 mm, compact (S50GS2MA…), high-torque (S50GT2MA…), and long (S50GL2MA…). The sixty-one Antivibration Flexible Couplings are available as standard catalog items and can be easily purchased through the sales department or online at the SDP/SI E-Store. Detailed product specifications are available on the website.

SDP/SI offers a wide variety of mechanical component choices for the engineer, including a comprehensive selection of rigid and flexible couplings. “The addition of this new precision flexible coupling line provides our customers with the very best solution for use in high speed and high precision servo systems,” said Sr. Development Engineer, Mike Yandolino. “Providing position accuracy, vibration reduction, zero backlash, and quiet operation, this coupling will become the preferred choice for many applications” added Yandolino. The high torque capability of the coupling results in the ability to downsize the component used.

For more information, visit www.sdp-si.com.

New RH-N gearbox kits from Nabtesco Motion Control are pre-engineered offering

January 28, 2019 By Lisa Eitel Leave a Comment

Nabtesco Motion Control now offers pre-engineered RH-N gearbox kits. RH-N kits use the manufacturer’s newest RV-N series of gearboxes … to 20% smaller and 30% lighter than the original RV-E series. RH-N gearbox kits make for turnkey motion solutions that trim lead, engineering, and installation times. The RH-N directly bolts onto servomotors without the need of additional components, as the gearbox kits eliminate the need to manufacture and machine motor plates and housings.

More specifically, RH-N kits include an RV-N-series gearbox; oil seals and O rings; RH-N middle flange and RH-N motor flange; all necessary fasteners; and input pinion. In fact, the input pinion requires no machining … so installers can simply bolt the design together.

Suitable applications for the RH-N include and array of servomotor-driven designs … and in fact, Nabtesco’s value-added gearbox-kit solution works on all RV-N series gear reducers with standard ratios.

RH-N Kits are designed and manufactured in the U.S. with a two-week lead time on all non-stocked items … though one Nabtesco Motion Control objective for 2019 is to increase stock levels to allow for JIT delivery.

Nabtesco Motion Control can design and manufacture various configurations from the RV-N gearbox body. Fully assembled RH-N variations (in the form of fully completed assemblies of the kit and gearbox excluding grease) are available. Oil seals are properly installed and all bolts torqued to the proper specs.

Note: Nabtesco Motion Control RD2-S and RD2-R use legacy RV-E series gearboxes. The newer RV-N series comes in sizes that are far larger (for much higher maximum rated torques). The manufacturer anticipates a migration to the RV-N Series (and the RH-N kits) for two reasons:

RV-N series gearboxes are smaller, lighter and more powerful than the traditional RV-E series
Pre-engineered solutions help design engineers as detailed above

For more information on RH-N Kits (and to provide feedback or submit requests) visit this deep link on nabtescomotioncontrol.com.

FAQ: What are mechanical, fluid-power, and elastomeric material dampers?

January 22, 2019 By Lisa Eitel Leave a Comment

Vibration in industrial machinery often originates from imbalances inherent to motors, gearboxes, and other turning component that excites natural frequencies. Dampers in this context are components that counteract and often isolate the vibration source from the rest of the design or machine — to prevent its propagation of mechanical oscillation. Watch the recent video on this topic for a full explanation:

Passive vibration mitigation includes passive isolators — such as closed-cell foam slabs, metal coil or wave springs, wire rope isolators (common in military applications) and rubber machine mounts.

These reduce system natural frequency to less than that of excitation frequency… though to be clear, traditional springs and rubber have near-zero damping capabilities.

Precision passive isolators include negative-stiffness isolators, which decrease system natural frequency upon loading via a kinematic linkage of beam columns and springs … typically stacked in series for tilt, horizontal, and vertical motion.

In fact, many isolators do impart a small amount of damping. Some (including wire-rope isolators) also attenuate shock impact at sudden move ends, hard stops, and collisions without recoil — on conveyor e-brakes or axis stroke ends, for example.

In contrast with isolators, passive dampers (such as material slabs and mechanical linkages) change the kinetic energy of vibration into heat. Passive damping usually employs viscous fluids, viscoelastic materials, piezo elements, or simple magnetics.

Though not our focus here, active dampers include an array of electronically controlled force cancellers that employ a power source, sensors, and actuation to counteract vibration with disruptive interference … out of phase with the source vibration. These include:

Shocks containing magnetorheological fluid that stiffen to solid with controllable yield strength under an applied magnetic field in milliseconds

Image courtesy Wikimedia Commons

Powered piezoelectric elements affixed to the design frame at critical points to execute active countermotions and address vibration (usually detected by acceleration sensors) and under the control of a DSP.

