How to Properly Choose Servo Couplings

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.

http://www.rw-america.com/index.php

High Torque Servo Couplings

Heavy duty torque ratings and high strength conical clamping hubs make BK3 couplings the choice for high torque servo gearboxes. Manufactured with a double-walled stainless steel bellows to absorb parallel, angular and axial shaft misalignment, the BK3 has an extremely high torsional stiffness to complement its relatively very low moment of inertia – allowing it to handle rapidly indexing and reversing servo applications.

These unique couplings are manufactured with a tapered conical clamping element, which results in the highest shaft clamping forces, without keys, compared to any other hub design. The BK3 coupling also incorporates unique disassembly screws to aid the mechanic in tight spaces.

The clamping sleeves are custom bored on each side for shaft diameters from 10 to 80 mm ( 0.39 to 3.13 in.). Sizes are available for torque capacities ranging from 15 to 10,000 Nm (133 to 88,500 in. lbs.).

R+W America
www.rw-america.com

Low-Cost EKC Servo Couplings from GAM

Mount Prospect, IL, USA – GAM introduces a complete range of low-cost elastomer couplings, the EKC Series, that combine high precision and custom configurability with an economical price. Starting at $34, these couplings contain all the features you would expect with other precision couplings from GAM.

The EKC Series is engineered to minimize space requirements as well as design and installation time. Key features of the EKC Coupling include a single bolt radial clamping hub, star-shaped elastomer element with involute tooth profile, and high shore hardness to ensure zero backlash over the life of product. Utilizing the EKC provides compensation for small shaft misalignments and oscillation resonance is dampened. The couplings are both cast and machined and offer same day delivery.

GAM
www.gamweb.com

Hydraulic Pumps Benefit From Zero-Max CD® Couplings

Plymouth, Minnesota: New CD Couplings® from Zero-Max are an ideal choice for use with fixed displacement hydraulic pumps driven by servo motors. CD Couplings provide the ideal combination of high dynamic load capacity and high torsional stiffness to ensure reliable system operation.

“This new pump drive technology has become increasingly popular because of dramatic improvements in their energy efficiency and noise reduction”, reports Robert Mainz, Zero-Max sales manager. “These pump systems utilize the power and precision that only a servo motor can provide. The system pressure is controlled by modulating the output volume of a fixed displacement pump. This is made possible utilizing a high performance control system and the high performance qualities of a CD shaft coupling.”

CD couplings have unique design qualities that are robust to ensure that these hydraulic pump applications are reliable and productive. CD Couplings are designed so that the working part is made of a composite material. The composite disc design withstands the punishment and stress of a servo motor, “everything a variable speed pump drive system can dish out,” report OEM designers. They also report that CD couplings enable these systems to not only perform well in test lab environments, but more importantly, on the production floor.

CD Couplings are available in single and double flex aluminum hub models with or without keyways. 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.

All CD couplings are environmentally friendly and are manufactured of RoHS compliant materials.

For more information, call 1-800-533-1731 for FREE brochure. Outside US and Canada, call 763-546-4300.

www.zero-max.com

For the Best Load Control Look to Bellows Couplings

Properly selected bellows couplings result in the best control over the load in any servo application. Here are tips to ensure you choose the right size for the application.

Bellows couplings help maintain tight controls over loads.

For years, bellows couplings have been a mainstay for efficient motion systems because they offer high torsional stiffness, low moment of inertia, and minimal restoring forces under misalignment. They may help maintain tight control over loads, which is especially critical when considering that the flexible coupling often represents the point of least stiffness in an electromechanical system. In this way, couplings have a significant effect on the stability of the entire system, as well as the postional accuracy of the load. Bellows couplings benefits include misalignment compensation paired with precise transmission of velocity, angular positioning, and torque.

Read more

Latest High Speed Tab Inserter Systems From UMG Technologies

 

Danvers, MA – 24/7 automated operation has become an industry standard for UMG Technologies high speed tab inserters used in the manufacture of electronic printed circuit devices. These systems are designed for continuous, unattended operation with minimal maintenance due largely to top notch design engineering and the use of the latest and best off-the-shelf component technology.

