ServoClass Couplings feature high torsional stiffness, zero backlash and low hysteresis to ensure repeatable precise positioning at speeds up to 10,000 rpm. Their robust design ensures precise system operation in automated 24/7 applications. That is especially true where stresses occur at increased speeds in a servo system. Designed with 304 stainless steel disc packs and 7075-T6 aluminum hubs, the couplings are inherently strong, durable and precisely balanced. To ensure precise alignment of the assembled components, ISO 4762 CL12.9 corrosion resistant socket head cap screws are used with a carefully controlled assembly process. The couplings are available in single and double flex models in inch and metric bore sizes from 0.157 in. (4mm) to 1.750 in. (45mm). All models and sizes feature clamp style hubs and operate in temperatures from -22° to +212° F (-30° to +100° C).

Zero-Max
www.zero-max.com

The 16 mm diameter size Servo Class coupling has operating torque of 4.43 in.-lb in both single (SD) and double disc (SC) models. They suit applications that need high torsional stiffness and low inertia.

The SD005 model delivers 43.3 torsional stiffness and 0.0009 in.lb² moment of inertia. The SC005 model delivers 30.5 torsional stiffness and 0.0013 in.lb² moment of inertia. All Servo Class couplings have zero-backlash, flexible metal stainless steel discs, and keyless clamp-style mounting hubs. Their robust design is maintenance free and they are easy to install.

The miniature sizes perform in all types of smaller servo motor applications including medical, electronic and assembly systems. “Reduced size doesn’t imply lower performance for these couplings,” reports Robert Mainz, Zero-Max sales manager. “They are as effective as any of the 18 larger sizes in the Servo Class coupling product line. They are a better option than beam style couplings.”

Performance specifications for Servo Class couplings:

SD005       SC005

Operating Torque              In.-lb (Nm)                           4.4 (0.5)      4.4 (0.5)
Maximum RPM                 RPM                                       10,000          10,000
Torsional Stiffness            In.lb./deg (Nm/rad)            77 (500)      39 (250)
Parallel Misalignment      In. (mm)                         0.001 (0.02)      0.002 (0.05)
Angular Misalignment     Degree 0.5 0.5
Axial Misalignment         +/- In. (mm)                     0.002 (0.05)    0.004 (0.10)
Weight                                Oz (gm)                                      0.25 (7)     0.35 (10)
Moment of Inertia            In.lb² (kgm2(x10-6)      0.0009 (0.25)   0.0012 (0.36)
Min Bore                             In. (mm)                                   0.157 (4)    0.157 (4)
Max Bore                            In. (mm)                                   0.236 (6)    0.236 (6)

Zero-Max

www.zero-max.com

The trend in industry to process more material faster and more efficiently calls for a high-torque, high-misalignment, low-inertia servo coupling, with minimal compromise to torsional stiffness. Stainless-steel bellows couplings have the highest torsional stiffness of commercially available flexible couplings, making them the best choice for aggressive servo-driven applications. But in cases where the two shafts to be connected are mounted to different bearing surfaces, it can be difficult to maintain the precise alignment tolerances normally required.

Utilizing a special, high-stiffness bellows and new, high-strength connection method, R+W’s BKZ handles an average of 2.6 times the traditional torque rating at a given outside diameter, and an average of 2.9 times more lateral misalignment, opening up the benefits of precision bellows couplings to a whole new segment of machine design and servo motion control.

Accepting bore diameters ranging from 15 to 60 mm and torque ratings from 20 to 1,000Nm, the BKZ range is available in four sizes, with a variety of materials, finishes and the optional self-opening clamp system.

www.rw-america.com

MISUMI Coupling types include high precision Single Disc and Double Disc Clamping models, many of which may be used with servomotors.  Also offered are Oldham, Slit and N Couplings, as well as Jaw, Sleeved, Bellows, and Resin types, in a variety of sizes and configurations.

The SCXW is a Double Disc type precision disc clamping coupling with high torque but no backlash.  Its torsional rigidity is up to 26% higher than conventional (standard) disc clamping couplings. It suits applications requiring fast positioning precision.  All the bolts are trivalent chromate plated and suitable for use in clean environments.

The MFJGWK is available as a high rigid Oldham coupling, set screw type. The MFJCGWK is a high rigid Oldham coupling, clamping type.  Both products feature an aluminum bronze spacer and have a keyed bore.  These couplings have allowable torque 2X higher compared to resin spacers.

The SCOC is a short Oldham coupling, clamping/spacer type. This space-saving version works with miniature devices because it is 17% shorter than conventional types.

Most MISUMI Couplings ship in six days, with the exception of the new High Rigid Oldham Couplings, which ship in eight days.  Some couplings offer optional express shipping for faster delivery.

MISUMI USA, Inc.
Http://us.misumi-ec.com

Specialist mechanical components supplier, Ondrives Ltd of Chesterfield, England have recently introduced a high quality range of servo-insert couplings into their extensive coupling range via their biggest ever catalogue, now that they have merged with sister company, Rino Industries Ltd.