On passive vibration damping — those in mechanical formats include tuned mass dampers that affix to machinery or structures to damp narrow frequency bands of vibration. Other options for passive mechanical damping are friction and piezoelectric action prompted by simple resistive shunt.

Passive vibration mitigation in fluid-power formats include hydraulic mounts, air springs, and bladders to isolate and damp industrial machines and other moving equipment. Passive air tables are another iteration, though increasingly displaced by other technologies. Gas springs (of the piston-type plunger design) act as kinematic holds.

Many pneumatic dampers have a similar structure — with a cylindrical chamber containing a piston and compressed air behind it — though work on moving axes. Oil dashpots employ a contained volume of fluid to resist motion with viscous friction to damp (though not isolate) vibration.

Last let’s consider passive vibration mitigation in elastomeric material formats — which offer simplicity in format and application. Foam slabs isolate well though lacks durability. Rubber and neoprene excel at isolation but not damping. In contrast, another option is viscoelastic Sorbothane material from Sorbothane Inc. that excels at vibration and shock control — absorbing up to 94.7% of the latter.

The material is classified as viscoelastic, as it exhibits both viscous and elastic characteristics when subject to deformation. A high delta tangent — also called the loss factor or damping coefficient — means Sorbothane out-of-phase time relationship between shock impact or vibration and force transmission. Sorbothane absorbs more than half the energies at 1 to 30,000 Hertz for powerful vibration damping … shedding the energy as heat (through hysteresis) and directing remaining energy perpendicularly — 90° out of phase from the vibration or shock source.

Formats abound … one includes layered blocks of Sorbothane that interlock — to let design engineers customize vibration-damping assemblies. The modular components include steel baseplates to keep their shape and boost column strength. For more information, visit sorbothane.com.

Zero backlash featured in Miki Pulley CSZ electromagnetic clutches

January 10, 2019 By Miles Budimir Leave a Comment

Miki Pulley’s CSZ electromagnetic clutches have a zero backlash design and provide an efficient connection between a motor and a load with low inertia, minimal drag and zero backlash.

CSZ clutches function using the magnetic force generated by the energized coil providing engagement of input and output members of the clutch. They feature an integrated bearing design making mounting fast and easy while ensuring application concentricity and excellent system runout. CSZ clutches operate well in temperatures from +14 to +104 °F (-10 to +40 °C).

Available in bores ranging from 10 to 15 mm, with brake torques ranging from 1.77 to 7.376 ft lb (2.4 to 10 Nm), the CSZ uses corrosion-resistant materials, and is RoHS compliant like all other Miki products.

“Miki Pulley’s CSZ clutches are a great choice for high performance printing, paper processing, packaging, food processing and textile manufacturing systems,” reports Jon Davidson, Miki Pulley sales specialist. “They are proven performers in system applications around the world.”

For more information about Miki Pulley CSZ clutches, visit www.mikipulley-us.com.

Why is viscosity important for bearing lubrication?

January 10, 2019 By Danielle Collins Leave a Comment

Lubrication — or, more correctly, improper or insufficient lubrication — is one of the leading causes of equipment failures in industrial applications. Without it, sliding, rolling, or meshing surfaces experience significant friction, heat, and wear, leading to increased noise, loss of accuracy, and reduced equipment life.

One of the most important characteristics of a lubricant is its viscosity (or, in the case of grease lubricant, the viscosity of the base oil). But viscosity is analogous to friction in fluids. So why do you need friction (in lubrication) in order to reduce friction (in bearings)?

Tribology is the study and application of the principles of friction, lubrication, and wear between two surfaces in relative motion.

Viscosity = friction in fluids

Viscosity is a property of fluids and is caused by their internal resistance to shear. When a fluid is moving under laminar flow conditions, with no turbulence — as is the case with most bearing lubrication scenarios — microscopic layers of the fluid flow over one another, much like a stack of paper, with each sheet moving slightly faster than the one below it. Cohesive forces between these microscopically thin fluid layers must be overcome as the layers move past one another. The resistance caused by these cohesive forces is the primary determinant of the fluid’s viscosity.

In laminar flow, microscopic layers of fluid flow over one another. The layers’ internal resistance to this shear force gives rise to viscosity.
Image credit: Michael Fowler, virginia.edu

The role of viscosity in reducing bearing friction

Bearing surfaces, no matter how well they’re machined, finished, and cleaned, will always have asperities (peaks) and valleys. When two bearing surfaces are in contact (for example, ball and raceway or roller and raceway), the asperities of the surfaces interfere with each other. One of the primary roles of lubrication is to separate the surfaces and reduce or eliminate the interference of their asperities, which significantly decreases friction and wear.

But when the surfaces are stationary (or moving at very low speeds), the pressure between them essentially “squeezes” the lubrication from between the surfaces. There is a very thin lubricating film, but it is not sufficient to separate the asperities of the two surfaces, and significant contact still exists. This is referred to as boundary lubrication.