The motion systems in these high speed automated inserters for example, employ servo motors connected to ball screws by means of zero-backlash ServoClass® couplings from Zero-Max. These tab inserter systems are used in the assembly of printed circuit boards for automotive and consumer interconnect devices and have insertion speeds up to 18,000 components an hour. The couplings damp out any backlash or harmonic tendencies that might occur in the system’s rapid step and repeat cycles as it precisely inserts connecting tabs into the circuit boards.

UMG Technologies PLT-901 Tab Insertion System used in the manufacture of electronic printed circuit board interconnect devices. It has an insertion speed up to 18,000 components an hour.	With a feed rate of 20 inches a second, these tab inserters have motion systems that employ servo motors connected to ball screws by means of zero-backlash ServoClass® Couplings from Zero-Max.

UMG Technologies, Inc. in Danvers, MA, specializes in designing and building these assembly interconnect systems with a focus on odd-form insertion, terminal, pin, eyelet, bulk wire, axial insert laser marking and continuous mechanical connector insertion systems for use in the consumer electronic, automotive, electronic manufacturing services, telecommunications and aerospace industries. They are programmable and can handle a full menu of different circuit boards.

Dual head inserter with in line conveyor. Note ball screw positioned behind inserter mechanism. The system features quick change anvil support tooling for flexible product changeover.

UMG’s PLT-901 dual head inline tab inserter is considered the industry standard in interconnect assembly machine technology, performance and reliability. The XY and rotary stage moves at speeds up to 20 inches a second with throughput rates of up to 18,000 insertions per hour. To achieve this high level of output, the interconnect material for these tabs must feed through the system with a high degree of accuracy and smooth motion. Tabs must align accurately at the cut and excise station where the system’s insert head transfers the interconnect into the printed circuit board while the lower anvils support the press-fit insertion.

In designing the drive system for these automated inserters, Robert Sooy, project engineer for UMG Technologies, decided the most effective connection of the servomotor (Yaskawa 200 watt brushless) to the ball screw (Kuroda 15 m X 10 mm) was with the ServoClass coupling because it is designed specifically to handle the specific sensitivities of servo systems. That means the coupling must take into account the mechanical as well as the electrical attributes of the system with the mechanical components keeping up with the electronic commands of the controller. The design specifications of the ServoClass coupling aid in making these two entities work well together.

Zero-Max Double Disc ServoClass couplings are specifically designed to meet the precision positioning requirements and high reverse load characteristics of today’s AC and DC servomotor applications.

“We tested the ServoClass coupling to verify it could handle the demands and high output of our servo system and were pleased with the coupling’s inertia and torsional stiffness features,” reported Sooy. “Tab alignment and positioning is really critical in these systems and with the high feed rate, any motion disparity when the anvil and insertion head meet has to be avoided or tabs can misalign and shut down the system. We needed a coupling that would operate reliably in this high speed, high volume 24/7 environment. We tried other steel, bellows-type couplings but preferred the Zero-Max single piece design with integral clamp style hubs. We ruled out couplings with steel spiral type center members because we needed torsional rigidity in our servo connections in order to eliminate any tendencies for harmonic vibration and backlash that could affect the servo controls positional and dynamic accuracy. The specs we saw and the tests we performed with the ServoClass Model SC035 gave us everything we needed to accomplish that.”

ServoClass SC035 couplings have torsional stiffness of 309 in-lb/degree and axial stiffness of 160 lb/in (N/mm).

ServoClass couplings are designed to meet the precision positioning requirements and high reverse-load characteristics of AC and DC servomotor applications. The couplings are flexible yet torque rigid because of their unique stainless steel double-flex disk design. It’s this design that provides the misalignment capacity, as well as the coupling flexibility to reduce reaction loads. The result is smoother system performance and longer operating life of the connected components.

The Zero-Max’s SC035 coupling that UMG Technologies uses has operating torque of 50 in-lb (6.0 Nm) at a maximum 10,000 r/m. It has torsional stiffness of 309 in-lb/deg and axial stiffness of 160 lb/in (N/mm). The coupling’s misalignment capacity is 0.009 inch (0.22 mm) parallel, 1.0 degree angular and 0.020 +/- inch (+/- 0.50) axial. It has moment of inertia of 0.0899 lb-in2 (26.3 kgm2 x106).

