Couplings (custom)
One of the greatest advantages of the specialist flexure beam product is in its ability to adapt into applications where simply other shaft coupling designs can not follow. Whether it is a standard shaft coupling with an unusual shaft attachment requirement or a design that requires a high degree of angular offset, the specialist flexure product can help solve your rotational challenges .
We like to refer to the adaptable flexible element in the product as the "FLEXURE"
The specialist flexure is determined by six major characteristics:
- Flexure outside diameter
- Flexure inside diameter
- Coil thickness
- Material
- Number of coils
- Number of coil starts
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| The Coil Width - By varying the thickness of the coils a flexure can accommodate increasing amounts of torque and radial loads. | The Number of Coils - When the number of coils is changed, the torque capability remains unchanged but the angular, parallel and skewed offset capability increases. | The Inside Diameter - When the inside diameter changes, so does the torque capacity, torsional stiffness and axial spring rate | The Number of Coil Starts - One, two or three helical beams provide higher torsional stiffness. |
In a rotating system, constant velocity refers to the relative rotational speed of the input and output shafts. In a constant velocity system the driven end of the coupling turns exactly the same rate as the driver end. When operating under a uniform load the helical flexure design provides constant velocity and can alleviate problems such as Backlash. The helical flexure has zero backlash. Angular misalignment can induce large fluctuations in rotational velocity in certain coupling designs. The Helical flexure has a constant spring rate at all points of rotation. Torsional Variations can induce differences in hub to hub velocity when subjected to dynamic loading are minimal in steady state applications on the helical flexure. Concentricity can be an issue when there is a lack of it, particularly in the case of couplings with backlash or where production variation is difficult to prevent. The Helical flexure one piece integrity minimises sinusoidal variations.
Backlash - the Helical flexure has zero backlash. Misalignment Compensation – The flexing capacity of the flexure can compensate for a variety of misalignments including parallel, angular, axial and skewed shaft misalignment. Optimised Torque Capacity – The basic requirement of a flexible coupling is to transmit torque loads without permanent distortion or damage and without imposing undue bending or radial loads upon the driver or driven components. Once the working torque rating of the flexure coupling is established, based on design criteria, its operational life is virtually unlimited. Configurable Torsional Stiffness - Every Flexible coupling has some torsional flexibility. Torsional flexibility reflects the amount of twist in a system; torsional stiffness the degree of resistance against twist. The flexure uniquely can be configured to provide the exact amount of torsional flexibility required in an application. In a rotating system, Constant Velocity refers to the relative rotational speed of the input and output shafts. In a constant velocity system the driven end of the coupling turns exactly the same rate as the driver end. When operating under a uniform load the helical flexure design provides constant velocity. Angular misalignment can induce large fluctuations in rotational velocity in certain coupling designs. The Helical flexure has a constant spring rate at all points of rotation. Torsional Variations, which can induce differences in hub to hub velocity when subjected to dynamic loading are minimal in steady state applications on the helical flexure. Concentricity, when there is a lack of it, particularly in the case of couplings with backlash or where production variation is difficult to prevent, the Helical flexure one piece integrity minimises sinusoidal variations. Bearing loads are primarily generated by a couplings natural resistance to bending and can be very destructive forces to an apparatus and its rotational components. The Helical flexure maintains a very constant radial and bending load at all points of rotation, providing exceptionally uniform and smooth bearing loads.
By altering these characteristics, torque capacity, angular and parallel misalignment capabilities, torsional and lateral bending rates of flexured u-joints can be modified to suit specific specifications and or requirements.
Utilising over 50 years of experience and flawless production techniques, the single piece construction totally eliminates any form of friction wear within its design, whilst also ensuring a zero-backlash and no torque loss operation. The following are examples of where we have helped;
Amalgamation of parts
Abssac recently enhanced the operation of a medical orthodontic machine by replacing a universal joint, plastic shaft coupling and a piece of shafting with just a one piece flexured drive shaft unit.
Abssac's customer had initially been using a traditional universal joint to connect a hand control, via a piece of shaft and through another plastic flexible shaft coupling, to a small gear box. The universal joint was expensive and was being utilised at the limit of its angular capability, which was causing cyclic torque variants on operation. A separate piece of bar stock was then used to span the drive mechanism to the gear box, which again required 3 degree shaft misalignment, which was accommodated by a small plastic multipart shaft coupling. The old design was inefficient, time consuming to build and had suffered from reliability issues.
Abssac's solution was to take 400mm of Aluminium bar stock, 15mm in diameter, which would provide the length requirement of the drive shaft. Then using the unique ability to adapt the "flexure" or beam part of the helical beam shaft coupling, they could provide the two angular misalignments required in the system, but all within the single part.
Utilising a double start coil flexure at each end to give the superior torsional stiffness, the drive shaft could accept angular misalignment up to 30 degrees at one end, whilst the other end would accept up to 5 degrees. The final design incorporated a split clamp design to lock the drive shaft into position onto the driven and drive ends.
The new design was then used in 4 other machines using different lengths as the single part provided a zeroblacklash drive solution, which did not require lubrication, maintenance or suffered from operational issues.
Resonance problems eliminated
The problem with shaft coupling resonance in a drive system is that once the shaft couplings physical size has been determined to transmit the torque and angular offsets required, the only way to escape a harmonic resonant frequency is to alter the couplings mass, normally requiring a reduction or increase in the physical size of the coupling. When you reduce the mass, you naturally reduce the torque capabilities too and if you increase the size, the price normally heads in the same direction.
We believe that we are one of the only companies to be able to over come this problem and still remain within the original dimensional characteristics that are often set within the application. The key lies with the flexure element. By altering the flexure configuration, for example, replacing a double start fine pitch coil with a single start thicker coil configuration, can change the mass of the coupling and therefore its resonant frequency.
Heat sink of shaft coupling?
Abssac has recently supplied a classic example of the flexures unique capability being utilised as a heat sink. A pancake shaped compression flexure 50mm in diameter but only 5mm in height has been produced to hold an ultra thin reflective mirror on its top surface, in a high wattage industrial laser machining application. High strength aluminium material was used because of its heat transfer characteristics and low cost. By incorporating the unique flexible element into the one piece design allows the easy alteration of the mirrors angle of incidence, whilst maintaining the mirrors position, rigidity and focus.
Stress Relief elongates life
Incorporating a stress relief hole reduces the stress concentration by taking the existing sharp edge and modifying it to be a smooth transition from the Flexure to the solid hubs. A stress relief can drastically increase the life of the shaft coupling.
Miniature flexure
A fully functional 3.1mm diameter shaft coupling was recent supplied for a medical application. Using a left and right handed thread shaft for attachment the coupling could accept up to 1mm of angular offset rotating up to 10,000 rpm. The same customer is now looking at a double start flexure with a 1.5mm outside diameter produced in titanium.
If you require further technical information on this product, please do not hesitate to contact our sales engineers who will be more than happy to help you