In boundary lubrication, friction, heat, and wear depend primarily on the interactions between the surfaces, although chemical reactions between the lubricant and the surfaces can also contribute to wear. The time spent in boundary lubrication conditions significantly affects bearing performance and life.

As bearing speed increases, lubrication is “pulled into” the contact zone.
Image credit: Wessex Petroleum Limited

As velocity increases, more lubrication is “pulled” into the space between the bearing surfaces, allowing a thicker lubrication film to develop. This causes the pressure on the lubrication film to increase, which, in turn, increases the lubricant’s viscosity (according to the lubricant’s pressure-viscosity coefficient). But there is a transition period where, as velocity increases, the surfaces are separated in some places, but in other places, interference between asperities still occurs. This is referred to as mixed lubrication.

Finally, when a sufficient velocity is reached, the lubricating layer becomes large enough to separate the asperities of the two surfaces, and the increased viscosity gives the lubricant sufficient film strength to support the load, by elastically deforming the bearing surface. This lubrication regime is referred to as elastohydrodynamic lubrication.

A Stribeck curve shows the development of the lubrication film and the resulting change in friction. As velocity increases, the bearing surfaces “pull in” more lubricant, creating a thicker lubricating layer under higher pressure, which results in higher viscosity. Finally, the layer is thick enough to separate the asperities of the surfaces, and the viscosity provides sufficient film strength for the lubricant to support the load.
Image credit: Anton Paar GmbH

Feature image credit: Exxon Mobil Corporation

New Spirawave nested wave spring series from Smalley

January 8, 2019 By Lisa Eitel Leave a Comment

Smalley now offers a new nested Spirawave wave spring series. Smalley has been producing nested wave springs as customs for over 30 years, but this will mark the first standard series on the market.

These multiple turn, flat wire wave springs are coiled in parallel to produce two to three times as much force as traditional single-turn wave springs. Nested Spirawave springs can be used to replace stacks of single-turn springs, eliminating misalignment and inconsistent loading.

The sturdy, tangle-resistant design allows for simple, time saving automated handling. Reduced costs can be realized from the use of a single spring and a simplified assembly process.

“Introducing a standard line of nested springs gives customers the ability to streamline production while meeting their high force requirements,” says Dan Frank, Research and Development Engineer.

Standard Nested Spirawave springs are available from 0.500 to 4 in. or 16 to 3,000 mm in carbon and stainless steel. Stock parts are available for overnight shipping.

Nested Spirawave springs are specified for many applications including heavy duty bearing preload, connectors, valves, and seals. The increased forces produced make them suitable for industries that need precision wave springs with high loads.

If a standard nested spring doesn’t meet the application requirements, Smalley has a team of experienced engineers capable of designing a custom nested spring. Custom or standard, Smalley will get the right part, in the right material, with No Tooling Charges.

Request a copy of the brochure or a free Nested Spirawave Wave Spring sample at nestedsprings.com.

For more than 50 years, Smalley has been the leading manufacturer of retaining rings and wave springs for OEM engineers worldwide. As an ISO 9001 and ISO 14001 company, we deliver quality products certified to: IATF 16949, AS9100 and ISO 13485. Custom or standard, we are dedicated to delivering the right part, in the right material for application. For manufacturing news and product updates, visit smalley.com/blog.

Laser marking now part of Gear Motions production

January 7, 2019 By Lisa Eitel Leave a Comment

Gear Motions now has a fiber laser marking machine which was recently installed at its Nixon Gear Division in Syracuse.

The Beamer Laser Systems Model FL53 uses a 50-watt high powered LED laser to mark products quickly and safely. The machine offers fast cycle times and a wide range of marking intensities. It has a 12.5 x 26-in. total marking field and can accommodate a part up to 3.5 ft long with the side panels attached, and even larger parts when the panels are removed.

An optional 5C collet indexer was also purchased for radial marking of shaft-type parts.

This is the first time that Gear Motions has been able to offer laser marking as a manufacturing service. Previously, operations such as dot peening and engraving were used as a method of marking parts for customers. Laser marking produces a higher quality mark with a better visual appearance, which is particularly desirable for customers that may resell their gears at retail. It can also provide a more data-dense marking solution, via 2D bar codes, QR codes , and so on. for those customers that need it.

Gear Motions is now able to meet the laser marking requirements of its existing customers without sending to an outside vendor. This will streamline the entire process and make complete gear manufacturing even quicker and more efficient. The company can now also offer this value-add service to attract new business from customers that need laser marking on their precision-made gears and may also consider laser mark only business in the future.

