Zero-backlash couplings handle servo demands

ServoClass couplings are designed to meet the precision positioning requirements and high reverse-load characteristics of AC and DC servomotor applications.

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 servomotors 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, in Danvers, Massachusetts, specialises 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.

UMG's PLT-901 dual head inline tab inserter is considered the industry standard in interconnect assembly machine technology, performance and reliability.

The x-y and rotary stage moves at speeds up to 20in/s 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 200W brushless) to the ball screw (Kuroda 15m x 10mm) 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.

"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 centre 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 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 6.0Nm at a maximum 10,000rev/min.

It has torsional stiffness of 35Nm/deg and axial stiffness of 18kN/mm.

The coupling's misalignment capacity is 0.22mm parallel, 1.0 degree angular and +/-0.50mm axial.

It has moment of inertia of 26.3kgm2 x10e6.

In the UMG application, the ServoClass coupling accelerates from 0 to 3000rev/min 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).

Reloading 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".

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