In the UMG application, the ServoClass coupling accelerates from 0 to 3000 rpm every half second and does so continuously. The only downtime needed with these systems is when a specific tab size insertion run is complete and a new one is started or when the interconnect inventory reels empty. (Reels have a capacity for approximately one hour of tab material.) Re-loading reels takes just two minutes for an operator to load. According to Sooy, there have been no coupling problems reported from any system users with over 600 machines in use for as long as 11 years.

“We also like the ServoClass coupling for its keyless clamp-type mounting hubs, “Sooy reported. “Their drop-in design makes them easy to connect and align during the machinery build cycle. There’s no need to align them with special tools or lasers. Once in place, they do the job they’re intended to do.”

For more information on UMG Technologies’ In-Line Tab Inserter systems:

Website: www.umgtinc.com Email: sales@umgtinc.com

For information on Zero-Max:
www.zero-max.com

Huco Tools Assist Coupling Selection for Design Engineers

Huco Dynatork, an Altra Industrial Motion company, offers the worlds most comprehensive range of small precision couplings from a single manufacturer. Huco’s precision couplings are ideal for use in high-end servo drives, pulse generators, scanners, X-Y positioning slides, high speed dynamometers, measuring instruments, robotics, machine tools and in many other applications where specific dimensional or performance criteria is required.

Because there is such a wide range of different motion control couplings from which the design engineer can choose, Huco offers a complete Design Guide to coupling performance characteristics on the company’s website.

The website also contains a unique Coupling Selector designers can use as a tool to identify the coupling types that meet their design criteria for angular, radial or axial misalignment, or a combination of all three. The interactive tool helps designers understand whether they need a bellows, membrane, sliding disc or helical beam, or another design.

The Coupling Selector takes the key information provided about the application and presents all the couplings that fit the criteria, with a link to the detailed specification of each coupling. Selection is based upon coupling type (mechanism), dimensions, shaft connections, performance, displacement and other conditions.

www.huco.com

Helical’s W-Series Coupling

SANTA MARIA, CA.—Helical’s W-Series coupling offers the convenience of metric sizing and fasteners for many designs. These single-piece, flexible couplings from Helical Products Co. compensate for mechanical movement irregularities such as angular and skewed misalignment, parallel offset and axial motion. The unique operating characteristics provide performance benefits such as no maintenance, no backlash, no lubrication, constant rotational velocity, and smooth bearing loads. Helical’s “W” Series couplings are manufactured in outside diameters (OD) of 15mm, 20mm,25mm, 30mm, 40mm and 50 mm. Inch and metric bore sizes are available and may also be combined. All are available in 7075-T6 Aluminum or 17-4PH Stainless Steel materials.

The W-Series can be used in a wide range of applications from driving components with light torque requirements, such as encoders and tachometers, to lead screw and pump applications requiring greater torque.

www.Heli-Cal.com

CD Couplings from Zero-Max

Plymouth, Minnesota: Motion system designers needing to fit a high performance coupling into a small space will find the solution with a specially designed CD coupling from Zero-Max.

High power custom CD coupling for small space application

Many other difficult coupling needs such as higher misalignment, greater torque capacity and greater torsional stiffness than that of standard couplings are available in Zero-Max specially designed CD couplings.

Key to these special coupling designs is the patented Zero-Max CD disc that has high torsional stiffness and yet allows for misalignment in high stress applications. Everything about this unique CD disc contributes to its high performance characteristics. The shape, the cutting process, the material used, the coating and the order and orientation of the disc layers – all have important significance to solving difficult motion system needs.

Custom stiff CD coupling for critical positioning application

Using finite element analysis (FEA), the CD disc can be easily modified along with changes in the composite material. Custom disc designs (manufactured on state-of-the-art laser cutting machines) can add to or lessen coupling flexibility or increase strength and stiffness as required for a particular application. And with 40 standard CD coupling models and sizes to work from, Zero-Max can configure a just-right custom coupling solution in a fraction of the time required for a custom coupling using all metallic components requiring special dies and tooling.

High precision CD coupling for small space application

In addition to the special CD couplings pictured, Zero-Max provides special large scale floating shaft couplings, very high speed couplings, stainless steel and/or nickel plated couplings, phase adjustable couplings, high misalignment and high torque couplings, shrink disc clamping hub couplings and many more.

A custom coupling proposal from Zero-Max includes complete engineering approval CAD drawings.

www.zero-max.com