Gear Motions, Inc. is an employee-owned company, with gear manufacturing facilities in Syracuse and Buffalo, NY. Specialists in precision ground gears, the company manufactures custom cut and ground gears for OEMs all around the world. Products include precision ground helical gears, spur gears, pump gears, bevel gears and worm gears, as well as multiple types of sprockets, timing pulleys, shafts and splines. For more information, visit gearmotions.com.

Why is static friction greater than kinetic friction?

January 4, 2019 By Danielle Collins Leave a Comment

Solid surfaces are subjected to two types of friction: static friction and kinetic friction. Static friction acts when the surfaces are stationary — think of a box on the floor. Static friction is what keeps the box from moving without being pushed, and it must be overcome with a sufficient opposing force before the box will move. Kinetic friction (also referred to as dynamic friction) is the force that resists the relative movement of the surfaces once they’re in motion.

The static friction between two surfaces is always higher than the kinetic friction (at least, in practical, real-world applications). But why is this? To find out, let’s look at the causes behind each type of friction.

Static friction

There are several theories regarding the causes of static friction, and like most friction-related concepts, each one proves valid under some conditions, but fails under other circumstances. For real-world applications (especially those related to industrial machinery and motion control) the two most widely-accepted theories behind static friction have to do with the microscopic roughness of surfaces.

Static friction keeps the box from moving until the applied force (F) exceeds the static friction force (f_s).

Regardless of how “perfectly” a surface is machined, finished, and cleaned, it will inevitably have asperities — essentially “roughness,” consisting of peaks and valleys, much like a mountain range. (Technically the “peaks” are the asperities.) When two surfaces are in contact, it may appear that they have a large, well-defined area of contact, but in reality, contact occurs only at certain places — that is, where the asperities of both surfaces interfere. The sum of these small areas of contact between the asperities is referred to as the “real” or “effective” area of contact.

Because these individual areas of contact are very small, the pressure (pressure = force/area) between the surfaces at these points is very high. This extreme pressure allows adhesion to occur between the surfaces, via a process known as cold welding, which occurs at the molecular level. Before the surfaces can move relative to each other, the bonds that cause this adhesion must be broken.

Because the surfaces are microscopically rough, with asperities and valleys, the real contact area between them is much smaller than the apparent contact area.

In addition, the roughness of the surfaces means that at some locations, the asperities of one surface will settle into the valleys of the other surface — in other words, the surfaces will interlock. These interlocked areas must be broken or plastically deformed before the surfaces can move. In other words, abrasion must occur.

So, in most applications, static friction is caused by both adhesion and abrasion of the contacting surfaces.

Kinetic friction

Overcoming the static friction between two surfaces essentially removes both the molecular obstacles (cold welding between asperities) and, to some degree, the mechanical obstacles (interference between the asperities and valleys of the surfaces) to movement. Once movement is initiated, some abrasion continues to occur, but at a much reduced level than during static friction. And the relative velocity between the surfaces provides insufficient time for additional cold welding to occur (except in the case of extremely low velocity).

Once the static friction is overcome, the box will move. Now, the friction opposing movement is much lower and is referred to as kinetic friction (F_k).

With most of the adhesion and abrasion being overcome to induce movement, the resistance to motion between the surfaces is reduced, and the surfaces are now moving under the influence of kinetic friction, which is much lower than static friction.

Assumptions regarding friction

Friction is an incredibly complex force that manifests differently under various conditions, making it difficult to express in terms of physical laws and mathematic equations. However, there are three assumptions regarding friction that apply in most real-world situations:

The frictional force is proportional to the normal force.
The frictional force is independent of the apparent area of contact.
The frictional force is independent of the relative velocity.

You might notice that assumption #2 (friction is independent of area of contact) seems to contradict the idea presented earlier that because the points of contact between the asperities are very small, pressure between the surfaces is high and adhesion (via cold welding) occurs, which increases friction. But notice that assumption #2 specifies the “apparent” area of contact.

Using the box example from above: Assume you move the contents of the box to a different box with a larger footprint. The mass (and hence, the normal force) hasn’t changed, but the apparent area of contact is larger. Despite the larger apparent area of contact, the friction force remains the same, as predicted by assumption #2.

Why does rolling motion experience friction?

In theory, a ball makes point contact with the surface. But in reality, the ball (and/or the surface) deforms due to the load, and the contact area becomes elliptical.
Image credit: SKF

Note that the discussion above relates to non-lubricated, sliding surfaces. In theory, rolling surfaces, such as those found in most rotary and linear bearings (except plain bearings), should not encounter friction forces. But in real-world applications, three factors cause friction in rolling surfaces:

Micro-slip between the surfaces (the surfaces slide relative to one another)
Inelastic properties (i.e. deformation) of the materials
Roughness of the surfaces