SERVOPLUS Couplings – Made for Servo Drives
Patented modular design simplifies machine servicing and allows for more efficient component use and storage.
In this article, we turn our particular attention to advanced industries requiring maximum precision in machine motion – we focus on the Italian SIT SERVOPLUS shaft couplings.
- Precisely: SIT SERVOPLUS Bellows Couplings
- Modular Design
- How Much Misalignment Can the Coupling Handle?
- Dimensions and Parameters
We are now offering these bellows couplings as standard items in our online store. With the previous inquiry-based process no longer necessary, you can select and order the individual coupling components, and assemble the coupling yourself, exactly to your application's requirements. Simply and conveniently in the TYMA CZ online store.
Precisely: SIT SERVOPLUS Bellows Couplings
A solution tailored specifically for precise positioning at high speeds and frequent load reversals.
A servo drive knows exactly where it is, the control system trusts it, and the machine components connecting the motor to the driven part must not compromise that. That's why SERVOPLUS shaft couplings, made by the Italian manufacturer SIT, transmit torque completely backlash-free and with exceptionally high torsional rigidity.
Bellows couplings are found on the axes of CNC machines, in robotic arms, on laser heads, and on packaging and printing lines. Wherever every command from the motor must have an immediate and precise effect on actual movement. And, of course, they compensate for axial, radial and angular shaft misalignment at the same time.
SERVOPLUS Shaft Couplings in the TYMA CZ Eshop
We are an authorized SIT distributor and can support you from the initial design stage in selecting the right solution for your application.
Alternative designs exist too. Are they equally suited? When do they fit, and when not?
Other Backlash-Free Couplings – What About TRASCO ES?
Being backlash-free alone isn't enough. TRASCO ES couplings are also free of backlash, but torque is transmitted through a flexible polyurethane element. Deliberately flexible, so it can effectively damp shocks and torsional vibration. The trouble is that very property works against the servo loop: the more compliant the coupling, the harder it is for the controller to tell whether it's correcting an actual position error, or just deflection within the coupling itself.
SERVOPLUS couplings, by contrast, are torsionally rigid. No flexing, no uncertainty. Backlash-free and rigid at the same time, not one instead of the other.
Other Torsionally Rigid Couplings – What About Disc-Type SERVOMATE?
That's more complicated. Disc couplings are just as backlash-free and torsionally rigid as bellows couplings, and a blanket statement about which design suits servo drives better would be misleading. The difference usually comes down to a trade-off between stiffness, misalignment tolerance, temperature or chemical resistance, and coupling dimensions. Whether bellows or disc, it always depends on the specific type, configuration and size.
SERVOMATE couplings are likewise designed specifically for servo motors and are offered in two configurations that nicely illustrate the trade-off principle: a single version with one disc pack, without the ability to compensate for radial misalignment, or a double version with two disc packs and a spacer ring, which handles radial misalignment at the cost of a longer design, higher moment of inertia and half the torsional stiffness.
However, while SERVOMATE is offered in only three sizes, SERVOPLUS covers a wider performance and dimensional range.
Modular Design of SIT SERVOPLUS Bellows Couplings
SERVOPLUS are all-metal bellows couplings. They transmit torque through a highly durable bellows element, connected to hubs on both sides, which compensates for shaft misalignment.
The design of SERVOPLUS couplings is modular. This fundamentally sets it apart from many other bellows couplings, where the element is permanently welded or bonded to the hubs. SIT takes a different approach and offers a demountable mechanical connection.
The bellows element is fitted into a groove on each hub and secured by a set of smaller set screws. These fix it in both the radial and axial directions. To replace a damaged bellows, these screws and the hub's clamping screw can simply be loosened, the hub slid along the shaft, and the element removed – without needing to move the shaft or disassemble the drive.
GSPM/GSPMF Hubs
The hubs are of the clamping type and are secured to the shaft with a single radial screw. As standard, they therefore work without a key and keyway, although the manufacturer also offers this as a custom option.
They are made of aluminum alloy, in two versions:
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GSPM – a semi-finished part with a pilot bore that must be machined to the required diameter before use,
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GSPMF – with a finished bore with an F7 tolerance, ready for immediate mounting.
Hub size is indicated by the maximum bore diameter it can accommodate (in mm).
GSPS Elements
The bellows is shaped like a thin-walled cylinder with a series of parallel, concentric corrugations. It's exactly this shape that gives the bellows element its key characteristics – torsional rigidity combined with the ability to absorb axial, radial and angular deflection.
The material is stainless steel – the standard choice for bellows, since it ensures fatigue strength under repeated cyclic loading. It flexes and straightens at least slightly with practically every rotation. Resistance to corrosion and related defects is, of course, also essential. Stainless steel is also a good choice for its temperature resistance and dimensional stability. The manufacturer states an operating temperature of up to +300 °C.
How Much Misalignment Can the SERVOPLUS Coupling Handle?
As with any shaft coupling, the range of permissible misalignment is one of the key characteristics.
Axial displacement usually arises from thermal expansion of the shafts during operation. Depending on coupling size, the manufacturer allows a value in the range of ±0.5 to ±1.0 mm. While angular misalignment is generally fine up to 2°, radial misalignment requires the most attention. Misalignment above 0.2 to 0.3 mm can cause undesirable deformation of the bellows.
These maximum values, however, cannot be used simultaneously. For a given application, each type of misalignment is converted into a percentage of the maximum for that coupling size, and the sum of all three must not exceed 100%. So if axial misalignment uses 50% of its maximum, only 50% remains for radial and angular combined.
Dimensions and Parameters
The five available sizes – 16, 20, 30, 38 and 45, denoting the maximum bore diameter in mm – correspond to nominal torques of 5 to 150 Nm, with the couplings able to briefly withstand up to 1.5 times those values. Outer diameter ranges from 34 to 83 mm, and overall coupling length from 50.5 to 103 mm.
Maximum speed decreases with increasing size – from 14,000 min−1 for the smallest to 5,800 min−1 for the largest.
Selected parameters of SIT SERVOPLUS bellows couplings
| Size: Maximum Bore Fmax [mm] |
Pilot Bore Ø Fg [mm] |
Torsional Rigidity CT [Nm/rad] |
Nominal Torque TKN [Nm] |
Maximum Speed nmax [min−1] |
|---|---|---|---|---|
| 16 | 4.5 | 3,050 | 5 | 14,000 |
| 20 | 7.5 | 6,600 | 15 | 11,900 |
| 30 | 9.5 | 14,800 | 35 | 8,700 |
| 38 | 13.5 | 24,900 | 65 | 7,300 |
| 45 | 13.5 | 64,000 | 150 | 5,800 |
Of course, you'll find more information in the manufacturer's catalog sheets, available for download in the online store.
SIT SERVOPLUS Bellows Couplings in the TYMA CZ Online Store
Selecting the Right Couplings for Your Application?
Send us your drive parameters and we will be happy to assist you with the design proposal.
We are an authorized distributor of shaft couplings from the Italian manufacturer SIT S.p.A.