Typically, they are used in applications where vibrations and crushes may appear. The dampening attributes of those couplings are caused by the spider element which is positioned between the two hubs. This spider element is available in different shore hardnesses. Depending on the requirements it is recommended customers use a spider element with low dampening properties for applications with low vibrations and crushes (higher torsional stiffness of the coupling) and to use a spider element with high dampening properties for application of high grades of vibrations or crushes (lower torsional stiffness of the coupling).

A further positive property of the servo insert couplings is that they are pluggable, so they can be assembled quickly and easily even under difficult assembly conditions. The many different varieties of the hub style include shaft fixing with set screws, with clamp hubs and with outer conical hubs. Customers will find that the most popular type, as always, is with the clamping hubs as they ensure the fastest assembly/disassembly without leaving marks on the shafts. Torque range varies from as low as 1.2Nm up to 940Nm on the largest sizes. Other advantages include an extremely compact design and minimum mass and inertia as standard. They offer high resistance against environmental influences and temperatures as well as being non-wearing and therefore maintenance free.

A misalignment of the shafts in axial, lateral and angular directions can be compensated by a servo insert coupling as well but it should only be a minimum of misalignment because relatively high reset forces are caused by the coupling which do negatively influence the lifetime of components such as bearings in this environment, the company states.

Typical applications include -

Stepping motors, servo drives, machine tools, CNC machines, wood working and packaging machines, factory automation machinery, printing machines, sheet metal forming machines, industrial robots, textile machines and control and feedback control systems.

www.ondrives.com

The GERWAH® line of products consists of magnetic couplings, metal bellows couplings, servo-insert couplings, line shafts, RING-flex® couplings and safety couplings. These couplings are available in a range of sizes and torque capacities to 3,800 lb-ft. The low mass of the lightweight construction helps increase machine performance and reduce energy costs.

Ringfeder Power Transmission USA Corporation markets a range of power transmission components and keyless shaft/hub technology.  Other power transmission products include shock absorbing devices, flexible elastomeric couplings, flexible disc couplings and torque limiters along with other specialty and custom made products.

RINGFEDER

www.ringfeder.com

The aluminum CD® model is a low inertia, lightweight coupling with high torsional stiffness for servo motor applications. It is available in single and double flex versions.

“We surveyed design engineers to find out what was the most desirable feature when specifying couplings for servo motor applications,” reports Robert Mainz, Zero-Max sales manager. “Low inertia was the most important.” These engineers said they continually look for ways to reduce cycle time and improve system productivity. A lightweight yet high strength coupling design will let you increase the speed of the actuator. Lightweight couplings will also have an effect on the energy consumption in their designs.

The working part of the CD® coupling is made of a special composite material. The composite disc design withstands the stresses of a servomotor’s high acceleration rates and high torque capacity better than other coupling designs. This results in lower energy requirements, and longer life of the motor and other operating components while ensuring uninterrupted system operation.

Zero-Max CD couplings are available in single and double flex models with or without keyways. The double-flex version is for precision applications requiring misalignment capacity greater than the single flex design. The single flex models have a torque capacity range from 40 Nm to 1436 Nm and beyond with speed ratings from 4400 RPM to 17,000 RPM.

Zero-Max
www.zero-max.com

Physical values such as torque, torsional rigidity, spring stiffness, moment of inertia, imbalance, and zero-backlash play a major role in coupling design. Here are a few facts to keep in mind when you design your motion system.

Torque (Nm): is the product of an acting force and the effective length of the acting force’s lever arm.

T = Fxr

T = Torque (Nm)

F = Force (N)

r = Lever arm (m)

With a force of 100 N and a 1 m long lever arm, you can generate a torque of 100 Nm. Or, you can generate a torque of 100 Nm with a force of 1000 N and a 0.1 m long lever arm. For couplings, a specific amount of torque can be achieved with a large outer diameter of the coupling and a correspondingly low acting force or with a small outer diameter and a correspondingly high acting force.

Torsional rigidity (Nm/rad): refers to the rigidity of a coupling when it is subjected to a torsional load. If the torque exceeds the maximum torsional value of the coupling, the coupling will no longer be strong enough to transmit the acting rotational force. Ex: If a coupling with a torsional rigidity of 10 000 Nm/rad is subjected to 10 Nm, the connection element will twist by 1/1000 rad. That is equal to an angle of twist of about 0.057 degrees (1 rad = 57°17’44.8”). For a torsionally rigid or vibration damping coupling, this angle of twist may still be within the admissible range.  In practice, torsionally rigid couplings normally have a maximum angle of twist of less than 0.05 degrees and vibration damping couplings have a maximum angle of twist of less than 5 degrees.

Spring Stiffness (N/mm): is the counterforce exerted by the coupling in case of differentiated position of the axes in an axial, radial, and lateral direction. Ex: If the axial spring stiffness of a coupling is 30 N/mm, the coupling will exert a force of 30 N in the case of an axial displacement of 1 mm. These forces are important in a design with couplings, particularly when selecting bearings or other drive system components.

Moment of inertia: is the moment resistance when the rotational speed is changed. Normally, the lower the total weight and the smaller the outer diameter of the coupling body, the lower the moment of inertia. The reverse is also true, the higher the weight and larger the outer diameter, the higher the moment of inertia. This feature is important in highly dynamic applications because the drive has to generate sufficient torque to overcome a body’s moment of inertia to accelerate and decelerate.

Imbalance: in a drive system, imbalance should be as low as possible for smooth operation. Caused by asymmetries in the drive system where mass is distributed unevenly, it affects centrifugal forces on the entire drive system. It can be rectified by “balancing bores,” which are normally drilled directly into the location of the disproportionally high concentration of mass.

Zero backlash: is a lack of empty space or “play” when the rotational speed, direction of rotation, or torque changes. It does not mean that there is no angle of twist. Backlash is an important factor in predicting bearing life.

Information courtesy of R+W America

Rw-america.com

ServoClass® Couplings suit applications using ac and dc servomotors that need precise positioning and the ability to handle high reverse loads. These couplings have zero-backlash and low hysteresis.

Three new sizes have been added to the ServoClass coupling line. They handle bore diameters from 0.875 in. (20 mm) to 1.378 in. (35 mm) and operating torque from 3937 to 9843 lb-in., (100 to 250 Nm). Additional sizes are available starting with the smallest bore size 0.157 in. (4 mm) and larger.

All ServoClass couplings are manufactured of RoHS compliant materials. They are lightweight and designed with 304 stainless steel disc packs and 7075-T6 aluminum hubs and center members. They are available in single and double flex models in inch and metric sizes. All models and sizes feature clamp style hubs with corrosion resistant socket head cap screws.

“ServoClass couplings provide a better option compared to beam or bellow style couplings,” reports Robert Mainz, Zero-Max sales manager. “As the cycle becomes faster, they outperform beam couplings, which experience harmful windup. Their robust design also outperforms the fragile design of bellows couplings.”

Zero-Max
www.zero-max.com

R+W Coupling Technology recently proposed a system on how to properly select your servo couplings.  They state that servo systems require mechanical components with  high torsional stiffness in order to perform properly in applications requiring rapid acceleration and deceleration of high inertia loads. Flexible couplings usually have the lowest torsional stiffness of any component in a motion system. Couplings are often selected based on factors other than torsional stiffness, often to the detriment of system performance.  Proper servo coupling selection can pay off when considering the overall picture.
R+W also say engineers go to great lengths to ensure that inertia mismatch between the load and the servo motor is compensated for. Motors and gearheads must be selected in order to ensure the ability of the drive to be able to accelerate the load with ease. The mechanical connection between the drive and the load can however unvaryingly compromise the efforts of the drive system. The most compliant component in the mechanical system (e.g. the coupling) will be twisted back and forth by the settling motion of the load at any major velocity change. The formula provided by R+W for calculating torsional deflection based on load and stiffness is as follows:

	f	=	torsional deflection (degrees)
	TAS	=	peak torque (Nm)
	CT	=	torsional stiffness of coupling (Nm/rad)

Depending on the inertia of the load and its effect on peak torque, this can happen to varying degrees. In any case, more power is required in order to accelerate the load at the desired rate when a less rigid component is installed between the drive and the load. According to R+W, this may or may not pose a concern depending on the application, and tends to be of higher importance in cases with a high inertia load that must be rapidly indexed.

When tuning servo drives, R+W claims that velocity and position feedback loops must be set to a low enough frequency so as not to excite the most torsionally compliant component in the system by reaching its natural frequency. Higher coupling stiffness leads to a higher natural frequency of the entire system, which means that feedback loops can be set to a higher frequency. This leads to a faster moving, more accurate machine, and ultimately higher throughput and higher quality.

A commonly used calculation by R+W for determining required coupling stiffness, and / or maximum drive frequency, utilizes what is called the “two-mass system.” In practice, if the calculation is carried out based on coupling stiffness alone, the calculated resonant frequency of the load has to be at least twice as high as the excitation frequency of the drive.

	fe	=	Resonant frequency of the system (Hz)
	CT	=	torsional stiffness of coupling (Nm/rad)
	JL	=	Moment of inertia, load (kgm^2)
	JA	=	Moment of inertia, drive (kgm^2)

Bellows couplings quite simply posses the highest torsional stiffness of commercially available flexible couplings, and are considered by many to be the standard for servo applications. Hydroformed from a continuous tube of stainless steel, bellows can easily flex laterally, angularly, and axially with only very gentle restoring forces, while remaining highly rigid in rotation. This, paired with a low moment of inertia, according to R+W, makes bellows couplings appropriate for almost any application requiring optimum efficiency and performance in acceleration and positioning.

The exception lies, says R+W,  in cases where neither a high level of dynamic positioning accuracy, nor the ability to optimize servo loop gains is critical. A vibration damping coupling can be a very dependable and a low cost alternative in these cases. When pushing the limits of efficiency, accuracy, and speed, the most torsionally rigid coupling possible should be used in order to design the best servo system possible.

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